2,077 research outputs found
Assessment of the SBAC atmospheric correction technique applied to Landsat 8-TIRS from ground LST measurements in the Barrax test site
La peculiar estructura y propiedades físico-químicas del silicio poroso nanoestructurado ha estimulado el uso
de este material en una amplia variedad de aplicaciones. En el campo de la optoelectrónica, la posibilidad de producir
estructuras multicapa en las que cada una de las capas tiene propiedades ópticas particulares, permite la fabricación de
filtros ópticos interferenciales con un comportamiento predefinido. En este trabajo se han utilizado estructuras multicapa
de silicio poroso para filtrar la luz incidente sobre un sustrato fotosensible de silicio con la intención de modular su respuesta
espectral. El comportamiento óptico del filtro de silicio poroso fue simulado antes de su fabricación, y las medidas
ópticas demostraron un buen acuerdo entre el comportamiento del filtro obtenido y las predicciones teóricas. Mediciones
de fotocorriente han demostrado que los filtros de silicio poroso han reducido el rango espectral de fotosensibilidad del
silicio, de los >750 nm originales a unos 150 nm. Filtros con distintos diseños han permitido no sólo estrechar la banda
espectral de sensibilidad del detector pancromático de Si, sino también sintonizarla a lo lago de todo el rango visible. El
silicio poroso nanoestructurado es compatible con las técnicas convencionales de fabricación microelectrónica, lo que
hace posible incorporar estos filtros interferenciales sobre una amplia variedad de sensores y fotodiodos pancromáticos
VIS, NIR o SWIR convencionales. Los resultados presentados en este trabajo demuestran que los filtros interferenciales
de silicio poroso reestructurado resultan muy prometedores para el desarrollo de sensores multi- e hiperespectrales de
bajo costeThe particular structure and physico-chemical properties of nanostructured porous silicon has stimulated the
use of this material in many different applications. In the field of optoelectronics, the possibility of fabricating multilayer
stacks where each individual layer has different optical properties allows the formation of optical interference filters with
a predesigned behavior. In the present work, nanostructured porous silicon interference multilayer structures have been
used to filter incident light reaching a Si photosensitive wafer in order to tailor its spectral response. The optical behavior
of the porous silicon filters was simulated prior to their fabrication, and optical measurements showed good agreement
between the simulated and experimental spectra. Photocurrent measurements have shown that the porous silicon filters
narrowed the spectral responsitivity of silicon, from the original value of >750 nm down to around 150 nm. Different
filter designs allowed to not only narrowen, but also tune the Si panchromatic sensitivity along the whole visible range.
Porous silicon is compatible with standard microelectronic fabrication processes, making it possible to incorporate these
interference filters onto a wide variety of conventional panchromatic VIS, NIR or SWIR broad band sensors. These
results show that nanostructured silicon interference filters are a promising tool for developing cost-effective multi- and
hyperspectral narrowband sensor
A new approach to dealing with missing values in data-driven fuzzy modeling
Real word data sets often contain many missing elements. Most algorithms that automatically develop a rule-based model are not well suited to deal with incomplete data. The usual technique is to disregard the missing values or substitute them by a best guess estimate, which can bias the results. In this paper we propose a new method for estimating the parameters of a Takagi-Sugeno fuzzy model in the presence of incomplete data. We also propose an inference mechanism that can deal with the incomplete data. The presented method has the added advantage that it does not require imputation or iterative guess-estimate of the missing values. This methodology is applied to fuzzy modeling of a classification and regression problem. The performance of the obtained models are comparable with the results obtained when using a complete data set
Large scale numerical investigation of excited states in poly(phenylene)
A density matrix renormalisation group scheme is developed, allowing for the
first time essentially exact numerical solutions for the important excited
states of a realistic semi-empirical model for oligo-phenylenes. By monitoring
the evolution of the energies with chain length and comparing them to the
experimental absorption peaks of oligomers and thin films, we assign the four
characteristic absorption peaks of phenyl-based polymers. We also determine the
position and nature of the nonlinear optical states in this model.Comment: RevTeX, 10 pages, 4 eps figures included using eps
Estimation of flexible fuzzy GARCH models for conditional density estimation
