593 research outputs found
V39: an unusual object in the field of IC 1613
The variable star V39 in the field of IC 1613 is discussed in the light of
the available photometric and new spectroscopic data. It has strong emission
Balmer lines, and the observed characteristics could be explained by a W Vir
pulsating star with a period of 14.341 d, located at more than 115 kpc, that is
in the very outer halo of our Galaxy. It should have an apparent companion, a
long period (1118d) red variable, belonging to IC 1613. The main uncertainty in
this interpretation is an emission feature at 668.4 nm, which we tentatively
identified as a He I line.Comment: 5 pages; accepted for publication in Astronomy & Astrophysic
Spin Hall effect transistor
Spin transistors and spin Hall effects have been two separate leading
directions of research in semiconductor spintronics which seeks new paradigms
for information processing technologies. We have brought the two directions
together to realize an all-semiconductor spin Hall effect transistor. Our
scheme circumvents semiconductor-ferromagnet interface problems of the original
Datta-Das spin transistor concept and demonstrates the utility of the spin Hall
effects in microelectronics. The devices use diffusive transport and operate
without electrical current, i.e., without Joule heating in the active part of
the transistor. We demonstrate a spin AND logic function in a semiconductor
channel with two gates. Our experimental study is complemented by numerical
Monte Carlo simulations of spin-diffusion through the transistor channel.Comment: 11 pages, 3 figure
Immune responses in lactating Holstein cows supplemented with Cu, Mn, and Zn as sulfates or methionine hydroxy analogue chelates
The aim of this study was to compare effects of inorganic sulfate versus chelated forms of supplemental Cu, Mn, and Zn on milk production, plasma and milk mineral concentrations, neutrophil activity, and antibody titer response to a model vaccination. Holstein cows (n = 25) were assigned in 2 cohorts based on calving date to a 12-wk randomized complete block design study. The first cohort consisted of 17 cows that had greater days in milk (DIM; mean of 77 DIM at the start of the trial) than the second cohort of 8 cows (32 DIM at the start of the trial). Diets were formulated to supplement 100% of National Research Council requirements of Cu, Mn, and Zn by either inorganic trace minerals (ITM) in sulfate forms or chelated trace minerals (CTM) supplied as metal methionine hydroxy analog chelates, without accounting for trace mineral contribution from other dietary ingredients. Intake and milk production were recorded daily. Milk composition was measured weekly, and milk Cu, Mn, and Zn were determined at wk 0 and 8. Plasma Cu and Zn concentrations and neutrophil activity were measured at wk 0, 4, 8, and 12. Neutrophil activity was measured by in vitro assays of chemotaxis, phagocytosis, and reactive oxygen species production. A rabies vaccination was administered at wk 8, and vaccine titer response at wk 12 was measured by both rapid fluorescent focus inhibition test and ELISA. Analyzed dietary Cu was 21 and 23 mg/kg, Mn was 42 and 46 mg/kg, and Zn was 73 and 94 mg/ kg for the ITM and CTM diets, respectively. No effect of treatment was observed on milk production, milk composition, or plasma minerals. Dry matter intake was reduced for CTM compared with ITM cows, but this was largely explained by differences in body weight between treatments. Milk Cu concentration was greater for CTM than ITM cows, but this effect was limited to the earlier DIM cohort of cows and was most pronounced for multiparous compared with primiparous cows. Measures of neutrophil function were unaffected by treatment except for an enhancement in neutrophil phagocytosis with the CTM treatment found for the later DIM cohort of cows only. Rabies antibody titer in CTM cows was 2.8 fold that of ITM cows as measured by ELISA, with a trend for the rapid fluorescent focus inhibition test. Supplementation of Cu, Mn, and Zn as chelated sources may enhance immune response of early lactation dairy cows compared with cows supplemented with inorganic sources
Two-photon spin injection in semiconductors
A comparison is made between the degree of spin polarization of electrons
excited by one- and two-photon absorption of circularly polarized light in bulk
zincblende semiconductors. Time- and polarization-resolved experiments in
(001)-oriented GaAs reveal an initial degree of spin polarization of 49% for
