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10,100 |
Suppose that you have an abstract for a scientific paper: nuclear level densities and @xmath0-ray strength functions of @xmath1fe have been extracted from proton-@xmath0 coincidences .
the level densities are compared to previous experimental data , both from particle - evaporation spectra and @xmath2he - induced reactions .
the low - energy enhancement in the @xmath0-ray strength functions , first discovered in ( @xmath3he,@xmath3he@xmath4)@xmath5fe and ( @xmath3he,@xmath6)@xmath7fe data , is confirmed with the experiments reported here .
angular distributions of the low - energy enhancement in @xmath5fe indicate its dipole nature . the high statistics and the excellent energy resolution of the large - volume labr@xmath8(ce ) detectors allowed for a thorough analysis of the @xmath0-ray strength function as a function of excitation energy .
strong fluctuations were found for the direct decay to the ground band , while the decay into the quasi - continuum shows a more uniform behavior .
there is no indication of any significant excitation - energy dependence in the @xmath0-ray strength function , in support of the generalized brink - axel hypothesis .
october 2016 _ keywords _ : level density , @xmath0-strength function , angular distributions , brink hypothesis , iron + .
And you have already written the first three sentences of the full article: one of the long - standing experimental and theoretical challenges within nuclear physics is the determination of the nucleus available quantum levels and the decay properties of these levels in the excitation - energy region between the ground state and up to the particle threshold(s ) . in this intermediate excitation - energy region , often called the _ quasicontinuum _ , the _ nuclear level density _ ( nld ) and the average , reduced @xmath0-decay probability , i.e. the _ @xmath0-strength function _ ( @xmath0sf ) , shed light on the dynamic behavior of the nucleus . apart from providing information on basic nuclear properties ,
these quantities are also indispensable input for calculations of , e.g. , neutron - capture cross sections .
these cross sections are of great importance for applications such as the astrophysical heavy - element nucleosynthesis @xcite and modeling of next - generation nuclear power plants @xcite ..
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amongst a handful of experimental techniques , the oslo method @xcite has been established as one of the promising approaches to obtain experimental information on the nld and @xmath0sf .
the advantage of the oslo method compared to other techniques is that both these quantities can be extracted from one and the same experiment , utilizing typically a charged - particle reaction to record particle-@xmath0 coincidences , in which the structural shape of the nld and the @xmath0sf can be determined . by measuring the energy of the outgoing charged particle ,
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10,101 |
Suppose that you have an abstract for a scientific paper: the past year has seen an explosion of new and old ideas about black hole physics . prior to the firewall paper ,
the dominant picture was the thermofield model apparently implied by ads / cft duality@xcite .
while some seek a narrow response to almheiri , marolf , polchinski , and sully,(amps)@xcite , there are a number of competing models .
one problem in the field is the ambiguity of the competing proposals .
some are equivalent while others incompatible .
this paper will attempt to define and classify a few models representative of the current discussions . .
And you have already written the first three sentences of the full article: hawking set out early on to outline an information loss model@xcite , which drew some significant criticism@xcite .
the full consequences of information loss scenarios are still unknown .
it is easy for non - unitary theories to lose causality , though energy conservation can still be maintained with care@xcite ..
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this category is characterized by a many - to - one map of states , as well as an injective map from pure to mixed states .
the no - hair theorem is embodied in the first property , in which a nonunitary quantum bleaching operator is applied .
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10,102 |
Suppose that you have an abstract for a scientific paper: the vast majority of sampling systems operate in a standard way : at each tick of a fixed - frequency master clock a digitizer reads out a voltage that corresponds to the value of some physical quantity and translates it into a bit pattern that is either transmitted , stored , or processed right away . thus signal sampling at evenly spaced time intervals is the rule : however this is not always the case , and uneven sampling is sometimes unavoidable .
while periodic or quasi - periodic uneven sampling of a deterministic signal can reasonably be expected to produce artifacts , it is much less obvious that the same happens with noise : here i show that this is indeed the case only for long - memory noise processes , i.e. , power - law noises @xmath0 with @xmath1 .
the resulting artifacts are usually a nuisance although they can be eliminated with a proper processing of the signal samples , but they could also be turned to advantage and used to encode information . .
And you have already written the first three sentences of the full article: nearly all digital signal - measuring equipment found in laboratories throughout the world , from the humble voltmeter up to powerful computerized data - logging systems and high - frequency digitizing scopes , operate with an internal master clock that sets the pace for an analog - to - digital converter that translates the electrical output of a transducer into a bit pattern .
the master clock frequency is usually held as stable as possible and the sample intervals are fixed to a very high degree of precision .
correspondingly , most signal - analysis techniques are meant to be used on evenly spaced data : this is true for the discrete fourier transform ( dft ) and also for autoregressive ( ar ) or moving average ( ma ) modeling of data @xcite ..
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however some data happen to be unevenly sampled : this is especially true for astronomers , who are seldom so lucky as to have an uninterrupted series of clear nights , and in general are bound to observe whatever comes from the sky , whenever it comes , and have to search for periodicities amid these scattered data .
indeed it was the astronomical community that developed the first effective spectral estimation techniques for unevenly sampled data @xcite .
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10,103 |
Suppose that you have an abstract for a scientific paper: an appropriate gauge - invariant framework for the treatment of magnetized curvature and entropy modes is developed .
it is shown that large - scale magnetic fields , present after neutrino decoupling , affect curvature and entropy perturbations .
the evolution of different magnetized modes is then studied across the matter - radiation transition both analytically and numerically . from the observation
that , after equality ( but before decoupling ) the ( scalar ) sachs - wolfe contribution must be ( predominantly ) adiabatic , constraints on the magnetic power spectra are deduced .
the present results motivate the experimental analysis of more general initial conditions of cmb anisotropies ( i.e. mixtures of magnetized adiabatic and isocurvature modes during the pre - decoupling phase ) .
the role of the possible correlations between the different components of the fluctuations is partially discussed . 8.5 in 6.5 in -30pt 0.2 cm cern - ph - th/2006 - 056 + .
And you have already written the first three sentences of the full article: the observational evidence inferred from the spatial variations of the cosmic microwave background ( cmb ) temperature suggests that the curvature perturbations that are present prior to decoupling ( but after equality ) must be predominantly adiabatic and gaussian with an ( almost ) scale - invariant spectrum @xcite .
a mode is defined to be ( predominantly ) adiabatic if the fluctuations of the entropy density are subleading after matter - radiation equality ( but prior to decoupling ) .
an exactly adiabatic mode of curvature fluctuations may be produced , for instance , by single - field inflationary models ..
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if this is the case , the scalar fluctuations of the inflaton field ( with wavelength larger than the hubble radius ) are transferred to curvature fluctuations whose value stays ( almost ) frozen from the early stages of the evolution of the universe until the pre - decoupling epoch when the minute spatial variations of the geometry are imprinted , via the sachs - wolfe effect , on large - scale temperature inhomogeneities .
in addition to adiabatic fluctuations there may be one or more non - adiabatic modes sometimes named ( with a somehow confusing terminology ) isocurvature modes . the specific number of ( regular )
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10,104 |
Suppose that you have an abstract for a scientific paper: we search for spectral features in fermi - lat gamma - rays coming from regions corresponding to eighteen brightest nearby galaxy clusters determined by the magnitude of their signal line - of - site integrals .
we observe a double peak - like excess over the diffuse power - law background at photon energies 110 gev and 130 gev with the global statistical significance up to @xmath0 , confirming independently earlier claims of the same excess from galactic centre . interpreting this result as a signal of dark matter annihilations to two monochromatic photon channels in galaxy cluster haloes , and fixing the annihilation cross section from the galactic centre data , we determine the annihilation boost factor due to dark matter subhaloes from data .
our results contribute to discrimination of the dark matter annihilations from astrophysical processes and from systematic detector effects as the possible explanations to the fermi - lat excess . .
And you have already written the first three sentences of the full article: it is a prediction of the concordance cold - dark - matter cosmological model that galaxies and galaxy clusters are surrounded by a massive dark matter ( dm ) haloes .
firm evidence for the dm existence is coming from various gravitational effects in astrophysics and cosmology @xcite .
if the existing cosmological dm @xcite is a thermal relic consisting of weakly interacting massive particles , dm annihilations into the standard model particles should provide indirect evidence of dm in cosmic ray experiments @xcite ..
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unfortunately the direct @xcite and indirect @xcite searches for dm particles have all given either negative or contradictory results .
a notable exception to this result is the recent evidence for @xmath1-ray excess with energy 130 gev @xcite in the fermi large area telescope ( lat ) @xcite data .
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10,105 |
Suppose that you have an abstract for a scientific paper: the magnetic fields can change their topology through a process known as magnetic reconnection .
this process in not only important for understanding the origin and evolution of the large - scale magnetic field , but is seen as a possibly efficient particle accelerator producing cosmic rays mainly through the first order fermi process . in this work we study the properties of particle acceleration in reconnection zones and show that the velocity component parallel to the magnetic field of test particles inserted in nearly non - resistive magnetohydrodynamic ( mhd ) domains of reconnection without including kinetic effects , such as pressure anisotropy , the hall term , or anomalous effects , increases exponentially . also , the acceleration of the perpendicular component is always possible in such models .
we have found that within contracting magnetic islands or current sheets the particles accelerate predominantly through the first order fermi process , as previously described , while outside the current sheets and islands the particles experience mostly drift acceleration due to magnetic fields gradients .
considering two dimensional mhd models without a guide field , we find that the parallel acceleration stops at some level .
this saturation effect is however removed in the presence of an out - of - plane guide field or in three dimensional models .
therefore , we stress the importance of the guide field and fully three dimensional studies for a complete understanding of the process of particle acceleration in astrophysical reconnection environments . .
And you have already written the first three sentences of the full article: acceleration of energetic particles is important for a wide range of astrophysical environments , from stellar magnetospheres , accretion disk / jet systems , supernova remnants and gamma ray bursts to clusters of galaxies .
several mechanisms for particle acceleration have been discussed in the literature which include varying magnetic fields in compact sources , stochastic second order fermi process in turbulent interstellar and intracluster media , and the first order fermi process behind shocks .
an alternative , less explored mechanism so far , involves particle acceleration in magnetic reconnection sites , and this will be the focus of the present work which is a first of a series of papers on this subject . for a comprehensive recent review on particle acceleration mechanisms the reader is referred to @xcite ..
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magnetic reconnection may occur when two magnetic fluxes of opposite polarity encounter each other . in the presence of finite magnetic resistivity , the converging magnetic lines annihilate at the discontinuity surface and a current sheet forms there .
it is common knowledge that magnetic fields stay frozen in highly conductive fluids .
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10,106 |
Suppose that you have an abstract for a scientific paper: the structures of odd - odd @xmath0 nuclei in the lower _ fp _ shell have been investigated with a new isospin - nonconserving microscopical interaction .
the interaction is derived from a high - precision charge - dependent bonn nucleon - nucleon potential using the folded - diagram renormalization method .
excellent agreements with experimental data have been obtained up to band terminations .
particularly , the relative positions of @xmath1 and @xmath2 bands were well reproduced .
calculations with another interaction obtained from the idaho - a chiral potential showed similar results .
our calculations also give a good description of the existence of high - spin isomeric states in the @xmath3 sub - shell . as examples , the spectroscopies and isospin structures of @xmath4v and @xmath5mn
have been discussed in detail , with the useful predictions of level structures including electromagnetic properties .
results for @xmath5mn were analyzed where experimental observations are still insufficient . .
And you have already written the first three sentences of the full article: nuclei with the equal numbers of neutrons and protons ( @xmath0 ) have become a special ground to investigate neutron - proton ( _ np _ ) correlations . in @xmath0 nuclei ,
neutrons and protons occupy the same shell - model orbits , leading to large spatial overlaps between neutron and proton wave functions .
the _ np _ pairing is further enhanced in odd - odd @xmath0 nuclei due to odd neutron and odd proton correlation ..
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the _ np _ residual pairing interaction can be equally important as the neutron - neutron ( _ nn _ , @xmath6 ) and proton - proton ( _ pp _ , @xmath7 ) pairings .
while _ nn _ and _ pp _ pairings have been well established in terms of the simple bcs model , the _ np _ pairing is still an open question that has motivated many recent theoretical and experimental works @xcite .
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10,107 |
Suppose that you have an abstract for a scientific paper: the understanding of complex systems has become a central issue because complex systems exist in a wide range of scientific disciplines .
time series are typical experimental results we have about complex systems . in the analysis of such time series ,
stationary situations have been extensively studied and correlations have been found to be a very powerful tool . yet most natural processes are non - stationary . in particular , in times of crisis , accident or trouble , stationarity is lost . as examples
we may think of financial markets , biological systems , reactors ( both chemical and nuclear ) or the weather . in non - stationary situations analysis
becomes very difficult and noise is a severe problem .
following a natural urge to search for order in the system , we endeavor to define states through which systems pass and in which they remain for short times .
success in this respect would allow to get a better understanding of the system and might even lead to methods for controlling the system in more efficient ways .
we here concentrate on financial markets because of the easy access we have to good data , because of our previous experience and last but not least because of the strong non - stationary effects recently seen .
we analyze the s&p 500 stocks in the 19-year period 1992 - 2010 . here , we propose such an above mentioned definition of state for a financial market and use it to identify points of drastic change in the correlation structure .
these points are mapped to occurrences of financial crises .
we find that a wide variety of characteristic correlation structure patterns exist in the observation time window , and that these characteristic correlation structure patterns can be classified into several typical `` market states '' .
using this classification we recognize transitions between different market states . a similarity measure
we develop thus affords means of understanding changes in states and of recognizing developments not previously seen .
the....
And you have already written the first three sentences of the full article: our findings offer insight for constructing an `` early warning system '' for financial markets . by providing a simple instrument to identify similarities to previous states during an upcoming crisis
, one can judge the current situation properly and be prepared to react if the crisis materializes .
another indication for a crisis is given when the correlation structure undergoes rapid changes ..
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using the similarity measure we were able to classify several typical market states between which the market jumps back and forth .
some of these states can easily be identified in the similarity measure .
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10,108 |
Suppose that you have an abstract for a scientific paper: fermion zero modes for abelian bps monopoles are considered . in the spherically symmetric case
the normalisable zero modes are determined for arbitrary monopole charge @xmath0 .
if @xmath1 the zero modes are zero along @xmath2 half - lines emanating from the monopole .
keywords : abelian gauge theory , bps monopoles , weyl equation , fermion zero modes .
fermion zero modes for bps monopoles can be constructed via the same nahm transform used to obtain the monopoles @xcite .
the construction is , however , cumbersome for magnetic charge @xmath3 . in this letter
we obtain zero modes for abelian bps monopoles .
our approach is to directly integrate the weyl equations in three - dimensional space rather than use nahm s method ( which has been adapted to abelian monopoles in @xcite ) .
the abelian bps equations read @xmath4 where @xmath5 is a real higgs field and @xmath6 is a magnetic field derived from a vector potential @xmath7 .
the maxwell equation @xmath8 implies that the higgs field @xmath5 obeys the laplace equation . the higgs field
@xmath9 with @xmath10 and @xmath11 constant , is harmonic away from @xmath0 singularities @xmath12 ( @xmath13 ) .
physically , the system comprises @xmath0 dirac monopoles each with magnetic charge @xmath11 interacting with a higgs field . here
@xmath10 fixes the asymptotic value of the higgs field .
consider the weyl operators @xmath14 where @xmath15 is the electric charge of the fermion and @xmath16 .
these weyl operators assume a real yukawa coupling in minkowski space .
however , identifying @xmath5 as @xmath17 they are also weyl operators for self - dual monopoles defined in euclidean space .
the dirac quantisation condition requires @xmath18 with @xmath19 integer . if @xmath20 and @xmath21 , @xmath22 has @xmath0 normalisable zero modes . in the @xmath23 case
we have @xmath24 taking the origin as the location of the monopole and @xmath25 denote spherical polar coordinates . here
the dirac string lies on the positive....
And you have already written the first three sentences of the full article: the components of @xmath22 associated with ( [ higgsn ] ) are ( @xmath67 ) w. nahm , phys . lett .
b * 93 * ( 1980 ) 42 .
r. jackiw and c. rebbi , phys ..
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d * 13 * ( 1976 ) 3398 .
a. gonzalez - arroyo and y. a. simonov , nucl .
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10,109 |
Suppose that you have an abstract for a scientific paper: we study confluent @xmath0-hypergeometric functions introduced by adolphson @xcite . in particular
, we give their integral representations by using rapid decay homology cycles of hien @xcite and @xcite .
the method of toric compactifications introduced in @xcite and @xcite will be used to prove our main theorem .
moreover we apply it to obtain a formula for the asymptotic expansions at infinity of confluent @xmath0-hypergeometric functions . .
And you have already written the first three sentences of the full article: the theory of @xmath0-hypergeometric systems introduced by gelfand - kapranov - zelevinsky @xcite is a vast generalization of that of classical hypergeometric differential equations . as in the case of hypergeometric equations , the holomorphic solutions to
their @xmath0-hypergeometric systems ( i.e. the @xmath0-hypergeometric functions ) admit @xmath1-series expansions ( @xcite ) and integral representations ( @xcite ) .
moreover this theory has deep connections with many other fields of mathematics , such as toric varieties , projective duality , period integrals , mirror symmetry , enumerative algebraic geometry and combinatorics . also from the viewpoint of the @xmath2-module theory ( see @xcite and @xcite etc . ) , @xmath0-hypergeometric @xmath2-modules are very elegantly constructed in @xcite ..
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for the recent development of this subject see @xcite and @xcite etc . in @xcite , @xcite , @xcite and @xcite etc .
the monodromies of their @xmath0-hypergeometric functions were studied . in
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10,110 |
Suppose that you have an abstract for a scientific paper: we use high - resolution hydrodynamic re - simulations to investigate the properties of the thermal sunyaev - zeldovich ( sz ) effect from galaxy clusters . we compare results obtained using different physical models for the intracluster medium ( icm ) , and
show how they modify the sz emission in terms of cluster profiles and scaling relations .
we also produce realistic mock observations to verify whether the results from hydrodynamic simulations can be confirmed .
we find that sz profiles depend marginally on the modelled physical processes , while they exhibit a strong dependence on cluster mass .
the central and total sz emission strongly correlate with the cluster x - ray luminosity and temperature .
the logarithmic slopes of these scaling relations differ from the self - similar predictions by less than 0.2 ; the normalization of the relations is lower for simulations including radiative cooling .
the observational test suggests that sz cluster profiles are unlikely to be able to probe the icm physics .
the total sz decrement appears to be an observable much more robust than the central intensity , and we suggest using the former to investigate scaling relations .
[ firstpage ] cosmic microwave background galaxies : clusters : general hydrodynamics methods : numerical .
And you have already written the first three sentences of the full article: galaxy clusters are ideal probes for studies of large scale structures .
they have typical masses of order @xmath0 ; within a radius of a few mpc they contain hundreds of galaxies orbiting in a gravitational potential well due primarily to dark matter ( dm ) .
they are also filled with icm : hot ionized gas , typically at a temperature of 1 - 15 kev , that can be observed via its bremsstrahlung emission in the soft x - ray band , and via the sunyaev - zeldovich ( sz ) effect in the millimetric band . several observational evidences.
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demonstrate that the picture of an icm in hydrostatic equilibrium in the dm potential well of the cluster is an over - simplification : above all , scaling relations between various cluster properties , like mass , temperature and x - ray luminosity , differ from the self - similar predictions ( see , e.g. , the recent reviews by * ? ? ?
* ; * ? ? ?
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10,111 |
Suppose that you have an abstract for a scientific paper: a large sample of low surface brightness ( lsb ) disk galaxies is selected from sdss with b - band central surface brightness @xmath0(b ) from 22 to 24.5 mag arcsec@xmath1 .
some of their properties are studied , such as magnitudes , surface brightness , scalelengths , colors , metallicities , stellar populations , stellar masses and multiwavelength seds from uv to ir etc .
these properties of lsb galaxies have been compared with those of the galaxies with higher surface brightnesses .
then we check the variations of these properties following surface brightness . .
And you have already written the first three sentences of the full article: low surface brightness galaxies ( lsbgs ) are important populations in galaxy field .
however , their contributions to galaxy population have been underestimated for a long time since they are hard to find owing to their faintness compared with the night sky .
an initial quantitative study was made by freeman ( 1970 ) , who noticed that the central surface brightness of their 28 out of 36 disc galaxies fell within a rather narrow range , @xmath0(b)[email protected] mag arcsec@xmath1 ..
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this could be caused by selection effects ( disney 1976 ) .
since then , many efforts have been made to search for large number of lsbgs from surveys ( bothun & impey 1997 ; impey & bothun 1997 ; zhong et al .
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10,112 |
Suppose that you have an abstract for a scientific paper: in a previous paper [ j. chem .
phys . * 121 * 4501 ( 2004 ) ] a unique bipolar decomposition , @xmath0 was presented for stationary bound states @xmath1 of the one - dimensional equation , such that the components @xmath2 and @xmath3 approach their semiclassical wkb analogs in the large action limit . moreover , by applying the madelung - bohm ansatz to the components rather than to @xmath1 itself , the resultant bipolar bohmian mechanical formulation satisfies the correspondence principle . as a result ,
the bipolar quantum trajectories are classical - like and well - behaved , even when @xmath1 has many nodes , or is wildly oscillatory . in this paper ,
the previous decomposition scheme is modified in order to achieve the same desirable properties for stationary scattering states .
discontinuous potential systems are considered ( hard wall , step , square barrier / well ) , for which the bipolar quantum potential is found to be _
zero _ everywhere , except at the discontinuities .
this approach leads to an exact numerical method for computing stationary scattering states of any desired boundary conditions , and reflection and transmission probabilities .
the continuous potential case will be considered in a future publication . .
And you have already written the first three sentences of the full article: much attention has been directed by theoretical / computational chemists towards developing reliable and accurate means for solving dynamical quantum mechanics problems i.e . , for obtaining solutions to the time - dependent equation for molecular systems .
insofar as `` exact '' quantum methods are concerned , two traditional approaches have been used : ( 1 ) representation of the system hamiltonian in a finite , direct - product basis set ; ( 2 ) discretization of the wavefunction onto a rectilinear grid of lattice points over the relevant region of configuration space . both approaches
, however , suffer from the drawback that the computational effort scales exponentially with system dimensionality.@xcite recently , a number of promising new methods have emerged with the potential to alleviate the exponential scaling problem once and for all ..
