1,304 research outputs found
Bose-Einstein condensate collapse: a comparison between theory and experiment
We solve the Gross-Pitaevskii equation numerically for the collapse induced
by a switch from positive to negative scattering lengths. We compare our
results with experiments performed at JILA with Bose-Einstein condensates of
Rb-85, in which the scattering length was controlled using a Feshbach
resonance. Building on previous theoretical work we identify quantitative
differences between the predictions of mean-field theory and the results of the
experiments. Besides the previously reported difference between the predicted
and observed critical atom number for collapse, we also find that the predicted
collapse times systematically exceed those observed experimentally. Quantum
field effects, such as fragmentation, that might account for these
discrepancies are discussed.Comment: 4 pages, 2 figure
Mean-field description of collapsing and exploding Bose-Einstein condensates
We perform numerical simulation based on the time-dependent mean-field
Gross-Pitaevskii equation to understand some aspects of a recent experiment by
Donley et al. on the dynamics of collapsing and exploding Bose-Einstein
condensates of Rb atoms. They manipulated the atomic interaction by an
external magnetic field via a Feshbach resonance, thus changing the repulsive
condensate into an attractive one and vice versa. In the actual experiment they
changed suddenly the scattering length of atomic interaction from positive to a
large negative value on a pre-formed condensate in an axially symmetric trap.
Consequently, the condensate collapses and ejects atoms via explosion. We find
that the present mean-field analysis can explain some aspects of the dynamics
of the collapsing and exploding Bose-Einstein condensates.Comment: 9 Latex pages, 10 ps and eps files, version accepted in Physical
Review A, minor changes mad
Eating disorders in the preoperative phase of bariatric surgery
Introduction: Bariatric surgery is considered the most effective obesity treatment. Obese patients have a high prevalence of eating disorders. Objectives: Evaluate the occurrence of eating disorders and eating patterns in candidates for bariatric surgery and associate eating disorders with sociodemographic and clinical characteristics. Methods: A retrospective study was conducted using electronic charts of candidates for bariatric surgery. Data were collected on sex, age, marital status, schooling, occupation, non-communicable diseases, body mass index (BMI), eating disorders, and eating patterns. Results: Among the 281 patients evaluated, eating disorders were detected in 26.7%; 10.3% had binge eating disorder, 6.6% had bulimia nervosa, and 5.3% had the night-eating syndrome. The specific eating patterns were overeating (46.6%), binge eating during periods of stress (9.3%), eating sweets (4%), and snaking (1.3%). BMI ranged from 35.38 to 59.03 kg/m (mean: 44.37 ± 5.89). All individuals (100%) had systemic arterial hypertension, and 23.3% had type 2 diabetes mellitus or dyslipidemia. Conclusions: The frequency of eating disorders was low in the sample studied, the most common of which was binge eating disorder. Non-communicable diseases were associated with eating disorders. Among the eating patterns observed, the most frequent was overeating
Determinacy analysis for logic programs using mode and type information
We propose an analysis for detecting procedures and goals
that are deterministic (i.e. that produce at most one solution), or predicates whose clause tests are mutually exclusive (which implies that at most one of their clauses will succeed) even if they are not deterministic (because they cali other predicates that can produce more than one solution). Applications of such determinacy information include detecting programming errors, performing certain high-level program transformations for improving search efñciency, optimizing low level code generation and parallel execution, and estimating tighter upper bounds on the computational costs of goals and data sizes, which can be used for program debugging, resource consumption and granularity control, etc. We have implemented the analysis and integrated it in the CiaoPP system, which also infers automatically the mode and type information that our analysis takes as input. Experiments performed on this implementation show that the analysis is fairly accurate and efncient
Low energy electron/recoil discrimination for directional Dark Matter detection
Directional detection is a promising Dark Matter search strategy. Even though
it could accommodate to a sizeable background contamination, electron/recoil
discrimination remains a key and challenging issue as for direction-insensitive
detectors. The measurement of the 3D track may be used to discriminate
electrons from nuclear recoils. While a high rejection power is expected above
20 keV ionization, a dedicated data analysis is needed at low energy. After
identifying discriminant observables, a multivariate analysis, namely a Boosted
