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1
Le Losq, Charles, et Matthieu Micoulaut. « Simuler le verre ». Reflets de la physique, no 74 (décembre 2022) : 34–38. http://dx.doi.org/10.1051/refdp/202274034.
Texte intégralRésumé :
Simuler les propriétés des verres et fontes vitreuses est un besoin fondamental pour résoudre différents problèmes scientifiques et industriels, mais aussi pour mieux décrire le phénomène de la transition vitreuse dont la compréhension complète nous échappe. Parmi les méthodes de prédiction des propriétés des matériaux, les simulations par dynamique moléculaire (classique ou ab initio) apportent une masse de connaissances importantes et permettent de mieux comprendre la formation et les propriétés des verres. L’apprentissage machine permet maintenant d’épauler ces simulations et aussi de valoriser de nombreuses mesures expérimentales existantes. Il offre ainsi de nouveaux horizons pour la compréhension et l’utilisation du verre dans de multiples domaines, de l’industrie à la volcanologie.
2
Abdelkader, Bougara, Ezziane Karim et Kadri Abdelkader. « Prédiction des résistances du ciment au laitier durcissant sous une temperature variable ». Canadian Journal of Civil Engineering 28, no 4 (1 août 2001) : 555–61. http://dx.doi.org/10.1139/l01-017.
Texte intégralRésumé :
The prediction of concrete strength has become a major concern that is forcing the construction industry to look closely at determining the appropriate time when to strip the form work or to apply prestress forces to new concrete. Normal concrete has different constitutions and can be subjected to different curing methods depending on the means available. Its characteristics are defined by the presence of mineral additives used to improve its efficiency. This has led us to establish a work plan to predict the strength of slag concrete, tested at different temperatures, from the data obtained from some control specimens of normal concrete, made only from clinker and subjected to a constant temperature of 20°C. The slag material was obtained from El-Hadjar (Algeria).Key words: slag, activation, temperature, finesse, thermal treatment, prediction, equivalent time, mortar, compression, cement, additives.
3
Chachuat, B., N. Roche et M. A. Latifi. « Réduction du modèle ASM 1 pour la commande optimale des petites stations d'épuration à boues activées ». Revue des sciences de l'eau 16, no 1 (12 avril 2005) : 5–26. http://dx.doi.org/10.7202/705496ar.
Texte intégralRésumé :
L'adoption par l'Union Européenne de normes de rejets plus contraignantes implique une meilleure gestion des stations d'épuration. L'utilisation de modèles de simulation dynamique dans des schémas de commande en boucle fermée constitue une alternative intéressante pour répondre à ce problème. Sur la base du modèle ASM 1, un modèle réduit est ici élaboré pour le procédé à boues activées en aération séquentielle, en vue de la commande optimale du système d'aération. Les simplifications considérées sont de deux types : (i) les dynamiques lentes du système sont identifiées au moyen d'une méthode d'homotopie, puis éliminées du modèle ; (ii) des simplifications plus heuristiques consistant à prendre en compte un composé organique unique et à éliminer la concentration des composés organiques azotés sont ensuite appliquées. Elles conduisent à un modèle simplifié de 5 variables. L'application d'une procédure d'identification paramétrique permet alors de démontrer que le comportement dynamique du modèle simplifié est en bonne adéquation avec celui du modèle ASM 1 sur un horizon de prédiction de plusieurs heures, même lorsque les concentrations de l'influent ne sont pas connues. Il est également vérifié que le modèle proposé est observable et structurellement identifiable, sous des conditions d'aérobiose et d'anoxie, à partir des mesures en ligne des concentrations en oxygène dissous, ammoniaque et nitrate. Le modèle simplifié développé présente ainsi toutes les propriétés requises pour une future utilisation au sein de schémas de commande en boucle fermée, en vue de la commande optimale des petites stations d'épuration à boues activées.
4
Finkelhor3, David, Anne Shattuck, Heather Turner et Sherry Hamby. « La polyvictimisation comme facteur de risque de revictimisation sexuelle12 ». Criminologie 47, no 1 (25 mars 2014) : 41–58. http://dx.doi.org/10.7202/1024006ar.
Texte intégralRésumé :
L’objectif était de tester l’hypothèse selon laquelle une exposition générale à la victimisation, ou victimisation multiple, expliquerait une conclusion de recherche fréquente : la victimisation sexuelle accroît le risque de victimisation sexuelle ultérieure. L’étude utilise les données de deux phases de la National Survey of Children’s Exposure to Violence (NatSCEV), menées en 2008 et en 2010. La NatSCEV est une enquête téléphonique auprès d’un échantillon représentatif d’enfants des États-Unis dont les ménages ont été sélectionnés par une composition aléatoire des numéros de téléphone. La présente analyse porte sur les 1186 enfants qui ont participé aux deux phases et qui étaient âgés de 10 à 17 ans lors de la Phase 1. Le nombre total de victimisations à la Phase 1 constituait la meilleure variable prédictive de la victimisation sexuelle à la Phase 2. À la Phase 1, la victimisation sexuelle n’apportait aucune contribution indépendante lorsque d’autres victimisations non sexuelles étaient incluses dans la prédiction. Les recherches futures sur la prédiction de la victimisation sexuelle et sur la récidive de la victimisation sexuelle devront également inclure et contrôler un large éventail d’autres victimisations non sexuelles.
5
Carter, R. E., et L. E. Lowe. « Lateral variability of forest floor properties under second-growth Douglas-fir stands and the usefulness of composite sampling techniques ». Canadian Journal of Forest Research 16, no 5 (1 octobre 1986) : 1128–32. http://dx.doi.org/10.1139/x86-197.
Texte intégralRésumé :
Lateral variability of forest floor physical and chemical properties is examined in LF and H horizons under six naturally regenerated, second-growth Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) stands in coastal southwestern British Columbia. The number of samples required to predict a mean value at two confidence levels (P = 0.01 and 0.05) and two allowable errors (10 and 20%) are given for each variable. Total C, N, P, S, Zn, pH, and lipids were the least variable, requiring 2–13 samples to estimate a plot mean with a 10% allowable error at the 95% confidence level in LF horizons and 3–51 samples per lot in H horizons. Total K, Cu, and Mn were found to have moderately high lateral variability, while total Ca, Mn, Al, and Fe all required large numbers of samples to estimate the plot mean. In the second part of the paper, composite samples weighted by field depth and bulk density are compared with the depth and bulk density–weighted arithmetic mean of subsamples analyzed individually. Values from analysis of composite samples were within one standard deviation of the mean, with the exception of P and Cu in the LF horizons and lipids in both horizons. Composite values and mean values were significantly correlated across the six sites for all variables except lipids in LF horizons and total C and Mn in both horizons. Composite samples are suggested to provide an adequate estimate of the mean value of subsamples analyzed individually for most purposes and, for some variables (i.e., Ca, Fe, Al, and Mn), the only feasible method of obtaining an estimate of the mean.
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Camus, F., M. Gabsi et B. Multon. « Prédiction des vibrations du stator d'une machine à réluctance variable en fonction du courant absorbé ». Journal de Physique III 7, no 2 (février 1997) : 387–404. http://dx.doi.org/10.1051/jp3:1997129.
Texte intégral
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Acevedo-Sandoval, Otilio A., Francisco Prieto-García, Judith Prieto-Méndez, Yolanda Marmolejo-Santillán et Claudia Romo-Gómez. « Chemical weathering in hardened volcanic horizons (tepetates) of the State of Mexico ». Revista Mexicana de Ciencias Geológicas 39, no 2 (26 juillet 2022) : 116–27. http://dx.doi.org/10.22201/cgeo.20072902e.2022.2.1644.
Texte intégralRésumé :
Weathering is one of the most important phenomena that affect the balance dynamics of the Earth's crust. The chemical composition of soil samples and hardened horizons from seven profiles (P1 to P7) of the State of Mexico was compared to detect the degree of alteration by means of weathering indices. In hardened horizons, the dominant elements are SiO2, Al2O3, Na2O, K2O and TiO2, corresponding to 86.8 % of the total oxides. The weathering indices based on the mobility and immobilization of alkaline and alkaline earth elements reveal that the B horizons and the hardened horizons of profiles P4, P5, P6 and P7 are generally more altered than the surface horizons, therefore they have a greater pedogenic development. Profiles P1, P2 and P3 show incipient weathering. The geochemical indices and chemical relationships used in this study to evaluate weathering and associated basic alteration processes showed consistent results. These coincide in indicating incipient to moderate weathering acting in the seven profiles, with variable intensity in all the hardened horizons. The intensity variation defines a sequence of chemical weathering for the hardened horizons: P6> P4> P5> P7> P2> P3> P1, where P6 has the highest degree of weathering in the indices: CIA, CPA, CIA-K, CIW, PIA,IPark, V.
