Extremes of deterministic sub‐sampled moving averages with heavy‐tailed innovations

Let {X_k}_k?1 be a strictly stationary time series. For a strictly increasing sampling function g:?→? define Y_k=X_g(k) as the deterministic sub‐sampled time series. In this paper, the extreme value theory of {Y_k} is studied when X_k has representation as a moving average driven by heavy‐tailed innovations. Under mild conditions, convergence results for a sequence of point processes based on {Y_k} are proved and extremal properties of the deterministic sub‐sampled time series are derived. In particular, we obtain the limiting distribution of the maximum and the corresponding extremal index. Copyright © 2003 John Wiley & Sons, Ltd.     

Characterization of porosity in a 19th century painting ground by synchrotron radiation X-ray tomography

The study of the early oeuvre of the Swiss painter Cuno Amiet (1868–1961) has revealed that, up to 1907, many of his grounds were hand applied and are mainly composed of chalk, bound in protein. These grounds are not only lean and absorbent, but also, as Synchrotron radiation X-ray microtomography has shown, porous. Our approach to the characterization of pore structure and quantity, their connectivity, and homogeneity is based on image segmentation and application of a clustering algorithm to high-resolution X-ray tomographic data. The issues associated with the segmentation of the different components of a ground sample based on X-ray imaging data are discussed. The approach applied to a sample taken from “Portrait of Max Leu” (1899) by Amiet revealed the presence of three sublayers within the ground with distinct porosity features, which had not been observed optically in cross-section. The upper and lower layers are highly porous with important connectivity and thus prone to water uptake/storage. The middle layer however shows low and nonconnected porosity at the resolution level of the X-ray tomography images, so that few direct water absorption paths through the entire sample exist. The potential of the method to characterize porosity and to understand moisture-related issues in paint layer degradation are discussed.     

Critical Evaluation of Analytical Procedures for the Determination of Lead in Seawater

Abstract: This article presents a critical evaluation of the analytical procedures used for the determination of lead in seawater, which is important because lead is a good indicator of marine pollution caused by human activities. Sampling, storage, and pretreatment techniques are briefly overviewed, including the significance of systematic errors that cannot be corrected later on. The main techniques in this article are electrothermal–atomic absorption spectrometry (ET-AAS), inductively coupled plasma–mass spectrometry (ICP-MS), and voltammetry. Flame atomic absorption spectrometry (FAAS) and inductively coupled plasma–optical emission spectrometry (ICP-OES) are treated as well, although their limits of quantification are not sufficient for a determination of lead in unpolluted seawater. Even when separation and preconcentration techniques are applied, these techniques are only capable of detecting lead in polluted coastal seawater. Separation and preconcentration are actually also required for ET-AAS and ICP-MS in order to determine the lowest concentrations of lead found in unpolluted open-ocean seawater, which is still a challenge for the analytical chemist.     

Non-compact symmetric spaces and the Toda molecule equations

It has been shown by Olshanetsky and Perelomov that the Toda molecule equations associated with any Lie groupG describe special geodesic motions on the Riemannian non-compact symmetric space which is the quotient of the normal real form ofG, G ^N, by its maximal compact subgroup. This is explained in more detail and it is shown that the fundamental Poisson bracket relation involving the Lax operatorA and leading to the Yang-Baxter equation and integrability properties is a direct consequence of the fact that the Iwasawa decomposition forG ^N endows the symmetric space with a hidden group theoretic structure.Supported by CNP _q (Brasil)     

Cathodic and anodic pre-treated boron doped diamond with different sp content: Morphological,structural, and impedance spectroscopy characterizations

In this work, the influence of cathodic (Red) and anodic (Ox) pre-treatment on boron doped diamond (BDD) films grown with different sp²/sp³ ratios was systematically studied. The sp²/sp³ ratios were controlled by the addition of CH₄ of 1,3,5 and 7 sccm in the gas inlet during the growth process. The electrodes were treated in 0.5 mol L⁻¹ H₂SO₄ at −3 and 3 V vs Ag/AgCl, respectively, for 30 min. The electrochemical response of BDD films was investigated using electrochemical impedance spectroscopy (EIS) and Mott–Schottky Plot (MSP) measurements. Four film sample sets were produced in a hot filament chemical vapor deposition reactor. During the growth process, an additional H₂ line passing through a bubbler containing the B₂O₃ dissolved in methanol was used to carry the boron. The scanning electron microscopy morphology showed well faced films with a small decrease in their grain size as the CH₄ concentration increased. The Raman spectra depicted a pronounced sp² band, mainly for films with 5 and 7 sccm of CH₄. MSP showed a decrease in the acceptor concentration as the CH₄ increased indicating the CH₄ influence on the doping process for Red–BDD and Ox–BDD samples. Nonetheless, an apparent increase in the acceptor concentrations for both Ox–BDD samples was observed compared to that for Red–BDD samples, mainly attributed to the surface conductive layer (SCL) formation after this strong oxidation process. The EIS Nyquist plots for Red–BDD showed a capacitance increase for the films with higher sp² content (5 and 7 sccm). On the other hand, the Nyquist plots for Ox–BDD can be described as semicircles near the origin, at high frequencies, where their charge transfer resistance strongly varied with the sp² increase in such films.     

