844 research outputs found
Stimulated Raman adiabatic passage into continuum
We propose a technique which produces nearly complete ionization of the
population of a discrete state coupled to a continuum by a two-photon
transition via a lossy intermediate state whose lifetime is much shorter than
the interaction duration. We show that using counterintuitively ordered pulses,
as in stimulated Raman adiabatic passage (STIRAP), wherein the pulse coupling
the intermediate state to the continuum precedes and partly overlaps the pulse
coupling the initial and intermediate states, greatly increases the ionization
signal and strongly reduces the population loss due to spontaneous emission
through the lossy state. For strong spontaneous emission from that state,
however, the ionization is never complete because the dark state required for
STIRAP does not exist. We demonstrate that this drawback can be eliminated
almost completely by creating a laser-induced continuum structure (LICS) by
embedding a third discrete state into the continuum with a third control laser.
This LICS introduces some coherence into the continuum, which enables a
STIRAP-like population transfer into the continuum. A highly accurate analytic
description is developed and numerical results are presented for Gaussian pulse
shapes
Incoherent matter-wave solitons
The dynamics of matter-wave solitons in Bose-Einstein condensates (BEC) is
considerably affected by the presence of a surrounding thermal cloud and by
condensate depletion during its evolution. We analyze these aspects of BEC
soliton dynamics, using time-dependent Hartree-Fock-Bogoliubov (TDHFB) theory.
The condensate is initially prepared within a harmonic trap at finite
temperature, and solitonic behavior is studied by subsequently propagating the
TDHFB equations without confinement. Numerical results demonstrate the collapse
of the BEC via collisional emission of atom pairs into the thermal cloud,
resulting in splitting of the initial density into two solitonic structures
with opposite momentum. Each one of these solitary matter waves is a mixture of
condensed and noncondensed particles, constituting an analog of optical
random-phase solitons.Comment: 4 pages, 2 figures, new TDHFB result
Neuro-protective effects of Crocin on brain and cerebellum tissues in diabetic rats
Background: Increase in free oxygen radicals and the disruption of defense system make the neurons and astrocytes more sensitive against oxidative damage.Materials and Methods: Rats were divided into three groups containing 10, rats in each group namely: control (C) group, Diabetes Mellitus (DM) group, and Diabetes Mellitus + crocin (DM+crocin) group. Tissue samples were processed by routine histological and biochemical procedures. The sections were stained with Hematoxylen-eosin. Malondialdehyde (MDA), glutathione (GSH), blood glucose, HbA1c levels and xanthine oxidase (XO) activities were assayed.Results: The histological appearence of the cerebrum and cerebellum were normal in the control group. DM group showed some histopathological changes including congestion, perivascular and perineuronal edema in cerebrum. In DM + crocin group, histopathological changes in cerebrum and cerebellum markedly reduced. MDA level and XO activities increased significantly in DM group (P<0.01), but decreased significantly in DM + crocin group when compared to DM group (P<0.01). Blood glucose concentrations increased significantly (p<0.01) in DM group), but decreased significantly in DM + crocin group when compared with DM group (p<0.05). Blood HbA1c levels were normal in control group. But there were significant differences between control and DM groups (p<0.01). On the other hand, blood HbA1c levels decreased in DM+crocin group when compared with the DM group, but it was not statistically significant (p > 0.05).Conclusion: Due to the fact that crocin has an antioxidant and anti-hyperglycemic effects, it can protect the brain and cerebellum tissue against the complications of oxidative stress.Key words: Diabetes mellitus, oxidative stress, crocin, brain, cerebellum
Coherently Controlled Nanoscale Molecular Deposition
Quantum interference effects are shown to provide a means of controlling and
enhancing the focusing a collimated neutral molecular beam onto a surface. The
nature of the aperiodic pattern formed can be altered by varying laser field
characteristics and the system geometry.Comment: 13 pages (inculding 4 figures), LaTeX (Phys. Rev. Lett., 2000, in
Press
ADDMC: Weighted Model Counting with Algebraic Decision Diagrams
We present an algorithm to compute exact literal-weighted model counts of
Boolean formulas in Conjunctive Normal Form. Our algorithm employs dynamic
programming and uses Algebraic Decision Diagrams as the primary data structure.
We implement this technique in ADDMC, a new model counter. We empirically
evaluate various heuristics that can be used with ADDMC. We then compare ADDMC
to state-of-the-art exact weighted model counters (Cachet, c2d, d4, and
miniC2D) on 1914 standard model counting benchmarks and show that ADDMC
significantly improves the virtual best solver.Comment: Presented at AAAI 202
Formation of Two Component Bose Condensate During the Chemical Potential Curve Crossing
In this article we study the formation of the two modes Bose-Einstein
condensate and the correlation between them. We show that beyond the mean field
approximation the dissociation of a molecular condensate due to the chemical
potential curve crossing leads to the formation of two modes condensate. We
also show that these two modes are correlated in a two mode squeezed state.Comment: 10 page
Spatial methods for event reconstruction in CLEAN
In CLEAN (Cryogenic Low Energy Astrophysics with Noble gases), a proposed
neutrino and dark matter detector, background discrimination is possible if one
can determine the location of an ionizing radiation event with high accuracy.
We simulate ionizing radiation events that produce multiple scintillation
photons within a spherical detection volume filled with liquid neon. We
estimate the radial location of a particular ionizing radiation event based on
the observed count data corresponding to that event. The count data are
collected by detectors mounted at the spherical boundary of the detection
volume. We neglect absorption, but account for Rayleigh scattering. To account
for wavelength-shifting of the scintillation light, we assume that photons are
absorbed and re-emitted at the detectors. Here, we develop spatial Maximum
Likelihood methods for event reconstruction, and study their performance in
computer simulation experiments. We also study a method based on the centroid
of the observed count data. We calibrate our estimates based on training data
Collisional shifts in optical-lattice atom clocks
We theoretically study the effects of elastic collisions on the determination
of frequency standards via Ramsey fringe spectroscopy in optical-lattice atom
clocks. Interparticle interactions of bosonic atoms in multiply-occupied
lattice sites can cause a linear frequency shift, as well as generate
asymmetric Ramsey fringe patterns and reduce fringe visibility due to
interparticle entanglement. We propose a method of reducing these collisional
effects in an optical lattice by introducing a phase difference of
between the Ramsey driving fields in adjacent sites. This configuration
suppresses site to site hopping due to interference of two tunneling pathways,
without degrading fringe visibility. Consequently, the probability of double
occupancy is reduced, leading to cancellation of collisional shifts.Comment: 15 pages, 11 figure
On a q-analogue of the multiple gamma functions
A -analogue of the multiple gamma functions is introduced, and is shown to
satisfy the generalized Bohr-Morellup theorem. Furthermore we give some
expressions of these function.Comment: 8 pages, AMS-Late
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