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191.
192.
Mohammad Shaharuzzaman James ChickosCheok N. Tam Timothy A. Keiderling 《Tetrahedron: Asymmetry》1995,6(12):2929-2932
The synthesis of (2R,3R) and (2S,3S) dideuteriosuccinic acid in 63 ± 10% enantiomeric excess by reduction of the half acid ester of ethyl fumarate from (R) and (S) BINAP ruthenium (II) diacetate complex, respectively, is reported. (2R,3R) and (2S,3S)-Dideuteriosuccinic acid has also been prepared from (R)-BINAP ruthenium (II) dicarboxylate complex directly in similar optical purity by reversing the sequence of introduction of the isotopic label. 相似文献
193.
This paper proves that circular vortex patches in the plane are stable for the nonlinear dynamical system generated by the Euler equations of incompressible fluids. This is achieved by establishing a relative variational principle in terms of either energy or angular momentum. Thus, we exploit and extend Arnold's idea in (1965, 1969) to a nonsmooth setting as well.Research partially supported by DOE contract DE-AT03-82ER12097 to the University of California, Berkeley 相似文献
194.
David G. Whitten Mohammad S. Farahat Elizabeth R. Gaillard 《Photochemistry and photobiology》1997,65(1):23-32
Abstract— Characterization of short-lived intermediates in homogeneous and microheterogeneous systems has been carried out using time-resolved spectroscopic techniques. The data obtained from these techniques have been analyzed in a relatively unconventional manner to elucidate complex transient behavior for two reactive systems. The highly nonexponential fluorescence decay for a series of fraws-stilbene-derivatized amphiphiles that readily form bilayer systems in aqueous media has been analyzed using a distribution of lifetimes analysis (DLA). The utility of DLA for quantitative studies was first determined by simulation of artificial decay data. Despite some limitations in DLA, qualitative conclusions as to the nature of the fluorescing species may be drawn when supplementary information such as steady-state spectroscopic data are also considered. The results indicate that the observed fluorescence originates from different types of excited-state species that consist of two or more trans-stilbene units; one of the emissions is attributed to the excited state of a ground-state aggregate while the other is assigned to an excimer that may arise from a 'defect'in the bilayer. The nonexponential nature of the decays is attributed to distributions of environments experienced by the fluorescing species. Electron transfer (ET) reactions between several excited pinacols and carbon tetrachloride in solution have been found to yield products with quantum yields that are higher than unity in the presence of oxygen, suggesting a chain mechanism for product formation. In these systems both the donor and the acceptor undergo bond fragmentation following the initial ET step. The individual steps involved in the proposed mechanism for these systems have been investigated in part using different steady-state and time-resolved laser spectroscopic techniques. However, it was also necessary to utilize pulse radiolysis in order to confirm the involvement of certain radical intermediates that were not observable by the usual flash photolysis techniques. 相似文献
195.
A. J. Abu El-Haija K. A. Al-Saleh N. A. Halim J. M. Khalifeh N. S. Saleh 《Journal of Radioanalytical and Nuclear Chemistry》1988,120(2):387-392
The ion-beam mixing of Sn thin film evaporated on silicon has been investigated by continuously measuring the electrical resistivity of the sample during irradiation by Kr ions. The resistivity results exhibit a tendency toward a saturation process and allow the determination of the critical dose corresponding to the total mixing condition. The variation of the volume fraction of intermixed atoms as a function of the ion dose has been deduced and compared with a semiempirical formula to explain the observed mixing kinetics. A linear dependence of the volume fraction of the intermixed atoms on the fluence is observed, which is a signature of recoil type mixing. 相似文献
196.
Mohammad Malakootian Hakimeh Mahdizadeh Abbas Dehdarirad 《Journal of Dispersion Science and Technology》2019,40(6):846-854
Ciprofloxacin is used in the treatment of bacterial infections. Because ciprofloxacin is not effectively degraded by biological processes, advanced oxidation processes such as photocatalytic ozonation are applied to remove this antibiotic from wastewater. The aim of this study was to investigate photocatalytic ozonation for the removal of ciprofloxacin from aquatic environments and optimization of the effective parameters of the process. For this purpose, ZnO nanoparticles were synthesized using the thermal method and immobilized on the surface of stones. The structural properties of the nanoparticles were determined by XRD, TEM, Photoluminescence (PL) and SEM. Experiments were carried out in a Plexiglas reactor supported with the continuous injection of ozone. The effective parameters for removal efficiency were reaction time, initial concentration of ciprofloxacin, pH, photocatalyst concentration and reaction kinetics. The highest ciprofloxacin removal efficiency occurred at the following optimal conditions: pH of 7, reaction time of 30?min, photocatalyst concentration of 3?g/L and initial ciprofloxacin concentration of 10?mg/L. Removal efficiency of 96% was obtained under these conditions. Linear kinetic models showed that the process followed pseudo-first order and Langmuir-Hinshelwood kinetics. This process had a high removal efficiency and suitable for removal of ciprofloxacin from aquatic environments.GRAPHICAL ABSTRACT 相似文献
197.
单胺类神经递质,多巴胺(DA)、去甲肾上腺素(NA)和肾上腺素(A)是哺乳动物和人类中枢重要的信息传递物质。了解脑组织中各部位单胺类神经递质的含量对于研究其生理功能、有关疾病的诊断和药物及手术疗效的评价均有重要的意义。 相似文献
198.
199.
氧化物、盐类在氧化物载体表面的自发分散是一种广泛存在的现象,文献中已报导过大量氧化物和盐类在高比表面载体上分散的研究结果['-3]TIO。作为一种较新型的载体,与Y-AI。O。、硅胶等传统载体相比,有许多不同特性.活性组分在TIO。表面的分散状态及所得催化剂的性能已有不少报导['-'],但所用的TIOZ主要是较高比表面的锐钛矿型TIOZ(刘金红石型TIO。(r)和锐钛矿型TIOZ(a)的结构不同,它是高温生成相,比表面较小['].氧化物在金红石上的分散行为仍未见报导.我们制备了三种具有不同比表面的TIO水),系统地研… 相似文献
200.