Incoherent Patterns Research Articles

Generation and absorption of characteristic X-rays under dynamical electron diffraction conditions

The theory for formation of incoherent channelling patterns (ICPs), produced by variations in characteristic X-ray emission in response to a systematic scan in the direction of the incident electron beam for orientations near a zone axis, is extended to account for absorption of X-rays within the specimen. This is achieved by calculating the probability of X-ray generation as a function of depth within a crystal prior to the inclusion of an absorptive term which is dependent on the geometry of the X-ray detector relative to the crystal as well as the absorption characteristics of the specimen for the particular X-ray energy. ICPs from three major zones of the L1 0 phase in Ti Al and Ti Ga alloys are compared and effects of different absorption due to variation of goniometer tilt with respect to the X-ray detector are calculated. Although fast electron quantum states that are peaked on Ti atomic sites have similar eigenvalues (binding energies) in both alloys, it is shown that differences in complex eigenvalues (including absorption) occur between states that are localized on Al or Ga, and that this results in substantially different contrast between the two alloys in ICPs from Al and Ga characteristics X-rays.

Statistical ALCHEMI: Aeneral formulation and method with application to Ti[sbnd]Al ternary alloys

Abstract Recent advances in the theory of characteristic X-ray emission from crystals under dynamic electron diffraction conditions are used in developing a new fully quantitative statistical method for atom location by channelling-enhanced microanalysis (ALCHEMI). Limitations imposed by delocalization, disorder and occupancy of interstitial sites are clarified. A fully computerized method for automated data collection and analysis from incoherent channelling patterns formed by the variation in characteristic X-ray emission as a function of orientation is used for the fist time. The precision and accuracy of this method are investigated using both experimental and simulated data from the ordered γ phase in ternary Ti[sbnd]Al alloys. It is shown that 1 at. % Ga, Hf and Mo additions partition onto Al sites, Ti sites and both sites respectively, and contrast in X-ray incoherent channelling patterns conforms that these ternary atoms are not located on interstitial sites. The traditional ratio ALCHEMI techniqu...

Zone-axis convergent-beam electron diffraction and ALCHEMI analysis of Ti[sbnd]Al alloys with ternary additions

Abstract A new statistical method for atom location by channelling-enhanced micro-analysis is applied to γ [sbnd] α2 duplex Ti[sbnd]Al based alloys containing ternary element additions of V, Cr, Mn, Ga, Y, Zr, Nb, Mo, La, Hf, Ta and W at the 1 at.% level. Incoherent channelling patterns, formed by the variation in characteristic X-ray emission as a function or orientation, are collected from a number of different zone axes from both phases. Comparisons of experimental patterns with calculated maps for various crystallographic sites indicate that the ternary atoms are incorporated substitutionally in the atomic structure of both the γ and the α2-phases and do not occupy interstitial sites. The crystallographic site distribution of the ternary elements is determined through χ2-minimization techniques, together with quantitative error limits. The structure of the non-stoichiometric α2-phase is investigated by convergent-beam electron diffraction.

Incoherent pattern detection using a liquid-crystal active lens

Incoherent pattern detection by a simple imaging system using a liquid-crystal active lens is proposed. The imaging system works as a spatial filtering system with a rewritable phase-only filter. We found that, in the incoherent matched filtering system, a conventional phase-only filter has a higher optical efficiency but a lower pattern discrimination than a complex filter. To improve the pattern discrimination ability, we optimized the phase-only filter by using simulated annealing and a genetic algorithm. We designed phase-only filters that have discrimination ability comparable with that in a complex filter. The performance of optimized phase-only filters is experimentally demonstrated.

Optical Image Combination and Logic AND Operation Using Beam Fanning Effect

Using the beam fanning effect in a BaTiO3 crystal, we propose two simple set-ups to perform the function of an optical image combiner and an optical AND gate respectively. The optical image combiner combines two mutually coherent as well as mutually incoherent patterns transmitted to it separately into a single coherent pattern. This set-up can also be used as an optical OR gate. For the AND gate, the two input signals may also be mutually coherent or incoherent. Experimental results showed the response time of these two devices to range from 0.01 second to 2.5 seconds.

