1,489 research outputs found
Dynamics of Vesicles in shear and rotational flows: Modal Dynamics and Phase Diagram
Despite the recent upsurge of theoretical reduced models for vesicle shape
dynamics, comparisons with experiments have not been accomplished. We review
the implications of some of the recently proposed models for vesicle dynamics,
especially the Tumbling-Trembling domain regions of the phase plane and show
that they all fail to capture the essential behavior of real vesicles for
excess areas, \Delta, greater than 0.4. We emphasize new observations of shape
harmonics and the role of thermal fluctuations.Comment: (removed forgotten leftover figure files
Photoinduced Changes of Reflectivity in Single Crystals of YBa2Cu3O6.5 (Ortho II)
We report measurements of the photoinduced change in reflectivity of an
untwinned single crystal of YBa2Cu3O6.5 in the ortho II structure. The decay
rate of the transient change in reflectivity is found to decrease rapidly with
decreasing temperature and, below Tc, with decreasing laser intensity. We
interpret the decay as a process of thermalization of antinodal quasiparticles,
whose rate is determined by an inelastic scattering rate of quasiparticle
pairs.Comment: 4 pages, 4 figure
Competition and Post-Transplant Outcomes in Cadaveric Liver Transplantation under the MELD Scoring System
Previous researchers have modelled the decision to accept a donor organ for transplantation as a Markov decision problem, the solution to which is often a control-limit optimal policy: accept any organ whose match quality exceeds some health-dependent threshold; otherwise, wait for another. When competing transplant centers vie for the same organs, the decision rule changes relative to no competition; the relative size of competing centers affects the decision rules as well. Using center-specific graft and patient survival-rate data for cadaveric adult livers in the United States, we have found empirical evidence supporting these predictions.liver transplantation, competition, optimal stopping
Competition and Post-Transplant Outcomes in Cadaveric Liver Transplantation under the MELD Scoring System
Previous researchers have modelled the decision to accept a donor organ for transplantation as a Markov decision problem, the solution to which is often a control-limit optimal policy: accept any organ whose match quality exceeds some health-dependent threshold; otherwise, wait for another. When competing transplant centers vie for the same organs, the decision rule changes relative to no competition; the relative size of competing centers affects the decision rules as well. Using center-specific graft and patient survival-rate data for cadaveric adult livers in the United States, we have found empirical evidence supporting these predictions.liver transplantation; competition; optimal stopping
Levi umbilical surfaces in complex space
We define a complex connection on a real hypersurface of \C^{n+1} which is
naturally inherited from the ambient space. Using a system of Codazzi-type
equations, we classify connected real hypersurfaces in \C^{n+1}, ,
which are Levi umbilical and have non zero constant Levi curvature. It turns
out that such surfaces are contained either in a sphere or in the boundary of a
complex tube domain with spherical section.Comment: 18 page
MLIP: using multiple processors to compute the posterior probability of linkage
<p>Abstract</p> <p>Background</p> <p>Localization of complex traits by genetic linkage analysis may involve exploration of a vast multidimensional parameter space. The posterior probability of linkage (PPL), a class of statistics for complex trait genetic mapping in humans, is designed to model the trait model complexity represented by the multidimensional parameter space in a mathematically rigorous fashion. However, the method requires the evaluation of integrals with no functional form, making it difficult to compute, and thus further test, develop and apply. This paper describes MLIP, a multiprocessor two-point genetic linkage analysis system that supports statistical calculations, such as the PPL, based on the full parameter space implicit in the linkage likelihood.</p> <p>Results</p> <p>The fundamental question we address here is whether the use of additional processors effectively reduces total computation time for a PPL calculation. We use a variety of data – both simulated and real – to explore the question "how close can we get?" to linear speedup. Empirical results of our study show that MLIP does significantly speed up two-point log-likelihood ratio calculations over a grid space of model parameters.</p> <p>Conclusion</p> <p>Observed performance of the program is dependent on characteristics of the data including granularity of the parameter grid space being explored and pedigree size and structure. While work continues to further optimize performance, the current version of the program can already be used to efficiently compute the PPL. Thanks to MLIP, full multidimensional genome scans are now routinely being completed at our centers with runtimes on the order of days, not months or years.</p
Monte-Carlo simulation of events with Drell-Yan lepton pairs from antiproton-proton collisions
The complete knowledge of the nucleon spin structure at leading twist
requires also addressing the transverse spin distribution of quarks, or
transversity, which is yet unexplored because of its chiral-odd nature.
Transversity can be best extracted from single-spin asymmetries in fully
polarized Drell-Yan processes with antiprotons, where valence contributions are
involved anyway. Alternatively, in single-polarized Drell-Yan the transversity
happens convoluted with another chiral-odd function, which is likely to be
responsible for the well known (and yet unexplained) violation of the Lam-Tung
sum rule in the corresponding unpolarized cross section. We present Monte-Carlo
simulations for the unpolarized and single-polarized Drell-Yan at different center-of-mass energies in both
configurations where the antiproton beam hits a fixed proton target or it
collides on another proton beam. The goal is to estimate the minimum number of
events needed to extract the above chiral-odd distributions from future
measurements at the HESR ring at GSI. It is important to study the feasibility
of such experiments at HESR in order to demonstrate that interesting spin
physics can be explored already using unpolarized antiprotons.Comment: Deeply revised text with improved discussion of kinematics and
results; added one table; 12 figures. Accepted for publication in Phys. Rev.
The Finite Field Kakeya Problem
A Besicovitch set in AG(n,q) is a set of points containing a line in every
direction. The Kakeya problem is to determine the minimal size of such a set.
We solve the Kakeya problem in the plane, and substantially improve the known
bounds for n greater than 4.Comment: 13 page
On Binary Matroid Minors and Applications to Data Storage over Small Fields
Locally repairable codes for distributed storage systems have gained a lot of
interest recently, and various constructions can be found in the literature.
However, most of the constructions result in either large field sizes and hence
too high computational complexity for practical implementation, or in low rates
translating into waste of the available storage space. In this paper we address
this issue by developing theory towards code existence and design over a given
field. This is done via exploiting recently established connections between
linear locally repairable codes and matroids, and using matroid-theoretic
characterisations of linearity over small fields. In particular, nonexistence
can be shown by finding certain forbidden uniform minors within the lattice of
cyclic flats. It is shown that the lattice of cyclic flats of binary matroids
have additional structure that significantly restricts the possible locality
properties of -linear storage codes. Moreover, a collection of
criteria for detecting uniform minors from the lattice of cyclic flats of a
given matroid is given, which is interesting in its own right.Comment: 14 pages, 2 figure
Shear-induced quench of long-range correlations in a liquid mixture
A static correlation function of concentration fluctuations in a (dilute)
binary liquid mixture subjected to both a concentration gradient and uniform
shear flow is investigated within the framework of fluctuating hydrodynamics.
It is shown that a well-known long-range correlation at
large wave numbers crosses over to a weaker divergent one for wave numbers
satisfying , while an asymptotic shear-controlled
power-law dependence is confirmed at much smaller wave numbers given by , where , , and are the
mass concentration, the rate of the shear, the mass diffusivity and the
kinematic viscosity of the mixture, respectively. The result will provide for
the first time the possibility to observe the shear-induced suppression of a
long-range correlation experimentally by using, for example, a low-angle light
scattering technique.Comment: 8pages, 2figure
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