445 research outputs found

    MAGNITUDE OF SOIL LOSSES THROUGHOUT THE CARIBBEAN

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    MAGNITUDE OF SOIL LOSSES THROUGHOUT THE CARIBBEA

    Tuning the Kondo effect with a mechanically controllable break junction

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    We study electron transport through C60 molecules in the Kondo regime using a mechanically controllable break junction. By varying the electrode spacing, we are able to change both the width and height of the Kondo resonance, indicating modification of the Kondo temperature and the relative strength of coupling to the two electrodes. The linear conductance as a function of T/T_K agrees with the scaling function expected for the spin-1/2 Kondo problem. We are also able to tune finite-bias Kondo features which appear at the energy of the first C60 intracage vibrational mode.Comment: 4 pages with 4 figure

    3-D Tracking and Visualization of Hundreds of Pt-Co Fuel Cell Nanocatalysts During Electrochemical Aging

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    We present an electron tomography method that allows for the identification of hundreds of electrocatalyst nanoparticles with one-to-one correspondence before and after electrochemical aging. This method allows us to track, in three-dimensions (3-D), the trajectories and morphologies of each Pt-Co nanocatalyst on a fuel cell carbon support. The use of atomic-scale electron energy loss spectroscopic imaging enables the correlation of performance degradation of the catalyst with changes in particle/inter-particle morphologies, particle-support interactions and the near-surface chemical composition. We found that, aging of the catalysts under normal fuel cell operating conditions (potential scans from +0.6 V to +1.0 V for 30,000 cycles) gives rise to coarsening of the nanoparticles, mainly through coalescence, which in turn leads to the loss of performance. The observed coalescence events were found to be the result of nanoparticle migration on the carbon support during potential cycling. This method provides detailed insights into how nanocatalyst degradation occurs in proton exchange membrane fuel cells (PEMFCs), and suggests that minimization of particle movement can potentially slow down the coarsening of the particles, and the corresponding performance degradation.Comment: Nano Letters, accepte

    Facile synthetic procedure for and electrochemical properties of hexa(2-thienyl)benzenes directed toward electroactive materials

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    In the presence of RhCl3 center dot 3H(2)O and i-Pr2NEt, the cyclotrimerization of di(2-thienyl)acetylenes proceeded smoothly to afford hexa(2-thienyl)benzenes. CV analysis of the hexa(2-thienyl)benzenes showed that they may be useful as electroactive materials.</p

    Getter sputtering system for high-throughput fabrication of composition spreads

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    We describe a sputtering system that can deposit composition spreads in an effectively UHV environment but which does not require the high-throughput paradigm to be compromised by a long pump down each time a target is changed. The system deploys four magnetron sputter guns in a cryoshroud (getter sputtering) which allows elements such as Ti and Zr to be deposited with minimal contamination by oxygen or other reactive background gases. The system also relies on custom substrate heaters to give rapid heating and cool down. The effectiveness of the gettering technique is evaluated, and example results obtained for catalytic activity of a pseudoternary composition spread are presented

    Getter sputtering system for high-throughput fabrication of composition spreads

    Get PDF
    We describe a sputtering system that can deposit composition spreads in an effectively UHV environment but which does not require the high-throughput paradigm to be compromised by a long pump down each time a target is changed. The system deploys four magnetron sputter guns in a cryoshroud (getter sputtering) which allows elements such as Ti and Zr to be deposited with minimal contamination by oxygen or other reactive background gases. The system also relies on custom substrate heaters to give rapid heating and cool down. The effectiveness of the gettering technique is evaluated, and example results obtained for catalytic activity of a pseudoternary composition spread are presented

    El Reglamento, ¿acto administrativo en el Derecho peruano?

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    This essay focuses on the difference between normative acts [Rules] and non normative acts [adjudications] of the Public administration and, despite the verification of this difference, is possible to include them in the only category of administrative acts, defined as Public Administration’s declarations that produce juridical effects in exercise of an administrative legal power. From a doctrinal perspective, this is the conclusion of the authors, to which they come after analyzing the criteria proposed to distinguish the normative acts (general regulations or Rules) of non normative acts (single decisions or adjudications), and of highlighting their similarities. About Peruvian Law, the authors analyze the Law 27444, Administrative General Procedure&nbsp;Act, in which they can find arguments to affirm that the Rules are also administrative acts [adjudications], though this norm will not be applied to them fully, because they are abstract and ordinamental measures. This last criterion could be used to distinguish between normative and non normative administrative acts, since in the administrative area is possible to affirm that those acts belong to one or another category «by nature», and not only form a formal criterion.Este trabajo se ocupa de la diferencia entre actos de la Administración normativos y actos no normativos y si, pese a la constatación de esta diferencia, es posible incluirlos en una categoría única de actos administrativos, definidos por ser declaraciones de la Administración productoras de efectos jurídicos dictados en ejercicio de una potestad administrativa. Desde una perspectiva doctrinal, esta es la posición de los autores, a la que llegan luego de analizar los criterios propuestos en la doctrina para distinguir las normas de los actos no normativos y de resaltar sus similitudes. Por su parte, en el Derecho peruano se analiza lo dispuesto por la Ley 27444, del Procedimiento Administrativo General, en la cual pueden encontrarse argumentos para afirmar que los Reglamentos son también actos administrativos, aunque no se les aplicará plenamente esta norma, al tratarse de medidas no consuntivas y abstractas. Este sería el criterio de distinción entre actos normativos y actos no normativos, pues en el ámbito administrativo sí puede defenderse que los actos pertenecen a una u otra categoría «por naturaleza» y no únicamente por un criterio formal

    The Oxygen Reduction Pathway for Spinel Metal Oxides in Alkaline Media: An Experimentally Supported Ab Initio Study

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    Precious-metal-free spinel oxide electrocatalysts are promising candidates for catalyzing the oxygen reduction reaction (ORR) in alkaline fuel cells. In this theory-driven study, we use joint density-functional theory in tandem with supporting electrochemical measurements to identify a novel theoretical pathway for the ORR on cubic Co3O4 nanoparticle electrocatalysts. This pathway aligns more closely with experimental results than previous models. The new pathway employs the cracked adsorbates *(OH)(O) and *(OH)(OH), which, through hydrogen bonding, induce spectator surface *H. This results in an onset potential closely matching experimental values, in stark contrast to the traditional ORR pathway, which keeps adsorbates intact and overestimates the onset potential by 0.7 V. Finally, we introduce electrochemical strain spectroscopy (ESS), a groundbreaking strain analysis technique. ESS combines ab initio calculations with experimental measurements to validate proposed reaction pathways and pinpoint rate-limiting steps
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