Modèle probabiliste de propagation de fissures de fatigue

Le caractère aléatoire de la propagation des fissures de fatigue conduit à l'utilisation de modèles probabilistes . Nous proposons, en utilisant la loi de Paris et à partir des données de Virkler, de comparer deux modélisations différentes : un modèle des paramètres m et C de la loi de Paris et un modèle de cette propagation par un processus markovien déterministe par morceaux (PDMP) avec un seul saut. Les résultats montrent que globalement le modèle PDMP donne de meilleurs résultats pour prédire le comportement d'une fissure à partir des premières mesures de sa propagation

Barriers to contraceptive uptake among women of reproductive age in a semi-urban community of Ekiti State, Southwest Nigeria

Background: Globally, unplanned pregnancy and sexually transmitted infections (STIs) persist as a significant threat to women’s reproductive health. In Nigeria, despite huge resources committed to family planning programs by stakeholders, contraceptive use has been very low. This study aimed at unraveling the barriers to the use of modern contraceptives among women of reproductive age (15-49 years) in Ise-Ekiti community, Ekiti State, Southwest Nigeria.Methods: This study was a cross sectional study among women aged 15-49 years. A multi-stage sampling technique was used in the recruitment of respondents from the community. An interviewer-administered questionnaire was used to collect data. Data were analyzed using SPSS version 15.Results: Although contraceptive awareness among respondents was high 496(98.6%), only 254 of the 503 respondents were using modern contraceptive methods giving a Contraceptive Prevalence Rate (CPR) of 50.5%. Among those not using any form of contraceptives, some identifiable barriers to contraceptive use includes desire for more children, 62(39.5%), partner disapproval, 40(25.5%), and fear of side-effects, 23(14.6%). Factors associated with contraceptive uptake include marital status (p=0.028), educational level (p=0.041) and religion (p=0.043) with traditional worshippers having the least uptake.Conclusion: This study showed that awareness to modern forms of contraceptives does translate into use. The identified barriers to contraceptive uptake suggest the need to improve uptake of contraceptives through a community-based and culturally acceptable intervention as doing this will go a long way in addressing some of these barriers.Keywords: Contraceptives uptake, barriers, women of reproductive ag

Early sexual debut: prevalence and risk factors among secondary school students in Ido-ekiti, Ekiti state, South-West Nigeria

Background: Early adolescent sexual activity remains a recurring problem with negative psychosocial and health outcomes. The age at sexual debut varies from place to place and among different individuals and is associated with varying factors. The aim was to determine the prevalence and risk factors of early sexual debut among secondary school students in Ido-Ekiti, South-West Nigeria.Methodology: This was a cross-sectional study. The respondents were selected using multi-stage sampling technique. Pre-tested, semi-structured, self-administered questionnaire was used to collect data. Data was analyzed using SPSS version 15.Results: More than two-thirds, 40(67.8%), had early sexual debut. The prevalence of early sexual debut was about 11%. The mean age of sexual debut was 13.10±2.82; the mean age for early sexual debutants was 11.68±1.98. The mean number of sexual partners was 2.44±1.99. Male gender, having friends who engaged in sexual activities had association with early sexual exposure (p<0.05). Alcohol intake had the strongest strength of association for early sexual debut among the students.Conclusion: The high prevalence of early sexual exposure among the students calls for urgent interventions to stem the trend. This will help to reduce the devastating negative psycho-social and health sequels.Keywords: Sexual debut, prevalence, risk factors, Nigeri

Early sexual debut: prevalence and risk factors among secondary school students in Ido-ekiti, Ekiti state, South-West Nigeria.

