New methods for proving the existence and stability of periodic solutions in singularly perturbed delay systems

We carry out a detailed analysis of the existence, asymptotics, and stability problems for periodic solutions that bifurcate from the zero equilibrium state in systems with large delay. The account is based on a specific meaningful example given by a certain scalar nonlinear second-order differential-difference equation that is a mathematical model of a single-circuit RCL oscillator with delay in a feedback loop.     

Inhomogeneous configurations of magnetization of ferromagnetic films with biaxial anisotropy

The system of the Landau-Lifshitz equations and magnetostatic equations for a ferromagnetic film with biaxial anisotropy and a Q-factor smaller than unity is reduced to a single scalar equation for the magnetostatic potential. Such a procedure is possible if the magnetization modulation scale in the sample considerably exceeds the characteristic magnetic length. The solutions to this equation describing inhomogeneous periodic magnetic configurations are obtained. The energy analysis of these configurations is carried out.     

Identification of dislocations and their influence on the recombination of charge carriers in gallium nitride

The relation between the density of etch pits revealed in GaN by etching in a KOH/NaOH eutectic and the density of dislocations determined by transmission electron microscopy (TEM) is studied along with the relation between the density of dislocations and the density of dark spot defects observed in GaN by microcathodoluminescence (MCL) and electron-beam-induced current (EBIC). It is demonstrated that selective etching is a reliable rapid method for the determination of the type and density of dislocations in GaN in the range 10⁶–10⁸ cm^?2, while MCL and EBIC can be used for the rapid nondestructive determination of the density of dislocations in the range 10⁶–10⁸ cm^?2. It is also found that some deep electron and hole traps are related to dislocations.     

Determination of the electric field gradient asymmetry from Berry’s phase in NQR of powder samples

An effect of Berry’s phase on the NQR spectrum of the rotating powder sample is described and applied for the determination of the electric field gradient asymmetry. The proposed method involves the analysis of the frequency singularities in the NQR powder patterns of the rotating samples. The Berry’s phases for the eigenstates, associated with an adiabatically changing quadrupole hamiltonian, are calculated for nuclei with a spin I = 3/2 and I = 1 as a function of the asymmetry parameter.     

Oxidative destruction of dinitrophenols by Fenton’s reagent in the presence of inorganic salts

The influence of inorganic salts on the kinetics of oxidation of 2,4-and 2,6-dinitrophenols by Fenton’s reagent, hydrogen peroxide, in the presence of iron(II) ions was studied.     

Intermolecular interactions of p-nitrophenol with butyl acetate,according to IR spectroscopic data

Infrared difference spectroscopy has been used to study the association of p-nitrophenol (NP) with butyl acetate (BA) in CCl₄ and in undiluted BA. It has been shown that in CCl₄, an associate is formed, [NP·BA] ·BA (Ia), in which one molecule of BA is linked to the NP by a hydrogen bond, and the second BA molecule is linked to the H-complex NP·BA by outer-sphere (dipole-dipole) interaction. In undiluted BA with low concentrations of NP, (Ia) is formed; with high concentrations of NP, an associate [(NP)₂BA] ·mBA is formed, in which two molecules of NP are bonded successively to each other and with a BA molecule; and the number of outer-sphere BA molecules may depend on the concentration of free BA molecules in the solutions.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 593–599, March, 1991.     

Anodic stripping coulometry with collection for absolute trace analysis of lead, using flow-through electrochemical cells with porous working electrodes

Summary Flow-through electrochemical cells with porous working electrodes made of crushed reticulated vitreous carbon and plated with mercury were used for absolute analysis of trace amounts of lead by anodic stripping coulometry with collection (ASCWC) in a flow system. The role of mercury coating, flow rate and pH were investigated. The coulombic content of the collection peak corresponded to the theoretical values calculated by Faraday's law in a concentration range from about 10^–9 to 10^–6 mol/l. The relative error and the relative standard deviation was +0.15% and 0.8%, respectively for 2×10^–6 mol/l analyte concentration. The absolute detection limit (3 s) was 0.1 ng of Pb, the linear response range 7×10⁴. One leave from: Department of Analytical Chemistry, Slovak Technical University, CS-812 37 Bratislava, Czechoslovakia