1,667 research outputs found
The effect of direct interactions on Brownian diffusion
The effect of direct interactions between suspended particles on their diffusion coefficient is investigated starting from the generalized Einstein relation. It is shown that an attractive potential added to the hard core repulsion leads to a decrease of the diffusion coëfficiënt, whereas a repulsive term has the opposite effect. Simple examples of attractive and repulsive potentials are considered in some detail. Using these results the possibility to obtain information on the interaction potential between suspended particles from their diffusion coefficient is discussed
TIGER: A data analysis pipeline for testing the strong-field dynamics of general relativity with gravitational wave signals from coalescing compact binaries
The direct detection of gravitational waves with upcoming second-generation
gravitational wave detectors such as Advanced LIGO and Virgo will allow us to
probe the genuinely strong-field dynamics of general relativity (GR) for the
first time. We present a data analysis pipeline called TIGER (Test
Infrastructure for GEneral Relativity), which is designed to utilize detections
of compact binary coalescences to test GR in this regime. TIGER is a
model-independent test of GR itself, in that it is not necessary to compare
with any specific alternative theory. It performs Bayesian inference on two
hypotheses: the GR hypothesis , and , which states that one or more of the post-Newtonian coefficients in
the waveform are not as predicted by GR. By the use of multiple sub-hypotheses
of , in each of which a different number of
parameterized deformations of the GR phase are allowed, an arbitrarily large
number of 'testing parameters' can be used without having to worry about a
model being insufficiently parsimonious if the true number of extra parameters
is in fact small. TIGER is well-suited to the regime where most sources have
low signal-to-noise ratios, again through the use of these sub-hypotheses.
Information from multiple sources can trivially be combined, leading to a
stronger test. We focus on binary neutron star coalescences, for which
sufficiently accurate waveform models are available that can be generated fast
enough on a computer to be fit for use in Bayesian inference. We show that the
pipeline is robust against a number of fundamental, astrophysical, and
instrumental effects, such as differences between waveform approximants, a
limited number of post-Newtonian phase contributions being known, the effects
of neutron star spins and tidal deformability on the orbital motion, and
instrumental calibration errors.Comment: 12 pages, 9 figures. Version as appears in Phys. Rev.
Determination of Dark Energy by the Einstein Telescope: Comparing with CMB, BAO and SNIa Observations
A design study is currently in progress for a third generation
gravitational-wave (GW) detector called Einstein Telescope (ET). An important
kind of source for ET will be the inspiral and merger of binary neutron stars
(BNS) up to . If BNS mergers are the progenitors of short-hard
-ray bursts, then some fraction of them will be seen both
electromagnetically and through GW, so that the luminosity distance and the
redshift of the source can be determined separately. An important property of
these `standard sirens' is that they are \emph{self-calibrating}: the
luminosity distance can be inferred directly from the GW signal, with no need
for a cosmic distance ladder. Thus, standard sirens will provide a powerful
independent check of the CDM model. In previous work, estimates were
made of how well ET would be able to measure a subset of the cosmological
parameters (such as the dark energy parameter ) it will have access to,
assuming that the others had been determined to great accuracy by alternative
means. Here we perform a more careful analysis by explicitly using the
potential Planck CMB data as prior information for these other parameters. We
find that ET will be able to constrain and with accuracies and , respectively. These results are compared
with projected accuracies for the JDEM Baryon Acoustic Oscillations project and
the SNAP Type Ia supernovae observations.Comment: 28 pages, 5 figures, 5 tables; Published Versio
Thermoelectric efficiency at maximum power in a quantum dot
We identify the operational conditions for maximum power of a
nanothermoelectric engine consisting of a single quantum level embedded between
two leads at different temperatures and chemical potentials. The corresponding
thermodynamic efficiency agrees with the Curzon-Ahlborn expression up to
quadratic terms in the gradients, supporting the thesis of universality beyond
linear response.Comment: 4 pages, 3 figure
Continuous and discontinuous phase transitions and partial synchronization in stochastic three-state oscillators
We investigate both continuous (second-order) and discontinuous (first-order)
transitions to macroscopic synchronization within a single class of discrete,
stochastic (globally) phase-coupled oscillators. We provide analytical and
numerical evidence that the continuity of the transition depends on the
coupling coefficients and, in some nonuniform populations, on the degree of
quenched disorder. Hence, in a relatively simple setting this class of models
exhibits the qualitative behaviors characteristic of a variety of considerably
more complicated models. In addition, we study the microscopic basis of
synchronization above threshold and detail the counterintuitive subtleties
relating measurements of time averaged frequencies and mean field oscillations.
Most notably, we observe a state of suprathreshold partial synchronization in
which time-averaged frequency measurements from individual oscillators do not
correspond to the frequency of macroscopic oscillations observed in the
population
Reconstructing Colonization Dynamics of the Human Parasite Schistosoma mansoni following Anthropogenic Environmental Changes in Northwest Senegal
© 2015 Van den Broeck et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The attached file is the published version of the article
Alternative derivation of Mie theory with electromagnetic potentials for diffuse particles
Mie's theory of light scattering on spherical particles is being increasingly used in nanophotonics, and these demanding applications have laid bare some shortcomings of Mie theory in its standard formulation. One problem that deserves special attention is the electron spill-out in small metallic nanoparticles, which invalidates the assumption of an abrupt interface. Here we present an alternative derivation of Mie theory without this assumption. To avoid the usual electromagnetic boundary conditions suitable for a hard-wall interface, we set up equations for the electromagnetic potentials instead of the electric and magnetic field. We show that in the limit of a hard-wall interface, the results of the standard Mie theory are recovered. Additionally, a numerical solution scheme is proposed for the equations for the vector potential and the scalar potential. Analysis of the optical cross sections of soft-interface nanospheres shows that the absorption increases and occurs at lower frequencies as compared to hard-walled nanospheres. This effect is rather dramatic in large spheres with large spill-out, due to the disappearance of high-frequency resonance peaks
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