1,950 research outputs found
On the shape of vortices for a rotating Bose Einstein condensate
For a Bose-Einstein condensate placed in a rotating trap, we study the
simplified energy of a vortex line derived in Aftalion-Riviere Phys. Rev. A 64,
043611 (2001) in order to determine the shape of the vortex line according to
the rotational velocity and the elongation of the condensate. The energy
reflects the competition between the length of the vortex which needs to be
minimized taking into account the anisotropy of the trap and the rotation term
which pushes the vortex along the z axis. We prove that if the condensate has
the shape of a pancake, the vortex stays straight along the z axis while in the
case of a cigar, the vortex is bent
Pulsed Adiabatic Photoassociation via Scattering Resonances
We develop the theory for the Adiabatic Raman Photoassociation (ARPA) of
ultracold atoms to form ultracold molecules in the presence of scattering
resonances. Based on a computational method in which we replace the continuum
with a discrete set of "effective modes", we show that the existence of
resonances greatly aids in the formation of deeply bound molecular states. We
illustrate our general theory by computationally studying the formation of
Rb molecules from pairs of colliding ultracold Rb atoms. The
single-event transfer yield is shown to have a near-unity value for wide
resonances, while the ensemble-averaged transfer yield is shown to be higher
for narrow resonances. The ARPA yields are compared with that of (the
experimentally measured) "Feshbach molecule" magneto-association. Our findings
suggest that an experimental investigation of ARPA at sub-K temperatures
is warranted.Comment: 20 pages, 11 figure
Dissipative dynamics of vortex arrays in trapped Bose-condensed gases: neutron stars physics on K scale
We develop a theory of dissipative dynamics of large vortex arrays in trapped
Bose-condensed gases. We show that in a static trap the interaction of the
vortex array with thermal excitations leads to a non-exponential decay of the
vortex structure, and the characteristic lifetime depends on the initial
density of vortices. Drawing an analogy with physics of pulsar glitches, we
propose an experiment which employs the heating of the thermal cloud in the
course of the decay of the vortex array as a tool for a non-destructive study
of the vortex dynamics.Comment: 4 pages, revtex; revised versio
The effects of temperature on Bosmina longirostris susceptibility to microcystin-LR acute toxicity
Harmful algal blooms are an ongoing threat to many aquatic systems throughout the world. In the Chowan River, North Carolina, the frequency of toxin producing Microcystis aeruginosa blooms has increased since 1975 along with an average 0.71°C rise in water temperature. The combined effect of microcystin-LR toxin and rising temperatures on a dominant zooplankter in the system, Bosmina longirostris, was the focus of this study. Laboratory studies were conducted to determine how microcystin-LR, produced from M. aeruginosa blooms, affected B. longirostris mortality under different temperature regimes. At 25°C, the LC50 for B. longirostris was 26.3 μg L-1 suggesting that B. longirostris can survive typical current bloom microcystin-LR concentrations ranging 0.1μg L-1 to 2.0 μg L-1, but would be susceptible to higher concentrations they may be periodically exposed to. Mortality was assessed at a constant microcystin-LR concentration of 26.3 μg L-1 over 15–35°C, and it was found that B. longirostris mortality increased at higher temperatures. B. longirostris mortality increased approximately 18% due to microcystin-LR alone over 2°C between 25°C and 27°C when exposed to the LC50 concentration. The increased prevalence of toxic M. aeruginosa blooms and increasing temperatures due to climate change may reduce B. longirostris populations, potentially affecting larval fish and fisheries in the Chowan River, North Carolina
Vortex Lattice Structures of a Bose-Einstein Condensate in a Rotating Lattice Potential
We study vortex lattice structures of a trapped Bose-Einstein condensate in a
rotating lattice potential by numerically solving the time-dependent
Gross-Pitaevskii equation. By rotating the lattice potential, we observe the
transition from the Abrikosov vortex lattice to the pinned lattice. We
investigate the transition of the vortex lattice structure by changing
conditions such as angular velocity, intensity, and lattice constant of the
rotating lattice potential.Comment: 6 pages, 8 figures, submitted to Quantum Fluids and Solids Conference
(QFS 2006
Manifestation of superfluidity in an evolving Bose-condensed gas
We study the generation of excitations due to an ''impurity''(static
perturbation) placed into an oscillating Bose-condensed gas in the
time-dependent trapping field. It is shown that there are two regions for the
position of the local perturbation. In the first region the condensate flows
around the ''impurity'' without generation of excitations demonstrating
superfluid properties. In the second region the creation of excitations occurs,
at least within a limited time interval, revealing destruction of
superfluidity. The phenomenon can be studied by measuring the damping of
