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A. Farina A. ProtopapaRadar Dpt Selenia S. p. A. Via Tiburtina Km. - Rome Italy 《系统工程与电子技术(英文版)》1992,(3)
After a brief recall of the Sidelobe Canceler (SLC) working principle, including the derivation of a general formula for the Cancellation Ratio (CR), the effects of channel mismatching are investigated. In particular, curves providing CRvalues as a function of amplitude and phase channel mismatching, radar bandwidth, and jammer direction of arrival (JDOA) are provided for the cases of one and two auxiliary antennas. Subsequently, a time -space processor for performance restoration is analyzed in detail. In addition to the above mentioned quantities, the attainable CR value is expressed as a function of the space-time processor parameters. The contribution of the paper is related to the derivation of a number of mathematical equations of CR for several cases of practical interest for the radar engineer. In addition, several curves are presented to assist design of SLC systems. 相似文献
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骨质疏松治疗将进入一个新时代饶新华编译骨质疏松是全身骨骼因骨质减少而变得脆弱的一种病症,有关这种病症的介绍文字日见增多,人们对此已不再觉得陌生了。“矮个子大娘”和“驼背子奶奶”这类措词所描述的就是那些患有此病的中老年妇女。“过去,人们每次见到自己的祖... 相似文献
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面向二十一世纪的生物学 总被引:1,自引:0,他引:1
21世纪将属于生物学,但是在哪些领域有可能最先取得重大突破呢?请看来自《新科学家》杂志千年生物学会议的报道── 如今,我们能够克隆猪,培育胚胎干细胞,甚至截取基因并任意将其植入不同的生物物种;而且,我们很快就能将含有30亿个碱基对的人类遗传密码全部破译。那么,哪些领域有可能在新世纪率先取得重大突破呢? 当 38位世界一流生物学家在当代最有影响的生物学家之一、加州理工学院院长戴维·巴尔的摩(David Bal-timore)的带领下,在2000年4月初相聚于科罗拉多州的落基山脉高峰基斯通时,这一问题便… 相似文献
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一直主要是在理论上争论是否应进行人类生殖性克隆的问题上周变得更实际了。列克星敦市肯塔基州立大学的生殖生理学家帕纳斯·扎沃斯 (PanosZavos)和意大利生育医学专家塞维里诺·安蒂诺里 (SeverinoAntinori,见图 )在 2 0 0 1年 1月 2 6日举行的一次生育问题专家会议上宣布 :他们将和几位合作者一道 ,在近两年内尝试通过克隆技术来生产婴儿。这项计划将在地中海的某个国家进行。尽管这种尝试面临着巨大的障碍和极高的风险 ,但此次宣布的计划决不会像其他科研小组所宣称要开展克隆人的计划那样轻而易举地撤消。此… 相似文献
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Tschöp M Castañeda TR Joost HG Thöne-Reineke C Ortmann S Klaus S Hagan MM Chandler PC Oswald KD Benoit SC Seeley RJ Kinzig KP Moran TH Beck-sickinger AG Koglin N Rodgers RJ Blundell JE Ishii Y Beattie AH Holch P Allison DB Raun K Madsen K Wulff BS Stidsen CE Birringer M Kreuzer OJ Schindler M Arndt K Rudolf K Mark M Deng XY Whitcomb DC Halem H Taylor J Dong J Datta R Culler M Craney S Flora D Smiley D Heiman ML Withcomb DC 《Nature》2004,430(6996):1 p following 165; discussion 2 p following 165
Batterham et al. report that the gut peptide hormone PYY3-36 decreases food intake and body-weight gain in rodents, a discovery that has been heralded as potentially offering a new therapy for obesity. However, we have been unable to replicate their results. Although the reasons for this discrepancy remain undetermined, an effective anti-obesity drug ultimately must produce its effects across a range of situations. The fact that the findings of Batterham et al. cannot easily be replicated calls into question the potential value of an anti-obesity approach that is based on administration of PYY3-36. 相似文献
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大家还记得芹菜事件的教训么?80年代中期,美国的芹菜培植者曾推崇过一种他们认为非常好的新品种,不仅抗虫性强,而且可以使产量显著提高。但是有一个小问题,触弄过此芹菜梗的人不久就开始为发生严重皮疹而抱怨。皮肤病学家发现,这种芹菜会不断分泌出扫若仑(psoralen),一种在阳光下会变成刺激物和诱变物的天然化学物质。实际上,人们全都搞错了,许多生物技术业内人士和政府食品管理机构官员(尤其是美国)如是说。到“基因食品”上了人们餐桌的时候,它并非只是同传统食物一样没有危险,而且在某些方面其实还更安全,因为有管理部门… 相似文献
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The latest issue of Nature reported in its Research Highlights ( see " Lithography: Luminous Lizards", Nature, Vol. 451, p868, Feb. 21, 2008) that a group of researchers from the Technical Institute of Physics and Chemistry (TIPC), Chinese Academy of Sciences (CAS) achieved the new progress in 3D microstructures of nanometer composites using the multiphoton nanoprocessing technology. 相似文献
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