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these include various basis set optimization methods,@xcite and build - and - prune methods,@xcite such as those based on wavelet techniques.@xcite on the other hand , a completely different approach to the exponential scaling problem is to use basis sets or grid points , that themselves evolve over time .
the idea is that at any given point in time , one need sample a much smaller hilbert subspace , or configuration space region , than would be required at all times thus substantially reducing the size of the calculation . for basis set calculations , much progress along these lines has been achieved by the multi - configurational time - dependent hartree ( mctdh ) method , developed by meyer , manthe and co - workers.@xcite more recently , time - evolving grid , or `` quantum trajectory '' methods@xcite ( qtms ) have also been developed , and for certain types of systems , successfully applied at quite high dimensionalities.@xcite qtms are based on the hydrodynamical picture of quantum mechanics , developed over half a century ago by bohm@xcite and takabayasi,@xcite who built on the earlier work of madelung@xcite and van vleck.@xcite qtms are inherently appealing for a number of reasons .
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10,113 |
Suppose that you have an abstract for a scientific paper: does the imf vary ? is it significantly different in metal - rich environments than in metal - poor ones ?
theoretical work predicts this to be the case .
but in order to provide robust empirical evidence for this , the researcher _ must _ understand _ all _ possible biases affecting the derivation of the stellar mass function .
apart from the very difficult observational challenges , this turns out to be highly non - trivial relying on an exact understanding of how _ stars evolve _ , and how stellar populations in galaxies are assembled dynamically and how individual star clusters and associations evolve .
_ @xmath0-body modelling _ is therefore an unavoidable tool in this game : the case can be made that without complete dynamical modelling of star clusters and associations any statements about the variation of the imf with physical conditions are most probably wrong . the calculations that do exist demonstrate time and again that the imf is invariant : there exists no statistically meaningful evidence for a variation of the imf from metal - poor to metal - rich populations .
this means that currently existing star - formation theory fails to describe the stellar outcome .
indirect evidence , based on chemical evolution calculations , however indicate that extreme star - bursts that assembled bulges and elliptical galaxies may have had a top - heavy imf .
[ 1996/06/01 ] .
And you have already written the first three sentences of the full article: the stellar initial mass function ( imf ) , @xmath1 , where @xmath2 is the stellar mass , is the parent distribution function of the masses of stars formed in _ one _ event . here
, the number of stars in the mass interval @xmath3 is @xmath4 .
salpeter ( 1955 ) inferred the imf from solar - neighbourhood star - counts applying corrections for stellar evolution and galactic - disk structure finding @xmath5 , for @xmath6 ..
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miller & scalo ( 1979 ) and scalo ( 1986 ) derived the imf for @xmath7 using better data and a more sophisticated analysis establishing that the imf flattens or turns - over at small masses .
modern studies of solar - neighbourhood star - count data which also apply detailed corrections for unknown multiple systems in the star - counts , confirm that @xmath8 for @xmath9 ( kroupa , tout & gilmore 1993 ; kroupa 1995b ; reid , gizis & hawley 2002 ) .
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10,114 |
Suppose that you have an abstract for a scientific paper: we use model selection forecasting to assess the ability of the planck satellite to make a positive detection of spectral index running .
we simulate planck data for a range of assumed cosmological parameter values , and carry out a three - way bayesian model comparison of a harrison zeldovich model , a power - law model , and a model including running .
we find that planck will be able to strongly support running only if its true value satisfies @xmath0 .
cosmology : theory .
And you have already written the first three sentences of the full article: results from the wilkinson microwave anisotropy probe ( wmap ) , especially the first - year data @xcite and to some extent the three - year data @xcite , have placed a focus on possible running of the spectral index of density perturbations ( see e.g. lidsey & tavakol 2003 ; kawasaki , yamaguchi & yokoyama 2003 ; chung , shiu & trodden 2003 ; bastero - gil , freese & mersini - houghton 2003 ; chen et al . 2004 ; covi et al . 2004 ; ashoorioon , hovdebo & mann 2005 ; ballesteros , casas & espinosa 2006 ; cline & hoi 2006 ; corts & liddle 2006 ; easther & peiris 2006 ) .
it is certainly premature to draw any strong conclusions based on existing evidence , especially as it remains controversial whether current data even support power - law models over the harrison
zeldovich ( hz ) model , but it is timely to investigate the extent to which the upcoming planck satellite may resolve the situation . as we have stressed in several recent papers ( e.g. mukherjee , parkinson & liddle 2006a ; parkinson , mukherjee & liddle 2006 ; liddle , mukherjee & parkinson 2006a ) , the appropriate statistical tool for assessing the need to introduce new parameters is _ model selection _ @xcite ..
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model selection assigns probabilities to _ sets _ of parameters , i.e. models , in addition to the usual probability distributions for parameter values within each model .
for example , bayesian model selection applied to data compilations including wmap3 shows that the case for including even just the spectral index @xmath1 as a variable fit parameter is inconclusive @xcite . in a recent paper @xcite
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10,115 |
Suppose that you have an abstract for a scientific paper: we present numerical results concerning the solution of the time - harmonic maxwell equations discretized by discontinuous galerkin methods . in particular ,
a numerical study of the convergence , which compares different strategies proposed in the literature for the elliptic maxwell equations , is performed in the two - dimensional case . ,
, , time - harmonic maxwell s equations , discontinuous galerkin methods . .
And you have already written the first three sentences of the full article: this work is concerned with the numerical solution of the time - harmonic maxwell equations discretized by discontinuous galerkin methods on unstructured meshes .
our motivation for using a discontinuous galerkin method is the enhanced flexibility compared to the conforming edge element method @xcite : for instance , dealing with non - conforming meshes is straightforward and the choice of the local approximation space is not constrained .
nonetheless , before taking full advantage of these features , it is required to carefully study the basic ingredients of the method such as the choice of the numerical flux at the interface between neighboring elements . in the context of time - harmonic problems ,.
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the design of efficient solution strategies for the resulting sparse linear systems is an equally important question .
previous works have shown convergence results for discontinuous galerkin methods applied to the time - harmonic maxwell equations , studied in the form of second - order vector wave equations .
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10,116 |
Suppose that you have an abstract for a scientific paper: this paper introduces a number of new intrinsically 3-linked graphs through five new constructions .
we then prove that intrinsic 3-linkedness is not preserved by @xmath0 moves .
we will see that the graph @xmath1 , which is obtained through a @xmath0 move on @xmath2 , is not intrinsically 3-linked . .
And you have already written the first three sentences of the full article: a graph , @xmath3 , is _ intrinsically knotted _ if every embedding of @xmath3 in @xmath4 contains a nontrivial knot .
a link @xmath5 is _ splittable _ if there is an embedding of a 2-sphere @xmath6 in @xmath7 such that each component of @xmath8 contains at least one component of @xmath5 .
if @xmath5 is not splittable it is called _ non - split_. a graph , @xmath3 , is _ intrinsically linked _.
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if every embedding of @xmath3 in @xmath4 contains a non - split link . a graph , @xmath3 , is _ minor minimal with respect to being intrinsically linked _ ( or simply _ minor minimal intrinsically linked _ ) if @xmath3 is intrinsically linked and no minor of @xmath3 is intrinsically linked .
the combined work of conway and gordon @xcite , sachs @xcite , and robertson , seymour , and thomas @xcite fully characterizes intrinsically linked graphs .
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10,117 |
Suppose that you have an abstract for a scientific paper: we present an effective hamiltonian for a bilayer quantum hall system at filling factor @xmath0 neglecting charge fluctuations .
our model is formulated in terms of spin and pseudospin operators and is an exact representation of the system within the above approximation .
we analyze its low - lying excitations in terms of spin - wave theory .
moreover we add to previous first - principle exact - diagonalization studies concentrating on the quantum phase transition seen in this system . .
And you have already written the first three sentences of the full article: at small layer separations , the ground state of a @xmath0 bilayer quantum hall system exhibits spontaneous interlayer phase coherence .
interest in this issue has been renewed by intriguing tunneling transport measurements by spielman _
_ showing a very pronounced conductance peak at zero bias voltage @xcite for sufficiently small values of the ratio of layer separation to magnetic length ..
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the quantum phase transiton underlying this phenomenon has been investigated recently in an exact diagonalization study using the spherical geometry @xcite .
the results suggest that a single phase transition , likely of first order , separates incompressible states with strong interlayer correlations from compressible states with weak interlayer correlations . in the present work we report on a study of @xmath0 quantum hall bilayer using a different approach introducing an effective spin - pseudospin model on an imaginary lattice in the lowest landau level ( lll ) orbital space
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10,118 |
Suppose that you have an abstract for a scientific paper: we study three transient x - ray sources , that were bright in the central region of m31 galaxy in the year 2000
. observations with _
chandra _ and _ xmm - newton _ allowed us for the first time in the history of x - ray astronomy , to build light curves of transient sources in m31 suitable for studying their variability on a time scale of months and , in some periods , weeks .
the three sources demonstrate distinctly different types of x - ray variability and spectral evolution .
xmmu j004234.1 + 411808 is most likely a black hole candidate based on the similarity of its x - ray light curve and spectra to typical transient low - mass x - ray binaries observed in our galaxy .
the outburst of cxo j004242.0 + 411608 lasted longer than a year , which makes the source an unusual x - ray transient .
the supersoft transient xmmu j004319.4 + 411759 is probably a classical nova - like system containing a magnetized , rapidly - spinning white dwarf .
we estimate a total rate of x - ray transient outbursts in the central bulge of m31 to be of the order @xmath0 per year . the rate of the hard x - ray transients ( @xmath1 year@xmath2 ) in the central part of the andromeda galaxy appears to be comparable to that of the central part of our own galaxy . *
# 1#1 .
And you have already written the first three sentences of the full article: there are about 200 known x - ray binaries in our galaxy .
these contain either a neutron star or a black hole ( @xcite ) .
about one third of them are classified as transients ( see @xcite for a review).some of the x - ray transients , most notably be - binary pulsars , erupt on regular intervals , while others erupt dramatically , but irregularly , with peak luminosities above 10@xmath3 erg / s and typical decay timesorder a month ..
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this last group represent the majority of known galactic black hole candidates , and provides the best opportunity to study the processes near black hole in relative proximity to the earth .
galactic transients have been therefore a focus of substantial observational and theoretical effort by x - ray astronomers .
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10,119 |
Suppose that you have an abstract for a scientific paper: a quasi one dimensional system of trapped , repulsively interacting atoms ( e.g. , an ion chain ) exhibits a structural phase transition from a linear chain to a zigzag structure , tuned by reducing the transverse trap potential or increasing the particle density .
since it is a one dimensional transition , it takes place at zero temperature and therefore quantum fluctuations dominate . in [ fishman , _ et al .
_ , phys .
rev .
b * 77 * , 064111 ( 2008 ) ] it was shown that the system close to the linear - zigzag instability is described by a @xmath0 model .
we propose a mapping of the @xmath0 field theory to the well known ising chain in a transverse field , which exhibits a quantum critical point .
based on this mapping , we estimate the quantum critical point in terms of the system parameters .
this estimate gives the critical value of the transverse trap frequency for which the quantum phase transition occurs , and which has a finite , measurable deviation from the critical point evaluated within the classical theory .
a measurement is suggested for atomic systems which can probe the critical trap frequency at sufficiently low temperatures @xmath1 .
we focus in particular on a trapped ion system , and estimate the implied limitations on @xmath1 and on the interparticle distance .
we conclude that the experimental observation of the quantum critical behavior is in principle accessible . .
And you have already written the first three sentences of the full article: the structural transition from a linear chain of repulsively interacting particles to a planar configuration , in the form of a zigzag structure , has been often discussed in theoretical studies on atomic and condensed matter systems .
examples include electrons in nanowires @xcite , ultracold dipolar gases @xcite , vortex lines in bose - einstein condensates @xcite , and ion coulomb crystals in traps @xcite .
specifically in ion coulomb crystals this transition has been experimentally observed and characterized @xcite , thereby determining a phase diagram of the ionic structures as a function of the trap aspect ratio and of the mean interparticle distance @xcite ..
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theoretical studies demonstrated that the transition from the string to the zigzag chain is associated with a symmetry breaking .
more specifically , if the hamiltonian is invariant under rotation about the string axis , it is the rotational symmetry around the chain which is broken in the zigzag phase .
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10,120 |
Suppose that you have an abstract for a scientific paper: magic currently is the largest imaging atmospheric cerenkov telescope world - wide . since 2004 , @xmath0-ray emission from several active galactic nuclei in the gev / tev energy range has been detected , some of which were newly discovered as very - high energy @xmath0-ray sources .
the @xmath0-rays are assumed to originate from particle acceleration processes in the agn jets .
we give an overview of the agn observed and detected by magic , discuss spectral and temporal properties of these and show physics implications of some selected observations . .
And you have already written the first three sentences of the full article: the study of very high energy ( vhe , @xmath1 gev ) @xmath0-ray emission from active galactic nuclei ( agn ) is one of the major goals of ground - based @xmath0-ray astronomy .
the sensitivity of the current imaging air cerenkov telescopes ( iact ) enables phenomenological studies of the physics inside the relativistic jets in blazars , and in particular advances in understanding both the origin of the vhe @xmath0-rays as well as the relations between photons of different energies ( from radio to vhe ) . except for the radio galaxy m87 ,
all 17 currently known vhe gamma - ray emitting agns @xcite are blazars , rwagner / sources/ for an up - to - date source list . ] which are characterized by a close orientation of the jets with the line of sight ..
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their spectra are dominated by non - thermal emission that consists of two distinct broad components . while the low energy bump , located at optical to x - ray energies , is unisonously explained by synchrotron emission of electrons , the origin of the high - energy part of the spectrum is still debated .
leptonic models ascribe it to inverse compton processes that either up - scatter synchrotron photons , or to external photons that originate from the accretion disk , from nearby massive stars , or are reflected into the jet by surrounding material . in hadronic models , interactions of a highly relativistic jet outflow with ambient matter , proton - induced cascades , or synchrotron radiation off protons , are responsible for the high energy photons .
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10,121 |
Suppose that you have an abstract for a scientific paper: we consider the gravastar model where the vacuum phase transition between the de sitter interior and the schwarzschild or schwarzschild de sitter exterior geometries takes place at a single spherical @xmath0-shell .
we derive sharp analytic bounds on the surface compactness ( @xmath1 ) that follow from the requirement that the dominant energy condition ( dec ) holds at the shell . in the case of schwarzschild exterior ,
the highest surface compactness is achieved with the stiff shell in the limit of vanishing ( dark ) energy density in the interior . in the case of schwarzschild
de sitter exterior , in addition to the gravastar configurations with the shell under surface pressure , gravastar configurations with vanishing shell pressure ( dust shells ) , as well as configurations with the shell under surface tension , are allowed by the dec .
respective bounds on the surface compactness are derived for all cases .
we also consider the speed of sound on the shell as derived from the requirement that the shell is stable against the radial perturbations .
the causality requirement ( sound speed not exceeding that of light ) further restricts the space of allowed gravastar configurations . .
And you have already written the first three sentences of the full article: the gravastar model has been proposed by mazur and mottola ( mm ) as a possible end point of the gravitational collapse of a massive body @xcite .
as opposed to the classical scenario of the gravitational collapse into a schwarzschild black hole , the gravastar concept avoids the formation of the black hole horizon . technically , the gravastar is a global , static , spherically symmetric solution to the einstein equations . in the interior
there is a segment of the de sitter geometry which is matched to the exterior schwarzschild geometry by means of a spherical shell of matter . in the original mm model the quantum phase transition takes place within the boundary layer / shell , but the full quantum treatment is immediately replaced by the mean field approximation in which ( classical ) einstein equations are valid ..
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the de sitter geometry in the interior of the gravastar implies constant positive ( dark ) energy density @xmath2 accompanied by the isotropic negative pressure @xmath3 .
such energy - momentum content of the spacetime is equivalent to introducing the positive cosmological constant @xmath4 into the einstein equations , and can be understood as the gravitational vacuum , or gravitational condensate , which motivated the coining of the term gravastar ( _ _ gra__vitational _ _ va__cuum _ star _ ) . in this original model of mm ,
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10,122 |
Suppose that you have an abstract for a scientific paper: we predict the coexistence of both te- and tm - polarized localized electromagnetic waves that can propagate _ in the same frequency range _ along a graphene layer inserted in a photonic crystal .
in addition , we studied the excitation of these modes by an external wave and have shown that the resonance peaks of the sample transmissivity should be observed due to the excitation of the localized waves , independently of the polarization of the exciting wave .
the simplicity of the derived dispersion relations for the localized modes and the possibility to excite waves of both polarizations provide a method for measuring graphene conductivity . .
And you have already written the first three sentences of the full article: the unusual and remarkable transport properties of graphene have attracted considerable attention , including : an unconventional quantum hall effect @xcite ; the possibility of testing the klein paradox @xcite ; the aharonov - bohm effect in graphene rings @xcite , as well as mesoscopic effects , such as weak localization @xcite , conductance fluctuations @xcite , quantum noise @xcite , coulomb blockade @xcite , and anderson localization @xcite ; specular andreev reflection and josephson effect @xcite ; formation of a wigner crystal @xcite ; voltage - driven quantum oscillations of the conductance @xcite ; intriguing electron lensing @xcite , and other fascinating phenomena ( see , e.g. , refs . and references therein ) .
studies of graphene are also inspired by its potential application in nanoelectronic devices , because the electron concentration can vary considerably due to applied electric fields , and graphene can have both electrons and holes as high - mobility charge carriers .
a main feature of the graphene electron structure , which is very different from conventional two - dimensional electron systems , is the existence of six dirac cones at the corners of an hexagon - shaped brillouin zone with a massless linear electron - hole dispersion ..
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this specific spectrum for the charge carriers leads to a number of interesting transport properties , or imparts new features to them .
the phenomena listed above are caused by the quantum peculiarities of graphene , and these manifest at the _ quantum _ level .
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10,123 |
Suppose that you have an abstract for a scientific paper: common methods for calculating a planet s annual insolation by latitude have relied on computationally heavy or complex computer algorithms . in this paper , we show that mean annual insolation by latitude of a planet with obliquity angle @xmath0 can be found by taking the definite integral of a function of longitude . this leads to faster computations and more accurate results .
we discuss differences between our method and selected computational results for insolation found in the literature . .
And you have already written the first three sentences of the full article: incoming solar radiation at the top of the atmosphere is an important quantity in many areas of earths systems modeling .
this physical quantity is needed in areas ranging from low dimensional energy balance models ( e.g. the budyko energy balance model @xcite ) to large global circulation models , gcms , ( e.g. nasa s modele ar5 @xcite ) .
it is common practice to compute insolation by latitude using computer algorithms ..
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for example , nasa s latitudinal insolation calculations for modele ar5 rely on three fortran subroutines that 1 ) calculate earth s orbital parameters ( eccentricity , obliquity , and longitude of perihelion ) as a function of year , 2 ) calculate distance to the sun and declination angle as functions of time of year and orbital parameters , and 3 ) calculate the time integrated zentih angle as a function of the declination angle and the time interval of the day @xcite .
these computer calculations are useful if you are working with a grid version of a planet ( as is typical in gcm s ) , however , to convert this information to useable data for other modeling scenarios is not always straightforward .
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10,124 |
Suppose that you have an abstract for a scientific paper: spectra of the qso pair q0307 - 195a , b have been obtained in the ly@xmath0forest ( 36603930 ) and ( 47204850 ) regions with a fwhm resolution between 0.7 and 0.5 .
46 lines have been detected in the spectrum of object a while 36 in the spectrum of object b , of them 29 and 20 were identified as ly@xmath0absorptions respectively .
the present observations have been supplemented with data of comparable quality on other 7 qso pairs available in the literature to give an enlarged sample of 217 ly@xmath0 lines with rest equivalent width @xmath1 .
the analysis of the hits ( i.e. when an absorption line appears in both qso spectra ) and misses ( i.e. when a line is seen in any of the qso spectra , but no line is seen in the other ) , carried out with an improved statistical approach , indicates that the absorbers have typically a large size km s@xmath2 mpc@xmath2 ) , @xmath3 . ] : @xmath4 kpc , with 95% confidence limits @xmath5 kpc and @xmath6 kpc , with 95% confidence limits @xmath7 kpc for the radius of idealized spherical and disc geometries , respectively .
the present data do not allow to establish any correlation of the typical inferred size with the proper separation or with the redshift of the pairs .
the correlation between the observed equivalent widths of the absorbers in the adjacent lines of sight becomes poorer and poorer with increasing proper separation .
a disc geometry with a column density profile @xmath8 , @xmath9 , is found to reasonably reproduce the data with @xmath10 kpc , but also spherical clouds with the same column density profile and a power - law distribution of radii may give a satisfactory representation of the observations . .
And you have already written the first three sentences of the full article: closely separated qso pairs and gravitationally lensed qsos provide two or more adjacent lines of sight ( los ) , which allow to sample the size and clustering of the absorbers .
the ray path separation of gravitationally lensed qsos usually spans subgalactic scales ; studies of these spectra have shown that the ly@xmath0 clouds are much larger than a few kiloparsecs ( weymann & foltz 1983 ; foltz et al .
1984 ; smette et al ..
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1992 , 1995 ) .
further results again pointing at very large sizes have been obtained for los separations of a few arcminutes or less ( shaver & robertson 1983 , sr83 ; crotts 1989 ; dinshaw et al .
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10,125 |
Suppose that you have an abstract for a scientific paper: using a cell dynamic system ( cds ) simulation scheme , we investigate the phase - ordering dynamics of non - conserved @xmath0 models without topological defects , i.e. for @xmath1 where @xmath2 is the spatial dimensionality .
in particular , we consider zero - temperature quenches for @xmath3 , @xmath4 , and for @xmath5 , @xmath6 .
we find , in agreement with previous simulations using fixed - length spins , that dynamical scaling is obtained , with characteristic length @xmath7 .
we show that the asymptotic behaviour of the structure - factor scaling function @xmath8 is well fitted by the stretched exponential form @xmath9 , with an exponent @xmath10 that appears to depend on both @xmath11 and @xmath2 .
an analytical treatment of an approximate large-@xmath11 equation for the pair correlation function yields @xmath12 , with @xmath13 for large @xmath11 , in agreement with recent simulations of the same equation . .
And you have already written the first three sentences of the full article: the phase - ordering dynamics of systems quenched from a high - temperature disordered state into an ordered state is a problem of great relevance in the description of out - of - equilibrium pattern formation @xcite .
one well established property is the onset of dynamic scaling , where the late - time behaviour of the order - parameter correlation functions is described by scaling forms with a single time - dependent length scale @xmath14 .
thus the real - space correlation function is found to have the scaling form @xmath15 while its fourier transform , the structure factor , has the corresponding scaling form @xmath16^d g(kl(t))\ ..
