29,417 research outputs found
Born-Oppenheimer study of two-component few-particle systems under one-dimensional confinement
The energy spectrum, atom-dimer scattering length, and atom-trimer scattering
length for systems of three and four ultracold atoms with -function
interactions in one dimension are presented as a function of the relative mass
ratio of the interacting atoms. The Born-Oppenheimer approach is used to treat
three-body ("HHL") systems of one light and two heavy atoms, as well as
four-body ("HHHL") systems of one light and three heavy atoms. Zero-range
interactions of arbitrary strength are assumed between different atoms, but the
heavy atoms are assumed to be noninteracting among themselves. Both fermionic
and bosonic heavy atoms are considered.Comment: 22 pages, 6 figures. Includes both positive and negative parity cases
for the four-body secto
Few-Boson Processes in the Presence of an Attractive Impurity under One-Dimensional Confinement
We consider a few-boson system confined to one dimension with a single
distinguishable particle of lesser mass. All particle interactions are modeled
with -functions, but due to the mass imbalance the problem is
nonintegrable. Universal few-body binding energies, atom-dimer and atom-trimer
scattering lengths are all calculated in terms of two parameters, namely the
mass ratio: , and ratio
of the -function couplings. We
specifically identify the values of these ratios for which the atom-dimer or
atom-trimer scattering lengths vanish or diverge. We identify regions in this
parameter space in which various few-body inelastic process become
energetically allowed. In the Tonks-Girardeau limit (), our results are relevant to experiments involving trapped fermions
with an impurity atom
Computational aerodynamics and artificial intelligence
The general principles of artificial intelligence are reviewed and speculations are made concerning how knowledge based systems can accelerate the process of acquiring new knowledge in aerodynamics, how computational fluid dynamics may use expert systems, and how expert systems may speed the design and development process. In addition, the anatomy of an idealized expert system called AERODYNAMICIST is discussed. Resource requirements for using artificial intelligence in computational fluid dynamics and aerodynamics are examined. Three main conclusions are presented. First, there are two related aspects of computational aerodynamics: reasoning and calculating. Second, a substantial portion of reasoning can be achieved with artificial intelligence. It offers the opportunity of using computers as reasoning machines to set the stage for efficient calculating. Third, expert systems are likely to be new assets of institutions involved in aeronautics for various tasks of computational aerodynamics
Smoothing of sandpile surfaces after intermittent and continuous avalanches: three models in search of an experiment
We present and analyse in this paper three models of coupled continuum
equations all united by a common theme: the intuitive notion that sandpile
surfaces are left smoother by the propagation of avalanches across them. Two of
these concern smoothing at the `bare' interface, appropriate to intermittent
avalanche flow, while one of them models smoothing at the effective surface
defined by a cloud of flowing grains across the `bare' interface, which is
appropriate to the regime where avalanches flow continuously across the
sandpile.Comment: 17 pages and 26 figures. Submitted to Physical Review
A study of the factors affecting boundary layer two-dimensionality in wind tunnels
The effect of screens, honeycombs, and centrifugal blowers on the two-dimensionality of a boundary layer on the test section floors of low-speed blower tunnels is studied. Surveys of the spanwise variation in surface shear stress in three blower tunnels revealed that the main component responsible for altering the spanwise properties of the test section boundary layer was the last screen, thus confirming previous findings. It was further confirmed that a screen with varying open-area ratio, produced an unstable flow. However, contrary to popular belief, it was also found that for given incoming conditions and a screen free of imperfections, its open-area ratio alone was not enough to describe its performance. The effect of other geometric parameters such as the type of screen, honeycomb, and blower were investigated. In addition, the effect of the order of components in the settling chamber, and of wire Reynolds number were also studied
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