Individual Differences in Representational Precision Predict Spatial Working Memory Span

Perhaps the signature feature of working memory is that it is limited. In the same subjects, we used two different retrieval tasks to independently measure two different limits of spatial memory. Precision was measured by asking participants to localize a missing target item among a field of other targets and distracters. Capacity was measured with a similar task where participants identified, rather than localized, a set of remembered targets from within a larger set of identical items. Across participants, the precision of localization was positively correlated with the number of successfully retrieved items. These data suggest that an individual's representational capacity may ultimately be constrained by their ability to form precise representations of space.     

Spatially resolved genomic, stable isotopic, and lipid analyses of a modern freshwater microbialite from cuatro ciénegas, Mexico

Abstract Microbialites are biologically mediated carbonate deposits found in diverse environments worldwide. To explore the organisms and processes involved in microbialite formation, this study integrated genomic, lipid, and both organic and inorganic stable isotopic analyses to examine five discrete depth horizons spanning the surface 25?mm of a modern freshwater microbialite from Cuatro Ciénegas, Mexico. Distinct bacterial communities and geochemical signatures were observed in each microbialite layer. Photoautotrophic organisms accounted for approximately 65% of the sequences in the surface community and produced biomass with distinctive lipid biomarker and isotopic (δ(13)C) signatures. This photoautotrophic biomass was efficiently degraded in the deeper layers by heterotrophic organisms, primarily sulfate-reducing proteobacteria. Two spatially distinct zones of carbonate precipitation were observed within the microbialite, with the first zone corresponding to the phototroph-dominated portion of the microbialite and the second zone associated with the presence of sulfate-reducing heterotrophs. The coupling of photoautotrophic production, heterotrophic decomposition, and remineralization of organic matter led to the incorporation of a characteristic biogenic signature into the inorganic CaCO(3) matrix. Overall, spatially resolved multidisciplinary analyses of the microbialite enabled correlations to be made between the distribution of specific organisms, precipitation of carbonate, and preservation of unique lipid and isotopic geochemical signatures. These findings are critical for understanding the formation of modern microbialites and have implications for the interpretation of ancient microbialite records. Key Words: Microbial ecology-Microbe-mineral interactions-Microbial mats-Stromatolites-Genomics. Astrobiology 12, 685-698.     

低特征信号绝热层用硅氧烷树脂研究

简述了用于固体火箭发动机低特征信号绝热层研制的发展现状。对多种硅氧烷树脂（ＲＴＶ）进行了筛选和信号透过率，热失重，力学及粘接笥能试验。试验结果表明，与使用ＥＰＤＭ绝热层材料相比，使用ＲＴＶ绝热层材料，火箭发动机燃烧室羽流具有较高的信号透过率；ＲＴＶ还具有较好的热性、力学及粘接性能，适于用作低特征信号绝热层的基体材料。     

Terahertz circular dichroism spectroscopy: a potential approach to the in situ detection of life's metabolic and genetic machinery

We propose a terahertz (far-infrared) circular dichroism-based life-detection technology that may provide a universal and unequivocal spectroscopic signature of living systems regardless of their genesis. We argue that, irrespective of the specifics of their chemistry, all life forms will employ well-structured, chiral, stereochemically pure macromolecules (>500 atoms) as the catalysts with which they perform their metabolic and replicative functions. We also argue that nearly all such macromolecules will absorb strongly at terahertz frequencies and exhibit significant circular dichroism, and that this circular dichroism unambiguously distinguishes biological from abiological materials. Lastly, we describe several approaches to the fabrication of a terahertz circular dichroism spectrometer and provide preliminary experimental indications of their feasibility. Because terahertz circular dichroism signals arise from the molecular machinery necessary to carry out life's metabolic and genetic processes, this life-detection method differs fundamentally from more well-established approaches based on the detection of isotopic fractionation, "signature" carbon compounds, disequilibria, or other by-products of metabolism. Moreover, terahertz circular dichroism spectroscopy detects this machinery in a manner that makes few, if any, assumptions as to its chemical nature or the processes that it performs.     

空间重离子辐照效应评述

文章对生物、半导体、光学材料、金属、聚合物的空间重离子辐照效应的研究工作进行了评述,也阐明了深入开展重离子空间环境模型以及重离子辐照效应与演化规律的研究具有重要意义。研究表明空间环境中重离子的含量虽少,但由于其高的电离能力和穿透力,对生物、半导体、光学材料、金属、聚合物等会产生各种辐射损伤效应,导致卫星信号故障、光学器件失效、金属与聚合物性能及形貌改变,甚至影响航天员的生命安全。     

数字签名卡的实现

数字签名是保证网络通信安全可靠的重要技术手段。文中介绍数字签名的原理 ,在原有的智能卡系统中加入公钥文件和私钥文件 ,并添加相关的指令 ,在智能卡中实现了数字签名及其验证技术 ,成功地将智能卡应用到 PKI中 ,为网络应用提供一种完全符合 X.5 0 9标准的密钥管理平台     

