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81.
We consider a certain combinatorial game on a digraph for two cases of the price function. For one case the game in question extends the cyclical game studied in Ehrenfeucht and Mycielski (1979) and Gurvitch, Karzanov and Khachiyan (1988) which, in its turn, is a generalization of the well-known problem of finding a minimum mean cycle in an edge-weighted digraph. We prove the existence of optimal uniform stationary strategies for both cases and give algorithms to find such strategies.This work was partially supported by Chaire municipale, Mairie de Grenoble. 相似文献
82.
综述了近8年来液相平行合成和组合合成中应用的不同技术, 包括可溶性载体、氟合成技术、离子液体、固相试剂树脂以及低聚乙烯二醇(OEG)衍生物的应用等几方面内容. 论述了它们的基本原理以及相关的应用实例, 并着重强调了目标化合物的分离纯化方法. 相似文献
83.
《Arabian Journal of Chemistry》2022,15(11):104302
Traditional Chinese medicine (TCM) is the key to unlock treasures of Chinese civilization. TCM and its compound play a beneficial role in medical activities to cure diseases, especially in major public health events such as novel coronavirus epidemics across the globe. The chemical composition in Chinese medicine formula is complex and diverse, but their effective substances resemble “mystery boxes”. Revealing their active ingredients and their mechanisms of action has become focal point and difficulty of research for herbalists. Although the existing research methods are numerous and constantly updated iteratively, there is remain a lack of prospective reviews. Hence, this paper provides a comprehensive account of existing new approaches and technologies based on previous studies with an in vitro to in vivo perspective. In addition, the bottlenecks of studies on Chinese medicine formula effective substances are also revealed. Especially, we look ahead to new perspectives, technologies and applications for its future development. This work reviews based on new perspectives to open horizons for the future research. Consequently, herbal compounding pharmaceutical substances study should carry on the essence of TCM while pursuing innovations in the field. 相似文献
84.
We investigate the trapping of a random walker in fractal structures (Sierpinski gaskets) with randomly distributed traps. The survival probability is determined from the number of distinct sites visited in the trap-free fractals. We show that the short-time behavior and the long-time tails of the survival probability are governed by the spectral dimensiond. We interpolate between these two limits by introducing a scaling law. An extension of the theory, which includes a continuous-time random walk on fractals, is discussed as well as the case of direct trapping. The latter case is shown to be governed by the fractal dimensiond. 相似文献
85.
Lumbierres M Palomo JM Kragol G Roehrs S Müller O Waldmann H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(24):7405-7415
A new flexible and efficient methodology for the solid-phase synthesis of lipidated peptides has been developed. The approach is based on the use of previously synthesized building blocks and overcomes the limitations of previously reported methods, since long doubly lipidated peptides can be synthesized by using this route. Furthermore, it was thus possible to prepare a large number of N- and H-Ras peptides bearing a wide range of reporter and/or linking groups--efficient tools for the investigation of biological processes. In terms of efficiency and flexibility this solid-phase method is superior to the solution-phase synthesis. It gives pure peptides in multimilligram amounts within a much shorter time and with superior overall yield. 相似文献
86.
Theab initio SCF method is used for computing the main electronic properties of the ribose unit of the nucleic acids. The present study is devoted to the ribose in the C3-endo,gg conformation. The properties investigated include the distribution of the electronic charges, the electrostatic molecular potential around the four oxygens of the unit, the hydration and the Na+ binding schemes studied in the supermolecule approximation. The possibilities of through-water binding of the cation to the sugar are also explored. The predictions of the computation in particular with regard to cation binding to the ribose ring are correlated with recent experimental results. 相似文献
87.
Yan-Tao He 《Tetrahedron letters》2005,46(32):5393-5397
Longimicin C, a naturally occurring annonaceous acetogenin possessing a C2-symmetrical bis-THF moiety and a short hydrocarbon chain between its THF-containing region and a terminal γ-lactone, was synthesized for the first time. The total synthesis was successfully achieved by an iterative acetylene-epoxide coupling strategy. d-Mannitol was used to establish the bis-THF-containing segment, in which the additional stereochemistries were introduced by Sharpless dihydroxylations and intramolecular Williamson etherifications. Regioselective epoxide-openings by the appropriate terminal acetylenes allowed coupling and elaboration of all four fragments including the introduction of three essential hydroxyls into the proper sites of the target skeleton. 相似文献
88.
Massey University is a world-leading university in remote-instruction, online and mixed teaching based on the Stream teaching platform. This paper analyzed the advantages of the Stream teaching platform, resource utilization, course format, teaching team cooperation and course evaluation in Massey University. The paper also analyzed the enlightenment of teaching experience of Massey University to undergraduate teaching. During the outbreak of COVID-19 epidemic, drawing on Massey's experience, combined with the rapid development of information technology in China, the teaching team of organic chemistry adopted the multi-teaching strategy of "teacher-centered and student-centered", and the teaching mode of "teacher-led and self-taught by students". The online teaching practice of organic chemistry was carried out in agriculture university. It has been demonstrated that this model can effectively improve teaching effects. 相似文献
89.
L. Malherbe 《Accreditation and quality assurance》2002,7(5):189-194
Human health risk assessment is a site-based approach used to identify the potential health hazards which are induced by an
old site contamination. For a proper evaluation of the daily doses of contaminants to which people will be exposed given the
future occupation of the site, both a characterization and a quantification of soil pollution are needed. Such information
can be provided by soil sampling. Thus the choice of the location, the number, depth and type of soil samples is very important
and ought to follow a well-defined strategy. A review of contaminated site sampling practices in Europe and North America
could not identify any completely formalized sampling strategy for human health risk assessment. On the contrary there are
several approaches which can be roughly classified into two categories: a systematic sampling scheme over the whole site,
on the one hand, and a sampling design driven by an initial knowledge of the contamination sources and fitted to the suspected
pollution pattern, on the other. The first approach provides a complete coverage of the site but it may be rather expensive
and entail useless sampling. The performance of the second depends on the quality of prior information. Actually both methods
can be combined as explained hereafter. In view of the specificity of each site, the requirements of health risk assessment
and the time and cost constraints, it seems difficult to work out a typical soil sampling strategy suitable for all sites.
However, some recommendations can be made according to the site dimensions, the nature, degree and heterogeneity of contamination,
and the (future) use of the site. The scientist should thus rely on a thorough examination of all available information (site
history, geology and hydrogeology, soil properties, contaminants behaviour , etc.) to delimit contaminated areas as homogeneous
as possible and then distribute the sampling points (e.g.using a sampling grid). They should also take the potential exposure
paths into account in order to define the areas and soil strata to be sampled as a priority. Statistical and geostatistical
tools can be helpful for formulating a sampling strategy as well as for interpreting the collected data.
Received: 7 December 2001 Accepted: 24 February 2002 相似文献
90.
激发极化法(简称激电法)不受地形起伏及围岩电阻率不均匀性的影响。因此。利用激电法找水,特别是在山区找水受到了重视,并取得了良好的效果。介绍了激发极化现象和激电找水中的常用参数,给出了利用激电法找水的具体实例。 相似文献