Hybrid static/dynamic scheduling for already optimized dense matrix factorization

We present the use of a hybrid static/dynamic scheduling strategy of the task dependency graph for direct methods used in dense numerical linear algebra. This strategy provides a balance of data locality, load balance, and low dequeue overhead. We show that the usage of this scheduling in communication avoiding dense factorization leads to significant performance gains. On a 48 core AMD Opteron NUMA machine, our experiments show that we can achieve up to 64% improvement over a version of CALU that uses fully dynamic scheduling, and up to 30% improvement over the version of CALU that uses fully static scheduling. On a 16-core Intel Xeon machine, our hybrid static/dynamic scheduling approach is up to 8% faster than the version of CALU that uses a fully static scheduling or fully dynamic scheduling. Our algorithm leads to speedups over the corresponding routines for computing LU factorization in well known libraries. On the 48 core AMD NUMA machine, our best implementation is up to 110% faster than MKL, while on the 16 core Intel Xeon machine, it is up to 82% faster than MKL. Our approach also shows significant speedups compared with PLASMA on both of these systems

Prevalence of HIV, HBV and Chlamydia infections in Cameroonian University context: case of the University of Dschang, in the Western Region

Introduction: In sub-Saharan Africa HIV infection remains largely epidemic, whereas HBV infection is highly endemic (>8%). In Cameroon, HIV prevalence is 4.3%. Concerning HBV and chlamydia infections, their prevalence are both ≥10%. Young adults, including university students, are the population groups mostly affected. Epidemiological data on these infections, among university students could be helpful to implement specific prevention strategies. Methods: A descriptive study was performed in May 2013 among 624 students from the University of Dschang, Cameroon. Participants were screened for HIV, HBV and Chlamydia infections. Data was collected by a standard questionnaire and analyzed by Epi Info. Results: Average age of participants was 23.3 years (σ = 3.2) with female predominance (58.7%). Prevalence of HIV, HBV and Chlamydia infection was 1.1% (7/624), 2.8% (5/176) and 2.0% (2/100) respectively. 83.2% of participants were sexually active. Concerning sexual risk behaviors, participants reported having multi partners (14.8%), using condom occasionally (58.6%) or never (5.0%). 100%, 62.6% and 52.2% reported to be aware on HIV, HBV and Chlamydia infections respectively. In addition, only 5.5% and 21.3% of the participants were aware of their HBV and Chlamydia status respectively, versus 64.4% for HIV. The excessive cost of HBV and Chlamydia tests has been identified as the major barrier to testing (87.6%). Conclusion: Among college Cameroonian students the prevalence of HIV, HBV and Chlamydia infections seems to be relatively low if compared to general population. However, having multiple sexual partners in addition to non-systematic use of condoms during sexual intercourse represents risk behaviors among students. Awareness campaigns and screening facilitation on HBV and chlamydia infections need to be strengthened

Spacing of Hydraulically Fractured Horizontal Laterals in Low Permeability Formations

The discovery of unconventional reservoirs such as tight gas sands and shale gas, the resolve for the United States to become independent of foreign hydrocarbons, toppled with depleting conventional fields around the world, has pushed for new technologies and effective and efficient approaches in unconventional reservoirs long-term production to supply their ever-growing demand.;Horizontal drilling along with hydraulic fracturing are the two most popular methods used to render low-permeability formations such as the Marcellus Shale economically productive. Nowadays, coupled with horizontal drilling and hydraulic fracturing, new strategies and tools such as coil tubing and multi-lateral horizontal wells are being strategized and used for unconventional reservoirs as well as conventional reservoirs to maximize recovery. However, the understanding of the production performance of recently drilled hydraulically fractured horizontal wells in low-permeability formations represents a challenge because of the lack extensive production history on these new producing wells. The same is true about the multi-lateral horizontal wells, though they have great potential for improving the recovery. The objective of this study was to conduct a modeling study, to investigate the impact of wells spacing on the production performance of hydraulically fractured multi-lateral horizontal wells in low permeability formations

