3,628 research outputs found
Entropy Distance: New Quantum Phenomena
We study a curve of Gibbsian families of complex 3x3-matrices and point out
new features, absent in commutative finite-dimensional algebras: a
discontinuous maximum-entropy inference, a discontinuous entropy distance and
non-exposed faces of the mean value set. We analyze these problems from various
aspects including convex geometry, topology and information geometry. This
research is motivated by a theory of info-max principles, where we contribute
by computing first order optimality conditions of the entropy distance.Comment: 34 pages, 5 figure
Generalized Drude model: Unification of ballistic and diffusive electron transport
For electron transport in parallel-plane semiconducting structures, a model
is developed that unifies ballistic and diffusive transport and thus
generalizes the Drude model. The unified model is valid for arbitrary magnitude
of the mean free path and arbitrary shape of the conduction band edge profile.
Universal formulas are obtained for the current-voltage characteristic in the
nondegenerate case and for the zero-bias conductance in the degenerate case,
which describe in a transparent manner the interplay of ballistic and diffusive
transport. The semiclassical approach is adopted, but quantum corrections
allowing for tunneling are included. Examples are considered, in particular the
case of chains of grains in polycrystalline or microcrystalline semiconductors
with grain size comparable to, or smaller than, the mean free path. Substantial
deviations of the results of the unified model from those of the ballistic
thermionic-emission model and of the drift-diffusion model are found. The
formulation of the model is one-dimensional, but it is argued that its results
should not differ substantially from those of a fully three-dimensional
treatment.Comment: 14 pages, 5 figures, REVTEX file, to appear in J. Phys.: Condens.
Matte
Theory of double resonance magnetometers based on atomic alignment
We present a theoretical study of the spectra produced by
optical-radio-frequency double resonance devices, in which resonant linearly
polarized light is used in the optical pumping and detection processes. We
extend previous work by presenting algebraic results which are valid for atomic
states with arbitrary angular momenta, arbitrary rf intensities, and arbitrary
geometries. The only restriction made is the assumption of low light intensity.
The results are discussed in view of their use in optical magnetometers
A room temperature 19-channel magnetic field mapping device for cardiac signals
We present a multichannel cardiac magnetic field imaging system built in
Fribourg from optical double-resonance Cs vapor magnetometers. It consists of
25 individual sensors designed to record magnetic field maps of the beating
human heart by simultaneous measurements on a grid of 19 points over the chest.
The system is operated as an array of second order gradiometers using
sophisticated digitally controlled feedback loops.Comment: 3 pages, 3 figures, submitted to Applied Physics Letter
A Model for the Strings of Eta Carinae
We propose a model based on ionization shadows to explain the formation of
the long and narrow strings of Eta Carinae. Five strings are known, all located
along the symmetry axis outside the Homunculus. The model assumes that each
string is formed in a shadow behind a dense clump near the symmetry axis. The
surrounding gas is ionized first, becomes much hotter, and compresses the gas
in the shadow. This leads to the formation of a radial, dense, long, and narrow
region, i.e., a string. Later the neutral material in the strings is ionized,
and becomes brighter. Still later it re-expands, and we predict that in about
200 years the strings will fade. The condition for the model to work is that
the ionization front, due to the diffuse ionizing recombination radiation of
the surrounding gas, proceeds into the shadow at a velocity slower than the
compression speed. From that we get a condition on the mass loss rate of the
mass loss episode that formed the strings, which should be less than 10^{-4}
Mo/year. The model can also explain the strings in the planetary nebula NGC
6543.Comment: 8 pages; Submitted to A&
Physical Structure of Small Wolf-Rayet Ring Nebulae
We have selected the seven most well-defined WR ring nebulae in the LMC (Br
2, Br 10, Br 13, Br 40a, Br 48, Br 52, and Br 100) to study their physical
nature and evolutionary stages. New CCD imaging and echelle observations have
been obtained for five of these nebulae; previous photographic imaging and
echelle observations are available for the remaining two nebulae. Using the
nebular dynamics and abundances, we find that the Br 13 nebula is a
circumstellar bubble, and that the Br 2 nebula may represent a circumstellar
bubble merging with a fossil main-sequence interstellar bubble. The nebulae
around Br 10, Br 52, and Br 100 all show influence of the ambient interstellar
medium. Their regular expansion patterns suggest that they still contain
significant amounts of circumstellar material. Their nebular abundances would
be extremely interesting, as their central stars are WC5 and WN3-4 stars whose
nebular abundances have not been derived previously. Intriguing and tantalizing
implications are obtained from comparisons of the LMC WR ring nebulae with ring
nebulae around Galactic WR stars, Galactic LBVs, LMC LBVs, and LMC BSGs;
however, these implications may be limited by small-number statistics. A SNR
candidate close to Br 2 is diagnosed by its large expansion velocity and
nonthermal radio emission. There is no indication that Br 2's ring nebula
interacts dynamically with this SNR candidate.Comment: 20 pages, Latex (aaspp4.sty), 2 figures, accepted by the Astronomical
Journal (March 99 issue
The plasma level of soluble urokinase receptor is elevated in patients with Streptococcus pneumoniae bacteraemia and predicts mortality
ABSTRACTThis multicentre prospective study was conducted to investigate whether the level of the soluble form of urokinase-type plasminogen activator receptor (suPAR) is elevated during pneumococcal bacteraemia and is of predictive value in the early stage of the disease. Plasma levels of suPAR were increased significantly (median 5.5; range 2.4–21.0 ng/mL) in 141 patients with pneumococcal bacteraemia, compared to 31 healthy controls (median 2.6, range 1.5–4.0 ng/mL, p 0.001). Furthermore, suPAR levels were elevated significantly in patients who died from the infection (n = 24) compared to survivors (n = 117; p < 0.001). No correlation was found between suPAR levels and C-reactive protein. In univariate logistic regression analysis, hypotension, renal failure, cerebral symptoms and high serum concentrations of protein YKL-40 and suPAR were associated significantly with mortality (p < 0.05). In multivariate analysis, only suPAR remained a significant predictor of death (mortality rate of 13 for suPAR levels of > 10 ng/mL; 95% CI: 1.1–158). The increase in suPAR levels may reflect increased expression by vascular or inflammatory cells in the setting of pneumococcal sepsis. This plasma protein may be used to identify patients who are severely ill with pneumococcal bacteraemia
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