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\label{scaling : fourier}\ ] ] conventional experimental systems such as binary alloys and binary liquids are described by a scalar order parameter .
recently , however , there has been much interest in systems with more complicated order parameters such as @xmath11-component vectors ( the @xmath0 model ) @xcite@xcite and traceless symmetric tensors ( nematic liquid crystals ) @xcite . in this paper
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10,126 |
Suppose that you have an abstract for a scientific paper: delamination is a typical failure mode of composite materials caused by weak bonding .
it arises when a crack initiates and propagates under a destructive loading .
given the physical law characterizing the properties of the interlayer adhesive between the bonded bodies , we consider the problem of computing the propagation of the crack front and the stress field along the contact boundary .
this leads to a hemivariational inequality , which after discretization by finite elements we solve by a nonconvex bundle method , where upper-@xmath0 criteria have to be minimized . as this is in contrast with other classes of mechanical problems with non - monotone friction laws and in other applied fields , where criteria are typically lower-@xmath0 ,
we propose a bundle method suited for both types of nonsmoothness .
we prove its global convergence in the sense of subsequences and test it on a typical delamination problem of material sciences .
* key words . *
composite material @xmath1 delamination @xmath1 crack front propagation @xmath1 hemivariational inequality @xmath1 clarke directional derivative @xmath1 nonconvex bundle method @xmath1 lower- and upper-@xmath0 function @xmath1 convergence .
institut de mathmatiques , universit de toulouse , france ] institute of mathematics , department of aerospace engineering , universitt der bundeswehr mnchen , germany ] .
And you have already written the first three sentences of the full article: we develop a bundle technique to solve nonconvex variational problems arising in contact mechanics and in other applied fields .
we are specifically interested in the delamination of composite structures with an adhesive bonding under destructive loading , a failure mode which is studied in the material sciences .
when the properties of the interlayer adhesive between the bonded bodies are given in the form of a physical law relating the normal component of the stress vector to the relative displacement between the upper and lower boundaries at the crack tip , the challenge is to compute the displacement and stress fields in order to assess the reactive destructive forces along the contact boundary , as the latter are difficult to measure in situ ..
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this leads to minimization of an energy functional , where a specific form of nonsmoothness arises in the boundary integral at the contact boundary .
after discretization via piecewise linear finite elements using the trapezoidal quadrature rule , this leads to a finite - dimensional nonsmooth optimization problem of the form @xmath2 where @xmath3 is locally lipschitz and neither smooth nor convex . depending on the nature of the frictional forces , the criterion
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Suppose that you have an abstract for a scientific paper: the crystal structure and magnetic ordering pattern of pdas@xmath0o@xmath1 were investigated by neutron powder diffraction .
while the magnetic structure of pdas@xmath0o@xmath1 is identical to the one of its isostructural @xmath2-homologue nias@xmath0o@xmath1 , its nel temperature ( 140 k ) is much higher than the one of nias@xmath0o@xmath1 ( 30 k ) .
this is surprising in view of the long distance and indirect exchange path between the magnetic pd@xmath3 ions .
density functional calculations yield insight into the electronic structure and the geometry of the exchange - bond network of both pdas@xmath0o@xmath1 and nias@xmath0o@xmath1 , and provide a semi - quantitative explanation of the large amplitude difference between their primary exchange interaction parameters . .
And you have already written the first three sentences of the full article: the magnetic properties of transition metal compounds with @xmath2 valence electrons have been one of the central research themes in solid - state physics for the past three decades . in view of the interplay between magnetism and high - temperature superconductivity ,
particular attention has been focused on oxides and arsenides .
recently , the electronic structure and ordering phenomena of transition metal compounds with @xmath4 and @xmath5 valence electrons ( such as ruthenates and iridates ) have also captured much attention ..
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the electronic correlations in these materials are generally weaker than those of their @xmath2 counterparts , while the spin - orbit coupling is stronger .
the quantitative description of the influence of these parameters on the electronic phase behavior of @xmath6-electron compounds is an important topic of current research .
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10,128 |
Suppose that you have an abstract for a scientific paper: we study the out - of - equilibrium current through a quantum dot which is placed between two superconducting leads held at fixed voltage bias , considering both cases of the absence and the presence of an additional normal lead connected to the dot . using the non - equilibrium keldysh technique
, we focus on the subgap bias region , where multiple andreev reflections ( mar ) are responsible for charge transfer through the dot . attention is put on the dc current and on the first harmonics of the supercurrent .
varying the position and/or the width of the dot level , we first investigate the crossover between a quantum dot and quantum point contact regimes in the absence of a normal lead .
we then study the effect of the normal electrode connected to the dot , which is understood to lead to dephasing , or alternatively to induce reverse proximity effect . by increasing the dot coupling to the normal probe
, we show the full crossover from zero dephasing to the incoherent case .
we also compute the josephson current in the presence of the normal lead , and find it in excellent agreement with the values of the non - equlibrium current extrapolated at zero voltage . .
And you have already written the first three sentences of the full article: non equilibrium transport between superconductors with a dc voltage bias gives rise to a subgap structure in the current voltage characteristics which can be described in terms of multiple andreev reflections ( mar)@xcite . indeed , it has been understood since the sixties@xcite that when the bias potential between two superconductors is smaller than the superconducting energy gap , electrons have to be transferred in bunches in order to satisfy energy requirements .
the calculation of the current in the presence of such mar processes can proceed along several directions .
early work@xcite considered a formulation of transport in terms of transmission probabilities rather than amplitudes . during the last decade or so , mar processes have been studied theoretically in the coherent regime for point contacts , using either scattering theory@xcite or microscopic tight binding hamiltonians@xcite ..
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the coherent current which flows between the two superconductors is then time dependent : it contains all harmonics of the josephson frequency . of particular interest in ref .
was the fact that in addition to the dc current , the cosine and sine harmonics of the current were computed .
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Suppose that you have an abstract for a scientific paper: we provide a derivation of a spin skyrmion number classification for two - dimensional topological superconductors constructed from ferromagnetic and rashba spin - orbit coupled semiconductor - superconductor heterostructures .
we show that in the non - trivial topological phase , characterized by a non - zero chern number , there is always a topological spin texture in the occupied bands represented by a skyrmion number .
the skyrmion number has the advantage of being both physically intuitive and directly measurable using spin - sensitive band structure imaging techniques .
in addition , we show that the skyrmion classification can be extended to the equivalent one - dimensional topological superconductors . .
And you have already written the first three sentences of the full article: classification of matter into different ordered phases is a central theme in condensed matter physics .
traditionally , ordered phases have been understood using the ginzburg - landau paradigm,@xcite where spontaneous symmetry breaking gives rise to a finite order parameter , such as a finite magnetization in a ferromagnet .
starting with the integer quantum hall effect,@xcite another classification paradigm based on the topological properties of the band structure has also emerged.@xcite with the recent discovery of topological insulators it has now become a reoccurring task to classify different phases of matter according to the topological properties of their ( single - particle ) band structure.
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. superconductors with a full pairing gap can be classified into different topological classes in much the same way as band insulators.@xcite non - trivial topological superconductors have lately received an enormous amount of attention,@xcite due to the possibility of them hosting majorana fermions at e.g. interfaces and vortices.@xcite the majorana fermion is its own anti - particle and obeys non - abelian statistics , which can be used for fault - tolerant topological quantum computation.@xcite the majorana state is a consequence of the bulk - boundary correspondence , which establishes that non - trivial topological order in the bulk necessarily gives rise to boundary states crossing the bulk energy gap.@xcite in some topological superconductors the resulting zero energy modes are majorana fermions . proposals for 2d topological superconductors with majorana fermions exist already , in e.g. superconducting hybrid structures between a conventional @xmath0-wave superconductor and topological insulators or ferromagnetic and rashba spin - orbit coupled semiconductors with finite magnetization.@xcite the latter alternative is particularly interesting since semiconductor technology is very mature , there exists semiconductors with large spin - orbit coupling@xcite and with demonstrated superconducting proximity effect@xcite , while ferromagnetism can be introduced either through proximity to a ferromagnetic insulator or through an applied magnetic field .
all key ingredients are thus in place for finding majorana fermions.@xcite in fact , possible experimental signatures of majorana fermions have already been reported in similar one - dimensional ( 1d ) nanowire semiconductor structures.@xcite although topological classification is a very powerful concept , the topological invariant usually remains a rather abstract quantity .
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Suppose that you have an abstract for a scientific paper: making use of the energetics and equations of state of defective uranium dioxide that calculated with first - principles method , we demonstrate a possibility of constraining the formation energy of point defects by measuring the transition pressures of the corresponding pseudo - phase of defects . the mechanically stable range of fluorite structure of uo@xmath0 , which dictates the maximum possible pressure of relevant pseudo - phase transitions , gives rise to defect formation energies that span a wide band and overlap with the existing experimental estimates .
we reveal that the knowledge about pseudo - phase boundaries can not only provide important information of energetics that is helpful for reducing the scattering in current estimates , but also be valuable for guiding theoretical assessments , even to validate or disprove a theory . in order to take defect interactions into account and to extrapolate the physical quantities at finite stoichiometry deviations to that near the stoichiometry
, we develop a general formalism to describe the thermodynamics of a defective system .
we also show that it is possible to include interactions among defects in a simple expression of point defect model ( pdm ) by introducing an auxiliary constant mean - field .
this generalization of the simple pdm leads to great versatility that allows one to study nonlinear effects of stoichiometry deviation on materials behavior .
it is a powerful tool to extract the defect energetics from finite defect concentrations to the dilute limit . besides these , the full content of the theoretical formalism and some relevant and interesting issues , including reentrant pseudo - transition , multi - defect coexistence , charged defects , and possible consequence of instantaneous defective response in a quantum crystal , are explored and discussed . .
And you have already written the first three sentences of the full article: defects usually play a prominent role in various properties of a solid . for this reason , the physics and chemistry of defects have been the subjects of much study for several decades.@xcite many of these works focused mainly at the dilute limit , _
i.e. _ , with a small defect concentration .
this is the case of interest in doped semiconductors and/or compounds in the immediate vicinity of the stoichiometry . at certain conditions ( usually with high temperature ) deviation from the stoichiometry.
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can span over a wide range of chemical composition .
binary oxides ceo@xmath0 and uo@xmath0 represent the paradigms for such kind of non - stoichiometry in the fluorite - related structures , and many others exist as well.@xcite for a comprehensive understanding of these materials , knowledge from just near the stoichiometry is insufficient .
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Suppose that you have an abstract for a scientific paper: we study the possibility that further advancement in the understanding of the order of chaos may demand a certain reconsideration of the approach to the classical mechanics . for this
we suggest to consider the viewpoint that spatio - temporal relations between objects are emergent and that they are but a result of complex interactions of objects .
such an approach is a natural continuation of the revision of the notions of space and time started by the general theory of relativity .
it leads to a possible extension of the structure of the classical mechanics .
namely , the result of the objects interactions can be wider than the spatio - temporal relations . in this case interactions
form a generalized space ( `` field - space '' ) wider than its spatio - temporal section ( while the known interactions are embedded within that section ) .
the study of such hypothesis demands constructing a theory , not relying on space and time as primitive notions . as primary elements of such a theory
we consider objects and purely informational connections between them , not expressed in spatio - temporal terms . following the logic of this theory
, the world constitutes a complex information web .
the web is in the state of a constant flux ( of a more general category than the one of the quantum fields ) - an incessant change of connections , the complex order of which comprises the order of chaos . reminding the space build - up from the regge skeleton ,
the web builds a unified field - space of pure information , manifested in space as energy distribution .
we describe the emergence of spatio - temporal laws from the viewpoint of purely informational physics .
the suggested construction of physics on the purely informational basis is a candidate for the theory of quantum gravity . .
And you have already written the first three sentences of the full article: physics developed from attempts to find order in the changes of spatial configurations of natural objects , such as celestial bodies . on the base of the classical mechanics , applicable in everyday situations , a picture emerged within which the relations between objects in space and time are a closed , self - explaining entity with future uniquely determined by the current spatial configuration of objects and the instantaneous rate of its change .
the subsequent discovery of chaos showed , however , that practically in every real situation the freedom of possible motions of the system , left after imposing the laws of classical mechanics , is extremely vast .
the relations between objects in space and time that are realized in reality , remain largely inexplicable . in other words , in complex situations , the constraints constituted by the laws of mechanics are extremely loose and they bring little information , making us to search for additional connections ..
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we are brought back to the original question - what is the order behind the changes of spatial configurations of objects around us ?
can it be that the laws of mechanics are emergent from some more fundamental processes the understanding of which would shed new light on chaos ?
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Suppose that you have an abstract for a scientific paper: the feynman - vernon path integral formalism is used to derive the density matrix of a quantum oscillator that is linearly coupled to an environmental reservoir .
although low - temperature reservoirs thermalize the oscillator to the usual boltzmann distribution , reservoirs at intermediate temperatures reduce this distribution to a single , coherent ground state .
associated with this state is an imaginary frequency indicating an environment which absorbs energy from the oscillator through the suppression of all excited modes .
further increase of the environmental temperature results again in the thermalization of the quantum oscillator to the expected boltzmann distribution .
qualitatively , this result could account for high - temperature quantum effects including the superconducting properties of graphite grains as well as the quantum coherence observed in photosynthetic systems .
decoherence , thermalization , imaginary eigenvalue , excited state decay , photosynthesis , high - temperature superconductivity .
And you have already written the first three sentences of the full article: quantum coherence is a phenomenon that could have profound impact on technological development .
usually understood to appear in temperature regimes much lower than those encountered in everyday practice , quantum coherence effects are not directly utilized in the operation of most conventional devices . superconducting sensors , magnets and transmission cables are examples where macroscopic quantum coherence is maintained at relatively high temperature .
nonetheless , even the highest-@xmath0 materials currently remain in the realm of cryogenic temperatures , thus significantly hampering their potential applicability ..
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consequently , much effort has been expended in the quest for higher temperature materials , as room - temperature superconductivity remains one of the most prominent issues in condensed matter physics .
although recent experimental evidence may suggest that superconductivity is possible at room temperature @xcite , what is perhaps even more compelling is the emerging evidence that photosynthetic systems found in nature may have already evolved a means of exploiting quantum coherence effects at physiological temperatures @xcite . due to the broad array of organisms sustained by trapping
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Suppose that you have an abstract for a scientific paper: microphysics of weakly magnetized relativistic collisionless shock waves , corroborated by recent high performance numerical simulations , indicate the presence of a microturbulent layer of large magnetic field strength behind the shock front , which must decay beyond some hundreds of skin depths .
the present paper discusses the dynamics of such microturbulence , borrowing from these same numerical simulations , and calculates the synchrotron signature of a powerlaw of shock accelerated particles .
the decaying microturbulent layer is found to leave distinct signatures in the spectro - temporal evolution of the spectrum @xmath0 of a decelerating blast wave , which are potentially visible in early multi - wavelength follow - up observations of gamma - ray bursts .
this paper also discusses the influence of the evolving microturbulence on the acceleration process , with particular emphasis on the maximal energy of synchrotron afterglow photons , which falls in the gev range for standard gamma - ray burst parameters .
finally , this paper argues that the evolving microturbulence plays a key role in shaping the spectra of recently observed gamma - ray bursts with extended gev emission , such as grb090510 .
[ firstpage ] acceleration of particles shock waves gamma - ray bursts .
And you have already written the first three sentences of the full article: the acceleration of particles at a decelerating relativistic collisionless shock front constitutes a key building block of the afterglow model of gamma - ray bursts ( grb , mszros & rees 1997 ) .
the standard phenomenology models the accelerated electron population as powerlaw @xmath1 , which radiates powerlaw photon spectra of the form @xmath2 , with a temporal decay index @xmath3 and a frequency index @xmath4 that are direct functions of @xmath5 , see e.g. piran ( 2005 ) for a review , or e.g. sari et al .
( 1998 ) , panaitescu & kumar ( 2000 ) for detailed formulae . from both microscopic and observational points of view.
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, the situation however appears more complex , in spite of several remarkable results of the past decade . on the microscopic level , for instance ,
one understands the formation of a relativistic collisionless shock front in a weakly magnetized medium such as the interstellar medium ( ism ) through the self - generation of intense small scale electromagnetic fields that act as the mediating agents for the transition from the far upstream unshocked state to the far downstream shocked state . the accelerated particles , as forerunners of the shock front , play a central role in triggering the microinstabilities that build the self - generated field .
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Suppose that you have an abstract for a scientific paper: the diagonal of a multivariate power series @xmath0 is the univariate power series @xmath1 generated by the diagonal terms of @xmath0 .
diagonals form an important class of power series ; they occur frequently in number theory , theoretical physics and enumerative combinatorics .
we study algorithmic questions related to diagonals in the case where @xmath0 is the taylor expansion of a bivariate rational function .
it is classical that in this case @xmath1 is an algebraic function .
we propose an algorithm that computes an annihilating polynomial for @xmath1 .
generically , it is its minimal polynomial and is obtained in time quasi - linear in its size .
we show that this minimal polynomial has an exponential size with respect to the degree of the input rational function .
we then address the related problem of enumerating directed lattice walks .
the insight given by our study leads to a new method for expanding the generating power series of bridges , excursions and meanders .
we show that their first @xmath2 terms can be computed in quasi - linear complexity in @xmath2 , without first computing a very large polynomial equation .
= 10000 = 10000 * categories and subject descriptors : * + i.1.2 [ * computing methodologies * ] : symbolic and algebraic manipulations _ algebraic algorithms _ * general terms : * algorithms , theory .
* keywords : * diagonals , walks , algorithms . .
And you have already written the first three sentences of the full article: * context . * the _ diagonal _ of a multivariate power series with coefficients @xmath3 is the univariate power series with coefficients @xmath4 . particularly interesting is the class of diagonals of _ rational _ power series ( ie , taylor expansions of rational functions ) . in particular , diagonals of _ bivariate _ rational power series are always roots of nonzero bivariate polynomials ( ie , they are algebraic series ) @xcite . since it is also classical that algebraic series are d - finite ( ie , satisfy linear differential equations with polynomial coefficients ) ,
their coefficients satisfy linear recurrences and this leads to an optimal algorithm for the computation of their first terms @xcite . in this article , we determine the degrees of these polynomials , the cost of their computation and related applications
. * previous work . *.
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the algebraicity of bivariate diagonals is classical .
the same is true for the converse ; also the property persists for multivariate rational series in positive characteristic @xcite .
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Suppose that you have an abstract for a scientific paper: crum s theorem in one - dimensional quantum mechanics asserts the existence of an associated hamiltonian system for any given hamiltonian with the complete set of eigenvalues and eigenfunctions .
the associated system is iso - spectral to the original one except for the lowest energy state , which is deleted .
a modification due to krein - adler provides algebraic construction of a new complete hamiltonian system by deleting a finite number of energy levels . here
we present a discrete version of the modification based on the crum s theorem for the ` discrete ' quantum mechanics developed by two of the present authors .
yukawa institute kyoto + dpsu-10 - 1 + yitp-10 - 15 + * modification of crum s theorem for ` discrete ' quantum mechanics + + * * leonor garca - gutirrez@xmath0 , satoru odake@xmath1 and ryu sasaki@xmath0 * @xmath0 yukawa institute for theoretical physics , + kyoto university , kyoto 606 - 8502 , japan + @xmath1 department of physics , shinshu university , + matsumoto 390 - 8621 , japan .
And you have already written the first three sentences of the full article: crum s seminal paper of 1955 @xcite has played an essential role in elucidating the structure of one - dimensional quantum mechanical systems in general and exactly solvable ones , in particular . throughout this paper ,
we mean ` exact solvability ' in the schrdinger picture , namely a quantum system is exactly solved when the complete set of eigenvalues and eigenfunctions are known .
many exactly solvable quantum mechanical hamiltonians were constructed and investigated by combining shape invariance @xcite and crum s theorem @xcite , or the factorisation method @xcite or the method of the so - called supersymmetric quantum mechanics @xcite ..
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it is interesting to note that most of these shape invariant systems are also solvable in the heisenberg picture @xcite .
exactly solvable quantum mechanical systems of one and many degrees of freedom are not only important in their own right but also have fundamental applications in various disciplines of physics / mathematics , _
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Suppose that you have an abstract for a scientific paper: the present uncertainties in the knowledge of the neutrino cross sections for @xmath0 gev , that is in the energy range most important for atmospheric and long baseline accelerator neutrinos , are large .
these uncertainties do not play a significant role in the interpretation of existing data , however they could become a limiting factor in future studies that aim at a complete and accurate determination of the neutrino oscillation parameters .
new data and theoretical understanding on nuclear effects and on the electromagnetic structure functions at low @xmath1 and in the resonance production region are available , and can be valuable in reducing the present systematic uncertainties .
the collaboration of physicists working in different subfields will be important to obtain the most from this available information .
it is now also possible , with the facilities developed for long baseline beams , to produce high intensity and well controlled @xmath2beams to measure the neutrino interaction properties with much better precision that what was done in the past .
several projects and ideas to fully exploit these possibilities are under active investigation .
these topics have been the object of the first @xmath2interaction ( nuint01 ) workshop . .
And you have already written the first three sentences of the full article: neutrino physics is living in a `` golden era '' .
experiments with atmospheric and solar neutrinos have given strong evidence for the existence of flavor oscillations , or ( less likely ) some other form of ` new physics ' beyond the standard model @xcite .
the study of the @xmath2 flavor transitions offer the possibility to obtain information about the neutrino masses and mixing , and the knowledge about these quantities hopefully represents a fundamental window on the physics of the unification ..
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theorists are busy trying to make sense of the unexpected results that have been obtained so far , on the other hand new experimental studies are planned to measure with greater precision the properties of the @xmath2 flavor transitions .
these future studies , are designed to determine if the @xmath2 flavor evolution is completely described by the 3-flavor mixing model , or if a more complex dynamics ( transitions to additional sterile states , neutrino decay , flavor changing neutral currents ) is necessary , and should measure the entire set of parameters ( 2 squared mass differences , 3 mixing angles and one cp violating phase ) that determine the @xmath2 flavor evolution in space time in the 3flavor scenario . the discovery of @xmath2 oscillations has been performed with natural ( solar and atmospheric ) neutrino sources , however most of the future studies will be performed with artificial neutrinos . in particular , long baseline ( lbl ) accelerator neutrino beams will play a fundamental role .
