2,144 research outputs found
Constraining the Progenitor Companion of the Nearby Type Ia SN 2011fe with a Nebular Spectrum at +981 Days
We present an optical nebular spectrum of the nearby Type Ia supernova
2011fe, obtained 981 days after explosion. SN 2011fe exhibits little evolution
since the +593 day optical spectrum, but there are several curious aspects in
this new extremely late-time regime. We suggest that the persistence of the
~\AA\ feature is due to Na I D, and that a new emission feature at
~\AA\ may be [Ca II]. Also, we discuss whether the new emission
feature at ~\AA\ might be [Fe I] or the high-velocity hydrogen
predicted by Mazzali et al. The nebular feature at 5200~\AA\ exhibits a linear
velocity evolution of per 100 days from at least
+220 to +980 days, but the line's shape also changes in this time, suggesting
that line blending contributes to the evolution. At days after
explosion, flux from the SN has declined to a point where contribution from a
luminous secondary could be detected. In this work we make the first
observational tests for a post-impact remnant star and constrain its
temperature and luminosity to and
. Additionally, we do not see any evidence for narrow H
emission in our spectrum. We conclude that observations continue to strongly
exclude many single-degenerate scenarios for SN 2011fe.Comment: 11 pages, 10 figures, published by MNRA
Constraints on the Progenitor System of the Type Ia Supernova 2014J from Pre-Explosion Hubble Space Telescope Imaging
We constrain the properties of the progenitor system of the highly reddened
Type Ia supernova (SN) 2014J in Messier 82 (M82; d ~ 3.5 Mpc). We determine the
SN location using Keck-II K-band adaptive optics images, and we find no
evidence for flux from a progenitor system in pre-explosion near-ultraviolet
through near-infrared Hubble Space Telescope (HST) images. Our upper limits
exclude systems having a bright red giant companion, including symbiotic novae
with luminosities comparable to that of RS Ophiuchi. While the flux constraints
are also inconsistent with predictions for comparatively cool He-donor systems
(T < ~35,000 K), we cannot preclude a system similar to V445 Puppis. The
progenitor constraints are robust across a wide range of R_V and A_V values,
but significantly greater values than those inferred from the SN light curve
and spectrum would yield proportionally brighter luminosity limits. The
comparatively faint flux expected from a binary progenitor system consisting of
white dwarf stars would not have been detected in the pre-explosion HST
imaging. Infrared HST exposures yield more stringent constraints on the
luminosities of very cool (T < 3000 K) companion stars than was possible in the
case of SN Ia 2011fe.Comment: Accepted by ApJ 14 May 2014 with only minor revision
Bose-Einstein Condensation from a Rotating Thermal Cloud: Vortex Nucleation and Lattice Formation
We develop a stochastic Gross-Pitaveskii theory suitable for the study of
Bose-Einstein condensation in a {\em rotating} dilute Bose gas. The theory is
used to model the dynamical and equilibrium properties of a rapidly rotating
Bose gas quenched through the critical point for condensation, as in the
experiment of Haljan et al. [Phys. Rev. Lett., 87, 21043 (2001)]. In contrast
to stirring a vortex-free condensate, where topological constraints require
that vortices enter from the edge of the condensate, we find that phase defects
in the initial non-condensed cloud are trapped en masse in the emerging
condensate. Bose-stimulated condensate growth proceeds into a disordered vortex
configuration. At sufficiently low temperature the vortices then order into a
regular Abrikosov lattice in thermal equilibrium with the rotating cloud. We
calculate the effect of thermal fluctuations on vortex ordering in the final
gas at different temperatures, and find that the BEC transition is accompanied
by lattice melting associated with diminishing long range correlations between
vortices across the system.Comment: 15 pages, 12 figure
Development and use of Bacteroides 16S rRNA polymerase chain reaction assay for source tracking dog faecal pollution in bathing waters
