基于自联想网络的发动机传感器解析余度技术

本文提出了一种基于自联想神经网络的传感器解析余度技术。在这种网络中,冗余传感器的信息被压缩、重组进入网络的第一部分,网络的第二部分将压缩信息恢复出来。基于数据融合原理,若一个传感器发生故障,其它传感器仍可提供足够的信息代替发生故障的传感器。理论分析和用于涡轴发动机的仿真结果表明,这种特殊结构的自联想网络具有良好的过滤噪声和故障信号的作用,特别适合于用作不易建模的复杂对象的传感器信号重构     

A study of some interplanetary shock wave tendencies

The configuration, and the structure of shock waves from isolated solar flares and from a series of flares are discussed and classified.An invited paper presented at STIP Workshop on Shock Waves in the Solar Corona and Interplanetary Space, 15–19 June, 1980, Smolenice, Czechoslovakia.     

Acceleration of the solar wind

In this review, we discuss critically recent research on the acceleration of the solar wind, giving emphasis to high-speed solar wind streams emanating from solar coronal holes. We first explain why thermally driven wind models constrained by solar and interplanetary observations encounter substantial difficulties in explaining high speed streams. Then, through a general discussion of energy addition to the solar wind above the coronal base, we indicate a possible resolution of these difficulties. Finally, we consider the question of what role MHD waves might play in transporting energy through the solar atmosphere and depositing it in the solar wind, and we conclude by examining, in a simple way, the specific mechanism of solar wind acceleration by Alfvén waves and the related problem of accelerating massive stellar winds with Alfvén waves.Paper presented at the IX-th Lindau Workshop The Source Region of the Solar Wind.On leave from the Auroral Observatory, Institute of Mathematical and Physical Sciences, University of Tromsø, N-9001 Tromsø, Norway.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Solar microwave bursts — A review

We review the observational and theoretical results on the physics of microwave bursts that occur in the solar atmosphere. We particularly emphasize the advances made in burst physics over the last few years with the great improvement in spatial and time resolution especially with instruments like the NRAO three element interferometer, Westerbork Synthesis Radio Telescope and more recently the Very Large Array (VLA).We review the observations on pre-flare build-up of an active region at centimeter wavelengths. In particular we discuss the observations that in addition to the active region undergoing brightness and polarization changes on time scales of the order of an hour before a flare, there can be a change of the sense of polarization of a component of the relevant active region situated at the same location as the flare, implying the emergence of a flux of reverse polarity at coronal levels. The intensity distribution of cm- bursts is similar to that of soft X-ray and hard X-ray bursts. Indeed, it appears that the flaring behavior of the Sun at cm wavelengths is similar to that of some other cosmic transients such as flare stars and X-ray bursters.We discuss three distinct phases in the evolution of cm bursts, namely, impulsive phase, post-burst phase, and gradual rise and fall. The radiation mechanism for the impulsive phase of the microwave burst is gyrosynchrotron emission from mildly relativistic electrons that are accelerated near the energy release site and spiral in the strong magnetic field in the low corona. The details of the velocity distribution function of the energetic electrons and its time evolution are not known. We review the spectral characteristics for two kinds of velocity distribution, e.g., Maxwellian and Maxwellian with a power law tail for the energetic electrons. In the post-burst phase the energetic electrons are gradually thermalized. The thermal plasma released in the energy release region as well as the expanded parts of the overheated upper chromosphere may alter the emission mechanism. Thus, in the post-burst phase, depending on the average density and temperature of the thermal plasma, the emission mechanism may change from gyrosynchrotron to collisional bremsstrahlung from a thermal plasma. The gradual rise and fall (GFR) burst represents the heating of a flare plasma to temperatures of the order of 10⁶ K, in association with a flare or an X-ray transient following a filament disruption.We discuss the flux density spectra of centimeter bursts. The great majority of the bursts have a single spectral maximum, commonly around 6 cm- The U-shaped signature sometimes found in cm-dcm burst spectrum of large bursts is believed to a be a reflection of only the fact that there are two different sources of burst radiation, one for cm- and the other for dcm-, with different electron energy distributions and different magnetic fields.Observations of fine structures with temporal resolutionof 10–100 ms in the intensity profiles of cm- bursts are described. The existence of such fine time structures imply brightness temperatures in burst sources of order 10¹⁵ K; their interpretation in terms of gyrosynchrotron measuring or the coherent interaction of upper hybrid waves excited by percipitating electron beams in a flaring loop is discussed.High spatial resolution observations (a few seconds of arc to 1 arc) are discussed, with special reference to the one- and two-dimensional maps of cm burst sources. The dominance of one sense of circular polarization in some weak 6 cm bursts and its interpretation in terms of energetic electrons confined in an asymmetric magnetic loop is discussed. Two-dimensional snapshot maps obtained with the VLA show that multi-peak impulsive 6 cm burst phase radiation originates from several arcades of loops and that the burst source often occupies a substantial portion of the flaring loop, and is not confined strictly to the top of the loop. This phenomenon is interpreted in terms of the trapping of energetic electrons due to anomalous doppler resonance instability and the characteristic scale length of the magnetic field variation along the loop. The VLA observations also indicate that the onset of the impulsive phase of a 6 cm burst can be associated with the appearance of a new system of loops. The presence of two loop systems with opposite polarities or a quadrupole field configuration is reminiscent of flare models in which a current sheet develops in the interface between two closed loops.We provide an extensive review of the emission and absorption processes in thermal and non-thermal velocity distributions. Unlike the thermal plasma where absorption and emission are inter-related through Kirchoff's law, the radiation emitted from a small population of non-thermal electrons can be reabsorbed from the same electrons (self-absorption) or from the background (thermal) electrons through gyro-resonance absorption, and free-free absorption. We also suggest that the non-thermal electrons can be unstable and these instabilities can be the source of very high brightness temperature, fine structure ( 10 ms) pulsations.Finally in the last part of this review we present several microwave burst models-the magnetic trap model, the two-component model, thermal model and the flaring loop model and give a critical discussion of the strength and weakness of these models.     

