Diversité des pratiques d'élevage bovin à viande dans le massif du Dahra (Algérie)

Pour appréhender la diversité des pratiques d’élevage bovin à viande dans les zones rurales du massif du Dahra (nord-ouest algérien), une typologie a été réalisée à partir des résultats d’une enquête dans 56 exploitations. Les groupes définis diffèrent par les structures et sont de 5 types (A, B, C, D et E). L’analyse technico - économique de 20 exploitations réparties sur les différents types préalablement identifiés révèle 4 systèmes de pratiques différents selon l’objectif de production, le plus souvent en cohérence avec les structures disponibles. Le contrôle des performances réalisé au niveau de 9 exploitations montre que lorsqu'on exclut le système d’élevage bovin commercial sans femelles reproductrices (engraisseur), le système à logique de capitalisation apparaît alors comme le plus performant

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

Recent trends on analytic properties of matrix orthonormal polynomials

Abstract. In this paper we give an overview of recent results on analytic properties of matrix orthonormal polynomials. We focus our attention on the distribution of their zeros as well as on the asymptotic behavior of such polynomials under some restrictions about the measure of orthogonality. Key words. matrix orthogonal polynomials, zeros, asymptotic behavior. AMS subject classifications. 42C05, 15A15, 15A23

Solution of internal erosion equations by asymptotic expansion

One dimensional coupled soil internal erosion and consolidation equations are considered in this work for the special case of well determined sand and clay mixtures with a small proportion of clay phase. An enhanced modelling of the effect of erosion on elastic soil behavior was introduced through damage mechanics concepts. A modified erosion law was proposed. The erosion phenomenon taking place inside the soil was shown to act like a perturbation affecting the classical soil consolidation equation. This interpretation has enabled considering an asymptotic expansion of the coupled erosion consolidation equations in terms of a perturbation parameter linked to the maximum expected internal erosion. A robust analytical solution was obtained via direct integration of equations at order zero and an adequate finite difference scheme that was applied at order one