Modèle multi-agents pour la simulation de la dynamique de carbone à l'échelle du terroir villageois

Un système multi-agents (SMA) a été conçu et mis en oeuvre en vue d'étudier la dynamique des ressources organiques et azotée d'un terroir africain. Les simulations réalisées ont permis de mesurer l'impact des modes de gestion sur les ressources dans le long terme. Trois types d'enquêtes ont été nécessaires pour collecter les données nécessaires. Un premier modèle à l'échelle de la parcelle a permis de simuler le stockage du carbone et de l'azote dans les sols et dans la biomasse végétale. Ensuite la définition des règles individuelles et collectives de décision et de gestion des exploitations agricoles et du terroir ont nécessité des enquêtes approfondies avec les principaux groupes utilisant le terroir. . Pour la conception informatique du modèle, le formalisme UML a été utilisé. La représentation statique et dynamique du modèle a été formalisée sur la plate forme de modélisation CORMAS. . La méthode développée est appelée MIROT Modélisation Intégrée de la dynamique des Ressources Organiques et analyse de viabilité de Terroirs agro-sylvo-pastoraux des savanes ouest africaines). Le modèle MIROT utilise un fond de carte du terroir avec des contraintes spatiales pour simuler le fonctionnement de celui-ci

HIV Treatment as Prevention: Considerations in the Design, Conduct, and Analysis of Cluster Randomized Controlled Trials of Combination HIV Prevention

The rigorous evaluation of the impact of combination HIV prevention packages at the population level will be critical for the future of HIV prevention. In this review, we discuss important considerations for the design and interpretation of cluster randomized controlled trials (C-RCTs) of combination prevention interventions. We focus on three large C-RCTs that will start soon and are designed to test the hypothesis that combination prevention packages, including expanded access to antiretroviral therapy, can substantially reduce HIV incidence. Using a general framework to integrate mathematical modelling analysis into the design, conduct, and analysis of C-RCTs will complement traditional statistical analyses and strengthen the evaluation of the interventions. Importantly, even with combination interventions, it may be challenging to substantially reduce HIV incidence over the 2- to 3-y duration of a C-RCT, unless interventions are scaled up rapidly and key populations are reached. Thus, we propose the innovative use of mathematical modelling to conduct interim analyses, when interim HIV incidence data are not available, to allow the ongoing trials to be modified or adapted to reduce the likelihood of inconclusive outcomes. The preplanned, interactive use of mathematical models during C-RCTs will also provide a valuable opportunity to validate and refine model projections

Wage losses in the year after breast cancer: Extent and determinants among Canadian women

This article is available open access through the publisher’s website at the link below. © The Author 2008.Background - Wage losses after breast cancer may result in considerable financial burden. Their assessment is made more urgent because more women now participate in the workforce and because breast cancer is managed using multiple treatment modalities that could lead to long work absences. We evaluated wage losses, their determinants, and the associations between wage losses and changes for the worse in the family's financial situation among Canadian women over the first 12 months after diagnosis of early breast cancer. Methods - We conducted a prospective cohort study among women with breast cancer from eight hospitals throughout the province of Quebec. Information that permitted the calculation of wage losses and information on potential determinants of wage losses were collected by three pretested telephone interviews conducted over the year following the start of treatment. Information on medical characteristics was obtained from medical records. The main outcome was the proportion of annual wages lost because of breast cancer. Multivariable analysis of variance using the general linear model was used to identify personal, medical, and employment characteristics associated with the proportion of wages lost. All statistical tests were two-sided. Results - Among 962 eligible breast cancer patients, 800 completed all three interviews. Of these, 459 had a paying job during the month before diagnosis. On average, these working women lost 27% of their projected usual annual wages (median = 19%) after compensation received had been taken into account. Multivariable analysis showed that a higher percentage of lost wages was statistically significantly associated with a lower level of education (Ptrend = .0018), living 50 km or more from the hospital where surgery was performed (P = .070), lower social support (P = .012), having invasive disease (P = .086), receipt of chemotherapy (P < .001), self-employment (P < .001), shorter tenure in the job (Ptrend < .001), and part-time work (P < .001). Conclusion - Wage losses and their effects on financial situation constitute an important adverse consequence of breast cancer in Canada.The Canadian Breast Cancer Research Alliance, Canadian Institutes of Health Research, and Fondation de l’Université Laval

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

Information transmission in oscillatory neural activity

Periodic neural activity not locked to the stimulus or to motor responses is usually ignored. Here, we present new tools for modeling and quantifying the information transmission based on periodic neural activity that occurs with quasi-random phase relative to the stimulus. We propose a model to reproduce characteristic features of oscillatory spike trains, such as histograms of inter-spike intervals and phase locking of spikes to an oscillatory influence. The proposed model is based on an inhomogeneous Gamma process governed by a density function that is a product of the usual stimulus-dependent rate and a quasi-periodic function. Further, we present an analysis method generalizing the direct method (Rieke et al, 1999; Brenner et al, 2000) to assess the information content in such data. We demonstrate these tools on recordings from relay cells in the lateral geniculate nucleus of the cat.Comment: 18 pages, 8 figures, to appear in Biological Cybernetic

Long-lived photoexcited states in polydiacetylenes with different molecular and supramolecular organization

With the aim of determining the importance of the molecular and supramolecular organization on the excited states of polydiacetylenes, we have studied the photoinduced absorption spectra of the red form of poly[1,6-bis(3,6-didodecyl-N-carbazolyl)-2,4-hexadiyne] (polyDCHD-S) and the results compared with those of the blue form of the same polymer. An interpretation of the data is given in terms of both the conjugation length and the interbackbone separation also in relation to the photoinduced absorption spectra of both blue and red forms of poly[1,6-bis(N-carbazolyl)-2,4-hexadiyne] (polyDCHD), which does not carry the alkyl substituents on the carbazolyl side groups. Information on the above properties is derived from the analysis of the absorption and Raman spectra of this class of polydiacetylenes

Choice of activity-intensity classification thresholds impacts upon accelerometer-assessed physical activity-health relationships in children

It is unknown whether using different published thresholds (PTs) for classifying physical activity (PA) impacts upon activity-health relationships. This study explored whether relationships between PA (sedentary [SED], light PA [LPA], moderate PA [MPA], moderate-to-vigorous PA, vigorous PA [VPA]) and health markers differed in children when classified using three different PTs