Determination of Ascorbic Acid by Electrocatalytic Response of an Electrode Coated with Polyvinylpyridine Film and Palladium-Plated

A procedure was developed for analysis of ascorbic acid with a carbon glass electrode coated with a palladium-modified poly(2-vinylpyridine) film.     

Eigenvalues of the antiplane-shear crack problem for a power-law material

This paper discusses the problem of finding the eigenvalue spectrum in determining the stress and strain fields at the tip of an antiplane-shear crack in a power-law material. It is shown that the perturbation method provides an analytical dependence of the eigenvalue on the material nonlinearity parameter and the eigenvalue of the linear problem. Thus, it is possible to find the entire spectrum of eigenvalues and not only the eigenvalue of the Hutchinson-Rice-Rosengren problem. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 1, pp. 173–180, January–February, 2008.     

High pressure elastic and plastic deformations of silica: In situ diamond anvil cell Raman experiments

Normal silica glass is usually referred to as low density amorphous silica as it can be converted to high density amorphous silica by a hydrostatic pressure (polyamorphic transition). In this work in situ Raman experiments are performed in a diamond anvil cell up to 18 GPa. The pressure effects on the structure of silica after successive compression decompression experiments are analyzed. The mode Grüneisen parameters corresponding to the elastic compression of high density amorphous silica are obtained and compared with those of normal silica. A reorganization of the high density amorphous silica below 3 GPa is evidenced.     

Specific features of the formation of submicron inclusion in Ti:sapphire

Specific features of the formation of submicron (70–300 nm) inclusions in Ti:sapphire (Al₂O₃:Ti) grown in a carbon-containing medium have been investigated. These inclusions are caused by deviation from the melt stoichiometry and are formed during the melt-crystal phase transition. These defects are submicropores containing excess aluminum and its suboxides; they can be destroyed by thermal loading of a crystal.     

Predicting the onset of DNA supercoiling using a non-linear hemitropic elastic rod

Elastic rod models provide a means to interpret single molecule DNA experiments as well as predict DNA behavior under physiological conditions. Here we use an elastic rod model to predict the stability boundary (critical torque vs. applied tension) for single molecule DNA experiments in which the molecule is subjected to applied tension and twist. We discuss the shortcomings of the usual isotropic rod model. We then derive a consistent non-linear material law from the general representation for a hemitropic (chiral) rod. Finally, we present results of a standard bifurcation analysis predicting the stability boundary. We find results from the non-linear hemitropic rod to match the data closely.     

Thermal degradation of composites of poly(methyl methacrylate) with alkoxysilane hydrolyzates

Organic-inorganic composites of poly(methyl methacrylate) with alkoxysilane hydrolyzates form transparent films. Their thermal and oxidative thermal degradation were studied by differential scanning calorimetry and thermogravimetric analysis.     

Diethoxyphosphinyl acetic acid hydrazide: a uniquely versatile reagent for the preparation of fused [5,5]-, [5,6]-, and [5,7]-3-[(E)-2-(arylvinyl)]-1,2,4-triazoles

Diethoxyphosphinyl acetic acid hydrazide is a unique reagent that provides a convenient and efficient process to prepare fused [5,5]-, [5,6]-, and [5,7]-3-[(E)-2-(arylvinyl)]-1,2,4-triazoles from aldehydes and alkoxyimines. The process involves three steps without isolation of any intermediates to afford 1,2,4-triazoles in modest to excellent overall yield.     

Basins of Attraction of Periodic Oscillations in Suspension Bridges

We consider the dynamics of the lowest order transversal vibration mode of a suspension bridge, for which the hangers are treated as one-sided springs, according to the model of Lazer and McKeena [SIAM Review 58, 1990, 537]. We analyze in particular the multi-stability of periodic attractors and the basin of attraction structure in phase space and its dependence with the model parameters. The parameter values used in numerical simulations have been estimated from a number of bridges built in the United States and in the United Kingdom, thus taking into account realistic, yet sometimes simplified, structural, aerodynamical, and physical considerations.