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Dinoflagellate cysts from two Middle-Late Jurassic sections in the Wenquan and Yanshiping regions of the Qiangtang Basin comprise 24 genera and 36 species including one new taxon of the genus Tenua. Based on their stratigraphic distribution, six assemblage zones are recognized in ascending order as follows: 1) Tubotuberella egemenii Zone, probably Callovian, in the mid-upper part of the Xiali Formation; 2) Pareodinia ceratophora Zone, probably Oxfordian, in the lower part of the Suowa Formation; 3) Batiacasphaera floralis Zone, probably Oxfordian, in the middle part of the Suowa Formation; 4) Amphorula metaelliptica Zone, probably Early Kimmeridgian, in the upper part of the Suowa Formation; 5) Alisocysta spp. Zone, probably Early Kimmeridgian, in the base of the Xueshan Formation; 6) Tenua wenquanensis sp. nov. -Dichadogonyaulax schizoblata Zone, probably Late Kimmeridgian-Tithonian, in the lower part of the Xueshan Formation. Based on our analysis the Jurassic-Cretaceous Boundary in the Wenquan section is placed higher than previously.  相似文献   

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Dinoflagellate cysts from two Middle-Late Jurassic sections in the Wenquan and Yanshiping regions of the Qiangtang Basin comprise 24 genera and 36 species including one new taxon of the genus Tenua. Based on their stratigraphic distribution, six assemblage zones are recognized in ascending order as follows: 1) Tubotuberella egemenii Zone, probably Callovian, in the mid-upper part of the Xiali Formation; 2) Pareodinia ceratophora Zone, probably Oxfordian, in the lower part of the Suowa Formation; 3) Batiacasphaera floralis Zone, probably Oxfordian, in the middle part of the Suowa Formation; 4) Amphorula metaelliptica Zone, probably Early Kimmeridgian, in the upper part of the Suowa Formation; 5) Alisocysta spp. Zone, probably Early Kimmeridgian, in the base of the Xueshan Formation; 6) Tenua wenquanensis sp. nov. -Dichadogonyaulax schizoblata Zone, probably Late Kimmeridgian-Tithonian, in the lower part of the Xueshan Formation. Based on our analysis the Jurassic-Cretaceous Boundary in the Wenquan section is placed higher than previously.  相似文献   

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Activation of the aryl hydrocarbon receptor (AHR) by environmental xenobiotic toxic chemicals, for instance 2,3,7,8-tetrachlorodibenzo-p-dioxin (dioxin), has been implicated in a variety of cellular processes such as embryogenesis, transformation, tumorigenesis and inflammation. But the identity of an endogenous ligand activating the AHR under physiological conditions in the absence of environmental toxic chemicals is still unknown. Here we identify the tryptophan (Trp) catabolite kynurenine (Kyn) as an endogenous ligand of the human AHR that is constitutively generated by human tumour cells via tryptophan-2,3-dioxygenase (TDO), a liver- and neuron-derived Trp-degrading enzyme not yet implicated in cancer biology. TDO-derived Kyn suppresses antitumour immune responses and promotes tumour-cell survival and motility through the AHR in an autocrine/paracrine fashion. The TDO-AHR pathway is active in human brain tumours and is associated with malignant progression and poor survival. Because Kyn is produced during cancer progression and inflammation in the local microenvironment in amounts sufficient for activating the human AHR, these results provide evidence for a previously unidentified pathophysiological function of the AHR with profound implications for cancer and immune biology.  相似文献   

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海洋环境现场监测手段的开发与应用   总被引:8,自引:0,他引:8  
阐述了国际上化学传感器、化学分析器、生物传感器,以及基于这些传感器和分析器的多学科交叉现场观测系统等海洋环境现场监测手段的开发与应用概况,并略涉一些现场采样手段,重点列举了pCO2微电极、中性浮式沉积物采样器,以及用于研究海洋上层输出通量的锚式系统,可为我国引进和开发海洋观测高技术提供借鉴。  相似文献   

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工业化的快速发展,大量工业废弃物的无达标排放,使环境承受着越来越巨大的压力,其中重金属污染更是引起了人们的高度重视,很多学者对重金属的生态效应及毒性作用进行了比较深入、系统的研究.仅以重金属镉为例,就近年来国内外学者对其的生态效应、毒性作用研究进行了综述,为以后进一步探讨镉污染问题提供有益的借鉴.  相似文献   

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环境和能源约束下的内生经济增长模型   总被引:2,自引:0,他引:2  
综合考虑环境和能源这两个制约经济高速发展的因素,建立经济增长和环境质量与能源强度之间的关系。引入人的身体健康指数去衡量环境的质量,并将其引入效用函数,揭示了基于代表性个体的消费和健康的效用函数达到最大化的经济发展需要满足的条件。  相似文献   

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Under the CES production technology, an improved Cass-Coopmans model with solvable endogenous fertility is given. We prove that there are multiple growth paths and multiple steady states when CES 0<δ<1 and the technology level is high enough; the growth path and the steady state is unique when δ>1 and the ratio of capital is smaller than a constant. So, the dynamic system which describes the model undergoes a bifurcation when δ=1 We discuss the economic sense of the main results we give. Cai Donghan, born in Sep. 1960, Ph.D graduate student  相似文献   

