Integral heats of solution and enthalpies of ionization of 100% nitric acid at 298 K 3. Aqueous solutions of sulfuric acid containing 70–90% H2SO4 and ionization of HNO3 as a base

The integral heats of solution of 100% HNO₃ at =0.1mole/liter in aqueous solutions of H₂SO₄ of <90% by wt. were measured. A scheme was proposed and proved for ionization of HNO₃ as a base in 82–90% aqueous solutions of H₂SO₄, according to which un-ionized HNO₃ exists in the form of an aqueous solvate H₂O-HNO₃ and the ionized form as the ion pair NO₂ ⁺·HSO₄ ^–. The value of the enthalpy of ionization of nitric acid H(NO₂ ⁺ HSO₄ ^–)=H(NO₂ ⁺·HSO₄ ^–) drops from 2.05 at 89.99% H₂SO₄ to 0.18 kcal/mole in 84.07% H₂SO₄.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 306–310, February, 1990.     

Kinetic method by using calorimetry to mechanism of epoxy-amine cure reaction

Four epoxy-amine reactions differing a number of the functional groups are compared. It has been shown that the main features of kinetics are similar for a whole family of model reactions. In series of epoxy-amine reactions analyzed, the reaction between resorcinol diglycidyl ether and m-phenylenediamine is one where increasing the viscosity of the reaction mixture leads to its vitrification during the reaction. This reaction proceeds very rapid compared with the model reactions. We demonstrate that application of kinetic techniques to analytical problems is facilitated by an understanding of the reaction mechanism involved. We report that thermokinetic method can be used for finding the activation energy in similar epoxy-amine systems through the use of times to point of the maximum in the experimental curve of the heat release rate vs. time. Our results indicate that independent of the initial reagent ratio, the conversion at the peak rate in the total curve the heat release ranges from 47 to 49%.     

Experimental evidence of time-delay-induced death in coupled limit-cycle oscillators

Experimental observations of time-delay-induced amplitude death in two coupled nonlinear electronic circuits that are individually capable of exhibiting limit-cycle oscillations are described. The existence of multiply connected death islands in the parameter space of coupling strength and time delay for coupled identical oscillators is established. The existence of such regions was predicted earlier on theoretical grounds [Phys. Rev. Lett. 80, 5109 (1998); Physica (Amsterdam) 129D, 15 (1999)]. The experiments also reveal the occurrence of multiple frequency states, frequency suppression of oscillations with increased time delay, and the onset of both in-phase and antiphase collective oscillations.     

Kinetic description of vacuum particle production in collisions of ultrarelativistic nuclei

The dynamics of partons that emerge as the result of quantum tunneling in a spatially uniform time-dependent field is studied under conditions prevalent in ultrarelativistic heavy-ion collisions. A self-consistent set of coupled equations that consists of the renormalized Maxwell equation and the Vlasov kinetic equation that involves a source and which is derived on a dynamical basis is solved numerically. The time dependence of the distributions of internal fields and currents for bosons and fermions is investigated within this back-reaction mechanism, and their momentum spectra are constructed. Clear evidence that oscillations in the time dependence of parton distributions in phase-space cells are of a stochastic character is obtained, and a significant irregularity in the momentum distribution on large time scales is found. If the influence of the back reaction is disregarded, these effects disappear completely, the oscillations becoming regular. A possible thermalization scenario for such a quasiparticle plasma is considered in the relaxation-time approximation. A locally equilibrium state is described within the two-component thermodynamics of particles and antiparticles. The possibility of introducing temperature under conditions of a strong vacuum polarization is discussed.     

Electromagnetic properties of zinc–nickel ferrites in the frequency range of 0.05–10 GHz

Zn_x-1Ni_xFe₂O₄ samples have been synthesized by solid-state reactions. Data on the chemical composition and the surface morphology of the samples have been obtained using a scanning electron microscope. X-ray powder diffractometer has been used to establish the phase purity and to determine the unit cell parameters. It has been found that the obtained samples had the spinel structure with Fd-3m (No. 227) space group. The unit cell parameters decrease with increasing nickel concentration. The magnetic characteristics of the obtained samples are determined and discussed. The Curie point of obtained samples varies in the range of 803.5–572.7 K. The maximum spontaneous magnetization of ~74.6 emu/g at room temperature was fixed for the solid solution with x = 0.6. The maximum value of the μ^/real part of ~12 and μ^//imaginary part of 6 of the permeability in the frequency range of 50 MHz–10 GHz is observed for the composition with x = 0.3. The composite samples for microwave study were prepared by mixing the ferrite powders with molten paraffin wax. The largest value of the μ^/ real part of ~3 and μ^// imaginary part of 0.63 of permeability is found for the x = 0.4 composite. The formation of the composite significantly reduces permeability.     

Anisotropy of the heat conduction,thermal emf,and Lorentz number in degenerate semimetals at low temperatures

The anisotropy of the heat conduction, thermal emf, and Lorentz number of degenerate semimetals at low temperatures, whose carriers possess an anisotropic energy spectrum, is investigated. It is shown that the anisotropy of heat conduction decreases with the reduction in temperature. At ultralow temperatures the diffusion thermal emf decreases proportionately to the temperature. The insignificant anisotropy of the thermal emf is due to the inelasticity of the electron collision.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 50–53, July, 1979.