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排序方式: 共有134条查询结果,搜索用时 15 毫秒
1.
5-bromodeoxyuridine (BUdR) injected to rats in the neonatal period is shown to produce a pronounced carcinogenic effect which brings about the appearance of various benign and malignant tumours. Exposure of females to X-ray total-body irradiation (1.5 Gy) was followed by intensification of the carcinogenic effect of BUdR. Assuming that this pyrimidine analog reacts solely with DNA substituting thymidine during DNA synthesis and induces point mutations due to tautomerization, the data obtained demonstrate the possibility of tumour induction by a selective DNA perturbation. 相似文献
2.
B. I. Zhukov V. N. Likhachev Yu. G. Sikharulidze A. G. Tuchin D. A. Tuchin V. P. Fedotov 《Journal of Computer and Systems Sciences International》2016,55(2):260-270
An algorithm is developed for terminal guidance during the main deceleration section of the lunar landing trajectory of a spacecraft with an integrated propulsion system, which has a main engine with variable thrust and four auxiliary nonthrottleable engines. A method of guidance adaptation to the actual motion conditions by measuring the thrust acceleration with jumps in time is proposed. 相似文献
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A pattern of DNA methylation and carcinogenesis has been studied in young (3 month-old) and old (14 month-old) female rats following a single intravenous injection (13 mg/kg) of methyl(acetoxymethyl)nitrosamine (DMN-OAc). The incidence of various tumours as well as the incidence of tumours in some peculiar sites were found to be similar in young and old DMN-OAc-treated rats. The life time of old rats was less than that in young animals; the average period of tumour detection was also shorter in old rats. In both young and old animals the highest concentrations of methylated purines were found in lung and kidney DNA. However, the level of DNA methylation in old rats was higher than in corresponding tissues of young animals. Efficiency of O6-meG repair in methylated template DNA was found to be the highest in liver extracts of 1- and 12-month-old rats. Further, by the age of 2 years, the activity of O6-meGT decreased. The findings suggest that different age periods could be characterized by different efficiency of DNA alkylation, synthesis and repair. 相似文献
5.
M. M. Bubnov A. N. Guryanov E. M. Dianov L. A. Ketkova M. E. Likhachev M. Yu. Salganskii V. F. Khopin 《Inorganic Materials》2010,46(5):556-562
We have studied the size distribution of silica glass particles in the fabrication of heavily doped germanosilicate glass
fiber preforms by modified chemical vapor deposition (MCVD) at different Freon 113 concentrations in the gas mixture. The
addition of Freon 113 to the gas mixture is shown to reduce the particle size in the deposited core glass layer and the optical
loss in the fiber. A mechanism is proposed which accounts for the effect of the initial particle size in the core glass layer
on the anomalous scattering and total optical loss in heavily doped step- and graded-index fibers. 相似文献
6.
S. Fvrier D. Gaponov M. Devautour P. Roy L. Daniault M. Hanna D.N. Papadopoulos F. Druon P. Georges M.E. Likhachev M.Y. Salganskii M.V. Yashkov 《Optical Fiber Technology》2010,16(6):419-427
In the search for ever higher output power or energy from fibre oscillators or amplifiers a nowadays mature technology relies on enlarging the fibre mode area. Broadening of the core diameter, all other things being equal, inevitably yields a multimode fibre, thereby dramatically limiting the device usefulness. Various strategies have been deployed to design and manufacture single transverse mode fibre oscillators and amplifiers, among which making use of the so-called photonic bandgap effect to restrict the modal population seems promising. Helped by efficient and reliable numerical tools the design of large mode area singlemode photonic bandgap fibres is presented. Two fibres with 20-μm and 40-μm core diameter, both of them heavily doped with Yb3+ ions, have been fabricated by the widespread modified chemical vapour deposition process and are shown to behave properly when used as the core element of either continuous wave oscillators or femtosecond amplifiers. Good output beam quality (M2 parameter spanning from 1.12 to 1.5 for the set of fibres studied) and high slope efficiency of 80% in cw oscillation regime are demonstrated. Furthermore the 40-μm core diameter fibre is shown to be resilient to tight bending down to 7.5-cm radius. The stack-and-draw process makes it easy to tailor the outer cladding so that a large numerical aperture can be reached. Subsequently, from this air-clad fibre, 500 fs 47 W pulses at 35 MHz are obtained from a two-stage chirped pulse amplification system. 相似文献
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We have proposed a mathematical model of the combustion of bubble reactive media in which the heat of the reaction is initially expended on the heating of a vapor-gas mixture contained within bubbles, and then the fluid is transferred through the interphase surface, as a consequence of which the fluid becomes heated and vaporizes. Under certain assumptions (a low volumetric gas-phase content, intensive mixing of the original components and the final products, quasiequilibrium of the vapor-formation process) we have derived approximate analytical expressions for the heat-release and heat-transfer functions, and we have solved numerically the heat-balance equation. We have investigated the possible combustion regimes and have determined the regions in which the steady state exists.Ukhta. Translated from Fizika Goreniya i Vzryva, No. 2, pp. 66–75, March–April, 1991. 相似文献
9.
A. Deppman O.A.P. TavaresS.B. Duarte E.C. de OliveiraJ.D.T. Arruda-Neto S.R. de PinaV.P. Likhachev O. Rodriguez J. MesaM. Gonçalves 《Computer Physics Communications》2002,145(3):385-394
We present an object oriented algorithm, written in the Java programming language, which performs a Monte Carlo calculation of the evaporation-fission process taking place inside an excited nucleus. We show that this nuclear physics problem is very suited for the object oriented programming by constructing two simple objects: one that handles all nuclear properties and another that takes care of the nuclear reaction. The MCEF code was used to calculate important results for nuclear reactions, and here we show examples of possible uses for this code. 相似文献
10.