Kinetics of nucleation of the solid phase in supercooled solutions or liquids under heat-insulating conditions: Intensive nucleation stage

The kinetics of decomposition of a supercooled melt or a viscous fluid under heat-insulating conditions during intensive nucleation has been investigated. Particles of a new phase have been studied, whose size is larger than the critical value, and for which the times are longer than the settling time of the classical quasi-steady state, which is characteristic of subcritical nuclei. The heat removal from the phase boundary is assumed to be the key process in the vicinity of a growing particle. The estimates of the duration of the stage of intensive nucleation, the maximum number of nucleated particles, and their average “size” have been obtained. Numerical simulations have been performed for nickel.     

Production and decay of subcritical nuclei in a solid solution

The decay of “subcritical” nuclei in a solid solution has been revealed in the investigation of the CuCl phase nucleation kinetics in glass. As soon as “supercritical” nuclei with an average radius R = 1.1 nm are created at 500°C, a sharp temperature increase up to 650°C transforms most nuclei created in the first annealing stage into “subcritical” ones, and this results in the decay of 80% of the nuclei in 5 min, while the remaining 20% of the nuclei grow in size to 2.4 nm. Their growth provides a sixfold increase in the CuCl phase growth rate against that in conventional annealing at 650°C. The kinetic dependences of the nucleation parameters—the amount of the phase and the average radius and concentration of the particles—were determined by the intrinsic absorption spectra of the CuCl nanocrystals. The critical radius of the CuCl nanomelt at 650°C has been estimated as 1.3 nm and the evaporation heat of the CuCl phase molecules in glass, as 13 kJ/mol. It is shown that multistage annealing makes it possible not only to control the parameters of the particles of the new phase, but also to determine the critical parameters of the initial nucleation stage.     

Influence of one-dimensional “defects” on the new-phase nucleation dynamics near the first-order transition in magnets

The evolution of a new-phase nucleus near the first-order spin-reorientation phase transition in magnets has been investigated. A strong influence of one-dimensional magnetic anisotropy “defects” on the nucleation dynamics has been shown. The conditions of the localization of the new-phase nucleus in the region of the magnetic anisotropy “defect” have been determined.     

Cold processing of green state LTCC with a CO2 laser

We report a novel “cold” self-cleaning technique for processing low temperature co-fired ceramic (LTCC) in the “green” state at high resolution and high speed, using a low power carbon dioxide laser. A particle ejection process involving both the ceramic grains and the organic binder produces material removal rates of >100 μm per pulse with lateral processing resolution of 50 μm and depth resolution comparable to ceramic grain size with no heat-effected zone or other deleterious thermal effects. The process has been used to drill microvias and to machine arbitrary shapes with high resolution. PACS 79.20.Ds; 42.62.Cf; 42.55.Lt; 81.20.Wk     

“Left-handed” state and polarization characteristics of waves in “semiconductor-magnet” superlattices

Dispersion properties of circularly polarized eigenwaves propagating in the “semiconductor-magnet” layered periodic structure along the axis of its periodicity and external magnetic field have been considered. The possibility of controlling the effective material parameters of the structure and the feasibility of negative refractive index for the wave with right (resonant) circular polarization has been shown. High magneto-optical activity of this gyrotropic structure has been ascertained, which leads to large Faraday rotation angles if the structure is in the state of “left-handed” medium.     

The impact of collisions on platelet distribution in the blood flow

The impact of platelet collisions on their distribution in a viscous liquid flow has been analyzed. It has been shown that platelet distribution in the flow perpendicular to current lines resulting from their collisions can be described as “shear” diffusion. In the wide physiological range of shear velocities specific for blood, the coefficient of “shear” diffusion is much larger than the coefficient of “Brownian” diffusion. For a parabolic fluid velocity profile (Poiseuille flow) in cylindrical vessel “shear” diffusion causes uneven radial distribution of platelets over the vessel radius. “Shear” diffusion causes platelet concentration to grow from the wall toward the center (vessel axis). This effect appears to be a consequence of the specific distribution of platelet collision frequency reaching its maximum at the vessel wall.     

