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101.
Middle Paleolithic assemblages from the Indian subcontinent before and after the Toba super-eruption
Petraglia M Korisettar R Boivin N Clarkson C Ditchfield P Jones S Koshy J Lahr MM Oppenheimer C Pyle D Roberts R Schwenninger JL Arnold L White K 《Science (New York, N.Y.)》2007,317(5834):114-116
The Youngest Toba Tuff (YTT) eruption, which occurred in Indonesia 74,000 years ago, is one of Earth's largest known volcanic events. The effect of the YTT eruption on existing populations of humans, and accordingly on the course of human evolution, is debated. Here we associate the YTT with archaeological assemblages at Jwalapuram, in the Jurreru River valley of southern India. Broad continuity of Middle Paleolithic technology across the YTT event suggests that hominins persisted regionally across this major eruptive event. 相似文献
102.
Sutter NB Bustamante CD Chase K Gray MM Zhao K Zhu L Padhukasahasram B Karlins E Davis S Jones PG Quignon P Johnson GS Parker HG Fretwell N Mosher DS Lawler DF Satyaraj E Nordborg M Lark KG Wayne RK Ostrander EA 《Science (New York, N.Y.)》2007,316(5821):112-115
The domestic dog exhibits greater diversity in body size than any other terrestrial vertebrate. We used a strategy that exploits the breed structure of dogs to investigate the genetic basis of size. First, through a genome-wide scan, we identified a major quantitative trait locus (QTL) on chromosome 15 influencing size variation within a single breed. Second, we examined genetic variation in the 15-megabase interval surrounding the QTL in small and giant breeds and found marked evidence for a selective sweep spanning a single gene (IGF1), encoding insulin-like growth factor 1. A single IGF1 single-nucleotide polymorphism haplotype is common to all small breeds and nearly absent from giant breeds, suggesting that the same causal sequence variant is a major contributor to body size in all small dogs. 相似文献
103.
Suntivich J May KJ Gasteiger HA Goodenough JB Shao-Horn Y 《Science (New York, N.Y.)》2011,334(6061):1383-1385
The efficiency of many energy storage technologies, such as rechargeable metal-air batteries and hydrogen production from water splitting, is limited by the slow kinetics of the oxygen evolution reaction (OER). We found that Ba(0.5)Sr(0.5)Co(0.8)Fe(0.2)O(3-δ) (BSCF) catalyzes the OER with intrinsic activity that is at least an order of magnitude higher than that of the state-of-the-art iridium oxide catalyst in alkaline media. The high activity of BSCF was predicted from a design principle established by systematic examination of more than 10 transition metal oxides, which showed that the intrinsic OER activity exhibits a volcano-shaped dependence on the occupancy of the 3d electron with an e(g) symmetry of surface transition metal cations in an oxide. The peak OER activity was predicted to be at an e(g) occupancy close to unity, with high covalency of transition metal-oxygen bonds. 相似文献
104.
The vast majority of materials shrink in all directions when hydrostatically compressed; exceptions include certain metallic or polymer foam structures, which may exhibit negative linear compressibility (NLC) (that is, they expand in one or more directions under hydrostatic compression). Materials that exhibit this property at the molecular level--crystalline solids with intrinsic NLC--are extremely uncommon. With the use of neutron powder diffraction, we have discovered and characterized both NLC and extremely anisotropic thermal expansion, including negative thermal expansion (NTE) along the NLC axis, in a simple molecular crystal (the deuterated 1:1 compound of methanol and water). Apically linked rhombuses, which are formed by the bridging of hydroxyl-water chains with methyl groups, extend along the axis of NLC/NTE and lead to the observed behavior. 相似文献
105.
Trenberth K 《Science (New York, N.Y.)》2005,308(5729):1753-1754
106.
Smith JD Cappa CD Wilson KR Messer BM Cohen RC Saykally RJ 《Science (New York, N.Y.)》2004,306(5697):851-853
A strong temperature dependence of oxygen K-edge x-ray absorption fine structure features was observed for supercooled and normal liquid water droplets prepared from the breakup of a liquid microjet. Analysis of the data over the temperature range 251 to 288 kelvin (-22 degrees to +15 degrees C) yields a value of 1.5 +/- 0.5 kilocalories per mole for the average thermal energy required to effect an observable rearrangement between the fully coordinated ("ice-like") and distorted ("broken-donor") local hydrogen-bonding configurations responsible for the pre-edge and post-edge features, respectively. This energy equals the latent heat of melting of ice with hexagonal symmetry (ice Ih) and is consistent with the distribution of hydrogen bond strengths obtained for the "overstructured" ST2 model of water. 相似文献
107.
Arkin IT Xu H Jensen MØ Arbely E Bennett ER Bowers KJ Chow E Dror RO Eastwood MP Flitman-Tene R Gregersen BA Klepeis JL Kolossváry I Shan Y Shaw DE 《Science (New York, N.Y.)》2007,317(5839):799-803
Na+/H+ antiporters are central to cellular salt and pH homeostasis. The structure of Escherichia coli NhaA was recently determined, but its mechanisms of transport and pH regulation remain elusive. We performed molecular dynamics simulations of NhaA that, with existing experimental data, enabled us to propose an atomically detailed model of antiporter function. Three conserved aspartates are key to our proposed mechanism: Asp164 (D164) is the Na+-binding site, D163 controls the alternating accessibility of this binding site to the cytoplasm or periplasm, and D133 is crucial for pH regulation. Consistent with experimental stoichiometry, two protons are required to transport a single Na+ ion: D163 protonates to reveal the Na+-binding site to the periplasm, and subsequent protonation of D164 releases Na+. Additional mutagenesis experiments further validated the model. 相似文献
108.
Krajick K 《Science (New York, N.Y.)》2002,296(5567):454-456
109.
110.
Phototropins are light-activated kinases important for plant responses to blue light. Light initiates signaling in these proteins by generating a covalent protein-flavin mononucleotide (FMN) adduct within sensory Per-ARNT-Sim (PAS) domains. We characterized the light-dependent changes of a phototropin PAS domain by solution nuclear magnetic resonance spectroscopy and found that an alpha helix located outside the canonical domain plays a key role in this activation process. Although this helix associates with the PAS core in the dark, photoinduced changes in the domain structure disrupt this interaction. We propose that this mechanism couples light-dependent bond formation to kinase activation and identifies a signaling pathway conserved among PAS domains. 相似文献