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Suppose that you have an abstract for a scientific paper: in this work the interaction of electromagnetic field with quasi - periodic media has been scrutinized .
we have obtained the formula for a distorted medium polarizability tenzor in the x - ray frequency band .
also there have been obtained the x - rays dynamic diffraction equations for the mediums with arbitrary smooth distortion . for these equations
the takagi - tuipin equations are obtained as a particular case .
we have got a very simple formula for the coefficient of x - rays reflection on the bent bragg mirror .
we have scrutinized the example of calculating the x - rays reflection and focusing by the bent bragg mirror .
also in this work one could find the rezults of calculating the reflected x - rays caustics form .
it is shown that there exists a possibility of linear dimensions of the x - rays focusing area having typical values of @xmath0 .
# 1@xmath1#1 .
And you have already written the first three sentences of the full article: in this article we consider interaction of electromagnetic field with quasi - periodic media which we define as media obtained by some smooth deformation of perfect periodic structures .
mathematically , the term smooth deformation means the biunivocal smooth mapping of the medium under consideration on the medium with perfect periodic structure .
the main goal of this article is to show that the electrodynamics of quasi - periodic media can be reduced to the electrodynamics of the perfect periodic media , and , thus , to make possible application to quasi - periodical structures of well - developed classical approaches.the correspondence between perfect and quasi - periodical media is possible when the later one is considered as the riemannian manifold with the fundamental metric tensor @xmath2 @xmath3 , where @xmath4 is the kronecker symbol and @xmath5 is the deformation tensor . to clarify this statement ,.
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let us remind , that in the mechanics of continuous medium there are two methods describing the deformation processes : the euler method and the lagrange method .
the co - ordinates coincide with the observer s frame of reference in the euler method .
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Suppose that you have an abstract for a scientific paper: we implement a double - pixel , compressive sensing camera to efficiently characterize , at high resolution , the spatially entangled fields produced by spontaneous parametric downconversion .
this technique leverages sparsity in spatial correlations between entangled photons to improve acquisition times over raster - scanning by a scaling factor up to @xmath0 for @xmath1-dimensional images .
we image at resolutions up to @xmath2 dimensions per detector and demonstrate a channel capacity of @xmath3 bits per photon . by comparing the entangled photons classical mutual information in conjugate bases , we violate an entropic einstein - podolsky - rosen separability criterion for all measured resolutions . more broadly , our result indicates compressive sensing can be especially effective for higher - order measurements on correlated systems . .
And you have already written the first three sentences of the full article: spatially entangled biphotons , such as those generated by spontaneous parametric downconversion ( spdc ) , exhibit strong einstein - podolsky - rosen ( epr ) type correlations @xcite in the transverse position and transverse momentum degrees of freedom @xcite .
because these variables are continuous , the entanglement can be very high - dimensional with a typical schmidt number greatly exceeding @xmath4 @xcite .
this provides high information density which can be leveraged to increase channel capacity and security for quantum key distribution @xcite and dense coding @xcite ..
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other applications include ghost imaging @xcite , quantum computing @xcite , and quantum teleportation @xcite .
experimentally characterizing the spdc state is unfortunately difficult due to weak sources and low resolution detectors .
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Suppose that you have an abstract for a scientific paper: the high density of evanescent modes in the vicinity of a metal leads to enhancement of the near - field frster resonant energy transfer ( fret ) rate .
we present a classical approach to calculate the fret rate based on the dyadic green s function of an arbitrary dielectric environment , and consider non - local limit of material permittivity in case of metallic halfspace and thin film . in a dimer system , we find that the fret rate is enhanced due to shared evanescent photon modes bridging a donor and an acceptor .
furthermore , a general expression for the fret rate for multimer systems is derived .
the presence of a dielectric environment and the path interference effect enhance the transfer rate , depending on the combination of distance and geometry . .
And you have already written the first three sentences of the full article: the short range energy transfer phenomena find applications in wide areas of physics and chemistry from mesoscopic to molecular systems , @xcite and is critical to our understanding of physical , chemical and biological processes at the molecular level .
@xcite understanding the physics of an exciton transfer from a donor to an acceptor is also crucial for designing better solar cells and photo - voltaic materials .
this has fueled great interest in the study of the effect of electromagnetic environment on the resonant energy transfer , which offers the possibility of controlling and enhancing the energy transfer in molecular systems ..
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@xcite therefore , obtaining an exact classical description of the resonant energy transfer under the influence of an electromagnetic environment is imperative to improve the energy transfer mechanism in molecular systems .
the interaction between a dipole emitter and its mirror image under the metallic surface , or equivalently , the scattered evanescent waves from the metal , has been studied in varieties of nanoscale systems .
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Suppose that you have an abstract for a scientific paper: one of the most important problems in large scale inference problems is the identification of variables that are highly dependent on several other variables .
when dependency is measured by partial correlations these variables identify those rows of the partial correlation matrix that have several entries with magnitude close to one ; i.e. , hubs in the associated partial correlation graph .
this paper develops theory and algorithms for discovering such hubs from a few observations of these variables .
we introduce a hub screening framework in which the user specifies both a minimum ( partial ) correlation @xmath0 and a minimum degree @xmath1 to screen the vertices .
the choice of @xmath0 and @xmath1 can be guided by our mathematical expressions for the phase transition correlation threshold @xmath2 governing the average number of discoveries .
we also give asymptotic expressions for familywise discovery rates under the assumption of large @xmath3 , fixed number @xmath4 of multivariate samples , and weak dependence . under the null hypothesis that the covariance matrix is sparse
these limiting expressions can be used to enforce fwer constraints and to rank these discoveries in order of statistical significance ( p - value ) . for @xmath5
the computational complexity of the proposed partial correlation screening method is low and is therefore highly scalable .
thus it can be applied to significantly larger problems than previous approaches .
the theory is applied to discovering hubs in a high dimensional gene microarray dataset .
* keywords * gaussian graphical models , correlation networks , nearest neighbor dependency , node degree and connectivity , asymptotic poisson limits , discovery rate phase transitions , p - value trajectories .
And you have already written the first three sentences of the full article: this paper treats the problem of screening a @xmath3-variate sample for strongly and multiply connected vertices in the partial correlation graph associated with the the partial correlation matrix of the sample .
this problem , called hub screening , is important in many applications ranging from network security to computational biology to finance to social networks . in the area of network security ,
a node that becomes a hub of high correlation with neighboring nodes might signal anomalous activity such as a coordinated flooding attack . in the area of computational biology.
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the set of hubs of a gene expression correlation graph can serve as potential targets for drug treatment to block a pathway or modulate host response . in the area of finance a hub
might indicate a vulnerable financial instrument or sector whose collapse might have major repercussions on the market . in the area of social networks
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Suppose that you have an abstract for a scientific paper: one of the findings of the recent literature is that the 2008 financial crisis caused reduction in international diversification benefits . to fully understand the possible potential from diversification
, we build an empirical model which combines generalised autoregressive score copula functions with high frequency data , and allows us to capture and forecast the conditional time - varying joint distribution of stock returns . using this novel methodology and fresh data covering five years after the crisis
, we compute the conditional diversification benefits to answer the question , whether it is still interesting for an international investor to diversify . as diversification tools , we consider the czech px and the german dax broad stock indices , and we find that the diversification benefits strongly vary over the 20082013 crisis years .
portfolio diversification , dynamic correlations , high frequency data , time - varying copulas c14 , c32 , c51 , f37 , g11 .
And you have already written the first three sentences of the full article: a proper quantification of the joint distribution allowing for the time - varying dependence between assets is critical for asset pricing , portfolio allocation and risk reduction . for a number of years
, finance literature has been studying the risk reduction benefit from international diversification .
after the recent 2008 financial crisis , many researchers have documented possible reduction of these benefits due to rising dependence between markets ..
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the literature concentrating on the central european markets has been limited though , as it is widely believed that after the enlargement of the european union , these markets became integrated with very limited opportunities for diversification . in this paper , we revisit this line of research , and study the possible benefits from diversification between the czech px and the german dax stock market indices using data covering the five years crisis period . while it is reasonable to believe that the czech and german stock markets show large degree of dependence due to integration of the czech republic into the euro area as well as large dependence of the czech economy on the german one , we aim to study , whether the german and czech stock indices can be considered for the reduction of risk of an international investor .
a number of researchers have addressed the issue of central and eastern european ( cee ) markets integration with the euro area .
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Suppose that you have an abstract for a scientific paper: we study the cauchy problem for a semilinear stochastic partial differential equation driven by a finite - dimensional wiener process .
in particular , under the hypothesis that all the coefficients are sufficiently smooth and have bounded derivatives , we consider the equation in the context of power scale generated by a strongly elliptic differential operator .
application of semigroup arguments then yields the existence of a continuous strong solution . .
And you have already written the first three sentences of the full article: in the present paper , we consider the following semilinear stochastic partial differential equation driven by a finite - dimensional wiener process : @xmath0{\mathrm{d}}t+\sigma(u)\,{\mathrm{d}}w,\quad x\in{\mathbb{t}}^n,\;t\in(0,t),\\ u(0)&=u_0 , \end{split}\ ] ] where @xmath1 is a strongly elliptic differential operator , @xmath2 is generally nonlinear unbounded operator and the diffusion coefficient in the stochastic term is also nonlinear .
it is a well known fact in the field of pdes and spdes that many equations do not , in general , have classical or strong solutions . unlike deterministic problems , in the case of stochastic equations we can only ask whether the solution is smooth in the space variable . thus , the aim of the present work is to determine conditions on coefficients and initial data under which there exists a spatially smooth solution to .
the literature devoted to the regularity for linear spdes is quite extensive mainly due to krylov ( see @xcite ) , krylov and rozovskii ( see @xcite , @xcite and the references therein ) and flandoli ( see @xcite ).
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. however , there seems to be less papers concentrated on regularity for nonlinear spdes .
a class of second order parabolic semilinear spdes was studied by gyngy and rovira ( see @xcite ) but they were only concerned with @xmath3-valued solutions .
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Suppose that you have an abstract for a scientific paper: in this article , we study the null controllability of linearized compressible navier - stokes system in one and two dimension .
we first study the one - dimensional compressible navier - stokes system for non - barotropic fluid linearized around a constant steady state .
we prove that the linearized system around @xmath0 , with @xmath1 @xmath2 is not null controllable by localized interior control or by boundary control .
but the system is null controllable by interior controls acting everywhere in the velocity and temperature equation for regular initial condition .
we also prove that the the one - dimensional compressible navier - stokes system for non - barotropic fluid linearized around a constant steady state @xmath3 , with @xmath1 @xmath4 @xmath5 is not null controllable by localized interior control or by boundary control for small time @xmath6 next we consider two - dimensional compressible navier - stokes system for barotropic fluid linearized around a constant steady state @xmath7 we prove that this system is also not null controllable by localized interior control . * key words . * linearized compressible navier - stokes system , null controllability , localized interior control , boundary control , gaussian beam .
* ams subject classifications .
* 35q30 , 93c20 , 93b05 .
And you have already written the first three sentences of the full article: control of fluid flow has been an important area of research and has many practical applications .
the question about controllability of fluid flows has attracted the attention of many researchers , more for incompressible flow but much less for compressible flow . in this paper
we are interested in controllability properties of linearized compressible navier - stokes system . for a compressible ,.
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isothermal barotropic fluid ( density is a function of only pressure ) , the navier - stokes system in @xmath8 consists of equation of continuity @xmath9 = 0 , \end{array}\ ] ] and the momentum equation @xmath10 \\ [ 3.mm ] \displaystyle = -\nabla p(x , t ) + \mu \bigtriangleup { \bf u}(x , t ) + ( \lambda + \mu ) \nabla [ \mbox{div } { \bf u}(x , t ) ] , \end{array}\ ] ] where @xmath11 is the density of the fluid , @xmath12 denotes the velocity vector in @xmath13 and @xmath14 is an external force field in @xmath15 the pressure satisfies the following constitutive law @xmath16 for some constants @xmath17 , @xmath18 the viscosity coefficients @xmath19 and @xmath20 are assumed to be constant satisfying the following thermodynamic restrictions , @xmath21 , @xmath22 for non - barotropic fluid ( when density is a function of pressure and temperature of the fluid ) , the navier - stokes system consists of the equation of continuity , the momentum equation and an additional thermal energy equation @xmath23(x , t ) + \theta(x , t ) \frac{\partial p}{\partial \theta}(x , t ) \mbox{div } { \bf u}(x , t ) \\ [ 3.mm ] \displaystyle = \kappa \bigtriangleup \theta ( x , t ) + \lambda ( \mbox{div } { \bf u}(x , t))^2 + 2 \mu \sum_{i , j=1}^n \frac{1}{4 } \left(\frac{\partial { \bf u}_i}{\partial x_j } + \frac{\partial { \bf u}_j}{\partial x_i}\right)^2 , \end{array}\ ] ] where @xmath24 denotes the temperature of the fluid , @xmath25 is the specific heat constant and @xmath26 is the heat conductivity constant . for ideal gas , the pressure is given by boyle s law : @xmath27 where @xmath28 is the universal gas constant ( see @xcite ) . in this article
, we first consider the compressible navier - stokes system for non - barotropic fluid in a bounded interval @xmath29 linearized around a constant steady state @xmath30 with @xmath31 and @xmath32 more precisely we consider the system @xmath33 where @xmath34 is the characteristic function of an open subset @xmath35 we choose the following initial and...
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Suppose that you have an abstract for a scientific paper: we study in a bottom - up approach the theoretically consistent description of additional resonances in the electroweak sector beyond the discovered higgs boson as simplified models .
we focus on scalar and tensor resonances .
our formalism is suited for strongly coupled models , but can also be applied to weakly interacting theories .
the spurious degrees of freedom of tensor resonances that would lead to bad high - energy behavior are treated using a generalization of the stckelberg formalism .
we calculate scattering amplitudes for vector - boson and higgs boson pairs .
the high - energy region is regulated by the t - matrix unitarization procedure , leading to amplitudes that are well behaved on the whole phase space .
we present numerical results for complete partonic processes that involve resonant vector - boson scattering , for the current and upcoming runs of lhc . .
And you have already written the first three sentences of the full article: after the discovery of a @xmath0 higgs boson , phenomenological high - energy physics has entered a new era .
the new particle fits the expectation of the minimal standard model ( sm ) .
this model is thus established as an effective field theory ( eft ) that correctly describes all current particle data ( except for still missing possible particle signals for dark matter and additional cp violation ) ..
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we know about high - energy scales where the effective theory eventually breaks down the scale of neutrino mass generation , the planck scale but those are far outside the reach of collider physics .
the hierarchy between those scales and the electroweak symmetry breaking scale , combined with the fact that all known elementary particles are weakly interacting , puzzles us due to the apparent fine - tuning in perturbative renormalization .
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Suppose that you have an abstract for a scientific paper: the reduced dynamics of a single or two qubits coupled to an interacting quantum spin bath modeled by a xxz spin chain is investigated . by using the method of time - dependent density matrix renormalization group ( t - dmrg ) , we go beyond the uniform coupling central spin model and evaluate nonperturbatively the induced decoherence and entanglement .
it is shown that both decoherence and entanglement strongly depend on the phase of the underlying spin bath .
we show that in general , spin baths can induce entanglement for an initially disentangled pair of qubits .
furthermore , when the spin bath is in the ferromagnetic phase , because qubits directly couple to the order parameter , the reduced dynamics shows oscillatory type behavior . on the other hand , only for paramagnetic and antiferromagnetic phases , initially entangled states suffer from the entanglement sudden death . by calculating concurrence , the finite disentanglement time is mapped out for all phases in the phase diagram of the spin bath . .
And you have already written the first three sentences of the full article: spin qubits are promising candidates for quantum information processing due to their long decoherence and relaxation time.@xcite some schemes , such as solid state spin qbuits , further enjoy the potential scalability via the integration with nanotechnology.@xcite however , spin qubits are not totally immune from the ubiquitous decoherence . to describe the bath that causes the decoherence of spin qubits , it is known that in some cases , the bath is better modeled by spins instead of delocalized oscillators , resulting in the so - called spin baths.@xcite
it has been argued that the influence of spin baths may be qualitatively different from bosonic baths and non - markovian dynamics can easily emerge.@xcite due to the growing interest in spin baths , the decoherence behavior and the entanglement dynamics of few qubits coupled to spin baths have been studied extensively in recent years .
early works focus on the decoherence due to independent spins.@xcite here although the proposed model formally resembles a spin boson model , non - markovian already emerges even when bath modes are not interacting.@xcite in real baths , however , spins are not independent ..
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it is therefore important to include effects due to interactions of spins in the bath .
nonetheless , the inclusion of the intra - spin interaction in the bath complicates the problem and only for some limited models with high symmetry , exact reduced dynamics can be identified .
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Suppose that you have an abstract for a scientific paper: we study the graviton self - energy function in a general gauge , using a hard thermal loop expansion which includes terms proportional to @xmath0 , @xmath1 and @xmath2 .
we verify explicitly the gauge independence of the leading @xmath0 term and obtain a compact expression for the sub - leading @xmath1 contribution .
it is shown that the logarithmic term has the same structure as the ultraviolet pole part of the @xmath3 self - energy function .
we argue that the gauge - dependent part of the @xmath1 contribution is effectively canceled in the dispersion relations of the graviton plasma , and present the solutions of these equations . # .
And you have already written the first three sentences of the full article: when the temperature @xmath5 is high compared with the typical momentum scale but well below the planck scale , all the n - graviton thermal green functions can be computed in the one - loop approximation using the hard thermal loop expansion .
there have been many investigations where this approach has been employed @xcite . an important property which is now well established is the gauge invariance of the leading high temperature contributions of all n - graviton thermal green functions .
the explicit from of these contributions can be obtained using the equivalence which exists between the formalism of boltzmann transport equation and the high temperature limit of the thermal green functions in field theory@xcite . using this approach ( which is explicitly gauge invariant ).
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one can easily show that the leading part of all n - point one - loop thermal green functions is proportional to @xmath0 @xcite .
these results have also been obtained by standard feynman diagrammatic calculation in the feynman - dedonder gauge for the one- and two - graviton functions @xcite as well as for the three - graviton function @xcite .
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Suppose that you have an abstract for a scientific paper: we compare the thermal conductance @xmath0 ( at temperature @xmath1 ) and the electrical shot noise power @xmath2 ( at bias voltage @xmath3 ) of majorana fermions on the two - dimensional surface of a three - dimensional topological superconductor .
we present analytical and numerical calculations to demonstrate that , for a local coupling between the superconductor and metal contacts , @xmath4 ( with @xmath5 the lorenz number ) .
this relation is ensured by the combination of electron - hole and time - reversal symmetries , irrespective of the microscopics of the surface hamiltonian , and provides for a purely electrical way to detect the charge - neutral majorana surface states .
a surface of aspect ratio @xmath6 has the universal shot - noise power @xmath7 . .
And you have already written the first three sentences of the full article: topological superconductors are analogous to topological insulators:@xcite both combine an excitation gap in the bulk with gapless states at the surface , without localization by disorder as long as time - reversal symmetry is preserved . however , the nature of the surface excitations is entirely different : in a topological insulator these are dirac fermions , relativistic electrons or holes of charge @xmath8 , while a topological superconductor has _
charge - neutral _ majorana fermions on its surface .
a transport experiment that aims to detect the majorana surface states can not be as routine as electrical conduction the direct analogue for majorana fermions of the _ electrical _ conductance of dirac fermions is the _ thermal _ conductance @xmath0 ..
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the challenge of low - temperature thermal measurements is one reason why majorana surface states have not yet been detected in a transport experiment on candidate materials for topological superconductivity.@xcite there exists a purely electrical alternative to thermal detection of majorana fermions.@xcite particle - hole symmetry enforces that a majorana fermion at the fermi level is an equal - weight electron - hole superposition , so while the average charge is zero , the charge fluctuations have a quantized variance of @xmath9 quantum fluctuations of the charge can be detected electrically in a shot noise measurement , and for a single fully transmitted majorana mode these produce a quantized shot noise power @xmath2 of @xmath10 per @xmath11 of applied bias.@xcite ( the factor @xmath12 reminds us that a majorana fermion is `` half a dirac fermion '' . ) is obtained by applying a temperature difference @xmath1 , @xmath13 between the contacts and measuring the resulting heat current @xmath14 . for the shot noise measurement one would bias contact @xmath15 at voltage @xmath16 , while keeping the superconductor and @xmath17 grounded .
the electrical current @xmath18 into contact @xmath17 fluctuates with noise power @xmath2 . both @xmath19 and @xmath20
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Suppose that you have an abstract for a scientific paper: we analyse the @xmath0 modes in the light of the most recent @xmath1-factory data , and obtain the following new results : ( i ) the @xmath2 modes prefer @xmath3 , which together with @xmath4 allows us to determine the `` true '' unitarity triangle and to search for cp - violating new - physics contributions to @xmath5@xmath6 mixing ; ( ii ) the @xmath7 puzzle reflected in particular by the low experimental value of the ratio @xmath8 of the neutral @xmath7 rates persists and still favours new physics in the electroweak penguin sector with a new cp - violating phase @xmath9 , although now also @xmath10 can bring us rather close to the data ; ( iii ) the mixing - induced @xmath11 cp asymmetry is a sensitive probe of the sign of this phase , and would currently favour @xmath10 , as well as the direct cp asymmetry of @xmath12 , which suffers , however , from large hadronic uncertainties ; ( iv ) we investigate the sensitivity of our @xmath7 analysis to large non - factorizable @xmath13-breaking effects and find that their impact is surprisingly small so that it is indeed exciting to speculate on new physics ; ( v ) assuming that new physics enters through @xmath14 penguins , we study the interplay between @xmath7 and rare @xmath1 , @xmath15 decays and point out that the most recent @xmath1-factory constraints for the latter have interesting implications , bringing us to a few scenarios for the future evolution of the data , where also the mixing - induced cp violation in @xmath11 plays a prominent rle .
cern - ph - th/2005 - 241 + tum - hep-610/05 + mpp-2005 - 156 + hep - ph/0512032 * andrzej j. buras,@xmath16 robert fleischer,@xmath17 stefan recksiegel@xmath16 and felix schwab@xmath18 * @xmath16 _ physik department , technische universitt mnchen , d-85748 garching , germany _
@xmath17 _ theory division , department of physics , cern , ch-1211 geneva 23 , switzerland _
@xmath19 _ max - planck - institut fr physik werner - heisenberg - institut , d-80805 munich , germany
_ december 2005 .
