13,584 research outputs found
The MUCHFUSS photometric campaign
Hot subdwarfs (sdO/Bs) are the helium-burning cores of red giants, which lost
almost all of their hydrogen envelopes. This mass loss is often triggered by
common envelope interactions with close stellar or even substellar companions.
Cool companions like late-type stars or brown dwarfs are detectable via
characteristic light curve variations like reflection effects and often also
eclipses. To search for such objects we obtained multi-band light curves of 26
close sdO/B binary candidates from the MUCHFUSS project with the BUSCA
instrument. We discovered a new eclipsing reflection effect system
(~d) with a low-mass M dwarf companion ().
Three more reflection effect binaries found in the course of the campaign were
already published, two of them are eclipsing systems, in one system only
showing the reflection effect but no eclipses the sdB primary is found to be
pulsating. Amongst the targets without reflection effect a new long-period sdB
pulsator was discovered and irregular light variations were found in two sdO
stars. The found light variations allowed us to constrain the fraction of
reflection effect binaries and the substellar companion fraction around sdB
stars. The minimum fraction of reflection effect systems amongst the close sdB
binaries might be greater than 15\% and the fraction of close substellar
companions in sdB binaries might be as high as . This would result in a
close substellar companion fraction to sdB stars of about 3\%. This fraction is
much higher than the fraction of brown dwarfs around possible progenitor
systems, which are solar-type stars with substellar companions around 1 AU, as
well as close binary white dwarfs with brown dwarf companions. This might be a
hint that common envelope interactions with substellar objects are
preferentially followed by a hot subdwarf phase.Comment: accepted for A&
Perceived etiology of foodborne illness among public health personnel.
Few data exist about perceptions regarding the etiology of foodborne illness. Among public health staff throughout Tennessee, the three pathogens most commonly believed to cause foodborne illness in the United States actually account for only 12% of disease. Fewer than 3% of respondents correctly identified the leading cause of foodborne illness
Pion gas viscosity at low temperature and density
By using Chiral Perturbation Theory and the Uehling-Uhlenbeck equation we
compute the viscosity of a pion gas, in the low temperature and low density
regime, in terms of the temperature, and the pion fugacity. The viscosity turns
out to be proportional to the squared root of the temperature over the pion
mass. Next to leading corrections are proportional to the temperature over the
pion mass to the 3/2.Comment: 15 pages, 4 figures. RevTeX
Ab initio calculation of the anomalous Hall conductivity by Wannier interpolation
The intrinsic anomalous Hall effect in ferromagnets depends on subtle
spin-orbit-induced effects in the electronic structure, and recent ab-initio
studies found that it was necessary to sample the Brillouin zone at millions of
k-points to converge the calculation. We present an efficient first-principles
approach for computing the anomalous Hall conductivity. We start out by
performing a conventional electronic-structure calculation including spin-orbit
coupling on a uniform and relatively coarse k-point mesh. From the resulting
Bloch states, maximally-localized Wannier functions are constructed which
reproduce the ab-initio states up to the Fermi level. The Hamiltonian and
position-operator matrix elements, needed to represent the energy bands and
Berry curvatures, are then set up between the Wannier orbitals. This completes
the first stage of the calculation, whereby the low-energy ab-initio problem is
transformed into an effective tight-binding form. The second stage only
involves Fourier transforms and unitary transformations of the small matrices
set up in the first stage. With these inexpensive operations, the quantities of
interest are interpolated onto a dense k-point mesh and used to evaluate the
anomalous Hall conductivity as a Brillouin zone integral. The present scheme,
which also avoids the cumbersome summation over all unoccupied states in the
Kubo formula, is applied to bcc Fe, giving excellent agreement with
conventional, less efficient first-principles calculations. Remarkably, we find
that more than 99% of the effect can be recovered by keeping a set of terms
depending only on the Hamiltonian matrix elements, not on matrix elements of
the position operator.Comment: 16 pages, 7 figure
Exciton states in monolayer MoSe2: impact on interband transitions
We combine linear and non-linear optical spectroscopy at 4K with ab initio
calculations to study the electronic bandstructure of MoSe2 monolayers. In
1-photon photoluminescence excitation (PLE) and reflectivity we measure a
separation between the A- and B-exciton emission of 220 meV. In 2-photon PLE we
detect for the A- and B-exciton the 2p state 180meV above the respective 1s
