Acceleration Rates and Injection Efficiencies in Oblique Shocks

The rate at which particles are accelerated by the first-order Fermi mechanism in shocks depends on the angle, \teq{\Tbone}, that the upstream magnetic field makes with the shock normal. The greater the obliquity the greater the rate, and in quasi-perpendicular shocks rates can be hundreds of times higher than those seen in parallel shocks. In many circumstances pertaining to evolving shocks (\eg, supernova blast waves and interplanetary traveling shocks), high acceleration rates imply high maximum particle energies and obliquity effects may have important astrophysical consequences. However, as is demonstrated here, the efficiency for injecting thermal particles into the acceleration mechanism also depends strongly on obliquity and, in general, varies inversely with \teq{\Tbone}. The degree of turbulence and the resulting cross-field diffusion strongly influences both injection efficiency and acceleration rates. The test particle \mc simulation of shock acceleration used here assumes large-angle scattering, computes particle orbits exactly in shocked, laminar, non-relativistic flows, and calculates the injection efficiency as a function of obliquity, Mach number, and degree of turbulence. We find that turbulence must be quite strong for high Mach number, highly oblique shocks to inject significant numbers of thermal particles and that only modest gains in acceleration rates can be expected for strong oblique shocks over parallel ones if the only source of seed particles is the thermal background.Comment: 24 pages including 6 encapsulated figures, as a compressed, uuencoded, Postscript file. Accepted for publication in the Astrophysical Journa

Inverse Bremsstrahlung in Shocked Astrophysical Plasmas

There has recently been interest in the role of inverse bremsstrahlung, the emission of photons by fast suprathermal ions in collisions with ambient electrons possessing relatively low velocities, in tenuous plasmas in various astrophysical contexts. This follows a long hiatus in the application of suprathermal ion bremsstrahlung to astrophysical models since the early 1970s. The potential importance of inverse bremsstrahlung relative to normal bremsstrahlung, i.e. where ions are at rest, hinges upon the underlying velocity distributions of the interacting species. In this paper, we identify the conditions under which the inverse bremsstrahlung emissivity is significant relative to that for normal bremsstrahlung in shocked astrophysical plasmas. We determine that, since both observational and theoretical evidence favors electron temperatures almost comparable to, and certainly not very deficient relative to proton temperatures in shocked plasmas, these environments generally render inverse bremsstrahlung at best a minor contributor to the overall emission. Hence inverse bremsstrahlung can be safely neglected in most models invoking shock acceleration in discrete sources such as supernova remnants. However, on scales > 100pc distant from these sources, Coulomb collisional losses can deplete the cosmic ray electrons, rendering inverse bremsstrahlung, and perhaps bremsstrahlung from knock-on electrons, possibly detectable.Comment: 13 pages, including 2 figures, using apjgalley format; to appear in the January 10, 2000 issue, of the Astrophysical Journa

Table-lookup algorithm for pattern recognition: ELLTAB (Elliptical Table)

Remotely sensed unit is assigned to category by merely looking up its channel readings in four-dimensional table. Approach makes it possible to process multispectral scanner data using a minicomputer

A Study for a Tracking Trigger at First Level for CMS at SLHC

It is expected that the LHC accelerator and experiments will undergo a luminosity upgrade which will commence after several years of running. This part of the LHC operations is referred to as Super-LHC (SLHC) and is expected to provide beams of an order of magnitude larger luminosity (1035cm-2sec-1) than the current design. Preliminary results are presented from a feasibility study for a First Level Tracking Trigger for CMS at the SLHC using the data of the inner tracking detector. As a model for these studies the current CMS pixel detector with the same pixel size and radial distances from the beam has been used. Monte Carlo studies have been performed using the full CMS simulation package (OSCAR) and the occupancy of such a detector at SLHC beam conditions has been calculated. The design of an electron trigger which uses both the calorimeter energy depositions and the pixel data to identify isolated electrons and photons has been investigated. Results on the tracker occupancy and the electron trigger performance are presentedComment: Presented at LECC, Heidelberg 200

FT-IR microanalysis of mineral separates from primitive meteorites: techniques, problems and solutions

From the Introduction: We compared several methods of infrared micro spectroscopy using an FT-IR microscope and workbench. This is part of a project to assemble a database of infrared and optical spectra from mineral separates from meteorites, for comparison with astronomical data. Since we usually have to work with small amounts of material (original grain sizes often <50 m), special sample preparation and analytical procedures have to be applied

Biodetection grinder

Work on a biodetection grinder is summarized. It includes development of the prototype grinder, second generation grinder, and the production version of the grinder. Tests showed the particle size distribution was satisfactory and biological evaluation confirmed the tests

Single stage experimental evaluation of slotted rotor and stator blading. Part I - Analysis and design

Analysis and design of slotted rotor and stator blading for application to compressors in advanced airbreathing propulsion system

Procedure for analysis of nickel-cadmium cell materials

Quality control procedures include analyses on electrolyte, active materials, and separators for nickel cadmium cell materials. Tests range from the visual/mechanical inspection of cells to gas sampling, electrolyte extract, electrochemical tests, and physical measurements