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.     

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.     

Isotopic Signatures of Presolar Materials in Interplanetary Dust

Interplanetary dust particles collected in the stratosphere frequently exhibit enrichments in deuterium (D) and ¹⁵N relative to terrestrial materials. These effects are most likely due to the preservation of presolar interstellar materials. While the elevated D/H ratios probably resulted from mass fractionation during chemical reactions at very low < 100 K temperatures, the origin of the N isotopic anomalies remains unresolved. The bulk of the N-bearing material may have obtained its isotopic signatures from low temperature chemistry, but a nucleosynthetic origin is also possible. This revised version was published online in August 2006 with corrections to the Cover Date.     

Genesis on-board determination of the solar wind flow regime

Some of the objectives of the Genesis mission require the separate collection of solar wind originating in different types of solar sources. Measurements of the solar wind protons, alpha particles, and electrons are used on-board the spacecraft to determine whether the solar-wind source is most likely a coronal hole, interstream flow, or a coronal mass ejection. A simple fuzzy logic scheme operating on measurements of the proton temperature, the alpha-particle abundance, and the presence of bidirectional streaming of suprathermal electrons was developed for this purpose. Additional requirements on the algorithm include the ability to identify the passage of forward shocks, reasonable levels of hysteresis and persistence, and the ability to modify the algorithm by changes in stored constants rather than changes in the software. After a few minor adjustments, the algorithm performed well during the initial portion of the mission. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Cassini Visual And Infrared Mapping Spectrometer (Vims) Investigation

The Cassini visual and infrared mapping spectrometer (VIMS) investigation is a multidisciplinary study of the Saturnian system. Visual and near-infrared imaging spectroscopy and high-speed spectrophotometry are the observational techniques. The scope of the investigation includes the rings, the surfaces of the icy satellites and Titan, and the atmospheres of Saturn and Titan. In this paper, we will elucidate the major scientific and measurement goals of the investigation, the major characteristics of the Cassini VIMS instrument, the instrument calibration, and operation, and the results of the recent Cassini flybys of Venus and the Earth–Moon system.This revised version was published online in July 2005 with a corrected cover date.     

Polar format algorithm for bistatic SAR

Matched filtering (MF) of phase history data is a mathematically ideal but computationally expensive approach to bistatic synthetic aperture radar (SAR) image formation. Fast backprojection algorithms (BPAs) for image formation have recently been shown to give improved O(N/sup 2/ log/sub 2/N) performance. An O(N/sup 2/ log/sub 2/N) bistatic polar format algorithm (PFA) based on a bistatic far-field assumption is derived. This algorithm is a generalization of the popular PFA for monostatic SAR image formation and is highly amenable to implementation with existing monostatic image formation processors. Limits on the size of an imaged scene, analogous to those in monostatic systems, are derived for the bistatic PFA.     

UVCS/SOHO Observations of Spectral Line Profiles in Polar Coronal Holes

Ultraviolet emission line profiles have been measured on 15-29 September 1997 for H I 1216 Å, O VI 1032, 1037 Å and Mg X 625 Å in a polar coronal hole, at heliographic heights ? (in solar radii) between 1.34 and 2.0. Observations of H I 1216 Å and the O VI doublet from January 1997 for ? = 1.5 to 3.0 are provided for comparison. Mg X 625 Å is observed to have a narrow component at ? = 1.34 which accounts for only a small fraction of the observed spectral radiance, and a broad component that exists at all observed heights. The widths of O VI broad components are only slightly larger than those for H I at ? = 1.34, but are significantly larger at ? = 1.5 and much larger for ? > 1.75. In contrast, the Mg X values are less than those of H I up to 1.75 and then increase rapidly up to at least ? = 2.0, but never reach the values of O VI.     

Track-before-detect procedures for early detection of moving target from airborne radars

In this paper we present a family of track-before-detect (TBD) procedures for early detection of moving targets from airborne radars. Upon a sectorization of the coverage area, the received echoes are jointly processed in the azimuth-range-Doppler domain and in the time domain through a Viterbi-like algorithm that exploits the physically admissible target transitions between successive illuminations, in order to collect all of the energy back-scattered during the time on target (TOT). A reduced-complexity implementation is derived assuming, at the design stage, that the target does not change resolution cell during the TOT in each scan. The constant false alarm rate (CFAR) constraint is also englobed in the proposed procedures as well as the possibility of working with quantized data. Simulation results show that the proposed algorithms have good detection and tracking capabilities even for high target velocities and low quantization rates.     

高深径比TC4钛合金筒形件普旋成型有限元数值模拟

采用有限元法对特定高深径比TC4钛合金筒形件普旋成型进行了数值模拟,分析了运动轨迹、旋压道次间距和间隙对成型的影响.结果表明普旋时坯料不同部位的应力应变状态不同,采用凹曲线轨迹,间隙为3.5 mm,首道次间距为9 mm,分6道次旋压成型效果好.同时在有限元数值模拟基础上,成功旋制了高精度试验件,说明有限元模拟对旋压具有很好指导意义.     

激波风洞重模型气动力试验研究

在激波风洞上进行气动力试验时,风洞启动时巨大的冲击载荷使模型-天平受到充分的激励,从而形成惯性干扰力,并与真实气动力混杂在一起,甚至完全覆盖气动力,降低了试验精准度,使得试验模型的质量受到极大的限制。本文介绍了CARDC-dia.2米激波风洞进行大、重模型的压电天平气动力试验研究情况,包括天平设计、天平校准、惯性补偿和风洞试验等几个方面。研究结果表明:气动力试验模型质量可从过去的500g增加到8kg,模型长度可达1m。从而提高了激波风洞测力试验能力,能满足高超声速飞行器试验的需求。