1,644 research outputs found
Controlling quasiparticle excitations in a trapped Bose-Einstein condensate
We describe an approach to quantum control of the quasiparticle excitations
in a trapped Bose-Einstein condensate based on adiabatic and diabatic changes
in the trap anisotropy. We describe our approach in the context of Landau-Zener
transition at the avoided crossings in the quasiparticle excitation spectrum.
We show that there can be population oscillation between different modes at the
specific aspect ratios of the trapping potential at which the mode energies are
almost degenerate. These effects may have implications in the expansion of an
excited condensate as well as the dynamics of a moving condensate in an atomic
wave guide with a varying width
Structural phase transitions of vortex matter in an optical lattice
We consider the vortex structure of a rapidly rotating trapped atomic
Bose-Einstein condensate in the presence of a co-rotating periodic optical
lattice potential. We observe a rich variety of structural phases which reflect
the interplay of the vortex-vortex and vortex-lattice interactions. The lattice
structure is very sensitive to the ratio of vortices to pinning sites and we
observe structural phase transitions and domain formation as this ratio is
varied.Comment: 4 pages, 3 figure
Atmospheric frontal zone studies
The research supported by this contract and directed Activities in the inversion and interpretation of data produced by the Nimbus-7 scanning multichannel microwave radiometer (SMMR) are reported. There were five principal subjects: (1) modeling of the emissivity of foam patches on the ocean surface; (2) inversion of radiometric data by a multidimensional algorithm; (3) an operational water vapor retrieval algorithm; (4) inference of Antarctic firm accumulation rates; and (5) inference of water vapor over the Arctic sea ice
CisOrtho: A program pipeline for genome-wide identification of transcription factor target genes using phylogenetic footprinting
BACKGROUND: All known genomes code for a large number of transcription factors. It is important to develop methods that will reveal how these transcription factors act on a genome wide level, that is, through what target genes they exert their function. RESULTS: We describe here a program pipeline aimed at identifying transcription factor target genes in whole genomes. Starting from a consensus binding site, represented as a weight matrix, potential sites in a pre-filtered genome are identified and then further filtered by assessing conservation of the putative site in the genome of a related species, a process called phylogenetic footprinting. CisOrtho has been successfully used to identify targets for two homeodomain transcription factors in the genomes of the nematodes Caenorhabditis elegans and Caenorhabditis briggsae. CONCLUSIONS: CisOrtho will identify targets of other nematode transcription factors whose DNA binding specificity is known and can be easily adapted to search other genomes for transcription factor targets
Photon lifetime in a cavity containing a slow-light medium
We investigate experimentally the lifetime of the photons in a cavity
containing a medium exhibiting strong positive dispersion. This intracavity
positive dispersion is provided by a metastable helium gas at room temperature
in the electromagnetically induced transparency (EIT) regime, in which light
propagates at a group velocity of the order of 10000 m/s. The results
definitely prove that the lifetime of the cavity photons is governed by the
group velocity of light in the cavity, and not its phase velocity.Comment: Accepted for publication in Optics Letter
A Simulation Engine to Predict Multi-Agent Work in Complex, Dynamic, Heterogeneous Systems
©2011 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.DOI: 10.1109/COGSIMA.2011.5753432This paper documents a simulation engine developed
to accurately and efficiently simulate work by multiple agents in
complex dynamic systems. Agents (human or mechanical) are
modeled as responding to, and changing, their environment by
executing the actions that get and set the value of resources in the
environment. Each action comprises the processes that need to
be evaluated at the same time by the same agent, which are used
to reference (get) resources, consider them according to simple
or complicated processes, and then interact back on the environment by setting resources appropriately. This paper specifically
addresses timing within the simulation. The simplest approach
would update all actions at the smallest unit of conceivable time,
an approach that is not only computationally inefficient, but also
not an accurate representation of situated behavior. Instead, every
action declares its next update time as required to accurately
model its internal dynamics and the simulation engine executes
them asynchronously. Thus, an action and the resources it ’gets’
from the environment are not inherently contemporary; instead,
each action also specifies, for each resource value that it gets,
the quality of service required in terms of its temporal currency.
This reflects dynamics of the real processes being simulated:
when, in actual operations, would the environment be sampled,
and how accurately must its state be known? Additionally, this
also reflects dynamics of environmental resources how often (or
how fast) does each inherently change? Using these constructs,
the list of actions to be simulated are sorted by the simulation
engine according to their next update time. Each action, when its
time comes, is given to their agent model to be executed, and then
is sorted back into the action list according to its self-reported
next update time. Thus, actions are each updated when they need
to be. In situations where, for example, action Y needs to get a
resource which, because action X has not set it recently, does not
meet action Ys required Quality of Service. The simulation engine
will invoke action X immediately before action Y, mimicking
cases in the real system where one process calls on another to
establish the conditions it needs. The presented simulation engine
is a complete redevelopment, designed and written from scratch
at the Cognitive Engineering Center at the Georgia Institute of Technology
Bridging the Gap: Cognitive and social approaches to research in second language learning and teaching.
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/139862/1/SSLA2014.pd
Watching a superfluid untwist itself: Recurrence of Rabi oscillations in a Bose-Einstein condensate
The order parameter of a condensate with two internal states can continuously
distort in such a way as to remove twists that have been imposed along its
length. We observe this effect experimentally in the collapse and recurrence of
Rabi oscillations in a magnetically trapped, two-component Bose-Einstein
condensate of ^87Rb
Spin Excitations in a Fermi Gas of Atoms
We have experimentally investigated a spin excitation in a quantum degenerate
Fermi gas of atoms. In the hydrodynamic regime the damping time of the
collective excitation is used to probe the quantum behavior of the gas. At
temperatures below the Fermi temperature we measure up to a factor of 2
reduction in the excitation damping time. In addition we observe a strong
excitation energy dependence for this quantum statistical effect.Comment: 4 pages, 3 figure
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