Geometric Interface Research Articles

Current-in-plane magnetoresistance: An approach to boundary conditions

The giant magnetoresistance effect is calculated for metallic magnetic superlattices with current-in-plane geometry by solving the semiclassical Boltzmann transport equation. Two types of interface roughness will be taken into account, geometrical interface roughness and scattering at defects, impurities, etc. located at the interface. Within this approach, geometrical interface roughness with a finite correlation length is considered. It is shown that geometrical interface roughness, without any other form of spin-dependent scattering, can result in a considerable magnetoresistance.

Liberation of composite waste from manufactured products

With regard to liberation, composite materials resulting from industrial manufacturing processes differ from locked mineral resources. The simultaneous requirements of low weight, high strength and apparent softness etc., ask for the combination of materials with different mechanical properties. These composites can be liberated by selective comminution, where a defined stress by impact or pressure causes breakage of only one component of the composite. Similarly by shear it is possible to detach different components at their interface due to focusing of strains at the transition of materials. In our experiments good results were obtained for various samples of manufacturing waste and used products. In addition, the interface between different materials of manufactured composites is rather small, i.e. the bond is considerably lower than for natural mineral resources where the interface dimension is sometimes a fractal. This is due to geometrical simplicity of manufactured goods like cables and other layer composites. For the case of known interface area A and volume V of a sinle part of composite, a useful length x = V A can be derived. This geometrical interface factor x enables us to predict the particle size D necessary to achieve a certain liberation rate L = 1 - D/x. These explanations indicate that the particularities of manufactured composites lead to new possibilities of liberation by comminution.

An Evolutionary Trace Method Defines Binding Surfaces Common to Protein Families

X-ray or NMR structures of proteins are often derived without their ligands, and even when the structure of a full complex is available, the area of contact that is functionally and energetically significant may be a specialized subset of the geometric interface deduced from the spatial proximity between ligands. Thus, even after a structure is solved, it remains a major theoretical and experimantal goal to localize protein functional interfaces and understand the role of their constituent residues. The evolutionary trace method is a systematic, transparent and novel predictive technique that identifies active sites and functional interfaces in proteins with known structure. It is based on the extraction of functionally important residues from sequence conservation patterns in homologous proteins, and on their mapping onto the protein surface to generate clusters identifying functional interfaces. The SH2 and SH3 modular signaling domains and the DNA binding domain of the nuclear hormone receptors provide tests for the accuracy and validity of our method. In each case, the evolutionary trace deliineates the functional epitope and identifies residues critical to the binding specificity. Based on mutational evolutionary analysis and on the structural homology of protein families, this simple and versatile approach should help focus site-directed mutagenesis studies of structure-function relationships in macromolecules, as well as studies of specificity in molecular recognitionl. More generally, it provedes an evolutionary perspective for judging the functional or structural role of each residue in a protein structure.

Theoretical and experimental studies of structural integrity of dovetail joints in aeroengine discs

Comprehensive finite element analysis and photoelastic studies using the stress freezing technique are made of the behaviour of aeroengine compressor discs under centrifugal loading. Specifically, the work is concerned with examining the effect of some of the critical geometric features and interface conditions in the dovetail region upon the least damage fail-safe design condition. These features included: inner and outer radii, flank length and flank angle, and coefficient of friction at the blade-disc interface. Two aspects of the work were accordingly examined. The first was concerned with the stressing of a number of discs containing the pertinent geometric features. The second was concerned with the initiation and subsequent propagation of cracks in regions exhibiting maximum stress concentration; the propagating cracks were then tracked using the maximum-minimum principal stress criterion. Finally, the theoretical predictions were compared with photoelastic spin tests. In this case, cracks which were introduced in the photoelastic models by careful sawing were extended incrementally along the theoretically predicted fracture path and isochromatic fringe patterns were recorded for each crack length. These fringe patterns were then used to analyse the stress field in the neighbourhood of the crack-tip.

