Analysis of complete positivity conditions for quantum qutrit channels

We present an analysis of complete positivity (CP) constraints on qutrit quantum channels that have a form of affine transformations of generalized Bloch vector. For diagonal (damping) channels we derive conditions analogous to the ones that in qubit case produce tetrahedron structure in the channel parameter space.Comment: 12 pages, 8 figures (.eps), minor changes in the text and formula

Discovery of 15-second oscillations in Hubble Space Telescope observations of WZ Sagittae following the 2001 outburst

We report the discovery of 15-s oscillations in ultraviolet observations of WZ Sge obtained with the Hubble Space Telescope approximately one month after the peak of the 2001 outburst. This is the earliest detection of oscillations in WZ Sge following an outburst and the first time that a signal near 15 s has been seen to be dominant. The oscillations are quite strong (amplitude about 5%), but not particularly coherent. In one instance, the oscillation period changed by 0.7 s between successive observations separated by less than 1 hour. We have also found evidence for weaker signals with periods near 6.5 s in some of our data. We discuss the implications of our results for the models that have been proposed to account for the 28-s oscillations seen in quiescence. If the periods of the 15-s oscillations can be identified with the periods of revolution of material rotating about the white dwarf, the mass of the white dwarf must satisfy M_WD > 0.71 M_sun. The corresponding limit for the 6.5-s signals is M_WD > 1.03 M_sun.Comment: accepted for publication in ApJ Letters; 13 pages, 4 postscript figures; new version corrects a few typos and matches version that will appear in ApJ

Computing a Knot Invariant as a Constraint Satisfaction Problem

We point out the connection between mathematical knot theory and spin glass/search problem. In particular, we present a statistical mechanical formulation of the problem of computing a knot invariant; p-colorability problem, which provides an algorithm to find the solution. The method also allows one to get some deeper insight into the structural complexity of knots, which is expected to be related with the landscape structure of constraint satisfaction problem.Comment: 6 pages, 3 figures, submitted to short note in Journal of Physical Society of Japa

Quantum Cryptography using entangled photons in energy-time Bell states

We present a setup for quantum cryptography based on photon pairs in energy-time Bell states and show its feasability in a laboratory experiment. Our scheme combines the advantages of using photon pairs instead of faint laser pulses and the possibility to preserve energy-time entanglement over long distances. Moreover, using 4-dimensional energy-time states, no fast random change of bases is required in our setup : Nature itself decides whether to measure in the energy or in the time base.Comment: 4 pages including 2 figure

Kepler-47: A Transiting Circumbinary Multi-Planet System

We report the detection of Kepler-47, a system consisting of two planets orbiting around an eclipsing pair of stars. The inner and outer planets have radii 3.0 and 4.6 times that of the Earth, respectively. The binary star consists of a Sun-like star and a companion roughly one-third its size, orbiting each other every 7.45 days. With an orbital period of 49.5 days, eighteen transits of the inner planet have been observed, allowing a detailed characterization of its orbit and those of the stars. The outer planet's orbital period is 303.2 days, and although the planet is not Earth-like, it resides within the classical "habitable zone", where liquid water could exist on an Earth-like planet. With its two known planets, Kepler-47 establishes that close binary stars can host complete planetary systems.Comment: To appear on Science Express August 28, 11 pages, 3 figures, one table (main text), 56 pages, 28 figures, 10 table

HLA alleles determine human T-lymphotropic virus-I (HTLV-I) proviral load and the risk of HTLV-I-associated myelopathy

The risk of disease associated with persistent virus infections such as HIV-I, hepatitis B and C, and human T-lymphotropic virus-I (HTLV-I) is strongly determined by the virus load. However, it is not known whether a persistent class I HLA-restricted antiviral cytotoxic T lymphocyte (CTL) response reduces viral load and is therefore beneficial or causes tissue damage and contributes to disease pathogenesis. HTLV-I-associated myelopathy (HAM/TSP) patients have a high virus load compared with asymptomatic HTLV-I carriers. We hypothesized that HLA alleles control HTLV-I provirus load and thus influence susceptibility to HAM/TSP. Here we show that, after infection with HTLV-I, the class I allele HLA-A*02 halves the odds of HAM/TSP (P < 0.0001), preventing 28% of potential cases of HAM/TSP. Furthermore, HLA-A*02+ healthy HTLV-I carriers have a proviral load one-third that (P = 0.014) of HLA-A*02− HTLV-I carriers. An association of HLA-DRB1*0101 with disease susceptibility also was identified, which doubled the odds of HAM/TSP in the absence of the protective effect of HLA-A*02. These data have implications for other persistent virus infections in which virus load is associated with prognosis and imply that an efficient antiviral CTL response can reduce virus load and so prevent disease in persistent virus infections

