176,944 research outputs found
Three-Body Losses in Trapped Bose-Einstein Condensed Gases
A time-dependent Kohn-Sham (KS)-like equation for N bosons in a trap is
generalized for the case of inelastic collisions. We derive adiabatic equations
which are used to calculate the nonlinear dynamics of the Bose-Einstein
condensate (BEC) and non-mean field corrections due to the three-body
recombination. We find that the calculated corrections are about 13 times
larger for 3D trapped dilute bose gases and about 7 times larger for 1D trapped
weakly interacting bose gases when compared with the corresponding corrections
for the ground state energy and for the collective frequencies.Comment: 11 pages, 2 figure
Approximate Coulomb distortion effects in (e,e'p) reactions
In this paper we apply a well-tested approximation of electron Coulomb
distortion effects to the exclusive reaction (e,e'p) in the quasielastic
region. We compare the approximate treatment of Coulomb distortion effects to
the exact distorted wave Born approximation evaluated by means of partial wave
analysis to gauge the quality of our approximate treatment. We show that the
approximate M\"oller potential has a plane-wave-like structure and hence
permits the separation of the cross section into five terms which depend on
bilinear products of transforms of the transition four current elements. These
transforms reduce to Fourier transforms when Coulomb distortion is not present,
but become modified with the inclusion of Coulomb distortion. We investigate
the application of the approximate formalism to a model of 208Pb(e,e'p) using
Dirac-Hartree single particle wave functions for the ground state and
relativistic optical model wave functions for the continuum proton. We show
that it is still possible to extract, albeit with some approximation, the
various structure functions from the experimentally measured data even for
heavy nuclei.Comment: 32 pages, 11 figures, 19 reference
Cold Bose Gases near Feshbach Resonances
The lowest order constrained variational method [Phys. Rev. Lett. 88, 210403
(2002)] has been generalized for a dilute (in the sense that the range of
interatomic potential is small compared with inter-particle spacing) uniform
gas of bosons near the Feshbach resonance using the multi-channel zero-range
potential model. The method has been applied to Na (F=1, m_F=1) atoms near the
G Feshbach resonance. It is shown that at high densities, there are
significant differences between our results for the real part of energy per
particle and the one-channel zero-range potential approximation. We point out
the possibility of stabilization of the uniform con densate for the case of
negative scattering length.Comment: Revised version of cond-mat/0212196. Added Eqs. (21,22) and
references for section
Extraction of Structure Functions from Quasielastic Electron Scattering (e,e') from Medium and Heavy Nuclei
Using a relativistic mean-field single particle knock-out model for (e,e')
reactions on nuclei, we investigate approximate treatments of Coulomb
distortion effects and the extraction of longitudinal and transverse structure
functions. We show that an effective momentum approximation (EMA) when coupled
with a focusing factor provides a good description of the transverse
contributions to the (e,e') cross sections for electron energies above 300 MeV
on 208Pb. This approximation is not as good for the longitudinal contributions
even for incident electron eneriges above 1 GeV and if one requires very
precise extraction of longitudinal and transverse structure functions in the
quasielastic region it is necessary to utilize distortion factors based on a
nuclear model and a more accurate inclusion of Coulomb distortion effects.Comment: 5 pages, 7 figures, submitted to Phys. Rev.
A strongly goal-directed close-range vision system for spacecraft docking
In this presentation, we will propose a strongly goal-oriented stereo vision system to establish proper docking approach motions for automated rendezvous and capture (AR&C). From an input sequence of stereo video image pairs, the system produces a current best estimate of: contact position; contact vector; contact velocity; and contact orientation. The processing demands imposed by this particular problem and its environment dictate a special case solution; such a system should necessarily be, in some sense, minimalist. By this we mean the system should construct a scene description just sufficiently rich to solve the problem at hand and should do no more processing than is absolutely necessary. In addition, the imaging resolution should be just sufficient. Extracting additional information and constructing higher level scene representations wastes energy and computational resources and injects an unnecessary degree of complexity, increasing the likelihood of malfunction. We therefore take a departure from most prior stereopsis work, including our own, and propose a system based on associative memory. The purpose of the memory is to immediately associate a set of motor commands with a set of input visual patterns in the two cameras. That is, rather than explicitly computing point correspondences and object positions in world coordinates and trying to reason forward from this information to a plan of action, we are trying to capture the essence of reflex behavior through the action of associative memory. The explicit construction of point correspondences and 3D scene descriptions, followed by online velocity and point of impact calculations, is prohibitively expensive from a computational point of view for the problem at hand. Learned patterns on the four image planes, left and right at two discrete but closely spaced instants in time, will be bused directly to infer the spacecraft reaction. This will be a continuing online process as the docking collar approaches
- …