4,622 research outputs found
Periodic Modulation Effect on Self-Trapping of Two weakly coupled Bose-Einstein Condensates
With phase space analysis approach, we investigate thoroughly the
self-trapping phenomenon for two weakly coupled Bose-Einstein condensates (BEC)
in a symmetric double-well potential. We identify two kinds of self-trapping by
their different relative phase behavior. With applying a periodic modulation on
the energy bias of the system we find the occurrence of the self-trapping can
be controlled, saying, the transition parameters can be adjusted effectively by
the periodic modulation. Analytic expressions for the dependence of the
transition parameters on the modulation parameters are derived for high and low
frequency modulations. For an intermediate frequency modulation, we find the
resonance between the periodic modulation and nonlinear Rabi oscillation
dramatically affects the tunnelling dynamics and demonstrate many novel
phenomena. Finally, we study the effects of many-body quantum fluctuation on
self-trapping and discuss the possible experimental realization of the model.Comment: 7 pages, 11 figure
Strong cosmic censorship for the massless Dirac field in the Reissner-Nordstrom-de Sitter spacetime
We present the Fermi story of strong cosmic censorship in the near-extremal
Reissner-Nordstrom-de Sitter black hole. To this end, we first derive from
scratch the criterion for the quasi-normal modes of Dirac field to violate
strong cosmic censorship in such a background, which turns out to be exactly
the same as those for Bose fields, although the involved energy momentum tensor
is qualitatively different from that for Bose fields. Then to extract the
low-lying quasi-normal modes by Prony method, we apply Crank-Nicolson method to
evolve our Dirac field in the double null coordinates. As a result, it shows
that for a fixed near-extremal black hole, strong cosmic censorship can be
recovered by the black hole family mode once the charge of our
Dirac field is greater than some critical value, which is increased as one
approaches the extremal black hole.Comment: JHEP published versio
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Analysis of Down syndrome failed to be diagnosed after prenatal screening: A multicenter study.
To analyze the characters of Down syndrome (DS) who failed to be diagnosed after prenatal screening and hope to be able to improve the programs of prenatal screening and reduce the missed diagnosis of DS. In this multicenter study, we collected the missed cases from 3 prenatal diagnosis centers and analyzed their characters. A total of 126 DS babies failed to be diagnosed after prenatal screening. Their mothers accepted the prenatal screening in second trimester. We collected the mothers' blood and detected the levels of alpha-fetoprotein (AFP) and the free beta subunit of human chorionic gonadotropin (fβhCG) by time-resolved fluoroimmunoassay. The values were also presented as multiples of the median (MoM) and determined the risk of carrying a fetus with DS by Wallace LifeCycle Elipse analysis software. Compared with normal control group, the level of fβhCG and hCG MoM were dramatically increased, while AFP and AFP MoM were decreased. The area under the receiver-operating-characteristic curve of trisomy 21 was 0.8387 for hCG-MoM and AFP-MoM testing. The sensitivity, specificity, positive predictive value, and negative predictive value were 84.6%, 74.8%, 75.4%, and 83.6%, respectively. Meanwhile, the prediction mode was "0.39957 + 1.90897HCG-MOM -3.32713AFP-MOM". It was worthwhile noting that the risk of 65.9% DS missed diagnosis group were higher than 1/1000, 92.9% higher than 1/3000. However, 72.5% cases in normal control group were lower than 1/3000. Only 9.2% mothers would be higher than the value of risk in 1/1000. The prediction mode of hCG MoM and AFP MoM might be able to help us reduce the missed diagnosis. It is also necessary to adjust more reasonable range of noninvasive prenatal testing with further clinical researches
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