Mixing in plasma and low density jets

This study was undertaken to examine the mechanisms which produce the large entrainment measured near the exit of thermal plasma torches. A research facility was constructed to examine low density jet behavior under similar dimensionless conditions as those produced by thermal plasma spray torches; the Reynolds number based on jet diameter and average properties was 1000, and the ratio of jet to ambient density was 0.07. This very low density jet produced organized vortex structures which were partially responsible for the rapid entrainment of external air. The formation of these organized structures could be disrupted by introducing turbulence, but the rapid entrainment process was not significantly affected. The structure of the jet produced by a commercial plasma torch was examined and compared to the low density research jet. At low gas flow rates the plasma jet also displayed the formation of coherent vortex structures, the passage frequency of which compared favorably with that measured in the low density research jet. At higher gas flow rates the shear layer of the plasma jet rapidly broke down producing relatively small scale turbulence. Visualizations of the hot plasma core were compared against measurements of the torch voltage fluctuations caused by arc instabilities. At low flow rates the arc voltage fluctuations were quite low and the plume was very steady. At higher flow rates the arc voltage fluctuations increased and produced surging and whipping in the hot potential core. It is believed that this low frequency unsteadiness is partially responsible for the rapid entrainment measured in plasma torches.The authors would like to thank Dr. Ron Spores for the extensive use of his data and Mr. Stuart Malmberg for help with the plasma core visualizations. This work was supported by IBM and ONR graduate fellowships. Additional funding for the plasma jet research was provided by the National Science Foundation Grant No. ECR-87-2145 and for the low density jet research by the American Chemical Society Grant No. PFR25238-G7E.     

Erd?s-Ko-Rado theorems for simplicial complexes

A recent framework for generalizing the Erd?s-Ko-Rado theorem, due to Holroyd, Spencer, and Talbot, defines the Erd?s-Ko-Rado property for a graph in terms of the graph's independent sets. Since the family of all independent sets of a graph forms a simplicial complex, it is natural to further generalize the Erd?s-Ko-Rado property to an arbitrary simplicial complex. An advantage of working in simplicial complexes is the availability of algebraic shifting, a powerful shifting (compression) technique, which we use to verify a conjecture of Holroyd and Talbot in the case of sequentially Cohen-Macaulay near-cones.     

Numerically stable solution of coupled channel equations: The wave function

In two earlier papers a numerically stable solution of the stationary Schrödinger equation for coupled channels was presented. The Schrödinger function and its first derivative were expressed in terms of two matrices: A so-calledlocal reflection matrix (LORE) and aninverse local transmission matrix (INTRA). These matrices obey very simple boundary conditions: They approach asymptotically zero (one) on one side of the reaction path and the reflection (transmission) matrix on the other side. Hence by propagating both matrices along the reaction path one can determine directly the observable scattering matrix elements without ever having to calculate wave functions. On the other hand it is often useful to know the wave functions, for instance in order to interpret scattering data in terms of flow patterns etc. Although the relation between theINTRA-LORE and the wave function is simple, a straight forward calculation is not possible. It would involve an inversion of theINTRA which is numerically ill behaved. In this paper we describe a numerically stable method of computing the wave function and illustrate by two examples of surface reactions.Dedicated to Herbert Wagner on the occasion of his 60th birthday. One of the authors (W.B.) also recalls with great pleasure the stimulating discussions he had with his first graduate student     

MxDC and MxLIVE: software for data acquisition,information management and remote access to macromolecular crystallography beamlines

An integrated computer software system for on‐site and remote collection of macromolecular crystallography (MX) data at the Canadian Light Source (CLS) is described. The system consists of an integrated graphical user interface for data collection and beamline control [MX Data Collector (MxDC)] which provides experiment‐focused control of beamline devices, and a laboratory information management system [MX Laboratory Information Virtual Environment (MxLIVE)] for managing sample and experiment information through a web browser. The system allows remote planning and transmission of sample and experiment parameters to the beamline through MxLIVE, on‐site or remote data collection through MxDC guided by information from MxLIVE, and remote monitoring and download of experimental results through MxLIVE. The system is deployed and in use on both MX beamlines at the CLS which constitute the Canadian Macromolecular Crystallography Facility.     

Development of XUV lasers at the RAL Central Laser Facility

Recent progress in the development of XUV lasers by research teams using high-power and ultrashort-pulse Nd: glass and KrF laser facilities at the Rutherford Appleton Laboratory is reviewed. Injector-amplifier operation and prepulse enhanced output of the Ge XXIII collisional laser driven by a kilojoule glass laser, enhanced gain in CVI recombination with picosecond CPA drive pulses from a glass laser, and optical field ionization and XUV harmonic generation with a KrF CPA laser are described.     

Establishing reactor operations from uranium targets used for the production of plutonium

This paper presents results from the examination of a number of archived neutron-irradiated uranium targets used for past plutonium production testing. Three of these targets were destructively characterized using Los Alamos National Laboratory actinide analytical chemistry capabilities. A validated conduct-of-operations protocol was followed for this characterization effort. Chemical analyses included measurements for radionuclides, uranium assay, uranium isotopic abundances, trace actinides, trace metals, and non-metals. Material scientists also examined materials for morphological and microstructural properties and individual particles were examined for trace impurities. After characterization of the targets was completed, a reactor modeling effort was undertaken to corroborate target details in historical records. Time since irradiation calculations utilized both activation and fission products. The described examination of uranium targets has a tremendous impact from a safeguards verification and nuclear forensics perspective.