123 research outputs found
Sur la symétrie et l'asymétrie des structures combinatoires
RĂ©sumĂ©Le but de ce texte est de prĂ©senter un panorama des propriĂ©tĂ©s fondamentales et de quelques applications concrĂ©tes des sĂ©ries indicatrices des cycles et des Ćeries indicatrices d'asymĂ©trie en combinatoire Ă©numĂ©rative. Ces sĂ©ries sont des outils permettant de calculer diverses statistiques concernant les symĂ©tries ou l'absence de symĂ©trie des structures appartenant Ă des espĂšces donnĂ©es. Nous mettons l'emphase sur le comportement de ces sĂ©ries devant les principales opĂ©rations combinatoires que l'on peut utiliser pour dĂ©finir (rĂ©cursivement ou explicitement) des espĂ©ces de structures.AbstractThe goal of this paper is to present a panorama of the fundametal properties of cycle index series and asymmetry index series within enumerative combinatorics, as well as a few concrete applications. These series are tools by means of which one can compute various statistics concerning the symmetries or lack of symmetry of structures belonging to given species. Emphasis is laid on the behaviour of these series with respect to the main operations that can be used to define (recursively or explicitly) species of structures
Enumeration of m-ary cacti
The purpose of this paper is to enumerate various classes of cyclically
colored m-gonal plane cacti, called m-ary cacti. This combinatorial problem is
motivated by the topological classification of complex polynomials having at
most m critical values, studied by Zvonkin and others. We obtain explicit
formulae for both labelled and unlabelled m-ary cacti, according to i) the
number of polygons, ii) the vertex-color distribution, iii) the vertex-degree
distribution of each color. We also enumerate m-ary cacti according to the
order of their automorphism group. Using a generalization of Otter's formula,
we express the species of m-ary cacti in terms of rooted and of pointed cacti.
A variant of the m-dimensional Lagrange inversion is then used to enumerate
these structures. The method of Liskovets for the enumeration of unrooted
planar maps can also be adapted to m-ary cacti.Comment: LaTeX2e, 28 pages, 9 figures (eps), 3 table
On extensions of the Newton-Raphson iterative scheme to arbitrary orders
Abstract. The classical quadratically convergent Newton-Raphson iterative scheme for successive approximations of a root of an equation f (t) = 0 has been extended in various ways by different authors, going from cubical convergence to convergence of arbitrary orders. We introduce two such extensions, using appropriate differential operators as well as combinatorial arguments. We conclude with some applications including special series expansions for functions of the root and enumeration of classes of tree-like structures according to their number of leaves. Résumé. Le schéma itératif classiqueà convergence quadratique de Newton-Raphson pour engendrer des approximations successives d'une racine d'uneéquation f (t) = 0 aétéétendu de plusieurs façons par divers auteurs, allant de la convergence cubiqueà des convergences d'ordres arbitraires. Nous introduisons deux telles extensions en utilisant des opérateurs différentiels appropriés ainsi que des arguments combinatoires. Nous terminons avec quelques applications incluant des développements en séries exprimant des fonctions de la racine et l'énumération de classes de structures arborescentes selon leur nombre de feuilles
The explicit molecular expansion of the combinatorial logarithm
Just as the power series of is the analytical substitutional inverse of the series of , the (virtual) combinatorial species, , is the combinatorial substitutional inverse of the combinatorial species, , of non-empty finite sets. This , , has been introduced by A. Joyal in 1986 by making use of an iterative scheme. Given a species (with ), one of its main applications is to express the species, , of -structures through the formula where denotes the species of non-empty -structures. Since its creation, equivalent descriptions of the combinatorial logarithm have been given by other combinatorialists (G. L., I. Gessel, J. Li), but its exact decomposition into irreducible components (molecular expansion) remained unclear. The main goal of the present work is to fill this gap by computing explicitly the molecular expansion of the combinatorial logarithm and of , a "cousin'' of the tensorial species, , of free Lie algebras
New combinatorial computational methods arising from pseudo-singletons
Since singletons are the connected sets, the species of singletons can be considered as the combinatorial logarithm of the species of finite sets. In a previous work, we introduced the (rational) species of pseudo-singletons as the analytical logarithm of the species of finite sets. It follows that in the context of rational species, where denotes the classical analytical power series for the exponential function in the variable . In the present work, we use the species to create new efficient recursive schemes for the computation of molecular expansions of species of rooted trees, of species of assemblies of structures, of the combinatorial logarithm species, of species of connected structures, and of species of structures with weighted connected components
Closed paths whose steps are roots of unity
We give explicit formulas for the number of closed polygonal paths of length (starting from the origin) whose steps are roots of unity, as well as asymptotic expressions for these numbers when . We also prove that the sequences are -recursive for each fixed and leave open the problem of determining the values of for which the sequences are -recursive
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Influence of Acidic pH on Hydrogen and Acetate Production by an Electrosynthetic Microbiome
Production of hydrogen and organic compounds by an electrosynthetic microbiome using electrodes and carbon dioxide as sole electron donor and carbon source, respectively, was examined after exposure to acidic pH (âŒ5). Hydrogen production by biocathodes poised at â600 mV vs. SHE increased>100-fold and acetate production ceased at acidic pH, but âŒ5â15 mM (catholyte volume)/day acetate and>1,000 mM/day hydrogen were attained at pH âŒ6.5 following repeated exposure to acidic pH. Cyclic voltammetry revealed a 250 mV decrease in hydrogen overpotential and a maximum current density of 12.2 mA/cm2 at â765 mV (0.065 mA/cm2 sterile control at â800 mV) by the Acetobacterium-dominated community. Supplying â800 mV to the microbiome after repeated exposure to acidic pH resulted in up to 2.6 kg/m3/day hydrogen (â2.6 gallons gasoline equivalent), 0.7 kg/m3/day formate, and 3.1 kg/m3/day acetate (â=â4.7 kg CO2 captured).</p
Counting unlabelled toroidal graphs with no K33-subdivisions
We provide a description of unlabelled enumeration techniques, with complete
proofs, for graphs that can be canonically obtained by substituting 2-pole
networks for the edges of core graphs. Using structure theorems for toroidal
and projective-planar graphs containing no K33-subdivisions, we apply these
techniques to obtain their unlabelled enumeration.Comment: 25 pages (some corrections), 4 figures (one figure added), 3 table
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