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71.
Lambert F Delmonte B Petit JR Bigler M Kaufmann PR Hutterli MA Stocker TF Ruth U Steffensen JP Maggi V 《Nature》2008,452(7187):616-619
Dust can affect the radiative balance of the atmosphere by absorbing or reflecting incoming solar radiation; it can also be a source of micronutrients, such as iron, to the ocean. It has been suggested that production, transport and deposition of dust is influenced by climatic changes on glacial-interglacial timescales. Here we present a high-resolution record of aeolian dust from the EPICA Dome C ice core in East Antarctica, which provides an undisturbed climate sequence over the past eight climatic cycles. We find that there is a significant correlation between dust flux and temperature records during glacial periods that is absent during interglacial periods. Our data suggest that dust flux is increasingly correlated with Antarctic temperature as the climate becomes colder. We interpret this as progressive coupling of the climates of Antarctic and lower latitudes. Limited changes in glacial-interglacial atmospheric transport time suggest that the sources and lifetime of dust are the main factors controlling the high glacial dust input. We propose that the observed approximately 25-fold increase in glacial dust flux over all eight glacial periods can be attributed to a strengthening of South American dust sources, together with a longer lifetime for atmospheric dust particles in the upper troposphere resulting from a reduced hydrological cycle during the ice ages. 相似文献
72.
Krishnan MN Ng A Sukumaran B Gilfoy FD Uchil PD Sultana H Brass AL Adametz R Tsui M Qian F Montgomery RR Lev S Mason PW Koski RA Elledge SJ Xavier RJ Agaisse H Fikrig E 《Nature》2008,455(7210):242-245
West Nile virus (WNV), and related flaviviruses such as tick-borne encephalitis, Japanese encephalitis, yellow fever and dengue viruses, constitute a significant global human health problem. However, our understanding of the molecular interaction of such flaviviruses with mammalian host cells is limited. WNV encodes only 10 proteins, implying that it may use many cellular proteins for infection. WNV enters the cytoplasm through pH-dependent endocytosis, undergoes cycles of translation and replication, assembles progeny virions in association with endoplasmic reticulum, and exits along the secretory pathway. RNA interference (RNAi) presents a powerful forward genetics approach to dissect virus-host cell interactions. Here we report the identification of 305 host proteins that affect WNV infection, using a human-genome-wide RNAi screen. Functional clustering of the genes revealed a complex dependence of this virus on host cell physiology, requiring a wide variety of molecules and cellular pathways for successful infection. We further demonstrate a requirement for the ubiquitin ligase CBLL1 in WNV internalization, a post-entry role for the endoplasmic-reticulum-associated degradation pathway in viral infection, and the monocarboxylic acid transporter MCT4 as a viral replication resistance factor. By extending this study to dengue virus, we show that flaviviruses have both overlapping and unique interaction strategies with host cells. This study provides a comprehensive molecular portrait of WNV-human cell interactions that forms a model for understanding single plus-stranded RNA virus infection, and reveals potential antiviral targets. 相似文献
73.
In each decade, population estimates are rebased using data from the most recent census. However, this would lead to a step change in the population estimates series. To avoid this discontinuity the backseries for 1992 to 2000, was revised to bring it into line with the 2001 Census. This article discusses the methodology used to produce the final revised backseries for 1992 to 2000 published by ONS in October 2004. The final estimates were produced after a long period of research into the best methodology to use. Traditionally, the backseries have been revised using an interim simple period method, followed by a final simple cohort method. The approach taken following the 2001 Census was much more comprehensive. This article outlines this approach, summarises the range of methods available and describes in detail the final method selected. 相似文献
74.
Summary Impaired breeding performance of aged female mice was associated with reduced numbers of ovulations and increased mortality of embryos. The amounts of progesterone in the sera, corpora lutea and uterine flushings of these animals were similar to those of young animals when measured by radioimmunoassay.Financial support was provided by the Medical Research Council (R.G.G.) and the Ford Foundation and one of us (R.E.F.) wishes to thank Lucy Cavendish College, Cambridge, for their support with a Calouste Gulbenkian Research Fellowship. 相似文献
75.