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Goldstein, Benjamin A., Michael J. Pencina, Maria E. Montez-Rath et Wolfgang C. Winkelmayer. « Predicting mortality over different time horizons : which data elements are needed ? » Journal of the American Medical Informatics Association 24, no 1 (29 juin 2016) : 176–81. http://dx.doi.org/10.1093/jamia/ocw057.
Texte intégralRésumé :
Objective: Electronic health records (EHRs) are a resource for “big data” analytics, containing a variety of data elements. We investigate how different categories of information contribute to prediction of mortality over different time horizons among patients undergoing hemodialysis treatment. Material and Methods: We derived prediction models for mortality over 7 time horizons using EHR data on older patients from a national chain of dialysis clinics linked with administrative data using LASSO (least absolute shrinkage and selection operator) regression. We assessed how different categories of information relate to risk assessment and compared discrete models to time-to-event models. Results: The best predictors used all the available data (c-statistic ranged from 0.72–0.76), with stronger models in the near term. While different variable groups showed different utility, exclusion of any particular group did not lead to a meaningfully different risk assessment. Discrete time models performed better than time-to-event models. Conclusions: Different variable groups were predictive over different time horizons, with vital signs most predictive for near-term mortality and demographic and comorbidities more important in long-term mortality.
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JONG, E. DE, D. F. ACTON et H. B. STONEHOUSE. « ESTIMATING THE ATTERBERG LIMITS OF SOUTHERN SASKATCHEWAN SOILS FROM TEXTURE AND CARBON CONTENTS ». Canadian Journal of Soil Science 70, no 4 (1 novembre 1990) : 543–54. http://dx.doi.org/10.4141/cjss90-057.
Texte intégralRésumé :
The soil water contents at the liquid and plastic limits (the Atterberg limits) are widely used in the classification of soils for engineering purposes. Approximately 500 soil samples (129 Ap horizons and 417 B and C horizons) collected over several years as part of the ongoing soil survey program in Saskatchewan were analyzed for texture and Atterberg limits. On about half of the samples water retention (−33 kPa and −1500 kPa matric potential and air dryness), and organic and inorganic C were also determined. The relationship between the Atterberg limits and soil properties was explored through correlation and regression analysis. Clay and organic matter content explained most of the observed variation in the Atterberg limits of the Ap horizons. Clay was the most important independent variable in the B and C horizons, while inorganic C had only a relatively small impact. Key words: Atterberg limits, texture, organic and inorganic C
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Orlova, L. A., et V. A. Panychev. « The Reliability of Radiocarbon Dating Buried Soils ». Radiocarbon 35, no 3 (1993) : 369–77. http://dx.doi.org/10.1017/s0033822200060379.
Texte intégralRésumé :
Variable 14C ages of paleosol organic matter (OM) cause difficulties in interpreting 14C data. We attempt to determine the reliability of OM 14C dates by examining different carbon-containing materials from soil horizons and paleosol fractions.
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J.B, Koto, T. R. Ramahefy et S. Randrianja. « Détection Des Anomalies Du Donnée De Démographie Par Région A Madagascar Par La Méthode Iforest ». International Journal of Progressive Sciences and Technologies 34, no 1 (27 septembre 2022) : 367. http://dx.doi.org/10.52155/ijpsat.v34.1.4578.
Texte intégralRésumé :
La détection des anomalies a connu dernièrement une grande attention, tant au niveau académique qu’au niveau industriel. La prédiction automatique pour la détection d’anomalie s’applique également aux données démographies à Madagascar. Une approche alternative qui se montre prometteuse, est l’utilisation de la méthode des forêts d’isolation (iForest).Cet article nous démontre que la détection des anomalies peut être appliquer sur tous les différents domaines, comme sur les données de la démographie par rapport au nombre de bureau de l’état civil à Madagascar. Les résultats de l’algorithme iForest présentent des réponses qui sont difficiles à l’interpréter. Il est toujours difficile de savoir la contribution de chaque variable dans cet algorithme d’isolation et de comprendre pourquoi des observations particulières reçoivent un score plus élevé.
12
Abduljabbar, Rusul L., Hussein Dia et Pei-Wei Tsai. « Unidirectional and Bidirectional LSTM Models for Short-Term Traffic Prediction ». Journal of Advanced Transportation 2021 (26 mars 2021) : 1–16. http://dx.doi.org/10.1155/2021/5589075.
Texte intégralRésumé :
This paper presents the development and evaluation of short-term traffic prediction models using unidirectional and bidirectional deep learning long short-term memory (LSTM) neural networks. The unidirectional LSTM (Uni-LSTM) model provides high performance through its ability to recognize longer sequences of traffic time series data. In this work, Uni-LSTM is extended to bidirectional LSTM (BiLSTM) networks which train the input data twice through forward and backward directions. The paper presents a comparative evaluation of the two models for short-term speed and traffic flow prediction using a common dataset of field observations collected from multiple freeways in Australia. The results showed BiLSTM performed better for variable prediction horizons for both speed and flow. Stacked and mixed Uni-LSTM and BiLSTM models were also investigated for 15-minute prediction horizons resulting in improved accuracy when using 4-layer BiLSTM networks. The optimized 4-layer BiLSTM model was then calibrated and validated for multiple prediction horizons using data from three different freeways. The validation results showed a high degree of prediction accuracy exceeding 90% for speeds up to 60-minute prediction horizons. For flow, the model achieved accuracies above 90% for 5- and 10-minute prediction horizons and more than 80% accuracy for 15- and 30-minute prediction horizons. These findings extend the set of AI models available for road operators and provide them with confidence in applying robust models that have been tested and evaluated on different freeways in Australia.
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PEREZ, J. M. « Prévision de l’energie digestible des aliments pour le porc : intérêt du dosage des parois végétales par voie enzymatique ». INRAE Productions Animales 3, no 3 (3 juillet 1990) : 171–79. http://dx.doi.org/10.20870/productions-animales.1990.3.3.4371.
Texte intégralRésumé :
Dans le cadre d’un programme général de recherches sur la prévision de la valeur énergétique des aliments composés destinés au Porc, cette étude avait pour objet d’évaluer l’intérêt d’une nouvelle méthode rapide de dosage des parois végétales par voie enzymatique mise au point par l’INRA (PAR : Parois insolubles dans l’eau). L’expérimentation portait sur un ensemble de 43 régimes complexes, dont on a cherché en particulier à diversifier la nature des sources de fibres alimentaires. Les mesures de valeur énergétique (ED) ont été réalisées sur des porcs mâles castrés appartenant à la même gamme de poids (40 kg environ), à raison de quatre animaux par régime (172 bilans digestifs au total). Pour accroître la précision des résultats analytiques et la portée des équations de prédiction, les aliments expérimentaux ont fait l’objet de dosages répétés dans plusieurs laboratoires. Sur la base des critères classiques de sélection des équations (écart-type résiduel, R2), les modèles de prédiction mettant en jeu la variable PAR apparaissent dans l’ensemble les plus précis. Cependant, ils ne présentent pas d’avantage décisif par rapport aux modèles de prévision incluant la cellulose brute ou les résidus pariétaux selon Van Soest. Si on combine les erreurs liées aux modèles (ETR) et les erreurs associées aux analyses (SLAB), les équations avec PAR s’avèrent toujours préférables à celles utilisant les autres indicateurs de parois. Les meilleurs modèles faisant intervenir PAR aboutissent à des équations de prévision de l’énergie digestible dont l’incertitude totale (équation + analyses) n’excède pas 75 kcal par kg de matière sèche. L’équation 25 (Lipides, PAR, Cendres, MAT) s’avère la plus intéressante.
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Glina, Bartłomiej, Jarosław Waroszewski et Cezary Kabała. « Water retention of the loess-derived Luvisols with lamellic illuvial horizon in the Trzebnica Hills (SW Poland) ». Soil Science Annual 65, no 1 (1 mars 2014) : 18–24. http://dx.doi.org/10.2478/ssa-2014-0003.
