Early Man Site Found in Highland Ecuador     

Mayer-Oakes WJ  Bell RE 《Science (New York, N.Y.)》1960,131(3416):1805-1806

Field investigations in Ecuador have produced archeological evidence for the occupation of the northern Andes by early nomadic hunters. Surface collections and test excavations have demonstrated a complex of stone tools with typological relationships to level I at Fell's Cave in southern Chile, and technological relationships to the late Pleistocene "fluted point" complexes of North America. The date of these materials is estimated at 7000 to 8000 B.C.  相似文献   

Water in Earth's Mantle: The Role of Nominally Anhydrous Minerals   总被引：8，自引：0，他引：8  

Bell DR  Rossman GR 《Science (New York, N.Y.)》1992,255(5050):1391-1397

Most minerals of Earth's upper mantle contain small amounts of hydrogen, structurally bound as hydroxyl (OH). The OH concentration in each mineral species is variable, in some cases reflecting the geological environment of mineral formation. Of the major mantle minerals, pyroxenes are the most hydrous, typically containing approximately 200 to 500 parts per million H(2)O by weight, and probably dominate the water budget and hydrogen geochemistry of mantle rocks that do not contain a hydrous phase. Garnets and olivines commonly contain approximately 1 to 50 parts per million. Nominally anhydrous minerals constitute a significant reservoir for mantle hydrogen, possibly accommodating all water in the depleted mantle and providing a possible mechanism to recycle water from Earth's surface into the deep mantle.  相似文献   

Conservation of brain amyloid proteins in aged mammals and humans with Alzheimer's disease   总被引：37，自引：0，他引：37  

D J Selkoe  D S Bell  M B Podlisny  D L Price  L C Cork 《Science (New York, N.Y.)》1987,235(4791):873-877

The formation of clusters of altered axons and dendrites surrounding extracellular deposits of amyloid filaments (neuritic plaques) is a major feature of the human brain in both aging and Alzheimer's disease. A panel of antibodies against amyloid filaments and their constituent proteins from humans with Alzheimer's disease cross-reacted with neuritic plaque and cerebrovascular amyloid deposits in five other species of aged mammals, including monkey, orangutan, polar bear, and dog. Antibodies to a 28-amino acid peptide representing the partial protein sequence of the human amyloid filaments recognized the cortical and microvascular amyloid of all of the aged mammals examined. Plaque amyloid, plaque neurites, and neuronal cell bodies in the aged animals showed no reaction with antibodies to human paired helical filaments. Thus, with age, the amyloid proteins associated with progressive cortical degeneration in Alzheimer's disease are also deposited in the brains of other mammals. Aged primates can provide biochemically relevant models for principal features of Alzheimer's disease: cerebrovascular amyloidosis and neuritic plaque formation.  相似文献   

Replacements of Pro86 in phage T4 lysozyme extend an alpha-helix but do not alter protein stability   总被引：10，自引：0，他引：10  

T Alber  J A Bell  D P Sun  H Nicholson  J A Wozniak  S Cook  B W Matthews 《Science (New York, N.Y.)》1988,239(4840):631-635

To investigate the relation between protein stability and the predicted stabilities of individual secondary structural elements, residue Pro86 in an alpha-helix in phage T4 lysozyme was replaced by ten different amino acids. The x-ray crystal structures of seven of the mutant lysozymes were determined at high resolution. In each case, replacement of the proline resulted in the formation of an extended alpha-helix. This involves a large conformational change in residues 81 to 83 and smaller shifts that extend 20 angstroms across the protein surface. Unexpectedly, all ten amino acid substitutions marginally reduce protein thermostability. This insensitivity of stability to the amino acid at position 86 is not simply explained by statistical and thermodynamic criteria for helical propensity. The observed conformational changes illustrate a general mechanism by which proteins can tolerate mutations.  相似文献   

Surficial deposits at Gusev Crater along Spirit Rover traverses     

Grant JA  Arvidson R  Bell JF  Cabrol NA  Carr MH  Christensen P  Crumpler L  Des Marais DJ  Ehlmann BL  Farmer J  Golombek M  Grant FD  Greeley R  Herkenhoff K  Li R  McSween HY  Ming DW  Moersch J  Rice JW  Ruff S  Richter L  Squyres S  Sullivan R  Weitz C 《Science (New York, N.Y.)》2004,305(5685):807-810

The Mars Exploration Rover Spirit has traversed a fairly flat, rock-strewn terrain whose surface is shaped primarily by impact events, although some of the landscape has been altered by eolian processes. Impacts ejected basaltic rocks that probably were part of locally formed lava flows from at least 10 meters depth. Some rocks have been textured and/or partially buried by windblown sediments less than 2 millimeters in diameter that concentrate within shallow, partially filled, circular impact depressions referred to as hollows. The terrain traversed during the 90-sol (martian solar day) nominal mission shows no evidence for an ancient lake in Gusev crater.  相似文献   

Biological Control of Yellow Nutsedge with the Indigenous Rust Fungus Puccinia canaliculata     

Phatak SC  Sumner DR  Wells HD  Bell DK  Glaze NC 《Science (New York, N.Y.)》1983,219(4591):1446-1447

Yellow nutsedge (Cyperus esculentus L.) is a serious weed problem in the United States and other countries. An indigenous rust fungus [Puccinia canaliculata (Schw.) Lagerh.], pathogenic on yellow nutsedge, was released in early spring as a potential biological control agent. The fungus inhibited nutsedge flowering and new tuber formation. The fungus also dehydrated and killed nutsedge plants. The successful control of yellow nutsedge by a rust epiphytotic under experimental conditions demonstrates the potential use of the rust in an integrated weed management system.  相似文献   

Scent organ development in creatonotos moths: regulation by pyrrolizidine alkaloids     

Schneider D  Boppré M  Zweig J  Horsley SB  Bell TW  Meinwald J  Hansen K  Diehl EW 《Science (New York, N.Y.)》1982,215(4537):1264-1265

7-Hydroxy-6,7-dihydro-5H-pyrolizine-1-carboxaldehyde is the major volatile component of the scent organs in males of two species of Creatonotos (Lepidoptera, Arctiidae). The biosynthesis of this presumed pheromone depends on the presence of pyrrolizidine alkaloids in plants that are ingested by the larvae. In addition, these secondary plant substances control the morphogenesis of the scent organs. This morphogenetic effect of an alkaloid has not been observed previously.  相似文献   

A UNIVERSAL LANGUAGE AND ITS VEHICLE,--A UNIVERSAL ALPHABET     

Bell AM 《Science (New York, N.Y.)》1883,2(32):350-353

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THE INFLUENCE OF NUTRITION UPON THE ANIMAL FORM     

Bell ET 《Science (New York, N.Y.)》1910,32(822):435

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Insulators and boundaries: versatile regulatory elements in the eukaryotic genome     

Bell AC  West AG  Felsenfeld G 《Science (New York, N.Y.)》2001,291(5503):447-450

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