贴地飞行时旋翼空气动力学实验研究

 本文对贴地飞行时的旋翼进行了流场显示和桨盘处下洗速度测量的实验研究。揭示并研究了环流和地面涡现象及其对旋翼平面下洗速度分布的影响,指出了旋翼贴地飞行时拉力、力矩等剧烈变化的原因。     

一种低功率易校准的温度传感器

本文描述一种具有内部参考的改进的线性集成电路温度传感器,其主要的性能是:易校准(只有一个步骤),在宽温度范围内(-4.6mv/℃;-50℃到+125℃)具有高灵敏度,低输出阻抗(40Q),低功耗(200μw)。此器件中的扩散电阻以通用线性集成电路的工艺过程制造。文中还讨论了这种传感器在热电偶冷接点补偿中的应用。     

Travel, Sex, and Food: What's Speciation Got to Do with It?

Abstract We discuss the potential interactions among travel (dispersal and gene flow), bacterial "sex" (mainly as horizontal gene transfer), and food (metabolic plasticity and responses to nutrient availability) in shaping microbial communities. With regard to our work at a unique desert oasis, the Cuatro Ciénegas Basin in Coahuila, Mexico, we propose that diversification and low phosphorus availability, in combination with mechanisms for nutrient recycling and community cohesion, result in enhanced speciation through reproductive as well as geographic isolation. We also discuss these mechanisms in the broader sense of ecology and evolution. Of special relevance to astrobiology and central to evolutionary biology, we ask why there are so many species on Earth and provide a working hypothesis and a conceptual framework within which to consider the question. Key Words: Microbial ecology-Microbial mats-Evolution-Horizontal gene transfer-Metabolism. Astrobiology 12, 634-640.     

Potential of cathodoluminescence microscopy and spectroscopy for the detection of prokaryotic cells on minerals

Detecting mineral-hosted ecosystems to assess the extent and functioning of the biosphere from the surface to deep Earth requires appropriate techniques that provide, beyond the morphological criteria, indubitable clues of the presence of prokaryotic cells. Here, we evaluate the capability of cathodoluminescence microscopy and spectroscopy, implemented on a scanning electron microscope, to identify prokaryotes on mineral surfaces. For this purpose, we used, as a first step, a simple model of either unstained or stained cultivable cells (Escherichia coli, Deinococcus radiodurans) deposited on minerals that are common in the oceanic crust (basaltic glass, amphibole, pyroxene, and magnetite). Our results demonstrate that the detection of cells is possible at the micrometric level on the investigated minerals through the intrinsic fluorescence of their constituting macromolecules (aromatic amino and nucleic acids, coenzymes). This allows us to distinguish biomorph inorganic phases from cells. This easily implemented technique permits an exploration of colonized rock samples. In addition, the range of spectrometric techniques available on a scanning electron microscope can provide additional information on the nature and chemistry of the associated mineral phases, which would lead to a simultaneous characterization of cells, their microhabitats, and a better understanding of their potential relationships.     

Establishment of a rearing system of the extremotolerant tardigrade Ramazzottius varieornatus: a new model animal for astrobiology

Studies on the ability of multicellular organisms to tolerate specific environmental extremes are relatively rare compared to those of unicellular microorganisms in extreme environments. Tardigrades are extremotolerant animals that can enter an ametabolic dry state called anhydrobiosis and have high tolerance to a variety of extreme environmental conditions, particularly while in anhydrobiosis. Although tardigrades have been expected to be a potential model animal for astrobiological studies due to their excellent anhydrobiotic and extremotolerant abilities, few studies of tolerance with cultured tardigrades have been reported, possibly due to the absence of a model species that can be easily maintained under rearing conditions. We report the successful rearing of the herbivorous tardigrade, Ramazzottius varieornatus, by supplying the green alga Chlorella vulgaris as food. The life span was 35 +/- 16.4 d, deposited eggs required 5.7 +/- 1.1 d to hatch, and animals began to deposit eggs 9 d after hatching. The reared individuals of this species had an anhydrobiotic capacity throughout their life cycle in egg, juvenile, and adult stages. Furthermore, the reared adults in an anhydrobiotic state were tolerant of temperatures of 90 degrees C and -196 degrees C, and exposure to 99.8% acetonitrile or irradiation with 4000 Gy (4)He ions. Based on their life history traits and tolerance to extreme stresses, R. varieornatus may be a suitable model for astrobiological studies of multicellular organisms.     

