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Geometrical Arrangement (geometrical + arrangement)
Selected AbstractsThe Effect of Ring Size on Catenane SynthesisEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2003Stefan Duda Abstract The synthesis of a [2]catenane with 87-membered rings was improved and extended to [2]catenanes with 63- and 147-membered rings. One of the key features is the carbonate linkage between phenols with tolane substituents in the 2- and 6-positions, which serves as a covalent template for the geometrical arrangement of a macrocycle and a ring precursor. Subsequent cyclization of the threaded ring precursor gives the precatenane as the main product, and this is converted into the catenane by carbonate hydrolysis. As well as the precatenane, its dumbbell shaped isomer is formed in the cyclization step. From the known conformation of the templating carbonate moiety and the strong dependence of the ratio of precatenane and dumbbell on the ring size, the dumbbell's origin is attributed to the conformational flexibility of the large rings and not to geometrical ambiguity of the carbonate moiety. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Elasto-plastic analysis of block structures through a homogenization methodINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2010G. de Felice Abstract The paper describes the development and numerical implementation of a constitutive relationship for modeling the elasto-plastic behavior of block structures with periodic texture, regarded at a macroscopic scale as homogenized anisotropic media. The macroscopic model is shown to retain memory of the mechanical characteristics of the joints and of the shape of the blocks. The overall mechanical properties display anisotropy and singularities in the yield surface, arising from the discrete nature of the block structure and the geometrical arrangement of the units. The model is formulated in the framework of multi-surface plasticity. It is implemented in an finite element (FE) code by means of two different algorithms: an implicit return mapping scheme and a minimization algorithm directly derived from the Haar,Karman principle. The model is validated against analytical and experimental results: the comparison between the homogenized continuum and the original block assembly shows a good agreement in terms of ultimate inelastic behavior, when the size of the block is small as compared with that of the whole assembly. Copyright © 2009 John Wiley & Sons, Ltd. [source] pKa optimized catalysis in serine proteinases, an ab initio study on the catalaytic HisINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 11 2007Péter Hudáky Abstract First principle models of catalytic apparatus of enzymes can be used for studying stability as well as the atomic details of a catalytic mechanism. For example, the catalytic triad of chymotrypsin was recently investigated by using an ab initio geometry optimized (Hudáky and Perczel, Proteins: Struct Funct Genet, 2006, 62, 749) self-stabilizing molecule ensemble without the presence of the complete enzyme and substrate. Several parameters of the above catalytic reaction turned out to be the same within the model and the in vitro enzymatic reaction. Among the numerous parameters of the catalytic process geometrical changes of the catalytic histidine was investigated here and the variation of its pKa value was determined. A relatively large range, 3.5 unit, was determined as the variation of pKa as function of the conformational subspace available in serine proteases. Comparing PDB structures of the free and the complex enzymes it was shown, that histidine, after accepting the proton from the OH group of the catalytic serine, undergoes a minor conformational change accompanied by a 2.5 unit decrease in pKa. We conclude that the changes of pKa during catalysis are predominantly determined by the geometrical arrangement of the histidine moiety and this change serves as a significant driving force in the catalytic process. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Strain rates from snowball garnetJOURNAL OF METAMORPHIC GEOLOGY, Issue 3 2003C. Biermeier Abstract Spiral inclusion trails in garnet porphyroblasts are likely to have formed due to simultaneous growth and rotation of the crystals, during syn-metamorphic deformation. Thus, they contain information on the strain rate of the rock. Strain rates may be interpreted from such inclusion trails if two functions are known: (1) The relationship between rotation rate and shear strain rate; (2) the growth rate of the crystal. We have investigated details of both functions using a garnetiferous mica schist from the eastern European Alps as an example. The rotation rate of garnet porphyroblasts was determined using finite element modelling of the geometrical arrangement of the crystals in the rock. The growth rate of the porphyroblasts was determined by using the major and trace element distributions in garnet crystals, thermodynamic pseudosections and information on the grain size distribution. For the largest porphyroblast size fraction (size L=12 mm) we constrain a growth interval between 540 and 590 °C during the prograde evolution of the rock. Assuming a reasonable heating rate and using the angular geometry of the spiral inclusion trails we are able to suggest that the mean strain rate during crystal growth was of the order of =6.6 × 10,14 s,1. These estimates are consistent with independent estimates for the strain rates during the evolution of this part of the Alpine orogen. [source] A Family of Symmetrical Lower-Mobility Parallel Mechanisms with Spherical and Parallel SubchainsJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 6 2003Q. C. Li This paper presents a new family of symmetrical lower-mobility parallel mechanisms (PMs) with spherical and parallel subchains, which consists of two 5-DOF (degrees of freedom) PMs, one 4-DOF PM and five 3-DOF PMs. The basic feature of this family is that each limb consists of five revolute pairs and can be constructed with two subchains, a 2R pointing subchain and a 3R parallel subchain, or a 3R spherical subchain and a 2R parallel subchain. Different geometrical arrangements of the limbs lead to different degrees of freedom. All the PMs of this family can be modularized easily due to the simple structure of the subchains. © 2003 Wiley Periodicals, Inc. [source] Flow of Newtonian and power law liquids in tube bundlesTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2009U. K. Singh Abstract In this work, the annular (tangential) flow of Newtonian and non-Newtonian fluids in tube bundles has been studied experimentally. Extensive pressure drop data has been obtained embracing wide ranges of the Reynolds number (13,6600) and for two test modules of different geometrical arrangements, but of similar overall void fraction. Preliminary experiments suggest that the pressure drop is mainly determined by the overall void fraction of the bundle and is relatively insensitive to the detailed geometrical configuration of the bundle. A simple predictive correlation has been developed which reconciles the present results for Newtonian and power law fluids with acceptable levels of reliability. Dans le cadre de ces travaux, on a examiné de façon expérimentale l'écoulement annulaire (tangentiel) des fluides newtoniens et non newtoniens dans des faisceaux tubulaires. On a obtenu de nombreuses données de chute de pression englobant de vastes plages du nombre de Reynolds (13-6600), et pour deux modules d'essai de différentes dispositions géométriques, mais à taux de vide global similaire. Les expériences préliminaires suggèrent que la chute de pression est déterminée principalement par le taux de vide global du faisceau et est relativement insensible à la configuration géométrique détaillée du faisceau. La création d'une simple corrélation prédictive a permis de rapprocher les présents résultats pour les fluides newtoniens et des fluides en loi de puissance avec des niveaux acceptables de fiabilité. 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