Ion transport and solid state battery studies on a new silver molybdate superionic glass system: x[0.75AgI: 0.25AgCl]: (1-x)[Ag2O: MoO3]

Preparation, material characterization, ion transport and battery discharge characteristic studies are reported for a new silver molybdate glass system: x[0.75AgI: 0.25AgCl]: (1-x)[Ag₂O: MoO₃], where 0<x<1 in molar weight fraction. The traditional host AgI has been replaced by an alternate compound: “a quenched [0.75AgI: 0.25 AgCl] mixed system/solid solution”. Electrical conductivity (σ), ionic mobility (μ) and mobile ion concentration (n) measurements were carried out as a function of “x”. The composition: 0.8[0.75AgI: 0.25AgCl]: 0.2[Ag₂O: MoO₃] exhibited the highest conductivity (∼ 6×10⁻³ S·cm⁻¹) at room temperature and has been referred to as ‘optimum conducting composition (OCC)’. The compositional variation of “μ” and “n” revealed that the enhancement in the room temperature conductivity of OCC is predominantly due to the increase in mobile ion concentration. The XRD and DSC analysis on OCC indicated the formation of glassy phase with partial presence of unreacted polycrystalline phase of the host salt. The temperature dependence of various ionic transport parameters viz. “σ”, “μ”, “n” and ionic transference number (t_ion) were carried out on the OCC and the results have been discussed on the basis of theoretical models suggested for superionic glasses. In addition to this, solid state batteries were fabricated using OCC as electrolyte and discharge characteristics were studied under varying load conditions.     

Accelerated simulation of heat transfer in magnetic fluid hyperthermia

We have created a fast algorithm for calculating the temperature profile in a living tissue treated by magnetic fluid hyperthermia. Our algorithm solves an equation by the finite difference method. This equation includes the “heat sink” and “K-effective” effects. The algorithm need not an initial solution and it has the peculiarity that it makes a recursive division of the network, reducing thus the calculation period 5–9 times.     

Stochastic statistical theory of nucleation and evolution of nano-sized precipitates in alloys with application to precipitation of copper in iron

A consistent and computationally efficient stochastic statistical approach (SSA) is developed to study the kinetics of nucleation and evolution of nano-sized precipitates in alloys. To increase the accuracy of the method, many refinements of the previous simplified versions of this approach have been made. We consider a realistic vacancy-mediated exchange kinetics rather than the simplified direct-atomic-exchange model; use quantitative, cluster statistical methods rather than simple mean-field-type approximations; allow strong concentration and temperature dependences of generalized mobilities in the resulting kinetic equations; consider realistic alloy models based on first-principle calculations, and so on. We also introduce the “maximum thermodynamic gain” principle to determine the key kinetic parameter of the SSA, the characteristic length of local equilibrium in the course of the nucleation process. For several realistic models of iron-copper alloys studied, the results of the SSA-based simulations of precipitation kinetics made in this work agree well with the kinetic Monte Carlo simulation results for all main characteristics of the microstructure. The approach developed is also used to study the kinetics of nucleation and changes in microstructural evolution under variations of temperature or concentration.     

Development of carbon-carbon nozzle extension for liquid fuel rocket motors

Successful experience of RSC “Energy” and SPA “Iskra” in the development of carbon-carbon extension for oxygen-kerosene liquid fuel rocket motor has been summarized. Methodological approach that served to completion of carbon-carbon extension development in full and at comparatively small expenses has been described. Results of practical application of carbon-carbon extension for liquid fuel rocket motor 11D58M have been presented within the framework of International Space Program “Sea Launch”.     

Conductively-cooled,high-energy,single-frequency diode pumped slab laser for space applications

A laser-diode-pumped high efficiency, high pulse energy and single-frequency oscillator and amplifier for potential space environment applications have been developed and demonstrated using conductively-cooled heat removal. A diode-pumped injection seeded single-frequency oscillator was achieved by using the resonance-detection technique in Q-Switching operation, and Nd: YAG zigzag slabs based on “pump on bounce” are used in power amplifier stage for high-efficiency pulse energy extraction. Output pulse energy of 800 mJ with 11 ns pulse duration is obtained at a repetition rate of 100 Hz, with a near 3× diffraction-limit beam and an optical-to-optical efficiency of 18%. The experimental result shows that the laser has compact structure, high efficiency, reliability, conductive cooling and can be used for space environments.     

