Nitrification process in a packed bed reactor with a chemically active bed

A laboratory scale submerged filter filled with crushed marble was used for the nitrification process investigation. The results obtained showed that the alkaline reactor filling material react with the hydrogen ions released during the process course which enables reactor exploitation without any pH value or alkalinity control.     

Changes occurring in the complex of cardenolide glycosides caused by phytoparasitic digitalis in fungi. IV. Determination of main regeneration of lanatosides A and C caused by Colletotrichum fuscum Laub

Groups of dogs were exercised immediately before, and immediately after occlusion of the left anterior descending coronary artery. Coronary occlusion by a staged procedure resulted in a low mortality and rare ventricular ectopic beats. The combination of simultaneous exercise with coronary occlusion reproducibly provoked ventricular fibrillation (VF). Exercise before and after occlusion frequently produced ventricular tachycardia but no VF. The risk of major arrhythmias was related to the peak heart rate resulting from the exercise.     

Investigation of the morphotropic region in the Sr-doped lead hafnate-titanate solid solution Pb0.94Sr0.06Hf1-TixO3

Sr-doped lead hafnate titanate (PHT) oxides were synthesized by solid-state reaction and carefully studied in order to identify the reaction mechanisms. The reaction sequences in the formation of Sr-doped PbHfO₃, Sr-doped PbTiO}_{3 and Sr-doped PbHf_{1 - x}Ti_xO₃ were investigated using X-ray powder diffraction and differential thermal analysis. The Sr-doped PbHfO₃ oxide is mainly elaborated from the reaction between PbO and HfO₂, while Sr-doped PbTiO₃ oxide is formed from the reaction between Pb₃O₄ and TiO₂. The Sr-doped PbHf_1-xTi_xO₃ oxide is obtained from a solid-state reaction between Sr-doped PbHfO₃ and Sr-doped PbTiO₃ solid solutions. For x close to 0.5, tetragonal and rhombohedral ferroelectric phases coexist in a region commonly called the morphotropic region which presents the best dielectric and electromechanical properties. By means of X-ray powder diffraction, the boundaries of the morphotropic region in the (Pb_0.94Sr_0.06)Hf_1-xTi_xO₃ system have been determined for x ranging between 0.42 and 0.58. Finally, electrical and piezoelectric characterizations have been performed on Sr-doped PHT ceramics crystallizing in the morphotropic region. The compositional dependence of the electromechanical coupling factor (k_P), piezoelectric coefficients (d_{33 and g₃₃) and relative permittivity (_r) has been studied. An optimum composition has been determined as x equal to 0.51. © 2001 Kluwer Academic Publishers     

Sulphidation and oxidation of the Ni22Cr10Al1Y alloy in H2/H2S and SO2 atmospheres at high temperatures

The Ni22Cr10Al1Y alloy was exposed in H₂/H₂S gas mixture under the sulphur pressure 10^–3 and 1 Pa as well as in SO₂ at 1173 and 1273 K. At p_s = 1 Pa the sulphidation rate was relatively high and the reaction obeyed the linear rate law. Under these conditions a nickel/nickel sulphide eutectic was formed. At p_s = 10^–3 Pa nickel sulphides became unstable and the sulphidation rate was significantly lower. The reaction obeyed the parabolic rate law. The oxidation rate of the alloy in SO₂ was lower than that in any of the H₂/H₂S atmospheres. The sulphide scales formed during sulphidation in H₂/H₂S had complex microstructures and compositions, with sulphospinel and sulphide phases being present, e.g. NiCr₂S₄, Ni₃S₂, Cr_xS_y. As the temperature increased and the sulphur pressure decreased, these phases were replaced by the chromium-rich sulphide phase. Various oxides formed during oxidation of the alloy in SO₂.     

STRESSES IN VISCOELASTIC PLATE DRIED CONVECTIVELY

The deformations and drying-induced stresses in a saturated porous plate insulated on one side and dried convectively on the others were analysedPlate material is assumed to be elastic and viscoelastic. A rigorous solution of the problem is presented using Laplace transformations and the method of variable separation. The results are presented in the form of a series resulting from the solution of a Sturm-Liouville problem. The shrinkage stresses in the plate are caused by non-uniform distribution of the moisture content. The thermal stresses are not included as the consideration were confined to only constant rate drying period.     

A Gas Scintillation Proportional Counter for the X-Ray Astronomy Satellite SAX

A driftless gas scintillation proportional counter is described. The instrument has several advantages over conventional GSPCs especially for applications at low x-ray energies (~0.l - 30 keV) and small dimensions such as imaging focal plane detectors for x-ray telescopes or concentrators. The x-ray astronomy satellite project SAX has such a requirement and an imaging GSPC of this configuration is presented in this context.     

Road transport energy conservation in Costa Rica

Transportation is typically the largest petroleum-using sector in less developed countries and is generally dominated by road transport. Despite this fact, energy planning and conservation assistance have concentrated on other sectors, partly because of a lack of experience with transport-energy conservation in less developed countries. Studies of short-term energy conservation in taxi and bus fleets under actual operating conditions in San Jose, Costa Rica, have shown that efficiency improvements on the order of 10% are obtainable. Training in fuel-efficient driving strategies reduced taxi-fuel use by 14% and bus-fuel use by 3% on the average. Implementation of fuel-efficient maintenance practices reduced bus-fuel consumption by an average of 6%. Radial tires were ineffective and possibly counter-productive in saving fuel. Because of the complex experimental design, the results were not readily perceived by vehicle operators. Future demonstrations should concentrate on showing monetary savings to vehicle operators.     

A simple and novel method for measuring the chirp parameter of anintensity modulated light source

A new and simple method of measuring the chirp parameter α of a modulated light source is presented. The technique involves modulating the optical source in a particular manner, and then directly examining the resulting optical spectrum. This experimental measurement technique allows us to directly measure the phase of the optical signal in the frequency domain. In addition, the method is very easy and accurate. Experimental results demonstrate the use of this measurement technique for measuring the chirp parameter of a source modulated at 10 GHz