text:
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arXiv:0909.1946v1 [cond-mat.soft] 10 Sep 2009
Slip effects in polymer thin films
O B¨ aumchen and K Jacobs
Experimental Physics, Saarland University, Campus, D-66123 Saarbr¨ ucken, Germany
E-mail: firstname.lastname@example.com
solid/liquid boundary condition. There is no need for external stimulation or pumping
of the liquid due to the fact that the dewetting process, an internal mechanism, acts
as a driving force for liquid flow. Viscous dissipation within the liquid and slippage
balance interfacial forces. Thereby, friction at the solid/liquid interface plays a key role
towards the flow dynamics of the liquid. Probing the temporal and spatial evolution
of growing holes or retracting straight fronts gives, in combination with theoretical
models, information of the liquid flow field and especially the boundary condition at the
interface. We review the basic models and experimental results obtained during the last
years with exclusive regard to polymers as ideal model liquids for fluid flow. Moreover,
concepts that aim on explaining slippage on the molecular scale are summarized and
Probing the fluid dynamics of thin films is an excellent tool to study the
PACS numbers: 68.15.+e, 83.50.Lh, 83.80.Sg, 47.15.gm
Submitted to: J. Phys.: Condens. Matter
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Slip effects in polymer thin films2
1. Introduction
Understanding liquid flow in confined geometries plays a huge role in the field of micro-
and nanofluidics [1]. Nowadays, microfluidic or so-called lab-on-chip devices are utilized
in a wide range of applications. Pure chemical reactions as well as biological analysis
performed on such a microfluidic chip allow a high performance while solely small
amounts of chemicals are needed. Thereby, analogies to electronic large-scale integrated
circuits are evident. Thorsen et al fabricated a microfluidic chip with a high density of
micromechanical valves and hundreds of individually addressable chambers [2]. Recent
developments tend to avoid huge external features such as pumps to control the flow by
designing analogues to capacitors, resistors or diodes that are capable to control currents
in electronic circuits [3].
By reducing the spacial dimensions of liquid volume in confined geometries, slippage
can have a huge impact on flow dynamics. Especially the problem of driving small
amounts of liquid volume through narrow channels has drawn the attention of many
researchers on slip effects at the solid/liquid interface. The aim is to reduce the pressure
that is needed to induce and to maintain the flow. Hence, the liquid throughput is
increased and, what is important in case of polydisperse liquids or mixtures, a low
dispersity according to lower velocity gradients perpendicular to the flow direction is
generated. Confined geometries are realized in various types of experiments: The physics
and chemistry of the imbibition of liquids by porous media is of fundamental interest
and enormous technological relevance [4]. Channel-like three-dimensional structures
can be used to artificially model the situation of fluids in confinement. Moreover, the
small gap between a colloidal probe and a surface filled with a liquid (e.g realized in
surface force apparatus or colloidal probe atomic force microscopy experiments) is a
common tool to study liquid flow properties. Besides the aforementioned experimental
systems, knowledge in preparation of thin polymer films has been extensively gained due
to its enormous relevance in coating and semiconductor processing technology. Such a
homogeneous nanometric polymer film supported by a very smooth substrate, as for
example a piece of a silicon (Si) wafer, exhibits two relevant interfaces, the liquid/air
and the substrate/liquid interface. Si wafers are often used according to their very low
roughness and controllable oxide layer thickness. Yet, also highly viscous and elastically
deformable supports, such as e.g. polydimethylsiloxane (PDMS) layers, are versatile
The stability of a thin film is governed by the effective interface potential φ as
function of film thickness h. In case of dielectric systems, φ(h) is composed of an
attractive van-der-Waals part and a repulsive part [5, 6, 7, 8]. For the description of
van-der-Waals forces of a composite substrate, the layer thicknesses and their respective
polarisation properties have to be taken into account [9]. Thereby, three major situations
of a thin liquid film have to be distinguished: stable, unstable and metastable films. As
illustrated in Fig. 1 by the typical curves of φ(h), a stable liquid film is obtained if
the effective interface potential is positive and monotonically decaying (cf. curve (1) in
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Slip effects in polymer thin films3
Figure 1. Different shapes of the effective interface potential φ(h) associated with
different wetting conditions. Curve (1) characterizes a stable liquid film. Curve (2)
represents a metastable, curve (3) and (4) an unstable situation.
Fig. 1). The equilibrium film thickness heqis infinite and the liquid perfectly wets the
substrate. In case of a global minimum of φ(h), curves (2) and (3) in Fig. 1, the system
can minimize its energy and a finite value for heqresults. The metastable situation is
furthermore characterized by a potential barrier that the system has to overcome to
reduce its potential energy (cf. curve (2) in Fig. 1). Curve (3) and (4) characterize
unstable conditions, since every slight fluctuation in film height will drive the system
towards the global minimum. The wettability of the substrate by the liquid is correlated
to the depth of the minimum at φ(heq). The deeper the global minimum of φ, the larger
is the equilibrium contact angle of the liquid on the surface. A nearly 180◦situation is
depicted in curve (4) of Fig. 1.
For a 100nm polystyrene (PS) film on a hydrophobized Si wafer with a native oxide
layer, dewetting starts after heating the sample above the glass transition temperature
of the polymer. Holes nucleate according to thermal activation or nucleation spots (dust
particles, inhomogeneities of the substrate or of the polymer film) and grow with time,
cf. Fig. 2. The subsequent stages of dewetting are characterized by the formation
of liquid ridges by coalescence of growing holes and traveling fronts. Very thin films
in the range of several nanometers may become unstable and can dewet according to
thermally induced capillary modes, that are amplified by forces contributing to the
effective interface potential. This phenomenon is characterized by the occurrence of
a preferred wavelength and is called spinodal dewetting. To study thin film flow with
regard to the influence of slippage, especially nucleated holes enable an easy experimental
access for temporal and spatial observation.
While fronts retract from the substrate and holes grow, a liquid rim is formed at the
three-phase contact line due to conservation of liquid volume. A common phenomenon
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Slip effects in polymer thin films4
Figure 2.
hydrophobized Si substrate captured by optical microscopy (adapted from [10]).
Dewetting of a 80nm PS(65kg/mol) film at T = 135◦C from a
is the formation of liquid bulges and so-called "fingers" due to the fact that the liquid
rim becomes unstable, similar to the instability of a cylindrical liquid jet that beads up
into droplets (e.g. in case of a water tap). This so-called Rayleigh-Plateau instability
is based on the fact that certain modes of fluctuations become amplified and surface
corrugations of a characteristic wavelength become visible. If two holes coalesce, a
common ridge builds up that in the end decays into single droplets due to the same
mechanism. The final stage is given by an equilibrium configuration of liquid droplets
arranged on the substrate exhibiting a static contact angle. Actually, the final state
would be one single droplet, since the Laplace pressure in droplets of different size is
varying. Yet then, a substantial material transport must take place, either over the gas
phase or via an equilibrium film between the droplets. This phenomenon is also called
Ostwald ripening. In polymeric liquids, these transport pathways are usually extremely
slow so that a network-like pattern of liquid droplets is already termed "final stage".
Besides the dynamics and stability of thin liquid films driven by intermolecular forces,
a recent article by Craster and Matar reviews further aspects such as e.g thermally or
surfactant driven flows [11].
In the first part of this topical review, basic concepts from hydrodynamic theories in
the bulk situation to corresponding models with regard to confinement are introduced.
Polymers are regarded as ideal model liquids due to their low vapor pressure, the
available chemical pureness and furthermore the fact that their viscosity can be
controlled in a very reliable manner. By setting the viscosity via temperature, the
experimental conditions can be tuned so that dewetting dynamics can be easily captured.
Mass conservation can safely be assumed, which consequently simplifies the theoretical
description. The dewetting dynamics governed by the driving forces and the mechanisms
of energy dissipation will be discussed also with regard to the shape of liquid ridges. The
second part summarizes experimental studies concerning the dynamics of two different
dewetting geometries: the straight front geometry and the growth of holes. Especially
the influence of parameters such as dewetting temperature, viscosity and molecular
weight of the polymer will be discussed in detail. Moreover, we focus on various scenarios
at the solid/liquid interface on the molecular level. Simulations such as for example
molecular-dynamic (MD) studies help to obtain more information and are supportive
to gain insight into the molecular mechanism of slippage.
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2. Basic theoretical concepts
In this section we aim to describe the main concepts of fluid dynamics especially in
a confined geometry. Depending on the type of liquid, viscous or even viscoelastic
effects have to be considered and deviations from Newtonian behavior might become
non-negligible. Since we concentrate in this article on polymer melts, viscosity and
viscoelasticity can be varied by chain length and branching of the polymer.
important aspect of a moving liquid is the velocity profile.
2.1. Polymer properties
For a comprehensive understanding of slippage, some important polymer properties
like glass transition temperature, viscosity and viscoelasticity have to be taken into
account. Especially in geometries like in a liquid film, confinement effects are a concern.
A detailed description can be found in textbooks [12, 13].
