9. Life On Earth... And Elsewhere?     

Thierry Montmerle  Philippe Claeys  Muriel Gargaud  Purificatión López-García  Hervé Martin  Robert Pascal  Jacques Reisse  Franck Selsis 《Earth, Moon, and Planets》2006,98(1-4):299-312

This concluding chapter is divided into two main parts. The first part is a summary of the main facts and events which constitute the present body of knowledge of the chronology of life in the solar system, in the form of “highlights” in astronomy, geology, chemistry and biology. The second part raises the interrogation “Is life universal?”, and tries to provide answers based on these facts and events. These answers turn out to differ widely among the various disciplines, depending on how far they feel able to extrapolate their current knowledge.  相似文献   

中国卤虫(Artemia sinica)早期胚胎发育相关基因表达序列标签(ESTs)分析          下载免费PDF全文

侯林  邹向阳  姚锋  林盛国  徐明玉  陈志娟  姜丽娟  孙文静 《海洋与湖沼》2008,39(2):139-144

以mRNA差异显示技术分析了中国两性生殖卤虫早期胚胎发育相关基因的表达序列标签(ESTs),共回收了2000条差异条带并进行了克隆、测序,在GenBank/DDBJ/EMBL数据库中用BLASTX和BLASTN软件分别与NCBI上的非冗余核酸序列数据库进行同源性比对,得到分值较高、长度在100bp—2kb以内的ESTs序列133条。所发现的133条ESTs的生物学功能分类为:能量代谢占24%、细胞生长、分裂相关基因占23%、RNA相关占17%、体节形成占12%、蛋白质合成占3%、转录因子占3%、离子转运占5%、细胞信号转导占4%、未知占9%。对所发现的ESTs进行了RT-PCR测定,排除假阳性能够提供足够数量的信息用于获取其全长cDNA,进而获得其全长基因序列以用于功能研究。另外,研究发现了包括小热休克蛋白基因家族、Hox基因家族的abdA和Dfd基因、A-trh基因(排盐器官及盐调节基因)、HIF(缺氧诱导因子)、CK-M2(肌肉型磷酸激酶基因)和GRP基因(富甘氨酸蛋白基因)等20个具有明显功能的相关基因的ESTs和完整基因序列和开放阅读框(ORF)。经初步推断这些ESTs和基因的功能大多为与卤虫发育的生理、生化相关的基因有关。所研究的133条ESTs基本代表了卤虫早期胚胎发育相关功能基因的表达谱。  相似文献   

成都区域大气探测技术支持与保障信息系统     

纪奎秀  郑伟  蒋小平  彭涛  刘兴忠 《成都信息工程学院学报》2009,24(4):393-397

基于Web采用"三层架构"分离和"B/S"(浏览器/月艮务器)模式,使用windows服务技术,选用SQL Server2000数据库平台,实现西南区域对气象探测设备智能化实时监控、实时语音报警、短信息报警功能,切实有效地减轻了各个台站值班人员的工作压力,促进西南区域内气象信息资源共享,为大气探测设备更新发展提供信息交流平台.  相似文献   

山东聊城阿城地区含煤地层蜓类化石及其分带          下载免费PDF全文

宋香锁  王明镇  张锡麒  李敏 《山东国土资源》2008,24(12)

山东聊城地区隐伏的晚古生代含煤地层发育,其中晚石炭—早二叠世太原组灰岩中富含类化石。由三灰、七灰、十灰共鉴定出化石11属45种,自上而下可建立1个类组合带(Pseudoschw agerina带),2个类组合亚带(Triticites paramontiparus亚带;Pseudofusulina firma-Rugosofusulina complicata亚带),该地区所产类组合与华北其他地区及国外相关组合具可比性,Pseudoschw agerina带的时代为早二叠世早期。  相似文献   

太湖蓝藻水华遥感动态监测预警模型的建立   总被引：7，自引：0，他引：7  

魏清宇  江南  吕恒  王甡 《地球信息科学学报》2008,10(2):156-160

湖泊富营养化和蓝藻水华暴发是当前我国湖泊面临的最重要的环境问题之一。本文分析了内陆湖泊太湖蓝藻监测的主要问题。并详细阐述了蓝藻水华遥感动态监测预警模型的建立,即,采用生物光学模型与气象环境预警模型相结合的方式,辅以图形图像学的模块匹配验证,对蓝藻水华暴发前进行临界状态的灾害等级警示,理论上较单纯监测微囊藻叶绿素a浓度值来实现水华暴发预警更为准确。这样,提前采取相应的技术措施,减少蓝藻水华暴发带来的影响和损失。  相似文献   

