A Blume-Capel spin glass with competing crystal-field interactions on a hierarchical lattice

Renormalization-group methods are used with a hierarchical lattice to model a Blume-Capel spin glass with annealed vacancies and competing crystal-field interactions. The strength of competing cross-link interactions is progressively increased as the effects, upon the phase diagrams, are investigated. A series of phase diagrams have been produced, sinks interpreted, and critical exponents calculated for higher order transitions.     

Microstructures in interpenetrating polymer networks

Prevalence of patterned microstructures in interpenetrating polymer networks is well documented experimentally. Thermodynamic theories explaining this feature nonetheless have not been forthcoming. These enmeshed structures carry elastic energy and elevate in the thermodynamic limit the free energy of mixing. Yet why is the deviation from a supposed macroscopic phase separation? This confounding question needs to be answered; and in this paper a thermodynamic explanation is offered. Crosslinking is shown to reduce the effective driving force for macrophase separation. Long-range free energy of deformation gives rise to sinks in the phase evolution, suppressing long-wavelength (hydrodynamic mode) composition fluctuations which usually implode during spinodal decompositions, prodding macrophase separations. Consequently, nonequilibrium metastable structures with small phase domains would evolve. This study highlights lineaments of pattern in physical systems: a competition between short- and long-range forces or a time evolution of nonconserved order parameters or both. A new free energy of mixing is formulated to elucidate the structural novelties.     

A renormalization-group analysis of a spin-1 Ising ferromagnet with competing crystal-field and repulsive biquadratic interactions

Phase diagrams have been produced and critical exponents calculated for a Blume-Emery-Griffiths system with competing biquadratic and crystal-field interactions with uniform ferromagnetic bilinear interactions. This competition directly effects the clustering and density of nonmagnetic impurities. These results have been produced using renormalization-group methods with a hierarchical lattice. A series of planes of constant, repulsive biquadratic coupling have been probed while varying the temperature and concentration of annealed vacancies in the system. The sinks have been analyzed and interpreted, and critical exponents calculated for the higher order transitions.     

A study of over-reflection in Hartmann flow

Summary It is observed that Hartmann flow sustains wave propagation in its centre region for waves whose phase speed is less than the maximum flow speed. Similar to the previous observations it is found that viscous boundary layers around the critical level and at the wall replace the exponential regions and wave sinks required for over-reflection in the inviscid flow. The uniform magnetic field stabilizes the flow for small-wave-number disturbances along thez-direction. Over-reflection is confined to a few ranges of phase speeds for which the two boundary layers are close together rather than widely separated. These ranges correspond exactly to those for which unstable eigenmodes exist. Over-reflection is associated with a wave phase tilt opposite in direction to the shear. The authors of this paper have agreed to not receive the proofs for correction.     

Precipitation of γ′ phase and helium bubbles during proton and α-particle irradiation of nickel–silicon

Segregation of silicon was induced by light-ion irradiation at elevated temperatures in Ni–8Si specimens. Its occurrence at external surfaces, helium-induced cavities, dislocation loops, coherent twin boundaries, grain boundaries, and precipitate-matrix interfaces has been investigated by transmission electron microscopy. Layers of ordered γ^′ (Ni₃Si) phase were formed at most of these point defect sinks. The behaviour of grain boundary precipitation was found to be exceptional in various respects. In particular, a high rate of precipitation distinguishes grain boundaries from all other kinds of point defect sinks investigated here. This phenomenon of rapid precipitation was found to be adjoined to precipitation-driven grain boundary migration and is attributed to a radiation-induced “discontinuous” precipitate reaction. Observations of helium bubble distributions created during α-particle irradiations at growing dislocation loops and at migrating grain boundaries are also briefly discussed.     

On the theory of void formation during irradiation

A simple theory of the swelling of materials subjected to high energy particle irradiation is developed. Chemical reaction rate equations are used as a basis. Point defects, interstitials and vacancies, are assumed to be produced randomly throughout the solid. They move by random walk through the material until they cease to exist either by recombination with the opposite type of defect or by incorporation into the crystal at sinks such as dislocations, grain boundaries and voids. The rate equations for interstitials and for vacancies, which are coupled via the recombination term, are solved for steady state conditions under irradiation. Defect concentrations, supersaturations, recombination and total sink annihilation rates are obtained in terms of the production rate, sink annihilation probabilities, jump frequencies and thermal equilibrium concentrations of defects. The swelling rate is derived using sink annihilation probabilities at three principally different types of sinks, i.e. voids, sinks which have a bias with regard to the annihilation of interstitials and vacancies (such as dislocations), and sinks with no bias. The defect annihilation probabilities at void, precipitate, dislocation and grain boundary sinks are estimated by using a cellular model and solving the diffusion equation for geometries approximating that of the cells, e.g. a concentric sphere around a void. The relative effects of different types of sinks, i.e. the microstructure, on the swelling rate is discussed. The swelling rate is integrated to give swelling-time or swelling-dose relations, making some simplifying assumptions about the changes in the sink structure as the irradiation proceeds. It is shown that the relation obtained is rather sensitive to the type of assumptions made.     

