排序方式: 共有14条查询结果,搜索用时 15 毫秒
1.
The chemisorption of acetylene on various faces of bcc tungsten, modelled by clusters of various sizes, has been studied by the Extended Hückel method. Relative binding energies on the various sites have been obtained, and the bonding modes of acetylene are discussed, also in comparison with experiment. It is concluded that, whenever possible, acetylene is di-jp47026502373r23/xxlarge963.gif" alt="sgr" align="BASELINE" BORDER="0"> bonded to the surface, and sp
2hybridization is considered likely in all cases.This paper is dedicated to Professor Hermann Hartmann on the occasion of his 65th birthday. 相似文献
2.
N. Kouvaris A. Provata 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(1):97-106
An ecosystem containing three interacting species is studied using both Mean Field approach and Kinetic Monte Carlo
simulations on a lattice substrate. The so called 3rd order LLV model involves birth, death and reaction
processes with 3rd order nonlinearities and feedbacks. At the mean field level this system exhibits conservative
oscillations; the analytic form of the constant of motion is presented. The stochastic simulations show that the
density oscillations disappear for sufficiently large lattices, while they are present locally, on small lattice
windows. Introduction of mixing via long range migration in the two reacting species changes this picture. For small
migration rates p, the behavior remains as with p = 0 and the system is divided into local asynchronous oscillators.
As p increases the system passes through a phase transition and exhibits a weak disorder limit cycle through a supercritical
Hopf-like bifurcation. The amplitude of the limit cycle depends on the rate p, on the range of migration
r and on the system kinetic rates k1, k2 and k3. 相似文献
3.
C. Donzé A. Chatjigakis A. W. Coleman 《Journal of inclusion phenomena and macrocyclic chemistry》1992,13(2):155-161
The solubility ofjp250r/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-CD, which is increased to 87 gL–1 in 75% water - 25% isopropanol mixtures, does not behave in a linear fashion as a function of the water/isopropanol ratio. Application of this increased solubility to the formation of inclusion complexes betweenjp250r/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-cyclodextrin and cineole : eugenol, cineole : pinene and eugenol : pinene shows strong solvent modulation of the inclusion selectivity. The proportion of guests complexed is in inverse ratio to the compatibility of the guests in the solvent mixture. 相似文献
4.
Buncha Pulpoka Zouhair Asfari Jacques Vicens 《Journal of inclusion phenomena and macrocyclic chemistry》1997,27(1):21-30
Co-receptor 1,3-calix[4]-di(aza-benzo)crown-crown-6 (1-H) designed with one calix[4]arene in a 1,3-alternate conformation and jp240m0u63jj/xxlarge8216.gif" alt="lsquo" align="BASELINE" BORDER="0">hardjp240m0u63jj/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0"> and jp240m0u63jj/xxlarge8216.gif" alt="lsquo" align="BASELINE" BORDER="0">softjp240m0u63jj/xxlarge8217.gif" alt="rsquo" align="BASELINE" BORDER="0"> metal ion binding sites has been prepared according to three pathways (A-C). Pathway B, consisting of two different 1 + 1 condensations with ditosylate derivatives, was shown to be the most efficient. 相似文献
5.
The development of new photovoltaic approach to improve costs and efficiencies is focused on the new materials and new technologies. InGaP is, in this sense, a key material for solar conversion. In particular, in the solar concentration approach, this material is part of multiple junction solar cells. Its low lattice mismatch with germanium and its adequate bandgap make it very promising. This paper shows how compositional modulation can affect the InGaP emitter and the AlGaAs tunnel junctions. The influence of the growth conditions, on the compositional modulation and misfit and threading dislocations, in In0.49Ga0.51P layers is demonstrated by TEM on purposely grown single InGaP layers. High resolution electron microscopy (HREM) intensity profiles showed no elastic lattice related modulation. 相似文献
6.
The properties of GaAs/AlGaAs solar cells irradiated with 40, 70, 100 and 170 keV protons have been studied. Current-voltage (IV) measurement showed that the worst degradation was found in the cells irradiated by 100 keV protons. The degradation was found defect dependent. Defect profile was obtained by the stopping and range of ions in matter (SRIM) simulation and deep-level transient spectroscopy (DLTS) measurement. In order to obtain the deep-level defect profile in depletion layer by DLTS measurement, the traditional calculation formula of defect concentration has been modified. DLTS measurement showed good agreement with that of the SRIM simulation. 相似文献
7.
