72,971 research outputs found
Computation of group table alphanumeric display
Computer program, using only group elements as input data, provides machine computation of group tables used for proving theorems and algorithms of finite groups. Program is written for second generation computers
Adaptive high-order finite element solution of transient elastohydrodynamic lubrication problems
This article presents a new numerical method to solve transient line contact elastohydrodynamic lubrication (EHL) problems. A high-order discontinuous Galerkin (DG) finite element method is used for the spatial discretization, and the standard Crank-Nicolson method is employed to approximate the time derivative. An h-adaptivity method is used for grid adaptation with the time-stepping, and the penalty method is employed to handle the cavitation condition.
The roughness model employed here is a simple indentation, which is located on the upper surface. Numerical results are presented comparing the DG method to standard finite difference (FD) techniques. It is shown that micro-EHL features are captured with far fewer degrees of freedom than when using low-order FD methods
Automatic analysis of Swift-XRT data
The Swift spacecraft detects and autonomously observes ~100 Gamma Ray Bursts
(GRBs) per year, ~96% of which are detected by the X-ray telescope (XRT). GRBs
are accompanied by optical transients and the field of ground-based follow-up
of GRBs has expanded significantly over the last few years, with rapid response
instruments capable of responding to Swift triggers on timescales of minutes.
To make the most efficient use of limited telescope time, follow-up astronomers
need accurate positions of GRBs as soon as possible after the trigger.
Additionally, information such as the X-ray light curve, is of interest when
considering observing strategy. The Swift team at Leicester University have
developed techniques to improve the accuracy of the GRB positions available
from the XRT, and to produce science-grade X-ray light curves of GRBs. These
techniques are fully automated, and are executed as soon as data are available.Comment: 4 pages, 2 figures, to appear in the proceedings of ADASS XVII (ASP
Conference Series
FORTRAN program for machine computation of group tables of finite groups
FORTRAN program for computation of finite group table
Asymptotic decay of pair correlations in a Yukawa fluid
We analyse the asymptotic decay of the total correlation
function, , for a fluid composed of particles interacting via a (point)
Yukawa pair potential. Such a potential provides a simple model for dusty
plasmas. The asymptotic decay is determined by the poles of the liquid
structure factor in the complex plane. We use the hypernetted-chain closure to
the Ornstein-Zernike equation to determine the line in the phase diagram,
well-removed from the freezing transition line, where crossover occurs in the
ultimate decay of , from monotonic to damped oscillatory. We show: i)
crossover takes place via the same mechanism (coalescence of imaginary poles)
as in the classical one-component plasma and in other models of Coulomb fluids
and ii) leading-order pole contributions provide an accurate description of
at intermediate distances as well as at long range.Comment: 5 pages, 3 figure
Density functional theory for colloidal mixtures of hard platelets, rods, and spheres
A geometry-based density functional theory is presented for mixtures of hard
spheres, hard needles and hard platelets; both the needles and the platelets
are taken to be of vanishing thickness. Geometrical weight functions that are
characteristic for each species are given and it is shown how convolutions of
pairs of weight functions recover each Mayer bond of the ternary mixture and
hence ensure the correct second virial expansion of the excess free energy
functional. The case of sphere-platelet overlap relies on the same
approximation as does Rosenfeld's functional for strictly two-dimensional hard
disks. We explicitly control contributions to the excess free energy that are
of third order in density. Analytic expressions relevant for the application of
the theory to states with planar translational and cylindrical rotational
symmetry, e.g. to describe behavior at planar smooth walls, are given. For
binary sphere-platelet mixtures, in the appropriate limit of small platelet
densities, the theory differs from that used in a recent treatment [L. Harnau
and S. Dietrich, Phys. Rev. E 71, 011504 (2004)]. As a test case of our
approach we consider the isotropic-nematic bulk transition of pure hard
platelets, which we find to be weakly first order, with values for the
coexistence densities and the nematic order parameter that compare well with
simulation results.Comment: 39 pages, 8 figure
- …