6,056 research outputs found
2D and 3D Dense-Fluid Shear Flows via Nonequilibrium Molecular Dynamics. Comparison of Time-and-Space-Averaged Tensor Temperature and Normal Stresses from Doll's, Sllod, and Boundary-Driven Shear Algorithms
Homogeneous shear flows (with constant strainrate du/dy) are generated with
the Doll's and Sllod algorithms and compared to corresponding inhomogeneous
boundary-driven flows. We use one-, two-, and three-dimensional smooth-particle
weight functions for computing instantaneous spatial averages. The nonlinear
stress differences are small, but significant, in both two and three space
dimensions. In homogeneous systems the sign and magnitude of the shearplane
stress difference, P(xx) - P(yy), depend on both the thermostat type and the
chosen shearflow algorithm. The Doll's and Sllod algorithms predict opposite
signs for this stress difference, with the Sllod approach definitely wrong, but
somewhat closer to the (boundary-driven) truth. Neither of the homogeneous
shear algorithms predicts the correct ordering of the kinetic temperatures,
T(xx) > T(zz) > T(yy).Comment: 34 pages with 12 figures, under consideration by Physical Review
Microscopic and Macroscopic Stress with Gravitational and Rotational Forces
Many recent papers have questioned Irving and Kirkwood's atomistic expression
for stress. In Irving and Kirkwood's approach both interatomic forces and
atomic velocities contribute to stress. It is the velocity-dependent part that
has been disputed. To help clarify this situation we investigate [1] a fluid in
a gravitational field and [2] a steadily rotating solid. For both problems we
choose conditions where the two stress contributions, potential and kinetic,
are significant. The analytic force-balance solutions of both these problems
agree very well with a smooth-particle interpretation of the atomistic
Irving-Kirkwood stress tensor.Comment: Fifteen pages with seven figures, revised according to referees'
suggestions at Physical Review E. See also Liu and Qiu's arXiv contribution
0810.080
Phase-change materials handbook
Handbook describes relationship between phase-change materials and more conventional thermal control techniques and discusses materials' space and terrestrial applications. Material properties of most promising phase-change materials and purposes and uses of metallic filler materials in phase-change material composites are provided
Remarks on NonHamiltonian Statistical Mechanics: Lyapunov Exponents and Phase-Space Dimensionality Loss
The dissipation associated with nonequilibrium flow processes is reflected by
the formation of strange attractor distributions in phase space. The
information dimension of these attractors is less than that of the equilibrium
phase space, corresponding to the extreme rarity of nonequilibrium states. Here
we take advantage of a simple model for heat conduction to demonstrate that the
nonequilibrium dimensionality loss can definitely exceed the number of
phase-space dimensions required to thermostat an otherwise Hamiltonian system.Comment: 5 pages, 2 figures, minor typos correcte
An automatic lightning detection and photographic system
Conventional 35-mm camera is activated by an electronic signal every time lightning strikes in general vicinity. Electronic circuit detects lightning by means of antenna which picks up atmospheric radio disturbances. Camera is equipped with fish-eye lense, automatic shutter advance, and small 24-hour clock to indicate time when exposures are made
Nonlinear Stresses and Temperatures in Transient Adiabatic and Shear Flows via Nonequilibrium Molecular Dynamics -- Three Definitions of Temperature
We compare nonlinear stresses and temperatures for adiabatic shear flows,
using up to 262,144 particles, with those from corresponding homogeneous and
inhomogeneous flows. Two varieties of kinetic temperature tensors are compared
to the configurational temperatures. This comparison leads to an improved form
for the local and instantaneous smooth-particle averaged stream velocity and to
a recognition of rotational contributions to the configurational temperature.Comment: 16 pages, 8 figures, stimulated by Denis Evans' comments on Hoover et
alii, Physical Review E 78, 046701 (2008). Augmented 30 January 2009 in
response to referees' comments at Physical Review
Exact Wave Solutions to 6D Gauged Chiral Supergravity
We describe a broad class of time-dependent exact wave solutions to 6D gauged
chiral supergravity with two compact dimensions. These 6D solutions are
nontrivial warped generalizations of 4D pp-waves and Kundt class solutions and
describe how a broad class of previously-static compactifications from 6D to 4D
(sourced by two 3-branes) respond to waves moving along one of the
uncompactified directions. Because our methods are generally applicable to any
higher dimensional supergravity they are likely to be of use for finding the
supergravity limit of time-dependent solutions in string theory. The 6D
solutions are interesting in their own right, describing 6D shock waves induced
by high energy particles on the branes, and as descriptions of the near-brane
limit of the transient wavefront arising from a local bubble-nucleation event
on one of the branes, such as might occur if a tension-changing phase
transition were to occur.Comment: 22 pages, 1 figure. Minor clarifications added. Accepted in JHE
Nose-Hoover dynamics for coherent states
The popular method of Nose and Hoover to create canonically distributed
positions and momenta in classical molecular dynamics simulations is
generalized to a genuine quantum system of infinite dimensionality. We show
that for the quantum harmonic oscillator, the equations of motion in terms of
coherent states can easily be modified in an analogous manner to mimic the
coupling of the system to a thermal bath and create a quantum canonical
ensemble. Possible applications to more complex systems, especially interacting
Fermion systems, are proposed.Comment: 13 pages, 3 figure
Lyapunov instability for a periodic Lorentz gas thermostated by deterministic scattering
In recent work a deterministic and time-reversible boundary thermostat called
thermostating by deterministic scattering has been introduced for the periodic
Lorentz gas [Phys. Rev. Lett. {\bf 84}, 4268 (2000)]. Here we assess the
nonlinear properties of this new dynamical system by numerically calculating
its Lyapunov exponents. Based on a revised method for computing Lyapunov
exponents, which employs periodic orthonormalization with a constraint, we
present results for the Lyapunov exponents and related quantities in
equilibrium and nonequilibrium. Finally, we check whether we obtain the same
relations between quantities characterizing the microscopic chaotic dynamics
and quantities characterizing macroscopic transport as obtained for
conventional deterministic and time-reversible bulk thermostats.Comment: 18 pages (revtex), 7 figures (postscript
Configurational temperature control for atomic and molecular systems
A new configurational temperature thermostat suitable for molecules with holonomic constraints is derived. This thermostat has a simple set of motion equations, can generate the canonical ensemble in both position and momentum space, acts homogeneously through the spatial
coordinates, and does not intrinsically violate the constraints. Our new configurational thermostat is
closely related to the kinetic temperature Nosé-Hoover thermostat with feedback coupled to the position variables via a term proportional to the net molecular force. We validate the thermostat by comparing equilibrium static and dynamic quantities for a fluid of n-decane molecules under
configurational and kinetic temperature control. Practical aspects concerning the implementation of the new thermostat in a molecular dynamics code and the potential applications are discussed
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