Two-temperature coronal flow above a thin disk

We extended the disk corona model (Meyer & Meyer-Hofmeister 1994; Meyer, Liu, & Meyer-Hofmeister 2000a) to the inner region of galactic nuclei by including different temperatures in ions and electrons as well as Compton cooling. We found that the mass evaporation rate and hence the fraction of accretion energy released in the corona depend strongly on the rate of incoming mass flow from outer edge of the disk, a larger rate leading to more Compton cooling, less efficient evaporation and a weaker corona. We also found a strong dependence on the viscosity, higher viscosity leading to an enhanced mass flow in the corona and therefore more evaporation of gas from the disk below. If we take accretion rates in units of the Eddington rate our results become independent on the mass of the central black hole. The model predicts weaker contributions to the hard X-rays for objects with higher accretion rate like narrow-line Seyfert 1 galaxies (NLS1s), in agreement with observations. For luminous active galactic nuclei (AGN) strong Compton cooling in the innermost corona is so efficient that a large amount of additional heating is required to maintain the corona above the thin disk.Comment: 17 pages, 6 figures. ApJ accepte

Hubble Space Telescope Observations of UV Oscillations in WZ Sagittae During the Decline from Outburst

We present a time series analysis of Hubble Space Telescope observations of WZ Sge obtained in 2001 September, October, November and December as WZ Sge declined from its 2001 July superoutburst. Previous analysis of these data showed the temperature of the white dwarf decreased from ~29,000 K to ~18,000 K. In this study we binned the spectra over wavelength to yield ultraviolet light curves at each epoch that were then analyzed for the presence of the well-known 27.87 s and 28.96 s oscillations. We detect the 29 s periodicity at all four epochs, but the 28 s periodicity is absent. The origin of these oscillations has been debated since their discovery in the 1970s and competing hypotheses are based on either white dwarf non-radial g-mode pulsations or magnetically-channelled accretion onto a rotating white dwarf. By analogy with the ZZ Ceti stars, we argue that the non-radial g-mode pulsation model demands a strong dependence of pulse period on the white dwarf's temperature. However, these observations show the 29 s oscillation is independent of the white dwarf's temperature. Thus we reject the white dwarf non-radial g-mode pulsation hypothesis as the sole origin of the oscillations. It remains unclear if magnetically-funnelled accretion onto a rapidly rotating white dwarf (or belt on the white dwarf) is responsible for producing the oscillations. We also report the detection of a QPO with period ~18 s in the September light curve. The amplitudes of the 29 s oscillation and the QPO vary erratically on short timescales and are not correlated with the mean system brightness nor with each other.Comment: 20 pages, 3 figures, 1 table; accepted for publication in Ap

A new clue to the transition mechanism between optical high and low states of the supersoft X-ray source RX J0513.9-6951, implied from the recurrent nova CI Aquilae 2000 outburst model

We have found a new clue to the transition mechanism between optical high/X-ray off and optical low/X-ray on states of the LMC supersoft X-ray source RX J0513.9-6951. A sharp ~1 mag drop is common to the CI Aql 2000 outburst. These drops are naturally attributed to cessation of optically thick winds on white dwarfs. A detailed light-curve analysis of CI Aql indicates that the size of a disk drastically shrinks when the wind stops. This causes ~1-2 mag drop in the optical light curve. In RX J0513.9-6951, the same mechanism reproduces sharp ~1 mag drop from optical high to low states. We predict this mechanism also works on the transition from low to high states. Interaction between the wind and the companion star attenuates the mass transfer and drives full cycles of low and high states.Comment: 9 pages including 5 figures, to appear in the Astrophysical Journa

A geoneutrino experiment at Homestake

A significant fraction of the 44TW of heat dissipation from the Earth's interior is believed to originate from the decays of terrestrial uranium and thorium. The only estimates of this radiogenic heat, which is the driving force for mantle convection, come from Earth models based on meteorites, and have large systematic errors. The detection of electron antineutrinos produced by these uranium and thorium decays would allow a more direct measure of the total uranium and thorium content, and hence radiogenic heat production in the Earth. We discuss the prospect of building an electron antineutrino detector approximately 700m^3 in size in the Homestake mine at the 4850' level. This would allow us to make a measurement of the total uranium and thorium content with a statistical error less than the systematic error from our current knowledge of neutrino oscillation parameters. It would also allow us to test the hypothesis of a naturally occurring nuclear reactor at the center of the Earth.Comment: proceedings for Neutrino Sciences 2005, submitted to Earth, Moon, and Planet

Optical Monitoring of 3C 390.3 from 1995 to 2004 and Possible Periodicities in the Historical Light Curve

We report V, R, and I band CCD photometry of the radio galaxy 3C 390.3 obtained with the 1.56-m telescope of the Shanghai Astronomical Observatory from March 1995 to August 2004. Combining these data with data from the literature, we have constructed a historical light curve from 1894 to 2004 and searched for periodicities using the CLEANest program. We find possible periods of 8.30+-1.17, 5.37+-0.49, 3.51+-0.21, and 2.13+-0.08 years.Comment: Accepted by AJ, 34 pages, 11 figure

