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921.
This paper considers the effect of the rocket exhaust turbulence and scattering within the surrounding medium upon the propagation characteristics of incident electromagnetic waves. The exhaust is represented by a cylindrical plasma beam, diffusing through the surrounding medium. The equations of propagation of EM waves are derived for both TE and TM modes. By using a quasi-linear perturbation technique the exhaust is further separated into an inner homogeneous cylindrical plasma beam, and an outer conical inhomogeneous turbulent region. The isotropic change in the temperature of the outer region and its effects on the fluctuations in the density of electrons, collision frequency, and plasma index of refraction are analyzed in detail. It is found that the exhaust turbulence and scattering effects produce linear fluctuations in the E and H fields computed from the exhaust inner region effect. The equations of this paper can be used in the prediction of the radar cross sections and the attenuation of microwaves by rocket exhaust plumes. 相似文献
922.
A Loran-C Receiver is used as an example to show how an analog system could be converted to a digital one to take advantage of the expanding integrated circuit technology. The digital equivalents of the analog servo elements are described. Criteria for the design of a phase-tracking servomechanism is developed in detail. The Loran performance requirements are used to illustrate their application. The noise performance of a critically damped Type II servomechanism is derived in detail. Since the system will be employed in aircraft, tracking velocity becomes an important consideration. An analysis is made showing that an adaptive control is desirable. 相似文献
923.
924.
Krishnaswamy P. B. Fegley K. A. 《IEEE transactions on aerospace and electronic systems》1965,(1):29-38
The human centrifuge is used to train pilots and astronauts for flights where they are subject to large accelerations. This paper deals with the problems of simulating such linear accelerations with a rotating device and presents suitable means of reducing undesirable simulation error. The advantages of using three gimbals rather than the usual two are considered. Numerical results illustrate the problems of simulation and the improvement achieved by the use of a third gimbal. 相似文献
925.
A review is given of the present state of the problem of upper atmospheric emission, in relation to the processes which take
place in that region.
Translated by the Express Translation Service, Wimbledon, London, W-2. 相似文献
926.
M Schwarzenberg P Pippia M A Meloni G Cossu M Cogoli-Greuter A Cogoli 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1999,24(6):793-800
In this paper we discuss the effect of microgravity on T cells and we present the data of studies with two new machines for 0 g simulations. Several experiments in space show that mitogenic T cell activation is lost at 0 g. Immunocytochemistry indicates that such effect is associated with changes of the cytoskeleton. Biochemical studies suggest that the lack of expression of the interleukin-2 receptor is one of the major causes of the loss of activity. In fact, interleukin-2 is the third signal required for full activation. In order to deepen our investigations we are now working with the free-fall machine, FFM, invented by D. Mesland, and with the random positioning machine, RPM, or three-dimensional clinostat, developed by T. Hoson. The FFM produces periods of free-fall lasting approximately 800 ms followed by bounces of 15-30 g lasting 45-60 ms. The RPM eliminates the effect of gravity by rotating biological specimen randomly around two orthogonal axes. While the FFM failed to reproduce the results obtained with T lymphocytes in space, the data from the RPM are in good agreement with those in real microgravity. In fact, the inhibition of the mitotic index in the RPM is 89% compared to static controls. The RPM (as the FFM) can carry markedly larger specimen than the fast rotating clinostat and thus allows to conduct comprehensive studies to select suitable biological objects for further investigations in space. 相似文献
927.
The dynamics of the rotational motion of a satellite, moving in the central Newtonian force field under the influence of gravitational and aerodynamic torques, is investigated. The paper proposes a method for determining all equilibrium positions (equilibrium orientations) of a satellite in the orbital coordinate system for specified values of aerodynamic torque and the major central moments of inertia; the sufficient conditions for their existence are obtained. For each equilibrium orientation the sufficient stability conditions are obtained using the generalized energy integral as the Lyapunov function. The detailed numerical analysis of the regions where the stability conditions of the equilibrium positions are satisfied is carried out depending on four dimensionless parameters of the problem. It is shown that, in the general case, the number of satellite’s equilibrium positions, for which the sufficient stability conditions are satisfied, varies from 4 to 2 with an increase in the value of the aerodynamic torque magnitude. 相似文献
928.
J. B. Blake B. H. Mauk D. N. Baker P. Carranza J. H. Clemmons J. Craft W. R. Crain A. Crew Y. Dotan J. F. Fennell R. H. Friedel L. M. Friesen F. Fuentes R. Galvan C. Ibscher A. Jaynes N. Katz M. Lalic A. Y. Lin D. M. Mabry T. Nguyen C. Pancratz M. Redding G. D. Reeves S. Smith H. E. Spence J. Westlake 《Space Science Reviews》2016,199(1-4):309-329
929.
Prateek R. Srivastava Sneha A. Gokani Ajeet K. Maurya Rajesh Singh Sushil Kumar B. Veenadhari R. Selvakumaran Abhay K. Singh Devendraa Siingh Janos Lichtenberger 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
One-to-one relation with its causative lightning discharges and propagation features of night-time whistlers recorded at low-latitude station, Allahabad (geomag. lat. 16.05°N, L = 1.08), India, from continuous observations made during 1–7 April, 2011 have been studied. The whistler observations were made using the Automatic Whistler Detector (AWD) system and AWESOME VLF receiver. The causative lightning strikes of whistlers were checked in data provided by World-Wide Lightning Location Network (WWLLN). A total of 32 whistlers were observed out of which 23 were correlated with their causative lightnings in and around the conjugate location (geom. lat. 9.87°S) of Allahabad. A multi-flash whistler is also observed on 1 April with dispersions 15.3, 17.5 and 13.6 s1/2. About 70% (23 out of 32) whistlers were correlated with the WWLLN detected causative lightnings in the conjugate region which supports the ducted mode of propagation at low latitude. The multi-flash and short whistlers also propagated most likely in the ducted mode to this station. 相似文献
930.
A. A. Abdyushev 《Russian Aeronautics (Iz VUZ)》2013,56(2):117-125
The equilibrium between the rods and panels in the ribbed shells is considered based on the total system of structural mechanics equations as applied to a discrete model. Also shown is an approach to solving the problems that permits the stiffness matrix of shear panels to be obtained with regard for the equilibrium along the boundary with rods. The connection with the standard hybrid method of constructing stiffness matrices is indicated. The solutions for separate elements and examples illustrating the approach being proposed are presented. 相似文献