The Computational Complexity of Knot and Link Problems

We consider the problem of deciding whether a polygonal knot in 3-dimensional Euclidean space is unknotted, capable of being continuously deformed without self-intersection so that it lies in a plane. We show that this problem, {\sc unknotting problem} is in {\bf NP}. We also consider the problem, {\sc unknotting problem} of determining whether two or more such polygons can be split, or continuously deformed without self-intersection so that they occupy both sides of a plane without intersecting it. We show that it also is in NP. Finally, we show that the problem of determining the genus of a polygonal knot (a generalization of the problem of determining whether it is unknotted) is in {\bf PSPACE}. We also give exponential worst-case running time bounds for deterministic algorithms to solve each of these problems. These algorithms are based on the use of normal surfaces and decision procedures due to W. Haken, with recent extensions by W. Jaco and J. L. Tollefson.Comment: 32 pages, 1 figur

GALEX UV Spectroscopy and Deep Imaging of LIRGs in the ELAIS S1 field

The ELAIS S1 field was observed by GALEX in both its Wide Spectroscopic and Deep Imaging Survey modes. This field was previously observed by the Infrared Space Observatory and we made use of the catalogue of multi-wavelength data published by the ELAIS consortium to select galaxies common to the two samples. Among the 959 objects with GALEX spectroscopy, 88 are present in the ELAIS catalog and 19 are galaxies with an optical spectroscopic redshift. The distribution of redshifts covers the range $0<z<1.6$. The selected galaxies have bolometric IR luminosities $10<Log(L_{IR})<13$ (deduced from the $15 \mu m$ flux using ISOCAM) which means that we cover a wide range of galaxies from normal to Ultra Luminous IR Galaxies. The mean ($\sigma$) UV luminosity (not corrected for extinction) amounts to $Log(\lambda.L_{1530}) = 9.8 (0.6)$ L_\sun for the low-z ($z \le 0.35$) sample. The UV slope $\beta$ (assuming $f_\lambda \propto \lambda^\beta$) correlates with the GALEX FUV-NUV color if the sample is restricted to galaxies below $z < 0.1$. Taking advantage of the UV and IR data, we estimate the dust attenuation from the IR/UV ratio and compare it to the UV slope $\beta$. We find that it is not possible to uniquely estimate the dust attenuation from $\beta$ for our sample of galaxies. These galaxies are highly extinguished with a median value $A_{FUV} = 2.7 \pm 0.8$. Once the dust correction applied, the UV- and IR-based SFRs correlate. For the closest galaxy with the best quality spectrum, we see a feature consistent with being produced by a bump near 220nm in the attenuation curve.Comment: This paper has been published as part of the GALEX ApJL Special Issue (ApJ 619, L63

First Observation of the Rare Decay Mode K-long -> e+ e-

In an experiment designed to search for and study very rare two-body decay modes of the K-long, we have observed four examples of the decay K-long -> e+ e-, where the expected background is 0.17+-0.10 events. This observation translates into a branching fraction of 8.7^{+5.7}_{-4.1} X 10^{-12}, consistent with recent theoretical predictions. This result represents by far the smallest branching fraction yet measured in particle physics.Comment: 9 pages, 3 figure

Distribution and Kinematics of O VI in the Galactic Halo

FUSE spectra of 100 extragalactic objects are analyzed to obtain measures of O VI absorption along paths through the Milky Way thick disk/halo. Strong O VI absorption over the approximate velocity range from -100 to 100 km/s reveals a widespread but highly irregular distribution of thick disk O VI, implying the existence of substantial amounts of hot gas with T ~ 3x10^5 K in the Milky Way halo. Large irregularities in the distribution of the absorbing gas are found to be similar over angular scales extending from less than one to 180 degrees, indicating a considerable amount of small and large scale structure in the gas. The overall distribution of Galactic O VI is not well described by a symmetrical plane-parallel layer of patchy O VI absorption. The simplest departure from such a model that provides a reasonable fit to the observations is a plane-parallel patchy absorbing layer with a scale height of 2.3 kpc, and a 0.25 dex excess of O VI in the northern Galactic polar region. The O VI absorption has a Doppler parameter b = 30 to 99 km/s, with an average value of 60 km/s . Thermal broadening alone cannot explain the large observed profile widths. The average O VI absorption velocities toward high latitude objects range from -46 to 82 km/s, with a sample average of 0 km/s and a standard deviation of 21 km/s. O VI associated with the thick disk moves both toward and away from the plane with roughly equal frequency. A combination of models involving the radiative cooling of hot fountain gas, the cooling of supernova bubbles in the halo, and the turbulent mixing of warm and hot halo gases is required to explain the presence of O VI and other highly ionized atoms found in the halo. (abbreviated)Comment: 70 pages, single-spaced, PDF format. Bound copies of this manuscript and two accompanying articles are available upon request. Submitted to ApJ