Faecal pollution on bathing beaches poses a potential threat to human health and as a result may also negatively affect the local economy. In instances where the source of such pollution is not obvious, it may be necessary to track such sources using a host-specific genetic markers technique. Bacteroides species are potential indicators for source tracking of faecal pollution in bathing waters. This study designed specific primer sets to amplify sections of the 16S rRNA gene unique to Bacteroides from domestic dogs and used quantitative PCR (qPCR) to quantify such genetic markers in environmental samples. The sensitivity and specificity of the primer sets was determined; they were specific in silico against known dog Bacteroides sequences and in vitro against Bacteroides sequences originating from human and livestock faeces. Dog faecal Bacteroides contamination was then detected in sea water during the bathing season at a local beach where dogs are banned during the summer months, in spite of the fact that these waters had met EU directive standards based on the culture-based enumeration of faecal indicator bacteria. Quantitative PCR was used to determine the limit of detection (LOD) of the dog Bacteroides genetic markers in these water samples. The copy number of dog Bacteroides genetic markers in the water was low and the LOD of those markers was 4 copies per reaction. The use of these dog primers has the potential to supply important additional information when source tracking faecal pollution at bathing beaches and maintaining water quality
Semiclassical wave functions and energy levels of Bose-condensed gases in spherically symmetric traps
The WKB-approximation for the Bogoliubov-equations of the quasi-particle
excitations in Bose-gases with condensate is worked out in the case of
spherically symmetric trap potentials on the basis of the resulting
quantization rule. The excitation spectrum is calculated numerically and also
analytically in certain limiting cases. It is found that the energy levels of a
Bohr-Sommerfeld type quantization may be considerably shifted when the
classical turning point gets close to the surface of the condensate.Comment: 4 pages Latex, 1 ps-fil
A pivotal role of GSK-3 in synaptic plasticity
Glycogen synthase kinase-3 (GSK-3) has many cellular functions. Recent evidence suggests that it plays a key role in certain types of synaptic plasticity, in particular a form of long-term depression (LTD) that is induced by the synaptic activation of N-methyl-D-aspartate receptors (NMDARs). In the present article we summarize what is currently known concerning the roles of GSK-3 in synaptic plasticity at both glutamatergic and GABAergic synapses. We summarize its role in cognition and speculate on how alterations in the synaptic functioning of GSK-3 may be a major factor in certain neurodegenerative disorders
The GSK-3 inhibitor CT99021 enhances the acquisition of spatial learning and the accuracy of spatial memory
Glycogen synthase kinase 3 (GSK-3) is a Ser/Thr protein kinase that regulates many cellular processes, including synaptic plasticity. Previously, we reported that inhibition of GSK-3 prevents the induction of one of the major forms of synaptic plasticity, N-methyl-D-aspartate receptor (NMDAR)-dependent long-term depression (LTD), in hippocampal slices. In the present study, we have investigated the effects of inhibiting GSK-3 on learning and memory in healthy naïve animals. Systemic administration of a highly selective GSK-3 inhibitor, CT99021, reversibly blocked NMDAR-dependent LTD in the CA1 region of the hippocampus in anesthetized adult mice. In behavioral tasks, CT99021 had no effect on locomotor activity, anxiety, hippocampus-dependent contextual fear memory, and hippocampus-dependent reversal learning. However, CT99021 facilitated the rate of learning in the Morris water maze (MWM) and T-maze and enhanced the accuracy of long-term spatial memory in the MWM. These findings suggest that GSK-3 regulates the accuracy of spatial memory acquisition and recall
Linking Life Skills and Norms with adolescent substance use and delinquency in South Africa
We examined factors targeted in two popular prevention approaches with adolescent drug use and
delinquency in South Africa. We hypothesized adolescent life skills to be inversely related, and
perceived norms to be directly related to later drug use and delinquency. Multiple regression and a
relative weights approach were conducted for each outcome using a sample of 714 South African
adolescents ages 15 to 19 years (M = 15.8 years, 57% female). Perceived norms predicted gateway
drug use. Conflict resolution skills (inversely) and perceived peer acceptability (directly) predicted
harder drug use and delinquency. The “culture of violence” within some South African schools
may make conflict resolution skills more salient for preventing harder drug use and delinquency.Department of HE and Training approved lis
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