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  • 1
    Electronic Resource
    Electronic Resource
    A model for crack connectivity in rocks, a discussion (1995)
    Springer
    Mathematical geology 27 (1995), S. 23-39 
    Details
    ISSN: 1573-8868
    Keywords: rock fracture ; renormalizalion-group ; percolation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract We reanalyzed a model introduced by T. R. Madden for the evaluation of the state of connectivity among the microcrack population existing inside crystalline rocks. The model assumes that cracks are distributed randomly in a cubic lattice with a basic occupation probability, p.Depending on the value of p, the stale of connectivity can give rise to macroscopic paths, which allow electrical conduction of the sample, or to extended crack surfaces, which would be responsible for rock failure. The position of the phase boundaries, that is, the threshold values of pfor the onset of conductivity or macroscopic fracture, are estimated by a real-space renormalizalion-group (RG) technique. By identifying all the relevant configurations of the lattice model, we have been able to provide explicit analytic formulae for the critical lines. The criterion used by Madden to “accept” the existence of microscopic linear connectivity is modified and the new consequences discussed. We analyze the limitations of simple versions of the RG technique, in particular when concerned with anisotropic spatial distributions of cracks. Finally, we emphasize the interest of acquiring experimental data, especially to test the position of the conduction thresholds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02083566
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Structure-based thermodynamic design of peptide ligands: Application to peptide inhibitors of the aspartic protease endothiapepsin (1998)
    New York, NY : Wiley-Blackwell
    Proteins: Structure, Function, and Genetics 30 (1998), S. 74-85 
    Details
    ISSN: 0887-3585
    Keywords: folding and binding ; kinetics ; pepstatin A ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The prediction of binding affinities from structure is a necessary requirement in the development of structure-based molecular design strategies. In this paper, a structural parameterization of the energetics previously developed in this laboratory has been incorporated into a molecular design algorithm aimed at identifying peptide conformations that minimize the Gibbs energy. This approach has been employed in the design of mutants of the aspartic protease inhibitor pepstatin A. The simplest design strategy involves mutation and/or chain length modification of the wild-type peptide inhibitor. The structural parameterization allows evaluation of the contribution of different amino acids to the Gibbs energy in the wild-type structure, and therefore the identification of potential targets for mutation in the original peptide. The structure of the wild-type complex is used as a template to generate families of conformational structures in which specific residues have been mutated. The most probable conformations of the mutated peptides are identified by systematically rotating around the side-chain and backbone torsional angles and calculating the Gibbs potential function of each conformation according to the structural parametrization. The accuracy of this approach has been tested by chemically synthesizing two different mutants of pepstatin A. In one mutant, the alanine at position five has been replaced by a phenylalanine, and in the second one a glutamate has been added at the carboxy terminus of pepstatin A. The thermodynamics of association of pepstatin A and the two mutants have been measured experimentally and the results compared with the predictions. The difference between experimental and predicted Gibbs energies for pepstatin A and the two mutants is 0.23 ± 0.06 kcal/mol. The excellent agreement between experimental and predicted values demonstrates that this approach can be used in the optimization of peptide ligands. Proteins 30:74-85, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
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