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An antioxidant function for DMSP and DMS in marine algae   总被引:29,自引:0,他引:29  
Sunda W  Kieber DJ  Kiene RP  Huntsman S 《Nature》2002,418(6895):317-320
The algal osmolyte dimethylsulphoniopropionate (DMSP) and its enzymatic cleavage product dimethylsulphide (DMS) contribute significantly to the global sulphur cycle, yet their physiological functions are uncertain. Here we report results that, together with those in the literature, show that DMSP and its breakdown products (DMS, acrylate, dimethylsulphoxide, and methane sulphinic acid) readily scavenge hydroxyl radicals and other reactive oxygen species, and thus may serve as an antioxidant system, regulated in part by enzymatic cleavage of DMSP. In support of this hypothesis, we found that oxidative stressors, solar ultraviolet radiation, CO(2) limitation, Fe limitation, high Cu(2+) (ref. 9) and H(2)O(2) substantially increased cellular DMSP and/or its lysis to DMS in marine algal cultures. Our results indicate direct links between such stressors and the dynamics of DMSP and DMS in marine phytoplankton, which probably influence the production of DMS and its release to the atmosphere. As oxidation of DMS to sulphuric acid in the atmosphere provides a major source of sulphate aerosols and cloud condensation nuclei, oxidative stressors--including solar radiation and Fe limitation--may be involved in complex ocean atmosphere feedback loops that influence global climate and hydrological cycles.  相似文献   

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磁通门磁力仪中的时钟电路是以单片机MSP430为核心,协调控制电源模块、时钟电路模块、数据通讯模块以及人机交互功能模块。详细分析了各功能模块设计的原理电路,测试结果表明,该时钟电路能正常工作,可以准确显示年、月、日、时、分、秒,且可将数据通过USB在PC上显示。  相似文献   

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本文简要介绍了基准原子钟的发展历程;目前,光学原子钟的频率不确定度已达到了10-18量级,是现在人们公认的最可能新的时间基准.国家授时中心担负着国家综合原子时的建立和保持,是国际原子时TAI建立的主要参加单位.文中介绍了国家授时中心锶光学原子钟研制工作的最新进展.  相似文献   

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T Roenneberg  H Nakamura  J W Hastings 《Nature》1988,334(6181):432-434
The circadian clock is considered to be a universal feature of eucaryotic organisms, controlling the occurrence and rates of many different aspects of life, ranging from single enzymatic reactions and metabolism to complex behaviours such as activity and rest. Although the nature of the underlying cellular/biochemical oscillator is still unknown, many substances are known to influence either phase or period of circadian rhythms in different organisms. These include D2O, electrolytes and ion channel inhibitors, small organic molecules such as alcohols and aldehydes, inhibitors of protein synthesis and amino-acid analogues. Certain transmitter and neurochemical drugs also influence the circadian clock in higher animals. We report here that the period of free-running circadian rhythms in the unicellular marine alga Gonyaulax polyedra is shortened by extracts from mammalian cells. The effect is dose-dependent, accelerating the circadian clock by as much as 4 hours per day. The substance responsible for this effect has been isolated from bovine muscle and identified as creatine. Authentic creatine has identical biological effects at micromolar concentrations and is known in animal systems for its involvement in cellular energy metabolism. A period shortening substance with similar chemical properties is also present in extracts of Gonyaulax itself.  相似文献   

17.
Chabot JR  Pedraza JM  Luitel P  van Oudenaarden A 《Nature》2007,450(7173):1249-1252
Recent advances in measuring gene expression at the single-cell level have highlighted the stochastic nature of messenger RNA and protein synthesis. Stochastic gene expression creates a source of variability in the abundance of cellular components, even among isogenic cells exposed to an identical environment. Recent integrated experimental and modelling studies have shed light on the molecular sources of this variability. However, many of these studies focus on systems that have reached a steady state and therefore do not address a large class of dynamic phenomena including oscillatory gene expression. Here we develop a general protocol for analysing and predicting stochastic gene expression in systems that never reach steady states. We use this framework to analyse experimentally stochastic expression of genes driven by the Synechococcus elongatus circadian clock. We find that, although the average expression at two points in the circadian cycle separated by 12 hours is identical, the variability at these two time points can be different. We show that this is a general feature of out-of-steady-state systems. We demonstrate how intrinsic noise sources, owing to random births and deaths of mRNAs and proteins, or extrinsic noise sources, which introduce fluctuations in rate constants, affect the cell-to-cell variability. To distinguish experimentally between these sources, we measured how the correlation between expression fluctuations of two identical genes is modulated during the circadian cycle. This quantitative framework is generally applicable to any out-of-steady-state system and will be necessary for understanding the fidelity of dynamic cellular systems.  相似文献   

18.
Etchegaray JP  Lee C  Wade PA  Reppert SM 《Nature》2003,421(6919):177-182
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Weeks SJ  Currie B  Bakun A 《Nature》2002,415(6871):493-494
Recurrent eruptions of toxic hydrogen sulphide gas in the waters along the Namibian coast off southwestern Africa have been considered to be local features with only limited ecosystem-scale consequences. But satellite remote sensing has revealed that these naturally occurring events are much more extensive and longer-lasting than previously suspected, and that the resultant hypoxia may last for much longer. The effects on the marine ecology and valuable coastal fisheries of this region are likely to be important.  相似文献   

20.
刘志堂  邵保华  孟克 《应用科技》2004,31(10):12-14
提出了一种分析高速数据传输中时钟抖动的解决方案——Matlab方法.分析了高速数据通讯中时钟抖动产生的原因及对通信系统的影响,介绍了用TDS7000系列数字荧光示波器和Matlab捕获信号数据并随后对不归零制(NRZ)时钟信号进行简单抖动分析的方法,完成了高速数据通信中的时钟信号的采集以及时钟抖动的鉴定和分析.试验验证,本方法大大提高了抖动鉴定工作的精度和效率.  相似文献   

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