Aqueous corrosion of phosphide minerals from iron meteorites: a highly reactive source of prebiotic phosphorus on the surface of the early Earth

We present the results of an experimental study of aqueous corrosion of Fe-phosphide under conditions relevant to the early Earth. The results strongly suggest that iron meteorites were an important source of reactive phosphorus (P), a requirement for the formation of P-based life. We further demonstrate that iron meteorites were an abundant source of phosphide minerals early in Earth history. Phosphide corrosion was studied in five different solutions: deionized water, deionized water buffered with sodium bicarbonate, deionized water with dissolved magnesium and calcium chlorides, deionized water containing ethanol and acetic acid, and deionized water containing the chlorides, ethanol, and acetic acid. Experiments were performed in the presence of both air and pure Ar gas to evaluate the effect of atmospheric chemistry. Phosphide corrosion in deionized water results in a metastable mixture of mixed-valence, P-bearing ions including pyrophosphate and triphosphate, key components for metabolism in modern life. In a pH-buffered solution of NaHCO(3), the condensed and reduced species diphosphonate is an abundant corrosion product. Corrosion in ethanol- and acetic acid-containing solutions yields additional P-bearing organic molecules, including acetyl phosphonate and a cyclic triphosphorus molecule. Phosphonate is a major corrosion product of all experiments and is the only P-bearing molecule that persists in solutions with high concentrations of magnesium and calcium chlorides, which suggests that phosphonate may have been a primitive oceanic source of P. The stability and reactivity of phosphonate and hypophosphite in solution were investigated to elucidate reaction mechanisms and the role of mineral catalysts on P-solution chemistry. Phosphonate oxidation is rapid in the presence of Fe metal but negligible in the presence of magnetite and in the control sample. The rate of hypophosphite oxidation is independent of reaction substrate.     

A sulfur-based survival strategy for putative phototrophic life in the venusian atmosphere

Several observations indicate that the cloud deck of the venusian atmosphere may provide a plausible refuge for microbial life. Having originated in a hot proto-ocean or been brought in by meteorites from Earth (or Mars), early life on Venus could have adapted to a dry, acidic atmospheric niche as the warming planet lost its oceans. The greatest obstacle for the survival of any organism in this niche may be high doses of ultraviolet (UV) radiation. Here we make the argument that such an organism may utilize sulfur allotropes present in the venusian atmosphere, particularly S(8), as a UV sunscreen, as an energy-converting pigment, or as a means for converting UV light to lower frequencies that can be used for photosynthesis. Thus, life could exist today in the clouds of Venus.     

Production of neutrons from interactions of GCR-like particles

In order to help assess the risk to astronauts due to the long-term exposure to the natural radiation environment in space, an understanding of how the primary radiation field is changed when passing through shielding and tissue materials must be obtained. One important aspect of the change in the primary radiation field after passing through shielding materials is the production of secondary particles from the breakup of the primary. Neutrons are an important component of the secondary particle field due to their relatively high biological weighting factors, and due to their relative abundance, especially behind thick shielding scenarios. Because of the complexity of the problem, the estimation of the risk from exposure to the secondary neutron field must be handled using calculational techniques. However, those calculations will need an extensive set of neutron cross section and thicktarget neutron yield data in order to make an accurate assessment of the risk. In this paper we briefly survey the existing neutron-production data sets that are applicable to the space radiation transport problem, and we point out how neutron production from protons is different than neutron production from heavy ions. We also make comparisons of one the heavy-ion data sets with Boltzmann-Uehling-Uhlenbeck (BUU) calculations.     

星图识别质心提取算法研究

采用对星图中星体的灰度值进行加权的方法，计算星图中星体的质心坐标。分析了星图预处理的方法，在此基础上进行了噪声条件下的仿真研究，并获得了满意的结果。     

Spatial orientation during locomotion [correction of locomation] following space flight

To investigate changes in spatial orientation ability and walking performance following space flight, 7 astronaut subjects were asked pre- and post-flight to perform a goal directed locomotion paradigm which consisted of walking a triangular path with and without vision. This new paradigm, involving inputs from different sensory systems, allows quantification of several critical parameters, like orientation performance, walking velocities and postural stability, in a natural walking task. The paper presented here mainly focusses on spatial orientation performance quantified by the errors in walking the previously seen path without vision. Errors in length and reaching the corners did not change significantly from pre- to post-flight, while absolute angular errors slightly increased post-flight. The significant decrease in walking velocity and a change in head-trunk coordination while walking around the corners of the path observed post-flight may suggest that during re-adaptation to gravity the mechanisms which are necessary to perform the task have to be re-accomplished.     

Modeling and Control for Magnetostrictive Hysteresis

To deal with the rate-dependent hysteresis presented in a magnetostrictive actuator, a new method of modeling and control is pro-posed. The relationship between inputs and outputs of the actuator is approximately described by a dynamic differential equation with two rate-dependent coefficients, each expressed as a polynomial of frequency. For a given frequency, the coefficients will be able to be estimated by approximating the experimental data of the outputs of the magnetostrictive actuator. Based on this model, a quasi-PID con-troller is designed. In the space of the coefficients and frequency, the stable domain of closed loop system with hysteresis is analyzed. The numerical simulation and experiments have born witness to the feasibility of the proposed new method.     

某型涡扇发动机地面起动试验研究

本文基于某型涡扇发动机地面试验情况,分析讨论了地面起动这一动态过程中主要参数的变化情况及原因,并结合试验数据,利用简单三段积分法计算了某型起动机特性,为地面起动控制规律和起动机设计计算提供了一定的参考依据。     

肯尼迪航天中心用于推进剂系统监视的知识库专家系统

液氧加注专家系统是建立实时专家系统的第一次尝试。它能在液体系统分析和故障寻找方面模仿 NASA 系统工程师的思维过程。软件的概述介绍了所使用的技术以及在其它过程控制系统中的可能应用。液氧专家系统现在正处于深入研究阶段,计划在一九八五年底全部完成。     

空间运输系统对空军卫星控制网的影响

二十多年来,空军卫星控制网(AFSCN)为许多军用航天器和发射运载器提供了实时跟踪、遥测和遥控支持。随着国防部航天任务测控要求的变化,空军卫星控制网的测控、通信和数据处理能力的扩展和现代化都已稳步增长。空间运输系统的发展促进了空军卫星控制网的发展。本文介绍了为满足空间运输系统的要求对空军卫星控制网目前已进行的和预期进行的一系列改造。