2,786 research outputs found
Finite temperature effects in light scattering off Cooper-paired Fermi atoms
We study stimulated light scattering off a superfluid Fermi gas of atoms at
finite temperature. We derive response function that takes into account vertex
correction due to final state interactions; and analyze finite temperature
effects on collective and quasiparticle excitations of a uniform superfluid
Fermi gas. Light polarization is shown to play an important role in
excitations. Our results suggest that it is possible to excite
Bogoliubov-Anderson phonon at a large scattering length by light scattering.Comment: 18 pages, 4 figures, Accepted in J. Phys. B: At. Mol. & Opt. Phy
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
Correlating contexts and NFR conflicts from event logs
In the design of autonomous systems, it is important to consider the preferences of the interested parties to improve the user experience. These preferences are often associated with the contexts in which each system is likely to operate. The operational behavior of a system must also meet various non-functional requirements (NFRs), which can present different levels of conflict depending on the operational context. This work aims to model correlations between the individual contexts and the consequent conflicts between NFRs. The proposed approach is based on analyzing the system event logs, tracing them back to the leaf elements at the specification level and providing a contextual explanation of the system’s behavior. The traced contexts and NFR conflicts are then mined to produce Context-Context and Context-NFR conflict sequential rules. The proposed Contextual Explainability (ConE) framework uses BERT-based pre-trained language models and sequential rule mining libraries for deriving the above correlations. Extensive evaluations are performed to compare the existing state-of-the-art approaches. The best-fit solutions are chosen to integrate within the ConE framework. Based on experiments, an accuracy of 80%, a precision of 90%, a recall of 97%, and an F1-score of 88% are recorded for the ConE framework on the sequential rules that were mined
Reinforcing age Hardenable Al-Cr Matrix Alloy In-Situ and by SiC/Al2O3
The achievable high ductility value of Al-Cr alloys (over 35% total elongation) has led to the attempt to produce in-situ composites with Al-Cr solid solution as the matrix
phase and excess insoluble intermetallics CrAL as the reinforcing constituent.The alloy produced with 1.20 wt% Cr results in in-situ composites which gives a good
combination of high tensile strength and ductility (approx. 30% elongation). Composites based on Al-Cr matrix alloy with SiC or A1,03 as the reinforcing phase showed
that the increase in strength is quite considerable even at a relatively good ductility
Light scattering in Cooper-paired Fermi atoms
We present a detailed theoretical study of light scattering off superfluid
trapped Fermi gas of atoms at zero temperature. We apply Nambu-Gorkov formalism
of superconductivity to calculate the response function of superfluid gas due
to stimulated light scattering taking into account the final state
interactions. The polarization of light has been shown to play a significant
role in response of Cooper-pairs in the presence of a magnetic field.
Particularly important is a scheme of polarization-selective light scattering
by either spin-component of the Cooper-pairs leading to the single-particle
excitations of one spin-component only. These excitations have a threshold of
where is the superfluid gap energy. Furthermore,
polarization-selective light scattering allows for unequal energy and momentum
transfer to the two partner atoms of a Cooper-pair. In the regime of low energy
() and low momentum (, being the Fermi
velocity) transfer, a small difference in momentum transfers to the two
spin-components may be useful in exciting Bogoliubov-Anderson phonon mode. We
present detailed results on the dynamic structure factor (DSF) deduced from the
response function making use of generalized fluctuation-dissipation theorem.
Model calculations using local density approximation for trapped superfluid
Fermi gas shows that when the energy transfer is less than , where
refers to the gap at the trap center, DSF as a function of energy
transfer has reduced gradient compared to that of normal Fermi gas.Comment: single column, 26 pages, 10 figures; Title changed, discussion on
experimental implication added in concluding section. Accepted for
publication in J. Phys.
A Multi-objective Exploratory Procedure for Regression Model Selection
Variable selection is recognized as one of the most critical steps in
statistical modeling. The problems encountered in engineering and social
sciences are commonly characterized by over-abundance of explanatory variables,
non-linearities and unknown interdependencies between the regressors. An added
difficulty is that the analysts may have little or no prior knowledge on the
relative importance of the variables. To provide a robust method for model
selection, this paper introduces the Multi-objective Genetic Algorithm for
Variable Selection (MOGA-VS) that provides the user with an optimal set of
regression models for a given data-set. The algorithm considers the regression
problem as a two objective task, and explores the Pareto-optimal (best subset)
models by preferring those models over the other which have less number of
regression coefficients and better goodness of fit. The model exploration can
be performed based on in-sample or generalization error minimization. The model
selection is proposed to be performed in two steps. First, we generate the
frontier of Pareto-optimal regression models by eliminating the dominated
models without any user intervention. Second, a decision making process is
executed which allows the user to choose the most preferred model using
visualisations and simple metrics. The method has been evaluated on a recently
published real dataset on Communities and Crime within United States.Comment: in Journal of Computational and Graphical Statistics, Vol. 24, Iss.
1, 201
Entangling two Bose Einstein condensates in a double cavity system
We propose a scheme to transfer the quantum state of light fields to the
collective density excitations of a Bose Einstein condensate (BEC) in a cavity.
This scheme allows to entangle two BECs in a double cavity setup by
transferring the quantum entanglement of two light fields produced from a
nondegenerate parametric amplifier (NOPA) to the collective density excitations
of the two BECs. An EPR state of the collective density excitations can be
created by a judicious choice of the system parameters.Comment: 3 figure
- …