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排序方式: 共有280条查询结果,搜索用时 31 毫秒
61.
Daffonchio D Borin S Brusa T Brusetti L van der Wielen PW Bolhuis H Yakimov MM D'Auria G Giuliano L Marty D Tamburini C McGenity TJ Hallsworth JE Sass AM Timmis KN Tselepides A de Lange GJ Hübner A Thomson J Varnavas SP Gasparoni F Gerber HW Malinverno E Corselli C Garcin J McKew B Golyshin PN Lampadariou N Polymenakou P Calore D Cenedese S Zanon F Hoog S;Biodeep Scientific Party 《Nature》2006,440(7081):203-207
The chemical composition of the Bannock basin has been studied in some detail. We recently showed that unusual microbial populations, including a new division of Archaea (MSBL1), inhabit the NaCl-rich hypersaline brine. High salinities tend to reduce biodiversity, but when brines come into contact with fresher water the natural haloclines formed frequently contain gradients of other chemicals, including permutations of electron donors and acceptors, that may enhance microbial diversity, activity and biogeochemical cycling. Here we report a 2.5-m-thick chemocline with a steep NaCl gradient at 3.3 km within the water column betweeen Bannock anoxic hypersaline brine and overlying sea water. The chemocline supports some of the most biomass-rich and active microbial communities in the deep sea, dominated by Bacteria rather than Archaea, and including four major new divisions of Bacteria. Significantly higher metabolic activities were measured in the chemocline than in the overlying sea water and underlying brine; functional analyses indicate that a range of biological processes is likely to occur in the chemocline. Many prokaryotic taxa, including the phylogenetically new groups, were confined to defined salinities, and collectively formed a diverse, sharply stratified, deep-sea ecosystem with sufficient biomass to potentially contribute to organic geological deposits. 相似文献
62.
The distillation and volatility of ionic liquids 总被引:2,自引:0,他引:2
Earle MJ Esperança JM Gilea MA Lopes JN Rebelo LP Magee JW Seddon KR Widegren JA 《Nature》2006,439(7078):831-834
It is widely believed that a defining characteristic of ionic liquids (or low-temperature molten salts) is that they exert no measurable vapour pressure, and hence cannot be distilled. Here we demonstrate that this is unfounded, and that many ionic liquids can be distilled at low pressure without decomposition. Ionic liquids represent matter solely composed of ions, and so are perceived as non-volatile substances. During the last decade, interest in the field of ionic liquids has burgeoned, producing a wealth of intellectual and technological challenges and opportunities for the production of new chemical and extractive processes, fuel cells and batteries, and new composite materials. Much of this potential is underpinned by their presumed involatility. This characteristic, however, can severely restrict the attainability of high purity levels for ionic liquids (when they contain poorly volatile components) in recycling schemes, as well as excluding their use in gas-phase processes. We anticipate that our demonstration that some selected families of commonly used aprotic ionic liquids can be distilled at 200-300 degrees C and low pressure, with concomitant recovery of significant amounts of pure substance, will permit these currently excluded applications to be realized. 相似文献
63.
令G=(V,E)为一个图,它的节点数为n,不仅是一个双循环也是一个上循环.记β(G)为G的双循环空间的维数.对于G的一个子图H,用φ(G,H)表示G的支撑森数目,使得它的每个树均恰含H的一条边.图G的H扩张X(G,H)在G上增添一个新节点ν,连ν与H的每一个奇次节点以一边所得到的图.本文证明,φ(G,H)是个偶数,要么X(G,H)不连通,要么X(G,H)有一个非零双循环.对于一个欧拉图G,令λ(G)为G中这样边的最小数目,使得在将它们从G中收缩掉而得到的图G中,所有那些落在奇数个完满对集上的边,形成一个非零双循环.同时还得到,在G的最大对集中边数为μ(G)的一个下界,即μ(G)≥(n-|β(G)-1|)/2.对于非欧拉图G,令ψ(G)=β(X(G,G)),和用γ(G)表示这样边的最小数目,使得在将它们从G中收缩掉而得到的图上,有边属于奇数个完满对集.我们证明,γ(G)=ψ(G)以及μ(G)≥(n-ψ(G))/2. 相似文献
64.
Chin K de Solorzano CO Knowles D Jones A Chou W Rodriguez EG Kuo WL Ljung BM Chew K Myambo K Miranda M Krig S Garbe J Stampfer M Yaswen P Gray JW Lockett SJ 《Nature genetics》2004,36(9):984-988
Transition through telomere crisis is thought to be a crucial event in the development of most breast carcinomas. Our goal in this study was to determine where this occurs in the context of histologically defined breast cancer progression. To this end, we assessed genome instability (using fluorescence in situ hybridization) and other features associated with telomere crisis in normal ductal epithelium, usual ductal hyperplasia, ductal carcinoma in situ and invasive cancer. We modeled this process in vitro by measuring these same features in human mammary epithelial cell cultures during ZNF217-mediated transition through telomere crisis and immortalization. Taken together, the data suggest that transition through telomere crisis and immortalization in breast cancer occurs during progression from usual ductal hyperplasia to ductal carcinoma in situ. 相似文献
65.
