Electrochemical reduction of nitrate and nitrite in simulated liquid nuclear wastes.

The electrochemical reduction of nitrate and nitrite in simulated low-level nuclear wastes containing 1.8 M NaNO(3)+0.55 M NaNO(2)+1.16 M NaOH was studied under galvanostatic polarization on tin and bismuth cathodes. The rate of the reduction of nitrate was about the same on both metals. The selectivity (%S) to ammonia was similar on the two metals (12% at 450 mA/cm(2)) and that to nitrogen 82% on Sn and 72% on Bi. On the other hand, the %S to nitrous oxide was lower on Sn (8%) than that on Bi (18%) under the same conditions. The current efficiency (%CE) on both metals was 80% when the 99% of the initial nitrogen was removed. The %CE gradually decreases as the concentration of the nitrogen containing species in the solution decreases during the electrolysis. The energy consumption for the removal of 1g of N was 100 Wh at 450 mA/cm(2) but it can be significantly reduced by a better design of the electrolysis cell.The presence of chromate in the electrolyte, which is a known inhibitor of the cathodic reduction of nitrate, has no influence on the rate of the reduction and the distribution of the products.

Characterization of a laminar flow cell for the prevention of biosensor fouling.

A flow cell using dual parallel laminar flows was designed and fabricated with the aim to prevent biosensor fouling. Y-shaped entrances allowed the introduction of sample and electrolyte streams, with the electrolyte serving as a mobile protective layer near the biosensor. Potassium permanganate was used to quantify the diffusion in the flow cell. Optical intensity analysis of potassium permanganate along a series of transverse lines across the flow cell was carried out under different flow conditions. It was found that the error function, erf(y/[square root](Dt)), where y was the position along the transverse line, D the diffusion coefficient of the solute and t was the time, gave reasonable approximation to the diffusion of potassium permanganate in the cell. The diffusion coefficient of potassium permanganate was determined in stop-flow measurements and the value, D=4.0 x 10(-5)cm(2)/s, agreed to previously reported values. Velocity distribution in the flow cell was simulated numerically to reveal the development of two inflows into one single laminar flow. Results from the study provided preliminary data on solute diffusion characteristics in the flow cell and supported the working principle of laminar flow cells in preventing biosensor fouling.

Photocatalytic degradation of p-coumaric acid over TiO2 suspensions.

The photocatalytic degradation of p-coumaric acid, a biorecalcitrant phenolic compound typically found in olive processing and wine distillery waste waters, has been investigated in aqueous heterogeneous solutions containing semiconductor powders as photocatalysts. The disappearance of the organic molecule follows approximately a pseudo-first kinetic order according to the Langmuir-Hinselwood model. The most important reaction intermediates were determined by GS-MS and HPLC measurements, suggesting a reaction pathway for the photodegradation. Various commercial photocatalysts were compared with respect to their overall efficiency, as well as the production of CO2. The effect of H2O2 on the reaction rate was ascertained.

A realistic three dimensional FEM of the human head.

A realistic three-dimensional finite element model (FEM) of the human head has been developed. Separate layers for the scalp, skull, cerebrospinal fluid (CSF) and brain were modelled. Hexahedral elements, a special master matrix assembly technique and an iterative successive over-relaxation (SOR) solution scheme were employed. This approach enabled rapid modelling with minimal memory requirements, which makes this method practical if used for electrical impedance tomography (EIT) or source localization inverse problems. Compared to scalp electrodes, subdural voltage sensing electrodes were three to four times more sensitive close to an oedema or source region, if it was peripheral, but this decreased to 30%-40% for central oedema or source regions. Scalp current injecting electrodes are preferable, since the maximum allowable current is 10 times larger than that of the subdural ones. The distance of voltage sensing electrodes from a region to be imaged highly affects sensitivity, so depth electrodes will be more sensitive, provided that they are close to the region of interest. Finally, the electrode size has significant effects on the input or transfer impedance.

A 32-electrode data collection system for electrical impedance tomography.

A 32-electrode data collection system for Electrical Impedance Tomography (EIT) will be presented. In this system, the demodulator is a multiplexed sample and hold (S&H) circuit followed by a voltage difference stage. This configuration provides high CMRR due to the low (almost DC) operating frequency of the signals the difference stage is required to process.

An efficient finite-element algorithm for 3D layered complex structure modelling.

In this paper an efficient finite-element method (FEM) algorithm for complicated three-dimensional (3D) layered type models has been developed. Its unique feature is that it can handle, with memory requirements within the abilities of a simple PC, arbitrarily shaped 3D elements. This task is achieved by storing only the non-zero coefficients of the sparse FEM system of equations. The algorithm is applied to the solution of the Laplace equation in models with up to 79 layers of trilinear general hexahedron elements. The system of equations is solved with the Gauss-Seidel iterative technique.

A reconstruction algorithm of electrical impedance tomography with optimal configuration of the driven electrodes.

A reconstruction algorithm for electrical impedance tomography (EIT) is presented. The least-squares (LS) method is applied and a formulation similar to that of the perturbation method is found. The main difference from perturbation lies with the sensitivity matrix, which here is replaced by the Jacobian matrix, defined in terms of the partial derivatives of every sensing electrode pair voltage difference with respect to every element's conductivity. The mutual position between the active electrodes is chosen to give optimum sensitivity. The results shown that the algorithm presented here has a better convergence and needs fewer iterations than the perturbation method.

Electrical impedance measurements for pulmonary disease diagnosis.

An investigation of the physical state of the human thorax and the associated thoracic electrical impedance is presented. From an experimental study with 60 subjects (23 without pulmonary disease and 37 with obstruction or restriction) it is concluded that the percentage change in the measured input impedance from the predicted value is a good index to estimate the size of oedema and the physical state of the lungs. These results are in good agreement with the theoretical analysis of the problem and the patient's physical state.

Reconstruction of impedance images using a modified perturbation method.

A modified perturbation method (MPM) arising from the replacement of the sensitivity matrix by the Jacobian matrix is presented. Our results have been made using an array processor board with four T-800 INMOS transputers. The numerical algorithm has been matched to the new system and the procedure reached a minimum 50 times faster than for a single PC/AT with mathematical co-processor. Several phantoms have been reconstructed. From the results one can see the applicability of the MPM algorithm to complicated models.