Competitive homolytic and heterolytic dediazoniation mechanisms: Rate constants and product distribution of methoxy‐, hydroxy‐, and hydro‐dediazoniation of 3‐ and 4‐methylbenzenediazonium salts in acidic MeOH/H2O mixtures

The rates and product distribution for methoxy‐, hydroxy‐ and hydro‐dediazoniation and the rate constants for disappearance of 3‐ and 4‐methylbenzenediazonium tetrafluoroborate in acidic MeOH/H₂O mixtures, in the presence and absence of electrolytes like HCl, NaCl, and CuCl₂, are reported. Data were obtained by using a combination of VIS‐UV and HPLC techniques. The kinetics and product distributions are completely consistent with competitive homolytic and heterolytic mechanisms, the heterolytic one being predominant at any solvent composition. Heterolytic data are in agreement with the predictions of a D_N + A_N mechanism; that is, rate determining formation of an aryl cation that reacts immediately with available nucleophiles. Selectivity values, determined from product yields, are low and independent of solvent composition. Product formation is discussed in terms of a preassociation step between aryl cations and the nucleophile, which does not account for much of the trapping, and a nucleophilic attack on a “free” arenediazonium cation. Activation parameters were also determined at 99.5% MeOH: enthalpies of activation are high and entropies of activation are positive, and they are similar to those reported for pure water. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 210–220, 2000     

MRI and diabetic foot infections

The role of magnetic resonance imaging and plain radiographs in evaluating osteomyelitis in the diabetic foot was studied. Fifty patients were prospectively examined by magnetic resonance imaging and plain radiographs to determine the extent of infection. Thirty-seven patients had positive MRI for osteomyelitis and 19 were positive with conventional radiography. Thirteen patients had negative MRI healed with short course of antibiotics. Five patients with positive MRI received four weeks' course of intravenous antibiotics with two still having persistent infection in the six weeks follow-up. Thirty-two patients underwent surgery with favorable results. Sixty-two bone specimens were obtained for histologic evaluation of osteomyelitis. In cases with histologic proof of diagnosis, magnetic resonance sensitivity was 99%, specificity was 81%, and accuracy was 94%. Thus magnetic resonance imaging was shown to have a high sensitivity, specificity, and accuracy in detecting osteomyelitis.     

Experiments and analysis on the melting of a semitransparent material by radiation

The purpose of this study was to obtain an improved understanding of the physical processes which occur during the melting of a semitransparent material for the case where the melting is effected by irradiation of the material. An analytical model was developed for predicting radiative and thermal conditions, as well as the liquid/solid interface displacement, during the radiation induced phase-change process. Parametric calculations were performed to determine the extent of the influence of some fourteen identifiable dimensionless parameters on the temperature distribution and liquid/solid interface motion. Experimental simulations were conducted in the laboratory using a high intensity lamp to melt a phase-change material within a carefully controlled environment. Provisions were made for measurement of the temperature and the liquid-solid interface displacement. Comparison between the model predictions and the experimental data is shown to be in very good agreement.     

Determination of Weibull's parameters on flexure strength of round beams of aluminum-copper alloy and cast iron

Weibull's parameters for the three-point bending of a round bar specimen made of aluminum-copper alloy and cast iron, both white and grey, are obtained to predict the cumulative probability of fracture. Unlike the rectangular beam specimens which are more sensitive to changes in the boundary conditions, results for the round bar specimens are better behaved and expressed in terms of the cumulative probabilities of fracture. Specimen size effects were overshadowed by variations in the material properties caused by unequal cooling rates and inhomogeneities in the material microstructure.     

Vapor-liquid equilibria forn-tetradecane-benzene mixtures at 25 and 50°C

Vapor pressures for the benzene+n-tetradecane system have been measured using a static apparatus. The excess Gibbs free energy was calculated using a modified Barker method and a Pade approximant equation. The selection of the most adequate approximation is discussed. Results are compared with those corresponding to other thermodynamic properties. The activity coefficient of benzene at infinite dilution calculated from these data agrees well with the value obtained from the literature.     

On polynomial EkP matrices

In this paper the relation betweenEP--matrices andE ^k P--matrices over an arbitrary filedF is studied. Further, conditions for the product ofE ^k P--matrices to be anE ^k P--matrix and for the reverse order law to hold for the polynomial Moore-Penrose inverse of the product ofE ^k P--matrices are determined     

Evaluation of a fibre optic device in solution equilibria studies. Application to 3-hydroxybenzoic acid ionization

The use of a fibre optic device for spectrophotometric measurements in solution equilibria studies is presented. In particular the precision obtainable with such equipment is evaluated as a function of different experimental conditions, such as path length, averaging time and stirring of the solution. Analysis of 3-hydroxybenzoic acid ionization is presented to assess the results obtained in the study of an equilibrium system.