Heat flow of the Earth and resonant capture of solar 57-Fe axions

In a very conservative approach, supposing that total heat flow of the Earth is exclusively due to resonant capture inside the Earth of axions, emitted by 57-Fe nuclei on Sun, we obtain limit on mass of hadronic axion: m_a<1.8 keV. Taking into account release of heat from decays of 40-K, 232-Th, 238-U inside the Earth, this estimation could be improved to the value: m_a<1.6 keV. Both the values are less restrictive than limits set in devoted experiments to search for 57-Fe axions (m_a<216-745 eV), but are much better than limits obtained in experiments with 83-Kr (m_a<5.5 keV) and 7-Li (m_a<13.9-32 keV).Comment: 8 page

RX J0513.9-6951: The first example of accretion wind evolution, a key evolutionary process to Type Ia supernovae

A new self-sustained model for long-term light curve variations of RX J0513.9-6951 is proposed based on an optically thick wind model of mass-accreting white dwarfs (WDs). When the mass accretion rate to a WD exceeds the critical rate of \sim 1 x 10^{-6} M_\sun yr^{-1}, optically thick strong winds begin to blow from the WD so that a formation of common envelope is avoided. The WD can accrete and burn hydrogen-rich matter atop the WD at the critical rate. The excess matter transferred to the WD above the critical rate is expelled by winds. This is called the accretion wind evolution. This ejection process, however, occurs intermittently because the mass transfer is attenuated by strong winds: the strong winds collide with the secondary surface and strip off the very surface layer of the secondary. The matter stripped-off is lost from the binary system. Properly formulating this mass stripping effect and the ensuing decay of mass transfer rate, we are able to reproduce, in a self-sustained manner, the transition between the optical high/X-ray off and optical low/X-ray on states of RX J0513.9-6951. Thus RX J0513.9-6951 is the first example of the accretion wind evolution, which is a key evolutionary process in a recently developed evolutionary path to Type Ia supernovae.Comment: 22 pages including 13 figures, to appear in the Astrophysical Journa

Three Stages of Lysozyme Thermal Stabilization by High and Medium Charge Density Anions

Addition of high and medium charge density anions (phosphate, sulfate, and chloride) to lysozyme in pure water demonstrates three stages for stabilization of the protein structure. The first two stages have a minor impact on lysozyme stability and are probably associated with direct interaction of the ions with charged and partial charges on the protein’s surface. There is a clear transition between the second and third stages; in the case of sodium chloride, disodium sulfate and disodium hydrogen phosphate this is at 550, 210, and 120 mM, respectively. Stabilization of lysozyme can be explained by the free energy required to hydrate the protein as it unfolds. At low ion concentrations, the protein’s hydration layer is at equilibrium with the bulk water. After the transition, bulk water is depleted and the protein is competing for water with the ions. With competition for water between the protein and the ions at higher salt concentrations, the free energy required to hydrate the interior of the protein rises and it is this that stabilizes the protein structure

Isolation and characterization of equine native MSC populations

Abstract Background In contrast to humans in which mesenchymal stem/stromal cell (MSC) therapies are still largely in the clinical trial phase, MSCs have been used therapeutically in horses for over 15 years, thus constituting a valuable preclinical model for humans. In human tissues, MSCs have been shown to originate from perivascular cells, namely pericytes and adventitial cells, which are identified by the presence of the cell surface markers CD146 and CD34, respectively. In contrast, the origin of MSCs in equine tissues has not been established, preventing the isolation and culture of defined cell populations in that species. Moreover, a comparison between perivascular CD146+ and CD34+ cell populations has not been performed in any species. Methods Immunohistochemistry was used to identify adventitial cells (CD34+) and pericytes (CD146+) and to determine their localization in relation to MSCs in equine tissues. Isolation of CD34+ (CD34+/CD146–/CD144–/CD45–) and CD146+ (CD146+/CD34–/CD144–/CD45–) cell fractions from equine adipose tissue was achieved by fluorescence-activated cell sorting. The isolated cell fractions were cultured and analyzed for the expression of MSC markers, using qPCR and flow cytometry, and for the ability to undergo trilineage differentiation. Angiogenic properties were analyzed in vivo using a chorioallantoic membrane (CAM) assay. Results Both CD34+ and CD146+ cells displayed typical MSC features, namely growth in uncoated tissue culture dishes, clonal growth when seeded at low density, expression of typical MSC markers, and multipotency shown by the capacity for trilineage differentiation. Of note, CD146+ cells were distinctly angiogenic compared with CD34+ and non-sorted cells (conventional MSCs), demonstrated by the induction of blood vessels in a CAM assay, expression of elevated levels of VEGFA and ANGPT1, and association with vascular networks in cocultures with endothelial cells, indicating that CD146+ cells maintain a pericyte phenotype in culture. Conclusion This study reports for the first time the successful isolation and culture of CD146+ and CD34+ cell populations from equine tissues. Characterization of these cells evidenced their distinct properties and MSC-like phenotype, and identified CD146+ cells as distinctly angiogenic, which may provide a novel source for enhanced regenerative therapies