CFAR data fusion center with inhomogeneous receivers

Detection systems with distributed sensors and data fusion are increasingly used by surveillance systems. A system formed by N inhomogeneous constant false alarm rate (CFAR) detectors (cell-averaging (CA) and ordered statistic (OS) CFAR detectors) is studied. A recursive formulation of an algorithm that permits a fixed level of false alarms in the data fusion center is presented, to set the optimum individual threshold levels in the CFAR receivers and the optimum `K out of N' decision rule in order to maximize the total probability of detection. The algorithm also considers receivers of different quality or with different communication channel qualities connecting them with the fusion center. This procedure has been applied to several hypothetical networks with distributed CA-CFAR and OS-CFAR receivers and for Rayleigh targets and interference, and it was seen that in general the fusion decision OR rule is not always the best     

The autocorrelation of m-sequences over nonprime finitefields

Nonbinary m-sequences (maximal length sequences) for spread-spectrum communication systems that have a two-level autocorrelation are presented. The autocorrelation function of an m -sequence over the Galois field of q elements GF(q), where q=p^k, for p a prime and k an integer greater than 1, is developed and shown to be bilevel when the elements of GF(q) are expressed as elements of a vector space over the pth roots of unity     

A design procedure for the phase-controlled parallel-loadedresonant inverter

High-frequency-link power conversion and distribution based on a resonant inverter has been recently proposed. The design of several topologies is reviewed and a simple approximate design procedure is developed for the phase-controlled parallel-loaded resonant inverter. This design procedure seeks to ensure the expected benefits of resonant conversion and is verified by data from a laboratory 2.5 kVA, 20-kHz converter. A simple phasor analysis is introduced as a useful approximation for design purposes. Experimental results show that under transient conditions such as load short-circuit, a reversal of the expected commutation sequence is possible. This should be accounted for in the design of the power circuit, or prevented by the design of the controller     

平板边界层转捩的数值模拟

对于自由湍流引起的压力梯度为零的平板边界层转捩过程的数值模拟,本文提出了一个单方程湍流模型 (VL M模型),对湍流粘性系数和湍流长度尺度都进行了修正以正确引入低雷诺数效应。数值计算表明,该模型在自由来流湍流度为 0.03～8%的大范围内能正确模拟边界层转捩全过程,包括转捩区起点位置和转捩区长度、边界层内的平均及脉动参数分布等。本文还提出了上述转捩过程的时均化五阶段模型。      

Ulysses observations of a coronal origin particle event at 32° south heliographic latitutde

A remarkable streaming beam-like particle event of 60 keV-5 MeV ions and of 38–315 keV electrons has been reported previously. This event has been associated with the passage of a Coronal Mass Ejection (CME) over the Ulysses spacecraft on June 9–13, 1993. At this time, the spacecraft was located at 4.6 AU from the sun and at an heliolatitude of 32° south. It was proposed (Armstrong et al., 1994) that the particle injection source could have been of coronal origin. In this study, we analyse the solar activity during this period. We identify a region of solar radio noise storms in the corona and in particular, a flare on June 7 that presents all the required characteristics to produce the hot plasma beam observed in the interplanetary medium.     

Pioneer and Voyager observations of large-scale spatial and temporal variations in the solar wind

The Pioneer 10, Pioneer 11, and Voyager 2 spacecraft were launched in 1972, 1974, and 1977, respectively. While these three spacecraft are all at compartively low heliographic latitudes compared with Ulysses, their observation span almost two solar cycles, a range of heliocentric distances from 1 to 57 AU, and provide a unique insight into the long-term variability of the global structure of the solar wind. We examine the spatial and temporal variation of average solar wind parameters and fluxes. Our obsevations suggest that the global structure of the outer heliosphere during the declining phase of the solar cycle at heliographic latitudes up to 17.5°N was charaterized by two competing phenomena: 1) a large-scale increase of solar wind density, temperature, mass flux, dynamic pressure, kinetic energy flux, and thermal enery flux with heliographic latitude, similar to the large-scale latitudinal gradient of velocity seen in IPS observations, 2) a small-scale decrease in velocity and temperature, and increase in density near the heliospheric current sheet, which is associated with a band of low speed, low temperature, and high density solar wind similar to that observed in the inner heliosphere.     

Reconnection on open field lines ahead of coronal mass ejections

Plasma and magnetic field signatures from 29 November 1990 indicate that the Ulysses spacecraft passed through a series of interplanetary structures that were most likely formed by magnetic reconnection on open field lines ahead of a coronal mass ejection (CME). This reconnection changed the magnetic topology of the upstream region by converting normal open interplanetary magnetic field into a pair of regions: one magnetically disconnected from the Sun and the other, a tongue, connected back to the Sun at both ends. This process provides a new method for producing both heat flux dropouts and counterstreaming suprathermal electron signatures in interplanetary space. In this paper we expand upon the 29 November case study and argue that reconnection ahead of CMEs should be less common at high heliolatitudes.