445 research outputs found
MAGNITUDE OF SOIL LOSSES THROUGHOUT THE CARIBBEAN
MAGNITUDE OF SOIL LOSSES THROUGHOUT THE CARIBBEA
Tuning the Kondo effect with a mechanically controllable break junction
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
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
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
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
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?
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 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 categorÃa única de actos administrativos, definidos por ser declaraciones de la Administración productoras de efectos jurÃdicos 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 serÃa el criterio de distinción entre actos normativos y actos no normativos, pues en el ámbito administrativo sà puede defenderse que los actos pertenecen a una u otra categorÃa «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
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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