Benchtop nuclear magnetic resonance spectrometer

A Benchtop nuclear magnetic resonance spectrometer (Benchtop NMR spectrometer) refers to a Fourier transform nuclear magnetic resonance (FT-NMR) spectrometer that is significantly more compact and portable than the conventional equivalents, such that it is portable and can reside on a laboratory benchtop. This convenience comes from using permanent magnets, which have a lower magnetic field and decreased sensitivity compared to the much larger and more expensive cryogen cooled superconducting NMR magnets. Instead of requiring dedicated infrastructure, rooms and extensive installations these benchtop instruments can be placed directly on the bench in a lab and moved as necessary ("e.g.," to the fumehood). These spectrometers offer improved workflow, even for novice users, as they are simpler and easy to use. They differ from relaxometers in that they can be used to measure high resolution NMR spectra and are not limited to the determination of relaxation or diffusion parameters ("e.g.," T1, T2 and D).
Magnet development.
This first generation of NMR spectrometers used large Electromagnets weighing hundreds of kilograms or more. Slightly smaller permanent magnet systems were developed in the 1960s-70s at proton resonance frequencies at 60 and 90 MHz and were widely used for chemical analysis using continuous wave methods but these permanent magnets still weighed hundreds of kilograms and could not be placed on a benchtop. Superconducting magnets were developed to achieve stronger magnetic fields for higher resolution and increased sensitivity. However, these superconducting magnets are expensive, large, and require specialized building facilities. In addition, the cryogens needed for the superconductors are hazardous, and represent an ongoing maintenance cost. As a result, these instruments are usually installed in dedicated NMR rooms or facilities for use by multiple research groups.
Since the early 2000s there has been a renaissance in permanent-magnet technology and design, with advances sufficient to allow development of much smaller NMR instruments with useful resolution and sensitivity for education, research and industrial applications. Samarium–cobalt and neodymium magnets in particular are strong enough for instruments up to 90 MHz. These smaller designs, which operate with magnet temperatures from room temperature to 60°C, allow instruments to be made small enough to fit on a lab bench, and safe to operate in a typical lab environment. They require only single phase local power and with UPS systems can be made portable and can perform NMR analyses at different points in the manufacturing area.
Disadvantage of Small-Size Magnets and Method to Overcome It.
One of the biggest disadvantages of low-field (0.3-1.5T) NMR spectrometers is the temperature dependence of the permanent magnets used to produce the main magnetic field. For small magnets there was a concern that the intensity of external magnetic fields may adversely affect the main field, however the use of magnetic shielding materials inside the spectrometer eliminates this problem. The currently available spectrometers are easily moved from one location to another, including some that are mounted on portable trolleys with continuous power supplies. Another related difficulty is that currently available spectrometers do not support elevated sample temperatures which may be required for some in-situ measurements in chemical reactions.
A recent paper suggests that a special experimental setup, with two or more coils and synchronous oscillators, may help overcome this problem and allow it to work with unstable magnetic fields and with affordable oscillators.
Applications.
NMR spectroscopy can be used for chemical analysis, reaction monitoring, and quality assurance/quality control experiments. Higher-field instruments enable unparalleled resolution for structure determination, particularly for complex molecules. Cheaper, more robust, and more versatile medium and low field instruments have sufficient sensitivity and resolution for reaction monitoring and QA/QC analyses. As such permanent magnet technology offers the potential to extend the accessibility and availability of NMR to institutions that do not have access to super-conducting spectrometers ("e.g.," beginning undergraduates or small-businesses).
Many automated applications utilizing multivariate statistical analyses (chemometrics) approaches to derive structure-property and chemical and physical property correlations between 60 MHz 1H NMR spectra and primary analysis data particularly for petroleum and petrochemical process control applications have been developed over the past decade.
Available Benchtop NMR Spectrometers.
Development of this new class of spectrometers began in the mid-2000s leaving this one of the last molecular spectroscopy techniques to be made available for the benchtop.
Spinsolve.
New Zealand- and Germany-based Magritek's Spinsolve instrument, operating at 80 MHz, 60 MHz and 42.5 MHz, offers very good sensitivity and resolution less than 0.5 Hz and weighs under 73 kg, 60 kg and 55 kg respectively. The ULTRA model has an even higher resolution of 0.2 Hz with a lineshape of 0.2 Hz/ 6 Hz/ 12 Hz comparable to high field NMR specifications. 1D Proton, 19F Fluorine, 13C Carbon and 31P Phosphorus as well as T1, T2 and 2D HETCOR, HMBC, HMQC, COSY and JRES spectra can be measured. The magnet is stabilised with an external lock, which means it does not require the use of deuterated solvents. Samples are measured using standard 5 mm NMR tubes and the spectrometer is controlled through an external computer where standard NMR data collection and processing takes place.
picoSpin.
In 2009, picoSpin LLC, based in Boulder, Colorado, launched the first benchtop NMR spectrometer with the picoSpin 45. A small (7 x 5.75 x 11.5”) 45 MHz spectrometer with good resolution (< 1.8 Hz) and mid-to-low-range sensitivity that weighs 4.76 kg (10.5 lbs) and can acquire a 1D 1H or 19F spectra. PicoSpin was acquired by Thermo Fisher Scientific in December 2012, and subsequently renamed the product Thermo Scientific picoSpin 45. Instead of the traditional static 5 mm NMR tubes, the picoSpin 45 spectrometer uses a flow-through system that requires sample injection into a 1/16” PTFE and quartz capillary. Deuterated solvents are optional due to the presence of a software lock. It needs only a web browser on any external computer or mobile device for control as the spectrometer has a built-in web server board; no installed software on a dedicated PC is required. In August 2013 a second version was introduced, the Thermo Scientific picoSpin 80, that operates at 82 MHz with a resolution of 1.2 Hz and ten times the sensitivity of the original picoSpin 45.
NMReady.
Calgary, AB, Canada based Nanalysis Corp offers two NMReady 60 MHz benchtop NMR instruments that weigh 25 kg. The spectrometers are all-in-one units, controlled by a touchscreen computer that is contained within the same enclosure as the magnet. The NMReady 60e model performs 1D 1H and 19F experiments as well as T1, T2, JRES and COSY. In addition, the NMReady 60Pro is a dual nuclei instrument that can also be tuned to 13C, 31P, 11B, and 7Li and perform DEPT, HSQC, HMBC, with options for additional experiments like signal suppression. The magnet is stabilized with an internal 2H lock so the use of deuterated solvents is recommended but not required. These spectrometers offer resolution < 1.2 Hz, use standard 5 mm NMR tubes, and are compatible with most third-party software suites.
In late 2020, Nanalysis made the 100e and the 100PRO models available. They offer 1D and 1D+2D modes, at 100 MHz, and 2.35 T. The machine weights about 25 kg
X-Pulse / Pulsar.
In 2019, Oxford Instruments launched a new 60 MHz spectrometer called X-Pulse. This instrument is a significant improvement on the previous Pulsar system, launched in 2013. X-Pulse has the highest, as standard, resolution (<0.35 Hz / 10Hz) of the currently available benchtop, cryogen-free NMR analysers. It incorporates a 60 MHz rare-earth permanent magnet. X-Pulse is the only benchtop NMR system to offer a full broadband X channel for the allowing the measurement of 1H,19F, 13C, 31P, 7Li, 29Si, 11B and 23Na on a single probe. A large range of 1D and 2D measurements can be performed on all nuclei, 1D spectra, T1, T2, HETCOR, COSY, HSQC, HMBC, JRES, and many others including solvent suppression and selective excitation. X-Pulse also has options for flow NMR and a variable temperature probe allowing the measurement of samples in NMR tubes at temperatures from 20°C to 60°C. The magnet and spectrometer are in two separate boxes with the magnet weighing 149 kg and the electronics weighing 22 kg. X-Pulse requires a standard mains electrical supply and uses standard 5mm NMR tubes. Instrument control comes from the SpinFlow workflow package, while the processing and manipulation of data is achieved using third-party NMR software suites. Pulsar instruments were discontinued in 2019 following the launch of X-Pulse.
Bruker.
In 2019, Bruker, a long time manufacturer and market leader of high performance NMR machines, introduced a Benchtop NMR, Fourier 80 FT-NMR. The machine uses permanent magnets, and operates using Bruker standard software (a full futured TopSpin 4 software for Windows and Linux; as well Python based API from Windows and Linux; and a simplified app called GoScan). Machine can be configured for 1H and 13C spectra (possibly more by a custom order) in 1D and 2D modes, and operates at 80 MHz (1.88 T). The machine weighs about 93 kg and consumes less than 300W when operating.