Positron emission tomography after MPTP: observations relating to the cause of Parkinson's disease 总被引:5,自引:0,他引:5
D B Calne J W Langston W R Martin A J Stoessl T J Ruth M J Adam B D Pate M Schulzer 《Nature》1985,317(6034):246-248
The dopa analogue 6-fluorodopa (6-FD) used with positron emission tomography (PET) allows in vivo visualization of dopamine and its metabolites in nigrostriatal nerve endings. We have now found abnormal 6-FD scans in four subjects exposed to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). None had parkinsonism. The results suggest subclinical damage to the nigrostriatal pathway. This is the first direct evidence that dopaminergic impairment can exist without clinical deficits. Here we discuss this finding in the context of the hypothesis that Parkinson's disease may stem from clinically silent damage to the substantia nigra, followed by slow attrition of neurones in this region because of its particular vulnerability to cell loss as a normal consequence of ageing. 相似文献
76.
77.
Beat Trueb Ruth Amann Simon D. Gerber 《Cellular and molecular life sciences : CMLS》2013,70(14):2505-2518
The mammalian kidney develops from the ureteric bud and the metanephric mesenchyme. In mice, the ureteric bud invades the metanephric mesenchyme at day E10.5 and begins to branch. The tips of the ureteric bud induce the metanephric mesenchyme to condense and form the cap mesenchyme. Some cells of this cap mesenchyme undergo a mesenchymal-to-epithelial transition and differentiate into renal vesicles, which further develop into nephrons. The developing kidney expresses Fibroblast growth factor (Fgf)1, 7, 8, 9, 10, 12 and 20 and Fgf receptors Fgfr1 and Fgfr2. Fgf7 and Fgf10, mainly secreted by the metanephric mesenchyme, bind to Fgfr2b of the ureteric bud and induce branching. Fgfr1 and Fgfr2c are required for formation of the metanephric mesenchyme, however the two receptors can substitute for one another. Fgf8, secreted by renal vesicles, binds to Fgfr1 and supports survival of cells in the nascent nephrons. Fgf9 and Fgf20, expressed in the metanephric mesenchyme, are necessary to maintain survival of progenitor cells in the cortical region of the kidney. FgfrL1 is a novel member of the Fgfr family that lacks the intracellular tyrosine kinase domain. It is expressed in the ureteric bud and all nephrogenic structures. Targeted deletion of FgfrL1 leads to severe kidney dysgenesis due to the lack of renal vesicles. FgfrL1 is known to interact mainly with Fgf8. It is therefore conceivable that FgfrL1 restricts signaling of Fgf8 to the precise location of the nascent nephrons. It might also promote tight adhesion of cells in the condensed metanephric mesenchyme as required for the mesenchymal-to-epithelial transition. 相似文献
78.
Margaret A. Fletcher Ortrun Zuber-Skerritt Brendan Bartlett Ruth Albertyn Judith Kearney 《Systemic Practice and Action Research》2010,23(6):487-507
Our purpose in this paper is to contribute to the field of systemic practice by sharing a process of professional learning based on meta-action research. The process emerged as we engaged with evaluation data from a leadership development program (LDP). The aim of this LDP had been to help leaders design their team projects on poverty reduction through action research methods in six African countries. As facilitators of the program we discuss our experiential learning based on critical reflection. We explain how meta-action research can transform understandings of ways to improve professional practice in future applications. We present three process models: (1) a model of reflection on action, (2) a meta-action research model, and (3) a model for lifelong learning through meta-action research. These models may be of benefit and interest to readers who facilitate systemic practice and action research in education, higher education, communities, industry and government. 相似文献
79.
This article describes a new method for the simultaneous determination of trace rare earth elements (REEs) and non rare earth elements (NREEs) in high purity terbium oxide by ICP-AES after HPLC separation using P507 resin. The chromatographic separation of the analytes from the matrix using dilute nitric acid as mobile phase was studied. The experimental results showed that a favorable separation of trace metals (Cu and Gd) from the matrix (Tb) can easily be achieved by elution with dilute nitric acid within 25 min. The proposed method was applied to the determination of trace metals (Ca, Cu, Mg, Mn, Ni, Si, La, Ce, Pr, Nd, Sm, Eu and Gd) in high purity terbium oxide. The detection limits (DLs) for the analytes ranged from 0.4-4.0 μg\5g-1, and the recoveries are from 78%-105%. 相似文献
80.