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51.
Multi-university research teams: shifting impact, geography, and stratification in science 总被引:1,自引:0,他引:1
This paper demonstrates that teamwork in science increasingly spans university boundaries, a dramatic shift in knowledge production that generalizes across virtually all fields of science, engineering, and social science. Moreover, elite universities play a dominant role in this shift. By examining 4.2 million papers published over three decades, we found that multi-university collaborations (i) are the fastest growing type of authorship structure, (ii) produce the highest-impact papers when they include a top-tier university, and (iii) are increasingly stratified by in-group university rank. Despite the rising frequency of research that crosses university boundaries, the intensification of social stratification in multi-university collaborations suggests a concentration of the production of scientific knowledge in fewer rather than more centers of high-impact science. 相似文献
52.
Fossilized nuclei and germination structures identify Ediacaran "animal embryos" as encysting protists 总被引:1,自引:0,他引:1
Huldtgren T Cunningham JA Yin C Stampanoni M Marone F Donoghue PC Bengtson S 《Science (New York, N.Y.)》2011,334(6063):1696-1699
Globular fossils showing palintomic cell cleavage in the Ediacaran Doushantuo Formation, China, are widely regarded as embryos of early metazoans, although metazoan synapomorphies, tissue differentiation, and associated juveniles or adults are lacking. We demonstrate using synchrotron-based x-ray tomographic microscopy that the fossils have features incompatible with multicellular metazoan embryos. The developmental pattern is comparable with nonmetazoan holozoans, including germination stages that preclude postcleavage embryology characteristic of metazoans. We conclude that these fossils are neither animals nor embryos. They belong outside crown-group Metazoa, within total-group Holozoa (the sister clade to Fungi that includes Metazoa, Choanoflagellata, and Mesomycetozoea) or perhaps on even more distant branches in the eukaryote tree. They represent an evolutionary grade in which palintomic cleavage served the function of producing propagules for dispersion. 相似文献
53.
Increasing river discharge to the Arctic Ocean 总被引:10,自引:0,他引:10
Peterson BJ Holmes RM McClelland JW Vörösmarty CJ Lammers RB Shiklomanov AI Shiklomanov IA Rahmstorf S 《Science (New York, N.Y.)》2002,298(5601):2171-2173
Synthesis of river-monitoring data reveals that the average annual discharge of fresh water from the six largest Eurasian rivers to the Arctic Ocean increased by 7% from 1936 to 1999. The average annual rate of increase was 2.0 +/- 0.7 cubic kilometers per year. Consequently, average annual discharge from the six rivers is now about 128 cubic kilometers per year greater than it was when routine measurements of discharge began. Discharge was correlated with changes in both the North Atlantic Oscillation and global mean surface air temperature. The observed large-scale change in freshwater flux has potentially important implications for ocean circulation and climate. 相似文献
54.
Robledo L Elzerman J Jundt G Atatüre M Högele A Fält S Imamoglu A 《Science (New York, N.Y.)》2008,320(5877):772-775
Conditional quantum dynamics, where the quantum state of one system controls the outcome of measurements on another quantum system, is at the heart of quantum information processing. We demonstrate conditional dynamics for two coupled quantum dots, whereby the probability that one quantum dot makes a transition to an optically excited state is controlled by the presence or absence of an optical excitation in the neighboring dot. Interaction between the dots is mediated by the tunnel coupling between optically excited states and can be optically gated by applying a laser field of the right frequency. Our results represent substantial progress toward realization of an optically effected controlled-phase gate between two solid-state qubits. 相似文献
55.
The reversible blockage of synthetic pores formed by rigid-rod beta barrels, either by substrates or products, was used to sense a variety of enzymatic reactions in high-throughput format with "naked-eye" fluorescent detection. Improvement of sensor sensitivity beyond three orders of magnitude by straightforward internal mutations underscores the functional plasticity of rigid-rod beta barrels. Such detectors of enzyme activity with the aforementioned characteristics are needed in areas as diverse as proteomics and environmentally benign organic synthesis. 相似文献
56.
During the Archean, massive amounts of iron were deposited in the form of banded iron formations. It has been suggested that sedimenting particles of ferric oxyhydroxide may have stripped dissolved phosphate from the oceans, causing a reduction in phytoplankton productivity. However, that model does not take into account the high concentration of dissolved silica that was present in seawater at that time. We show experimentally that silica effectively competes with phosphate for sorption sites on ferrihydrite particles. Furthermore, coprecipitation of silica with ferrihydrite reduces particle reactivity toward phosphate. Hence, Archean oceans probably contained considerably more phosphate than previously predicted. 相似文献
57.
耐盐性Imt1基因表达载体的构建及其在酵母中的高效表达 总被引:2,自引:0,他引:2
将Imt1(Inositol O-methyltransferase,肌醇甲基转移酶)构建成酵母表达载体pBD#-3,在酵母双突变体gpd#+(-)(glycerol 3-phosphate-dehydrogenase,3-磷酸甘油脱氢酶)中高效表达,使gpd#+(-)突变株对氯化钠的耐性由2.5%提高到5.0%。生化分析表明,在每mg干酵母细胞内积累高达2.2nmol的Ononitol(芒柄醇)含量。Western blot分析证明了Imt1基因的表达。这一研究为植物耐盐基因工程开辟了一条新途径。 相似文献
58.
A global view of gene activity and alternative splicing by deep sequencing of the human transcriptome 总被引:6,自引:0,他引:6
59.
Armstead I Donnison I Aubry S Harper J Hörtensteiner S James C Mani J Moffet M Ougham H Roberts L Thomas A Weeden N Thomas H King I 《Science (New York, N.Y.)》2007,315(5808):73
A key gene involved in plant senescence, mutations of which partially disable chlorophyll catabolism and confer stay-green leaf and cotyledon phenotypes, has been identified in Pisum sativum, Arabidopsis thaliana, and Festuca pratensis by using classical and molecular genetics and comparative genomics. A stay-green locus in F. pratensis is syntenically equivalent to a similar stay-green locus on rice chromosome 9. Functional testing in Arabidopsis of a homolog of the rice candidate gene revealed (i) senescence-associated gene expression and (ii) a stay-green phenotype after RNA interference silencing. Genetic mapping in pea demonstrated cosegregation with the yellow/green cotyledon polymorphism (I/i) first reported by Gregor Mendel in 1866. 相似文献
60.