Multivariate optical computing

Multivariate optical computing, also known as molecular factor computing, is an approach to the development of compressed sensing spectroscopic instruments, particularly for industrial applications such as process analytical support. "Conventional" spectroscopic methods often employ multivariate and chemometric methods, such as multivariate calibration, pattern recognition, and classification, to extract analytical information (including concentration) from data collected at many different wavelengths. Multivariate optical computing uses an optical computer to analyze the data as it is collected. The goal of this approach is to produce instruments which are simple and rugged, yet retain the benefits of multivariate techniques for the accuracy and precision of the result.
An instrument which implements this approach may be described as a multivariate optical computer. Since it describes an approach, rather than any specific wavelength range, multivariate optical computers may be built using a variety of different instruments (including Fourier Transform Infrared (FTIR) and Raman).
The "software" in multivariate optical computing is encoded directly into an optical element spectral calculation engine such as an interference filter based multivariate optical element (MOE), holographic grating, liquid crystal tunable filter, spatial light modulator (SLM), or digital micromirror device (DMD) and is specific to the particular application. The optical pattern for the spectral calculation engine is designed for the specific purpose of measuring the magnitude of that multi-wavelength pattern in the spectrum of a sample, without actually measuring a spectrum.
Multivariate optical computing allows instruments to be made with the mathematics of pattern recognition designed directly into an optical computer, which extracts information from light without recording a spectrum. This makes it possible to achieve the speed, dependability, and ruggedness necessary for real time, in-line process control instruments.
Multivariate optical computing encodes an analog optical regression vector of a transmission function for an optical element. Light which emanates from a sample contains the spectral information of that sample, whether the spectrum is discovered or not. As light passes from a sample through the element, the normalized intensity, which is detected by a broad band detector, is proportional to the dot product of the regression vector with that spectrum, i.e. is proportional to the concentration of the analyte for which the regression vector was designed. The quality of the analysis is then equal to the quality of the regression vector which is encoded. If the resolution of the regression vector is encoded to the resolution of the laboratory instrument from which that regression vector was designed and the resolution of the detector is equivalent, then the measurement made by Multivariate Optical Computing will be equivalent to that laboratory instrument by conventional means. The technique is making headway in a niche market for harsh environment detection. Specifically the technique has been adopted for use in the oil industry for detection of hydrocarbon composition in oil wells and pipeline monitoring. In such situations, laboratory quality measurements are necessary, but in harsh environments.
History.
Although the concept of using a single optical element for analyte regression and detection was suggested in 1986, the first full MOC concept device was published in 1997 from the Myrick group at the University of South Carolina, with a subsequent demonstration in 2001. The technique has received much recognition in the optics industry as a new method to perform optical analysis with advantages for harsh environment sensing. The technique has been applied to Raman spectroscopy, fluorescence spectroscopy, absorbance spectroscopy in the UV-Vis, NIR and MIR, microscopy, reflectance spectroscopy and hyperspectral imaging. In the years since first demonstration, applications have been demonstrated for defence, forensics, monitoring of chemical reactions, environmental monitoring, recycling, food and drug, medical and life sciences, and the petroleum industry. The first published demonstration for use of MOC in the harsh environments, was 2012 with a laboratory study with temperatures from 150F to 350F and pressures from 3000psi to 20,000psi, followed in 2013 with field trials in oil wells.


Speed camera


B share (NYSE)

B shares are a special class of shares on the New York Stock Exchange.
Comparison with A shares.
B shares carry a back-end load, whereas A shares carry a front-end load.


Fourths (angle)


762 Pulcova

762 Pulcova is a main-belt asteroid. It was discovered by Grigoriy N. Neujmin in 1913, and is named after Pulkovo Observatory, near Saint Petersburg. Pulcova is 137 km in diameter, and is a C-type asteroid, which means that it is dark in colouring with a carbonate composition.
Photometric observations of this asteroid from Leura, Australia during 2006 gave a light curve with a period of 5.8403 ± 0.0005 hours and a brightness variation of 0.20 ± 0.02 in magnitude. This result is in agreement with previous studies.
Satellite.
On February 22, 2000, astronomers at the Canada-France-Hawaii Telescope on Mauna Kea, Hawaii, discovered a small, 15-km moon (roughly a 10th the size of the primary) orbiting Pulcova at a distance of 800 km. Its orbital period is 4 days. The satellite is about 4 magnitudes fainter than the primary. It was one of the first asteroid moons to be identified.
Density.
In the year 2000, Merline estimated Pulcova to have a density of 1.8 g/cm³, which would make it more dense than the trinary asteroid 45 Eugenia, and binary 90 Antiope. But estimates by Marchis in 2008 suggest a density of only 0.90 g/cm³, suggesting it may be a loosely packed rubble pile, not a monolithic object.


HD 2039

HD 2039 is a yellow dwarf or yellow subgiant star in the constellation Phoenix. The star is not visible to the naked eye, and lies 280 light years away from the Sun. HD 2039 is a relatively stable star, and an exoplanet at least three times the mass of the planet Jupiter has been discovered in its orbit; this exoplanet, known as HD 2039 b, was the 100th exoplanet to be discovered.
Nomenclature.
The designation "HD 2039" from the Henry Draper Catalogue. The catalogue, which was published between 1918 and 1924, was based on the work of Annie Jump Cannon and her team between 1911 and 1915. HD 2039 does not have a common, colloquial name that is characteristic of stars like Sirius, Procyon, and Aldebaran.
Characteristics.
HD 2039 is a stable G-type star, meaning it shines with white light that can be seen in the Sun. HD 2039 exhibits a radius approximately 40 percent larger than the Sun's. The star is slightly hotter than the Sun; while HD 2039 has a temperature of 5935 K, the Sun's surface temperature lies nearly 200 kelvins lower at 5778 K. HD 2039 is unusually metal-rich, which has attracted the attention of astrophysicists.
Distance and visibility.
The star's magnitude as observed from Earth is 9; this signifies that the body is not visible with the naked eye, but can be seen with a telescope. HD 2039 lies roughly 280 light years from the Sun, which is about as far from the Sun as the second brightest star in the night sky, Canopus.
Planetary system.
In 2002, a planet was found by the Anglo-Australian Planet Search team to be orbiting the star in a very eccentric orbit. It has a minimum mass more than four times that of Jupiter and has an orbital period of over three years. The planet orbits its star at a distance of approximately two AU away; the planet Earth, in comparison, orbits at a distance of one AU away from the Sun. HD 2039 b's discovery was reported quietly; no press release was provided by the observatory that discovered the star's planet, and no formal announcement of the planet's existence was made. The entity was the 100th exoplanet to have been verified by the scientific community.


A-sharp minor

A-sharp minor is a minor scale based on A, consisting of the pitches A, B, C, D, E, F, and G. Its key signature has seven sharps, while the direct enharmonic equivalent, B-flat minor, has five flats.
Its relative major is C-sharp major (or enharmonically D-flat major), and its parallel major is A-sharp major, usually replaced by B-flat major, since A-sharp major's three double-sharps make it impractical to use.
A-sharp minor is likely the least used minor key in music as it is not generally considered a practical key for composition. The enharmonic equivalent B-flat minor, which only contains five flats as opposed to A-sharp minor's seven sharps, is preferable to use.
The A-sharp natural minor scale is:
\override Score.TimeSignature #'stencil = ##f
\relative c" {
 \clef treble \key ais \minor \time 7/4
 ais4^\markup "Natural minor scale" bis cis dis eis fis gis ais gis fis eis dis cis bis ais2
</score>
Changes needed for the melodic and harmonic versions of the scale are written in with accidentals as necessary. The A-sharp harmonic minor and melodic minor scales are:
\override Score.TimeSignature #'stencil = ##f
\relative c" {
 \clef treble \key ais \minor \time 7/4
 ais4^\markup "Harmonic minor scale" bis cis dis eis fis gisis ais gisis fis eis dis cis bis ais2
</score>
\override Score.TimeSignature #'stencil = ##f
\relative c" {
 \clef treble \key ais \minor \time 7/4
 ais4^\markup "Melodic minor scale (ascending and descending)" bis cis dis eis fisis gisis ais gis! fis! eis dis cis bis ais2
</score>
In Rinck's 30 Preludes and Exercises in all major and minor keys, the 16th Prelude and Exercise is in A-sharp minor. In Bach's Prelude and Fugue in C-sharp major, a brief section near the beginning of the piece modulates to A-sharp minor.


Milli mass unit

The milli mass unit or (mmu) is used as a unit of mass by some scientific authors even though this unit is not defined by the IUPAP red book nor by the IUPAC green book. It is a short form of the tongue-breaking but formally more correct "milli unified atomic mass unit" (mu) and equivalent to of the unified atomic mass unit (u). A more modern name is the millidalton (mDa)
since the "unified atomic mass unit" is more and more displaced by the unit dalton. (1 Da = 1 u)
Since 1961 the unified atomic mass unit "u" has been defined as the mass of C. Before that the atomic mass unit "amu" was defined as the mass of O (physics) and as the mass of O (chemistry). Thus the publication date in literature ought to be heeded when reading about the milli mass unit as its name does not reveal whether it refers to the old amu or the newer u.
The mass excess is usually indicated in mu or mmu.
In mass spectrometry the mass accuracy of a mass analyzer is often indicated in mu, even though a more correct unit would be mTh (millithomson) since mass spectrometers measure the mass-to-charge ratio, not the mass. The relative mass accuracy is often indicated in ppm, even though this is no longer supported by the IUPAC green book which suggests using units like μTh/Th instead of ppm.