2.1.1. Polymer physics Polymers are synthesized by polymerization of monomers of
molar mass Mmono. To characterize the polydispersity of polymer chains in a solution
or in a melt, the polydispersity index Mw/Mnis calculated as the ratio of mean values
given by the weight Mw and number averaged Mn molecular weight. Polymers are
able to change their conformations. The radius of gyration characterizes the spatial
dimension of the polymer and is given as the mean square displacement between
monomers and the polymer's center of mass. In an isotropic configuration, the shape of
the polymer chain can be approximated as a spherical entity. Polystyrene, abbreviated
PS, which is commonly used as a melt in dewetting experiments, is a linear homopolymer
with Mmono = 104g/mol. Besides other properties concerning the micro-structure of
polymer chains such as the tacticity and the architecture (linear, branched, ring-shaped),
physical properties are of special interest. If a melt is heated above its glass transition
temperature Tg, a phase transition from the glassy phase to the liquid phase occurs
and the polymer becomes liquid. Randomly structured macromolecules such as atactic
polymers avoid the formation of semi-crystalline domains below Tgand exhibit a pure
amorphous phase. The glass transition of a bulk polymer or of a polymeric thin film
can be observed e.g. via probing its linear expansion coefficient. Although, the glass
transition is based on a kinematic effect and does not occur due to a rearrangement
process of polymer chains. Therefore, the glass transition usually takes place on a
specific temperature range and not at a exactly allocable temperature. According to
the increased mobility of shorter chains, their glass transition temperature is decreased
significantly. For PS with a sufficiently large chain-length, Tg=100◦C.
The viscosity η of a polymer melt measures the inner friction of polymer chains
and governs the time scale of flow processes. Due to the fact that the mobility of chains
increases while the temperature increases, the viscosity decreases. Internal stresses relax
and dynamical processes proceed faster. The most common description of the functional
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dependency of the viscosity η of a polymer on temperature T was developed by Williams,
Landel and Ferry:
η = ηgexpB(Tg− T)
fg(T − T∞).(2.1)
In this so-called WLF-equation, ηgdenotes the viscosity at Tg, B an empirically obtained
constant, T∞the so-called Vogel temperature and fgthe free liquid volume fraction.
Besides the above discussed impact of temperature on the viscosity of a polymer
melt, also the molecular weight Mw strongly influences η. While Mw increases, the
chain mobility decreases and therefore the relaxation times and thus η increase. For
sufficiently small Mw, the Rouse model predicts a linear increase of η for increasing Mw.
At this point, another characteristic number of polymer physics has to be introduced:
the critical chain length for entanglements Mc. Above Mc, the polymer chains form chain
entanglements exhibiting a specific mean strand length called entanglement length Me.
For PS, Mc=35kg/mol and Me=17kg/mol is found [12]. According to the reptation
model of de Gennes [14], the viscosity increases stronger in the presence of chain
entanglements and an algebraic behavior of η ∝ M3
regime below Mcis well reproduced, above Mcan exponent of 3.4 is found experimentally
for different polymers. For a detailed description of chemical and physical properties of
polymers as well as for the Rouse or the reptation theory we refer to the book Polymer
physics by Rubinstein and Colby [12].
wis expected. Empirically, the linear
volume properties of the polymers are measured, liquids in confined geometries such as
a thin film often show deviations from the behavior in the volume due to additional
interface effects.One of these properties is the aforementioned glass transition
temperature. It has been shown in numerous studies, that Tgchanges with film thickness
h.On the one hand, in case of free-standing or supported films exhibiting no or
repulsive interactions with the substrate, Tg(h) decreases with decreasing film thickness
[15, 16, 17, 18]. On the other hand, Keddie and Jones have shown that an increase of
the glass transition temperature with decreasing film thickness is possible for attractive
interactions between substrate and polymer film [19]. The influence of the interfacial
energy on the deviation of Tgfrom its bulk value has been studied and quantified by
Fryer and co-workers for different polymers [20]. In case of PS on a solid support, a
significant change of Tg is found for films thinner than 100nm (see Fig. 3) [21]. For
PS(2k) below 10nm for instance, the glass transition temperature and the viscosity of
the polymer film are affected such that these films are liquid at room temperature and
may dewet spinodally.
Several attempts have been made to explain the change of Tg according to the
film thickness. Besides interface-related effects such as reorientation of polymer chains
or accumulation of chain-ends at the interface, finite-size effects have been proposed
to be responsible. Herminghaus et al discussed the strain relaxation behavior of thin
Properties in confined geometries In contrast to the bulk situation, where
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Figure 3. Glass transition temperature Tg of polystyrene films of 2kg/mol against
film thickness (adapted from [21]).
viscoelastic polymer films with regard to surface melting and the shift of the glass
transition temperature [21].Kawana and Jones studied the thermal expansivity of
thin supported polymer films using ellipsometry and attributed their results concerning
Tg to a liquid-like surface layer [22], a result that was also found by other authors
[23, 24]. Besides confinement effects on Tg, further interface-related phenomena have
been studied: Si et al have shown that polymers in thin films are less entangled than
bulk polymers and that the effective entanglement molecular weight Meis significantly
larger than the bulk value [25].
general or a polymer in particular is its viscosity η. Applying shear stress σ to a liquid,
it usually reacts with a strain γ. If stress and strain rate ˙ γ are proportional, the fluid is
called Newtonian. The constant of proportionality is identified as the viscosity η of the
Viscosity and viscoelasticity One of the major characteristics of a liquid in
σ = η˙ γ.(2.2)
Liquids such as long-chained polymers show a shear rate dependent viscosity η(˙ γ)
due to the fact that the liquid molecules are entangled. If the viscosity increases while
shearing the liquid, we call this behavior shear thickening, whereas in case of lowered
viscosity so-called shear thinning is responsible. In contrast to the elastic deformation
of a solid, a deformation of a viscoelastic liquid might induce an additional flow and can
relax on a specific time scale τ. On short time scales (t < τ), the liquid behaves in an
elastic, on long time scales (t > τ) in a viscous manner. Thereby, strain γ is connected
to stress σ via the elastic modulus G of the liquid:
σ = Gγ.(2.3)
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Figure 4. Maxwell model represented by a dashpot and a spring in a serial connection.
To cover the stress relaxation dynamics of a polymer film, several modelling
attempts have been proposed. Mostly, so-called Maxwell or Jeffreys models are applied.
The simplest model is the Maxwell model (see Fig. 4), which assumes a serial connection
of a perfectly elastic element (represented by a spring) and a perfectly viscous one
(represented by a dashpot). Consequently, the total shear strain γ is given by the sum
of the corresponding shear strains γeand γvof both mechanisms:
γ = γe+ γv.(2.4)
With (2.3) and (2.2) we get
σ = GMγe= ηM˙ γv
since both react on the same shear stress σ. Thereby, the ratio of viscosity of the viscous
element to the elastic modulus of the elastic one can be identified with a specific time
scale, the relaxation time τM:
The relaxation of stress after a step strain γ leads to a time-dependent stress function
σ(t) for a viscoelastic liquid. Due to the fact that the total strain γ is constant, a first
order differential equation for the time-dependent strain γv(t) is obtained:
τM˙ γv= γ − γv(t).(2.7)
Solving this differential equation using the initial condition γv(t = 0) = 0 gives a simple
exponential decay of σ(t) on the time scale of the stress relaxation time τM in the
Maxwell model:
γe(t) = γ exp(−t/τM),σ(t) = GMγe(t) = GMγ exp(−t/τM).(2.8)
A situation of special interest is the linear response region: For sufficiently small values
of γ, the stress/strain-relation (2.3) is valid and the stress relaxation modulus G(t) is
independent of the strain γ. In this regime, a linear superposition of stresses resulting
from an infinite number of strain steps can be used to model a steady simple shear flow
of a viscoelastic liquid. For larger applied shear rates, linear response and the linear
superposition fails. The viscosity is still defined as the ratio of stress and strain rate,
but it has to be regarded as an apparent viscosity which differs from the above described
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Slip effects in polymer thin films9
"zero shear rate" viscosity. Polymers with shear-thinning or shear-thickening properties
can be described by the function
σ ∝ ˙ γn,(2.9)
where the exponent n can be extracted from experimental data. These type of fluids are
also called "power law fluids". Moreover, also other nontrivial stress-strain relations can
be considered or alternatively non-linear extensions can be applied to the linear Maxwell
models. In case of the linear Jeffreys model, the stress tensor σijrelaxes according to
the following constitutive relaxation equation:
(1 + λ1∂t)σ = η(1 + λ2∂t)˙ γ,(2.10)
where the strain rate is given by the gradient of the velocity field ˙ γij = ∂jui+ ∂iuj.
Hereby, λ1 governs the relaxation of stress, whereas λ2 (λ2 < λ1) describes the
relaxation of the strain rate, respectively. This model accounts for the viscous and
the elastic properties of a fluid and was used by Blossey, Rauscher, Wagner and M¨ unch
as basis for the development of a thin-film equation that incorporates viscoelastic effects
[26, 27, 28]. For a more elaborate description of non-Newtonian flows we refer e.g. to
the correspondent work of Te Nijenhuis et al [29].
