Energy characteristics of a carbon monoxide gasdynamic laser

The characteristics of gasdynamic lasers based on mixtures of carbon monoxide with nitrogen and inert gases were investigated and the populations of vibrational levels of CO molecules, the gain of the mixture, and the generation power were determined in [1–8]. But the parameters of a gasdynamic laser (GDL) in the optimum emission mode have not been determined up to now. The difficulties in calculating the optimum energy characteristics are connected with the complexity of the calculating model and the large number of parameters of the system. The energy characteristics of a CO gasdynamic laser are calculated and optimized in the present report on the basis of a simple model.Translated from Zhurnal Prikladnoi Mekhaniki Tekhnicheskoi Fiziki, No. 5, pp. 16–23, September–October, 1978.     

Interaction between phase transformations and dislocations at the nanoscale. Part 1. General phase field approach

Thermodynamically consistent, three-dimensional (3D) phase field approach (PFA) for coupled multivariant martensitic transformations (PTs), including cyclic PTs, variant–variant transformations (i.e., twinning), and dislocation evolution is developed at large strains. One of our key points is in the justification of the multiplicative decomposition of the deformation gradient into elastic, transformational, and plastic parts. The plastic part includes four mechanisms: dislocation motion in martensite along slip systems of martensite and slip systems of austenite inherited during PT and dislocation motion in austenite along slip systems of austenite and slip systems of martensite inherited during reverse PT. The plastic part of the velocity gradient for all these mechanisms is defined in the crystal lattice of the austenite utilizing just slip systems of austenite and inherited slip systems of martensite, and just two corresponding types of order parameters. The explicit expressions for the Helmholtz free energy and the transformation and plastic deformation gradients are presented to satisfy the formulated conditions related to homogeneous thermodynamic equilibrium states of crystal lattice and their instabilities. In particular, they result in a constant (i.e., stress- and temperature-independent) transformation deformation gradient and Burgers vectors. Thermodynamic treatment resulted in the determination of the driving forces for change of the order parameters for PTs and dislocations. It also determined the boundary conditions for the order parameters that include a variation of the surface energy during PT and exit of dislocations. Ginzburg–Landau equations for dislocations include variation of properties during PTs, which in turn produces additional contributions from dislocations to the Ginzburg–Landau equations for PTs. A complete system of coupled PFA and mechanics equations is presented. A similar theory can be developed for PFA to dislocations and other PTs, like reconstructive PTs and diffusive PTs described by the Cahn–Hilliard equation, as well as twinning and grain boundaries evolution.     

Amplification of the emission of a CO2 laser in the products of the reaction of carbon monoxide and nitrous oxide

To produce laser-active gaseous media, and to investigate their characteristics, it is convenient to use expanding gasdynamic flows [1–4], and high-speed chemical reactions [5, 6]. The idea of a chemical-gasdynamic laser [7, 8], based on a combination of the chemical and gasdynamic methods of producing population inversion is of interest. In this paper we investigate the conditions under which population inversion of the vibrational levels of the CO₂ molecule can be produced in expanding flows of different gaseous mixtures containing CO₂, including the products of the reaction between NO and CO with the addition of a small amount of hydrogen, and when the initial mixture is diluted with nitrogen or argon. The effect of the composition of the initial mixture and the temperature in front of the nozzle on the gain of the coherent emission at a wavelength of 10.6 μm in the working cross section of the flow is investigated.     

Characterization of phase detection optical probes for the measurement of the dispersed phase parameters in sprays

In order to be able to investigate the characteristics and the spatial evolution of dense sprays produced by coaxial injectors for instance, a measuring technique based on a phase detection optical probe has been developed. Conical optical probes have previously been successfully used in bubbly flows. Aside local concentration, the velocity of gas inclusions was deduced from the analysis of the dewetting time, and, combined with the gas residence time, the bubble size was obtained. Here, it is shown that this technique can also be helpful for the measurements of drop characteristics in dense sprays. Using controlled conditions in terms of drop size, velocity and trajectory, it is demonstrated that for drops above 30 μm in diameter, the velocity and size are evaluated with an uncertainty less than about 15% including variations in the impact conditions. An adapted signal processing has been developed which is shown to be weakly sensitive to the various criteria introduced. When applied to sprays generated by a two-dimensional gas–liquid mixing layer, volumetric fluxes measured by the probe are shown to agree within 15% with a sampling technique. To illustrate the capability of this fairly objective tool, some results are provided and analyzed for the drop velocities and chords as well as for the concentration and the interfacial area density in the near field of dense sprays with a wide size distribution.     

Synchronization and phase relations in the motion of two-pendulum system

The synchronization phenomenon in non-linear oscillating system is studied by means of examination of the coupled pendulums. Dependence of the phase shift between pendulum states on system parameters and initial conditions is studied both analytically and numerically. The harmonic linearization technique is applied for analytical examinations.     

