Quantitative analysis of the elemental composition and electron concentration in AlGaN/GaN heterostructures with a two-dimensional electron channel by means of SIMS and C-V profiling

The elementary composition and electron concentration in series of delta doped heterostructures Al _X Ga_{1 − X} N/GaN with a two-dimensional electron channel are investigated. Separation of the electron channel and the doping Si admixture is shown by a combination of SIMS and C-V profiling.     

Thermally activated diffusion of magnesium from bioapatite crystals

We have attempted to use heat treatment followed by ultrasonic treatment to separate the apatite from the non-apatite components of bone mineral in samples from different animals. The Mg content and the Ca/P ratio in the temperature range 560°C–720°C in the samples before and after ultrasonic treatment were determined by electron-probe x-ray microanalysis. Furthermore, we used atomic absorption spectrometry to measure the Mg content in powdered bone samples only after annealing and in distilled water, which was the “sonication” medium. We obtained evidence for thermally activated transition of Mg from a structurally bound state to a labile state at 680°C–720°C. At the same temperature, the Ca-deficient apatite is transformed to stoichiometric apatite. The data presented are evidence that crystals of Ca-deficient bioapatite are surrounded by Ca-enriched surface layers. As a result of thermal transformations at 680°C-720°C, all the Mg in the biomineral is found in the non-apatite environment surrounding the crystals and is removed by ultrasonic treatment, while the surface-localized Ca penetrates into the apatite lattice, restoring its stoichiometry. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 385–391, May–June, 2006.     

Numerical study of axisymmetric waves in an elastic cylindrical shell partially filled with a viscous liquid

Moscow Institute of Electronics and Mechanical Engineering. Translated from Prikladnaya Mekhanika, Vol. 24, No. 2, pp. 50–54, February, 1988.     

Conditions for the Formation of a Nonequilibrium Nonstoichiometric Layer on Pyrrhotite in Acid Solutions

Conditions for the formation of a nonequilibrium nonstoichiometric metal-deficient layer (NL) on natural pyrrhotites are studied, together with the NL electroreduction and the role NL plays in a nonoxidizing dissolution of pyrrhotite in solutions of sulfuric and hydrochloric acids. To estimate the NL weight, the charge connected with a cathodic peak at about –0.2 V (Ag/AgCl) is used. The peak reflects the irreversible reduction of NL with the formation of hydrogen sulfide, which is confirmed by SEM and XES data. Bulky NL forms in 0.5 M H₂SO₄at –0.1 to 0.0 V, where the nonoxidizing dissolution rate sharply alters, and at 0.5–1.1 V, where the pyrrhotite oxidation rate is high. The NL growth is controlled by solid-state diffusion, whereas nonoxidizing dissolution of iron is limited by diffusion at 20–30°C and a kinetic stage of dissolution of sulfur at higher temperatures.     

Electrochemical behavior of manganese in chloride-bromide-ammonium electrolytes

Halide-ammonium electrolytes were developed for electrochemical production of high-purity manganese.     

Some aspects of the behavior of shock-compressed polymers

The changes in the properties of certain polymeric materials subjected to the action of plane shocks of varying amplitude are discussed. Three loading techniques are employed — single, multiple, and high-frequency multiple loading — each accompanied by a different rise in the temperature of the polymeric material. The results show that the change in physicomechanical properties also varies with the loading technique.Volgograd Polytechnic Institute. Translated from Mekhanika Polimerov, No. 1, pp. 76–80, January–February, 1970.     

One-pot synthesis of 4-heteroaryl-1,2-dihydro-3-benzazepines from 3,4-dihydroisoquinolinium salts or pseudo bases

A novel one-pot synthetic route to the poorly studied 4-heteroaryl-1,2-dihydro-3-benzazepine motif from 3,4-dihydroisoquinolinium compounds is described. The synthetic approach is based on heterocyclic ring expansion of isoquinoline substrates upon reaction with chloromethyl-substituted heterocycles. The scope and limitations of the reaction were investigated to give a series of novel heteroaryl-3-benzazepines.     

Heats of solution of 1:1 electrolytes in 1,2- and 1,1-dichloroethane and derived enthalpies and entropies of transfer of electrolytes from water to these solvents

Heats of solution of nine electrolytes in 1,2-dichloroethane and of three electrolytes in 1,1-dichloroethane have been determined calorimetrically at various electrolyte concentrations and extrapolated to zero concentration to yield H _s ^o values for these electrolytes. It is shown that values of H _t ^o for transfer from water to the dichloroethanes of 11 electrolytes are often negative, so that these electrolytes can be more stable enthalpically in the less polar solvents. Combinations of the H _t ^o values with previously determined G _t ^o values yield values of S _t ^o for transfer of 11 electrolytes from water to the dichloroethanes. These S _t ^o values are mostly very negative; they can be correlated very well by the method of Abraham, and in this way S _t ^o values for transfer of numerous other anions and cations have been predicted. The Ph₄As⁺/Ph₄B^– convention yields single-ion entropies of transfer from water to the dichloroethanes in reasonable agreement with values calculated by the correspondence-plot method.     

MFI zeolite as adsorbent for selective recovery of hydrocarbons from ABE fermentation broths

1-Butanol and butyric acid are two interesting compounds that may be produced by acetone, butanol, and ethanol fermentation using e.g. Clostridium acetobutylicum. The main drawback, restricting the commercialization potential of this process, is the toxicity of butanol for the cell culture resulting in low concentrations of this compound in the broth. To make this process economically viable, an efficient recovery process has to be developed. In this work, a hydrophobic MFI type zeolite with high silica to alumina ratio was evaluated as adsorbent for the recovery of butanol and butyric acid from model solutions. Dual component adsorption experiments revealed that both butanol and butyric acid showed a high affinity for the hydrophobic MFI zeolite when adsorbed from aqueous model solutions. Multicomponent adsorption experiments using model solutions, mimicking real fermentation broths, revealed that the adsorbent was very selective to the target compounds. Further, the adsorption of butyric and acetic acid was found to be pH dependent with high adsorption below, and low adsorption above, the respective pKa values of the acids. Thermal desorption of butanol from MFI type zeolite was also studied and a suitable desorption temperature was identified.