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Infinitely many homoclinic solutions for damped vibration systems with locally defined potentials
Wafa Selmi,Mohsen Timoumi 대한수학회 2022 대한수학회논문집 Vol.37 No.3
In this paper, we are concerned with the existence of infinitely many fast homoclinic solutions for the following damped vibration system $$\ddot{u}(t)+q(t)\dot{u}(t)-L(t)u(t)+\nabla W(t,u(t))=0,\ \forall t\in\mathbb{R}, \leqno(1)$$ where $q\in C(\mathbb{R},\mathbb{R})$, $L\in C(\mathbb{R},\mathbb{R}^{N^{2}})$ is a symmetric and positive definite matix-valued function and $W\in C^{1}(\mathbb{R}\times\mathbb{R}^{N},\mathbb{R})$. The novelty of this paper is that, assuming that $L$ is bounded from below unnecessarily coercive at infinity, and $W$ is only locally defined near the origin with respect to the second variable, we show that $(1)$ possesses infinitely many homoclinic solutions via a variant symmetric mountain pass theorem.
CEO Characteristics and Firm Performance: A Study of Saudi Arabia Listed Firms
Wafa GHARDALLOU,Hela BORGI,Hibah ALKHALIFAH 한국유통과학회 2020 The Journal of Asian Finance, Economics and Busine Vol.7 No.11
This paper aims to investigate the impact of chief executive officer’s (CEO) attributes on firms’ performance. Specifically, it examines the influence of CEOs’ education, professional experience, and tenure on Saudi firms’ performance. We look at a sample of 120 listed firms on Tadawul stock exchange from 2014 to 2017. Data on financial and accounting variables are obtained from the annual reports of the selected companies. We follow the existing empirical literature and use a panel model and formulate three different equations using the GMM estimator. Findings prove that CEO educational background does matter. In particular, companies employing CEOs with business administration, economics, finance, or accounting degree will perform outstandingly better. Similarly, stock performance gets improved when the CEO has a postgraduate qualification, i.e., when the CEO holds an MBA, a master, or a PhD degree. Besides, results reveal that executives who have an experience in a related field will positively affect the firm’s performance. Finally, evidence shows that high CEOs tenure improves corporate performance. Overall, these findings demonstrate that executives’ attributes are key factors that would explain differences in Saudi firms’ performance. These results would help shareholders to make the right decision in selecting CEOs to manage the company.
Wafa Boukadida,Anouar Benamor,Hassani Messaoud,Patrick Siarry 제어·로봇·시스템학회 2019 International Journal of Control, Automation, and Vol.17 No.6
The paper introduces a new design control strategy for finite time stabilization of uncertain discrete systems. The proposed control method uses the First Order Sliding Mode Control (FOSMC), the Linear Quadratic Regulator (LQR) and Genetic Algorithms (GA). The key idea of combining two control strategies lies in the fact that a robust controller tackles the uncertainties when the optimal controller performances are unaffected. Firstly, as the performances of the Sliding Mode Control (SMC) greatly depends on the choice of the sliding surface, a novel method based on the resolution of a Sylvester equation is proposed. Secondly, to ensure the robustness in the whole space, the Integral Sliding Mode Control (ISMC) is combined with the above LQR method. Rigorous stability analysis for the closed-loop system is given and proves that the system states are always bounded even the unknown disturbances. In order to handle the problem accompanying the LQR synthesis as well as the gain of the robust compensator, a multi-objective optimization problem considering a set of competing objectives is solved using GA.For that,a novel dynamically aggregated objective function is proposed. A set of non dominated optimal solutions are provided to the control engineer and then may select the most adequate solution among the resulting optimal Pareto set. The novel method has successfully solved the robust stabilization of two known benchmarks and the different results asserts not merely the efficiency as well as the quality of the designed controller but also its supremacy compared to some existing ones.
Wafa Tourab,Abdesselam Babouri 한국산업안전보건공단 산업안전보건연구원 2016 Safety and health at work Vol.7 No.2
Background: This work presents an experimental and modeling study of the electromagnetic environment in the vicinity of a high voltage substation located in eastern Algeria (Annaba city) specified with a very high population density. The effects of electromagnetic fields emanating from the coupled multilines high voltage power systems (MLHV) on the health of the workers and people living in proximity of substations has been analyzed. Methods: Experimental Measurements for the Multi-lines power system proposed have been conducted in the free space under the high voltage lines. Field’s intensities were measured using a referenced and calibrated electromagnetic field meter PMM8053B for the levels 0 m, 1 m, 1.5 m and 1.8 m witch present the sensitive’s parts as organs and major functions (head, heart, pelvis and feet) of the human body. Results: The measurement results were validated by numerical simulation using the finite element method and these results are compared with the limit values of the international standards. Conclusion: We project to set own national standards for exposure to electromagnetic fields, in order to achieve a regional database that will be at the disposal of partners concerned to ensure safety of people and mainly workers inside high voltage electrical substations.
Wafa Cherif,Leila Ktari,Monia El Bour,Abdellatif Boudabous,Micheline Grignon-Dubois 한국조류학회I 2016 ALGAE Vol.31 No.2
The Mediterranean Sea is currently facing dramatic changes and threats, including change in native species and accidental introductions. The introduced green alga Codium fragile subsp. fragile (Suringar) Hariot influences diversity and community structure in some parts of the world. This paper documents the distribution of this species in Tunisia and provides a morphological description of C. fragile subsp. fragile in Northern Tunisia. Results confirm the identity of Tunisian specimens as the invasive subspecies C. fragile subsp. fragile. This is the first morphological characterization of this subspecies in Tunisia.
Wafa Tebboune,Abdelouahed Tounsi,Kouider Halim Benrahou,Mohammed Sid Ahmed Houari 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.18 No.2
In this paper, an efficient and simple trigonometric shear deformation theory is presented for thermal buckling analysis of functionally graded plates. It is assumed that the plate is in contact with elastic foundation during deformation. The theory accounts for sinusoidal distribution of transverse shear stress, and satisfies the free transverse shear stress conditions on the top and bottom surfaces of the plate without using shear correction factor. Unlike the conventional trigonometric shear deformation theory, the proposed sinusoidal shear deformation theory contains only four unknowns. It is assumed that the mechanical and thermal non-homogeneous properties of functionally graded plate vary smoothly by distribution of power law across the plate thickness. Using the non-linear strain-displacement relations, the equilibrium and stability equations of plates made of functionally graded materials are derived. The boundary conditions for the plate are assumed to be simply supported on all edges. The elastic foundation is modelled by two-parameters Pasternak model, which is obtained by adding a shear layer to the Winkler model. The effects of thermal loading types and variations of power of functionally graded material, aspect ratio, and thickness ratio on the critical buckling temperature of functionally graded plates are investigated and discussed.