1,466 research outputs found
Sagnac Effect of Goedel's Universe
We present exact expressions for the Sagnac effect of Goedel's Universe. For
this purpose we first derive a formula for the Sagnac time delay along a
circular path in the presence of an arbitrary stationary metric in cylindrical
coordinates. We then apply this result to Goedel's metric for two different
experimental situations: First, the light source and the detector are at rest
relative to the matter generating the gravitational field. In this case we find
an expression that is formally equivalent to the familiar nonrelativistic
Sagnac time delay. Second, the light source and the detector are rotating
relative to the matter. Here we show that for a special rotation rate of the
detector the Sagnac time delay vanishes. Finally we propose a formulation of
the Sagnac time delay in terms of invariant physical quantities. We show that
this result is very close to the analogous formula of the Sagnac time delay of
a rotating coordinate system in Minkowski spacetime.Comment: 26 pages, including 4 figures, corrected typos, changed reference
Collective Feshbach scattering of a superfluid droplet from a mesoscopic two-component Bose-Einstein condensate
We examine the collective scattering of a superfluid droplet impinging on a
mesoscopic Bose-Einstein condensate (BEC) as a target. The BEC consists of an
atomic gas with two internal electronic states, each of which is trapped by a
finite-depth external potential. An off-resonant optical laser field provides a
localized coupling between the BEC components in the trapping region. This
mesoscopic scenario matches the microscopic setup for Feshbach scattering of
two particles, when a bound state of one sub-manifold is embedded in the
scattering continuum of the other sub-manifold. Within the mean-field picture,
we obtain resonant scattering phase shifts from a linear response theory in
agreement with an exact numerical solution of the real time scattering process
and simple analytical approximations thereof. We find an energy-dependent
transmission coefficient that is controllable via the optical field between 0
and 100%.Comment: 4 Latex pages, including 4 figure
Formation of Pairing Fields in Resonantly Coupled Atomic and Molecular Bose-Einstein Condensates
In this paper, we show that pair-correlations may play an important role in
the quantum statistical properties of a Bose-Einstein condensed gas composed of
an atomic field resonantly coupled with a corresponding field of molecular
dimers. Specifically, pair-correlations in this system can dramatically modify
the coherent and incoherent transfer between the atomic and molecular fields.Comment: 4 pages, 4 figure
Equivalence of Kinetic Theories of Bose-Einstein Condensation
We discuss the equivalence of two non-equilibrium kinetic theories that
describe the evolution of a dilute, Bose-Einstein condensed atomic gas in a
harmonic trap. The second-order kinetic equations of Walser et al. [PRA 63,
013607 (2001)] reduce to the Gross-Pitaevskii equation and the quantum
Boltzmann equation in the low and high temperature limits, respectively. These
kinetic equations can thus describe the system in equilibrium (finite
temperature) as well as in non-equilibrium (real time). We have found this
theory to be equivalent to the non-equilibrium Green's function approach
originally proposed by Kadanoff and Baym and more recently applied to
inhomogeneous trapped systems by M. Imamovi\'c-Tomasovi\'c and A. Griffin
[arXiv:cond-mat/9911402].Comment: REVTeX3, 6 pages, 2 eps figures, published version, minor change
Laser-noise-induced correlations and anti-correlations in Electromagnetically Induced Transparency
High degrees of intensity correlation between two independent lasers were
observed after propagation through a rubidium vapor cell in which they generate
Electromagnetically Induced Transparency (EIT). As the optical field
intensities are increased, the correlation changes sign (becoming
anti-correlation). The experiment was performed in a room temperature rubidium
cell, using two diode lasers tuned to the Rb line (nm). The cross-correlation spectral function for the pump and probe fields
is numerically obtained by modeling the temporal dynamics of both field phases
as diffusing processes. We explored the dependence of the atomic response on
the atom-field Rabi frequencies, optical detuning and Doppler width. The
results show that resonant phase-noise to amplitude-noise conversion is at the