2.1.4. Reynolds and Weissenberg number
specific numbers. One of these numbers is the so-called Reynolds number Re, which
describes the ratio of inertia effects to viscous flow contributions. In case of thin liquid
films, Re can be written as
The flow of a liquid can be characterized by
Re =ρuh
where ρ denotes the density of the liquid, u describes the flow velocity and h stands
for the film thickness [30]. For thin dewetting polymer films, the Reynolds number is
very small, i.e. Re ≪ 1, and a low-Re lubrication theory can be applied. To quantify
and to judge the occurrence of viscoelastic effects versus pure viscous flow, the so-called
Weissenberg number Wi has been introduced as
Wi = τ ˙ γ.(2.12)
Thereby, τ denotes the relaxation time and ˙ γ the strain rate as introduced in the previous
section. If Wi ≪ 1, an impact of viscoelasticity on flow dynamics can be neglected and
viscous flow dominates.
2.2. Navier-Stokes equations
The Navier-Stokes equations for a Newtonian liquid mark the starting point for the
discussion of fluid dynamics in confined geometries. According to conservation of mass,
the equation of continuity can be formulated as
∂tρ + ∇ · (ρu) = 0,(2.13)
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where u = (ux,uy,uz) is the velocity field of the fluid. For an incompressible liquid,
which implies a temporally and spatially constant liquid density ρ, (2.13) can be
simplified to
∇u = 0. (2.14)
With the conservation of momentum, the Navier-Stokes equations for an incompressible
liquid can be written as
ρ(∂t+ u · ∇)u = −∇p + η△u + f,
with the pressure gradient ∇p and the volume force f of external fields acting as driving
forces for the liquid flow. We already stated that for small Reynolds numbers, i.e.
Re ≪ 1, the terms on the left hand side of (2.15) can be neglected as compared to terms
describing the pressure gradient, external volume forces and viscous flow. By that, we
can simplify (2.15) to the so-called Stokes equation
0 = −∇p + η△u + f.(2.16)
In section 2.5, we will demonstrate how these basic laws of bulk fluid dynamics can be
applied to the flow geometry of a thin film supported by a solid substrate.
2.3. Free interface boundary condition
At the free interface of a supported liquid film, i.e. at the liquid/gas or usually the
liquid/air interface, no shear forces can be transferred to the gas phase due to the
negligible viscosity of the gas. In general, the stress tensor σ∗
tension σij, see (2.2), and the pressure p:
ijis given by the stress
ij= σij+ pδij= η(∂jui+ ∂iuj) + pδij.(2.17)
The tangential t and normal n (perpendicular to the interface) components of the stress
tensor are:
(σ∗· n) · t = 0(σ∗· n) · n = γlvκ, (2.18)
where κ denotes the mean curvature and γlv the interfacial tension (i.e. the surface
tension of the liquid) of the liquid/vapor interface. If the liquid is at rest, i.e. the
stationary case u = 0, the latter boundary condition gives the equation for the Laplace
pressure pL:
pL= γlvκ = γlv(1
R1 and R2 are the principal radii of curvature of the free liquid/gas boundary; the
appropriate signs of the radii are chosen according to the condition that convex
boundaries give positive signs. Such convex liquid/gas boundaries lead to an additional
pressure within the liquid due to its surface tension. In the next section, the solid/liquid
boundary condition will be discussed, which yields a treatment of slip effects.
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Figure 5. Different velocity profiles in the vicinity of the solid/liquid interface and
illustration of the slip (extrapolation) length b. The situation of so-called "apparent"
slip is illustrated on the right: According to a thin liquid layer of thickness z0
that obtains a significantly reduced viscosity, the slip velocity ux|z=0 is zero, but a
substantial slip length is measured.
2.4. Slip/no-slip boundary condition
2.4.1. Navier slip boundary condition
where the assumption that the tangential velocity u|| at the solid/liquid interface
vanishes (no-slip boundary condition), confined geometries require a more detailed
investigation as slippage becomes important. In 1823, Navier [31] introduced a linear
boundary condition: The tangential velocity u||is proportional to the normal component
of the strain rate tensor; the constant of proportionality is described as the so-called
slip length b:
In contrast to fluid dynamics in a bulk volume,
u||= bn · ˙ γ(2.20)
In case of simple shear flow in x-direction, the definition of the slip length can be
alternatively written as
b =
where ξ = σ/uxdenotes the friction coefficient at the solid/liquid interface. The xy-
plane thereby represents the substrate surface. According to these definitions, the slip
length can be illustrated as the extrapolation length of the velocity profile "inside" the
substrate, cf. Fig. 5. Moreover, both limiting cases are included within this description:
For b = 0, we obtain the no-slip situation, whereas b = ∞ characterizes a full-slip
situation. The latter case corresponds to "plug-flow", where the liquid behaves like a
solid that slips over the support.
2.4.2. How to measure the slip length?
were published using diverse methods to probe the slip length at the boundary of
different simple or complex liquids and solid supports. For details concerning these
experimental methods we refer to the review articles from Lauga et al [32], Neto et
In recent years, numerous experimental studies
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al [33] and Bocquet and Barrat [34] (and references therein). To probe the boundary
condition, scientists performed either drainage experiments or direct measurements of
the local velocity profile using e.g. tracer particles.
In case of drainage experiments, the liquid is squeezed between two objects, e.g. a
flat surface and a colloidal probe at the tip of an AFM cantilever, and the corresponding
force for dragging the probe is measured (colloidal probe AFM). Alternatively, in an
surface force apparatus (SFA), two cylinders arranged perpendicular to each other are
brought in closer contact and force/distance measurements are performed to infer the
slip length.
The use of tracer particles as a probe of the local flow profile might bring some
disadvantages.The chemistry of these particles is usually different from the liquid
molecules and their influence on the results might not be negligible. A similar method
is called fluorescence recovery after photo bleaching.
fluorescent liquid is bleached by a laser pulse and the flow of non-bleached liquid into
that part is measured. The disadvantage of this method is that diffusion might be a
further parameter that is hard to control. Recently, Joly et al showed that also thermal
motion of confined colloidal tracers in the vicinity of the solid/liquid interface can be
used as a probe of slippage without relying on external driving forces [35].
Thereby, a distinct part of a
2.4.3. Which parameters influence slippage?
field of micro- and nanofluidics are related to intrinsic parameters that govern slippage
of liquid molecules at the solid/liquid interface. For simple liquids on smooth surfaces,
the contact angle is one of the main parameters influencing slippage [36, 37, 38, 39].
This originates from the effect of molecular interactions between liquid molecules
and the solid surface: If the molecular attraction of liquid molecules and surface
decreases (and thereby the contact angle increases), slippage is enlarged.
studies aim to quantify the impact of roughness [37, 40, 41, 42] or topographic structure
[43, 44, 45, 46, 47] of the surface on slippage. For different roughness length scales,
a suppression (see e.g. [37, 40]) or an amplification (see e.g. [43]) of slippage can be
observed. Moreover, the shape of molecular liquids itself has been experimentally shown
to impact the boundary condition. Schmatko et al found significantly larger slip lengths
for elongated linear compared to branched molecules [48]. This might be associated
with molecular ordering effects [49] and the formation of layers of the fluid in case of the
capability of these liquids to align in the vicinity of the interface [50]. Cho et al identified
the dipole moment of Newtonian liquids at hydrophobic surfaces as a crucial parameter
for slip [51]. De Gennes proposed a thin gas layer at the interface of solid surface and
liquid as a possible source of large slip lengths [52]. Recently, MD studies for water on
hydrophobic surfaces by Huang et al revealed a dependence of slippage on the amount of
water depletion at the surface and a strong increase of slip with increasing contact angle
[53]. Such depletion layers for water in the vicinity of smooth hydrophobic surfaces
have also been experimentally observed using scattering techniques [54, 55, 56, 57].
Contamination by nanoscale air bubbles (so-called nanobubbles) and its influence on
Of course, many interesting aspects in the
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u (u ,u )
Figure 6. Illustration of the nomenclature of the thin film length scales (x and y are
parallel to the substrate) and the velocity contribution u||= (ux,uy).
slippage has been controversially discussed in literature (see e.g. [58, 59, 60, 61]). In
case of more complex liquids such as polymer melts further concepts come into play.
They will be illustrated in section 3.4.
2.5. Thin-film equation for Newtonian liquids
thin film, we can assume that the velocity contribution perpendicular to the substrate
is much smaller than the parallel one. Furthermore, the lateral length scale of film
thickness variations is much smaller than the film thickness itself. On the basis of these
assumptions, Oron et al [62] developed a thin-film equation from the rather complex
equations of motion, (2.13) and (2.15). In case of film thicknesses smaller than the
capillary length lc=
?γlv/ρg, (which is typically in the order of magnitude of 1mm)
0 = −∇(p + φ′(h)) + η△u
Additional external fields such as gravitation can be neglected, but a secondary
contribution φ′(h), the disjoining pressure, has been added to the capillary pressure
p. The disjoining pressure originates from molecular interactions of the fluid molecules
with the substrate. The effective interface potential φ(h) summarizes the inter-molecular
interactions and describes the energy that is required to bring two interfaces from infinity
to the finite distance h. As already discussed in the introductory part, the stability of a
thin liquid film is also governed by φ(h). For a further description of thin film stability,
we refer to [8] and the references therein.