Fresnel diffraction

In optics, the Fresnel diffraction equation for near-field diffraction is an approximation of the Kirchhoff–Fresnel diffraction that can be applied to the propagation of waves in the near field. It is used to calculate the diffraction pattern created by waves passing through an aperture or around an object, when viewed from relatively close to the object. In contrast the diffraction pattern in the far field region is given by the Fraunhofer diffraction equation.
The near field can be specified by the Fresnel number, , of the optical arrangement. When formula_1 the diffracted wave is considered to be in the near field. However, the validity of the Fresnel diffraction integral is deduced by the approximations derived below. Specifically, the phase terms of third order and higher must be negligible, a condition that may be written as
where formula_3 is the maximal angle described by formula_4, and the same as in the definition of the Fresnel number.
The multiple Fresnel diffraction at closely spaced periodical ridges (ridged mirror) causes the specular reflection; this effect can be used for atomic mirrors.
Early treatments of this phenomenon.
Some of the earliest work on what would become known as Fresnel diffraction was carried out by Francesco Maria Grimaldi in Italy in the 17th century. In his monograph entitled "Light", Richard C. MacLaurin explains Fresnel diffraction by asking what happens when light propagates, and how that process is affected when a barrier with a slit or hole in it is interposed in the beam produced by a distant source of light. He uses the Principle of Huygens to investigate, in classical terms, what transpires. The wave front that proceeds from the slit and on to a detection screen some distance away very closely approximates a wave front originating across the area of the gap without regard to any minute interactions with the actual physical edge.
The result is that if the gap is very narrow only diffraction patterns with bright centers can occur. If the gap is made progressively wider, then diffraction patterns with dark centers will alternate with diffraction patterns with bright centers. As the gap becomes larger, the differentials between dark and light bands decrease until a diffraction effect can no longer be detected.
MacLaurin does not mention the possibility that the center of the series of diffraction rings produced when light is shone through a small hole may be black, but he does point to the inverse situation wherein the shadow produced by a small circular object can paradoxically have a bright center. (p. 219)
In his "Optics", Francis Weston Sears offers a mathematical approximation suggested by Fresnel that predicts the main features of diffraction patterns and uses only simple mathematics. By considering the perpendicular distance from the hole in a barrier screen to a nearby detection screen along with the wavelength of the incident light, it is possible to compute a number of regions called half-period elements or Fresnel zones. The inner zone is a circle and each succeeding zone will be a concentric annular ring. If the diameter of the circular hole in the screen is sufficient to expose the first or central Fresnel zone, the amplitude of light at the center of the detection screen will be double what it would be if the detection screen were not obstructed. If the diameter of the circular hole in the screen is sufficient to expose two Fresnel zones, then the amplitude at the center is almost zero. That means that a Fresnel diffraction pattern can have a dark center. These patterns can be seen and measured, and correspond well to the values calculated for them.
The Fresnel diffraction integral.
The electric field diffraction pattern at a point "(x, y, z)" is given by:
where
Analytical solution of this integral is impossible for all but the simplest diffraction geometries. Therefore, it is usually calculated numerically.
The Fresnel approximation.
The main problem for solving the integral is the expression of "r". First, we can simplify the algebra by introducing the substitution:
Substituting into the expression for "r", we find:
Next, by the binomial expansion,
We can express formula_14 as
If we consider all the terms of binomial series, then there is no approximation. Let us substitute this expression in the argument of the exponential within the integral; the key to the Fresnel approximation is to assume that the third term is very small and can be ignored and henceforth any higher orders. In order to make this possible, it has to contribute to the variation of the exponential for an almost null term. In other words, it has to be much smaller than the period of the complex exponential; i.e., formula_16:
expressing "k" in terms of the wavelength,
we get the following relationship:
Multiplying both sides by formula_20, we have
or, substituting the earlier expression for ρ2,
If this condition holds true for all values of "x", "x' ", "y" and "y' ", then we can ignore the third term in the Taylor expression. Furthermore, if the third term is negligible, then all terms of higher order will be even smaller, so we can ignore them as well.
For applications involving optical wavelengths, the wavelength λ is typically many orders of magnitude smaller than the relevant physical dimensions. In particular:
and
Thus, as a practical matter, the required inequality will always hold true as long as
We can then approximate the expression with only the first two terms:
This equation, then, is the Fresnel approximation, and the inequality stated above is a condition for the approximation's validity.
Fresnel diffraction.
The condition for validity is fairly weak, and it allows all length parameters to take comparable values, provided the aperture is small compared to the path length. For the "r" in the denominator we go one step further, and approximate it with only the first term, formula_27. This is valid in particular if we are interested in the behaviour of the field only in a small area close to the origin, where the values of "x" and "y" are much smaller than "z". In general, Fresnel diffraction is valid if the Fresnel number is approximately 1.
For Fresnel diffraction the electric field at point "(x, y, z)" is then given by :
This is the Fresnel diffraction integral; it means that, if the Fresnel approximation is valid, the propagating field is a spherical wave, originating at the aperture and moving along "z". The integral modulates the amplitude and phase of the spherical wave. Analytical solution of this expression is still only possible in rare cases. For a further simplified case, valid only for much larger distances from the diffraction source, see Fraunhofer diffraction. Unlike Fraunhofer diffraction, Fresnel diffraction accounts for the curvature of the wavefront, in order to correctly calculate the relative phase of interfering waves.
Alternative forms.
Convolution.
The integral can be expressed in other ways in order to calculate it using some mathematical properties. If we define the following function:
then the integral can be expressed in terms of a convolution:
in other words we are representing the propagation using a linear-filter modeling. That is why we might call the function "h(x, y, z)" the impulse response of free space propagation.
Fourier transform.
Another possible way is through the Fourier transform. If in the integral we express "k" in terms of the wavelength:
and expand each component of the transverse displacement:
then we can express the integral in terms of the two-dimensional Fourier transform. Let us use the following definition:
where "p" and "q" are spatial frequencies (wave numbers). The Fresnel integral can be expressed as
That is, first multiply the field to be propagated by a complex exponential, calculate its two-dimensional Fourier transform, replace ("p", "q") with formula_35 and multiply it by another factor. This expression is better than the others when the process leads to a known Fourier transform, and the connection with the Fourier transform is tightened in the linear canonical transformation, discussed below.
Linear canonical transformation.
From the point of view of the linear canonical transformation, Fresnel diffraction can be seen as a shear in the time-frequency domain, corresponding to how the Fourier transform is a rotation in the time-frequency domain.


List of language proficiency tests

The following is a non-exhaustive, but growing, list of standardized tests that assess a person's language proficiency of a foreign/secondary language. Various types of such exams exist per many languages—some are organized at an international level even through national authoritative organizations, while others simply for specific limited business or study orientation.
Bulgarian.
(STBFL) (Стандартизиран тест по
български език като чужд език (СТБЕЧ))
http://www.deo.uni-sofia.bg/bg/certificate/bg
https://www.mon.bg/upload/7447/reglament_BG_online.pdf
http://www.legacy.deo.uni-sofia.bg/alte/index.htm
http://www.deo.uni-sofia.bg/bg/coursis
http://www.deo.uni-sofia.bg/bg/language/bulgarian
German.
DSD II, DSH, and TestDaF are accepted by any university in Germany. They are officially recognised as university entrance qualifications. Other tests may be considered, but no guarantees are given. In other German-speaking countries the situation varies.
Hungarian.
 The certificate examinations are staged on four levels of language proficiency according to the Common European Framework of Reference for Languages:
Italian.
According to the Ministero degli Esteri (Italian Foreign Affairs), there are four officials Italian certifications approved CLIQ (Certificato di Lingua Italiana di Qualità): CILS, CELI, PLIDA and .IT ROMA TRE
Kazakh.
 Levels : Reasonable grade
 Elementary : 31-64 grades
 Pre-Intermediate : 65-104 grades
 Intermediate : 105-119 grades
 Upper-Intermediate : 120-134 grades
 Advanced : 135-145 grades
 Higher advanced : 146-150 grades
Norwegian.
- Bergenstest for voksne innvandrere - Level B2


Paraguayan units of measurement

A number of units of measurement were used in Paraguay to measure quantities including length, mass, area, capacity, etc. Metric system had been optional since 1890, and adopted since 1899 in Paraguay.
System before metric system.
Spanish system was used before metric system.
Length.
A number of units were used to measure length. According to legal equivalents, one vara (old) was 0.83856 m. One cuerda or One cordel was vara or 69.88 m, according to legal equivalents. One vara was 0.866 m, according to legal equivalents. Some other units and their legal equivalents are given below:
1 pulgada (inch) = vara
1 linea (line) = vara
1 piede (foot) = vara
1 pouce = vara
1 ligne = vara
1 cuadra = 100 vara
1 lieue (league) = 5000 vara.
Mass.
Several units were used to measure mass. According to legal equivalents, One libra was 0.459 kg (One libra (old) was 460.08 kg). Some other units and their legal equivalents were given below:
1 onza (once) = libra
1 arroba = 25 libra
1 quintal (hundredweight) = 100 libra
1 tonelada (tonne) = 2000 libra.
Area.
Several units were used to measure area. Some units and their legal equalents are given below:
1 lifio (old) = 4883.2 m2
1 lifio = 100 square vara = 75 m2.
Capacity.
Two main systems, dry and liquid, were used to measure capacity.
Dry.
One fanega was 288 l and one almude was fanega.
Liquid.
Several units were used to measure liquid capacity. One frasco was 3.029 litres. Some other units and their legal equivalents are given below:
1 cuarto = frasco
1 baril = 32 frasco
1 pipe = 192 frasco.


Blumlein pair

Blumlein pair is the name for a stereo recording technique invented by Alan Blumlein for the creation of recordings that, upon replaying through headphones or loudspeakers, recreate the spatial characteristics of the recorded signal.
The pair consists of an array of two matched microphones that have a bi-directional (figure-8) pickup pattern. They are positioned 90° from each other. Ideally, the transducers should occupy the same physical space; since this cannot be achieved, the microphone capsules are placed as close to each other as physically possible, generally with one centered directly above the other. The array is oriented so that the line bisecting the angle between the two microphones points towards the sound source to be recorded (see diagram). The pickup patterns of the pair, combined with their positioning, delivers a high degree of stereo separation in the source signal, as well as the room ambiance.
The Blumlein pair produces an exceptionally realistic stereo image, but the quality of recordings is highly dependent on the acoustics of the room and the size of the sound source.
Both ribbon and condenser microphones can be used for Blumlein-pair recording. A few types of stereo ribbon microphones (B & O, Royer, AEA) have even been purpose-built for just this type of recording. Several types of stereo condenser microphone (Neumann, AKG, Schoeps, Nevaton BPT) have also offered a Blumlein arrangement as one of their possible configurations. Individual microphones with variable patterns (such as those from Pearl/Milab) can be used. The Soundfield microphone used to make Ambisonic recordings can be adjusted to mimic two microphones of any pattern at any angle to each other, including a Blumlein pair.
In his early experiments at EMI with what he called "binaural" sound, Blumlein did not use this actual technique because he did not have access to figure-8 microphones. This meant that he had to develop ways of using omnidirectional microphones to record what we now know as stereo sound. In the claims he made in his U.K. patent application in 1931, as well as details of these techniques, he included the theoretical possibility of using directional microphones in what later became known as a Blumlein pair. During the period when Blumlein's patent (British Patent 394325) was being written, Harry F. Olson published a patent for the first practical ribbon microphone, and much of the later experimental work was carried out with this type of microphone
It is unclear when this approach became known as the Blumlein pair, although it does not appear to have been known by that name during his lifetime.


