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排序方式: 共有79条查询结果,搜索用时 125 毫秒
11.
Extremes - In the context of bivariate random variables $\left (Y^{(1)},Y^{(2)}\right )$ , the marginal expected shortfall, defined as $\mathbb {E}\left (Y^{(1)}|Y^{(2)} \ge Q_{2}(1-p)\right )$ for... 相似文献
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In view of a study of the atypical bases of the nucleic acids, the integral values appropriate for the methyl substituent have been determined in the SCF approximation previously described [1]. Both the inductive and the hyperconjugation effects have been introduced. An application to thymine is described. 相似文献
14.
Fozia A. Adem Victor Kuete Armelle T. Mbaveng Matthias Heydenreich Andreas Koch Albert Ndakala 《Natural product research》2019,33(18):2609-2617
A new isoflavone, 4′-prenyloxyvigvexin A (1) and a new pterocarpan, (6aR,11aR)-3,8-dimethoxybitucarpin B (2) were isolated from the leaves of Lonchocarpus bussei and the stem bark of Lonchocarpus eriocalyx, respectively. The extract of L. bussei also gave four known isoflavones, maximaisoflavone H, 7,2′-dimethoxy-3′,4′-methylenedioxyisoflavone, 6,7,3′-trimethoxy-4′,5′-methylenedioxyisoflavone, durmillone; a chalcone, 4-hydroxylonchocarpin; a geranylated phenylpropanol, colenemol; and two known pterocarpans, (6aR,11aR)-maackiain and (6aR,11aR)-edunol. (6aR,11aR)-Edunol was also isolated from the stem bark of L. eriocalyx. The structures of the isolated compounds were elucidated by spectroscopy. The cytotoxicity of the compounds was tested by resazurin assay using drug-sensitive and multidrug-resistant cancer cell lines. Significant antiproliferative effects with IC50 values below 10 μM were observed for the isoflavones 6,7,3′-trimethoxy-4′,5′-methylenedioxyisoflavone and durmillone against leukemia CCRF-CEM cells; for the chalcone, 4-hydroxylonchocarpin and durmillone against its resistant counterpart CEM/ADR5000 cells; as well as for durmillone against the resistant breast adenocarcinoma MDA-MB231/BCRP cells and resistant gliobastoma U87MG.ΔEGFR cells. 相似文献
15.
Romeo D. Tadjouate Nago Paul Nayim Armelle T. Mbaveng James D. Simo Mpetga Gabin T. Mbahbou Bitchagno Badawe Garandi Pierre Tane Bruno N. Lenta Norbert Sewald Mathieu Tene Victor Kuete Augustin Silvere Ngouela 《Molecules (Basel, Switzerland)》2021,26(16)
The local botanical Imperata cylindrica in Cameroon was investigated for its antibacterial potency. The methanol extract afforded a total of seven compounds, including five hitherto unreported compounds comprising three flavonoids (1–3) and two C-15 isoprenoid analogues (4 and 5) together with known derivatives (6 and 7). The novelty of the flavonoids was related to the presence of both methyl and prenyl groups. The potential origin of the methyl in the flavonoids is discussed, as well as the chemophenetic significance of our findings. Isolation was performed over repeated silica gel and Sephadex LH-20 column chromatography and the structures were elucidated by (NMR and MS). The crude methanol extract and isolated compounds showed considerable antibacterial potency against a panel of multi-drug resistant (MDR) bacterial strains. The best MIC values were obtained with compound (2) against S. aureus ATCC 25923 (32 µg/mL) and MRSA1 (16 µg/mL). 相似文献
16.
