71,870 research outputs found
Phase Diagrams for Deformable Toroidal and Spherical Surfaces with Intrinsic Orientational Order
A theoretical study of toroidal membranes with various degrees of intrinsic
orientational order is presented at mean-field level. The study uses a simple
Ginzburg-Landau style free energy functional, which gives rise to a rich
variety of physics and reveals some unusual ordered states. The system is found
to exhibit many different phases with continuous and first order phase
transitions, and phenomena including spontaneous symmetry breaking, ground
states with nodes and the formation of vortex-antivortex quartets. Transitions
between toroidal phases with different configurations of the order parameter
and different aspect ratios are plotted as functions of the thermodynamic
parameters. Regions of the phase diagrams in which spherical vesicles form are
also shown.Comment: 40, revtex (with epsf), M/C.TH.94/2
Transforming from time to frequency without artefacts
I review a simple method, recently introduced to convert rheological
compliance measurements into frequency-dependent moduli. New experimental data
are presented, and the scientific implications of various data conversion
methods discussed
Factorised steady states for multi-species mass transfer models
A general class of mass transport models with Q species of conserved mass is
considered. The models are defined on a lattice with parallel discrete time
update rules. For one-dimensional, totally asymmetric dynamics we derive
necessary and sufficient conditions on the mass transfer dynamics under which
the steady state factorises. We generalise the model to mass transfer on
arbitrary lattices and present sufficient conditions for factorisation. In both
cases, explicit results for random sequential update and continuous time limits
are given.Comment: 11 page
Product Measure Steady States of Generalized Zero Range Processes
We establish necessary and sufficient conditions for the existence of
factorizable steady states of the Generalized Zero Range Process. This process
allows transitions from a site to a site involving multiple particles
with rates depending on the content of the site , the direction of
movement, and the number of particles moving. We also show the sufficiency of a
similar condition for the continuous time Mass Transport Process, where the
mass at each site and the amount transferred in each transition are continuous
variables; we conjecture that this is also a necessary condition.Comment: 9 pages, LaTeX with IOP style files. v2 has minor corrections; v3 has
been rewritten for greater clarit
Soft core fluid in a quenched matrix of soft core particles: A mobile mixture in a model gel
We present a density-functional study of a binary phase-separating mixture of
soft core particles immersed in a random matrix of quenched soft core particles
of larger size. This is a model for a binary polymer mixture immersed in a
crosslinked rigid polymer network. Using the replica `trick' for
quenched-annealed mixtures we derive an explicit density functional theory that
treats the quenched species on the level of its one-body density distribution.
The relation to a set of effective external potentials acting on the annealed
components is discussed. We relate matrix-induced condensation in bulk to the
behaviour of the mixture around a single large particle. The interfacial
properties of the binary mixture at a surface of the quenched matrix display a
rich interplay between capillary condensation inside the bulk matrix and
wetting phenomena at the matrix surface.Comment: 20 pages, 5 figures. Accepted for Phys. Rev.
Perturbative polydispersity: Phase equilibria of near-monodisperse systems
The conditions of multi-phase equilibrium are solved for generic polydisperse
systems. The case of multiple polydispersity is treated, where several
properties (e.g. size, charge, shape) simultaneously vary from one particle to
another. By developing a perturbative expansion in the width of the
distribution of constituent species, it is possible to calculate the effects of
polydispersity alone, avoiding difficulties associated with the underlying
many-body problem. Explicit formulae are derived in detail, for the
partitioning of species at coexistence and for the shift of phase boundaries
due to polydispersity. `Convective fractionation' is quantified, whereby one
property (e.g. charge) is partitioned between phases due to a driving force on
another. To demonstrate the ease of use and versatility of the formulae, they
are applied to models of a chemically-polydisperse polymer blend, and of
fluid-fluid coexistence in polydisperse colloid-polymer mixtures. In each case,
the regime of coexistence is shown to be enlarged by polydispersity.Comment: 22 pages, 3 figure
Boundary layer integral matrix procedure code modifications and verifications
A summary of modifications to Aerotherm's Boundary Layer Integral Matrix Procedure (BLIMP) code is presented. These modifications represent a preliminary effort to make BLIMP compatible with other JANNAF codes and to adjust the code for specific application to rocket nozzle flows. Results of the initial verification of the code for prediction of rocket nozzle type flows are discussed. For those cases in which measured free stream flow conditions were used as input to the code, the boundary layer predictions and measurements are in excellent agreement. In two cases, with free stream flow conditions calculated by another JANNAF code (TDK) for use as input to BLIMP, the predictions and the data were in fair agreement for one case and in poor agreement for the other case. The poor agreement is believed to result from failure of the turbulent model in BLIMP to account for laminarization of a turbulent flow. Recommendations for further code modifications and improvements are also presented
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