34,278 research outputs found
Thermal stability of the cu-ceo2 interface on silica and alumina, and its relation with activity in the oxidation reaction of co and the decomposition of n2o
Indexación: Scopus; Scielo.The effect of the support on the formation of the Cu-CeO2 interface and its thermal stability after calcination at 500, 700 and 900 °C is studied. The supports used are SiO2, because of its inert character, and Al2O3, because it can interact with the Cu and Ce species on the surface. The catalysts were characterized by BET, XRD, UV-vis DRS, and TPR with H2. The catalytic activity in the CO oxidation reactions with O2 at low temperature and the decomposition of N2O were selected to visualize the effect of temperature on the concentration of Cu-CeO2 interfacial sites. The results show that at a calcination temperature of 500 °C the formation of the Cu-CeO2 interface is favored over the SiO2 support. However, the stability of the Cu-CeO2 interface on SiO2 is much lower than on Al2O3, causing a substantial decrease of the interfacial sites calcining at 700 °C, and segregation of the Cu and Ce species on the surface of the silica, with complete loss of the catalytic activity in both reactions when calcining at 900 °C. In contrast, on alumina the Cu-CeO2 interface is more stable and presents a significant catalytic activity in both reactions, even when calcining at 900 °C. The characterization results show that the sintering process of Cu species and CeO2 particles is less on the alumina support due to the greater interaction of the Cu and Ce with this support. © 2018 Sociedad Chilena de Quimica.all rights reserved.https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0717-97072018000304102&lng=en&nrm=iso&tlng=e
Activity of alumina supported fe catalysts for N2O decomposition: Effects of the iron content and thermal treatment
Indexación: Scopus.The activity of Fe2O3/Al2O3 catalysts prepared by impregnation of Al2O3 with different amounts of Fe and calcination temperatures (650 and 900 °C) in the direct N2O decomposition reaction was studied. High calcination temperature was introduced to study the effect of "aging", which are the conditions prevailing in the process-gas option for N2O abatement. The catalysts were characterized by BET, XRD, UV-DRS, and H2-TPR. The incorporation of Fe promotes the alumina phase transition (g-Al2O3 to a-Al2O3) when the catalysts are calcined at 900 °C, which is accompanied by a decrease in the specifc area. The activity of the catalysts and the specifc surface area depend on Fe loading and calcination temperature. It was found that highly dispersed Fe species are more active than bulk type Fe2O3 particles. We conclude that Fe2O3/Al2O3 catalysts prepared by impregnation method are active in the decomposition of N2O, to be used at low or high reaction temperatures (tail-gas or process-gas treatments, respectively), as part of nitric acid production plant. © 2018 Sociedad Chilena de Quimica. All rights reserved.https://scielo.conicyt.cl/pdf/jcchems/v62n4/0717-9324-jcchems-62-04-3752.pd
Direct T-violation measurements and T-odd effects in decay experiments
Motivated by the recent experimental announcements for direct measurements of
time-reversal non-invariance in the neutral kaon system, we make a comparative
discussion of the CPLEAR and KTeV measurements. The most suitable way to
consistently incorporate the mixing, the time evolution and the decays of
kaons, is to describe the neutral kaon system as a system with a non-Hermitean
Hamiltonian. In this framework, the physical (decaying) incoming and outgoing
states are distinct and belong to dual spaces. Moreover, since they are
eigenstates of the full Hamiltonian, they never oscillate. This is directly
manifest in the orthogonality conditions of the physical states, which entirely
determine the evolution of the kaon system. Along these lines we conclude:
CPLEAR studies K0-bar{K0} oscillations, a process where initial and final
states can be reversed, the CPLEAR asymmetry being an effect directly related
to the definition of time-reversal. Conclusively, CPLEAR provides a direct
measurement of T-violation without any assumption either on unitarity or on
CPT-invariance. The KTeV experiment studies in particular the process KL -> pi+
pi- e+ e- where they measure a T-odd effect. However, using unitarity together
with estimates of the final state interactions, it should be possible to
determine whether this effect can be identified with a genuine T-reversal
violation.Comment: 11 pages, no figures. Presented at the 34th Rencontres de Moriond on
Electroweak Interactions and Unified Theories, Les Arcs, 13-20 March, 199
Space-time noncommutativity and (1+1) Higgs Model
We compare the classical scattering of kinks in (1+1) Higgs model with its
analogous noncommutative counterpart. While at a classical level we are able to
solve the scattering at all orders finding a smooth solution, at a
