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181.
McFarland KS Naples D Arroyo CG Auchincloss P de Barbaro P Bazarko AO Bernstein RH Bodek A Bolton T Budd H Conrad J Drucker RB Harris DA Johnson RA Kim JH King BJ Kinnel T Koizumi G Koutsoliotas S Lamm MJ Lefmann WC Marsh W McNulty C Mishra SR Nienaber P Nussbaum M Oreglia MJ Perera L Quintas PZ Romosan A Sakumoto WK Schumm BA Sciulli FJ Seligman WG Shaevitz MH Smith WH Spentzouris P Steiner R Stern EG Vakili M Yang UK 《Physical review letters》1995,75(22):3993-3996
182.
Wilson William L. Curtis K. Tackitt M. Hill A. Hale A. Schilling M. Boyd C. Campbell S. Dhar L. Harris A. 《Optical and Quantum Electronics》2000,32(3):393-404
The long held promise of using volume holography to deliver high performance optical storage is reviewed. The problems, which limited the development for many years, are accessed. Finally, we describe a series of innovations, which may make the technology viable at last. 相似文献
183.
Chung MK Orlova G Goddard JD Schlaf M Harris R Beveridge TJ White G Hallett FR 《Journal of the American Chemical Society》2002,124(35):10508-10518
Palladium(0)-catalyzed silane alcoholysis was applied to sugars for the first time using tert-butyldimethylsilane (TBDMS-H) and Ph(3)SiH as the silanes. The catalyst is a colloidal solution of Pd(0) generated in situ from PdX(2) (X = Cl(-), OAc(-)) and TBDMS-H in N,N-dimethylacetamide. The colloid has been characterized by dynamic light scattering and transmission electron microscopy and consists of catalytically highly active nanoparticles of approximately 2 nm diameter. The silane alcoholysis reaction is an effective method for the regioselective silylation of methyl and phenyl glycosides and generates hydrogen gas as the only side product. For many of the sugar substrates investigated, the distribution of regioisomers obtained is complementary to that of the traditional R(3)SiCl/base (base = pyridine, imidazole) methodology and gives convenient access to the 3,6- rather than the 2,6-silylated pyranosides, obtained as the main product by the silyl chloride method. The method also allows a selective axial silylation of levoglucosan and 1,3,5-O-methylidene-myo-inositol. In an attempt to rationalize the observed regioselectivities, ab initio predictions (HF/3-21G) have been made on the relative energies of some of the silylated products. They suggest that the observed regioselectivities do not reflect a kinetic vs thermodynamic product distribution but are induced by the silylation agent employed. Models for the possible origin of the observed regioselectivity in both silylation methods (silane- and silyl chloride-based) are discussed. 相似文献
184.
Several representative examples are given of the successful application of negative staining across the holes of holey carbon support films using 5% (w/v) ammonium molybdate solution containing trehalose. The inclusion of 0.1% (w/v) trehalose is considered to be most satisfactory, although good data have also been obtained in the presence of 0.01 and 1.0% (w/v) trehalose. The examples given fall into the following groups: protein molecules in the absence of polyethylene glycol (PEG), protein molecules in the presence of PEG (Mr 1000), lipoproteins, lipids and membranes, filaments and tubules, viruses in the absence of PEG, viruses in the presence of PEG, aqueous polymer solutions, and finally for comparison purposes, four unstained samples studied in the presence of trehalose alone. In all these cases, and many others not documented here, successful spreading of the sample across holes has been achieved, with the sample embedded within a thin film of air-dried ammonium molybdate+trehalose. These specimens can be rapidly produced and provide an alternative to negatively stained specimens on carbon support films. Specimen stability in the electron bean is good and such specimens can usually generate superior negatively stained TEM images without flattening and adsorption artefacts. The formation of 2-D arrays/crystals of protein molecules and viruses, suspended across holes in the presence of ammonium molbybdate+trehalose, and trehalose alone, is also demonstrated. 相似文献
185.
A flow system has been developed to study relative rate coefficients of hydroxyl radicals reacting with alkanes under conditions relating to tropospheric chemistry. Relative Arrhenius parameters have been measured over the temperature range 243–328 K for pairs of alkanes from a list consisting of n-butane, 2-methylpropane, n-pentane, n-hexane, 2,2- and 2,3-dimethylbutane, 2,3,3-trimethylbutane, and 2,3,4-trimethylpentane. The results have been incorporated into a Structure-Activity Relation for hydroxylalkane reactions which leads to the following group rate coefficients for a temperature range of 240–500 K. 相似文献
186.
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188.
We describe the operating characteristics of a compact, frequency tunable, electron-beam-controlled, 15 atmosphere CO2 laser. Two intracavity Fabry-Perot etalons have been used to obtain laser line narrowing and continuous tuning within the 10.4 μm and 9.4μm bands of the CO2 gain spectrum. The laser output consists of a 100 nsec pulse (fwhm) with energy up to 100 mJ. The overall laser tuning range is 70 cm-1 and we have measured a laser linewidth of 0.03 cm-1. 相似文献
189.
The effects of librational anharmonicity in solid α-N2 are studied. Anharmonic frequencies are obtained using a boson representation for torsional motion. Two-libron and (one stretch + one libron) processes observed via Raman spectroscopy are discussed. Cubic libron-phonon interactions are shown to account for anomalies in the widths of the optical phonons as observed in infrared absorption. 相似文献
190.