英国防部发起新型航空母舰的竞争

日前，英国国防部向全球航空航天制造商发起了价值244亿美元、为英国海军制造两艘航空母舰的竞标活动。有6家公司参与了竞标，它们是波音、英国宇航防御系统、洛克希德、马丁、马可尼电子系统、雷神和汤姆逊一CSF公司。这6家公司都具有较强的海军系统综合能力。但英国政府坚持，新型航空母舰必须在英国制造。计划的第一阶段是在今年秋季选出3家承包商进行初步研究，台问价值830万美元。然后再从中选出两家公司进行减少风险的研究，台同价值3300万美元。最终承包商的确定预计将在2001年，第一艘航空母舰计划于2012年投入使用。该项目由国防…     

美国空军关注下一代电子战飞机

USAFSizesUpNextElectronicCombatAircraft美国一些制造商现在又开始忙于向空军提出用来替代EA—6B“徘徊者”老龄电于战飞机的后继机方案了。其中一种是“联合攻击战斗机”（JS）的派生型，还有就是考虑将F—22改装为具有电子战能力，使其能偷偷突防到敌空防区纵深，并将目标摧毁之。新电子战飞机计划被如此关注的主要原因是对科索沃冲突详细评估的结果。美国空军认为这场冲突显示对于各种信息收集和电子战飞机的需求要大大增加，特别是像EA—6B的后继机，并要大大扩展战术干扰空中力量，以保护隐身和常规的攻击飞机。如果能在2001…     

欧洲的研究和发展计划旨在更清洁的发动机

AVIATIONWEEK》》&SPACETECHNOLOGYEuropeanRεDprojectsTargetCleanerEngines为在未来的民用发动机市场上占更多的份额，欧洲发动机公司正在实施环保型发动机研究计划，目标是大大减少CO。和NOX的排放，并降低拥有费用欧洲委员会已同意投资两项研究计划，旨在为商用飞机研究更清洁和更高效的发动机。这些称为技术平台的飞机发动机计划是根据欧洲委员会研究指挥部第5框架计划进行的，这些计划从2000年到2004年实施，是提高欧洲航字工业竞争性的一系列主要研究和发展计划的首批计划。根据第5框架计划投资的其他技术平台计划…     

机械师短缺,航空安全令人堪忧

AVIATIONWEEK&SPACETECHNOLOGYMechanicShortageRaisesGrowth，SafetyConcernsEdwaPdHPhilips据预测，在今后几年，除非采取快捷有效的方法改变现状，否则美国飞机机械师和航电技术人员的人力资源的短缺会威胁到航空运输的发展和安全问题据美国劳工部所作的统计表明，在今后几年需要12000名新的飞机、发动机机械师（A＆P）加盟，以保持现有的航空运输业发展速度和补充退休的有经验的机械师，几乎每年缺4000名机械师。到2006年，全美维修业应达到155000名机械师，比现有人员增加13％。航空技术教育委员会（ATEC）的总裁文…     

A viable microbial community in a subglacial volcanic crater lake, Iceland

We describe a viable microbial community in a subglacial lake within the Grímsv?tn volcanic caldera, Iceland. We used a hot water drill to penetrate the 300-m ice shelf and retrieved lake water and volcanic tephra sediments. We also acquired samples of borehole water before and after penetration to the lake, overlying glacial ice and snow, and water from a nearby subaerial geothermal lake for comparative analyses. Lake water is at the freezing point and fresh (total dissolved solids = 260 mg L(-1)). Detectable numbers of cells were found in samples of the lake water column and tephra sediments: 2 x 10(4) ml(-1) and 4 x 10(7) g(-1), respectively. Plate counts document abundant cold-adapted cultivable organisms in the lake water, but not in the borehole (before penetration) or glacial ice. Denaturing gradient gel electrophoresis (DGGE) of 16S rRNA gene fragments amplified from genomic DNA extracted from Grímsv?tn samples indicates that the lake community is distinct from the assemblages of organisms in borehole water (before penetration) and the overlying ice and snow. Sequencing of selected DGGE bands revealed that many sequences are highly similar to known psychrophilic organisms or cloned DNA from other cold environments. Significant uptake of 14C-labeled bicarbonate occurred in dark, low-temperature incubations of lake water samples, indicating the presence of autotrophs. Acetylene reduction assays under similar incubation conditions showed no significant nitrogen fixation potential by lake water samples. This may be a consequence of the inhibition of diazotrophy by nitrogen in the lake.     