Texte intégralRésumé :
Abstract The aim of work was to characterize the water retention in the silt-textured Luvisols with lamellic illuvial horizon (argic) that occur in the loess covered northern part of the Silesian Lowland. Soil pits were localized on the Trzebnica Hills near the villages: Machnice (profile 1), Skarszyn (profile 2) and Zaprężyn (profile 3 and 4). Profiles Machnice 1 and Skarszyn 2 were situated in the upper parts of the hills covered with beech stands with an admixture of oak, linden and maple. Profiles Zaprężyn 3 and 4 were situated in the central and lower parts of the arable slope. During the field work conducted in April 2011, 29 soil samples were collected for texture, bulk density and water properties analysis. The soils under study were characterized by texture of silt loam with lower clay content in humus horizons (.loamy silt. according to Polish classification), and higher clay content (.clayey silt.) in the illuvial and subsoil horizons. The texture of all examined profiles was dominated by the „loess“ fractions. Variable abundance of the massive lamellae causes variations in water properties of the illuvial (sub-)horizons. It was found that lamellic illuvial horizons in the loess-derived Luvisols have higher field water capacity than the homogenous illuvial horizons, apart of the clay content. There was no apparent effect of the horizon kind (homogeneous versus lamellic) on the soil bulk density. These properties mainly depended on the total clay content in a particular horizon (sub-horizon).
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Chaikham, Nonthamon, et Wannika Sawangtong. « Sub-Optimal Control in the Zika Virus Epidemic Model Using Differential Evolution ». Axioms 7, no 3 (23 août 2018) : 61. http://dx.doi.org/10.3390/axioms7030061.
Texte intégralRésumé :
A dynamical model of Zika virus (ZIKV) epidemic with direct transmission, sexual transmission, and vertical transmission is developed. A sub-optimal control problem to counter against the disease is proposed including three controls: vector elimination, vector-to-human contact reduction, and sexual contact reduction. Each control variable is discretized into piece-wise constant intervals. The problem is solved by Differential Evolution (DE), which is one of the evolutionary algorithm developed for optimization. Two scenarios, namely four time horizons and eight time horizons, are compared and discussed. The simulations show that models with controls lead to decreasing the number of patients as well as epidemic period length. From the optimal solution, vector elimination is the prioritized strategy for disease control.
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Wu, Hao, Bo Zhang, Tengfei Lin, Danping Cao et Yihuai Lou. « Semiautomated seismic horizon interpretation using the encoder-decoder convolutional neural network ». GEOPHYSICS 84, no 6 (1 novembre 2019) : B403—B417. http://dx.doi.org/10.1190/geo2018-0672.1.
Texte intégralRésumé :
The seismic horizon is a critical input for the structure and stratigraphy modeling of reservoirs. It is extremely hard to automatically obtain an accurate horizon interpretation for seismic data in which the lateral continuity of reflections is interrupted by faults and unconformities. The process of seismic horizon interpretation can be viewed as segmenting the seismic traces into different parts and each part is a unique object. Thus, we have considered the horizon interpretation as an object detection problem. We use the encoder-decoder convolutional neural network (CNN) to detect the “objects” contained in the seismic traces. The boundary of the objects is regarded as the horizons. The training data are the seismic traces located on a user-defined coarse grid. We give a unique training label to the time window of seismic traces bounded by two manually picked horizons. To efficiently learn the waveform pattern that is bounded by two adjacent horizons, we use variable sizes for the convolution filters, which is different than current CNN-based image segmentation methods. Two field data examples demonstrate that our method is capable of producing accurate horizons across the fault surface and near the unconformity which is beyond the current capability of horizon picking method.
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Leopoldino Oliveira, Karen M., Heather Bedle et Karelia La Marca Molina. « Identification of polygonal faulting from legacy 3D seismic data in vintage Gulf of Mexico data using seismic attributes ». Interpretation 9, no 3 (7 juillet 2021) : C23—C28. http://dx.doi.org/10.1190/int-2019-0255.1.
Texte intégralRésumé :
Geological feature: Polygonal faults Seismic appearance: Variable-amplitude plane-parallel horizons without clear discontinuities Features with similar appearance: Seismic noise in stratigraphic sequences without brittle deformation Age: Cenozoic Location: Northern Gulf of Mexico Seismic data: Survey B-01-91-MS obtained by the U.S. National Archive of Marine Seismic Surveys Analysis tools: Geometric seismic attributes
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Green, J. W., A. H. Knoll et K. Swett. « Microfossils from silicified stromatolitic carbonates of the Upper Proterozoic Limestone-Dolomite 'Series', central East Greenland ». Geological Magazine 126, no 5 (1 septembre 1989) : 567–85. http://dx.doi.org/10.1017/s0016756800022858.
Texte intégralRésumé :
AbstractSilicified flake conglomerates andin situstratiform stromatolites of the Upper Proterozoic (c.700–800 Ma) Limestone-Dolomite ‘Series’, central East Greenland, contain well preserved microfossils. Five stratigraphic horizons within the 1200 m succession contain microbial mat assemblages, providing a broad palaeontological representation of late Proterozoic peritidal mat communities. Comparison of assemblages demonstrates that the taxonomy and diversity of mat builder, dweller, and allochthonous populations all vary considerably within and among horizons. The primary mat builder in most assemblages isSiphonophycus inornatum, a sheath-forming prokaryote of probable but not unequivocally established cyanobacterial affinities. An unusual low diversity unit in Bed 17 is dominated by a different builder,Tenuofilum septatum, while a thin cryptalgal horizon in Bed 18 is built almost exclusively bySiphonophycus kestron.Although variable taphonomic histories contribute to observed assemblage variation, most differences within and among horizons appear to reflect the differential success or failure of individual microbial populations in colonizing different tidal flat microenvironments. Twenty-two taxa are recognized, of which two are described as new:Myxococcoides stragulescensn.sp. andScissilisphaera gradatan. sp.
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Ghiculescu, Daniela, Niculae Marinescu, Daniel Ghiculescu et Claudiu Pirnău. « Customer Matrix with Different Time Horizons Applied to Electrodischarge Machines ». Applied Mechanics and Materials 371 (août 2013) : 220–24. http://dx.doi.org/10.4028/www.scientific.net/amm.371.220.
Texte intégralRésumé :
A very effective method to evaluate the products is the Customer Matrix (CM) that uses two coordinates: Perceived Used Value (PUV) and Perceived Price. Our researches extend this basic concept by adding the time variable, creating CM with different time horizons that assures a better understanding of competitive environment. In the first stage, the Customer Matrix is associated with a forecast method. The relevance tree method was used to predict the most probable evolution paths of electrodischarge machines. In the second stage, the CM with different time horizons is constructed, considering products evaluation for short, medium and long time. Finally, a strategy is conceived for an organization that attempts to ameliorate and consolidate its long term position against the main competitors, aiming at obtaining sustainable competitive advantage.
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Sédar Paluku, Mutsotsya, Mpia Héritier Nsenge, Munga Manassé Nzanzu, Baelani Nephtali Inipaivudu et Kasolene Moïse Katembo. « Prédiction des notes finales des étudiants en fin du premier cycle : Utilisation de Data Mining éducatif ». Revue Internationale Multidisciplinaire Etincelle 25, no 2 (6 septembre 2024) : 1–17. http://dx.doi.org/10.61532/rime252114.
Texte intégralRésumé :
L'analyse des performances académiques est basée sur un certain nombre de facteurs qui mesurent les capacités intellectuelles. Cette mesure de la performance est basée sur un certain nombre de variables qui peuvent être utilisées pour prédire la performance académique et les notes finales. Les outils statistiques permettent avant tout de mesurer l'impact des données les unes sur les autres. À cette fin, l'étude des corrélations est le meilleur compromis pour identifier les vrais et les faux prédicteurs entre les variables. Aussi, par le biais des statistiques descriptives, la distribution des données est d'ordre important pour mesurer les différentes dispersions des données dans leur exploration, ces analyses minutieuses amènent le chercheur à devoir cibler les éléments nécessaires à la prédiction des outputs. Pour prédire les performances académiques des étudiants, il est important d'avoir une idée de l'historique de leurs études, afin de pouvoir identifier les facteurs qui peuvent être déterminants pour prédire le résultat final à la fin du cycle. Les modèles d'apprentissage automatique ont joué un rôle clé dans la prédiction des performances. Après avoir exploré les données, nous avons pu comparer les performances des différents algorithmes. Nous avons comparé six algorithmes, dont deux ont atteint une performance acceptable de 80% pour le coefficient de détermination : la régression linéaire et le SVM. L'algorithme le plus performant est la régression linéaire, étant donné que le problème abordé est basé sur la régression. La régression est un type d'algorithme souvent adapté à l'analyse quantitative où la variable cible supporte des valeurs continues. Une fois les modèles entraînés, ils ont été déployés sur la plateforme web à l'aide du Framework Python Flask, en vue de mettre les résultats à la disposition du grand public. Pour illustrer notre modèle, nous avons utilisé 6 variables susceptibles de déterminer les meilleurs prédicteurs. Une fois le modèle entraîné, il peut être utilisé et sauvegardé pour un déploiement ultérieur.
