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991.
The degree of circular polarization ( Weierstrass p ) of the nonlinear emission in semiconductor microcavities is controlled by changing the exciton-cavity detuning. The polariton relaxation towards K approximately 0 cavitylike states is governed by final-state stimulated scattering. The helicity of the emission is selected due to the lifting of the degeneracy of the +/-1 spin levels at K approximately 0. At short times after a pulsed excitation Weierstrass p reaches very large values, either positive or negative, as a result of stimulated scattering to the spin level of lowest energy (+1/-1 spin for positive/negative detuning). 相似文献
992.
在地平式折轴望远镜中开展自适应光学激光导星实验,研究了共孔径发射接收信标激光束偏振耦合分光效率随望远镜方位角和天顶角变化的补偿技术。提出了一种由四分之一波片和法拉第旋光器构成的相位补偿器,通过旋转四分之一波片以实时补偿由于望远镜旋转导致的光路相位延迟量的变化。数值计算表明,望远镜处于任意方位角和天顶角位置时,通过1°步长旋转四分之一波片,可使补偿后的偏振分光效率理论上达到99.90%以上。实验从原理上定性地验证了该方法的有效性。只要测量出镜面的相位延迟,便可计算得到望远镜处于不同方位角和天顶角情况下有效补偿所需的四分之一波片旋转角度,据此可建立实用的旋转波片偏振补偿装置。 相似文献
993.
The optimization of a HPLC method for caffeine, 8-chlorotheophylline and diphenhydramine separation with UV detection at 229 nm is described. The conditions studied included: stationary phase, compositions of mobile phases with pH modulators. Optimal conditions were: SymmetryShield RP8 column and acetonitrile–(0.01 M H3PO4–triethylamine, pH 2.8) (22:78, v/v). Validation was performed using standards and a pharmaceutical preparation containing the compounds described above. Results from both standards and samples show suitable validation parameters. The pharmaceutical grade substances were tested by factors that could influence the chemical stability. These reaction mixtures were analyzed to evaluate the capability of the method to separate degradation products. Degradation products did not interfere with the determination of the substances tested by the assay. 相似文献
994.
An improved design of the transport detector is described that uses a pre-oxidized titanium ribbon as the transport medium. The titanium ribbon has a high loading capacity that permits a large proportion of the total column eluent to be taken into the sensing system. The solute is sensed by pyrolysis and the subsequent detection of pyrolysis products by a miniature argon detector. The pyrolyzer and sensor system is designed to ensure that all the pyrolysis products enter the detector with minimum dilution and band dispersion. As a result, the sensitivity of the detector (or minimum detectable concentration) has been reduced by approximately two orders of magnitude compared with the original design. The sensitivity of the system described to sucrose is 8 x 10(-8) g/mL, which is similar to the sensitivity of the fixed-wavelength UV detector to benzene (approximately 5 x 10(-8) g/mL). It would appear that the new design has potentially a sensitivity at least an order of magnitude lower than that reported here. 相似文献
995.
Cordero BM Pérez Pavón JL García Pinto C Fernández Laespada ME Carabias Martínez R Rodriguez Gonzalo E 《Journal of chromatography. A》2000,902(1):195-204
An overview of the analytical applications of membrane-based systems for sample enrichment in chromatography and capillary electrophoresis is presented. A brief introduction to the different types of membranes and the main forces related to the transport through them is also given. 相似文献
996.
The application of two extreme models for diffusion in two-component systems to electrochemically determine equilibrium constants is discussed. The application of cyclic voltammetric, diferential pulse and rotating-disc electrode voltammetric data to elucidate the stoichiometry and formation constant of complex species by applying a generalization of the molar-ratio method is described. Molar-ratio experiments permit the distinction between the limiting diffusive regimes. The values of the equilibrium stability constants for complexation of phenethylamine and phenethylammonium ions by a 26-membered dioxotetraester crown of 3,5-disubstituted 1H-pyrazole as free ligand 1[L] and as dipyrazolate anion 1'[L(2-)]2Na(+), respectively, were determined. 相似文献
997.
Muñoz de la Peña A Mahedero MC Espinosa-Mansilla A Bautista Sánchez A Reta M 《Talanta》1999,48(1):15-21
The spectral characteristics of the inclusion of 1-naphthalenacetamide in beta-cyclodextrin have been studied by luminescence methods. The addition of bromoalcohols or bromoalkanes produces a decrease of the fluorescence of the inclusion complex, giving rise to a new band corresponding to phosphorescence emission. The emission intensity is much higher in the presence of bromoalkanes than in the presence of bromoalcohols. The deoxygenation of the solutions is achieved by flowing nitrogen, by the addition of sodium sulphite and by a combination of both methods, which results in the most effective approach. The phosphorescence emission is produced in the turbid suspension formed in the presence of the bromoalkane. The formation of microcrystals seems necessary to obtain phosphorescence emission from the ternary system. 相似文献
998.
We have developed an experimental method based on the visibility factor of light-scattering minima to obtain size-polydispersity information from contaminants upon a flat substrate. We verify the method by using double-interaction-model calculations and use this technique to examine experimentally the radial variation of a micrometer-sized fiber and the size polydispersity of spherical particles upon a substrate. 相似文献
999.
一类描述混沌映射的符号动力系统 总被引:11,自引:0,他引:11
本文定义了符号空间上的拟移位映射,并用该类映射描述了Cantor集及平面Cantor集上的混沌映射,本文结果可看作Smale马蹄模型的简化。 相似文献
1000.