state. In second harmonic generation (SHG) spectroscopy we record an
enhancement by more than 2 orders of magnitude of the SHG signal at resonances
of the charged exciton and the 1s and 2p neutral A- and B-exciton. Our
post-Density Functional Theory calculations show in the conduction band along
the direction a local minimum that is energetically and in k-space
close to the global minimum at the K-point. This has a potentially strong
impact on the polarization and energy of the excitonic states that govern the
interband transitions and marks an important difference to MoS2 and WSe2
monolayers.Comment: 8 pages, 3 figure
Direct observation of the quantum critical point in heavy fermion CeRhSi
We report on muon spin rotation studies of the noncentrosymmetric heavy
fermion antiferromagnet CeRhSi. A drastic and monotonic suppression of the
internal fields, at the lowest measured temperature, was observed upon an
increase of external pressure. Our data suggest that the ordered moments are
gradually quenched with increasing pressure, in a manner different from the
pressure dependence of the N\'eel temperature. At \unit{23.6}{kbar}, the
ordered magnetic moments are fully suppressed via a second-order phase
transition, and is zero. Thus, we directly observed the quantum
critical point at \unit{23.6}{kbar} hidden inside the superconducting phase
of CeRhSi
Vortex lattice studies in CeCoIn5 with H perpendicular to c
We present small angle neutron scattering studies of the vortex lattice (VL)
in CeCoIn5 with magnetic fields applied parallel (H) to the antinodal [100] and
nodal [110] directions. For H || [100], a single VL orientation is observed,
while a 90 degree reorientation transition is found for H || [110]. For both
field orientations and VL configurations we find a distorted hexagonal VL with
an anisotropy, Gamma = 2.0 +/- 0.05. The VL form factor shows strong Pauli
paramagnetic effects similar to what have previously been reported for H ||
[001]. At high fields, above which the upper critical field (Hc2) becomes a
first-order transition, an increased disordering of the VL is observed.Comment: 5 pages, 4 figure
Fractal Analysis of Protein Potential Energy Landscapes
The fractal properties of the total potential energy V as a function of time
t are studied for a number of systems, including realistic models of proteins
(PPT, BPTI and myoglobin). The fractal dimension of V(t), characterized by the
exponent \gamma, is almost independent of temperature and increases with time,
more slowly the larger the protein. Perhaps the most striking observation of
this study is the apparent universality of the fractal dimension, which depends
only weakly on the type of molecular system. We explain this behavior by
assuming that fractality is caused by a self-generated dynamical noise, a
consequence of intermode coupling due to anharmonicity. Global topological
features of the potential energy landscape are found to have little effect on
the observed fractal behavior.Comment: 17 pages, single spaced, including 12 figure
Morphological Abnormalities in Vitamin B6 Deficient Tarsometatarsal Chick Cartilage
The aim of this study was to test the hypothesis that deficiency of vitamin B6 would produce morphological characteristics of osteochondral lathyrism. To accomplish this goal, morphological characteristics of chick cartilage in which lathyrism was produced by two separate dietary regimens was compared to morphological changes encountered in vitamin B6 deficiency. Vitamin B6 deficiency should reduce activity of lysyloxidase needed for producing intermolecular cross-links. The question to be addressed was: would this latter deficiency impair collagen morphological features and secondarily other structures indirectly by reducing collagen molecular assembly? Failure of cross-linking of collagen in the positive controls was related to a lack of functional aldehyde cross-link intermediates which are blocked by homocysteine and aminoacetonitrile.
Day-old-male Lohmann chicks were fed adequate (6 mg/kg) or vitamin B6-deficient diets. Cross-link defects were induced by homocysteine-rich diets (0.6% w/w) or a diet containing aminoacetonitrile (0.1% w/w). Animals were sacrificed at 6 weeks of age and Ossa tarsalia articular cartilage specimens, as well as the proximal end of tarsometatarsus were dissected from the tibial metatarsal joint, a major weight-bearing site. Light microscopic observations revealed reduction of subarticular trabecular bone formation, concurrent with overexpansion of the hypertrophic cell zone. Ultrastructural electron microscopy observations of articular fibro-cartilage indicated significant thickening of collagen fibers in vitamin B6 deficient birds, as well as the positive controls in comparison to that of cage-matched control birds. It was concluded that vitamin B6 deficient cross-linking may be responsible for the observed delay in bone development and aforementioned cartilage histological alterations
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