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Orewa, Gregory, Akbar Ghiasi, Shivani Gupta, Rohit Pradhan et Robert Weech-Maldonado. « FINANCIAL HORIZONS : EXAMINING RURAL AND URBAN NURSING HOME FINANCIAL PERFORMANCE ». Innovation in Aging 8, Supplement_1 (décembre 2024) : 130. https://doi.org/10.1093/geroni/igae098.0418.
Texte intégralRésumé :
Abstract Rural nursing homes (NH) struggle with financial sustainability due to sparse populations, high costs, and scarce healthcare resources. Urban counterparts face increased operational costs and resource competition, despite larger populations and better infrastructure. Addressing these distinct challenges is essential for the sector’s financial health and strategic relevance. This study examines financial performance differences between rural and urban nursing homes. The study utilized secondary data from 2017 to 2022 from the Medicare Cost Report, LTC Focus, Care Compare, and Area Health Resource File. The data were modeled using hierarchical linear regression controlling for year and state fixed effects. The dependent variable was operating margin, and the independent variable was nursing home location (Rural vs. Urban). Two models were run, the first controlling for organizational factors (size, quality, ownership, occupancy rate, payer mix, and percent minorities) and the second for organizational and environmental factors (population 65 and older, competition, and Medicare Advantage) that may be associated with financial performance. Results suggest that urban nursing homes had significantly higher operating margins compared to rural facilities (β=1.95, p< 0.01) after controlling for organizational factors. After controlling for environmental factors, urban nursing homes still had higher operating margins (β=0.90, p< 0.01) than rural facilities, but to a lesser extent. As such, rural nursing homes have lower financial performance than urban, even after accounting for organizational and environmental differences. To the extent that lower financial performance may affect quality and access to long-term care, policymakers should explore reimbursement strategies to address these financial disparities.
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Ebner, F. H., J. S. Marquardt, B. Hirt, G. C. Feigl, M. Tatagiba et M. U. Schuhmann. « Broadening horizons of neuroendoscopy with a variable-view rigid endoscope : An anatomical study ». European Journal of Surgical Oncology (EJSO) 36, no 2 (février 2010) : 195–200. http://dx.doi.org/10.1016/j.ejso.2009.07.185.
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Wang, Haowei, Kin On Kwok et Steven Riley. « Forecasting influenza incidence as an ordinal variable using machine learning ». Wellcome Open Research 9 (8 janvier 2024) : 11. http://dx.doi.org/10.12688/wellcomeopenres.19599.1.
Texte intégralRésumé :
Background: Many mechanisms contribute to the variation in the incidence of influenza disease, such as strain evolution, the waning of immunity and changes in social mixing. Although machine learning methods have been developed for forecasting, these methods are used less commonly in influenza forecasts than statistical and mechanistic models. In this study, we applied a relatively new machine learning method, Extreme Gradient Boosting (XGBoost), to ordinal country-level influenza disease data. Methods: We developed a machine learning forecasting framework by adopting the XGBoost algorithm and training it with surveillance data for over 32 countries between 2010 and 2018 from the World Health Organisation’s FluID platform. We then used the model to predict incidence 1- to 4-week ahead. We evaluated the performance of XGBoost forecast models by comparing them with a null model and a historical average model using mean-zero error (MZE) and macro-averaged mean absolute error (mMAE). Results: The XGBoost models were consistently more accurate than the null and historical models for all forecast time horizons. For 1-week ahead predictions across test sets, the mMAE of the XGBoost model with an extending training window was reduced by 78% on average compared to the null model. Although the mMAE increased with longer prediction horizons, XGBoost models showed a 62% reduction in mMAE compared to the null model for 4-week ahead predictions. Our results highlight the potential utility of machine learning methods in forecasting infectious disease incidence when that incidence is defined as an ordinal variable. In particular, the XGBoost model can be easily extended to include more features, thus capturing complex patterns and improving forecast accuracy. Conclusion: Given that many natural extreme phenomena are often described on an ordinal scale when informing planning and response, these results motivate further investigation of using similar scales for communicating risk from infectious diseases.
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Foggin, Peter. « L’évolution des valeurs foncières à Montréal (1964-1969) ». Cahiers de géographie du Québec 19, no 46 (12 avril 2005) : 87–118. http://dx.doi.org/10.7202/021249ar.
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On peut résumer ainsi les conclusions de cette étude. 1) Il existe un lien de causalité réciproque entre l'utilisation du sol et les valeurs foncières. 2) À l'échelle de la zone d'analyse, on observe un effet systématique minimal du facteur autoroutes sur les modifications relatives de la surface des valeurs foncières à l'intérieur du périmètre urbain. 3) Quand il se produit des changements dans la position relative des classes de valeurs foncières, ils apparaissent comme la conséquence de la construction des principales stations du nouveau métro. L'effet « régional » considérable que l'on observe n'a rien d'étonnant. .En ce qui concerne les facteurs sociaux, on a vu que le statut familial, représenté par la variable substitut de la taille de la famille, contribue de façon significative à la prédiction de la surface des valeurs foncières intra-urbaines. Il nous paraît évident qu'on pourrait accorder un caractère plus définitif au modèle si l'analyse en coupe portait sur deux moments d'observation plus éloignés dans le temps.
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Jarnuszewski, Grzegorz. « Chemical properties of organic soils developed from lacustrine chalk near the lakes Strzeszowskie, Sitno, and Sierakowo (Western Pomerania, north Poland) ». Soil Science Annual 66, no 4 (1 décembre 2015) : 168–79. http://dx.doi.org/10.1515/ssa-2015-0034.
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Abstract The genesis of organic soils is closely connected with water. The occurrence of carbonate deposits in the central and lower part of organic soil profile points to the link between their genesis and post-glacial lakes. The studies conducted in the years 2009–2012 focused on organic soils near lakes: Strzeszowskie, Sitno (Myśliborskie Lakeland) and Sierakowo (Ińskie Lakeland), north Poland. The goal of the present study was to characterize chemical properties of organic soils developed on carbonate deposits. The examined soils belonged to organic muck and sapric peat soils. They contained variable amount of organic matter (32,4–66,6%). The C/N ratio depended on the degree of mineralization. The soils under study, had a high level of available forms of Ca and low level of P, K, Cu, and Zn. Both in surface and subsurface horizons of muck and sapric peat soils the content of exchangeable cations may be ranked as follows: Ca > Mg > K > Na. Basic cations total in organic horizons was distinctly higher than in calcareous sediments. In organic horizons and limnic deposits, the share of exchangeable form of Ca in the sum of basic cations exceeded 95%.
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Gustafsson, J. P., D. G. Lumsdon et M. Simonsson. « Aluminium solubility characteristics of spodic B horizons containing imogolite-type materials ». Clay Minerals 33, no 1 (mars 1998) : 77–86. http://dx.doi.org/10.1180/000985598545444.
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AbstractFifteen Swedish and Finnish soil samples from spodic B horizons containing imogolite-type materials were equilibrated with dilute NaCl and HC1 at 8°C. For the NaCl extracts, apparent equilibrium with respect to an AI(OH)3 phase was reached in one to two weeks. Equilibrium with respect to an imogolite-type phase was slower, especially at large soil:solution ratios. The results show that log *Ks (gibbsite), i.e. the logarithm of the solubility constant for reactive AI(OH)3 at 8°C was ~9.40 (8.29 at 25°C) while log *Ks (imogolite) was variable; for the soil studied in most detail it was 7.66 (6.64 at 25°C) As well-ordered gibbsite rarely forms in spodic B horizons, it is suggested that Al(OH)3 and poorly-ordered allophanic materials may be slowly converted to less soluble and less reactive imogolite-type materials.
