On adaptive multiband signal detection with the SMI algorithm

In a nonstationary and/or nonhomogeneous interference environment, an adaptive system for target detection may suffer a severe performance degradation due to the lack of a sufficient amount of data from which the system can learn (estimate) the statistics of the environment. The detection performance of an adaptive system, which employs a frequency diversity (multiband) signaling waveform and a multiband sample matrix inversion algorithm (SMI), is analyzed. By comparison with the corresponding single-band system under the chosen system constraint, it is shown that the multiband system can significantly outperform the single band when the amount of data available from a single frequency band is severely limited by the environment     

Small-Signal Model for the Series Resonant Converter

The results of a previous discrete-time model of the series resonant dc-dc converter are reviewed and from these a small signal dynamic model is derived. This model is valid for low frequencies and is based on the modulation of the diode conduction angle for control. The basic converter is modeled separately from its output filter to facilitate the use of these results for design purposes. Experimental results are presented.     

Late Stages of Stellar Evolution

A large fraction of ISO observing time was used to study the late stages of stellar evolution. Many molecular and solid state features, including crystalline silicates and the rotational lines of water vapour, were detected for the first time in the spectra of (post-)Asymptotic Giant Branch (AGB) stars. Their analysis has greatly improved our knowledge of stellar atmospheres and circumstellar environments. A surprising number of objects, particularly young planetary nebulae with Wolf-Rayet (WR) central stars, were found to exhibit emission features in their ISO spectra that are characteristic of both oxygen-rich and carbon-rich dust species, while far-IR observations of the PDR around NGC 7027 led to the first detections of the rotational line spectra of CH and CH⁺. Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, The Netherlands, and the United Kingdom), and with the participation of ISAS and NASA.     

Differential flank growth.

With the mathematical basis for the precise analysis of developmental processes in plants, the patterns of growth in phototropic and gravitropic responses have become better understood. A detailed temporal and spatial quantification of a growth process is an important tool for evaluating hypotheses about the underlying physiological mechanisms. Studies of growth rates and curvature show that the original Cholodny-Went hypothesis cannot explain the complex growth patterns during tropic responses of shoots and roots. In addition, regulating factors other than the lateral redistribution of hormones must be taken into account. Electrophysiological studies on roots led to a modification of the Cholodny-Went hypothesis in that redistributions of bioelectrical activities are observed.     

A method for improving extended Kalman filter performance forangle-only passive ranging

A relatively simple method is presented which eliminates previously reported (Oct. 1985) erratic estimation performance associated with Cartesian formulations of the extended Kalman filter (EKF) for the 2D angle-only emitter location problem. The technique is based on an initialization procedure which combines a priori probability density function (pdf) information with single measurement a posteriori pdf information in a manner which is more efficient than the EKF. Simulation results are presented which demonstrate the utility of the technique as compared with a previously offered modified gain EKF     

The Electron Beam Instrument (F6) on Freja

The Electron Beam Instrument (F6) onFreja is the first attempt to apply the electron drift technique in a region of large ambient magnetic fields. The paper describes the operational principles, the technical realization, and the difficulties encountered in the derivation of the electric fields.     

Field formation around negatively biased solar arrays in the LEO-plasma

Heavy emission caused by impacting plasma ions results in a fast discharging effect of the initially large surface potentials on the dielectric solar cells. This eventually counteracts the energization process of the plasma ions to the cover glasses and leaves no significant electric fields. Thus, with an existing thermal plasma, electrons are again able to reach dielectric surfaces. Strong localized electric fields of the order of several 10 kV/cm form near the interconnector-cover glass interface.     

EUROPEAN NETWORK FOR THE NUMERICAL SIMULATION OF SPACE PLASMAS

The Cluster mission of the European Space Agency (ESA) will allow, for the first time three-dimensional measurements in key regions of the Earth's magnetosphere to be carried out. The European Numerical Simulation Network (ENSN) aims at providing a theoretical support to the mission. We describe the achievements of the ENSN during its first period of activity 1991–1994, during which the network was funded by the European Union. In particular, the ENSN has set up (i) thematic Working Groups on the prime scientific goals of the mission, (ii) a code development Working Group to develop numerical simulation codes specifically adapted to studying magnetospheric boundaries and the corresponding scale mixing, and (iii) software models of Cluster instruments to test in a numerical simulation what the set of four instruments will measure.