MULTICOMPONENT NON-ISOTHERMAL ADSORPTION DYNAMICS

The present state of the theoretical basis of adsorption dynamics of multicomponent mixture with account for thermal effects accompanying adsorption is presented. Theoretical models for the non-isothermal kinetics and dynamics of adsorption in multicomponent mixtures are analyzed. A classification of these models is given, and model equations accounting for all major qualitative physicochemical features of heat and mass transfer through interfaces and in the intergranular space of porous media are presented. The following topics are considered: (1) Considerable role of thermal effects in the adsorption and desorption processes; (2) Considerable interaction of mixture components due to the non-linear nature of the adsorption isotherms of the mixture; (3) Considerable dependence of heat and mass transfer coefficients on concentration of mixture component and temperature; (4) Considerable effect of the mutual diffusion of the mixture component; (5) The role of the thermal diffusion effect (the Soret effect) and the diffusion-thermal effect (the Dufour effect) on heat and mass transfer when local concentration and temperature gradient inside the porous grains of the adsorbents are significant. The effect of slow heat and mass kinetics on the nature of distribution of concentration and temperature in the adsorber is considered. The qualitative differences between the equilibrium theory and non-equilibrium theory of multicomponent non-isothermal adsorption dynamics are shown. The coherent (steady) and incoherent (transient) patterns of concentration and thermal waves in the adsorber are analysed. The conditions of existence of the frontal patterns of mixture separation are found, and simple formulae estimating major parameters of frontal behavior in adsorption separation of mixture, which take into account of all basic qualitative features of interphase heat and mass transfer outlined in items (1) trough (5) above, are given

Coherent and incoherent frontal patterns of multicomponent adsorption dynamics for variable linear fluid velocity in the fixed bed—I. Frontal patterns for linear adsorption isotherms

The coherent constant and proportional patterns for the equilibrium and nonequilibrium models of adsorption dynamics have been analyzed for linear adsorption isotherms at variable linear fluid velocity in the fixed bed. The Riemann, R k , and L i invariants are found in the simple analytical form. The conditions of existence of the coherent patterns are obtained for the equilibrium and nonequilibrium models. The influence of the dispersive factors (kinetics and longitudinal dispersion) on the nature of the concentrations distributions is considered. For different nonequilibrium theoretical models, the simple formula is derived to calculate the mass transfer zone for the coherent constant patterns. It is shown that the dispersive factors can convert coherent patterns into incoherent ones.

Incoherent pattern recognition with phase-only filters

Phase-only and binary-phase spatial light modulators can be employed in the filter plane of incoherent pattern recognitionsystems. We employ computer simulations to show that advanced filter design techniques can be used to achieve a close approximation to classical matched filtering.

Medium-energy electron diffraction from Cu(100).

We have investigated the polar-angle dependence of medium-energy electron diffraction (MEED) from a Cu(100) surface. It is observed that MEED is characterized by a combination of coherent and incoherent scattering, and the incoherent part is governed by the forward-scattering mechanism. The incoherent MEED pattern differs from that of x-ray photoelectron diffraction and Auger electron diffraction because of the angular distribution of the initial electron scattering. The asymmetry between the incident-beam and exit-beam diffraction is also observed and discussed.

Coherent and incoherent frontal patterns for multicomponent dynamics of adsorption—I. Analysis of frontal-pattern isothermal adsorption dynamics for convex mixture isotherms of adsorption

Abstract Theoretical models have been analysed taking into account all major distinctive features of the interphase mass exchange within the porous grains and their surfaces, and the conditions entailing the type of frontal patterns for various isotherms of adsorption (including Langmuir's isotherms). The essential influence of mass exchange kinetics is shown.

Coherent and incoherent frontal patterns for multicomponent adsorption dynamics—II. Non-uniqueness of frontal patterns in the isothermal case for convex isotherms of two-component mixtures

Abstract It has been shown that of frontal patterns can be non-unique in the isothermal case for convex adsorption isotherms of two-component mixtures with variable coefficients of separation. The uniqueness of frontal patterns have been analysed by using extreme conditions. The influence of the dispersive factors on the nature of the concentration distribution is considered. It has shown that the dispersive factors can qualitatively change the nature of concentration distribution in the adsorber too: (a) convert coherent patterns into incoherent ones; (b) transform some coherent patterns into other coherent ones.

Hartley transformation for hybrid pattern matching

A hybrid pattern matching system using the binary versions of the Hartley and related transformations is presented. These transformations can be obtained by an incoherent optical system described in this paper. Using them, the spurious correlation signals inherent in an incoherent pattern matching system based on the optical cosine transformation are removed. Experimental demonstrations in an incoherent-optical/digitalel ectronic hybrid system are also presented.