Entropy and Nonlinear Nonequilibrium Thermodynamic Relation for Heat Conducting Steady States

Among various possible routes to extend entropy and thermodynamics to nonequilibrium steady states (NESS), we take the one which is guided by operational thermodynamics and the Clausius relation. In our previous study, we derived the extended Clausius relation for NESS, where the heat in the original relation is replaced by its “renormalized” counterpart called the excess heat, and the Gibbs-Shannon expression for the entropy by a new symmetrized Gibbs-Shannon-like expression. Here we concentrate on Markov processes describing heat conducting systems, and develop a new method for deriving thermodynamic relations. We first present a new simpler derivation of the extended Clausius relation, and clarify its close relation with the linear response theory. We then derive a new improved extended Clausius relation with a “nonlinear nonequilibrium” contribution which is written as a correlation between work and heat. We argue that the “nonlinear nonequilibrium” contribution is unavoidable, and is determined uniquely once we accept the (very natural) definition of the excess heat. Moreover it turns out that to operationally determine the difference in the nonequilibrium entropy to the second order in the temperature difference, one may only use the previous Clausius relation without a nonlinear term or must use the new relation, depending on the operation (i.e., the path in the parameter space). This peculiar “twist” may be a clue to a better understanding of thermodynamics and statistical mechanics of NESS.     

Hysteresis Phenomenon in Deterministic Traffic Flows

We study phase transitions of a system of particles on the one-dimensional integer lattice moving with constant acceleration, with a collision law respecting slower particles. This simple deterministic “particle-hopping” traffic flow model being a straightforward generalization to the well known Nagel–Schreckenberg model covers also a more recent slow-to-start model as a special case. The model has two distinct ergodic (unmixed) phases with two critical values. When traffic density is below the lowest critical value, the steady state of the model corresponds to the “free-flowing” (or “gaseous”) phase. When the density exceeds the second critical value the model produces large, persistent, well-defined traffic jams, which correspond to the “jammed” (or “liquid”) phase. Between the two critical values each of these phases may take place, which can be interpreted as an “overcooled gas” phase when a small perturbation can change drastically gas into liquid. Mathematical analysis is accomplished in part by the exact derivation of the life-time of individual traffic jams for a given configuration of particles. This research has been partially supported by Russian Foundation for Fundamental Research and French Ministry of Education grants.     

Breather states and compound solitons in a ferromagnet-insulator-metal structure

Nonlinear dynamic states with a fine internal structure, such as breathers, “breather lattices,” kinks, kink-antikink bound states, and their spatially periodic generalizations have been constructed in terms of a modified Korteweg-de Vries equation for a system of magnetostatic waves in a ferromagnet-insulator-metal structure. Specific features of the nucleation, interaction, and transformation of these states have been studied in layered magnetic structures.     

Half-life estimation under indefinite “mother-daughter” relation

An algorithm has been proposed to build an estimate of the half-life of a “daughter” nucleus in case, when it is unknown, which nucleus is its “mother” (“indefinite start time”). For a decay of the “mother” at an instant t we can determine P—a probability of such a decay, if we assume that each “mother”, which has been decayed before t has equal chances to be “mother” of this “daughter”:

Kinetics of magnetization reversal in a thin La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> manganite film

The kinetics of magnetization reversal of a thin LSMO film has been studied for the first time. It is shown that the magnetic domain structure critically depends on the conditions of structure formation. In the demagnetized state (after zero-field cooling from T _c ), a maze-like domain microstructure with perpendicular magnetization is formed in the film. However, after field cooling and/or saturating magnetization by a field of arbitrary orientation, the [110] direction of spontaneous magnetization in the film plane is stabilized; this pattern corresponds to macrodomains with in-plane magnetization. Further film magnetization reversal (both quasi-static and pulsed) from this state is implemented via nucleation and motion of 180° “head-to-head” domain walls. Upon pulse magnetization reversal, the walls “jump” at a distance proportional to the applied field strength and then undergo thermally activated drift. All dynamic characterisitcs critically depend on the temperature when the latter varies around the room temperature.     