Hiroshi Yamawaki Hiroshi Fujihisa Mami Sakashita Kazumasa Honda 《Physica B: Condensed Matter》2008,403(17):2643-2648
Proton-deuteron mutual diffusion in a CsHSO4/CsDSO4 solid at 373 K was examined up to 3 GPa by an infrared mapping measurement. Phases HPHT1 and HPHT2 appeared at 1.5 and 2.3 GPa, respectively, after heating. These phases were found to be stable at room temperature, while phase IV, which appeared on compression at room temperature, was metastable. The pressure dependence of the proton-deuteron mutual diffusion coefficient was determined from the temporal change in the deuteron distribution of the solid. The coefficient decreased from 7×10−16 to 1×10−16 m2/s during the transition from phase II to HPHT1 at 1.5 GPa, and showed no significant change during the transition to phase HPHT2. These results suggested that in addition to the hydrogen bond length, other structural factors might also have had an influence on the rate of diffusion. 相似文献
8.
The purpose of this paper is to study the biological and economic risks involved in the management of the Norwegian springjp504755r10417q5/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">spawning herring fishery. We use a discrete time and agejp504755r10417q5/xxlarge8208.gif" alt="dash" align="MIDDLE" BORDER="0">structured model based on historical data. The current paper investigates, under different levels of fishing mortalities, the risk probabilities related to the time behaviour of the spawning stock and profit. We show that the exploitation of the herring stock is vulnerable to small changes in harvesting and price level. 相似文献
9.
John D. Barrow 《General Relativity and Gravitation》2000,32(6):1111-1124
We describe how theories incorporating time-varying coupling constants can drive the Universe to a late-time near-flat attractor in which the cosmological constant is very small. We also discuss some consequences of allowing time-varying constants to vary in space as well. 相似文献
10.
V. A. Mamedov I. A. Litvinov O. N. Kataeva I. Kh. Rizvanov I. A. Nuretdinov 《Monatshefte für Chemie / Chemical Monthly》1994,125(12):1427-1435
Summary TheDarzens reaction of dichloroacetophenone (DCAP) with substituted benzaldehydes has been studied. The structure of the products was shown to depend on the phenyl group substituents. Reaction of benzaldehyde, 4-bromo-, and 2,4-dichlorobenzaldehydes results in 1-phenyl-3-aryl-3-chloropropane-1,2-diones (2a–c), reaction ofpara- ormeta-nitrobenzaldehydes yields 1-phenyl-2-chloro-3-aryl-2,3-epoxypropane-1-ones (3a, b). Upon the introduction of an alkoxy group into the phenyl ring of benzaldexyde and/or dichloroacetophenone, symmetrically substituted dioxines were obtained (6a–c). The structure of the reaction products has been established by single crystal X-ray investigations.
Darzens-Reaktion als bequemes Verfahren zur Synthese von jp6u56l7h6r5875l/xhuge945.gif" alt="agr" align="BASELINE" BORDER="0">-Chloroketonen, jp6u56l7h6r5875l/xhuge945.gif" alt="agr" align="BASELINE" BORDER="0">-Chloroepoxiden und symmetrisch substituierten Dioxinen
Zusammenfassung DieDarzens-Reaction von Dichloracetophenon (DCAP) mit substituierten Benzaldehyden wurde untersucht. Die Struktur der Produkte ist von den Substituenten an der Phenylgruppe abhängig. Die Umsetzung mit Benzaldehyd, 4-Brom- und 2,4-Dichlorbenzaldehyd liefert 1-Phenyl-3-aryl-3-chloropropan-1,2-dione (2a–c), die Reaktion vonpara- odermeta-Nitrobenzaldehyd 1-Phenyl-2-chloro-3-aryl-2,3-epoxipropan-1-one (3a,b). Durch Einführung einer Alkoxygruppe in den Phenylring des Benzaldehyds und/oder des Dichloracetophenons erhält man symmetrisch substituierte Dioxine (6a–c). Die Struktur der Reaktionsprodukte wurde mittels Röntgenstrukturanalyse bestätigt.相似文献