5,963 research outputs found
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
POWER OUTPUT DURING THE 1ST AND 2ND PULL PHASES IN THE SNATCH BY WOMEN WEIGHTLIFTERS
The purpose of this study was to compare the power outputs of the 1st, 2nd, and total pulls in the snatch lift for women competing in the 1999 United States national championships. The performance of ten lifters was recorded and analyzed using a Peak5 2D Motion Analysis system. The power output values for the 1st, 2nd, and total pulls ranged from 604.41 W to 2329.45 W, 756.45 W to 4532.75 W, and 702.39 W to 1909.67 W, respectively. These lifters demonstrated statistically significant differences (p < 0.05) during each phase of the snatch pull, and total power output values were comparable to values previously reported (Garhammer, 1991). Knowledge of the power output during each phase of the pull may help athletes to fully refine the training leading to competition
Kicking the Rugby Ball: Perturbations of 6D Gauged Chiral Supergravity
We analyze the axially-symmetric scalar perturbations of 6D chiral gauged
supergravity compactified on the general warped geometries in the presence of
two source branes. We find all of the conical geometries are marginally stable
for normalizable perturbations (in disagreement with some recent calculations)
and the nonconical for regular perturbations, even though none of them are
supersymmetric (apart from the trivial Salam-Sezgin solution, for which there
are no source branes). The marginal direction is the one whose presence is
required by the classical scaling property of the field equations, and all
other modes have positive squared mass. In the special case of the conical
solutions, including (but not restricted to) the unwarped `rugby-ball'
solutions, we find closed-form expressions for the mode functions in terms of
Legendre and Hypergeometric functions. In so doing we show how to match the
asymptotic near-brane form for the solution to the physics of the source
branes, and thereby how to physically interpret perturbations which can be
singular at the brane positions.Comment: 21 pages + appendices, references adde
HORIZONTAL BAR DISPLACEMENTS OF WOMEN WEIGHTLIFTERS DURING THE SNATCH
The purpose of this study was to analyze the horizontal bar displacement of women weightlifters while performing the snatch. Thirty lifts performed at the 1999 United States National Weightlifting Championships were recorded and analyzed using a Peak5 2D Motion Analysis System. Three key displacement values were obtained for each lift: first pull, second pull, and just after peak height. The magnitude of bar displacement ranged from –3 to 8cm, for the first pull –14 to 14cm, for the second pull, and –3 to 21cm just after peak height is attained. Lifters did not display the horizontal displacement pattern that is described for men in the current literature
KINEMATIC ANALYSIS OF THE BAR DROP DISPLACEMENT IN THE SNATCH
The purpose of this study was to analyze drop-under time, maximum vertical barbell displacement, vertical barbell drop and maximum vertical barbell velocity during the 1999 United States National Weightlifting Championships. The performance of ten female lifters performing 30 lifts was recorded and analyzed using a Peak5 2D Motion Analysis System. These variables were observed for lifters who successfully performed multiple lifts to determine the trends that take place as the load of the barbell increases. Average maximum vertical barbell displacement was 101.5(cm) with a SD of 7.4. Average vertical barbell drop displacement was 20.8(cm) with a SD of 5.9. Average maximum vertical velocity of the barbell was 164.8(cm/s) with a SD of 19.1. Average drop-under time was .47(s) with a SD of .09
Scaling Solutions to 6D Gauged Chiral Supergravity
We construct explicitly time-dependent exact solutions to the field equations
of 6D gauged chiral supergravity, compactified to 4D in the presence of up to
two 3-branes situated within the extra dimensions. The solutions we find are
scaling solutions, and are plausibly attractors which represent the late-time
evolution of a broad class of initial conditions. By matching their near-brane
boundary conditions to physical brane properties we argue that these solutions
(together with the known maximally-symmetric solutions and a new class of
non-Lorentz-invariant static solutions, which we also present here) describe
the bulk geometry between a pair of 3-branes with non-trivial on-brane
equations of state.Comment: Contribution to the New Journal of Physics focus issue on Dark
Energy; 28 page
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
Miniature Triaxial Shear Testing of a Quaternary Ammonium Chloride Stabilized Loess
Compressive bearing characteristics of a stabilized soil may be determined by several methods, in each of which the soil specimens are loaded to failure. The resistance to failure of the stabilized soil depends on the maximum cohesion and internal friction between the soil particles after compaction. The Triaxial Shear Test is employed to provide a measure of these two soil properties. In most highway base and sub-base design problems, or in any similar soil foundation study, the capacity of the underlying soil to withstand and support vertical and/or lateral forces is directly related to the cohesive and frictional forces present in the soil mass. The purpose of the investigation was to determine the effect of a quaternary ammonium chloride soil stabilizing agent on the cohesive and frictional properties of a sample of western Iowa loess. A miniature triaxial shear testing apparatus, developed by the Iowa Engineering Experiment Station Soil Research Laboratory, was used for the investigation
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