太平洋东部ES0103柱状样品中可溶有机质的组成变化及其早期成岩作用   总被引：1，自引：1，他引：0  

张海生  于培松  倪建宇  武光海  姚旭莹 《海洋学研究》2008,26(3):1-8

利用2001年采自太平洋东部ES0103站位的多管沉积物柱状样品,采用GC/MS对沉积物中的可溶有机质(氯仿沥青"A")及其族组成(饱和烃、芳烃、非烃和沥青质)、正构烷烃、类异戊二烯烃和萜类化合物进行了定量分析,结果表明:(1)氯仿沥青"A"中的非烃较饱和烃和芳烃的含量高,反映出该海区沉积物中有机质的演化程度较低.(2)正构烷烃的碳分子数范围多为nC14～nC34,CPI值略显奇偶优势,轻重烃比值(nC23-/nC24 )较低;类异戊二烯烃的Pr/Ph值较低,显示出该海区沉积物中的烃类是在较强的还原环境下形成的低成熟烃类,其母质来源主要为大型低等水生生物.(3)总有机碳与显晶蜡产率、氯仿沥青"A"均呈明显正相关关系,表明有机质相对富集层位所处的沉积环境也有利于高蜡烃的形成,成烃演化与成岩作用阶段有较好的对应关系.而萜类化合物的Ts/Tm值在表层和深部差别不大,显示出典型的低成熟烃类的特征.由此可见, ES0103柱状样品所处海区的沉积物为在较强还原环境中形成的,其有机质演化程度较低,为早期成岩作用阶段的产物.  相似文献   

Stellar populations and Lyα emission in two lensed  z≳ 6  galaxies     

Daniel Schaerer  Roser Pelló 《Monthly notices of the Royal Astronomical Society》2005,362(3):1054-1064

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The end of the dark ages in modified Newtonian dynamics     

S. Stachniewicz  M. Kutschera 《Monthly notices of the Royal Astronomical Society》2005,362(1):89-94

We study the evolution of a spherically symmetric density perturbation in the Modified Newtonian Dynamics model applied to the net acceleration over Hubble flow. The background cosmological model is a Λ-dominated, low-Ω_b Friedmann model with no cold dark matter. We include thermal processes and non-equilibrium chemical evolution of the collapsing gas. We find that under these assumptions the first low-mass objects  ( M ≤ 3 × 10⁴ M_⊙)  may collapse already for   z ∼ 30  , which is in quite good agreement with the recent Wilkinson Microwave Anisotropy Probe results. A lower value of a ₀ would lead to much slower collapse of such objects.  相似文献   

宇宙微波背景辐射极化的近似解析公式     

张杨  郝蘅  赵文 《天文学报》2005,46(1):1-11

在宇宙早期的退耦过程中，光子与电子发生Thompson散射．光子气体空间分布的各向异性通过Thompson散射而产生宇宙微波背景辐射的极化，并为最近WMAP观测到．从光子气体的Boltzmann方程出发，采用一般的光深函数，分别积分给出原初密度扰动和残余引力波产生的微波背景辐射极化的近似解析解，结果适用于一般的复合过程．密度扰动FS所产生极化的近似解析解为βS≌-CFs(Td)ΔTd，其中Td和△Td分别为退耦时刻和退耦宽度，系数C≌(0．08—0．12)，明显依赖于复合模型．残余引力波扰动FT产生极化的积分稍微复杂，在长波近似下我们对原初扰动按波数进行幂级数展开，保留到两项FT≌FT^(1) FT(2)，分别积分，给出近似解析解βT≌-[CFT^(1)(Td) DFT^(2)(Td)]ΔTd.第一项的极化与密度扰动类似，结论也相同；但第二项的系数D≌(0．22—0．32)，远大于系数C，我们的近似解析解有助于理解背景辐射的温度一极化交叉关联和检测残余引力波对背景辐射各向异性的贡献．  相似文献   

Lines in the cosmic microwave background spectrum from the epoch of cosmological hydrogen recombination     

J. A. Rubiño-Martín  J. Chluba  R. A. Sunyaev 《Monthly notices of the Royal Astronomical Society》2006,371(4):1939-1952

We compute the spectral distortions of the cosmic microwave background (CMB) arising during the epoch of cosmological hydrogen recombination within the standard cosmological (concordance) model for frequencies in the range 1–3500 GHz. We follow the evolution of the populations of the hydrogen levels including states up to principle quantum number   n = 30  in the redshift range  500 ≤ z ≤ 3500  . All angular momentum substates are treated individually, resulting in a total number of 465 hydrogen levels. The evolution of the matter temperature and the fraction of electrons coming from He  ii are also included. We present a detailed discussion of the distortions arising from the main dipolar transitions, for example Lyman and Balmer series, as well as the emission due to the two-photon decay of the hydrogen 2s level. Furthermore, we investigate the robusteness of the results against changes in the number of shells considered. The resulting spectral distortions have a characteristic oscillatory behaviour, which might allow experimentalists to separate them from other backgrounds. The relative distortion of the spectrum exceeds a value of 10⁻⁷ at wavelengths longer than 21 cm. Our results also show the importance of detailed follow-up of the angular momentum substates, and their effect on the amplitude of the lines. The effect on the residual electron fraction is only moderate, and mainly occurs at low redshifts. The CMB angular power spectrum is changed by less than 1 per cent. Finally, our computations show that if the primordial radiation field is described by a pure blackbody, then there is no significant emission from any hydrogen transition at redshifts greater than   z ∼ 2000  . This is in contrast to some earlier works, where the existence of a 'pre-recombination' peak was claimed.  相似文献