origin of the observed signal and the change in sign for the correlation
coefficient can be explained as a consequence of the competition between EIT
and Raman resonance processes.Comment: Accepted for publication in EPJ
The Stanley Foundation Bipolar Network: Results of the naturalistic follow-up study after 2.5 years of follow-up in the German centres
The Stanley Foundation Bipolar Network (SFBN) is an international, multisite network investigating the characteristics and course of bipolar disorder. Methods (history, ratings and longitudinal follow-up) are standardized and equally applied in all 7 centres. This article describes demographics and illness characteristics of the first 152 German patients enrolled in them SFBN as well as the results of 2.5 years of follow-up. Patients in Germany were usually enrolled after hospitalisation. More than 72% of the study population suffered from bipolar I disorder and 25% from bipolar 11 disorder. The mean +/- SD age of the study participants was 42.08 +/- 13.5 years, and the mean SD age of onset 24.44 +/- 10.9 years. More than 40% of the sample reported a rapid-cycling course in history, and even more a cycle acceleration overtime. 37% attempted suicide at least once. 36% had an additional Axis I disorder, with alcohol abuse being the most common one, followed by anxiety disorders. During the follow-up period, only 27% remained stable, 56% had a recurrence, 12.8% perceived subsyndromal symptoms despite treatment and regular visits. 27% suffered from a rapid-cycling course during the follow-up period. Recurrences were significantly associated with bipolar I disorder, an additional comorbid Axis I disorder, rapid cycling in history, a higher number of mood stabilizers and the long-term use of typical antipsychotics. Rapid cycling during follow-up was only associated with a rapidcycling course in history, a higher number of mood stabilizers and at least one suicide attempt in history. Copyright (c) 2003 S. Karger AG, Basel
Gap-filling strategies for annual VOC flux data sets
Up to now the limited
knowledge about the exchange of volatile organic compounds (VOCs) between the
biosphere and the atmosphere is one of the factors which hinders more
accurate climate predictions. Complete long-term flux data sets of several
VOCs to quantify the annual exchange and validate recent VOC models are
basically not available. In combination with long-term VOC flux measurements
the application of gap-filling routines is inevitable in order to replace
missing data and make an important step towards a better understanding of the
VOC ecosystem–atmosphere exchange on longer timescales.
<br><br>
We performed VOC flux measurements above a mountain meadow in Austria during
two complete growing seasons (from snowmelt in spring to snow reestablishment
in late autumn) and used this data set to test the performance of four
different gap-filling routines, mean diurnal variation (MDV), mean gliding
window (MGW), look-up tables (LUT) and linear interpolation (LIP), in terms
of their ability to replace missing flux data in order to obtain reliable VOC
sums. According to our findings the MDV routine was outstanding with regard
to the minimization of the gap-filling error for both years and all
quantified VOCs. The other gap-filling routines, which performed gap-filling
on 24 h average values, introduced considerably larger uncertainties. The
error which was introduced by the application of the different filling
routines increased linearly with the number of data gaps. Although average
VOC fluxes measured during the winter period (complete snow coverage) were
close to zero, these were highly variable and the filling of the winter
period resulted in considerably higher uncertainties compared to the
application of gap-filling during the measurement period.
<br><br>
The annual patterns of the overall cumulative fluxes for the quantified VOCs
showed a completely different behaviour in 2009, which was an exceptional
year due to the occurrence of a severe hailstorm, compared to 2011. Methanol
was the compound which, at 381.5 mg C m<sup>−2</sup> and 449.9 mg
C m<sup>−2</sup>, contributed most to the cumulative VOC carbon emissions in
2009 and 2011, respectively. In contrast to methanol emissions, however,
considerable amounts of monoterpenes (−327.3 mg C m<sup>−2</sup>) were
deposited onto the mountain meadow during 2009 caused by a hailstorm. Other
quantified VOCs had considerably lower influences on the annual patterns
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