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691.
T.E. Moore M.O. Chandler M.-C. Fok B.L. Giles D.C. Delcourt J.L. Horwitz C.J. Pollock 《Space Science Reviews》2001,95(1-2):555-568
The discovery of terrestrial O+ and other heavy ions in magnetospheric hot plasmas, combined with the association of energetic ionospheric outflows with geomagnetic activity, led to the conclusion that increasing geomagnetic activity is responsible for filling the magnetosphere with ionospheric plasma. Recently it has been discovered that a major source of ionospheric heavy ion plasma outflow is responsive to the earliest impact of coronal mass ejecta upon the dayside ionosphere. Thus a large increase in ionospheric outflows begins promptly during the initial phase of geomagnetic storms, and is already present during the main phase development of such storms. We hypothesize that enhancement of the internal source of plasma actually supports the transition from substorm enhancements of aurora to storm-time ring current development in the inner magnetosphere. Other planets known to have ring current-like plasmas also have substantial internal sources of plasma, notably Jupiter and Saturn. One planet having a small magnetosphere, but very little internal source of plasma, is Mercury. Observations suggest that Mercury has substorms, but are ambiguous with regard to the possibility of magnetic storms of the planet. The Messenger mission to Mercury should provide an interesting test of our hypothesis. Mercury should support at most a modest ring current if its internal plasma source is as small as is currently believed. If substantiated, this hypothesis would support a general conclusion that the magnetospheric inflationary response is a characteristic of magnetospheres with substantial internal plasma sources. We quantitatively define this hypothesis and pose it as a problem in comparative magnetospheres. 相似文献
692.
SAR ATR performance using a conditionally Gaussian model 总被引:1,自引:0,他引:1
O'Sullivan J.A. DeVore M.D. Kedia V. Miller M.I. 《IEEE transactions on aerospace and electronic systems》2001,37(1):91-108
A family of conditionally Gaussian signal models for synthetic aperture radar (SAR) imagery is presented, extending a related class of models developed for high resolution radar range profiles. This signal model is robust with respect to the variations of the complex-valued radar signals due to the coherent combination of returns from scatterers as those scatterers move through relative distances on the order of a wavelength of the transmitted signal (target speckle). The target type and the relative orientations of the sensor, target, and ground plane parameterize the conditionally Gaussian model. Based upon this model, algorithms to jointly estimate both the target type and pose are developed. Performance results for both target pose estimation and target recognition are presented for publicly released data from the MSTAR program 相似文献
693.
Comparison of two measurement fusion methods forKalman-filter-based multisensor data fusion 总被引:3,自引:0,他引:3
Currently there exist two commonly used measurement fusion methods for Kalman-filter-based multisensor data fusion. The first (Method I) simply merges the multisensor data through the observation vector of the Kalman filter, whereas the second (Method II) combines the multisensor data based on a minimum-mean-square-error criterion. This paper, based on an analysis of the fused state estimate covariances of the two measurement fusion methods, shows that the two measurement fusion methods are functionally equivalent if the sensors used for data fusion, with different and independent noise characteristics, have identical measurement matrices. Also presented are simulation results on state estimation using the two measurement fusion methods, followed by the analysis of the computational advantages of each method 相似文献
694.
气固紊流剪切流中颗粒弥散的拉格朗日模拟 总被引:1,自引:0,他引:1
本文提出了一种对于气固两相紊流剪切流中圆形固体颗粒弥散的拉格朗日拟计算方法,其中考虑了颗粒间的磁撞对流体相和颗料相的影响,应用该方法对一气固紊流剪切流场进行了模拟计算,并对有、无颗粒间磁撞情况下的模拟计算结果与Lavieville用大涡模拟方法的研究结果进行了比较,并进行了讨论。 相似文献
695.
696.
L. Ofman M. Romoli G. Noci G. Poletto J. L. Kohl R. A. Howard C. St. Cyr C. E. Deforest 《Space Science Reviews》1999,87(1-2):287-290
In recent UVCS/SOHO White Light Channel (WLC) observations we found quasi-periodic variations in the polarized brightness
(pB) in the polar coronal holes at heliocentric distances of 1.9 to 2.45 solar radii. The motivation for the observation is
the 2.5D MHD model of solar wind acceleration by nonlinear waves, that predicts compressive fluctuations in coronal holes.
In February 1998 we performed new observations using the UVCS/WLC in the coronal hole and obtained additional data. The new
data corroborate our earlier findings with higher statistical significance. The new longer observations show that the power
spectrum peaks in the 10–12 minute range. These timescales agree with EIT observations of brightness fluctuations in polar
plumes. We performed preliminary LASCO/C2 observations in an effort to further establish the coronal origin of the fluctuations.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
697.
The radio observations of Venus are reviewed and compared with theoretical microwave spectra computed for a variety of models of the Venusian environment. The models considered are (a) a CO2-N2 atmosphere, (b) an atmosphere of dust (the aeolosphere model), and (c) a cloud model with various loss mechanisms in the cloud. The effect of polarization on the surface emissivity has been included in all the computations. It is shown how the radio observations place limits upon the acceptable models, for example, the density and size of dust particles required in the aeolosphere model. It is shown how some models place severe restrictions on radar observations at short centimeter wavelengths, thereby emphasizing the importance of such experiments. These same models show that the Mariner II observations can not be interpreted in terms of surface phenomena and provide a new interpretation for the microwave phase effect.This work was supported in part by the U.S. Army, Navy and Air Force under Contract DA36-039-AMC-03200(E); and in part by the National Aeronautics and Space Administration (Grants NsG-250-62 and NsG-419). 相似文献
698.
699.
Sarles F.W. Stanley A.G. Roberge J.K. Godfrey B.W. 《IEEE transactions on aerospace and electronic systems》1973,(6):921-924
For direct measurement of the integrated radiation dose experienced in Earth synchronous orbit, p-i-n diodes were flown as radiation dosimeters on LES-6. The diode, which has a lifetime of 10-4 seconds in the intrinsic region, was originally developed as a neutron dosimeter, but can detect 1-MeV electron fluences as low as 1013 e·cm-2. Observations over three years in orbit are presented. 相似文献
700.
A direction-finding technique is presented that is capable of simultaneously estimating the arrival angles of multiple signals. Pulsed as well as continuous signals can be handled with the signal form only approximately specified. An adaptive antenna array is used as a processing device in the estimation technique. The effect of input signal and feedback loop parameters upon estimate bias is discussed. 相似文献