Electrochemical technique to measure Fe(II) and Fe(III) concentrations simultaneously

An electrochemical technique is presented to simultaneously determine the concentrations of Fe(II) and Fe(III) ions using a rotating disk electrode. The method consists of using a steady state polarization technique where the developed limiting currents are measured and related to the concentration of the cations present in solution. Two linear equations were derived which correlate the limiting currents with the concentrations of the pair cations. The equations are used to easily and simultaneously determine the concentrations of the multivalent species. The precision and accuracy of the technique were found to be comparable to other advanced methods for the quantification of cations, such as capillary zone electrophoresis and spectro-photometric sequential injection analysis.     

Early bacterial accumulation on guided tissue regeneration membrane materials. An in vivo study

The aim of the study was to compare the in vivo early bacterial plaque colonization of 3 different guided tissue regeneration (GTR) membrane materials using a morphological (scanning electron microscope) method. Rectangular-shaped strips were cut from 3 periodontal membranes (expanded polytetrafluoroethylene, polyglactin 910, and polylactic acid) and glued to the buccal aspect of removable acrylic devices, which were applied to the molar-premolar region of the upper quadrants in 8 dental students. Each device held 3 strips: one ePTFE, one polyglactin 910, and one polylactic acid. The surface roughness of each membrane material was measured by means of a laser profilometer. During a 24-hour period, the students had to refrain from any oral hygiene procedures and did not use chlorhexidine mouthrinses. In each subject, one device was removed after 4 hours and the other after 24 hours. After removal, the devices were placed in a 2.5% gluteraldehyde solution to fix the membranes, which were then processed for SEM analysis. Fifty-four microscopic fields (at 200x magnification) were randomly selected and analyzed in each strip. Magnification was increased to determine the presence of bacterial morphotypes. The presence or absence of bacteria was assessed in a binomial fashion. In such a system, the field was bacteria-positive when bacteria constituted the deposits covering the surface of the membrane. The microscopic field was considered bacteria-negative when no bacteria were present. Bacteria-positive fields showing rods and filaments as prevalent bacterial morphotypes were recorded as rod-positive fields. A different pattern of plaque accumulation was demonstrated on different membrane materials. The 4-hour results indicated a statistically significant difference (P = 0.008, ANOVA) in the proportion of bacteria-positive fields among the 3 membranes; a greater amount of bacteria was demonstrated on the ePTFE membrane compared to the other 2 membranes. At 24 hours, the difference in the proportion of bacteria-positive fields was statistically significant (P = 0.002, ANOVA); a lesser amount of bacterial plaque was present on the polylactic acid membrane compared to the ePTFE and polyglactin 910 membranes. No difference in the proportion of rod/bacteria-positive fields was demonstrated among the 3 membranes at either 4 or 24 hours. It was concluded that quantitative differences in early plaque accumulation on various membranes seem to be related to the textural and structural characteristics of the surface, which is not adequately represented by the surface Ra value measured with a profilometric instrument.     

Rhodium electrodeposition on nickel electrodes used for urea electrolysis

A procedure for the constant potential electrodeposition of rhodium onto nickel electrodes, the subsequent surface characterizations, and electrochemical evaluation is presented. The resulting Ni/Rh electrodes were evaluated for their activity as anode catalysts for the electro-oxidation of urea. A detailed procedure for the electrodeposition of Rh onto Ni foil is provided. It is shown that the electrocatalytic performance of Ni/Rh electrodes on the oxidation of urea in alkaline medium is primarily influenced by two electrodeposition parameters: the applied electrodeposition potential and the loading of Rh (mg?cm^?2). An optimization for electrocatalytic performance based on the electrodeposition potential and Rh loading is demonstrated. The effect of these parameters on visual finish, surface morphology, and crystal structure was also studied.     

Comparison of finite difference and control volume methods for solving differential equations

Comparisons are made between the finite difference method (FDM) and the control volume formulation (CVF). An analysis of truncation errors for the two methods is presented. Some rules-of-thumb related to the accuracy of the methods are included. It is shown that the truncation error is the same for both methods when the boundary conditions are of the Dirichlet type, the system equations are linear and represented in Cartesian coordinates. A technique to analyze the accuracy of the methods is presented. Two examples representing different physical situations are solved using the methods. The FDM failed to conserve mass for a small number of nodes when both boundary conditions include a derivative term (i.e. either a Robin or Neumann type boundary condition) whereas the CVF method did conserve mass for these cases. The FDM is more accurate than the CVF for problems with interfaces between adjacent regions. The CVF is (ΔX) order of accuracy for a Neumann type boundary condition whereas the FDM is (ΔX)² order.     

High electroactivity performance in Pt/MWCNT and PtNi/MWCNT electrocatalysts

This work presents the synthesis, characterization and electrochemical evaluation of electrocatalysts for PEM fuel cells base on Pt and Pt–Ni nanoparticles over multi-walled carbon nanotubes (MWCNT). The MWCNT were synthesized by spray pyrolysis of toluene, using ferrocene and nickelocene as catalytic agents. The Pt nanoparticles were deposited using the ultrasound assisted aqueous deposition method, followed by either thermal or chemical reduction. The materials were characterized by scanning and transmission electron microscopy, as well as X-ray diffraction. The MWCNT exhibit lengths of 200 μm (using ferrocene) and 30 μm (using nickelocene) and diameters around 50–70 nm. Pt nanoparticles showed sizes between 4 and 8 nm. The electrochemical active area toward the hydrogen oxidation reaction was evaluated by cyclic voltammetry (CV) in a standard three electrodes cell. In addition to corroborate the electrochemical active area, CO stripping tests were done. From both, the CV and CO stripping analyses, it was found that the synthesized electrocatalysts exhibited an electrochemical activity higher (140–230 m²gr⁻¹) than 10%Pt/Vulcan (Etek).     

Fatal intracerebral hemorrhage following thrombolytic therapy of embolic myocardial infarction in unsuspected infective endocarditis

Cerebral hemorrhage occurs in 0.2% of patients under the age of 60 years treated with thrombolytic therapy for acute myocardial infarction. A case of fatal cerebral hemorrhage following TPA therapy for myocardial infarction due to probable coronary artery embolism during unsuspected native valve infective endocarditis is reported.