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811.
Comets with a high content of organics and light molecules are expected under cosmic radiation to gain a relatively unreactive crust and less volatile material to some ten metres deep. Interstellar dust impacts act to loosen and turn over 1 cm of the surface. We discuss how far this accords with observations of cometary dust halos and new versus old comets. Two key material properties have emerged from recent studies. Firstly, the source of cometary volatiles is not ice in the sense of material with a single sublimation energy. Secondly, the particulates are not simply mineral dust but include much organic material, some of which undergoes chemical processing and exchanges with the gaseous environment. Consistent with these properties, a coherent crust rather than a mantle of loose grains would build up to cover much of the nucleus of periodic comets. It would consolidate by cooking in the solar radiation, especially at peak temperatures around perihelion. There are two disjoint surface phases: one of volatile material, the other the refractory crust, the former deepening into crater-like hollows over successive apparitions. The transition to non-volatile crust is unstable, subject to competing consolidation and disruption processes, and sensitive to seasonal changes. A comet dims and becomes asteroidal as the inert crust extends over the erosion craters, and may only be rejuvenated via collision with a boulder-sized impactor or perturbation of the orbit to smaller perihelion distance. 相似文献
812.
A plan of the health care system for the crew on the lunar base is described in this study. The health care system consists of two subsystems. The first is the daily health care system. The system contains health care menus, similar to those on Earth, and some biochemical and ordinary medical examinations. The second system is a periodic medical inspection for the crew's bones and the determination of natural radioisotopes in the body. These care systems are automatically treated with the examination and data filing. Usually these examinations are carried out without the presence of a medical doctor. Examinations and files of the whole results are controlled by a computer. The daily results of examinations are compared with data in the file. If any abnormal values are found in the results, an appropriate message is sent advising whether he must receive an in-depth examination by a medical doctor, or be reexamined by the same submenu. The automatic health care system also records transactions with the life support monitoring system. 相似文献
813.
We discuss the use of multilayered annular-plate dampers as rotor supports in turbopumps of the RD-0120 and RD-0146 rocket engines. We present a technique of calculating the elastic and damping characteristics of multilayer corrugated annular supports in the case of the conical precession of the rotor. 相似文献
814.
V. T. Grumondz E. I. Karpezhnikov M. A. Polishchuk M. V. Polishchuk 《Russian Aeronautics (Iz VUZ)》2017,60(4):534-541
The algorithms of controlled descent for unmanned winged gliders are designed taking into account the requirements to the flight trajectory. The calculation results are represented to show the efficiency of the algorithms. 相似文献
815.
Features of fuel atomization and propagation in the flow behind a gas-dynamic stabilizer are considered. Estimations of the influence of transverse jets impulse magnitude on characteristics of mixing behind the stabilizer are obtained by numerical and experimental methods. 相似文献
816.
R.A. Gowen A. Smith A.D. Fortes S. Barber P. Brown P. Church G. Collinson A.J. Coates G. Collins I.A. Crawford V. Dehant J. Chela-Flores A.D. Griffiths P.M. Grindrod L.I. Gurvits A. Hagermann H. Hussmann R. Jaumann A.P. Jones K.H. Joy O. Karatekin K. Miljkovic E. Palomba W.T. Pike O. Prieto-Ballesteros F. Raulin M.A. Sephton S. Sheridan M. Sims M.C. Storrie-Lombardi R. Ambrosi J. Fielding G. Fraser Y. Gao G.H. Jones G. Kargl W.J. Karl A. Macagnano A. Mukherjee J.P. Muller A. Phipps D. Pullan L. Richter F. Sohl J. Snape J. Sykes N. Wells 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
817.
An approach to the analysis of electric arc process stability in plasma systems of ignition is considered depending on the
ignition system power circuit parameters, speed of plasma-generating air, and combustion chamber inlet pressure. Also solved
is the problem on determination of the calculated value of the maximum admissible speed of plasma-generating air that corresponds
to the critical regime of stable arcing in plasma spark plug at the GTE start. 相似文献
818.
A technique of evaluating the micromechanical characteristics (namely, microhardness, microdurability, microbrittleness and
static crack resistance coefficient) using microindentation as applied to plasma zirconia-based thermal barrier coatings is
presented. 相似文献
819.
The results of studying the characteristics of a two-phase flow being formed during adiabatic water efflux through axisymmetric
cylindrical and Laval nozzle channels are presented. Experiments were carried out with saturated water in the range of initial
pressures 0.6–4.0 MPa. The fluid efflux was performed into the air with atmospheric pressure. The generalizing relations for
calculating thrust pulse and critical flowrate were obtained. 相似文献
820.
A. L. Tukmakov V. G. Tonkonog A. G. Kochenkov S. A. Kusyumov 《Russian Aeronautics (Iz VUZ)》2011,54(4):402-411
A physical and mathematical model of a boiling-up fluid flow in the variable crosssection channels is proposed. The numerical
model is based on the solution of the Navier-Stokes nonstationary equations for compressible fluid by the implicit finite-difference
method. We present the results of the numerical modeling for two-phase flow characteristics at the initial stage of the evaporation
process and the steady-state quasistationary flow of a two-phase medium. 相似文献