Systematic generation of high-resolution deletion coverage of the Drosophila melanogaster genome 总被引:1,自引:0,他引:1
Parks AL Cook KR Belvin M Dompe NA Fawcett R Huppert K Tan LR Winter CG Bogart KP Deal JE Deal-Herr ME Grant D Marcinko M Miyazaki WY Robertson S Shaw KJ Tabios M Vysotskaia V Zhao L Andrade RS Edgar KA Howie E Killpack K Milash B Norton A Thao D Whittaker K Winner MA Friedman L Margolis J Singer MA Kopczynski C Curtis D Kaufman TC Plowman GD Duyk G Francis-Lang HL 《Nature genetics》2004,36(3):288-292
In fruit fly research, chromosomal deletions are indispensable tools for mapping mutations, characterizing alleles and identifying interacting loci. Most widely used deletions were generated by irradiation or chemical mutagenesis. These methods are labor-intensive, generate random breakpoints and result in unwanted secondary mutations that can confound phenotypic analyses. Most of the existing deletions are large, have molecularly undefined endpoints and are maintained in genetically complex stocks. Furthermore, the existence of haplolethal or haplosterile loci makes the recovery of deletions of certain regions exceedingly difficult by traditional methods, resulting in gaps in coverage. Here we describe two methods that address these problems by providing for the systematic isolation of targeted deletions in the D. melanogaster genome. The first strategy used a P element-based technique to generate deletions that closely flank haploinsufficient genes and minimize undeleted regions. This deletion set has increased overall genomic coverage by 5-7%. The second strategy used FLP recombinase and the large array of FRT-bearing insertions described in the accompanying paper to generate 519 isogenic deletions with molecularly defined endpoints. This second deletion collection provides 56% genome coverage so far. The latter methodology enables the generation of small custom deletions with predictable endpoints throughout the genome and should make their isolation a simple and routine task. 相似文献
66.
67.
68.
Hepatocyte nuclear factor 4alpha controls the development of a hepatic epithelium and liver morphogenesis 总被引:10,自引:0,他引:10
Parviz F Matullo C Garrison WD Savatski L Adamson JW Ning G Kaestner KH Rossi JM Zaret KS Duncan SA 《Nature genetics》2003,34(3):292-296
Although advances have been made in understanding cell differentiation, only rudimentary knowledge exists concerning how differentiated cells form tissues and organs. We studied liver organogenesis because the cell and tissue architecture of this organ is well defined. Approximately 60% of the adult liver consists of hepatocytes that are arranged as single-cell anastomosing plates extending from the portal region of the liver lobule toward the central vein. The basal surface of the hepatocytes is separated from adjacent sinusoidal endothelial cells by the space of Disse, where the exchange of substances between serum and hepatocytes takes place. The hepatocyte's apical surface forms bile canaliculi that transport bile to the hepatic ducts. Proper liver architecture is crucial for hepatic function and is commonly disrupted in disease states, including cirrhosis and hepatitis. Here we report that hepatocyte nuclear factor 4alpha (Hnf4alpha) is essential for morphological and functional differentiation of hepatocytes, accumulation of hepatic glycogen stores and generation of a hepatic epithelium. We show that Hnf4alpha is a dominant regulator of the epithelial phenotype because its ectopic expression in fibroblasts induces a mesenchymal-to-epithelial transition. Most importantly, the morphogenetic parameters controlled by Hnf4alpha in hepatocytes are essential for normal liver architecture, including the organization of the sinusoidal endothelium. 相似文献
69.
Association of cadherin 23 with polygenic inheritance and genetic modification of sensorineural hearing loss 总被引:20,自引:0,他引:20
Age-related hearing loss (AHL) in common inbred mouse strains is a genetically complex quantitative trait. We found a synonymous single-nucleotide polymorphism in exon 7 of Cdh23 that shows significant association with AHL and the deafness modifier mdfw (modifer of deafwaddler). The hypomorphic Cdh23(753A) allele causes in-frame skipping of exon 7. Altered adhesion or reduced stability of CDH23 may confer susceptibility to AHL. Homozygosity at Cdh23(753A) or in combination with heterogeneous secondary factors is a primary determinant of AHL in mice. 相似文献
70.
Compartments revealed in food-web structure 总被引:1,自引:0,他引:1
Compartments in food webs are subgroups of taxa in which many strong interactions occur within the subgroups and few weak interactions occur between the subgroups. Theoretically, compartments increase the stability in networks, such as food webs. Compartments have been difficult to detect in empirical food webs because of incompatible approaches or insufficient methodological rigour. Here we show that a method for detecting compartments from the social networking science identified significant compartments in three of five complex, empirical food webs. Detection of compartments was influenced by food web resolution, such as interactions with weights. Because the method identifies compartmental boundaries in which interactions are concentrated, it is compatible with the definition of compartments. The method is rigorous because it maximizes an explicit function, identifies the number of non-overlapping compartments, assigns membership to compartments, and tests the statistical significance of the results. A graphical presentation reveals systemic relationships and taxa-specific positions as structured by compartments. From this graphic, we explore two scenarios of disturbance to develop a hypothesis for testing how compartmentalized interactions increase stability in food webs. 相似文献