Incoherent pattern recognition with limited rotation invariance

The application of circular cosine expansion to intensity pattern recognition is investigated. Choosing one modified component of the circular cosine expansion, a positive reference pattern is composed and limited rotation-invariant incoherence pattern recognition is achieved. Computer simulation shows that it is in good agreement with the theoretical prediction.

Dissipative structures in a reaction-diffusion system

A transient analysis of reaction-diffusion equations associated with the model reaction of Prigogine and Lefever (Brusselator model), has been performed. For low system lengths and for fixed boundary conditions, steady state solutions with the low amplitude are unstable. For zero flux boundary conditions the multiplicity of symmetric solutions with the same wave number may exist and the majority of them are unstable. The diffusion of initial components induces relaxation oscillations in space for fixed as well as zero flux boundary conditions. The amplitude of the oscillations increases as the diffusion coefficient of the initial component decreases. For conditions of relaxation oscillations the spatial profiles result in single or multiple propagating fronts. High system lengths for both zero flux and periodic boundary conditions, may give rise to a multipeak incoherent wave pattern. For periodic boundary conditions the multiplicity of waves has been observed. Numerical simulation of two-dimensional spatial structures reveals the existence of certain similarities between the one- and two-dimensional cases.

The hybrid constraint equation for motion extraction

A new derivation of the constraint equation for motion extraction in the image flow is presented. The derivation was obtained by applying the constraint equation to the Fourier transform of the 2D images. It resulted in a hybrid equation joining time-space and frequency notations. The hybrid equation was numerically solved for the 1D case and tested with many image sequences representing coherent, rigid and incoherent motion patterns. Outlines of the 2D case are also presented with some solved examples. The algorithm seems superior to former derivations of the constraint equation for its ability to extract the movement parameters (magnitude and direction) in non-homogeneous movement fields for displacements greater than pixel size. The relevance of the present procedures to machine and organic motion detection is discussed.

Educational psychology: New pressures, new solutions?

Abstract This paper inspects recent pressures on educational psychology services with particular reference to legislation pertaining to special educational needs. An examination of these pressures indicates that a confused and incoherent pattern of responses appears to have been adopted by professionals working within a rather bureaucratic framework. Although the critique is specifically directed towards practice in Scotland, many of its implications have validity in other European countries, particularly England and Wales. In the search for solutions it is argued that educational psychologists must re‐examine their duties and obligations towards special educational needs within a systems‐orientated model. Emphasis should be placed on the promotion of a constructive policy regarding the requirements of pupils with learning difficulties and on a problem‐solving approach to the shortcomings of the educational system.

Random (Speckle) Patterns For Displacement And Strain Measurement: Some Recent Advances

Major advances in using coherent and incoherent speckle patterns for displacement and strain measurements are reviewed. Topics include the laws of spatial movement of laser speckle, the halo functions of coherent and incoherent speckle patterns, decorrelation factors and their effect on the fringe visibility and the upper limit of measurement, new techniques of holospeckle interferometry, real-time and electron microscopic speckle photographies, and the automatic processing of Young's fringes.

High-power multiple-emitter AlGaAs superluminescent diodes

A superluminescent AlGaAs diode emitting 350 mW of cw optical power at room temperature has been demonstrated for the first time. This extraordinarily high power for nonlasing operation was achieved by combining efficient quantum well material with an edge-emitting, multiple-emitter, short (250 μm) Fabry–Perot cavity incorporating one highly reflective mirror. Lasing action is suppressed by applying a ZrO2 coating with an ultralow reflectivity to the laser’s output facet. Suppression of the lasing in this way produces the uniform and incoherent radiation pattern required for many applications.

Diffraction halo functions of coherent and incoherent random speckle patterns

A theoretical analysis based on statistical optics is presented for the diffraction halo functions of random speckle patterns either generated by a coherent source such as a laser or artificially created and illuminated by an incoherent radiation such as white light. It is shown that for a coherent speckle pattern the halo function is given by the autocorrelation of the squared aperture function of the recording system, whereas for a incoherent speckle pattern it is governed by the squared autocorrelation of the aperture function.

Hybrid incoherent optical pattern recognition system

A pattern recognition system that uses incoherent spatial filtering to recognize images directly from a narrowband phosphor television monitor is described. Images of real objects are captured with a television camera. These images are then edge-enhanced electronically and displayed on the TV monitor. The monitor output is used directly as the input to a holographic correlator. An optical multichannel analyzer at the correlation plane is used to analyze the shape of the correlation function and to determine the position of its peak. Experimental results agree well with theory. Concepts for handling rotation, aspect angle, and scale variations of the input are discussed.