Alfvn Waves in the Solar Wind

Alfvn waves are found to be ubiquitous in the solar wind.Recent progress in observational studies of the waves is reviewed to formulate a microscopic picture for the Alfvenic fluctuations. The main aspects of the observational properties of these waves,including the wave intervals, propagation,evolution,origin and generation,are presented.Then Alfven wave heating and acceleration of the solar wind plasma are briefly introduced.The relation of the waves to rotational and tangential discontinuities,magnetic decreases,and other relatively large-scale structures such as flux tubes/ropes,magnetic clouds and interplanetary coronal mass ejections in the solar wind is particularly investigated.Finally,some remaining open questions are also indicated due to their fundamental importance of understanding of the physical nature of Alfven waves and the role of the waves in heating and accelerating the solar wind.     

Is the presence of oxygen on an exoplanet a reliable biosignature?

We revisit the validity of the presence of O(2) or O(3) in the atmosphere of a rocky planet as being a biosignature. Up to now, the false positive that has been identified applies to a planet during a hot greenhouse runaway, which is restricted to planets outside the habitable zone (HZ) of the star that are closer to the star. In this paper, we explore a new possibility based on abiotic photogeneration of O(2) at the surface of a planet that could occur inside the HZ. The search for such a process is an active field of laboratory investigation that has resulted from an ongoing interest in finding efficient systems with the capacity to harvest solar energy on Earth. Although such a process is energetically viable, we find it to be a very unlikely explanation for the observation of O(2) or O(3) in the atmosphere of a telluric exoplanet in the HZ. It requires an efficient photocatalyst to be present and abundant under natural planetary conditions, which appears unlikely according to our discussion of known mineral photochemical processes. In contrast, a biological system that synthesizes its constituents from abundant raw materials and energy has the inherent adaptation advantage to become widespread and dominant (Darwinist argument). Thus, O(2) appears to continue to be a good biosignature.     

Prebiotic significance of extraterrestrial ice photochemistry: detection of hydantoin in organic residues

The delivery of extraterrestrial organic materials to primitive Earth from meteorites or micrometeorites has long been postulated to be one of the origins of the prebiotic molecules involved in the subsequent apparition of life. Here, we report on experiments in which vacuum UV photo-irradiation of interstellar/circumstellar ice analogues containing H(2)O, CH(3)OH, and NH(3) led to the production of several molecules of prebiotic interest. These were recovered at room temperature in the semi-refractory, water-soluble residues after evaporation of the ice. In particular, we detected small quantities of hydantoin (2,4-imidazolidinedione), a species suspected to play an important role in the formation of poly- and oligopeptides. In addition, hydantoin is known to form under extraterrestrial, abiotic conditions, since it has been detected, along with various other derivatives, in the soluble part of organic matter of primitive carbonaceous meteorites. This result, together with other related experiments reported recently, points to the potential importance of the photochemistry of interstellar "dirty" ices in the formation of organics in Solar System materials. Such molecules could then have been delivered to the surface of primitive Earth, as well as other telluric (exo-) planets, to help trigger first prebiotic reactions with the capacity to lead to some form of primitive biomolecular activity.     

缺口件疲劳寿命预测新方法

采用有限元方法针对缺口件多轴疲劳实验结果进行模拟。结果表明,相同路径条件下,随着缺口半径减小缺口根部附近的应力梯度显著增加。基于缺口根部应变值,采用等效应变法进行疲劳寿命预测,预测结果随缺口半径的减小而偏于保守。采用应力梯度法确定有效距离,相同路径下,随着缺口半径的减小有效距离减小;依据该有效距离处的等效应变进行疲劳寿命预测,总体预测结果较为分散且偏于不安全。基于实验及有限元模拟结果,提出了基于应变梯度的有效距离确定的新方法,大部分疲劳寿命预测结果位于2倍分散带内。     

