Today parametric associative CAD systems must help companies to create more efficient virtual development processes. While dealing with complex parts (e.g. the number of surfaces of the solid) no CAD modeling methodology is existing. Based on the analysis of industrial designers' practices as well as student practices on CAD, we identified key factors that lead to better performance. Our objective in this article is to propose a practical method for complex parts modeling in parametric CAD system. An illustration of the performances and the results obtained by this method are presented comparing the traditional method with the proposed one while using an academic case and then an industrial case. 相似文献
Scanning probe microscopy (SPM) is in a period of rapid development. It shows great promise for characterizing coating surfaces. This paper describes modification of an SPM so that it can be used to mar the surfaces of coatings under controlled conditions and to characterize the mars. Mar resistance of coatings is analyzed in terms of a ‘three response, two mechanism model.' The three responses (fracture, elastic, and plastic) can be measured quantitatively using the SPM. Of the three responses, only two (fracture and plastic deformation) are marring mechanisms – elastic deformations recover instantaneously. In some cases mars resulting from plastic deformation may recover slowly with time or with immersion in water; this phenomenon is attributed to viscoelastic creep. Microhardness is also measured with the modified SPM. Some thermoset coatings appear to be substantially harder near their surfaces than in the mass of material, and such materials may respond quite differently to stress applied at different levels near the surface. This finding has important implications for all coating properties that are strongly influenced by the surface. A quantity called ‘micro mar resistance' is defined. It may be useful for comparing different coatings under specified conditions of marring. However, there can be no single quantity that expresses ‘mar resistance' of a coating under all conditions. 相似文献
Model-driven engineering introduces additional challenges for controlling and managing software evolution. Today, tools exist for generating model editors and for managing models with transformation, validation, merging and weaving. There is limited support, however, for model migration—a development activity in which instance models are updated in response to metamodel evolution. In this paper, we propose conservative copy—a style of model transformation that we believe is well-suited to model migration—and Epsilon Flock—a compact model-to-model transformation language tailored for model migration. The proposed structures are evaluated by comparing the conciseness of model migration strategies written in different styles of transformation language, using several examples of evolution taken from UML and the graphical modelling framework. 相似文献
A Sulzer SMX mixer was used to disperse gas into viscous, Newtonian and non-Newtonian fluids. The investigation covered the effect of the dispersed phase volume fraction, the viscosity of the continuous phase, the mixer length and the power draw. The flow regime was kept laminar in all the experiments. The dispersion of gas was carried out with gas concentrations between 1% and 7% in volume. Using the “process viscosity” concept, it was possible to collapse all the measured sizes on a single master curve by using the energy consumption in the mixer as the common variable between the experiments. Comparison was made with a Kenics mixer. The SMX mixer was found to be better adapted to the dispersion task due to its internal structure. 相似文献
The human plasma high density lipoproteins (HDL) are a heterogeneous ensemble of five proteins associated with both neutral
and polar lipids. The sequences of all five proteins are known. ApoA-I and apoA-II are the major protein components; apoC-I,
apoC-II and apoC-III are the minor protein components. All these apoproteins spontaneously recombine with phospholipids to
give stable lipid-protein complexes and freely exchange between the two major HDL subclasses, HDL2 and HDL3. In addition, ApoC-I, apoC-II, and apoC-III exchange between HDL and very low density lipoproteins. Furthermore, certain
HDL apoproteins are activators for plasma enzymes that are important in lipid metabolism. ApoA-I and apoC-I activate lecithin/cholesterol
acyltransferase; apoC-II is an activator of lipoprotein lipase. The regions of apoC-I and apoC-II that are involved in the
activation of these enzymes have been localized with synthetic peptides. Studies of synthetic and native fragments of apoA-II,
apoC-I, apoC-II, and apoC-III as well as model lipid-binding peptides have identified specific regions with structural features
common to lipid-binding proteins. These special properties, which include helical potential, sequences with a critical amphipathic
length, and high hydrophobicity of the nonpolar side of the amphipathic helix, are the determinants of HDL structure and metabolism. 相似文献
The effects of platinum (Pt) and silver (Ag) metallisation in the photocatalytic oxidation of resorcinol at pH 3 ± 0.5 have been investigated. The photocatalytic degradation of resorcinol was significantly improved by Pt/TiO2, while the presence of Ag/TiO2 enhanced the initial photocatalytic degradation rate of resorcinol slightly. Likewise, the photocatalytic mineralisation of resorcinol continued to be enhanced by Pt/TiO2, but it was retarded when Ag/TiO2 was used.
The function of Pt and Ag deposits on the surface of TiO2 has been found to be markedly influenced by the interaction of resorcinol and its degradation products with the metal deposits. The presence of Pt or Ag on the surface of TiO2 altered the distribution of degradation products of resorcinol as well as the production of photoactive species for the photocatalytic oxidation of resorcinol. The X-ray photoelectron spectroscopy (XPS), zeta potential and transmission electron microscopy (TEM) analyses have indicated that the contrasting effect of Pt and Ag deposits were governed by the oxidation states and the catalytic property of metal deposits. In addition to that, it has been found that the roles of metal deposits are specific and should not be generalised. 相似文献
Most heterogeneous catalysts are either supported on some kind of porous material or the catalyst itself is porous. To satisfy practical constraints such as pressure drop, handling, and separation from products, these catalysts are generally pelletized. Very often the overall chemical reaction rates within these catalyst pellets are determined by a complicated interaction of internal and external transport effects with the intrinsic kinetic rate at the active surface. 相似文献
Torsion and normal force measurements were made during single step stress relaxation experiments on a polymeric glass (PMMA). Isochronal data were analysed using an approach adapted from that developed by Penn and Kearsley1 (for incompressible elastic materials) to determine the derivatives , and of the time dependent strain potential function. and are determined from existing solution to the torsion of an incompressible cylinder. A special solution to the torsion of a compressible cylinder is presented and it is shown that the values of and obtained using this solution to analyse the data do not differ greatly from those obtained using the incompressible solution. It is found from both solutions that is negative and increases towards zero with increasing time and deformation while is positive, greater in magnitude than and decreases towards zero with increasing time and deformation. These results were unexpected and a full understanding of their meaning has yet to be reached. 相似文献