An examination of the carbon isotope effects associated with amino acid biosynthesis

Stable carbon isotope ratios (delta(13)C) were determined for alanine, proline, phenylalanine, valine, leucine, isoleucine, aspartate (aspartic acid and asparagine), glutamate (glutamic acid and glutamine), lysine, serine, glycine, and threonine from metabolically diverse microorganisms. The microorganisms examined included fermenting bacteria, organotrophic, chemolithotrophic, phototrophic, methylotrophic, methanogenic, acetogenic, acetotrophic, and naturally occurring cryptoendolithic communities from the Dry Valleys of Antarctica. Here we demonstrated that reactions involved in amino acid biosynthesis can be used to distinguish amino acids formed by life from those formed by nonbiological processes. The unique patterns of delta(13)C imprinted by life on amino acids produced a biological bias. We also showed that, by applying discriminant function analysis to the delta(13)C value of a pool of amino acids formed by biological activity, it was possible to identify key aspects of intermediary carbon metabolism in the microbial world. In fact, microorganisms examined in this study could be placed within one of three metabolic groups: (1) heterotrophs that grow by oxidizing compounds containing three or more carbon-to-carbon bonds (fermenters and organotrophs), (2) autotrophs that grow by taking up carbon dioxide (chemolitotrophs and phototrophs), and (3) acetoclastic microbes that grow by assimilation of formaldehyde or acetate (methylotrophs, methanogens, acetogens, and acetotrophs). Furthermore, we demonstrated that cryptoendolithic communities from Antarctica grouped most closely with the autotrophs, which indicates that the dominant metabolic pathways in these communities are likely those utilized for CO(2 )fixation. We propose that this technique can be used to determine the dominant metabolic types in a community and reveal the overall flow of carbon in a complex ecosystem.     

F-16XL为HSCT进行超音速层流试飞

目前一架F-16XL研究机已经被改装成一架超音速层流控制概念研究机。该机的左机翼被装上了一个带有很大的吸气表面翼套。这项试验将对美国高速民用运输机(HSCT),即下一代超音速民用飞机的研制具有重要的意义。装上新翼套的F-16XL已完成了首次飞行。为其制订的一系列试验计划将要验证仅仅使用目前的吸气技术是否能在超音速飞行下维持机翼表面的大部分区域为层流区,从理论上讲,通过对机翼前段翼型外形的正确设计,组     

美国空军关注下一代电子战飞机

USAFSizesUpNextElectronicCombatAircraft美国一些制造商现在又开始忙于向空军提出用来替代EA—6B“徘徊者”老龄电于战飞机的后继机方案了。其中一种是“联合攻击战斗机”（JS）的派生型,还有就是考虑将F—22改装为具有电子战能力,使其能偷偷突防到敌空防区纵深,并将目标摧毁之。新电子战飞机计划被如此关注的主要原因是对科索沃冲突详细评估的结果。美国空军认为这场冲突显示对于各种信息收集和电子战飞机的需求要大大增加,特别是像EA—6B的后继机,并要大大扩展战术干扰空中力量,以保护隐身和常规的攻击飞机。如果能在2001…     

增大表征振荡器能力的修正阿仑方差

阿仑方差σ_y~2(τ)事实上现在已经成为测量振荡器在时域中不稳定度的实用标准。振荡器的频率不稳定度常常可以用幂律谱S_y(f)～f~a拟出适当的模型,这里的y是归一化频率差,f是傅氏频率,a在某一傅氏频率范围内为常数。已经证明,用幂律谱,则有σ_y~2(τ)～τ~μ,当-3相似文献   

一种测定精密惯性制导系统性能的方法

本文介绍一种先进的方法,即采用一套附加的惯性测量装置(以下用IMU表示)——高级惯性参考球(AIRS)来提供高质量速度数据,用以测定民兵导弹惯性制导系统的性能。文章简要介绍了先前用陆上雷达的外测数据来鉴定民兵制导系统的方法,并闸述了双套IMU方案的演变。文章介绍了方案、校准方法、所需的弹上和地面保障设备以及分析方法;还讨论了随后进行的火箭橇试验计划,在这里可以基本不经改动即能使用弹上设备和地面保障设备。     

叶片CAT型线图的自适应生成

介绍在计算机集成信息系统中（ＣＩＩＳ），利用三坐标测量机测量叶片、自适应生成型线图的方法，包括曲线类型、曲线段数、分段点和曲线参数的自适应选择，通过试用对文中提出的方法进行了验证评价．关键词     

在未来战场上无人机对卫星通信系统的补充作用

在军事通信领域,刚刚出现但却意义深远的变革很快就将向单兵、车辆和飞机提供战场的全面情况,并确保他们与世界各地的通信联络。高空、长航时无人机将会被用作准卫星系统进行宽范围的通信中继。不久的将来,新技术的发展将使所有士兵都装备一套便携式个人通信系统用于了解战场形势。民用个人通信系统技术上的发展也将有助于它们在军事上的应用。目前,世界军事力量对来自多渠道的地理空间数据的合成有更高的要求。任何有关     

A FINITE ELEMENT ADAPTIVE METHOD FOR SOLVING GENERALIZED STOKES PROSLEM

ＡＦＩＮＩＴＥＥＬＥＭＥＮＴＡＤＡＰＴＩＶＥＭＥＴＨＯＤＦＯＲＳＯＬＶＩＮＧＧＥＮＥＲＡＬＩＺＥＤＳＴＯＫＥＳＰＲＯＳＬＥＭＤ．Ａ．ＦｏｋｉｎＹａｎｇＺｕｏｓｈｅｎｇ（ＤｅｐａｒｔｍｅｎｔｏｆＡｅｒｏｄｙｎａｍｉｃｓ，ＮＵＡＡ２９ＹｕｄａｏＳｔｒｅｅ...     

Physiological problems for man in space

This article discusses some of the problems facing man in space. Many of these problems are manifested only on return to Earth when the de-conditioned body again has to withstand the effects of gravity.