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排序方式: 共有467条查询结果,搜索用时 203 毫秒
461.
462.
Experimental and theoretical studies of the physical processes occurring in thin plane targets irradiated by intense X-ray pulses 总被引:1,自引:0,他引:1
A. É. Bugrov I. N. Burdonskiĭ V. V. Gavrilov A. Yu. Gol’tsov E. V. Grabovskiĭ V. P. Efremov E. V. Zhuzhukalo M. V. Zurin N. G. Koval’skiĭ V. N. Kondrashov G. M. Oleĭnik A. I. Potapenko A. A. Samokhin V. P. Smirnov V. E. Fortov I. N. Frolov 《Plasma Physics Reports》2007,33(6):444-454
Results are presented from experimental and theoretical studies of the interaction of intense X-ray pulses with different types of plane targets, including low-density (~10 mg/cm3) ones, in the Angara-5-1 facility. It is found experimentally that a dense low-temperature plasma forms on the target surface before the arrival of the main heating X-ray pulse. It is demonstrated that the contrast of the X-ray pulse can be increased by placing a thin organic film between the target and the discharge gap. The expansion velocity of the plasma created on the target surface irradiated by Z-pinch-produced X rays was found to be (3–4) × 106 cm/s. A comparison between the simulation and experimental results confirms the validity of the physical-mathematical model used. 相似文献
463.
Addition of chloroazide to 3,4,6-tri-O-acetyl-1,5-anhydro-2-deoxy-d-lyxo- (1) and -d-arabino-hex-1-enitol (2) under u.v. irradiation proceeds regio- and stereo-selectively yielding mainly O-acetyl derivatives of 2-azido-2-deoxy-d-galactopyranose and -d-glucopyranose, respectively. 3,4,6-Tri-O-acetyl-2-chloro-2-deoxy-α-d-galactopyranosyl azide and 3,4,6-tri-O-acetyl-2-azido-2-deoxy-α-d-talopyranose (from 1), and 1,3,4,6-tetra-O-acetyl-2-chloro-2-deoxy-α-d-glucopyranosyl azide and 1,3,4,6-tetra-O-acetyl-2-azido-2-deoxy-α-d-mannopyranose (from 2) are byproducts. 1,5-Anhydro-3,4,6-tri-O-benzyl-2-deoxy-d-lyxo- and -d-arabino-hex-1-enitol reacted more rapidly with chloroazide, to give, under irradiation, derivatives of 2-azido-2-deoxy-d-galactose and -d-glucose, respectively. However, reaction in the dark gave mainly O-benzyl derivatives of 2-chloro-2-deoxy-α-d-galacto- and -α-d-glucopyranosyl azide. The difference between the products obtained may depend on the existence of two parallel processes, one radical (under irradiation), and the other ionic (reaction in the dark). 相似文献
464.
Paule Bénit Eric Letouzé Malgorzata Rak Laetitia Aubry Nelly Burnichon Judith Favier Anne-Paule Gimenez-Roqueplo Pierre Rustin 《BBA》2014
Seventy years from the formalization of the Krebs cycle as the central metabolic turntable sustaining the cell respiratory process, key functions of several of its intermediates, especially succinate and fumarate, have been recently uncovered. The presumably immutable organization of the cycle has been challenged by a number of observations, and the variable subcellular location of a number of its constitutive protein components is now well recognized, although yet unexplained. Nonetheless, the most striking observations have been made in the recent period while investigating human diseases, especially a set of specific cancers, revealing the crucial role of Krebs cycle intermediates as factors affecting genes methylation and thus cell remodeling. We review here the recent advances and persisting incognita about the role of Krebs cycle acids in diverse aspects of cellular life and human pathology. 相似文献
465.
É. Deniaud-Alexandre 《Médecine Nucléaire》2008,32(10):530-535
The prognosis of patients with localized non-small-cell lung carcinoma and treated with radiation therapy remains poor. The three-dimensional conformational radiotherapy aims to increase the dose of radiation at the tumor volume to increase the local control, while sparing the healthy tissue neighborhood. The reduction of the safety margins and the irradiated volumes obliges to determine with most acute precision the exact tumor volume. However, the scanner alone is insufficient, particularly at the mediastinal level and at a distance. The positron emission tomography allows distinguishing a biological tumor volume. It helps to define the lung tumor volume, especially when the tumor is accompanied by atelectasis, and to recover the lymph node staging at the mediastinal level and at a distance. Even if the sensibility and the specificity are not 100 %, positron emission tomography now becomes essential before considering an escalation of thoracic radiation dose. 相似文献
466.
E. É. Saftenku 《Neurophysiology》1998,30(4-5):230-231
Programs are represented that permit us to solve the following three problems of single channel kinetic activity: 1) to fulfill
a preliminary analysis of single channel activity, i.e., to estimate the minimum number of agonist molecules that bind with
a channel structure, the minimum number of open and closed kinetic states of the channel, and possible connections between
these states, to check the condition of thermodynamic equilibrium and adequacy of a Markovian assumption for modeling of the
channel kinetics; 2) to select the model of channel gating: for a given number of kinetic states, the potential models that
permit us to fit a list of dwell-times observed in an experiment are examined; the model is selected by a criterium of the
maximum likelihood; 3) to simulate the response to a rapid change of the agonist concentration of single channels that demonstrate
processes of adaptation or inactivation. 相似文献
467.
A Aubry G Pietrzynski B Rzeszotarska G Boussard M Marraud 《International journal of peptide and protein research》1991,37(1):39-45
The crystal structure of the tBuCO-D,L-Ala-delta Z-Phe-NHiPr dipeptide has been solved by X-ray diffraction. The peptide crystallizes in monoclinic space group P2(1)/c with a = 13.445 (3) A, b = 35.088 (4) A, c = 14.755 (3) A, beta = 116.73 (1) degree, Z = 12 and dc = 1.151 g.cm-3. The three independent molecules per asymmetric unit accommodate a beta II-folded conformation, but only one of them contains the typical i + 3----i interaction characterizing a beta-turn. In the other two molecules, the N...O distance exceeds 3.2 A, a value generally considered the upper limit for hydrogen bonds in peptides. In solution, the beta II-turn conformation is largely predominant. 相似文献