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Search Results: 1 - 10 of 201246 matches for " P. Durand "
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Simulating nitrogen budgets in complex farming systems using INCA: calibration and scenario analyses for the Kervidy catchment (W. France)
P. Durand
Hydrology and Earth System Sciences (HESS) & Discussions (HESSD) , 2004,
Abstract: The integrated nitrogen model INCA (Integrated Nitrogen in Catchments) was used to analyse the nitrogen dynamics in a small rural catchment in Western France. The agrosystem studied is very complex, with: extensive use of different organic fertilisers, a variety of crop rotations, a structural excess of nitrogen (i.e. more animal N produced by the intensive farming than the N requirements of the crops and pastures), and nitrate retention in both hydrological stores and riparian zones. The original model features were adapted here to describe this complexity. The calibration results are satisfactory, although the daily variations in stream nitrate are not simulated in detail. Different climate scenarios, based on observed climate records, were tested; all produced a worsening of the pollution in the short term. Scenarios of alternative agricultural practices (reduced fertilisation and catch crops) were also analysed, suggesting that a reduction by 40% of the fertilisation combined with the introduction of catch crops would be necessary to stop the degradation of water quality. Keywords: diffuse pollution, nitrate, climate change, model
Does Raising Type 1 Error Rate Improve Power to Detect Interactions in Linear Regression Models? A Simulation Study
Casey P. Durand
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0071079
Abstract: Introduction Statistical interactions are a common component of data analysis across a broad range of scientific disciplines. However, the statistical power to detect interactions is often undesirably low. One solution is to elevate the Type 1 error rate so that important interactions are not missed in a low power situation. To date, no study has quantified the effects of this practice on power in a linear regression model. Methods A Monte Carlo simulation study was performed. A continuous dependent variable was specified, along with three types of interactions: continuous variable by continuous variable; continuous by dichotomous; and dichotomous by dichotomous. For each of the three scenarios, the interaction effect sizes, sample sizes, and Type 1 error rate were varied, resulting in a total of 240 unique simulations. Results In general, power to detect the interaction effect was either so low or so high at α = 0.05 that raising the Type 1 error rate only served to increase the probability of including a spurious interaction in the model. A small number of scenarios were identified in which an elevated Type 1 error rate may be justified. Conclusions Routinely elevating Type 1 error rate when testing interaction effects is not an advisable practice. Researchers are best served by positing interaction effects a priori and accounting for them when conducting sample size calculations.
Paleohydrological Reconstruction from Late Holocene Records in Interdune Lakes (N’Guigmi, Northern Bank of the Lake Chad, Niger)  [PDF]
David Sebag, Alain Durand, Zibo Garba, Eric P. Verrecchia
Open Journal of Geology (OJG) , 2013, DOI: 10.4236/ojg.2013.32018

An old erg covers the northern part of the Lake Chad basin. This dune landform allowed the formation of many interdune ponds of various sizes. Still present in certain zones where the groundwater level is high (e.g. Kanem, southern Manga), these ponds formed in the past a vast network of lacustrine microsystems, as shown by the nature and the distribution of their deposits. In the Manga, these interdune deposits represent the main sedimentary records of the Holocene environmental succession. Their paleobiological (pollens, diatoms, ostracods) and geochemical (δ18O, δ13C, Sr/Ca) contents are often the basis for paleoenvironmental reconstruction. On the other hand, their sedimentological characters are rarely exploited. This study of palustro-lacustrine deposits of the Holocene N’Guigmi lake (northern bank of the Lake Chad; Niger) is based on the relationships between the sedimentological features and the climato-hydrological fluctuations. The mineralogical parameters (e.g. calcium carbonate content, clay mineralogy) and the nature of autochthonous mineralization (i.e. amorphous silica, clays, calcium carbonates) can be interpreted using a straightforward hydro-sedimentary model. Established to explain the geochemical dynamics of Lake Chad, this model is based on a biogeochemical cycle of the main elements (i.e. silicium, calcium) directly controlled by the local hydrological balance (i.e. rainfall/evaporation ratio). All these results show that a detailed study of sedimentological features can provide important paleohydrological informations about the regional aridification since ca 6500 14C BP.

