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991.
High-performance capillary electrophoresis with electrochemical detection was employed to analyse active ingredients of Rhododendron dauricum L., an important crude herb frequently used in Chinese medicines. Farrerol, quercetin, syringic acid, vanillic acid, 4-hydroxybenzoic acid, protocatechuic acid are major important active ingredients. Operated in a wall-jet configuration, a 300-microm diameter carbon-disk electrode was used as the working electrode, which exhibits a good response at +950 mV (vs. saturated calomel electrodes) for six analytes. Under the optimum conditions, the analytes were baseline separated within 16 min in a borax buffer (pH 8.7). Notably, excellent linearity was obtained over two orders of magnitude with detection limits (S/N=3) ranged from 9 x 10(-7) to 3.0 x 10(-6) M for all analytes. This method was successfully used in the analysis of Rhododendron dauricum L. with relatively simple extraction procedures, and the assay results were satisfactory. 相似文献
992.
We report the generation and coherent detection of freely propagating ultrashort baseband electromagnetic pulses. Using optical rectification in ?110? GaAs for wideband emission and electro-optic sampling in a poled polymer for wideband detection, we demonstrate spectral sensitivity that extends from the far infrared (lambda~100 mum) to ~33 THz(lambda = 9 mum) . Over a band of nearly 20 THz, a relatively flat frequency response is observed. We discuss issues that limit the response bandwidth. 相似文献
993.
We have studied the enhancement of spontaneous emission rates for InAs quantum dots embedded in GaAs microdisks in a time-resolved photoluminescence experiment. Inhomogeneous broadening of the quantum dot energy levels and random spatial distribution of the quantum dots in a microdisk lead to a broad distribution of the spontaneous emission rates. Using a nonnegative least-norm algorithm, we extract the distribution of spontaneous emission rates from the temporal decay of emission intensity. The maximum spontaneous emission enhancement factor exceeds 10. 相似文献
994.
995.
制备了Sm2-xCexCuO4的多晶样品.X-射线粉末衍射结果表明,该系列样品为K2NiF4214结构,当0.090.17时,为T'相.电阻率测量在0.15,0.17,0.19样品上观测到超导转变.最高Tc对应于x=0.17为13.6K,均远低于(Pr0.8La1.2)1.85Ce1.2CuO4 的超导转变温度(30K).这是由于该系列样品在远高于超导转变温度时就存在更强的载流子局域化效应.磁化率测量结果表明x=0.17的样品为体超导.该体系样品的Tc低、抗磁信号小与载流子的强局域化效应有关.热电势测量结果表明,在最佳超导组份附近斜率改变符号,欠掺杂区域载流子为电子型,过掺杂区域载流子为空穴型. 相似文献
996.
997.
998.
Cao An Wang 《BIT Numerical Mathematics》1991,31(2):230-236
An algorithm for finding a polygon with minimum number of edges nested in two simplen-sided polygons is presented. The algorithm solves the problem in at mostO(n logn) time, and improves the time complexity of two previousO(n
2) algorithms.The work was supported by NSERC grant OPG0041629. 相似文献
999.
A scheme is developed for analysing the interaction between a foundation and a nonlinear rock and soil medium, in which the
foundation is considered as a linear elastic body and a typical boundary integral equation method (BIEM) is employed. On the
basis of taking the nonlinear properties of the medium into account, a perturbation BIEM is developed. The fundamental equations
for the nonlinear coupling analysis are formulated, and typical problems are solved and discussed by the present method. 相似文献
1000.
The copolymer system HBA (4-hydroxybenzoic acid) and HNA (2,6-hydroxyhaphthoic acid) has been studied mainly by means of differential scanning calorimetry. Heat capacities for the two homopolymers and three copolymers are reported from 175 to 650 K. The heat capacities are additive with composition. The whole copolymer system represents an example of a mesophase intermediate between the liquid-crystalline and the condis-crystalline state with a small amount of crystallinity. The disordering transitions (520–620 K) have a eutecticlike phase diagram. The transitions to the isotropic states occur above the decomposition temperatures (600–700 K). The glass transitions (377–434 K) show normal changes in heat capacity (31–34 J/K mol), but are broadened to as much as 200 K. 相似文献