Pattern recognition applications for power system disturbance classification

This paper presents an automated online disturbance classification technique. This technique is based on wavelet multiresolution analysis and pattern recognition techniques. The wavelet-multiresolution transform is introduced as a powerful tool for feature extraction in order to classify different disturbances. Minimum Euclidean distance, k-nearest neighbor, and neural network classifiers are used to evaluate the efficiency of the extracted features.     

X-ware reliability and availability modeling

The problem of modeling a system's reliability and availability with respect to the various classes of faults (physical and design, internal and external) which may affect the service delivered to its users is addressed. Hardware and software models are currently exceptions in spite of the user's requirements; these requirements are expressed in terms of failures independently of their sources, i.e., the various classes of faults. The causes of this situation are analyzed; it is shown that there is no theoretical impediment to deriving such models, and that the classical reliability theory can be generalized in order to cover both hardware and software viewpoints that are X-Ware     

On the electronic nature of silicon and germanium based oxynitrides and their related mechanical,optical and vibrational properties as obtained from DFT and DFPT

Electronic structure, bonding and optical properties of the orthorhombic oxynitrides Si₂N₂O and Ge₂N₂O are studied using the density function theory as implemented in pseudo-potential plane wave and full-potential (linearized) augmented plane wave plus local orbitals methods. Generalized gradient approximation is employed in order to determine the band gap energy. Indeed, the Si₂N₂O exhibits a large direct gap whereas Ge₂N₂O have an indirect one. Bonding is analyzed via the charge densities and Mulliken population, where the role of oxygen is investigated. The analysis of the elastic constants show the mechanical stability of both oxynitrides. Their bulk and shear modulus are slightly smaller than those reported on nitrides semiconductors due to the oxygen presence. The optical properties, namely the dielectric function, optical reflectivity, refractive index and electron energy loss, are reported for radiation up to 30 eV. The phonon dispersion relation, zone-center optical mode frequency, density of phonon states are calculated using the density functional perturbed theory. Thermodynamic properties of Si₂N₂O and Ge₂N₂O, such as heat capacity and Debye temperature, are given for reference. Our study suggests that Si₂N₂O and Ge₂N₂O could be a promising potential materials for applications in the microelectronics and optoelectronics areas of research.     

Web service availability—impact of error recovery and traffic model

Internet is often used for transaction based applications such as online banking, stock trading and shopping, where the service interruption or outages are unacceptable. Therefore, it is important for designers of such applications to analyze how hardware, software and performance related failures affect the quality of service delivered to the users. This paper presents analytical models for evaluating the service availability of web cluster architectures. A composite performance and availability modeling approach is defined considering various causes of service unavailability. In particular, web cluster systems are modeled taking into account: two error recovery strategies (client transparent and non-client-transparent) as well as two traffic models (Poisson and modulated Poisson). Sensitivity analysis results are presented to show their impact on the web service availability. The obtained results provide useful guidelines to web designers.     

Investigation of the ground thermal potential in tunisia focused towards heating and cooling applications

In this paper, an experiment has been conducted in order to record the ground temperature at different depths during 2006 in a suburb of Sfax (Tunisia) which represents an example of the South-Mediterranean climate. The temperature of the soil has also been calculated using a thermal model taking into account properties of the soil and meteorological conditions. Experimental results are compared with theoretical predictions. In order to estimate the influence of the soil properties on the ground temperature, different soil thermal conductivities are tested. A simplified model of an earth pipe system is developed. The cooling and heating capabilities produced by such a system are evaluated. This model is validated against an other published experimental model.     

Construction and stepwise refinement of dependability models

This paper presents a stepwise approach for dependability modeling, based on generalized stochastic Petri nets (GSPNs). The first-step model called functional-level model, is built based on the system’s functional specifications and then completed by the structural model as soon as the system’s architecture is known. It can then be refined according to three complementary aspects: component decomposition, state and event fine-tuning and distribution adjustment to take into account increasing event rates. We define specific rules to make the successive transformations as easy and systematic as possible. This approach allows the various dependencies to be taken into account at the right level of abstraction: functional dependency, structural dependency and those induced by non-exponential distributions. A part of the approach is applied to an instrumentation and control (I&C) system in power plants.