4,954 research outputs found
Cold inelastic collisions between lithium and cesium in a two-species magneto-optical trap
We investigate collisional properties of lithium and cesium which are
simultaneously confined in a combined magneto-optical trap. Trap-loss
collisions between the two species are comprehensively studied. Different
inelastic collision channels are identified, and inter-species rate
coefficients as well as cross sections are determined. It is found that loss
rates are independent of the optical excitation of Li, as a consequence of the
repulsive Li-Cs interaction. Li and Cs loss by inelastic inter-species
collisions can completely be attributed to processes involving optically
excited cesium (fine-structure changing collisions and radiative escape). By
lowering the trap depth for Li, an additional loss channel of Li is observed
which results from ground-state Li-Cs collisions changing the hyperfine state
of cesium.Comment: submitted to Euro. Phys. J. D, special issue on Laser Cooling and
Trappin
TRUSTING REVIEW MECHANISMS IN KNOWLEDGE MANAGEMENT SYSTEMS: ANTECEDENTS, OUTCOMES, AND THE ROLE OF PERCEIVED RISK
In recent years, the success of social media in the private realm has entailed an increasing awareness of opportunities that are linked to user-generated content in knowledge management systems. Alongside the benefits in terms of knowledge quantity, new quality risks arise from an unregulated knowledge contribution. Considering that, review mechanisms have been implemented to monitor the content and provide a basis to distinguish between good and poor quality knowledge assets. This paper proposes a model to uncover the role of trust in expert and peer reviews during the knowledge application process by considering its antecedents, its outcomes, and the influnce of perceived risk. The model suggests that trust in expert and peer reviews is based on the ability, benevolence, and integrity of the respective group and is positively influnced by a higher trustor´s propensity to trust. Perceived risk in a particular situation influnces the decision whether to apply knowledge based on trust in expert or in peer reviews. It is assumed that high-risk decisions are based on expert reviews more likely because the organizational and individual risk is perceived to be lowered, whereas peer reviews can only mitigate organizational risk
Genetic and serological heterogeneity of the supertypic HLA-B locus specificities Bw4 and Bw6
Gene cloning and sequencing of the HLA-B
locus split antigens B38 (B16.1) and B39 (B16.2) allowed
localization of their subtypic as well as their public
specificities HLA-Bw4 or -Bw6 to the c~-helical region of
the c~ 1 domain flanked by the amino acid positions 74-83.
Comparison of their amino acid sequences with those of
other HLA-B-locus alleles established HLA-Bw6 to be
distinguished by Ser at residue 77 and Asn at residue 80.
In contrast, HLA-Bw4 is characterized by at least seven
different patterns of amino acid exchanges at positions 77
and 80-83. Reactivity patterns of Bw4- or Bw6-specific
monoclonal antibodies reveal two alloantigenic epitopes
contributing to the HLA-Bw4 or -Bw6 specificity residing
next to the region of highest diversity of the cr domain
Liquid Scintillator Time Projection Chamber Concept
Results are presented from a small-scale experiment to investigate the use of
room temperature organic liquid scintillators as the active medium for a time
projection chamber (TPC). The optical properties of liquid scintillators have
long been known, but their ability to transport charge has remained, until now,
largely untested. The idea of using room temperature liquids as an active
medium for an ionisation chamber was first presented in \cite{EnglerTMS}. Since
then the range of liquid scintillators available has been greatly developed. We
present successful transport of ionization charges in a selection of both, pure
organic liquid solvents and liquid scintillator cocktails over 20mm using a
variety of electric drift field strengths. The target of this research is to
offer a cost effective alternative to liquid noble gas detectors in neutrino
physics.Comment: 6 pages, 5 figures, submitted to Proceedings 12th Pisa Meeting on
Advanced Detectors, La Biodola, Isola d'Elba, Ital
Detection of scattered light from the hot dust in HD 172555
Debris disks or belts are important signposts for the presence of colliding
planetesimals and, therefore, for ongoing planet formation and evolution
processes in young planetary systems. Imaging of debris material at small
separations from the star is very challenging but provides valuable insights
into the spatial distribution of so-called hot dust produced by solid bodies
located in or near the habitable zone. We report the first detection of
scattered light from the hot dust around the nearby (d = 28.33 pc) A star HD
172555. We want to constrain the geometric structure of the detected debris
disk using polarimetric differential Imaging (PDI) with a spatial resolution of
25 mas and an inner working angle of about 0.1. We measured the polarized
light of HD 172555, with SPHERE-ZIMPOL, in the very broad band (VBB;
nm) filter for the projected separations between 0.08 (2.3
au) and 0.77 (22 au). We constrained the disk parameters by fitting models
for scattering of an optically thin dust disk taking the limited spatial
resolution and coronagraphic attenuation of our data into account. The
geometric structure of the disk in polarized light shows roughly the same
orientation and outer extent as obtained from thermal emission at 18 m.
Our image indicates the presence of a strongly inclined (),
roughly axisymmetric dust belt with an outer radius in the range between
0.3 (8.5 au) and 0.4 (11.3 au). We derive a lower limit for the
polarized flux contrast ratio for the disk of in the VBB filter. This ratio is small, only
9 %, when compared to the fractional infrared flux excess (). The model simulations show that more polarized light could be
produced by the dust located inside 2 au, which cannot be detected with the
instrument configuration used.Comment: 16 pages, 10 figure
Testing the proposed link between cosmic rays and cloud cover
A decrease in the globally averaged low level cloud cover, deduced from the
ISCCP infra red data, as the cosmic ray intensity decreased during the solar
cycle 22 was observed by two groups. The groups went on to hypothesise that the
decrease in ionization due to cosmic rays causes the decrease in cloud cover,
thereby explaining a large part of the presently observed global warming. We
have examined this hypothesis to look for evidence to corroborate it. None has
been found and so our conclusions are to doubt it. From the absence of
corroborative evidence, we estimate that less than 23%, at the 95% confidence
level, of the 11-year cycle change in the globally averaged cloud cover
observed in solar cycle 22 is due to the change in the rate of ionization from
the solar modulation of cosmic rays
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