Filtered thermal contrast based technique for testing of material by infrared thermography

A new kind of thermal contrast, called “filtered contrast” is presented, which allows detecting and characterizing material defects using active thermography under some assumptions on physical and thermal parameters of materials. In opposition to known definitions of the thermal contrast, knowledge about defect-free area is not necessary and this contrast is less sensitive to nonuniformity of heat disposal to the material surface. The measurements were performed on an experimental setup equipped with a ThermaCAM PM 595 infrared camera and frame grabber. The step heating was chosen as heat excitation. The results demonstrate usefulness of the 1D model of heat transfer used for determination of depth of subsurface defects. The influence of the parameter of the smoothing filter, required for filtered contrast implementation, thermal parameters of the tested material and defect on expanded uncertainty of determination of defect depth is also presented. Due to significant complexity of the model of heat transfer, the conditions for the “law of propagation of uncertainty” were not fulfilled and a numerical method, i.e., Monte Carlo simulation is applied for the propagation of distributions.     

Transition to Longitudinal Instability of Detonation Waves is Generically Associated with Hopf Bifurcation to Time-Periodic Galloping Solutions

We show that transition to longitudinal instability of strong detonation solutions of reactive compressible Navier–Stokes equations is generically associated with Hopf bifurcation to nearby time-periodic “galloping”, or “pulsating”, solutions, in agreement with physical and numerical observation. In the process, we determine readily numerically verifiable stability and bifurcation conditions in terms of an associated Evans function, and obtain the first complete nonlinear stability result for strong detonations of the reacting Navier–Stokes equations, in the limit as amplitude (hence also heat release) goes to zero. The analysis is by pointwise semigroup techniques introduced by the authors and collaborators in previous works.     

Energetic and thermal performance of high-gain diode-side-pumped Nd:YAG rods

We investigated the energetic and thermal performance of a diode-side-pumped Nd:YAG rod laser with up to 50 W power deposited as excess heat into a 3-mm-diameter, 10-cm-length rod. The rod design produces an extremely flat gain profile resulting in “textbook” expressions of thermal lensing and birefringence. Thermal and energetic measurements are compared to corresponding “textbook” theoretical expressions. Discrepancies between various published thermo-mechanical YAG parameters are resolved by a self-consistent set of measured and calculated data for rod thermal lens focal lengths, birefringence depolarization and ratio of heat to stored energy (χ). Measured thermal and energetic performance under lasing and nonlasing conditions are presented, which agree with published theoretical expressions and measurements. Compensation of rod thermal lensing with simple spherical concave lenses is demonstrated. In addition various methods for compensating birefringence depolarization are theoretically and experimentally analyzed and compared. Received: 19 July 1999 / Revised version: 22 October 1999 / Published online: 23 February 2000     

Thermodynamic crisis of boiling

The procedure of calculation of the dynamics of rapid near-wall vaporization near a metallic heater is considered. A physical model of explosive boiling-up on bubbles of fluctuation origin is used. The model is limited to regimes when the motion of bubbles can be ignored and convective flows do not have enough time to develop. It is assumed that the dry spot under a bubble thermally insulates the heater wall. The heat removal is provided by the vicinity of the wetting line (WL). An analytical calculation has become possible on the basis of the well-known exact solution to the problem of the temperature field near the wetting line. Generalization of this solution has led to two new problems. These are the problem of allowance for the difference of the dynamic wetting angle from the right angle and that of allowance for thermocapillary flows. A numerical comparison of the results of calculation of the dry area with the use of different methods of allowing for the “tightness” effect in the dynamics of bubble generation and growth has been made. The evolution of bubbles from their generation to growth limited by the heat supply has been investigated. It has been found that the transition stage in the development of bubbles from Rayleigh to thermal ones is of considerable importance in the processes of explosive boiling-up. The dynamics of change in the dry area and wetting line length prior to the stage of bubble merging into a vapor film has been calculated. A condition of passage of the heat flux through a maximum is found. The applicability of the idea of thermodynamic crisis to calculations of miniature devices is justified. The problem of constructing a model to calculate the interphase surface shape near the wetting line under a developed thermocapillary flow and considerable reactive forces of the vapor flow is formulated. The model is in good agreement with the results of experiments on pulsed superheating of liquids at a rate higher than 1 K/μs.