Piezoelectric sensor

A piezoelectric sensor is a device that uses the piezoelectric effect to measure changes in pressure, acceleration, temperature, strain, or force by converting them to an electrical charge. The prefix "piezo-" is Greek for 'press' or 'squeeze'.
Applications.
Piezoelectric sensors are versatile tools for the measurement of various processes. They are used for quality assurance, process control, and for research and development in many industries. Pierre Curie discovered the piezoelectric effect in 1880, but only in the 1950s did manufacturers begin to use the piezoelectric effect in industrial sensing applications. Since then, this measuring principle has been increasingly used, and has become a mature technology with excellent inherent reliability.
They have been successfully used in various applications, such as in medical, aerospace, nuclear instrumentation, and as a tilt sensor in consumer electronics or a pressure sensor in the touch pads of mobile phones. In the automotive industry, piezoelectric elements are used to monitor combustion when developing internal combustion engines. The sensors are either directly mounted into additional holes into the cylinder head or the spark/glow plug is equipped with a built-in miniature piezoelectric sensor.
The rise of piezoelectric technology is directly related to a set of inherent advantages. The high modulus of elasticity of many piezoelectric materials is comparable to that of many metals and goes up to . Even though piezoelectric sensors are electromechanical systems that react to compression, the sensing elements show almost zero deflection. This gives piezoelectric sensors ruggedness, an extremely high natural frequency and an excellent linearity over a wide amplitude range. Additionally, piezoelectric technology is insensitive to electromagnetic fields and radiation, enabling measurements under harsh conditions. Some materials used (especially gallium phosphate or tourmaline) are extremely stable at high temperatures, enabling sensors to have a working range of up to . Tourmaline shows pyroelectricity in addition to the piezoelectric effect; this is the ability to generate an electrical signal when the temperature of the crystal changes. This effect is also common to piezoceramic materials. Gautschi in "Piezoelectric Sensorics" (2002) offers this comparison table of characteristics of piezo sensor materials vs other types:
One disadvantage of piezoelectric sensors is that they cannot be used for truly static measurements. A static force results in a fixed amount of charge on the piezoelectric material. In conventional readout electronics, imperfect insulating materials and reduction in internal sensor resistance causes a constant loss of electrons and yields a decreasing signal. Elevated temperatures cause an additional drop in internal resistance and sensitivity. The main effect on the piezoelectric effect is that with increasing pressure loads and temperature, the sensitivity reduces due to twin formation. While quartz sensors must be cooled during measurements at temperatures above , special types of crystals like GaPO4 gallium phosphate show no twin formation up to the melting point of the material itself.
However, it is not true that piezoelectric sensors can only be used for very fast processes or at ambient conditions. In fact, numerous piezoelectric applications produce quasi-static measurements, and other applications work in temperatures higher than .
Piezoelectric sensors can also be used to determine aromas in the air by simultaneously measuring resonance and capacitance. Computer controlled electronics vastly increase the range of potential applications for piezoelectric sensors.
Piezoelectric sensors are also seen in nature. The collagen in bone is piezoelectric, and is thought by some to act as a biological force sensor.
Principle of operation.
The way a piezoelectric material is cut defines one of its three main operational modes:
Transverse effect.
A force applied along a neutral axis (y) displaces charges along the (x) direction, perpendicular to the line of force. The amount of charge (formula_1) depends on the geometrical dimensions of the respective piezoelectric element. When dimensions formula_2 apply,
Longitudinal effect.
The amount of charge displaced is strictly proportional to the applied force and independent of the piezoelectric element size and shape. Putting several elements mechanically in series and electrically in parallel is the only way to increase the charge output. The resulting charge is
Shear effect.
The charge produced is exactly proportional to the applied force and is generated at a right angle to the force. The charge is independent of the element size and shape. For formula_10 elements mechanically in series and electrically in parallel the charge is
In contrast to the longitudinal and shear effects, the transverse effect make it possible to fine-tune sensitivity on the applied force and element dimension.
Electrical properties.
A piezoelectric transducer has very high DC output impedance and can be modeled as a proportional voltage source and filter network. The voltage "V" at the source is directly proportional to the applied force, pressure, or strain. The output signal is then related to this mechanical force as if it had passed through the equivalent circuit.
A detailed model includes the effects of the sensor's mechanical construction and other non-idealities. The inductance "L"m is due to the seismic mass and inertia of the sensor itself. "C"e is inversely proportional to the mechanical elasticity of the sensor. "C"0 represents the static capacitance of the transducer, resulting from an inertial mass of infinite size. "R"i is the insulation leakage resistance of the transducer element. If the sensor is connected to a load resistance, this also acts in parallel with the insulation resistance, both increasing the high-pass cutoff frequency.
For use as a sensor, the flat region of the frequency response plot is typically used, between the high-pass cutoff and the resonant peak. The load and leakage resistance must be large enough that low frequencies of interest are not lost. A simplified equivalent circuit model can be used in this region, in which "C"s represents the capacitance of the sensor surface itself, determined by the standard formula for capacitance of parallel plates. It can also be modeled as a charge source in parallel with the source capacitance, with the charge directly proportional to the applied force, as above.
Sensor design.
Based on piezoelectric technology various physical quantities can be measured the most common are pressure and acceleration. For pressure sensors, a thin membrane and a massive base is used, ensuring that an applied pressure specifically loads the elements in one direction. For accelerometers, a seismic mass is attached to the crystal elements. When the accelerometer experiences a motion, the invariant seismic mass loads the elements according to Newton's second law of motion formula_13.
The main difference in working principle between these two cases is the way they apply forces to the sensing elements. In a pressure sensor, a thin membrane transfers the force to the elements, while in accelerometers an attached seismic mass applies the forces.
Sensors often tend to be sensitive to more than one physical quantity. Pressure sensors show false signal when they are exposed to vibrations. Sophisticated pressure sensors therefore use acceleration compensation elements in addition to the pressure sensing elements. By carefully matching those elements, the acceleration signal (released from the compensation element) is subtracted from the combined signal of pressure and acceleration to derive the true pressure information.
Vibration sensors can also harvest otherwise wasted energy from mechanical vibrations. This is accomplished by using piezoelectric materials to convert mechanical strain into usable electrical energy.
Sensing materials.
Three main groups of materials are used for piezoelectric sensors: piezoelectric ceramics, single crystal materials and thin film piezoelectric materials.
The ceramic materials (such as PZT ceramic) have a piezoelectric constant/sensitivity that is roughly two orders of magnitude higher than those of the natural single crystal materials and can be produced by inexpensive sintering processes. The piezoeffect in piezoceramics is "trained", so their high sensitivity degrades over time. This degradation is highly correlated with increased temperature.
The less-sensitive, natural, single-crystal materials (gallium phosphate, quartz, tourmaline) have a higher – when carefully handled, almost unlimited – long term stability. There are also new single-crystal materials commercially available such as Lead Magnesium Niobate-Lead Titanate (PMN-PT). These materials offer improved sensitivity over PZT but have a lower maximum operating temperature and are currently more complicated to manufacture due to four compound vs. three compound material PZT.
Thin film piezoelectric materials can be manufactured utilizing sputtering, CVD (Chemical vapour deposition), ALD (atomic layer epitaxy) etc. methods. Thin film piezoelectric materials are used in applications where high frequency (> 100 MHz) is utilised in the measurement method and/or small size is favored in the application.


Phi3 Ceti

Phi3 Ceti is a solitary, orange-hued star in the equatorial constellation of Cetus. It is faintly visible to the naked eye with an apparent visual magnitude of 5.31. Based upon an annual parallax shift of 5.92 mas as seen from Earth, it is located roughly 550 light years from the Sun, give or take 30 light years.
This is an evolved K-type giant star with a stellar classification of K5 III. The measured angular diameter of Phi3 Ceti is . At the estimated distance of the star, this yields a physical size of about 44 times the Sun's radius. It has about 1.4 times the mass of the Sun and radiates 429 times the solar luminosity from its photosphere at an effective temperature of 3,940 K.
References.
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Dror Feiler