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Kreye, Jesse K., J. Morgan Varner et Christopher J. Dugaw. « Spatial and temporal variability of forest floor duff characteristics in long-unburnedPinus palustrisforests ». Canadian Journal of Forest Research 44, no 12 (décembre 2014) : 1477–86. http://dx.doi.org/10.1139/cjfr-2014-0223.
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Duff fires (smouldering in fermentation and humus forest floor horizons) and their consequences have been documented in fire-excluded ecosystems but with little attention to their underlying drivers. Duff characteristics influence the ignition and spread of smouldering fires, and their spatial patterns on the forest floor may be an important link to the heterogeneity of consumption observed following fires. We evaluated fuel bed characteristics (depths, bulk densities, and moisture) of duff in a long-unburned longleaf pine (Pinus palustris Mill.) forest and corresponding spatial variation across 100to 103m scales. Fermentation and humus horizon depths both varied (∼100% coefficient of variation) but with moderate to strong spatial autocorrelation at fine scales. Fermentation bulk density varied less than humus bulk density, which varied considerably at fine scales. Fermentation horizons held more moisture (average 49%–172%) and were much more variable than humus following rainfall, which remained stable and relatively dry (average 28%–62%). Humus moisture was moderately autocorrelated at fine scales, but fermentation moisture was highly variable, showing no evidence of spatial autocorrelation under dry, intermediate, or wet conditions. Observations from this study highlight the underlying spatial variability in duff, informing future sampling and fire management efforts in these long-unburned coniferous forests.
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Zajícová, Kateřina, et Tomáš Chuman. « O and A soil horizons’ boundaries detection using GPR under variable soil moisture conditions ». Geoderma 422 (septembre 2022) : 115934. http://dx.doi.org/10.1016/j.geoderma.2022.115934.
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Saha, Sajal, Anwar Haque et Greg Sidebottom. « Multi-Step Internet Traffic Forecasting Models with Variable Forecast Horizons for Proactive Network Management ». Sensors 24, no 6 (14 mars 2024) : 1871. http://dx.doi.org/10.3390/s24061871.
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The ISP (Internet Service Provider) industry relies heavily on internet traffic forecasting (ITF) for long-term business strategy planning and proactive network management. Effective ITF frameworks are necessary to manage these networks and prevent network congestion and over-provisioning. This study introduces an ITF model designed for proactive network management. It innovatively combines outlier detection and mitigation techniques with advanced gradient descent and boosting algorithms, including Gradient Boosting Regressor (GBR), Extreme Gradient Boosting (XGB), Light Gradient Boosting Machine (LGB), CatBoost Regressor (CBR), and Stochastic Gradient Descent (SGD). In contrast to traditional methods that rely on synthetic datasets, our model addresses the problems caused by real aberrant ISP traffic data. We evaluated our model across varying forecast horizons—six, nine, and twelve steps—demonstrating its adaptability and superior predictive accuracy compared to traditional forecasting models. The integration of the outlier detection and mitigation module significantly enhances the model’s performance, ensuring robust and accurate predictions even in the presence of data volatility and anomalies. To guarantee that our suggested model works in real-world situations, our research is based on an extensive experimental setup that uses real internet traffic monitoring from high-speed ISP networks.
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Aramendia, Iñigo, Ekaitz Zulueta, Jose Manuel Lopez-Guede, Daniel Teso-Fz-Betoño et Unai Fernandez-Gamiz. « Optimization of the Design and Control System of a Backup Power System Based on Batteries and Generator Set ». Sustainability 17, no 5 (6 mars 2025) : 2313. https://doi.org/10.3390/su17052313.
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Grid complexity is expected to increase in the near future, and therefore, research on it is highly increasing due to the interest in optimizing power distribution along with the implementation of renewable energy sources. The grid presented in the current work uses a hybrid storage system with batteries and a generator set. A supervisor is also added to the model in order to distribute the load between the batteries and the generator when a power grid outage is detected. The main objective of this study is to find optimal supervisor operating values and battery capacity sizing. To that end, a recently developed intelligent algorithm, called Basque optimization (BO), is applied to model the battery capacity sizing and its depth of discharge. The results obtained provided an optimum value of 0.7267, which implies a battery sizing of 72.67% of the maximum battery capacity proposed in the optimization algorithm. Additionally, an optimal state of charge (SoC_lim) of the battery of 3.87% is obtained, corresponding to a depth of discharge (DoD_lim) of 96.13%. A sensitivity analysis is also performed to evaluate different time horizons and load profiles. The results showed that longer simulation horizons reduce the DoD, preserving battery life, while battery utilization increases in longer time horizons and variable load conditions, ensuring energy availability.
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Flader, Anna, Barbara Gworek et Jolanta Kostrzewa-Szulc. « Modified Wallschläger Sequential Extraction as a Tool for Evaluating the Mobility of Mercury ». Archives of Environmental Protection 40, no 1 (1 mars 2014) : 23–31. http://dx.doi.org/10.2478/aep-2014-0005.
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Abstract The presented studies were focused on evaluating the utility of one of sequential extraction methods for evaluating the bioavailability of mercury in soils polluted by this element. Soil samples collected from horizons 0-20 cm and 20-80 cm were subject to analysis of the basic physical and chemical properties of soils. Moreover, the total content of mercury was determined and sequential extraction of mercury was conducted using a modified five-stage Wallschläger method. The analyses show that the studied soils are characterized by a variable mercury content, the highest in the surface soil horizons. Sequential extraction of mercury in the analyzed soils has indicated that the highest percentage content in the total content had mercury linked with sulphides. A high content of mercury linked with organic matter was also noted. The content of bioavailable mercury did not exceed 1.5% of the total content.
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Heidari, H. « Alternative bvar models for forecasting inflation ». Acta Oeconomica 61, no 1 (1 mars 2011) : 61–75. http://dx.doi.org/10.1556/aoecon.61.2011.1.4.
Texte intégralRésumé :
This paper investigates the use of different priors to improve the inflation forecasting performance of BVAR models with Litterman’s prior. A Quasi-Bayesian method, with several different priors, is applied to a VAR model of simulated data as well as to the Australian economy from 1978:Q2 to 2006:Q4. A novel feature with this paper is the use of g-prior in the BVAR models to alleviate poor estimation of drift parameters of Traditional BVAR models. Some results are as follows: (1) In the Quasi-Bayesian framework, BVAR models with Normal-Wishart prior provide the most accurate forecasts of Australian inflation; (2) Generally in the parsimonious models, the BVAR with g-prior performs better than BVAR with Litterman’s prior; (3) In simulated data, the BVAR model with g-prior produces more accurate forecasts of driftless variable in the long-run horizons (first and second year forecast horizons).
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Connidis, Ingrid Arnet. « David K. Foot with Daniel Stoffman. Boom, Bust, and Echo : How to Profit from the Coming Demographic Shift. Toronto : Macfarlane, Walter and Ross, 1996. » Canadian Journal on Aging / La Revue canadienne du vieillissement 16, no 2 (1997) : 373–80. http://dx.doi.org/10.1017/s0714980800014409.
Texte intégralRésumé :
RésuméDans leur trés populaire Boom, Bust, and Echo, Foot et Stoffman posent comme principe que “la démographie explique presque les deux tiers de tout” (p. 2). Dans un style trés vivant, ils traitent de l'effet des données démographiques (surtout de la fluctuation des taux de fécondité et de ses conséquences sur les différences de niveaux au sein des cohortes d'âge) sur l'immobilier, l'investissement, l'emploi, le commerce de détail, les loisirs, les villes, l'éducation, les soins de santé, la famille et les politiques en matière d'aînés. La distinction entre l'explication et la prédiction demeure équivoque tout au long du livre mais en réalité, la prédiction est beaucoup plus définie que l'explication. On trouve peu d'insistance sur certains éléments critiques comme la structure sociale, l'organisation humaine et le changement social de notre siècle. Le changement social important est ramené aux données démographiques en tant que variable causale et les enjeux sociaux majeurs sont souvent réduits à leurs conséquences économiques. La concentration sur l'âge comme indicateur prévisionnel du comportement mène à une analyse résolument déterministe du vieillissement et tend à présenter comme homogènes tous les membres d'un même groupe d'âge. Bien que le coeur de l'argumentation repose sur le nombre relatif de membres d'une même cohorte d'âge, on relève parfois de la confusion en matière de changements réels du comportement (qui se reflète dans le changement des proportions, et non seulement dans les nombres, d'un groupe d'âge donné engagé dans un comportement donné) et par les hypothèses de systèmes de changement de valeurs reposant sur la taille d'une cohorte. Les auteurs n'ont virtuellementpas tenu compte de la vaste recherche déjà effectuée dans le domaine. Dans l'ensemble, ils nʼembrassent pas la vision démographique apocalyptique si chère aux politiciens et aux économistes actuels, lesquels favorisent l'approche comptable transgénérationnelle, et terminent sur une note optimiste en ce qui a trait à l'avenir du Canada, notamment sur notre capacité à gérer les facteurs numériques variés en matière de retraite.
