299 research outputs found
An Atom Faucet
We have constructed and modeled a simple and efficient source of slow atoms.
From a background vapour loaded magneto-optical trap, a thin laser beam
extracts a continuous jet of cold rubidium atoms. In this setup, the extraction
column that is typical to leaking MOT systems is created without any optical
parts placed inside the vacuum chamber. For detailed analysis, we present a
simple 3D numerical simulation of the atomic motion in the presence of multiple
saturating laser fields combined with an inhomogeneous magnetic field. At a
pressure of mbar, the moderate laser power of
10 mW per beam generates a jet of flux atoms/s with a
mean velocity of 14 m/s and a divergence of mrad.Comment: Submitted to EPJD. 1 TeX file (EPJ format), 7 picture
Vortex formation in a stirred Bose-Einstein condensate
Using a focused laser beam we stir a Bose-Einstein condensate of 87Rb
confined in a magnetic trap and observe the formation of a vortex for a
stirring frequency exceeding a critical value. At larger rotation frequencies
we produce states of the condensate for which up to four vortices are
simultaneously present. We have also measured the lifetime of the single vortex
state after turning off the stirring laser beam.Comment: 4 pages, 3 figure
Vortex lattices in a stirred Bose-Einstein condensate
We stir with a focused laser beam a Bose-Einstein condensate of Rb
atoms confined in a magnetic trap. We observe the formation of a single vortex
for a stirring frequency exceeding a critical value. At larger rotation
frequencies we produce states of the condensate for which up to eleven vortices
are simultaneously present. We present measurements of the decay of a vortex
array once the stirring laser beam is removed
Specific-heat, magnetic-susceptibility and transport-properties of polycrystalline CeInAu and CeInAu2
Computing and Representing Sea Ice Trends: Toward a Community Consensus
Estimates of the recent decline in Arctic Ocean summer sea ice extent can vary due to differences in sea ice data sources, in the number of years used to compute the trend, and in the start and end years used in the trend computation. Compounding such differences, estimates of the relative decline in sea ice cover (given in percent change per decade) can further vary due to the choice of reference value (the initial point of the trend line, a climatological baseline, etc.). Further adding to the confusion, very often when relative trends are reported in research papers, the reference values used are not specified or made clear. This can lead to confusion when trend studies are cited in the press and public reports
Comparison of metal-based nanoparticles and nanowires: Solubility, reactivity, bioavailability and cellular toxicity
While the toxicity of metal-based nanoparticles (NP) has been investigated in an increasing number of studies, little is known about metal-based fibrous materials, so-called nanowires (NWs). Within the present study, the physico-chemical properties of particulate and fibrous nanomaterials based on Cu, CuO, Ni, and Ag as well as TiO and CeO NP were characterized and compared with respect to abiotic metal ion release in different physiologically relevant media as well as acellular reactivity. While none of the materials was soluble at neutral pH in artificial alveolar fluid (AAF), Cu, CuO, and Ni-based materials displayed distinct dissolution under the acidic conditions found in artificial lysosomal fluids (ALF and PSF). Subsequently, four different cell lines were applied to compare cytotoxicity as well as intracellular metal ion release in the cytoplasm and nucleus. Both cytotoxicity and bioavailability reflected the acellular dissolution rates in physiological lysosomal media (pH 4.5); only Ag-based materials showed no or very low acellular solubility, but pronounced intracellular bioavailability and cytotoxicity, leading to particularly high concentrations in the nucleus. In conclusion, in spite of some quantitative differences, the intracellular bioavailability as well as toxicity is mostly driven by the respective metal and is less modulated by the shape of the respective NP or NW
Specific heat, magnetic susceptibility and transport properties of polycrystalline CeInAu and CeInAu 2
Possibility of long-range order in clean mesoscopic cylinders
A microscopic Hamiltonian of the magnetostatic interaction is discussed. This
long-range interaction can play an important role in mesoscopic systems leading
to an ordered ground state.
The self-consistent mean field approximation of the magnetostatic interaction
is performed to give an effective Hamiltonian from which the spontaneous,
self-sustaining currents can be obtained.
To go beyond the mean field approximation the mean square fluctuation of the
total momentum is calculated and its influence on self-sustaining currents in
mesoscopic cylinders with quasi-1D and quasi-2D conduction is considered. Then,
by the use of the microscopic Hamiltonian of the magnetostatic interaction for
a set of stacked rings, the problem of long-range order is discussed. The
temperature below which the system is in an ordered state is
determined.Comment: 14 pages, REVTeX, 5 figures, in print in Phys. Rev.
Electron Dephasing in Mesoscopic Metal Wires
The low-temperature behavior of the electron phase coherence time,
, in mesoscopic metal wires has been a subject of controversy
recently. Whereas theory predicts that in narrow wires should
increase as as the temperature is lowered, many samples exhibit
a saturation of below about 1 K. We review here the experiments
we have performed recently to address this issue. In particular we emphasize
that in sufficiently pure Ag and Au samples we observe no saturation of
down to our base temperature of 40 mK. In addition, the measured
magnitude of is in excellent quantitative agreement with the
prediction of the perturbative theory of Altshuler, Aronov and Khmelnitskii. We
discuss possible explanations why saturation of is observed in
many other samples measured in our laboratory and elsewhere, and answer the
criticisms raised recently by Mohanty and Webb regarding our work.Comment: 14 pages, 3 figures; to appear in proceedings of conference
"Fundamental Problems of Mesoscopic Physics", Granada, Spain, 6-11 September,
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