用于低轨卫星精密轨道确定的简化动力学法

全球定位系统(GPS)的测量量可促成一种简化动力学法，用于近地卫星的近厘末级定轨。利用这种方法，不同观测时刻的卫星状态间的转移由正规的动力学模型和由连续GPS载波相位数据以运动学法导出的卫星位置变化来完成。动力学信息和运动学信息间的相对权重可自由变化。协方差分析表明：当观测几何差而动力学模型好时，模型支配着状态转移的计算；动力模型差而观测几何好时，载波相位统治着状态转移的计算；而当运动学和动力学信息间没有明显优劣时，简化动力学联合法可显著提高轨道精度。本文给出简化动力学法中准最佳的择权准则，并研究了求解精度对权的敏感性。     

格鲁门将放弃一些关键机体技术工作

格鲁门将放弃其现有的独立设计、发展和试验新一代战术飞机的能力,以有效地实施公司从原先的机体主承包商向系统综合商转变的五年发展计划。 格鲁门公司董事长兼首席执行官雷索·卡波拉里近期要求公司的高级管理层清查那些能被放弃的设施,并制订好一份详细的清理计划。     

卡恩劝告美国航空运输业:耐心等候,削减成本

美国国会于1978年通过了对航空运输业放松管制的法律,结束了40年之久的在政府干预下的行业竞争。许多观察家认为,这一举措改变了航空运输业的经营思路。 为应付日益加剧的竞争并时刻关注自己的财政状况,航空公司开始根据自己的资产负债表和盈利情况来调整计划航班业务、收费和业务扩充。 目前,国内航空运输业陷入严重的财政危机。面对高达数亿美元的财政失衡和亏损,许多航空公司正被迫收缩业务。难道真像某些人所说的那样,这一切应归罪于放松管制政策吗? 带着这一疑问和其他问题,美国     

全球定位系统用于空间超高动态飞行器的跟踪

全球定位系统(GPS)将提供非常有吸引力的跟踪空间动能武器的方法,以进行战略防御创新计划的系统试验和鉴定。然而,小体积高动态的武器使GPS的使用复杂化了。本文针对这些问题进行论述并提出解决办法。     

三叉戟Ⅰ型导弹利用转发GPS信号进行实时跟踪的现场试验结果

GPS接收机可以用来跟踪和确定单兵、轰炸机和洲际导弹等一切物体的位置。当体积和成本问题而不宜使用弹载接收机的场合,常利用转发GPS跟踪方案。三叉戟Ⅱ型潜射导弹提出的靶场安全跟踪问题正是这种情况。美国海军签订了一项合同,研制一套验证转发GPS跟踪方案的系统,以此来评价GPS用于靶场安全的技术风险,并检验其跟踪精度。利用预定的三叉戟Ⅰ型(C-4)试验发射,对整个系统进行了现场试验。本文叙述了转发GPS跟踪系统方案,所做的现场试验及其结果。     

航天飞机运载器的靶场安全指令接收/解码器

靶场安全用的停飞分系统是所有航天器发射运载器的一个组成部分。该分系统中的指令接收和解码器接收上行射频信号,启动停飞动作。对于无人航天器运载器,靶场安全上行指令信号由一组选定的IRIG单音组成(按特定的顺序,对射频载波进行调频)。航天飞机的发射,则采用了一种更为复杂的主字母(High-Alphabet)调制技术,这种技术能更好地防止干扰信号所引起的误炸。航天飞机系统使用了一种复合指令调制格式,即由几种不同的单音组成,对标准的UHF载皮进行调频。指令字中的字母由两个同时发送的单音组成,这两个单音选自7个可供使用的单音频率。这7个单音一次使用两个,可形成一个21个字母的字母表,用这些字母构成指令字。每次任务可选择发射字母序列。对于任何一次任务,大约有10~(12)种可供选用的代码组合。对于航天飞机发射,空间运输系统的固体助推器和外储箱要加靶场安全指令接收—解码器。接收机部分设计成单超外差式,在制造过程中固定调谐在一个合适的射频中心频率上。解码器部分采用一个微处理器进行解码。解码器在飞行前编好程,使之仅能识别这次任务的代码。此外,借助微处理器利用快速付利叶变换(FFT)完成单音解调。由固态输出开关给停飞炸毁机构输出解码器输出电压