Determination of selenium in soil by hydride generation AAS

Hydride generation AAS was applied for the determination of total selenium in soil. The influence of various anions and cations present in the sample solution on the generation of selenium hydride was investigated. Special attention was paid to the wet oxidation procedure for the sample dissolution. The proposed procedure involves microwave sample preparation by using a mixture of H₂O₂/HNO₃/H₂SO₄. The accuracy of the procedure was checked by the analysis of the standard reference material Buffalo River Sediment (SRM-2704, NIST). Satisfactory agreement of the results obtained with the values reported was achieved. The detection limit of the procedure was 25 ng Se/g of soil. The relative standard deviation of the measurements varied from 5.5% for SRM-2704 up to 10% for the real soil samples. Received: 20 January 1997 / Revised: 24 February 1997 / Accepted: 1 March 1997     

Iodine in mineral waters: A comparison of results from two analytical techniques

A comparative study of the determination of iodine in mineral waters is presented. Iodine was first determined by a standard titrimetric method and the results obtained were compared with those obtained by the faster and more sensitive radiochemical neutron activation method. For a series of waters, the results obtained by the two techniques were in fair agreement for the higher concentration levels of iodine, but for very low iodine levels the titrimetric method was insufficiently sensitive. The RNAA procedure was checked by standard addition experiments, and shown to be also valid when iodine was present as iodate.The paper was presented in part at the ISM XI, Wiesbaden, August 1989     

The Relationship Between Perceptual Evaluation and Objective Multiparametric Evaluation of Dysphonia Severity

SUMMARY: The purpose of this study was to investigate the usefulness of the Dysphonia Severity Index (DSI) as an objective multiparametric measurement in assessing dysphonia. The DSI was compared with the score on Grade of the GRBAS scale. Investigated was also whether the DSI is related to severity of dysphonia, which was represented by different diagnosis groups. Furthermore, it was investigated whether the DSI can differentiate between a group of patients and a control group. A total of 294 patients with different voice pathologies were included. A control group consisted of 118 volunteers without any voice complaints. The voices of all participants were perceptually evaluated on Grade, and the DSI was measured. The groups of patients with voice complaints have a lower DSI and higher scores on Grade than the control group. The DSI was significantly lower when the score on Grade was higher. The DSI discriminates between patients with nonorganic voice disorders, vocal fold mass lesions, and vocal fold paresis/paralysis. To determine whether the DSI discriminates between patients and controls, the sensitivity and specificity for different DSI cutoff points were calculated. With a DSI cutoff of 3.0, maximum sensitivity (0.72) and specificity (0.75) were found. We conclude that the DSI is a useful instrument to objectively measure the severity of dysphonia.     

Monte Carlo simulation of electron avalanches and avalanche size distributions in methane

The simulation of electron avalanches and avalanche size distributions in methane is presented in this paper. A model for electron transport under the influence of a constant electric field based on the Monte Carlo method is described in detail. The model is verified and then used to simulate the avalanche development, to calculate the number of electrons in the avalanche (avalanche size), and to determine the avalanche size distribution. The simulated avalanche size distributions in methane are compared with the experimental results, and a good agreement is observed. The influence of inter‐electrode distance, pressure, and reduced electric field on the shape of the avalanche size distribution is discussed. The assumption from the literature that for a constant reduced electric field the shape of the reduced avalanche size distribution is independent of the mean size of the avalanche is confirmed for a wide range of experimental conditions. The simulations have shown that avalanche size distributions depend only on the reduced electric field, confirming the similarity principle.     

Heat and fluid flow analysis of metal foam embedded in a double-layered sinusoidal heat sink under local thermal non-equilibrium condition using nanofluid

The present study aims to enhance the hydrothermal performance of a porous sinusoidal double-layered heat sink using nanofluid. The optimum thickness of metal foam (nickel) for different Reynolds numbers ranging from 10 to 100 for the laminar regime and Darcy numbers ranging from 10^?4 to 10^?2 is obtained. At the optimum porous thicknesses, nanofluid (silver–water) with three volume fractions of nanoparticles equal to 2, 3, and 4% is employed to enhance the heat sink thermal performance. Darcy–Brinkman–Forchheimer model and the local thermal non-equilibrium model or two equations method are employed to model the momentum equation and energy equations in the porous region, respectively. It was found that in the cases of Darcy numbers 10^?4, 10^?3, and 10^?2 the dimensionless optimum porous thicknesses are 0.8, 0.8, and 0.2, respectively. It was also obtained that the maximum PEC number is 2.12 and it corresponds to the case with Darcy number 10^?2, Reynolds number 40, and volume fraction of nanoparticles 0.04. The validity of local thermal equilibrium (LTE) assumption was investigated, and it was found that increasing the Darcy number which results in an enhancement in porous particle diameter leads to some errors in results, under LTE condition.

     

Toluene methylation to para-xylene

To investigate the effect of operational parameter and transport phenomena on para-xylene production from toluene methylation with methanol, a fixed bed tubular reactor packed with Al-HMS-5 mesoporous catalyst was numerically studied. A mechanistic Longmuir–Hinshelwood-type kinetic study has been implemented on a proposed reaction network based on former experimental observation and theoretical background. Kinetic parameters and activation energy related to proposed reaction network for toluene methylation were evaluated using nonlinear regression and Arrhenius plot, respectively. In addition, heat transfer, fluid flow, and chemical reaction equations consisting of toluene methylation and xylene isomerization were solved using finite element method. In order to optimize toluene methylation process, reaction temperature and residence time were investigated. The results showed that uniform distribution of temperature exists at the reactor. There is only deviation from uniform temperature at the reactor entrance, but in other places, the temperature distribution is uniform. As a result, fluid temperature quickly becomes the same as the wall temperature, making the toluene methylation reaction highly efficient. Finally, the residence time of 60 s and wall temperature of 425 K were recommended as optimum working values.

     

Biomedical simulation of heat transfer in a human heart

Theory and practical experiences from numerical simulations of heat transfer in the field of medicine are presented in this paper. The cooling of a human heart during surgery was taken as an illustrative example. All phases of the simulation process are described starting with the construction of an irregularly shaped 3-dimensional model. The mathematical model is based on diffusion and Navier-Stokes equations. The system of partial differential equations is solved by finite difference approximation using an explicit time-stepping scheme to obtain the time evolution of the solution for the complete simulated interval, which is typically 1 h. A typical domain is composed of several million voxels; therefore, the program was parallelized to speed up the simulation. A speed-up of 8.2 was obtained on 16 processors in a Linux cluster.     

On a Measure on the Inductive Limit of Projection Logics

The aim of the paper is to measure the logic of J-projections from inductive limit of W J-algebras studied. The main result isTheorem. Let А be a W^∗ J-factor of countable type (type of А is different from I₂) and let А be the inductive limit of W^∗ J-factors А_α different from I₂. If (1) А be a W^∗ P-factor or (2) А and all А_α are W^∗ K-factors, then any indefinite measure ν : ∪_αА^h_α→ R can be unique by the strong operator topology extended to an indefinite measure on A^h.