Perturbations in the Nevai matrix class of orthogonal matrix polynomials

24 pages, no figures.-- MSC2000 codes: 15A54, 15A21, 42C05.MR#: MR1855403 (2002i:42037)Zbl#: Zbl 0992.15022In this paper we study a Jacobi block matrix and the behavior of the limit of its entries when a perturbation of its spectral matrix measure by the addition of a Dirac delta matrix measure is introduced.The work of the second author was supported by Dirección General de Enseñanza Superior (DGES) of Spain under grant PB96-0120-CO3-01 and INTAS Project INTAS-93-0219 Ext, and the work of the third author was supported by DGES under grant PB 95-1205, INTAS-93-0219-ext and Junta de Andalucía, Grupo de Investigación FQM 229.Publicad

Analyse de la diversité génétique des plasmides d'Escherichia coli antibiorésistants causant la colibacillose aviaire

Les souches d’Escherichia coli aviaires antibiorésistantes sont porteuses de plasmides à une fréquence très élevée. Dans une étude antérieure, l’hétérogénéité de ces plasmides a été montrée. Une sonde d’ADN plasmidique (2 kb) extraite de l’une de ces souches a été utilisée dans la technique du Southern blot pour analyser les relations existantes entre les plasmides. À partir de poulets atteints de colibacillose et provenant de différentes fermes d’élevage, les plasmides de 22 souches d’E. coli ont été isolées. La sonde s’est hybridée avec tous les profils plasmidiques de ces souches, ce qui est en faveur de la présence d’une grande homologie de séquence entre ces plasmides ainsi que leur appartenance au même groupe d’hybridation. Le profil d’hybridation confirme l’hétérogénéité des plasmides contenus dans ces souches

Relative asymptotics for orthogonal matrix polynomials with respect to a perturbed matrix measure on the unit circle

19 pages, no figures.-- MSC2000 codes: 42C05, 47A56.MR#: MR1970413 (2004b:42058)Zbl#: Zbl 1047.42021Given a positive definite matrix measure Ω supported on the unit circle T, then main purpose of this paper is to study the asymptotic behavior of L_n(\tilde{\Omega}) L_n(\Omega) -1} and \Phi_n(z, \tilde{\Omega}) \Phi_n(z, \tilde{\Omega}) -1} where $\tilde{\Omega}(z) = \Omega(z) + M \delta ( z - w)$, $1$, M is a positive definite matrix and δ is the Dirac matrix measure. Here, Ln(·) means the leading coefficient of the orthonormal matrix polynomials Φn(z; •).Finally, we deduce the asymptotic behavior of $\Phi_n(omega, \tilde{\Omega}) \Phi_n(omega, \Omega)$ in the case when M=I.The work of the second author was supported by Dirección General de Enseñanza Superior (DGES) of Spain under grant PB96-0120-C03-01 and INTAS Project INTAS93-0219 Ext.Publicad

Ectomycorrhizal fungal diversity and community structure associated with cork oak in different landscapes

Cork oak (Quercus suber L.) forests play an important ecological and economic role. Ectomycorrhizal fungi (ECMF) are key components for the sustainability and functioning of these ecosystems. The community structure and composition of ECMF associated with Q. suber in different landscapes of distinct Mediterranean bioclimate regions have not previously been compared. In this work, soil samples from cork oak forests residing in different bioclimates (arid, semi-arid, sub-humid, and humid) were collected and surveyed for ectomycorrhizal (ECM) root tips. A global analysis performed on 3565 ECM root tips revealed that the ECMF community is highly enriched in Russula, Tomentella, and Cenoccocum, which correspond to the ECMF genera that mainly contribute to community differences. The ECMF communities from the rainiest and the driest cork oak forests were distinct, with soils from the rainiest climates being more heterogeneous than those from the driest climates. The analyses of several abiotic factors on the ECMF communities revealed that bioclimate, precipitation, soil texture, and forest management strongly influenced ECMF structure. Shifts in ECMF with different hyphal exploration types were also detected among forests, with precipitation, forest system, and soil texture being the main drivers controlling their composition. Understanding the effects of environmental factors on the structuring of ECM communities could be the first step for promoting the sustainability of this threatened ecosystem.This work was supported by Fundacao Ciencia e Tecnologia (FCT/MCTES/PIDDAC, Portugal), under the project (PEst-OE/BIA/UI4046/2014; UID/MULTI/04046/2013) and PhD grant to F.R. (SFRH/BD/86519/2012)

