45,119 research outputs found
Spontaneous creation of non-zero angular momentum modes in tunnel-coupled two-dimensional degenerate Bose gases
We investigate the dynamics of two tunnel-coupled two-dimensional degenerate
Bose gases. The reduced dimensionality of the clouds enables us to excite
specific angular momentum modes by tuning the coupling strength, thereby
creating striking patterns in the atom density profile. The extreme sensitivity
of the system to the coupling and initial phase difference results in a rich
variety of subsequent dynamics, including vortex production, complex
oscillations in relative atom number and chiral symmetry breaking due to
counter-rotation of the two clouds.Comment: 7 pages, 5 figure
Quantifying Finite Temperature Effects in Atom Chip Interferometry of Bose-Einstein Condensates
We quantify the effect of phase fluctuations on atom chip interferometry of
Bose-Einstein condensates. At very low temperatures, we observe small phase
fluctuations, created by mean-field depletion, and a resonant production of
vortices when the two clouds are initially in anti-phase. At higher
temperatures, we show that the thermal occupation of Bogoliubov modes makes
vortex production vary smoothly with the initial relative phase difference
between the two atom clouds. We also propose a technique to observe vortex
formation directly by creating a weak link between the two clouds. The position
and direction of circulation of the vortices is subsequently revealed by kinks
in the interference fringes produced when the two clouds expand into one
another. This procedure may be exploited for precise force measurement or
motion detection.Comment: 7 pages, 5 figure
Design definition of a mechanical capacitor
A design study and analyses of a 10 kW-hr, 15 kW mechanical capacitor system was studied. It was determined that magnetically supported wheels constructed of advanced composites have the potential for high energy density and high power density. Structural concepts are analyzed that yield the highest energy density of any structural design yet reported. Particular attention was paid to the problem of 'friction' caused by magnetic and I to the second power R losses in the suspension and motor-generator subsystems, and low design friction levels have been achieved. The potentially long shelf life of this system, and the absence of wearing parts, provide superior performance over conventional flywheels supported with mechanical bearings. Costs and economies of energy storage wheels were reviewed briefly
JPL preferred parts list: Reliable electronic components
The JPL Preferred Parts List was prepared to provide a basis for selection of electronic parts for JPL spacecraft programs. Supporting tests for the listed parts were designed to comply with specific spacecraft environmental requirements. The list tabulates the electronic, magnetic, and electromechanical parts applicable to all JPL electronic equipment wherein reliability is a major concern. The parts listed are revelant to equipment supplied by subcontractors as well as fabricated at the laboratory
Transmission and Reflection of Bose-Einstein Condensates Incident on a Gaussian Potential Barrier
We investigate how Bose-Einstein condensates, whose initial state is either
irrotational or contains a single vortex, scatter off a one-dimensional
Gaussian potential barrier. We find that for low atom densities the vortex
structure within the condensate is maintained during scattering, whereas at
medium and high densities, multiple additional vortices can be created by the
scattering process, resulting in complex dynamics and disruption of the atom
cloud. This disruption originates from two different mechanisms associated
respectively with the initial rotation of the atom cloud and the interference
between the incident and reflected matter waves. We investigate how the
reflection probability depends on the vorticity of the initial state and on the
incident velocity of the Bose-Einstein condensate. To interpret our results, we
derive a general analytical expression for the reflection coefficient of a
rotating Bose-Einstein condensate that scatters off a spatially-varying
one-dimensional potential.Comment: 9 pages, 9 figure
Formation of fundamental structures in Bose-Einstein Condensates
The meanfield interaction in a Bose condensate provides a nonlinearity which
can allow stable structures to exist in the meanfield wavefunction. We discuss
a number of examples where condensates, modelled by the one dimensional Gross
Pitaevskii equation, can produce gray solitons and we consider in detail the
case of two identical condensates colliding in a harmonic trap. Solitons are
shown to form from dark interference fringes when the soliton structure,
constrained in a defined manner, has lower energy than the interference fringe
and an analytic expression is given for this condition.Comment: 7 pages, 3 figures, requires ioplppt.st
Anomalous quantum reflection of Bose-Einstein condensates from a silicon surface: the role of dynamical excitations
We investigate the effect of inter-atomic interactions on the
quantum-mechanical reflection of Bose-Einstein condensates from regions of
rapid potential variation. The reflection process depends critically on the
density and incident velocity of the condensate. For low densities and high
velocities, the atom cloud has almost the same form before and after
reflection. Conversely, at high densities and low velocities, the reflection
process generates solitons and vortex rings that fragment the condensate. We
show that this fragmentation can explain the anomalously low reflection
probabilities recently measured for low-velocity condensates incident on a
silicon surface.Comment: 5 figures, 5 pages, references correcte
Soil Aggregate Dynamics, Particulate Organic Matter and Phosphate under Dryland and Irrigated Pasture
Soil aggregate formation and turnover affects the rate of occlusion or release of soil organic matter and therefore the availability for mineralisation or stabilisation of soil carbon (C) and phosphorus (P). Furthermore, differences in soil type, management and the quantity and quality of organic inputs can affect aggregate turnover rates (Six et al., 2000). Under pastoral farming the ratio of coarse particulate organic matter (inter-POM) inside macroaggregates but outside microaggregates to fine POM (intra-POM) within microaggregates may provide an indication of physical processes influencing mineralisation and stabilisation of soil C and organic P (Po). Our aim was to determine the coarse and fine POM and associated C and P contents in water stable macro and microaggregates under long term irrigated and dryland pasture grazed by sheep
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