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5月25日<<Science>>的两篇摘要-----希望对大家有用
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Science 25 May 2007: Vol. 316. no. 5828, pp. 1178 - 1181 DOI: 10.1126/science.1141040 Prev | Table of Contents | Next Reports Evidence for a Late Supernova Injection of 60Fe into the Protoplanetary Disk Martin Bizzarro,1,2* David Ulfbeck,1 Anne Trinquier,1 Kristine Thrane,1 James N. Connelly,1,3 Bradley S. Meyer4 High-precision 60Fe-60Ni isotope data show that most meteorites originating from differentiated planetesimals that accreted within 1 million years of the solar system's formation have 60Ni/58Ni ratios that are 25 parts per million lower than samples from Earth, Mars, and chondrite parent bodies. This difference indicates that the oldest solar system planetesimals formed in the absence of 60Fe. Evidence for live 60Fe in younger objects suggests that 60Fe was injected into the protoplanetary disk 1 million years after solar system formation, when 26Al was already homogeneously distributed. Decoupling the first appearance of 26Al and 60Fe constrains the environment where the Sun's formation could have taken place, indicating that it occurred in a dense stellar cluster in association with numerous massive stars. Science 25 May 2007: Vol. 316. no. 5828, pp. 1144 - 1148 DOI: 10.1126/science.1137591 Prev | Table of Contents | Next Review Single-Molecule Experiments in Vitro and in Silico Marcos Sotomayor and Klaus Schulten* Single-molecule force experiments in vitro enable the characterization of the mechanical response of biological matter at the nanometer scale. However, they do not reveal the molecular mechanisms underlying mechanical function. These can only be readily studied through molecular dynamics simulations of atomic structural models: "in silico" (by computer analysis) single-molecule experiments. Steered molecular dynamics simulations, in which external forces are used to explore the response and function of macromolecules, have become a powerful tool complementing and guiding in vitro single-molecule experiments. The insights provided by in silico experiments are illustrated here through a review of recent research in three areas of protein mechanics: elasticity of the muscle protein titin and the extracellular matrix protein fibronectin; linker-mediated elasticity of the cytoskeleton protein spectrin; and elasticity of ankyrin repeats, a protein module found ubiquitously in cells but with an as-yet unclear function. [ Last edited by luo.henry on 2008-4-25 at 15:45 ] |
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