Reconstruction Creation

In Chapter 12, Cemescu et al. present a reverse engineering application in the context of dental engineering. The aim is to efficiently and effectively assess the mechanical quality of manufactured complete dentures in terms of their behavior to mechanical stresses e.g. detect areas likely to underperform or crack in normal operation mode. The reverse engineering pipeline presented covers the steps of 3D model acquisition by means of scanning and surface reconstruction, creation of a finite element mesh suitable for numerical simulations, and the actual computation of stress and strain factors in presence of induced model defects. 

The purpose of our researches is a study of variants for creation of an economic means for 3D tomographic inspection. For this purpose it is necessary to carry out the analysis of existing methods of 3D reconstruction, directed on solving problems of NDT a wide class of industrial products. 

Abstract. We describe the state-of-the-art in the creation of ordered superlattices of adsorbed atoms, molecules, semiconductor quantum dots, and metallic islands, by means of self-assembly during atomic-beam growth on single crystal surfaces. These surfaces often have long-period reconstructions or strain relief patterns which are used as template for heterogeneous nucleation. However, repulsive adsorbate-adsorbate interactions may also stabilize ordered superlattices, and vertical correlations of growth sequences of buried islands will be discussed in the case of semiconductor quantum dots. We also present new template surfaces considered as particularly promising for the creation of novel island superlattices. 

Silicon forms a diamond lattice. As Si single crystals are cut, some of the sp3 bonds that stabilize the diamond structure are cleaved, resulting in the creation of unsaturated, or dangling bonds at the surface. To reduce its surface energy, the system tends to minimize the number of dangling bonds. In this process, new bonds between adjacent Si atoms are formed, associated with geometric surface reconstruction. The reactivity of specific Si surface sites strongly depends on their... 

Surface reconstruction is driven by stabilization of the adsorbate after adsorption of carbon atoms on more reactive surface atoms. Ciobica et al. (74) demonstrated that an overlayer of Cads leads to the Co(lll) to Co(lOO) reconstruction on fee cobalt (the stable phase of small cobalt particles). Because of the change in metal atom density in the surface layer, the reconstruction may be associated with faceting and hence creation of step-edge sites, which are highly active in the Fischer-Tropsch reaction (5). Hence, surface reconstruction and formation of a stable carbide overlayer may actually be the processes occurring during the initial activation of the catalyst. This phenomenon has been described by Schulz (101) as self-organization. 

Pd were deposited on Ni(llO) the period of alignments along the [llO] direction is about 5 nm, instead of 2.5 nm for 4 ML Pd on Ni(llO). As previously discussed for Pd on Ni(llO) one can suppose that the surface reconstructs to relax the stress, at least partially, with here again creation of a specific structural arrangement, generating very active surface sites. The understanding of the modified chemical reactivity would recquire complementary informations relative to the electronic properties of the considered thin films. 

Landsberg, however, did not accept assumptions (62) and postulated (L2) in so doing he postulated that chemisorption has two contrasting effects on one side the chemisorption of a molecule deactivates one site, but on another side it is also responsible for the creation of newly exposed area and hence of new adsorption sites. This can be restated by assuming that the active area lost per unit time and unit geometric area is bdN/dt, where b represents the net lost area per chemisorbed molecule. If the reconstruction mechanism is such that (L3) is satisfied, the number of available sites per unit geometric area evolves with time as... 

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