Three-body non-additive forces between spin-polarized alkali atoms

Three-body non-additive forces in systems of three spin-polarized alkali atoms (Li, Na, K, Rb and Cs) are investigated using high-level ab initio calculations. The non-additive forces are found to be large, especially near the equilateral equilibrium geometries. For Li, they increase the three-atom potential well depth by a factor of 4 and reduce the equilibrium interatomic distance by 0.9 A. The non-additive forces originate principally from chemical bonding arising from sp mixing effects.Comment: 4 pages, 3 figures (in 5 files

The First VERITAS Telescope

The first atmospheric Cherenkov telescope of VERITAS (the Very Energetic Radiation Imaging Telescope Array System) has been in operation since February 2005. We present here a technical description of the instrument and a summary of its performance. The calibration methods are described, along with the results of Monte Carlo simulations of the telescope and comparisons between real and simulated data. The analysis of TeV $\gamma$-ray observations of the Crab Nebula, including the reconstructed energy spectrum, is shown to give results consistent with earlier measurements. The telescope is operating as expected and has met or exceeded all design specifications.Comment: Accepted by Astroparticle Physic

On Solving the Coronal Heating Problem

This article assesses the current state of understanding of coronal heating, outlines the key elements of a comprehensive strategy for solving the problem, and warns of obstacles that must be overcome along the way.Comment: Accepted by Solar Physics; Published by Solar Physic

Milagro limits and HAWC sensitivity for the rate-density of evaporating Primordial Black Holes

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BIOMEDICAL AND ENVIRONMENTAL APPLICATIONS OF SECONDARY ION EMISSION MICROANALYSIS

Le SIMS est appliqué à la caractérisation de contaminations dues au milieu ambiant et à l'étude cytopathologique de particules respirables dans les macrophages alvéolaires. La quantification des données SIMS provenant d'échantillons biologiques est en partie limitée par des irrégularités de surface dues au rétrécissement différentiel de l'échantillon pendant sa deshydratation et par une vaporisation hétérogène ou différentielle des divers constituants tissulaires. Dans les études préliminaires on a comparé les effets morphologiques du décapage par plasma ou par bombardement ionique sur différentes préparations.The application of SIMS to the characterization of environmental contaminants is described, including the study of the cytopathology of respirable particles in alveolar macrophages. Quantification of SIMS data of biological specimens is limited in part by surface topography introduced by differential shrinkage during specimen dehydration and by non-uniform or differentials puttering of various tissue components. Preliminary studies are discussed comparing the morphologic effects of radiofrequency plasma etching vs. ion beam sputtering on various tissue preparations

Effects of polypeptide conformation and surface bonding on static secondary ion mass spectra

Abstract For the first time, the α‐helical homopolypeptide poly(γ‐benzyl‐L‐glutamate) (PBLG) was synthesized by solid‐phase methods. A 10 residue PBLG sample (10‐mer) was prepared which exhibited a β‐sheet configuration, and a 15 repeat unit PBLG sample (15‐mer) was made which displayed partial α‐helical character. Solvent‐cast thin films of these peptides were deposited on both gold and silver and analyzed by time‐of‐flight static secondary ion mass spectrometry (ToF‐SSIMS). The PBLG 10‐mer spectra consisted of a strong molecular ion (cationized with Na or Ag) and less‐pronounced fragments spaced by the benzyl glutamate mass ( n ‐mers) attributed to SSIMS fragmentation. Contrary to this, the PBLG 15‐mer did not provide an intact molecular ion, and only low‐mass n ‐mer species were observed. These n ‐mers are believed to be a product of SSIMS‐induced molecular fragmentation that is enhanced by the peptide α‐helical conformation. A disulfide moiety (SS) was also coupled to the 10‐mer and 15‐mer N‐termini (10‐merSS and 15‐merSS) to provide a functional group for self‐assembly on gold. Molecular ions were observed from solvent‐cast films of these samples, verifying the presence of the SS cap. However, self‐assembled monolayers of these peptides on gold generated weak SSIMS signals which primarily reflect the strong binding of the SS group to the substrate