The derivation of a thin-film equation for Newtonian liquids starts with the
kinematic condition
Derivation Confining the flow of a liquid to the geometry to the one of a
(2.16) can be written as
∂th = −∇||
i.e. the coupling of the time derivative of h(x,y,t) to the flow field, where the index
|| in general denotes the components parallel to the substrate (∇|| = (∂x,∂y) and
u||= (ux,uy)) as illustrated in Fig. 6.
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For thin liquid films, film thickness variations on lateral scale L are much larger
than the length scale of the film thickness H. Introducing the parameter ǫ = H/L ≪ 1
yields the so-called lubrication approximation and is used in the following to re-scale
the variables to dimensionless values. In a first approximation, linearized equations are
obtained while neglecting all terms of the order O(ǫ2). For reasons of simplicity and due
to translational invariance in the surface plane, a one-dimensional geometry is used:
∂x(p + φ′) = ∂2
zux,∂z(p + φ′) = 0,∂xux+ ∂zuz= 0.(2.24)
While the substrate is supposed to be impenetrable for the liquid, i.e. uz= 0 for z = 0,
friction at the interface implies a velocity gradient ∂zux= ux/b for z = 0. Moreover,
the tangential and normal boundary condition at the free interface, i.e. z = h(x), can
be simplified in the following manner:
∂zux= 0,p + ∂2
xh = 0. (2.25)
From (2.24) and the boundary conditions, the velocity profile ux(z) can be obtained.
Using the kinematic condition (2.23), the equation of motion for thin films in three
dimensions is derived:
∂th = −∇[m(h)∇(γlv△h − φ′(h))],
where m(h) denotes the mobility given by
3η(h3+ 3bh2).
m(h) =
2.5.2. Lubrication models including slippage
derivation of the thin-film equation is based on the so-called lubrication approximation
and the re-scaling of relevant values in ǫ. As a consequence, the slip length b is supposed
to obtain values smaller than the film thickness h, i.e. b ≪ h. To extend this so-called
weak-slip situation with regard to larger slip b ≫ h, M¨ unch et al [30] and Kargupta et
al [63] developed independently so-called strong-slip models. Thereby, the slip length is
defined as b = β/ǫ2. The corresponding equation of motion together with the kinematic
condition in one dimension for a Newtonian thin liquid film read as:
u =2b
∂th = −∂x(hu).
In fact, a family of lubrications models, cf. Tab. 1, accounting for different slip
situations have been derived. In the limit b → 0, i.e. the no-slip situation, the mobility
is given by m(h) = h3/3η. If the slip length is in the range of the film thickness b ∼ h,
the mobility in the corresponding intermediate-slip model is m(h) = bh2/η. Recently,
Fetzer et al [64] derived a more generalized model based on the full Stokes equations,
developed up to third order of a Taylor expansion. The authors were able to show that
this model is in good agreement with numerical simulations of the full hydrodynamic
equations and is not restricted to a certain slip regime as the aforementioned lubrication
As discussed in the previous section, the
η∂x(2ηh∂xu) +bh
xh − φ′(h))
Page 15
Slip effects in polymer thin films15
Table 1.
Summary of lubrication models for Newtonian flow and different slip
modelvalidity equationlimiting casesref.
weak-slipb ≪ h(2.26), (2.27)
b → 0 (no-slip)
b → ∞ (intermediate-slip)
β → 0 (intermediate-slip)
β → ∞ ("free"-slip)
strong-slipb ≫ h(2.28)[63, 30]
2.5.3. Lubrication models including viscoelasticity
a thin film equation for the weak-slip case including linear viscoelastic effects of Jeffreys
type (such as described by equation (2.10) in section 2.1.3) has been achieved (see [26]).
To cover relaxation dynamics of the stress tensor σ, an additional term ∇ · σ on the
right hand side of (2.22) has to be included to the aforementioned model for Newtonian
liquids. Furthermore, the treatment of linear viscoelastic effects was also achieved for
the strong-slip situation by Blossey et al [27]. To summarize these extensions, the
essential result is the fact that linear viscoelastic effects are absent in the weak-slip case
and the Newtonian thin-film model is still valid. The strong-slip situation, however,
is more complicated. Slippage and viscoelasticity are combined and strongly affect the
corresponding equations. In the meanwhile, the authors were able to fully incorporate
the non-linearities of the co-rotational Jeffreys model for viscoelastic relaxation into
their thin-film model [28].
The extensions of the aforementioned thin-film models for different slip conditions
with or without the presence of viscoelastic relaxation (Newtonian and non-Newtonian
models) affect on the one hand the rupture conditions, but also on the other hand
the shape of a liquid ridge. These two phenomena will be discussed in the next two
subsections. A elaborate description of these theoretical aspects can be found in a
recent review article by Blossey [65].
In the meanwhile, the derivation of
theoretical thin-film models is the dewetting of thin polymer films. As introduced in
section 1 and illustrated by Fig. 1, the stability of a thin liquid film is governed by the
effective interface potential. Basically, long-range attractive van der Waals forces add
to short-range repulsive forces. Due to the planar geometry of two interfaces of distance
d, the van der Waals contribution to the potential is φ(d)vdW∝ −A/d2, where A is the
Hamaker constant. For the description of the explicit calculation of Hamaker constants
from the dielectric functions of the involved materials we refer to [8] and to the book by
Israelachvili [66]. Experimental systems often exhibit multi-layer situations, cf. Fig. 7.
A hydrophobic film and/or an oxide layer of distinct thicknesses diexhibiting Hamaker
constants Airequire a superposition of contributions to the potential:
Application I - Spinodal dewetting One of the main applications of the
φ(d)vdw= −
12π(d + d1)2−
12π(d + d1+ d2)2


text:
Story in photos: Chandler Jones gets the Pats a night off
Check out the way Herald photographer John Wilcox captured Chandler Jones' twisting, falling, hold-on-for-dear-life catch of Zoltan Mesko's punt at the end of today's practice. Jones' catch earned the players a night off.
- Blog:
- The Blitz [1]
81ff92_2.jpg [2]

subset: commoncrawl


text:
The Pikeur® Gotha II Competition Coat is made of a lightweight soft shell fabric that retains its shape, is breathable, moisture-wicking and water-resistant. Superior features make this easy-care coat a great choice to help you stay at the top of your game. Pikeur® branding on left sleeve and just above right pocket.
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Experience Grand Prix's signature fit in incredibly lightweight fabric! The Grand Prix TechLite Shadbelly is machine washable, wrinkle-resistant and fast to dry. It wicks moisture and offers the stretch you need for full range of motion. Points are not machine washable.


text:
With a production capacity of 5,000 tpd of oxygen, the ultra-modern facility pushes the technical boundaries that have existed up to now, also with regard to efficiency, reliability and safety.
When the new liquefaction facility becomes operational in 2018, it will enable bi-directional service between the terminal and the liquefaction plant.
The new site manufactures compression-molded components for the oil and gas industry as well as critical components for semiconductor and heavy equipment applications.
Especially when handling hydrogen, reciprocating compressors must provide ruggedness, operating flexibility and energy efficiency at pressures up to 3,000 psi (200 bar).
The project will convert low-value Antwerp refinery off-gases into a low-cost petrochemical feedstock by recovering valuable hydrocarbons that would otherwise be burned as fuel.
Linde officials are hoping to help commercialize fuel-cell cars with better hydrogen infrastructure, saying they need more flexibility to meet rising demand in different markets.
A searchable database of project activity in the global hydrocarbon processing industry
Engineers and designers are highly skilled individuals. Forcing them to enter design changes using tables, forms and spreadsheets is unproductive and uneconomical, and it increases the likelihood of human error—this is the way that most instrumentation software systems currently work. For too long, software vendors have denied engineers and designers the simple practicality of a graphical visual engineering interface with "drag and drop" capability and inbuilt intelligence, ensuring changes are automatically replicated into all the associated data and databases.
Will previously-planned downstream investments be cut back in 2015 due to lower global oil prices?
Depends how long current prices last
March 2015


text:
- Specials
App Attack #015: Mango Appetizers
In this episode of App Attack, we revisit some essential apps for the new Windows Phone adopters, and feature those that have been updated and are ready for the Windows Phone 7.5 Mango experience.
A Taste of Windows Phone 7.5 Mango
The Windows Phone 7.5 update, otherwise commonly known as Mango, is finally here. If you're still finding your way around it, here are some pointers from us to familiarize you with the major features of this update.
First Looks: Windows 8 Preview
With official blog entries and a Facebook page, Windows 8 has kept us enthralled in anticipation. We jumped right into the thick of action with the release of its Developer Preview.
App Attack #014: Vroom Vroom!
Everyone is caught up with F1's fever and we are no exception. For this edition of App Attack, we have compiled a list of five apps for to keep you on the edge of the driver's seat!
Diablo III Beta - Performance Review
Blizzard's Diablo III beta is finally live! But can your system handle it in all its dark, fantasy glory? We find out with three variously configured machines.
