Did cooling oceans trigger Ordovician biodiversification? Evidence from conodont thermometry     

Trotter JA  Williams IS  Barnes CR  Lécuyer C  Nicoll RS 《Science (New York, N.Y.)》2008,321(5888):550-554

The Ordovician Period, long considered a supergreenhouse state, saw one of the greatest radiations of life in Earth's history. Previous temperature estimates of up to approximately 70 degrees C have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time. We present a very different global climate record determined by ion microprobe oxygen isotope analyses of Early Ordovician-Silurian conodonts. This record shows a steady cooling trend through the Early Ordovician reaching modern equatorial temperatures that were sustained throughout the Middle and Late Ordovician. This favorable climate regime implies not only that the oxygen isotopic composition of Ordovician seawater was similar to that of today, but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period.  相似文献   

T cell activation by lipopeptide antigens   总被引：2，自引：0，他引：2  

Moody DB  Young DC  Cheng TY  Rosat JP  Roura-Mir C  O'Connor PB  Zajonc DM  Walz A  Miller MJ  Levery SB  Wilson IA  Costello CE  Brenner MB 《Science (New York, N.Y.)》2004,303(5657):527-531

Unlike major histocompatibility proteins, which bind peptides, CD1 proteins display lipid antigens to T cells. Here, we report that CD1a presents a family of previously unknown lipopeptides from Mycobacterium tuberculosis, named didehydroxymycobactins because of their structural relation to mycobactin siderophores. T cell activation was mediated by the alphabeta T cell receptors and was specific for structure of the acyl and peptidic components of these antigens. These studies identify a means of intracellular pathogen detection and identify lipopeptides as a biochemical class of antigens for T cells, which, like conventional peptides, have a potential for marked structural diversity.  相似文献   

CoRoT measures solar-like oscillations and granulation in stars hotter than the Sun     

Michel E  Baglin A  Auvergne M  Catala C  Samadi R  Baudin F  Appourchaux T  Barban C  Weiss WW  Berthomieu G  Boumier P  Dupret MA  Garcia RA  Fridlund M  Garrido R  Goupil MJ  Kjeldsen H  Lebreton Y  Mosser B  Grotsch-Noels A  Janot-Pacheco E  Provost J  Roxburgh IW  Thoul A  Toutain T  Tiphène D  Turck-Chieze S  Vauclair SD  Vauclair GP  Aerts C  Alecian G  Ballot J  Charpinet S  Hubert AM  Lignières F  Mathias P  Monteiro MJ  Neiner C  Poretti E  de Medeiros JR  Ribas I  Rieutord ML  Cortés TR  Zwintz K 《Science (New York, N.Y.)》2008,322(5901):558-560

Oscillations of the Sun have been used to understand its interior structure. The extension of similar studies to more distant stars has raised many difficulties despite the strong efforts of the international community over the past decades. The CoRoT (Convection Rotation and Planetary Transits) satellite, launched in December 2006, has now measured oscillations and the stellar granulation signature in three main sequence stars that are noticeably hotter than the sun. The oscillation amplitudes are about 1.5 times as large as those in the Sun; the stellar granulation is up to three times as high. The stellar amplitudes are about 25% below the theoretic values, providing a measurement of the nonadiabaticity of the process ruling the oscillations in the outer layers of the stars.  相似文献   

The global circulation of seasonal influenza A (H3N2) viruses     

Russell CA  Jones TC  Barr IG  Cox NJ  Garten RJ  Gregory V  Gust ID  Hampson AW  Hay AJ  Hurt AC  de Jong JC  Kelso A  Klimov AI  Kageyama T  Komadina N  Lapedes AS  Lin YP  Mosterin A  Obuchi M  Odagiri T  Osterhaus AD  Rimmelzwaan GF  Shaw MW  Skepner E  Stohr K  Tashiro M  Fouchier RA  Smith DJ 《Science (New York, N.Y.)》2008,320(5874):340-346

