Water solubility in aluminous orthopyroxene and the origin of Earth's asthenosphere   总被引：3，自引：0，他引：3  

Mierdel K  Keppler H  Smyth JR  Langenhorst F 《Science (New York, N.Y.)》2007,315(5810):364-368

Plate tectonics is based on the concept of rigid lithosphere plates sliding on a mechanically weak asthenosphere. Many models assume that the weakness of the asthenosphere is related to the presence of small amounts of hydrous melts. However, the mechanism that may cause melting in the asthenosphere is not well understood. We show that the asthenosphere coincides with a zone where the water solubility in mantle minerals has a pronounced minimum. The minimum is due to a sharp decrease of water solubility in aluminous orthopyroxene with depth, whereas the water solubility in olivine continuously increases with pressure. Melting in the asthenosphere may therefore be related not to volatile enrichment but to a minimum in water solubility, which causes excess water to form a hydrous silicate melt.  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   

A new strategy for the synthesis of glycoproteins     

Zhang Z  Gildersleeve J  Yang YY  Xu R  Loo JA  Uryu S  Wong CH  Schultz PG 《Science (New York, N.Y.)》2004,303(5656):371-373

Posttranslational modifications of proteins regulate many biological processes, including metabolism, signal transduction, and gene expression. The synthetic challenges associated with generating homogeneous populations of selectively modified proteins, however, have hindered detailed studies of the effects of these modifications on protein structure and function. Here, we report an approach to the cotranslational synthesis of selectively glycosylated proteins in which the modified amino acid is genetically encoded. We show that myoglobin containing beta-N-acetylglucosamine (GlcNAc)-serine at a defined position can be expressed in Escherichia coli in good yield and with high fidelity. The beta-GlcNAc moiety can be recognized by a saccharide-binding protein, or subsequently modified with a galactosyltransferase to build more complex carbohydrates. This approach should be generally applicable to other posttranslational modifications such as protein phosphorylation, acetylation, and methylation.  相似文献   

Anatomy of a conformational change: hinged "lid" motion of the triosephosphate isomerase loop   总被引：14，自引：0，他引：14  

D Joseph  G A Petsko  M Karplus 《Science (New York, N.Y.)》1990,249(4975):1425-1428

Triosephosphate isomerase (TIM) is used as a model system for the study of how a localized conformational change in a protein structure is produced and related to enzyme reactivity. An 11-residue loop region moves more than 7 angstroms and closes over the active site when substrate binds. The loop acts like a "lid" in that it moves rigidly and is attached by two hinges to the remainder of the protein. The nature of the motion appears to be built into the loop by conserved residues; the hinge regions, in contrast, are not conserved. Results of molecular dynamics calculations confirm the structural analysis and suggest a possible ligand-induced mechanism for loop closure.  相似文献   

Crystal structure of an ancient protein: evolution by conformational epistasis   总被引：1，自引：0，他引：1  

Ortlund EA  Bridgham JT  Redinbo MR  Thornton JW 《Science (New York, N.Y.)》2007,317(5844):1544-1548

The structural mechanisms by which proteins have evolved new functions are known only indirectly. We report x-ray crystal structures of a resurrected ancestral protein-the approximately 450 million-year-old precursor of vertebrate glucocorticoid (GR) and mineralocorticoid (MR) receptors. Using structural, phylogenetic, and functional analysis, we identify the specific set of historical mutations that recapitulate the evolution of GR's hormone specificity from an MR-like ancestor. These substitutions repositioned crucial residues to create new receptor-ligand and intraprotein contacts. Strong epistatic interactions occur because one substitution changes the conformational position of another site. "Permissive" mutations-substitutions of no immediate consequence, which stabilize specific elements of the protein and allow it to tolerate subsequent function-switching changes-played a major role in determining GR's evolutionary trajectory.  相似文献   

Three-dimensional polarimetric imaging of coronal mass ejections     

Moran TG  Davila JM 《Science (New York, N.Y.)》2004,305(5680):66-70

We present three-dimensional reconstructions of coronal mass ejections (CMEs), which were obtained through polarization analysis of single-view images recorded with the use of the Large Angle and Spectrometric Coronagraph (LASCO) C2 coronagraph on board the Solar and Heliospheric Observatory (SOHO) spacecraft. Analysis of a loop-like CME shows a complex three-dimensional structure centered at 40 degrees from the plane of the sky, moving radially at 250 kilometers/second. Reconstruction of two halo CMEs suggests that these events are expanding loop arcades.  相似文献   

Newsgathering     

Hirschberg E  Joseph Fu SC  Frisell WR  Farber E  Potter VR  Rusch HP  Saffiotti U  Shimkin MB  Brennan MJ  Nowell PC  Creech HJ  Taylor RM  Schabel FM  Frei E  Lepage GA  Weinhouse S  Hall TC 《Science (New York, N.Y.)》1972,176(4041):1288-1289

  相似文献   

Building a space weather aerie in Armenia     

Dagdigian J 《Science (New York, N.Y.)》2003,302(5652):1893

  相似文献   

Identifying autism loci and genes by tracing recent shared ancestry   总被引：2，自引：0，他引：2  

Morrow EM  Yoo SY  Flavell SW  Kim TK  Lin Y  Hill RS  Mukaddes NM  Balkhy S  Gascon G  Hashmi A  Al-Saad S  Ware J  Joseph RM  Greenblatt R  Gleason D  Ertelt JA  Apse KA  Bodell A  Partlow JN  Barry B  Yao H  Markianos K  Ferland RJ  Greenberg ME  Walsh CA 《Science (New York, N.Y.)》2008,321(5886):218-223

To find inherited causes of autism-spectrum disorders, we studied families in which parents share ancestors, enhancing the role of inherited factors. We mapped several loci, some containing large, inherited, homozygous deletions that are likely mutations. The largest deletions implicated genes, including PCDH10 (protocadherin 10) and DIA1 (deleted in autism1, or c3orf58), whose level of expression changes in response to neuronal activity, a marker of genes involved in synaptic changes that underlie learning. A subset of genes, including NHE9 (Na+/H+ exchanger 9), showed additional potential mutations in patients with unrelated parents. Our findings highlight the utility of "homozygosity mapping" in heterogeneous disorders like autism but also suggest that defective regulation of gene expression after neural activity may be a mechanism common to seemingly diverse autism mutations.  相似文献   

Beating crystallization in glass-forming metals by millisecond heating and processing     

Johnson WL  Kaltenboeck G  Demetriou MD  Schramm JP  Liu X  Samwer K  Kim CP  Hofmann DC 《Science (New York, N.Y.)》2011,332(6031):828-833

The development of metal alloys that form glasses at modest cooling rates has stimulated broad scientific and technological interest. However, intervening crystallization of the liquid in even the most robust bulk metallic glass-formers is orders of magnitude faster than in many common polymers and silicate glass-forming liquids. Crystallization limits experimental studies of the undercooled liquid and hampers efforts to plastically process metallic glasses. We have developed a method to rapidly and uniformly heat a metallic glass at rates of 10(6) kelvin per second to temperatures spanning the undercooled liquid region. Liquid properties are subsequently measured on millisecond time scales at previously inaccessible temperatures under near-adiabatic conditions. Rapid thermoplastic forming of the undercooled liquid into complex net shapes is implemented under rheological conditions typically used in molding of plastics. By operating in the millisecond regime, we are able to "beat" the intervening crystallization and successfully process even marginal glass-forming alloys with very limited stability against crystallization that are not processable by conventional heating.  相似文献