condensate oscillations at different positions of the ''impurity''
Allosteric HIV-1 integrase inhibitors lead to premature degradation of the viral RNA genome and integrase in target cells
ABSTRACT
Recent evidence indicates that inhibition of HIV-1 integrase (IN) binding to the viral RNA genome by allosteric integrase inhibitors (ALLINIs) or through mutations within IN yields aberrant particles in which the viral ribonucleoprotein complexes (vRNPs) are eccentrically localized outside the capsid lattice. These particles are noninfectious and are blocked at an early reverse transcription stage in target cells. However, the basis of this reverse transcription defect is unknown. Here, we show that the viral RNA genome and IN from ALLINI-treated virions are prematurely degraded in target cells, whereas reverse transcriptase remains active and stably associated with the capsid lattice. The aberrantly shaped cores in ALLINI-treated particles can efficiently saturate and be degraded by a restricting TRIM5 protein, indicating that they are still composed of capsid proteins arranged in a hexagonal lattice. Notably, the fates of viral core components follow a similar pattern in cells infected with eccentric particles generated by mutations within IN that inhibit its binding to the viral RNA genome. We propose that IN-RNA interactions allow packaging of both the viral RNA genome and IN within the protective capsid lattice to ensure subsequent reverse transcription and productive infection in target cells. Conversely, disruption of these interactions by ALLINIs or mutations in IN leads to premature degradation of both the viral RNA genome and IN, as well as the spatial separation of reverse transcriptase from the viral genome during early steps of infection.
IMPORTANCE
Recent evidence indicates that HIV-1 integrase (IN) plays a key role during particle maturation by binding to the viral RNA genome. Inhibition of IN-RNA interactions yields aberrant particles with the viral ribonucleoprotein complexes (vRNPs) eccentrically localized outside the conical capsid lattice. Although these particles contain all of the components necessary for reverse transcription, they are blocked at an early reverse transcription stage in target cells. To explain the basis of this defect, we tracked the fates of multiple viral components in infected cells. Here, we show that the viral RNA genome and IN in eccentric particles are prematurely degraded, whereas reverse transcriptase remains active and stably associated within the capsid lattice. We propose that IN-RNA interactions ensure the packaging of both vRNPs and IN within the protective capsid cores to facilitate subsequent reverse transcription and productive infection in target cells.
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Periodically-dressed Bose-Einstein condensates: a superfluid with an anisotropic and variable critical velocity
Two intersecting laser beams can produce a spatially-periodic coupling
between two components of an atomic gas and thereby modify the dispersion
relation of the gas according to a dressed-state formalism. Properties of a
Bose-Einstein condensate of such a gas are strongly affected by this
modification. A Bogoliubov transformation is presented which accounts for
interparticle interactions to obtain the quasiparticle excitation spectrum in
such a condensate. The Landau critical velocity is found to be anisotropic and
can be widely tuned by varying properties of the dressing laser beams.Comment: 5 pages, 4 figure
Calibration of distorted wave Born approximation for electron impact excitation of Ne and Ar at incident energies below 100 eV
We calibrate the distorted wave Born approximation (DWBA) for electron impact
excitation processes empirically. Differential cross sections (DCS) for the
excitation of the , ,, and configurations of
Ne and the and configurations of Ar by electron impact are
calculated using DWBA for incident energies between 20 and 100 eV. The
calculated results are compared with the absolute experimental measurements and
other theoretical results. We found that the structure of the DCS can be well
reproduced by the DWBA model while the magnitude is overestimated for most
cases considered here. The differences in magnitude between DWBA and experiment
are used to test the calibration of DWBA such that the DWBA can be used to
describe laser-induced electron impact excitation processes. These processes
are involved in the non-sequential double ionization of atoms in strong laser
fields.Comment: 10 pages, 8 figure
Two-component Bose-Einstein Condensates with Large Number of Vortices
We consider the condensate wavefunction of a rapidly rotating two-component
Bose gas with an equal number of particles in each component. If the
interactions between like and unlike species are very similar (as occurs for
two hyperfine states of Rb or Na) we find that the two components
contain identical rectangular vortex lattices, where the unit cell has an
aspect ratio of , and one lattice is displaced to the center of the
unit cell of the other. Our results are based on an exact evaluation of the
vortex lattice energy in the large angular momentum (or quantum Hall) regime.Comment: 4 pages, 2 figures, RevTe
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