218 research outputs found
Invariant Kekulé structures in fullerene graphs
No full textFullerene graphs are trivalent plane graphs with only hexagonal and pentagonal faces. They are often used to model large carbon molecules. A totally symmetric Kekule structure in a fullerene graph is a set of independent edges which is fixed by each automorphism of the fullerene. Starting from the complete catalog of all fullerenes with at least ten symmetries, we establish exactly which of them have at least one totally symmetric Kekule structure
A stoichiometric reaction scheme for Saccharothrix algeriensis growth and thiolutin production
No full textA new bacterial species, Saccharothrix algeriensis NRRL B-24137, was isolated in 1992 in the Sahara desert. This filamentous bacterium is able to produce dithiolopyrrolones, molecules presenting antibacterial, antifungal, and anticancer properties. In this study, a “reaction engineering” approach was adopted to gain more knowledge on the growth of Sa. algeriensis and its dithiolopyrrolone production on a semi-synthetic liquid medium. The objective is to establish a reaction scheme of the bacterium metabolism from extracellular experimental information, relatively easy to obtain. The approach enabled us to show that Sa. algeriensis could grow using several substrates that were sequentially consumed and that substrate limitation may induce a secondary metabolism in antibiotic production. From these qualitative data, a general reaction scheme was extracted consisting of four reactions: growth via amino acids, glucose consumption for maintenance, growth using glucose, and thiolutin production. The stoichiometric coefficients and the reaction extends were identified using a factorial analysis based on the bilinear structure of the component mass balances in a batch reactor. The analysis of the reaction stoichiometry enabled us to draw some conclusions concerning the substrate consumption pathway
Totally Symmetric Kekule Structures in Fullerene Graphs with Ten or More Symmetries
No full textGraph theoretic fullerenes are designed to model large carbon molecules: each vertex represents a carbon atom and the edges represent chemical bonds. A totally symmetric Kekulé structure in a fullerene is a set of independent edges which is fixed by all symmetries of the fullerene. It was suggested in a paper by S. J. Austin, J. Baker, P. W. Fowler, D. E. Manolopoulos and in a paper by K. M. Rogers and P. W. Fowler that molecules with totally symmetric Kekulé structures could have special physical and chemical properties. Starting from a catalog given by J.E.Graver, we study all graph theoretic fullerenes with at least ten symmetries and we establish exactly which of them have at least one totally symmetric Kekulé structure.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Isometries and construction of permutation arrays
No full textAn (n,d)-permutation code is a subset C of Sym(n) such that the Hamming distance dH between any two distinct elements of C is at least equal to d. In this paper, we use the characterization of the isometry group of the metric space (Sym(n),dH) in order to develop generating algorithms with rejection of isomorphic objects. To classify the (n,d) -permutation codes up to isometry, we construct invariants and study their efficiency. We give the numbers of nonisometric (4,3) - and (5,4)- permutation codes. Maximal and balanced (n,d)-permutation codes are enumerated in a constructive way. © 2006 IEEE.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Spatial flood extent modelling. A performance based comparison
No full textThe rapid development of Geographical Information Systems (GIS) has together with the inherent spatial nature of hydrological modelling led to an equally rapid development in the integration between GIS and hydrological models. The advantages of integration are particularly apparent in flood extent modelling. In this thesis, the integration of hydrological models and GIS is approached on the basis of performance, with performance taken as the balance of computational efficiency, flexibility of application, and most importantly the reliability of the integrated model. It is shown that predictive reliability is dominated by model uncertainties, particularly in model roughness parameters. These roughness parameters are found to be more conceptual than physical as they represent bulk momentum loss parameters at the reach scale. Limited data on spatial extent of flooding is available to constrain these uncertainties, and where such data is lacking the simplest numerical approach may be as reliable as more complex approaches. The overall performance of the simple approach is then higher as this is more easily integrated within GIS. Observations of flood extent from aerial photographs may help constrain uncertainties, though much more value is found from distributed water level observations in the floodplain. The lack of hydrological data also results in high resolution GIS data of elevation or land use being of limited value. As sufficient hydrological data is unavailable and perhaps impossible to acquire, model predictions made are recommended to be considered probabilistically, irrespective the level of integration with GIS.Civil Engineering and Geoscience
Permutation codes and permutations arrays: construction, enumeration and automorphisms
No full text<p>Un code de permutations G(n,d) un sous-ensemble C de Sym(n) tel que la distance de Hamming D entre deux éléments de C est supérieure ou égale à d. Dans cette thèse, le groupe des isométries de (Sym(n),D) est déterminé et il est prouvé que ces isométries sont des automorphismes du schéma d'association induit sur Sym(n) par ses classes de conjugaison. Ceci mène, par programmation linéaire, à de nouveaux majorants de la taille maximale des G(n,d) pour n et d fixés et n compris entre 11 et 13. Des algorithmes de génération avec rejet d'objets isomorphes sont développés. Pour classer les G(n,d) non isométriques, des invariants ont été construits et leur efficacité étudiée. Tous les G(4,3) et les G(5,4) ont été engendrés à une isométrie près, il y en a respectivement 61 et 9445 (dont 139 sont maximaux et décrits explicitement). D’autres classes de G(n,d) sont étudiées.<p><p><p><p> <p><p><p><p>A permutation code G(n,d) is a subset C of Sym(n) such that the Hamming distance D between two elements of C is larger than or equal to d. In this thesis, we characterize the isometry group of the metric space (Sym(n),D) and we prove that these isometries are automorphisms of the association scheme induced on Sym(n) by the conjugacy classes. This leads, by linear programming, to new upper bounds for the maximal size of G(n,d) codes for n and d fixed and n between 11 and 13. We develop generating algorithms with rejection of isomorphic objects. In order to classify the G(n,d) codes up to isometry, we construct invariants and study their efficiency. We generate all G(4,3) and G(4,5)codes up to isometry; there are respectively 61 and 9445 of them. Precisely 139 out of the latter codes are maximal and explicitly described. We also study other classes of G(n,d)codes.<p><p><p><p>Doctorat en sciences, Spécialisation mathématiquesinfo:eu-repo/semantics/nonPublishe
Computer-assisted cartography for monitoring spatio-temporal aspects of urban air pollution
No full textCivil Engineering and Geoscience
New Upper Bounds for the Size of Permutation Codes via Linear Progamming
No full textAn (n, d)-permutation code of size s is a subset C of Sn with s elements such that the Hamming distance dH between any two distinct elements of C is at least equal to d. In this paper, we give new upper bounds for the maximal size μ(n, d) of an (n, d)-permutation code of degree n with 11 =< n =<14. In order to obtain these bounds, we use the structure of association scheme of the permutation group Sn and the irreducible characters of Sn .The upper bounds for μ(n, d) are determined solving an optimization problem with linear inequalities.info:eu-repo/semantics/publishe
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