Kinetic relations and the propagation of phase boundaries in solids

This paper treats the dynamics of phase transformations in elastic bars. The specific issue studied is the compatibility of the field equations and jump conditions of the one-dimensional theory of such bars with two additional constitutive requirements: a kinetic relation controlling the rate at which the phase transition takes place and a nucleation criterion for the initiation of the phase transition. A special elastic material with a piecewise-linear, non-monotonic stress-strain relation is considered, and the Riemann problem for this material is analyzed. For a large class of initial data, it is found that the kinetic relation and the nucleation criterion together single out a unique solution to this problem from among the infinitely many solutions that satisfy the entropy jump condition at all strain discontinuities.     

On the phase transitions in fluid mixtures

Summary The integral equations of balance for a binary fluid mixture are stated when the mixture presents two phases which are separated by an interface. The equilibrium conditions are derived together with the Gibbs phase rule for plane interfaces. The theory is extended to the mixture with three phases.

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Sommario Si scrivono le equazioni integrali del bilancio per una miscela fluida binaria che una interfaccia separa dalla miscela del suo vapore. Si derivano le condizioni di equilibrio e, nel caso di interfaccia piana, la regola delle fasi di Gibbs. La teoria proposta è poi estesa a sistemi di miscela binaria con tre fasi.

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This paper is made under the auspices of G.N.F.M. of the Italian C.N.R.     

Visual receiver for the phase contrast refractometer

Summary The accuracy of a visual photometric meter is limited by the luminance discrimination ratio ΔB/B of the eye, which, in the present case, is about 2 per cent. The unit, utilizing polarizers, measures optical paths to within 0.003 λ. The efficiency is compared with that of the photoelectric receiver, and accuracy values for some applications, including analyses of the isotope mixtures D₂O¹⁶/H₂O¹⁶ and H₂O¹⁸/H₂O¹⁶, are given.     

Interface propagation and microstructure evolution in phase field models of stress-induced martensitic phase transformations

Analytical solutions for diffuse interface propagation are found for two recently developed Landau potentials that account for the phenomenology of stress-induced martensitic phase transformations. The solutions include the interface profile and velocity as a function of temperature and stress tensor. An instability in the interface propagation near lattice instability conditions is studied numerically. The effect of material inertia is approximately included. Two methods for introducing an athermal interface friction in phase field models are discussed. In the first method an analytic expression defines the location of the diffuse interface, and the rate of change of the order parameters is required to vanish if the driving force is below a threshold. As an alternative and more physical approach, we demonstrate that the introduction of spatially oscillatory stress fields due to crystal defects and the Peierls barrier, or to a jump in chemical energy, reproduces the effect of an athermal threshold. Finite element simulations of microstructure evolution with and without an athermal threshold are performed. In the presence of spatially oscillatory fields the evolution self-arrests in realistic stationary microstructures, thus the system does not converge to an unphysical single-phase final state, and rate-independent temperature- and stress-induced phase transformation hysteresis are exhibited.     

饱和砂土相变和峰值状态的研究

在实验室内运用TSZ-1全自动三轴仪,对重塑饱和砂土进行了一系列不同排水条件下的三轴剪切试验。通过控制土样的初始孔隙比、围压及其排水条件,设计了三轴试验的方案。对试验结果进行了分析,研究了相变点、峰值点与饱和砂土的初始孔隙比、围压之间的线性规律,并建立了相应关系式,为进一步基于相变和峰值建立饱和砂土的本构关系提供基础。     

Bounds on the phase speed and growth rate of the extended Taylor-Goldstein problem

In this paper we consider the extended Taylor-Goldstein problem of hydrodynamic stability dealing with the stability of stratified shear flows in sea straits of arbitrary cross section. For this problem we have obtained the upper and lower bounds on the phase velocity of neutral modes and estimates for the growth rate of unstable modes. Furthermore, we have found a semielliptical instability region depending on the minimum Richardson number and parabolic instability regions which intersect the semielliptical instability region for a class of basic flows.     

RESEARCH ON METHOD TO CALCULATE VELOCITIES OF SOLID PHASE AND LIQUID PHASE IN DEBRIS FLOW

Velocities of solid phase and liquid phase in debris flow are one key problem to research on impact and abrasion mechanism of banks and control structures under action of debris flow. Debris flow was simplified as two-phase liquid composed of solid phase with the same diameter particles and liquid phase with the same mechanical features. Assume debris flow was one-dimension two-phase liquid moving to one direction, then general equations of velocities of solid phase and liquid phase were founded in two-phase theory. Methods to calculate average pressures, volume forces and surface forces of debris flow control volume were established. Specially, surface forces were ascertained using Bingham's rheology equation of liquid phase and Bagnold's testing results about interaction between particles of solid phase. Proportional coefficient of velocities between liquid phase and solid phase was put forward, meanwhile, divergent coefficient between theoretical velocity and real velocity of solid phase was provided too. To state succinctly before, method to calculate velocities of solid phase and liquid phase was obtained through solution to general equations. The method is suitable for both viscous debris flow and thin debris flow. Additionally, velocities every phase can be identified through analyzing deposits in-situ after occurring of debris flow. It is obvious from engineering case the result in the method is consistent to that in real-time field observation.