Sensor validation using hardware-based on-line learning neuralnetworks

The objective of this document Is to show the capabilities of parallel hardware-based on-line learning neural networks (NNs). This specific application is related to an on-line estimation problem for sensor validation purposes. Neural-network-based microprocessors are starting to be commercially available. However, most of them feature a learning performed with the classic back-propagation algorithm (BPA). To overcome this lack of flexibility a customized motherboard with transputers was implemented for this investigation, The extended BPA (EBPA), a modified and more effective BPA, was used for the on-line learning, These parallel hardware-based neural architectures were used to implement a sensor failure detection, identification, and accommodation scheme in the model of a night control system assumed to be without physical redundancy in the sensory capabilities. The results of this study demonstrate the potential for these neural schemes for implementation in actual flight control systems of modern high performance aircraft, taking advantage of the characteristics of the extended back-propagation along with the parallel computation capabilities of NN customized hardware     

Information security: from reference monitors to wrappers

Information system security has turned out to be much more challenging than at first thought. In the 1980s, a great deal of energy was expended in an attempt to create a broad market of security-enhanced systems. This market, however, did not develop, and most computer systems today include only rudimentary security mechanisms. New technologies, such as extensible systems and security wrappers, hold promise to reintroduce security as an effective and ubiquitous system service     

Hydrodynamic modeling of mass loss from cataclysmic variable secondaries

Results of detailed computer simulations of mass loss from a cataclysmic variable secondary are presented. The calculations involve solution of the nonlinear hydrodynamical equations of stellar structure under varying degrees of approximation in an attempt to determine stability of the mass loss process. For comparison with previous theoretical studies dynamical sequences were computed assuming spherically symmetric mass loss from the secondary. The assumption of spherical symmetry is very poor since nearly all of the transferred material is lost within a small region about the inner Lagrangian point. Dynamical sequences treating only the region near the Lagrangian point were constructed in a manner consistent with the assumption of Roche geometry. Finally the effects of mass flow nonorthogonal to the Roche equipotential surfaces were treated in a very simple way. The last generalization produces stable mass loss in a model which was unstable for the less realistic approximation schemes. The finding of stable mass transfer implies that instability of the secondary star is not the mechanism leading to cataclysmic variable outbursts. This conclusion is consistent with published observations of dwarf novae made just prior to outburst.A detailed account of this study will be published elsewhere.Now at National Center for Atmospheric Research, P. O. Box 3000, Boulder, CO 80307     

The Impact of Integrated Electronics on Aerospace Avionic Subsystems

Integrated electronics or microelectronics is one of today's major technical frontiers. Possibilities offered to the designer of avionics subsystems, for aerospace vehicles, by these techniques, are almost limitless, from the point of view of performance capabilities as well as reliability and maintainability. Application will change current engineering practices in avionics design. Some changes will be easy; in others, problems will appear. This paper discusses these changes, indicating potential gains to be expected as well as potential problem areas. The rise in the application of integrated electronics is expected to be high for the next 10 to 15 years. By 1980, integrated circuitry will have largely replaced the use of discrete components, and the rate-of-increase-of-application curves will level off.     

The use of model-based test requirements throughout the productlife cycle

Test requirements, which are generally collected in multiple disparate formats throughout the life cycle of an electronic product, could be used in various applications that reduce test and development cycle times and increase the confidence in the final test program. Unfortunately, test requirements are seldom captured in a consistent format that may be processed by a computer, thus eliminating the possibility of using such requirements in an engineering application. Additionally, such an approach disallows test requirements captured in one segment of the product life cycle to be reused in subsequent life cycle stages. This paper describes a model-based methodology, specifically the Test Requirements Model (TeRM), which can be shown to facilitate the transfer of test-related product information between various stages of the life cycle. This transportability, in conjunction with an exchange format that can be processed by a computer, permits test requirement information to support value-added applications in the engineering process throughout the life cycle of a product     

An adventure in technology and marketing: a personal account. Tripto the Orient via the Moon