Dror Elimelech Feiler (; born 31 August 1951) is an Israeli-born Swedish musician, artist and left-wing activist. He is married to the artist Gunilla Sköld-Feiler.
Early life and career.
Feiler was born in Tel Aviv in 1951 to Eliezer and Pnina Feiler, and moved with his family to kibbutz Yad Hana in 1967. His father, Eliezer Feiler, was a left-wing activist. In 1978, he and others secretly met with a group of Palestine Liberation Organization representatives in Bucharest while it was still illegal. Eliezer Feiler was tried and eventually sentenced to six months of community service and a 4,000 Israeli lira fine. The fine was paid, but the sentence was never served because, while the legal process was ongoing, the law had changed and it was no longer illegal to meet with members of the PLO. His mother, Pnina Feiler, born 1923, was among the founders of Yad Hana. She worked with mobile health centrals in Palestinian villages in the West Bank that have to travel far to get access to health-care and other services until 2015, when she stopped due to her advanced age. Dror Feiler served as a paratrooper in the Israel Defense Forces.
Feiler went abroad in the early 70s to pursue his musical studies in Sweden, where he met his wife. Swedish law at that time did not recognize dual citizenship, and Feilor had to relinquish his Israeli rights in order to become a citizen of Sweden.He studied avant-garde music and its interpretation at the Fylkingen Institut for New Music from 1975 to 1977, musicology at Stockholm University from 1977 to 1978 and composition at the Music Academy of Stockholm from 1978 to 1983.
Feiler also plays saxophone in the jazz band Lokomotiv Konkret, and founded the Too Much Too Soon Orchestra. In January 2004 he and Gunilla Sköld-Feiler made international news with their art installation "Snow White and The Madness of Truth", which referred to female suicide bomber Hanadi Jaradat, which was vandalised by the then Israeli ambassador to Sweden Zvi Mazel. The installation consisted of a long pool of water coloured blood red, upon which floated a small white boat named "Snövit" ("Snow White") carrying a portrait of Hanadi Jaradat. She had blown herself up in October 2003 in an attack on Maxim's restaurant in the northern Israeli city of Haifa, killing 21 people and injuring 51.
Feiler is now the chairman of the Swedish organization Jews for Israeli–Palestinian Peace (JIPF) and the European organization European Jews for a Just Peace (EJJP). He is also a member of the editorial board of the New Colombia News Agency (ANNCOL).
He runs the artspace TEGEN 2 in Stockholm together with Gunilla Sköld Feiler.
He is active as a composer of modern music, which includes composition music for symphonic orchestras, opera, chamber music and electro-acoustic music. In April 2008, the Bavarian Radio Symphony Orchestra dropped the world premiere of his composition "Halat Hisar" (State of Siege), after musicians complained that the music, which includes machine gun sounds, was so loud that it gave them ear problems and headaches.
On 31 May 2010 Feiler was aboard one of the ships involved in the Gaza flotilla raid and sustained some minor injuries to the face during the raid. For his participation in the raid, Feiler was banned from entering Israel for 10 years. In July 2010, he flew to Israel together with Swedish MP Mehmet Kaplan, who had also received a 10-year entry ban over his participation in the Gaza flotilla, planning to lodge a complaint with the Israel Police over the flotilla raid. They were refused entry at Ben Gurion Airport and deported. In 2011, Feiler was involved in the Freedom Flotilla II, and was among the 15 activists arrested by Israeli authorities aboard the boat Dignité. He was subsequently deported from Israel.
In the 2010 Swedish general election, Feiler was a candidate for the Left Party () in Stockholm. He obtained 1,784 personal preference votes in Stockholm Municipality (4.51% of the Left Party votes, the second most voted candidate on the list after party chairman Lars Ohly) and 629 personal preference votes in Stockholm County (1.99% of the Left Party votes).
Feiler took part in Freedom Flotilla III, aboard the Swedish vessel "Marianne". The ship was intercepted by the Israeli Navy on June 29, and Feiler was arrested.
Attempts to visit his mother.
In 2013, Feiler appealed this ban in order to visit his ailing 90-year-old mother. His mother, then 90, had to fly to Sweden to meet up with her son, though bsubsequently, due to health problems, that option ceased to be available. She therefore repeatedly requested the Israeli Ministry for the Interior to lift his ban, without success. In 2018, after Swedish law dropped its ban on dual citizenship, Feiler asked for his citizenship to be restored on the basis of his right to make aliyah and be with his aging mother. No reply was forthcoming. In response to a petition by the family's attorney in December 2019, the director of the Population and Immigration Authority Prof. Shlomo Mor-Yosef in January 2020 conceded permission for a 2 week visit on condition he post a $28,910 bond. This condition was appealed and, in September, a judge extended his visa by a further 2 weeks, since, were he to visit, he would have to stay in quarantine for 14 days, given the Covid19 crisis. That crisis had also affected Feiler's concert schedule, depriving him of adequate financial means to post the bond.


Remote Differential Compression

Remote Differential Compression (RDC) is a client–server synchronization algorithm that allows the contents of two files to be synchronized by communicating only the differences between them. It was introduced with Microsoft Windows Server 2003 R2, is included with later Windows client and server operating systems, but by 2019 is not being developed and is not used by any Microsoft product.
Unlike Binary Delta Compression (BDC), which is designed to operate only on known versions of a single file, RDC does not make assumptions about file similarity or versioning. The differences between files are computed on the fly, therefore RDC is suitable for efficient synchronization of files that have been updated independently, where network bandwidth is small, or where the files are large but the differences between them are small.
The algorithm used is based on fingerprinting blocks on each file locally at both ends of the replication partners. Since many types of file changes can cause the file contents to move without other significant change (for example, a small insertion or deletion at the beginning of a file can cause the rest of the file to become misaligned to the original content) the blocks used for comparison are not based on static arbitrary cut points but on cut points defined by the contents of each file segment. This means that if a part of a file changes in length, or blocks of the contents get moved to other parts of the file, the block boundaries for the parts that have not changed remain fixed related to the contents, and thus the series of fingerprints for those blocks do not change, they just change position. By comparing all hashes in a file to the hashes for the same file at the other end of the replication pair, RDC is able to identify which blocks of the file have changed and which have not, even if the contents of the file have been significantly reshuffled.
Since comparing large files could imply making large numbers of signature comparisons, the algorithm is recursively applied to the hash sets to detect which blocks of hashes have changed or moved around, significantly reducing the amount of data that needs to be transmitted for comparing files.
Later versions of Windows support cross-file RDC, which finds files similar to the one being replicated, and uses blocks of the similar files that are identical to the replicating file to minimize data transferred over the WAN. Cross-file RDC can use blocks of up to five similar files.
RDC is similar in many ways to the older (1996) rsync protocol, but with some useful innovations, in particular the recursive algorithm and cross-file RDC.
RDC is implemented in Windows operating systems by a DLL file, MSRDC.DLL, which will be present in the %SYSTEMROOT%\System32 directory if and only if RDC is enabled. Very little software is available which makes use of it, particularly on non-server systems. According to Internet rumor, enabling RDC significantly slows local file transfers, and it should not be enabled; a Microsoft TechNet web page disputes this in great detail, despite frequent anecdotal posts of its removal having worked to restore transfer speeds.
Discontinuation.
With the release of Microsoft's Windows Server 2019, RDC support was included in the section "Features we’re no longer developing" (which may be removed from a future update), with the comment "This support isn’t currently used by any Microsoft product".


2929 Harris


Gramm (record label)

Gramm was an Icelandic record label created by Ásmundur Jónsson and Einar Örn Benediktsson in 1981.
Located in Reykjavík, Gramm’s first release was a 10-track 7" vinyl titled "Tilf" by Purrkur Pillnikk, a punk group led by Einar Örn.
Besides releasing all Purrkur Pillnikk's records, Gramm also issued works of artists like the English experimental group Psychic TV, Björk's first band Tappi Tíkarrass and Kukl (featuring Björk and Einar Örn). Rock band Þeyr and punk groups such as Vonbrigði were also associated with Gramm.
In 1987, Gramm went bankrupt. Ásmundur and some of the musicians who were playing in Kukl created Smekkleysa, which ultimately became Bad Taste, known worldwide by the Sugarcubes.


Tau Piscium

Tau Piscium (τ Piscium) is an orange-hued star in the zodiac constellation of Pisces. With an apparent visual magnitude of +4.52, it is a dim star but visible to the naked eye. Based upon an annual parallax shift of 19.32 mas as seen from Earth, it is located around 169 light years from the Sun. It is most likely (96% chance) a member of the thin disk population.
This is an evolved K-type giant star with a stellar classification of K0.5 IIIb. It is about 2.27 billion years and is a red clump star on the horizontal branch, which indicates it is generating energy through helium fusion at its core. The star has 1.7 times the mass of the Sun and has expanded to about 10 times the Sun's radius. It is radiating 45 times the Sun's luminosity from its photosphere at an effective temperature of 4,624 K.
Naming.
In Chinese, (), meaning "Legs", refers to an asterism consisting of τ Piscium, η Andromedae, 65 Piscium, ζ Andromedae, ε Andromedae, δ Andromedae, π Andromedae, ν Andromedae, μ Andromedae, β Andromedae, σ Piscium, 91 Piscium, υ Piscium, φ Piscium, χ Piscium and ψ¹ Piscium. Consequently, the Chinese name for τ Piscium itself is (, .)


347 Pariana

347 Pariana ("prov. designation": "or" ) is a metallic background asteroid from the central region of the asteroid belt. It was discovered by French astronomer Auguste Charlois at the Nice Observatory on 28 November 1892. The M-type asteroid has a short rotation period of 4.1 hours and measures approximately in diameter. The origin of the asteroid's name remains .


Two-sample hypothesis testing

In statistical hypothesis testing, a two-sample test is a test performed on the data of two random samples, each independently obtained from a different given population. The purpose of the test is to determine whether the difference between these two populations is statistically significant.
There are a large number of statistical tests that can be used in a two-sample test. Which one(s) are appropriate depend on a variety of factors, such as:
Relevant tests.
Statistical tests that may apply for two-sample testing include:


Shaker (testing device)

A shaker is a device used in vibration testing to excite the structure either for endurance testing or modal testing.


694 Ekard

694 Ekard is a minor planet orbiting the Sun that was discovered by American astronomer Joel Hastings Metcalf on November 7, 1909.
Photometric observations of this asteroid gave a light curve with a period of 5.925 hours and a brightness variation of 0.50 in magnitude. Measurements of the thermal inertia of 694 Ekard give a value of around 100–140 J m−2 K−1 s−1/2, compared to 50 for lunar regolith and 400 for coarse sand in an atmosphere.
13-cm radar observations of this asteroid from the Arecibo Observatory between 1980 and 1985 were used to produce a diameter estimate of 101 km. Four separate stellar occultation events involving this asteroid were observed from multiple sites in 2009. The resulting chords matched a least squares equivalent diameter of .