Antigenic and genetic analysis of the hemagglutinin of approximately 13,000 human influenza A (H3N2) viruses from six continents during 2002-2007 revealed that there was continuous circulation in east and Southeast Asia (E-SE Asia) via a region-wide network of temporally overlapping epidemics and that epidemics in the temperate regions were seeded from this network each year. Seed strains generally first reached Oceania, North America, and Europe, and later South America. This evidence suggests that once A (H3N2) viruses leave E-SE Asia, they are unlikely to contribute to long-term viral evolution. If the trends observed during this period are an accurate representation of overall patterns of spread, then the antigenic characteristics of A (H3N2) viruses outside E-SE Asia may be forecast each year based on surveillance within E-SE Asia, with consequent improvements to vaccine strain selection.  相似文献   

Coeval large-scale magmatism in the Kalahari and Laurentian cratons during Rodinia assembly     

Hanson RE  Crowley JL  Bowring SA  Ramezani J  Gose WA  Dalziel IW  Pancake JA  Seidel EK  Blenkinsop TG  Mukwakwami J 《Science (New York, N.Y.)》2004,304(5674):1126-1129

We show that intraplate magmatism occurred 1106 to 1112 million years ago over an area of two million square kilometers within the Kalahari craton of southern Africa, during the same magnetic polarity chron as voluminous magmatism within the cratonic core of North America. These contemporaneous magmatic events occurred while the Rodinia supercontinent was being assembled and are inferred to be parts of a single large igneous province emplaced across the two cratons. Widespread intraplate magmatism during Rodinia assembly shows that mantle upwellings required to generate such provinces may occur independently of the supercontinent cycle.  相似文献   

Service-oriented science   总被引：1，自引：0，他引：1  

Foster I 《Science (New York, N.Y.)》2005,308(5723):814-817

New information architectures enable new approaches to publishing and accessing valuable data and programs. So-called service-oriented architectures define standard interfaces and protocols that allow developers to encapsulate information tools as services that clients can access without knowledge of, or control over, their internal workings. Thus, tools formerly accessible only to the specialist can be made available to all; previously manual data-processing and analysis tasks can be automated by having services access services. Such service-oriented approaches to science are already being applied successfully, in some cases at substantial scales, but much more effort is required before these approaches are applied routinely across many disciplines. Grid technologies can accelerate the development and adoption of service-oriented science by enabling a separation of concerns between discipline-specific content and domain-independent software and hardware infrastructure.  相似文献   

Lead isotopic ages of chondrules and calcium-aluminum-rich inclusions     

Amelin Y  Krot AN  Hutcheon ID  Ulyanov AA 《Science (New York, N.Y.)》2002,297(5587):1678-1683

The lead-lead isochron age of chondrules in the CR chondrite Acfer 059 is 4564.7 +/- 0.6 million years ago (Ma), whereas the lead isotopic age of calcium-aluminum-rich inclusions (CAIs) in the CV chondrite Efremovka is 4567.2 +/- 0.6 Ma. This gives an interval of 2.5 +/- 1.2 million years (My) between formation of the CV CAIs and the CR chondrules and indicates that CAI- and chondrule-forming events lasted for at least 1.3 My. This time interval is consistent with a 2- to 3-My age difference between CR CAIs and chondrules inferred from the differences in their initial 26Al/27Al ratios and supports the chronological significance of the 26Al-26Mg systematics.  相似文献   

Extracellular proteins limit the dispersal of biogenic nanoparticles     

Moreau JW  Weber PK  Martin MC  Gilbert B  Hutcheon ID  Banfield JF 《Science (New York, N.Y.)》2007,316(5831):1600-1603

High-spatial-resolution secondary ion microprobe spectrometry, synchrotron radiation-based Fourier-transform infrared spectroscopy, and polyacrylamide gel analysis demonstrated the intimate association of proteins with spheroidal aggregates of biogenic zinc sulfide nanocrystals, an example of extracellular biomineralization. Experiments involving synthetic zinc sulfide nanoparticles and representative amino acids indicated a driving role for cysteine in rapid nanoparticle aggregation. These findings suggest that microbially derived extracellular proteins can limit the dispersal of nanoparticulate metal-bearing phases, such as the mineral products of bioremediation, that may otherwise be transported away from their source by subsurface fluid flow.  相似文献   

Human embryonic stem cells     

Wilmut I  West MD  Lanza RP  Gearhart JD  Smith A  Colman A  Trounson AO  Campbell KH 《Science (New York, N.Y.)》2005,310(5756):1903

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Ecology and evolution. Sex differences in mortality rate     

Owens IP 《Science (New York, N.Y.)》2002,297(5589):2008-2009

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