Artefacts

To search for the forms of potentials we are considering here simple mechanical models. Two of them, namely cluster support algorithm (CSA) and plane support algorithm (PSA), were described in details in [6]. Providing the experiments with simulated and experimental data, it was shown that the iteration procedure yields the sweeping of the structures which are not volumetric-like or surface-like, correspondingly. While the number of required projections for the reconstruction is reduced by 10 -100 times, the quality of reconstruction estimated quantitatively remained quite comparative (sometimes even with less artefacts) with that result obtained by classic Computer Tomography (CT). 

Correction for beam hardening artefacts in computerised tomography... 

The main disadvantage of Feldkamp s approaeh is the fact, that it is mathematically correct only in tire midplane of the beam. With larger Cone-Beam angles the error grows and over 30 degrees severe artefacts can be observed In the reconstruction. 

The are essentially adjustable parameters and, clearly, unless some of the parameters in A2.4.70 are fixed by physical argument, then calculations using this model will show an improved fit for purely algebraic reasons. In principle, the radii can be fixed by using tables of ionic radii calculations of this type, in which just the A are adjustable, have been carried out by Friedman and co-workers using the HNC approach [12]. Further rermements were also discussed by Friedman [F3], who pointed out that an additional temi is required to account for the fact that each ion is actually m a cavity of low dielectric constant, e, compared to that of the bulk solvent, e. A real difficulty discussed by Friedman is that of making the potential continuous, since the discontinuous potentials above may lead to artefacts. Friedman [F3] addressed this issue and derived... 

Saito, M Molecular dynamics simulations of proteins in solution artefacts caused by the cutoff approximation. J. Chem. Phys. 101 (1994) 4055-4061. 

Solutions in contact with polyvinyl chloride can become contaminated with trace amounts of lead, titanium, tin, zinc, iron, magnesium or cadmium from additives used in the manufacture and moulding of PVC. V-Phenyl-2-naphthylamine is a contaminant of solvents and biological materials that have been in contact with black rubber or neoprene (in which it is used as an antioxidant). Although it was only an artefact of the separation procedure it has been isolated as an apparent component of vitamin K preparations, extracts of plant lipids, algae, livers, butter, eye tissue and kidney tissue [Brown Chem Br 3 524 1967]. 

The following is a summary of visual aids (slides, artefacts and demonstrations) that may be found helpful in presenting the material in this book. Material for slides may be found in this book in the further reading at the ends of the chapters and in other readily available sources (indicated by references [1] to [5] and listed at the end of Appendix 2). Where material for slides needs to be found from more specialised publications and reports we have given appropriate references. Copyright permission should, of course, be obtained where applicable. 

Artefacts Screwdrivers dismantled spark plug PVC yachting anorak, polymer rope, etc. 

Artefacts Damaged piece of GFRP to show opacity caused by debonding. 

Artefacts Galvanised steel sheet, new and old anodised Al polymeric roofing material corroded exhaust system. 

Artefacts Skis sectioned to show layered construction. 

Pottery is one of the oldest materials. Clay artefacts as old as the pyramids (5000 bc) are sophisticated in their manufacture and glazing and shards of pottery of much earlier date are known. Then, as now, the clay was mined from sites where weathering had deposited them, hydroplastieally formed, fired and then glazed. 

The temperature dependences of k, calculated by Hancock et al. [1989], are given in fig. 48. The crossover temperature equals 25-30 K. The weak increase of k T) with decreasing temperature below is an artefact caused by extending the gas-phase theory prefactor to low temperatures without taking into account the zero-point vibrations of the H atom in the crystal. For the same reason the values of the constants differ by 1-2 orders of magnitude from the experimental ones. 

Heintz, E.A., Influence of coke structure on the properties of the carbon-graphite artefact, FUEL, 1985, 64, 1192 1196. 

Cahn, R.W. (1992) Artifice and Artefacts 100 Essays in Materials Science (Institute of Physics Publishing, Bristol and Philadelphia) p. 314. 

Martin, G. (2000) Stasis in complex artefacts, in Technological Innovation as an Evolutionary Process, ed. Ziman, J. (Cambridge University Press, Cambridge) p. 90. Marzke. O.T. (editor) (1955) Impurities and Imperfections (American Society for Metals, Cleveland, Ohio). 

Novel Methods for Making Carbon and Ceramic Materials and Artefacts... 

Novel methods for making carbon and ceramic materials and artefacts... 

A particularly simple lattice model has been utilized by Harris and Rice [129] and subsequently by Stettin et al. [130] to simulate Langmuir mono-layers at the air/water interface chains on a cubic lattice which are confined to a plane at one end. Haas et al. have used the bond-fluctuation model, a more sophisticated chain model which is common in polymer simulations, to study the same system [131]. Amphiphiles are modeled as short chains of monomers which occupy a cube of eight sites on a cubic lattice and are connected by bonds of variable length [132], At high surface coverage, Haas et al. report various lattice artefacts. They conclude that the study... 

Lattice models for bulk mixtures have mostly been designed to describe features which are characteristic of systems with low amphiphile content. In particular, models for ternary oil/water/amphiphile systems are challenged to reproduce the reduction of the interfacial tension between water and oil in the presence of amphiphiles, and the existence of a structured disordered phase (a microemulsion) which coexists with an oil-rich and a water-rich phase. We recall that a structured phase is one in which correlation functions show oscillating behavior. Ordered lamellar phases have also been studied, but they are much more influenced by lattice artefacts here than in the case of the chain models. 

Gays are an essential component of soils, to which we owe our survival, and they are also the raw materials for some of mankind s most ancient and essential artefacts pottery, bricks, tiles, etc. Clays are formed by the weathering and decomposition of igneous rocks and occur typically as very fine panicles e.g. kaolinite is formed as hexagonal plates of edge. 1-3 p m by the weathering of alkaline feldspar... 

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