3,937 research outputs found
Magneto-optical Feshbach resonance: Controlling cold collision with quantum interference
We propose a method of controlling two-atom interaction using both magnetic
and laser fields. We analyse the role of quantum interference between magnetic
and optical Feshbach resonances in controlling cold collision. In particular,
we demonstrate that this method allows us to suppress inelastic and enhance
elastic scattering cross sections. Quantum interference is shown to modify
significantly the threshold behaviour and resonant interaction of ultracold
atoms. Furthermore, we show that it is possible to manipulate not only the
spherically symmetric s-wave interaction but also the anisotropic higher
partial-wave interactions which are particularly important for high temperature
superfluid or superconducting phases of matter.Comment: 7 pages 3 figures, some minor errors are corrected, Accepted in J.
Phys.
Modelling of laboratory data of bi-directional reflectance of regolith surface containing Alumina
Bidirectional reflectance of a surface is defined as the ratio of the
scattered radiation at the detector to the incident irradiance as a function of
geometry. The accurate knowledge of the bidirectional reflection function (BRF)
of layers composed of discrete, randomly positioned scattering particles is
very essential for many remote sensing, engineering, biophysical applications
and in different areas of Astrophysics. The computations of BRF's for plane
parallel particulate layers are usually reduced to solve the radiative transfer
equation (RTE) by the existing techniques. In this work we present our
laboratory data on bidirectional reflectance versus phase angle for two sample
sizes of 0.3 and 1 of Alumina for the He-Ne laser at 632.8 nm (red) and
543.5nm(green) wavelength. The nature of the phase curves of the asteroids
depends on the parameters like- particle size, composition, porosity, roughness
etc. In our present work we analyse the data which are being generated using
single scattering phase function i.e. Mie theory considering particles to be
compact sphere. The well known Hapke formula will be considered along with
different particle phase function such as Mie and Henyey Greenstein etc to
model the laboratory data obtained at the asteroid laboratory of Assam
University.Comment: 5 pages, 5 figures [accepted for publication in Publications of the
Astronomical Society of Australia (PASA) on 8 June, 2011
Interference of stochastic resonances: Splitting of Kramers' rate
We consider the escape of particles located in the middle well of a symmetric
triple well potential driven sinusoidally by two forces such that the potential
wells roll as in stochastic resonance and the height of the potential barrier
oscillates symmetrically about a mean as in resonant activation. It has been
shown that depending on their phase difference the application of these two
synchronized signals may lead to a splitting of time averaged Kramers' escape
rate and a preferential product distribution in a parallel chemical reaction in
the steady state
Suppression of power-broadening in strong-coupling photoassociation in the presence of a Feshbach resonance
Photoassociation (PA) spectrum in the presence of a magnetic Feshbach
resonance is analyzed. Nonperturbative solution of the problem yields
analytical expressions for PA linewidth and shift which are applicable for
arbitrary PA laser intensity and magnetic field tuning of Feshbach Resonance.
We show that by tuning magnetic field close to Fano minimum, it is possible to
suppress power broadening at increased laser intensities. This occurs due to
quantum interference of PA transitions from unperturbed and perturbed
continuum. Line narrowing at high laser intensities is accompanied by large
spectral shifts. We briefly discuss important consequences of line narrowing in
cold collisions.Comment: 12 pages, 5 figure
Linear systems with adiabatic fluctuations
We consider a dynamical system subjected to weak but adiabatically slow
fluctuations of external origin. Based on the ``adiabatic following''
approximation we carry out an expansion in \alpha/|\mu|, where \alpha is the
strength of fluctuations and 1/|\mu| refers to the time scale of evolution of
the unperturbed system to obtain a linear differential equation for the average
solution. The theory is applied to the problems of a damped harmonic oscillator
and diffusion in a turbulent fluid. The result is the realization of
`renormalized' diffusion constant or damping constant for the respective
problems. The applicability of the method has been critically analyzed.Comment: Plain Latex, no figure, 21 page
Multi-Objective Big Data Optimization with jMetal and Spark
Big Data Optimization is the term used to refer to optimization problems which have to manage very large amounts of data. In this paper, we focus on the parallelization of metaheuristics with the Apache Spark cluster computing system for solving multi-objective Big Data Optimization problems. Our purpose is to study the influence of accessing data stored in the Hadoop File System (HDFS) in each evaluation step of a metaheuristic and to provide a software tool to solve these kinds of problems. This tool combines the jMetal multi-objective optimization framework with Apache Spark. We have carried out experiments to measure the performance of the proposed parallel infrastructure in an environment based on virtual machines in a local cluster comprising up to 100 cores. We obtained interesting results for computational e ort and propose guidelines to face multi-objective Big Data Optimization
problems.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech
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Heading direction with respect to a reference point modulates place-cell activity.
The tuning of neurons in area CA1 of the hippocampus emerges through a combination of non-spatial input from different sensory modalities and spatial information about the animal's position and heading direction relative to the spatial enclosure being navigated. The positional modulation of CA1 neuronal responses has been widely studied (e.g. place tuning), but less is known about the modulation of these neurons by heading direction. Here, utilizing electrophysiological recordings from CA1 pyramidal cells in freely moving mice, we report that a majority of neural responses are modulated by the heading-direction of the animal relative to a point within or outside their enclosure that we call a reference point. The finding of heading-direction modulation relative to reference points identifies a novel representation encoded in the neuronal responses of the dorsal hippocampus
Electronic properties of doped magnesium thioindate ternary spinel in the normal and in the inverse structure
We present a theoretical study of the structural and electronic properties of the M-doped MgIn2S4 ternary spinel semiconductor with M = V, Cr, and Mn. All substitutions, in the normal and in the inverse structure, are analyzed. Some of these possible substitutions present intermediate-band states in the band gap with a different occupation for a spin component. It increases the possibilities of inter-band transitions and could be interesting for applications in optoelectronic devices. The contribution to, and the electronic configuration of, these intermediate bands for the octahedral and tetrahedral sites is analyzed and discussed. The study of the substitutional energies indicates that these substitutions are favorable. Comparison between the pure and doped hosts absorption coefficients shows that this deeper band opens up more photon absorption channels and could therefore increase the solar-light absorption with respect to the host
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