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Mignini, Irene, Valentina Blasi, Fabrizio Termite, Giorgio Esposto, Raffaele Borriello, Lucrezia Laterza, Franco Scaldaferri, Maria Elena Ainora, Antonio Gasbarrini et Maria Assunta Zocco. « Fibrostenosing Crohn’s Disease : Pathogenetic Mechanisms and New Therapeutic Horizons ». International Journal of Molecular Sciences 25, no 12 (7 juin 2024) : 6326. http://dx.doi.org/10.3390/ijms25126326.
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Bowel strictures are well recognized as one of the most severe complications in Crohn’s disease, with variable impacts on the prognosis and often needing surgical or endoscopic treatment. Distinguishing inflammatory strictures from fibrotic ones is of primary importance due to the different therapeutic approaches required. Indeed, to better understand the pathogenesis of fibrosis, it is crucial to investigate molecular processes involving genetic factors, cytokines, alteration of the intestinal barrier, and epithelial and endothelial damage, leading to an increase in extracellular matrix synthesis, which ultimately ends in fibrosis. In such a complex mechanism, the gut microbiota also seems to play a role. A better comprehension of molecular processes underlying bowel fibrosis, in addition to radiological and histopathological findings, has led to the identification of high-risk patients for personalized follow-up and testing of new therapies, primarily in preclinical models, targeting specific pathways involving Transforming Growth Factor-β, interleukins, extracellular matrix balance, and gut microbiota. Our review aims to summarize current evidence about molecular factors involved in intestinal fibrosis’ pathogenesis, paving the way for potential diagnostic biomarkers or anti-fibrotic treatments for stricturing Crohn’s disease.
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Balter, Anne G., et Bas J. M. Werker. « THE EFFECT OF THE ASSUMED INTEREST RATE AND SMOOTHING ON VARIABLE ANNUITIES ». ASTIN Bulletin 50, no 1 (31 octobre 2019) : 131–54. http://dx.doi.org/10.1017/asb.2019.27.
Texte intégralRésumé :
AbstractIn this paper, we consider the risk–return trade-off for variable annuities in a Black–Scholes setting. Our analysis is based on a novel explicit allocation of initial wealth over the payments at various horizons. We investigate the relationship between the optimal consumption problem and the design of variable annuities by deriving the optimal so-called assumed interest rate for an investor with constant relative risk aversion preferences. We investigate the utility loss due to deviations from this. Finally, we show analytically how habit-formation-type smoothing of financial market shocks over the remaining lifetime leads to smaller year-to-year volatility in pension payouts, but to increases in the longer-term volatility.
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Kamra, S. K., J. Michaelsen, W. Wichtmann et P. Widmoser. « Preferential solute movement along the interface of soil horizons ». Water Science and Technology 40, no 2 (1 juillet 1999) : 61–68. http://dx.doi.org/10.2166/wst.1999.0086.
Texte intégralRésumé :
Preferential flow significantly contributes to groundwater contamination due to rapid bypass of large fractions of applied agrochemicals through the vadose zone. Transport of surface-applied non-reactive tracer (bromide) and pesticides was studied from 1991/92 to 1994/95 in an experimental drain plot in northern Germany. The soil of the study site was sandy loam in texture with high bulk density and a distinct structural change from sub-angular to angular at the interface of two soil horizons at 30-40 cm. Each year, bromide and pesticides appeared in drain water with the first drainage event followed by steep concentration peaks indicating preferential solute movement. The general shape of the breakthrough curves, magnitude and time of occurrence of the main concentration peaks of bromide and pesticides were comparable in different years despite notable differences in rainfall, drain discharge and areas of chemical application. Further, it was observed that variable drain discharges occurred without significant changes in water table levels, and a major fraction of surface-applied bromide and pesticides appeared in drainage effluent without apparently leaching through the deeper layers. It appears that water and solutes, after vertical movement through the upper plough layer, moved horizontally along the interface of two soil horizons towards and through the porous drain trench to the drain.
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Hall, R. P., B. Chadwick, J. C. Escher et V. N. Vasudev. « Supracrustal rocks in the Ammassalik region, South-East Greenland ». Rapport Grønlands Geologiske Undersøgelse 146 (31 décembre 1989) : 17–22. http://dx.doi.org/10.34194/rapggu.v146.8091.
Texte intégralRésumé :
Large belts of supracrustal rocks are abundant in the Ammassalik region of S.E. Greenland, and are referred to collectively as the Siportoq supracrustal association. They comprise overwhelmingly metasediments, mainly of quartz-rich or semipelitic composition, with variable proportions of quartz, kyanite, sillimanite, garnet and biotite. Graphitic schists are also common and marble horizons occur up to a kilometre thick. Garnet amphibolites are volumetrically minor, and ultramafic rocks are extremely rare. Lithological banding representing relict bedding and rare cross-bedding are locally well preserved. The compositions of the metasedimentary rocks suggest that their provenance was dominantly sialic and the great thickness of semi-pelitic rocks suggests that additions of immature minerals kept pace with gentle subsidence of a basin or shelf environment. The thick marble horizons indicate periods of relative stability. Unlike the surrounding quartzo-feldspathic gneisses in the north of the area, the supracrustal rocks do not appear to have undergone granulite facies metamorphism.
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Jeske, Agnieszka, et Barbara Gworek. « Content and Mobility of Strontium in Forest Soils According to North-South Transect in Poland ». Archives of Environmental Protection 39, no 4 (1 décembre 2013) : 113–22. http://dx.doi.org/10.2478/aep-2013-0032.
Texte intégralRésumé :
Abstract The investigation was carried out on forest soils collected from areas subject to variable pollution. The fraction of strontium was analyzed in soil samples from north-eastern Poland (Borki forest division), treated as a non-polluted region (natural background) and in soil samples from central (Rogów forest division) and south-western Poland (Świerklaniec forest division). The sequential extraction procedure was applied in this study to separate the fractions of strontium. Five fractions were analyzed in every genetic horizon according to the Tessier method. The concentration of strontium was also analyzed in the plants. Both results were compared in order to evaluate the mobility and bioavailability of the trace elements in the environment. The content, distribution and bioavailability of the strontium fractions were investigated with particular emphasis on the contaminated study sites. Total content of strontium in surface horizons depended on the localization. Among analysed fractions strontium, in organic soil horizons, regardless of localization, occurred predominantly in mobile fractions in all examined soils.
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Boone, Richard D. « Influence of sampling date and substrate on nitrogen mineralization : comparison of laboratory-incubation and buried-bag methods for two Massachusetts forest soils ». Canadian Journal of Forest Research 22, no 12 (1 décembre 1992) : 1895–900. http://dx.doi.org/10.1139/x92-248.
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Nitrogen (N) mineralization potential and net N mineralization insitu were measured monthly over 7 months for the forest floor horizons (Oi, Oe, Oa) and mineral soil (0–15 cm) of a pine stand and the mineral soil (0–15 cm) of a maple stand in Massachusetts, United States. In all cases, N mineralization potential per unit organic matter (anaerobic laboratory incubation) varied significantly by sampling month but was unrelated to the seasonal pattern for net N mineralization (buried-bag method). The organic horizons in the pine stand exhibited the most variable N mineralization potential, with the Oe horizon having more than a fourfold seasonal range. For the pine stand the Oe horizon also had the highest N mineralization potential (per unit organic matter) and the highest net N mineralization insitu (per unit area). In general, temporal and depth-wise variability should be considered when sites are assessed with respect to the pool of mineralizable N.
