3,177 research outputs found
Black Hole Radiation and Volume Statistical Entropy
The simplest possible equation for Hawking radiation, and other black hole
radiated power is derived in terms of black hole density. Black hole density
also leads to the simplest possible model of a gas of elementary constituents
confined inside a gravitational bottle of Schwarzchild radius at tremendous
pressure, which yields identically the same functional dependence as the
traditional black hole entropy. Variations of Sbh can be obtained which depend
on the occupancy of phase space cells. A relation is derived between the
constituent momenta and the black hole radius which is similar to the Compton
wavelength relation.Comment: 11 pages, no figures. Key Words: Black Hole Entropy, Hawking
Radiation, Black Hole density. This is a better pdf versio
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Quantitative analysis of acetyl-CoA production in hypoxic cancer cells reveals substantial contribution from acetate
Background
Cell growth requires fatty acids for membrane synthesis. Fatty acids are assembled from 2-carbon units in the form of acetyl-CoA (AcCoA). In nutrient and oxygen replete conditions, acetyl-CoA is predominantly derived from glucose. In hypoxia, however, flux from glucose to acetyl-CoA decreases, and the fractional contribution of glutamine to acetyl-CoA increases. The significance of other acetyl-CoA sources, however, has not been rigorously evaluated. Here we investigate quantitatively, using 13C-tracers and mass spectrometry, the sources of acetyl-CoA in hypoxia.<p></p>
Results
In normoxic conditions, cultured cells produced more than 90% of acetyl-CoA from glucose and glutamine-derived carbon. In hypoxic cells, this contribution dropped, ranging across cell lines from 50% to 80%. Thus, under hypoxia, one or more additional substrates significantly contribute to acetyl-CoA production. 13C-tracer experiments revealed that neither amino acids nor fatty acids are the primary source of this acetyl-CoA. Instead, the main additional source is acetate. A large contribution from acetate occurs despite it being present in the medium at a low concentration (50–500 μM).<p></p>
Conclusions
Acetate is an important source of acetyl-CoA in hypoxia. Inhibition of acetate metabolism may impair tumor growth.<p></p>
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Earthquake slip surfaces identified by biomarker thermal maturity within the 2011 Tohoku-Oki earthquake fault zone.
Extreme slip at shallow depths on subduction zone faults is a primary contributor to tsunami generation by earthquakes. Improving earthquake and tsunami risk assessment requires understanding the material and structural conditions that favor earthquake propagation to the trench. We use new biomarker thermal maturity indicators to identify seismic faults in drill core recovered from the Japan Trench subduction zone, which hosted 50 m of shallow slip during the Mw9.1 2011 Tohoku-Oki earthquake. Our results show that multiple faults have hosted earthquakes with displacement ≥ 10 m, and each could have hosted many great earthquakes, illustrating an extensive history of great earthquake seismicity that caused large shallow slip. We find that lithologic contrasts in frictional properties do not necessarily determine the likelihood of large shallow slip or seismic hazard
Basic Connection between Superconductivity and Superfluidity
A basic and inherently simple connection is shown to exist between
superconductivity and superfluidity. It is shown here that the author's
previously derived general equation which agrees well with the superconducting
transition temperatures for the heavy-electron superconductors, metallic
superconductors, oxide supercon- ductors, metallic hydrogen, and neutron stars,
also works well for the superfluid transition temperature of 2.6 mK for liquid
3He. Reasonable estimates are made from 10^-3 K to 10^9K -- a range of 12
orders of magnitude. The same paradigm applies to the superfluid transition
temperature of liquid 4He, but results in a slightly different equation. The
superfluid transition temperature for dilute solutions of 3He in superfluid 4He
is estimated to be ~ 1 to 10mK. This paradigm works well in detail for
metallic, cuprate, and organic superconductors.Comment: 16 pages, 2 figure
Discovery of near-Earth asteroids by CCD scanning
The found near-Earth asteroid are different objects with peculiar orbits. With the new technique of CCD scanning we entered the domain of the smallest, the fastest, and the closest near-Earth asteroids. The results are presented
Keck Observatory Laser Guide Star Adaptive Optics Discovery and Characterization of a Satellite to the Large Kuiper Belt Object 2003 EL_(61)
The newly commissioned laser guide star adaptive optics system at Keck Observatory has been used to discover and characterize the orbit of a satellite to the bright Kuiper Belt object 2003 EL_(61). Observations over a 6 month period show that the satellite has a semimajor axis of 49,500 ± 400 km, an orbital period of 49.12 ± 0.03 days, and an eccentricity of 0.050 ± 0.003. The inferred mass of the system is (4.2 ± 0.1) × 10^(21) kg, or ~32% of the mass of Pluto and 28.6% ± 0.7% of the mass of the Pluto-Charon system. Mutual occultations occurred in 1999 and will not occur again until 2138. The orbit is fully consistent neither with one tidally evolved from an earlier closer configuration nor with one evolved inward by dynamical friction from an earlier more distant configuration
Satellites of the largest Kuiper Belt objects
We have searched the four brightest objects in the Kuiper Belt for the presence of satellites using the newly commissioned Keck Observatory Laser Guide Star Adaptive Optics system. Satellites are seen around three of the four objects: Pluto (whose satellite Charon is well-known and whose recently discovered smaller satellites are too faint to be detected), 2003 EL61 (where a second satellite is seen in addition to the previously known satellite), and 2003 UB313 (where a satellite is seen for the first time). The object 2005 FY9, the brightest Kuiper Belt object (KBO) after Pluto, does not have a satellite detectable within 0".4 with a brightness of more than 1% of the primary. The presence of satellites around three of the four brightest KBOs is inconsistent with the fraction of satellites in the Kuiper Belt at large at the 99.2% confidence level, suggesting a different formation mechanism for these largest KBO satellites. The two satellites of 2003 EL61, and the one satellite of 2003 UB313, with fractional brightnesses of 5% and 1.5%, and 2%, of their primaries, respectively, are significantly fainter relative to their primaries than other known KBO satellites, again pointing to possible differences in their origin
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