3,053 research outputs found
Chaoticity without thermalisation in disordered lattices
We study chaoticity and thermalization in Bose-Einstein condensates in
disordered lattices, described by the discrete nonlinear Schr\"odinger equation
(DNLS). A symplectic integration method allows us to accurately obtain both the
full phase space trajectories and their maximum Lyapunov exponents (mLEs),
which characterize their chaoticity. We find that disorder destroys ergodicity
by breaking up phase space into subsystems that are effectively disjoint on
experimentally relevant timescales, even though energetically, classical
localisation cannot occur. This leads us to conclude that the mLE is a very
poor ergodicity indicator, since it is not sensitive to the trajectory being
confined to a subregion of phase space. The eventual thermalization of a BEC in
a disordered lattice cannot be predicted based only on the chaoticity of its
phase space trajectory
Two stochastic models for simulation of correlated random processes
Mathematical models for simulation of correlated stochastic processes with stationary Gaussian propertie
Strongly interacting bosons in a 1D optical lattice at incommensurate densities
We investigate quantum phase transitions occurring in a system of strongly
interacting ultracold bosons in a 1D optical lattice. After discussing the
commensurate-incommensurate transition, we focus on the phases appearing at
incommensurate filling. We find a rich phase diagram, with superfluid,
supersolid and solid (kink-lattice) phases. Supersolids generally appear in
theoretical studies of systems with long-range interactions; our results break
this paradigm and show that they may also emerge in models including only
short-range (contact) interactions, provided that quantum fluctuations are
properly taken into account
A method for the measurement and the statistical analysis of atmospheric turbulence
The instantaneous values of output voltages representing the wind velocity vector and the temperature at different elevations of the 250-foot meteorological tower located at NASA Wallops Flight Center are provided with the three dimensional split-film TSI Model 1080 anemometer system. The output voltages are sampled at a rate of one every 5 milliseconds, digitized and stored on digital magnetic tapes for a time period of approximately 40 minutes, with the use of a specially designed data acqusition system. A new calibration procedure permits the conversion of the digital voltages to the respective values of the temperature and the velocity components in a Cartesian coordinate system connected with the TSI probe with considerable accuracy. Power, cross, coincidence and quadrature spectra of the wind components and the temperature are obtained with the use of the fast Fourier transform. The cosine taper data window and ensemble and frequency smoothing techniques are used to provide smooth estimates of the spectral functions
Supersolid phases of dipolar bosons in optical lattices with a staggered flux
We present the theoretical mean-field zero-temperature phase diagram of a
Bose-Einstein condensate (BEC) with dipolar interactions loaded into an optical
lattice with a staggered flux. Apart from uniform superfluid, checkerboard
supersolid and striped supersolid phases, we identify several supersolid phases
with staggered vortices, which can be seen as combinations of supersolid phases
found in earlier work on dipolar BECs and a staggered-vortex phase found for
bosons in optical lattices with staggered flux. By allowing for different
phases and densities on each of the four sites of the elementary plaquette,
more complex phase patterns are found.Comment: 11 pages; added references, minor changes in tex
Het stedelijk landschap van Amsterdam
__Abstract__
De afgelopen decennia is een ‘maelstrom’ van
structurele veranderingen door Amsterdam
getrokken, afkomstig van zowel nationaal als
internationaal niveau. De stad zelf is daardoor
sterk van aard en bevolking veranderd en
welvarender geworden. Deze bijdrage
beschrijft de bewegingen in het stedelijk landschap
van Amsterdam, via een rondgang langs
de veranderlijke wijken en hun bewoners. De
verschillende stadswijken hebben altijd een
eigen karakter gehad. Dit karakter is echter
door de jaren heen vaak ingrijpend veranderd,
zodat prestigieuze nieuwbouwprojecten vaak
daalden in de stedelijke hiërarchie, en soms
zelfs vervielen tot verzamelplaatsen van
sociaal-economische ellende, terwijl voormalige
probleemwijken zich ontwikkelden tot
broedplaatsen van vernieuwing. Over deze
veranderingen gaat deze bijdrage
Statistical analysis of low level atmospheric turbulence
The statistical properties of low-level wind-turbulence data were obtained with the model 1080 total vector anemometer and the model 1296 dual split-film anemometer, both manufactured by Thermo Systems Incorporated. The data obtained from the above fast-response probes were compared with the results obtained from a pair of Gill propeller anemometers. The digitized time series representing the three velocity components and the temperature were each divided into a number of blocks, the length of which depended on the lowest frequency of interest and also on the storage capacity of the available computer. A moving-average and differencing high-pass filter was used to remove the trend and the low frequency components in the time series. The calculated results for each of the anemometers used are represented in graphical or tabulated form
An experimental study of the atmospheric boundary layer modified by a change in surface roughness and surface temperature
Turbulent flow, resembling an on-shore flow from the ocean crossing the beach at an oblique angle, is investigated. Measurements of this flow have been taken at high sample rates and include measurements at various heights, high enough to describe the portion of the mean wind and temperature profiles and fluxes that are of interest for the solution of practical engineering problems. These problems could include air pollution (fumigation and plume trapping), operation of low flying aircraft, crop-spraying and crop-dusting operations
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