371 research outputs found
A ROSAT Survey of Contact Binary Stars
Contact binary stars are common variable stars which are all believed to emit
relatively large fluxes of x-rays. In this work we combine a large new sample
of contact binary stars derived from the ROTSE-I telescope with x-ray data from
the ROSAT All-Sky Survey (RASS) to estimate the x-ray volume emissivity of
contact binary stars in the galaxy. We obtained x-ray fluxes for 140 contact
binaries from the RASS, as well as 2 additional stars observed by the
XMM-Newton observatory. From these data we confirm the emission of x-rays from
all contact binary systems, with typical luminosities of approximately 1.0 x
10^30 erg s^-1. Combining calculated luminosities with an estimated contact
binary space density, we find that contact binaries do not have strong enough
x-ray emission to account for a significant portion of the galactic x-ray
background.Comment: 19 pages, 5 figures, accepted by A
A Catalog of 1022 Bright Contact Binary Stars
In this work we describe a large new sample of contact binary stars extracted
in a uniform manner from sky patrol data taken by the ROTSE-I telescope.
Extensive ROTSE-I light curve data is combined with J, H, and K band
near-infrared data taken from the Two Micron All-Sky Survey (2MASS) to add
color information. Contact binaries candidates are selected using the observed
period-color relation. Candidates are confirmed by visual examination of the
light curves. To enhance the utility of this catalog, we derive a new J-H
period-color-luminosity relation and use this to estimate distances for the
entire catalog. From these distance estimates we derive an estimated contact
binary space density of (1.7 +/- 0.6) x 10^-5 pcs^-3.Comment: 26 pages, 12 figures, accepted for publication in A
Comportamento de cultivares de milho em relação fungo Sclerospora sorghi (Kulk) Weston e Uppal.
Identification of super-infected Aedes triseriatus mosquitoes collected as eggs from the field and partial characterization of the infecting La Crosse viruses
Catalytic partial oxidation of methane on platinum investigated by spatial reactor profiles, spatially resolved spectroscopy, and microkinetic modeling
Spatially resolved profile measurements, Raman spectroscopy, electron microscopy, and microkinetic modeling have been used to study the catalytic partial oxidation of methane on Pt. The measured species profiles through Pt coated foam catalysts exhibit a two-zone structure: an abrupt change in reaction rates separates the fast exothermic oxidation chemistry at the entrance of the reactor from the slow endothermic reforming chemistry. Spatially resolved Raman spectroscopy and electron microscopy confirm that the position of the mechanistic change could be correlated with Pt transportation and formation of carbonaceous deposits blocking the majority of active Pt sites in the reforming zone. The species profiles were simulated using a pseudo-2D heterogeneous model, which includes heat and mass transport limitations, and two state-of-the-art chemical kinetic mechanisms. Although both mechanisms are in quantitative agreement with the oxygen profiles, the two mechanisms differ substantially in their predictions of the branching ratio between partial and complete oxidation, as well as surface site coverages. The experimentally observed change in reaction rates is attributed to carbon formation, which the mechanisms are unable to reproduce, since they do not include carbon–carbon coupling reactions
Molecular Mechanism of Capacitative Calcium Entry Deficits in Familial Alzheimer’s Disease
Poster PresentationPresenilin (PS) is the catalytic subunit of the gamma-secretase which is responsible for the cleavage of
amyloid precursor protein to form beta amyloid (Aβ). Mutations in PS associated with familial
Alzheimer’s disease (FAD) increase the Aβ plaques formation in the brain and cause neurodegeneration.
Apart from this, FAD-linked PS mutations have been demonstrated to disrupt intracellular calcium (Ca2+)
regulation. Accumulating evidence suggests that Ca2+ disruption may play a proximal role in the AD
pathogenesis. Mutant PS exaggerated Ca2+ release from the endoplasmic reticulum (ER). It also attenuated
Ca2+ entry through the capacitative Ca2+ entry (CCE) pathway, yet, the mechanism is not fully understood.
Using a human neuroblast cell line SH-SY5Y and Ca2+ imaging technique, we observed CCE deficits in
FAD-linked PS1-M146L retroviral infected cell. The attenuation of CCE in PS1 mutant cells was not
mediated by the down-regulation of STIM1 and Orai1 expression, the known essential molecular players
in the CCE pathway. Instead, we identified a molecular interaction between PS and STIM1 proteins by
immunoprecipitation. On the other hand, immunofluorescence staining showed a significant reduction in
puncta formation after ER Ca2+ depleted by thapsigargin in cells infected with PS1-M146L as compared to
the wild type PS1 infected cells. Taken together, our results suggest a molecular mechanism for the CCE
deficits in FAD associated with PS1 mutations. The interaction of mutant PS1 with STIM1 exerts a
negative impact on its oligomerization and/or its interaction with Orai1. Our results may suggest molecular
targets for the development of therapeutic agents that help to treat the disease.published_or_final_versio
The H1 Forward Proton Spectrometer at HERA
The forward proton spectrometer is part of the H1 detector at the HERA
collider. Protons with energies above 500 GeV and polar angles below 1 mrad can
be detected by this spectrometer. The main detector components are
scintillating fiber detectors read out by position-sensitive photo-multipliers.
These detectors are housed in so-called Roman Pots which allow them to be moved
close to the circulating proton beam. Four Roman Pot stations are located at
distances between 60 m and 90 m from the interaction point.Comment: 20 pages, 10 figures, submitted to Nucl.Instr.and Method
Potential for La Crosse virus segment reassortment in nature
The evolutionary success of La Crosse virus (LACV, family Bunyaviridae) is due to its ability to adapt to changing conditions through intramolecular genetic changes and segment reassortment. Vertical transmission of LACV in mosquitoes increases the potential for segment reassortment. Studies were conducted to determine if segment reassortment was occurring in naturally infected Aedes triseriatus from Wisconsin and Minnesota in 2000, 2004, 2006 and 2007. Mosquito eggs were collected from various sites in Wisconsin and Minnesota. They were reared in the laboratory and adults were tested for LACV antigen by immunofluorescence assay. RNA was isolated from the abdomen of infected mosquitoes and portions of the small (S), medium (M) and large (L) viral genome segments were amplified by RT-PCR and sequenced. Overall, the viral sequences from 40 infected mosquitoes and 5 virus isolates were analyzed. Phylogenetic and linkage disequilibrium analyses revealed that approximately 25% of infected mosquitoes and viruses contained reassorted genome segments, suggesting that LACV segment reassortment is frequent in nature
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