Chronic orthostatic and antiorthostatic restraint induce neuroendocrine, immune and neurophysiologial disorders in rats

The tail-cast suspension rat model has been developed in ground laboratories interested in space physiology for extensive study of mechanisms causing the pathophysiological syndrome associated with space flights. We used individually-caged male rats to explore the effects of acute and chronic (7d) orthostatic restraint (OR) and head-down anti-orthostatic restraint (AOR) on a series of physiological variables. The acute restraint study showed that (1) the installation of the OR device induced an acute reaction for 2 days, with a substantial rise in ACTH (x2) and CORT (x6), and that (2) the head-down tilt from OR to AOR induced (i) within 10 min and lasting 60 min a 2-fold rise in the intra-cerebro-ventricular pressure (Picv) monitored with an icv telemetric recording system, which receded to normal between 60 and 120 min; and (ii) within 30 min a short-lived 4-fold rise in plasma ACTH and CORT levels. Chronic OR induced (1) the suppression of the diurnal ACTH/CORT rhythm, with increased mean levels, especially for ACTH, (2) a degraded circadian locomotor activity rhythm manifested by a significant reduction in the spectral power of the 24h periodicity and a concomitant emergence of shorter (ultradian) periodicities, (3) an associated, but less pronounced alteration of the diurnal rhythm in body temperature; and (4) a marked increase in baseline plasma levels of IL-1β and an increased reactivity in cytokine release following an E. coli endotoxin (LPS) challenge. AOR induced (1) a similar obliteration of the circadian ACTH/CORT rhythm, (2) the loss of close correlation between ACTH and CORT, (3) a generalized increase in baseline plasma IL-1β levels and (4) more extensive degradation of the arcadian periodicity for both locomotor activity and, to a lesser extent, body temperature, replaced by dominant spectral powers for ultradian periodicities (3 to 10h). In conclusion, both experimental paradigms — but AOR more than OR — caused a blockade of the arcadian rhythmicity of major physiological variables, the loss of normal correlations between ACTH and CORT, and inflammatory-immune hyperreactivity. These pathophysiological disorders may all be parts of a complex chronic stress syndrome.     

Cardiac and vascular adaptation to 0g with and without thigh cuffs (Antares 14 and Altair 21 day Mir spaceflights)

Cardiovascular Actaptation was evaluated on 2 astronauts: one wearing thigh cuffs from flight day 1 to 8 (14d flight), the second without cuffs (21d flight). Ultrasound investigations were performed at rest and during LBNP. Results: Without thigh cuffs the cardiovascular Actaptation consists in (1) the development of a hypovolemia with an increase of the heart rate and the cardiac output, (2) the decrease of the vascular tone in the deep (mesenteric and splanchnic) and peripheral (Lower limbs) vascular areas. The use of thigh cuffs maintains the volemia and the cardiac output at the preflight level (without heart rate increase) and prevents the loss of vascular tone in the deep and peripheral areas. Moreover the adaptative process changes since the cuffs are removed and even the volemia seems to be unaffected at this stage the vascular tone decreases to a comparable extend as during the flight without cuffs. Nevertheless during the flight without cuffs or 3 days after removing the cuffs hemodynamic signs of decreased orthostatic tolerance are present during the inflight and the 3 days post flight LBNP. Presently the possible contribution of the thigh cuffs to the reduction of the vascular deconditioning has not been tested yet.     

自适应序列概率比检验型PCM帧同步器的分析

本文用一简单的自适应算法来决定序列概率比检验(SPRT)型 PCM 帧同步器的工作参数。由计算机仿真得到了在很大的误码率范围内的性能数据。数据表明:序列概率比检验型在锁定态到搜索态转换性质上,比通用型同步器有重要的改进。     

数字波束形成合成孔径雷达

阐述了最近在Astrium完成的两项SAR研究，简述了大地测量合成孔径成像雷达X型（TSX）卫星的能力。两项研究是在SAR成像模式时采用新颖天线波束形成概念的高分辨率宽条带成像雷达（HRWS）和LCMA（低成本多个馈电天线）。分析了它们的设计、性能和样机框图，并将它们与采用有源相控阵天线的TSX—SAR进行了比较。     

液氧/甲烷高压补燃火箭燃烧室研究

采用一台小型推力室对液氧/甲烷推进剂的高压补燃火箭燃烧室进行了实验评估,富燃预燃室和主燃室均单独进行了试验.预燃室/主燃室装置的试验条件是:主燃室压力7—9.6MPa,混合比3.1—3.7.预燃的燃气温度760—1070K,推力范围4.6—6.4kN.试验评估了在使用不同类型的主喷注器和预燃室喷注器时,预燃室和主燃室的燃烧性能、主燃室内的热通量分布以及室壁和喷嘴表面的积碳特性.此外,还推导了表征主燃室燃烧效率的经验公式.实验装置的任何部位均未出现严重的积碳,也未检测到由于室壁的积碳而引起热通量的明显减小.     

MX导弹第三级样机评价

本文评述赫克力斯公司正在为空军研制的MX导弹第三级的设计。第三级固体发动机的许多部件和材料都选用了最新的技术。这些新技术包括:带有碳复合材料裙的凯夫拉49发动机壳体;二维和三维碳/碳复合材料的轻型喷管;硝酸酯增塑的聚醚推进剂(NEPE),这种推进剂比冲高、延伸率大;以及两节套筒式可延伸出口锥(EEC)。这些新技术的应用提高了整个发动机的性能。本文对第三级的设计及其主要部件都作了概要介绍。为了说明MX第三级的设计是切实可行的,还将MX第三级各部件设计与以前研制的发动机作了比较。     

Long-term manipulations of intact microbial mat communities in a greenhouse collaboratory: simulating earth's present and past field environments

Photosynthetic microbial mat communities were obtained from marine hypersaline saltern ponds, maintained in a greenhouse facility, and examined for the effects of salinity variations. Because these microbial mats are considered to be useful analogs of ancient marine communities, they offer insights about evolutionary events during the >3 billion year time interval wherein mats co-evolved with Earth's lithosphere and atmosphere. Although photosynthetic mats can be highly dynamic and exhibit extremely high activity, the mats in the present study have been maintained for >1 year with relatively minor changes. The major groups of microorganisms, as assayed using microscopic, genetic, and biomarker methodologies, are essentially the same as those in the original field samples. Field and greenhouse mats were similar with respect to rates of exchange of oxygen and dissolved inorganic carbon across the mat-water interface, both during the day and at night. Field and greenhouse mats exhibited similar rates of efflux of methane and hydrogen. Manipulations of salinity in the water overlying the mats produced changes in the community that strongly resemble those observed in the field. A collaboratory testbed and an array of automated features are being developed to support remote scientific experimentation with the assistance of intelligent software agents. This facility will permit teams of investigators the opportunity to explore ancient environmental conditions that are rare or absent today but that might have influenced the early evolution of these photosynthetic ecosystems.     

史密森天文物理观测台研制的冷氢激射器及有关装置

低温冷却激射器为测量频率偏移和存储壁涂敷材料的弛豫特性创造了有利条件。这种涂敷材料是从常态变为气态物质而被冻结在存储壁上的。我们对FEP—120聚四氟乙烯在77K至48K之间的原始测试结果作了报道,并把这些测量结果和法国de Saintfuscien在372K至77K之间的测试数据进行了比较。对激射器的某些设计性能作了说明。低溫激射器的氢分离器,完全密封在真空环境中,其温度77k。本文还介绍了在真空中工作的分离器和其它一些装置。这些装置已在常温激射器中被采用并进行了测试。它们既适合于太空环境又适合于在地面使用。