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Search Publications by: Stephen Langer (Fed)

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Displaying 26 - 50 of 54

Velocity Fluctuations in a Steadily Sheared Model Foam

June 18, 2003
Author(s)
I K. Ono, S Tewari, Stephen A. Langer, A J. Liu
Numerical simulations are conducted to calculate velocity fluctuations in a simple two-dimensional model of foam under steady shear. The width of the velocity distribution increases sublinearly with the shear rate, indicating that velocity fluctuations are

Microstructure-Based Simulation of Thermomechanical Behavior of Composite Materials by Object-Oriented Finite Element Analysis

December 1, 2002
Author(s)
N Chawla, B V. Patel, M Koopman, K K. Chawla, R Saha, B R. Patterson, Lin-Sien H. Lum, Stephen A. Langer
While it is well recognized that microstructure controls the physical and mechanical properties of a material, the complexity of the microstructure often makes it difficult to simulate by analytical or numerical techniques. In this paper we present a

Effective Temperatures of a Driven System Near Jamming

August 26, 2002
Author(s)
I K. Ono, C S. O'Hern, Stephen A. Langer, A J. Liu, S R. Nagel, D J. Durian
Fluctuations in a model of a sheared, zero-temperature foam are studied numerically. Five different quantities that reduce to the true temperature in an equilibrium thermal system are calculated. All five have the same shear-rate dependence, and three have

Random Packings of Frictionless Particles

February 18, 2002
Author(s)
C S. O'Hern, Stephen A. Langer, A J. Liu, S R. Nagel
We study random packings of frictionless particles at T=0. The packing fraction where the pressure becomes nonzero is the same as the jamming threshold, where the static shear modulus becomes nonzero. The distribution of threshold packing fractions narrows

OOF: An Image-Based Finite Element Analysis of Material Microstructure

June 1, 2001
Author(s)
Stephen A. Langer, W Carter, Lin-Sien H. Lum
The determination of macroscopic properties of a material given its microscopic structure is of fundamental importance to materials science. We present an overview of two public domain programs which jointly predict macroscopic behavior, starting from an

Force Distributions Near the Jamming and Glass Transitions

January 1, 2001
Author(s)
C S. O'Hern, Stephen A. Langer, A J. Liu, S R. Nagel
We measure the distributions of interparticle normal forces P(F) near the glass transition in supercooled liquids and near the jamming transition in foams and compare them to those obtained in recent experiments on static granular packings. We find that

Sheared Foam as a Supercooled Liquid?

January 1, 2000
Author(s)
Stephen A. Langer, A J. Liu
We conduct numerical simulations on a simple model of a two-dimensional steady-state sheared foam, and define a quantity Γ that measures pressure fluctuations in the constant-area system. This quantity reduces to the temperature in an equilibrium system

Statistics of Shear-Induced Rearrangements in a Two-Dimensional Model Foam

October 1, 1999
Author(s)
S Tewari, D Schiemann, D J. Durian, C M. Knobler, Stephen A. Langer, A J. Liu
Under steady shear, a foam relaxes stress through intermittent rearrangements of bubbles accompanied by sudden drops in the stored elastic energy. We use a simple model of foam that incorporates both elasticity and dissipation to study the statistics of

Effect of Ordering on Spinodal Decomposition of Liquid-Crystal/Polymer Mixtures

January 1, 1999
Author(s)
A M. Lapena, S C. Glotzer, Stephen A. Langer, A J. Liu
Partially phase-separated liquid-crystal/polymer dispersions display highly fibrillar domain morphologies that are dramatically different from the typical structure found in isotropic mixtures. To explain this, we explore the coupling between phase

The OOF Manual: Version 1.0

November 1, 1998
Author(s)
W C. Carter, Stephen A. Langer, Lin-Sien H. Lum
OOF and PPM200F are programs developed at NIST to investigate the properties of microstructures. The user starts with an image of a real or simulated microstructure, assigns material properties to the features in the image, and performs virtual experiments