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排序方式: 共有58条查询结果,搜索用时 15 毫秒
1.
Rodriguez JA Liu G Jirsak T Hrbek J Chang Z Dvorak J Maiti A 《Journal of the American Chemical Society》2002,124(18):5242-5250
Synchrotron-based high-resolution photoemission and first-principles density-functional slab calculations were used to study the interaction of gold with titania and the chemistry of SO(2) on Au/TiO(2)(110) surfaces. The deposition of Au nanoparticles on TiO(2)(110) produces a system with an extraordinary ability to adsorb and dissociate SO(2). In this respect, Au/TiO(2) is much more chemically active than metallic gold or stoichiometric titania. On Au(111) and rough polycrystalline surfaces of gold, SO(2) bonds weakly and desorbs intact at temperatures below 200 K. For the adsorption of SO(2) on TiO(2)(110) at 300 K, SO(4) is the only product (SO(2) + O(oxide) --> SO(4,ads)). In contrast, Au/TiO(2)(110) surfaces (theta;(Au) < or = 0.5 ML) fully dissociate the SO(2) molecule under identical reaction conditions. Interactions with titania electronically perturb gold, making it more chemically active. Furthermore, our experimental and theoretical results show quite clearly that not only gold is perturbed when gold and titania interact. The adsorbed gold, on its part, enhances the reactivity of titania by facilitating the migration of O vacancies from the bulk to the surface of the oxide. In general, the complex coupling of these phenomena must be taken into consideration when trying to explain the unusual chemical and catalytic activity of Au/TiO(2). In many situations, the oxide support can be much more than a simple spectator. 相似文献
2.
Tokumasu F Hwang J Dvorak JA 《Langmuir : the ACS journal of surfaces and colloids》2004,20(3):614-618
Membrane domains contribute important structural and functional attributes to biological membranes. We describe the heterogeneous nanoscale distribution of lipid molecules within microscale membrane domains in multicomponent lipid bilayers composed of dipalmitoylphosphatidylcholine (DPPC), dilauroylphosphatidylcholine (DLPC), and cholesterol (chol). The lipids were labeled with the fluorescent lipid analogues Bodipy-PC and DiI-C20:0 to identify the distribution of individual membrane components. We used a near-field scanning optical microscope (NSOM) at room temperature to identify the nanoscale structures in the membrane. Simultaneous multicolor NSOM imaging at the emission maxima of the fluorescent analogues revealed a patchy distribution of Bodipy-PC and DiI-C20:0 indicative of phase separations in the bilayer. In a cholesterol-free system (DPPC/DLPC = 1:1), NSOM images proved that the two phosphatidylcholine molecules can coexist in domains at the micrometer level but form nanoscopic patches within the domains; DPPC occurs at the edge of the domains, whereas DLPC is present throughout the domains. In the presence of cholesterol (DPPC/DLPC = 7:3, chol = 18.9%), the two lipid molecules were more miscible but incomplete phase separations also occurred. The average domain sizes were 140-200 nm, well below the resolution capabilities of diffraction-limited light microscopy techniques; the domains were unresolvable by confocal microscopy. Our high-resolution NSOM studies of membrane domain behavior provide a better understanding of complex membrane phase phenomena in multicomponent biological membranes. 相似文献
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4.
Ryan P. Jansonius Phil A. Schauer David J. Dvorak Benjamin P. MacLeod David K. Fork Curtis P. Berlinguette 《Angewandte Chemie (International ed. in English)》2020,59(29):12192-12198
Strain engineering can increase the activity and selectivity of an electrocatalyst. Tensile strain is known to improve the electrocatalytic activity of palladium electrodes for reduction of carbon dioxide or dioxygen, but determining how strain affects the hydrogen evolution reaction (HER) is complicated by the fact that palladium absorbs hydrogen concurrently with HER. We report here a custom electrochemical cell, which applies tensile strain to a flexible working electrode, that enabled us to resolve how tensile strain affects hydrogen absorption and HER activity for a thin film palladium electrocatalyst. When the electrodes were subjected to mechanically‐applied tensile strain, the amount of hydrogen that absorbed into the palladium decreased, and HER electrocatalytic activity increased. This study showcases how strain can be used to modulate the hydrogen absorption capacity and HER activity of palladium. 相似文献
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6.
