Resolution of phenolic antioxidant mixtures employing a voltammetric bio-electronic tongue

This work reports the application of a Bio-Electronic Tongue (BioET) system made from an array of enzymatic biosensors in the analysis of polyphenols, focusing on major polyphenols found in wine. For this, the biosensor array was formed by a set of epoxy-graphite biosensors, bulk-modified with different redox enzymes (tyrosinase and laccase) and copper nanoparticles, aimed at the simultaneous determination of the different polyphenols. Departure information was the set of voltammograms generated with the biosensor array, selecting some characteristic features in order to reduce the data for the Artificial Neural Network (ANN). Finally, after the ANN model optimization, it was used for the resolution and quantification of each compound. Catechol, caffeic acid and catechin formed the three-analyte case study resolved in this work. Good prediction ability was attained, therefore allowing the separate quantification of the three phenols with predicted vs. expected slope better than 0.970 for the external test set (n = 10). Finally, BioET has been also tested with spiked wine samples with good recovery yields (values of 104%, 117% and 122% for catechol, caffeic acid and catechin, respectively).     

On the growth kinetics and structure of the NiSi compound on silicon single crystals

Summary The growth kinetics of NiSi has been evaluated by depositing a Ni film on <111> and <100> Si substrates. X-ray diffraction and MeV⁴He⁺ backscattering have been used to identify the compounds formed and to measure their thicknesses. Carbon and oxygen impurities have been detected with Auger electron spectrometry with Ar sputtering. During thermal annealing Ni₂Si is formed first, while NiSi appears only after the total exhaustion of the Ni film. It has been found that, on both Si substrates, the thickness of NiSi increases with the square root of time. Different growth rates have been observed for the two different Si orientations. The activation energy in the (300÷370)°C temperature range is 1.83 eV for NiSi grown on <111> and 1.23 eV for NiSi on <100> Si. The two competing mechanisms of Ni diffusion through NiSi by grain boundary and by substitutional processes are correlated with the different microcrystalline structure of the NiSi silicide layers grown on different Si-oriented substrates.

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Riassunto Sono state studiate, con la diffrattometria ai raggi X e con la tecnica RBS di ioni⁴He accelerati ad energie dell'ordine del MeV, la formazione e la velocità di crescita del composto NiSi ottenuto per trattamento termico di uno strato sottile di Ni depositato su Si monocristallino <111> e <100>. La presenza di eventuali impurezze, tipo carbone e ossigeno, è stata osservata con la spettrometria Auger combinata con la rimozione catodica del materiale. Il primo composto che si forma dalla reazione Si−Ni è l'Ni₂Si. Successivamente l'NiSi cresce per la reazione dell'Ni₂Si con il Si e ciò avviene solo dopo che tutto il ni si è consumato nella formazione dell'Ni₂Si. Lo spessorex dell'NiSi cresce col tempot secondo una legge del tipo su entrambi i tipi di Si monocristallino. La velocità di crescita su Si <100> è però maggiore di quella su Si <111>. Sono diverse anche le energie di attivazione del processo di diffusione che determina la crescta dell'NiSi. Infatti, nell'intervallo di temperatura (300÷370)°C, si ottiene un'energia di attivazione di 1.83 eV per l'NiSi cresciuto su Si<111> e 1.23 eV su Si<100>. Dall'analisi ai raggi X si correla la diversa microstruttura dell'NiSi cresciuto su substrati di Si diversamente orientati con le cinetiche di crescita e con le energie di attivazione del processo. Due meccanismi di diffusione competitivi sono responsabili dei diversi risultati ottenuti sui due tipi di substrato monocristallino. Su Si <100> predomina la diffusione di atomi attraverso i bordi di grano dell'NiSi, mentre sul <111> predomina la diffusione per sostituzione successiva degli atomi del composto.

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Резюме Оценивается кинематика роста соединения NiSi, образованного посредством осаждения пленки Ni на подложках <111> и <100> Si. Используется дифракция ренттеновских лучей и обратное рассеяние МэВ-ных⁴He⁺ для идентификации полученных соединений и измерения их толщины. Примеси углерода и кислорода определяются с помощью спектроскопии Оже-электронов при Ar распылении. Во время термического отжига сначала овразуется Ni₂Si, тогда как NiSi появляется только после полного истошения пленки Ni. Обнаружено, что на обоих подложках <111> и <1000> Si толшина NiSi увеличивается как квадратный корень из времени. Для двух различных ориентаций Si наблюдаются различные скорости роста. Энергия активации в области температур (300÷370)°C составляет 1.83 эВ при вырашивании NiSi на <111> Si и 1.23 эв при вырашивании NiSi на <100> Si. Два конкурируюших механизма диффузии Ni через NiSi на границе зерна или в результате процессов замещения коррелируют с различными микрокристаллическими структурами слоев NiSi, выращенных на подложках кремния с различной ориестациеи.

     

Analytical approach to relaxation dynamics of condensed Bose gases

The temporal evolution of a perturbation of the equilibrium distribution of a condensed Bose gas is investigated using the kinetic equation which describes collision between condensate and noncondensate atoms. The dynamics is studied in the low momentum limit where an analytical treatment is feasible. Explicit results are given for the behavior at large times in different temperature regimes.     

Fast invisible neutrino decays

Any value for the lifetime of neutrinos decaying into invisible modes (another neutrino and a Goldstone boson) is possible in theories in which the lepton number is a spontaneously broken global symmetry with different charges for every family. There are two types of models. Only in one of them neutrinos could, in a natural way, be relevant for cosmology.     

New synthetic entries to γ-heteromethyl-substituted α,β-butenolides

The title compounds have been obtained from C₃ plus C₂ synthons by a variety of chemical and photochemical methods.