6,680 research outputs found
Adiabatic radio frequency potentials for the coherent manipulation of matter waves
Adiabatic dressed state potentials are created when magnetic sub-states of
trapped atoms are coupled by a radio frequency field. We discuss their
theoretical foundations and point out fundamental advantages over potentials
purely based on static fields. The enhanced flexibility enables one to
implement numerous novel configurations, including double wells, Mach-Zehnder
and Sagnac interferometers which even allows for internal state-dependent atom
manipulation. These can be realized using simple and highly integrated wire
geometries on atom chips.Comment: 13 pages, 2 figure
Numerical simulation of the turbulent convective buoyant flow of sodium over a backward- facing step
A forced convective and a buoyancy-aided turbulent liquid sodium flow over a backward-facing step with a constant heat flux applied on the indented wall is simulated. Linear eddy viscosity models are used for the Reynolds stresses. Turbulent heat fluxes are modelled with a single gradient diffusion hypotheses with two different approaches to evaluate the turbulent Prandtl number. Moreover, the inuence of turbulence on heat transfer to sodium is also assessed through simulations with zero turbulent thermal diffusivity. The results are compared with DNS data from literature. The velocity and turbulent kinetic energy profiles predicted by all models are in good agreement with the DNS data. The local Nusselt number trend is qualitatively well captured, however, its magnitude is underestimated by all models for the mixed convection case. For forced convection, the heat transfer is overestimated by all heat flux models. The simulation with neglected turbulent heat transfer shows the best overall agreement for the forced convection case. For the mixed convection best agreement is obtained using a correlation to locally evaluate the turbulent thermal diffusivity
Numerical simulation of the turbulent convective buoyant flow of sodium over a backward- facing step
A forced convective and a buoyancy-aided turbulent liquid sodium flow over a
backward-facing step with a constant heat flux applied on the indented wall is simulated.
Linear eddy viscosity models are used for the Reynolds stresses. Turbulent heat fluxes are
modelled with a single gradient diffusion hypotheses with two different approaches to evaluate
the turbulent Prandtl number. Moreover, the influence of turbulence on heat transfer to sodium
is also assessed through simulations with zero turbulent thermal diffusivity. The results are
compared with DNS data from literature. The velocity and turbulent kinetic energy profiles
predicted by all models are in good agreement with the DNS data. The local Nusselt number
trend is qualitatively well captured, however, its magnitude is underestimated by all models
for the mixed convection case. For forced convection, the heat transfer is overestimated by all
heat flux models. The simulation with neglected turbulent heat transfer shows the best overall
agreement for the forced convection case. For the mixed convection best agreement is obtained
using a correlation to locally evaluate the turbulent thermal diffusivity
Reproducible Research Using Stata
In this presentation we shall address two issues concerning the research process: (1) the need for an efficient way to transfer results obtained using a statistical package into a written report, and (2) the need to organize and to package one's work so that those results are easily reproducible. Previous work addressing these issues has concentrated on tools written specifically for use with S-Plus/R and LaTeX, and has involved mixing code and written material in a single document (e.g., Sweave). In contrast, our approach involves a method for extracting results (e.g., estimation results, graphs, and even pieces of code and/or raw output) generated by a suitably organized do-file (or files) into a series of intermediary files which can then be easily imported into a second, written document. Although the document could be constructed in a variety of formats, we shall demonstrate how this may done using reStructuredText -- an intuitive and easy-to-use markup syntax which can then be automatically translated into a variety of final formats (e.g., LaTeX, HTML). This system may be used not only for research but also when teaching statistics with Stata as a method for students to organize and to submit their work.
Dual-species quantum degeneracy of potassium-40 and rubidium-87 on an atom chip
In this article we review our recent experiments with a 40K-87Rb mixture. We
demonstrate rapid sympathetic cooling of a 40K-87Rb mixture to dual quantum
degeneracy on an atom chip. We also provide details on efficient BEC
production, species-selective magnetic confinement, and progress toward
integration of an optical lattice with an atom chip. The efficiency of our
evaporation allows us to reach dual degeneracy after just 6 s of evaporation -
more rapidly than in conventional magnetic traps. When optimizing evaporative
cooling for efficient evaporation of 87Rb alone we achieve BEC after just 4 s
of evaporation and an 8 s total cycle time.Comment: 8 pages, 4 figures. To be published in the Proceedings of the 20th
International Conference on Atomic Physics, 2006 (Innsbruck, Austria
Prospects for measuring the 229Th isomer energy using a metallic magnetic microcalorimeter
The Thorium-229 isotope features a nuclear isomer state with an extremely low
energy. The currently most accepted energy value, 7.8 +- 0.5 eV, was obtained
from an indirect measurement using a NASA x-ray microcalorimeter with an
instrumental resolution 26 eV. We study, how state-of-the-art magnetic metallic
microcalorimeters with an energy resolution down to a few eV can be used to
measure the isomer energy. In particular, resolving the 29.18 keV doublet in
the \gamma-spectrum following the \alpha-decay of Uranium-233, corresponding to
the decay into the ground and isomer state, allows to measure the isomer
transition energy without additional theoretical input parameters, and increase
the energy accuracy. We study the possibility of resolving the 29.18 keV line
as a doublet and the dependence of the attainable precision of the energy
measurement on the signal and background count rates and the instrumental
resolution.Comment: 32 pages, 8 figures, eq. (3) correcte
Alternative Stacking Sequences in Hexagonal Boron Nitride
The relative orientation of successive sheets, i.e. the stacking sequence, in
layered two-dimensional materials is central to the electronic, thermal, and
mechanical properties of the material. Often different stacking sequences have
comparable cohesive energy, leading to alternative stable crystal structures.
Here we theoretically and experimentally explore different stacking sequences
in the van der Waals bonded material hexagonal boron nitride (h-BN). We examine
the total energy, electronic bandgap, and dielectric response tensor for five
distinct high symmetry stacking sequences for both bulk and bilayer forms of
h-BN. Two sequences, the generally assumed AA' sequence and the relatively
unknown (for h-BN) AB (Bernal) sequence, are predicted to have comparably low
energy. We present a scalable modified chemical vapor deposition method that
produces large flakes of virtually pure AB stacked h-BN; this new material
complements the generally available AA' stacked h-BN
Armies of Misfits: Mobility Disabilities and Activism in the Biblical Studies Classroom
This article argues for the disabled body as a site of resistance and for the biblical studies classroom as one venue to mobile towards world-changing activism. After reviewing a range of models from disability studies (the medical, social/minority, religious and political/relational models) this article advocates for what the authors call “misfitting”. Using select biblical stories that feature characters with mobility disabilities and that also demonstrate discriminatory attitudes toward these characters, namely 2 Samuel 5:6-8 and Mark 2:1-12, misfitting is illustrated
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