App Attack #013: One Button Games
While some clamor for motion sensitive, 3D immersive, next-next-gen gaming, many mobile developers know that simple is often better - and what's more simple than a one button game? We share with you some of top gaming apps of this class.
Tablets Round-up (Q3, 2011)
2011 is certainly the Year of the Tablet. With so many tablets currently in the market and more on the way, choices are aplenty. Here's a quick summary of the tablet scene and their respective reviews.
Dual-Core Smartphones Round-up
Looking for a powerful smartphone? Take a quick look at our compilation of dual-core smartphone related articles, from previews to full reviews. Hit the jump to get a quick overview of the scene and choices available in this hotly contested arena.
App Attack #012: Traveler's Special
Although Singapore is a small island, we have problems getting to our destinations sometimes. Here's a list of five apps to be your eyes and ears as you roam the sunny island.
HP webOS and TouchPad Hands-On
HP's webOS brings a fresh perspective to the tablet space that is currently dominated by Apple iOS and Google Android. Our hands-on experience with the OS and its accompanying hardware, the HP TouchPad, will shed some light on its standing against the matured mobile OS.
- Canon announces launch of Canon Print Hub at the Singapore Sports Hub
- Aftershock is offering the NVIDIA GeForce GTX Titan X card with their desktop systems
- Sony announces the launch of new 4K and Full HD Action cams
- Canon's new ultra-short throw projectors let you write on the screen
- Google unveils new Chromebooks and Chromebit, the dongle that turns your display into a Chromebook
- Intel releases 14nm "Braswell" SoCs, targeted at entry-level PCs and notebooks
- Wakka Wakka! Pac-Man runs wild on Google Maps
- Would you buy a camera called the Podo?


text:
It all started one day after lunch, sometime back in 2011. We sat in the lab's living room (Yeah, we have a living room. And a bedroom. And a blind pet cat. But that's a different story), when Noam asked – ever wonder why people shake hands?
– To show you don't have a saber up your sleeve – I immediately retorted.
– But that seems odd, doesn't it? After all, we're not in the Middle Ages anymore, he responded.
Noam had just gotten back from an international conference, one of many, and did there what all better scientists do in their leisure time: observed.
– and what if I tell you people sniff their own hands right after they shake someone's hand?
–You're kidding right? what are we, rodents?!
–Well, you should know by now we're not that far from that…
So we devised a simple paradigm to test this. Do people really sniff their hands following a handshake? And is it directly related to the handshake? And more importantly – is it related to our sense of smell?.. Which is our lab's frame of reference for, well, almost anything.
We already had most of what it takes – we have rooms where we can put human subjects and sit them relatively comfortably on a dentist-style chair (talk about comfortable…), we have CCTV cameras that only need to be set up, and plenty of subjects that come and go for the various experiments taking place in the lab. So off we went. We knew we needed a big sample of subjects to be able to say something meaningful, so we started with 60. The paradigm was pretty simple – A person was seated alone in the room, unaware at that point that they are being filmed. After three minutes of idle seating, one of my lab mates (or myself at times) would enter and either shake or not shake the subject's hand, saying the same "greet" sentence. The subject thought they're waiting for the "real" experiment to ensue, so we told them we are getting everything ready, and that the experiment will start momentarily. After an additional three-minute period, the experiment was essentially over.
Then the fun part started. Watching this quantity of videos could be "a bit" tedious, but it has its perks embedded – people do the most hilarious things when they are alone… the most interesting for us – they constantly touch their faces. Much as Noam and that late-90's song both foresaw – "you and me baby ain't nothing but mammals," and may we add – indeed not very far from rodents so it seems. We constantly "groom."
One of the more perplexing results was the "self-sampling" behavior after encountering another individual — as if to assess or validate one's own place within some sort of hierarchy.
But the jackpot was the statistics of before and after handshake – there was a significant and substantial increase if a handshake was involved!
Though we got nice results with 60 subjects, and presented those in two international conferences, we wanted something more comprehensive to tell. Is this effect happening only between males and females? Is it gender specific at all? So up went the count – to 160 subjects, 20 in each possible combination of subject, experimenter and shake/no shake. And this number continued to swell as we added more conditions and more controls. You can check the article to see what we did there. Calvin Klein was unwittingly involved as well…
Along the way the paper got some pretty and colorful additions. One day Ofer came and asked – did you check and see WHERE people touch their faces? I replied "Well it's a very interesting question which I am not going to address, but feel free to check that". So he did just that, and the answer became figure 2C – which I must say is one of my favorite pieces of art since. Another day Yaara wondered what actual chemicals are transferred when we shake hands, and that's Figure 1.
When people ask why study such stuff, and what scientific field or discipline do such studies fall under anyway – we have several answers. First – because it's there – and it's interesting. Everyone shakes hands and if the common explanation as to why is partial – we need to amend it. We do basic science – and the notion of applicability is important but not the main thing. Second, this really serves a broader argument – in which our stand is quite obvious – there is no advantage for man over beast, and we're a part of the greater evolutionary tree.
So here you have it – a story that started off as a casual conversation in the living room of a lab, and 280 subjects / cups of coffee / new grey hair later became the paper you ought to read, if you haven't done so already!
With a skull and Keats, there was little choice but to write about the new online items in rhyme. So with apologies to Shakespeare, Keats and the scientists, as well as the people at SpaceIL, here are today's grab bag of poems. As usual, follow the links.
On a Lone Cranium
Alas poor Yorick – We can only know
Where you lived all those eons ago
Walking, did you take those others in stride;
Human, yet strange, as they strode alongside?
Did your children wander forth,
Searching for a greener North?
Can your skull, a bit of bone,
Tell us where our seeds were sown?
To the Moon
There was a fine crew in Rehovot
That aimed for the Moon with a "space boat"
It's barely a cart
But they've built it quite smart,
For cool science it's bound to promote
In a Heartbeat
"Two hearts that beat as one,"
Just one beat? Where's the fun?
Just one cell can beat as twenty
For your heart, love, that is plenty
Oh yes, and we have women PhDs, too. If you're an outstanding female Israeli PhD looking for help with your postdoc, click here.]]>
Prof. Benny Shilo knows the value of a good picture. We recently mentioned his book: Life's Blueprint, which uses photographs of things like bread dough and yeast cells to illustrate the process of biological development. Here is the image from the most recent piece we have uploaded on his research:
This is an individual Islet of Langerhans, as you've never seen it before. The white dots are the insulin-containing vesicles inside the beta cells, which both sense glucose levels and secrete insulin. Shilo and his team managed to get "close-up shots" of the individual cell membranes, and found that they have straight edges where both sensing and secretion functions are located.
We love the images in this new article on the work of Prof. Talila Volk because, aside from their eye-catching colors, these ones really do illustrate the story her work tells.
Volk's work investigates how muscle fibers get renewed through exercise. It may all come down to a protein that senses muscle contraction and tells the DNA in the cell nucleus to make more muscle proteins.
In this image, red is muscle fiber in fruit fly larvae, green is nuclei (muscle fibers are large cells with multiple nuclei) (A) shows normal muscle fiber, the others show what happens when the protein is missing.
How does it work? This image says it all:
In the left image you can see how the protein structure encircles the cell nucleus. At the other end of its arms (red) it connects to the cell's skeletal structure – the cytoskeleton. On the right, in green, you can see the protein structure. Its arms are springy – so that a pull on the end transmits a signal to the middle.
Volk and her group refer to the protein as a biological "mechanosensor," and, indeed, there is something rather mechanical about the right-hand image.
Assuming that form follows function, Volk has surmised that similarly-shaped proteins in human muscle fibers do the same thing.
Third, we have some cancer research images from the lab of Prof. Lea Eisenbach:
These tell the story of anti-cancer immune activity. Tissue and tumor cells appear in blue, pink shows immune cells that attack the cancer cells. When tumor cells appear in the back, there are many immune cells (left); but in the brain (middle) the same tumor cells attract relatively few immune cells. In fact, the normal brain tissue (in the same brain) on the right has no immune cells. If you first inject the tumor into the rat's back, where there is immune activity, and then inject the tumor cells from the back into the brain, the brain will be protected from the cancer.
And, oh yes, they are pretty too. This image, again from Talila Volk, of a 3-D computer model of a fruit fly larva muscle fiber was the inspiration for a sewing project:
Science Teaching researcher Prof. Nir Orion recently returned from Peru, where his award-winning Blue Planet teaching unit was adopted by the Peruvian Ministry of Education
Q: You have been working for many years to get schoolchildren out of the classroom setting. Why?
A: Schools in general and science teaching in particular are supposed to teach children about the world they live in. But they do it in a sterile environment that is disengaged from the real world; and thus many students do not find relevance or personal meaning in the subjects they "learn."
There are, of course, many types of important, abstract subjects that a child living in the 21st century needs to know well (for example the concept of an atom); these can't be taught by hands-on experience in the out-of-classroom setting. But most subjects of study include elements that can be directly experienced and investigated in the physical (out-of-school) environment, and built into lesson plans that then progress from the concrete to the conceptual.
