Two-dimensional radiation-hydrodynamic model for limit-cycle oscillations of luminous accretion disks

We investigate the time evolution of luminous accretion disks around black holes, conducting the two-dimensional radiation-hydrodynamic simulations. We adopt the alpha prescription for the viscosity. The radial-azimuthal component of viscous stress tensor is assumed to be proportional to the total pressure in the optically thick region, while the gas pressure in the optically thin regime. The viscosity parameter, alpha, is taken to be 0.1. We find the limit-cycle variation in luminosity between high and low states. When we set the mass input rate from the outer disk boundary to be 100 L_E/c^2, the luminosity suddenly rises from 0.3L_E to 2L_E, where L_E is the Eddington luminosity. It decays after retaining high value for about 40 s. Our numerical results can explain the variation amplitude and duration of the recurrent outbursts observed in microquasar, GRS 1915+105. We show that the multi-dimensional effects play an important role in the high-luminosity state. In this state, the outflow is driven by the strong radiation force, and some part of radiation energy dissipated inside the disk is swallowed by the black hole due to the photon-trapping effects. This trapped luminosity is comparable to the disk luminosity. We also calculate two more cases: one with a much larger accretion rate than the critical value for the instability and the other with the viscous stress tensor being proportional to the gas pressure only even when the radiation pressure is dominant. We find no quasi-periodic light variations in these cases. This confirms that the limit-cycle behavior found in the simulations is caused by the disk instability.Comment: 6 pages, 4 figures, accepted for publication in ApJ (ApJ 01 April 2006, v640, 2 issue

Unbounded-error One-way Classical and Quantum Communication Complexity

This paper studies the gap between quantum one-way communication complexity $Q(f)$ and its classical counterpart $C(f)$, under the {\em unbounded-error} setting, i.e., it is enough that the success probability is strictly greater than 1/2. It is proved that for {\em any} (total or partial) Boolean function $f$, $Q(f)=\lceil C(f)/2 \rceil$, i.e., the former is always exactly one half as large as the latter. The result has an application to obtaining (again an exact) bound for the existence of $(m,n,p)$-QRAC which is the $n$-qubit random access coding that can recover any one of $m$ original bits with success probability $\geq p$. We can prove that $(m,n,>1/2)$-QRAC exists if and only if $m\leq 2^{2n}-1$. Previously, only the construction of QRAC using one qubit, the existence of $(O(n),n,>1/2)$-RAC, and the non-existence of $(2^{2n},n,>1/2)$-QRAC were known.Comment: 9 pages. To appear in Proc. ICALP 200

Chandra X-ray Observatory Arcsecond Imaging of the Young, Oxygen-rich Supernova Remnant 1E0102.2-7219

We present observations of the young, Oxygen-rich supernova remnant 1E0102.2-7219 taken by the Chandra X-ray Observatory during Chandra's Orbital Activation and Checkout phase. The boundary of the blast wave shock is clearly seen for the first time, allowing the diameter of the remnant and the mean blast wave velocity to be determined accurately. The prominent X-ray bright ring of material may be the result of the reverse shock encountering ejecta; the radial variation of O VII vs. O VIII emission indicates an ionizing shock propagating inwards, possibly through a strong density gradient in the ejecta. We compare the X-ray emission to Australia Telescope Compact Array 6 cm radio observations (Amy and Ball) and to archival Hubble Space Telescope [O III] observations. The ring of radio emission is predominantly inward of the outer blast wave, consistent with an interpretation as synchrotron radiation originating behind the blast wave, but outward of the bright X-ray ring of emission. Many (but not all) of the prominent optical filaments are seen to correspond to X-ray bright regions. We obtain an upper limit of ~9e33 erg/s (3 sigma) on any potential pulsar X-ray emission from the central region.Comment: Accepted for pulication in Ap. J. Letters. 4 pages, 6 figures (one color figure). Formatted with emulateapj5. Revised to incorporate copyediting changes. High-resolution postscript (3.02MB) and tiff versions of the color figure are available from http://chandra.harvard.edu/photo/cycle1/0015multi/index.htm

Entanglement measures and approximate quantum error correction

It is shown that, if the loss of entanglement along a quantum channel is sufficiently small, then approximate quantum error correction is possible, thereby generalizing what happens for coherent information. Explicit bounds are obtained for the entanglement of formation and the distillable entanglement, and their validity naturally extends to other bipartite entanglement measures in between. Robustness of derived criteria is analyzed and their tightness compared. Finally, as a byproduct, we prove a bound quantifying how large the gap between entanglement of formation and distillable entanglement can be for any given finite dimensional bipartite system, thus providing a sufficient condition for distillability in terms of entanglement of formation.Comment: 7 pages, two-columned revtex4, no figures. v1: Deeply revised and extended version: different entanglement measures are separately considered, references are added, and some remarks are stressed. v2: Added a sufficient condition for distillability in terms of entanglement of formation; published versio