Control of Lunar and Martian dust--experimental insights from artificial and natural cyanobacterial and algal crusts in the desert of Inner Mongolia, China

Studies on the colonization of environmentally extreme ground surfaces were conducted in a Mars-like desert area of Inner Mongolia, People's Republic of China, with microalgae and cyanobacteria. We collected and mass-cultured cyanobacterial strains from these regions and investigated their ability to form desert crusts artificially. These crusts had the capacity to resist sand wind erosion after just 15 days of growth. Similar to the surface of some Chinese deserts, the surface of Mars is characterized by a layer of fine dust, which will challenge future human exploration activities, particularly in confined spaces that will include greenhouses and habitats. We discuss the use of such crusts for the local control of desert sands in enclosed spaces on Mars. These experiments suggest innovative new directions in the applied use of microbe-mineral interactions to advance the human exploration and settlement of space.     

通过事后分析提高GPS的外测精度

通过事后分析可以提高GPS的外测精度。为了试验和鉴定目的,欲测量被试验体的时间空间位置信息(TSPI),现在已有不少方法。如果使用GPS,可考虑两种方案。一是在被试验体上装载GPS接收机,在运功体上测定TSPI,再通过遥测将数据送到地面。二是在运动体上装载一个GPS变频转发器,传送宽带GPS信息到地面。在地面站完成TSPI测量。本文指出,与装载接收机相比,装载GPS转发器的方案可以获得更高的测量精度。精度的提高来自两点:装载GPS接收机时仅处理来自4颗卫星的距离,得到运动体的位置。在某一位置上,所选用的4颗GPS卫星的GDOP值,可能是,也可能不是最佳。在转发方案中,运动体视场内所有信息都转送到地面进行处理。来自所有卫星的宽带数据都加以记录,以便作事后处理。作节后分析时,可按最佳GDOP选择最有利的卫星,或处理视场内所有卫星的数据,得到最高精度。记录宽带数据的能力还带来另外一些重要的事后处理好处。在飞行试验之前,只能估计试验体的飞行动态。飞行体上接收机跟踪滤波器参数依此作调整。如果飞行体运动异常(试验飞行中完全有可能这样),接收机就有可能对卫星失锁,所有的TSPI数据都会丢失。如果用GPS转发器,在地面站记录所有卫星的数据,在事后分析中重放该数据,可根据实际飞行动态,将滤波器最佳化,不会丢失TSPJ数据。此外,还可由数据处理来填补丢失的数据。     

CMOS集成电路中的交扰分析

本文指出CMOS(互补—金属—氧化物—半导体)集成电路内传输线间的交扰耦合如何通过影响逻辑和模拟元件的传播延迟而引起错误状态。提出了用于寄生电容耦合效应计算的简化模型,计算了交扰对基本功能部件如逻辑门电路、锁存器、RAM存储器和模/数转换器性能的影响。     

直接数字式合成器中寄生的抑制

一、前言本文介绍一种能消除直接数字式合成器(DDS)输出中通常存在的离散寄生谱线的极好方法。所研究的 DDS 的型式主要由一个 N 位累加器组成,其容量在时钟频率 Fc 时增加一 K值。虽然在用这种方法来合成周期波方面有许多方案,但是,最简单可行的方案是只利用累加器溢出发生的时间来确定“方”波的两沿。对于幂次为2的输入数 K,输出频率是时钟频率的直接分谐波。但是,所有其它的数,电路的性能如同非均匀输出周期序列的分数分频器一样。这些周期序列和可确定的图形重复,以给出与所需信号周期相等的平均值。遗憾的是,寄生谱线或边带都是由输出的周期性调相所引起的。在过去,这样的谱线都是利用累加