Two sources of magnetosheath ions observed by Cluster in the mid-altitude polar cusp

Double cusps have been observed on a few occasions by polar orbiting spacecraft and ground-based observatories. The four Cluster spacecraft observed two distinct regions, showing characteristics of a double cusp, during a mid-altitude cusp pass on 7 August 2004. The Wind spacecraft detected a southward turning of the Interplanetary Magnetic Field (IMF) at the beginning of the cusp crossings and IMF–Bz stayed negative throughout. Cluster 4 observed a high energy step in the ion precipitation around 1 keV on the equatorward side of the cusp and a dense ion population in the cusp centre. Cluster 1, entering the cusp around 1 min later, observed only a partial ion dispersion with a low energy cutoff reaching 100 eV, together with the dense ion population in the cusp centre. About 9 min later, Cluster 3 entered the cusp and observed full ion dispersion from a few keV down to around 50 eV, together with the dense ion population in the centre of the cusp. The ion flow was directed poleward and eastward in the step/dispersion, whereas in the centre of the cusp the flow was directed poleward and westward. In addition the altitude of the source region of ion injection in the step/dispersion was found 50% larger than in the cusp centre. This event could be explained by the onset of dayside reconnection when the IMF turned southward. The step would be the first signature of component reconnection near the subsolar point, and the injection in the centre of the cusp a result of anti-parallel reconnection in the northern dusk side of the cusp. A three-dimensional magnetohydrodynamic (MHD) simulation is used to display the topology of the magnetic field and locate the sources of the ions during the event.     

Training, career development and registration for safety criticalsoftware systems specialists

A career development program for information systems practitioners currently being used widely by employers in the UK and now becoming available in North America is described. The program, called the Professional Development Scheme (PDS), was developed by the British Computer Society to address the lack of structure and quality control generally present in the way computing professionals were being trained. The performance standards underpinning the program (The British Computer Society Industry Structure Model) have been thoroughly updated and now include material specific to the development, maintenance, and management of software for safety-critical applications. The use of the program for this purpose and potential developments in the field of training and registration for safety-critical software specialists are discussed     

The response of the high-latitude thermosphere to geomagnetic substorms

Enhanced ionization and electric fields associated with geomagnetic substorms lead to time-varying momentum (ion drag) and heat (Joule dissipation) sources in the high latitude thermosphere. These momentum and heat sources, in turn, cause changes in the structure of the wind, pressure and temperature fields, and, in addition, provide a mechanism for the generation of atmospheric gravity waves. We have developed a model which has been used to simulate, on a spatial scale of tens of kilometers, the response of the high latitude thermosphere to these momentum and heat sources, which constitute a major factor in the coupling between the magnetosphere, the ionosphere and the upper atmosphere. Simulations reported herein indicate that, because the coupling between ions and neutrals is highly dependent on the neutral-ion collision frequency, the response of the neutral atmosphere varies, not only as a function of total ionization, but also as a function of the details of the electron density profile.     

Models of the structure of the atmosphere of Venus from the surface to 100 kilometers altitude

From a critical comparison and synthesis of data from the four Pioneer Venus Probes, the Pioneer Venus Orbiter, and the Venera 10, 12, and 13 landers, models of the lower and middle atmosphere of Venus are derived. The models are consistent with the data sets within the measurement uncertainties and established variability of the atmosphere. The models represent the observed variations of state properties with latitude, and preserve the observed static stability. The rationale and the approach used to derive the models are discussed, and the remaining uncertainties are estimated.     

Modulation of dayside ion and neutral distributions at Venus: Evidence of direct and indirect solar energy inputs

In-situ measurements of ion and neutral composition and temperature across the dayside of Venus during 1979–1980 exhibit long and short-term changes attributed to solar variations. Following solar maximum, dayside concentrations of CO⁺ and the neutral gas temperature are relatively smoothly modulated with a 28-day cycle reasonably matching that of the solar F_10.7 and EUV fluxes. Measurements some 6–8 months earlier show less pronounced and more irregular modulation, and short-term day-to-day fluctuations in the ions and neutrals are relatively more conspicuous than in the later period. During the earlier period, the solar wind at Venu exhibits relatively large velocity enhancements, which appear to be consistent with differences in solar coronal behavior during the two periods. It is suggested that through the solar wind variations and associated changes in the draping of the interplanetary magnetic field about the dayside, fluctuating patterns of joule heating may occur, producing the observed short term ion and neutral variations. This indirect energy effect, if verified, presents a complication for quantitatively analyzing the modulation in neutral temperature and ion concentration produced by changes in direct EUV radiation.     

8. The thermal balance of the atmosphere of venus

Current knowledge of the temperature structure of the atmosphere of Venus is briefly summarized. The principal features to be explained are the high surface temperature, the small horizontal temperature contrasts near the cloud tops in the presence of strong apparent motions, and the low value of the exospheric temperature. In order to understand the role of radiative and dynamical processes in maintaining the thermal balance of the atmosphere, a great deal of additional data on the global temperature structure, solar and thermal radiation fields, structure and optical properties of the clouds, and circulation of the atmosphere are needed. The ability of the Pioneer Venus Orbiter and Multiprobe Missions to provide these data is indicated.     

Equatorial cloud properties on Venus from pioneer orbiter infrared observations

Infrared observations of Venus from the Pioneer Orbiter have been used to study the limb darkening properties of the cloud tops at wavelengths and spatial resolutions not previously attained. The preliminary results show evidence for an extensive haze feature over the equatorial morning terminator and for small amounts of a far-infrared absorber concentrated near local noon, also near the equator. The evidence for these features is reviewed and their possible origins briefly discussed.     

False alarm analysis of the envelope detection GO-CFAR processor

The greatest of constant false alarm rate processor (GO CFAR) is a useful architecture for adaptively setting a radar detection threshold in the presence of clutter edges. The GO CFAR input is often the envelope detected in-phase (I) and quadrature (Q) channels of the baseband signal (x_e=√(I²+Q²)). This envelope detection can also be approximated using x=a max{|I|,|Q|}+b min{|I|,|Q|} which requires less complex hardware (a and b are simple multiplying coefficients). The envelope GO CFAR processor and several envelope approximation GO CFAR processors are compared in terms of the probability of false alarm (PFA) performance. Closed-form expressions which describe the PFA performance are given and their accuracy evaluated. It is shown that for all cases, the PFA is proportional to the number of reference cells n for small threshold multiplier T and inversely proportional to n for large T. A region of intersection occurs where the PFA is the same for two different values of n. For example, at T'=1.68 in the |I|+|Q| GO CFAR (a=1, b=1) the PFA for n=1 is equal to the optimal n=∞ fixed-threshold PFA (PFA=0.112)     

快速反应部队对于台海作战的影响——台湾观点

随着中国集中于军事现代化，解放军越来越重视如何在局部高技术条件下获得决定性作战优势，特别是美军近年来在历次区域性冲突中展现的快速部署和战场掌握能力更是让意图借助速战速决避免美国必然的介入，为了能够在短时间内消除台湾的有抵抗和作战意志，解放军显然须要另辟蹊径才能够在第一时间直捣黄龙，避免陷入传统军事作战的泥沼。