A thermodynamic analysis of the formation of zirconium nitride from zirconium tetrachloride

Conclusions On the basis of a thermodynamic calculation of the heterogeneous system zirconium-nitrogen-hydrogen-chlorine the feasibility is demonstrated of obtaining zirconium nitride in the condensed state, with a virtually complete transformation of the metal into the nitride and a comparatively low expenditure of energy (about 80,000 kJ/kg), at temperatures of 2000–2400°K, a pressure of 1 bar, and a 50-fold dilution of the stoichiometric composition to a ZrNClH ratio of 1504200. Use of ammonia instead of nitrogen at the same ratio of the elements increases the amount of energy expended to 106,000 kJ/kg.Translated from Poroshkovaya Metallurgiya, No. 12 (156), pp. 1–3, December, 1975.     

Adaptive control system for the viscosity of viscose

Conclusions A structure and algorithm have been developed for an adaptive system for control of viscose viscosity in the manufacture of artificial fibres.The control system has been introduced into the ACS TP for viscose tire cord manufacture of the Svetlogorodsk Khimvolokno PO.Translated from Khimicheskie Volokna, No. 5, pp. 22–25, September–October, 1986.     

Increasing the wear-resistance of yarn-guide bend elements in liquid treatment of yarns

Conclusions The frictional force of yarns on yarn-guide bends in spinning and washing essentially does not depend on the linear density of the yarn or its rate of movement within the range 60–300 m/min.The frictional force of yarns on rings of artificial corundum is less than on rings of metal, Pyroceram, or glass.Special constructions of the elements of yarn-guid bends, which make it possible to reduce the length of contact of the yarn with the friction body, considerably reduce frictional force and, consequently, the yarn tension in the system.Translated from Khimicheskie Volokna, No. 3, pp. 43–44, May–June, 1986.     

Heat of combustion of liquid halogen-organic compounds

It is noted that in determining the heat of combustion of halogen-containing wastes, it is necessary to perform a multicomponent analysis, and know the heat of combustion of each component. A simplified algorithm is proposed for calculation of the calorific value of a halogen-organic mixture with respect to the lowest heat of combustion of chlorine and fluorine-containing organic substances. Results of the calculations differ negligibly from experimental data. __________ Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 1, pp. 13–14, January, 2007.     

Physical model of the formation of a periodic structure on the surface of pyrolytic graphite under high-energy ion bombardment

A physical model is proposed for the formation of a structure consisting of “micropoints” and “cavities” on the surface of pyrolytic graphite bombarded by 210 MeV Kr⁺ ions. This structure may be explained in terms of the depth distribution of the energy deposited by the bombardment. Pis’ma Zh. Tekh. Fiz. 23, 89–93 (July 26, 1997)     

Damping of bloch oscillations in quantum dot superlattices: A general approach

A quantum kinetic equation describing damping of the Bloch oscillations in ideal quantum-dot (QD) superlattices of various dimensionalities (1D, 2D, 3D) has been derived using the density matrix formalism. The possibility of suppressing completely single-phonon scattering by optical phonons and considerably suppressing the acoustic-phonon scattering in the QD superlattice by effectively controlling the spectrum by varying the DC electric field magnitude and orientation is demonstrated. Conditions ensuring that the only photon-scattering mechanism responsible for damping of the Bloch oscillations is scattering by acoustic phonons within transverse minibands of the Stark carrier-state ladder are obtained.     

Theory of threshold characteristics of semiconductor quantum dot lasers

A comprehensive theory of threshold characteristics of quantum dot (QD) lasers, which provides a basis for optimization of their design, is reviewed. The dependences of the gain, transparency current, threshold current, characteristic temperature, and multimode generation threshold on the parameters of the QD ensemble (surface density and size dispersion of QDs), cavity (stripe length and thickness of the waveguide region), heterocontacts (band offsets), and temperature are considered in detail. The limiting characteristics of the laser (optimum structure parameters, minimum threshold current density, and characteristic temperature of the optimized structure) are discussed at length. The results of the analysis may serve as direct recommendations for the development of QD lasers that significantly outperform the semiconductor lasers currently in use.     

Role of thermal ejection of carriers in the burning of spatial holes in quantum dot lasers

The role of thermal carrier ejection from quantum dots and free carrier diffusion in the burning of spatial holes in semiconductor quantum dot lasers is analyzed. The balance of the spatially inhomogeneous population inversion in the longitudinal direction of the cavity is shown to be controlled by thermal ejection from quantum dots. Because of this circumstance, hole burning in quantum dot lasers can show up more strongly and the threshold for multimode lasing can be lower than in semiconductor lasers with three-dimensional active regions or quantum-well lasers. The threshold for multimode lasing is determined as a function of the dispersion in the quantum dot size, cavity length, and temperature for structures that have been optimized to minimize the threshold current density of the fundamental mode. Fiz. Tekh. Poluprovodn. 33, 1076–1079 (September 1999)     

Electron localization and bloch oscillations in quantum-dot superlattices under a constant electric field

It is demonstrated that the electron spectrum in ideal two-dimensional and three-dimensional quantum-dot superlattices (SLs) under a constant electric field can be either discrete or continuous depending on the field orientation with respect to the SL crystallographic axes. In the latter case, the width of the resulting transverse miniband depends exponentially on the crystallographic index corresponding to the direction of the field. The electron localization area undergoes dramatic variations with the field orientation in the vicinity of the directions corresponding to the continuous energy spectrum. The Bloch oscillations in this kind of SL are considered. It is established that the scattering of oscillating electrons can be strongly suppressed by an appropriate choice of the field strength and direction.