Black Hole Formation and Explosion from Rapidly Rotating Very Massive Stars

We explore the formation process of a black hole (BH) through the pair-instability collapse of a rotating Population III very massive star in axisymmetric numerical relativity. As the initial condition, we employ a progenitor star which is obtained by evolving a rapidly rotating zero-age main sequence (ZAMS) star with mass $320M_\odot$ until it reaches a pair instability region. We find that for such rapidly rotating model, a fraction of the mass, $\sim 10M_\odot$, forms a torus surrounding the remnant BH of mass $\sim 130M_\odot$ and an outflow is driven by a hydrodynamical effect. We also perform simulations, artificially reducing the initial angular velocity of the progenitor star, and find that only a small or no torus is formed and no outflow is driven. We discuss the possible evolution scenario of the remnant torus for the rapidly rotating model by considering the viscous and recombination effects and show that if the energy of $\sim 10^{52}$ erg is injected from the torus to the envelope, the luminosity and timescale of the explosion could be of the orders of $10^{43}$ erg/s and yrs, respectively. We also point out the possibility for observing gravitational waves associated with the BH formation for the rapidly rotating model by ground-based gravitational-wave detectors.Comment: 19 pages, 16 figures, submitted to Ap

Neutrino-driven explosions of ultra-stripped type Ic supernovae generating binary neutron stars

We study explosion characteristics of ultra-stripped supernovae (SNe), which are candidates of SNe generating binary neutron stars (NSs). As a first step, we perform stellar evolutionary simulations of bare carbon-oxygen cores of mass from 1.45 to 2.0 $M_\odot$ until the iron cores become unstable and start collapsing. We then perform axisymmetric hydrodynamics simulations with spectral neutrino transport using these stellar evolution outcomes as initial conditions. All models exhibit successful explosions driven by neutrino heating. The diagnostic explosion energy, ejecta mass, Ni mass, and NS mass are typically $\sim 10^{50}$ erg, $\sim 0.1 M_\odot$, $\sim 0.01M_\odot$, and $\approx 1.3 M_\odot$, which are compatible with observations of rapidly-evolving and luminous transient such as SN 2005ek. We also find that the ultra-stripped SN is a candidate for producing the secondary low-mass NS in the observed compact binary NSs like PSR J0737-3039.Comment: 9 pages, 8 figures, 2 tables; accepted for publication in MNRA

Stand development and regeneration during a 33-year period in a seral Picea glehnii forest, northern Japan

The original publication is available at www.springerlink.comArticleECOLOGICAL RESEARCH. 21(1):35-42(2006)journal articl

Vascular changes in the rat brain during chronic hypoxia in the presence and absence of hypercapnia.

Changes in brain vascularity in adult rats during adaptation to chronic normobaric hypoxia with or without elevated CO(2) were morphometrically investigated. Immunohistochemistry with anti-rat endothelial cell antigen (RECA-1) antibody was carried out for the vascular analysis. After the rats were subjected to hypoxia for 2 to 8 weeks (wks)(10 percent O(2) in N(2)), the total area of blood vessels was measured in 6 brain regions. After 2 wks of hypoxia, the blood vessel area was found to be significantly increased in the frontal cortex, striatum, hippocampus, thalamus, cerebellum, and medulla oblongata, by 44% , 96% , 65% , 50% , 102% and 97% , respectively. The ratio of large vessels with an area &#62; 500 micro m(2) was also increased in all brain regions. Hypoxic adaptation in brain vascularity did not change during 8 wks of hypoxia, and the hypoxia-induced levels measured in the vasculature returned to control levels 2 wks after the termination of hypoxia in areas of the brain other than the cortex and thalamus. In addition, hypoxia-induced changes in terms of the total vascular area and vessel size distribution were significantly inhibited by the elevation in CO(2), whereas chronic hypercapnia without hypoxia had no effect on brain vascularity. These findings suggested that adaptations in brain vascularity in response to hypoxia are rapidly induced, and there are regional differences in the reversibility of such vascular changes. Carbon dioxide is a potent suppressor of hypoxia-induced vascular changes, and may play an important role in vascular remodeling during the process of adaptation to chronic hypoxia.</p

Surface tension measurement of glass melts by the maximum bubble pressure method

The maximum bubble pressure method was used to obtain accurate surface tension measurements. The dependence of apparent surface tension value on bubble growth time was measured for times from several to longer than a thousand seconds. The static surface tension value was obtained by extrapolating bubble growth time to infinity. The dynamic surface tension, which is familiar in colloids, could not be directly obtained because of the high viscosity of glass melt. The effects of capillary tip material and shape were also examined. This method is applicable to melts with viscosity less than 10^3.5 dPa s. The reproducibility in the measurement was within a few percent