World Space Congress: a vision quest

The World Space Congress (WSC) in October, 2002, brought together luminaries, aerospace engineers, students, and scientists to discuss strategies for reviving the world's space agency. WSC lectures and plenary sessions focused on future research in space. Among topics discussed are the use of the Hubble Space Telescope to scan for habitable planets and obtain data about the beginning of the universe, new weather satellites, planetary protection from comets or asteroids, exploration and establishment of colonies on the Moon and Mars, medical advances, the role of space exploration in the world economy.     

UV photochemistry of DNA in vitro and in Bacillus subtilis spores at earth-ambient and low atmospheric pressure: implications for spore survival on other planets or moons in the solar system

Two major parameters influencing the survival of Bacillus subtilis spores in space and on bodies within the Solar System are UV radiation and vacuum, both of which induce inactivating damage to DNA. To date, however, spore survival and DNA photochemistry have been explored only at the extremes of Earth-normal atmospheric pressure (101.3 kPa) and at simulated space vacuum (10(-3)-10(-6) Pa). In this study, wild-type spores, mutant spores lacking alpha/beta-type small, acid-soluble spore proteins (SASP), naked DNA, and complexes between SASP SspC and DNA were exposed simultaneously to UV (254 nm) at intermediate pressure (1-2 Pa), and the UV photoproducts cis,syn-thymine-thymine cyclobutane dimer (c,sTT), trans,syn-thymine-thymine cyclobutane dimer (t,sTT), and "spore photoproduct" (SP) were quantified. At 101.3 kPa, UV-treated wild-type spores accumulated only SP, but spores treated with UV radiation at 1-2 Pa exhibited a spectrum of DNA damage similar to that of spores treated at 10(-6) Pa, with accumulation of SP, c,sTT, and t,sTT. The presence or absence of alpha/beta-type SASP in spores was partly responsible for the shift observed between levels of SP and c,sTT, but not t,sTT. The changes observed in spore DNA photochemistry at 1-2 Pa in vivo were not reproduced by irradiation of naked DNA or SspC:DNA complexes in vitro, suggesting that factors other than SASP are involved in spore DNA photochemistry at low pressure.     

鸭翼位置对前掠翼气动特性的影响

本文依据在低速风洞所取得的测力、油流观察及旋涡测量结果,研究了前掠翼鸭式布局的鸭翼位置对气动性能的影响机理。研究表明,鸭翼位置对气动性能的影响是极为显著的。前掠翼鸭式布局大迎角性能的提高取决于鸭、主翼前缘涡的相对位置及其相互控制,也就是它们间的相互干扰。文中根据前掠及后掠鸭翼与主翼组合的实验结果,提出了采用鸭式布局时鸭、主翼应具有的平面形状及它们的相对位置。文中还对双前掠翼布局提出了一些看法。     

磁层氧离子向磁鞘泄漏的机制和效应

１９９７年 １月 １０日磁暴期间， Ｇｅｏｔａｉｌ卫星在向阳侧的磁鞘中观测到了磁层氧离子突增事件．这些氧离子的出现和磁鞘中存在很强的南向行星际磁场有关．事件期间向阳面发生了准静态的磁重联，氧离子流存在由北向南的速度分量．通量突增过程具有逆向和正向能量色散现象，磁层内部只有氧离子有可能被梯度漂移输送到重联区，所以只有氧离子在磁鞘中持续地被观测到．估计氧离子的逃逸速率为 ０．６１× １０２３／ｓ，大约为环电流氧离子输入率的 ３３％．大量的环电流氧离子由磁层跑到了磁鞘，导致环电流指数 ＡＳＹ－Ｈ呈现明显的非对称性．     

相控阵雷达技术发展水平及趋势

本报告首先简介雷达和天文学领域中相控阵天线的形状；评述了雷达技术发展的各种趋势一方面受到成本问题的驱动，另一方面受到增长的性能需求驱动；讨论的技术发展方向有增加带宽、收／发模块功率增加效率的改进、移相器技术、辐射器设计、用数字技术替代模拟技术以及稀疏阵的引入。通过评述，本文断定在雷达应用中，目前相控阵虽有商业生存力，但其复杂性却使得它们的成本居高不下。