14,402 research outputs found
Topological vortices in generalized Born-Infeld-Higgs electrodynamics
A consistent BPS formalism to study the existence of topological axially
symmetric vortices in generalized versions of the Born-Infeld-Higgs
electrodynamics is implemented. Such a generalization modifies the field
dynamics via introduction of three non-negative functions depending only in the
Higgs field, namely, , and . A set of
first-order differential equations is attained when these functions satisfy a
constraint related to the Ampere law. Such a constraint allows to minimize the
system energy in such way that it becomes proportional to the magnetic flux.
Our results provides an enhancement of topological vortex solutions in
Born-Infeld-Higgs electrodynamics. Finally, we analyze a set of models such
that a generalized version of Maxwell-Higgs electrodynamics is recovered in a
certain limit of the theory.Comment: 8 pages, 8 figures, to appear in EPJ
Deformation method for generalized Abelian Higgs-Chern-Simons models
We present an extension of the deformation method applied to self-dual
solutions of generalized Abelian Higgs-Chern-Simons models. Starting from a
model defined by a potential and a non-canonical kinetic term
whose analytical domain wall solutions are
known, we show that this method allows to obtain an uncountable number of new
analytical solutions of new models defined by other functions
and . We present some examples of deformation functions
leading to new families of models and their associated analytic solutions.Comment: 6 pages, 10 figure
Minimização da toxidez do resÃduo gerado na determinação de nitrogênio total (método Kjeldahl) pela eliminação do selênio.
Nanocrystalline cathodes for PC-SOFCs based on BCZY
Perovskites based on BaCeO3-δ exhibit the highest proton conductivity among this class of materials, however, they are susceptible to hydration and carbonation in presence of water vapor and CO2 [1]. In contrast, the chemical stability of BaZrO3-based protonic conductors is better, but they require sintering temperatures as high as 1700 ºC and suffer from high intrinsic grain boundary resistance, limiting the final performance. Partial substitution of Zr for Ce in Ba(Ce0.9-xZrx)Y0.2O3-δ allows obtaining electrolytes with both high proton conductivity and good chemical stability.
The performance of a PC-SOFC at low temperatures depends significantly on the ohmic resistance of the electrolyte, although it can be lowered by reducing the electrolyte thickness. Another important limiting factor is the increase of the cathode polarization resistance due to the thermally activated nature of the oxygen reduction reaction. For this reason, it is essential to obtain high efficiency cathodes operating at reduced temperatures.
In this work, BaCe0.6Zr0.2Y0.2O3-δ (BCZY) powders were prepared by freeze-drying precursor method. These powders were mixed with a Zn-containing solution as sintering additive in order to obtain dense pellets with submicrometric grain size at only 1200 ºC. After that, La0.6Sr0.4Co0.8Fe0.2O3 nanocrystalline electrodes were deposited symmetrically onto dense pellets BCZY by conventional spray-pyrolysis [3]. The structure, microstructure and electrochemical properties of these electrodes have been examined by XRD, FE-SEM and impedance spectroscopy. The stability of these electrodes at intermediate temperatures was evaluated as a function of time.
These nanocrystalline cathodes exhibit a substantial improvement of the electrode polarization resistance with respect to the same materials prepared by screen-printing method at high sintering temperatures, e.g. 0.7 and 3.2 cm2 at 600 ºC for LSCF cathodes prepared by spray-pyrolysis and screen-printing method respectively (Figure). An anode supported cell with composition LSCF/BCZY/NiO-BCZY was also prepared to test the electrochemical performance.Universidad de Málaga. Campus de Excelencia Internacional AndalucÃa Tech
Signatures of magnetic activity in the seismic data of solar-type stars observed by Kepler
In the Sun, the frequencies of the acoustic modes are observed to vary in
phase with the magnetic activity level. These frequency variations are expected
to be common in solar-type stars and contain information about the
activity-related changes that take place in their interiors. The unprecedented
duration of Kepler photometric time-series provides a unique opportunity to
detect and characterize stellar magnetic cycles through asteroseismology. In
this work, we analyze a sample of 87 solar-type stars, measuring their temporal
frequency shifts over segments of length 90 days. For each segment, the
individual frequencies are obtained through a Bayesian peak-bagging tool. The
mean frequency shifts are then computed and compared with: 1) those obtained
from a cross-correlation method; 2) the variation in the mode heights; 3) a
photometric activity proxy; and 4) the characteristic timescale of the
granulation. For each star and 90-d sub-series, we provide mean frequency
shifts, mode heights, and characteristic timescales of the granulation.
Interestingly, more than 60% of the stars show evidence for (quasi-)periodic
variations in the frequency shifts. In the majority of the cases, these
variations are accompanied by variations in other activity proxies. About 20%
of the stars show mode frequencies and heights varying approximately in phase,
in opposition to what is observed for the Sun.Comment: Accepted for publication in ApJS, 19(+86) pages, 11(+89) figures,
2(+87) table
Seismic signatures of magnetic activity in solar-type stars observed by Kepler
The properties of the acoustic modes are sensitive to magnetic activity. The
unprecedented long-term Kepler photometry, thus, allows stellar magnetic cycles
to be studied through asteroseismology. We search for signatures of magnetic
cycles in the seismic data of Kepler solar-type stars. We find evidence for
periodic variations in the acoustic properties of about half of the 87 analysed
stars. In these proceedings, we highlight the results obtained for two such
stars, namely KIC 8006161 and KIC 5184732.Comment: 4 pages, 1 figure, to appear in the Proceedings of the IAUS34
CaracterÃsticas das cultivares de arroz recomendadas para Rondônia.
A EMBRAPA/Centro de Pesquisa Agroflorestal de Rondônia (CPAF-Rondônia) vem conduzindo, anualmente, em colaboração com a EMBRAPA Centro Nacional de Pesquisa de Arroz e Feijão (CNPAF), um Programa de Melhoramento Genético do Arroz, onde procura avaliar e selecionar genótipos agronomicamente superiores, com o objetivo de recomendar aos produtores rondonienses, novas cultivares que apresentam alto potencial produtivo, além de resistência a doenças e ao acamamento, e boa qualidade de grãos.bitstream/item/112982/1/CPAFRO-Documentos-29.pd
SPACE SIMULATION OF THE CHINA-BRAZIL EARTH RESOURCES SATELLITE CBERS
Space Simulation Tests are performed in spacecraft in order to verify equipment proper
operation under thermal vacuum conditioning and to verify the correct workmanship in
the assembling of the flight spacecraft as a whole. This paper presents the space simulation
(thermal vacuum test) developed in the China Brazil Earth Resources Satellite, Flight
Model no. 2, that took place at the Integration and Tests Laboratory LIT, INPE. Measuring
approximately 1.8 x 2.0 x 2.2m, weighting 1,500 kg and carrying three cameras as the
main payload, this spacecraft is scheduled to be launched in China. The spacecraft was
installed in the 3x3m space simulation chamber and the tests run 24 hours a day completing
a total of 350 hours. Using the technique of skin-heaters complemented by the thermal
vacuum chamber thermally conditioned shrouds and cold plates, dedicated heat inputs
and heat sink where applied at the spacecraft surfaces in order to obtain the required high
and low acceptance values of temperature and, subsequently, simulating the operational
conditions for the necessary electronic subsystems functioning tests of the spacecraft.
This test campaign included teams from both China and Brazil, summing a total of 67
people directly involved
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