Eutectic phases in ice facilitate nonenzymatic nucleic acid synthesis

Polymeric compounds similar to oligonucleotides are relevant to the origin of life and particularly to the concept of an RNA world. Although short oligomers of RNA can be synthesized nonenzymatically under laboratory conditions by second-order reactions in concentrated solutions, there is no consensus on how these polymers could have been synthesized de novo on the early Earth from dilute solutions of monomers. To address this question in the context of an RNA world, we have explored ice eutectic phases as a reaction medium. When an aqueous solution freezes, the solutes become concentrated in the spaces between the ice crystals. The increased concentration offsets the effect of the lower temperature and accelerates the reaction. Here we show that in the presence of metal ions in dilute solutions, frozen samples of phosphoimidazolide-activated uridine react within days at -18 degrees C to form oligouridylates up to 11 bases long. Product yields typically exceed 90%, and approximately 30% of the oligomers include one or more 3'-5' linkages. These conditions facilitate not only the notoriously difficult oligouridylate synthesis, but also the oligomerization of activated cytidylate, adenylate, and guanylate. To our knowledge, this represents the first report to indicate that ice matrices on the early Earth may have accelerated certain prebiotic polymerization reactions.     

一种经济效益很高的校准无线电外测系统的方法——卫星校准法

一、鉴定和校准的重要性和紧迫性导弹武器系统和航天器的运载火箭在研制过程中,需要经过靶场飞行试验的全面鉴定。弹道式导弹(运载火箭)制导系统的鉴定,航天器的指挥控制,都需要靶场测量设备和跟踪网站提供精确的位置和速度数据。可以说,导弹武器系统和航天器的实际效能在很大程度上取决于靶场外测数据的质量。而高精度的外测数据在很大程度上又取决于外测系统本身的鉴定和校准工作。因为,确保规定的测量精度,是对外测系统提出的最重要的要求之一,而对一切     

Discovery of abundant cellulose microfibers encased in 250 Ma Permian halite: a macromolecular target in the search for life on other planets

In this study, we utilized transmission electron microscopy to examine the contents of fluid inclusions in halite (NaCl) and solid halite crystals collected 650 m below the surface from the Late Permian Salado Formation in southeastern New Mexico (USA). The halite has been isolated from contaminating groundwater since deposition approximately 250 Ma ago. We show that abundant cellulose microfibers are present in the halite and appear remarkably intact. The cellulose is in the form of 5 nm microfibers as well as composite ropes and mats, and was identified by resistance to 0.5 N NaOH treatment and susceptibility to cellulase enzyme treatment. These cellulose microfibers represent the oldest native biological macromolecules to have been directly isolated, examined biochemically, and visualized (without growth or replication) to date. This discovery points to cellulose as an ideal macromolecular target in the search for life on other planets in our Solar System.     

On laboratory simulation and the effect of small temperature oscillations about the freezing point and ice formation on the evaporation rate of water on Mars

We report measurements of the evaporation rate of water under Mars-like conditions (CO2 atmosphere at 7 mbar and approximately 0 degrees C) in which small temperature oscillations about the freezing point repeatedly formed and removed a thin layer of ice. We found that the average evaporation at 2.7 +/- 0.5 degrees C without an ice layer (corrected for the difference in gravity on Earth and on Mars) was 1.24 +/- 0.12 mm/h, while at -2.1 +/- 0.3 degrees C with an ice layer the average evaporation rate was 0.84 +/- 0.08 mm/h. These values are in good agreement with those calculated for the evaporation of liquid water and ice when it is assumed that evaporation only depends on diffusion and buoyancy. Our findings suggest that such differences in evaporation rates are entirely due to the temperature difference and that the ice layer has little effect on evaporation rate. We infer that the formation of thin layers of ice on pools of water on Mars does not significantly increase the stability of water on the surface of Mars.     

