377 research outputs found
Transport dynamics of ultracold atoms in a triple-well transistor-like potential
The transport of atoms is experimentally studied in a transistor-like
triple-well potential consisting of a narrow gate well surrounded by source and
drain wells. Atoms are initially loaded into the source well with
pre-determined temperature and chemical potential. Energetic atoms flow from
the source, across the gate, and into the drain where they are removed using a
resonant light beam. The manifestation of atom-atom interactions and
dissipation is evidenced by a rapid population growth in the initially vacant
gate well. The transport dynamics are shown to depend strongly on a feedback
parameter determined by the relative heights of the two barriers forming the
gate region. For a range of feedback parameter values, experiments establish
that the gate atoms develop a larger chemical potential and lower temperature
than those in the source.Comment: 13 pages, 5 figures, accepted for publication in NJ
Undamped nonequilibrium dynamics of a nondegenerate Bose gas in a 3D isotropic trap
We investigate anomalous damping of the monopole mode of a non-degenerate 3D
Bose gas under isotropic harmonic confinement as recently reported by the JILA
TOP trap experiment [D. S. Lob- ser, A. E. S. Barentine, E. A. Cornell, and H.
J. Lewandowski (in preparation)]. Given a realistic confining potential, we
develop a model for studying collective modes that includes the effects of
anharmonic corrections to a harmonic potential. By studying the influence of
these trap anharmonicities throughout a range of temperatures and collisional
regimes, we find that the damping is caused by the joint mechanisms of
dephasing and collisional relaxation. Furthermore, the model is complimented by
Monte Carlo simulations which are in fair agreement with data from the JILA
experiment.Comment: 11 pages, 6 figure
Collapse and revival of the monopole mode of a degenerate Bose gas in an isotropic harmonic trap
We study the monopole (breathing) mode of a finite temperature Bose-Einstein condensate in an isotropic harmonic trap recently developed by Lobser et al. [Nat. Phys. 11, 1009 (2015)]. We observe a nonexponential collapse of the amplitude of the condensate oscillation followed by a partial revival. This behavior is identified as being due to beating between two eigenmodes of the system, corresponding to in-phase and out-of-phase oscillations of the condensed and noncondensed fractions of the gas. We perform finite temperature simulations of the system dynamics using the Zaremba-Nikuni-Griffin methodology [J. Low Temp. Phys. 116, 277 (1999)], and find good agreement with the data, thus confirming the two mode description
GronOR:Massively parallel and GPU-accelerated non-orthogonal configuration interaction for large molecular systems
GronOR is a program package for non-orthogonal configuration interaction calculations for an electronic wave function built in terms of anti-symmetrized products of multi-configuration molecular fragment wave functions. The two-electron integrals that have to be processed may be expressed in terms of atomic orbitals or in terms of an orbital basis determined from the molecular orbitals of the fragments. The code has been specifically designed for execution on distributed memory massively parallel and Graphics Processing Unit (GPU)-accelerated computer architectures, using an MPI+OpenACC/OpenMP programming approach. The task-based execution model used in the implementation allows for linear scaling with the number of nodes on the largest pre-exascale architectures available, provides hardware fault resiliency, and enables effective execution on systems with distinct central processing unit-only and GPU-accelerated partitions. The code interfaces with existing multi-configuration electronic structure codes that provide optimized molecular fragment orbitals, configuration interaction coefficients, and the required integrals. Algorithm and implementation details, parallel and accelerated performance benchmarks, and an analysis of the sensitivity of the accuracy of results and computational performance to thresholds used in the calculations are presented
A comparative study of the activity of free and immobilized enzymes and its application to glucose isomerase
PCR-GLOBWB 2: a 5 arcmin global hydrological and water resources model
We present PCR-GLOBWB 2, a global hydrology and water resources model. Compared to previous versions of PCR-GLOBWB, this version fully integrates water use. Sector-specific water demand, groundwater and surface water withdrawal, water consumption, and return flows are dynamically calculated at every time step and interact directly with the simulated hydrology. PCR-GLOBWB 2 has been fully rewritten in Python and PCRaster Python and has a modular structure, allowing easier replacement, maintenance, and development of model components. PCR-GLOBWB 2 has been implemented at 5 arcmin resolution, but a version parameterized at 30 arcmin resolution is also available. Both versions are available as open-source codes on https://github.com/UU-Hydro/PCR-GLOBWB_model (Sutanudjaja et al., 2017a). PCR-GLOBWB 2 has its own routines for groundwater dynamics and surface water routing. These relatively simple routines can alternatively be replaced by dynamically coupling PCR-GLOBWB 2 to a global two-layer groundwater model and 1-D–2-D hydrodynamic models. Here, we describe the main components of the model, compare results of the 30 and 5 arcmin versions, and evaluate their model performance using Global Runoff Data Centre discharge data. Results show that model performance of the 5 arcmin version is notably better than that of the 30 arcmin version. Furthermore, we compare simulated time series of total water storage (TWS) of the 5 arcmin model with those observed with GRACE, showing similar negative trends in areas of prevalent groundwater depletion. Also, we find that simulated total water withdrawal matches reasonably well with reported water withdrawal from AQUASTAT, while water withdrawal by source and sector provide mixed results
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