both one- and two-photon spin injection at wavelengths of 775 and 1550 nm, in
agreement with theory. The macroscopic symmetry and microscopic theory for
two-photon spin injection are reviewed, and the latter is generalized to
account for spin-splitting of the bands. The degree of spin polarization of
one- and two-photon optical orientation need not be equal, as shown by
calculations of spectra for GaAs, InP, GaSb, InSb, and ZnSe using a 14x14 k.p
Hamiltonian including remote band effects. By including the higher conduction
bands in the calculation, cubic anisotropy and the role of allowed-allowed
transitions can be investigated. The allowed-allowed transitions do not
conserve angular momentum and can cause a high degree of spin polarization
close to the band edge; a value of 78% is calculated in GaSb, but by varying
the material parameters it could be as high as 100%. The selection rules for
spin injection from allowed-allowed transitions are presented, and interband
spin-orbit coupling is found to play an important role.Comment: 12 pages including 7 figure
Kepler photometry of RRc stars: peculiar double-mode pulsations and period doubling
We present the analysis of four first overtone RR Lyrae stars observed with the Kepler space telescope, based on data obtained over nearly 2.5 yr. All four stars are found to be multiperiodic.
The strongest secondary mode with frequency f2 has an amplitude of a few mmag, 20–45 times lower than the main radial mode with frequency f1. The two oscillations have a period ratio of P2/P1 = 0.612–0.632 that cannot be reproduced by any two radial modes. Thus, the secondary mode is non-radial. Modes yielding similar period ratios have also recently been discovered in other variables of the RRc and RRd types. These objects form a homogenous group and constitute a new class of multimode RR Lyrae pulsators, analogous to a similar class of multimode classical Cepheids in the Magellanic Clouds. Because a secondary mode with P2/P1 ∼ 0.61 is found in almost every RRc and RRd star observed from space, this form of multiperiodicity must be common. In all four Kepler RRc stars studied, we find subharmonics of f2 at ∼1/2f2 and at ∼3/2f2. This is a signature of period doubling of the secondary oscillation, and is the first detection of period doubling in RRc stars. The amplitudes and phases of f2 and its subharmonics are variable on a time-scale of 10–200 d. The dominant radial mode also shows variations on the same time-scale, but with much smaller amplitude. In three Kepler RRc stars we detect additional periodicities, with amplitudes below 1 mmag, that must correspond to non-radial g-modes. Such modes never before have been observed in RR Lyrae variables
The Population Structure of Acinetobacter baumannii: Expanding Multiresistant Clones from an Ancestral Susceptible Genetic Pool
Outbreaks of hospital infections caused by multidrug resistant Acinetobacter baumannii strains are of increasing concern worldwide. Although it has been reported that particular outbreak strains are geographically widespread, little is known about the diversity and phylogenetic relatedness of A. baumannii clonal groups. Sequencing of internal portions of seven housekeeping genes (total 2,976 nt) was performed in 154 A. baumannii strains covering the breadth of known diversity and including representatives of previously recognized international clones, and in 19 representatives of other Acinetobacter species. Restricted amounts of diversity and a star-like phylogeny reveal that A. baumannii is a genetically compact species that suffered a severe bottleneck in the recent past, possibly linked to a restricted ecological niche. A. baumannii is neatly demarcated from its closest relative (genomic species 13TU) and other Acinetobacter species. Multilocus sequence typing analysis demonstrated that the previously recognized international clones I to III correspond to three clonal complexes, each made of a central, predominant genotype and few single locus variants, a hallmark of recent clonal expansion. Whereas antimicrobial resistance was almost universal among isolates of these and a novel international clone (ST15), isolates of the other genotypes were mostly susceptible. This dichotomy indicates that antimicrobial resistance is a major selective advantage that drives the ongoing rapid clonal expansion of these highly problematic agents of nosocomial infections
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