Alexander (satellite)

Alexander, also known as PhoneSat 2.0 Beta or PhoneSat v2a is a technology demonstration satellite operated by NASA's Ames Research Center, which was launched in April 2013. Part of the PhoneSat programme, it was one of the first three PhoneSat spacecraft, and the first Phonesat-2.0 satellite, to be launched.
A PhoneSat-2.0 satellite, "Alexander" was built to the single-unit (1U) CubeSat specification, and measures in each dimension. The satellite is based on an off-the-shelf Samsung Electronics Nexus S smartphone which serves in place of an onboard computer. The satellite is equipped with a two-way S-band transponder and solar cells for power generation. The spacecraft uses the phone's gyroscopes, along with a GPS receiver, to determine its position and orientation, and a system of reaction wheels and magnetorquer coils for attitude control.
"Alexander" was named after Alexander Graham Bell, the inventor of the telephone. The two other PhoneSat spacecraft launched aboard the same rocket were named "Graham" and "Bell". The three PhoneSat spacecraft, along with the commercial Dove 1 satellite, were launched as secondary payloads aboard the maiden flight of the Antares launch vehicle; flight A-ONE. The primary payload was the Cygnus Mass Simulator.
Liftoff occurred at 21:00 UTC on 21 April 2013, from Pad 0A of the Mid-Atlantic Regional Spaceport (MARS), following attempts on 17 and 20 April which had been scrubbed due to an umbilical problem and high-level winds respectively. The launch was conducted by Orbital Sciences Corporation, however the CubeSats were launched under a contract with Spaceflight Services, using dispensers produced by Innovative Solutions In Space (ISIS). "Alexander", "Graham" and "Bell" were deployed from a single ISIPod dispenser, while Dove 1 was deployed from a second such dispenser.
On 27 April 2013, the satellite was confirmed to have burned up in the atmosphere, with instruments still running up until then.


944 Hidalgo

944 Hidalgo is a centaur and unusual object on an eccentric, cometary-like orbit between the asteroid belt and the outer Solar System, approximately in diameter. Discovered by German astronomer Walter Baade in 1920, it is the first member of the dynamical class of centaurs ever to be discovered. The dark D-type object has a rotation period of 10.1 hours and likely an elongated shape. It was named after Mexican revolutionary Miguel Hidalgo y Costilla.
Discovery and naming.
"Hidalgo" was discovered by German astronomer Walter Baade on 31 October 1920 at Bergedorf Observatory in Hamburg, Germany. It is named for Miguel Hidalgo y Costilla (1753–1811), who was responsible for declaring Mexico's independence in 1810 and the ensuing Mexican War of Independence. German astronomers who were in Mexico to observe a total eclipse on 10 September 1923 had an audience with President Álvaro Obregón. During this meeting, they asked his permission to name the asteroid after Hidalgo ().
Orbit and classification.
"Hidalgo" orbits the Sun at a distance of 1.9–9.5 AU once every 13 years and 9 months (5,024 days; semi-major axis of 5.74 AU). Its orbit has a high eccentricity of 0.66 and an inclination of 43° with respect to the ecliptic. The body's observation arc begins with its official discovery observation on 31 October 1920.
With a semi-major axis between that of Jupiter (5.2 AU) and Neptune (30.1 AU), "Hidalgo" is a member of the dynamically unstable population of centaurs, located between the classical asteroids and the trans-Neptunian objects. The Minor Planet Center classifies it both as main-belt asteroid and unusual object due to an orbital eccentricity higher than 0.5. "Hidalgo" has traditionally been considered an asteroid because centaurs were not recognized as a distinct class until the discovery of 2060 Chiron in 1977. Alternatively, cis-Neptunian object and distant object are more generic terms that also includes objects further out the Solar System.
"Hidalgo" orbit takes it to the inner edge of the asteroid belt and as far out as to the orbit of Saturn (9.0–10.1 AU), a characteristic normally associated with Saturn's family of comets. Some astronomers therefore suspect that it was once a comet. It is a Jupiter- and Saturn-crosser. Strictly speaking, "Hidalgo" is a Saturn-grazer rather than a crosser as its aphelion does not clear Saturn's. The object's severe orbital inclination is suspected to be the result of a close encounter with Jupiter. Even as recently as 1922, "Hidalgo" passed within 0.89 AU of Jupiter. Its orbit has a Jupiter minimum orbit intersection distance of only .
It is unlikely there are any large satellites orbiting Hidalgo larger than about 15 kilometers across. Observations from the Very Large Telescope in 2003 ruled out any secondary objects brighter than V=19.5 further than 200 kilometers from the asteroid. However, smaller moons have not been ruled out.
Physical characteristics.
In the Tholen and Bus–DeMeo classification, "Hidalgo" is a dark, carbonaceous D-type asteroid.
According to the surveys carried out by the Japanese Akari satellite and the NEOWISE mission of NASA's Wide-field Infrared Survey Explorer, "Hidalgo" measures 52.45 and 61.4 kilometers in diameter and its surface has a low albedo of 0.042 and 0.028, respectively. The prominent JPL Small-Body Database currently gives a diameter of 38 kilometers taken from the publication "Hazards due to Comets and Asteroids" (Tom Gehrels, 1994). The "Collaborative Asteroid Lightcurve Link" assumes a standard albedo for a carbonaceous asteroid of 0.057 and derives a diameter of 44.6 km based on an absolute magnitude of 10.48, while Johnston's archive adopts Akari's diameter of 52 km with an albedo of 0.042.
In the late 1990s, a network of astronomers worldwide gathered lightcurve data that was ultimately used to derive the spin states and shape models of 10 new asteroids, including "Hidalgo". The authors describe the shape model as having 'very large flat areas and a "rectangular" pole-on silhouette, which are strong indications of a highly nonconvex shape'. Some of the light curves show sharp minima, which indicates the object shape may have two lobes. Lightcurve data has also been recorded by observers at the Antelope Hills Observatory in Colorado, United States. When Pluto was discovered "Hidalgo" was the furthest known minor planet from the Sun.


Stem-and-leaf display

A stem-and-leaf display or stem-and-leaf plot is a device for presenting quantitative data in a graphical format, similar to a histogram, to assist in visualizing the shape of a distribution. They evolved from Arthur Bowley's work in the early 1900s, and are useful tools in exploratory data analysis. Stemplots became more commonly used in the 1980s after the publication of John Tukey's book on "exploratory data analysis" in 1977. The popularity during those years is attributable to their use of monospaced (typewriter) typestyles that allowed computer technology of the time to easily produce the graphics. Modern computers' superior graphic capabilities have meant these techniques are less often used.
This plot has been implemented in Octave and R.
A stem-and-leaf plot is also called a stemplot, but the latter term often refers to another chart type. A simple stem plot may refer to plotting a matrix of "y" values onto a common "x" axis, and identifying the common" x" value with a vertical line, and the individual "y "values with symbols on the line.
Unlike histograms, stem-and-leaf displays retain the original data to at least two significant digits, and put the data in order, thereby easing the move to order-based inference and non-parametric statistics.
Construction.
To construct a stem-and-leaf display, the observations must first be sorted in ascending order: this can be done most easily if working by hand by constructing a draft of the stem-and-leaf display with the leaves unsorted, then sorting the leaves to produce the final stem-and-leaf display. Here is the sorted set of data values that will be used in the following example:
Next, it must be determined what the stems will represent and what the leaves will represent. Typically, the leaf contains the last digit of the number and the stem contains all of the other digits. In the case of very large numbers, the data values may be rounded to a particular place value (such as the hundreds place) that will be used for the leaves. The remaining digits to the left of the rounded place value are used as the stem.
In this example, the leaf represents the ones place and the stem will represent the rest of the number (tens place and higher).
The stem-and-leaf display is drawn with two columns separated by a vertical line. The stems are listed to the left of the vertical line. It is important that each stem is listed only once and that no numbers are skipped, even if it means that some stems have no leaves. The leaves are listed in increasing order in a row to the right of each stem.
It is important to note that when there is a repeated number in the data (such as two 72s) then the plot must reflect such (so the plot would look like 7 | 2 2 5 6 7 when it has the numbers 72 72 75 76 77).
Rounding may be needed to create a stem-and-leaf display. Based on the following set of data, the stem plot below would be created:
For negative numbers, a negative is placed in front of the stem unit, which is still the value X / 10. Non-integers are rounded. This allowed the stem and leaf plot to retain its shape, even for more complicated data sets. As in this example below:
Usage.
Stem-and-leaf displays are useful for displaying the relative density and shape of the data, giving the reader a quick overview of the distribution. They retain (most of) the raw numerical data, often with perfect integrity. They are also useful for highlighting outliers and finding the mode. However, stem-and-leaf displays are only useful for moderately sized data sets (around 15–150 data points). With very small data sets a stem-and-leaf displays can be of little use, as a reasonable number of data points are required to establish definitive distribution properties. A dot plot may be better suited for such data. With very large data sets, a stem-and-leaf display will become very cluttered, since each data point must be represented numerically. A box plot or histogram may become more appropriate as the data size increases.