This usually does not happen because the fundamental basis of the classic school (all over the world) is the disengagement from the real world. Going outside the school walls to engage with that world is mostly seen as a waste of time and money.
Learning is really an innate instinct that exists in many species. In most species, this instinct serves their most basic survival; but for the human species, the ability to learn is much more than that. It serves our best urges: curiosity and the tendency to look for novelty and challenges. But, like any instinct, the urge to learn is only called into play by a stimulus or need. The classic schoolroom stifles the natural learning instinct of most of its students and thus it encourages boredom, truancy and rebellion. To deal with the 'anti'-attitudes, the classic school must use force and manipulation that ultimately makes it less of an educator, more of a policing body.
Because of its failures, the educational system runs in circles, adopting the latest teaching plans that look, at least on paper, to be very successful. But in reality, none of them touch upon the root of the problem: Most of what is learned in school has no "internal" relevance to most of the students. In the teaching materials that I have been developing for around 30 years, the out-of-school "real-world" approach is an integral element in the curriculum; the research that accompanies the application of these learning materials consistently points to the fact that the correct integration of this method into the lesson plan can contribute to creating relevance for the subject matter among students and thus awaken their learning instinct.
Q: What is unique about the approach of the Blue Planet unit?
A: The Blue Planet is one among dozens of units developed in my group over the past 30 years under the title Thinking Science – Understanding Environment. The underlying concept for all of these units is that they try to awaken the students' natural learning instinct by making it personally relevant to them. Thus every unit is based on a lesson plan that begins with the concrete and then moves to the abstract, based on a well-considered inclusion of the out-of-school environment into its lesson plan.
The Thinking Science – Understanding Environment program is designed to really advance the development of thinking skills, especially thinking skills that then enable the development of environmental insight. Blue Planet and the rest of the collection in Thinking Science – Understanding Environment is the result of the many years of research and development. The consistent results of this research are what have enabled us to say that what is really unique about the program is the way in which the principles of making the subject matter relevant have been translated so completely into practice. These programs reveal that the student must be the main focus of learning, and the starting point of teaching must be emotional (motivation) – this is the key to generating complex cognitive processes.
Q: Why do you think UNESCO gave Blue Planet the recognition it did? What has this meant for you and your work?
A: UNESCO recognized and rewarded the program because it identified in it the same unique elements that I emphasized above, as well as the uncommon methods of using science teaching as a tool for developing environmental insight.
For me, it was a great honor, and it was very important to me personally. I feel there is a sad lack of recognition in the Israeli educational system, which still bows to the golden calf of international testing — to the detriment of the students.
Q: Have you had any interesting experiences traveling around leading workshops for teachers on the approach?
A: For over a decade I have been invited to conduct workshops for teachers around the world. I have held these workshops for teachers in Portugal, Argentina, Chile, the US, Brazil, India, Peru, Uruguay, South Africa. The demand for these workshops is increasing from year to year. Next summer, I'll split my time between India and Peru.
Q: Have you seen any changes in Israeli science education in classes that have adopted the out-of-classroom approach?
A: Absolutely, yes. In every study we have conducted on the development and application of our teaching plans, we see that out-of-school environmental methods become central to creating relevance (motivation) in learning; we can show that lesson plans that are built on the transition from the concrete to the abstract promote the development of complex thinking abilities.]]>
For Dr. Jacob (Yaqub) Hanna, the way forward lies in taking a step back and asking the fundamental questions: How does reprogramming work on the basic molecular level? Why does the reprogramming process – inserting four genes into adult cells – create cells that are almost, but not quite, the equivalent of embryonic stem cells? Why is it that mouse embryonic stem cells tend to be stable and easily manipulated in the lab, but human stem cells stubbornly insist on differentiating or degrading, as well as resisting methods that have been shown to work on mouse cells?
That last question has turned out to be crucial: It is by comparing mouse and human cells that Hanna and his lab group have gained an understanding of the genetic pathways in human cells that drive differentiation, and this understanding led them to create "better iPS cells." We wrote about these "naïve" cells, which appear to be closer to the earliest embryonic stem cells, around a year ago saying: "The next step, of course, is directing the differentiation of the embryonic tissue to produce specific human tissues and organs. Hanna and his group are already on it."
We are now pleased to report progress in that area. The cells that Hanna and his group have created in the lab in the course of their latest research are some of the most challenging: primordial germ cells, the precursor cells that appear just a week or two into embryonic development and eventually give rise to the sperm and ova. A group in Japan had produced them in mouse cells, but that feat was proving particularly tricky to reproduce in human cells.
Using the naïve cell technique they invented, Hanna and his team went on to create human primordial germ cells – in quantity. "We can produce enough of these cells in the petri dish to use them for further research," says Hanna. "One of the most important things we discovered is that the process is regulated by a different master gene in humans than in mice. This shows that we need to learn more about how these cells are produced in humans."
Images: Clusters of human embryonic stem cells that were differentiated to an early germ cell (PGC) state. Each color reveals the expression of a different gene. (top to bottom) NANOS3, NANOG, OCT4 and all three combined in a single image
Not everyone gets their research written about by this week's Nobel Prize winners:
All mammals face the challenge of navigating in complex, three-dimensional (3D) environments, whether they are swinging from branch-to-branch in forests or burrowing underground tunnels. How does the brain maintain a sense of place and direction in 3D? In a beautiful study published on Nature's website today, Finkelstein et al. report that bats have an internal neural compass that tracks direction in 3D during both surface locomotion and flight.
That's from Prof. May-Britt Moser in Nature's "News and Views." It turns out that the whole place-cell-grid-cell community is quite excited by today's prize, not just because the Mosers are apparently well-loved, but because it boosts all the research in this field. And the fact that cells in our brain form little hexagonal grids that keep us oriented, map-like, in our surroundings is not just an important insight into the workings of our brain; it is a pyrotechnic flash of insight that changes how we understand the brain to work.
Arseny Finkelstein is in the group of Prof. Nachum Ulanovsky, and to tell the truth, their work does not need a lot of extra boosting. Watch the video of bats flying around their lab to see why: http://www.nature.com/news/bat-nav-system-enables-three-dimensional-manoeuvres-1.16475. Among other things, they show that you can really apply mathematical models to understand how our mammalian brains get their bearings.
Understanding bats' internal compasses, by the way, could have real implications for research into human brain malfunctions, among them the sudden vertigo occasionally experienced by pilots, when they lose their sense of up and down.
On the ocean beds, microorganisms "breathe" sulfur: They take in sulfate – an abundant compound of oxidized sulfur, and use it to digest organic matter that sinks to the seafloor. Thus in addition to sulfur, a great deal of the ocean's carbon and oxygen cycle through these microorganisms. When we last mentioned these sulfate-reducing microorganisms, it was to highlight Halevy's previous research, which traced the global sulfur cycle over the past 500 million years by accounting for the exit of sulfur from the ocean. This study revealed the importance of one destination of the microbes' waste products: the iron-sulfide mineral pyrite, which gets buried in seafloor sediments.
In his recent research, Halevy developed a model for a closer understanding how the day-to-day activity of these microbes relates to their environment. Dr. Boswell Wing of McGill University, Montreal, who worked on this research with Halevy while on sabbatical in Halevy's lab, says: "Along with the fact that sulfate-reducing microbes play a critical role in controlling atmospheric oxygen levels when their waste products are buried as the mineral pyrite, a.k.a. fools' gold, what drew us to this problem was the huge amount of outstanding experimental data that was begging for an explanation."
The two developed the model to explain a long-standing curiosity: The deep-sea microbes prefer light sulfur isotopes over heavier ones. They will, however, use the slightly heavier isotopes, and the resulting isotope ratios vary according to the availability of sulfur in their surroundings and their respiration rates. Halevy and Wing basically brought together models and formulas from across biochemistry and isotope chemistry to create a physical model that explains how the metabolic processes of the microorganisms interact with their environment. This model is already being used to uncover the planet's sulfurous past, and it may help us to predict the future, as well, since environmental change will affect the habitats of crucial microbe populations and thus their metabolic activity. In addition, says Halevy, the basic model they developed could be adapted to work out the microbiological exchange of such other vital substances as nitrogen or methane.
On Mars, the driver of the sulfur cycle is not biological, but may be primarily volcanic – or at least it was in the planet's more turbulent past. The signs of past volcanic activity on Mars – including the tallest volcano in the solar system – suggest that eruptions were hundreds of times more forceful than those on Earth, some lasting for up to a decade. These would have had a profound effect on the planet's atmosphere. On Earth, the ash and sulfur compounds flung into the atmosphere from eruptions tend to have a cooling effect. But a climate model developed by Halevy suggests that the large amounts of sulfur-dioxide would act as a greenhouse gas, warming the surface below. The compounds that cool on Earth would have less of a chilling effect on Mars, as they would coat the dust particles already present in the atmosphere.
What does this model tell us? Volcanoes may have warmed the planet enough that water could have once flowed on Mars, at least in the lower latitudes for short periods of time – decades to centuries. Were such brief wet periods enough to sustain life on early Mars? Such questions are still being debated, but Halevy's work gives us a much clearer picture of the conditions that may have prevailed on Mars' ancient surface.]]>
Volunteers given the same conditioning while awake did not reduce their nicotine consumption.
Arzi and Sobel had first demonstrated true sleep learning in 2012. This is the same conditioning that Pavlov discovered when he trained dogs to salivate at the sound of a bell: Teach the mind to subconsciously associate one sensation with another. Their twist was to use smell instead of the bell: We can register and even react to odors while we sleep without waking up. So when the volunteers were exposed throughout the night to the smell of cigarette smoke together with that of rotten fish, they did not remember it in the morning. And yet their need for a "ciggie" was not as strong as it had been.
The second trick was to monitor the sleepers' brain waves and administer the smells at the right stage of sleep. The group's previous research had suggested that the associations are formed and cemented in the brain during non-rapid-eye-movement (NREM) sleep – the stage in which researchers believe that memories from the previous day are being consolidated. The new study supported this finding quite strongly.
Arzi assiduously points out that the research has proven a point about the workings of the sleeping brain. She will be pleased, of course, if clinical researchers adopt the method and improve on it. She, herself, intends to use this window on the brain's activity to keep investigating the mysterious phenomena of sleep and learning, and the apparently unique place of smell among our senses.]]>
Life's Blueprint – The Science and Art of Embryo Creation; Benny Shilo, Yale University Press, 174 pages.
When a stem cell divides, one daughter maintains the stem cell fate while the other produces a differentiated progeny. Stem cells are positioned in a restricted spatial niche that provides signals maintaining them in a proliferative, nondifferentiated state. After division, only the undifferentiated progeny is retained in the niche. Top: Once the eye of the zebrafish (Danio rerio) is specified, cells differentiate and produce neurons that sense light. Retinal stem cells (red) are maintained throughout the animal's life in a niche located next to the lens (K. Cerveny and S. Wilson, University College London); bottom: The live yeast stock, or mother, is carefully maintained in the bakery. Portions are allocated to produce dough and bread. A fine balance is kept to ensure a steady production of bread while continuing to propagate the yeast stock (B. Shilo, Hi Rise Bakery, Cambridge, Massachusetts)
One and one can equal one – or two. But sometimes one and one goes way beyond the question of quantity – into the realm of elaborate qualification. When a sperm penetrates an egg – the two begin as one: a single, fertilized cell. That cell, of course, begins another operation: division. At first the cells are identical, but soon a process begins that leads, in the end, to a many-celled, autonomous organism. The same process occurs in flies, humans and pretty much all the life that was can see.
In Life's Blueprint, Prof. Benny Shilo of the Weizmann Institute of Science describes the precisely-orchestrated concert that is embryonic development (at least everything we know today about the process). This is one of the most complex processes in nature, from the point of view of the number of factors involved, the precision timing required for each step, regulating the concentrations of substances that shape the developing embryo, the ability to copy information with great accuracy (though not absolute – a few "typos" are necessary to drive natural selection and thus evolution), and more.
The compound eye of the fruit fly is made up of eight hundred repeated units called ommatidia. During eye development, patterning takes place progressively from the bottom to the top of the picture, generating a new row of ommatidia every two hours. Once an ommatidium is established, it signals to inhibit cells at the immediate radius from assuming a similar fate. The newly formed ommatidia become spaced at fixed distances, just outside this radius. Once created, they will now generate their own inhibitory spheres, to outline spacing of the next row of ommatidia that will form. Top: Establishment of the founder cells (blue) for ommatidia during eye development (A. Shwartz and B. Shilo, Weizmann Institute); bottom: Pigeons sitting on a railing establish a fixed spacing (B. Shilo, Moss Landing, California)
Shilo's book, written for a popular readership, avoids excess detail and scientific jargon. Other books may describe embryonic development, but with the photos, this book adds a level of philosophical treatise to the concise descriptions. The photos – all taken by Shilo – are presented in pairs (one plus one); each pair contains one image of an important stage in embryonic development alongside a photo from the world of our human, everyday objects. Their message is unambiguous and precise: a statement about the rules and plans that shape our world – both the seen and the unseen.
Cancer, according to a new Weizmann Institute study, may grow and spread more at night. In this scenario, our cells are getting messages left and right, day and night, and taking them in through the specialized receptors on their outer membranes. During the daytime, our bodies produce natural "wake-up" hormones, and these apparently, take precedence over other incoming messages, their receptors overriding those receiving growth factor messages. At night, when the wake-up hormones have gone to bed, the growth receptor messages are heard in the cell loud and clear, especially in cancer cells that tend to amplify growth signals.
The message: Certain anti-cancer drugs that target the growth factor receptors could be more effective if given at night.
How does a population of internal bacteria, which sit in the deepest intestinal dark, tell day from night? The scientists who brought us the news on the connection between artificial sweeteners, gut bacteria and glucose intolerance are back with a new study on our close relationship with our microbiome. This time, they have shown that our gut bacteria change and adapt throughout the day in synchronization with our eating schedule. So jet lag, for example, does not just screw with your head; it can temporarily upset the balance of bacteria in your gut. And constant upsets in that balance, as we know from their previous study, can lead to metabolic disorders. Indeed, the gut bacteria from a jet-lagged person implanted in the intestines of a sterile mouse caused weight gain and a rise in blood sugar levels.
The message: If you are gaining too much weight while rotating through shift work or flying around the world, blame it on your gut bacteria. Eventually, according to the scientists, we might be able to develop ways of "tricking" our gut bacteria into revising their schedules to fit the unnatural ones we adopt.


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Over the years, I have really grown to appreciate the work of the coaches in the Dayton city league. The City League teams are getting better and better.
Last Sunday, both Thurgood Marshall and Belmont had players at the MSROHIO Combine at the D1 Sports Training facility. Both head coaches were there with their players.
Belmont football has been down in recent years. Veteran Earl White is now leading Belmont. Coach White brought 10 players to our combine. Most were a mixture of freshman and eighth graders. Also some juniors and sophomores made the trip.
Coach White is teaching and exposing young players as to what it takes to be good.
Thurgood Marshall's football program has really improved overs the last few years and continues to improve. Coach Robert Brown brought 4 veteran players. Four juniors and two sophomores.
Last fall, I watched them against powerful Akron St.V's. They lost the game, but played hard, and until a lack of depth got the best of them, were doing well.
RB Daryl McCleskey measured 5'8-172 (no shoes) and ran really well. Ran 4.56/40. Needs to work on change of direction – 4.63/proshuttle and 7.4/L-cone. Gets north/south well. Excellent vision.
RB Bobby Brown Jr measured 5'7-163 (no shoes) and showed excellent change of direction and burst. Ran a 7.2/L-cone. Needs to improve speed, but more a north/south runner. Good strength – powerballed 30'1. Broad jumped – 8'9. Continue ReadingRead More »


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Jim Williams has been watching birds and writing about their antics since before "Gilligan's Island" went into reruns. Join him for his unique insights, his everyday adventures and an open conversation about the birds in your back yard and beyond.
Another Black-capped Chickadee with a deformed bill is being seen in Minnesota. This bird is coming to feeders at the Duluth home of author/birder/blogger Laura Erickson.
The bird previously mentioned here was seen in Maple Grove in February. These two join several other reports of Minnesota birds with this deformity (photo below by Laura Erickson), including more chickadees.
If you see such a bird, any species with a deformed bill, please report it to http://alaska.usgs.gov/science/biology/landbirds/beak_deformity/observerreport.php
Biologists at U.S. Geological Survey offices in Alaska are tracking these sightings. Several thousand birds with this deformity have been reported in Alaska and the Pacific Northwest in the past several years. Reason for the deformities, unknown at present, is being sought.
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Vault Guides are THE source for insider insight on career information and employer reviews. Shop Vault Guides
Call it truth in advertising -- Nationwide Mutual Insurance Company has offices throughout the US. The company is a leading US property/casualty insurer that also provides life insurance and retirement products through its Nationwide Financial Services subsidiary. Its property/casualty products range from general personal and commercial coverage -- including auto, home, and business owners policies -- to such specialty lines as professional liability, workers' compensation, agricultural, loss-control, pet insurance, and other coverage. The company sells its products and provides services through Allied Group, Harleysville Group, Nationwide Agribusiness Insurance, GatesMcDonald, Scottsdale Insurance, and other subsidiaries.
Nationwide earns about 80% of annual revenues from premiums and policy charges, most of which come from its property/casualty insurance subsidiaries. As the US insurance industry has been mature for a long time, Nationwide has sought growth by moving into assorted niches, including specialty auto coverage and financial services. The company created its workplace benefits Nationwide Better Health program and has grown it through acquisitions to provide health, productivity, and disease management services to employers.
Operating as Nationwide Bank, Nationwide Financial Services provides deposit products and ATM access for its property/casualty and financial services customers. The company also established its Nationwide Advantage Mortgage business, which provides both mortgages and home equity loans. Consumers can access its services online, over the phone, and through Nationwide agents.
Geographic Reach
Nationwide offers its products in all 50 US states.
Sales and Marketing
Nationwide Mutual Insurance Company distributes its property/casualty products through a network of some 3,200 exclusive agents across the US. It also relies upon more than 5,200 independent agents, as well as general agents and brokers for its specialty products. Nationwide Financial Services distributes its group retirement programs through its own sales team, while it sells its individual investment products through affiliated and unaffiliated investment advisors.
Financial Performance
Nationwide's 2012 and 2013 financial results showed a 22% and 8% increase in revenues to some $22 billion and $24 billion, respectively, due to higher premium and policy income across all major business lines (including premium growth from acquisitions), as well as higher investment income and gains. Revenues have seen varying levels of growth over recent years; Nationwide reported flat earnings in 2011 due to market volatility and higher claims from severe weather conditions ranging from hurricanes and wildfires to tornadoes and drought.
The company reported profits of $2 billion in 2013, more than doubling the $940 million it netted in 2012, attributed to higher revenues and increased client assets in the financial services operations. A decrease in weather-related claims also helped net income, as did efforts to improve expense efficiencies in the property/casualty business.
To leverage the strength of its brand, the group is working towards aligning its various operations under the Nationwide name.
The growth efforts of Nationwide have focused on its investment management operations, as demand for new and existing products has risen. The firm added several new mutual funds during 2012 and 2013, adding new investment opportunities; it also expanded its sales and distribution networks for the investment offerings and launched an online investment management support tool (Investment Solutions Builder). In 2014, Nationwide Funds added three new mutual funds. Also that year, Nationwide teamed up with annuity designer and marketer Annexus to launch a new fixed indexed annuity product.
Through Crestbrook Insurance, Nationwide in 2013 began providing niche property/casualty products, including various specialty lines for wealthy clients.
Mergers and Acquisitions
To expand the breadth of its commercial product lines, Nationwide spent some $760 million to acquire Pennsylvania-based Harleysville Group and its majority shareholder Harleysville Mutual in 2012. Following the transaction, Harleysville Mutual was absorbed and its policyholders became policyholders of Nationwide. Harleysville Group became a subsidiary of Nationwide. Operating from its headquarters in Harleysville, the subsidiary is a distinct brand that serves small and midsized businesses in the northeastern and midwestern states. Harleysville Group became a major component of Nationwide's property/casualty independent agency business, alongside its Allied Insurance subsidiary.
To expand its mutual fund operations, Nationwide purchased two funds from UBS in 2012. It followed that purchase up with the buy of 17 bond and equity mutual funds from HighMark Capital in 2013.
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News » Published months ago
Is this Jennie Garth the Actor?
Share your thoughts on this image?
26th January 2015 @ 04:44am
Jennie Garth's 2015 is off to a great start as she has a new 'man' in her life which ironically is confirmed as she is pictured looking gorgeous in 'Ang ...
26th October 2014 @ 02:23pm
Jennie Garth is starring in her new reality show "The Jennie Garth Project" on HGTV and in the process has expanded her brand while reinventing herself.


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Wallpaper Repair
I have a small section of a wall where a piece of wallpaper was torn off by a child. If we still had the piece, I would try to patch it back in, but we don't. In the same room, there are areas covered by the same wallpaper which are out of view. Is there a way to cut out a piece and transplant it to the area which is visible? Thanks.
eddieg 2008,
Yes you can do it. Be careful to match the piece you need when you find out where your taking it from. Oversize the piece.
Using a level and a pencil, mark the area you are going to remove. Score the outline with a wallpaper razor knife gently. Sanitest comes off real easy, paper is harder.
Using warm water with a sponge and 1" scraper start wetting the area your removing. Apply and apply and each time start working the knife under the paper. After a while, you will eventually remove the piece you want.
You can either just paste it over the area thats missing, a fair job. Or you can wallpaper razor knife through both pieces of wallpaper and remove the new piece and then carefully remove the edging remaining. Now paste the new piece right in place.
Whalla! Done.
Patience helps. Let the warm water have time to work its' way into the paper.
Good Luck,
All the best,
The PorchGuy
Here is a link that might be useful: My Album


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Latest Kyoto Protocol Stories
New modeling released on Tuesday by the United Nations says emission cuts pledges made by 60 countries will not be enough to keep the average global temperature rise at 2 degrees Celsius or less.
Yvo de Boer, head of the UN's climate change convention, announced on Thursday that he would resign from his position as of July 1.
WASHINGTON, Jan. 28 /PRNewswire-USNewswire/ -- In a letter to the UN Climate Change Convention Secretariat, the European Union and its member states today confirmed their willingness to be associated with the Copenhagen Accord negotiated during the UN climate change conference in December 2009.
FARMINGDALE, N.Y., Jan. 13 /PRNewswire-FirstCall/ -- Cemtrex Inc.
President Obama's visit to China before December's Copenhagen conference underlined views that the international strategy to tackle climate change truly hinges on cooperation between the United States and the developing Asian economies.
Amid new diplomatic wrangling over the failure of the Copenhagen summit, UN Secretary General Ban Ki-moon appealed for world powers to make a new effort to secure a legally binding climate deal next year.
FARMINGDALE, N.Y., Dec. 15 /PRNewswire-FirstCall/ -- Cemtrex Inc.
Several developing countries temporarily withdrew their co-operation for negotiations at the UN climate summit on Monday.
Panasonic has unveiled an eco-dream house in Tokyo Bay, Japan.
The UN climate talks have produced the first official draft blueprint for a deal that would set targets for limiting global warming.
- Forsooth! indeed! originally a parenthetical phrase used in repeating the words of another with more or less contempt or disdain.


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Does Riot plan on bringing more game modes into LoL? Or having a Map Editor so we can create our own maps? I think it would be fun, even if you had to remove IP and EXP on the user-created maps, as they probably wouldn't be balanced.
I'd love to have more then just 2 teams competing in the same arena, such as 3v3v3v3 or 4v4v4. Or a huge map that has many fronts, like 20v20. I'm not sure how much stress this would put on the servers but over the years I've experienced almost 0 lag in 99% of my games, would increasing player capacity to 12 or 16 be too much trouble?
How about a weekly or monthly event where you can join a side (much like the Ionia vs Noxus event you held earlier, but for the whole player-base to participate in) to play against the opposite champs?
What about timed games where the team that reaches victory is determined by whoever earns the most gold?
These are just a few ideas, the possibilities are endless, I'm just curious on how far Riot is planning on expanding the game.
© 2015 Riot Games, Inc. All rights reserved. Riot Games, League of Legends and PvP.net are trademarks, services marks, or registered trademarks of Riot Games, Inc.


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Could Ceramides solve your dry skin?
March 27, 2015
Ceramides play a central role in conserving supple, healthy-looking skin. A family of waxy molecules, they are a crucial lipid element of the skin's membrane. Composed of sphingosine and a fatty acid, ceramides maintain the … [Read More...]
How to stop scratching
March 25, 2015
Anyone who has eczema, psoriasis or urticaria will have experienced the burning, uncontrollable and completely overwhelming urge to itch! Having had hives, I've woken up in the middle of the night ready to tear my skin … [Read More...]
An update from Pai HQ
March 20, 2015
Early spring always seems to be a busy time at Pai HQ – in between getting some beautiful new photography shot (stay tuned for the outcome!), planning new launches and pizza-making it's been a particularly exciting week! Here … [Read More...]
The rise of organics: Exciting news from the Soil Association report
March 19, 2015
News just in – the new Soil Association report on the rise of organic sales makes for really encouraging reading! There has been a growth in sales of organic health and beauty products since 2010. A sudden increase of 17% from … [Read More...]
Super foods: supporting your skin as it ages
March 11, 2015
The saying is 'you are what you eat'. I couldn't agree more -especially when you're seeking to maintain healthy skin! Using the right skincare products is just one part of the jigsaw. For a calm and radiant complexion you also … [Read More...]
My advice on starting a business and being bold!
March 8, 2015
Today is International Women's Day and its theme this year is 'Make it Happen' This message can apply to a million different things but I'd like to shine a light on female entrepreneurship. Women account for 17% of business … [Read More...]
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riding lawnmower, sears craftsman
It started out as I had issues with my steering on my lawnmower. I recently replace my steering shaft on my sears craftsman automatic transmission riding lawn mower. (its an electric start.) After fixing my steering shaft, I notice my forward pedal gets stuck while pressing it down. When I put it in reverse, its hard to press the pedal down. I had the lawn mower sitting on its side. I don't know if that had something to do with it. Before I work on the lawn mower, I never had any issues with them until after I fix the steering shaft. Can anyone help??
I believe you are talking about tie rods, which are horizontal and move the wheels left or right. If so, did you put them in the correct position? If not, it might be that a tie rod is coming in contact with part of the speed pedal assembly and if so, you should be able to see that happening from underneath.


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Try one of these articles:
- Will Firefox work on my mobile device? This article lists mobile devices that are supported by Firefox for Android.
- Is Firefox available for iPhone or iPad? Good news! The Firefox experience is coming to iOS users in 2015. Stay tuned!
- Update to the latest version of Firefox for Android This article shows you how to update to the latest version of Firefox for Android so you can use all the newest features.
- How do I install Firefox on an Android device? This article shows you how to download and install Firefox for Android on your Android device.


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