Modeling Planetary Interiors in Laser Based Experiments Using Shockless Compression

X-ray diffraction is a widely used technique for measuring the crystal structure of a compressed material. Recently, short pulse x-ray sources have been used to measure the crystal structure in-situ while a sample is being dynamically loaded. To reach the ultra high pressures that are unattainable in static experiments at temperatures lower than using shock techniques, shockless quasi-isentropic compression is required. Shockless compression has been demonstrated as a successful means of accessing high pressures. The National Ignition Facility (NIF), which will begin doing high pressure material science in 2010, it should be possible to reach over 2 TPa quasi-isentropically. This paper outlines how x-ray diffraction could be used to study the crystal structure in laser driven, shocklessly compressed targets the same way it has been used in shock compressed samples. A simulation of a shockless laser driven iron is used to generate simulated diffraction signals, and recent experimental results are presented.     

Correlation between solar microwave bursts and hard X-ray flares

We compared the microwave bursts with short timescale fine structure observed at 2.84 GHZ at Beijing Astronomical Observatory with the hard X-ry bursts (HXB) observed by the YOHKOH satellite during the period 1991 Oct–1992 Dec, and found that of the 20 microwave events, 12 had HXB counterparts. For the typical event of 1992-06-07, we analyzed the common quasi-period oscillations on the order of 10² s and calculated the parameters of the source region, together with a brief discussion.     

An interpretation of the semicircular structure of the supernova remnant CTB-109

The supernova exploded at the boundary of a dense molecular cloud in a diffuse gas. The eastern half of the shock wave entered the diffuse gas and is now in the stage of adiabatic expansion, forming the observed semicircular remnant; the western half entered the dense cloud, moved at a much slower speed and is now in the pressure-driven snowplow phase, the radiation it emits is in the uv, and is completely absorbed by the interstellar gas along the line of sight.     

A hard X-ray survey of the Sagittarius Arm tangent with the IBIS telescope of the INTEGRAL observatory: A catalog of sources

We analyze the images of the Sagittarius Arm tangent obtained with the IBIS telescope of the INTEGRAL observatory in the energy range 18–120 keV during its observations in the spring of 2003. We detected 28 sources at a statistically significant level with fluxes above 1.4 mCrab in the energy range 18–60 keV. Of these sources, 16 were previously identified as binaries of various classes in our Galaxy, 3 were identified as extragalactic objects, 2 were identified as pulsars in supernova remnants, and 7 sources were of an unknown nature. These observations revealed three new sources. A statistically significant flux in the energy range 60–120 keV was recorded from 13 sources.     

Type-I X-ray bursts from voids: tracers of weakly accreting bursters?

We obtained long-term (10–20 years) light curves for seven X-ray bursters. These sources exhibited no prolonged episodes of luminosities exceeding several percent of the Eddington luminosity over the entire observing period. For four sources, we found upper limits for the luminosity of over 5 years. These limits proved to be below 10³⁶ erg s^?1. We estimated the total number of such sources in our Galaxy.     

The Velocity Dispersion in the X-Ray Scaling Laws

We used a sample of 20 poor groups of galaxies to study the low mass tail of the relationships among the X-ray temperature T, the X-ray luminosity L_x and the optical velocity dispersion σ. We obtained redshifts for the fainter members of these groups. We find that X-ray bright groups have more members and higher velocity dispersions on average. Using the fainter group members and MonteCarlo tests, we define the number of group members required to calculate a robust velocity dispersion. There is a tendency to underestimate the group velocity dispersion for samples of fewer than∼ 10 members that introduces systematic errors in the slope of the relationships among L_x, T, and σ. A comparison with the data of Ponman and Mahdavi shows that our improved velocity dispersions provide better constraints on the relationship between the kinematics of the hot gas and galaxies in these common environments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Observations of the X-ray pulsar GX 301-2 with the ART-P telescope of the GRANAT Observatory

The variability of the X-ray flux from the pulsar GX 301-2 is analyzed by using data from the ART-P telescope of the GRANAT Observatory. The intensity variations with time scales of several thousand seconds are studied at various orbital phases. The high-state flux from the source exceeds its low-state flux by as much as a factor of 10. The hardness and spectrum of the source are shown to change greatly with its intensity. These intensity variations are most likely caused by substantial inhomogeneities in the stellar wind from the companion star.     

Period variation of X-ray pulsars and Kelvin-Helmholtz instability at the accretion disk boundary

We introduce between the magnetosphere of a neutron star and its accretion disk a sheared layer of finite thickness in which the velocity, density, pressure and magnetic field vary continuously and we discuss the Kelvin-Helmholtz instability of plane wave purturbations for the case of a compressible plasma. The results show that the K-H instability is still present and radial wave vector perturbation is the main mode of instability. We particularly considered the effect of the thickness of the sheared layer on the rotation of the neutron star, showing that by suitably adjusting the thickness we can explain the period changes in the X-ray pulsars. Application of this model to Her X-1 gave a good result.     

Accuracy of formation factors for three-dimensional pore-scale images of geo-materials estimated by renormalization technique

The formation factor, the dimensionless electric resistivity of porous rock/sediment saturated with conductive fluid, is an important quantity in geophysical exploration for petroleum reservoirs and groundwater aquifers. The renormalization technique is a promising approximation method for the quick estimation of the formation factors from large three-dimensional images of porous geo-materials obtained by X-ray microtomography. In the present study, we applied the renormalization technique to various pore-scale image sets of real geo-materials (sandstones, pumice, lava, and sandy sediments). The purpose is to explore the factors controlling the estimation accuracy of the formation factor. The results revealed that the accuracy increases with increasing (i) porosity, (ii) degree of the pore elongation along the direction of the applied electric field, and (iii) size of the initial subsystem with which the renormalization step starts and with decreasing (iv) pore or grain size. Most importantly, a high degree of elongation of the pore structure along the applied field ensures good accuracy even if the porosity is low, the initial subsystem is small, and the pore or grain size is large.     

心律不齐患者64层螺旋CT冠脉成像的临床应用

目的:与DSA结果进行对照,评价MSCTA对心律不齐患者冠脉病变的诊断价值.方法:收集2009年1月至2010年11月在煤炭总医院临床诊断和怀疑冠心病的心律不齐患者31例,在一个月内分别完成MSCT和DSA检查.以DSA为参考标准,评价MSCTA在心律不齐患者中冠脉病变的诊断价值.结果:30例图像(96.77%,30/...