AVantage lié au génotype Hi hi pour l'intensité de ponte chez la poule
P Mérat, L Durand
Genetics Selection Evolution , 1973, DOI: 10.1186/1297-9686-5-4-469
Agglutinogène ? Hi ? et performances chez la poule
L Durand, P Mérat
Genetics Selection Evolution , 1971, DOI: 10.1186/1297-9686-3-1-5
Proportion Mendélienne Anormale Pour Le Gène ? Cou Nu ? Chez La Poule Domestique
P Mérat, L Durand
Genetics Selection Evolution , 1970, DOI: 10.1186/1297-9686-2-2-135
Fréquence et comparaison des performances pour les génotypes à quatre loci affectant des protéines de l'?uf chez la poule
L Durand, P Mérat
Genetics Selection Evolution , 1982, DOI: 10.1186/1297-9686-14-1-49
Gène Hi et production d'?ufs chez la poule: intensité de ponte et ?pauses?
P Mérat, L Durand
Genetics Selection Evolution , 1976, DOI: 10.1186/1297-9686-8-1-1
Modification of Wax Crystallization in Petroleum Products Modification de la cristallisation des paraffines dans les produits pétroliers
Denis J.,Durand J. P.
Oil & Gas Science and Technology , 2006, DOI: 10.2516/ogst:1991031
Abstract: The low temperature properties of petroleum products are improved either by refinery processing or by adding wax crystallization modifiers. The crystallization of paraffins in waxy crudes and petroleum products is governed by three phenomena : nucleation, growth and agglomeration or gelling. Different wax crystal modifiers can have a specific effect on these various steps of crystallization. Research in this field discussed in this article has the dual aim first to describe these specific actions and then, to define more and more efficient structures of additives in applications having to do with wax crystallization :(a) Production, transportation and storage of waxy crudes (b) Diesel fuel behavior at low temperatures(c) Base stock dewaxing process(d) Low temperature operability of lubricating oils. Les paraffines lourdes présentes dans les produits pétroliers sont la cause de nombreuses difficultés, notamment dans la production, le transport, le stockage des bruts paraffiniques, ainsi que dans le stockage et l'opérabilité de produits tels que gazoles, fuels lourds et huiles. Pour remédier à ces inconvénients des additifs susceptibles de modifer la cristallisation des paraffines sont fréquemment utilisés. La cristallisation des paraffines est gouvernée par trois phénomènes successifs : nucléation, croissance et agglomération. La nucléation est due à l'accroissement à basse température des forces d'attraction entre les molécules de paraffines. La croissance a tendance à se faire surtout sous forme de plaquettes de l'épaisseur d'une molécule de paraffine; la croissance en épaisseur beaucoup plus lente se fait sous forme de pyramides très fines, soit par nucléation au-dessus des premières couches (fig. 1) soit par développement de spirales autour des imperfections qui prennent naissance au cours de l'alignement des molécules (fig. 2). L'agglomération des cristaux conduit soit à des dép ts, soit à la formation de réseaux rigides responsables de la congélation. Les additifs peuvent modifier l'un ou plusieurs de ces phénomènes : certains initient la cristallisation; d'autres solubilisent les cristaux naissants; d'autres encore conduisent à des morphologies en blocs de tailles diverses; d'autres maintiennent une grande finesse de cristaux de l'ordre du micron; d'autres enfin dispersent les cristaux, les empêchant de s'agglomérer. Considérons les applications dans les différents domaines : Lors de la production, du transport et du stockage des bruts paraffiniques les principaux problèmes rencontrés, résultant de la cristallisation des paraffines, concernent l'ac
Dosage direct des alcools dans les carburols par chromatographie en phase gazeuse Direct Gas Chromatographie Determination of Alcohols in Gasolines Blended by Oxygenated Compounds
Durand J. P.,Petroff N.
Oil & Gas Science and Technology , 2006, DOI: 10.2516/ogst:1982027
Abstract: Dans cette étude, on décrit une méthode de chromatographie en phase gazeuse utilisant une colonne remplie ; elle permet de doser, sans préfractionnement, les alcools jusqu'aux butanols dans les carburols (carburants additionnés de composés oxygénés). La phase stationnaire sélectionnée est le glycérol. This report describes a gas chromatographie method using a packed column. It allows the direct determination of alcohols up to butanols in gasolines blended with oxygenated compounds without prefractionation. Glycerol has been selected as stationary phase.
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