3020 Naudts


Mister Heartbreak

Mister Heartbreak is the second album by avant-garde artist, singer and composer Laurie Anderson, released in 1984.
Like its predecessor, it contains reworked elements of Anderson's "United States" ("Langue d'Amour", "Kokuku", based on musical elements from "Rising Sun", and "Blue Lagoon"). However, Anderson also introduced new material ("Sharkey's Day"/"Sharkey's Night" and "Gravity's Angel") while "Excellent Birds", written in collaboration with Peter Gabriel, was written for a 1984 project for video artist Nam June Paik called "Good Morning, Mr. Orwell".
Background.
"Gravity's Angel" borrows imagery from Thomas Pynchon's "Gravity's Rainbow". Anderson had "wanted to make an opera of that book ... and asked him if that would be OK... He said, 'You can do it, but you can only use banjo.' And so I thought, 'Well, thanks. I don't know if I could do it like that." "Blue Lagoon" contains allusions to other tales of the sea (William Shakespeare's "The Tempest" (Ariel's song) and Herman Melville's "Moby-Dick").
Considered more mainstream than its predecessor, "Big Science", the album's lead track, "Sharkey's Day" formed the basis of a popular music video. Author William S. Burroughs read the lyrics of the closing track, "Sharkey's Night", while Peter Gabriel provided vocals on "Excellent Birds", an alternate version of which, titled "This is the Picture (Excellent Birds)", also appeared on his album "So". According to Anderson, she and Gabriel "could never agree on what a bassline was. (I think I probably don’t hear so well down there.) I wanted to learn from him, but it turned into a standoff and so we each put out our own version of the song." A third version of the song can be heard in the music video version, directed by Dean Winkler.
Most of the songs on this album were later performed in Anderson's 1986 concert film "Home of the Brave". Burroughs appears in that film and appears in two brief segments reciting lines from "Sharkey's Night", although it is Anderson herself who performs a complete version of the song at the film's conclusion. "Sharkey's Night" featured in the Australian short documentary film "Ladies Please!" (1995).
It has sold 44,000 copies in France.
Track listing.
All songs written by Laurie Anderson except as indicated.
Charts.
Album


HTML5 Chinese Interest Group

The HTML5 Chinese Interest Group, is part of the HTML Working Group Activity, its mission of is to facilitate focused discussion of the HTML5 specification and of specifications closely related to HTML5.
The HTML5 Chinese IG will not produce Recommendation-track deliverables but may produce Interest Group Notes on HTML5 and related technologies, currently the Chinese IG has over 1000 members.
The Group's initial chair was Zi Bin Cheah.


Equivalent Martingale Measure


Optimistic replication

Optimistic replication, also known as lazy replication, is a strategy for replication, in which replicas are allowed to diverge.
Traditional pessimistic replication systems try to guarantee from the beginning that all of the replicas are identical to each other, as if there was only a single copy of the data all along. Optimistic replication does away with this in favor of eventual consistency, meaning that replicas are guaranteed to converge only when the system has been quiesced for a period of time. As a result, there is no longer a need to wait for all of the copies to be synchronized when updating data, which helps concurrency and parallelism. The trade-off is that different replicas may require explicit reconciliation later on, which might then prove difficult or even insoluble.
Algorithms.
An optimistic replication algorithm consists of five elements:
There are two strategies for propagation: state transfer, where sites propagate a representation of the current state, and operation transfer, where sites propagate the operations that were performed (essentially, a list of instructions on how to reach the new state).
Scheduling and conflict resolution can either be syntactic or semantic. Syntactic systems rely on general information, such as when or where an operation was submitted. Semantic systems are able to make use of application-specific information to make smarter decisions. Note that state transfer systems generally have no information about the semantics of the data being transferred, and so they have to use syntactic scheduling and conflict resolution.
Examples.
One well-known example of a system based on optimistic replication is the CVS version control system, or any other version control system which uses the copy-modify-merge paradigm. CVS covers each of the five elements:
A special case of replication is synchronization, where there are only two replicas. For example, personal digital assistants (PDAs) allow users to edit data either on the PDA or a computer, and then to merge these two datasets together. Note, however, that replication is a broader problem than synchronization, since there may be more than two replicas.
Other examples include:
Implications.
Applications built on top of optimistic replicated databases need to be careful about ensuring that the delayed updates observed do not impair the correctness of the application.
As a simple example, if an application contains a way of viewing some part of the database state, and a way of editing it, then users may edit that state but then not see it changing in the viewer. Alarmed that their edit "didn't work", they may try it again, potentially more than once. If the updates are not idempotent (e.g., they increment a value), this can lead to disaster. Even if they are idempotent, the spurious database updates can lead to performance bottlenecks, especially when the database systems are processing heavy loads; this can become a vicious circle.
Testing of applications is often done on a testing environment, smaller in size (perhaps only a single server) and less loaded than the "live" environment. The replication behaviour of such an installation may differ from a live environment in ways that mean that replication lag is unlikely to be observed in testing, masking replication-sensitive bugs. Application developers must be very careful about the assumptions they make about the effect of a database update, and must be sure to simulate lag in their testing environments.
Optimistically replicated databases have to be very careful about offering features such as validity constraints on data. If any given update may or may not be accepted based on the current state of the record, then two updates (A and B) may be individually legal against the starting state of the system, but one or more of the updates may not be legal against the state of the system after the other update (e.g., A and B are both legal, but AB or BA are illegal). If A and B are both initiated at roughly the same time within the database, then A may be successfully applied on some nodes and B on others, but as soon as A and B "meet" and one is attempted on a node which has already applied the other, a conflict will be found. The system must, in this case, decide which update finally "wins", and arrange for any nodes that have already applied the losing update to revert it. However, some nodes may temporarily expose the state with the reverted update, and there may be no way to inform the user who initiated the update of its failure, without requiring them to wait (potentially forever) for confirmation of acceptance at every node.


Room synchronization

The room synchronization technique is a form of concurrency control in computer science.
The room synchronization problem involves supporting a set of "m" mutually exclusive "rooms" where any number of users can execute code simultaneously in a shared room (any one of them), but no two users can simultaneously execute code in separate rooms.
Room synchronization can be used to implement asynchronous parallel queues and stacks with constant time access (assuming a fetch-and-add operation).


2382 Nonie


William C. Hetzel

Dr. William C. Hetzel is an expert in the field of software testing. He compiled the papers from the 1972 Computer Program Test Methods Symposium, also known as the Chapel Hill Symposium, into the book "Program Test Methods." The book, published in 1973, details the problems of software validation and testing.
The International Conference and Exposition on Testing Computer Software, which is the first conference with a focus on software testing, is convened in 1984 by the US Professional Development Institute (USPDI) in Washington, D.C. Hetzel and Dr. David Gelperin are the joint program chairs.
Hetzel and Dave Gelperin co-found the Software Quality Engineering consultancy firm in 1986. Their motto was, "Test, then code." Together they worked to establish software testing as a stand-alone computer discipline. In 1988 they classified the phases and goals of software testing into the following stages:
In 1988 Gelperin and Heztel write the article The Growth of Software Testing. In it they discuss four major models for software testing. The first two are Phase Models, and the second two are Life Cycle Models.
Hetzel's book "The Complete Guide to Software Testing" which provides methodologies, testing techniques, and the principles of software testing, is released in 1988. The book is released in a 2nd edition later the same year, and several other printings are made through 1994.
In 1992 Gelperin and Hetzel firm organized the first "Software Testing, Analysis & Review," the "STAR" conference, in Las Vegas, Nevada and in 1993 introduced a European equivalent, the EuroSTAR Conference. The US-based conferences are now produced by TechWell Corporation which is the new name for their Software Quality Engineering company.
Gelperin and Hetzel developed the STEP methodology for implementing the original IEEE-829-1998 Standard for Software and System Test Documentation. Their firm was instrumental in gaining recognition for testing as a separate discipline within the software industry.


2446 Lunacharsky


Surendranath Evening College

Surendranath Evening College, established in 1961, is an undergraduate college in Sealdah, Kolkata, West Bengal, India. It is affiliated with the University of Calcutta.
Accreditation.
Surendranath Evening College is recognized by the University Grants Commission (UGC).


WiTrack

A WiTrack is a 3-D motion tracking sensor that is capable of monitoring human body movements. This sensor is able to serve three main purposes, such functions being the following: turning on/off home appliances, tracking a lethal fall, and improving gaming experience. This new piece of technology, currently in its developing stages, was developed primarily by Fadel Adib and Dina Katabi at MIT. The WiTrack functions through the use of radio signals, which help perform the task of finding a person's current location, the radio signals not been affected at all by walls and other physical obstacles present.
Technology.
WiTrack functions through the use of radio signals that reflect off a person, this does not require a user to hold on to a wireless device like other previous similar inventions. WiTrack uses a total of four antennas, one antenna is used for transmitting signals and three antennas are used for receiving the signals. Through the use of these antennas, a geometric model is created which is able to calculate the distance between the antennas receiving the signals and the user where the signals derive from.
Time-of-flight estimation.
The time it takes for the signal to travel from the transmitter to the person's body, and back again to the transmitter.
3-D localization.
Through the use of the antennas, a geometric model is created which is able to calculate the distance between the antennas and the person's body.
Fall detection and pointing.
WiTrack classifies a fall as a rapid change on the elevation of a person. WiTrack can track the motion of a person's arm and detect on what direction the arm is pointing at.
Future goals.
The WiTrack was well received, this led to the creation of Emerald. Emerald was an extension to the WiTrack's ability to track falls among the elderly. Just like WiTrack, Emerald tracks the motion of a person through the use of radio signals reflected off the person's body. Once a fall is detected it alerts the person taking care of the elder, or 911. Emerald was presented to President Barack Obama at the White House on August 4, 2015 and was seen as a huge innovation towards tracking falls among the elderly.
Applications.
Controlling home appliances.
A simple gesture, raising your arm and pointing at an appliance, is all it would take in order to transmit a signal. This simple gesture is detected by the use of radio signals, which are then able to turn on/off appliances. This action of turning on and off home appliances doesn't only have to be done in one room, a person is able to control a household appliance even through walls. WiTrack is still able to detect a person's arm gesture even through physical objects.
Identifying dangerous falls among the elderly.
WiTrack's ability to track motion with such ease and simplicity will make it useful in tracking elderly patients at high risk of falling. WiTrack is able to differentiate a fall from sitting down or standing, it's able to recognize a fall as a fast change in the distance between the person and the ground. WiTrack is able to detect a lethal fall with a high accuracy percentage of 96.9%, making it easy and reliable to use.
Gaming.
Gamers are able to roam around the comfort of their home, being able to truly interact with the game. WiTracker gives players the ability to run down real hallways, hide behind furniture, and go into different rooms of their home, all while the game is still going.
Similar inventions.
WiTrack is one of many attempts at 3-D motion tracking technology. This kind of technology has been attempted on both the gaming field and on the field dealing with the tracking of lethal falls among the elderly. Worldwide known gaming consoles, such as the Wii and Xbox Kinect, have long been praised for interacting with their players, involving them in physical activity. These gaming consoles require users to stand at a certain distance and can't stand behind furniture nor behind walls. Current attempts at trying to detect falls amongst the elderly require users to continuously wear sensors or place cameras around their home. These other medical alarms can detect the fall of a person through the use of 3-D motion sensors, similar to the WiTrack.
Issues and improvements.
A challenge would derive from multipath effects, which create errors in mapping the delay of a reflection to the distance from the target. Sometimes the transmitted signal is reflected from walls and any home appliances. A major issue that is currently being fixed is the measuring time of flight is difficult since RF signals travel very fast. The MIT team is currently trying to fix this issue by using a technique named FMCW, which stands for frequency modulated carrier wave.
Another obstacle that stands on the way is the fact that WiTrack is only able to identify one person at a time, but this is being resolved at the time by the MIT team.


