Nonlinear four-way kinetic-excitation-emission fluorescence data processed by a variant of parallel factor analysis and by a neural network model achieving the second-order advantage: malonaldehyde determination in olive oil samples

Four-way data were obtained by recording the kinetic evolution of excitation-emission fluorescence matrices for the product of the Hantzsch reaction between the analyte malonaldehyde and methylamine. The reaction product, 1,4-disubstituted-1,4-dihydropyridine-3,5-dicarbaldehyde, is a highly fluorescent compound. The nonlinear nature of the kinetic fluorescence data has been demonstrated, and therefore the four-way data were processed with parallel factor analysis combined with a nonlinear pseudounivariate regression, based on a quadratic polynomial fit, and also with a recently introduced neural network methodology, based on the combination of unfolded principal component analysis, residual trilinearization, and radial basis functions. The applied chemometric strategies are not only able to adequately model the nonlinear data but also to successfully determine malonaldehyde in olive oil samples. This is possible since the experimentally recorded four-way data, modeled with the above-mentioned advanced chemometric approaches, permit the achievement of the second-order advantage. This allows us to predict the analyte concentration in a complex background, in spite of the nonlinear behavior and in the presence of uncalibrated interferences. The present work is a new example of the use of higher-order data for the resolution of a complex nonlinear system, successfully employed in the context of food chemical analysis.     

Unsupervised word sense disambiguation with N-gram features

The present paper concentrates on the issue of feature selection for unsupervised word sense disambiguation (WSD) performed with an underlying Naïve Bayes model. It introduces web N-gram features which, to our knowledge, are used for the first time in unsupervised WSD. While creating features from unlabeled data, we are “helping” a simple, basic knowledge-lean disambiguation algorithm to significantly increase its accuracy as a result of receiving easily obtainable knowledge. The performance of this method is compared to that of others that rely on completely different feature sets. Test results concerning nouns, adjectives and verbs show that web N-gram feature selection is a reliable alternative to previously existing approaches, provided that a “quality list” of features, adapted to the part of speech, is used.     

Electrical Conductivity and Thermodynamic Properties of Some Alkaline Earth-Doped Lanthanum Chromites

Alkaline-earth doped lanthanum chromites are currently the interconnecting materials of choice for solid oxide fuel cells (SOFCs). Since these materials in SOFC operating conditions are under a large oxygen potential gradient and at high temperature (1273 K), a thorough knowledge of their physical and thermochemical properties is very important. In the present study, the alkaline-earth doped lanthanum chromites La_1-xSr_xCrO₃ (x=0–0.3) and La_0.7Ca_0.3CrO₃ were prepared from complex precursors isolated from the La(NO₃)₃–Cr(NO₃)₃–urea system. The oxide powders were characterized by means of X-ray diffraction (XRD). The DC electrical conductivities of the samples were measured in the temperature range of 295–1273 K in air. The thermodynamic properties represented by the relative partial molar free energies, enthalpies, and entropies of oxygen dissolution in the perovskite phase, as well as the partial pressures of oxygen, have been investigated by the solid electrolyte galvanic cells method coupled with the solid-state coulometric titration technique, within the temperature range of 1073–1273 K and in a reducing atmosphere (10^–5 Pa). The variation of the electrical conductivities and thermodynamic properties with changing oxygen stoichiometry is discussed. The study demonstrates new correlations existing between the structural, electrical, and thermodynamic properties in the doped lanthanum chromites.Paper presented at the Sixteenth European Conference on Thermophysical Properties, September 1–4, 2002, London, United Kingdom.     

Determination of danofloxacin in milk combining second-order calibration and standard addition method using excitation–emission fluorescence data

For this paper we propound a new procedure for fast detection and determination of danofloxacin (DANO) in commercial bovine milks. For this aim, a spectrofluorimetric method coupled with chemometric (PARAFAC) tools has been optimized. This method provides valuable information about the total amount of DANO in the selected sample in a short analysis time. After a cleanup step, consisting in protein precipitation in acidic medium, excitation–emission fluorimetric scans (EMMs) were recorded and a standard addition calibration method, using second order multivariate procedures, was applied. The analytical method has been validated according to the European Community directive related to the decision limit (CCα) and detection capability (CCβ). The obtained values, 7.3 and 12 ng mL⁻¹, respectively calculated are well below the MRL for DANO in milk (30 ng mL⁻¹). This procedure has been applied to different commercial milks in order to accomplish the strength of this methodology by PARAFAC standard addition. Recoveries around 100% were observed for all the samples. The high sensitivity of the fluorimetric technique and the fast cleanup step make this method an easy and fast way for quality and antibiotic residues surveys in commercial milks.     

