A TRANSIENT MODEL FOR INSULATED GATE BIPOLAR TRANSISTORS (IGBTs)

The Insulated Gate Bipolar Transistor is widely accepted as the preferred switching device in a variety of power converters and motor drive applications. The device combines the advantages of high current density bipolar operation that results in low conduction losses with the advantages of the fast switching and low drive power of MOSFET gated devices. The basic idea behind IGBT is to increase the conductivity of a thick lightly doped epitaxial layer, thus reducing the on-resistance and losses associated with power MOSFET. This reduction in resistivity resulting from high level of carrier injection is referred to as conductivity modulation. When the IGBT is turned off, however, injected carriers must be extracted first before the device can sustain the reverse blocking voltage. Several models have been proposed in the literature to describe both DC and transient behaviors of IGBTs. These models can be broadly classified into two main categories: physics based models and behavioral or compact models. The dissertation compares the various approaches made in the literature to model the transient behavior of IGBTs. A new physics-based model for a Non Punch Through (NPT) IGBT during transient turn off period is presented. The steady state part of the model is derived from the solution of the ambipolar diffusion equation in the drift region of the IGBT. The transient component of the model is based on the availability of a newly developed expression for the excess carrier distribution in the base. The transient voltage is obtained numerically from this model. Alternatively, an analytical solution for the transient voltage is presented. The theoretical predictions of both approaches are found to be in good agreement with the experimental data. The model is used to calculate the instantaneous power dissipation and the switching losses in IGBT for different device carrier lifetimes

Perturbed integral equations in modular function spaces

We focus our attention on a class of perturbed integral equations in modular spaces, by using fixed point Theorem I.1 (see [1])

Histological exploration of follicular population of the Moroccan bovine (Oulmes-Zaers) breed

Follicular population and repartition in the ovarian cortex was investigated in the ovaries of the Oulmès-Zaers cattle breed and its crosses. A total of 30 ovaries were collected at slaughterhouse in Casablanca and Rabat from Oulmes-Zaers breed and its crosses (2 genotypes) of 3 age groups (5 years). The histological study of the ovary revealed that the ovarian cortex is composed of different areas (from the periphery to the medulla), the non stratified epithelium of the ovary, the tunica albuginea composed of two areas rich of collagen fibers directed into different ways white variable thickness. The primordial and antral follicles appear in underlying areas. Therefore, the follicles cannot appear on the ovarian surface when situated under thicker Layers. At the quantitative level, the ovary of the Oulmes-Zaears breed seems to contain less follicles in animals less than 3 years of age as compared to the crossbreed (P< 0.05). Between 3 and 5 years of age, the follicles occupied similar areas of the ovaries (17% and 18% for oulmes-Zaers and its crosses, respectively). This study shows that the ovary of the Moroccan local cattle breed (Oulmes-Zaers) is equipped with a whole plain follicular population that is more important than the one visible on the surface of the ovary and which is exploited by aspiration and picking techniques. Key words: Ovary, Oulmès-Zaers, follicular population, bovine, age. African Journal of Biotechnology Vol.3(5) 2004: 294-29

Numerical method for solving a class of nonlinear elliptic inverse problems

AbstractThis paper discusses a method to solve a family of nonlinear inverse problems with Cauchy conditions on a part of the boundary and no condition at all on another part. An iterative boundary element procedure is proposed. The scheme uses a dynamically estimated relaxation parameter on the under-specified boundary. Various types of convergence, boundary condition formulations and effects of added small perturbations into the input data are investigated. The numerical results show that the method produces a stable reasonably approximate solution

La Drépanocytose Chez Les Enfants Hospitaliers Au Service De Pédiatrie (CHR El Idriss De Kénitra, Maroc): A Propos De 53 Cas.

The objective of this work is to study sickle cell in children 1 to 16 years at El Idrissi regional hospital of Kenitra (Morocco) The study was conducted between March and June 2012. The population includes 53 patients, 39 male and 14 female. The studied parameters were age, sex, socioeconomic status, origin, age of diagnosis and schooling. Data on sickle cell patients was collected from information sheets available from the archives department at the El Idrissi regional hospital of Kenitra and a patient's verbal consent or that of the child's parents. Sickle cell disease is the third leading cause of admission (10.16 % of total admissions). 47.16 % of patients are under the age of 6 years. The diagnosis of disease is made in 32.07 % of the cases around 9 months. In 94.3% of cases, patients are from family whose father has a low and irregular income. The main causes of hospitalization are painful crises (69.81 %), acute anemia (28.30%), and infections (28.30%). As a medical treatment, the rehydration, analgesics, antibiotics and blood transfusions are the most prescribed. The transfusion was performed in 96.22 % of cases. The lack of early detection and socio –economic pressures and environmental conditions seems to put our patients in a vulnerable state.The focus should be on prevention and strengthening the capacity of families

Analyse de la variabilité germinative de la vesce commune sous l’impact d’un stress Ferrique-Cadmique-Salin

Ce travail a pour but de voir l’impact de l’application d’une combinaison de stress abiotique sur la germination des graines de vesce commune ainsi que de visualiser les modifications physiologiques et histologiques au niveau des tissus racinaires sous l’influence de ces contraintes. De ce fait, une conduite de germination a été réalisée avec des graines de vesce commune dans différentes situations de combinaisons entre trois types de stress métallique-cadmique-salin et un suivi a été fait en se basant sur des caractères végétatifs bien déterminés. Les résultats montrent bien une nette différence entre les réponses des graines à l’application de stress séparément et entre les combinaisons de stress ainsi qu’une variabilité intra-espèce énorme vis-à-vis de différentes types de contraintes.Mots-clés : vesce commune, stress métallique-cadmique-salin, caractères végétatifs, modifications physiologiques et histologiques