4,018 research outputs found
Universality Class of the Reversible-Irreversible Transition in Sheared Suspensions
Collections of non-Brownian particles suspended in a viscous fluid and
subjected to oscillatory shear at very low Reynolds number have recently been
shown to exhibit a remarkable dynamical phase transition separating reversible
from irreversible behaviour as the strain amplitude or volume fraction are
increased. We present a simple model for this phenomenon, based on which we
argue that this transition lies in the universality class of the conserved DP
models or, equivalently, the Manna model. This leads to predictions for the
scaling behaviour of a large number of experimental observables. Non-Brownian
suspensions under oscillatory shear may thus constitute the first experimental
realization of an inactive-active phase transition which is not in the
universality class of conventional directed percolation.Comment: 4 pages, 2 figures, final versio
Simulating mixed-phase Arctic stratus clouds: sensitivity to ice initiation mechanisms
The importance of Arctic mixed-phase clouds on radiation and the Arctic climate is well known. However, the development of mixed-phase cloud parameterization for use in large scale models is limited by lack of both related observations and numerical studies using multidimensional models with advanced microphysics that provide the basis for understanding the relative importance of different microphysical processes that take place in mixed-phase clouds. To improve the representation of mixed-phase cloud processes in the GISS GCM we use the GISS single-column model coupled to a bin resolved microphysics (BRM) scheme that was specially designed to simulate mixed-phase clouds and aerosol-cloud interactions. Using this model with the microphysical measurements obtained from the DOE ARM Mixed-Phase Arctic Cloud Experiment (MPACE) campaign in October 2004 at the North Slope of Alaska, we investigate the effect of ice initiation processes and Bergeron-Findeisen process (BFP) on glaciation time and longevity of single-layer stratiform mixed-phase clouds. We focus on observations taken during 9–10 October, which indicated the presence of a single-layer mixed-phase clouds. We performed several sets of 12-h simulations to examine model sensitivity to different ice initiation mechanisms and evaluate model output (hydrometeors' concentrations, contents, effective radii, precipitation fluxes, and radar reflectivity) against measurements from the MPACE Intensive Observing Period. Overall, the model qualitatively simulates ice crystal concentration and hydrometeors content, but it fails to predict quantitatively the effective radii of ice particles and their vertical profiles. In particular, the ice effective radii are overestimated by at least 50%. However, using the same definition as used for observations, the effective radii simulated and that observed were more comparable. We find that for the single-layer stratiform mixed-phase clouds simulated, process of ice phase initiation due to freezing of supercooled water in both saturated and subsaturated (w.r.t. water) environments is as important as primary ice crystal origination from water vapor. We also find that the BFP is a process mainly responsible for the rates of glaciation of simulated clouds. These glaciation rates cannot be adequately represented by a water-ice saturation adjustment scheme that only depends on temperature and liquid and solid hydrometeors' contents as is widely used in bulk microphysics schemes and are better represented by processes that also account for supersaturation changes as the hydrometeors grow
Surface melting of the vortex lattice
We discuss the effect of an (ab)-surface on the melting transition of the
pancake-vortex lattice in a layered superconductor within a density functional
theory approach. Both discontinuous and continuous surface melting are
predicted for this system, although the latter scenario occupies the major part
of the low-field phase diagram. The formation of a quasi-liquid layer below the
bulk melting temperature inhibits the appearance of a superheated solid phase,
yielding an asymmetric hysteretic behavior which has been seen in experiments.Comment: 4 pages, 3 figure
Observations on the effect of bottom trawling on dislocation of non-edible biota in the Palk Bay and Gulf of Mannar, South East Coast of India
Observations on the dislocated non- edible biota by bottom
trawlers in the Palk Bay and Gulf of Mannar wcre made during 1995- 1998. Data was cullected at trawl landing centres. Rameswaram (Palk Bay) and Pamban (Gulf of Mannar). The average composition of non edible biota to the total trawl discard was 38. Mt and 33.9% at
