Measurement of Isothermal Pressure of Lattice Gas by Random Walk

We present a computational random walk method of measuring the isothermal pressure of the lattice gas with and without the excluded volume interaction. The method is based on the discretization of the exact thermodynamic relation for the pressure. The simulation results are in excellent agreement with the theoretical predictions.Comment: 10 Pages, 2 Figures, Teaching Material. To Appear in Physica

Stability of Elastic Glass Phases in Random Field XY Magnets and Vortex Lattices in Type II Superconductors

A description of a dislocation-free elastic glass phase in terms of domain walls is developed and used as the basis of a renormalization group analysis of the energetics of dislocation loops added to the system. It is found that even after optimizing over possible paths of large dislocation loops, their energy is still very likely to be positive when the dislocation core energy is large. This implies the existence of an equilibrium elastic glass phase in three dimensional random field X-Y magnets, and a dislocation free, bond-orientationally ordered ``Bragg glass'' phase of vortices in dirty Type II superconductors.Comment: 12 pages, Revtex, no figures, submitted to Phys Rev Letter

Condensation of Hard Spheres Under Gravity

Starting from Enskog equation of hard spheres of mass m and diameter D under the gravity g, we first derive the exact equation of motion for the equilibrium density profile at a temperature T and examine its solutions via the gradient expansion. The solutions exist only when \beta\mu \le \mu_o \approx 21.756 in 2 dimensions and \mu_o\approx 15.299 in 3 dimensions, where \mu is the dimensionless initial layer thickness and \beta=mgD/T. When this inequality breaks down, a fraction of particles condense from the bottom up to the Fermi surface.Comment: 9 pages, one figur

Taphonomic Interpretation of Enamel-Less Teeth in the Shotgun Local Fauna (Paleocene, Wyoming)

259-275http://deepblue.lib.umich.edu/bitstream/2027.42/48503/2/ID354.pd

Underwater carcass storage and processing of marrow, brains, and dental pulp: evidence for the role of proboscideans in human subsistence

Skeletal material of Late Pleistocene proboscideans in the North American Great Lakes region is often preserved in fine-grained, organic-rich sediment characteristic of small lakes and wetlands. Patterns of spatial distribution and articulation of bones often suggest that carcass parts were emplaced as multiple clusters of anatomically disparate butch- ery units, each including multiple bones. Clusters of skeletal material are sometimes associated with features that may have served as anchors intend- ed to keep carcass parts tethered to a selected lo- cation within a pond, despite gas accumulation within soft tissues. One type of anchor consists of lithic material ranging from sand to gravel, where these sediments appear to have occupied a cylin- drical container that was probably a length of in- testine from the butchered animal. One site with well-documented “clastic anchors” also preserved two “marking posts” (an inverted main axis of spruce and an unidentified lateral axis) extending into sediment below the bone horizon but trun- cated by decomposition at the bone horizon. Each post probably extended to the pond surface at the time of emplacement and would have been visi- ble from shore. These features suggest a practice of securing, concealing, and returning to utilize groups of nutritionally significant carcass parts stored underwater. Ethnographic parallels and ra- tionales (extended time and reduced uncertainty of resource access) for this behavior are known, and experimental studies of subaqueous meat storage using deer heads, legs of lamb, and an adult draft horse show it to be effective over timescales rang- ing from months to years.The symposium and the volume "Human-elephant interactions: from past to present" were funded by the Volkswagen Foundation

Mode of Preservation of the Shotgun Local Fauna (Paleocene, Wyoming) and Its Implication for the Taphonomy of a Microvertebrate Concentration

247-257http://deepblue.lib.umich.edu/bitstream/2027.42/48502/2/ID353.pd

Distributions of gaps and end-to-end correlations in random transverse-field Ising spin chains

A previously introduced real space renormalization-group treatment of the random transverse-field Ising spin chain is extended to provide detailed information on the distribution of the energy gap and the end-to-end correlation function for long chains with free boundary conditions. Numerical data, using the mapping of the problem to free fermions, are found to be in good agreement with the analytic finite size scaling predictions.Comment: 12 pages revtex, 10 figures, submitted to Phys. Rev.

Depinning with dynamic stress overshoots: A hybrid of critical and pseudohysteretic behavior

A model of an elastic manifold driven through a random medium by an applied force F is studied focussing on the effects of inertia and elastic waves, in particular {\it stress overshoots} in which motion of one segment of the manifold causes a temporary stress on its neighboring segments in addition to the static stress. Such stress overshoots decrease the critical force for depinning and make the depinning transition hysteretic. We find that the steady state velocity of the moving phase is nevertheless history independent and the critical behavior as the force is decreased is in the same universality class as in the absence of stress overshoots: the dissipative limit which has been studied analytically. To reach this conclusion, finite-size scaling analyses of a variety of quantities have been supplemented by heuristic arguments. If the force is increased slowly from zero, the spectrum of avalanche sizes that occurs appears to be quite different from the dissipative limit. After stopping from the moving phase, the restarting involves both fractal and bubble-like nucleation. Hysteresis loops can be understood in terms of a depletion layer caused by the stress overshoots, but surprisingly, in the limit of very large samples the hysteresis loops vanish. We argue that, although there can be striking differences over a wide range of length scales, the universality class governing this pseudohysteresis is again that of the dissipative limit. Consequences of this picture for the statistics and dynamics of earthquakes on geological faults are briefly discussed.Comment: 43 pages, 57 figures (yes, that's a five followed by a seven), revte

Nonequilibrium dynamics of random field Ising spin chains: exact results via real space RG

Non-equilibrium dynamics of classical random Ising spin chains are studied using asymptotically exact real space renormalization group. Specifically the random field Ising model with and without an applied field (and the Ising spin glass (SG) in a field), in the universal regime of a large Imry Ma length so that coarsening of domains after a quench occurs over large scales. Two types of domain walls diffuse in opposite Sinai random potentials and mutually annihilate. The domain walls converge rapidly to a set of system-specific time-dependent positions {\it independent of the initial conditions}. We obtain the time dependent energy, magnetization and domain size distribution (statistically independent). The equilibrium limits agree with known exact results. We obtain exact scaling forms for two-point equal time correlation and two-time autocorrelations. We also compute the persistence properties of a single spin, of local magnetization, and of domains. The analogous quantities for the spin glass are obtained. We compute the two-point two-time correlation which can be measured by experiments on spin-glass like systems. Thermal fluctuations are found to be dominated by rare events; all moments of truncated correlations are computed. The response to a small field applied after waiting time $t_w$, as measured in aging experiments, and the fluctuation-dissipation ratio $X(t,t_w)$ are computed. For $(t-t_w) \sim t_w^{\hat{\alpha}}$, $\hat{\alpha} <1$, it equals its equilibrium value X=1, though time translational invariance fails. It exhibits for $t-t_w \sim t_w$ aging regime with non-trivial $X=X(t/t_w) \neq 1$, different from mean field.Comment: 55 pages, 9 figures, revte

Spin Reduction Transition in Spin-3/2 Random Heisenberg Chains

Random spin-3/2 antiferromagnetic Heisenberg chains are investigated using an asymptotically exact renormalization group. Randomness is found to induce a quantum phase transition between two random-singlet phases. In the strong randomness phase the effective spins at low energies are S_eff=3/2, while in the weak randomness phase the effective spins are S_eff=1/2. Separating them is a quantum critical point near which there is a non-trivial mixture of S=1/2, S=1, and S=3/2 effective spins at low temperatures.Comment: 4 pages, 3 figures. Typos correcte