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Evdokimova, Elizaveta, Ekaterina Ivanova, Grigory Gladkov, Aleksei Zverev, Anastasiia Kimeklis, Elena Serikova, Alexandr Pinaev et al. « Structural Shifts in the Soil Prokaryotic Communities Marking the Podzol-Forming Process on Sand Dumps ». Soil Systems 8, no 1 (9 janvier 2024) : 9. http://dx.doi.org/10.3390/soilsystems8010009.
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This work describes the microbial community structure of the continuously revegetated chronosequence of a former sand quarry, which demonstrates a unique example of nearly complete soil restoration in less than 100 years. Samples were collected at five time points (0, 3, 30, 70 years and mature soil) from the entire set of soil horizons, revealing the history of pedogenesis. Real-time PCR was applied to quantitatively describe the bacterial and archaeal communities. High-throughput sequencing of the bacterial and archaeal V4 variable region of the 16S rRNA gene was used to identify abundant microbial taxa. A beta-diversity analysis revealed that the prokaryotic community structure responded strongly to the processes of organic matter accumulation and the corresponding evolution of the soil into discrete horizons. Changes in soil microbiota in the course of soil profile evolution revealed three groups of prokaryotes, which tended to accumulate in the specific soil horizons and might be associated with the certain soil-forming processes, including plant roots growth. This research showed the heuristic potential of soil horizon profiling in microbiological studies as opposed to the formal depth-dependent separation of the soil layers. The results allowed us to trace the relationship between the structure of the soil prokaryotic community and the peculiarities of the evolution of the podzolic soil profile as well as to identify the microbial indicators and drivers of primary pedogenesis.
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Behrendt, Karl, Oscar Cacho, James M. Scott et Randall Jones. « Optimising pasture and grazing management decisions on the Cicerone Project farmlets over variable time horizons ». Animal Production Science 53, no 8 (2013) : 796. http://dx.doi.org/10.1071/an11174.
Texte intégralRésumé :
This study addresses the problem of balancing the trade-offs between the need for animal production, profit, and the goal of achieving persistence of desirable species within grazing systems. The bioeconomic framework applied in this study takes into account the impact of climate risk and the management of pastures and grazing rules on the botanical composition of the pasture resource, a factor that impacts on livestock production and economic returns over time. The framework establishes the links between inputs, the state of the pasture resource and outputs, to identify optimal pasture development strategies. The analysis is based on the application of a dynamic pasture resource development simulation model within a seasonal stochastic dynamic programming framework. This enables the derivation of optimum decisions within complex grazing enterprises, over both short-term tactical (such as grazing rest) and long-term strategic (such as pasture renovation) time frames and under climatic uncertainty. The simulation model is parameterised using data and systems from the Cicerone Project farmlet experiment. Results indicate that the strategic decision of pasture renovation should only be considered when pastures are in a severely degraded state, whereas the tactical use of grazing rest or low stocking rates should be considered as the most profitable means of maintaining adequate proportions of desirable species within a pasture sward. The optimal stocking rates identified reflected a pattern which may best be described as a seasonal saving and consumption cycle. The optimal tactical and strategic decisions at different pasture states, based on biomass and species composition, varies both between seasons and in response to the imposed soil fertility regime. Implications of these findings at the whole-farm level are discussed in the context of the Cicerone Project farmlets.
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Mencagli, G. « Adaptive model predictive control of autonomic distributed parallel computations with variable horizons and switching costs ». Concurrency and Computation : Practice and Experience 28, no 7 (18 mai 2015) : 2187–212. http://dx.doi.org/10.1002/cpe.3495.
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Jensen, Mogens H., Anders Johansen et Ingve Simonsen. « Inverse Fractal Statistics in Turbulence and Finance ». International Journal of Modern Physics B 17, no 22n24 (30 septembre 2003) : 4003–12. http://dx.doi.org/10.1142/s021797920302199x.
Texte intégralRésumé :
We consider inverse statistics in turbulence and financial data. By inverse statistics, also sometimes called exit time statistics, we "turn" the variables around such that the fluctuating variable becomes the fixed variable, while the fixed variable becomes fluctuating. In that sense we can probe distinct regimes of the data sets. In the case of turbulence, we obtain a new set of (multi)-scaling exponents which monitor the dissipation regime. In the case of economics, we obtain a distribution of waiting times needed to achieve a predefined level of return. Such a distribution typically goes through a maximum at a time called the optimal investment horizon[Formula: see text], since this defines the most likely waiting time for obtaining a given return ρ. By considering equal positive and negative levels of return, we report on a quantitative gain-loss asymmetry most pronounced for short horizons.
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Piotrowska-Długosz, Anna, Jacek Długosz, Agata Gryta et Magdalena Frąc. « Responses of N-Cycling Enzyme Activities and Functional Diversity of Soil Microorganisms to Soil Depth, Pedogenic Processes and Cultivated Plants ». Agronomy 12, no 2 (20 janvier 2022) : 264. http://dx.doi.org/10.3390/agronomy12020264.
Texte intégralRésumé :
The rates of N cycling and soil enzyme activities involved in the transformation of soil N-related nutrients are rarely measured in soils below a 30 cm depth, even though substantial amounts of nitrogen are also stored in deep soils. The aim of this study was to determine how soil microbial and enzymatic properties changed as a function of depth across soil profiles that were developed on the same parent material but differed in terms of soil-forming processes. Two soil profiles were excavated in fields with lucerne and two under winter wheat. We assessed the N-cycling enzymes, the microbial utilization of the N-substrates, the microbial biomass carbon and nitrogen (MBC, MBN) content, and the related physicochemical properties. The most beneficial enzymatic (on a soil mass) and microbial properties, as well as nitrogen substrate utilization, were found in the Ap horizons and decreased with depth to varying degrees. The specific enzymatic activity (per unit of soil TOC and MBC), was more variable in response to the depth of the profile, but did not exhibit clear trends. The potential enzyme activities in the subsurface layers were also affected by factors that are associated with the pedogenic processes (e.g., the lessivage process, clay content). Only nitrate reductase activity was significantly higher in the horizons with potential reducing conditions compared to oxidative horizons, while the opposite trend was found for N-acetyl-β-D-glucosaminidase (NAG) activity. The cultivated plants had a significant impact on the degree of enzymatic activity and N-substrate utilization. The lessivage process significantly reduced microbial biomass and enzymatic activity (except for NAG activity). In general, nitrogen substrate utilization decreased with increasing soil depth and was greater in lucerne than the winter wheat profiles. Mollic Stagnic Gleysols (MSG) and Cambic Stagnic Phaeozems (CSP) horizons also have higher nitrogen substrate utilization than Luvisol profiles.
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Szymański, Wojciech, Janusz Siwek, Joanna Waścińska et Bronisław Wojtuń. « Texture and geochemistry of surface horizons of Arctic soils from a non-glaciated catchment, SW Spitsbergen ». Polish Polar Research 37, no 3 (1 septembre 2016) : 361–77. http://dx.doi.org/10.1515/popore-2016-0019.
Texte intégralRésumé :
AbstractPhysical and chemical properties of Arctic soils and especially the properties of surface horizons of the soils are very important because they are responsible for the rate and character of plant colonization, development of vegetation cover, and influence the rate and depth of thawing of soils and development of active layer of permafrost during summer. The main aim of the present study is to determine and explain the spatial diversity of selected physical and chemical properties of surface horizons of Arctic soils from the non-glaciated Fuglebekken catchment located in the Hornsund area (SW Spitsbergen) by means of geostatistical approach. Results indicate that soil surface horizons in the Fuglebekken catchment are characterized by highly variable physical and chemical properties due to a heterogeneous parent material (marine sediments, moraine, rock debris), tundra vegetation types, and non-uniform influence of seabirds. Soils experiencing the strongest influence of seabird guano have a lower pH than other soils. Soils developed on the lateral moraine of the Hansbreen glacier have the highest pH due to the presence of carbonates in the parent material and a lack or presence of a poorly developed and discontinuous A horizon. The soil surface horizons along the coast of the Hornsund exhibit the highest content of the sand fraction and SiO2. The surface of soils occurring at the foot of the slope of Ariekammen Ridge is characterized by the highest content of silt and clay fractions as well as Al2O3, Fe2O3, and K2O. Soils in the central part of the Fuglebekken catchment are depleted in CaO, MgO, and Na2O in comparison with soils in the other sampling sites, which indicates the highest rate of leaching in this part of the catchment.