Early in the sixties when President Kennedy announced the goal to land a man on the Moon and return him safely to Earth, there was no way to gauge, accurately and reliably, the millions of pounds of fuel and oxidizer in the proposed rocket. Late in the sixties, when Phillips Petroleum and Marathon Oil contracted to provide large-scale, long term, ocean transport of Liquefied Natural Gas, no system existed to satisfactorily gauge this stream of high value cargoes for commercial transactions. The adventure in solving these related problems led to a worldwide market for LNG Custody Transfer Systems, a successful transfer of technology from a NASA program to commercial use     

In-Situ CHAMP Observation of Ionosphere-Thermosphere Coupling

The coupling between the ionised plasma and the neutral thermospheric particles plays an important role for the dynamics of the upper atmosphere. Significant progress in understanding the related processes has been achieved thanks to the availability of continuous accurate measurements of thermospheric parameters like mass density and wind by high resolution accelerometers on board the satellites CHAMP and GRACE. Here we present some examples of ionosphere-thermosphere coupling where CHAMP observations contributed considerably to their interpretation. We start with the derived properties of the thermosphere at altitudes around 400 km. A new aspect is the significant control of the geomagnetic field geometry on thermospheric features. Phenomena discussed in some depths are the equatorial mass density anomaly, the cusp-related mass density enhancement and the thermospheric response to magnetospheric substorms. Here we consider both the effect on the density and on the wind. A?long predicted process is the wind-driven ionospheric F region dynamo. The high-resolution magnetic field measurements of CHAMP enabled for the first time a systematic study of that phenomenon considering longitudinal, local time, seasonal and solar flux dependences. Some open issues that require further investigations are mentioned at the end.     

Alice: The rosetta Ultraviolet Imaging Spectrograph

We describe the design, performance and scientific objectives of the NASA-funded ALICE instrument aboard the ESA Rosetta asteroid flyby/comet rendezvous mission. ALICE is a lightweight, low-power, and low-cost imaging spectrograph optimized for cometary far-ultraviolet (FUV) spectroscopy. It will be the first UV spectrograph to study a comet at close range. It is designed to obtain spatially-resolved spectra of Rosetta mission targets in the 700–2050 Å spectral band with a spectral resolution between 8 Å and 12 Å for extended sources that fill its ～0.05^ × 6.0^ field-of-view. ALICE employs an off-axis telescope feeding a 0.15-m normal incidence Rowland circle spectrograph with a toroidal concave holographic reflection grating. The microchannel plate detector utilizes dual solar-blind opaque photocathodes (KBr and CsI) and employs a two-dimensional delay-line readout array. The instrument is controlled by an internal microprocessor. During the prime Rosetta mission, ALICE will characterize comet 67P/Churyumov-Gerasimenko's coma, its nucleus, and nucleus/coma coupling; during cruise to the comet, ALICE will make observations of the mission's two asteroid flyby targets and of Mars, its moons, and of Earth's moon. ALICE has already successfully completed the in-flight commissioning phase and is operating well in flight. It has been characterized in flight with stellar flux calibrations, observations of the Moon during the first Earth fly-by, and observations of comet C/2002 T7 (LINEAR) in 2004 and comet 9P/Tempel 1 during the 2005 Deep Impact comet-collision observing campaign.     

缝隙宽度对频率选择表面透波特性的影响

从物理本质上分析了频率选择表面FSS(Frequency Selective Surfaces)单元的缝隙宽度对FSS平板透波特性的影响.FSS平板单元的缝隙越宽,则单元的谐振波长缩短就越多,谐振频率也随之升高.利用Floquet定理,计算分析了缝隙宽度对FSS平板透波特性的影响;采用蚀刻技术加工FSS平板小矩形缝隙单元.实验测试的结果表明,缝隙宽度变大时,谐振频率升高,同时,FSS平板的透波率和谐振带宽变大.实验数据与计算结果在误差允许的范围内基本一致.