Asymétrie des cycles économiques et changement de régimes : cas de la Tunisie

Le papier s’intéresse à l’identification et à la datation des points de retournement de l’activité économique en Tunisie en utilisant l’approche changement de régimes, innovée par Hamilton (1989) pour l’analyse des cycles économiques. On identifie les changements de régimes dans le processus stochastique de la croissance économique, en utilisant des données mensuelles relatives à la croissance de la production industrielle couvrant la période 1994-2004. Notre recherche est basée sur les probabilités de lissage déterminées en estimant le modèle à changement de régimes à deux états. Les résultats obtenus nous permettent d’identifier sept points de retournement durant cette période tout en signalant la récession débutant en septembre 2001.In this paper we are interested in the identification and the dating of the turning points of the economic activity in Tunisia, by using the Markov switching approach innovated by Hamilton (1989) for the analysis of the business cycles. We identify the changes of regimes in the stochastic process of the economic growth, by using monthly data relating to the growth of the industrial production covering the period 1994-2004. We base our research on the smoothing probabilities determined by estimating the model of two states Markov switching regimes. The results obtained enable us to identify seven turning points during this period. And, using this approach of two states, we can detect the recession of september 2001

Asymétrie des cycles économiques et changement de régimes : cas de la Tunisie*

In this paper we are interested in the identification and the dating of the turning points of the economic activity in Tunisia, by using the Markov switching approach innovated by Hamilton (1989) for the analysis of the business cycles. We identify the changes of regimes in the stochastic process of the economic growth, by using monthly data relating to the growth of the industrial production covering the period 1994-2004. We base our research on the smoothing probabilities determined by estimating the model of two states Markov switching regimes. The results obtained enable us to identify seven turning points during this period. And, using this approach of two states, we can detect the recession of september 2001. Le papier s’intéresse à l’identification et à la datation des points de retournement de l’activité économique en Tunisie en utilisant l’approche changement de régimes, innovée par Hamilton (1989) pour l’analyse des cycles économiques. On identifie les changements de régimes dans le processus stochastique de la croissance économique, en utilisant des données mensuelles relatives à la croissance de la production industrielle couvrant la période 1994-2004. Notre recherche est basée sur les probabilités de lissage déterminées en estimant le modèle à changement de régimes à deux états. Les résultats obtenus nous permettent d’identifier sept points de retournement durant cette période tout en signalant la récession débutant en septembre 2001.

Architectures et mécanismes de fédération dans les environnements cloud computing et cloud networking

Presented in the literature as a new technology, Cloud Computing has become essential in the development and delivery of IT services. Given the innovative potential of Cloud, our thesis was conducted in the context of this promising technology. It was clear that the Cloud would change the way we develop, manage and use information systems. However, the adoption and popularization of Cloud were slow and difficult given the youth of the concepts and heterogeneity of the existing solutions. This difficulty in adoption is reflected by the lack of standard, the presence of heterogeneous architectures and APIs, the introduction of Vendor Lock-In imposed by the market leaders and the lack of cloud federation principles and facilitators. The main motivation for our PhD is to simplify the adoption of the cloud paradigm and the migration to cloud environments and technologies. Our goal has consequently been to improve interoperability and enable federation in the cloud. The thesis focused on two main areas. The first concerns the convergence of future networks and clouds and the second the improvement of federation and interoperability between heterogeneous cloud solutions and services. Based on our work in state of the art about Cloud Computing and Cloud Networking, we defined in this thesis two architectures for Cloud federation. The first architecture enables the merging (convergence) of Cloud Computing and Cloud Networking. The second architecture addresses interoperability between services and proposes cloud-brokering solutions. The study enabled the identification of two essential components for cloud federation, namely: a generic interface and a message exchange system. These two components have been two contributions of our thesis. The proposed federation architectures and these two components summarize the four major contributions of our workPrésenté dans la littérature comme une nouvelle technologie, le Cloud Computing est devenu incontournable dans la mise en place et la fourniture des services informatiques. Cette thèse s’inscrit dans le contexte de cette nouvelle technologie qui est en mesure de transformer la mise en place, la gestion et l’utilisation des systèmes d’information. L'adoption et la vulgarisation du Cloud ont été ralenties par la jeunesse même des concepts et l'hétérogénéité des solutions existantes. Cette difficulté d'adoption se manifeste par l'absence de standard, l'hétérogénéité des architectures et des API, le Vendor Lock-In imposé par les leaders du marché et des manques qui ralentissent la fédération. La motivation principale de la thèse est de simplifier l'adoption du cloud et la migration vers ses environnements et technologies. Notre objectif est de proposer des solutions d'interopérabilité et de fédération dans le Cloud. Le travail de recherche s’est aussi articulé autour de deux grands axes. Le premier concerne le rapprochement des réseaux du futur et des Clouds. Le deuxième axe concerne l'interopérabilité et la fédération entre solutions et services cloud. Une analyse de l’état de l’art sur le Cloud Computing et le Cloud Networking, a permis de confirmer des manques pressentis et de proposer deux architectures de fédération Cloud. La première architecture permet le rapprochement entre le Cloud Computing et le Cloud Networking. La seconde architecture facilite l'interopérabilité et le courtage de services Cloud. L'étude des deux architectures a fait ressortir deux composants primordiaux et essentiels pour assurer la fédération: une interface générique et un système d'échange de messages. Ces deux composants correspondent à deux contributions centrales de la thèse et reflètent l’ensemble des contributions (quatre au total) du travail de recherch