Ultrathin metal film growth on TiO 2(110): an overview

The interface between an oxide substrate and a metal overlayer may crucially influence the macroscopic behavior of technological devices such as sensors, catalysts, ceramics, and semiconductor chips. Hence investigations of adsorption, nucleation and growth of ultrathin metal films on metal oxide surfaces have attracted increasing interest during recent years. Experimental results on the growth of metal overlayers on a model oxide, TiO 2(110), are reviewed. The emphasis is on the very initial stages of overlayer growth and on extracting general trends on metal/metal-oxide interaction by comparing results from different metal overlayers. The electronic and geometric structure, growth mode, interface formation, and thermal stability of metal films are discussed. The strength of the oxidation/reduction reaction at the interface, the wetting ability and the tendency to form a disordered layer are all related to the reactivity of the overlayer metal towards oxygen. We propose that ‘reactive adsorption’ accounts for the observed trends.

Photoluminescent volumetric imaging: A technique for the exploration of multiphase flow and transport in porous media

A new measurement technique, photoluminescent volumetric imaging (PVI), has been developed for the visualization and quantification of multiphase flows and interface behavior in porous media. For this technique, a transparent, multiphase porous‐medium system is constructed of optical‐quality quartz sand, and two immiscible fluids matched to the optical refractive index of fused silica. Doping the fluids with property‐selective fluorophores allows planar areas of the system to be successively excited with a shaped laser light to reveal the structure of the system. The resulting illumination is recorded by a high‐resolution, cooled, slow scan charged‐coupled device (CCD) camera. The planar digital images produced are then processed to generate a true three‐dimensional data set that allows for quantitative study of the distribution of phases and interfaces within the porous medium. Sample volumes up to 125 mm³ in size with a resolution of better than 1 µm have been measured. Because of the large sample size and the high resolution of the measured data, geometric, flow, and phase interface information can be visualized and extracted at both subpore and system scales.

THEORETICAL AND EXPERIMENTAL STUDIES OF FRETTING‐INITIATED FATIGUE FAILURE OF AEROENGINE COMPRESSOR DISCS

Abstract— A finite element analysis and fatigue crack growth studies are made of dovetail joints in aeroengine compressor discs. Three aspects are examined: the first deals with the finite element stress analysis of the critical geometrical features and interface conditions of different dovetail configurations, thus enabling an assessment to be made of the critically loaded regions in the disc. The second deals with the prediction of the direction of potential fatigue cracks, which were allowed to initiate in the finite element model at the regions where fretting damage is most likely to occur, using an incremental crack tracking criterion. The third is concerned with the verification of the above modelling techniques with fatigue tests on a uniaxial back‐to‐back arrangement, which attempts to simulate the stress fields of a rotating disc.

A study of the adsorption of acetonitrile on a gold electrode from aqueous solutions using in situ vibrational spectroscopy

The structure of the interphase at the gold/aqueous solution interface with adsorbed acetonitrile was studied by subtractively normalized FTIR spectroscopy (SNIFTIRS). Two types of acetonitrile and water molecules were observed in the interphasal region. The first involved chemisorbed molecules in which important vibrational modes are shifted strongly in frequency with respect to that observed in the bulk of the solution. In the case of acetonitrile, adsorption resulted in a CN stretching band at 2342 cm −1, and for water, a bending mode at 1688 cm −1. The second type of molecule in the double layer with a band at 2261 cm −1 in the case of acetonitrile, and at 1628 cm −1 in the case of water, was assumed to be hydrogen bonded to chemisorbed water molecules, and thus located further away from the geometrical interface. A band due to perchlorate ion at 1107 cm −1 is attributed to anions attracted into the double layer by the positive charge on the electrode. No evidence was obtained for contact adsorption of this anion.

