7,138 research outputs found
Low Reynolds number multiple-time-scale turbulence model and calculations of steady and pulsating shear layers
A low Reynolds number multiple-time-scale turbulence model (LMS) and its application to fully developed turbulent channel flows and pulsating pipe flows are presented. The LMS can describe the inequilibrium turbulence phenomena down to the viscous sublayer. The calculated fluid flow and turbulence fields for the channel flows are in better agreement with the direct numerical simulation (DNS) results than those obtained using a Reynolds stress turbulence model, and the calculated near-wall dissipation rates are in qualitatively correct agreement with the DNS results. The LMS also successfully predicts the rapidly varying phase-lead of the wall shearing stress that occurs in a narrow range of the dimensionless frequency omega (+) = (omega x nu)/(upsilon x tau(exp2)) for the pulsating pipe flows while various other turbulence models fail to predict this phenomenon, and the LMS yields significantly improved numerical results for a wide range of the dimensionless frequency compared with those obtained using a rapid distortion theory (RDT)
Improvement of conversion efficiency of atom-molecule Bose-Einstein condensate
We investigate the stimulated Raman adiabatic passage in two-color
photoassociation for a atom-molecule Bose-Einstein condensate. By applying two
time-varying Guassian laser pulses that fulfill generalized two-photon
resonance condition, we obtain highly efficient atom-molecule conversion. The
efficiency depends on the free-bound detuning and the delay time between the
two pulses. By adjusting the parameters optimally, we achieve 92% conversion
efficiency.Comment: 4 pages, 4 figures. To be appeared in J. Korean Phys. Society (JKPS
Storage of spin squeezing in a two-component Bose-Einstein condensate
Efficient control of spin squeezing in a two-component Bose-Einstein
Condensate is studied by rapidly turning-off the external field at a time that
maximal spin squeezing appears. We show that strong reduction of spin
fluctuation can be maintained in a nearly fixed direction for a long time. We
explain the underlying physics unambiguously, and present analytical
expressions of the maximal-squeezing time.Comment: 10 pages, 5 figures. This version is slightly different from the one
published in Phys. Rev. Let
Statistical properties of chaotic microcavities in small and large opening cases
We study the crossover behavior of statistical properties of eigenvalues in a
chaotic microcavity with different refractive indices. The level spacing
distributions change from Wigner to Poisson distributions as the refractive
index of a microcavity decreases. We propose a non-hermitian matrix model with
random elements describing the spectral properties of the chaotic microcavity,
which exhibits the crossover behaviors as the opening strength increases.Comment: 22 pages, 6 figure
- …