And you have already written the first three sentences of the full article: decays of @xmath1 mesons into @xmath20 and @xmath21 final states offer valuable information about strong interactions , weak interactions and possible new - physics ( np ) effects . in a series of recent papers @xcite
, we developed a strategy to address these aspects in a systematic manner .
it uses the following working hypotheses : * @xmath13 flavour symmetry of strong interactions ( but taking factorizable @xmath13-breaking corrections into account ) ; * neglect of penguin annihilation and exchange topologies ..
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we may gain confidence in these assumptions through internal consistency checks , which worked well within the experimental uncertainties for our previous numerical analyses .
since the @xmath1 factories reported updated results for several of the input quantities , we would like to explore the implications for the picture emerging from our strategy . for a detailed overview of the current experimental status of the @xmath0 observables ,
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Suppose that you have an abstract for a scientific paper: acyclicity of individual preferences is a minimal assumption in social choice theory .
we replace that assumption by the direct assumption that preferences have maximal elements on a fixed agenda .
we show that the core of a simple game is nonempty for all profiles of such preferences if and only if the number of alternatives in the agenda is less than the nakamura number of the game .
the same is true if we replace the core by the _ core without majority dissatisfaction _
, obtained by deleting from the agenda all the alternatives that are non - maximal for all players in a winning coalition . unlike the core , the core without majority dissatisfaction depends only on the players sets of maximal elements and is included in the union of such sets .
a result for an extended framework gives another sense in which the core without majority dissatisfaction behaves better than the core .
_ journal of economic literature _
classifications : c71 , d71 , c02 .
_ keywords : _ core , nakamura number , kappa number , simple games , voting games , maximal elements , acyclic preferences , limit ordinals . .
And you have already written the first three sentences of the full article: _ preference aggregation theory _ is concerned with aggregating individual preferences into a ( collective ) social preference , which is then maximized to yield a set of best alternatives .
the theory investigates the extent to which social preferences inherit desirable properties from individual preferences . we typically restrict ( strict ) individual and social preferences to those asymmetric relations @xmath0 on a set @xmath1 of alternatives that are either ( i ) acyclic or ( ii ) transitive or ( iii ) negatively transitive . by @xmath2 .
@xmath0 is asymmetric iff @xmath3 is complete ( reflexive and total ) ..
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( i ) @xmath0 is _ acyclic _ if for any finite set @xmath4 , whenever @xmath5 , , @xmath6
, we have @xmath7 . if @xmath0 is acyclic , it is asymmetric and irreflexive .
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Suppose that you have an abstract for a scientific paper: the systematic errors in the virial mass - to - light ratio , @xmath0 , of galaxy clusters as an estimator of the field @xmath1 value are assessed .
we overlay 14 clusters in redshift space to create an ensemble cluster which averages over substructure and asymmetries .
the combined sample , including background , contains about 1150 galaxies , extending to a projected radius of about twice 200 .
the radius 200 , defined as where the mean interior density is 200 times the critical density , is expected to contain the bulk of the virialized cluster mass .
the dynamically derived @xmath2 of the ensemble is @xmath3 .
the @xmath0 overestimate is attributed to not taking into account the surface pressure term in the virial equation . under the assumption that the velocity anisotropy parameter is in the range @xmath4
, the galaxy distribution accurately traces the mass profile beyond about the central @xmath5 .
there are no color or luminosity gradients in the galaxy population beyond @xmath6 , but there is @xmath7 mag fading in the @xmath8 band luminosities between the field and cluster galaxies .
we correct the cluster virial mass - to - light ratio , @xmath9 ( calculated assuming @xmath10 ) , for the biases in @xmath11 and mean luminosity to estimate the field @xmath12 . with our self - consistently derived field luminosity density , @xmath13 ( at @xmath14 ) , the corrected @xmath1 indicates @xmath15 ( formal @xmath16 random error and estimated potential systematic errors ) for those components of the mass field in rich clusters . 1 200 200 .
And you have already written the first three sentences of the full article: the existence of dark matter was discovered in galaxy clusters where the velocity dispersions are nearly an order of magnitude higher than expected from the gravitational binding provided by the stellar masses of their visible galaxies ( @xcite ) .
clusters are gravitationally bound , quasi - equilibrium systems assembled over a hubble time via the infall of the mass in the surrounding field ( @xcite ) , which implies that both the dark matter and the galaxies within clusters have their origins in the field . because clusters are large systems that draw their mass and galaxy content from regions 20 across , measurements of cluster @xmath1 values should be representative of the field value , although not necessarily identical to it because of differential galaxy evolution .
the product of the field @xmath1 with the field luminosity density , @xmath17 , is equal to the mean mass density of the universe , @xmath18 ( @xcite ) ..
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the cosmological density parameter , @xmath19 , is therefore estimated as the ratio of the cluster @xmath1 ( corrected to the field ) to the @xmath20 for closure ( @xcite ) .
the resulting @xmath21 estimate has no dependence on @xmath22 for dynamically measured cluster masses ( @xcite ) .
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Suppose that you have an abstract for a scientific paper: astronomers are always anxious to push their observations to the limit basing results on objects at the detection threshold , spectral features barely stronger than the noise , or photometry in very crowded regions . in this paper
we present a careful analysis of photometry in crowded regions , and show how image blending affects the results and interpretation of such data .
although this analysis is specifically for our nicmos observations in m31 , the techniques we develop can be applied to any imaging data taken in crowded fields ; we show how the effects of image blending will even limit ngst .
we have obtained hst - nicmos observations of five of m31 s most metal rich globular clusters .
these data allow photometry of individual stars in the clusters and their surrounding fields . however , to achieve our goals
obtain accurate luminosity functions to compare with their galactic counterparts , determine metallicities from the slope of the giant branch , identify long period variables , and estimate ages from the agb tip luminosity , we must be able to disentangle the true properties of the population from the observational effects associated with measurements made in very crowded fields .
we thus use three different techniques to analyze the effects of crowding on our data , including the insertion of artificial stars ( traditional completeness tests ) and the creation of completely artificial clusters .
these computer simulations have proven invaluable in interpreting our data .
they are used to derive threshold- and critical - blending radii for each cluster , which determine how close to the cluster center reliable photometry can be achieved .
the simulations also allow us to quantify and correct for the effects of blending on the slope and width of the rgb at different surface brightness levels .
we then use these results to estimate the limits blending will place on future space - based observations . .
And you have already written the first three sentences of the full article: the main objective of our observations was to obtain physical parameters for a selection of metal - rich globular clusters in m31 .
these parameters are usually straight - forward to derive from color - magnitude diagrams ( cmds ) , however , we have found the effects of crowding to be particularly severe .
we therefore present our analysis in two parts ..
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this paper describes in detail the effects of crowding , how we quantify them , the techniques used to correct for them , and their implications for future space - based observations such as with ngst . a second paper ( * ? ? ?
* hereafter paper ii ) presents the science obtained from our observations using these techniques .
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Suppose that you have an abstract for a scientific paper: we report the study on the low - temperature heat transport of ba@xmath0mn@xmath1o@xmath2 single crystal , a layered spin - dimer compound exhibiting the magnetic - field - induced magnetic order or the magnon bose - einstein condensation .
the thermal conductivities ( @xmath3 ) along both the @xmath4 plane and the @xmath5 axis show nearly isotropic dependence on magnetic field , that is , @xmath3 is strongly suppressed with increasing field , particularly at the critical fields of magnetic phase transitions .
these results indicate that the magnetic excitations play a role of scattering phonons and the scattering effect is enhanced when the magnetic field closes the gap in the spin spectrum .
in addition , the magnons in the bec state of this materials do not show notable ability of carrying heat . .
And you have already written the first three sentences of the full article: low - dimensional or frustrated quantum magnets were revealed to exhibit exotic ground states , magnetic excitations , and quantum phase transitions ( qpts).@xcite for a particular case of the spin - gapped antiferromagnets , the external magnetic field can close the gap in the spectrum , which results in a qpt between a low - field disordered paramagnetic phase and a high - field long - range ordered one .
an intriguing finding is that this ordered phase can be approximately described as a bose - einstein condensation ( bec ) of magnons.@xcite many experimental investigations on the critical properties of the bec - related qpt have been carried out , including the characterizations of the magnon spectrum , the magnetization , the specific heat and the thermal transport , etc.@xcite in a recent study , the heat transport properties of a magnon bec material , nicl@xmath1-@xmath6sc(nh@xmath1)@xmath1 ( dtn ) , were found to display strong anomalies at the qpts and the heat conductivity of the bec state seemed to be much enhanced upon lowering temperatures ( approaching the absolute zero).@xcite this result shows an analogy between the magnon bec and the superfluid of @xmath7he in the aspect of the ability of transporting heat . however , one notable facet is that magnons act as heat carriers only in the direction of the spin chains of this compound , whereas they only scatter phonons in the transverse direction.@xcite so the exchange anisotropy may play the key role in the heat transport of magnetic excitations .
a later experimental work confirmed the main features of transport properties of dtn , but an alternative picture based on the mass renormalization and impurity scattering effects was proposed to explain the thermal transport data.@xcite in any case , the qpts associated with the magnon bec are believed to significantly affect the heat transport properties and the low - energy magnetic excitations provide a substantial contribution to the heat transport . to get the general principals of the heat....
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ba@xmath0mn@xmath1o@xmath2 ( bmo ) is an @xmath8 = 1 quantum spin - dimer system exhibiting the bec of spin degrees of freedom .
it crystallizes in the rhombohedral @xmath9 structure with the pairs of mn@xmath10 3@xmath11 ions ( @xmath8 = 1 ) arranged vertically on the hexagonal layers.@xcite the spins of mn@xmath10 ions of each pair are coupled antiferromagnetically to form spin dimers.@xcite neutron scattering results indicated an intradimer exchange energy @xmath12 = 1.642 mev , an interdimer coupling between mn ions in the same plane @xmath13 = 0.1136 mev , an interdimer coupling between mn ions in the adjacent planes @xmath14 mev , and the next nearest neighbor interdimer interactions between bilayers ( along the @xmath5 axis ) @xmath15 mev.@xcite the strong in - plane spin - dimer interaction results in a spin - singlet ground state , with a spin gap of 1.05 mev to the lowest triplet state and a second larger gap to the quintuplet state .
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10,153 |
Suppose that you have an abstract for a scientific paper: we investigate direct above - threshold ionization in diatomic molecules , with particular emphasis on how quantum interference is altered by a driving field of non - vanishing ellipticity
. this interference may be either temporal , i.e. , related to ionization events occurring at different times , or spatial , i.e. , related to the electron emission at different centers in the molecule . employing the strong - field approximation and saddle - point methods , we find that , in general , for non - vanishing ellipticity , there will be a blurring of the temporal and spatial interference patterns .
the former blurring is caused by the electron velocity component perpendicular to the major polarization axis , while spatial interference is washed out as a consequence either of @xmath0 mixing , or of the temporal dependence of the ionization prefactor .
both types of interference are analyzed in detail in terms of electron trajectories , and specific conditions for which sharp fringes occur are provided . .
And you have already written the first three sentences of the full article: atoms and molecules interacting with a strong laser field may be ionized by absorbing more photons than necessary .
this highly nonlinear phenomenon is called above - threshold ionization ( ati ) and has attracted increasing attention since its 1979 discovery by agostini and co - workers @xcite . recently
, impressive progress has been achieved in the study of ati ..
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for example , great emphasis has been placed on employing ati as a tool for the attosecond imaging of molecular orbitals @xcite .
imaging applications are based on the physical mechanism behind this phenomenon , in which the active electron ( i ) is released in the continuum , ( ii ) is accelerated by the field , and ( iii ) reaches the detector without returning or after rescattering with its parent molecule .
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10,154 |
Suppose that you have an abstract for a scientific paper: collective charge density excitation spectra of both a spatially separated two - component quasi - one dimensional ( 1d ) quantum plasma , as existing in a semiconductor double quantum wire structure , and a 1d homogeneous electron - hole plasma , as appropriate for a photoexcited semiconductor quantum wire system , are calculated within the two - component random - phase - approximation .
we find two phase fluctuation collective modes , one ( optical plasmon , op ) with energy proportional to @xmath0 is the _ total _ in - phase ( out - of - phase ) charge density oscillation of the system and the other ( acoustic plasmon , ap ) with a linear energy dispersion as @xmath1 is the _ neutral _ out - of - phase ( in - phase ) charge density oscillation of the system for the situation where the two components have the same ( opposite ) charges , where @xmath2 is the 1d wave vector and @xmath3 is a characteristic 1d confinement size .
in contrast to higher dimensional systems we find the neutral long wavelength ap mode to be generically undamped by landau damping effects due to the severe suppression of single particle excitations in 1d systems .
we also investigate the effect of impurity scattering on the collective mode dispersion and damping , and calculate the collective mode spectral weight by obtaining the dynamical structure factor .
we find that both op and ap modes are overdamped by impurity scattering below some critical wave vector .
we find that in the long wavelength limit the spectral weight is carried mostly by the op , but the spectral weight of the undamped ap mode at finite ( but not too large ) wave vectors is comparable with that of the op mode , making it viable to observe the ap mode in semiconductor quantum wire systems .
the effect of the interwire electron tunneling in a biwire system on the collective charge density excitation spectra is also studied .
we discuss the mode dispersion and damping from an effective luttinger liquid perspective as well and in some cases include....
And you have already written the first three sentences of the full article: recent advances in fabrication techniques involving molecular beam epitaxy and lithography have now made it possible to make narrow gaas - based quasi - one dimensional ( 1d ) electronic systems with lateral dimensions of the order of the bohr radius @xcite . in these so - called quantum wire structures , the motion of charge carriers is confined in two transverse directions but is essentially free ( in the effective mass sense ) in the longitudinal direction .
study of collective modes in reduced dimensional electron systems in semiconductor nanostructures is a subject of growing experimental and theoretical interest .
experimentally , far - infrared optical spectroscopy@xcite and resonant inelastic light scattering spectroscopy@xcite have been used to study quasi-1d elementary electronic excitations ..
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several theoretical studies , mostly based on the random phase approximation ( rpa ) , have been reported on the energy dispersion of elementary excitations in semiconductor quantum wires .
the measured 1d intrasubband plasmon dispersion agrees remarkably well with the rpa predictions @xcite .
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Suppose that you have an abstract for a scientific paper: we present a complete next - to - leading order ( nlo ) calculation for the total cross section for inclusive higgs pair production via bottom - quark fusion at the cern large hadron collider ( lhc ) in the minimal supersymmetric standard model ( mssm ) and the minimal supergravity model ( msugra ) .
we emphasize the contributions of squark and gluino loops ( sqcd ) and the decoupling properties of our results for heavy squark and gluino masses .
the enhanced couplings of the @xmath0 quark to the higgs bosons in supersymmetric models with large @xmath1 yield large nlo sqcd corrections in some regions of parameter space . .
And you have already written the first three sentences of the full article: in the standard model ( sm ) , only one higgs doublet is introduced and one neutral higgs boson remains after electroweak symmetry breaking . in the minimal supersymmetric standard model ( mssm )
@xcite , two higgs doublets are required to break the electroweak symmetry .
the two higgs doublets , @xmath2 and @xmath3 , couple to fermions with weak isospin @xmath4 and @xmath5 respectively @xcite . after spontaneous symmetry breaking , there remain five physical higgs bosons : a singly charged higgs boson @xmath6 , two neutral cp - even scalars @xmath7 and @xmath8 , and a neutral cp - odd pseudoscalar @xmath9 ..
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the higgs potential is constrained by supersymmetry such that all tree - level higgs boson masses and couplings are determined by just two independent parameters , commonly chosen to be the mass of the cp - odd pseudoscalar ( @xmath10 ) and the ratio of vacuum expectation values of the neutral higgs fields ( @xmath11 ) . in the standard model ,
gluon fusion is the dominant process for producing a pair of higgs bosons via triangle and box diagrams with internal top quarks and bottom quarks @xcite .
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10,156 |
Suppose that you have an abstract for a scientific paper: we perform a systematic study of the multi wavelength signal induced by weakly interacting massive particle ( wimp ) annihilations at the galactic center ( gc ) .
referring to a generic wimp dark matter ( dm ) scenario and depending on astrophysical inputs , we discuss spectral and angular features and sketch correlations among signals in the different energy bands .
none of the components which have been associated to the gc source sgr a@xmath0 , nor the diffuse emission components from the gc region , have spectral or angular features typical of a dm source .
still , data - sets at all energy bands , namely the radio , near infrared , x - ray and gamma - ray bands , contribute to place significant constraints on the wimp parameter space . in general , the gamma - ray energy range is not the one with the largest signal to background ratio . in the case of large magnetic fields close to the gc ,
x - ray data give the tightest bounds .
the emission in the radio - band , which is less model dependent , is very constraining as well .
the recent detection by hess of a gc gamma - ray source , and of a diffuse gamma - ray component , limits the possibility of a dm discovery with the next generation of gamma - ray telescopes , like glast and cta .
we find that most of the region in the parameter space accessible to these instruments is actually already excluded at other wavelengths . on the other hand , there may be still an open window to improve constraints with wide - field radio observations . .
And you have already written the first three sentences of the full article: weakly interacting massive particles ( wimps ) are among the leading candidates for the dark matter ( dm ) component in the universe .
the framework is elegant and simple : stable wimps can be embedded in most extensions to the standard model of particle physics . in thermal equilibrium in the early universe ,
they decouple from the primordial bath in the non - relativistic regime ..
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their relic abundance scales approximatively with the inverse of their total pair annihilation rate into lighter particles : the weak - interaction coupling ensures that , within the standard cosmological scenario , such relic density is of the order of the mean density of dm in the universe today , as determined in cosmological observations ( for comprehensive reviews on wimp dm candidates and their detection , see , e.g. , @xcite ) in principle , one of the routes to test the hypothesis of wimp dm stems from the bases of the framework themselves .
supposing that wimps are indeed the building blocks of all structures in the universe , there is a ( small but finite ) probability that wimps in dm halos , including the halo of the milky way , annihilate in pairs into detectable species .
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Suppose that you have an abstract for a scientific paper: we study transport properties of weakly interacting one - dimensional electron systems including on an equal footing thermal equilibration due to three - particle collisions and the effects of large - scale inhomogeneities .
we show that equilibration in an inhomogeneous quantum wire is characterized by the competition of interaction processes which reduce the electrons total momentum and such which change the number of right- and left - moving electrons .
we find that the combined effect of interactions and inhomogeneities can dramatically increase the resistance of the wire .
in addition , we find that the interactions strongly affect the thermoelectric properties of inhomogeneous wires and calculate their thermal conductance , thermopower , and peltier coefficient . .
And you have already written the first three sentences of the full article: transport properties of low - dimensional systems have been subject of intensive research work over the last two decades .
one of the fundamental discoveries that has driven the field was the observation of conductance quantization in ballistic quantum wires and quantum point contacts . @xcite it was found that conductance exhibits a staircase - like dependence on the electron density with the universal step .
the understanding of this phenomenon follows already from the single - electron picture , which predicts for the conductance of a one - dimensional single channel - clean wire , @xcite @xmath0 the physical origin of conductance plateaus at certain gate voltages was associated with a fixed number of occupied electronic subbands , each supplying one quantum of conductance @xmath1 . within the same approach of noninteracting particles both charge and energy.
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are carried by electronic excitations .
this results in the universal relation between electric and thermal conductances , known as the wiedemann - franz law @xmath2 .
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Suppose that you have an abstract for a scientific paper: we present a pattern recognition method which use datapoints on a plane and estimates the parameters of a circle .
mc data are generated in order to test the method s efficiency over noise hits , uncertainty in the hits positions and number of datapoints .
the scenario were the hits from a quadrant of the circle are missing is also considered .
the method proposed is proven to be robust , accurate and very efficient . .
And you have already written the first three sentences of the full article: various types of detectors require algorithms that handle number of datapoints in a plane and reconstruct the parameters of a circle , @xcite,@xcite,@xcite .
these algorithms need to be robust against noise hits and analyse big amount of data relatively fast .
finally , the performance of the algorithm needs as independent as possible with the resolution of the detector . in a recent paper @xcite we examined the use of the legendre transform for the determination of a circle s characteristics . in this paper.
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we revisit this problem and describe in detail an alternative method , based on gaussian sums , proposed for the reconstruction of the circle s center @xmath0 and radius @xmath1 from a given set of datapoints .
following the notation and train of though of @xcite , using @xmath2 datapoints ( @xmath3 , @xmath4 and @xmath5 ) , we can have a first estimation of the center @xmath6 and the radius , @xmath7 , of the circle ( see figure [ fig : circle_circle ] ) . and radius @xmath7 . ]
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Suppose that you have an abstract for a scientific paper: we consider the time evolution of a particle subjected to both a uniform electrostatic field @xmath0 and a one - dimensional delta - function potential well .
we derive the propagator @xmath1 of this system , directly leading to the wavefunction @xmath2 , in which its essential ingredient @xmath3 , accounting for the ionization - recombination in the bound - continuum transition , is exactly expressed in terms of the multiple hypergeometric functions @xmath4 .
and then we obtain the ingredient @xmath3 in an appropriate approximation scheme , expressed in terms of the generalized hypergeometric functions @xmath5 being much more transparent to physically interpret and much more accessible in their numerical evaluation than the functions @xmath4 . .
And you have already written the first three sentences of the full article: the ionization of atoms in an external electric field is , as well - known , one of the oldest subjects in quantum physics . as a simple example of the ionization , hydrogen - like atoms in a uniform electrostatic field
have been extensively considered ( see , e.g. , @xcite ) . here
the background potential caused by the field decreases without limit in one direction , and the electron initially in the bound state will eventually tunnel through the `` barrier '' created by the field , so leading to ionization of the atom . the tunneling rate for an _ ensemble _ of many independent electrons has been calculated based on the exponential decay law following from the statistical assumption that the tunneling rate is proportional to the number of available atoms . on the other hand , big experimental advances in the field of nano - scale physics have highly enlarged a need for a detailed understanding of the ( time - dependent ) tunneling process of _ individual _ electrons subjected to an external field ..
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in fact , the nano - scale devices have been designed and fabricated , examples of which are molecular switches @xcite and resonant tunnel junctions @xcite , etc . however , in exploring the time evolution of the electron tunneling process leading to ionization , we have a considerable mathematical difficulty that there are no exactly solvable models for a transition from a bound state to the continuum .
further , even obtaining the numerical solution , with high accuracy , to this problem can not be considered an easy task either , especially in the strong - field limit where a highly oscillatory behavior is found in the time evolution of the bound - continuum transition .
