54 research outputs found
Magnetohydrodynamics and Plasma Cosmology
We study the linear magnetohydrodynamic (MHD) equations, both in the
Newtonian and the general-relativistic limit, as regards a viscous magnetized
fluid of finite conductivity and discuss instability criteria. In addition, we
explore the excitation of cosmological perturbations in anisotropic spacetimes,
in the presence of an ambient magnetic field. Acoustic, electromagnetic (e/m)
and fast-magnetosonic modes, propagating normal to the magnetic field, can be
excited, resulting in several implications of cosmological significance.Comment: 9 pages, RevTeX, To appear in the Proceedings of the Peyresq X
Meeting, IJTP Conference Serie
Gamma-Ray Bursts: The Underlying Model
A pedagogical derivation is presented of the ``fireball'' model of gamma-ray
bursts, according to which the observable effects are due to the dissipation of
the kinetic energy of a relativistically expanding wind, a ``fireball.'' The
main open questions are emphasized, and key afterglow observations, that
provide support for this model, are briefly discussed. The relativistic outflow
is, most likely, driven by the accretion of a fraction of a solar mass onto a
newly born (few) solar mass black hole. The observed radiation is produced once
the plasma has expanded to a scale much larger than that of the underlying
``engine,'' and is therefore largely independent of the details of the
progenitor, whose gravitational collapse leads to fireball formation. Several
progenitor scenarios, and the prospects for discrimination among them using
future observations, are discussed. The production in gamma- ray burst
fireballs of high energy protons and neutrinos, and the implications of burst
neutrino detection by kilometer-scale telescopes under construction, are
briefly discussed.Comment: In "Supernovae and Gamma Ray Bursters", ed. K. W. Weiler, Lecture
Notes in Physics, Springer-Verlag (in press); 26 pages, 2 figure
An update for cladoceran fauna (Crustacea, Branchiopoda) from Lake Paranoá, Central Brazil, with the first description of a male of Leydigiopsis ornata Daday, 1905
Effects of exposure to Diazinon on the lung and small intestine of Guinea pig, histological and some histochemical changes
The parental care behaviour of Paratilapia polleni (Perciformes, Labroidei), a phylogenetically primitive cichlid from Madagascar, with a discussion of the evolution of maternal care in the family Cichlidae
The parental behaviour of the Madagascan cichlid, Paratilapia polleni , was studied in the laboratory. According to current hypotheses of phylogenetic intrarelationship for the family Cichlidae, Paratilapia is a representative of a phylogenetically primitive cichlid lineage, and as such is of particular interest in comparative evolutionary studies. Given the basal phylogenetic placement of Paratilapia it seems reasonable to expect that, if maternal participation in brood care arose within the extant Cichlidae, then the proposed plesiomorphic system of extensive male care of eggs and embryos may be retained in this taxon. This is not the case, and already by the fertilized-egg interval male and female roles in Paratilapia are strongly differentiated with the female as the primary care giver. In addition to specialized behavioural roles, a unique egg morphology and mobile egg mass is described for Paratilapia . The results of the study are discussed in the context of theories of the evolution of maternal brood care within the Cichlidae.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42636/1/10641_2004_Article_BF00004768.pd
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Heavy element production in a compact object merger observed by JWST
The mergers of binary compact objects such as neutron stars and black holes are of central interest to several areas of astrophysics, including as the progenitors of gamma-ray bursts (GRBs)1, sources of high-frequency gravitational waves (GW)2 and likely production sites for heavy element nucleosynthesis via rapid neutron capture (the r-process)3. Here we present observations of the exceptionally bright gamma-ray burst GRB 230307A. We show that GRB 230307A belongs to the class of long-duration gamma-ray bursts associated with compact object mergers4–6, and contains a kilonova similar to AT2017gfo, associated with the gravitational-wave merger GW1708177–12. We obtained James Webb Space Telescope mid-infrared (mid-IR) imaging and spectroscopy 29 and 61 days after the burst. The spectroscopy shows an emission line at 2.15 microns which we interpret as tellurium (atomic mass A=130), and a very red source, emitting most of its light in the mid-IR due to the production of lanthanides. These observations demonstrate that nucleosynthesis in GRBs can create r-process elements across a broad atomic mass range and play a central role in heavy element nucleosynthesis across the Universe
The electromagnetic counterpart of the binary neutron star merger LIGO/Virgo GW170817. I. Discovery of the optical counterpart using the Dark Energy Camera
We present the Dark Energy Camera (DECam) discovery of the optical counterpart of the first binary neutron star merger detected through gravitational wave emission, GW170817. Our observations commenced 10.5 hours post-merger, as soon as the localization region became accessible from Chile. We imaged 70 deg2 in the i and z bands, covering 93% of the initial integrated localization probability, to a depth necessary to identify likely optical counterparts (e.g., a kilonova). At 11.4 hours post-merger we detected a bright optical transient located 10:600 from the nucleus of NGC4993 at redshift z = 0:0098, consistent (for H0 = 70 km s-1 Mpc-1) with the distance of 40±8 Mpc reported by the LIGO Scientific Collaboration and the Virgo Collaboration (LVC). At detection the transient had magnitudes i=17.3 and z=17.4, and thus an absolute magnitude of Mi = -15.7, in the luminosity range expected for a kilonova. We identified 1,500 potential transient candidates. Applying simple selection criteria aimed at rejecting background events such as supernovae, we find the transient associated with NGC4993 as the only remaining plausible counterpart, and reject chance coincidence at the 99.5% confidence level. We therefore conclude that the optical counterpart we have identified near NGC4993 is associated with GW170817. This discovery ushers in the era of multi-messenger astronomy with gravitational waves, and demonstrates the power of DECam to identify the optical counterparts of gravitational-wave sources
Studies on the biochemical development of human lung and brain
In 2 volsAvailable from British Library Document Supply Centre- DSC:DX171039 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo
243 The Association of Sex Hormone Binding Globulin with Mortality is Mediated by Age in Men with Type 2 Diabetes
Studies on glutathione S-transferase GSTM1 and GSTT1 genotypes and susceptibility to laryngeal cancer,ERSTE ERGEBNISSE UBER GLUTATHION-S-TRANSFERASE GSTM1 UND GSTT1 GENOTYPEN UND DIE GENETISCHE PRADISPOSITION BEIM LARYNXKARZINOM
BackgroundWhile cigarette smoking and alcohol consumption have been linked to laryngeal carcinoma, the role of genetic factors in determining individual susceptibility is unknown. We describe the role of allelism at glutathione-S-transferase GSTM1, GSTT1, and cytochrome P 450 CYP2D6 loci in determining individual susceptibility to laryngeal squamous cell carcinoma.MethodsEnzyme genotypes were determined using the polymerase chain reaction in 169 patients suffering T1-T4 laryngeal carcinoma and in 145 controls.ResultsWhile the frequency of the heterozygote GSTM1 A/B genotype was statistically significantly lower in the cases than controls, the frequency of the GSTT1 null genotype was higher in cases than controls.ConclusionThese initial data suggest that allelism at GST loci mediates susceptibility to squamous cell carcinoma of the larynx. Thus, GSTM1 A/B appears to be associated with a reduced risk while GSTT1 null confers increased risk. The findings are compatible with the view that genetic predisposition is important in determining risk of this cancer
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