5,706 research outputs found
Synthesis and properties of Co-doped titanate nanotubes and their optical sensitization with methylene blue
Here we report on a novel chemical route to synthesize homogenous cobalt
doped titanate nanotubes (CoTNT), using an amorphous Co-doped precursor. The
influence of the synthesis temperature, autoclave dwell time and metal doping
on the structural and microstructural as well as on the optical properties of
the synthesized titanate nanotubes is studied and discussed. The optical band
gaps of the CoTNT samples are red shifted in comparison with the values
determined for the undoped samples, such red shifts bringing the absorption
edge of the CoTNT samples into the visible region. CoTNT materials also
demonstrate particular high adsorption ability for methylene blue, the amount
of the adsorbed dye being higher than the one predictable for a monolayer
formation. This suggests the possibility of intercalation of the dye molecule
between the TiO6 layers of the TNT structure. It is also shown that the
methylene blue sensitized Co-doped nanostructures are highly stable under UV
radiation and present a strong and broad absorption in the visible region.Comment: 31 pages, 3 tables, 7 figure
Free monadic Tarski and MMI3-algebras
MMI3-algebras are a generalization of the monadic Tarski algebras as defined by A. Monteiro and L. Iturrioz, and a particular case of the MMIn+1-algebras defined by A. Figallo. They can also be seen as monadic three-valued £ukasiewicz algebras without a first element. By using this point of view, and the free monadic extensions, we construct the free MMI3-algebras on a finite number of generators, and indicate the coordinates of the generators. As a byproduct, we also obtain a construction of the free monadic Tarski algebras.Fil: Entizne, Rosana V.. Universidad Nacional del Sur. Departamento de Matemática; ArgentinaFil: Monteiro, Luiz F.. Universidad Nacional del Sur. Departamento de Matemática; ArgentinaFil: Savini, Sonia M.. Universidad Nacional del Sur. Departamento de Matemática; ArgentinaFil: Viglizzo, Ignacio Dario. Universidad Nacional del Sur. Departamento de Matemática; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentin
Ages of White Dwarf-Red Subdwarf Systems
We provide the first age estimates for two recently discovered white
dwarf-red subdwarf systems, LHS 193AB and LHS 300AB. These unusual systems
provide a new opportunity for linking the reliable age estimates for the white
dwarfs to the (measurable) metallicities of the red subdwarfs. We have obtained
precise photometry in the bands and spectroscopy covering
from 6000\AA to 9000\AA for the two new systems, as well as for a comparison
white dwarf-main sequence red dwarf system, GJ 283 AB. Using model grids
available in the literature, we estimate the cooling age as well as
temperature, surface gravity, mass, progenitor mass and {\it total} lifetimes
of the white dwarfs. The results indicate that the two new systems are probably
ancient thick disk objects with ages of at least 6-9 Gyr. We also conduct
searches of red dwarf and white dwarf compendia from SDSS data and the
L{\'e}pine Shara Proper Motion (LSPM) catalog for additional common proper
motion white dwarf-red subdwarf systems. Only seven new candidate systems are
found, which indicates the rarity of these systems.Comment: accepted for publication in Ap
Some boundary effects in quantum field theory
We have constructed a quantum field theory in a finite box, with periodic
boundary conditions, using the hypothesis that particles living in a finite box
are created and/or annihilated by the creation and/or annihilation operators,
respectively, of a quantum harmonic oscillator on a circle. An expression for
the effective coupling constant is obtained showing explicitly its dependence
on the dimension of the box.Comment: 12 pages, Late
Band inversion driven by electronic correlations at the (111) LaAlO/SrTiO interface
Quantum confinement at complex oxide interfaces establishes an intricate
hierarchy of the strongly correlated -orbitals which is widely recognized as
a source of emergent physics. The most prominent example is the (001)
LaAlO/SrTiO(LAO/STO) interface, which features a dome-shaped phase
diagram of superconducting critical temperature and spin-orbit coupling (SOC)
as a function of electrostatic doping, arising from a selective occupancy of
orbitals of different character. Here we study (111)-oriented LAO/STO
interfaces - where the three orbitals contribute equally to the
sub-band states caused by confinement - and investigate the impact of this
unique feature on electronic transport. We show that transport occurs through
two sets of electron-like sub-bands, and the carrier density of one of the sets
shows a non-monotonic dependence on the sample conductance. Using tight-binding
modeling, we demonstrate that this behavior stems from a band inversion driven
by on-site Coulomb interactions. The balanced contribution of all
orbitals to electronic transport is shown to result in strong SOC with reduced
electrostatic modulation.Comment: 5 pages, 4 figures, (+ supplemental material
Produção de raízes finas em cultivos de palma de óleo (Elaeis guineensis) no Nordeste paraense.
O objetivo do trabalho foi avaliar a variabilidade espacial da produção de raízes finas (diâmetro ? 2 mm) em um cultivo convencional de palma de óleo (Elaeis guineensis). O estudo foi realizado no município de Tomé-Açu (PA), em área de agricultor familiar. As amostras foram coletadas entre 0 e 10 cm de profundidade por um cilindro telado (?ingrowth core?) de malha de abertura igual a 2 mm e diâmetro igual a 5 cm. Os locais de coleta avaliados foram: (a) entre plantas, (b) empilhamento e (c) carreador, e em diferentes distâncias a partir do estipe: 0,6; 1,2; 2; e 4 m. Os dados obtidos foram analisados e interpretados em relação à variação pluviométrica média regional. A produção mensal de raízes finas não diferiu nas diferentes distâncias da base da planta, exceto na camada foliar, em que a distância de 0,6 m apresentou uma maior produção de raízes com (média ± erro padrão = 54,20 ± 7,95 g m-2 ano-1, n = 5). A variação intranual da produção de raízes finas foi influenciada pela sazonalidade da precipitaçã
Improved voltage control of the electric vehicle operating as UPS in smart homes
As a contribution for sustainability, electric vehicles (EVs) are seen
as one of the most effective influences in the transport sector. As complement
to the challenges that entails the EVs integration into the grid considering the
bidirectional operation (grid-to-vehicle and vehicle-to-grid), there are new concepts
associated with the EV operation integrating various benefits for smart
homes. In this sense, this paper proposes an improved voltage control of the EV
operating as uninterruptible power supply (UPS) in smart homes. With the EV
plugged-in into the smart home, it can act as an off-line UPS protecting the
electrical appliances from power grid outages. Throughout the paper, the foremost
advantages of the proposed voltage control strategy are comprehensively
emphasized, establishing a comparison with the classical approach. Aiming to
offer a sinusoidal voltage for linear and nonlinear electrical appliances, a
pulse-width modulation with a multi-loop control scheme is used. A Kalman
filter is used for decreasing significantly the time of detecting power outages
and, consequently, the transition for the UPS mode. The experimental validation
was executed with a bidirectional charger containing a double stage power
conversion (an ac-dc interfacing the grid-side and a dc-dc interfacing the batteries-
side) and a digital stage. The computer simulations and the acquired experimental
results validate the proposed strategy in different conditions of operation.This work has been supported by COMPETE: POCI-01-0145-FEDER-007043 and FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2013. This work is financed by the ERDF – European Regional Development Fund through the Operational Programme for Competitiveness and Internationalisation – COMPETE 2020 Programme, and by National Funds through the Portuguese funding agency, FCT – Fundação para a Ciência e a Tecnologia, within project SAICTPAC/0004/2015 – POCI – 01–0145–FEDER–016434. This work is part of the FCT project 0302836 NORTE-01-0145-FEDER-030283.info:eu-repo/semantics/publishedVersio
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