Locally quasi-nilpotent elementary operators

Let $A$ be a unital dense algebra of linear mappings on a complex vector space $X$. Let $\phi=\sum_{i=1}^n M_{a_i,b_i}$ be a locally quasi-nilpotent elementary operator of length $n$ on $A$. We show that, if $\{a_1,\ldots,a_n\}$ is locally linearly independent, then the local dimension of V(\phi)=\spa\{b_ia_j: 1 \leq i,j \leq n\} is at most $\frac{n(n-1)}{2}$. If \lDim V(\phi)=\frac{n(n-1)}{2} , then there exists a representation of $\phi$ as $\phi=\sum_{i=1}^n M_{u_i,v_i}$ with $v_iu_j=0$ for $i\geq j$. Moreover, we give a complete characterization of locally quasi-nilpotent elementary operators of length 3.Comment: 15

Study into mechanical and electrochemical properties of coating deposits and welded-coated components using the HVOF (High Velocity Oxy-Fuel) process.

The present study examines the metallurgical, mechanical and corrosion properties of High Velocity Oxy-Fuel (HVOF) thermal spray coatings of Inconel 625 powders on plain and welded surfaces of mild carbon and stainless steel (304). The research work carried out focused on coating adherence to base substrate, coating integrity and mechanical behavior of coating at the weld-substrate interface when subjected to tensile and fatigue loads. The solid bar and sheet specimens were tested and prepared in accordance with the test standards "Standard Test Method for Adhesion or Cohesion Strength of Thermal Spray Coatings". The specimens were tensile and fatigue tested pre and post exposure to brine. SEM and EDS analysis were carried out to examine the surface morphology and microstructure of the coatings. The specimens that were subjected to a corrosion environment for an extended period of three weeks failed at a lower tensile load than those that were not exposed to corrosive environment. Shear deformation of the adjacent zones at the coating-substrate interface resulted in the total failure of the coating. However, in some cases, the coating was almost free from voids or pores and was impervious to electrolytic or any other contaminants. This result was observed from tests performed on different sets of specimens to identify brine exposure effects on coating adherence to the substrate. Foreign materials were observed beneath the coating due to improper surface preparation during the specimen preparation prior to coating. From tensile tests results it was observed that the bond strength of the coating reduced due to corrosion effect which caused degradation of the coating adhesion to the specimen's surface. This is probably due to the formation of oxides on carbon steel surfaces during coating. Due to expected progressive oxidation, coating adherence was continuously degraded with lowering bond strength. Fatigue results revealed that an excess of 15 thousand cycles without cracking was demonstrated by the stainless steel coated specimens assuring the fatigue strength. The fatigue life resistance of the stainless steel coated specimens exceeded .that of the coated carbon steel specimens. Moreover, the imperfection at the interface resulted during coating could cause early initiation of cracks in the coating, therefore, thus lowering the fatigue strength

Competitivite de la filiere huile d’olive en Algerie: Cas de la wilaya de bejaia

L'oléiculture algérienne a connu ces dernières décennies de profondes mutations, pour sa mise à niveau nécessaire à son intégration dans l’économie mondiale. En effet, la concurrence qui résulte de la libéralisation des échanges a incité les entreprises de ce secteur à améliorer leurs performances et leur compétitivité. Dans ce travail, nous nous proposons d'évaluer la position compétitive de la filière de l'huile d'olive en Algérie. Cette analyse porte d'une part sur la compétitivité, fondée sur le calcul des coûts de production dans les exploitations agricoles de la wilaya de Bejaia, principale zone de production oléicole en Algérie. D’autre part, elle aborde les aspects de compétitivité «hors-prix», déterminés par la qualité qui différencie les produits. L’Algérie ne dispose pas d’un avantage comparatif sur les prix ; mais paradoxalement ses traditions de consommation restent en faveur d’une qualité immatérielle qui exclut le goût algérien du standard international.Mots clés : Filière huile d’olive, Compétitivité, Bejaia, Algérie.Code Jel: Q1, R1

Natural families in evolution algebras

In this paper we introduce the notion of evolution rank and give a decomposition of an evolution algebra into its annihilator and extending evolution subspaces having evolution rank one. This decomposition can be used to prove that in nondegenerate evolution algebras any family of natural and orthogonal vectors can be extended to a natural basis. The central results are the characterization of those families of orthogonal linearly independent vectors which can be extended to a natural basis. We also consider ideals in perfect evolution algebras and prove that they coincide with basic ideals. Nilpotent elements of order three can be localized (in a perfect evolution algebra over a field in which every element is a square) by merely looking at the structure matrix: any vanishing principal minor provides one. Conversely, if a perfect evolution algebra over an arbitrary field has a nilpotent element of order three, then its structure matrix has a vanishing principal minor. We finish by considering the adjoint evolution algebra and relating its properties to the corresponding ones in the initial evolution algebra