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101.
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Survey of worldwide high-power wideband capabilities 总被引:2,自引:0,他引:2
Prather W.D. Baum C.E. Torres R.J. Sabath F. Nitsch D. 《Electromagnetic Compatibility, IEEE Transactions on》2004,46(3):335-344
Wideband and ultrawideband (UWB) technologies have achieved notable progress in recent years, aided immeasurably by improvements in solid-state manufacturing, computers, and digitizers. As a result, wideband systems that were difficult or impossible to implement ten years ago are now being built for an increasingly wide variety of applications including transient radar, concealed object detection, mine clearing, pipeline inspections, archeology, geology, electronic effects testing, and communications. In this paper, we discuss current wideband source technology around the world as well as laboratory and test facilities. We also will briefly touch on frequency limitations of anechoic chambers, design of transmission line simulators, frequency regulation requirements for outdoor ranges, and personnel exposure limits. 相似文献
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Michael D. Peck Emilio Mantero-Atienza Maria Jose Miguez-Burbano Mary Ann Fletcher Gail Shor-Posner Marianna K. Baum 《Lipids》1993,28(10):961
The online version of the original article can be found at 相似文献
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ES Sills JD Baum X Ling MM Harper DP Levy CJ Lockwood 《Canadian Metallurgical Quarterly》1997,26(7):704-710
The effect of long-term L-thyroxine (LT4) replacement therapy on bone mineral density and on biochemical markers of bone turnover were studied in children with congenital hypothyroidism (CH). Forty-four children and adolescents (mean age 8.5 +/- 3.5 years) with primary CH who began LT4 replacement therapy within the first month of life were studied. Bone mineral density (BMD) of the lumbar vertebrae and the upper femoral bone was measured by dual energy X-ray absorptiometry. Serum osteocalcin (OC) and bone alkaline phosphatase were measured as markers of bone formation and urinary deoxypyridinoline was taken as a marker of bone resorption. Bone mineral densities of CH children were not different from those in age-matched controls. The biochemical markers of bone turnover were normal except for the serum OC levels which were found to be higher than in controls and positively correlated with the free thyroid hormone levels (for FT4 r = 0.42, p = 0.02). Eight CH children demonstrated low BMD values (below -1 SDS) at -2 +/- 0.7 SDS for the lumbar spine and -1.6 +/- 0.5 SDS for the femoral site. These eight children showed lower mean weight (p < 0.05) and their dietary calcium intake tended to be less (p <0.06) than that seen in the normal BMD group. In conclusion, our results show that LT4 replacement therapy for 8 years is not detrimental to the skeletal mineralization of CH children. As in a healthy population, weight and current intake of calcium seem to be major determinants of bone density. Dietary recommendations, especially when calcium intake is below the recommended dietary allowance, may have to be reconsidered. 相似文献
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Reinhard Schneider Eckhard Pippel Jrg Woltersdorf Silke Strauß Hans Jürgen Grabke 《国际钢铁研究》1997,68(7):326-332
Microstructural and microchemical investigations were carried out on nickel and Inconel 600 after exposure to strongly carburizing atmospheres at temperatures of about 600 to 650°C to study their metal dusting behaviour. Contrary to iron and low-alloy steels, where metal dusting proceeds via the formation and disintegration of a metastable carbide M3C, both nickel and Inconel 600 directly disintegrate. Inside the metal this disintegration proceeds by formation of thin graphite filaments of nearly 10 nm in diameter, the atomic basal planes of which are oriented perpendicular to the surface thus effecting a high reactivity at the growth front. Subsequently, fine particles or larger parts of the metal surface layer are released, which are buried in the deposited graphite layer on the surface. In case of Inconel 600, containing Cr with mass contents of about 15%, the disintegration can be delayed by the formation of a chromium oxide layer, but no safe protection against metal dusting is obtained. 相似文献