Aloui R.,Tunis el Manar University |
Aissa M.S.B.,Tunis el Manar University
Journal of Banking and Finance | Year: 2011
The paper examines the extent of the current global crisis and the contagion effects it induces by conducting an empirical investigation of the extreme financial interdependences of some selected emerging markets with the US. Several copula functions that provide the necessary flexibility to capture the dynamic patterns of fat tail as well as linear and nonlinear interdependences are used to model the degree of cross-market linkages. Using daily return data from Brazil, Russia, India, China (BRIC) and the US, our empirical results show strong evidence of time-varying dependence between each of the BRIC markets and the US markets, but the dependency is stronger for commodity-price dependent markets than for finished-product export-oriented markets. We also observe high levels of dependence persistence for all market pairs during both bullish and bearish markets. © 2010 Elsevier B.V.
Barhoumi B.,Tunis el Manar University
Mechanics and Industry | Year: 2017
This paper presents an improved form of the convected Boundary Element Method (BEM) for axisymmetric problems in a subsonic uniform flow. The proposed formulation based on the axisymmetric Convected Helmholtz Equation (CHE) and its fundamental solution that describes the sound radiation from a monopole source. The variables in the new axisymmetric boundary integral formulation can be expressed explicitly in terms of the acoustic pressure and its particular normal derivative. Also, the constant coefficients are expressed only in terms of the axisymmetric convected Green's function and its convected normal derivative. The particular and convected derivatives reduce the flow effects of the normal and the flow direction derivatives incorporated in the conventional convected boundary integral formulas. The advanced form of the axisymmetric boundary integral representation with flow is a similar form of the axisymmetric boundary element method without flow. Precisely, the two new operators significantly reduce the computational burden of the classical BEM and then becomes the CPU time of BEM without flow. The formula is verified comparing to both analytical and Finite Element Methods (FEM) of an axisymmetric infinite rigid duct in a subsonic uniform flow. © AFM, EDP Sciences 2017.
Agency: European Commission | Branch: H2020 | Program: RIA | Phase: WATER-5c-2015 | Award Amount: 4.04M | Year: 2016
Climate change and population growth are expected to exacerbate the water crisis of Mediterranean African Countries (MACs), where agriculture accounts for 80-85% of freshwater consumption. The aim of MADFORWATER is to develop a set of integrated technological and management solutions to enhance wastewater treatment, reuse for irrigation and water efficiency in agriculture in three MACs (Tunisia, Morocco and Egypt). MADFORWATER will develop and adapt to three main hydrological basins in the selected MACs technologies for the production of irrigation-quality water from drainage canals, municipal, agro-industrial and industrial wastewaters, and technologies for water efficiency and reuse in agriculture, initially validated at laboratory scale. Selected technologies will be further adapted and validated in four field pilot plants of integrated wastewater treatment/reuse. Integrated strategies for wastewater treatment and reuse targeted to the selected basins will be developed, and guidelines for the development of integrated water management strategies in other basins of the three target MACs will be produced, considering climate change, population increase and economic growth scenarios. The social and technical suitability of the developed technologies and non-technological instruments in relation to the local context will be evaluated with the participation of MAC stakeholders and partners. Guidelines on economic instruments and policies for the effective implementation of the proposed water management solutions in the target MACs will be developed. The project will lead to a relevant long-term impact in Egypt, Morocco and Tunisia in terms of increased wastewater treatment, wastewater reuse, food production and income in the agricultural and water treatment sectors, and decreased groundwater exploitation, water pollution and food contamination. The MADFORWATER consortium consists of 18 partners, 5 of which from the 3 MACs and 1 from China.