设计测取精度信息的导弹飞行试验计划用的统计方法

决定导弹飞行试验计划测得精度能力的因素有:被试系统(即惯性制导系统、天文导航系统等)的误差模型;测量系统(即外测系统、遥测等)的误差模型;数据精度;飞行试验前得到的先验信息;弹道(或轨道)以及数据分析的方法。这些因素可以用数字计算机进行仿真,并且可以借助加权最小二乘回归法对具体的精度值求得定量的统计指标。在设计试验计划阶段,数字仿真和统计分析可用来进行综合研究,以便使弹道、测量系统和飞行前试验计划要求等试验条件达到最佳。通过正确的试验设计,常常可以把飞行试验计划测量精度的能力提高10-100倍。     

采用脉冲雷达数据鉴定导弹制导精度的最佳方法

一、引言——飞行试验鉴定概述为了有效地使用弹道式导弹,空军必须有效地鉴定其精度。为鉴定弹道导弹精度而制定的试验计划,随武器和负责部门的不同而不同,但一般都是地面试验和飞行试验相结合,然后加以分析。最能逼真模拟实战或预期运用情况的飞行试验计划,可按复杂性而分为两类。第一类试验通常称为验证性试验计划,其主要目的是测得武器系统的总误差,不注重分离各单项误差因素。第二类试验称为鉴定性试验计划,其目的是分离、鉴别和定量测定形成武器系统总误差的各主要误差源。这种飞行试验计划显然是最为复杂,因而实施起来也是最难成功的。而在洲际弹道式导弹比之用来鉴定其性能的基准系统更为精确的今天,尤为如此。本文详细讨论了在这种情况下鉴定惯性制导系统所遇到的问题,并介绍了一种分析方法,以此尽量减少其中一些问题所造成的影响。     

Key science questions from the second conference on early Mars: geologic, hydrologic, and climatic evolution and the implications for life

In October 2004, more than 130 terrestrial and planetary scientists met in Jackson Hole, WY, to discuss early Mars. The first billion years of martian geologic history is of particular interest because it is a period during which the planet was most active, after which a less dynamic period ensued that extends to the present day. The early activity left a fascinating geological record, which we are only beginning to unravel through direct observation and modeling. In considering this time period, questions outnumber answers, and one of the purposes of the meeting was to gather some of the best experts in the field to consider the current state of knowledge, ascertain which questions remain to be addressed, and identify the most promising approaches to addressing those questions. The purpose of this report is to document that discussion. Throughout the planet's first billion years, planetary-scale processes-including differentiation, hydrodynamic escape, volcanism, large impacts, erosion, and sedimentation-rapidly modified the atmosphere and crust. How did these processes operate, and what were their rates and interdependencies? The early environment was also characterized by both abundant liquid water and plentiful sources of energy, two of the most important conditions considered necessary for the origin of life. Where and when did the most habitable environments occur? Did life actually occupy them, and if so, has life persisted on Mars to the present? Our understanding of early Mars is critical to understanding how the planet we see today came to be.     

关于用近地卫星校准无线电外测设备的数据分析研究

1957年,东靶场首先提出了用近地卫星来校准导弹无线电外测系统的设想。这种方法的主要优点来自下述两个方面:①合作卫星处于自由下落状态,因此具有“平滑”的可预测的轨道;②卫星处于足够的高度,可由许多站进行重迭跟踪。1964年中期,这一计划终于作为一项专款项目来实施。在制定这一计划时,必须详细研究一下东靶场准备用于C波段和连续波雷达的飞行试验事后分析和处理的方法。第一步工作是作出完整的系统模型并尽量找出重要的误差源。找出了11种可能的误差源。对每一误差源开展了具体研究。有些作了深入的研究,有些仅仅浏览了有关文献,选择了校准工作所用的最理想的模型或方法。东靶场主要在下列几方面作了工作:①外测设备测量值及其误差的特性鉴定;②数据压缩和选择;③计算机程序鉴定;④卫星数据最佳区间的选择;⑤站址大地测量。最后将各项研究汇总起来形成初步处理校准卫星数据指导思想的雏型。本文扼要介绍这些研究结果以及初步处理校准卫星数据所得的某些结果。