29,524 research outputs found
Thermal Model Analysis of Particle Ratios at GSI Ni-Ni Experiments Using Exact Strangeness Conservation
The production of hadrons in Ni-Ni at the GSI is considered in a hadronic gas
model with chemical equilibrium. Special attention is given to the abundance of
strange particles which are treated using the exact conservation of
strangeness. It is found that all the data can be described using a temperature
T = 70 pm 10 MeV and a baryon chemical potential mu_B = 720 pm 20 MeV.Comment: Revtex, 7 pages, 3 figures in postscript forma
Phillips CO-oxidation catalyts for long-lived CO2 lasers: Activity and initial characterization studies
Four different catalysts have been developed specifically for use in sealed carbon dioxide lasers. The catalysts have been designed to be low dusting, stable to shock and vibration, have high activity at low temperatures and have long active lifetimes. Measured global CO oxidation rates range from 1.4 to 2.2 cc CO converted per minute per gram of catalyst at ambient temperature. The catalysts also retain substantial activity at temperatures as low as -35 C. The Phillips laser catalysts are prepared in a variety of different shapes to meet the different pressure drop and gas flow profiles present in the many different styles of lasers. Each catalyst has been tested in sealed TEA lasers and has been shown to substantially increase the sealed life of the laser. Activity measurements made on the precious metal catalysts which were prepared with and without activity promoters showed that the promoter materials increase catalyst CO oxidation activity at least an order of magnitude at ambient temperature. Initial studies using H2 and CO chemisorption, X ray diffraction (XRD) and X ray photoelectron spectroscopy (XPS) have shown that the activity promoters do not significantly affect the precious metal crystallite size or the electronic structure around the precious metal. In addition, the formation or lack of formation of solid solutions between the precious metal and promoters has also been shown not to affect the activity of the promoted catalyst
A Descriptive Study of the Population Dynamics of Adult \u3ci\u3eDiabrotica Virgifera Virgifera\u3c/i\u3e (Coleoptera: Chrysomelidae) in Artificially Infested Corn Fields
The influence of corn plant phenology on the dynamics of adult western corn rootworm, Diabrotica virgifera virgifera, populations was studied during 1988 and 1989 in com fields artificially infested with eggs. Fifty percent of adult emergence from the soil occurred by day 194 in 1988 and day 203 in 1989. In both years, adult emergence was synchronized with corn flowering, eggs were recovered in soil samples approximately four days after reproductive females were first observed in the population, and oviposition was essentially complete about 25 days after it began. The number of reproductive female beetle-days accumulating per m2 was similar in both years. Approximately two times as many eggs were laid in 1988 (1239 eggs 1m2) as in 1989 (590 eggs 1m2). The difference in egg density may have been caused by differences among years in the temporal synchrony of reproductive beetles with flowering corn. Daily survival rates of adults were high while corn was flowering; exhibited a gradual decline during grain filling; and decreased rapidly during the grain drying stage
The Lipkin Model in the su(M+1)-Algebra for Many-Fermion System and its Counterpart in the Schwinger Boson Representation
Following the Schwinger boson representation for the su(M+1)- and the
su(N,1)-algebra presented by two of the present authors (J. da P. and M. Y.)
and Kuriyama, a possible counterpart of the Lipkin model in the su(M+1)-algebra
formulated in the fermion space is presented. The free vacuum, which plays a
fundamental role in the conventional treatment of the Lipkin model, is
generalized in a quite natural way, and further, the excited state generating
operators such as the particle-hole pairs are also given in a natural scheme.
As concrete examples, the cases of the su(2)-, su(3)- and the su(4)-algebra are
discussed. Especially, the case of the su(4)-algebra is investigated in detail
in relation to the nucleon pairing correlations and the high temperature
superconductivity.Comment: 22 pages, 1 figure, using PTPTeX styl
Parasitism, Adult Emergence, Sex Ratio, and Size of \u3ci\u3eAphidius Colemani\u3c/i\u3e (Hymenoptera: Aphidiidae) on Several Aphid Species
Aphidius colemani Viereck parasitizes several economically important aphid pests of small grain crops including the greenbug, Schizaphis graminum and the Russian wheat aphid, Diuraphis noxia. The ability of A. colemani to switch from S. graminum to several species of aphids common to agricultural and associated non-agricultural ecosystems in the Great Plains, and the effects of host-change on several biological parameters that influence population growth rate were determined. Female A. colemani parasitized and developed to adulthood in nine of 14 aphid species to which they were exposed in the laboratory. All small grain feeding aphids except Sipha flava were parasitized. Two sunflower feeding species (Aphis nerii and A. helianthi) and two crucifer feeding species (Lipaphis erysimi and Brevicoryne brassicae) were parasitized, as was the cotton aphid. Aphis gossypii. The average percentage of aphids parasitized differed significantly among host aphid species. as did the percentage of parasitoids surviving from the mummy to the adult stage and the time required for immature development. The sex ratio of adults that enclosed from the various hosts did not differ significantly among species. Dry weights of adult parasitoids differed significantly among host species. Adults from S. graminum weighed most (0.054 mg) while those emerging from A. helianthi weighed least (0.020 mg). Results are discussed in terms of strategies for classical biological control of aphid pests of cereals
Rotor performance characteristics from an aeroacoustic helicopter wind-tunnel test program
An investigation of helicopter rotor noise at model scale was conducted in the Langley 4 by 7 meter tunnel. The program described was the first of a planned three-phase project whose purpose was to examine the characteristic noise mechanism involved in main rotor/tail rotor interaction noise. This first phase was conducted with a main rotor only, in order to identify the characteristic noise generated by only the main rotor. The aerodynamic operating conditions of the rotor system were defined during the test. The acoustic data were properly referenced
Nonabelian density functional theory
Given a vector space of microscopic quantum observables, density functional
theory is formulated on its dual space. A generalized Hohenberg-Kohn theorem
and the existence of the universal energy functional in the dual space are
proven. In this context ordinary density functional theory corresponds to the
space of one-body multiplication operators. When the operators close under
commutation to form a Lie algebra, the energy functional defines a Hamiltonian
dynamical system on the coadjoint orbits in the algebra's dual space. The
enhanced density functional theory provides a new method for deriving the group
theoretic Hamiltonian on the coadjoint orbits from the exact microscopic
Hamiltonian.Comment: 1 .eps figur
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