Ds0*(2317) and Ds1(2460) mesons in two-body B-meson decays

We analyze the branching ratios of B to D(*) + Ds0*(Ds1) decays using the factorization hypothesis. The B to D(*) transition form factors are taken from a model-independent analysis done by Caprini, Lellouch and Neubert based on heavy quark spin symmetry and dispersive constraints, including short-distance and power corrections. The leptonic decay constants fDs0* and fDs1 are calculated assuming a molecular structure for the Ds0* and Ds1 mesons. The calculated branching ratios of B-meson two-body decays are compared with experimental data and other theoretical results.Comment: 12 pages, 2 figure

Transient and Highly Polarized Double-Peaked H-alpha Emission in the Seyfert 2 Nucleus of NGC 2110

We have discovered an extremely broad, double-peaked H-alpha emission line in the polarized flux spectrum of NGC 2110, establishing that this well-studied Seyfert 2 galaxy contains a disk-like hidden broad-line region (BLR). Several properties of NGC 2110 suggest that it is an obscured twin of Arp 102B, the prototypical double-peaked emission-line active galactic nucleus (AGN). A comparison between our data and previous spectra of NGC 2110 indicates that the double-peaked H-alpha feature is transient. The presence of a disk-like BLR in NGC 2110 has important implications for AGNs: it expands the range of properties exhibited by Seyfert 2 galaxies, and the fact that the BLR is obscured by a torus-like structure provides the first evidence that double-peaked emitters and classical Seyfert nuclei may have the same basic parsec-scale geometry.Comment: 5 pages, including 3 postscript figures. Uses emulateapj. Accepted for publication in ApJ Letter

Conformal Couplings in Induced Gravity

It is found that the induced gravity with conformal couplings requires the conformal invariance in both classical and quantum levels for consistency. This is also true for the induced gravity with an extended conformal coupling interacting with torsion.Comment: 10 pages, Revtex3.0, to appear in General Relativity and Gravitatio

Broad Band X-Ray Observations of the Narrow Line X-Ray Galaxy NGC 5506

We present a detailed analysis of broad band X-ray data of the Seyfert 2 galaxy NGC5506. 2-10 keV band are detected during a 1-day ASCA observation, while no significant change in the 2-10 keV continuum shape is found. The ASCA spectrum consists of an absorbed power-law, a 'soft excess' below 2 keV, and an Fe K$\alpha$ emission line at 6.4 keV. The 'soft excess' can be well described by either thermal emission from very low abundance material at a temperature kT$\simeq$0.8 keV, or scattered/leaking flux from the primary power-law plus a small amount of thermal emission. Analysis of ROSAT HRI data reveals that the soft X-ray emission is extended on kpc scales in this object, and the extended component may account for most of the soft X-ray excess observed by the ASCA. The result suggests that in this type 2 AGN, the 'soft excess' at least partly comes from an extended region, imposing serious problem for the model in which the source is partially covered. Fe K$\alpha$ profile is complex and can not be satisfactorily modeled by a single gaussian. Models of either double gaussians, or a narrow gaussian plus a line from a relativistic accretion disk viewed at an inclination of about 40$\pm10^\circ$ provide good fits to the data. However, the inclination of the disk can be substantially larger if there is a small amount of excessive Fe K edge absorption. The intermediate inclinations for NLXGs are consistent with the ideas that the inner accretion disk is aligned with the outer obscuring torus.Comment: 8 pages, 5 postscript figures. to appear in Astrophy. J., 1999, April 2

GUT theories from Calabi-Yau 4-folds with SO(10) Singularities

We consider an SO(10) GUT model from F-theory compactified on an elliptically fibered Calabi-Yau with a D5 singularity. To obtain the matter curves and the Yukawa couplings, we use a global description to resolve the singularity. We identify the vector and spinor matter representations and their Yukawa couplings and we explicitly build the G-fluxes in the global model and check the agreement with the semi-local results. As our bundle is of type SU(2k), some extra conditions need to be applied to match the fluxes.Comment: 27 page

Iridium-Catalyzed Enantioselective Hydrogenation of Vinylsilanes

We have screened a diverse array of iridium complexes derived from chiral N,P ligands as catalysts for the asymmetric hydrogenation of vinylsilanes, a transformation for which generally applicable catalysts were lacking. Several catalysts emerged from this study that enabled the highly enantioselective hydrogenation of a wide range of vinylsilanes with trisubstituted or disubstituted terminal C=C bonds bearing aryl, alkyl, ethoxycarbonyl, or hydroxymethyl substituents. In addition to trimethylsilyl and dimethyl(phenyl) silyl derivatives, trialkoxysilyl- and silacyclobutyl-substituted alkenes were used as substrates