4,850 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
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
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
An instability of higher-dimensional rotating black holes
We present the first example of a linearized gravitational instability of an
asymptotically flat vacuum black hole. We study perturbations of a Myers-Perry
black hole with equal angular momenta in an odd number of dimensions. We find
no evidence of any instability in five or seven dimensions, but in nine
dimensions, for sufficiently rapid rotation, we find perturbations that grow
exponentially in time. The onset of instability is associated with the
appearance of time-independent perturbations which generically break all but
one of the rotational symmetries. This is interpreted as evidence for the
existence of a new 70-parameter family of black hole solutions with only a
single rotational symmetry. We also present results for the Gregory-Laflamme
instability of rotating black strings, demonstrating that rotation makes black
strings more unstable.Comment: 38 pages, 13 figure
Ultraspinning instability of anti-de Sitter black holes
Myers-Perry black holes with a single spin in d>5 have been shown to be
unstable if rotating sufficiently rapidly. We extend the numerical analysis
which allowed for that result to the asymptotically AdS case. We determine
numerically the stationary perturbations that mark the onset of the
instabilities for the modes that preserve the rotational symmetries of the
background. The parameter space of solutions is thoroughly analysed, and the
onset of the instabilities is obtained as a function of the cosmological
constant. Each of these perturbations has been conjectured to represent a
bifurcation point to a new phase of stationary AdS black holes, and this is
consistent with our results.Comment: 22 pages, 7 figures. v2: Reference added. Matches published versio
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