On the Progenitors of Core-Collapse Supernovae

Theory holds that a star born with an initial mass between about 8 and 140 times the mass of the Sun will end its life through the catastrophic gravitational collapse of its iron core to a neutron star or black hole. This core collapse process is thought to usually be accompanied by the ejection of the star's envelope as a supernova. This established theory is now being tested observationally, with over three dozen core-collapse supernovae having had the properties of their progenitor stars directly measured through the examination of high-resolution images taken prior to the explosion. Here I review what has been learned from these studies and briefly examine the potential impact on stellar evolution theory, the existence of "failed supernovae", and our understanding of the core-collapse explosion mechanism.Comment: 7 Pages, invited review accepted for publication by Astrophysics and Space Science (special HEDLA 2010 issue

Incoherent Interplane Conductivity of kappa-(BEDT-TTF)2Cu[N(CN)2]Br

The interplane optical spectrum of the organic superconductor kappa-(BEDT-TTF)2Cu[N(CN)2]Br was investigated in the frequency range from 40 to 40,000 cm-1. The optical conductivity was obtained by Kramers-Kronig analysis of the reflectance. The absence of a Drude peak at low frequency is consistent with incoherent conductivity but in apparent contradiction to the metallic temperature dependence of the DC resistivity. We set an upper limit to the interplane transfer integral of tb = 0.1 meV. A model of defect-assisted interplane transport can account for this discrepancy. We also assign the phonon lines in the conductivity to the asymmetric modes of the ET molecule.Comment: 7 pages with embedded figures, submitted to PR

Habitable Zones and UV Habitable Zones around Host Stars

Ultraviolet radiation is a double-edged sword to life. If it is too strong, the terrestrial biological systems will be damaged. And if it is too weak, the synthesis of many biochemical compounds can not go along. We try to obtain the continuous ultraviolet habitable zones, and compare the ultraviolet habitable zones with the habitable zones of host stars. Using the boundary ultraviolet radiation of ultraviolet habitable zone, we calculate the ultraviolet habitable zones of host stars with masses from 0.08 to 4.00 \mo. For the host stars with effective temperatures lower than 4,600 K, the ultraviolet habitable zones are closer than the habitable zones. For the host stars with effective temperatures higher than 7,137 K, the ultraviolet habitable zones are farther than the habitable zones. For hot subdwarf as a host star, the distance of the ultraviolet habitable zone is about ten times more than that of the habitable zone, which is not suitable for life existence.Comment: 5 pages, 3 figure

Transport properties of strongly correlated metals:a dynamical mean-field approach

The temperature dependence of the transport properties of the metallic phase of a frustrated Hubbard model on the hypercubic lattice at half-filling are calculated. Dynamical mean-field theory, which maps the Hubbard model onto a single impurity Anderson model that is solved self-consistently, and becomes exact in the limit of large dimensionality, is used. As the temperature increases there is a smooth crossover from coherent Fermi liquid excitations at low temperatures to incoherent excitations at high temperatures. This crossover leads to a non-monotonic temperature dependence for the resistance, thermopower, and Hall coefficient, unlike in conventional metals. The resistance smoothly increases from a quadratic temperature dependence at low temperatures to large values which can exceed the Mott-Ioffe-Regel value, hbar a/e^2 (where "a" is a lattice constant) associated with mean-free paths less than a lattice constant. Further signatures of the thermal destruction of quasiparticle excitations are a peak in the thermopower and the absence of a Drude peak in the optical conductivity. The results presented here are relevant to a wide range of strongly correlated metals, including transition metal oxides, strontium ruthenates, and organic metals.Comment: 19 pages, 9 eps figure

Hypoxia, not pulmonary vascular pressure induces blood flow through intrapulmonary arteriovenous anastomoses

Blood flow through intrapulmonary arteriovenous anastomoses (IPAVA) is increased with exposure to acute hypoxia and has been associated with pulmonary artery systolic pressure (PASP). We aimed to determine the direct relationship between blood flow through IPAVA and PASP in 10 participants with no detectable intracardiac shunt by comparing: (1) isocapnic hypoxia (control); (2) isocapnic hypoxia with oral administration of acetazolamide (AZ; 250 mg, three times-a-day for 48 h) to prevent increases in PASP, and (3) isocapnic hypoxia with AZ and 8.4% NaHCO3 infusion (AZ+HCO3-) to control for AZ-induced acidosis. Isocapnic hypoxia (20 min) was maintained by end-tidal forcing, blood flow through IPAVA was determined by agitated saline contrast echocardiography and PASP was estimated by Doppler ultrasound. Arterial blood samples were collected at rest before each isocapnic-hypoxia condition to determine pH, [HCO3-], and PaCO2. AZ decreased pH (-0.08 ± 0.01), [HCO3-] (-7.1 ± 0.7 mmol/l), and PaCO2 (-4.5 ± 1.4 mmHg; p<0.01), while intravenous NaHCO3 restored arterial blood gas parameters to control levels. Although PASP increased from baseline in all three hypoxic conditions (p<0.05), a main effect of condition expressed an 11 ± 2% reduction in PASP from control (p<0.001) following AZ administration while intravenous NaHCO3 partially restored the PASP response to isocapnic hypoxia. Blood flow through IPAVA increased during exposure to isocapnic hypoxia (p<0.01) and was unrelated to PASP, cardiac output and pulmonary vascular resistance for all conditions. In conclusion, isocapnic hypoxia induces blood flow through IPAVA independent of changes in PASP and the influence of AZ on the PASP response to isocapnic hypoxia is dependent upon the H+ concentration or PaCO2. Abbreviations list: AZ, acetazolamide; FEV1, forced expiratory volume in 1 second; FIO2, fraction of inspired oxygen; FVC, forced vital capacity; Hb, total haemoglobin; HPV, hypoxic pulmonary vasoconstriction; HR, heart rate; IPAVA, intrapulmonary arteriovenous anastomoses; MAP, mean arterial pressure; PASP, pulmonary artery systolic pressure; PETCO2, end-tidal partial pressure of carbon dioxide; PETO2, end-tidal partial pressure of oxygen; PFO, patent foramen ovale; PVR, pulmonary vascular resistance; Q̇c, cardiac output; RVOT, right ventricular outflow tract; SpO2, oxyhaemoglobin saturation; SV, stroke volume; TRV, tricuspid regurgitant velocity; V̇E, minute ventilation; VTI, velocity-time integra