11,421 research outputs found
Ground Band and a Generalized GP-equation for Spinor Bose-Einstein Condensates
For the spinor Bose-Einstein condensates both the total spin and its
Z-component should be conserved. However, in existing theories, only
the conservation of has been taken into account. To remedy, this paper
is the first attempt to take the conservation of both and into
account. For this purpose, a total spin-state with the good quantum numbers
and is introduced in the trial wave function, thereby a generalized
Gross-Pitaevskii equation has been derived. With this new equation, the ground
bands of the Na and Rb condensates have been studied, where the
levels distinct in split. It was found that the level density is extremely
dense in the bottom of the ground band of Na, i.e., in the vicinity of
the ground state. On the contrary, for Rb, the levels are extremely
dense in the top of the ground band,Comment: 7 page, 5 figure
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Two-phase flow and oxygen transport in the perforated gas diffusion layer of proton exchange membrane fuel cell
Liquid water transport in perforated gas diffusion layers (GDLs)is numerically investigated using a three-dimensional (3D)two-phase volume of fluid (VOF)model and a stochastic reconstruction model of GDL microstructures. Different perforation depths and diameters are investigated, in comparison with the GDL without perforation. It is found that perforation can considerably reduce the liquid water level inside a GDL. The perforation diameter (D = 100 μm)and the depth (H = 100 μm)show pronounced effect. In addition, two different perforation locations, i.e. the GDL center and the liquid water break-through point, are investigated. Results show that the latter perforation location works more efficiently. Moreover, the perforation perimeter wettability is studied, and it is found that a hydrophilic region around the perforation further reduces the water saturation. Finally, the oxygen transport in the partially-saturated GDL is studied using an oxygen diffusion model. Results indicate that perforation reduces the oxygen diffusion resistance in GDLs and improves the oxygen concentration at the GDL bottom up to 101% (D = 100 μm and H = 100 μm)
Repeating head-on collisions in an optical trap and the evaluation of spin-dependent interactions among neutral particles
A dynamic process of repeating collisions of a pair of trapped neutral
particles with weak spin-dependent interaction is designed and studied. Related
theoretical derivation and numerical calculation have been performed to study
the inherent coordinate-spin and momentum-spin correlation. Due to the
repeating collisions the effect of the weak interaction can be accumulated and
enlarged, and therefore can be eventually detected. Numerical results suggest
that the Cr-Cr interaction, which has not yet been completely clear, could be
thereby determined. The design can be in general used to determine various
interactions among neutral atoms and molecules, in particular for the
determination of very weak forces.Comment: 15 pages, 7 figure
Two-body scattering in a trap and a special periodic phenomenon sensitive to the interaction
Two-body scattering of neutral particles in a trap is studied theoretically.
The control of the initial state is realized by using optical traps. The
collisions inside the trap occur repeatedly; thereby the effect of interaction
can be accumulated. Two periodic phenomena with a shorter and a much longer
period, respectively, are found. The latter is sensitive to the interaction.
Instead of measuring the differential cross section as usually does, the
measurement of the longer period and the details of the periodic behavior might
be a valid source of information on weak interactions among neutral particles.Comment: 5 pages, 5 figure
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