Hamzaoui K.,Tunis el Manar University
Clinical and Experimental Rheumatology | Year: 2011
Accumulating evidence suggests that the abnormality of innate and adaptive immunity responses plays an important role in Behçet's disease (BD). T helper (Th) cells have a central role in modulating immune responses. Traditionally, BD is regarded as a Thl-mediated inflammatory disease. Recently, Thl7 cells were identified as a new subset of Th cells unrelated to Thl or Thl cells, and several cytokines are involved in regulating their activation and differentiation. Naive murine CD4 + Th can be induced to differentiate towards Thl, Th2, Thl7 and Treg phenotypes according to the local cytokine milieu. The committed cells are characterised by expression of specific transcription factors, T bet for Thl, GATA-3 for Thl, Foxp3 for Tregs and RORyt (RORyt/ RORC) for Thl 7 cells. It has been demonstrated that the skewing of murine Th towards Thl7 and Treg is mutually exclusive. Thl7 cells regulate inflammation via production of distinct cytokines such as interleukin (IL)-17. There is growing evidence that Thl7 cells are pathological in many human autoimmune and inflammatory diseases, leading to intense interest in defining their origins, functions and developing strategies to block their pathological effects. Evidence from human disease such as BD suggests that specialised antigen-presenting cells drive their in vivo development. Knowledge of how Thl7 cells interact with other immune cells is limited, but recent data suggest that Thl7 cells may not be subject to strict cellular regulation by T regulatory cells. Notably, Thl7 cells and Treg cells appear to share common developmental pathways and both cell types retain significant plasticity. Herein, we will discuss the molecular and cellular regulation of Thl7 cells with an emphasis on BD. The identification of Thl7 cells helps us to explain some of the anomalies seen in the ThllTh2 axis and has broadened our understanding of the immunopathological effects of Thl7 cells in the development of BD. © Copyright CLINICAL AND EXPERIMENTAL RHEUMATOLOGY 2011.
Kouidhi S.,Tunis el Manar University
Journal of endocrinological investigation | Year: 2011
Adiponectin has emerged over the last decade as a key adipokine linking obesity, insulin resistance, and Type 2 diabetes. However, the molecular mechanisms controlling adiponectin expression in adipose tissue are not fully elucidated. Furthermore, increasing evidence indicates that peroxisome proliferator-activated receptor- γ (PPAR-γ) plays an important, and beneficial, role in modulating adiponectin expression. The aim of the present study was to assess the separate role of obesity and Type 2 diabetes in the relationship between endogenous PPAR-γ signaling and adiponectin expression in subcutaneous adipose tissue. Enzyme-linked immuno sor bent assay and real time quantitative PCR analysis were carried out in overweight, obese, and/or diabetic Tunisian patients who underwent an abdominal surgery. These results collectively indicate that circulating levels of adiponectin were decreased in all overweight, obese, and/or diabetic (p<0.001). However, the subcutaneous mRNA expression of adiponectin was reduced only in diabetics (p<0.01) but presents some discrepancies in obese individuals. Moreover, mRNA levels of adiponectin were positively correlated with levels of mRNA encoding PPARγ and its heterodimeric partner retinoid X receptor-α (RXR-α), in both obese and diabetic patients. Our study on Tunisian patients shows impaired regulation of circulating and mRNA adiponectin levels dependent of metabolic disorders in obesity and Type 2 diabetes. The data suggest that subcutaneous adipose tissue may play an important role in modulating adiponectin expression in diabetes and obesity. Moreover, adiponectin mRNA could be potentially regulated by endogenous PPARγ/RXRα-dependent pathways.
Saanouni T.,Tunis el Manar University
Mathematical Methods in the Applied Sciences | Year: 2014
We investigate the initial value problem for a semilinear damped Schrödinger equation with exponential growth nonlinearity in two space dimensions. We obtain global well-posedness in the energy space. Copyright © 2013 John Wiley & Sons, Ltd. Copyright © 2013 John Wiley & Sons, Ltd.
Hachicha S.,Tunis el Manar University
Infinite Dimensional Analysis, Quantum Probability and Related Topics | Year: 2014
We prove two characterizations of the support projection of a state evolving under the action of a quantum Markov semigroup and a quantum analogue of the Lévy-Austin-Ornstein theorem. We discuss applications to open quantum systems. © World Scientific Publishing Company.