基于智能卡的数字签名系统的设计与实现

数字签名能够确认消息签署者的身份 ,并保证消息的完整性 ,是实现安全电子商务的重要手段。文中首先分析了数字签名的基本原理和实现数字签名的功能模型 ,进而设计并实现了基于智能卡的数字签名系统。系统采用标准的程序接口 ,实现了与 Windows平台的无缝集成 ,因而具有广阔的应用前景。     

改性双基低特征信号推进剂研究进展

综述了国外改性双基低特征信号推进剂研究的最新进展，提出了改性双基推进剂实现低特征信号并提高性能的主要技术途径和性能指标，重点介绍了几种含有新型含能材料、新型燃速改良剂和新型键合剂的改性双基低特征信号推进利配方。     

一种新的基于椭圆曲线的代理签名方案

数字签名和消息加密是信息安全的关键之一。文中利用椭圆曲线密码体制的高可靠性和短密钥等良好特性,提出一种指定接收者恢复消息的代理签名方案,并进行安全性和性能分析。该方案不需要使用专门的安全传输通道及分发代理签名密钥,而且将签名和加密较好地结合起来,可应用于电子现金和移动电子商务等场合。     

诊断键合图在液体火箭发动机故障诊断中的应用

研究了通过诊断键合图模型建立液体火箭发动机解析冗余关系的故障诊断方法。通过在液体火箭发动机键合图模型中加入观测信号和虚拟传感器的方法，建立其诊断键合图模型，并利用此模型构建了系统的解析冗余关系。提出了根据诊断键合图因果路径并利用解析冗余关系残差趋势分析建立具有残差变化方向故障特征矩阵的方法，使故障特征值能更好地反映故障特征。最后利用仿真数据对诊断结果进行验证和分析，表明该方法建模简单、诊断速度快、准确性高。     

Scouting the spectrum for interstellar travellers

Advanced civilizations capable of interstellar travel, if they exist, are likely to have advanced propulsion methods. Spaceships moving at high speeds would leave a particular signature which could be detected from Earth. We propose a search based on the properties of light reflecting from objects travelling at relativistic speeds. Based on the same principles, we also propose a simple interstellar beacon with a solar sail.     

Interplanetary transfer of photosynthesis: an experimental demonstration of a selective dispersal filter in planetary island biogeography

We launched a cryptoendolithic habitat, made of a gneissic impactite inoculated with Chroococcidiopsis sp., into Earth orbit. After orbiting the Earth for 16 days, the rock entered the Earth's atmosphere and was recovered in Kazakhstan. The heat of entry ablated and heated the rock to a temperature well above the upper temperature limit for life to below the depth at which light levels are insufficient for photosynthetic organisms ( approximately 5 mm), thus killing all of its photosynthetic inhabitants. This experiment shows that atmospheric transit acts as a strong biogeographical dispersal filter to the interplanetary transfer of photosynthesis. Following atmospheric entry we found that a transparent, glassy fusion crust had formed on the outside of the rock. Re-inoculated Chroococcidiopsis grew preferentially under the fusion crust in the relatively unaltered gneiss beneath. Organisms under the fusion grew approximately twice as fast as the organisms on the control rock. Thus, the biologically destructive effects of atmospheric transit can generate entirely novel and improved endolithic habitats for organisms on the destination planetary body that survive the dispersal filter. The experiment advances our understanding of how island biogeography works on the interplanetary scale.     

The Martian and extraterrestrial UV radiation environment--1. Biological and closed-loop ecosystem considerations

The Martian surface is exposed to both UVC radiation (<280 nm) and higher doses of UVB (280-315 nm) compared to the surface of the Earth. Terrestrial organisms have not evolved to cope with such high levels of UVC and UVB and thus any attempts to introduce organisms to Mars, particularly in closed-loop life support systems that use ambient sunlight, must address this problem. Here we examine the UV radiation environment of Mars with respect to biological systems. Action spectra and UV surface fluxes are used to estimate the UV stress that both DNA and chloroplasts would experience. From this vantage point it is possible to consider appropriate measures to address the problem of the Martian UV environment for future long term human exploration and settlement strategies. Some prospects for improving the UV tolerance of organisms are also discussed. Existing artificial ecosystems such as Biosphere 2 can provide some insights into design strategies pertinent to high UV environments. Some prospects for improving the UV tolerance of organisms are also discussed. The data also have implications for the establishment of closed-loop ecosystems using natural sunlight on the lunar surface and elsewhere in the Solar System.     

GAP高能低特征信号推进剂的研究

综述了四十二所GAP粘合剂和GAP高能低特征信号推进剂的研究及取得的进展、目前达到的技术水平。叠氮类推进剂可发展成高能、低特征信号和纯感推进剂，是今后战术发动机用固体推进剂的发展重点和方向。     

Should the Space Station be an ark?