X-rays from quasars and active galaxies

We review some of the most important theoretical ideas and observations for quasars and the nuclei of active galaxies, and suggest areas of future research. Emphasis is on the nature of the power source, the radiation processes, and the mechanism for formation and collimation of jets. Phenomena that produce X-rays are of particular concern. Particular topics discussed are the observed and expected time variability, the gas supply mechanisms and luminosity evolution, thermal and nonthermal radiation processes, observed and theoretical spectra, criteria for thermalization of electrons and ions, effects of electron-positron pairs on relativistic plasmas, hydrodynamic, electrodynamic and inertial methods for producing and confining jets. We conclude with a list of needed observations.Based on a lecture given at the Goddard Workshop on X-ray Astronomy (October 1981).     

Magnetic energy storage and conversion in the solar atmosphere

A review of the theoretical problems associated with preflare magnetic energy storage and conversion is presented. The review consists of three parts; preflare magnetic energy storage, magnetic energy conversion mechanisms, and preflare triggers. In Section 2, the relationship between magnetic energy storage and the electrodynamic coupling of the solar atmosphere is developed. By accounting for the electrodynamic coupling of the solar atmosphere, we are able to examine the fundamental problems associated with the concept of in situ versus remote magnetic-energy storage. Furthermore, this approach permits us to distinguish between the roles of local and global parameters in the storage process.Section 3 is focused on the conversion mechanisms that can explain, in principle, the rapid energy release of a flare. In addition, we discuss how electrodynamic coupling eventually dictates which mechanism(s) is responsible for releasing the stored magnetic energy, and how the global coupling dictates the final evolution of the relevant mechanism. Section 4 examines preflare triggers and Section 5, we examine the most promising directions for future research into the problem of magnetic-energy storage and conversion of the Sun.     

The plasma mantle: Composition and other characteristics observed by means of the PROGNOZ-7 satellite

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.     

GTD Terrain Reflection Model Applied to ILS Glide Scope

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.     

Asymptotically Stable Motions of a Gyro in a Spinning Vehicle

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.     

Eliminating Reference Loop Phase Shift in Adaptive Arrays

Adaptive array processors utilizing the Widrow LMS algroithm with an internally generated reference signal have been shown to be subject to weight cycling caused by phase shift in the reference extracting loop. Adaptive compensation schemes that eliminate the reference loop phase shift are suggested here. Two such schemes are proposed. They differ in the amount of hardware complexity needed as well as in the rate at which each one eliminates the phase shift. Computer calculations are used to compare the rates of convergence of the two schemes.