161 research outputs found
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Theoretical studies of chemisorption and surface reactions on nickel and silicon
The research is part of a theoretical program on the structure of molecules adsorbed on solid surfaces and dissociative chemisorption which emphasis on transition metal substrates and electronic materials. An embedding theory for treating chemisorption on metals is further developed and applied to the reaction of hydrocarbon fragments and hydrogen coadsorbed on nickel, the dissociation of water on nickel, and the system H/Ni, NH{sub 3}/Ni, and C{sub 6}H{sub 6}/Ni. The main emphasis of the work is on the energetics of adsorption as a function of surface site, the potential energy for adsorbate motion between surface sites and the energetics of surface reactions. Equilibrium geometries, vibrational frequencies and ionization potentials are also calculated. Preliminary work on the description of Si(100) surfaces has been completed in preparation of H/Si and N/Si adsorption studies. Studies of {pi} bonding on Si(111) were also completed and work was begun on the Auger ionization of F/Si. The original form of the embedding theory has been extended to make use of an effective potential representation of the bulk electrons interacting with the embedded surface region. Effective core potentials for Fe have been developed
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Calorimeter based detectors for high energy hadron colliders
This report discusses the following topics: the central calorimeter; and installation; commissioning; and calorimeter beam tests; the central drift chamber; cosmic ray and beam tests; chamber installation and commissioning; and software development; and SSC activities: the EMPACT project
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A connectionist model of the Drosophila blastoderm
The authors present a phenomenological modeling framework for development, and apply it to the network of segmentation genes operating in the blastoderm of Drosophila. Their purpose is to provide a systematic method for discovering and expressing correlations in experimental data on gene expression and other developmental processes. The modeling framework is based on a connectionist or neural net dynamics for biochemical regulators, coupled to grammatical rules which describe certain features of the birth, growth, and death of cells, synapses and other biological entities. They present preliminary numerical results regarding regulatory interactions between the genes Kruppel and knirps that demonstrate the potential utility of the model. 14 refs., 5 figs
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