The shakedown problem for a composite lamina made of an elastic-plastic matrix and elastic cylindrical fibers is studied. The plastic deformation modes of the lamina are reviewed, and it is concluded that significant shakedown effects can be caused only by the I1 = 1/2(T11 + T22) and I2 = T33 components of the remotely applied stress field which are symmetric about the axis x3 of the fiber; T11 and T22 are the normal composite stresses in the transverse plane. It is shown that the I1I2 stress system is needed also to represent thermal loads caused by a uniform change of temperature in the composite.Two methods for evaluation of shakedown limits in the I1I2-plane are described. First, the classical approach involving the determination of parametric families of self-stress fields and the solution of mathematical programming problems is used. Results are presented for selected B-Al, Be-Al, B-Ti and B-Mg composites.In the second method, the shakedown problem is related to the recently developed kinematic hardening rules for fibrous composites. It is shown that the composite will shake down for any loading program within a prescribed domain in the I1I2-plane, providing that the domain can be contained within a translated initial yield surface. This approach leads to a closed-form evaluation of shakedown limits for any arbitrary combination of mechanical and thermal variable cyclic loads in fibrous composites with temperaturedependent matrix yield strengths.The relationship between shakedown and fatigue in metal matrix composites is discussed. 相似文献
7.
U. Köster P. Carbonez A. Dorsival J. Dvorak R. Eichler S. Fernandes H. Frånberg J. Neuhausen Z. Novackova R. Wilfinger A. Yakushev 《The European physical journal. Special topics》2007,150(1):285-291
Refractory elements, i.e. elements with very high melting point and
low vapor pressure, cannot be released in atomic form from an ISOL target.
Therefore most of these elements are presently not available as ISOL beams.
However, when reactive gases are introduced
into the target, they may form volatile compounds with the refractory elements,
allowing for an easier transport to the ion source. Particularly useful are
high-temperature stable fluorides and oxides.
By these chemical evaporation methods so far ISOL beams of the refractory elements
C, Zr, Hf and Ta have been produced. We discuss how ISOL beams of B, Ti, Nb, Mo, Tc,
Ru, W, Re, Os and Ir could be produced in a similar way. 相似文献
8.
M. Merz P. Reutler B. Büchner D. Arena J. Dvorak Y. U. Idzerda S. Tokumitsu S. Schuppler 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,51(3):315-319
O1s and Mn2p near-edge X-ray absorption spectroscopy on
La1-xSr1+xMnO4 (0 ≤x ≤0.5) single crystals shows that Sr doping does not
only provide holes to the system but also induces a continuous transfer of electrons from
out-of-plane d3z2-r2 to in-plane d3x2-r2/d3y2-r2 orbitals. Furthermore, a
non-vanishing electron occupation of in-plane dx2-y2 and out-of-plane d3z2-r2
orbitals is observed up to relatively high doping contents. These findings demonstrate that the
energy difference between all these orbital types has to be very small and manifest that the
orbital degree of freedom is determined not just by crystal field effects but also by orbital
coupling. Moreover, the doping-dependent transfer of spectral weight observed in the current data
identifies La1-xSr1+xMnO4 as a charge-transfer insulator. 相似文献
9.
A strain-space formulation of plasticity theory for metal matrix fibrous composites is discussed. Specific results are obtained for a composite system in which the fibers are elastic until failure, while the matrix is of the Mises type, with kinematic hardening. The material model of the composite is based on the assumption that the fiber diameter is vanishingly small, and the fiber volume fraction is finite. Explicit expressions are obtained for instantaneous strain concentration factors in the phases, for the instantaneous overall stiffness, and for the overall loading surface and hardening rule during mechanical straining along a prescribed path. 相似文献
10.