Decision Tree, is proposed, enabling an efficient event tagging for Dark Matter
search. We show that it allows us to optimize rejection while keeping a rather
high efficiency which is compulsory for rare event search.With respect to a
sequential analysis, the rejection is about 20 times higher with a multivariate
analysis, for the same Dark Matter exclusion limit.Comment: 20 pages, 20 figure
Electromagnetic absorption of a pinned Wigner crystal at finite temperatures
We investigate the microwave absorption of a pinned, two-dimensional Wigner
crystal in a strong magnetic field at finite temperatures. Using a model of a
uniform commensurate pinning potential, we analyze thermal broadening of the
electromagnetic absorption resonance. Surprisingly, we find that the pinning
resonance peak should remain sharp even when the temperature is comparable or
greater than the peak frequency. This result agrees qualitatively with recent
experimental observations of the ac conductivity in two-dimensional hole
systems in a magnetically induced insulating state. It is shown, in analogy
with Kohn's theorem, that the electron-electron interaction does not affect the
response of a harmonically pinned Wigner crystal to a spatially uniform
external field at any temperature. We thus focus on anharmonicity in the
pinning potential as a source of broadening. Using a 1/N expansion technique,
we show that the broadening is introduced through the self-energy corrections
to the magnetophonon Green's functions.Comment: 21 pages, 9 eps figure
Photoionization of ultracold and Bose-Einstein condensed Rb atoms
Photoionization of a cold atomic sample offers intriguing possibilities to
observe collective effects at extremely low temperatures. Irradiation of a
rubidium condensate and of cold rubidium atoms within a magneto-optical trap
with laser pulses ionizing through 1-photon and 2-photon absorption processes
has been performed. Losses and modifications in the density profile of the
remaining trapped cold cloud or the remaining condensate sample have been
examined as function of the ionizing laser parameters. Ionization
cross-sections were measured for atoms in a MOT, while in magnetic traps losses
larger than those expected for ionization process were measured.Comment: 9 pages, 7 figure
Spectral method for the time-dependent Gross-Pitaevskii equation with a harmonic trap
We study the numerical resolution of the time-dependent Gross-Pitaevskii
equation, a non-linear Schroedinger equation used to simulate the dynamics of
Bose-Einstein condensates. Considering condensates trapped in harmonic
potentials, we present an efficient algorithm by making use of a spectral
Galerkin method, using a basis set of harmonic oscillator functions, and the
Gauss-Hermite quadrature. We apply this algorithm to the simulation of
condensate breathing and scissors modes.Comment: 23 pages, 5 figure
Zeta function method and repulsive Casimir forces for an unusual pair of plates at finite temperature
We apply the generalized zeta function method to compute the Casimir energy
and pressure between an unusual pair of parallel plates at finite temperature,
namely: a perfectly conducting plate and an infinitely permeable one. The high
and low temperature limits of these quantities are discussed; relationships
between high and low temperature limits are estabkished by means of a modified
version of the temperature inversion symmetry.Comment: latex file 9 pages, 3 figure
Chemical tools for study of phosphohistidine: generation of selective Τ‐phosphohistidine and Π‐phosphohistidine antibodies
Non-hydrolysable stable analogues of τ-phosphohistidine (τ-pHis) and π-pHis have been designed aided by electrostatic surface potential calculations, and subsequently synthesized. The τ-pHis and π-pHis analogues (phosphopyrazole 8 and pyridyl amino amide 13, respectively) were used as haptens to generate pHis polyclonal antibodies. Both τ-pHis and π-pHis conjugates in the form of a BSA-glutaraldehyde-τ-pHis and BSA-glutaraldehyde-π-pHis were synthesized and characterized by 31P NMR spectroscopy. Commercially available τ-pHis (SC56-2) and π-pHis (SC1-1; SC50-3) monoclonal antibodies were used to show that the BSA-G-τ-pHis and BSA-G-π-pHis conjugates could be used to assess the selectivity of pHis antibodies in a competitive ELISA. Subsequently, the selectivity of the generated pHis antibodies generated using phosphopyrazole 8 and pyridyl amino amide 13 as haptens was assessed by competitive ELISA against His, pSer, pThr, pTyr, τ-pHis and π-pHis. Antibodies generated using the phosphopyrazole 8 as a hapten were found to be selective for τ-pHis, and antibodies generated using the pyridyl amino amide 13 were found to be selective for π-pHis. Both τ- and π-pHis antibodies were shown to be effective in immunological experiments, including ELISA, western blot, and immunofluorescence. The τ-pHis antibody was also shown to be useful in the immunoprecipitation of proteins containing pHis
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