Biochemical constraints in a protobiotic earth devoid of basic amino acids: the "BAA(-) world"

It has been hypothesized in this journal and elsewhere, based on surveys of published data from prebiotic synthesis experiments and carbonaceous meteorite analyses, that basic amino acids such as lysine and arginine were not abundant on prebiotic Earth. If the basic amino acids were incorporated only rarely into the first peptides formed in that environment, it is important to understand what protobiotic chemistry is possible in their absence. As an initial test of the hypothesis that basic amino acid negative [BAA(-)] proteins could have performed at least a subset of protobiotic chemistry, the current work reports on a survey of 13 archaeal and 13 bacterial genomes that has identified 61 modern gene sequences coding for known or putative proteins not containing arginine or lysine. Eleven of the sequences found code for proteins whose functions are well known and important in the biochemistry of modern microbial life: lysine biosynthesis protein LysW, arginine cluster proteins, copper ion binding proteins, bacterial flagellar proteins, and PE or PPE family proteins. These data indicate that the lack of basic amino acids does not prevent peptides or proteins from serving useful structural and biochemical functions. However, as would be predicted from fundamental physicochemical principles, we see no fossil evidence of prebiotic BAA(-) peptide sequences capable of interacting directly with nucleic acids.     

用EM算法解决多目标／多传感器的跟踪问题

采用我种精度不同和特性不同的传感器的输出来跟踪杂波噪声环境中的多个运动目标是监视和侦察系统中的一个重要问题。人们提出了许多解决多目标／多传感器跟踪问题的方案，从难度适中（针对特定应用的方案）的到得复杂的、理论上是最佳的方案均有。本文描述了一种基于最大期望（ＥＭ）算法的时间递归多目标／多传感器的迭代跟踪方法。更具体地说，我们把多目标／多传感器跟踪问题当作是利用可观测传感器的输出表示不完全数据的不完全     

A study of metabolic balance in crewmembers of Skylab IV

A metabolic balance study was conducted on the three crewmembers of the 84-day Skylab IV earth orbital mission. Dietary intake was controlled, monitored, and kept very nearly constant for a period commencing 21 days prior to flight, throughout flight, and for a period of 18 days postflight. Within the first 30 days of flight urine calcium rose to a level approx. 100% above preflight levels and remained elevated for the remainder of the flight. Fecal calcium excretion increased more slowly but continued to accelerate throughout the flight and did not return to baseline levels during the postflight period. Urinary nitrogen increased to 25-30% above preflight levels within one month following launch and thereafter gradually subsided toward control values. The overall losses of calcium averaged approx. 200 mg per day throughout the mission while nitrogen losses averaged 590 mg. Various other indices of musculoskeletal deterioration are discussed and correlated. The parallelism between the effects of weightlessness and bed rest is reviewed. It is noted, that no evidence is yet available as to the identity of the initial biological response to the absence of gravity.     

AN／APG-79／79（V）有源电扫阵列火控雷达

雷声公司为美国海军制造的AN／APG-79（AESA）是一种有源电扫阵列雷达，是APG-73雷达的改进型。是一项对F／A-18E／F战斗机的重大改进项目，也是F／A-18E／F战斗机的第二批改进计划（blockⅡ）中的关键设备。本文介绍了该雷达的技术特点和工作方式，给出了AN／APG-79雷达较之APG-73雷达的改进，详细介绍了AN／APG-79雷达的研制进度、飞行试验和交付情况。     

Mars habitat modules: launch, scaling and functional design considerations

The Sasakawa International Center for Space Architecture (SICSA) is undertaking a multi-year research, planning and design study that is exploring near- and long-term commercial space development opportunities. The central goal of this activity is to conceptualize a scenario of sequential, integrated private enterprise initiatives that can carry humankind forward to Mars. Each development stage is planned as a building block to provide the economic foundation, technology advancements and operational infrastructure to support others that follow. This report presents fundamental issues and requirements associated with planning human Mars initiatives that can transfer crews, habitats and equipment from Earth to Mars orbit, deliver them to the planet's surface, and return people and samples safely back to Earth. The study builds in part upon previous studies which are summarized in SICSA's: Commercial Space Development Plan and the Artificial Gravity Science and Excursion Vehicle reports. Information and conclusions produced in this study provide assumptions and a conceptual foundation for a subsequent report titled The First Mars Outpost: Planning and Concepts.     

Blended control, predictor-corrector guidance algorithm: an enabling technology for Mars aerocapture

A guidance scheme designed for coping with significant dispersion in the vehicle's state and atmospheric conditions is presented. In order to expand the flyable aerocapture envelope, control of the vehicle is realized through bank angle and angle-of-attack modulation. Thus, blended control of the vehicle is achieved, where the lateral and vertical motions of the vehicle are decoupled. The overall implementation approach is described, together with the guidance algorithm macrologic and structure. Results of guidance algorithm tests in the presence of various single and multiple off-nominal conditions are presented and discussed.     

飞行测量和RCS的预测：对波音737机身侧部的雷达距离轮廓所做的比较

在实际测量中无法获取测量值时，确定雷达横截面预测技术是获取预测值可靠２性的关键。文中首次给出了对一维图像即雷达距离轮廓所做的比较结果。