18,752 research outputs found
Coherent Collisions between Bose-Einstein Condensates
We study the non-degenerate parametric amplifier for matter waves,
implemented by colliding two Bose-Einstein condensates. The coherence of the
amplified waves is shown by observing high contrast interference with a
reference wave and by reversing the amplification process. Since our
experiments also place limits on all known sources of decoherence, we infer
that relative number squeezing is most likely present between the amplified
modes. Finally, we suggest that reversal of the amplification process may be
used to detect relative number squeezing without requiring single-particle
detection.Comment: 4.2 pages, 4 figures, please take postscript version for best quality
of picture
Exact phase diagrams for an Ising model on a two-layer Bethe lattice
Using an iteration technique, we obtain exact expressions for the free energy
and the magnetization of an Ising model on a two - layer Bethe lattice with
intralayer coupling constants J1 and J2 for the first and the second layer,
respectively, and interlayer coupling constant J3 between the two layers; the
Ising spins also couple with external magnetic fields, which are different in
the two layers. We obtain exact phase diagrams for the system.Comment: 24 pages, 2 figures. To be published in Phys. Rev. E 59, Issue 6,
199
Efficient fault diagnosis of helicopter gearboxes
Application of a diagnostic system to a helicopter gearbox is presented. The diagnostic system is a nonparametric pattern classifier that uses a multi-valued influence matrix (MVIM) as its diagnostic model and benefits from a fast learning algorithm that enables it to estimate its diagnostic model from a small number of measurement-fault data. To test this diagnostic system, vibration measurements were collected from a helicopter gearbox test stand during accelerated fatigue tests and at various fault instances. The diagnostic results indicate that the MVIM system can accurately detect and diagnose various gearbox faults so long as they are included in training
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