89,159 research outputs found
Meanfield treatment of Bragg scattering from a Bose-Einstein condensate
A unified semiclassical treatment of Bragg scattering from Bose-Einstein
condensates is presented. The formalism is based on the Gross-Pitaevskii
equation driven by classical light fields far detuned from atomic resonance. An
approximate analytic solution is obtained and provides quantitative
understanding of the atomic momentum state oscillations, as well as a simple
expression for the momentum linewidth of the scattering process. The validity
regime of the analytic solution is derived, and tested by three dimensional
cylindrically symmetric numerical simulations.Comment: 21 pages, 10 figures. Minor changes made to documen
An Improved Procedure for Laboratory Rearing of the Corn Earworm, \u3ci\u3eHeliothis Zea\u3c/i\u3e (Lepidoptera: Noctuidae)
An improved method for the laboratory rearing of the corn earworm. Heliothis zea, described. The rearing medium is a modification of the commonly used wheat germ An oviposition chamber, a feeder for adults, and a simple and inexpensive contrnlled humidity chamber are described
Diffractive energy spreading and its semiclassical limit
We consider driven systems where the driving induces jumps in energy space:
(1) particles pulsed by a step potential; (2) particles in a box with a moving
wall; (3) particles in a ring driven by an electro-motive-force. In all these
cases the route towards quantum-classical correspondence is highly non-trivial.
Some insight is gained by observing that the dynamics in energy space, where
is the level index, is essentially the same as that of Bloch electrons in a
tight binding model, where is the site index. The mean level spacing is
like a constant electric field and the driving induces long range hopping
1/(n-m).Comment: 19 pages, 11 figs, published version with some improved figure
Recommended from our members
Nevus sebaceus with syringocystadenoma papilliferum, prurigo nodularis, apocrine cystadenoma, basaloid follicular proliferation, and sebaceoma: case report and review of nevus sebaceus-associated conditions
Nevus sebaceus is a benign skin hamartoma of congenital onset that grows during puberty, and in adulthood can develop secondary benign and malignant neoplasms. The most common benign neoplasms occurring in nevus sebaceus are believed to be syringocystadenoma papilliferum, trichilemmoma, and trichoblastoma. A patient with nevus sebaceus developed not only syringocystadenoma papilliferum but also prurigo nodularis within her hamartomatous lesion; multiple biopsies were necessary to establish the diagnoses. Excision of the residual nevus sebaceus also revealed an apocrine cystadenoma, basaloid follicular proliferation, and sebaceoma. Also, it is important to select the appropriate biopsy site and size when evaluating a patient for secondary neoplasms within their nevus sebaceous. Indeed, more than one biopsy may be required if additional diagnoses are suspected
Star formation in Carina OB1: Observations of a giant molecular cloud associated with the eta Carinae Nebula
A giant molecular cloud associated with the eta Carinae nebula was fully mapped in CO with the Columbia Millimeter-Wave Telescope at Cerro Tololo. The cloud comples has a mass of roughly 700,000 solar mass and extends about 140 pc along the Galactic plane, with the giant Carina HII region situated at one end of the complex. Clear evidence of interaction between the HII region and the molecular cloud is found in the relative motions of the ionized gas, the molecular gas, and the dust; simple energy and momentum considerations suggest that the HII region is responsible for the observed motion of a cloud fragment. The molecular cloud complex appears to be the parent material of the entire Car OB1 Association which, in addition to the young clusters in the Carine nebula, includes the generally older cluster NGC 3325, NGC 3293, and IC 2581. The overall star formation efficiency in the cloud complex is estimated to be approximately 0.02
Large Magnetic Fields and Motions of OH Masers in W75 N
We report on a second epoch of VLBA observations of the 1665 and 1667 MHz OH
masers in the massive star-forming region W75 N. We find evidence to confirm
the existence of very strong (~40 mG) magnetic fields near source VLA 2. The
masers near VLA 2 are dynamically distinct and include a very bright spot
apparently moving at 50 km/s relative to those around VLA 1. This fast-moving
spot may be an example of a rare class of OH masers seen in outflows in
star-forming regions. Due to the variability of these masers and the rapidity
of their motions, tracking these motions will require multiple observations
over a significantly shorter time baseline than obtained here. Proper motions
of the masers near VLA 1 are more suggestive of streaming along magnetized
shocks rather than Keplerian rotation in a disk. The motions of the easternmost
cluster of masers in W75 N (B) may be tracing slow expansion around an unseen
exciting source.Comment: 7 pages including 4 figures (2 color) & 3 tables, to appear in Ap
Charge Transfer in Partition Theory
The recently proposed Partition Theory (PT) [J.Phys.Chem.A 111, 2229 (2007)]
is illustrated on a simple one-dimensional model of a heteronuclear diatomic
molecule. It is shown that a sharp definition for the charge of molecular
fragments emerges from PT, and that the ensuing population analysis can be used
to study how charge redistributes during dissociation and the implications of
that redistribution for the dipole moment. Interpreting small differences
between the isolated parts' ionization potentials as due to environmental
inhomogeneities, we gain insight into how electron localization takes place in
H2+ as the molecule dissociates. Furthermore, by studying the preservation of
the shapes of the parts as different parameters of the model are varied, we
address the issue of transferability of the parts. We find good transferability
within the chemically meaningful parameter regime, raising hopes that PT will
prove useful in chemical applications.Comment: 12 pages, 16 figure
Life and death of a hero - Lessons learned from modeling the dwarf spheroidal Hercules: an incorrect orbit?
Hercules is a dwarf spheroidal satellite of the Milky Way, found at a
distance of about 138 kpc, and showing evidence of tidal disruption. It is very
elongated and exhibits a velocity gradient of 16 +/- 3 km/s/kpc. Using this
data a possible orbit of Hercules has previously been deduced in the
literature. In this study we make use of a novel approach to find a best fit
model that follows the published orbit. Instead of using trial and error, we
use a systematic approach in order to find a model that fits multiple
observables simultaneously. As such, we investigate a much wider parameter
range of initial conditions and ensure we have found the best match possible.
Using a dark matter free progenitor that undergoes tidal disruption, our
best-fit model can simultaneously match the observed luminosity, central
surface brightness, effective radius, velocity dispersion, and velocity
gradient of Hercules. However, we find it is impossible to reproduce the
observed elongation and the position angle of Hercules at the same time in our
models. This failure persists even when we vary the duration of the simulation
significantly, and consider a more cuspy density distribution for the
progenitor. We discuss how this suggests that the published orbit of Hercules
is very likely to be incorrect.Comment: accepted by MNRAS; 19 pages, 19 figures, 2 table
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