Different types of X-ray bursts from GRS 1915+105 and their origin

We report the X-ray observations of the Galactic X-ray transient source GRS 1915+105 with the PPCs of the Indian X-ray Astronomy Experiment(IXAE) onboard the Indian satellite IRS-P3 during 1997 June - August, which have revealed the presence of four types of intense X-ray bursts. All the observed bursts have a slow exponential rise, a sharp linear decay, and they can broadly be put in two classes: irregular and quasi-regular bursts in one class, and regular bursts in another class. The regular bursts are found to have two distinct time scales and they persist over extended durations. There is a strong correlation between the preceding quiescent time and the burst duration for the quasi-regular and irregular bursts. No such correlation is found for the regular bursts. The ratio of average flux during the burst time to the average flux during the quiescent phase is high and variable for the quasi- regular and irregular bursts while it is low and constant for the regular bursts. We suggest that the peculiar bursts that we have seen are charact- eristic of the change of state of the source. The source can switch back and forth between the low-hard state and the high-soft state near critical accretion rates in a very short time scale. A test of the model is presented using the publicly available 13-60 keV RXTE/PCA data for irregular and regular bursts concurrent with our observations.Comment: 13 pages, 12 figures, Accepted in APJ, emulateapj style use

Interaction Correction of Conductivity Near a Ferromagnetic Quantum Critical Point

We calculate the temperature dependence of conductivity due to interaction correction for a disordered itinerant electron system close to a ferromagnetic quantum critical point which occurs due to a spin density wave instability. In the quantum critical regime, the crossover between diffusive and ballistic transport occurs at a temperature $T^{\ast}=1/[\tau \gamma (E_{F}\tau)^{2}]$, where $\gamma$ is the parameter associated with the Landau damping of the spin fluctuations, $\tau$ is the impurity scattering time, and $E_{F}$ is the Fermi energy. For a generic choice of parameters, $T^{\ast}$ is few orders of magnitude smaller than the usual crossover scale $1/\tau$. In the ballistic quantum critical regime, the conductivity has a $T^{(d-1)/3}$ temperature dependence, where $d$ is the dimensionality of the system. In the diffusive quantum critical regime we get $T^{1/4}$ dependence in three dimensions, and $\ln^2 T$ dependence in two dimensions. Away from the quantum critical regime we recover the standard results for a good metal.Comment: 15 pages, 8 figure

Transverse "resistance overshoot" in a Si/SiGe two-dimensional electron gas in the quantum Hall effect regime

We investigate the peculiarities of the "overshoot" phenomena in the transverse Hall resistance R_{xy} in Si/SiGe. Near the low magnetic field end of the quantum Hall effect plateaus, when the filling factor \nu approaches an integer i, R_{xy} overshoots the normal plateau value h/ie^2. However, if magnetic field B increases further, R_{xy} decreases to its normal value. It is shown that in the investigated sample n-Si/Si_{0.7}Ge_{0.3}, overshoots exist for almost all \nu. Existence of overshoot in R_{xy} observed in different materials and for different \nu, where splitting of the adjacent Landau bands has different character, hints at the common origin of this effect. Comparison of the experimental curves R_{xy}(\nu) for \nu = 3 and \nu = 5 with and without overshoot showed that this effect exist in the whole interval between plateaus, not only in the region where R_{xy} exceeds the normal plateau value.Comment: 3 pages, 5 EPS figure

Penrose Diagram for a Transient Black Hole

A Penrose diagram is constructed for a spatially coherent black hole that smoothly begins an accretion, then excretes symmetrically as measured by a distant observer, with the initial and final states described by a metric of Minkowski form. Coordinate curves on the diagram are computationally derived. Causal relationships between space-time regions are briefly discussed. The life cycle of the black hole demonstrably leaves asymptotic observers in an unaltered Minkowski space-time of uniform conformal scale.Comment: 14 pages, 9 figures, spelling correction

Alternating magnetic anisotropy of Li2_2(Li1−xTx_{1-x}T_x)N with TT = Mn, Fe, Co, and Ni

