30,725 research outputs found

### Spherical Orbifolds for Cosmic Topology

Harmonic analysis is a tool to infer cosmic topology from the measured
astrophysical cosmic microwave background CMB radiation. For overall positive
curvature, Platonic spherical manifolds are candidates for this analysis. We
combine the specific point symmetry of the Platonic manifolds with their deck
transformations. This analysis in topology leads from manifolds to orbifolds.
We discuss the deck transformations of the orbifolds and give eigenmodes for
the harmonic analysis as linear combinations of Wigner polynomials on the
3-sphere. These provide new tools for detecting cosmic topology from the CMB
radiation.Comment: 17 pages, 9 figures. arXiv admin note: substantial text overlap with
arXiv:1011.427

### Surface structure of i-Al(68)Pd(23)Mn(9): An analysis based on the T*(2F) tiling decorated by Bergman polytopes

A Fibonacci-like terrace structure along a 5fold axis of i-Al(68)Pd(23)Mn(9)
monograins has been observed by T.M. Schaub et al. with scanning tunnelling
microscopy (STM). In the planes of the terraces they see patterns of dark
pentagonal holes. These holes are well oriented both within and among terraces.
In one of 11 planes Schaub et al. obtain the autocorrelation function of the
hole pattern. We interpret these experimental findings in terms of the
Katz-Gratias-de Boisseu-Elser model. Following the suggestion of Elser that the
Bergman clusters are the dominant motive of this model, we decorate the tiling
T*(2F) by the Bergman polytopes only. The tiling T*(2F) allows us to use the
powerful tools of the projection techniques. The Bergman polytopes can be
easily replaced by the Mackay polytopes as the decoration objects. We derive a
picture of ``geared'' layers of Bergman polytopes from the projection
techniques as well as from a huge patch. Under the assumption that no surface
reconstruction takes place, this picture explains the Fibonacci-sequence of the
step heights as well as the related structure in the terraces qualitatively and
to certain extent even quantitatively. Furthermore, this layer-picture requires
that the polytopes are cut in order to allow for the observed step heights. We
conclude that Bergman or Mackay clusters have to be considered as geometric
building blocks of the i-AlPdMn structure rather than as energetically stable
entities

### Theoretical Framework for Microscopic Osmotic Phenomena

The basic ingredients of osmotic pressure are a solvent fluid with a soluble
molecular species which is restricted to a chamber by a boundary which is
permeable to the solvent fluid but impermeable to the solute molecules. For
macroscopic systems at equilibrium, the osmotic pressure is given by the
classical van't Hoff Law, which states that the pressure is proportional to the
product of the temperature and the difference of the solute concentrations
inside and outside the chamber. For microscopic systems the diameter of the
chamber may be comparable to the length-scale associated with the solute-wall
interactions or solute molecular interactions. In each of these cases, the
assumptions underlying the classical van't Hoff Law may no longer hold. In this
paper we develop a general theoretical framework which captures corrections to
the classical theory for the osmotic pressure under more general relationships
between the size of the chamber and the interaction length scales. We also show
that notions of osmotic pressure based on the hydrostatic pressure of the fluid
and the mechanical pressure on the bounding walls of the chamber must be
distinguished for microscopic systems. To demonstrate how the theoretical
framework can be applied, numerical results are presented for the osmotic
pressure associated with a polymer of N monomers confined in a spherical
chamber as the bond strength is varied

### A Stochastic Immersed Boundary Method for Fluid-Structure Dynamics at Microscopic Length Scales

In this work it is shown how the immersed boundary method of (Peskin2002) for
modeling flexible structures immersed in a fluid can be extended to include
thermal fluctuations. A stochastic numerical method is proposed which deals
with stiffness in the system of equations by handling systematically the
statistical contributions of the fastest dynamics of the fluid and immersed
structures over long time steps. An important feature of the numerical method
is that time steps can be taken in which the degrees of freedom of the fluid
are completely underresolved, partially resolved, or fully resolved while
retaining a good level of accuracy. Error estimates in each of these regimes
are given for the method. A number of theoretical and numerical checks are
furthermore performed to assess its physical fidelity. For a conservative
force, the method is found to simulate particles with the correct Boltzmann
equilibrium statistics. It is shown in three dimensions that the diffusion of
immersed particles simulated with the method has the correct scaling in the
physical parameters. The method is also shown to reproduce a well-known
hydrodynamic effect of a Brownian particle in which the velocity
autocorrelation function exhibits an algebraic tau^(-3/2) decay for long times.
A few preliminary results are presented for more complex systems which
demonstrate some potential application areas of the method.Comment: 52 pages, 11 figures, published in journal of computational physic

### Orientational transition in nematic liquid crystals under oscillatory Poiseuille flow

We investigate the orientational behaviour of a homeotropically aligned
nematic liquid crystal subjected to an oscillatory plane Poiseuille flow
produced by an alternating pressure gradient. For small pressure amplitudes the
director oscillates within the flow plane around the initial homeotropic
position, whereas for higher amplitudes a spatially homogeneous transition to
out-of-plane director motion was observed for the first time. The orientational
transition was found to be supercritical and the measured frequency dependence
of the critical pressure amplitude in the range between 2 and 20 Hz was in
quantitative agreement with a recent theory.Comment: 11 pages, 4 figures, submitted to Europhys. Let

### B0 - B0 bar mixing, B -> J/psi K_S and B -> X_d gamma in general MSSM

We consider the gluino-mediated SUSY contributions to B0 - B0 bar mixing, B
-> J/psi K_S and B -> X_d gamma in the mass insertion approximation. We find
the LL mixing parameter can be as large as |delta_{13}^d_{LL}| < 2*10^-1, but
the LR mixing is strongly constrained by the B -> X_d gamma branching ratio and
we find |delta_{13}^d_{LR}| < 10^-2. The implications for the direct CP
asymmetry in B -> X_d gamma and the dilepton charge asymmetry (A_{ll}) are also
discussed, where substantial deviations from the standard model predictions are
possible.Comment: 14 pages, 4 figure

- …