2,168 research outputs found
Dimensional effects on the tunneling conductivity of gold-implanted nanocomposite films
We study the dependence of the electrical conductivity on the gold
concentration of Au-implanted polymethylmethacrylate (PMMA) and alumina
nanocomposite thin films. For Au contents larger than a critical concentration,
the conductivity of Au-PMMA and Au-alumina is well described by percolation in
two dimensions, indicating that the critical correlation length for percolation
is larger than the thickness of the films. Below the critical loading, the
conductivity is dominated by tunneling processes between isolated Au particles
dispersed in PMMA or alumina continuous matrices. Using an effective medium
analysis of the tunneling conductivity, we show that Au-PMMA behaves as a
tunneling system in two dimensions, as the film thickness is comparable to the
mean Au particle size. On the contrary, the conductivity of Au-alumina films is
best described by tunneling in three dimensions, although the film thickness is
only a few times larger than the particle size. We interpret the enhancement of
the effective dimensionality of Au-alumina films in the tunneling regime as due
to the larger film thickness as compared to the mean interparticle distances.Comment: 7 pages, 7 figure
Estimating strategies for Multiparameter Multivariate Extreme value copulas
Abstract. Multivariate Extreme Value models are a fundamental tool in order to assess potentially dangerous events. Exploiting recent theoretical developments in the theory of Copulas, new multiparameter models can be easily constructed. In this paper we suggest several strategies in order to estimate the parameters of the selected copula, according to different criteria: these may use a single station approach, or a cluster strategy, or exploit all the pair-wise relationships between the available gauge stations. An application to flood data is also illustrated and discussed
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Textural and minerochemical features of NWA 1807 and 2180, two new CV3 chondrites from northwest Africa
A textural and minerochemical study has been performed on NWA 1807 and 2180 chondrites in order to determine sizes and typologies of chondrules, relative abundances of mineral phases, compositions of main phases and bulk oxygen isotope composition
On the return period and design in a multivariate framework
Abstract. Calculating return periods and design quantiles in a multivariate environment is a difficult problem: this paper tries to make the issue clear. First, we outline a possible way to introduce a consistent theoretical framework for the calculation of the return period in a multi-dimensional environment, based on Copulas and the Kendall's measure. Secondly, we introduce several approaches for the identification of suitable design events: these latter quantities are of utmost importance in practical applications, but their calculation is yet limited, due to the lack of an adequate theoretical environment where to embed the problem. Throughout the paper, a case study involving the behavior of a dam is used to illustrate the new concepts outlined in this work
Deep into the structure of the first galaxies: SERRA views
We study the formation and evolution of a sample of Lyman Break Galaxies in
the Epoch of Reionization by using high-resolution (),
cosmological zoom-in simulations part of the SERRA suite. In SERRA, we follow
the interstellar medium (ISM) thermo-chemical non-equilibrium evolution, and
perform on-the-fly radiative transfer of the interstellar radiation field
(ISRF). The simulation outputs are post-processed to compute the emission of
far infrared lines ([CII], [NII], and [OIII]). At , the most massive
galaxy, `Freesia', has an age , stellar mass
, and a star formation rate
, due to a recent burst.
Freesia has two stellar components (A and B) separated by ; other 11 galaxies are found within . The
mean ISRF in the Habing band is and is spatially uniform; in
contrast, the ionisation parameter is , and
has a patchy distribution peaked at the location of star-forming sites. The
resulting ionising escape fraction from Freesia is .
While [CII] emission is extended (radius 1.54 kpc), [OIII] is concentrated in
Freesia-A (0.85 kpc), where the ratio . As many high- galaxies, Freesia lies below the local [CII]-SFR
relation. We show that this is the general consequence of a starburst phase
(pushing the galaxy above the Kennicutt-Schmidt relation) which
disrupts/photodissociates the emitting molecular clouds around star-forming
sites. Metallicity has a sub-dominant impact on the amplitude of [CII]-SFR
deviations.Comment: 22 pages, 14 figures, accepted by MNRA
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