排序方式: 共有44条查询结果,搜索用时 250 毫秒
31.
R. Abraham L. Serlet 《Stochastics An International Journal of Probability and Stochastic Processes》2013,85(3-4):287-308
We consider a path-valued process which is a generalization of the classical Brownian snake introduced by Le Gall. More precisely we add a drift term b to the lifetime process, which may depends on the spatial process. Consequently, this introduces a coupling between the lifetime process and the spatial motion. This process can be obtained from the standard Brownian snake by Girsanov's theorem or by killing of the spatial motion. It can also be viewed as the limit of discrete snakes or, in some special cases, as conditioned Brownian snakes. We also use this process to describe the solutions of the non-linear partial differential equation j u =4 u 2 +4 bu . 相似文献
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一种自动提取目标的主动轮廓法 总被引:28,自引:2,他引:26
提出一种新的广泛应用于数字图象分析和计算机视觉的主动轮廓(Snake)模型,引入作用方向可以自适应变化的外加强制力,使控制点能够不依赖于初始轮廓而快速地收敛到目标的真实轮廓;初始轮廓自动确定;控制点的数目可以自适应地改变;能够在背景比较复杂的图象中实现对目标轮廓的提取.用该模型对空中目标的红外图象进行的实验结果表明其具有很好的鲁棒性和实用性. 相似文献
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Hla Myoe Min Tohru Taniguchi Kenji Monde Toshiaki Nikai Yoshiaki Takaya 《Tetrahedron letters》2007,48(35):6155-6158
(+)-Alternamin (1), a new dihydrofuranocoumarin, was isolated from the aerial parts of Murraya alternans (Kurz) Swingle. The analysis 2-D NMR correlation of (+)-1 led to either of linear dihydrofuranocoumarin (2A, 2C) or angular one (2B). An IR and a vibrational circular dichroism (VCD) studies were conducted to distinguish the structure and to assign the absolute configuration. By comparison of the observed spectra with the calculated spectra for (S)-2A, (S)-2B, and (R)-2C, the molecular structure of (+)-1 was determined to be (S)-(+)-5,8-dimethoxymarmesin. The compound exhibited antidote activity against snake venom from Trimeresurus flavoviridis, affording experimental support for the pharmacological use of M. alternans. 相似文献
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Fractionation and proteomic analysis of the Walterinnesia aegyptia snake venom using OFFGEL and MALDI‐TOF‐MS techniques 下载免费PDF全文
Tarek Mohamed Abd El Aziz Sandrine Bourgoin‐Voillard Stéphanie Combemale Rémy Beroud Mahmoud Fadl Michel Seve Michel De Waard 《Electrophoresis》2015,36(20):2594-2605
Animal venoms are complex mixtures of more than 100 different compounds, including peptides, proteins, and nonprotein compounds such as lipids, carbohydrates, and metal ions. In addition, the existing compounds show a wide range of molecular weights and concentrations within these venoms, making separation and purification procedures quite tedious. Here, we analyzed for the first time by MS the advantages of using the OFFGEL technique in the separation of the venom components of the Egyptian Elapidae Walterinnesia aegyptia snake compared to two classical methods of separation, SEC and RP‐HPLC. We demonstrate that OFFGEL separates venom components over a larger scale of fractions, preserve respectable resolution with regard to the presence of a given compound in adjacent fractions and allows the identification of a greater number of ions by MS (102 over 134 total ions). We also conclude that applying several separating techniques (SEC and RP‐HPLC in addition to OFFGEL) provides complementary results in terms of ion detection (21 more for SEC and 22 more with RP‐HPLC). As a result, we provide a complete list of 134 ions present in the venom of W. aegyptia by using all these techniques combined. 相似文献
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为了更深入地研究核子性质,中国科学院近代物理研究所将在强流重离子加速器装置(HIAF)上利用极化质子束开展实验。HIAF增强器BRing能够提供最大能量9.3 GeV/u的极化质子束,在加速过程中极化束流会遇到多次退极化共振,需要特殊设计才能使束流保持较高的极化度。利用退极化共振强度模拟程序DEPOL,研究了BRing加速过程中不同退极化共振对束流极化度的影响。结果表明,加速过程遇到的两种退极化共振将会使束流完全退极化;在BRing电子冷却段加入Full Siberian Snake可以使质子束在加速时保持较高的极化度。In order to explore the nucleon properties in details, the polarized proton will be used for some special experiments at HIAF project in Institute of Modern Physics, Chinese Academy of Sciences (IMP,CAS). The maximum energy of 9.3 GeV/u for Polarized protons will be provided in the Booster Ring(BRing) at HIAF. The polarized beam experiences depolarizing resonances many times during acceleration process, so it's necessary to suppress those resonances to keep polarizability well by special design. In this paper, the code DEPOL is used to simulate the influence of depolarizing resonances process in BRing. According to the results, the beam's polarization has been destroyed completely by the depolarizing resonances in the acceleration process. And the Full Siberian Snake is chosen in the Electron Cooler part of BRing to preserve the beam's polarization during the acceleration, and its strength and location of the Siberian Snake are also presented here. 相似文献
