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91.
V. A. Grigoriev 《Space Science Reviews》1989,49(1-2):151-155
The scintillation time-of-flight triggering system of the Gamma-1 gamma-ray telescope provides for both the time-of-flight discrimination and the pulse height discrimination of the secondary particles. The paper gives some experimental results for energy dependence of the instrument efficiency in 30–300 MeV energy range for different trigger logics. 相似文献
92.
Krishna M. V. Apparao 《Space Science Reviews》1994,69(3-4):255-329
Observations of X-ray emission from Be star/X-ray binaries are reviewed. Some optical characteristics of these binaries are also presented. Theoretical aspects pertaining to the X-ray emissions are given. 相似文献
93.
A brief summary of the main results of magnetospheric ion composition measurements in general is first presented. PROGNOZ-7 measurements in the nightside plasma mantle are then described and analyzed. Some of the results are the following: In the nightside mantle not too far from midnight the properties of the mantle are sometimes consistent with the open magnetosphere model. However during most magnetic storm situations O+ ions appear in the mantle in large proportions and with high energies. The acceleration process affecting the ions has been found in several cases to give equal amounts of energy to all ions independent of mass. Along the flanks of the magnetosphere the flow of the plasma is often low or absent. The O+ content is high (up to 20%) and the energy spectrum of both ions and electrons may be very hot, even up to the level of the ring current plasma in the keV range.The O+ content in the plasma mantle is positively correlated with the magnetospheric activity level. The mantle, however, does not appear to be the dominating source for the storm time ring current. Direct acceleration of ionospheric ions onto the closed field lines of the plasma sheet and ring current is most likely the main source. The magnetopause on the nightside and along the flanks of the magnetosphere appears to be a fairly solid boundary for mantle ions of ionospheric origin. This is especially evident during periods with high geomagnetic activity, when the mantle is associated with fairly strong fluxes of O+ ions.An interesting observation in most of the mantle passages during geomagnetically disturbed periods is the occurrence of intense, magnetosheath like, regions deep inside the mantle. In some cases these regions with strong antisunward flow and with predominant magnetosheath ion composition was observed in the innermost part of the mantle, i.e. marking a boundary region between the lobe and the mantle. These magnetosheath penetration events are usually associated with strong fluxes of accelerated ionospheric ions in nearby parts of the mantle. Evanescent penetration regions with much reduced flow properties are frequently observed in the flank mantle. 相似文献
94.
An analysis of the motion of a single-axis rate gyroscope mounted in a space vehicle which is spinning with uncertain constant angular velocity xz about the spin axis of the gyro is presented. The nonlinearity in the equation of motion of the gimbal is retained. Using the Lyapunov approach, regions are obtained in the k-xz plane where k is the torsional spring constant, for asymptotic stability and for global asymptotic stability, and an estimate of the region of stability in state space is presented. Analytical relations for the selection of the gyro parameters are derived. 相似文献
95.
J. P. Cox J. C. Wheeler C. J. Hansen D. S. King A. N. Cox S. W. Hodson 《Space Science Reviews》1980,27(3-4):529-535
The radial pulsations of very luminous, low-mass models (L/M 104, solar units), which are possible representatives of the R CrB stars, have been examined. These pulsations are extremely nonadiabatic. We find that there are in some cases at least one extra (strange) mode which makes interpretation difficult. The blue instability edges are also peculiar, in that there is an abrupt excursion of the blue edge to the blue for L/M sufficiently large. The range of periods of the model encompasses observed periods of the Cepheid-like pulsations of actual R CrB stars. 相似文献
96.
Leith E.N. Friesem A.A. Funkhouser A.T. 《IEEE transactions on aerospace and electronic systems》1970,(6):832-840
Coherent optical systems, because of their basic similarity to coherent radar systems, can be used to simulate many of the characteristics of the latter. This paper discusses the use of a coherent optical system for the simulation of the range and azimuth ambiguities that sometimes occur in radar systems. The optical configurations for implementing these simulations are described in detail, and extensive experimental results are presented. 相似文献
97.
Simplified analysis of PWM converters using model of PWM switch.II. Discontinuous conduction mode 总被引:1,自引:0,他引:1
For pt.I see ibid., vol.26, no.3, p.490-6 (1990). According to the method of state-space averaging, when a pulsewidth modulation (PWM) converter enters discontinuous conduction mode (DCM), the inductor current state is lost from the average model of the converter. It is shown that there is neither theoretical nor experimental justification for the disappearance of the inductor state as claimed by the method of state-space averaging. For example, when the model of the PWM switch in DCM is substituted in the buck, boost, or buck-boost converter while the inductor is left intact, the average model has two poles: the first pole f p1 agrees with the single pole of state-space averaging, while the second pole f p2 occurs in the range f p2⩾F s/π. It is shown that the right-half plane zeros present in the control-to-output transfer functions of the boost, buck-boost, and Cuk converters in continuous conduction mode are also present in discontinuous conduction mode 相似文献
98.
99.
Dabbous T.E. Ahmed N.U. McMillan J.C. Liang D.F. 《IEEE transactions on aerospace and electronic systems》1988,24(1):85-102
A refined stochastic model for the errors of the Loran-C radio navigation aid is described, and it is shown how this model can be used to improve the performance of integrated navigation systems. In addition to the usual propagation errors, Loran-C time of arrival measurements are occasionally plagued with sudden intermittent errors of a particular magnitude and caused by receiver cycle selection errors. These result in sudden large jumps in the calculated position solution. The Loran-C error has been modeled as the sum of a diffusion process, representing the normal propagating errors, and a pure jump process of Poisson type, representing the cycle selection errors. A simple integrated navigation system is then described, based on the Loran-C model and the standard dead reckoning (heading and speed) system model. Assuming that the observed process is governed by a linear stochastic difference equation, a recursive linear unbiased minimum variance filter is developed, from which the Loran-C and dead reckoning errors, and hence position and velocity, can be estimated 相似文献
100.
GTD Terrain Reflection Model Applied to ILS Glide Scope 总被引:1,自引:0,他引:1
Luebbers R. Ungvichian V. Mitchell L. 《IEEE transactions on aerospace and electronic systems》1982,(1):11-20
The capability of calculating the reflection of electromagnetic signals from uneven terrain has many applications. One of these is the determination of instrument landing system (ILS) glide slope performance. For this application the wavelength is approximately 1 m, incidence angles are usually near grazing, and the fields are horizontally polarized, so that gross irregularities such as dropoffs and hills are more important than surface roughness. Past approaches used to calculate the ground reflections for this application have been three-dimensional physical optics models which were very cumbersome and time consuming and which neglected important diffraction and shadowing phenomenon; a two-dimensional physical optics model which was faster than the three-dimensional models but ignored many shadowing and transverse terrain variation effects; and a half-plane diffraction model which is applicable only to a specified type of terrain geometry. In this paper a terrain reflection model based on the geometrical theory of diffraction (GTD) is described which can accommodate any piecewise linear terrain profile, requires less computer time than the physical optics models, is capable of including transverse terrain effects, and determines the reflected fields with all important diffraction and blockage effects included. 相似文献