Osaka University

About: Osaka University is a education organization based out in Osaka, Japan. It is known for research contribution in the topics: Laser & Catalysis. The organization has 83778 authors who have published 185669 publications receiving 5158122 citations. The organization is also known as: Ōsaka daigaku.

Gravitationally redshifted emission implying an accretion disk and massive black hole in the active galaxy MCG-6-30-15

Abstract: ACTIVE galactic nuclei and quasars are probably powered by the accretion of gas onto a supermassive black hole at the centre of the host galaxy1, but direct confirmation of the presence of a black hole is hard to obtain. As the gas nears the event horizon, its velocity should approach the speed of light; the resulting relativistic effects, and a gravitational redshift arising from the proximity to the black hole, should be observable, allowing us to test specific predictions of the models with the observations. Here we report the detection of these relativistic effects in an X-ray emission line (the Kα line) from ionized iron in the galaxy MCG–6–30–15. The line is extremely broad, corresponding to a velocity of ∼100,000 km s−1, and asymmetric, with most of the line flux being redshifted. These features indicate that the line most probably arises in a region between three and ten Schwarzschild radii from the centre, so that we are observing the innermost region of the accretion disk.

Gauss-Bonnet black holes in AdS spaces

Abstract: We study the thermodynamic properties and phase structures of topological black holes in Einstein theory with a Gauss-Bonnet term and a negative cosmological constant. The event horizon of these topological black holes can be a hypersurface with positive, zero, or negative constant curvature. When the horizon is a zero curvature hypersurface, the thermodynamic properties of black holes are completely the same as those of black holes without the Gauss-Bonnet term, although the two black hole solutions are quite different. When the horizon is a negative constant curvature hypersurface, the thermodynamic properties of the Gauss-Bonnet black holes are qualitatively similar to those of black holes without the Gauss-Bonnet term. When the event horizon is a hypersurface with positive constant curvature, we find that the thermodynamic properties and phase structures of black holes drastically depend on the spacetime dimension d and the coefficient of the Gauss-Bonnet term: when dgreater than or equal to6, the properties of black holes are also qualitatively similar to the case without the Gauss-Bonnet term, but when d=5, a new phase of locally stable small blacks holes occurs under a critical value of the Gauss-Bonnet coefficient, and beyond the critical value, the black holes are always thermodynamically stable. However, the locally stable small black hole is not globally preferred; instead a thermal anti-de Sitter space is globally preferred. We find that there is a minimal horizon radius, below which the Hawking-Page phase transition will not occur since for these black holes the thermal anti-de Sitter space is always globally preferred.

Essential role of MD-2 in LPS responsiveness and TLR4 distribution.

Abstract: Toll-like receptor 4 (TLR4) mediates lipopolysaccharide (LPS) signaling in a variety of cell types. MD-2 is associated with the extracellular domain of TLR4 and augments TLR4-dependent LPS responses in vitro. We show here that MD-2(-/-) mice do not respond to LPS, do survive endotoxic shock but are susceptible to Salmonella typhimurium infection. We found that in MD-2(-/-) embryonic fibroblasts, TLR4 was not able to reach the plasma membrane and predominantly resided in the Golgi apparatus, whereas TLR4 was distributed at the leading edge surface of cells in wild-type embryonic fibroblasts. Thus, MD-2 is essential for correct intracellular distribution and LPS-recognition of TLR4.