634 research outputs found
Damped Bogoliubov excitations of a condensate interacting with a static thermal cloud
We calculate the damping of condensate collective excitations at finite
temperatures arising from the lack of equilibrium between the condensate and
thermal atoms. We neglect the non-condensate dynamics by fixing the thermal
cloud in static equilibrium. We derive a set of generalized Bogoliubov
equations for finite temperatures that contain an explicit damping term due to
collisional exchange of atoms between the two components. We have numerically
solved these Bogoliubov equations to obtain the temperature dependence of the
damping of the condensate modes in a harmonic trap. We compare these results
with our recent work based on the Thomas-Fermi approximation.Comment: 9 pages, 3 figures included. Submitted to PR
Prescription pattern of benzodiazepines for inpatients at a tertiary care university hospital in Pakistan
Objective: To determine the point prevalence of benzodiazepine prescriptions for inpatients at a tertiary care university hospital in Pakistan and to correlate it with prescription patterns of various specialties, indications and demographic variables of the patients.Methods: This 24-hours point prevalence study was done at The Aga Khan University Hospital, Karachi. By convenient random sampling, 208 inpatients were interviewed. Patients\u27 files were also studied to record the drugs administered. Data was entered into questionnaires and analyzed by SPSS 10.0.Results: The point prevalence of the benzodiazepines was 21.2%. It was higher among males than females and among surgical than non-surgical patients. Midazolam was the most commonly used benzodiazepine, followed by Alprazolam and Lorazepam. Pre-anesthesia and psychiatric symptoms were the two most common indications. Oral route was used in 84% patients for drug administration and mean Valium equivalent dosage was 4.86 mg/day. Mean length of prescription was 3 days. Longer duration of hospitalization was a significant predictor of the requirement of benzodiazepine prescription (p-value = 0.020).CONCLUSION: Prescription pattern of benzodiazepines at a tertiary care university hospital is similar to that reported in the developed countries through monitoring at various levels by physicians, clinical pharmacist and nursing staff. Data regarding the prescription pattern of benzodiazepines is scarce, and it needs to be expanded to formulate clear guidelines regarding their prescription
Dimensional and Temperature Crossover in Trapped Bose Gases
We investigate the long-range phase coherence of homogeneous and trapped Bose
gases as a function of the geometry of the trap, the temperature, and the
mean-field interactions in the weakly interacting limit. We explicitly take
into account the (quasi)condensate depletion due to quantum and thermal
fluctuations, i.e., we include the effects of both phase and density
fluctuations. In particular, we determine the phase diagram of the gas by
calculating the off-diagonal one-particle density matrix and discuss the
various crossovers that occur in this phase diagram and the feasibility of
their experimental observation in trapped Bose gases.Comment: One figure added, typos corrected, refernces adde
Vortex lattice formation in a rotating Bose-Einstein condensate
We study the dynamics of vortex lattice formation of a rotating trapped
Bose-Einstein condensate by numerically solving the two-dimensional
Gross-Pitaevskii equation, and find that the condensate undergoes elliptic
deformation, followed by unstable surface-mode excitations before forming a
quantized vortex lattice. The origin of the peculiar surface-mode excitations
is identified to be phase fluctuations at the low-density surface regime. The
obtained dependence of a distortion parameter on time and that on the driving
frequency agree with the recent experiments by Madison {\it et al.} [Phys. Rev.
Lett. {\bf 86}, 4443 (2001)].Comment: 4 pages, 4 figure
Quadrupole collective modes in trapped finite-temperature Bose-Einstein condensates
Finite temperature simulations are used to study quadrupole excitations of a
trapped Bose-Einstein condensate. We focus specifically on the m=0 mode, where
a long-standing theoretical problem has been to account for an anomalous
variation of the mode frequency with temperature. We explain this behavior in
terms of the excitation of two separate modes, corresponding to coupled motion
of the condensate and thermal cloud. The relative amplitudes of the modes
depends sensitively on the temperature and on the frequency of the harmonic
drive used to excite them. Good agreement with experiment is found for
appropriate drive frequencies.Comment: 4 pages, 3 figure
A thin film approach for SiC-derived graphene as an on-chip electrode for supercapacitors
© 2015 IOP Publishing Ltd. We designed a nickel-assisted process to obtain graphene with sheet resistance as low as 80 Ω square-1 from silicon carbide films on Si wafers with highly enhanced surface area. The silicon carbide film acts as both a template and source of graphitic carbon, while, simultaneously, the nickel induces porosity on the surface of the film by forming silicides during the annealing process which are subsequently removed. As stand-alone electrodes in supercapacitors, these transfer-free graphene-on-chip samples show a typical double-layer supercapacitive behaviour with gravimetric capacitance of up to 65 F g-1. This work is the first attempt to produce graphene with high surface area from silicon carbide thin films for energy storage at the wafer-level and may open numerous opportunities for on-chip integrated energy storage applications
Excitations of a Bose-Einstein condensate in a one-dimensional optical lattice
We investigate the low-lying excitations of a stack of weakly-coupled
two-dimensional Bose-Einstein condensates that is formed by a one-dimensional
optical lattice. In particular, we calculate the dispersion relations of the
monopole and quadrupole modes, both for the ground state as well as for the
case in which the system contains a vortex along the direction of the lasers
creating the optical lattice. Our variational approach enables us to determine
analytically the dispersion relations for an arbitrary number of atoms in every
two-dimensional condensate and for an arbitrary momentum. We also discuss the
feasibility of experimentally observing our results.Comment: 16 pages, 5 figures, minor changes,accepted for publication in Phys.
Rev.
Extension of Bogoliubov theory to quasi-condensates
We present an extension of the well-known Bogoliubov theory to treat low
dimensional degenerate Bose gases in the limit of weak interactions and low
density fluctuations. We use a density-phase representation and show that a
precise definition of the phase operator requires a space discretisation in
cells of size . We perform a systematic expansion of the Hamiltonian in
terms of two small parameters, the relative density fluctuations inside a cell
and the phase change over a cell. The resulting macroscopic observables can be
computed in one, two and three dimensions with no ultraviolet or infrared
divergence. Furthermore this approach exactly matches Bogoliubov's approach
when there is a true condensate. We give the resulting expressions for the
equation of state of the gas, the ground state energy, the first order and
second order correlations functions of the field. Explicit calculations are
done for homogeneous systems.Comment: 32 pages, 2 figures; typos corrected in revised versio
Exact calculation of the skyrmion lifetime in a ferromagnetic Bose condensate
The tunneling rate of a skyrmion in ferromagnetic spin-1/2 Bose condensates
through an off-centered potential barrier is calculated exactly with the
periodic instanton method. The prefactor is shown to depend on the chemical
potential of the core atoms, at which level the atom tunnels. Our results can
be readily extended to estimate the lifetime of other topological excitations
in the condensate, such as vortices and monopoles.Comment: 16 pages, 4 figures, to appear Phys. Rev.
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