Silvia Anthoine Dietrich Renate Lindauer Claire Stierlin Jürg Gertsch Dr. Ruth Matesanz Dr. Sara Notararigo José Fernando Díaz Dr. Karl‐Heinz Altmann Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(39):10144-10157
A series of epothilone B and D analogues bearing isomeric quinoline or functionalized benzimidazole side chains has been prepared by chemical synthesis in a highly convergent manner. All analogues have been found to interact with the tubulin/microtubule system and to inhibit human cancer cell proliferation in vitro, albeit with different potencies (IC50 values between 1 and 150 nM ). The affinity of quinoline‐based epothilone B and D analogues for stabilized microtubules clearly depends on the position of the N‐atom in the quinoline system, while the induction of tubulin polymerization in vitro appears to be less sensitive to N‐positioning. The potent inhibition of human cancer cell growth by epothilone analogues bearing functionalized benzimidazole side chains suggests that these systems might be conjugated with tumor‐targeting moieties to form tumor‐targeted prodrugs. 相似文献
17.
Davila J Chassepot A Longo J Boulmedais F Reisch A Frisch B Meyer F Voegel JC Mésini PJ Senger B Metz-Boutigue MH Hemmerlé J Lavalle P Schaaf P Jierry L 《Journal of the American Chemical Society》2012,134(1):83-86
Cell adhesion processes take place through mechanotransduction mechanisms where stretching of proteins results in biological responses. In this work, we present the first cyto-mechanoresponsive surface that mimics such behavior by becoming cell-adhesive through exhibition of arginine-glycine-aspartic acid (RGD) adhesion peptides under stretching. This mechanoresponsive surface is based on polyelectrolyte multilayer films built on a silicone sheet and where RGD-grafted polyelectrolytes are embedded under antifouling phosphorylcholine-grafted polyelectrolytes. The stretching of this film induces an increase in fibroblast cell viability and adhesion. 相似文献
18.
Armelle Anthoine 《International Journal of Solids and Structures》2010,47(11-12):1477-1489
The homogenisation theory for periodic composites is generalised to the case of quasi-periodic composites. In quasi-periodic composites, the unit cell does not repeat throughout the medium but gradually changes along one or more directions of periodicity (grading directions). Quasi-periodic composites are thus to functionally graded materials (FGMs) what periodic composites are to statistically uniform composite materials. Contrarily to most of the homogenisation methods applied to FGMs, the proposed second-order homogenisation theory takes explicitly into account the grading at the micro-level. The derived equivalent material happens to be a particular second gradient material in which few components of the strain gradient (second gradient of the displacement) should be taken into account in addition to the classical strains (first gradient of displacement). The second gradient theory therefore appears as the natural framework to appropriately handle functionally graded materials at the macro-level. It is worth mentioning that the presented second-order homogenisation procedure is somehow analogous to the one developed for periodic composite materials submitted to rapidly varying macroscopic strain fields as in regions of high gradients. In fact, both are a generalisation of the first-order homogenisation theory for periodic media and lead to a second gradient equivalent material. However, besides their different domains of application, they exhibit further substantial differences, which are highlighted in the paper. 相似文献
19.
In this paper, we consider the estimation of the extreme value index and extreme quantiles in the presence of random right
censoring. The generalization of the peaks over threshold method is discussed and an adaptation of the moment estimator is
proposed. The corresponding extreme quantile estimators are also introduced. We make a start with the analysis of the asymptotic
properties of the moment estimator and the corresponding extreme quantile estimator. The finite sample behaviour is illustrated
with a small simulation study and through practical examples from survival data analysis.
相似文献
20.
This abstract deals with the telomerization of butadiene with carbon tetrachloride. By changing experimental conditions (the nature of the catalyst [Cu+, Cu2+, Fe3+, Fe (CN)63?, Fe (CN)64?, Mg], the ratio “r” of the concentration of taxogen to that of telogen, the ratio “c” of the concentration of catalyst to that of telogen) we have obtained chlorinated liquid polymers; their molecular weights range between 208 and approx 70,000. The dispersity of these polymers is calculated to be between 1.4 and 1.6. Addition 1–4 is the most frequent, (>80%). The correspondence between ratios r and c and the average molecular weight is established. 相似文献