High‐order numerical methods for one‐dimensional parabolic singularly perturbed problems with regular layers

In this work we construct and analyze some finite difference schemes used to solve a class of time‐dependent one‐dimensional convection‐diffusion problems, which present only regular layers in their solution. We use the implicit Euler or the Crank‐Nicolson method to discretize the time variable and a HODIE finite difference scheme, defined on a piecewise uniform Shishkin mesh, to discretize the spatial variable. In both cases we prove that the numerical method is uniformly convergent with respect to the diffusion parameter, having order near two in space and order one or 3/2, depending on the method used, in time. We show some numerical examples which illustrate the theoretical results, in the case of using the Euler implicit method, and give better numerical behaviour than that predicted theoretically, showing order two in time and order N^?2log²N in space, if the Crank‐Nicolson scheme is used to discretize the time variable. Finally, we construct a numerical algorithm by combining a third order A‐stable SDIRK with two stages and a third‐order HODIE difference scheme, showing its uniformly convergent behavior, reaching order three, up to a logarithmic factor. © 2004 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2005     

Active role of buried ultrathin oxide layers in adsorption of O2 on Au films

Ultrathin oxide layers can exhibit special behavior by enabling the coupling of structural distortions and charge transfer beyond that allowed in the bulk. In this work, we show from first-principles calculations that ultrathin layers of titania, a prototypical oxide, are active in stabilizing adsorption of O₂ on Au overlayers. The adsorbed O₂ molecules induce charge redistribution in Au that penetrates to the Au-titania interface, which responds through structural distortions that lower the total energy of the system. We suggest that this effect may be of more general nature and useful in catalysis.     

Linear Key Predistribution Schemes

In a key predistribution scheme, some secret information is distributed among a set of users. For a given family of privileged groups, this secret information must enable every user in a privileged group to compute a common key associated with that group. Besides, this common key must remain unknown to some specified coalitions of users outside the privileged group. We present in this paper a new model, based on linear algebraic techniques, for the design of key predistribution schemes that unifies all previous proposals. This new model provides a common mathematical formulation and a better understanding of key predistribution schemes. Two new families of key predistribution schemes that are obtained by using this model are presented. Those families provide, for some specification structures, schemes that have better information rates than the ones given in previous proposals or fit in situations that have not been considered before.     

Mössbauer spectroscopic and SEM study of Campanian and Terra sigillata pottery from Spain

A combination of Mössbauer spectroscopy (CEMS and transmission) and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDAX) was employed to study the differences between coat and body in Campanian and Terra Sigillata wares. Conclusions about type of clay, origin of colour, and fabric and firing technology are established.     

Study of the photoluminescence spectrum in high purity CdTe

In this work, a study of the photoluminescence produced by a high purity sample of n-type CdTe of $\text{?}\text{N}{}_{\mathrm{<mtext>D</mtext>}}\text{?}\text{N}{}_{\mathrm{<mtext>A</mtext>}}\text{? < 10}{}^{14}$ impurities per cm³ was done at several temperatures, varying from 10 to 35 K. Several sharp lines were observed in the spectral region between 1.5 to 1.6 eV, plus the well-known 1.4 eV band with several well-defined structures on it. The observed temperature behaviour of the line positions, linewidths and relative intensities allowed us to establish the presence of a new transition, located at 10 K 21.3 meV below in energy from the free exciton (FE) line, as well as its first phonon replica. Its nature seems to be transitions originating from the conduction band to an acceptor level, 32 meV above the valence band. These two lines appear at the same position where previous works had reported the first and second phonon replicas of the FE. A scheme of impurity level is proposed to explain the observed transitions in terms of previously established levels and this new acceptor level.     

Dimension of the solution spaces of the matrix equations [A, [A, X]] = 0 and [A, [A, [A, X]]]= 0

In this paper, a formula for the dimension of spaces of solutions of these equations in terms of Segre characteristic of matrix A is given.     

Semipreparative-scale gas-chromatographic separation of filbertone enantiomers

The enantioselectivity of heptakis(2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl-beta-CD) toward racemic filbertone (E-5-methyl-hep-2-en-4-one) was studied by performing the chiral separation on a capillary column, a thick-film wide-bore column and a semipreparative column. The semipreparative enantioseparation of filbertone was achieved at 80 degrees C by using a packed column providing (R)- and (S)-enantiomers of filbertone with ee 90 and 96%, respectively. The isolated enantiomers (approximately 250 microg each, ee = 90-96%) may be used for studies on the relationship of chirality and biological activity by olfactory screening and toxicological studies.     

Wood identification using pressure DSC data

This work addresses the problem of supervised classification of industrial wood species (seven different types in the present study) through their thermo‐oxidative stability. This is evaluated by pressure differential scanning calorimetry (PDSC) using the ASTM E2009. The maximization of the ratio of correct classification and the reduction of the costs of this activity are intended. This supervised classification problem was carried out using two different proposals: applying novel nonparametric functional data analysis techniques, based on kernel estimation, to the original PDSC curves, and using machine learning classification approaches applied to different multivariate data sets. The multivariate data sets were obtained, on the one hand, by estimating the fractal (Hausdorff) dimension of the PDSC curves by several methods, jointly with selecting the parameters from fitting a nonlinear model to the PDSC curves and, on the other hand, applying principal component analysis or partial linear squares to the thermograms. The results obtained show that the PDSC curves can be used to discriminate wood samples when these innovative and traditional statistical techniques are applied. In the best of the cases, a probability of correct classification that equals to 0.92 was obtained. PDSC represents a new alternative to the use of images, spectra, and other thermal signals as thermogravimetric analysis for classification purposes.Copyright © 2013 John Wiley & Sons, Ltd.