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941.
In this article active non-linear optical effects in semiconductors are reviewed. These processes arise because of the dynamics of excited populations of charge carriers temporarily created in otherwise empty states when a beam of laser radiation is incident on the material. A large number of different effects have been observed in different semiconductor materials recently and the non-linearities cover a wide range of magnitudes both in time-scale and size of non-linearity. The theory and physical concepts relevant to these processes are described and experimental observations using both high power pulsed and low power c.w. lasers are reviewed. Applications in optical bistability, phase conjugation, optical gating and optoelectronic gating are discussed. 相似文献
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947.
Harry M. Smith 《Fresenius' Journal of Analytical Chemistry》1896,35(1):563
Ohne Zusammenfassung 相似文献
948.
Philip. J. Davies Stephen F. Lincoln Christopher B. Smith Max R. Taylor Kevin P. Wainwright Kia S. Wallwork 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(1):28-30
Crystallization of [Cd(S‐thpc12)](ClO4)2·H2O {S‐thpc12 is 1,4,7,10‐tetrakis[(S)‐2‐hydroxypropyl]‐1,4,7,10‐tetraazacyclo‐dodecane} in the presence of sodium p‐nitrophenolate forms the title complex, [Cd(C20H44N4O4)](C6H4NO3)(ClO4)·H2O, in which p‐nitrophenolate and water separately hydrogen bond to a different pair of cis‐related pendant hydroxyl groups which, together with the four N atoms, are themselves bound to CdII in an approximately square antiprismatic arrangement. The diastereoselectivity of the complex‐forming process is apparent from the fact that both different disymmetric cations in the asymmetric unit have the same Δ helicity. 相似文献
949.
The synthesis of alkyl-substituted 2-pyrrolecarboxylate esters has been accomplished by the condensation reaction of a symmetrical vinamidinium salt and glycine ester derivatives. 相似文献
950.
The insect population in grain stores can be kept under control by maintaining a high concentration of CO2 gas (greater than 35%) throughout the grain bed. In this paper the initial phase of this process is considered, where the gas is introduced into the bed. The flow of CO2 through the grain bulk is modelled as fluid flow in a porous medium and the effect of advection, dispersion, sorption and curvilinear isobars and streamlines are considered. An analytic solution to this problem is developed using perturbation expansions and the analysis is restricted to the dominant term in each expansion. In curvilinear flow, a useful variable is the traverse time; the time taken for the gas to travel from the inlet duct. It is shown that lines of constant traverse time are also lines of constant CO2 concentration throughout the grain bed except in the narrow region called the front, where the concentration gradient is large. For most grain stores the isobars have a negative curvature and in these situations the front moves more slowly than in uniform flow and the width of the front increases more rapidly as it travels through the grain bed. It is shown that sorption has an effect on the CO2 concentration in the air for some grains such as canola but not for others such as wheat. 相似文献