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841.
O. T. Demkiv E. L. Kordyum O. R. Kardash O. Ya. Khorkavtsiv 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,23(12):1999-2004
The gravitropism of protonemata of Pohlia nutans is described and compared with that of other mosses. In darkness, protonemata showed negative gravitropism. Under uniform illumination they grew radially over the substrate surface, whereas unilateral illumination induced positive phototropic growth. Gravitropism was coupled with starch synthesis and amyloplast formation. Protonematal gravitropic growth is more variable than the strict negative gravitropism of Ceratodon chloronema. 相似文献
842.
T Hoson 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,23(12):1971-1974
The life of plants and other organisms is governed by the constant force of gravity on earth. The mechanism of graviperception, signal transduction, and gravireaction is one of the major themes in space biology. When gravity controls each step of the life cycle such as growth and development, it does not work alone but operates with the interaction of other environmental factors. In order to understand the role of gravity in regulation of the life cycle, such interactions also should be clarified. Under microgravity conditions in space, various changes are brought about in the process of growth and development. Some changes would be advantageous to organisms, but others would be unfavorable. For overcoming such disadvantages, it may be required to exploit some other environmental factors which substitute for gravity in some properties. In terrestrial plants, gravity can be replaced by light under certain conditions. The gravity-substituting factors may play a principal role in future space development. 相似文献
843.
V. A. Gladyshev A. Yu. Shchekotov N. V. Yagova J. -J. Berthelier M. Parrot O. S. Akent’eva L. N. Baranskii E. N. Fedorov T. M. Mulyarchik O. A. Molchanov 《Cosmic Research》2012,50(2):103-115
Variations in concentration of ions H+, He+, and O+ are studied at a height of about 700 km using the data of continuous observations onboard the DEMETER satellite at the decline and in the minimum of solar activity from 2004 to 2008. Latitudinal distributions, seasonal behavior,
and irregular variations in ion concentrations and their dependence on solar and geomagnetic activity are considered. Within
this altitude range, for the first time an analysis is performed of the dataset of many-year continuous observations in both
hemispheres from the equatorial to subauroral latitudes. This made it possible to describe the seasonal and irregular variations
of the concentrations of main ion species with better time and spatial resolution than in the available empirical models.
The dependence of concentrations of three types of ions on solar and geomagnetic activity is studied at time scales from several
days to several years, and it is shown that the anti-phase change in concentrations of O+ and light ions known from publications is partly a result of mutual dependence of solar and geomagnetic activity and is observed
only at time scales beginning from several months. At time scales from several days to several weeks, variations in the concentration
of O+ and light ions are governed mainly by solar and geomagnetic activity, respectively. 相似文献
844.
O. B. Barysheva 《Russian Aeronautics (Iz VUZ)》2007,50(4):374-379
The behavior of generalized diffusion coefficients and diffusion flows of individual substances in the multicomponent gas mixture is investigated. The combustion products of liquid rocket propellants being used are considered. 相似文献
845.
R. A. Leske R. A. Mewaldt C. M. S. Cohen A. C. Cummings E. C. Stone M. E. Wiedenbeck T. T. von Rosenvinge 《Space Science Reviews》2007,130(1-4):195-205
Solar energetic particles (SEPs) provide a sample of the Sun from which solar composition may be determined. Using high-resolution
measurements from the Solar Isotope Spectrometer (SIS) onboard NASA’s Advanced Composition Explorer (ACE) spacecraft, we have
studied the isotopic composition of SEPs at energies ≥20 MeV/nucleon in large SEP events. We present SEP isotope measurements
of C, O, Ne, Mg, Si, S, Ar, Ca, Fe, and Ni made in 49 large events from late 1997 to the present. The isotopic composition
is highly variable from one SEP event to another due to variations in seed particle composition or due to mass fractionation
that occurs during the acceleration and/or transport of these particles. We show that various isotopic and elemental enhancements
are correlated with each other, discuss the empirical corrections used to account for the compositional variability, and obtain
estimated solar isotopic abundances. We compare the solar values and their uncertainties inferred from SEPs with solar wind
and other solar system abundances and find generally good agreement. 相似文献
846.
In this paper, the existing techniques of electrochemical dimensional machining are considered. The use of an additional current-conducting template makes it possible to improve the accuracy of materials separation with the aid of the electric field superimposed. 相似文献
847.
A technique for calculating the geometrically and physically nonlinear stress strain state of nonshallow shells of revolution under the nonaxisymmetric wind-like loading is proposed. The calculation results for a semispherical shell with the central hole and rigidly fixed edges depending on the loading nonaxisymmetry, material characteristics and thickness are presented. We demonstrate not only quantitative but also qualitative influence of taking into account the factor of joint nonlinearity on the process of shell deformation. 相似文献
848.
A. V. Sedel’nikov 《Russian Aeronautics (Iz VUZ)》2007,50(3):322-325
Making use of the Weierstrass-Mandelbrot fractal function, some problems connected with the adequate assessment of microaccelerations aboard a spacecraft are considered. The ranges of values for the function parameters that make it possible to simulate the quasi-static component of microaccelerations are also determined. 相似文献
849.
850.
The paper is devoted to studying the motion of meteor bodies with mass outflow in a planet’s atmosphere, taking into account the non-isothermal character of the latter. Analytical solutions are obtained at the constant parameter of mass outflow in the model of a nonfragmenting meteoroid. A theoretical analysis of the derived regularities of the ballistics of such bodies is presented. 相似文献