5,586 research outputs found
Excessive subdural hemorrhage associated with warfarin treatment in antiphospholipid antibody syndrome
Tailoring the Phonon Band Structure in Binary Colloidal Mixtures
We analyze the phonon spectra of periodic structures formed by
two-dimensional mixtures of dipolar colloidal particles. These mixtures display
an enormous variety of complex ordered configurations [J. Fornleitner {\it et
al.}, Soft Matter {\bf 4}, 480 (2008)], allowing for the systematic
investigation of the ensuing phonon spectra and the control of phononic gaps.
We show how the shape of the phonon bands and the number and width of the
phonon gaps can be controlled by changing the susceptibility ratio, the
concentration and the mass ratio between the two components.Comment: 4 pages 3 figure
Spin correlation functions in random-exchange s=1/2 XXZ chains
The decay of (disorder-averaged) static spin correlation functions at T=0 for
the one-dimensional spin-1/2 XXZ antiferromagnet with uniform longitudinal
coupling and random transverse coupling is investigated
by numerical calculations for ensembles of finite chains. At (XX
model) the calculation is based on the Jordan-Wigner mapping to free lattice
fermions for chains with up to N=100 sites. At Lanczos
diagonalizations are carried out for chains with up to N=22 sites. The
longitudinal correlation function is found to exhibit a
power-law decay with an exponent that varies with $\Delta$ and, for nonzero
$\Delta$, also with the width of the $\lambda_i$-distribution. The results for
the transverse correlation function show a crossover from
power-law decay to exponential decay as the exchange disorder is turned on.Comment: RevTex manuscript (7 pages), 4 postscript figure
Zero temperature phase diagram of the square-shoulder system
Particles that interact via a square-shoulder potential, consisting of an
impenetrable hard core with an adjacent, repulsive, step-like corona, are able
to self-organize in a surprisingly rich variety of rather unconventional
ordered structures. Using optimization strategies that are based on ideas of
genetic algorithms we encounter, as we systematically increase the pressure,
the following archetypes of aggregates: low-symmetry cluster and columnar
phases, followed by lamellar particle arrangements, until at high pressure
values compact, high-symmetry lattices emerge. These structures are
characterized in the NPT ensemble as configurations of minimum Gibbs free
energy. Based on simple considerations, i.e., basically minimizing the number
of overlapping coronae while maximizing at the same time the density, the
sequence of emerging structures can easily be understood.Comment: Submitted to J. Chem. Phy
Formation of Polymorphic Cluster Phases for Purely Repulsive Soft Spheres
We present results from density functional theory and computer simulations
that unambiguously predict the occurrence of first-order freezing transitions
for a large class of ultrasoft model systems into cluster crystals. The
clusters consist of fully overlapping particles and arise without the existence
of attractive forces. The number of particles participating in a cluster scales
linearly with density, therefore the crystals feature density-independent
lattice constants. Clustering is accompanied by polymorphic bcc-fcc
transitions, with fcc being the stable phase at high densities.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let
Testing a simple recipe for estimating galaxy masses from minimal observational data
The accuracy and robustness of a simple method to estimate the total mass
profile of a galaxy is tested using a sample of 65 cosmological
zoom-simulations of individual galaxies. The method only requires information
on the optical surface brightness and the projected velocity dispersion
profiles and therefore can be applied even in case of poor observational data.
In the simulated sample massive galaxies ( \kms) at
redshift have almost isothermal rotation curves for broad range of radii
(RMS for the circular speed deviations from a constant value over
). For such galaxies the method recovers the
unbiased value of the circular speed. The sample averaged deviation from the
true circular speed is less than with the scatter of
(RMS) up to . Circular speed estimates of massive
non-rotating simulated galaxies at higher redshifts ( and ) are also
almost unbiased and with the same scatter. For the least massive galaxies in
the sample ( \kms) at the RMS deviation is
and the mean deviation is biased low by about . We also derive the
circular velocity profile from the hydrostatic equilibrium (HE) equation for
hot gas in the simulated galaxies. The accuracy of this estimate is about RMS
for massive objects () and the HE
estimate is biased low by , which can be traced to the presence of
gas motions. This implies that the simple mass estimate can be used to
determine the mass of observed massive elliptical galaxies to an accuracy of
and can be very useful for galaxy surveys.Comment: 15 pages, 14 figures, 1 tabl
The Two-Dimensional, Rectangular, Guillotineable-Layout Cutting Problem with a Single Defect
In this paper, a two-dimensional cutting problem is considered in which a single plate (large object) has to be cut down into a set of small items of maximal value. As opposed to standard cutting problems, the large object contains a defect, which must not be covered by a small item. The problem is represented by means of an AND/OR-graph, and a Branch & Bound procedure (including heuristic modifications for speeding up the search process) is introduced for its exact solution. The proposed method is evaluated in a series of numerical experiments that are run on problem instances taken from the literature, as well as on randomly generated instances.Two-dimensional cutting, defect, AND/OR-graph, Branch & Bound
Computer Assembly of Cluster-Forming Amphiphilic Dendrimers
Recent theoretical studies have predicted a new clustering mechanism for soft
matter particles that interact via a certain kind of purely repulsive, bounded
potentials. At sufficiently high densities, clusters of overlapping particles
are formed in the fluid, which upon further compression crystallize into cubic
lattices with density-independent lattice constants. In this work we show that
amphiphilic dendrimers are suitable colloids for the experimental realization
of this phenomenon. Thereby, we pave the way for the synthesis of such
macromolecules, which form the basis for a novel class of materials with
unusual properties.Comment: 4 pages, 4 figures, 1 tabl
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