The Harris-Luck criterion for random lattices

The Harris-Luck criterion judges the relevance of (potentially) spatially correlated, quenched disorder induced by, e.g., random bonds, randomly diluted sites or a quasi-periodicity of the lattice, for altering the critical behavior of a coupled matter system. We investigate the applicability of this type of criterion to the case of spin variables coupled to random lattices. Their aptitude to alter critical behavior depends on the degree of spatial correlations present, which is quantified by a wandering exponent. We consider the cases of Poissonian random graphs resulting from the Voronoi-Delaunay construction and of planar, ``fat'' $\phi^3$ Feynman diagrams and precisely determine their wandering exponents. The resulting predictions are compared to various exact and numerical results for the Potts model coupled to these quenched ensembles of random graphs.Comment: 13 pages, 9 figures, 2 tables, REVTeX 4. Version as published, one figure added for clarification, minor re-wordings and typo cleanu

On the critical frontiers of Potts ferromagnets

We formulate a conjecture concerning the critical frontiers of q-state Potts ferromagnets on d-dimensional lattices (d > 1) which generalize a recent one stated for planar lattices. The present conjecture is verified within satisfactory accuracy (exactly in some cases) for all the lattices or arrays whose critical points are known. Its use leads to the prediction of : a) a considerable amount of new approximate critical points (26 on non-planar regular lattices, some others on Husimi trees and cacti) ; b) approximate critical frontiers for some 3-dimensional lattices; c) the possibly asymptotically exact critical point on regular lattices in the limit d → ∞ for all q ≽ 1; d) the possibly exact critical frontier for the pure Potts model on fully anisotropic Bethe lattices; e) the possibly exact critical frontier for the general quenched random-bond Potts ferromagnet (any P(J)) on isotropic Bethe lattices.Nous formulons une conjecture sur les frontières critiques du modèle de Potts à q états ferromagnétiques sur des réseaux d-dimensionnels (d > 1) qui généralise une proposition récente pour des réseaux plans. La conjecture présente est vérifiée de façon satisfaisante (exacte dans certains cas) pour tous les réseaux dont les points critiques sont connus. Son utilisation nous permet de prédire : a) un nombre considérable de points critiques approchés (26 sur des réseaux réguliers non planaires, quelques-uns sur des arbres de Husimi et des cacti); b) les frontières critiques approchées pour quelques réseaux tridimensionnels; c) le comportement asymptotique probablement exact du point critique pour des réseaux réguliers dans la limite d → oo pour tout q ≽ 1; d) la frontière critique probablement exacte pour le modèle de Potts pure sur des réseaux de Bethe complètement anisotropes; e) la frontière critique probablement exacte pour le modèle trempé ferromagnétique de Potts à liaisons aléatoires distribuées selon une loi quelconque (P(J)) sur des réseaux de Bethe isotropes

Streptococcus Agalactiae In Brazil: Serotype Distribution, Virulence Determinants And Antimicrobial Susceptibility

Background: Group B Streptococcus (GBS) remains a major cause of neonatal sepsis and is also associated with invasive and noninvasive infections in pregnant women and non-pregnant adults, elderly and patients with underlying medical conditions. Ten capsular serotypes have been recognized, and determination of their distribution within a specific population or geographical region is important as they are major targets for the development of vaccine strategies. We have evaluated the characteristics of GBS isolates recovered from individuals with infections or colonization by this microorganism, living in different geographic regions of Brazil.Methods: A total of 434 isolates were identified and serotyped by conventional phenotypic tests. The determination of antimicrobial susceptibility was performed by the disk diffusion method. Genes associated with resistance to erythromycin (ermA, ermB, mefA) and tetracycline (tetK, tetL, tetM, tetO) as well as virulence-associated genes (bac, bca, lmb, scpB) were investigated using PCR. Pulsed-field gel electrophoresis (PFGE) was used to examine the genetic diversity of macrolide-resistant and of a number of selected macrolide-susceptible isolates.Results: Overall, serotypes Ia (27.6%), II (19.1%), Ib (18.7%) and V (13.6%) were the most predominant, followed by serotypes IV (8.1%) and III (6.7%). All the isolates were susceptible to the beta-lactam antimicrobials tested and 97% were resistant to tetracycline. Resistance to erythromycin and clindamycin were found in 4.1% and 3% of the isolates, respectively. Among the resistance genes investigated, tetM (99.3%) and tetO (1.8%) were detected among tetracycline-resistant isolates and ermA (39%) and ermB (27.6%) were found among macrolide-resistant isolates. The lmb and scpB virulence genes were detected in all isolates, while bac and bca were detected in 57 (13.1%) and 237 (54.6%) isolates, respectively. Molecular typing by PFGE showed that resistance to erythromycin was associated with a variety of clones.Conclusion: These findings indicate that GBS isolates circulating in Brazil have a variety of phenotypic and genotypic characteristics, and suggest that macrolide-resistant isolates may arise by both clonal spread and independent acquisition of resistance genes. © 2014 Dutra et al.; licensee BioMed Central Ltd.141Schuchat, A., Epidemiology of group B streptococcal disease in the United States: shifting paradigms (1998) Clin Microbiol Rev, 11, pp. 497-513. , 88893, 9665980Skoff, T.H., Farley, M.M., Petit, S., Increasing burden of invasive group B streptococcal disease in nonpregnant adults, 1990-2007 (2009) Clin Infect Dis, 49, pp. 85-92. , 10.1086/599369, 19480572Maisey, H.C., Doran, K.S., Nizet, V., Recent advances in understanding the molecular basis of group B Streptococcus virulence (2008) Expert Rev Mol Med, 10, pp. 1-16Slotved, H.C., Kong, F., Lambertsen, L., Sauer, S., 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