Diamond genesis,seismic structure,and evolution of the Kaapvaal-Zimbabwe craton     

Shirey SB  Harris JW  Richardson SH  Fouch MJ  James DE  Cartigny P  Deines P  Viljoen F 《Science (New York, N.Y.)》2002,297(5587):1683-1686

The lithospheric mantle beneath the Kaapvaal-Zimbabwe craton of southern Africa shows variations in seismic P-wave velocity at depths within the diamond stability field that correlate with differences in the composition of diamonds and their syngenetic inclusions. Middle Archean mantle depletion events initiated craton keel formation and early harzburgitic diamond formation. Late Archean accretionary events involving an oceanic lithosphere component stabilized the craton and contributed a younger Archean generation of eclogitic diamonds. Subsequent Proterozoic tectonic and magmatic events altered the composition of the continental lithosphere and added new lherzolitic and eclogitic diamonds to the Archean diamond suite.  相似文献   

VARIETIES OF TRITICUM VULGARE PRACTICALLY IMMUNE IN ALL STAGES OF GROWTH TO STEM RUST     

Peterson RF  Johnson T  Newton M 《Science (New York, N.Y.)》1940,91(2361):313-314

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Experiences and perspectives of farmers from Upstate New York farmers' markets     

Matthew R. Griffin  Edward A. Frongillo 《Agriculture and Human Values》2003,20(2):189-203

Despite the growing popularityof farmers' markets (FMs) across the UnitedStates, the experiences and perspectives offarmers who sell at markets have received verylittle research attention. This study describesthe views of 18 farmers from Upstate New Yorkon the importance of FMs as part of theirlifestyle and livelihood, the challenges theyface selling at markets, and their conceptionsof ideal FMs. Through in-depth, semi-structuredinterviews, farmers expressed economic andsocial motivations for selling at FMs; socialbenefits from interacting with customers; andthe challenges they faced as small-scalefarmers and sellers, including extra-marketcompetition, uncooperative and problematicmarket vendors, rising farm input costs, andchanging consumer trends. Farmers alsodiscussed personal values associated withselling at FMs, such as pride in raising andmarketing one's own products, working togetherwith other farmer-vendors, and providingcustomers with honest information. Visions ofideal FMs were varied among farmers, but therewas general agreement that FMs should provide adiversity of products to attract customers andeducational opportunities for the public tolearn more about FMs and local produce. Theinterdependence of FM farmers was a majoremergent theme across interviews. Findingssuggested that market experiences of FMfarmers, including economic success, are notonly contingent on personal effort, but canalso be affected by the work of fellow vendors.Future research may look to further explore howFM farmers and other vendors interact ascooperative and competitive social and economicunits. At the community level, FM leadershipshould continue to focus on the experiences andperspectives of farmers and other marketvendors, in addition to identifying ways forenhancing cooperative FM enterprises.  相似文献   

Traces of human migrations in Helicobacter pylori populations     

Falush D  Wirth T  Linz B  Pritchard JK  Stephens M  Kidd M  Blaser MJ  Graham DY  Vacher S  Perez-Perez GI  Yamaoka Y  Mégraud F  Otto K  Reichard U  Katzowitsch E  Wang X  Achtman M  Suerbaum S 《Science (New York, N.Y.)》2003,299(5612):1582-1585

Helicobacter pylori, a chronic gastric pathogen of human beings, can be divided into seven populations and subpopulations with distinct geographical distributions. These modern populations derive their gene pools from ancestral populations that arose in Africa, Central Asia, and East Asia. Subsequent spread can be attributed to human migratory fluxes such as the prehistoric colonization of Polynesia and the Americas, the neolithic introduction of farming to Europe, the Bantu expansion within Africa, and the slave trade.  相似文献   

Dentate gyrus NMDA receptors mediate rapid pattern separation in the hippocampal network     

McHugh TJ  Jones MW  Quinn JJ  Balthasar N  Coppari R  Elmquist JK  Lowell BB  Fanselow MS  Wilson MA  Tonegawa S 《Science (New York, N.Y.)》2007,317(5834):94-99

Forming distinct representations of multiple contexts, places, and episodes is a crucial function of the hippocampus. The dentate gyrus subregion has been suggested to fulfill this role. We have tested this hypothesis by generating and analyzing a mouse strain that lacks the gene encoding the essential subunit of the N-methyl-d-aspartate (NMDA) receptor NR1, specifically in dentate gyrus granule cells. The mutant mice performed normally in contextual fear conditioning, but were impaired in the ability to distinguish two similar contexts. A significant reduction in the context-specific modulation of firing rate was observed in the CA3 pyramidal cells when the mutant mice were transferred from one context to another. These results provide evidence that NMDA receptors in the granule cells of the dentate gyrus play a crucial role in the process of pattern separation.  相似文献   

Quantitative analysis of culture using millions of digitized books   总被引：1，自引：0，他引：1  

Michel JB  Shen YK  Aiden AP  Veres A  Gray MK;Google Books Team  Pickett JP  Hoiberg D  Clancy D  Norvig P  Orwant J  Pinker S  Nowak MA  Aiden EL 《Science (New York, N.Y.)》2011,331(6014):176-182

We constructed a corpus of digitized texts containing about 4% of all books ever printed. Analysis of this corpus enables us to investigate cultural trends quantitatively. We survey the vast terrain of 'culturomics,' focusing on linguistic and cultural phenomena that were reflected in the English language between 1800 and 2000. We show how this approach can provide insights about fields as diverse as lexicography, the evolution of grammar, collective memory, the adoption of technology, the pursuit of fame, censorship, and historical epidemiology. Culturomics extends the boundaries of rigorous quantitative inquiry to a wide array of new phenomena spanning the social sciences and the humanities.  相似文献   

RECENT PROGRESS IN PALEONTOLOGY     

Eastman CR  Gregory WK  Matthew WD 《Science (New York, N.Y.)》1917,45(1153):117-121

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Shocked quartz at the triassic-jurassic boundary in Italy     

Bice DM  Newton CR  McCauley S  Reiners PW  McRoberts CA 《Science (New York, N.Y.)》1992,255(5043):443-446

Quartz grains that appear to have been shock-metamorphosed occur within three closely spaced shale beds from the uppermost Triassic ("Rhaetian") Calcare a Rhaetavicula in the Northern Apennines of Italy. The upper shale coincides with the abrupt termination of the distinctive, uppermost Triassic Rhaetavicula fauna and is overlain by the Hettangian (Lower Jurassic) Calcare Massiccio; no extinctions appear to be associated with the two lower layers, which occur 1.2 and 2.4 meters below the boundary shale. Approximately 5 to 10% of the quartz grains within these layers exhibit one or more sets of planar deformational features whose orientations cluster around the rational crystallographic planes (basal, omega, and pi) most commonly observed in shocked quartz. Textural and stratigraphic observations support an interpretation of at least three closely spaced impacts at the end of the Triassic.  相似文献   

THE ORIGIN OF PACIFIC ISLAND FAUNAS     

Matthew WD 《Science (New York, N.Y.)》1916,43(1115):686-687

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Adenovirus small e1a alters global patterns of histone modification     

Horwitz GA  Zhang K  McBrian MA  Grunstein M  Kurdistani SK  Berk AJ 《Science (New York, N.Y.)》2008,321(5892):1084-1085

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