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Klaus-Jürgen Schleifer 《Journal of computer-aided molecular design》1997,11(5):491-501
The identification and structural determination of the criticalamino acid residues causing the calcium channel blocking effects of theangusticeps type III toxin FS2 is described. Alignments withmore than 200 different short and long neuro-, cyto-, muscarinic and otherangusticeps-type toxins yielded 12 amino acid residues at the tips of loopsII and III which are unique to the type III toxins. The competitive bindingbehaviour between the 1,4-dihydropyridine derivative nifedipine and toxinFS2 was used for a further delimitation of the relevant toxinbinding domain. Using the ab initio geometry optimized nifedipine X-raystructure as a template, a model based on the sequenceMet45-Trp46-cis-Pro47-Tyr48has been elaborated. This sequence shows the same hydrophobic andhydrogen bond forming properties as nifedipine. In addition, qualitativelysimilar molecular electrostatic potentials are observed for both structures,leading to the assumption that these amino acid residues of the toxin act asthe potential attachment region at the calcium channel receptor site. 相似文献
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A review of research on snake neurotoxin is presented, with emphasis on the chemical modification studies and molecular cloning of postsynaptic and presynaptic neurotoxins from Naja naja atra (Taiwan cobra) (Fig. 1a) and Bungarus multicinctus (Taiwan banded krait) (Fig. 1b). Cobrotoxin and α-bungarotoxin are the primary postsynaptic neurotoxins isolated from the venom of N. naja atra and B. multicinctus, respectively. Although they share a common three-dimensional structure, the functional elements essential for the manifestation of their toxicity are different. Selective and stepwise chemical modification of cobrotoxin indicate that at least two cationic groups, an ?-amino group of Lys-47 and a guanidino group of Arg-33 common to all known postsynaptic neurotoxins, are functionally important for its neuromuscular blocking activity. However, for α-bungarotoxin, the side chains of several basic amino acid residues are involved in the multipoint contact between the toxin and acetylcholine receptor. Moreover, the conserved Trp residue is essential for the neurotoxicity of cobrotoxin, but not for α-bungarotoxin. The cDNAs encoding cobrotoxin and α-bungarotoxin was constructed from the cellular RNA isolated from the venom glands of N. naja atra and B. multicinctus by polymerase chain reaction. The sequence of their 3′-untranslational region, signal peptide and 5′-untranslational region share a high degree of homology, suggesting that they are evolutionarily related. Expression of both neurotoxic protein in E. coli generated polypeptide chains for reactions with the antisera against the native neurotoxins. Presynaptic neurotoxins constitute a different group of neurotoxic proteins in snake venom proteins. These presynaptic neurotoxins are either basic phospholipase A2 (PLA2) per se or contain basic PLA2 as an indispensible part of their structures. Thus, the presynaptic neurotoxins usually show both PLA2 activity and presynaptic neurotoxicity. β-Bungarotoxin (β-Bgt), the main presynaptic PLA2 neurotoxin isolated from the venom of B. multicinctus (Taiwan banded krait), consists of two dissimilar polypeptide chains, a PLA2 subunit (A chain) and potassium channel recognition subunit (B chain). Chemical modification studies show that the toxin might possess two functional sites, one responsible for the catalytic activity and the other for its pharmacological properties. Molecular cloning and expression of the A chain and B chain of β-Bgt reveal that the A chain of β-Bgt is an active subunit with PLA2 activity, and that the B chain is involved in voltage-gated potassium channel blocking action observed with β-Bgt. 相似文献
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Perkins等[1]用MALDI/TOF/MS对不同种类蛇毒中神经毒素进行了分析,彭嘉柔等[2,3]对江浙蝮蛇和蛇毒粗组份进行了初步质谱表征.但蛇毒蛋白纯化困难,因此对单一组份的研究较少且不系统.本文以白眉蝮蛇蛇毒(AgkistrodonblomhoffiiUssurensis,ABUV)为原料,纯化得到了精氨酸酯酶(Arginineesterase,AEase)、磷脂酶A2(PhospholipaseA2,PLA2)、纤溶酶(fibrinolyticenzyme)和L-氨基酸氧化酶(L-aminoacidoxidase),并且用MALDI/TOF/MS法对它们和蛇毒粗毒进行了系统研究.1 实验部分1.1 仪器和药品 激光解吸质谱仪为美国Molecular公司L… 相似文献