Properties of metallic nanowires: from conductance quantization to localization     

Pascual JI  Méndez J  Gómez-Herrero J  Baró AM  Garcia N  Landman U  Luedtke WD  Bogachek EN  Cheng HP 《Science (New York, N.Y.)》1995,267(5205):1793-1795

Material structures of reduced dimensions exhibit electrical and mechanical properties different from those in the bulk. Measurements of room-temperature electronic transport in pulled metallic nanowires are presented, demonstrating that the conductance characteristics depend on the length, lateral dimensions, state and degree of disorder, and elongation mechanism of the wire. Conductance during the elongation of short wires (length l approximately 50 angstroms) exhibits periodic quantization steps with characteristic dips, correlating with the order-disorder states of layers of atoms in the wire predicted by molecular dynamics simulations. The resistance R of wires as long as l approximately 400 angstroms exhibits localization characteristics with In R(l) approximately l(2).  相似文献   

Selective and efficient platinum(0)-carbene complexes as hydrosilylation catalysts     

Markó IE  Stérin S  Buisine O  Mignani G  Branlard P  Tinant B  Declercq JP 《Science (New York, N.Y.)》2002,298(5591):204-206

The hydrosilylation reaction enables the production of silicon polymers. Platinum-carbene complexes are reported that catalyze the hydrosilylation reaction of alkenes with remarkable efficiency and exquisite selectivity and avoid the formation of platinum colloids. By-products, typically encountered with previous catalytic systems, are suppressed with these platinum derivatives.  相似文献   

NANOTECHNOLOGY: Beyond Gedanken Experiments     

Forró L 《Science (New York, N.Y.)》2000,289(5479):560-561

For future nanomechanical devices to be realized, sophisticated ways of manipulating small structures must be developed, and fundamental elements of macroscopic machines, such as switches and bearings, must be reproduced in the nanoscale. Forró highlights the nanotube nanobearings and nanoswitches reported by Cumings and Zettl and concludes that multiwall nanotubes are ideal starting materials for future nanodevices.  相似文献   

Spain's Ramón y Cajal Program     

Axness C  Tornero P  Ricote J  Algueró M 《Science (New York, N.Y.)》2003,300(5616):52-53

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Ecology. Dipping into the rare biosphere     

Pedrós-Alió C 《Science (New York, N.Y.)》2007,315(5809):192-193

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Electronic transitions in perovskite: possible nonconvecting layers in the lower mantle     

Badro J  Rueff JP  Vankó G  Monaco G  Fiquet G  Guyot F 《Science (New York, N.Y.)》2004,305(5682):383-386

We measured the spin state of iron in magnesium silicate perovskite (Mg(0.9),Fe(0.1))SiO(3) at high pressure and found two electronic transitions occurring at 70 gigapascals and at 120 gigapascals, corresponding to partial and full electron pairing in iron, respectively. The proportion of iron in the low spin state thus grows with depth, increasing the transparency of the mantle in the infrared region, with a maximum at pressures consistent with the D" layer above the core-mantle boundary. The resulting increase in radiative thermal conductivity suggests the existence of nonconvecting layers in the lowermost mantle.  相似文献   

Biscrolling nanotube sheets and functional guests into yarns     

Lima MD  Fang S  Lepró X  Lewis C  Ovalle-Robles R  Carretero-González J  Castillo-Martínez E  Kozlov ME  Oh J  Rawat N  Haines CS  Haque MH  Aare V  Stoughton S  Zakhidov AA  Baughman RH 《Science (New York, N.Y.)》2011,331(6013):51-55

Multifunctional applications of textiles have been limited by the inability to spin important materials into yarns. Generically applicable methods are demonstrated for producing weavable yarns comprising up to 95 weight percent of otherwise unspinnable particulate or nanofiber powders that remain highly functional. Scrolled 50-nanometer-thick carbon nanotube sheets confine these powders in the galleries of irregular scroll sacks whose observed complex structures are related to twist-dependent extension of Archimedean spirals, Fermat spirals, or spiral pairs into scrolls. The strength and electronic connectivity of a small weight fraction of scrolled carbon nanotube sheet enables yarn weaving, sewing, knotting, braiding, and charge collection. This technology is used to make yarns of superconductors, lithium-ion battery materials, graphene ribbons, catalytic nanofibers for fuel cells, and titanium dioxide for photocatalysis.  相似文献   

Direct measurement of the current-phase relation of a superfluid 3He-B weak link     

S Backhaus  SV Pereverzev  A Loshak  JC Davis  RE Packard 《Science (New York, N.Y.)》1997,278(5342):1435-1438

Direct measurements of the current-phase relation, I versus Deltaphi, for a weak link coupling two reservoirs of B-phase superfluid helium-3 (3He-B) were made over a wide range of temperatures. The weak link consists of a square array of 100-nanometer-diameter apertures. For temperatures T such that T/Tc >/= 0.6 (where Tc is the superfluid transition temperature), I approximately sin(Deltaphi). At lower temperatures, I(Deltaphi) approaches a straight line. Several remarkable phenomena heretofore inaccessible to superconducting Josephson junctions, including direct observation of quantum oscillations and continuous knowledge of Deltaphi, were also observed.  相似文献   

Spin transition zone in Earth's lower mantle     

Lin JF  Vankó G  Jacobsen SD  Iota V  Struzhkin VV  Prakapenka VB  Kuznetsov A  Yoo CS 《Science (New York, N.Y.)》2007,317(5845):1740-1743

Mineral properties in Earth's lower mantle are affected by iron electronic states, but representative pressures and temperatures have not yet been probed. Spin states of iron in lower-mantle ferropericlase have been measured up to 95 gigapascals and 2000 kelvin with x-ray emission in a laser-heated diamond cell. A gradual spin transition of iron occurs over a pressure-temperature range extending from about 1000 kilometers in depth and 1900 kelvin to 2200 kilometers and 2300 kelvin in the lower mantle. Because low-spin ferropericlase exhibits higher density and faster sound velocities relative to the high-spin ferropericlase, the observed increase in low-spin (Mg,Fe)O at mid-lower mantle conditions would manifest seismically as a lower-mantle spin transition zone characterized by a steeper-than-normal density gradient.  相似文献   

SPME-GC-pyrolysis-AFS determination of methylmercury in marine fish products by alkaline sample preparation and aqueous phase phenylation derivatization   总被引：2，自引：0，他引：2  

Jókai Z  Abrankó L  Fodor P 《Journal of agricultural and food chemistry》2005,53(14):5499-5505

Characterization of a cost-efficient analytical method based on alkaline sample digestion with KOH and NaOH, followed by aqueous phase phenylation derivatization with NaBPh4 and solid phase microextraction (SPME) for the determination of methylmercury in typical fish-containing food samples commercially available in Hungary, is reported. The sample preparation procedure along with the applied SPME-GC-pyrolysis-AFS system was validated by measuring certified reference materials (CRM) BCR-464, TORT-2, and a candidate CRM BCR 710. To carry out an estimation of average Hungarian methylmercury exposures via marine fish and/or fish-containing food consumption, 16 commercially available products and 3 pooled representative seafood samples of-according to a previous European survey--the three most consumed fish species in Hungary, herring, sardines, and hake, were analyzed. Methylmercury concentrations of the analyzed samples were in the range 0.016-0.137 microg of MeHg g(-1) dry weight as Hg.  相似文献