4,987 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
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
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
Generalized quantum field theory: perturbative computation and perspectives
We analyze some consequences of two possible interpretations of the action of
the ladder operators emerging from generalized Heisenberg algebras in the
framework of the second quantized formalism. Within the first interpretation we
construct a quantum field theory that creates at any space-time point particles
described by a q-deformed Heisenberg algebra and we compute the propagator and
a specific first order scattering process. Concerning the second one, we draw
attention to the possibility of constructing this theory where each state of a
generalized Heisenberg algebra is interpreted as a particle with different
mass.Comment: 19 page
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
The electric vehicle in smart homes: a review and future perspectives
The electric mobility dissemination is forcing the adoption of new technologies and operation paradigms, not only focusing on smart grids, but also on smart homes. In fact, the emerging technologies for smart homes are also altering the conventional grids toward smart grids. By combining the key pillars of electric mobility and smart homes, this paper characterizes the paradigms of the electric vehicle (EV) in smart homes, presenting a review about the state of the art and establishing a relation with future perspectives. Since the smart home must be prepared to deal with the necessities of the EV, the analysis of both on board and off board battery charging systems are considered in the paper. Moreover, the in-clusion of renewable energy sources, energy storage systems, and dc electrical appliances in smart homes towards sustainability is also considered in this paper, but framed in the perspective of an EV off board battery charging system. As a pertinent contribution, this paper offers future perspectives for the EV in smart homes, including the possibility of ac, dc, and hybrid smart homes. Covering all of these aspects, exemplificative and key results are presented based on numerical simulations and experimental results obtained with a proof of concept prototype.FCT – Fundação para a Ciência e Tecnologia within the Project Scope: UID/CEC/00319/2019. This work has been supported by the FCT Project newERA4GRIDs PTDC/EEI-EEE/30283/2017, and by the FCT Project DAIPESEV PTDC/EEI-EEE/30382/2017. Tiago Sousa is supported by the doctoral scholarship SFRH/BD/134353/2017 granted by FC
Sacrococcygeal teratoma with malignant transformation in an adult female: CT and MRI findings
This report describes a case of sacrococcygeal teratoma with adenocarcinomatous
transformation in a 45-year-old woman. This is an infrequent location for teratoma in adults and
malignant transformation has rarely been described. Prognosis depends on complete excision.
Clinical manifestations, imaging aspects and histological findings of this case are presented. CT
and MRI adequately document the mixed cystic and solid nature of the tumour, its extension and
relations with adjacent structures, allowing accurate pre-operative planning
- …