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排序方式: 共有521条查询结果,搜索用时 203 毫秒
81.
82.
Amino acid analysis of elastin--a rapid method 总被引:1,自引:0,他引:1
83.
H. Braun D. Evrard A. Fridman J. -P. Gerber A. Givernaud J. Grunhaus R. Kahn G. Maurer A. Michalon B. Schiby R. Strub C. Voltolini 《Zeitschrift für Physik A Hadrons and Nuclei》1971,247(2):107-116
A study of a 150000-picture exposure of ¯pd at 5.5 GeV/c yielded 152 events satisfying the hypothesis ¯pd→p s π+2π?π0. For the events with proton spectator in the momentum range 100–280 MeV/c we obtained the cross section of 0.11±0.02 mb. Assuming the validity of the impulse approximation we estimate a cross section of 0.43±0.06 mb for the reaction ¯pn→ π+2π?π0. The rate for single ? meson production and an upper limit for double ? production are given. A modified multiperipheral Regge model was used in order to describe the general features of the data. 相似文献
84.
Electronic structure calculations predict the existence of a novel type of a chemically bound noble gas compound. The predicted species is an extended linear and periodic polymer, made of the repeat unit -(XeCC)-, where CC is the acetylenic group. The polymer has a strong partly ionic nature, with positive partial charge on the xenon atoms and a negative one on the CC groups. High energy barriers are found for the removal of a Xe atom from the chain, indicating high stability. This is the first polymer with a noble-gas-containing building block. 相似文献
85.
86.
The kinetics of the interaction between molecular oxygen and the Co2+-complexes of the three terdentate ligands Z, N-(2-picolyl)-ethylenediamine (PEN), N-(2-picolyl)-oxamide (POA) and diethylenetriamine (DIEN) have been studied spectrophotometrically and using an O2 specific Clark electrode. Starting from the respective 1:1- and 1:2-complexes, the binuclear species ZCoO2(OH)CoZ and Z2CoO2CoZ2 are formed with each ligand. The existence of the former product shows that a minimum of three chelating nitrogen donors is sufficient to make a Co2+-complex reactive towards O2. As derived from the empirical rate laws the same general reaction mechanism must be valid for all three systems. In the case of PEN- and DIEN-complexes the oxygen adducts are metastable intermediates and formed in stoichiometric quantities. With POA irreversible formation of cobaltic species is rapid, and O2-adducts are present in steady state concentrations only, except in strongly basic solutions. 相似文献
87.
88.
Paul R. Gerber 《Zeitschrift für Physik B Condensed Matter》1977,28(2):103-107
The effect of an isolated impurity on local static critical properties is examined by extrapolating exact high-temperature series. In accord with results of alternative methods no change in the critical exponents is found. The amplitudes of the singularities change in general, but a special choice of the nature of the impurity may even leave the amplitudes unchanged. This provides a convenient situation for numerical tests. 相似文献
89.
Cecelia M. DuBray Cody L. Gerber Ryan D. McCulla Angie J. Oakland Keith D. Schwartz Robert Eliason Jay H. Brown 《Journal of Physical Organic Chemistry》2010,23(12):1196-1201
The ring inversion process for a series of 3,5‐dialkyl‐1‐oxa‐3,5‐diazacyclohexanes was studied using proton dynamic nuclear magnetic resonance (1H DNMR) spectroscopy in conjunction with semiempirical calculations. At low temperature, the ring methylene protons decoalesced into two AB spin systems in a 2:1 ratio. Lineshape simulations of the DNMR spectra provided first‐order rate constants for magnetic exchange. The energy barrier for each inversion reaction was calculated from the respective rate constants. In general, as the size of the N‐alkyl group increased, the barrier to ring inversion decreased. A similar trend was seen in semiempirical calculations that modeled the ring inversion process. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
90.
Ramazan KA Wingen LM Miller Y Chaban GM Gerber RB Xantheas SS Finlayson-Pitts BJ 《The journal of physical chemistry. A》2006,110(21):6886-6897
Although heterogeneous chemistry on surfaces in the troposphere is known to be important, there are currently only a few techniques available for studying the nature of surface-adsorbed species as well as their chemistry and photochemistry under atmospheric conditions of 1 atm pressure and in the presence of water vapor. We report here a new laboratory approach using a combination of long path Fourier transform infrared spectroscopy (FTIR) and attenuated total reflectance (ATR) FTIR that allows the simultaneous observation and measurement of gases and surface species. Theory is used to identify the surface-adsorbed intermediates and products, and to estimate their relative concentrations. At intermediate relative humidities typical of the tropospheric boundary layer, the nitric acid formed during NO2 heterogeneous hydrolysis is shown to exist both as nitrate ions from the dissociation of nitric acid formed on the surface and as molecular nitric acid. In both cases, the ions and HNO3 are complexed to water molecules. Upon pumping, water is selectively removed, shifting the NO(3-)-HNO3(H2O)y equilibria toward more dehydrated forms of HNO3 and ultimately to nitric acid dimers. Irradiation of the nitric acid-water film using 300-400 nm radiation generates gaseous NO, while irradiation at 254 nm generates both NO and HONO, resulting in conversion of surface-adsorbed nitrogen oxides into photochemically active NO(x). These studies suggest that the assumption that deposition or formation of nitric acid provides a permanent removal mechanism from the atmosphere may not be correct. Furthermore, a potential role of surface-adsorbed nitric acid and other species formed during the heterogeneous hydrolysis of NO2 in the oxidation of organics on surfaces, and in the generation of gas-phase HONO on local to global scales, should be considered. 相似文献