In this work we introduce a new flexible fuzzy GARCH model for conditional density estimation. The model combines two different types of uncertainty, namely fuzziness or linguistic vagueness, and probabilistic uncertainty. The probabilistic uncertainty is modeled through a GARCH model while the fuzziness or linguistic vagueness is present in the antecedent and combination of the rule base system. The fuzzy GARCH model under study allows for a linguistic interpretation of the gradual changes in the output density, providing a simple understanding of the process. Such a system can capture different properties of data, such as fat tails, skewness and multimodality in one single model. This type of models can be useful in many fields such as macroeconomic analysis, quantitative finance and risk management. The relation to existing similar models is discussed, while the properties, interpretation and estimation of the proposed model are provided. The model performance is illustrated in simulated time series data exhibiting complex behavior and a real data application of volatility forecasting for the S&P 500 daily returns series
The critical Ising model via Kac-Ward matrices
The Kac-Ward formula allows to compute the Ising partition function on any
finite graph G from the determinant of 2^{2g} matrices, where g is the genus of
a surface in which G embeds. We show that in the case of isoradially embedded
graphs with critical weights, these determinants have quite remarkable
properties. First of all, they satisfy some generalized Kramers-Wannier
duality: there is an explicit equality relating the determinants associated to
a graph and to its dual graph. Also, they are proportional to the determinants
of the discrete critical Laplacians on the graph G, exactly when the genus g is
zero or one. Finally, they share several formal properties with the Ray-Singer
\bar\partial-torsions of the Riemann surface in which G embeds.Comment: 30 pages, 10 figures; added section 4.4 in version
Sustainability metrics for coal power generation in Australia
The basis of this work was to investigate the relative environmental impacts of various power generators knowing that all plants are located in totally different environments and that different receptors will experience different impacts. Based on IChemE sustainability metrics paradigm, we calculated potential environmental indicators (P-EI) that represent the environmental burden of masses of potential pollutants discharged into different receiving media. However, a P-EI may not be of significance, as it may not be expressed at all in different conditions, so to try and include some receiver significance we developed a methodology to take into account some specific environmental indicators (S-EI) that refer to the environmental attributes of a specific site. In this context, we acquired site specific environmental data related to the airsheds and water catchment areas in different locations for a limited number of environmental indicators such as human health (carcinogenic) effects, atmospheric acidification, photochemical (ozone) smog and eutrophication. The S-EI results from this particular analysis show that atmospheric acidification has highest impact value while health risks due to fly ash emissions are considered not to be as significant. This is due to the fact that many coal power plants in Australia are located in low population density air sheds. The contribution of coal power plants to photochemical (ozone) smog and eutrophication were not significant. In this study, we have considered emission related data trends to reflect technology performance (e.g., P-EI indicators) while a real sustainability metric can be associated only with the specific environmental conditions of the relevant sites (e.g., S-EI indicators)
A mathematical analysis of the evolution of perturbations in a modified Chaplygin gas model
One approach in modern cosmology consists in supposing that dark matter and
dark energy are different manifestations of a single `quartessential' fluid.
Following such idea, this work presents a study of the evolution of
perturbations of density in a flat cosmological model with a modified Chaplygin
gas acting as a single component. Our goal is to obtain properties of the model
which can be used to distinguish it from another cosmological models which have
the same solutions for the general evolution of the scale factor of the
universe, without the construction of the power spectrum. Our analytical
results, which alone can be used to uniquely characterize the specific model
studied in our work, show that the evolution of the density contrast can be
seen, at least in one particular case, as composed by a spheroidal wave
function. We also present a numerical analysis which clearly indicates as one
interesting feature of the model the appearence of peaks in the evolution of
the density constrast.Comment: 21 pages, accepted for publication in General Relativity and
Gravitatio
Schottky barrier heights at polar metal/semiconductor interfaces
Using a first-principle pseudopotential approach, we have investigated the
Schottky barrier heights of abrupt Al/Ge, Al/GaAs, Al/AlAs, and Al/ZnSe (100)
junctions, and their dependence on the semiconductor chemical composition and
surface termination. A model based on linear-response theory is developed,
which provides a simple, yet accurate description of the barrier-height
variations with the chemical composition of the semiconductor. The larger
barrier values found for the anion- than for the cation-terminated surfaces are
explained in terms of the screened charge of the polar semiconductor surface
and its image charge at the metal surface. Atomic scale computations show how
the classical image charge concept, valid for charges placed at large distances
from the metal, extends to distances shorter than the decay length of the
metal-induced-gap states.Comment: REVTeX 4, 11 pages, 6 EPS figure
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