Interface stress, tension and free energy density of condensed matter

A model of geometrical interface with inherent elastic stress is developed. The general formulas for interface stress, tension and free energy density of condensed matter as well as their relations are derived. The constitutive relationship of the interface is also discussed. The results so obtained all agree with the current theories, and some new conclusions are drawn.

Overview No. 98 I—Geometric models of crystal growth

Recent theoretical advances in the mathematical treatment of geometric interface motion make more tractable the theory of a wide variety of materials science problems where the interface velocity is not controlled by long-range-diffusion. Among the interface motion problems that can be modelled as geometric are certain types of phase changes, crystal growth, domain growth, grain growth, ion beam and chemical etching, and coherency stress driven interface migration. We provide an introduction to nine mathematical methods for solving such problems, give the limits of applicability of the methods, and discuss the relations among them theoretically and their uses in computation. Comparisons of some of them are made by displaying how the same physical problems are treated in the various applicable methods.

Defect modeling in HRTEM image simulation

One practical problem in High Resolution Transmission Electron Microscopy (HRTEM) image simulation is the creation of atomistic models of defect structures. The ideal crystal structures are readily represented by a relatively small number of “basis” atoms and the crystallographic space group. On the other hand, the specification of a grain boundary between two crystals requires the atomic location of possibly thousands of atoms, and a HRTEM simulation program will need all this information before a calculation can be carried out. Users comfortable with writing computer code will write a computer program to generate the hundreds or thousands of atomistic locations, while others may be forced to enter the data by hand or search around for a ready made program that can generate the required data To the authors knowledge, no such suitable program is readily available. There are existing programs that will generate geometric interface models, but these programs were designed to create input to atomistic relaxation calculations, not as generalized tools for creating defect structures.

Influence of the interface quality on the elastic properties of Co/Au multilayers investigated by Brillouin light scattering

We have determined the set of elastic constants of polycrystalline Co/Au multilayers by means of Brillouin light scattering. Annealing the samples enhances c33 by 14% and c55 by 30%, but leaves c11 unchanged. Increasing the modulation wavelength of the multilayers, c33 increases, but c11 and c55 remain unchanged. These results are discussed in the light of the known phenomena of chemical and geometrical interface modifications of the multilayered structures as a function of annealing temperature and time.

Donor cell-finite element descriptions of wire-duct precipitator fields, charges, and efficiencies

Computations of electric field and charge density structures and resultant efficiencies in wire-duct electrostatic precipitators are described. The computational method is based upon the finite-element method as a means for computing the potential and electric field for a known charge distribution and a donor cell method that imposes conservation of charge in integral form as a means for computing charge densities for a known field structure, with iterative convergence to self-consistent solutions. The solution region is discretized by the Delaunay algorithm. This division simultaneously provides the triangles needed for the finite-element method and the Voronoi polygons over which charge conservation is imposed. Thus, a natural geometric interface is established between the finite-element method and the donor cell description. Results are shown in models that include the time-averaged effect of turbulence through a diffusivity coefficient, bipolar ionic species modeling back ionization, and the effects of particulate and ionic space charge. >

Learning studies in the use of computer aided design systems for discrete-parts manufacture

Abstract Two-dimensional computer aided engineering design systems are recognized as having limitations in comparison with the alternative three-dimensional techniques of solid modelling. The mathematically sounder approach of solid modelling permits far greater integration between the activities of functional design, design analysis and manufacturing. However, the existing methods of specifying design geometry within typical solid modelling systems are deficient in that they relate more to the mathematical needs of the computer system than they do to the needs of the designer. CAPE-LUT (Computer Aided Production Engineering-Loughborough University of Technology) is a prototype system which provides a machining analogy so that geometric and manufacturing ideas can be expressed through familiar engineering terminology, to provide detail designs and outline process plans. CAPE-LUT is an experimental vehicle only and the system has been used to investigate the hypothesis that a ‘manufacturing features’ approach to design and manufacture is easy to learn, accurate and fast in use, and acceptable to practising designers and manufacturing engineers. This paper describes the experimental work, which provides statistical evidence that the manufacturing features method is significantly easier to learn than a similar CAD system that has a purely geometric interface. It is also shown that CAPE-LUT performed well when used by experienced subjects and was acceptable to a large number of practising engineers.

