Determination of formic and acetic acids in air by piezoelectric microweighing

The quantitative and kinetic parameters of sorption of formic and acetic acids on thin films of various modifiers of piezoelectric quartz resonator electrodes are determined. Parameters of film formation on the electrodes (application procedure and thickness) are optimized. Methods for joint and separate determination of formic and acetic acids in air by piezoelectric microweighing with single- and double-sensor devices are developed.     

<Superscript>40</Superscript>K activities and potassium concentrations in tobacco samples of Mexican cigarettes

Nine brands of tobacco cigarettes manufactured and distributed in the Mexican market were analyzed by γ-spectrometry to certify their non-artificial radioactive contamination. Since natural occurring radioactive materials (NORM) ⁴⁰K, ²³²Th, ²³⁵U, and ²³⁹U (and decay products from the latter three nuclides) are the main sources for human radiation exposure, the aim of this work was to determine the activity of ⁴⁰K and potassium concentration. Averages of ⁴⁰K and potassium concentration were of 1.29±0.18 Bq·g⁻¹, and 4.0±0.57%. The annual dose equivalents to the whole body from ingestion and inhalation of 26 Bq ⁴⁰K were 0.23 μSv and 15.8 μSv, respectively. The corresponding 50 years committed dose equivalents was 0.23 μSv. The total committed dose to the lungs due to inhalation of ⁴⁰K in tobacco was 16 μSv. Potassium concentrations obtained in this work were in the same range of those obtained by INAA, so showing that the used technique is acute, reproducible, and accessible to laboratories equipped with low background scintillation detectors.     

Growth and characterisation of Eu doped GaN thin films

We have studied the optical properties of Eu doped GaN thin films. We have grown high quality Eu doped GaN thin films by using Gas Source Molecular Beam Epitaxy (GSMBE), with 1.4% Eu concentration. The Full Width at Half Maximum (FWHM) of the X-ray diffraction in an omega scan was found to be 288 arcsecs. Low Eu concentration (0.08%) doped GaN thin films were grown, where Eu-related photoluminescence at 622 and 613 nm was detected using above band-gap excitation at 2 K. For high Eu concentration of 30% GaN:Eu crystal photoluminescence (PL) and cathodoluminescence (CL) spectra show strong and intense transitions at 622 and 664 nm, but also at 593 nm for CL spectra, with a similar transition observed from the low Eu concentration sample.     

Magnetic susceptibility and magnetic resonance study of acceptor doped fullerenes C60(MF6)2 (M=As, Sb, P)

In order to check whether superconductivity occurs in the acceptor doped fullerenes C₆₀(MF₆)₂ (M=As, P, Sb) and to study their magnetic and structural properties, we have carried out magnetic, EPR and NMR measurements of these compounds. Temperature dependences of magnetic susceptibility down to 5 K and field dependences of magnetic moment at 5 K show no ‘bulk’ transition in superconducting state. Some reasons of the absence of superconductivity, such as insufficient charge transfer between C₆₀ and intercalated species and inhomogeneity of the compounds under study, are discussed.     

Axial anomaly and index of the overlap hypercube operator

The overlap hypercube fermion is constructed by inserting a lattice fermion with hypercubic couplings into the overlap formula. One obtains an exact Ginsparg-Wilson fermion, which is more complicated than the standard overlap fermion, but which has improved practical properties and is of current interest for use in numerical simulations. Here we deal with conceptual aspects of the overlap hypercube Dirac operator. Specifically, we evaluate the axial anomaly and the index, demonstrating that the correct classical continuum limit is recovered. Our derivation is non-perturbative and therefore valid in all topological sectors. At the non-perturbative level this result had previously only been shown for the standard overlap Dirac operator with Wilson kernel. The new techniques which we develop to accomplish this also for hypercubic kernels are of a general nature and have the potential to be extended to overlap Dirac operators with even more general kernels.Received: 27 October 2003, Published online: 25 February 2004     

Modelling and optimal control of coupled structural acoustic systems with piezoelectric elements

We construct a model of a shell with piezoelectric elements (patches) that take into account the mutual influence of deformations and electric fields. Coupled problems for the shell with piezoelectric patches and an acoustic field, are studied and results on the existence and the uniqueness are obtained. For this system we consider an optimal control problem on noise attenuation and obtain results on the existence, the uniqueness, necessary and sufficient conditions of optimality. Copyright © 2003 John Wiley & Sons, Ltd.     

High pressure elastic and plastic deformations of silica: In situ diamond anvil cell Raman experiments

Normal silica glass is usually referred to as low density amorphous silica as it can be converted to high density amorphous silica by a hydrostatic pressure (polyamorphic transition). In this work in situ Raman experiments are performed in a diamond anvil cell up to 18 GPa. The pressure effects on the structure of silica after successive compression decompression experiments are analyzed. The mode Grüneisen parameters corresponding to the elastic compression of high density amorphous silica are obtained and compared with those of normal silica. A reorganization of the high density amorphous silica below 3 GPa is evidenced.     

Predicting the onset of DNA supercoiling using a non-linear hemitropic elastic rod

Elastic rod models provide a means to interpret single molecule DNA experiments as well as predict DNA behavior under physiological conditions. Here we use an elastic rod model to predict the stability boundary (critical torque vs. applied tension) for single molecule DNA experiments in which the molecule is subjected to applied tension and twist. We discuss the shortcomings of the usual isotropic rod model. We then derive a consistent non-linear material law from the general representation for a hemitropic (chiral) rod. Finally, we present results of a standard bifurcation analysis predicting the stability boundary. We find results from the non-linear hemitropic rod to match the data closely.