508 research outputs found
Making, probing and understanding Bose-Einstein condensates
Contribution to the proceedings of the 1998 Enrico Fermi summer school on
Bose-Einstein condensation in Varenna, Italy.Comment: Long review paper with ~90 pages, ~20 figures. 2 GIF figures in
separate files (4/5/99 fixed figure
Ultracold neutral plasma expansion in two dimensions
We extend an isothermal thermal model of ultracold neutral plasma expansion
to systems without spherical symmetry, and use this model to interpret new
fluorescence measurements on these plasmas. By assuming a self-similar
expansion, it is possible to solve the fluid equations analytically and to
include velocity effects to predict the fluorescence signals. In spite of the
simplicity of this approach, the model reproduces the major features of the
experimental data
Fluorescence measurements of expanding strongly-coupled neutral plasmas
We report new detailed density profile measurements in expanding
strongly-coupled neutral plasmas. Using laser-induced fluorescence techniques,
we determine plasma densities in the range of 10^5 to 10^9/cm^3 with a time
resolution limit as small as 7 ns. Strong-coupling in the plasma ions is
inferred directly from the fluorescence signals. Evidence for strong-coupling
at late times is presented, confirming a recent theoretical result.Comment: submitted to PR
On Fully Dynamic Graph Sparsifiers
We initiate the study of dynamic algorithms for graph sparsification problems and obtain fully dynamic algorithms, allowing both edge insertions and edge deletions, that take polylogarithmic time after each update in the graph. Our three main results are as follows. First, we give a fully dynamic algorithm for maintaining a -spectral sparsifier with amortized update time . Second, we give a fully dynamic algorithm for maintaining a -cut sparsifier with \emph{worst-case} update time . Both sparsifiers have size . Third, we apply our dynamic sparsifier algorithm to obtain a fully dynamic algorithm for maintaining a -approximation to the value of the maximum flow in an unweighted, undirected, bipartite graph with amortized update time
Atomic wave packet dynamics in finite time-dependent optical lattices
Atomic wave packets in optical lattices which are both spatially finite and
time-dependent exhibit many striking similarities with light pulses in photonic
crystals. We analytically characterize the transmission properties of such a
potential geometry for an ideal gas in terms of a position-dependent band
structure. In particular, we find that at specific energies, wave packets at
the center of the finite lattice may be enclosed by pairs of band gaps. These
act as mirrors between which the atomic wave packet is reflected, thereby
effectively yielding a matter wave cavity. We show that long trapping times may
be obtained in such a resonator and investigate the collapse and revival
dynamics of the atomic wave packet by numerical evaluation of the Schr\"odinger
equation
FLIGHT INFORMATION PRIORITY BY PHASE
Includes Supplementary MaterialMilitary helicopter pilots must receive, analyze, communicate, and react to large amounts of information during a flight. Pilots continuously filter through information to identify what is relevant at the current point in their mission based on the operational and flight-specific situation. While fusing information, pilots may experience cognitive overload that results in degraded performance and contributes to catastrophic events. This report investigates whether pilots require different information during different phases of flight, what specific information pilots need during these phases, and how pilots want to receive different types of information. A survey was sent to 3600 US Army UH-60 pilots (362 completed at least one portion of the survey; response rate of ~10%) asking them to prioritize 31 information items (very important, important, somewhat important) by phase of flight. The survey was followed by UH-60 pilot focus groups conducted at Fort Drum, NY. The research team found that desired information varies by phase, identified the specific information needed in each phase, and determined that pilots prefer most information to be presented visually. The conclusions of this study can inform future cockpit designs that integrate emerging technologies while reducing pilot cognitive load and increasing operational efficiency and safety.Captain, United States ArmyCaptain, United States ArmyCaptain, United States ArmyCaptain, United States ArmyCaptain, United States ArmyCaptain, United States ArmyApproved for public release. Distribution is unlimited
Extracting density-density correlations from in situ images of atomic quantum gases
We present a complete recipe to extract the density-density correlations and
the static structure factor of a two-dimensional (2D) atomic quantum gas from
in situ imaging. Using images of non-interacting thermal gases, we characterize
and remove the systematic contributions of imaging aberrations to the measured
density-density correlations of atomic samples. We determine the static
structure factor and report results on weakly interacting 2D Bose gases, as
well as strongly interacting gases in a 2D optical lattice. In the strongly
interacting regime, we observe a strong suppression of the static structure
factor at long wavelengths.Comment: 15 pages, 5 figure
Long-Term Stability of an Area-Reversible Atom-Interferometer Sagnac Gyroscope
We report on a study of the long-term stability and absolute accuracy of an
atom interferometer gyroscope. This study included the implementation of an
electro-optical technique to reverse the vector area of the interferometer for
reduced systematics and a careful study of systematic phase shifts. Our data
strongly suggests that drifts less than 96 deg/hr are possible after
empirically removing shifts due to measured changes in temperature, laser
intensity, and several other experimental parameters.Comment: 4 pages, 4 figures, submitted to PR
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