The influence of leadership styles on job performance in telecommunication company of Algeria (OTA)

This study attempts to present a picture of leadership style in Orascom Telecom Algeria (OTA). The primary purpose of this study is to analyse the relationship between transformational, transactional, servant, and participative leadership, and job performance. The study population is comprised of Telecommunications Company in Algeria located in Algiers, Oran. Data were collected from 205 employees. SmartPLS was used in order to determine whether the hypotheses were accepted. The results supported all of the hypotheses of this study, discovered that transformational, transactional, servant, and participative leadership have positive effects on job performance. The results affirmed that transformational leadership, transactional leadership, servant leadership, and participative leadership styles affect job performance of OTA’ employees. It is hoped that the outcome of this study can be used as guidance for OTA Algeria to empower their workforce

Influence du polyéthylène oxyde (PEO) de différentes masses moléculaires sur les propriétés rhéologiques des suspensions d’argile

Le but de ce travail est d’étudier l’effet du polyéthylène oxyde (PEO) (polymère non ionique), utilisé généralement dans la formulation des boues de forage, sur le comportement rhéologique de suspensions debentonite. Des mesures rhéologiques, granulométriques et zétamétriques ont été effectuées sur une suspension de bentonite, des solutions de PEO (polyéthylène oxyde de masse moléculaire de 4.106, 106, 4.105 et 105 g.mol- 1) et des mélanges bentonite-PEO à différentes concentrations de polymères. L’étude a révélé une forte augmentation (d’autant plus importante que la concentration et la masse moléculaire du PEO  augmentent) de la viscosité, de la contrainte seuil et des propriétés viscoélastiques de la suspension argileuse. L’origine de ce changement de comportement a été discutée sur la base de l'étude zétamétrique et granulométrique. Cette dernière a mis en évidence des liaisons pont assurées par les chaînes de polymères entre les particules de bentonite.Mots clés : Boues de forage, bentonite, polyéthylène oxyde

Nonlinear control of a grid connected hybrid energetic systems (HES) based on photovoltaic-fuel cells distributed power generation systems

This paper presents a discrete-time integral sliding mode control for a grid connected hybrid energetic systems (HES) based on photovoltaic-Solid oxide fuel cell (SOFC) for distributed power generation systems. The proposed HES systems employ solid oxide fuel cell (SOFC) and photovoltaic panels as main sources, supercapacitors as complementary sources, and controlled DC-DC boost converter and three levels NPC inverter. A maximum power point tracking (MPPT) control is used in order to maximize the power of the photovoltaic system. The proposed control consists of a power management grid interface inverter transferring the energy from the hybrid sources into the grid by controlling the main utility grid and the common DC voltage active and reactive power. The obtained simulation results show the effectiveness and robustness of the proposed control strategy. Keywords: Hybrid Energetic Systems (HES), Solid Oxide Fuel Cell (SOFC), Photovoltaic (PV), Sliding Mode Control, Maximum Power Point Tracking (MPPT), Grid power management

Annular interdigital transducer focuses piezoelectric surface waves to a single point

We propose and demonstrate experimentally the concept of the annular interdigital transducer that focuses acoustic waves on the surface of a piezoelectric material to a single, diffraction-limited, spot. The shape of the transducing fingers follows the wave surface. Experiments conducted on lithium niobate substrates evidence that the generated surface waves converge to the center of the transducer, producing a spot that shows a large concentration of acoustic energy. This concept is of practical significance to design new intense microacoustic sources, for instance for enhanced acouto-optical interactions

Formulation of a composite of date palm wood-cement

This work reports the results of an experimental study on the incorporation of wood waste date palm reduced in particles for the manufacture of wood – cement composites. These materials are chipper than the conventional insulator material and environmental friendly. Five types of wood – cement composites with various concentrations of the wood particles, ie. 2, 4, 6, 8 and 10% of total volume, were made according to defined protocol and mix design. Their thermal and mechanical properties were measured and compared to other conventional materials. The obtained results show that the thermal conductivity is positively correlated to the content of particles in the mixture. The compressive strength of composites decreases where the content of particles increase. However, taking account of the ASTM C 109 / C109-95 standard, the wood – cement composite contained 10% of wood particles, considered as lightweight concrete, could be used as non-structural material in construction

Experimental Characterization of a Functionally Graded Composite Using Recycled Steel Fiber

Many industries have recently focused on cost-effective materials with good mechanical properties. Steel fiber reinforced cementitious composites have proven their mechanical performance in industrial and structural components. The concept of recycled fiber-reinforced FGM is used as an alternative construction material, which can be one of the proposed cost-effective solutions. To achieve these objectives, an experimental program has been developed. A cementitious composite based on local materials was strengthened in two designs; one strengthened over the entire cross-section and the other strengthened only in the tensile zone. We also substituted a functional gradient material reinforced with recycled fibers considering the following volume fractions: 0, 0.5, 1, and 1.5%. This paper investigates the feasibility of using recycled fibers from industrial waste from steel wool manufacturing as reinforcement. We also characterized their mechanical properties using ultrasonic pulse velocity, compressive strength, flexural tensile strength, and shear strength. The results show that the corrugated recycled fibers are the ideal choice to increase the mechanical performance of the reinforced composite, including the improvement of flexural and shear behaviors. Therefore, the investigated FGC could be a valuable tool to optimize the design process in various structural applications and make the production of mechanically and environmentally economical composites possible. Doi: 10.28991/CEJ-2022-08-05-03 Full Text: PD

Thermal design of air cooled condenser of a solar adsorption refrigerator

The objective of this paper is to study the design of a condenser of a solar adsorption refrigerator which will be tested in the region of Biskra (Algeria). The LMTD (log mean temperature difference) method is used to calculate the size of the condenser applying experimental data obtained from the literature. For this purpose, a calculation code has been developed to determine the total heat transfer area of the heat exchanger. Therefore, we present a comparison between calculated and experimental results obtained from the literature. This comparison allowed the validation of the calculation method by applying the same experimental conditions. The discussion of the results indicates that we cannot use the ambient air in free convection mode as a cooling fluid if its temperature exceeds 30°C. This problem presents the greatest obstacle especially in the Saharan regions, such as in Biskra, where the average ambient air temperature during the summer exceeds 35°C. As a solution, we propose in this article the improvement of the heat transfer by the air-forced convection mode. Thus, it is established that the use of the air fan can extend the operating temperature limits of the condenser above 35°C