noncommutative level we present only perturbative results, suggesting the
existence of a smooth solution also in this case.Comment: 18 pages, 2 figure
A Simple Algebraic Derivation of the Covariant Anomaly and Schwinger Term
An expression for the curvature of the "covariant" determinant line bundle is
given in even dimensional space-time. The usefulness is guaranteed by its
prediction of the covariant anomaly and Schwinger term. It allows a parallel
derivation of the consistent anomaly and Schwinger term, and their covariant
counterparts, which clarifies the similarities and differences between them. In
particular, it becomes clear that in contrary to the case for anomalies, the
difference between the consistent and covariant Schwinger term can not be
extended to a local form on the space of gauge potentials.Comment: 16 page
Gravitational Instantons from Gauge Theory
A gauge theory can be formulated on a noncommutative (NC) spacetime. This NC
gauge theory has an equivalent dual description through the so-called
Seiberg-Witten (SW) map in terms of an ordinary gauge theory on a commutative
spacetime. We show that all NC U(1) instantons of Nekrasov-Schwarz type are
mapped to ALE gravitational instantons by the exact SW map and that the NC
gauge theory of U(1) instantons is equivalent to the theory of hyper-Kaehler
geometries. It implies the remarkable consequence that ALE gravitational
instantons can emerge from local condensates of purely NC photons.Comment: 4 pages with two columns; comments and references added, to appear in
Phys. Rev. Let
Fermionic Determinant of the Massive Schwinger Model
A representation for the fermionic determinant of the massive Schwinger
model, or , is obtained that makes a clean separation between the
Schwinger model and its massive counterpart. From this it is shown that the
index theorem for follows from gauge invariance, that the Schwinger
model's contribution to the determinant is canceled in the weak field limit,
and that the determinant vanishes when the field strength is sufficiently
strong to form a zero-energy bound state
1RXS J180408.9-342058: an ultra compact X-ray binary candidate with a transient jet
We present a detailed NIR/optical/UV study of the transient low mass X-ray
binary 1RXS J180408.9-342058 performed during its 2015 outburst, aimed at
determining the nature of its companion star. We obtained three optical spectra
at the 2.1 m San Pedro Martir Observatory telescope (Mexico). We performed
optical and NIR photometric observations with both the REM telescope and the
New Technology Telescope (NTT) in La Silla. We obtained optical and UV
observations from the Swift archive. Finally, we performed optical polarimetry
of the source by using the EFOSC2 instrument mounted on the NTT. The optical
spectrum of the source is almost featureless since the hydrogen and He I
emissions lines, typically observed in LMXBs, are not detected. Similarly,
carbon and oxygen lines are neither observed. We marginally detect the He II
4686 AA emission line, suggesting the presence of helium in the accretion disc.
No significant optical polarisation level was observed. The lack of hydrogen
and He I emission lines in the spectrum implies that the companion is likely
not a main sequence star. Driven by the tentative detection of the He II 4686
AA emission line, we suggest that the system could harbour a helium white
dwarf. If this is the case, 1RXS J180408.9-342058 would be an ultra-compact
X-ray binary. By combining an estimate of the mass accretion rate together with
evolutionary tracks for a He white dwarf, we obtain a tentative orbital period
of ~ 40 min. On the other hand, we also built the NIR-optical-UV spectral
energy distribution (SED) of the source at two different epochs. One SED was
gathered when the source was in the soft X-ray state, and it is consistent with
the presence of a single thermal component. The second SED, obtained when the
source was in the hard X-ray state, shows a thermal component together with a
tail in the NIR, likely indicating the presence of a (transient) jet.Comment: 8 pages, 5 figures, 4 tables. Accepted for publication in Astronomy &
Astrophysics (Section 7
Security Issues in a SOA-based Provenance System
Recent work has begun exploring the characterization and utilization of provenance in systems based on the Service Oriented Architecture (such as Web Services and Grid based environments). One of the salient issues related to provenance use within any given system is its security. Provenance presents some unique security requirements of its own, which are additionally dependent on the architectural and environmental context that a provenance system operates in. We discuss the security considerations pertaining to a Service Oriented Architecture based provenance system. Concurrently, we outline possible approaches to address them
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