5,408 research outputs found
Photoelectrocatalytic performances of nanostructured/decorated TiO 2 electrodes: Effect of wavelength and cell configuration
The behaviour of TiO2 based electrodes was investigated during the photoelectrocatalytic water splitting process. TiO2 nanotubes and compact oxide structures were obtained by electrochemical oxidation of Ti foils. A subsequent hydrothermal process carried out at both the nanotubular and compact oxide structures allowed decorating the structure by TiO2 nanoparticles. The synthesized TiO2 samples worked as photoanodes both in a bulk three electrode cell and in a thin gap cell. The results from measurements of the photocurrent and from electrochemical impedance spectroscopy were used to highlight a combined effect of the wavelength of the incident light and the kind of cell configuration, on the global performance of the systems. The results indicate that the decoration process does not result only in a simple increase of the specific surface, but it also determines a different concentration of the bulk and superficial sites in the electrode. The different response of the sites at different wavelengths, along with the accessibility of the electrolyte to the porous structure are evocated to justify the experimental behaviour observed
The Virtual Element Method with curved edges
In this paper we initiate the investigation of Virtual Elements with curved
faces. We consider the case of a fixed curved boundary in two dimensions, as it
happens in the approximation of problems posed on a curved domain or with a
curved interface. While an approximation of the domain with polygons leads, for
degree of accuracy , to a sub-optimal rate of convergence, we show
(both theoretically and numerically) that the proposed curved VEM lead to an
optimal rate of convergence
Multi-critical multi-field models: a CFT approach to the leading order
We present some general results for the multi-critical multi-field models in
d>2 recently obtained using CFT and Schwinger-Dyson methods at perturbative
level without assuming any symmetry. Results in the leading non trivial order
are derived consistently for several conformal data in full agreement with
functional perturbative RG methods. Mechanisms like emergent (possibly
approximate) symmetries can be naturally investigated in this framework.Comment: 12 pages, 1 figure, Contribution to the Conference QFT2018, Quantum
Fields From Fundamental Concepts to Phenomenological Questions, Mainz 26-28
September 201
The Denoised, Deconvolved, and Decomposed Fermi -ray sky - An application of the DPO algorithm
We analyze the 6.5yr all-sky data from the Fermi LAT restricted to gamma-ray
photons with energies between 0.6-307.2GeV. Raw count maps show a superposition
of diffuse and point-like emission structures and are subject to shot noise and
instrumental artifacts. Using the D3PO inference algorithm, we model the
observed photon counts as the sum of a diffuse and a point-like photon flux,
convolved with the instrumental beam and subject to Poissonian shot noise. D3PO
performs a Bayesian inference in this setting without the use of spatial or
spectral templates;i.e., it removes the shot noise, deconvolves the
instrumental response, and yields estimates for the two flux components
separately. The non-parametric reconstruction uncovers the morphology of the
diffuse photon flux up to several hundred GeV. We present an all-sky spectral
index map for the diffuse component. We show that the diffuse gamma-ray flux
can be described phenomenologically by only two distinct components: a soft
component, presumably dominated by hadronic processes, tracing the dense, cold
interstellar medium and a hard component, presumably dominated by leptonic
interactions, following the hot and dilute medium and outflows such as the
Fermi bubbles. A comparison of the soft component with the Galactic dust
emission indicates that the dust-to-soft-gamma ratio in the interstellar medium
decreases with latitude. The spectrally hard component exists in a thick
Galactic disk and tends to flow out of the Galaxy at some locations.
Furthermore, we find the angular power spectrum of the diffuse flux to roughly
follow a power law with an index of 2.47 on large scales, independent of
energy. Our first catalog of source candidates includes 3106 candidates of
which we associate 1381(1897) with known sources from the 2nd(3rd) Fermi
catalog. We observe gamma-ray emission in the direction of a few galaxy
clusters hosting radio halos.Comment: re-submission after referee report (A&A); 17 pages, many colorful
figures, 4 tables; bug fixed, flux scale now consistent with Fermi, even
lower residual level, pDF -> 1DF source catalog, tentative detection of a few
clusters of galaxies, online material
http://www.mpa-garching.mpg.de/ift/fermi
The Galaxy in circular polarization: all-sky radio prediction, detection strategy, and the charge of the leptonic cosmic rays
The diffuse Galactic synchrotron emission should exhibit a low level of
diffuse circular polarization (CP) due to the circular motions of the emitting
relativistic electrons. This probes the Galactic magnetic field in a similar
way as the product of total Galactic synchrotron intensity times Faraday depth.
We use this to construct an all sky prediction of the so far unexplored
Galactic CP from existing measurements. This map can be used to search for this
CP signal in low frequency radio data even prior to imaging. If detected as
predicted, it would confirm the expectation that relativistic electrons, and
not positrons, are responsible for the Galactic radio emission. Furthermore,
the strength of real to predicted circular polarization would provide
statistical information on magnetic structures along the line-of-sights.Comment: 11 pages, 5 figures, revise
Stochastic growth of quantum fluctuations during slow-roll inflation
We compute the growth of the mean square of quantum fluctuations of test
fields with small effective mass during a slowly changing, nearly de Sitter
stage which took place in different inflationary models. We consider a
minimally coupled scalar with a small mass, a modulus with an effective mass (with as the Hubble parameter) and a massless non-minimally
coupled scalar in the test field approximation and compare the growth of their
relative mean square with the one of gauge-invariant inflaton fluctuations. We
find that in most of the single field inflationary models the mean square gauge
invariant inflaton fluctuation grows {\em faster} than any test field with a
non-negative effective mass. Hybrid inflationary models can be an exception:
the mean square of a test field can dominate over the gauge invariant inflaton
fluctuation one on suitably choosing parameters. We also compute the stochastic
growth of quantum fluctuation of a second field, relaxing the assumption of its
zero homogeneous value, in a generic inflationary model; as a main result, we
obtain that the equation of motion of a gauge invariant variable associated,
order by order, with a generic quantum scalar fluctuation during inflation can
be obtained only if we use the number of e-folds as the time variable in the
corresponding Langevin and Fokker-Planck equations for the stochastic approach.
We employ this approach to derive some bounds in the case of a model with two
massive fields.Comment: 9 pages, 4 figures. Added references, minor changes, matches the
version to be published in Phys. Rev.
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