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171.
A Lazcano E Díaz-Villagómez T Mills J Oró 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1995,15(3):345-356
The most frequently invoked explanation for the origin of metabolic pathways is the retrograde evolution hypothesis. In contrast, according to the so-called "patchwork" theory, metabolism evolved by the recruitment of relatively inefficient small enzymes of broad specificity that could react with a wide range of chemically related substrates. In this paper it is argued that both sequence comparisons and experimental results on enzyme substrate specificity support the patchwork assembly theory. The available evidence supports previous suggestions that gene duplication events followed by a gradual neoDarwinian accumulation of mutations and other minute genetic changes lead to the narrowing and modification of enzyme function in at least some primordial metabolic pathways. 相似文献
172.
King CB Butterfield AJ Hypes WD Nealy JE Simonsen LC 《Journal of spacecraft and rockets》1990,27(3):225-226
The space shuttle external tank, which consists of a liquid oxygen tank, an intertank structure, and a liquid hydrogen tank, is an expendable structure used for approximately 8.5 min during each launch. A concept for outfitting the liquid oxygen tank-intertank unit for a 12-person lunar habitat is described. The concept utilizes existing structures and openings for both man and equipment access without compromising the structural integrity of the tank. Living quarters, instrumentation, environmental control and life support, thermal control, and propulsion systems are installed at Space Station Freedom. The unmanned habitat is then transported to low lunar orbit and autonomously soft landed on the lunar surface. Design studies indicate that this concept is feasible by the year 2000 with concurrent development of a space transfer vehicle and manned cargo lander for crew changeover and resupply. 相似文献
173.
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175.
E. G. Dem’yanenko 《Russian Aeronautics (Iz VUZ)》2014,57(2):204-211
In this paper, a new technique for shaping the thin-walled barrel-type parts is presented. 相似文献
176.
V.E. Kunitsyn A.M. Padokhin A.E. Vasiliev G.A. Kurbatov V.L. Frolov G.P. Komrakov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The purpose of this work is to report the experimental evidences for the influence of perturbations in the electron density in the dayside mid-latitude ionosphere, that are caused by high-frequency heating of the F2 layer, on the GNSS signals. The experiments were carried out at the Sura heater (Radio Physical Research Institute, N. Novgorod). During the sessions of ionospheric heating with different time modulations of the radiated power the rays linking the navigational satellites with the ground receiver intersected the heated region. Variations in the total electron content (TEC) were studied; these variations are proportional to the reduced phases of navigational signals. It is shown that with the square-wave modulation of the radiated power (with periods of 1, 6, 10 and 15 min), perturbations with periods of the main modulation of heating and its harmonics appear in the spectrum of TEC variations. Examples are presented of identification of the heating-induced variations in TEC, including determination of the amplitudes and time characteristics of these variations. 相似文献
177.
Using numerical modeling, the influence of the NO concentration on the intensity of 557.7 nm emission in aurora caused by electron precipitation has been studied. It has been shown that the O2 + NO reaction, which reduces the contribution of the dissociative recombination of the O2 + ion into the formation of the 1S state of atomic oxygen, is the main channel of suppression of the intensity of the emission at 557.7 nm. A method of estimating the NO concentration in the aurora based on the data of photometric measurements of emissions at 391.4, 557.7, and 630.0 nm has been proposed. The method has been tested using the data of simultaneous rocket measurements of emissions at 391.4, 557.7, and 630.0 nm and the NO content in aurora. A good agreement of estimates of the NO concentrations performed by the method to the results of direct measurements has been obtained. 相似文献
178.
The paper highlights significance of the interturbine transition duct as part of the high pressure and low pressure turbine spool. The correlations have been suggested allowing us to estimate variation of the average cross section flow swirl while its passing the interturbine transition duct. 相似文献
179.
G.?S.?ZaslavskiiEmail author M.?V.?Zakhvatkin N.?S.?Kardashev Yu.?Yu.?Kovalev E.?A.?Mikhailov M.?V.?Popov K.?V.?Sokolovskii V.?A.?Stepan’yants A.?G.?Tuchin 《Cosmic Research》2017,55(4):290-305
The results of updating the parameters of motion of the Spektr-R spacecraft at the end of 2016 have shown that, in January 2018, with a probability close to unity, the condition that a spacecraft stay in the Earth’s shadow is violated; however, in May of the same year, the ballistic life of the spacecraft will be terminated. Thus, in 2017, the question arose of how to design the correction of flight of this spacecraft using its onboard propulsion system. The correction was designed with allowance for the fact that, for the first time since it was launched, the spacecraft in the course of several years, beginning with 2017, repeatedly approaches the Moon, deeply immersing into its sphere of influence. This paper presents the technologically and organizationally convenient, allowable versions of upcoming correction of the Spektr-R spacecraft trajectory and justifies the particular scheme of its implementation. 相似文献
180.