Climatological Aspects of Aerosol Physical Characteristics in Tunisia Deduced from Sun Photometric Measurements

Atmospheric and climatic data measured at Thala site (Tunisia) for a long-time period (1977–2001) are used to analyse the monthly, seasonal, and annual variations of the aerosol optical depth at 1 μm wavelength. We have shown that aerosol and microphysical properties and the dominating aerosol types depend on seasons. A comparison of the seasonal cycle of aerosol optical characteristics at Thala site showed that the contribution of long-range transported particles is expected to be larger in summer as a consequence of the weather stability typical of this season. Also, the winter decrease in atmospheric turbidity may result from increases in relative humidity and decreases in temperature, leading to increased particle size and mass and increased fall and deposition velocities. The spring and autumn weather patterns usually carry fine dust and sand particles for the desert area to Thala region. The annual behaviour of the aerosol optical depth recorded a period of stead increase started in 1986 until 2001. Trends in atmospheric turbidity after 1988 could be explained other ways by the contribution of the eruption of Mount Pinatubo in 1991 and by local or regional changes in climate or in aerosol emissions

Characterization of Coolia spp. (Gonyaucales, Dinophyceae) from Southern Tunisia: first record of Coolia malayensis in the Mediterranean Sea.

This study provides the first report of the presence of Coolia malayensis in the Mediterranean Sea, co-occurring with C. monotis. Isolated strains from the Gulf of Gabes, Tunisia (South-eastern Mediterranean) were identified by morpho-logical characterization and phylogenetic analysis. Examination by light and scanning electron microscopy revealed no significant morphological differences between the Tunisian isolates and other geographically distant strains of C. monotis and C. malayensis. Phylogenetic trees based on ITS1-5.8S-ITS2 and D1-D3/28S rDNA sequences showed that C. monotis strains clustered with others from the Mediterranean and Atlantic whereas the C. malayensis isolate branched with isolates from the Pacific and the Atlantic, therefore revealing no geographical trend among C. monotis and C. ma-layensis populations. Ultrastructural analyses by transmission electron microscopy revealed the presence of numerous vesicles containing spirally coiled fibers in both C. malayensis and C. monotis cells, which we speculate to be involved in mucus production

Magnetic Study of the Heated and Unheated Sedimentary Fillings of Sebkha Mhabeul, Southeast Tunisia: A Geophysical Method for Paleoclimatic Investigation and Tephrochronological Dating

This paper is meant to investigate the climatic and volcanic signals within the sedimentary filling of sebkha Mhabeul through a thermomagnetic study of a 37 cm length core. Values of the magnetic susceptibility at ambient temperature show that the core encompasses four climatic stages: the Warming Present (WP), the Little Ice Age (Late LIA), Early Little Ice Age (ELIA), and the Medieval Climate Anomalies (MCA). Added to the subcycles, the spectral analysis shows the individualization of an 888 yr cycle probably related to solar activity. The heating at 250°C is good-for-nothing since it was useful neither for climatic investigation nor for tephras layers detection. Heating at 700°C generated the complete loss of the climatic signal. On the other hand, it allowed the detection of the previously identified tephras layers. Further, it highlighted the presence of other tephras layers. The extraction by the bromoform confirms the presence of these tephras. The use of the same methodology may allow the detection of tephras layers within other sebkhas