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941.
T S Wu M S Kao P L Wu F W Lin L S Shi M J Liou C Y Li 《Chemical & pharmaceutical bulletin》1999,47(3):375-382
Thirty-two new bakkenolides, bakkenolides-Db (1)--Dh(7), -Fa(8), -Fb(9), -I(10)--M(14), -Na(15), -Nb(16), -O(17)--T(22), -Ua (23), -Ub(24), -V(25)--X(27), -Ya(28), -Yb(29), -Za(30), -Zb(31) and -III(32), from the roots of Petasites formosanus together with thirty known compounds were isolated. The structures were characterized by spectral analysis. The locations, C-1 and/or C-9 of bakkenolide skeleton, of the substituents, such as acetoxy, isobutyroyloxy and isovaleroyloxy groups, can be determined by the chemical shifts of their signals and the H-1 and/H-9 in the 1H-NMR spectra. The cytotoxicity was also discussed. 相似文献
942.
The recently described pressure reaction in the presence of trithylamine with subsequent thermal (200°C) cyclization provided 13N‐pyridylcantharidinimides 4a‐4m from aminopyridines and cantharidin in yields of 15–83%. 2‐Amino‐3,5‐dichloropyridine failed to yield 4n . 相似文献
943.
Bin Liu Rong Zhang Zili Xie XiangQian Xiu Liang Li Jieying Kong Huiqiang Yu Pin Han Shulin Gu Yi Shi Zheng YouDou Tang ChenGuang Chen YongHai Wang ZhanGuo 《中国科学G辑(英文版)》2008,51(3):237-242
InN films grown on sapphire at different substrate temperatures from 550°C to 700°C by metalorganic chemical vapor deposition
were investigated. The low-temperature GaN nucleation layer with high-temperature annealing (1100°C) was used as a buffer
for main InN layer growth. X-ray diffraction and Raman scattering measurements reveal that the quality of InN films can be
improved by increasing the growth temperature to 600°C. Further high substrate temperatures may promote the thermal decomposition
of InN films and result in poor crystallinity and surface morphology. The photoluminescence and Hall measurements were employed
to characterize the optical and electrical properties of InN films, which also indicates strong growth temperature dependence.
The InN films grown at temperature of 600°C show not only a high mobility with low carrier concentration, but also a strong
infrared emission band located around 0.7 eV. For a 600 nm thick InN film grown at 600°C, the Hall mobility achieves up to
938 cm2/Vs with electron concentration of 3.9 × 1018 cm−3.
Supported by the National Basic Research Program of China (Grant No. 2006CB6049), the National Natural Science Foundation
of China (Grant Nos. 6039072, 60476030 and 60421003), the Great Fund of the Ministry of Education of China (Grant No. 10416),
the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20050284004), and the Natural
Science Foundation of Jiangsu Province of China (Grant Nos. BK2005210 and BK2006126) 相似文献
944.
The three-dimensional (3D) problem of the ground vibration isolation by an in-filled trench as a passive barrier is studied
theoretically. Integral equations governing Rayleigh wave scattering are derived based on the Green’s solution of Lamb problem.
The integral equations are solved accurately and efficiently with an iteration technique. They are used to evaluate the complicated
Rayleigh wave field generated by irregular scatterers embedded in an elastic half-space solid. The passive isolation effectiveness
of ground vibration by the in-filled trench for screening Rayleigh wave is further studied in detail. Effects of relevant
parameters on the effectiveness of vibration isolation are investigated and presented. The results show that a trench filled
with stiff backfill material gets a better isolation effect than a soft one, and increasing the depth or width of the in-filled
trench also improves its screening effectiveness. The effectiveness and the area of the screened zone are surging with the
increase in the length of the in-filled trench.
Supported by the National Natural Science Foundation of China (Grant Nos. 50678128 and 50538010) and the Research Fund for
PhD Student of Chinese College (Grant No. 20050247030) 相似文献
945.
L-Fuzzy拓扑空间中一种新型的强F仿紧性 总被引:8,自引:1,他引:8
本文引入一种新型的强F仿紧性─—Ⅲ型强F仿紧性,它是基于α-局部有限族概念提出的,这种α-局部有限族概念可用于刻划强F可数紧性。 相似文献
946.
In this paper, the idea of random selection in the theorem on gambling system is extended to Markov chains, by using the notion likelihood ratio and an analytic technique. A strong limit theorem on the relative frequency of ordered couple under random selection is established.AMS Subject Classification (2001)
primary 60F15 Secondary 60J10 相似文献
947.
Suppose that independent U(0, 1) weights are assigned to the ${d\choose 2}n^{2}$ edges of the complete d‐partite graph with n vertices in each of the d maximal independent sets. Then the expected weight of the minimum‐weight perfect d‐dimensional matching is at least $\frac{3}{16}n^{1-(2/d)}$. We describe a randomized algorithm that finds a perfect d‐dimensional matching whose expected weight is at most 5d3n1?(2/d)+d15 for all d≥3 and n≥1. © 2002 John Wiley & Sons, Inc. Random Struct. Alg., 20, 50–58, 2002 相似文献
948.
Yixun Shi 《Numerical Linear Algebra with Applications》2002,9(3):195-203
This paper studies the possibility of combining interior point strategy with a steepest descent method when solving convex programming problems, in such a way that the convergence property of the interior point method remains valid but many iterations do not request the solution of a system of equations. Motivated by this general idea, we propose a hybrid algorithm which combines a primal–dual potential reduction algorithm with the use of the steepest descent direction of the potential function. The complexity of the potential reduction algorithm remains valid but the overall computational cost can be reduced. Our numerical experiments are also reported. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
949.
950.
High aspect-ratio, single crystal BaWO4 nanowires with diameters as small as 3.5 nm and lengths up to more than 50 microns were synthesized in catanionic reverse micelles formed by an equimolar mixture of two surfactants: undecylic acid and decylamine. 相似文献