Substantial amounts of the transition metals Mn, Fe, Co, and Ni can be substituted for Li in single crystalline Li$_2$(Li$_{1-x}T_x$)N. Isothermal and temperature-dependent magnetization measurements reveal local magnetic moments with magnitudes significantly exceeding the spin-only value. The additional contributions stem from unquenched orbital moments that lead to rare-earth-like behavior of the magnetic properties. Accordingly, extremely large magnetic anisotropies have been found. Most notably, the magnetic anisotropy alternates as easy-plane $\rightarrow$ easy-axis $\rightarrow$ easy-plane $\rightarrow$ easy-axis when progressing from $T$ = Mn $\rightarrow$ Fe $\rightarrow$ Co $\rightarrow$ Ni. This behavior can be understood based on a perturbation approach in an analytical, single-ion model. The calculated magnetic anisotropies show a surprisingly good agreement with the experiment and capture the basic features observed for the different transition metals.Comment: 5 pages, 3 figures, published as PRB Rapid Communication, Fig. 3 update

Efficient optical quantum state engineering

We discuss a novel method of efficiently producing multi-photon states using repeated spontaneous parametric downconversion. Specifically, by attempting downconversion several times, we can pseudo-deterministically add photons to a mode, producing various several-photon states. We discuss both expected performance and experimental limitations.Comment: 4 pages, 4 figure

Cold Quark Matter

We perform an O(alpha_s^2) perturbative calculation of the equation of state of cold but dense QCD matter with two massless and one massive quark flavor, finding that perturbation theory converges reasonably well for quark chemical potentials above 1 GeV. Using a running coupling constant and strange quark mass, and allowing for further non-perturbative effects, our results point to a narrow range where absolutely stable strange quark matter may exist. Absent stable strange quark matter, our findings suggest that quark matter in compact star cores becomes confined to hadrons only slightly above the density of atomic nuclei. Finally, we show that equations of state including quark matter lead to hybrid star masses up to M~2M_solar, in agreement with current observations. For strange stars, we find maximal masses of M~2.75M_solar and conclude that confirmed observations of compact stars with M>2M_solar would strongly favor the existence of stable strange quark matter.Comment: 51 pages, 11 figures, v2: minor modifications and additional reference

Probability for Primordial Black Holes in Higher Derivative Theories

The probability for quantum creation of an inflationary universe with a pair of black holes in higher derivative theories has been studied. Considering a gravitational action which includes quadratic ($\alpha R^{2}$) and/or cubic term ($\beta R^{3}$) in scalar curvature in addition to a cosmological constant ($\Lambda$) in semiclassical approximation with Hartle-Hawking boundary condition, the probability has been evaluated. The action of the instanton responsible for creating such a universe, with spatial section with $S^{1}XS^{2}$ topology, is found to be less than that with a spatial $S^{3}$ topology, unless $\alpha < - \frac{1}{8 \Lambda}$ in $R^{2}$-theory. In the $R^{3}$ theory, however, there exists a set of solutions without a cosmological constant when $\beta R^{2} = 1$ and $\alpha = - 3 \sqrt{\beta}$ which admit primordial black holes (PBH) pair in an inflationary universe scenario. We note further that when $\beta R^{2} \neq 1$, one gets PBH pairs in the two cases : (i) with $\alpha$ and $\Lambda$ both positive and (ii) with $\Lambda$ positive and $\alpha$ negative satisfying a constraint $6 | \alpha | \Lambda > 1$. However, the relative probability for creation of an inflationary universe with a pair of black holes in the $R^{3}$-theory suppresses when $\alpha > - 2 \sqrt{\beta}$ or $|\alpha| < 2 \sqrt{\beta}$. However, if the above constraints are relaxed one derives interesting results leading to a universe with PBH in $R^{3}$-theory without cosmological constant. PACS No(s). : 04.20.Jb, 04.60.+n, 98.80.HwComment: 15 pages, No figures. accepted in Int. J. Mod. Phys. D (2001

Manual for starch gel electrophoresis: A method for the detection of genetic variation

The procedure to conduct horizontal starch gel electrophoresis on enzymes is described in detail. Areas covered are (I) collection and storage of specimens, (2) preparation of tissues, (3) preparation of a starch gel, (4) application of enzyme extracts to a gel, (5) setting up a gel for electrophoresis, (6) slicing a gel, and (7) staining a gel. Recipes are also included for 47 enzyme stains and 3 selected gel buffers. (PDF file contains 26 pages.