Rameswaram and Pamban respectively
Critical Point of a Symmetric Vertex Model
We study a symmetric vertex model, that allows 10 vertex configurations, by
use of the corner transfer matrix renormalization group (CTMRG), a variant of
DMRG. The model has a critical point that belongs to the Ising universality
class.Comment: 2 pages, 6 figures, short not
Density functional theory of vortex lattice melting in layered superconductors: a mean-field--substrate approach
We study the melting of the pancake vortex lattice in a layered
superconductor in the limit of vanishing Josephson coupling. Our approach
combines the methodology of a recently proposed mean-field substrate model for
such systems with the classical density functional theory of freezing. We
derive a free-energy functional in terms of a scalar order-parameter profile
and use it to derive a simple formula describing the temperature dependence of
the melting field. Our theoretical predictions are in good agreement with
simulation data. The theoretical framework proposed is thermodynamically
consistent and thus capable of describing the negative magnetization jump
obtained in experiments. Such consistency is demonstrated by showing the
equivalence of our expression for the density discontinuity at the transition
with the corresponding Clausius-Clapeyron relation.Comment: 11 pages, 4 figure
Surface Melting of the Vortex Lattice in Layered Superconductors: Density Functional Theory
We study the effects of an -surface on the vortex-solid to vortex-liquid
transition in layered superconductors in the limit of vanishing inter-layer
Josephson coupling. We derive the interaction between pancake vortices in a
semi-infinite sample and adapt the density functional theory of freezing to
this system. We obtain an effective one-component order-parameter theory which
can be used to describe the effects of the surface on vortex-lattice melting.
Due to the absence of protecting layers in the neighbourhood of the surface,
the vortex lattice formed near the surface is more susceptible to thermal
fluctuations. Depending on the value of the magnetic field, we predict either a
continuous or a discontinuous surface melting transition. For intermediate
values of the magnetic field, the surface melts continuously, assisting the
formation of the liquid phase and suppressing hysteresis above the melting
transition, a prediction consistent with experimental results. For very low and
very high magnetic fields, the surface melts discontinuously. The two different
surface melting scenarios are separated by two surface multicritical points,
which we locate on the melting line.Comment: 16 pages, 12 figure
Triangle percolation in mean field random graphs -- with PDE
We apply a PDE-based method to deduce the critical time and the size of the
giant component of the ``triangle percolation'' on the Erd\H{o}s-R\'enyi random
graph process investigated by Palla, Der\'enyi and VicsekComment: Summary of the changes made: We have changed a remark about k-clique
percolation in the first paragraph. Two new paragraphs are inserted after
equation (4.4) with two applications of the equation. We have changed the
names of some variables in our formula
Persistence in One-dimensional Ising Models with Parallel Dynamics
We study persistence in one-dimensional ferromagnetic and anti-ferromagnetic
nearest-neighbor Ising models with parallel dynamics. The probability P(t) that
a given spin has not flipped up to time t, when the system evolves from an
initial random configuration, decays as P(t) \sim 1/t^theta_p with theta_p
\simeq 0.75 numerically. A mapping to the dynamics of two decoupled A+A \to 0
models yields theta_p = 3/4 exactly. A finite size scaling analysis clarifies
the nature of dynamical scaling in the distribution of persistent sites
obtained under this dynamics.Comment: 5 pages Latex file, 3 postscript figures, to appear in Phys Rev.
Probing Disordered Substrates by Imaging the Adsorbate in its Fluid Phase
Several recent imaging experiments access the equilibrium density profiles of
interacting particles confined to a two-dimensional substrate. When these
particles are in a fluid phase, we show that such data yields precise
information regarding substrate disorder as reflected in one-point functions
and two-point correlations of the fluid. Using Monte Carlo simulations and
replica generalizations of liquid state theories, we extract unusual two-point
correlations of time-averaged density inhomogeneities induced by disorder.
Distribution functions such as these have not hitherto been measured but should
be experimentally accessible.Comment: 10 pages revtex 4 figure
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