Geometric optical optimization of the corneal lens of Notonecta glauca

The optimal shape of the corneal lens of the water bug backswimmer (Notonecta glauca) and the optimal shape and position of the thin transition layer between the distal and proximal units of its cornea are theoretically determined. Using a geometric optical method, first the shape of a geometric interface between the lens units is determined, which eliminates the longitudinal spherical aberration. This interface is investigated for differently formed thick lenses when the medium in contact with the entrance surface of the lens is water or air. The optimal transition layer for the amphibious backswimmer is that, the boundaries of which are the theoretical interfaces for water and air, and the refractive index varies continuously in it. The optimal shape of the corneal lens is determined, with the disadvantageous lenses, with respect to the possible minimal spherical aberration and amount of reflected light from the transition layer, being rejected. The optimal position of the transition layer in the cornea can be obtained from the minimization of the amount of diffracted light on the marginal connection of the layers. The optimal corneal lens for backswimmer has ellipsoid boundary surfaces; the optimal transition layer in it is thin bell-shaped, at the marginal connection of which there is no dimple, the maximum of the layer is on the margin of the cornea. The shape of the theoretically optimal corneal lens, the shape and position of the theoretically optimal transition layer agree well with those of Notonecta glauca. The question posed, the geometric optical method used and the results presented are of general importance, and not only with respect to vision in the bug Notonecta, but also in the fossil trilobites, or in the wave guide theories which have been employed in similar modelling problems, in design of system of lenses without spherical aberration, for example.

A knowledge-based system for process planning based on a solid modeller

The generation of planning and control data for the machining of mechanical components is a complex task which requires the application of skill and experience. With current interest in applying expert system (ES) techniques to problems in the area of CAD/CAM, this particular aspect of process planning appears to be well suited to a knowledge-based (KB) approach. However, the knowledge used to solve such problems involves the interpretation of three-dimensional (3-D) geometry. This paper outlines the development of a process planning system using knowledge-based techniques with derivation of component geometric information from a three-dimensional solid modeller. The knowledge-based components of the system are centred on a production rule based expert system, coexisting with a nonlinear knowledge-based planning system. These are in turn coupled to a solid modeller via a geometric interface. The knowledge resident within the system operates on the geometry of the component to produce the planning and control data. The system is targetted at planning the manufacture of components with 2½-D geometries, using a three-axis machining centre, from rectilinear blanks.

A supervised simulation system for process and device designs based on a geometrical data interface

A supervised simulation system for two-dimensional simulation has been developed covering the range from pattern layout to process simulation and also to device simulation. The system features a system controller for module programs, and the feasibility of module programs based on an intermediate topography data format with which data go between the module programs. The system controller can automatically generate appropriate jobs, assigning pertinent input data. The topography data acts as an interface through process simulation and up to device simulation. The system will eliminate laborious work for designers and greatly reduce the time required for process and device designs.

An Electrostatic Explanation of the Phenomenon of Flotation

THE explanation of the flotation processes with the aid of the cataphoretic and electroendosmotic potentials has failed completely. These potentials play an important part at a distance from the geometrical interface of the phase only.1 There are, however, suggestions in the literature2 that ideal chemical electrodes should have a positive electrostatic potential in water and the dielectrics a negative one. This suggestion has important consequences. Emulsions of dielectrics in water will wet unattackable electrodes immersed in water but not attackable electrodes which are coated with dielectric oxides (hydroxides) in water. The wetting must, however, reduce the positive charge of the unattackable electrode, and it is expected that the wetting will not take place on attackable electrodes coated with a dielectric hydroxide, as for example, zinc. This is actually observed.