Molecular mechanisms for the functionality of lubricant additives     

Mosey NJ  Müser MH  Woo TK 《Science (New York, N.Y.)》2005,307(5715):1612-1615

Wear limits the life-span of many mechanical devices with moving parts. To reduce wear, lubricants are frequently enriched with additives, such as zinc phosphates, that form protective films on rubbing surfaces. Using first-principles molecular dynamics simulations of films derived from commercial additives, we unraveled the molecular origin of how antiwear films can form, function, and dissipate energy. These effects originate from pressure-induced changes in the coordination number of atoms acting as cross-linking agents to form chemically connected networks. The proposed mechanism explains a diverse body of experiments and promises to prove useful in the rational design of antiwear additives that operate on a wider range of surface materials, with reduced environmental side effects.  相似文献   

Recombinant DNA: NIH rules broken in insulin gene project     

Wade N 《Science (New York, N.Y.)》1977,197(4311):1342-1345

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Early origin and recent expansion of Plasmodium falciparum     

Joy DA  Feng X  Mu J  Furuya T  Chotivanich K  Krettli AU  Ho M  Wang A  White NJ  Suh E  Beerli P  Su XZ 《Science (New York, N.Y.)》2003,300(5617):318-321

The emergence of virulent Plasmodium falciparum in Africa within the past 6000 years as a result of a cascade of changes in human behavior and mosquito transmission has recently been hypothesized. Here, we provide genetic evidence for a sudden increase in the African malaria parasite population about 10,000 years ago, followed by migration to other regions on the basis of variation in 100 worldwide mitochondrial DNA sequences. However, both the world and some regional populations appear to be older (50,000 to 100,000 years old), suggesting an earlier wave of migration out of Africa, perhaps during the Pleistocene migration of human beings.  相似文献   

Ultrahigh-density nanowire lattices and circuits     

Melosh NA  Boukai A  Diana F  Gerardot B  Badolato A  Petroff PM  Heath JR 《Science (New York, N.Y.)》2003,300(5616):112-115

We describe a general method for producing ultrahigh-density arrays of aligned metal and semiconductor nanowires and nanowire circuits. The technique is based on translating thin film growth thickness control into planar wire arrays. Nanowires were fabricated with diameters and pitches (center-to-center distances) as small as 8 nanometers and 16 nanometers, respectively. The nanowires have high aspect ratios (up to 10(6)), and the process can be carried out multiple times to produce simple circuits of crossed nanowires with a nanowire junction density in excess of 10(11) per square centimeter. The nanowires can also be used in nanomechanical devices; a high-frequency nanomechanical resonator is demonstrated.  相似文献   

Bond-selective control of a heterogeneously catalyzed reaction     

Killelea DR  Campbell VL  Shuman NS  Utz AL 《Science (New York, N.Y.)》2008,319(5864):790-793

Energy redistribution, including the many phonon-assisted and electronically assisted energy-exchange processes at a gas-metal interface, can hamper vibrationally mediated selectivity in chemical reactions. We establish that these limitations do not prevent bond-selective control of a heterogeneously catalyzed reaction. State-resolved gas-surface scattering measurements show that the nu1 C-H stretch vibration in trideuteromethane (CHD3) selectively activates C-H bond cleavage on a Ni(111) surface. Isotope-resolved detection reveals a CD3:CHD2 product ratio > 30:1, which contrasts with the 1:3 ratio for an isoenergetic ensemble of CHD3 whose vibrations are statistically populated. Recent studies of vibrational energy redistribution in the gas and condensed phases suggest that other gas-surface reactions with similar vibrational energy flow dynamics might also be candidates for such bond-selective control.  相似文献   

Materials science. Sweet, hairy, soft, and slippery     

Lee S  Spencer ND 《Science (New York, N.Y.)》2008,319(5863):575-576

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Four climate cycles of recurring deep and surface water destabilizations on the Iberian margin     

Martrat B  Grimalt JO  Shackleton NJ  de Abreu L  Hutterli MA  Stocker TF 《Science (New York, N.Y.)》2007,317(5837):502-507

Centennial climate variability over the last ice age exhibits clear bipolar behavior. High-resolution analyses of marine sediment cores from the Iberian margin trace a number of associated changes simultaneously. Proxies of sea surface temperature and water mass distribution, as well as relative biomarker content, demonstrate that this typical north-south coupling was pervasive for the cold phases of climate during the past 420,000 years. Cold episodes after relatively warm and largely ice-free periods occurred when the predominance of deep water formation changed from northern to southern sources. These results reinforce the connection between rapid climate changes at Mediterranean latitudes and century-to-millennial variability in northern and southern polar regions.  相似文献   

Transgenerational epigenetic instability is a source of novel methylation variants     

Schmitz RJ  Schultz MD  Lewsey MG  O'Malley RC  Urich MA  Libiger O  Schork NJ  Ecker JR 《Science (New York, N.Y.)》2011,334(6054):369-373

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Relationship between clinical signs and transmission of an infectious disease and the implications for control     

Charleston B  Bankowski BM  Gubbins S  Chase-Topping ME  Schley D  Howey R  Barnett PV  Gibson D  Juleff ND  Woolhouse ME 《Science (New York, N.Y.)》2011,332(6030):726-729

Control of many infectious diseases relies on the detection of clinical cases and the isolation, removal, or treatment of cases and their contacts. The success of such "reactive" strategies is influenced by the fraction of transmission occurring before signs appear. We performed experimental studies of foot-and-mouth disease transmission in cattle and estimated this fraction at less than half the value expected from detecting virus in body fluids, the standard proxy measure of infectiousness. This is because the infectious period is shorter (mean 1.7 days) than currently realized, and animals are not infectious until, on average, 0.5 days after clinical signs appear. These results imply that controversial preemptive control measures may be unnecessary; instead, efforts should be directed at early detection of infection and rapid intervention.  相似文献   

Ordered and dynamic assembly of single spliceosomes     

Hoskins AA  Friedman LJ  Gallagher SS  Crawford DJ  Anderson EG  Wombacher R  Ramirez N  Cornish VW  Gelles J  Moore MJ 《Science (New York, N.Y.)》2011,331(6022):1289-1295

The spliceosome is the complex macromolecular machine responsible for removing introns from precursors to messenger RNAs (pre-mRNAs). We combined yeast genetic engineering, chemical biology, and multiwavelength fluorescence microscopy to follow assembly of single spliceosomes in real time in whole-cell extracts. We find that individual spliceosomal subcomplexes associate with pre-mRNA sequentially via an ordered pathway to yield functional spliceosomes and that association of every subcomplex is reversible. Further, early subcomplex binding events do not fully commit a pre-mRNA to splicing; rather, commitment increases as assembly proceeds. These findings have important implications for the regulation of alternative splicing. This experimental strategy should prove widely useful for mechanistic analysis of other macromolecular machines in environments approaching the complexity of living cells.  相似文献