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Suppose that you have an abstract for a scientific paper: we derive a realistic microscopic model for doped colossal magnetoresistance manganites , which includes the dynamics of charge , spin , orbital and lattice degrees of freedom on a quantum mechanical level .
the model respects the @xmath0 spin symmetry and the full multiplet structure of the manganese ions within the cubic lattice . concentrating on the hole doped domain ( @xmath1 ) we study the influence of the electron - lattice interaction on spin and orbital correlations by means of exact diagonalisation techniques .
we find that the lattice can cause a considerable suppression of the coupling between spin and orbital degrees of freedom and show how changes in the magnetic correlations are reflected in dynamic phonon correlations .
in addition , our calculation gives detailed insights into orbital correlations and demonstrates the possibility of complex orbital states . .
And you have already written the first three sentences of the full article: the observation of the colossal magnetoresistance effect ( cmr ) @xcite in doped manganese oxides with perovskite structure , r@xmath2a@xmath3mno@xmath4 ( r = rare - earth , a = alkaline - earth metal ) , moved these materials into the focus of intense research activity @xcite .
it turned out soon that the complex electronic and magnetic properties of the manganites depend on a close interplay of almost all degrees of freedom known in solid state physics , namely itinerant charges , localised spins , orbitals , and lattice vibrations . on the one hand ,
the strong coulomb interaction @xmath5 and the hund s rule coupling @xmath6 introduce a spin background and affect the charge mobility via double - exchange @xcite . on the other hand , the cubic environment of the mn sites within the perovskite lattice results in a crystal field splitting of mn-@xmath7-orbitals into @xmath8 and @xmath9 and.
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gives rise to an orbital degeneracy in the ground - state of mn@xmath10 ions .
this orbital degeneracy , in turn , connects the electronic system to the lattice , making it sensible to jahn - teller distortion and polaronic effects @xcite .
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Suppose that you have an abstract for a scientific paper: we present the result of astrometric observations of the radio pulsar psr b0656 + 14 , made using the very long baseline array .
the parallax of the pulsar is @xmath0 mas , yielding a distance @xmath1 pc .
this independent distance estimate has been used to constrain existing models of thermal x - ray emission from the neutron star s photosphere .
simple blackbody fits to the x - ray data formally yield a neutron star radius @xmath2 km . with more realistic fits to a magnetized hydrogen atmosphere
, any radius between @xmath3 and @xmath4 km is allowed . .
And you have already written the first three sentences of the full article: the cooling of neutron stars offers a unique diagnostic of the physics of the interior .
because the emergent spectrum is nearly blackbody , the observed flux can be modeled to estimate the temperature , the intervening column of absorbing material , and the ratio of radius to distance .
astrometric measurement of the distance then allows an estimation of the photospheric radius , which is sensitively dependent on the high density equation of state ..
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psr b0656 + 14 is a middle - aged ( @xmath5 yr old ) pulsar , with a spectrum dominated at ultraviolet and soft - x - ray wavelengths by a @xmath6 k blackbody component , as expected in standard cooling models .
distance estimates obtained from measurements of radio dispersion in the ionized material between earth and the pulsar have led to a large estimated stellar radius , @xmath7 km . here
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Suppose that you have an abstract for a scientific paper: we propose a new way of defining entropy of a system , which gives a general form which may be nonextensive as tsallis entropy , but is linearly dependent on component entropies , like renyi entropy , which is extensive .
this entropy has a conceptually novel but simple origin and is mathematically easy to define by a very simple expression , though the probability distribution resulting from optimizing it gives rather complex , which is compared numerically with the other entropies .
it may , therefore , appear as the right candidate in a physical situation where the probability distribution does not suit any of the previously defined forms . .
And you have already written the first three sentences of the full article: entropy is a measure of disorder or randomness , and assumes its maximal value when a system can be in a number of states randomly with equal probability , and is minimally zero when the system is in a given state , with no uncertainty in its description .
apart from this common feature shared by all definitions of entropy at two ends of the scale , variations are possible in particularizing the functional form in between @xcite .
they lead to different forms of the probability distributions for states with different energies or some other conserved attribute ..
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some turn up as extensive , where the entropy of a combination of systems is simply the sum of the entropies of the systems , as in the classical case of the shannon form , while others can be defined to be not so .
renyi entropy @xcite is different from shannon , yet extensive , and hence the shannon form is not unique with respect to the property of extensivity .
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Suppose that you have an abstract for a scientific paper: we present the first results from a bayesian analysis of the _ wmap _ first year data using a gibbs sampling technique . using two independent , parallel supercomputer codes
we analyze the _ wmap _ q , v and w bands .
the analysis results in a full probabilistic description of the information the _ wmap _ data set contains about the power spectrum and the all - sky map of the cosmic microwave background anisotropies .
we present the complete probability distributions for each @xmath0 including any non - gaussianities of the power spectrum likelihood . while we find good overall agreement with the previously published _ wmap _ spectrum , our analysis uncovers discrepancies in the power spectrum estimates at low @xmath1 multipoles .
for example we claim the best - fit @xmath2cdm model is consistent with the @xmath3 inferred from our combined q+v+w analysis with a 10% probability of an even larger theoretical @xmath3 . based on our exact analysis
we can therefore attribute the `` low quadrupole issue '' to a statistical fluctuation . .
And you have already written the first three sentences of the full article: cosmic microwave background ( cmb ) power spectrum estimation from large datasets such as the wilkinson microwave anisotropy probe ( _ wmap _ ) @xcite presents a considerable computational challenge . with the exception of some specialized methods @xcite , obtaining the power spectrum and error bars for a generalized , large cmb dataset without introducing significant simplifications has , until now , been computationally impossible .
however , a new numerical approach based on gibbs sampling has been developed recently by jewell , levin , and anderson ( 2004 ) and wandelt , larson , and lakshminarayanan ( 2004 ) which offers the hope of overcoming these computational difficulties and allowing the analysis of large cmb datasets regardless of scanning strategy , noise characteristics and so on . in this letter
we present our results from the application of this new method to the first year _.
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wmap _ data .
we developed two independent , parallel codes to achieve this and a detailed description of the implementation of these codes is given in a companion publication @xcite .
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Suppose that you have an abstract for a scientific paper: a deep search for the potential glycine precursor hydroxylamine ( nh@xmath0oh ) using the caltech submillimeter observatory ( cso ) at @xmath1 mm and the combined array for research in millimeter - wave astronomy ( carma ) at @xmath2 mm is presented toward the molecular outflow l1157 , targeting the b1 and b2 shocked regions .
we report non - detections of nh@xmath0oh in both sources .
we a perform non - lte analysis of ch@xmath3oh observed in our cso spectra to derive kinetic temperatures and densities in the shocked regions . using these parameters , we derive upper limit column densities of nh@xmath0oh of @xmath4 @xmath5 and @xmath6 @xmath5 toward the b1 and b2 shocks , respectively , and upper limit relative abundances of @xmath7 and @xmath8 , respectively . .
And you have already written the first three sentences of the full article: glycine ( nh@xmath0ch@xmath0cooh ) , the simplest amino acid , has been identified in cometary @xcite and meteoritic samples @xcite , however it is not yet known whether the species is formed in these solid bodies , in the interstellar medium ( ism ) , or both . indeed , a detection in the ism has so far proven ellusive @xcite .
although chemical models predict the formation of glycine in the ism , in low abundance ( see , e.g. @xcite and refs . therein ) , it has been difficult to observationally constrain them without a detection of the species .
the relative likelihood of different possible formation routes can , however , be constrained by careful observation of the reactants used in the chemical models to form glycine ..
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one pathway which has garnered significant interest is the formation of glycine through the reaction of hydroxylamine ( nh@xmath0oh ) , or its protonated and ionized derivatives , with acetic acid ( ch@xmath3cooh ) , a known interstellar molecule @xcite .
ionization or protonation of nh@xmath0oh under interstellar conditions should be efficient @xcite , and subsequent laboratory work has demonstrated the formation of glycine from nh@xmath0oh and its ionized and protonated forms @xcite . although recent theoretical work has suggested that these gas - phase routes forming glycine through these reactions are inefficient under interstellar conditions @xcite , condensed - phase surface - mediated reactions remain a possibility , and observational constraints of the precursors are still desirable for the refinement of models .
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Suppose that you have an abstract for a scientific paper: first quasiclassical correction to the differential cross section of high - energy electron - positron photoproduction in the electric field of a heavy atom is obtained with the exact account of the field .
this correction is responsible for the charge asymmetry @xmath0 in this process .
when the transverse momentum of at least one of the produced particles is much larger than the electron mass @xmath1 , the charge asymmetry can be as large as tens percent .
we also estimate the contribution @xmath2 to the charge asymmetry coming from the compton - type diagram . for heavy nuclei ,
this contribution is negligible . for light nuclei ,
@xmath2 is noticeable only when the angle between the momenta of electron and positron is of order of @xmath3 ( @xmath4 is the photon energy ) while the transverse momenta of both particles are much larger than @xmath1 . .
And you have already written the first three sentences of the full article: the production of an electron - positron pair by a photon in an atomic field is one of the most important processes of qed . because of its importance for various applications ,
see refs .
@xcite , this process has been investigated in numerous theoretical and experimental papers ..
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the cross section of the process in the born approximation is known for arbitrary energy @xmath4 of the incoming photon , refs .
@xcite ( we set @xmath5 throughout the paper ) . for heavy atoms ,
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Suppose that you have an abstract for a scientific paper: as one of the extensions of the standard model , we investigate the anomalous four - point @xmath0 scalar- and tensor - type interactions , which originate from the gauge invariant dimension - five operators .
the coupling constants are constrained by the measured branching ratio of the @xmath1 decay : @xmath2 and @xmath3 at the 95% confidence level for the scalar and tensor interactions , respectively . .
And you have already written the first three sentences of the full article: the decays of @xmath4 lepton provide unique opportunities to search for the effects beyond the standard model ( bsm ) @xcite .
the large mass of @xmath4 ( @xmath5 mev/@xmath6 @xcite ) , in comparison with that of the electron or muon , allows one to expect an essential enhancement in the sensitivity to the effects of new physics ( np ) @xcite . of all tau decays , the leptonic ones are precisely calculated within electroweak sector of the sm ,
hence they offer a clean laboratory to search for the effects of np . through the measurement of michel parameters , @xmath7 , @xmath8 , @xmath9 and @xmath10 , in ordinary leptonic decays @xmath11 ( @xmath12 ) ,.
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the experimental verification of the lorentz structure of the charged weak interaction was carried out @xcite .
the most precision measurements were done by aleph @xcite and cleo @xcite collaborations .
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Suppose that you have an abstract for a scientific paper: we observed sgr a * using the very large array ( vla ) and the giant metrewave radio telescope ( gmrt ) at multiple cm and mm wavelengths on 17 june 2003 .
the measured flux densities of sgr a * , together with those obtained from the submillimeter array ( sma ) and the keck ii 10 m telescope on the same date , are used to construct a simultaneous spectrum of sgr a * from 90 cm to 3.8 @xmath0 m .
the simultaneous spectrum shows a spectral break at about 3.6 cm , a possible signature of synchrotron self - absorption of the strong radio outburst which occurred near epoch 17 july 2003 . at 90 cm ,
the flux density of sgr a * is @xmath1 jy , suggesting a sharp decrease in flux density at wavelengths longer than 47 cm .
the spectrum at long cm wavelengths appears to be consistent with free - free absorption by a screen of ionized gas with a cutoff @xmath2100 cm .
this cutoff wavelength appears to be three times longer than that of @xmath230 cm suggested by davies , walsh & booth based on observations in 1974 and 1975 .
our analysis suggests that the flux densities of sgr a * at wavelengths longer than 30 cm could be attenuated and modulated by stellar winds from massive stars close to sgr a*. .
And you have already written the first three sentences of the full article: soon after the discovery of the compact radio source sagittarius a * ( sgr a * ) at the galactic center ( gc ) @xcite , davies , walsh & booth ( 1976 , hereafter dwb ) carried out observations of sgr a * at 0.408 , 0.96 and 1.66 ghz .
sgr a * was only detected at the two higher frequencies .
the measurements showed a low - frequency turnover around 1 ghz in the spectrum of sgr a*. the authors attributed the decrease in flux density below 1 ghz to free - free absorption from ionized gas of sgr a west ..
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recent observations of sgr a * at both 620 and 330 mhz indicate that the spectrum below 1 ghz may indeed have a pronounced turnover . at 620 mhz ,
roy & rao ( 2004 ) detected sgr a * using the gmrt with a flux density of @xmath3 jy with an angular resolution of @xmath4 , while @xcite detected sgr a * at 330 mhz using the vla of the national radio astronomy observatory ( nrao ) with a flux density of @xmath5 jy ( resolution of @xmath29 ) .
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Suppose that you have an abstract for a scientific paper: we present a novel extension of thompson sampling for stochastic sequential decision problems with graph feedback , even when the graph structure itself is unknown and/or changing .
we provide theoretical guarantees on the bayesian regret of the algorithm , linking its performance to the underlying properties of the graph .
thompson sampling has the advantage of being applicable without the need to construct complicated upper confidence bounds for different problems .
we illustrate its performance through extensive experimental results on real and simulated networks with graph feedback .
more specifically , we tested our algorithms on power law , planted partitions and erds rnyi graphs , as well as on graphs derived from facebook and flixster data .
these all show that our algorithms clearly outperform related methods that employ upper confidence bounds , even if the latter use more information about the graph . .
And you have already written the first three sentences of the full article: sequential decision making problems under uncertainty appear in most modern applications , such as automated experimental design , recommendation systems and optimisation .
the common structure of these applications that , at each time step @xmath0 , the decision - making agent is faced with a choice . after each decision , it obtains some problem - dependent feedback @xcite . for the so - called _ bandit _
problem , the choices are between different _ arms _ , and the feedback consists of a single scalar reward obtained by the arm at time @xmath0 . for the _ prediction _ ( or full - information ) problem.
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, it obtains the reward of the chosen arm , but also observes the rewards of all other choices at time @xmath0 . in both cases ,
the problem is to maximise the total reward obtained over time .
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Suppose that you have an abstract for a scientific paper: in this paper , we investigate the simultaneous distribution of the fractional parts of @xmath0 , where @xmath1 , @xmath2 , @xmath3 , @xmath4 , and @xmath5 are fixed distinct positive real numbers and @xmath6 runs over the imaginary parts of the non - trivial zeros of the riemann zeta - function . .
And you have already written the first three sentences of the full article: let @xmath7 be a fixed positive real number , and @xmath6 run over the imaginary parts of the zeros of the riemann zeta - function .
we are interested in the distribution of the fractional parts @xmath8 .
rademacher @xcite was the first to consider this problem and he conjectured that , for a certain specific type of @xmath7 , there should be a `` predominance of terms which fulfill @xmath9 '' . since the fractional parts are uniformly distributed modulo @xmath10 , as proved by hlawka @xcite in 1975 , any discrepancy must be very subtle ..
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the first and third authors uncovered in @xcite this delicate inequity in the fractional parts and not only proved rademacher correct , but also gave a much more precise measure for this phenomenon .
let @xmath11 be the torus .
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Suppose that you have an abstract for a scientific paper: the workshop on small ionized and neutral structures in the interstellar medium featured many contributions on the theory of the objects which are responsible for `` tiny scale atomic structures '' ( tsas ) and `` extreme scattering events '' ( ese ) .
the main demand on theory is accounting for objects that have the high densities and small sizes apparently required by the observations , but also persist over a sufficiently long time to be observable .
one extensively - discussed mechanism is compressions by transonic turbulence in the warm interstellar medium , followed by thermal instabilities leading to an even more compressed state . in addressing the requirements for overpressured but persistent objects
, workshop participants also discussed fundamental topics in the physics of the interstellar medium , such as the timescale for evaporation of cool dense clouds , the relevance of thermodynamically - defined phases of the ism , the effect of magnetic fields , statistical effects , and the length and time scales introduced by interstellar processes . .
And you have already written the first three sentences of the full article: the sins meeting was dominated by an interesting and often disconnected mix of observational reports on `` small scale '' structure in various interstellar environments , and theoretical works attempting to explain such observed structures .
interestingly , there was a wider variety in the kinds and physical properties of the structures reported observationally than in the theoretical approaches presented as potential models .
this article includes a review of the theoretically - significant results presented at the sins workshop ..
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for reference , we first recall observational results that pose the challenge for the theoretical studies .
small - scale structure was reported to be observed in all three of the diffuse ionized , atomic and molecular components of the interstellar medium ( ism ) , although the physical properties of the structures in each component are as varied as the environments in which they are found ( see the observational review by heiles & stinebring in this volume ) .
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Suppose that you have an abstract for a scientific paper: the results of the ccd observations of the 2002 superoutburst of v1141 aql are described .
we have detected clear superhumps characterized by the period of 0.05930(5 ) days .
there was another , much weaker , modulation in the light curve of v1141 aql .
its amplitude is equal to @xmath0 mag and its period to 0.03923(8 ) days .
we have also discovered quasi periodic oscillations ( qpos ) with a mean period equal to 130 s and amplitude of @xmath1 mag .
* key words : * stars : individual : v1141 aql binaries : close novae , cataclysmic variables .
And you have already written the first three sentences of the full article: v1141 aql was suspected for variability by kukarkin
_ et al . _ ( 1951 ) and confirmed as a variable star by kukarkin _
et al . _ ( 1968 ) ..
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it was later classified as a dwarf nova by vogt and bateson ( 1982 ) . in subsequent documentation ,
v1141 aql is only referred to as a dwarf nova ( bruch _ et al .
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Suppose that you have an abstract for a scientific paper: we have carried out a search for 18-cm oh megamaser ( ohm ) emission with the green bank telescope .
the targeted galaxies comprise a sample of 121 ulirgs at @xmath0 , making this the first large , systematic search for ohms at @xmath1 .
nine new detections of ohms are reported , all at redshifts @xmath2 . for the remainder of the galaxies ,
observations constrain the upper limit on oh emission ; this rules out ohms of moderate brightness ( @xmath3 ) for 26% of the sample , and extremely bright ohm emission ( @xmath4 ) for 73% of the sample .
losses from rfi result in the ohm detection fraction being significantly lower than expected for galaxies with @xmath5 .
the new ohm detections are used to calculate an updated oh luminosity function , with @xmath6 ; this slope is in agreement with previous results .
non - detections of ohms in the cosmos field constrain the predicted sky density of ohms ; the results are consistent with a galaxy merger rate evolving as @xmath7 , where @xmath8 . .
And you have already written the first three sentences of the full article: oh megamasers ( ohms ) trace of some of the most extreme physical conditions in the universe - in particular , the presence of an ohm signals specific stages in the merger process of gas - rich galaxies .
ohms can thus be used as probes of their environments , both directly and indirectly .
characteristics of the maser emission itself can be used to measure extragalactic magnetic fields ( via zeeman splitting ) and gas kinematics , while the _ presence _ of an ohm is a signpost for phenomena associated with galaxy mergers , including extreme star formation and merging black holes ..
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ohms are a unique tool in this respect due to their extreme luminosities and ability to be seen at cosmic distances .
the total number of ohms detected to date is still low . as of 2012 , there are @xmath9 ohms published in the literature , with roughly 50% discovered in the arecibo survey of ( * ? ? ?
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Suppose that you have an abstract for a scientific paper: we present a list of @xmath0 scuti stars in double and multiple systems , ranging from the very wide binaries to the very close ones such as spectroscopic and eclipsing systems including the optical visual pairs which are of no further use here .
our aim is to group the information from the binarity on the one hand and the pulsational characteristics on the other hand for as complete a sample as possible of @xmath0 scuti stars in stellar systems .
a selection of 18 well - documented cases , taking care that every type of binary is being represented , is discussed more extensively . .
And you have already written the first three sentences of the full article: it is well known that the vast majority of stars belong to a binary or a multiple system , irrespective of their spectral type .
recent surveys with improved astrometric accuracy , either from space or from the ground , present clear evidence that the higher the accuracy , the larger the number of binary detections .
up to 3000 new binaries have thus been discovered during the hipparcos satellite mission ( lindegren 1997 ) ..
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the frequency of binaries is estimated to be at least 60% in the solar neighbourhood ( duquennoy & mayor 1991 ) but this is probably an underestimation as modelisation tends to show .
for example , odenkirchen and brosche ( 1999 ) found that a frequency of at least 70% was needed in some models to account for the existence of another 2400 ( up to now undetected ) astrometric binaries in the hipparcos catalogue .
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Suppose that you have an abstract for a scientific paper: we consider in this note a class of two - dimensional determinantal coulomb gases confined by a radial external field . as
the number of particles tends to infinity , their empirical distribution tends to a probability measure supported in a centered ring of the complex plane .
a quadratic confinement corresponds to the complex ginibre ensemble . in this case
, it is also already known that the asymptotic fluctuation of the radial edge follows a gumbel law .
we establish in this note the universality of this edge behavior , beyond the quadratic case .
the approach , inspired by earlier works of kostlan and rider , boils down to identities in law and to an instance of the laplace method . .
And you have already written the first three sentences of the full article: let us consider a gas of charged particles @xmath0 on the complex plane @xmath1 , confined individually by the external field @xmath2 and experiencing a coulomb pair repulsive interaction .
this corresponds to the probability distribution on @xmath3 with density proportional to @xmath4 where @xmath5 is a fixed parameter and where @xmath6 is a fixed smooth function .
we are mostly interested in asymptotics in @xmath7 of this particles system . to ensure the integrability for large enough @xmath8 , and following @xcite , it is convenient to assume that there exists some real number @xmath9 with @xmath10 such that @xmath11 . indeed ,.
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using the inequality @xmath12 valid for any @xmath13 , we get @xmath14 the factor @xmath8 in front of @xmath2 in the density is motivated by the remarkable formula @xmath15 where @xmath16 is the empirical distribution of the particles . indeed , following @xcite ( see @xcite for more general models ) , on the space @xmath17 of probability measures on @xmath1 equipped with the topology of narrow convergence ( i.e. the dual topology related to bounded continuous test functions ) , the functional @xmath18 is strictly convex , bounded from below with compact level sets , admits a unique minimizer @xmath19 , and the empirical distribution @xmath20 satisfies a large deviations principle for the weak topology at speed @xmath21 with good rate function @xmath22 . in particular , from the first borel - cantelli lemma , with probability one , @xmath23 weakly as @xmath7 . following ( * ? ? ?
* th.1.3 ) , it can be shown that @xmath19 has compact support when @xmath24 .
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Suppose that you have an abstract for a scientific paper: 28 size spectra of extensive air showers in the knee region from 7 different experiment are analysed consistently .
they are fitted by adjusting either 4 or 5 parameters : knee position , power law exponents above and below the knee region , overall intensity and , in addition , a parameter describing the smoothness of the bend .
the residuals are then normalized to the same knee position and averaged .
when 5 parameters are employed no systematic deviation from a simple smooth knee is apparent at the 1 % level up to about a factor of 4 above the knee . at larger shower sizes
a moderately significant deviation can be seen whose shape and position are compatible with a second knee caused by iron group nuclei .
cosmic rays ; knee ; eas .