Transverse-electric and transverse-magnetic beam modes beyond the paraxial approximation

Transverse-electric and transverse-magnetic beam modes are considered based on a theory in which complex dipole sources and sinks are oriented along the beam axis; the theory is similar to one that was previously presented for transverse dipoles. The field in the region of the waist is explored. Modes with such polarization have been reported from a wide range of laser types.     

Theoretical analysis of impurity precipitation in nanopores in crystals. II: Kinetics of impurity cluster growth in pores

The kinetics of the formation of impurity clusters in subsurface nanopores in crystals is studied theoretically. A physical model of precipitation of the impurity phase in nanopores in a sample with sinks of various types is developed. This model forms the basis for the calculation of the annealing kinetics of copper containing subsurface pores and cobalt impurity atoms. The optimal annealing conditions are determined in which cobalt atoms diffuse predominantly into pores and form impurity clusters in them.     

New phenomena in the adsorption of alkali metals on Al surfaces

Recent studies of the adsorption and co-adsorption of alkali metals on Al surfaces have revealed a wealth of hitherto unexpected phenomena, including: order-preserving phase transformations between metastable and stable structures; reconstruction of the substrate by adsorption at room temperature; and formation of binary and ternary surface alloys. The results of experimental structural determinations are reviewed, with the major emphasis on Low-Energy Electron Diffraction (LEED) studies of the ordered structures formed by adsorption of the alkalis on Al(111). The experimental results are compared where possible with corresponding results of ab initio calculations of total energy by Scheffler and co-workers. The experiment-theory comparisons provide valuable insight into the adsorption mechanisms, including the possible role of surface steps as both sources and sinks.     

A Neural Network-Based Optimization Of Thermal Performance Of Phase Change Material-Based Finned Heat Sinks—An Experimental Study

Experiments are conducted to determine the time to reach a set-point temperature for aluminum finned heat sinks filled with the phase change material n-eicosane. Results thus obtained are integrated with a feed-forward back-propagation artificial neural network to predict operating times. The artificial neural network prediction is then used to determine the optimum configuration that maximizes thermal performance. Four different plate-fin heat sink geometries filled with phase change materials giving rise to different volume fractions of the aluminum were experimentally investigated.     

Concentration dependence of diffusion-controlled processes among stationary reactive sinks

A multiple scattering theory of competition effects in diffusion-controlled reactions are presented. We consider a random array of stationary sinks which react with a density field of another reactant. Using the radiation boundary condition to describe the reaction at the surfaces of the sinks, we treat the modification of the density field due to reaction with sinks exactly. By keeping only the most divergent terms in a given order of scattering and summing them, we obtain the rate constant as a function of the sink concentration in the steady state. We also calculate the concentration-dependent diffusion constant of the density field. Both the rate and diffusion constants have nonanalytic behavior in the sink concentration.Alfred P. Sloan Foundation Fellow 1976–1980; John Simon Guggenheim Memorial Fellow 1979–1980.     

On the formation of defect clusters in neutron-irradiated Si

The formation of radiation-induced defect clusters in neutron-irradiated silicon have been studied by solving the semilinear parabolic reaction-diffusion coupled equations. It is found that most of primary displacement defects (interstitial and vacancy) would be annihilated by direct I–V recombination in an extremely short time, and a lot of divacancies would be formed meantime. In particular, the production of 4-vacancy defects is independent of the concentration of sinks and impurities in the sample, and of the energy of recoil particles. The threshold energy of vacancy cluster formation has also been investigated. The results are discussed and compared with experiment observations.     

散斑剪切干涉条纹特性的实验研究

本文通过位移位相存在的真实性实验、小孔滤波的必要性实验、位移梯度的解相关性实验,证实了散斑剪切于涉术的条纹是由物体变形所引起的“位移位相”和“位移微分位相”以及由位移和位移微分共同决定的“附加位相”之和的余弦条纹。实验证实这种余弦条纹的分布,随着滤波孔的位置而变化,它的衬比随着位移和位移梯度的增大而下降。特别是,当在象面上一点相遇的两个物点的象面散斑位移之差的模值大于散斑的直径时,两者相遇的象点上的条纹消失。     

