Tunis University

About: Tunis University is a education organization based out in Tunis, Tunisia. It is known for research contribution in the topics: Population & Thin film. The organization has 11745 authors who have published 15400 publications receiving 154900 citations. The organization is also known as: University of Tunis & UT.

Global financial crisis and weak-form efficiency of Islamic sectoral stock markets: An MF-DFA analysis

Abstract: This paper estimates the weak-form efficiency of Islamic stock markets using 10 sectoral stock indices (basic materials, consumer services, consumer goods, energy, financials, health care, industrials, technology, telecommunication, and utilities). The results based on the multifractal detrended fluctuation analysis (MF-DFA) approach show time-varying efficiency for the sectoral stock markets. Moreover, we find that they tend to show high efficiency in the long term but moderate efficiency in the short term, and that these markets become less efficient after the onset of the global financial crisis. These results have several significant implications in terms of asset allocation for investors dealing with Islamic markets.

Robust H ∞ sliding mode observer design for fault estimation in a class of uncertain nonlinear systems with LMI optimization approach

Abstract: This paper presents a new approach for the design of robust H∞ sliding mode observer (SMO) for a class of Lipschitz nonlinear systems where both faults and uncertainties are considered. A sufficient condition using linear matrix inequality (LMI) optimization is derived to guarantee the asymptotically stability of the estimation error dynamics and compute the observer gains. A fault estimation scheme is presented where the estimation signal can approximate the fault to some degree of accuracy. Our design approach has some advantages. The Lipschitz constant of the nonlinear term in the system and the disturbance attenuation level are maximized simultaneously through convex multiobjective optimization. For this reason, the Lipschitz constant is suitable to a large class of uncertain nonlinear systems. Moreover, the fault estimation is much more robust against disturbances and nonlinear uncertainty and can preserve the fault signal shape effectively. Finally, a simulation study on a robotic arm system is presented to show the effectiveness of this approach.

Structural optical magnetic properties of Co doped α-MoO3 sprayed thin films

Abstract: This works deals with the synthesis of Cobalt doped MoO 3 thin films which were grown on glass substrates by the spray pyrolysis at 460 °C. First, X-ray diffraction analysis shows an orthorhombic structure related to α-MoO 3 allotropic variety with (020) and (040) preferred orientations. The surface topography performed by atomic force microscopy (AFM) shows that the grain size varies from 150 to 280 nm. Second, optical parameters, such as optical band gap, Urbach energy, refractive index and dielectric constants were studied in terms of Co content. This optical study shows a direct transition of all prepared thin films and normal dispersion of the refractive index showing both Cauchy and Wemple & Di-dominico variations. On the other hand, PL measurements show transition bands mainly in blue and green domains related to band-to-band transitions as well as to oxygen vacancy in all films. Finally, magnetic measurements at room temperature using vibrating sample magnetometer (VSM) technique reveal a ferromagnetic behavior of such doped films.