Least-squares support vector machines and near infrared spectroscopy for quantification of common adulterants in powdered milk

This paper proposes the use of the least-squares support vector machine (LS-SVM) as an alternative multivariate calibration method for the simultaneous quantification of some common adulterants (starch, whey or sucrose) found in powdered milk samples, using near-infrared spectroscopy with direct measurements by diffuse reflectance. Due to the spectral differences of the three adulterants a nonlinear behavior is present when all groups of adulterants are in the same data set, making the use of linear methods such as partial least squares regression (PLSR) difficult. Excellent models were built using LS-SVM, with low prediction errors and superior performance in relation to PLSR. These results show it possible to built robust models to quantify some common adulterants in powdered milk using near-infrared spectroscopy and LS-SVM as a nonlinear multivariate calibration procedure.     

Multicommutation-NIR determination of Hexythiazox in pesticide formulations

A multicommutated flow-system was designed in order to increase analytical throughput and for controlling thermal effects on the NIR spectra for determination of Hexythiazox in pesticide formulations. An on-line standard addition was carried out showing the versatility and repeatability of multicommutation for the on-line mixing and dilution of solutions. Results obtained for commercial samples were statistically comparable with those obtained by an HPLC-reference method. Multicommutation-NIR allows the analysis of 52 samples per hour, in front of the 30 samples per hour analyzed by the NIR-batch procedure and the 7 samples per hour analyzed by HPLC-reference method.     

Current trends in the computational modelling of polyoxometalates

Computational chemistry applied to the study of polyoxometalates has achieved its maturity in the last years. During two decades, important advances have been made using theoretical tools in the comprehension and interpretation of many relevant issues. In the present mini-review, we want to stress that different techniques have been incorporated to the routine of computation: from the very first Hartree?CFock LCAO-SCF calculation on the decavanadate anion, followed by numerous density functional theory?Cbased studies on increasingly complex systems, also applying correlated ab initio techniques for magnetism and, more recently, using molecular dynamics to analyse properties in liquid media, the information provided by computational chemistry gets more and more relevant.     

Intensity and polarization self-pulsations in vertical-cavity surface-emitting lasers

We implement a dynamic model that describes the polarization behavior in vertical-cavity surface-emitting lasers that contain an absorbing region surrounding the active zone. We find four regions of qualitatively different behavior: stable linearly polarized operation, intensity pulsations of a linearly polarized component, pulsations of both total-intensity and polarization components, and polarization self-pulsation with constant total intensity. We characterize the four regions by computing the polarization-resolved optical and power spectra. The predicted behavior agrees with recent experimental results.     

Exploration of the ultimate patterning potential achievable with high resolution focused ion beams

Controlled and reproducible fabrication of nano-structured materials will be one of the main industrial challenges in the next few years. We have recently proposed exploitation of the nano-structuring potential of a high resolution Focused Ion Beam Tool, to overcome basic limitations of current nano-fabrication techniques. The aim of this article is to present some new routes for material patterning, which benefit from ion-induced local property modifications or damage. In the experiments we describe hereafter an ultra-sharp pencil of 30 keV gallium ions is used to tailor the characteristics of several materials at a scale of a few nanometres. The experimental results are then compared to simulations. First, we simulate the control of collisional defects generated in a thin magnetic layer under FIB irradiation. The results explain the stable magnetic structures we have obtained experimentally. This was achieved with a low surface ion dose (10¹² to 10¹⁴ ions/cm²). In addition we have explored the promising direction of Bottom-up or self-organization processes using a FIB instrument. We have defined artificial surface defects. These defects created by the impact of an 8-nm FWHM probe were used to pin the diffusion and to organize nanometre-sized gold clusters on a graphite surface. PACS 79.20.Rf; 81.07.-b     

2-Methoxy-6-oxo-1,4,5,6-tetrahydropyridine-3-carbonitriles: versatile starting materials for the synthesis of libraries with diverse heterocyclic scaffolds

Heterocyclic demonstration libraries for agrochemical screening were prepared from the common intermediates 2-methoxy-6-oxo-1,4,5,6-tetrahydropyridine-3-carbonitriles (1), using standard solution-phase techniques. A total of 18 screening libraries were prepared in good to excellent yields. Several members of these libraries were active in the first level of agrochemical screening, especially in the fungicide screen.     

Origin of the asymmetric magnetization reversal behavior in exchange-biased systems: competing anisotropies

The magnetization reversal in exchange-biased ferromagnetic-antiferromagnetic (FM-AFM) bilayers is investigated. Different reversal pathways on each branch of the hysteresis loop, i.e., asymmetry, are obtained both experimentally and theoretically when the magnetic field is applied at certain angles from the anisotropy direction. The range of angles and the magnitude of this asymmetry are determined by the ratio between the FM anisotropy and the interfacial FM-AFM exchange anisotropy. The occurrence of asymmetry is linked with the appearance of irreversibility, i.e., finite coercivity, as well as with the maximum of exchange bias, increasing for larger anisotropy ratios. Our results indicate that asymmetric hysteresis loops are intrinsic to exchange-biased systems and the competition between anisotropies determines the asymmetric behavior of the magnetization reversal.     

Deroughening of domain wall pairs by dipolar repulsion

As a magnetic domain wall propagates under small fields through a random potential, it roughens as a result of weak collective pinning, known as creep. Using Kerr microscopy, we report experimental evidence of a surprising deroughening of wall pairs in the creep regime, in a 0.5 nm thick Co layer with perpendicular anisotropy. A bound state is found in cases where two rough domains nucleated far away from one another and first growing under the action of a magnetic field eventually do not merge. The two domains remain separated by a strip of unreversed magnetization, characterized by flat edges and stabilized by dipolar fields. A creep theory that includes dipolar interactions between domains successfully accounts for (i) the domain wall deroughening as the width of the strip decreases and (ii) the quasistatic and dynamic field dependence of the strip width s.     

The index of a plane curve and green’s formula

In this paper we compute the line integral of a complex function on a rectifiable cycle homologous to zero obtaining a Green’s formula with multiplicities that involves the of the function and the index of the cycle. We consider this formula in several settings and we obtain a sharp version in terms of the Lebesgue integrability properties of the partial derivatives of the function. This result depends on the proven fact that the index of a rectifiable cycle is square integrable with respect to the planar Lebesgue measure. The work of both authors is partially supported by grants 2000SGR-00059, 2001SGR 00172 of Generalitat de Catalunya and BFM 2002-04072-C02-02 of Ministerio de Ciencia y Tecnologia