And you have already written the first three sentences of the full article: the existence of the knee in the spectra of extensive air showers ( eass ) has been known by now for more than 40 years @xcite .
first seen in the number of electrons ( the shower size ) observed near sea level it was later also observed in the muon number @xcite , hadron properties @xcite and muon densities @xcite .
in fact it seems to show up in all shower observables if investigated in sufficient detail ..
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nevertheless its origin is still obscure . of the explanations
proposed two seem to have found more general acceptance .
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Suppose that you have an abstract for a scientific paper: we study a model of stochastic deposition - evaporation with recombination , of three species of dimers on a line .
this model is a generalization of the model recently introduced by barma _ et .
al . _
( 1993 _ phys .
rev .
lett . _ * 70 * 1033 ) to @xmath0 states per site .
it has an infinite number of constants of motion , in addition to the infinity of conservation laws of the original model which are encoded as the conservation of the irreducible string .
we determine the number of dynamically disconnected sectors and their sizes in this model exactly . using the additional symmetry
we construct a class of exact eigenvectors of the stochastic matrix .
the autocorrelation function decays with different powers of @xmath1 in different sectors .
we find that the spatial correlation function has an algebraic decay with exponent @xmath2 , in the sector corresponding to the initial state in which all sites are in the same state .
the dynamical exponent is nontrivial in this sector , and we estimate it numerically by exact diagonalization of the stochastic matrix for small sizes . we find that in this case @xmath3 .
# 1 pacs numbers : 02.50+s , 75.10j , 82.20.m , 05.50+q .
And you have already written the first three sentences of the full article: recently a very interesting stochastic model with deposition and evaporation processes has been introduced by barma _ et .
_ @xcite . in this model one
deposits atoms on to @xmath4 adjacent vacant sites of a @xmath5-dimensional lattice and evaporates atoms from any @xmath4 adjacent occupied sites , with specific rates for deposition and evaporation ..
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the cases @xmath6 and @xmath7 are exactly solvable , the former being trivial , and the latter being equivalent to ferromagnetic heisenberg spin-@xmath8 chain . for @xmath9 , on a linear chain of length @xmath10 , the phase space of this @xmath4-mer model consisting of the @xmath11 possible configurations is found to break up into an exponentially large number of dynamically disconnected sectors @xcite . this may be understood as being due to the existence of an infinite number of independent conserved quantities in this model @xcite .
these conservation laws also give rise to a wide range of relaxation behavior @xcite .
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Suppose that you have an abstract for a scientific paper: it has been well recognized that channel state information ( csi ) feedback is of great importance for dowlink transmissions of closed - loop wireless networks . however , the existing work typically researched the csi feedback problem for each individual mobile station ( ms ) , and thus , can not efficiently model the interactions among self - interested mobile users in the network level . to this end
, in this paper , we propose an alternative approach to investigate the csi feedback rate control problem in the analytical setting of a game theoretic framework , in which a multiple - antenna base station ( bs ) communicates with a number of co - channel mss through linear precoder .
specifically , we first present a non - cooperative feedback - rate control game ( nfc ) , in which each ms selects the feedback rate to maximize its performance in a distributed way . to improve efficiency from a social optimum point of view ,
we then introduce pricing , called the non - cooperative feedback - rate control game with price ( nfcp ) .
the game utility is defined as the performance gain by csi feedback minus the price as a linear function of the csi feedback rate .
the existence of the nash equilibrium of such games is investigated , and two types of feedback protocols ( fdma and csma ) are studied .
simulation results show that by adjusting the pricing factor , the distributed nfcp game results in close optimal performance compared with that of the centralized scheme . .
And you have already written the first three sentences of the full article: the increasing demands for fast and reliable wireless communications have spurred development of multiple - antenna systems in order to efficiently harvest the capacity gains @xcite .
recent information - theoretic research indicates that a feedback channel can be further employed to furnish channel state information ( csi ) to the transmitter side , which may affect closed - loop capacity gains @xcite . with some form of knowledge of the wireless channel conditions
, the transmitter can adapt to the propagation conditions by the use of a variety of channel adaptive techniques @xcite . specifically , in a multiple mobile station ( ms ) scenario , with the knowledge of the channel to nearby co - channel mss , it is possible to actively suppress the signal to the interfered users and meanwhile maximize the effective signal power @xcite . in this case , the base station ( bs ) can obtain the required channel coefficients through a feedback channel from the ms ..
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then , mechanisms such as multiple - antenna precoding can be utilized to mitigate the effects of co - channel interference and exploit spatial dimensions to increase the capacity of wireless networks @xcite .
since csi is essential for closed - loop wireless communication systems , the techniques on how to effectively feedback csi from the transmitter to the receiver has been intensively studied @xcite . as perfect feedback of csi
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Suppose that you have an abstract for a scientific paper: we investigate the effects of the nuclear equation of state ( eos ) to the neutron star cooling .
new era for nuclear eos has begun after the discovery of @xmath0 neutron stars psr j1614@xmath12230 and psr j0348@xmath20432 @xcite .
also recent works on the mass and radius of neutron stars from low - mass x - ray binaries @xcite strongly constrain the eos of nuclear matter . on the other hand , observations of the neutron star in cassiopeia a ( cas a ) more than 10 years confirmed the existence of nuclear superfluidity @xcite .
nuclear superfluidity reduces the heat capacities as well as neutrino emissivities . with nuclear superfluidity the neutrino emission processes
are highly suppressed , and the existence of superfluidity makes the cooling path quite different from that of the standard cooling process .
superfluidity also allows new neutrino emission process , which is called ` pair breaking and formation'(pbf ) .
pbf is a fast cooling process and can explain the fast cooling rate of neutron star in cas a. therefore , it is essential to add the superfluidity effect in the neutron star cooling process . in this work ,
we simulate neutron star cooling curves using both non - relativistic and relativistic nuclear models .
the existence of too early direct urca process shows that some of nuclear models do not fit for the cooling simulation .
after this first selection process , the nuclear pairing gaps are searched using the observational neutron star s age and temperature data .
neutron star , nuclear equation of state , neutron star cooling , nuclear superfluidity # 1 # 1 .
And you have already written the first three sentences of the full article: a neutron star ( ns ) is born as a result of the core collapse supernova explosion if the initial mass of the main sequence star is around 8 to 20 solar mass ( @xmath3 ) .
various eos , relations between the density and the pressure , are used to describe the interior of neutron stars .
the resulting central density of a neutron star is expected to reach up to several times of the nuclear saturation density ( @xmath4 @xmath5 ) ..
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hence , a neutron star is one of the best astrophysical laboratories to study the physics of the extremely dense nuclear matter .
figure [ fig : ns_section ] shows the structure of neutron stars in the theoretical point of view . outside the envelope , there exists a very thin atmosphere which is composed of hydrogen and heavy elements @xcite . depending on the temperature , its thickness ranges from a few centimeters to a few millimeters and the thermal radiation is expected to occur in this region .
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Suppose that you have an abstract for a scientific paper: we consider polarized @xmath0 hyperon production in proton - proton scattering , @xmath1 , in the kinematical region of the lhc experiments , in particular the alice experiment .
we present a new @xmath0 polarization observable that arises from the sivers effect in the fragmentation process . it can be large even at midrapidity and therefore , is of interest for high energy hadron collider experiments .
apart from its potential to shed light on the mechanisms behind the phenomenon of @xmath0 polarization arising in unpolarized hadronic collisions , the proposed observable in principle also allows to test the possible color flow dependence of single spin asymmetries and the ( non)universality of transverse momentum dependent fragmentation functions . .
And you have already written the first three sentences of the full article: since the observation of large transverse polarization of produced @xmath0 hyperons in the inclusive reactions @xmath2 @xcite and @xmath3 @xcite in the middle of the 1970 s , there have been many experimental and theoretical investigations aimed at understanding this striking polarization phenomenon @xcite .
the polarization measurements of @xmath0 hyperons produced in these inclusive reactions have been performed in fixed target experiments , and the data showed that the @xmath0 polarizations are large only for large @xmath4 .
this poses a problem if one wants to investigate this observable further using high energy colliders such as rhic , tevatron or lhc , where the capabilities to measure @xmath0 polarization are restricted to the midrapidity region , where @xmath4 is very small ..
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however , in this paper we point out a way to by - pass this problem by making a less inclusive measurement : to select two - jet events and to measure the jet momenta @xmath5 and @xmath6 in addition to the momentum @xmath7 and polarization @xmath8 of the @xmath0 that is part of either of the two jets .
an asymmetry proportional to @xmath9 can then arise , which is neither power suppressed , nor needs to be zero the @xmath0 polarization needs to vanish at @xmath10 due to symmetry reasons . in @xmath11 nuclear effects could allow for a nonvanishing asymmetry at midrapidity .
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Suppose that you have an abstract for a scientific paper: we investigate the number of topological ends of the trace of branching random walk ( brw ) on a graph , showing that in many symmetric cases there are infinitely many ends .
we then describe some brws which have just one end , and conclude with some open problems . .
And you have already written the first three sentences of the full article: consider a branching random walk ( brw ) on a graph described as follows .
we are given a graph @xmath0 and a vertex @xmath1 .
we begin with one particle at @xmath2 at time @xmath3 . for each @xmath4 , each particle alive at time @xmath5 dies and gives birth to an independent random number of offspring particles according to some probability distribution @xmath6 , each of which independently takes a step according to a specified random walk on the graph with transition kernel @xmath7 ..
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we write @xmath8 for such a branching random walk .
we assume throughout that @xmath0 is infinite , @xmath7 is irreducible , @xmath6 has finite mean @xmath9 and @xmath10 .
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Suppose that you have an abstract for a scientific paper: we present an on - shell graphical framework for superamplitudes in super yang - mills theory with arbitrary supersymmetry .
our diagrammatic procedure is derived through manipulations of the full @xmath0 superamplitude and illustrated by a number of explicit examples . .
And you have already written the first three sentences of the full article: multiloop scattering amplitudes in maximally supersymmetric ( @xmath0 ) yang - mills theory have been studied extensively over the years @xcite in connection with for instance the famous ads / cft correspondence and possible finiteness of supergravity theories .
remarkable results have been uncovered including new favorable evaluation methods applicable to both tree- and loop - level amplitudes .
an essential part of this progress is the on - shell superspace formalism , which organizes on - shell states and scattering amplitudes in maximally supersymmetric super yang - mills theory very elegantly @xcite ..
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the principle is to arrange the entire supermultiplet as a convenient expansion labeled by @xmath1-symmetry indices and particle number into @xmath2 superfields , one for each external leg .
all possible scattering combinations are realized by formation of superamplitudes , defined as generating functions with the superfields as input , having all supersymmetric ward identities automatically satisfied .
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Suppose that you have an abstract for a scientific paper: i study the three parameters bipartite quantum gaussian state called squeezed asymmetric thermal state , calculate gaussian entanglement of formation analytically and the up bound of relative entropy of entanglement , compare them with coherent information of the state . based on the result obtained
, one can determine the relative entropy of entanglement of the state with infinitive squeezing . .
And you have already written the first three sentences of the full article: quantum entanglement is one of the most important phenomenon in quantum theory .
it exhibit the nature of nonlocal correlation between quantum systems , and plays an essential role in various fields of quantum information processing , such as quantum computation , quantum communication , quantum cryptography , quantum teleportation@xcite , and closely related to quantum [email protected] the first experiments @xcite on quantum teleportation using two - mode squeezed states @xcite@xcite , a significant amount of work has been devoted to develop a quantum information theory of continuous variable systems .
so far , most of the theoretical work has focused on the entanglement properties of the quantum states involved in all these experiments , the so - called gaussian states ..
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the first problem arisen is that if a given quantum gaussian state is entangled , the problem of qualifying entanglement has been solved in the general bipartite setting @xcite@xcite .
but the efficiency of entanglement manipulation protocols used in practical quantum information processing critically depends on the quality of the entanglement that one can generate .
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Suppose that you have an abstract for a scientific paper: shape from texture refers to the extraction of 3d information from 2d images with irregular texture .
this paper introduces a statistical framework to learn shape from texture where convex texture elements in a 2d image are represented through a point process . in a first step ,
the 2d image is preprocessed to generate a probability map corresponding to an estimate of the unnormalized intensity of the latent point process underlying the texture elements .
the latent point process is subsequently inferred from the probability map in a non - parametric , model free manner .
finally , the 3d information is extracted from the point pattern by applying a locally scaled point process model where the local scaling function represents the deformation caused by the projection of a 3d surface onto a 2d image .
_ keywords : _
3d scenes , convex texture elements , locally scaled point processes , near regular texture , perspective scaling , shape analysis .
And you have already written the first three sentences of the full article: natural images contain a variety of perceptual information enabling the viewer to infer the three - dimensional shapes of objects and surfaces @xcite .
@xcite observed that surface geometry mainly has three effects on the appearance of texture in images : foreshortening and scaling of texture elements , and a change in their density .
@xcite proposed the slant , the angle between a normal to the surface and a normal to the image plane , as a measure for surface orientation ..
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stevens amended this by introducing the tilt , the angle between the surface normal s projection onto the image plane and a fixed coordinate axis in the image plane . in this paper , we will directly infer the surface normal from a single image taken under standard perspective projection .
statistical procedures for estimating surface orientation often make strong assumptions on the regularity of texture .
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Suppose that you have an abstract for a scientific paper: from the naturalness point of view , the first lhc results seem to disfavour any constrained mssm realization with universal conditions at the susy - breaking scale . a more motivated scenario is given by split - family susy ,
in which the first two generations of squarks are heavy , compatible with a @xmath0 flavour symmetry . here , after reviewing the flavour structures obtained in this framework , we consider the flavour symmetry to be broken at a very high scale , and study the consequences at low energies through its rge evolution .
initial conditions compatible with a split scenario are found , and the preservation of correlations from minimal @xmath0 breaking are checked . .
And you have already written the first three sentences of the full article: when considering physics beyond the standard model ( sm ) , supersymmetry , in the form of the minimal supersymmetric standard model ( mssm ) is usually considered as one of the most appealing options . however , due to its vast parameter space , a standard procedure is to assume universality conditions of the soft terms at the gut scale , and allow the renormalization group equations ( rges ) to break the universality when running down to the weak scale .
this constrained realization is named cmssm , and leads to flavoured soft terms acquiring a structure following minimal flavour violation ( mfv ) @xcite .
mfv effectively suppresses all susy contributions to flavoured processes , solving the so - called susy flavour problem ..
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however , it also leads to sfermion masses with small splittings .
this can cause issues in the solution of the hierarchy problem , which depends mainly on having light third generation squark masses .
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Suppose that you have an abstract for a scientific paper: we discuss interstellar temperature determinations using the excitation equilibrium of the @xmath0 levels of si@xmath1ii and c@xmath1ii .
we show how observations of the @xmath2 fine structure levels of si@xmath1ii and c@xmath1ii ( which have significantly different excitation energies , corresponding to @xmath3 and 92 k , respectively ) can be used to limit gas kinetic temperatures .
we apply this method to the @xmath4 damped lyman-@xmath5 system toward the quasar pss 1443 + 27 . the lack of significant absorption out of the si@xmath1ii @xmath2 level and the presence of very strong c@xmath1ii @xmath2 provides an upper limit to the temperature of the c@xmath1ii@xmath6-bearing gas in this system . assuming a solar si / c ratio , the observations imply a @xmath7 limit @xmath8 k for this absorber ; a super - solar si / c ratio gives stricter limits , @xmath9 k. the observations suggest the presence of a cold neutral medium ; such cold gas may serve as the fuel for star formation in this young galaxy . .
And you have already written the first three sentences of the full article: high - redshift damped lyman-@xmath5 systems ( dlas ) are the highest column density class of qso absorption lines .
defined by @xmath10 ( wolfe et al .
1986 ) , these systems are thought to trace the interstellar medium ( ism ) of high - redshift galaxies . dedicated surveys over the past two decades.
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have helped trace the global properties of high - redshift dlas , including their contribution to the cosmological baryon density ( storrie - lombardi & wolfe 2000 ; prochaska & herbert - fort 2004 ) , their chemical enrichment ( e.g. , prochaska et al .
2003 ) , their dust content ( e.g. , pettini et al .
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Suppose that you have an abstract for a scientific paper: probing the higgs potential and new physics behind the electroweak symmetry breaking is one of the most important issues of particle physics .
in particular , nature of electroweak phase transition is essential for understanding physics at the early universe , such that the strongly first order phase transition is required for a successful scenario of electroweak baryogenesis . the strongly first order phase transition is expected to be tested by precisely measuring the triple higgs boson coupling at future colliders like the international linear collider .
it can also be explored via the spectrum of stochastic gravitational waves to be measured at future space - based interferometers such as elisa and decigo .
we discuss complementarity of both the methods in testing the strongly first order phase transition of the electroweak symmetry in models with additional isospin singlet scalar fields with and without classical scale invariance .
we find that they are synergetic in identifying specific models of electroweak symmetry breaking in more details . .
And you have already written the first three sentences of the full article: the discovery of the higgs boson ( @xmath0 ) , whose mass is 125 gev , at the large hadron collider ( lhc ) run - i @xcite and subsequent measurements of properties of the higgs boson @xcite have established the standard model ( sm ) of particle physics as a low energy effective theory at the electroweak scale .
nevertheless , the details of the higgs sector including the shape of the higgs potential are still unknown .
the higgs sector of the sm with one isospin doublet scalar field is constructed based merely on minimality , and not guided by any fundamental principle ..
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many models with extended higgs sectors can also satisfy current experimental data , and need to be distinguished in the future .
in addition to the ambiguity of the higgs potential , several phenomena that require physics beyond the sm ( bsm ) have been reported .
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Suppose that you have an abstract for a scientific paper: we consider the time evolution of massless gravitino perturbations in schwarzschild black holes , and show that as in the case of fields of other values of spin , the evolution comes in three stages , after an initial outburst as a first stage , we observe the damped oscillations characteristic of the quasinormal ringing stage , followed by long time tails . using the sixth order wkb method and prony fitting of time domain data we determine the quasinormal frequencies .
there is a good correspondence between the results obtained by the above two methods , and we obtain a considerable improvement with respect to the previously obtained third order wkb results . we also show that the response of a black hole depends crucially on the spin class of the perturbing field : the quality factor becomes a decreasing function of the spin for boson perturbations , whereas the opposite situation appears for fermion ones . .
And you have already written the first three sentences of the full article: the study of the evolution of small perturbations in black hole backgrounds is a very interesting subject . actually , we know that this evolution , at intermediate times , is dominated by damped single frequency oscillations .
these characteristic oscillations have been termed quasinormal modes and the associated frequencies quasinormal frequencies , and depend only on the parameters characterizing the black hole , as it mass , electric charge and angular momentum @xcite . in this sense
we can say that black holes have a characteristic sound , resembling for example the familiar sound produced bay the ringing of a bell or the strum of a guitar ..
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once one realizes the importance of black holes in fundamental physics , one can grasp the meaning and significance of their characteristic vibrations @xcite .
black holes have been called the hydrogen atom of general relativity , perfect comparison because like the hydrogen atom in quantum mechanics , a black hole , as a solution of the einstein s field equations has all the general relativistic properties embodied in it , but still is simple enough to be a model for starting a complete understanding of all the physics that go with einstein s gravitation theory .
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Suppose that you have an abstract for a scientific paper: we present spectropolarimetry of sn 2009ip throughout the evolution of its 2012 explosion . during the 2012a phase ,
when the spectrum exhibits broad p - cygni lines , we measure a @xmath0-band polarization of @xmath1% at a position angle of @xmath2 , indicating substantial asphericity for the 2012a outflow . near the subsequent peak of the 2012b phase ,
when the spectrum shows signs of intense interaction with circumstellar material ( csm ) , we measure @xmath3% and @xmath4 , indicating a separate component of polarization during 2012b , which exhibits a higher degree of asphericity than 2012a and an orthogonal axis of symmetry on the sky .
around 30 days past peak , coincident with a substantial bump in the declining light curve , we measure @xmath5% and another significant shift in @xmath6 . at this point ,
broad photospheric lines have again become prominent and exhibit significant variations in @xmath7 relative to the continuum , particularly he i / na i d. by 60 days past peak the continuum polarization has dropped below 0.2% , probably declining toward a low value of interstellar polarization .
the results are consistent with a scenario in which a prolate ( possibly bipolar ) explosion launched during the 2012a phase impacts an oblate ( toroidal ) distribution of csm in 2012b .
previous calculations that assumed spherical symmetry for the csm have substantially underestimated the required explosion energy , since only a small fraction of the sn ejecta appears to have participated in strong csm interaction . an ejecta kinetic energy of at least @xmath8 ergs is difficult to avoid , supporting the interpretation that the 2012 outburst of sn 2009ip was the result of a core - collapse explosion .
[ firstpage ] circumstellar matter stars : evolution stars : winds , outflows supernovae : general supernovae : individual ( sn 2009ip ) .
And you have already written the first three sentences of the full article: interacting supernovae ( sne ) are stellar explosions that collide with dense circumstellar material ( csm ) produced by the progenitor star . these events are raising critical new questions about the final evolutionary phases of massive stars and the mass - loss episodes that ensue before core collapse ( smith & arnett 2014 ) .
type - iin and ibn sne , in particular , are interacting sne that are characterized spectroscopically by the presence of relatively narrow emission lines of h and he in their spectra ( schlegel 1990 ; filippenko 1997 ; pastorello et al .
2008 ) , which arise from dense csm that becomes illuminated by the shock between the fast moving sn ejecta and slower moving csm ( chevalier & fransson 1994 ) . as such , observations of interacting sne probe the stellar progenitor s pre - sn mass - loss history , providing valuable information on its final evolutionary episodes ..
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various lines of evidence show that interacting sne require eruptive pre - sn mass loss that is reminiscent of luminous blue variable ( lbv ) stars , like @xmath9 car , although observations indicate a wide range of mass - loss properties ( e.g. , see the review by smith 2014 ) .
the eruptions are often detectable as extragalactic transients , commonly referred to as ` sn impostors ' ( van dyk 2000 ; smith et al . 2011a ; kochanek et al .
