Changes in crystallite size and microstrains of hematite derived from the thermal decomposition of synthetic akaganeite

The thermal decomposition of akaganeite, β-FeOOH, in air is studied. The structural properties of the dehydroxylation product, identified as hematite, are determined at different temperatures. From the results on crystallite size and microstrains, a change of crystallite shape has been shown to occur in the range of temperatures of 300 to 485°C. A marked increase in crystallite size and a diminution in microstrains is observed at 525°C. This change is related to the occurrence of an exothermic peak in the DTA and DSC curves of akaganeite at about 512°C. The peak is thus ascribed to a recrystallization process of hematite. Electron micrographs support the most relevant observations of changes in particle size and shape.     

Chemical characterization and quality of the waters used for hemodialyses in the INEF from 2002 to 2004

Summary The quality of the potable and purified for haemodialysis waters used in the National Institute of Nephrology was evaluated since 2002 up to now. A total of 20 chemical components were analyzed. The analytical results were compared with the admissible maximum concentrations according to the Cuban Standard NC 92-02:85 for potable water and with the Spanish Standard UNE 111-301-90, related to the quality of water for use in haemodialysis. The quality of both types of water was found to comply with the Standards regulations. The CEADEN analytical chemistry laboratory operates a quality management system since 1992, that was credited according to ISO/IEC 17025 requirements.     

Multielement analysis of lichen samples using XRF methods. Comparison with ICP‐AES and FAAS

This research presents the contents of Ca, Fe, Zn, Br, Rb, Sr and Pb in lichen samples used as biomonitors of air pollution collected in Havana. Statistical comparisons were made among the results obtained in three campaigns during three years. Two X‐Ray Fluorescence (XRF) methods were used, employing for excitation an annular ¹⁰⁹Cd source and a Mo X‐ray tube with a molybdenum secondary target. In both cases, matrix effects were corrected by the use of normalization for the Compton scattered peak; in this way the determination is more efficient. For quality control of the results, biological Certified Reference Materials were analyzed and were made comparisons between XRF, Inductively Coupled Plasma‐Atomic Emission Spectrometry and Flame Atomic Absorption Spectrophotometry. No significant differences were found between the different techniques. The elemental distribution patterns obtained for each metal were associated with different pollution sources, thus contributing to the assessment of air pollution in Havana. Copyright © 2015 John Wiley & Sons, Ltd.     

System for determination of ultrasonic wave speeds and their temperature dependence in liquids and in vitro tissues

An interferometric technique capable of accurately measuring wave speed in liquids is reported. The hardware is adapted from a design to measure nonlinear responses of biological tissues to pressure changes (pressure derivatives) and temperature changes (temperature derivatives). It is used with the highly sensitive variable frequency pulsed phase-locked loop (VFPPLL) instrument. The system uses well-understood and well-characterized components and systems. The apparatus covers a temperature range from below 5 degrees C to above 45 degrees C. The system with the high-sensitivity VFPPLL is capable of measurement of wave speed to an uncertainty of less than 0.1%, and changes in wave speed to better than 0.001%. The transducer is an undamped temperature-characterized PZT-5A 500-kHz plate, whose output is corrected for off-resonance operation and for diffraction effects. To test the accuracy of the technique, measurement of ultrasonic compressional wave speed in water at temperatures from 10 degrees C to 45 degrees C are reported, with an estimated uncertainty of 0.07% and a temperature uncertainty of 0.15 degrees C. The agreement between mean values and literature values is better than 0.05%.     

Ecriture de l'énergie cinétique à l'aide d'opérateurs quasi-moments

Cet article concerne l'utilisation des quasi-moments ?π _m , définis par

,

pour exprimer l'opérateur correspondant à l'énergie cinétique de N particules en Mécanique Quantique. La condition de Wilson-Howard portant sur les coefficients s^ml est interprétée comme la condition pour que les opérateurs ?π _m soient hermitiques quand on utilise l'élément de volume s dq ₁ … dq ₃ N (s=[dét {s^ml }]^-1). La condition générale pour qu'il soit possible de trouver un élément de volume avec lequel les opérateurs ?π _m sont hermitiques est donnée et différentes expressions de l'opérateur énergie cinétique sont établies quand cette condition est remplie et quand elle ne l'est pas.