Ultrastructural and geochemical characterization of Archean-Paleoproterozoic graphite particles: implications for recognizing traces of life in highly metamorphosed rocks

Abundant graphite particles occur in amphibolite-grade quartzite of the Archean-Paleoproterozoic Wutai Metamorphic Complex in the Wutaishan area of North China. Petrographic thin section observations suggest that the graphite particles occur within and between quartzite clasts and are heterogeneous in origin. Using HF maceration techniques, the Wutai graphite particles were extracted for further investigation. Laser Raman spectroscopic analysis of a population of extracted graphite discs indicated that they experienced a maximum metamorphic temperature of 513 +/- 50 degrees C, which is consistent with the metamorphic grade of the host rock and supports their indigenicity. Scanning and transmission electron microscopy revealed that the particles bear morphological features (such as hexagonal sheets of graphite crystals) related to metamorphism and crystal growth, but a small fraction of them (graphite discs) are characterized by a circular morphology, distinct marginal concentric folds, surficial wrinkles, and complex nanostructures. Ion microprobe analysis of individual graphite discs showed that their carbon isotope compositions range from -7.4 per thousand to -35.9 per thousand V-PDB (Vienna Pee Dee Belemnite), with an average of -20.3 per thousand, which is comparable to bulk analysis of extracted carbonaceous material. The range of their size, ultrastructures, and isotopic signatures suggests that the morphology and geochemistry of the Wutai graphite discs were overprinted by metamorphism and their ultimate carbon source probably had diverse origins that included abiotic processes. We considered both biotic and abiotic origins of the carbon source and graphite disc morphologies and cannot falsify the possibility that some circular graphite discs characterized by marginal folds and surficial wrinkles represent deflated, compressed, and subsequently graphitized organic-walled vesicles. Together with reports by other authors of acanthomorphic acritarchs from greenschist-amphibolite-grade metamorphic rocks, this study suggests that it is worthwhile to examine carbonaceous materials preserved in highly metamorphosed rocks for possible evidence of ancient life.     

CCD互相关粒子图像测速及其在对抗流流场测量中的应用

在常规自相关粒子图像测速（ＰＩＶ）系统的基础上,发展了一个采用ＣＣＤ像机的互相关粒子图像测速系统。用这一新系统测量了对抗流流场的结果表明,这一技术克服了自相关粒子图像测速技术在测量具有滞止点的流场中的困难。实验说明,与自相关粒子图像测速技术相比,这一技术更快捷有效。     

The influence of microgravity on invasive growth in Saccharomyces cerevisiae

This study investigates the effects of microgravity on colony growth and the morphological transition from single cells to short invasive filaments in the model eukaryotic organism Saccharomyces cerevisiae. Two-dimensional spreading of the yeast colonies grown on semi-solid agar medium was reduced under microgravity in the Σ1278b laboratory strain but not in the CMBSESA1 industrial strain. This was supported by the Σ1278b proteome map under microgravity conditions, which revealed upregulation of proteins linked to anaerobic conditions. The Σ1278b strain showed a reduced invasive growth in the center of the yeast colony. Bud scar distribution was slightly affected, with a switch toward more random budding. Together, microgravity conditions disturb spatially programmed budding patterns and generate strain-dependent growth differences in yeast colonies on semi-solid medium.     

Formation of nucleobases from formamide in the presence of iron oxides: implication in chemical evolution and origin of life

Simple compounds like HCN, which have one C and one N, are proposed as the probable precursors for biomonomers. Formamide, a hydrolysis product of HCN, is known as the precursor of various biologically important compounds, for example, nucleobases (purines and pyrimidines). In this paper, we report our results on the synthesis of nucleobases, adenine, cytosine, purine, 9-(hydroxyacetyl) purine, and 4(3H)-pyrimidinone from formamide, using iron oxide (hematite) and oxide hydroxides (goethite and akaganeite) as a catalyst. Goethite and hematite produced purine in higher yield. The products formed were characterized by high-performance liquid chromatography and electrospray ionization mass spectrometry techniques. Results of our study reveal that iron oxides might have worked as efficient prebiotic catalysts.     

通过时间拉伸预处理克服ADC的输入带宽限制时间拉伸预处理：第一部分

数字信号处理（ＤＳＰ）已经开始在现代通讯和雷达系统设计中起主导作用，不幸的是，商用模拟－数字变换器（ＡＤＣ０的速度尚不能满足通讯和雷达系统的数字化要求（尤其在微波段），可喜的是，我们已经发展了一种新的ＡＤＣ机理－在ＡＤ变换之前放慢模拟信号的速度，通过卫低输入信号（载波及其调制）的带宽的方法，ＡＤＣ的性能得到极大的改进，本文由于几个部分组成，还将研究时间压缩及其在高速数字－模拟变换器（ＤＡＣ）中的应用。     

冲压——火箭发动机的突扩喷射

对冲压——火箭发动机冲压级突扩喷射的重要性作了说明并简要地评论了这一领域最近的研究工作之后,本文介绍一种计算椭圆型内部反应流的数值方法。它是把算子分裂法用于物质守恒方程,使这些方程中通常是疑难的积分在两步演算中完成。对于无反应的第一阶段,应用Gosman等人的算法;而有反应的第二阶段,使方程式能改写成一组常微分方程。为处理常常与实际的化学动力学问题有关的刚性,应用Gear的方法对不同的几何构型解该常微分方程组。 实验结果同数值法的预估值很好地相符。发现在靠近喷射处有一强大的回流区。几何构型既影响化学反应又影响流动稳定性:45°喷射引起平均流率的增加,而90°时却不明显。垂直喷射比45°进气好象是更加稳定,这还取决于恰当的构型。     

航天飞机固体火箭发动机壳体的统计断裂力学和最佳断裂控制

本报告叙述了有关航天飞机固体火箭发动机壳体可靠性分析方法的研究。该分析方法是基于统计断裂力学理论监考虑到原始裂纹大小的概率分布情况。这种可靠性分析方法可用于设计变量的选择,例如,在最小预计成本和规定的可靠性范围的基础上,选择固体火箭发动机壳体的壁厚、设计使用期限和试验因子。断裂控制计划的作用,如在非破坏性试验中,以及在使用过程中材料的腐蚀,均可把它作为一种选择设计变量的研究方法。本报告中的以可靠性为基础的方法,经改进后就可推广应用在其它类似结构和各种断裂控制设计上。