Mycorrhization of fagaceae forests within mediterranean ecosystems

Mediterranean Fagaceae forests are valuable due to their ecological and socioeconomic aspects. Some profitable plant species, such as Castanea (timber and chestnut), Quercus (timber and cork), and Fagus (timber), encounter in this habitat the excellent edaphoclimatic conditions to develop. All Fagaceae plants are commonly associated to ECM fungal species, which are found in these forests in quite stable communities, mainly enriched in Russulaceae and Telephoraceae species. Currently, the Mediterranean Basin is considered as one of the global biodiversity hotspots, since many of their endemic plant species are not found elsewhere and are now under threat. Due to climate changing and introduction of disease agents, Fagaceae forests are facing an adaptation challenge to both biotic and abiotic threats. Although ECM communities are highly disturbed by climate factors and tree disease incidence, they could play an important role in increasing water availability to the plant and also improving plant tree defense against pathogens. Recent advances, namely, on genomics and transcriptomics, are providing tools for increasing the understanding of Fagaceae mycorrhization process and stress responses to biotic and abiotic stresses. Such studies can provide new information for the implementation of the most adequate management policies for protecting threaten Mediterranean forests.info:eu-repo/semantics/publishedVersio

The Possibilities of Phenomenology for Organizational Research

Qualitative researchers have developed and employed a variety of phenomenological methodologies to examine individuals’ experiences. However, there is little guidance to help researchers choose between these variations to meet the specific needs of their studies. The purpose of this article is to illuminate the scope and value of phenomenology by developing a typology that classifies and contrasts five popular phenomenological methodologies. By explicating each methodology’s differing assumptions, aims, and analytical steps, the article generates a series of guidelines to inform researchers’ selections. Subsequent sections distinguish the family of phenomenological methodologies from other qualitative methodologies, such as narrative analysis and autoethnography. The article then identifies institutional work and organizational identity as topical bodies of research with particular research needs that phenomenology could address

Managing Imaginary organizations

International audienc

Production et mise sur le marché du lait en Algérie, entre formel et informel : stratégies des éleveurs du périmètre irrigué du Haut-Cheliff

International audienceThe main problem of dairy industry in Algeria is aid to consumption of cheap milk, made from dry milk powder. In the area of Haut-Cheliff, the problem of developing fresh milk industry has taken centre stage because this is an important milk-producing region which reflects the current state of the national dairy sector. Whatever the segment of this supply chain, shortcomings and failures are clearly visible. The collection rate is low and ranges from 11 to 12% in the area under investigation. A poorly specialized production system and a collection system providing few incentives encourage milk distribution through uncontrolled marketing channels or informal channels. The sale of milk through informal channels is more profitable and is favoured by the proximity of many agglomerations. There is an increasing tendency towards legitimization and formalization of these circuits by integrating traditionally manufactured products, mainly butter, Raib (curd) and L'ben (fermented milk) into marketing channels (groceries, stores, etc).Le problème fondamental de la filière lait en Algérie a toujours été l’aide accordée à la consommation en mettant sur le marché un lait pas cher, fabriqué à partir de poudre de lait anhydre. Dans la zone du Haut-Cheliff, le problème du développement d’une filière de lait frais se pose directement car cette région est un bassin laitier important qui reflète la situation de la filière à l'échelle nationale. Quel que soit le segment de la filière, les insuffisances et les contre-performances sont évidentes. Le taux de collecte demeure faible, de 11 à 12 % dans la région d’étude. Un système de production très peu spécialisé et un système de collecte très peu incitatif sont à l’origine de l'écoulement de la production laitière vers les circuits non contrôlés ou informels. L’écoulement par l’informel, plus rémunérateur, est favorisé par la proximité de nombreuses agglomérations. Ces circuits tendent de plus en plus à se légitimer et à se formaliser par l’intégration des produits de production artisanale surtout le beurre, le lait caillé (Raib) et le lait fermenté (L’ben) dans les circuits de commerce (épicerie, points de vente, etc.)