18,250 research outputs found
Coherence and Josephson oscillations between two tunnel-coupled one-dimensional atomic quasicondensates at finite temperature
We revisit the theory of tunnel-coupled atomic quasicondensates in
double-well elongated traps at finite temperatures. Using the
functional-integral approach, we calculate the relative-phase correlation
function beyond the harmonic limit of small fluctuations of the relative phase
and its conjugate relative-density variable. We show that the thermal
fluctuations of the relative phase between the two quasicondensates decrease
the frequency of Josephson oscillations and even wash out these oscillations
for small values of the tunnel coupling.Comment: revtex4, 4 figures (.eps
Non trivial generalizations of the Schwinger pair production result II
It is suggested that Schwinger's (1951) vacuum persistence probability
against pair production by an intense but constant electric field is a very
good approximation to the corresponding quantity if the field does not vary
appreciably over distances less than m/e/E/5 pagesComment: 5 page
Soft gamma repeaters outside the Local group
We propose that the best sites to search for SGRs outside the Local group are
galaxies with active massive star formation. Different possibilities to observe
SGR activity from these sites are discussed. In particular we searched for
giant flares from nearby galaxies ( -- 4 Mpc) M82,
M83, NGC 253, and NGC 4945 in the BATSE data. No candidates alike giant SGR
flares were found. The absence of such detections implies that the rate of
giant flares with energy release in the initial spike above
erg is less then 1/25 yr in our Galaxy. However, hyperflares similar to
the one of 27 December 2004 can be observed from larger distances.
Nevertheless, we do not see any significant excess of short GRBs from the Virgo
galaxy cluster and from galaxies Arp 299 and NGC 3256 with extremely high star
formation rate. This implies that the galactic rate of hyperflares with energy
release erg is less than yr. With this
constraint the fraction of possible extragalactic SGR hyperflares among BATSE
short GRBs should not exceed few percents. We present a list of short GRBs
coincident with galaxies mentioned above, and discuss the possibility that some
of them are SGR giant flares. We propose that the best target for observations
of extragalactic SGR flares by {\it Swift} is the Virgo cluster.Comment: 14 pages with 3 figures; accepted to MNRAS (final version
Single-atom quantum memory with degenerate atomic levels
The storage and retrieval of a single-photon polarization q-bit by means of
STIRAP through the atoms with degenerate levels is studied theoretically for
arbitrary polarization of the driving laser field and arbitrary values of the
angular momenta of resonant atomic levels. The dependence of the probability of
long-term photon storage on the polarization of the driving field and on the
initial atomic state is examined.Comment: 12 pages, 1 figure. arXiv admin note: text overlap with
arXiv:1203.439
Finite Element Solution of Axisymmetrical Dynamic Problems of Shells of Revolution
Finite element solution for natural frequencies and mode shapes of free axisymmetrical vibrations and dynamic response of arbitrary rotationally symmetric shell
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