338 research outputs found
Low temperature vortex phase diagram of Bi2Sr2CaCu2O8 : a magnetic penetration depth study
We report measurements of the magnetic penetration depth \lambda_m(T) in the
presence of a DC magnetic field in optimally doped BSCCO-2212 single crystals.
Warming, after magnetic field is applied to a zero-field cooled sample, results
in a non-monotonic \lambda_m(T), which does not coincide with a curve obtained
upon field cooling, thus exhibiting a hysteretic behaviour. We discuss the
possible relation of our results to the vortex decoupling, unbinding, and
dimensional crossover.Comment: M2S-HTSC-V
Shear bands in granular flow through a mixing length model
We discuss the advantages and results of using a mixing-length, compressible
model to account for shear banding behaviour in granular flow. We formulate a
general approach based on two function of the solid fraction to be determined.
Studying the vertical chute flow, we show that shear band thickness is always
independent from flowrate in the quasistatic limit, for Coulomb wall boundary
conditions. The effect of bin width is addressed using the functions developed
by Pouliquen and coworkers, predicting a linear dependence of shear band
thickness by channel width, while literature reports contrasting data. We also
discuss the influence of wall roughness on shear bands. Through a Coulomb wall
friction criterion we show that our model correctly predicts the effect of
increasing wall roughness on the thickness of shear bands. Then a simple
mixing-length approach to steady granular flows can be useful and
representative of a number of original features of granular flow.Comment: submitted to EP
Domain Wall Depinning in Random Media by AC Fields
The viscous motion of an interface driven by an ac external field of
frequency omega_0 in a random medium is considered here for the first time. The
velocity exhibits a smeared depinning transition showing a double hysteresis
which is absent in the adiabatic case omega_0 --> 0. Using scaling arguments
and an approximate renormalization group calculation we explain the main
characteristics of the hysteresis loop. In the low frequency limit these can be
expressed in terms of the depinning threshold and the critical exponents of the
adiabatic case.Comment: 4 pages, 3 figure
Melting of Flux Lines in an Alternating Parallel Current
We use a Langevin equation to examine the dynamics and fluctuations of a flux
line (FL) in the presence of an {\it alternating longitudinal current}
. The magnus and dissipative forces are equated to those
resulting from line tension, confinement in a harmonic cage by neighboring FLs,
parallel current, and noise. The resulting mean-square FL fluctuations are
calculated {\it exactly}, and a Lindemann criterion is then used to obtain a
nonequilibrium `phase diagram' as a function of the magnitude and frequency of
. For zero frequency, the melting temperature of the
mixed phase (a lattice, or the putative "Bose" or "Bragg Glass") vanishes at a
limiting current. However, for any finite frequency, there is a non-zero
melting temperature.Comment: 5 pages, 1 figur
Facet Formation in the Negative Quenched Kardar-Parisi-Zhang Equation
The quenched Kardar-Parisi-Zhang (QKPZ) equation with negative non-linear
term shows a first order pinning-depinning (PD) transition as the driving force
is varied. We study the substrate-tilt dependence of the dynamic transition
properties in 1+1 dimensions. At the PD transition, the pinned surfaces form a
facet with a characteristic slope as long as the substrate-tilt is
less than . When , the transition is discontinuous and the critical
value of the driving force is independent of , while the transition
is continuous and increases with when . We explain these
features from a pinning mechanism involving a localized pinning center and the
self-organized facet formation.Comment: 4 pages, source TeX file and 7 PS figures are tarred and compressed
via uufile
Methyl 2,2-bis(2,4-dinitrophenyl)ethanoate
In the title compound, C15H10N4O10, the dihedral angle between the aromatic rings is 89.05 (16)°. One O atom of one of the nitro groups is disordered over two sites in a 0.70:0.30 ratio. In the crystal, the molecules are linked by weak C—H⋯O interactions
Phase ordering and roughening on growing films
We study the interplay between surface roughening and phase separation during
the growth of binary films. Already in 1+1 dimension, we find a variety of
different scaling behaviors depending on how the two phenomena are coupled. In
the most interesting case, related to the advection of a passive scalar in a
velocity field, nontrivial scaling exponents are obtained in simulations.Comment: 4 pages latex, 6 figure
Separation quality of a geometric ratchet
We consider an experimentally relevant model of a geometric ratchet in which
particles undergo drift and diffusive motion in a two-dimensional periodic
array of obstacles, and which is used for the continuous separation of
particles subject to different forces. The macroscopic drift velocity and
diffusion tensor are calculated by a Monte-Carlo simulation and by a
master-equation approach, using the correponding microscopic quantities and the
shape of the obstacles as input. We define a measure of separation quality and
investigate its dependence on the applied force and the shape of the obstacles
Roughness of Interfacial Crack Front: Correlated Percolation in the Damage Zone
We show that the roughness exponent zeta of an in-plane crack front slowly
propagating along a heterogeneous interface embeded in a elastic body, is in
full agreement with a correlated percolation problem in a linear gradient. We
obtain zeta=nu/(1+nu) where nu is the correlation length critical exponent. We
develop an elastic brittle model based on both the 3D Green function in an
elastic half-space and a discrete interface of brittle fibers and find
numerically that nu=1.5, We conjecture it to be 3/2. This yields zeta=3/5. We
also obtain by direct numerical simulations zeta=0.6 in excellent agreement
with our prediction. This modelling is for the first time in close agreement
with experimental observations.Comment: 4 pages RevTeX
On dual Rickart modules and weak dual Rickart modules
Let R be a ring. A right R-module M is called d-Rickart if for every endomorphism φ of M, φ(M) is a direct summand of M and it is called wd-Rickart if for every nonzero endomorphism φ of M, φ(M) contains a nonzero direct summand of M. We begin with some basic properties of (w)d-Rickart modules. Then we study direct sums of (w)d-Rickart modules and the class of rings for which every finitely generated module is (w)d-Rickart. We conclude by some structure results
- …