Screening of a moving charge in a nonequilibrium plasma

Based on the model of point sinks, we consider the problem on the screening of the charge of a moving macroparticle in a nonequilibrium plasma. The characteristic formation times of the polarization cloud around such a macroparticle have been determined by the method of a three-dimensional integral Fourier transformation in spatial variables and a Laplace transformation in time. The screening effect is shown to be enhanced with increasing macroparticle velocity. We consider the applicability conditions for the model of point sinks and establish that the domain of applicability of the results obtained expands with decreasing gas ionization rate and macroparticle size. We consider the problem of charge screening at low velocities and establish that the stationary potential of the moving charge has a dipole component that becomes dominant at large distances. We show that the direction of the force exerted on the dust particle by the induced charges generally depends on the relationship between the transport and loss coefficients of the plasma particles in a plasma. When the Langevin ion recombination coefficient β _iL = 4πeμ _i exceeds the electron-ion recombination coefficient β _ei , this force will accelerate the dust particles in the presence of sinks. In the absence of sinks or when β _ei > β _iL , this force will be opposite in direction to the dust particle velocity. We also consider the problem on the energy and force of interaction between a moving charged macroparticle and the induced charges.     

Kinetics of high-temperature precipitation in dislocation-free silicon single crystals

The defect structure of dislocation-free silicon single crystals has been calculated using the approximate solution of the Fokker-Planck partial differential equations. It has been demonstrated that the precipitation starts to occur near the crystallization front due to the disappearance of excess intrinsic point defects on sinks whose role is played by oxygen and carbon impurities.     

Radiation enhanced diffusion in face centered cubic cu-zn alloys

The enhancement of diffusion by neutron irradiation has been investigated on a Cu-36 percent Zn alloy for various neutron fluxes and irradiation temperatures by means of in-pile measurements of electrical resistivity. For fresh samples the diffusion rate depends on temperature with an activation energy of 0.35 eV. During repeated irradiations the diffusion rate decreases and becomes nearly temperature independent. The variation of the concentration of interstitials and vacancies with irradiation time has been numerically calculated for various neutron fluxes, irradiation temperatures and sink concentrations. A comparison of the experimental and theoretical results shows that the point defects annihilate in fresh samples mainly by pair recombination and in samples which had been repeatedly cycled by pair recombination and at fixed sinks. Point defect clusters acting as sinks are created during the course of the irradiation as shown by electron microscope investigations. The radiation enhanced diffusion rate was found to depend on interstitials only, the activation energy of which was determined to 0.70 eV.     

Adsorption of tungsten on stepped tungsten surfaces studied by work function measurement

Work function measurements have been performed during the deposition of W on the (110)W plane and several stepped W surfaces with (110) terraces and different terrace width. For each sample the work function decreases with growing coverage. The total work function drop diminishes strongly with decreasing terrace width. The results are interpreted in terms of a reduced nucleation process on stepped surfaces as compared to the flat (110) plane. The step edges act as sinks for the deposited adatonis and cause in their proximity a “dead” zone for nuclei formation. Details of the work function change with coverage are discussed in terms of an edge roughening effect on stepped surfaces.     

Ultraviolet and visible Raman spectroscopy characterization of diamond–like carbon film growth by pulsed laser deposition

Laser-induced removal of flash from heat sinks in integrated circuit (IC) packages has been studied. It is found that flash can be effectively removed from heat sinks in plastic IC packages by laser deflashing. An optical microscope, an α-step surface profiler and X-ray photoelectron spectroscopy are used to analyze the deflashing efficiency. Laser deflashing of IC packages is based on laser ablation of flash materials. With an increase of laser fluence, the ablation rate increases. The laser fluence is selected between the ablation threshold of flash materials and that of heat-sink materials. An acoustic wave is generated by laser ablation of flash materials. Acoustic wave detection is used to monitor the surface cleanness during laser deflashing and to determine the ablation threshold of flash materials. Received: 18 April 2001 / Accepted: 14 September 2001 / Published online: 17 October 2001     

Kinetic analysis of dynamic point defect pinning in aluminium initiated by strain rate changes

The role of point defect production during deformation was examined by sealing the vacancy sinks in the grain boundaries with solutes to magnify its effect upon instantaneous strain-rate changes. AA1100 aluminium sheets were thermal-mechanically treated to result in a grain size of about 25 µm and in grain boundaries that were not capable of acting as efficient vacancy sinks. Tensile tests at various temperatures ranging from 78 to 300 K showed that above 195 K, the pinning effect could be quantitatively analysed. A rate equation analysis for mono- and di-vacancy recovery was adopted to perform fits to the deduced change in flow stress with time after strain-rate change from which apparent activation energies were derived. This examination indicates that the migrating species are predominantly di-vacancies. It is concluded that point-defect atmospheres have the capacity to glide in unison with mobile dislocations and hence are sensitive to the magnitude of the strain rate and temperature.