Evolution of AQL X-1 During the Rising Phase of its 1998 Outburst

We present results from 16 snapshots of Aql X-1 with RXTE during the rising phase of its recent outburst. The observations were carried out at a typical rate of once or twice per day. The source shows interesting spectral evolution during this period. Phenomenologically, it bears remarkable similarities to ``atoll'' sources. Shortly after the onset of the outburst, the source is seen to be in an ``island'' state, but with little X-ray variability. It then appears to have made a rapid spectral transition (on a time scale less than half a day) to another ``island'' state, where it evolves slightly and stays for 4 days. In this state, the observed X-ray flux becomes increasingly variable as the source brightens. Quasi-period oscillation (QPO) in the X-ray intensity is detected in the frequency range 670--870 Hz. The QPO frequency increases with the X-ray flux while its fractional rms decreases. The QPO becomes undetectable following a transition to a ``banana'' state, where the source continues its evolution by moving up and down the ``banana'' branch in the color-color diagram as the flux (presumably, the mass accretion rate) fluctuates around the peak of the outburst. Throughout the entire period, the power density spectrum is dominated by very-low frequency noises. Little power can be seen above ~1 Hz, which is different from typical ``atoll'' sources. In the ``banana'' state, the overall X-ray variability remains low (with fractional rms ~3--4%) but roughly constant. The observed X-ray spectrum is soft with few photons from above $\sim$25 keV, implying the thermal origin of the emission. The evolution of both spectral and temporal X-ray properties is discussed in the context of disk-instability models.Comment: 13 pages, including one table and five figures. To appear in ApJ Letters (July 20

Fluctuation-Induced First Order Transition between the Quantum Hall Liquid and Insulator

We study the phase transition between the quantum Hall liquid state and the insulating state within the framework of the Chern-Simons-Landau-Ginzburg theory of the quantum Hall effect. For the transition induced by a background periodic potential in the absence of disorder, the model is described by a relativistic scalar field coupled to the Chern-Simons gauge field. For this system, we show that the transition is of the first order, induced by the fluctuations of the gauge field, rather than second order, with statistical angle-dependent scaling exponent.Comment: 5 pages, REVTEX 3.0, two PostScript pictures appended, preprint SU-ITP-94-

Interaction of Individual Skyrmions in Nanostructured Cubic Chiral Magnet

We report the direct evidence of field-dependent character of the interaction between individual magnetic skyrmions as well as between skyrmions and edges in B20-type FeGe nanostripes observed by means of high resolution Lorentz transmission electron microscopy. It is shown that above certain critical values of external magnetic field the character of such long-range skyrmion interactions change from attraction to repulsion. Experimentally measured equilibrium inter-skyrmion and skrymion-edge distances as function of applied magnetic field shows quantitative agreement with the results of micromagnetic simulations. Important role of demagnetizing fields and internal symmetry of three-dimensional magnetic skyrmions are discussed in details.Comment: accepted in PR

Cosmological Models and Latest Observational Data

In this note, we consider the observational constraints on some cosmological models by using the 307 Union type Ia supernovae (SNIa), the 32 calibrated Gamma-Ray Bursts (GRBs) at $z>1.4$, the updated shift parameter $R$ from WMAP 5-year data (WMAP5), and the distance parameter $A$ of the measurement of the baryon acoustic oscillation (BAO) peak in the distribution of SDSS luminous red galaxies with the updated scalar spectral index $n_s$ from WMAP5. The tighter constraints obtained here update the ones obtained previously in the literature.Comment: 10 pages, 5 figures, 1 table, revtex4; v2: discussions added, accepted by Eur. Phys. J. C; v3: published versio

Evidence for Frame-Dragging Around Spinning Black Holes in X-Ray Binaries

In the context of black hole spin in X-ray binaries, we propose that certain type of quasi-period oscillations (QPOs) observed in the light curves of black hole binaries (BHBs) are produced by X-ray modulation at the precession frequency of accretion disks, due to relativistic dragging of inertial frames around spinning black holes. These QPOs tend to be relatively stable in their centroid frequencies. They have been observed in the frequency range of a few to a few hundred Hz for several black holes with dynamically determined masses. By comparing the computed disk precession frequency with that of the observed QPO, we can derive the black hole angular momentum, given its mass. When applying this model to GRO J1655-40, GRS 1915+105, Cyg X-1, and GS 1124-68, we found that the black holes in GRO J1655-40 and GRS 1915+105, the only known BHBs that occasionally produce superluminal radio jets, spin at a rate close to the maximum limit, while Cyg X-1 and GS 1124-68, typical (persistent and transient) BHBs, contain only moderately rotating ones. Extending the model to the general population of black hole candidates, the fact that only low-frequency QPOs have been detected is consistent with the presence of only slowly spinning black holes in these systems. Our results are in good agreement with those derived from spectral data, thus strongly support the classification scheme that we proposed previously for BHBs.Comment: new title, minor revisions; change title to conform to ApJL rules; replaced with the updated version to avoid confusio

Hydraulic transient modeling and analysis of the district heating network

The hydraulic transients are obvious during the operation and adjustment of large-scale district heating (DH) network. Hydraulic transient modeling and simulation methods can provide basis for efficient operation of the DH network. In this paper, two hydraulic transient models, the distributed parameter model (DPM) and lumped parameter model (LPM), were established for DH network. Efficient numerical algorithms were presented for the two models. The proposed DPM and LPM were both applied to a DH network to simulate and analyze the network hydraulic transients caused by the valve and pump operations. Results indicate that with the increase of the distance from the adjustment location, the transient time for the flow rate and pressure gets longer. As the adjustment duration decreases, the transient time increases. Comparison of the simulation performances between the two models indicates that the DPM can capture the high-frequency hydraulic transients subtly. With the decrease of adjustment duration, more severe high-frequency hydraulic transients will occur. However, only the average hydraulic fluctuations can be described by LPM. The computation time of LPM is shorter than DPM because of the vectorizable calculation procedure and the less data to record, since the LPM neglects the pressure waves and the fluid compressibility

A Single Scalar Field Model of Dark Energy with Equation of State Crossing -1

In this paper we study the possibility of building models of dark energy with equation of state across -1 and propose explicitly a model with a single scalar field which gives rise to an equation of state larger than -1 in the past and less than -1 at the present time, consistent with the current observations.Comment: 4 pages, 1 figure, the version accepted by JCAP, presentation improved and references adde

Cytogenetic and Embryologic Analyses of the Mechanism of Parthenogenesis Induced by 1BL/1RS Male Sterile Lines in Wheat

In this study, we employed electron microscopy to investigate the cytogenetic and embryologic mechanisms of parthenogenesis induced in the 1BL/1RS male sterile lines of wheat. Analysis of the root tips and acid polyacrylamide gel electrophoresis indicated that all of the male sterile lines and their maintainer lines were 1BL/1RS translocation lines, whereas the restorer lines were non-1BL/1RS translocation lines. Furthermore, the chromosomes of 1BL/1RS wheat lines with T. aestivum cytoplasm and Aegilops cytoplasm (include Ae. kotschyi, Ae. ventricosa, Ae. variabilis) paired abnormally at different rates during meiotic metaphase I (MMI). The translocated segment size of the 1RS chromosome and the specific nuclear–alloplasm interaction impaired the pairing of homologous chromosome in the background of the specific Aegilops cytoplasm at MMI. In addition, the frequency of abnormal chromosomal pairing was directly affected by the frequency of haploid production induced by parthenogenesis. The results of this study provide significant insights into the mechanism of parthenogenesis, which is probably due to the abnormal fertilization of synergid cells in alloplasmic 1BL/1RS wheat