Science policy: house committee wants in on the action     

Carter LJ 《Science (New York, N.Y.)》1975,187(4181):1061

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Controversy over New Pesticide Regulations     

Carter LJ 《Science (New York, N.Y.)》1974,186(4167):904

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Energy: cannibalism in the bureaucracy     

Carter LJ 《Science (New York, N.Y.)》1974,186(4163):511

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Nader Queries Handler on Status of CONAES Study     

Carter LJ 《Science (New York, N.Y.)》1978,202(4373):1171

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Deformation of silicates from the sea of tranquillity     

Carter NL  Leung IS  Ave'lallemant HG 《Science (New York, N.Y.)》1970,167(3918):666-669

Plagioclase and olivine crystals in the crystalline rocks from the Sea of Tranquillity show little or no evidence of either static or dynamic deformation. The large disorientations in many of the pyroxene crystals are commonly consistent with slip on the system T -(100), t = [001], but these distortions are not due to plastic flow. They are ascribed to rapid growth and quenching phenomena as deduced from studies of chondrules and of quenched natural and experimentally produced melts. Some of the silicates in the breccias and regolith show evidence of shock deformation, from mild to intense, as indicated by pervasive featuring, shock lamallae, and partial transformatiion of pyroxene and plagioclase crystals to glass.  相似文献   

Engineering enzyme specificity by "substrate-assisted catalysis"   总被引：8，自引：0，他引：8  

P Carter  J A Wells 《Science (New York, N.Y.)》1987,237(4813):394-399

A novel approach to engineering enzyme specificity is presented in which a catalytic group from an enzyme is first removed by site-directed mutagenesis causing inactivation. Activity is then partially restored by substrates containing the missing catalytic functional group. Replacement of the catalytic His with Ala in the Bacillus amyloliquefaciens subtilisin gene (the mutant is designated His64Ala) by site-directed mutagenesis reduces the catalytic efficiency (kcat/Km) by a factor of a million when assayed with N-succinyl-L-Phe-L-Ala-L-Ala-L-Phe-p-nitroanilide (sFAAF-pNA). Model building studies showed that a His side chain at the P2 position of a substrate bound at the active site of subtilisin could be virtually superimposed on the catalytic His side chain of this serine protease. Accordingly, the His64Ala mutant hydrolyzes a His P2 substrate (sFAHF-pNA) up to 400 times faster than a homologous Ala P2 or Gln P2 substrate (sFAAF-pNA or sFAQF-pNA) at pH 8.0. In contrast, the wild-type enzyme hydrolyzes these three substrates with similar catalytic efficiencies. Additional data from substrate-dependent pH profiles and hydrolysis of large polypeptides indicate that the His64Ala mutant enzyme can recover partially the function of the lost catalytic histidine from a His P2 side chain on the substrate. Such "substrate-assisted catalysis" provides a new basis for engineering enzymes with very narrow and potentially useful substrate specificities. These studies also suggest a possible functional intermediate in the evolution of the catalytic triad of serine proteases.  相似文献   

Long-Term Mean Vertical Motion over the Tropical Pacific: Wind-Profiling Doppler Radar Measurements     

Gage KS  McAfee JR  Carter DA  Ecklund WL  Riddle AC  Reid GC  Balsley BB 《Science (New York, N.Y.)》1991,254(5039):1771-1773

Measurement from Christmas Island (2 degrees N, 157 degrees W) of long-term mean vertical motions in the tropical atmosphere using very-high-frequency wind-profiling Doppler radar show that there is a transition from downward motion in the free troposphere to upward motion in the upper troposphere and lower stratosphere. The observations in the free troposphere are consistent with a balance between adiabatic and diabatic heating and cooling rates in a clear atmosphere. Comparison of the results at Christmas Island during El Ni?o and non-El Ni?o conditions with earlier results obtained for stratiform rain conditions over Pohnpei, Federated States of Micronesia, show that cirrus clouds in the vicinity of the tropopause likely play an important role in determining the sense and magnitude of vertical motions in this region. These results have implications for the exchange of mass between the troposphere and stratosphere over the tropics.  相似文献   

Ultrafast flash thermal conductance of molecular chains     

Wang Z  Carter JA  Lagutchev A  Koh YK  Seong NH  Cahill DG  Dlott DD 《Science (New York, N.Y.)》2007,317(5839):787-790

At the level of individual molecules, familiar concepts of heat transport no longer apply. When large amounts of heat are transported through a molecule, a crucial process in molecular electronic devices, energy is carried by discrete molecular vibrational excitations. We studied heat transport through self-assembled monolayers of long-chain hydrocarbon molecules anchored to a gold substrate by ultrafast heating of the gold with a femtosecond laser pulse. When the heat reached the methyl groups at the chain ends, a nonlinear coherent vibrational spectroscopy technique detected the resulting thermally induced disorder. The flow of heat into the chains was limited by the interface conductance. The leading edge of the heat burst traveled ballistically along the chains at a velocity of 1 kilometer per second. The molecular conductance per chain was 50 picowatts per kelvin.  相似文献   

Congress: debate over science jurisdictions     

Carter LJ 《Science (New York, N.Y.)》1966,153(3742):1364-1366

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WIPP Goes Ahead, Amid Controversy: New Mexico's governor worries less about the nuclear waste project now planned than about the one he suspects DOE may have up its sleeve     

Carter LJ 《Science (New York, N.Y.)》1983,222(4628):1104-1106

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