Bit slip

In digital transmission, bit slip is the loss or gain of a bit or bits, caused by clock drift – variations in the respective clock rates of the transmitting and receiving devices.
One cause of bit slippage is overflow of a receive buffer that occurs when the transmitter's clock rate exceeds that of the receiver. This causes one or more bits to be dropped for lack of storage capacity.
One way to maintain timing between transmitting and receiving devices is to employ an asynchronous protocol such as start-stop. Alternatively, bit slip can be prevented by using a self-clocking signal (such as a signal modulated using OQPSK) or using a line coding such as Manchester encoding.
Another cause is "losing count", as on a hard drive: if a hard drive encounters a long string of 0s, without any 1s (or a string of 1s without 0s), it may lose track of the frame between fields, and suffer bit slip.
When a pulse of N consecutive zero bits are sent, clock drift may cause the hardware to apparently detect N-1 zero bits or N+1 zero bits—both kinds of errors are called bit slip.
Thus one prevents long strings without change via such devices as run length limited codes.
Many communication systems use linear-feedback shift register scrambling to prevent long strings of 0s (or other symbol),
including VSAT, 1000BASE-T, , etc.
While a scrambler makes the "losing count" type of bit slip error occur far less often,
when bit slip errors do occur (perhaps for other reasons),
scramblers have the property of expanding small errors that add or lose a single bit into a much longer burst of errors.
The optimized cipher feedback mode (OCFB), the statistical self-synchronization mode, and the "one-bit CFB mode" also expand small bit-slip errors into a longer burst of errors, but eventually recover and produce the correct decrypted plaintext.
A bit-slip error when using any other block cipher mode of operation generally results in complete corruption of the rest of the message.


3566 Levitan


Sentence completion tests

Sentence completion tests are a class of semi-structured projective techniques. Sentence completion tests typically provide respondents with beginnings of sentences, referred to as "stems", and respondents then complete the sentences in ways that are meaningful to them. The responses are believed to provide indications of attitudes, beliefs, motivations, or other mental states. Therefore, sentence completion technique, with such advantage, promotes the respondents to disclose their concealed feelings. Notwithstanding, there is debate over whether or not sentence completion tests elicit responses from conscious thought rather than unconscious states. This debate would affect whether sentence completion tests can be strictly categorized as projective tests.
A sentence completion test form may be relatively short, such as those used to assess responses to advertisements, or much longer, such as those used to assess personality. A long sentence completion test is the Forer Sentence Completion Test, which has 100 stems. The tests are usually administered in booklet form where respondents complete the stems by writing words on paper.
The structures of sentence completion tests vary according to the length and relative generality and wording of the sentence stems. Structured tests have longer stems that lead respondents to more specific types of responses; less structured tests provide shorter stems, which produce a wider variety of responses.
History.
Hermann Ebbinghaus is generally credited with developing the first sentence completion test in 1897. Ebbinghaus's sentence completion test was used as part of an intelligence test. Simultaneously, Carl Jung's word association test may also have been a precursor to modern sentence completion tests. Moreover, in recent decades, sentence completion tests have increased in usage, in part because they are easy to develop and easy to administer. As of the 1980s, sentence completion tests were the eighty-fifth most widely used personality assessment instruments. Another reason for the increased usage of sentence completion tests is because of their superiority to other measures in uncovering conflicted attitudes. Some sentence completion tests were developed as a way to overcome the problems associated with thematic apperception measures of the same constructs.
Uses.
The uses of sentence completion tests include personality analysis, clinical applications, attitude assessment, achievement motivation, and measurement of other constructs. They are used in several disciplines, including psychology, management, education, and marketing.
Sentence completion measures have also been incorporated into non-projective applications, such as intelligence tests, language comprehension, and language and cognitive development tests.
Examples.
There are many sentence completion tests available for use by researchers. Some of the most widely used sentence completion tests include:
Data analysis, validity and reliability.
The data collected from sentence completion tests can usually be analyzed either quantitatively or qualitatively. Usually, sentence completion tests can be interpreted in two different ways: subjective-intuitive analysis of the underlying motivations projected in the subject's responses, or objective analysis by means of scores assigned to each completed sentence. Multiple themes can occur in a short test, which gives the examinee multiple opportunities to reveal underlying motivations about each topic during data analysis. Of course, most sentence completion tests are much longer (anywhere from 40 to 100 stems) and contain more themes (anywhere from 4 to 15 topics).
Sentence completion tests usually include some formal coding procedure or manual. The validity of each sentence completion test must be determined independently and this depends on the instructions laid out in the scoring booklet.
Compared to positivist instruments, such as Likert-type scales, sentence completion tests tend to have high face validity (i.e., the extent to which measurement items accurately reflect the concept being measured). This is to be expected, because in many cases the sentence stems name or refer to specific objects and the respondent provides responses specifically focused on such objects.


Benchmark (computing)

In computing, a benchmark is the act of running a computer program, a set of programs, or other operations, in order to assess the relative performance of an object, normally by running a number of standard tests and trials against it.
The term "benchmark" is also commonly utilized for the purposes of elaborately designed benchmarking programs themselves.
Benchmarking is usually associated with assessing performance characteristics of computer hardware, for example, the floating point operation performance of a CPU, but there are circumstances when the technique is also applicable to software. Software benchmarks are, for example, run against compilers or database management systems (DBMS).
Benchmarks provide a method of comparing the performance of various subsystems across different chip/system architectures.
Test suites are a type of system intended to assess the correctness of software.
Purpose.
As computer architecture advanced, it became more difficult to compare the performance of various computer systems simply by looking at their specifications. Therefore, tests were developed that allowed comparison of different architectures. For example, Pentium 4 processors generally operated at a higher clock frequency than Athlon XP or PowerPC processors, which did not necessarily translate to more computational power; a processor with a slower clock frequency might perform as well as or even better than a processor operating at a higher frequency. See BogoMips and the megahertz myth.
Benchmarks are designed to mimic a particular type of workload on a component or system. Synthetic benchmarks do this by specially created programs that impose the workload on the component. Application benchmarks run real-world programs on the system. While application benchmarks usually give a much better measure of real-world performance on a given system, synthetic benchmarks are useful for testing individual components, like a hard disk or networking device.
Benchmarks are particularly important in CPU design, giving processor architects the ability to measure and make tradeoffs in microarchitectural decisions. For example, if a benchmark extracts the key algorithms of an application, it will contain the performance-sensitive aspects of that application. Running this much smaller snippet on a cycle-accurate simulator can give clues on how to improve performance.
Prior to 2000, computer and microprocessor architects used SPEC to do this, although SPEC's Unix-based benchmarks were quite lengthy and thus unwieldy to use intact.
Computer manufacturers are known to configure their systems to give unrealistically high performance on benchmark tests that are not replicated in real usage. For instance, during the 1980s some compilers could detect a specific mathematical operation used in a well-known floating-point benchmark and replace the operation with a faster mathematically equivalent operation. However, such a transformation was rarely useful outside the benchmark until the mid-1990s, when RISC and VLIW architectures emphasized the importance of compiler technology as it related to performance. Benchmarks are now regularly used by compiler companies to improve not only their own benchmark scores, but real application performance.
CPUs that have many execution units — such as a superscalar CPU, a VLIW CPU, or a reconfigurable computing CPU — typically have slower clock rates than a sequential CPU with one or two execution units when built from transistors that are just as fast. Nevertheless, CPUs with many execution units often complete real-world and benchmark tasks in less time than the supposedly faster high-clock-rate CPU.
Given the large number of benchmarks available, a manufacturer can usually find at least one benchmark that shows its system will outperform another system; the other systems can be shown to excel with a different benchmark.
Manufacturers commonly report only those benchmarks (or aspects of benchmarks) that show their products in the best light. They also have been known to mis-represent the significance of benchmarks, again to show their products in the best possible light. Taken together, these practices are called "bench-marketing."
Ideally benchmarks should only substitute for real applications if the application is unavailable, or too difficult or costly to port to a specific processor or computer system. If performance is critical, the only benchmark that matters is the target environment's application suite.
Challenges.
Benchmarking is not easy and often involves several iterative rounds in order to arrive at predictable, useful conclusions. Interpretation of benchmarking data is also extraordinarily difficult. Here is a partial list of common challenges:
Benchmarking Principles.
There are seven vital characteristics for benchmarks. These key properties are: