Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session G33: GSNP Student Award Session and Glasses |
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Sponsoring Units: GSNP Chair: Narayanan Menon, University of Massachusetts, Amherst Room: Baltimore Convention Center 336 |
Tuesday, March 14, 2006 8:00AM - 8:12AM |
G33.00001: Rate of Entropy Extraction in Compressible Turbulence Mahesh Bandi The rate of change of entropy is measured for a system of particles floating on the surface of a fluid maintained in a turbulent steady state. This rate of entropy ${\dot S}$ equals the time integral of the two point temporal velocity divergence correlation function with a negative prefactor. The measurements satisfactorily agree with the sum of Lyapunov exponents (Kolmogorov-Sinai entropy rate) measured from previous simulations, as expected of dynamical systems that are very chaotic (Sinai-Ruelle-Bowen statistics). [Preview Abstract] |
Tuesday, March 14, 2006 8:12AM - 8:24AM |
G33.00002: Toward Zero Surface Tension Limit: Granular Fingering Instability in a Radial Hele-Shaw Cell Xiang Cheng Because of the absence of cohesive forces between grains, dry granular material can, in many respects, be thought of as a fluid with zero surface tension. In the zero surface-tension limit, viscous fingering is known to possess singular behavior. We have studied the viscous fingering instability in such a granular ``fluid.'' In our experiment, we use a conventional radial Hele-Shaw cell consisting of two parallel glass plates separated by a gap. Gas with controlled pressures is blown through a hole at the center of one glass plate and displaces the surrounding dry granular material. We have systematically studied the fingering pattern as a function of gas pressure, gap thickness, and grain size. Two stages are observed during pattern growth. In the first stage, we find fluid-like fingering. However, as opposed to normal fluids, the pattern is more ramified at low pressure. In the second stage, we find several new behaviors in the system such as merging and pinching off of fingers and the existence of satellite bubbles. [Preview Abstract] |
Tuesday, March 14, 2006 8:24AM - 8:36AM |
G33.00003: The effect of packing density on self-assembled monolayer friction: Investigation of frictional contrast between OTS phase-separated regions Erin Flater Motivated by the lack of fundamental understanding of friction, and that friction and wear are major limiting factors for surface micromachined devices, we use atomic force microscopy (AFM) to determine the nanoscale frictional properties of alkylsilane monolayers commonly used in these microscale devices to reduce adhesion and friction. Quantitative nanoscale single asperity measurements of friction and contact stiffness are performed using monolayer-terminated AFM tips on monolayer-terminated silicon. By comparing the two structural phases present in octadecyltrichrolosilane (OTS) monolayers, we observe that friction depends on the local molecular packing density. The liquid condensed phase shows measurably lower friction at low loads than the liquid expanded phase, demonstrating that lower friction is associated with higher molecular packing density. However, the phases exhibit the same frictional response at higher loads, suggesting that compressed forms of both phases are structurally and tribologically equivalent. We discuss these results in terms of stress-induced molecular conformational changes in the confined interface. We acknowledge our collaborators: W. Robert Ashurst at Auburn University, who provided the OTS samples, and Maarten P. de Boer and Alex D. Corwin at Sandia National Laboratories. [Preview Abstract] |
Tuesday, March 14, 2006 8:36AM - 8:48AM |
G33.00004: Universal Impedance, Admittance and Scattering Fluctuations in Quantum-chaotic Systems Sameer Hemmady We experimentally investigate fluctuations in the eigenvalues of the impedance, admittance and scattering matrices of wave chaotic systems using a microwave analog of a quantum chaotic infinite square well potential. We consider a 2-D, time-reversal symmetric chaotic microwave resonator driven by two non-ideally coupled ports. The system-specific coupling effects are removed using the measured radiation impedance matrix ($\mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\leftrightarrow$}}\over {Z}} _{Rad} )$ [1] of the two ports. A normalized impedance matrix ($\mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\leftrightarrow$}}\over {z}} )$ is thus obtained, and the Probability Density Function (PDF) of its eigenvalues is predicted to be universal depending only on the cavity loss. We observe remarkable agreement between the statistical properties of $\mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\leftrightarrow$}}\over {z}} $ and $\mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\leftrightarrow$}}\over {y}} =\mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\leftrightarrow$}}\over {z}} ^{-1}$ for all degrees of loss, which is in accordance with [1, 2] and Random Matrix Theory (RMT). We compare the joint PDF of the eigenphases of the normalized scattering matrix ($\mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\leftrightarrow$}}\over {s}} )$ with that obtained from RMT for varying degrees of loss. We study the joint PDF of the eigenvalues of $\mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\leftrightarrow$}}\over {s}} \mathord{\buildrel{\lower3pt\hbox{$\scriptscriptstyle\leftrightarrow$}}\over {s}} ^{\dag }$ and find good agreement with [3]. [1] X. Zheng, \textit{et al.,} -- Electromagnetics (in press); condmat/0408317; S. Hemmady, \textit{et al}., Phys. Rev. Lett. \textbf{94}, 014102 (2005).[2] Y. V. Fyodorov, \textit{et al.},-- condmat/0507016.[3] P. W. Brouwer and C. W. J Beenakker -- PRB \textbf{55}, 4695 (1997). Work supported by DOD MURI AFOSR Grant F496200110374, DURIP Grants FA95500410295 and FA95500510240. [Preview Abstract] |
Tuesday, March 14, 2006 8:48AM - 9:00AM |
G33.00005: Plastic Failure Events in 2D Sheared Granular Systems Trush Majmudar We present experimental measurements of plastic failure events in a two dimensional granular system consisting of polymer photoelastic disks, placed horizontally, and confined within a rectangular biaxial cell. The bi-refringence of these disks allows us to determine the normal and tangential components of contact forces. We image the system at various deformation states and measure the stress changes and displacements of the disks during one complete shear cycle. The stress changes are found by computing the stress tensor of each disk and the displacements are measured by particle tracking. We obtain bulk stress-strain curves by spatial averaging and find that the system exhibits regions of reversible deformation interrupted by irreversible plastic failure events. We also obtain the behavior of shear modulus of the system. The spatial distribution of reversible and plastic deformations found by studying the displacements of the disks show that in two corners, the disks move uniformly but in a central band aligned along a principal strain direction, we observe multiple vortices. Reversing the direction of shear causes maximum plastic deformation which results in disruption of the vortex structure. We compare our results to the shear transformation zone (STZ) theory. [Preview Abstract] |
Tuesday, March 14, 2006 9:00AM - 9:12AM |
G33.00006: Locally fluctuating elasticity of vulcanized solids Xiaoming Mao, Paul Goldbart, Xiangjun Xing, Annette Zippelius The elastic properties of vulcanized solids, such as rubbery polymeric media, are characterized not only by their small mean shear moduli but also by the random spatial fluctuations of their local elasticity. These fluctuations originate in the randomness locked in, e.g., to a polymer network during the cross-linking process. We examine these fluctuations in the local elasticity of random solids via vulcanization theory, i.e., the replica field theory that describes cross-linking- driven random solidification transitions and their emergent rigidity. To do this we identify the Goldstone excitations of the random solid state as local shear deformations, and interpret their effective free energy in terms of a phenomenological model of inhomogeneous, nonlocal rubber elasticity. Thus, we arrive at predictions for the statistical properties of the fluctuating elasticity of vulcanized solids. [Preview Abstract] |
Tuesday, March 14, 2006 9:12AM - 9:24AM |
G33.00007: Rheological Fluids under Perturbation: Reconstruction and Relaxation Processes Elsa Maria De la Calleja, Jose Luis Carrillo We study the evolution of the structure of electro rheological as well as magneto rheological fluids in the presence of perturbation fields. We have previously shown that the fibrous structure acquired by these dispersions in the presence of a static, electric or magnetic, field has multifractal characteristics[1]. If in addition to the static field a perpendicular pulsed field is applied, under certain conditions it is possible to rearrange the structure into an ordered one[2]. Based on the measured mass fractal dimension and the radial distribution of mass, we discuss these processes and other structural characteristics of the system approaching these phenomena as a glass transition. [1] J. L. Carrillo, F. Donado, and M. E. Mendoza: Fractal patterns, cluster dynamics, and elastic properties. Phys. Rev. E 68, 061509 (2003); J. L. Carrillo, M. E. Mendoza, and F. Donado: Fractal patterns and aggregation processes in rheological dispersions. J. Stat. Mech. P06001 (2005). [2] J. L. Carrillo, E. M. De la Calleja, M. E. Mendoza, and F. Donado, Ferroelectrics (in press). [Preview Abstract] |
Tuesday, March 14, 2006 9:24AM - 9:36AM |
G33.00008: Low temperature solution of the Sherrington-Kirkpatrick model Sergey Pankov We propose a simple scaling ansatz for the full replica symmetry breaking solution of the Sherrington-Kirkpatrick model in the low energy sector. This solution is argued to become exact in the limit $x\to0$, $\beta x\to\infty$ of the Parisi replica symmetry breaking scheme parameter $x$. The distribution function $P(x,y)$ of the frozen fields $y$ has been known to develop a linear gap at zero temperature. We integrate the scaling equations to find an exact numerical value for the slope of the gap $\partial P(x,y)/\partial y|_{y\to0}=0.301046...$ We also use the scaling solution to devise an inexpensive numerical procedure for computing finite timescale ($x=1$) quantities. The entropy, the dynamical susceptibility at zero frequency and the local field distribution function are computed in the low temperature limit with high precision, barely achievable by other currently available methods. [Preview Abstract] |
Tuesday, March 14, 2006 9:36AM - 9:48AM |
G33.00009: Slowing dynamics of supercooled glycerol in the volume-temperature plane Narayanan Menon, K. Win We have measured\footnote{ K. Z. Win and N. Menon, cond-mat/0508648} the dielectric susceptibility of supercooled glycerol from 0.01 Hz to 100 kHz at up to 900 MPa and close to the glass transition temperature. We find that the glass transition temperature and isobaric fragility increase with pressure. We separate the effects on the relaxation frequency of volume and temperature by studying the glass transition in the V-T plane. By introducing a generalized fragility we quantify these effects and show that V and T contribute almost equally to dynamic slowing-down. We exploit a connection between the generalized fragility and a recently discovered scaling exponent to show that these results are likely to hold for other fluids. [Preview Abstract] |
Tuesday, March 14, 2006 9:48AM - 10:00AM |
G33.00010: Structure of solid metal ammonia systems Xue Wang, C. A. Burns, D. Hoogerheide, C. N. Kodituwakku Both crystalline and amorphous phases in metal ammonia solids have been studied using x-ray scattering. We have studied the structure of Li(NH$_{3})_{4}$ over a temperature range of 10 K to 90 K and also studied the structure of quenched sodium-ammonia solutions at concentrations of 0, 3, 6, 9, 12, and 15 mole percent metal. We find a mixture of amorphous and crystalline phases in lithium-ammonia with at least two different crystalline phases. An amorphous phase is also found in certain of the quenched sodium-ammonia solutions. [Preview Abstract] |
Tuesday, March 14, 2006 10:00AM - 10:12AM |
G33.00011: Relaxation Width and Ionic Conductivity of Supercooled Glycerol at High Pressure Kyaw Zin Win, Narayanan Menon We have measured the dielectric susceptibility of supercooled glycerol from 0.01 Hz to 100 kHz at up to 900 MPa and close to the glass transition temperature. We find that, at a fixed relaxation frequency, the relaxation width increases with pressure. We also establish a relation between isobaric fragility and the width of glycerol and compare it to a correlation \footnote{ R. Bohmer, K. L. Ngai, C. A. Angell, and D. J. Plazek, J. Chem. Phys. 99, 4201 (1993).} between these quantities at 1 atmosphere for a variety of liquids. We find that volume has a much bigger effect than temperature on the changes in the width. We are also for the first time able to study the ionic conductivity as a function of temperature and pressure, and study the Nernst-Einstein relation between the conductivity and the relaxation frequency. [Preview Abstract] |
Tuesday, March 14, 2006 10:12AM - 10:24AM |
G33.00012: Calculation of the configurational entropy for a binary Lennard-Jones fluid below the mode-coupling temperature using a hybrid Monte Carlo method Elijah Flenner, Grzegorz Szamel We developed a novel, hybrid Monte Carlo algorithm that combines configurational bias particle swaps with parallel tempering. We use this new method to simulate a standard model of a glass forming binary mixture above and below the so-called mode-coupling temperature, $T_{MCT}$. We find that an \textit{ansatz} that was used previously to extrapolate thermodynamic quantities to temperatures below $T_{MCT}$ breaks down in the vicinity of the mode-coupling temperature. Thus, previous estimates of the so-called Kauzmann temperature need to be reexamined. Also, we find that the Adam-Gibbs relations $D \propto \exp(-a/TS_c)$ and $\tau \propto \exp(b/TS_c)$, which connect the diffusion coefficient $D$ and the relaxation time $\tau$ with the configurational entropy $S_c$, are valid for all temperatures for which the configurational and vibrational contributions to the free energy decouple. [Preview Abstract] |
Tuesday, March 14, 2006 10:24AM - 10:36AM |
G33.00013: Enhanced Elasticity and Soft Glassy Rheology of a Smectic Liquid Crystal in a Random Porous Environment Dennis Liang, Ranjini Bandyopadhyay, Ralph Colby, James Harden, Robert Leheny We present rheometry studies of the frequency dependent shear modulus, $G^*(\omega)=G'(\omega)+iG''(\omega)$, of the smectic liquid crystal octylcyanobiphenyl (8CB) confined by a colloidal silica gel. When the 8CB is in the isotropic or nematic phase, the shear modulus is independent of temperature and dominated by the elasticity of the gel. With the onset of smectic order, $G'$ grows approximately linearly with decreasing temperature and reaches values that can exceed by more than 3 orders of magnitude the values for pure 8CB. The modulus in the smectic phase possesses a weak power-law dependence on frequency, $G^*(\omega) \sim \omega^\alpha$, with the exponent $\alpha$ approaching zero with increasing gel density. Within the soft glassy rheology model, such a decreasing exponent indicates an approach to a glass transition, which we correlate with the increasing random field coupling between the gel and smectic. We further interpret the enhanced elasticity and weak power law dependence of $G^*(\omega)$ as the result of a dense population of defects in the disordered smectic. [Preview Abstract] |
Tuesday, March 14, 2006 10:36AM - 10:48AM |
G33.00014: Concept of a Bond in Metallic Glasses. Bond's Lifetime in a Supercooled Liquid. MD Modeling. Valentin A. Levashov, Takeshi Egami, Rachel S. Aga, James R. Morris We have done constant volume MD simulations of a one component system of particles interacting via modified Johnson pair potential previously developed for iron. Negative curvature of the potential at the distances beyond potential minimum leads to the clear differentiation between the first and second nearest neighbors observed in the pair distribution function. Therefore a concept of a bond could be introduced. We studied the distribution of bond lifetimes in a liquid state. At high temperatures probability to find a long living bond is very small. As temperature decreases there appear bonds whose lifetime is very long. At the same time, the number of bonds whose lifetime is relatively small remains significant. This could be considered as an indication of the separation of the system into solid-like and liquid-like regions. Obtained bond lifetime distributions will be analyzed from this point of view of the presence in supercooled liquids different kinetic regimes at different temperatures. [Preview Abstract] |
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