Probing the heat‐induced structural changes in bovine serum albumin by fluorescence spectroscopy and molecular modelling

The fluorescence spectroscopy and in silico methods were used to evaluate the structural changes in bovine serum albumin (BSA) over a temperature range of 25–70 °C for 15 min. Experimental results indicated that the polypeptide chain rearrangements at temperatures higher than 40 °C lead to a lower exposure of hydrophobic residues causing the decrease in fluorescence intensity. The nonlinearity of the phase diagram indicated a sequential denaturation process involving several molecular species. The molecular dynamics simulations at the single‐molecule level showed the high stability of the BSA structure, compensating for the entropic costs associated with the prevalent helical folding.     

Performance and endurance of a high temperature PEM fuel cell operated on methanol reformate

This paper analyzes the effects of methanol and water vapor on the performance of a high temperature proton exchange membrane fuel cell (HT-PEMFC) at varying temperatures, ranging from 140 °C to 180 °C. For the study, a H₃PO₄ – doped polybenzimidazole (PBI) – based membrane electrode assembly (MEA) of 45 cm² active surface area from BASF was employed. The study showed overall negligible effects of methanol-water vapor mixture slips on performance, even at relatively low simulated steam methanol reforming conversion of 90%, which corresponds to 3% methanol vapor by volume in the anode gas feed. Temperature on the other hand has significant impact on the performance of an HT-PEMFC. To assess the effects of methanol-water vapor mixture alone, CO₂ and CO are not considered in these tests. The analysis is based on polarization curves and impedance spectra registered for all the test points. After the performance tests, endurance test was performed for 100 h at 90% methanol conversion and an overall degradation rate of −55 μV/h was recorded.     

Heterogeneous Catalytic Transformation of Citronellal to Menthol in a Single Step on Ir-Beta Zeolite Catalysts

The synthesis of menthol from citronellal was studied on bifunctional Ir/Beta zeolite catalysts, prepared via impregnation of Beta zeolite with different concentrations of Ir. The results show that Beta zeolites, impregnated with Ir, catalyze the one-pot full conversion of citronellal to menthol by consecutive acid-catalyzed cyclization and Ir-catalyzed hydrogenation. The best results (95% selectivity for the menthol isomers, of which 75% is the desired (±)-menthol) were recorded on 3% Ir/Beta zeolite catalyst. In contrast with earlier studies, 0.05 g Ir/Beta catalyst per mL of substrate leads to complete and selective substrate transformation. The textural properties, acidity and hydrogenation function were studied by liquid N₂ adsorption–desorption, FT-IR, XPS and hydrogen chemisorption techniques. To clarify the mechanism of the cyclization of citronellal, tests were also performed using zeolites with different acidity and loaded with other metals (Pt, Pd, Rh, Ru).     

Experimental Researches Regarding the Thermodynamic Activities in the Binary Pb-Sb Alloy System

We have determined the thermodynamic activity of Pb and Sb in the Pb-Sb binary system. For the experiments, we used a galvanic cell in which the measuring electrode was made of Pb-Sb alloys with different chemical compositions. The reference electrode was manufactured from pure lead, and a mixture of salts (35% KCl, 17% NaCl and 48% PbCl₂) was used as an electrolyte, which had a melting temperature of 399 °C (672 K). Tungsten wires were used for the contact conductors of the electrodes, and platinum wires were used for the electrical contacts between the measurement instrument and the contact conductors. The variations of activity coefficients depending on its atomic fraction were calculated for the Pb and Sb in the Pb-Sb binary alloy system. The experimental measurements were performed at a temperature of 650 °C (923 K). The obtained data are reliable and consistent, and now, based on these, thermodynamic functions can be obtained that can help the scientific community to correctly describe the behavior of the Pb-Sb binary alloy system.     

Soil and groundwater cleanup: benefits and limits of emerging technologies

Contaminated soil and groundwater have been the subject of study and research, so that the field of remediation has grown and evolved, continually developing and adopting new technologies in attempts to improve the decontamination. The cleanup of environmental pollution involves a variety of techniques, ranging from simple biological processes to advanced engineering technologies. Cleanup activities may also address a wide range of contaminants. This article is a short analysis of the technologies for cleaning up groundwater and soil, highlighting knowledge and information gaps. Challenges and strategies for cleaning up different types of contaminants, mainly heavy metals and persistent organic compounds are described. Included are technologies that treat ground water contaminants in place in the subsurface and soil technologies that treat the soil either in place or on site in a treatment unit. Emerging technologies such as those based on oxidation–reduction, bioremediation, and nanotechnologies are covered. It is evident that for a good efficiency of remediation, techniques or even whole new technologies may be incorporated into an existing technology as a treatment train, improving its performance or overcome limitations. Several economic and decision-making elements are developed in the final part, based on the analysis carried out throughout the article. The work highlights the fact that excellence in research and technology progress could be attained by the development of technologies to deal more effectively and economically with certain toxic contaminants such as heavy metals, volatile organic compounds, and persistent organic pollutants, associated with optimization of technologies under field remediation conditions and requirements, improving capacity and yields, and reducing costs. Moreover, increasing knowledge of the scope and problem of equipment development could improve the benefits.