808 research outputs found
Internal Stress in a Model Elasto-Plastic Fluid
Plastic materials can carry memory of past mechanical treatment in the form
of internal stress. We introduce a natural definition of the vorticity of
internal stress in a simple two-dimensional model of elasto-plastic fluids,
which generates the internal stress. We demonstrate how the internal stress is
induced under external loading, and how the presence of the internal stress
modifies the plastic behavior.Comment: 4 pages, 3 figure
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Simulations of hydrodynamic interactions among immersed particles in stokes flow using a massively parallel computer
In this paper, a massively parallel implementation of the boundary element method to study particle transport in Stokes flow is discussed. The numerical algorithm couples the quasistatic Stokes equations for the fluid with kinematic and equilibrium equations for the particles. The formation and assembly of the discretized boundary element equations is based on the torus-wrap mapping as opposed to the more traditional row- or column-wrap mappings. The equation set is solved using a block Jacobi iteration method. Results are shown for an example application problem, which requires solving a dense system of 6240 equations more than 1200 times
Simulated Annealing for Topological Solitons
The search for solutions of field theories allowing for topological solitons
requires that we find the field configuration with the lowest energy in a given
sector of topological charge. The standard approach is based on the numerical
solution of the static Euler-Lagrange differential equation following from the
field energy. As an alternative, we propose to use a simulated annealing
algorithm to minimize the energy functional directly. We have applied simulated
annealing to several nonlinear classical field theories: the sine-Gordon model
in one dimension, the baby Skyrme model in two dimensions and the nuclear
Skyrme model in three dimensions. We describe in detail the implementation of
the simulated annealing algorithm, present our results and get independent
confirmation of the studies which have used standard minimization techniques.Comment: 31 pages, LaTeX, better quality pics at
http://www.phy.umist.ac.uk/~weidig/Simulated_Annealing/, updated for
publicatio
Light Curves and Period Changes of Type II Cepheids in the Globular Clusters M3 and M5
Light curves in the B, V, and I_c passbands have been obtained for the type
II Cepheids V154 in M3 and V42 and V84 in M5. Alternating cycle behavior,
similar to that seen among RV Tauri variables, is confirmed for V84. Old and
new observations, spanning more than a century, show that V154 has increased in
period while V42 has decreased in period. V84, on the other hand, has shown
large, erratic changes in period that do not appear to reflect the long term
evolution of V84 through the HR diagram.Comment: 28 pages, 12 figure
α4β1-dependent adhesion strengthening under mechanical strain is regulated by paxillin association with the α4-cytoplasmic domain
The capacity of integrins to mediate adhesiveness is modulated by their cytoplasmic associations. In this study, we describe a novel mechanism by which α4-integrin adhesiveness is regulated by the cytoskeletal adaptor paxillin. A mutation of the α4 tail that disrupts paxillin binding, α4(Y991A), reduced talin association to the α4β1 heterodimer, impaired integrin anchorage to the cytoskeleton, and suppressed α4β1-dependent capture and adhesion strengthening of Jurkat T cells to VCAM-1 under shear stress. The mutant retained intrinsic avidity to soluble or bead-immobilized VCAM-1, supported normal cell spreading at short-lived contacts, had normal α4-microvillar distribution, and responded to inside-out signals. This is the first demonstration that cytoskeletal anchorage of an integrin enhances the mechanical stability of its adhesive bonds under strain and, thereby, promotes its ability to mediate leukocyte adhesion under physiological shear stress conditions
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