Evaluation of the nutritional status of infants from mothers tested positive to HIV/AIDS in the health district of Dschang, Cameroon

INTRODUCTION: Poor infant feeding practices are common in Africa, resulting in physical and intellectual developmental impairments. Good feeding practices are crucial, especially in the first year of growth. HIV/AIDS has worsened the clinical and nutritional status of both mothers and their children, exacerbating high rates of malnutrition. The aim of this study was to assess by participative approach, the nutritional status of infants from mothers tested positive to HIV in the health district of Dschang. METHODS: This is a cross sectional study with a period of recruitment of 2 years (2010-2012). Data Collection was done by the aim of a personal slip followed by training to strengthen the nutritional and hygienic capacity of targeted parents. Height and weight of infants were measured and body mass index (BMI) calculated. RESULTS: Significant difference (p ≤ 0.05) was noticed in height-for-age z-score (HAZ) of girls aged between 1 to 2 years compared to 1-year old girls as well as to boys of all ages, defining them as stunted. Furthermore, the weight-for-age z-score (WAZ) results indicate that both girls and boys of all age are in moderate state of malnutrition. The results of BMI thinness classified according to gender and age groups, indicates that most infants (68/130, 52.3%) showed grade 2 thinness predominantly in 2-years old both boys and girls. However, no participants fall within the normal category for age and sex, as well as overweight and obesity categories. CONCLUSION: Undernutrition exists among infants from mothers tested positive to HIV residing in Dschang, as most of the infants are underweight, and malnourished

Reboiser les sols dégradés sahéliens. Le cas des sols hardé de la région de Maroua

Dans la région soudano-sahélienne du Nord-Cameroun, existent de vastes surfaces de sols ayant un couvert de végétation très faible et très discontinu, désignés en langue peule par le terme de hardé. Poussés par les services de développement qui voulaient reboiser autoritairement ces terres, les chercheurs-forestiers ont tout d'abord essayé des méthodes exigeant de gros moyens mécaniques et des essences exotiques à croissance rapide, mais celles-ci ont échoué. Ils ont donc repris le problème en étudiant, tout d'abord, les pratiques paysannes et la dynamique naturelle de la végétation. En fait, les sociétés agro-pastorales de cette région font un usage non négligeable de ces sols pour l'élevage et la cueillette. De plus, elles ont mis au point une méthode de mise en valeur, fondée sur un carroyage de systèmes anti-ruissellement et sur une rotation entre pâturage de saison des pluies et culture de sorgho de saison sèche. Il a été possible de cartographier ces sols par télédétection et de décrire leurs caractères pédologiques et hydrologiques. La replantation de certaines terres a été étudiée en associant le reboisement à base d'espèces locales à usages multiples, avec une gestion de la strate herbacée spontanée. Les méthodes mises au point, bien que peu spectaculaires, se révèlent adaptées aux besoins et aux possibilités des sociétés rurales de cette région pour gérer rationnellement leur environnement

Essays on time series forecasting with neural-network or long-dependence autoregressive models and macroeconomic news effects on bond yields

