X-ray emission from PSR B1800-21, its wind nebula, and similar systems

We detected X-ray emission from PSR B1800-21 and its synchrotron nebula with the Chandra X-ray Observatory. The pulsar's observed flux is (1.4+/-0.2) 10^{-14} ergs cm^{-2} s^{-1} in the 1-6 keV band. The spectrum can be described by a two-component PL+BB model, suggesting a mixture of thermal and magnetospheric emission. For a plausible hydrogen column density n_{H}=1.4 10^{22} cm^{-2}, the PL component has a slope Gamma=1.4+/-0.6 and a luminosity L_{psr}^{nonth}=4 10^{31}(d/4 kpc)^2 ergs s^{-1}. The properties of the thermal component (kT=0.1-0.3 keV, L^{bol}=10^{31}-10^{33} ergs s^{-1}) are very poorly constrained because of the strong interstellar absorption. The compact, 7''\times4'', inner pulsar-wind nebula (PWN), elongated perpendicular to the pulsar's proper motion, is immersed in a fainter asymmetric emission. The observed flux of the PWN is (5.5+/-0.6) 10^{-14} ergs cm^{-2} s^{-1} in the 1-8 keV band. The PWN spectrum fits by a PL model with Gamma=1.6+/-0.3, L=1.6 10^{32} (d/4 kpc})^2 ergs s^{-1}. The shape of the inner PWN suggests that the pulsar moves subsonically and X-ray emission emerges from a torus associated with the termination shock in the equatorial pulsar wind. The inferred PWN-pulsar properties (e.g., the PWN X-ray efficiency, L_{pwn}/\dot{E}~10^{-4}; the luminosity ratio, L_{pwn}/L_{psr}^{nonth}=4; the pulsar wind pressure at the termination shock, p_s=10^{-9} ergs cm^{-3}) are very similar to those of other subsonically moving Vela-like objects detected with Chandra (L_{pwn}/\dot{E}=10^{-4.5}-10^{-3.5}, L_{pwn}/L_{psr}^{nonth}~5, p_s=10^{-10}-10^{-8} ergs cm^{-1}).Comment: 11 pages, 10 figures, 2 tables; submitted to ApJ. Version with the high-resolution figures is available at http://www.astro.psu.edu/users/green/B1800/B1800_ApJ.pd

Compressibility and structural stability of ultra-incompressible bimetallic interstitial carbides and nitrides

We have investigated by means of high-pressure x-ray diffraction the structural stability of Pd2Mo3N, Ni2Mo3C0.52N0.48, Co3Mo3C0.62N0.38, and Fe3Mo3C. We have found that they remain stable in their ambient-pressure cubic phase at least up to 48 GPa. All of them have a bulk modulus larger than 330 GPa, being the least compressible material Fe3Mo3C, B0 = 374(3) GPa. In addition, apparently a reduction of compressibility is detected as the carbon content increased. The equation of state for each material is determined. A comparison with other refractory materials indicates that interstitial nitrides and carbides behave as ultra-incompressible materials.Comment: 14 pages, 3 figures, 1 tabl

Illicit Methylphenidate Use in an Undergraduate Student Sample: Prevalence and Risk Factors

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90236/1/phco.23.5.609.32210.pd

Structure and Stability of Si(114)-(2x1)

We describe a recently discovered stable planar surface of silicon, Si(114). This high-index surface, oriented 19.5 degrees away from (001) toward (111), undergoes a 2x1 reconstruction. We propose a complete model for the reconstructed surface based on scanning tunneling microscopy images and first-principles total-energy calculations. The structure and stability of Si(114)-(2x1) arises from a balance between surface dangling bond reduction and surface stress relief, and provides a key to understanding the morphology of a family of surfaces oriented between (001) and (114).Comment: REVTeX, 4 pages + 3 figures. A preprint with high-resolution figures is available at http://cst-www.nrl.navy.mil/papers/si114.ps . To be published in Phys. Rev. Let

Illicit Use of Specific Prescription Stimulants Among College Students: Prevalence, Motives, and Routes of Administration

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90069/1/phco.26.10.1501.pd

A hard metallic material: Osmium Diboride

We calculate the structural and electronic properties of OsB2 using density functional theory with or without taking into account spin-orbit (SO) interaction. Our results show that the bulk modulus with and without SO interaction are 364 and 365 Gpa respectively, both are in good agreement with experiment (365-395 Gpa). The evidence of covalent bonding of Os-B, which plays an important role to form a hard material, is indicated both in charge density, atoms in molecules analysis, and density of states analysis. The good metallicity and hardness of OsB2 might suggest its potential application as hard conductors.Comment: Figures improve

Surface Quality of a Work Material Influence on Vibrations in a Cutting Process

The problem of stability in the machining processes is an important task. It is strictly connected with the final quality of a product. In this paper we consider vibrations of a tool-workpiece system in a straight turning process induced by random disturbances and their effect on a product surface. Basing on experimentally obtained system parameters we have done the simulations using one degree of freedom model. The noise has been introduced to the model by the Langevin equation. We have also analyzed the product surface shape and its dependence on the level of noise.Comment: 12 pages, PDF of figures can be obtained from http://archimedes.pol.lublin.pl/~raf/graf/fpic.pd

Separable Dual Space Gaussian Pseudo-potentials

We present pseudo-potential coefficients for the first two rows of the periodic table. The pseudo potential is of a novel analytic form, that gives optimal efficiency in numerical calculations using plane waves as basis set. At most 7 coefficients are necessary to specify its analytic form. It is separable and has optimal decay properties in both real and Fourier space. Because of this property, the application of the nonlocal part of the pseudo-potential to a wave-function can be done in an efficient way on a grid in real space. Real space integration is much faster for large systems than ordinary multiplication in Fourier space since it shows only quadratic scaling with respect to the size of the system. We systematically verify the high accuracy of these pseudo-potentials by extensive atomic and molecular test calculations.Comment: 16 pages, 4 postscript figure