214 research outputs found
Three-State Feshbach Resonances Mediated By Second-Order Couplings
We present an analytical study of three-state Feshbach resonances induced by
second-order couplings. Such resonances arise when the scattering amplitude is
modified by the interaction with a bound state that is not directly coupled to
the scattering state containing incoming flux. Coupling occurs indirectly
through an intermediate state. We consider two problems: (i) the intermediate
state is a scattering state in a distinct open channel; (ii) the intermediate
state is an off-resonant bound state in a distinct closed channel. The first
problem is a model of electric-field-induced resonances in ultracold collisions
of alkali metal atoms [Phys. Rev. A 75, 032709 (2007)] and the second problem
is relevant for ultracold collisions of complex polyatomic molecules, chemical
reaction dynamics, photoassociation of ultracold atoms, and electron - molecule
scattering. Our analysis yields general expressions for the energy dependence
of the T-matrix elements modified by three-state resonances and the dependence
of the resonance positions and widths on coupling amplitudes for the
weak-coupling limit. We show that the second problem can be generalized to
describe resonances induced by indirect coupling through an arbitrary number of
sequentially coupled off-resonant bound states and analyze the dependence of
the resonance width on the number of the intermediate states.Comment: 27 pages, 4 figures; added a reference; journal reference/DOI refer
to final published version, which is a shortened and modified version of this
preprin
Intestinal obstruction caused by a Meckel’s diverticulum adherent to an infected urachal cyst
Urachal remnant diseases are rare and frequently misdiagnosed, as the clinical presentation is similar to more common causes of intra-abdominal and pelvic disease. We report the rare case of a 1½-year-old boy with small-bowel obstruction caused by an adhesion band between a Meckel’s diverticulum and an infected urachal cyst. The condition was initially misdiagnosed and treated as a periappendiceal abscess on the basis of clinical examination and ultrasonography findings. In addition to the case report, we present an overview of urachal diseases
Blind signal separation using steepest descent method
A method that significantly improves the convergence rate of the gradient-based blind signal separation (BSS) algorithm for convolutive mixtures is proposed. The proposed approach is based on the steepest descent algorithm suitable for constrained BSS problems, where the constraints are included to ease the permutation effects associated with the convolutive mixtures. In addition, the method is realized using a modified golden search method plus parabolic interpolation, and this allows the optimum step size to be determined with only a few calculations of the cost function. Evaluation of the proposed procedure in simulated environments and in a real room environment shows that the proposed method results in significantly faster convergence for the BSS when compared with a fixed step-size gradient-based algorithm. In addition, for blind signal extraction where only a main speech source is desired, a combined scheme consisting of the proposed BSS and a postprocessor, such as an adaptive noise canceller, offers impressive noise suppression levels while maintaining low-target signal distortion level
Speech recognition enhancement using beamforming and a genetic algorithm
This paper proposes a genetic algorithm (GA) based beamformer to optimize speech recognition accuracy for a pretrained speech recognizer. The proposed beamformer is designed to tackle the non-differentiable and non-linear natures of speech recognition by employing the GA algorithm to search for the optimal beamformer weights. Specifically, a population of beamformer weights is reproduced by crossover and mutation until the optimal beamformer weights are obtained. Results show that the speech recognition accuracies can be greatly improved even in noisy environments
Incorporation of excluded volume correlations into Poisson-Boltzmann theory
We investigate the effect of excluded volume interactions on the electrolyte
distribution around a charged macroion. First, we introduce a criterion for
determining when hard-core effects should be taken into account beyond standard
mean field Poisson-Boltzmann (PB) theory. Next, we demonstrate that several
commonly proposed local density functional approaches for excluded volume
interactions cannot be used for this purpose. Instead, we employ a non-local
excess free energy by using a simple constant weight approach. We compare the
ion distribution and osmotic pressure predicted by this theory with Monte Carlo
simulations. They agree very well for weakly developed correlations and give
the correct layering effect for stronger ones. In all investigated cases our
simple weighted density theory yields more realistic results than the standard
PB approach, whereas all local density theories do not improve on the PB
density profiles but on the contrary, deviate even more from the simulation
results.Comment: 23 pages, 7 figures, 1 tabl
Design of broadband beamformers with low complexity
2011-2012 > Academic research: refereed > Publication in refereed journalVersion of RecordPublishe
Dynamics of ions in the selectivity filter of the KcsA channel
The statistical and dynamical properties of ions in the selectivity filter of the KcsA ion channel are considered on the basis of molecular dynamics (MD) simulations of the KcsA protein embedded in a lipid membrane surrounded by an ionic solution. A new approach to the derivation of a Brownian dynamics (BD) model of ion permeation through the filter is discussed, based on unbiased MD simulations. It is shown that depending on additional assumptions, ion’s dynamics can be described either by under-damped Langevin equation with constant damping and white noise or by Langevin equation with a fractional memory kernel. A comparison of the potential of the mean force derived from unbiased MD simulations with the potential produced by the umbrella sampling method demonstrates significant differences in these potentials. The origin of these differences is an open question that requires further clarifications
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