This essay explores the pros and cons of maximizing the number of species that can be maintained on the Space Station. It reviews some of the history of comparative space biology to show that different cultures have different perspectives on the study of non-traditional research organisms (ie non-rodents) in space. Despite these differences, there are simple principles that all international partners in the Space Station endeavour should be able to uphold when deciding what facilities to build and what species to fly. As an argument for maximizing the taxonomic diversity on the Space Station, examples are given to show how very similar organisms may have different reactions to microgravity. At the same time the political pressure in the USA to make the Space Station an institution specifically servicing the 'health, well-being and economic benefits of people on earth', is acknowledged. Ultimately the justification for what species will be on the Space Station should rest with the quality of the scientific questions being asked.     

基于Java和XML的家具城电子商务平台的设计和实现

本文介绍了家具城电子商务平台的设计和实现,在分析XML优点和数据签名原理的基础上,给出了数据签名在XML平台的实现,这一实现使得电子商务平台具有良好的安全性。     

Photochemical synthesis of citric acid cycle intermediates based on titanium dioxide

The emergence of the citric acid cycle is one of the most remarkable occurrences with regard to understanding the origin and evolution of metabolic pathways. Although the chemical steps of the cycle are preserved intact throughout nature, diverse organisms make wide use of its chemistry, and in some cases organisms use only a selected portion of the cycle. However, the origins of this cycle would have arisen in the more primitive anaerobic organism or even back in the proto-metabolism, which likely arose spontaneously under favorable prebiotic chemical conditions. In this context, we report that UV irradiation of formamide in the presence of titanium dioxide afforded 6 of the 11 carboxylic acid intermediates of the reductive version of the citric acid cycle. Since this cycle is the central metabolic pathway of contemporary biology, this report highlights the role of photochemical processes in the origin of the metabolic apparatus.     

Necessary, but not sufficient: Raman identification of disordered carbon as a signature of ancient life

To identify microscopic particles as actual fossil material, it would be useful to have a means of unambiguously recognizing which carbonaceous deposits found in rocks are residues from once-living organisms (i.e., biogenic material). Those residues consist of many different, mostly aromatic (i.e., benzene ring-containing), C-O-H-dominated molecules, and typically are called kerogens. Raman microprobe spectroscopy can be applied to minute samples of ancient kerogens either isolated from their host rocks or in situ in thin section. The Raman spectra generated by monochromatic blue or green laser excitation (e.g., at 488, 514, 532 nm) typically show only generic spectral features indicative of discontinuous arrays of condensed benzene rings (i.e., structures referred to as "disordered carbonaceous material"). Thus, despite the complex chemistry of kerogens and the expected presence of H, O, and N, the Raman spectra typically do not show any evidence of functional groups, such as CH, CH(2), CH(3), CO, and CN. Moreover, the same kind of Raman spectral signature as is obtained from kerogens also is obtained from many other poorly ordered carbonaceous materials that arise through nonbiological processes, such as in situ heating of organic or inorganic compounds (whether or not they are of biological origin), metamorphic mobilization of preexisting carbon compounds, and high-temperature precipitation from hydrothermal solutions. Thus, neither a Raman spectrum, nor a Raman image derived from such spectra, definitively can identify a sample as "kerogen," but only as "disordered carbonaceous material." Clearly, the fact that small, opaque grains consist of disordered carbonaceous material is necessary, but not sufficient, to prove them to be residues of cellular material and, thus, biogenic.     

Common freshwater cyanobacteria grow in 100% CO2

Cyanobacteria and similar organisms produced most of the oxygen found in Earth's atmosphere, which implies that early photosynthetic organisms would have lived in an atmosphere that was rich in CO2 and poor in O2. We investigated the tolerance of several cyanobacteria to very high (>20 kPa) concentrations of atmospheric CO2. Cultures of Synechococcus PCC7942, Synechocystis PCC7942, Plectonema boryanum, and Anabaena sp. were grown in liquid culture sparged with CO2-enriched air. All four strains grew when transferred from ambient CO2 to 20 kPa partial pressure of CO2 (pCO2), but none of them tolerated direct transfer to 40 kPa pCO2. Synechococcus and Anabaena survived 101 kPa (100%) pCO2 when pressure was gradually increased by 15 kPa per day, and Plectonema actively grew under these conditions. All four strains grew in an anoxic atmosphere of 5 kPa pCO2 in N2. Strains that were sensitive to high CO2 were also sensitive to low initial pH (pH 5-6). However, low pH in itself was not sufficient to prevent growth. Although mechanisms of damage and survival are still under investigation, we have shown that modern cyanobacteria can survive under Earth's primordial conditions and that cyanobacteria-like organisms could have flourished under conditions on early Mars, which probably had an atmosphere similar to early Earth's.     

固体火箭发动机羽烟特征信号的分类及测试评估概述

介绍了国外低特征信号固体推进剂分类标准和固体火箭发动机羽烟特征信号分类及测试技术等方面的工作,主要内容涉及发动机羽烟特征信号的定义、产生根源、对使用的影响、理论预估及特征信号测试评估的各种实验方法和设施,并预示了羽烟特征信号测试与评估的发展方向。