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Stock, James H., et Mark W. Watson. « Variable Trends in Economic Time Series ». Journal of Economic Perspectives 2, no 3 (1 août 1988) : 147–74. http://dx.doi.org/10.1257/jep.2.3.147.
Texte intégralRésumé :
The two most striking historical features of aggregate output are its sustained long run growth and its recurrent fluctuations around this growth path. Over horizons of a few years, these shorter cyclical swings can be pronounced; for example, the 1953, 1957, and 1974 recessions are evident as substantial temporary declines in aggregate activity. These cyclical fluctuations are, however, dwarfed in magnitude by the secular expansion of output. But just as there are cyclical swings in output, so too are there variations in the growth trend: growth in GNP in the 1960s was much stronger than it was in the 1950s. Thus, changes in long-run patterns of growth are an important feature of postwar aggregate economic activity. In this article, we discuss the implications of changing trends in macroeconomic data from two perspectives. The first perspective is that of a macroeconomist reassessing the conventional dichotomy between growth and stabilization policies. As an empirical matter, does this dichotomy make sense for the postwar United States? What is the relative “importance” of changes in the trend and cyclical swings in explaining the quarterly movements in economic aggregates? We next adopt the perspective of an econometrician interpreting empirical evidence based on data that contain variable trends. The presence of variable trends in time series data can lead one to draw mistaken inferences using conventional econometric techniques. How can these techniques -- or our interpretation of them -- be modified to avoid these mistakes?
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Leroux-Boudreault, Ariane, Jacques Forget et Pier-Olivier Caron. « Une analyse picoéconomique de l’attention à la tâched’écoliers et de l’attention de l’enseignant ». ACTA COMPORTAMENTALIA 22, no 1 (mars 2014) : 73–88. https://doi.org/10.32870/ac.v22i1.48852.
Texte intégralRésumé :
Dans le cadre de la picoéconomie, la contrainte exercée par un programme de renforcement est considérée comme le prix nécessaire à l’obtention d’un bien (Ainslie, 1992). L’allocation des réponses d’un sujet res-pecte alors la loi de la demande (Green et Kagel, 1987). La présente étude vise à illustrer l’intégration de la picoéconomie dans un contexte scolaire de salle de classe. Elle porte sur une analyse descriptive des relations entre le taux d’attention de trois écoliers d’une école primaire et différentes formes d’attention qu’ils obtiennent de leur enseignant. Ces relations sont analysées suivant trois programmes de renforcement, soit un programme à proportion variable, un programme à intervalle variable et un programme concurrent. L’étude vise à établir le type de contingences qui prédit le mieux le taux d’attention des écoliers en fonc-tion d’une perspective moléculaire (séquences comportement-conséquence de 5 minutes), locale (séquences de 10 minutes) ou molaire (moyenne quotidienne). Les résultats de cette étude de cas suggèrent qu’une analyse moléculaire permet une meilleure prédiction des comportements des enfants. En revanche, la loi de l’appariement est le meilleur prédicteur du taux d’attention des écoliers autant sur le plan moléculaire que molaire. Ces résultats sont abordés selon le modèle picoéconomique d’Ainslie (1992). Enfin, il est relevé que l’analyse quantitative des relations entre comportement et conséquence en termes de programme de renforcement telle que réalisée dans la présente étude est totalement négligée par les auteurs qui s’intéressent à l’analyse descriptive et fonctionnelle du comportement.
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Billot, Antoine, et Frédéric Gavrel. « Dispersion des prix et experiences Une étude de l'équilibre d'un marché à générations de clients en information imparfaite ». Recherches économiques de Louvain 59, no 3 (1993) : 379–88. http://dx.doi.org/10.1017/s0770451800008472.
Texte intégralRésumé :
RésuméNous proposons de fonder la dispersion des prix sur l'écart entre les horizons passés (les «expériences») des différentes générations de clients. L'argument de base est simple : la vieille génération dotée d'une certaine connaissance du marché sera naturellement plus exigeante que les jeunes qui ne savent rien encore. Nous nous plaçons dans un modèle à générations imbriquées. Supposant d'abord la population constante, nous caractérisons l'équilibre de marché. Puis, supposant la population variable, nous apprécions l'influence de son taux de croissance sur la distribution des prix.
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Dyck, M. F., et R. G. Kachanoski. « Scale-dependent covariance of soil physical properties above and below a soil horizon interface : Pedogenic versus anthropogenic influences on total porosity ». Canadian Journal of Soil Science 91, no 2 (mai 2011) : 149–59. http://dx.doi.org/10.4141/cjss10078.
Texte intégralRésumé :
Dyck, M. F. and Kachanoski, R. G. 2011. Scale-dependent covariance of soil physical properties above and below a soil horizon interface: Pedogenic versus anthropogenic influences on total porosity. Can. J. Soil Sci. 91: 149–159. The basic unit of soil – the pedon – is described as the minimum, three-dimensional unit of soil representative of the variability of soil horizon dimensions and morphology. Pedogenic processes responsible for soil horizon and soil profile formation are primarily hydrologic in nature. The spatially variable distribution of soil horizons (i.e., the variation among pedons within catenae or landscapes) is likely a reflection of the inherent variability of the soil parent material and the spatial variability of hydrological/pedogenic processes. This paper explores the spatial variability and spatially scale-dependent covariance between a basic soil property (porosity) above and below an A/B horizon interface under adjacent disturbed (cultivated) and undisturbed (forested) conditions. A combination of scale-dependent variance and Fourier-domain spectral analysis shows that the scale-dependent covariance of A and B horizon porosity varies significantly between the cultivated and forested sampling transects. The majority of these observed differences between the scale-dependent covariance of A and B horizon porosity under contrasting land uses is attributed to tillage. These results suggest that anthropogenic activities such as tillage may not only alter the surface horizons, but the nature of the spatial covariance between surface and underlying horizons which likely influences current soil hydrological processes.
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Whetter, D. A., P. R. Bullock et L. G. Fuller. « Bromide redistribution as influenced by landscape morphology and pedogenic properties in a variable glacial till landscape : A qualitative examination ». Canadian Journal of Soil Science 88, no 4 (1 août 2008) : 477–90. http://dx.doi.org/10.4141/cjss07072.
Texte intégralRésumé :
Redistribution of water and associated solutes in undulating to hummocky landscapes affects crop yield via losses of valuable nutrients and negatively impacts groundwater quality. The objective of this study was to determine the influence of qualitative soil-landscape complexes on vertical and lateral redistribution of solutes in a variable glacial till landscape under zero tillage agricultural management by employing a bromide tracer. Tracer plots were established in the fall of 1999 within three sites comprising three representative soil-slope associations. Values of soil development indicators (A horizon thickness, solum thickness, depth to CaCO3, profile development index and organic carbon) generally increased from crest to midslope to depression. Further to this, the occurrence and thickness of eluvial and illuvial horizons increased from crest to midslope to depression. Well-developed, clay-coated blocky Bt horizons with vertical cracking and overlying Ae horizons in depressions appeared to have favoured rapid, downward vertical bromide redistribution. Crest positions were the least anisotropic and vertical redistribution was more important than lateral redistribution at this position. A combination of topographic and pedologic factors resulted in more lateral redistribution at the midslope position relative to crests and depressions. Bromide recovery rates in the top 60 cm of the soil profile indicated that most of the recovered bromide remained within that depth following spring runoff, but had mostly leached below that depth after the growing season, particularly at the depression position. Low bromide recovery rates in the top 30 cm following spring runoff, indicated that reduced availability of fall-applied nutrients for early crop growth could be expected at crest and depression positions following spring runoff. Bromide redistribution was important during both spring recharge and over the growing season at the depression position. Bromide movement below crop rooting depths and into shallow groundwater sources provides evidence that fall-applied nutrients can enter groundwater following both spring melt and growing season runoff in depressional landscape positions, especially in recharge areas. Management practices to reduce over-application of soluble nutrients and surface water accumulation, or both, in depressional areas may be an effective means to lower the risk of groundwater contamination with soluble nutrients without jeopardizing crop yield potential across the majority of the landscape positions in undulating to hummocky glacial till terrain. Key words: Solute redistribution, bromide tracer, soil properties, topography, landscape