Cette thèse, organisée en trois chapitres, porte sur la modélisation et la prévision des séries chronologiques économiques et financières. Les deux premiers chapitres proposent de nouveaux modèles économétriques pour l'analyse des données économiques et financières en relaxant certaines hypothèses irréalistes habituellement faites dans la littérature. Le chapitre 1 développe un nouveau modèle de volatilité appelé TVP[indice ANN]-GARCH. Ce modèle offre une dynamique riche pour modéliser les données financières en considérant une structure GARCH (Generalized autoregressive conditional heteroscedasticity) dans laquelle les paramètres varient dans le temps selon un réseau de neurones artificiels (ANN). L'utilisation des ANNs permet de résoudre le problème de l'évaluation de la vraisemblance (présent dans les modèles à paramètres variables dans le temps (TVP)) et permet également l'utilisation de variables explicatives supplémentaires. Le chapitre développe également un algorithme Monte Carlo séquentiel (SMC) original et efficace pour estimer le modèle. Une application empirique montre que le modèle se compare favorablement aux processus de volatilité populaires en termes de prévisions de court et de long terme. L'approche peut facilement être étendue à tout modèle à paramètres fixes. Le chapitre 2 développe trois polynômes de retard autorégressifs (AR) parcimonieux qui génèrent des fonctions d'autocorrélation à décroissance lente, comme on l'observe généralement dans les séries chronologiques financières et économiques. La dynamique des polynômes de retard est similaire à celle de deux processus très performants, à savoir le modèle MSM (Multifractal Markov-Switching) et le modèle FHMV (Factorial Hidden Markov Volatility). Ils sont très flexibles car ils peuvent être appliqués à de nombreux modèles populaires tels que les processus ARMA, GARCH et de volatilité stochastique. Une analyse empirique met en évidence l'utilité des polynômes de retard pour la prévision de la moyenne conditionnelle et de la volatilité. Ils devraient être considérés comme des modèles de prévision alternatifs pour les séries chronologiques économiques et financières. Le dernier chapitre s'appuie sur une approche de régression prédictive en deux étapes pour identifier l'impact des nouvelles macroéconomiques américaines sur les rendements obligataires de trois petites économies ouvertes (Canada, Royaume-Uni et Suède). Nos résultats suggèrent que les nouvelles macroéconomiques américaines sont significativement plus importantes pour expliquer la dynamique de la courbe des taux dans les petites économies ouvertes (PEO) que les nouvelles nationales elles-mêmes. Les nouvelles relatives à la politique monétaire américaine ne sont pas les seuls facteurs importants des variations des rendements obligataires des PEO, mais les nouvelles relatives au cycle économique jouent également un rôle significatif.This thesis, organized in three chapters, focuses on modelling and forecasting economic and financial time series. The first two chapters propose new econometric models for analysing economic and financial data by relaxing unrealistic assumptions usually made in the literature. Chapter 1 develops a new volatility model named TVP[subscript ANN]-GARCH. The model offers rich dynamics to model financial data by allowing for a generalized autoregressive conditional heteroscedasticity (GARCH) structure in which parameters vary over time according to an artificial neural network (ANN). The use of ANNs for parameters dynamics is a valuable contribution as it helps to deal with the problem of likelihood evaluation (exhibited in time-varying parameters (TVP) models). It also allows for the use of additional explanatory variables. The chapter develops an original and efficient Sequential Monte Carlo sampler (SMC) to estimate the model. An empirical application shows that the model favourably compares to popular volatility processes in terms of out-of sample fit. The approach can easily be extended to any fixed-parameters model. Chapter 2 develops three parsimonious autoregressive (AR) lag polynomials that generate slowly decaying autocorrelation functions as generally observed financial and economic time series. The dynamics of the lag polynomials are similar to that of two well performing processes, namely the Markov-Switching Multifractal (MSM) and the Factorial Hidden Markov Volatility (FHMV) models. They are very flexible as they can be applied in many popular models such as ARMA, GARCH, and stochastic volatility processes. An empirical analysis highlights the usefulness of the lag polynomials for conditional mean and volatility forecasting. They could be considered as forecasting alternatives for economic and financial time series. The last chapter relies on a two steps predictive regression approach to identify the impact of US macroeconomic releases on three small open economies (Canada, United Kingdom, and Sweden) bond yields at high and low frequencies. Our findings suggest that US macro news are significantly more important in explaining yield curve dynamics in small open economies (SOEs) than domestic news itself. Not only US monetary policy news are important drivers of SOEs bond yield changes, but business cycle news also play a significant role

Utilisation et conservation des ressources en sol et en eau (Nord Cameroun) : rapport final

Après avoir étudié les principaux facteurs régionaux du milieu naturel, une partie de l'étude est consacrée à la caractérisation et à la cartographie des systèmes écologiques de la région de Mouda. Une troisième partie est axée sur les problèmes de fonctionnement des espèces ligneuses et herbacées et fait appel à la connaissance du régime hydrique des sols et à l'organisation des couvertures pédologiques. Une dernière étude, celle du ruissellement et de l'érosion peut être considérée comme la ligne principale du projet