Jammazi R.,Tunis el Manar University |
Aloui C.,Tunis el Manar University
Energy Economics | Year: 2012
Oil price prediction has usually proved to be an intractable task due to the intrinsic complexity of oil market mechanism. In addition, the recent oil shock and its consequences relaunch the debate on understanding the behavior underlying the expected oil prices. Combining the dynamic properties of multilayer back propagation neural network and the recent Harr A trous wavelet decomposition, a Hybrid model HTW-MPNN is implemented to achieve prominent prediction of crude oil price. While recent studies focus on the determination of the best forecasting model by comparing various neural architectures or applying several decomposition techniques to the ANN, the new insight of this paper is to target the issue of the transfer function selection providing robust simulations on both in sample and out of sample basis. Based on the work of Yonaba, H., Anctil, F., and Fortin, V. (2010) "Comparing Sigmoid Transfer Functions for Neural Network Multistep Ahead Stream flow forecasting". Journal of Hydrologic Engineering, April, 275-283, we use three variants of activation function namely sigmoid, bipolar sigmoid and hyperbolic tangent in order to test the model's flexibility. Furthermore, the forecasting robustness is checked through several levels of input-hidden nodes. Comparatively, results of HTW-MBPNN perform better than the conventional BPNN. Our conclusions add a major attribute to the previous studies corroborating the Occam razor's principle, especially when simulations are constructed through training and testing phases simultaneously. Finally, more eligible forecasting power is found according to the wavelet oil price signal which appears to be the closest to the real anticipations of future oil price fluctuations. © 2011 Elsevier B.V.
Jammazi R.,Tunis el Manar University
Energy | Year: 2012
Since oil prices are typically governed by nonlinear and chaotic behavior, it's become rather difficult to capture the dominant properties of their fluctuations. In recent years, unprecedented interest emerged on the decomposition methods in order to capture drifts or spikes relatively to this data. Together, our understanding of the nature of crude oil price shocks and their effects on the stock market returns has evolved noticeably. We accommodate these findings to investigate two issues that have been at the center of recent debates on the effect of crude oil shocks on the stock market returns of five developed countries (USA, UK, Japan, Germany and Canada). First, we analyze whether shocks and or volatility emanating from two major crude oil markets are transmitted to the equity markets. We do this by applying, the Haar A Trous Wavelet decomposition to monthly real crude oil series in a first step, and the trivariate BEKK Markov Switching GARCH model to analyze the effect of the smooth part on the degree of the stock market instability in a second step. The motivation behind the use of the former method is that noises and erratic behavior often appeared at the edge of the signal, can affect the quality of the shock and thus increase erroneous results of the shock transmission to the stock market. The proposed model is able to circumvent the path dependency problem that can influence the prediction's robustness and can provide useful information for investors and government agencies that have largely based their views on the notion that crude oil markets affect negatively stock market returns. Second, under the hypothesis of common increased volatility, we investigate whether these states happen around the identified international crises. Indeed, the results show that the A Haar Trous Wavelet decomposition method appears to be an important step toward improving accuracy of the smooth signal in detecting key real crude oil volatility features. Additionally, apart from UK and Japanese cases, the responses of the stock market to an oil shock depend on the geographic area for the main source of supply whether from the North Sea or from the North America (as we take two oil benchmarks WTI and Brent respectively). © 2011 Elsevier Ltd.
Jammazi R.,Tunis el Manar University
Energy | Year: 2012
The main aim of the present paper is to explore how the interactions between crude oil (CO) price changes and stock returns of five developed countries namely U.S.A, Canada, Germany, Japan and U.K., evolve simultaneously over time and frequency, in light of the conflicting evidence provided by much of recent studies on the sign and the direction of this relationship. To this end, we apply a more efficient wavelet tool, namely Haar à trous wavelet transform that helps circumvent the problems of the standard regression techniques and proves its effectiveness in encircling the real data features. In order to provide more credible conclusions, the wavelet variance, correlation and cross-correlation are implemented. In general, we extend the existing empirical works by providing more generalized and convincing results inherent to the stock-oil markets interactions which are usually reputed to be complicated. First, we find evidence that the wavelet variances of all the variables decrease with increasing scales. Second, from the analysis of the wavelet correlation, changes in CO and almost all the stock prices do not move together up to the intermediate scale, but since they abruptly shift their direction in unison. Third, results for the wavelet CCF at scales 2, 3 and/or 4 generally illustrate no transmission mechanism between CO and the stock market returns although we provide support for massive CO variations at these scales. In contrast, the CO-equity market relationships at higher scales become interconnected in a negative unidirectional pattern running from CO to stock market returns for only two oil importing countries but also Canada. For oil exporting countries, we have seen that while highly transient (scale 1) positive/negative causalities flowing from TSX stock market to CO changes are detected, highly persistent (scale 6) positive causality running from FTSE to the CO changes are rather found. Finally, the implications of the study's results vary depending on the oil - stock market linkages' sensitivity to the degree of improvement in energy efficiency of a given country, the degree of oil shock persistence, and to whether a country is oil importer or exporter (among other suggested factors). © 2012 Elsevier Ltd.