Background: Early adolescent sexual activity remains a recurring problem with negative psychosocial and health outcomes. The age at sexual debut varies from place to place and among different individuals and is associated with varying factors. The aim was to determine the prevalence and risk factors of early sexual debut among secondary school students in Ido-Ekiti, South-West Nigeria. Methodology: This was a cross-sectional study. The respondents were selected using multi-stage sampling technique. Pre-tested, semi-structured, self-administered questionnaire was used to collect data. Data was analyzed using SPSS version 15. Results: More than two-thirds, 40(67.8%), had early sexual debut. The prevalence of early sexual debut was about 11%. The mean age of sexual debut was 13.10\ub12.82; the mean age for early sexual debutants was 11.68\ub11.98. The mean number of sexual partners was 2.44\ub11.99. Male gender, having friends who engaged in sexual activities had association with early sexual exposure (p<0.05). Alcohol intake had the strongest strength of association for early sexual debut among the students. Conclusion: The high prevalence of early sexual exposure among the students calls for urgent interventions to stem the trend. This will help to reduce the devastating negative psycho-social and health sequels

Availability Allocation to Repairable Systems with Genetic Algorithms: A Multi-Objective Formulation

International audienceThis paper describes a methodology based on genetic algorithms (GA) and experiments plan to optimize the availability and the cost of reparable parallel-series systems. It is a NP-hard problem of multi-objective combinatorial optimization, modeled with continuous and discrete variables. By using the weighting technique, the problem is transformed into a single-objective optimization problem whose constraints are then relaxed by the exterior penalty technique. We then propose a search of solution through GA, whose parameters are adjusted using experiments plan technique. A numerical example is used to assess the method

Optimization of k/n-serial systems reliability by using genetic algorithms: three possible formulations

International audienceThis paper investigates the optimization of k/n serial system, which is a mixed discrete and continue combinatorial optimization problem. Three formulations of the problem are solved, including multi-objective optimization formulation. The formulations are NP-hard, and the objective functions obtained after constraint relaxation by penalty method are not derivable. So, genetic algorithms are used to solve these formulations of k/n optimization problems. The proposed algorithm gives suitable results with reasonable computing time.Dans ce papier, nous cherchons à optimiser un système série de type k/n qui constitue un problème d'optimisation combinatoire à la fois discrète et continue. Trois formulations différentes du problème incluant la forme d'optimisation multi-objectif, sont résolues. Les formulations sont non seulement NP-difficiles, mais en plus les fonctions objectives obtenues après relaxation des contraintes par la méthode de pénalité sont non dérivables. Les algorithmes génétiques ont donc été utilisés pour résoudre le problème d'optimisation sous ses différentes formulations. L'algorithme proposé donne des résultats convenables avec des temps de calculs informatiques raisonnables

Asymptotic availability allocation with genetic algorithms

International audienceThis paper proposes a genetic algorithm to allocate the availability goal to a parallel-serial system components. The problem is formulated as a multi-objective optimization problem in continue and discrete variables. It is a combinatorial optimization that is NP-hard, so genetics algorithms are suitable for attacking such a problem. We use the weighing approach and exact penalty method to relax the problem constraints. An experimental factorial plan is proposed to analyze each parameter's influence on the genetic algorithm's results. From this factorial plan, we have indications on how to choose the parameters of our algorithm. The approach used is relevant for genetics algorithms users. The results that we obtain are suitable and enable us to show how powerful are genetics algorithms. A numerical example is given to assess the algorithm

Reliability allocation to systems components following Weibull law using genetic algorithms and simulated annealing

International audienceIn this paper, a reliability allocation process is performed for parallel-serial systems, which components' uptime are assumed to follow that Weibull law. Generally, the uptime of components of a mechanical system follows Weibull law. The problem is formulated as two optimisations problems in which the decision variables are the parameters of the components up time law. The first problem consists of maximising the system's reliability under cost constraints, and the second one consists of minimising the cost of the system under reliability constraints. The optimisation problems are solved using Genetic Algorithms based on the real number and binary encoding on the one hand, and Simulated Annealing based on the previous encoding to create neighbour of feasible solutions on the other hand. A numerical example is given to compare the results obtained by each algorithm

State of the art in reliability allocation: a comparative study on a mechanical system

International audienceThis paper aims to present some reliability allocation methods and their application on a mechanical system. So, it enables us to point out the difficulties to use reliability allocation methods on such systems. The system studied is complex, we firstly present an approach to break it down and to model it in a serial system which is the form adapted to the methods here presented. Secondly, we present the reliability allocation method and compare the allocation results