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551.
An analysis is given of the tracking accuracy of a conopulse radar that angle-tracks on target echo pulses. The analysis includes effects of noises in both sum and difference channels, the effect of the tracking range gate's duration, and applies to any shape of radio frequency (RF) pulse envelope. For large single-pulse signalto-noise ratio and any shape of RF pulse envelope, accuracy approaches the theoretical accuracy of a conopulse system when a short-duration range gate is used. The inportant case of rectangular RF pulses is solved in detail. 相似文献
552.
In the present work, the asymptotic dependence of the reservation multiplicity on the failure danger diminution coefficient in both cases of reservation replacement and continually acting reserver is investigated. The comparison of the method of reservation for different multiplicities with the method of diminution of the failure intensity, related to the mean performance time shows that the decrease of the failure intensity of the plazma engine is the most rational. Nevertheless, there is a value of the time flight for which even a simple duplication is better than arbitrarily large, though finite, failure intensity decrease of the engine. The reliability of coupled MOD-thrusters is verified experimentally. The specific character of the thruster V-I curves and, in particular, their increase in the pubricrcrisis region, yield normally working couples, conformly to many types of feed sources with weakly decreasing of constant V-I characteristics. The parallel connection of a second thruster is shown to double the customed current and, as a consequence the thruster intermediary regimes of the thruster and the dynamics of switching on and by breaking the electric line and stopping the propellant rate flow are investigated. 相似文献
553.
P Todd 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(1):43-49
Several modifications of differentiated functions of animal cells cultivated in vitro have been reported when cultures have been exposed to increased or decreased inertial acceleration fields by centrifugation, clinorotation, and orbital space flight. Variables modified by clinorotation conditions include inertial acceleration, convection, hydrostatic pressure, sedimentation, and shear stress, which also affect transport processes in the extracellular chemical environment. Autocrine, paracrine and endocrine substances, to which cells are responsive via specific receptors, are usually transported in vitro (and possibly in certain embryos) by convection and in vivo by a circulatory system or ciliary action. Increased inertial acceleration increases convective flow, while microgravity nearly abolishes it. In the latter case the extracellular transport of macromolecules is governed by diffusion. By making certain assumptions it is possible to calculate the Peclet number, the ratio of convective transport to diffusive transport. Some, but not all, responses of cells in vitro to modified inertial environments could be manifestations of modified extracellular convective flow. 相似文献
554.
We examine the resonant non-linear interaction in the Earth's ionosphere of two powerful high frequency radio beams with frequencies f
1 and f
2 (both larger than the plasma frequency at F2max) and wave numbers k
1 and k
2 such that a whistler mode wave can be excited with a frequency f
3 = f
1 — f
2 and a wave number k
3 = k
1 – k
2. The feasibility of an effective ground based installation, sited at low latitudes, is discussed and the field strength of the wave emerging from a 10 km wide ionospheric region illuminated by the beams is evaluated for a range of transmitted frequencies, beam orientations and plasma frequencies in the interaction region. It is suggested that the longitude dependence of the enhancement of VLF noise bands detected by the Ariel 3 satellite may be due to a non-linear interaction of this type between any two or more medium wavelength signals from areas where there is a high concentration of commercial broadcasting stations, such as the NE region of the U.S.A. 相似文献
555.
We discuss evolutionary processes in binaries where the primary becomes a red giant with a deep convective envelope before it fills its Roche lobe. Such binaries (late Case B or late Case C, if they evolve conservatively) ought to suffer drastic mass transfer, on a hydrodynamic timescale. In some circumstances this may lead to a common envelope, spiral-in, and finally either a very short-period binary or coalescence. But there appear to be other circumstances in which the outcome is an ordinary Algol, or a wide binary with a white dwarf companion as in Barium stars and some symbiotics. We try to demonstrate that stellar-wind mass loss, enhanced one or two orders of magnitude by tidal interaction with a companion, can vitally affect the approach to RLOF, and indeed may prevent RLOF in binaries with periods over 1000 d. Such mass loss is probably accompanied by angular momentum loss, by magnetic braking combined with tidal friction. The result is that it will not be easy to predict definitively the outcome of evolution in a given zero-age binary. 相似文献
556.
557.
A novel symmetrically skewed configuration for an attitude reference system (ARS) using three dynamically tuned gyros (DTGs) is developed. Simple schemes for autonomous detection and identification of a faulty DTG in real time and subsequent reconfiguration of the attitude estimation algorithm are proposed. The performance of the present configuration is shown to be better than that of configurations proposed earlier, and it is shown to have better features. It tolerates all types of failures of DTG failures, requires very simple computations, and gives less error in attitude estimate than the other configurations 相似文献
558.
The difficult problem of synthesizing an optimal regulation scheme for linear time-invariant systems, assuming an integral quadratic cost functional, when the desired output is a constant nonzero vector and when the upper time limit approaches infinity, is studied in this paper. The problem is solved by properly redefining the cost functional, so that consistence with the stability requirement is achieved. The problem of the optimal closed-loop regulation of a singleinput/single-output system has always been an interesting topic for control engineers. The most common assumption is that the cost functional to minimize be of quadratic type, with infinity as an upper limit. The classical frequency domain approach, assuming the absence of initial conditions, suggests an optimal compensator in forward loop. On the other hand, the modern time-domain approach, based on the direct application of the maximum principle, yields a closed-form solution for the case in which the desired output is zero. This paper presents results which allow one to consider from a unifying point of view the two above approaches and, in addition, suggests a stable optimal scheme which is valid for any initial state and for any desired constant output. 相似文献
559.
This paper reviews the present state of knowledge concerning the diurnal and semidiurnal variations in the galactic cosmic ray intensity. The analytical procedures that are required for extracting from the original data the desired information concerning the characteristics of the anisotropies outside the magnetosphere are described. These include corrections for atmospheric fluctuations, the determination of the amplitudes and phases of the daily variations, and their interpretation in terms of the free space anisotropies that give rise to them. The experimental results concerning the 24-h wave, including its long-term variations with periods of one and two solar cycles, and the characteristics of the total diurnal anisotropy are then discussed. The semidiurnal anisotropy is considered next. Transient anisotropies which manifest themselves as day-to-day variations, recurrence tendencies, cosmic ray storms, and diurnal variation trains, and which can introduce appreciable changes in the spectral parameters, are also of interest. The evolution of theoretical models developed to account for the diurnal and semidiurnal anisotropies, and fluctuations thereof, are then discussed in the light of the experimental results. Finally, the general features that are now well established, and the nature of the remaining problems, are summarized. 相似文献
560.
M.M. Gogoshev B.P. Komitov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1981,1(8):155-160
In this paper the latest neutral and ionospheric models of the upper Martian atmosphere, created on the Viking data are used. For the calculations of the photoelectron spectra the Hinteregger's measurements of the solar flux together with the theoretical photoelectron distribution are also used. 相似文献