Optical properties of in situ doped and undoped titania nanocatalysts and doped titania sol-gel nanofilms

In this paper we present spectroscopic properties of doped and undoped titanium dioxide (TiO₂) as nanofilms prepared by the sol-gel process with rhodamine 6G doping and studied by photoacoustic absorption, excitation and emission spectroscopy. The absorption spectra of TiO₂ thin films doped with rhodamine 6G at very low concentration during their preparation show two absorption bands, one at 2.3 eV attributed to molecular dimmer formation, which is responsible for the fluorescence quenching of the sample and the other at 3.0 eV attributed to TiO₂ absorption, which subsequently yields a strong emission band at 600 nm. The electronic band structure and optical properties of the rutile phase of TiO₂ are calculated employing a fully relativistic, full-potential, linearized, augmented plane-wave (FPLAPW) method within the local density approximation (LDA). Comparison of this calculation with experimental data for TiO₂ films prepared for undoped sol-gels and by sputtering is performed.     

Interface-related effects on confined excitons in GaAs/AlxGa1−xAs single quantum wells

Confined excitons in non-abrupt GaAs/Al_xGa_1−xAs single quantum wells are studied. The graded interfaces are described taking into account fluctuations in their thickness a and positioning with respect to the abrupt interface picture. Numerical results for confined (0,0),(1,1) and (0,2) excitons in GaAs/Al_0.3Ga_0.7As quantum wells show that while the interfacial fluctuations produce small changes (<0.5 meV) in the exciton binding energies, the confined exciton energies can be red- or blue-shifted as much as 25 meV for wells with mean width of 50 Å and 2 ML wide interfaces.     

Pressure and temperature characterization of two interferometric configurations based on suspended-core fibers

In this work, two all-fiber interferometric configurations based on suspended core fibers (SCF) are investigated. A Fabry–Pérot cavity (FPC) made of SCF spliced in-between segments of single-mode and hollow-core fiber is proposed. The interferometric signals are generated by the refractive-index mismatches between the two fibers in the splice region and at the end of the suspended-core fiber. An alternative sensing head configuration formed by the insertion of a length of SCF as a birefringence element in a Sagnac loop interferometer is also demonstrated. In this structure, the interferometric signals are generated by interfering two counter propagating beams with different polarization states which propagate through a length of SCF as a birefringence element. The sensitivity to pressure and temperature was determined for both configurations. The results show that the pressure sensitivities are ? 4.68 × 10^? 5 nm/psi and 0.032 nm/psi for FPC and Sagnac loop interferometers, respectively. The temperature sensitivity of both structures has been obtained and the results have been discussed.     

Photophysical properties of a series of 4‐aryl substituted 1,4‐dihydropyridines

In this article, a series of Hantzsch 1,4‐dihydropyridines with different substituted aryl groups were synthesized and its spectral data obtained by UV–Vis absorption and fluorescence emission spectroscopies in solution. The dihydropyridines present absorption located around 350 nm and fluorescence emission in the blue–green region. A higher Stokes’ shift could be observed for the derivative 3b because of an intramolecular charge transfer in the excited state from the dimethylaniline to the dihydropyridine chromophores, which was corroborated by a linear relation of the fluorescence maxima (ν_max) versus the solvent polarity function (Δf) from the Lippert–Mataga correlation. A comparison between the experimental data and time‐dependent density functional theory‐polarizable continuum model calculations of the vertical transitions was performed to help on the elucidation of the photophysics of these compounds. For these calculations, the S₀ and S₁ states were optimized using Becke, three‐parameter, Lee–Yang–Parr/6‐31 G* and Configuration Interaction Singles/6‐31 G*, respectively. The predicted absorption maxima are in good agreement with the experimental; however, the theoretical fluorescence emission maxima do not match the experimental, which means that the excited specie cannot be related to neither a locally excited state nor to an aromatized structure. Copyright © 2012 John Wiley & Sons, Ltd.