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851.
An antenna array for wideband operation (up to 70%) is presented. The structure has low windloading area and consists of parallel printed circuit boards (PCB) with microstrip dipoles, feed network and metal fences placed between the PCBs. The low profile, low weight antenna array forms the main beam and three difference patterns for sidelobe cancellation. Experimental results are compared with calculations for both microstrip dipole and array 相似文献
852.
Kang-Ngee Chia Hea Joung Kim Lansing S. Mangione-Smith W.H. Villasensor J. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》1998,6(3):364-371
Under the Mojave configurable computing project, we have developed a system for achieving high performance on an automatic target recognition (ATR) application through the use of configurable computing technology. The ATR system studied here involves real-time image acquisition from a synthetic aperture radar (SAR). SAR images exhibit statistical properties which can be used to improve system performance. In this paper, the Mojave configurable computing system uses field programmable gate arrays (FPGA's) to implement highly specialized circuits while retaining the flexibility of programmable components. A controller sequences through a set of specialized circuits in response to real-time events. Computer-aided design (CAD) tools have been developed to support the automatic generation of these specialized circuits. The resulting configurable computing system achieves a significant performance advantage over the existing solution, which is based on application specific integrated circuit (ASIC) technology 相似文献
853.
854.
Although the precise pathoetiology of Beh?et's disease (BD) remains obscure, patients with BD have a high incidence of chronic infectious foci, indicating an enhanced susceptibility to chronic tonsillitis, and dental caries. Sometimes, clinical symptoms appear after treatment of these foci in BD patients. It is believed that BD might be related to an allergic reaction to a bacterial infection in view of the many clinical symptoms, especially the presence of aphthous and genital ulcerations. An attempt to obtain cutaneous responses to bacterial antigens has been carried out using various vaccines developed from bacteria isolated from the ulcerative lesions and oral cavities of BD patients. BD patients often show intense hypersensitivity to various strains of streptococci, not only by their cutaneous reactions but also by in vitro testing. In this report, we describe our previous studies on the correlation between streptococcal antigens and the pathogenesis of BD and also discuss the recent reports of other authors. The intense hypersensitivity to streptococcal antigens acquired after streptococcal infection is thought to play an important role in the appearance of symptoms in BD patients since the production of pro-inflammatory cytokines by peripheral blood mononuclear cells (PBMC) was enhanced when stimulated with streptococcal antigen in a culture system. Minocycline, an antibiotic to which certain strains of streptococci are sensitive, reduced the frequency of clinical symptoms in BD patients as well as the production of pro-inflammatory cytokines by BD-PBMC stimulated with streptococcal antigen. 相似文献
855.
Thin microtomed samples from hot-tool butt welds of polypropylene pipes are subjected to uniaxial tensile stress using a specially built instrumented microtesting machine. The deformation of the interface between the weld and the bulk polymer is measured by an optical method. An analysis of these measurements is carried out using the finite element method, and contours of the effective stress are obtained. There is a steep stress gradient at the junction of the weld flash and the bulk polymer, although the stress concentration factor is relatively low. The stress is essentially constant in the bulk polymer apart from the region near the weld zone. Tests on samples without the weld flash show that the maximum stress occurs within the weld zone. This is consistent with long-term tests on larger samples, where the fracture is found to initiate within the weld. The method of analysis enables the stress-strain response of the weld material to be determined. 相似文献
856.
857.
Dissolved organic carbon (DOC) dynamics were investigated over a two year period in the Upper Rhǒne River to examine the role of side-arms in providing DOC to the main channel in relation to discharge fluctuations, especially floods. Concentrations of DOC are shown to remain low in space and in time (average 1.5 mg ?1) and to be more related to global hydrological events (precipitation) than to any local flushing for backwaters during floods. The results do not support the general assumption that side-arms are the providers of DOC to the main channel. 相似文献
858.
A case of traumatic extracranial vertebral arterial dissection leading to vertebrobasilar thrombosis and respiratory compromise requiring mechanical ventilation was managed with intraarterial thrombolysis and stenting of the vertebral intimal dissection. In contrast to similar, previously reported cases, this critically ill patient made a full recovery, returning to his job as a secondary school teacher. 相似文献
859.
860.