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Suppose that you have an abstract for a scientific paper: the quantum interference effect on the quasiparticle density of states ( dos ) is studied with the diagrammatic technique in two - dimensional @xmath0-wave superconductors with dilute nonmagnetic impurities both near the born and near the unitary limits .
we derive in details the expressions of the goldstone modes ( cooperon and diffuson ) for quasiparticle diffusion .
the dos for generic fermi surfaces is shown to be subject to a quantum interference correction of logarithmic suppression , but with various renormalization factors for the born and unitary limits . upon approaching the combined limit of unitarity and nested fermi surface ,
the dos correction is found to become a @xmath1-function of the energy , which can be used to account for the resonant peak found by the numerical studies .
pacs numbers : 74.25.jb , 71.20.-b , 73.20.fz .
And you have already written the first three sentences of the full article: since the experiments revealed the @xmath0-wave symmetry of the order parameter in cuprate superconductors @xcite , the physics of low - energy quasiparticle excitations in disordered two - dimensional ( 2d ) @xmath0-wave superconductors has been a subject of ongoing intensive research @xcite .
the characteristic feature of the @xmath2-wave pairing state is the existence of four nodal points where the order parameter vanishes . in the vicinity of the gap nodes there
exist low - lying dirac - type quasiparticle excitations ..
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an understanding of the disorder effect induced by randomly - distributed impurities on these low - energy states is essential for the elucidation of the thermodynamic and transport properties of disordered @xmath0-wave superconductors . during the years
a number of theoretical approaches , such as the self - consistent approximation schemes [ 39 ] , non - perturbative methods [ 1017 ] , and numerical studies [ 18 - 22 ] , have been developed to calculate the quasiparticle density of states ( dos ) in the presence of disorder .
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Suppose that you have an abstract for a scientific paper: the critical behavior of charge - density waves ( cdws ) in the pinned phase is studied for applied fields increasing toward the threshold field , using recently developed renormalization group techniques and simulations of automaton models . despite the existence of many metastable states in the pinned state of the cdw
, the renormalization group treatment can be used successfully to find the divergences in the polarization and the correlation length , and , to first order in an @xmath0 expansion , the diverging time scale .
the automaton models studied are a charge - density wave model and a `` sandpile '' model with periodic boundary conditions ; these models are found to have the same critical behavior , associated with diverging avalanche sizes .
the numerical results for the polarization and the diverging length and time scales in dimensions @xmath1 are in agreement with the analytical treatment .
these results clarify the connections between the behaviour above and below threshold : the characteristic correlation lengths on both sides of the transition diverge with different exponents .
the scaling of the distribution of avalanches on the approach to threshold is found to be different for automaton and continuous - variable models . .
And you have already written the first three sentences of the full article: the static and dynamic behaviour of sliding charge density waves ( cdws ) is perhaps the most well studied example of a class of problems involving the transport of an elastic medium through a disordered background .
the cdw , which behaves like an elastic medium , is pinned by impurities distributed randomly throughout the material . as the magnitude of an externally applied electric field
is varied , a depinning transition is seen , from a stationary phase at weak fields , to a moving phase at strong fields where the cdw slides through the material . in the vicinity of this depinning transition ,.
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the dynamics of the cdw are correlated over long distances , with characteristic correlation lengths diverging at the threshold field .
it has been shown@xcite that the behaviour near the threshold field can be studied as a critical phenomenon associated with a second order phase transition.@xcite extensive numerical simulations@xcite on a number of classical models for cdws have helped in understanding the critical properties in the vicinity of the depinning transition . in particular ,
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Suppose that you have an abstract for a scientific paper: there are no square @xmath0-flat sequences of polynomials of the type @xmath1 where for each @xmath2 .
it follows that erds s conjectures on littlewood polynomials hold . consequently , turyn - golay s conjecture is true , that is , there are only finitely many barker sequences .
we further get that the spectrum of dynamical systems arising from continuous morse sequences is singular .
this settles an old question due to m. keane . .
And you have already written the first three sentences of the full article: the main purpose of this paper is to establish that there are no square @xmath0-flat sequences of polynomials of the type @xmath3 where for each @xmath4 and @xmath5 @xmath6 is the circle group .
it follows that there are only finitely many barker sequences .
we thus get an affirmative answer to turyn - golay s conjecture and erds s conjectures ..
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furthermore , our result implies that the spectrum of dynamical system arising from generalized morse sequences is singular for every continuous morse sequence .
this answer an old question due to m. keane @xcite .
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Suppose that you have an abstract for a scientific paper: ultra - clean crystals of sr@xmath0ru@xmath1o@xmath2 undergo a metamagnetic transition at low temperatures .
this transition shows a strong anisotropy in the applied field direction with the critical field @xmath3 ranging from @xmath4 t for @xmath5 perpendicular to @xmath6 to @xmath7 t for @xmath8 .
in addition , studies on ultra - pure samples revealed a bifurcation of the metamagnetic line for fields in @xmath6-direction and it has been argued that a nematic phase emerges between the magnetization jumps . the aim of this study is to explain the field - direction anisotropy of these phenomena .
based on a microscopic tight - binding model , we introduce the metamagnetic transition by means of a van hove singularity scenario .
we show that the rotation of the o - octahedra around the @xmath6-axis observed in this material introduces a staggered spin - orbit coupling within the planes and naturally leads to an anisotropy in the low - temperature behavior around the metamagnetic transition . in particular , the low - temperature ( nematic ) phase is affected .
we show that uniform in - plane magnetic fields induce a ( commensurate ) staggered magnetic moment component which can suppress the low - temperature phase .
in contrast , the response to fields along the c - axis remains unaffected and thus , also the corresponding low - temperature phase . as a concrete example
, we choose a nematic pomeranchuk instability for the low - temperature phase .
an experimentally testable prediction of this work is the occurrence of a staggered magnetic moment in response to a uniform magnetic field perpendicular to the c - axis , which should be accessible by neutron scattering . .
And you have already written the first three sentences of the full article: ru@xmath9o@xmath10 for fields @xmath5 applied with an angle @xmath11 versus the @xmath12-plane .
the surface represents first - order transitions separating a region with low ( spin ) polarization from a region with high polarization .
the thick black line connecting @xmath13 and @xmath14 is a line of critical endpoints ..
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for details see main text . ]
the ruthenium compounds of the ruddlesden - popper series , sr@xmath15ru@xmath16o@xmath17 , have been the subject of intensive research for over a decade due to their interesting ground - states .
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Suppose that you have an abstract for a scientific paper: it is studied to what extent the characteristics of multi - imf ( intermediate - mass fragments ) events can be derived from the properties of the observed single - imf transverse - energy spectra .
it is found that the spectra of total transverse imf energy ( @xmath0 ) in multi - imf events are well represented by `` synthetic '' spectra obtained by a multiple folding of the single - imf transverse energy spectrum .
further , it is shown that , using the experimental imf multiplicity distribution in the folding procedure , it is possible to reproduce the observed trends in the imf multiplicity distributions for fixed values of the total transverse energy @xmath0 .
accordingly , the `` synthetic '' multiplicity distributions show a binomial reducibility and an arrhenius - like scaling similar to that reported in the recent literature .
consistent with the concept of statistical independence of multiple imf production , similar results are obtained when the above folding - type synthesis is replaced with one based on mixing of events with different imf multiplicities .
for statistically independent imf emission , the observed binomial reducibility and arrhenius - like scaling are shown to be merely reflections of the shape of the single - imf transverse - energy spectrum .
hence , a valid interpretation of these imf distributions in terms of a particular production scenario has to explain independently the observed shape of the single - imf @xmath0 spectrum .
# 1@xmath1#1 ( pacs 25.70lm , 24.10.pa , 25.70.mn , 25.70.pq ) .
And you have already written the first three sentences of the full article: recently , in several studies@xcite of heavy - ion - induced nuclear multifragmentation it was concluded that certain characteristics of the intermediate - mass fragment ( imf ) data are suggestive of statistical independence of multiple imf production.@xcite concepts of a binomial or a poissonian reducibility@xcite have been suggested to express the particular observed independence in mathematical terms .
the concept of statistical independence or reducibility presumes that certain characteristics of multi - imf events are reflections of the single - imf production process .
for example , the concept of a binomial reducibility@xcite presumes that the probability of multiple imf production is a reflection of the single - imf production probability - the two quantities of interest being connected via the expression for a binomial distribution : @xmath2 where @xmath3 is the multiple - imf production probability and the parameters @xmath4 and @xmath5 are the number of ( binomial ) tries and the probability for success in any of these trials , respectively ..
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although so far , no theoretical model has been proposed that would explain a binomial reducibility , one would reasonably expect that a successful model would at the same time link other characteristics of multi - imf events to the characteristics of single - imf production . with these expectations in mind ,
the present paper investigates , to what extent the empirical systematic of multiple imf production can be derived from empirical characteristics of single - imf production and , specifically , from the single - imf transverse - energy spectrum .
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Suppose that you have an abstract for a scientific paper: the study of quantum mechanical bound states is as old as quantum theory itself . yet
, it took many years to realize that three - body borromean systems that are bound when any two - body subsystem is unbound are abundant in nature . here
we demonstrate the existence of borromean systems of spin - polarized ( spinless ) identical fermions in two spatial dimensions .
the ground state with zero orbital ( planar ) angular momentum exists in a borromean window between critical two- and three - body strengths . the doubly degenerate first excited states of angular momentum one appears only very close to the two - body threshold .
they are the lowest in a possible sequence of so - called super - efimov states .
while the observation of the super - efimov scaling could be very difficult , the borromean ground state should be observable in cold atomic gases and could be the basis for producing a quantum gas of three - body states in two dimensions .
unlike classical mechanics quantum mechanics allows bound @xmath0-body states without having bound subsystems .
these so - called borromean systems are discussed in a number of publications for the simplest example of three particles @xcite .
the phenomenon was recently even generalized to more particles and higher orders , see f.ex .
ref .
@xcite .
borromean three - body systems are abundant in three dimensions ( 3d ) for both bosonic and fermionic systems in nuclear , atomic and molecular physics @xcite . however , the behavior is strikingly different for bosonic systems in one or two ( 2d ) spatial dimensions @xcite . where bound states appear for infinitesimally small attractions . without an artificial repulsive barrier at large distance
it is virtually impossible to form a borromean bosonic 2d system @xcite .
furthermore , the celebrated efimov effect of infinitely many bound three - body states at the two - body threshold is not present in 2d @xcite .
three identical spin - polarized fermions are harder to bind than bosons ,....
And you have already written the first three sentences of the full article: borromean states are most easily found for potentials that can almost bind a two - body system .
the relative motion in two - body systems is described with the wave function given as a product of radial , @xmath2 , and angular , @xmath3 , parts , where @xmath4 are the polar relative coordinates , and @xmath5 is the 2d angular momentum quantum number .
the radial schrdinger equation is @xmath6 where the bounded potential , @xmath7 , of cylindrical symmetry is assumed to decrease faster than @xmath8 , @xmath9 , for large @xmath10 , or in practice treated as zero outside a finite radius @xmath11 ..
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the two - body energy is @xmath12 , @xmath13 , is a dimensionless strength parameter , and @xmath14 is the mass of one particle .
the doubly degenerate antisymmetric ground state for spin polarized fermions has @xmath15 , since @xmath16 describes a symmetric total wave function .
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Suppose that you have an abstract for a scientific paper: in this note we study la baxter @xcite the possible integrable manifolds of the asymmetric eight - vertex model .
as expected they occur when the boltzmann weights are either symmetric or satisfy the free - fermion condition but our analysis clarify the reason both manifolds need to share a universal invariant .
we also show that the free - fermion condition implies three distinct classes of integrable models .
= -0.33 in = -0.3 in ufscar - th-02 + + _ departamento de fsica , universidade federal de so carlos _ _ caixa postal 676 , 13565 - 905 , so carlos , brazil _
july 2002 exactly solved vertex models play a fundamental role in classical statistical mechanics .
the most important of these is the so - called eight - vertex model which contains as special cases most systems on a plane square lattice @xcite .
the general asymmetric eight - vertex model possesses six different boltzmann weights @xmath0 and @xmath1 whose transfer matrix can be written as @xmath2\ ] ] where the trace is over the ordered product of local operators @xmath3 which are given by the following @xmath4 matrix @xmath5 and @xmath6 are pauli matrices acting on the sites @xmath7 of an one - dimensional lattice .
the asymmetric eight - vertex model is known to be solvable in the manifolds @xmath8 @xmath9 @xmath10 where @xmath11 and @xmath12 are arbitrary constants .
the manifold ( 3 ) is the so - called free - fermion model whose free - energy was first calculated by fan and wu @xcite and later re - derived by felderhof @xcite who devised a method to diagonalize the corresponding transfer matrix .
the integrability of the free - fermion manifold is usually assumed from the fact that its transfer matrix commutes with the @xmath13 hamiltonian as shown by krinsky @xcite who used a procedure first developed by sutherland @xcite .
later on barouch @xcite and kasteleyn @xcite have revisited the problem of commuting asymmetric eight - vertex transfer matrices and generalized heisenberg hamiltonians....
And you have already written the first three sentences of the full article: this work has been partially supported by the brazilian research agencies cnpq and fapesp .
baxter , `` exactly solved models in statistical mechanics '' . academic press , 1982 , new york c. fan and f.y .
. 179 ( 1969 ) 560 _ b.u ..
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felderhof , _ physica 66 ( 1973 ) 279 , 509 _ s. krinsky , _
phys.letters.a 39 ( 1972 ) 169 _ b. sutherland , _
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Suppose that you have an abstract for a scientific paper: in the sixties , dewitt discovered that the advanced and retarded green functions of the wave operator on metric perturbations in the de donder gauge make it possible to define classical poisson brackets on the space of functionals that are invariant under the action of the full diffeomorphism group of spacetime .
he therefore tried to exploit this property to define invariant commutators for the quantized gravitational field , but the operator counterpart of such classical poisson brackets turned out to be a hard task . on the other hand , in the mathematical literature , it is by now clear that , rather than inverting exactly an hyperbolic ( or elliptic ) operator , it is more convenient to build a quasi - inverse , i.e. an inverse operator up to an operator of lower order which plays the role of regularizing operator .
this approximate inverse , the parametrix , which is , strictly , a distribution , makes it possible to solve inhomogeneous hyperbolic ( or elliptic ) equations .
we here suggest that such a construction might be exploited in canonical quantum gravity provided one understands what is the counterpart of classical smoothing operators in the quantization procedure .
we begin with the simplest case , i.e. fundamental solution and parametrix for the linear , scalar wave operator ; the next step are tensor wave equations , again for linear theory , e.g. maxwell theory in curved spacetime .
last , the nonlinear einstein equations are studied , relying upon the well - established choquet - bruhat construction , according to which the fifth derivatives of solutions of a nonlinear hyperbolic system solve a linear hyperbolic system .
the latter is solved by means of kirchhoff - type formulas , while the former fifth - order equations can be solved by means of well - established parametrix techniques for elliptic operators .
but then the metric components that solve the vacuum einstein equations can be obtained by convolution of such a parametrix with kirchhoff - type formulas . some....
And you have already written the first three sentences of the full article: the hamiltonian road to quantization has played a key role , over the last century , in the development of quantum mechanics @xcite , quantum field theory in flat spacetime @xcite , including quantum yang - mills @xcite and the particle physics standard model , as well as in the formulation of canonical quantum gravity @xcite .
the main drawback of the hamiltonian formulation , despite its beautiful and powerful applications to the classical cauchy problem of general relativity @xcite , lies in the loss of the full diffeomorphism group of four - dimensional spacetime , with the associated undoing of the unification of space and time into the spacetime manifold ( see , however , the valuable work in refs .
@xcite on the way to circumvent this problem ) . indeed , at classical level , the tools of global differential geometry make it possible to obtain a spacetime covariant formulation of the constraint equations @xcite , which turn out to be linear @xcite on a bigger space , the space of multimomenta ..
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even earlier , at quantum level , the work of peierls @xcite and dewitt @xcite made it possible to define a poisson bracket on the space of all field functionals that remain invariant under the action of the infinite - dimensional lie ( pseudo-)group of the theory ( for gravity , this is the group of spacetime diffeomorphisms ) .
if @xmath0 and @xmath1 are any two such functionals of the field variables @xmath2 , their classical peierls bracket reads as ( see appendix for the notation ) @xmath3 where @xmath4 , the supercommutator function @xcite , is the difference between advanced and retarded green functions for the invertible operator @xmath5 acting on fields : @xmath6 the advanced and retarded green functions are both left- and right - inverses of @xmath5 , i.e. @xmath7 @xmath8 in the framework of ref .
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10,197 |
Suppose that you have an abstract for a scientific paper: in this paper , based on the noda iteration , we present inexact noda iterations ( ini ) , to find the smallest eigenvalue and the associated positive eigenvector of a large irreducible nonsingular @xmath0-matrix .
the positivity of approximations is critical in applications , and if the approximations lose the positivity then they may be meaningless and could not be interpreted .
we propose two different inner tolerance strategies for solving the inner linear systems involved , and prove that the convergence of resulting ini algorithms is globally linear and superlinear with the convergence order @xmath1 , respectively .
the proposed ini algorithms are structure preserving and maintains the positivity of approximate eigenvectors .
we also revisit the exact noda iteration and establish a new quadratic convergence result .
all the above is first done for the problem of computing the perron root and the positive perron vector of an irreducible nonnegative matrix and is then adapted to computing the smallest eigenpair of the irreducible nonsingular @xmath0-matrix .
numerical examples illustrate that the proposed ini algorithms are practical , and they always preserve the positivity of approximate eigenvectors .
we compare them with the jacobi davidson method , the implicitly restarted arnoldi method and the explicitly restarted krylov
schur method , all of which can not guarantee the positivity of approximate eigenvectors , and illustrate that the overall efficiency of the ini algorithms is competitive with and can be considerably higher than the latter three methods .
example.eps gsave newpath 20 20 moveto 20 220 lineto 220 220 lineto 220 20 lineto closepath 2 setlinewidth gsave .4 setgray fill grestore stroke grestore .
And you have already written the first three sentences of the full article: irreducible nonsingular @xmath0-matrices are one class of the most important matrices from applications , such as discretized pdes , markov chains abate94,rober90 and electric circuits @xcite , and have been studied extensively in the literature ; see , for instance , ( * ? ? ?
* chapter 6 ) . in many applications ,
one is interested in finding the smallest eigenvalue @xmath2 and the associated eigenvector @xmath3 of an irreducible nonsingular @xmath0-matrix @xmath4 ..
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@xmath0-matrices are closely related to nonnegative matrices .
for instance , an @xmath5-matrix @xmath6 can be expressed in the form @xmath7 with a nonnegative matrix @xmath8 and some constant @xmath9 , the spectral radius of @xmath10 ; @xmath11 is nonnegative . for more properties and a systematic account of @xmath0-matrices and nonnegative matrices ,
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10,198 |
Suppose that you have an abstract for a scientific paper: a number of classical algorithms are based on random walks on graphs .
it is hoped that recently defined quantum walks can serve as the basis for quantum algorithms that will faster than the corresponding classical ones .
we discuss a particular kind of quantum walk on a general graph .
we affix two semi - infinite lines to a general finite graph , which we call tails . on the tails ,
the particle making the walk simply advances one unit at each time step , so that its behavior there is analogous to free propatation .
we are interested in how many steps it will take the particle , starting on one tail and propagating through the graph ( where its propagation is not free ) , to emerge onto the other tail .
the probability to make such a walk in @xmath0 steps and the hitting time for such a walk can be expressed in terms of the transmission amplitude for the graph , which is one element of its s matrix . demonstrating this neccessitates a study of the analyticity properties of the transmission and reflection coefficients of a graph .
we show that a graph can have bound states that can not be accessed by a particle entering the graph from one of the tails .
time - reversal invariance of a quantum walk is defined and used to show that the transmission amplitudes for the particle entering the graph from different directions are the same if the walk is time - reversal invariant . .
And you have already written the first three sentences of the full article: random walks on graphs serve as the basis of algorithms for solving a number of problems , including 2-sat , graph connectivity , and finding satsifying assignments for boolean functions . quantum algorithms
have shown promise in solving some problems faster than is possible using classical algorithms .
quantum walks represent an attempt to `` quantize '' classical random walk algorithms and thereby increase their speed ..
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quantum algorithms must be run on a quantum computer . in this kind of machine
, information is represented not in terms of bits , but in terms of quantum bits , or qubits .
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10,199 |
Suppose that you have an abstract for a scientific paper: we calculate the force operator for a charged particle in the field of an aharonov - bohm flux line .
formally this is the lorentz force , with the magnetic field operator modified to include quantum corrections due to anomolous commutation relations . for stationary states ,
the magnitude of the force is proportional to the product of the wavenumber @xmath0 with the amplitudes of the ` pinioned ' components , the two angular momentum components whose azimuthal quantum numbers are closest to the flux parameter @xmath1 .
the direction of the force depends on the relative phase of the pinioned components . for paraxial beams ,
the transverse component of our expression gives an exact version of shelankov s formula [ shelankov a 1998 _ europhys .
lett . _ * 43 * , 623 8 ] , while the longitudinal component gives the force along the beam .
nonstationary states are treated by integrating the force operator in time to obtain the impulse operator .
expectation values of the impulse are calculated for two kinds of wavepackets . for slow wavepackets , which spread faster than they move
, the impulse is inversely proportional to the distance from the flux line . for fast wavepackets , which spread only negligibly before their closest approach to the flux line ,
the impulse is proportional to the probability density transverse to the incident direction evaluated at the flux line . in this case
, the transverse component of the impulse gives a wavepacket analogue of shelankov s formula .
the direction of the impulse for both kinds of wavepackets is flux dependent .
we give two derivations of the force and impulse operators , the first a simple derivation based on formal arguments , and the second a rigorous calculation of wavepacket expectation values .
we also show that the same expressions for the force and impulse are obtained if the flux line is enclosed in an impenetrable cylinder , or distributed uniformly over a flux cylinder , in the limit that the radius of the cylinder goes to....
And you have already written the first three sentences of the full article: there have been a number of investigations of the force exerted on a charged particle by an aharonov - bohm flux line .
classically , of course , there is no force , so it , like the aharonov - bohm effect itself , is essentially quantum mechanical , vanishing as @xmath2 .
olariu & popescu ( 1983 , 1985 ) show that for certain localized wavepackets ( these are the fast wavepackets described in below ) , the force , along with the momentum it imparts , is negligible unless the centre of the wavepacket hits the flux line ..
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nielson and hedegrd ( 1995 ) and shelankov ( 2000 ) compute matrix elements of the force operator for stationary states of the same energy .
shelankov ( 1998 ) calculates the transverse force on a stationary incident beam of finite angular width using a paraxial approximation , a result we refer to as _ shelankov s
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