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Articles de revues sur le sujet "Avion (avion) – Probabilités"
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Evans, Allen F., Quinn Payton, Nathan J. Hostetter, Ken Collis, Bradley M. Cramer et Daniel D. Roby. « Cumulative effects of piscivorous colonial waterbirds on juvenile salmonids : A multi predator-prey species evaluation ». PLOS ONE 17, no 8 (10 août 2022) : e0272875. http://dx.doi.org/10.1371/journal.pone.0272875.
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We investigated the cumulative effects of predation by piscivorous colonial waterbirds on the survival of multiple salmonid (Oncorhynchus spp.) populations listed under the U.S. Endangered Species Act (ESA) and determined what proportion of all sources of fish mortality (1 –survival) were due to birds in the Columbia River basin, USA. Anadromous juvenile salmonids (smolts) were exposed to predation by Caspian terns (Hydroprogne caspia), double-crested cormorants (Nannopterum auritum), California gulls (Larus californicus), and ring-billed gulls (L. delawarensis), birds known to consume both live and dead fish. Avian consumption and survival probabilities (proportion of available fish consumed or alive) were estimated for steelhead trout (O. mykiss), yearling Chinook salmon (O. tshawytscha), sub-yearling Chinook salmon, and sockeye salmon (O. nerka) during out-migration from the lower Snake River to the Pacific Ocean during an 11-year study period (2008–2018). Results indicated that probabilities of avian consumption varied greatly across salmonid populations, bird species, colony location, river reach, and year. Cumulative consumption probabilities (consumption by birds from all colonies combined) were consistently the highest for steelhead, with annual estimates ranging from 0.22 (95% credible interval = 0.20–0.26) to 0.51 (0.43–0.60) of available smolts. The cumulative effects of avian consumption were significantly lower for yearling and sub-yearling Chinook salmon, with consumption probabilities ranging annually from 0.04 (0.02–0.07) to 0.10 (0.07–0.15) and from 0.06 (0.3–0.09) to 0.15 (0.10–0.23), respectively. Avian consumption probabilities for sockeye salmon smolts was generally higher than for Chinook salmon smolts, but lower than for steelhead smolts, ranging annually from 0.08 (0.03–0.22) to 0.25 (0.14–0.44). Although annual consumption probabilities for birds from certain colonies were more than 0.20 of available smolts, probabilities from other colonies were less than 0.01 of available smolts, indicating that not all colonies of birds posed a substantial risk to smolt mortality. Consumption probabilities were lowest for small colonies and for colonies located a considerable distance from the Snake and Columbia rivers. Total mortality attributed to avian consumption was relatively small for Chinook salmon (less than 10%) but was the single greatest source of mortality for steelhead (greater than 50%) in all years evaluated. Results suggest that the potential benefits to salmonid populations of managing birds to reduce smolt mortality would vary widely depending on the salmonid population, the species of bird, and the size and location of the breeding colony.
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Pérez-Losada, Marcos, Ryan G. Christensen, David A. McClellan, Byron J. Adams, Raphael P. Viscidi, James C. Demma et Keith A. Crandall. « Comparing Phylogenetic Codivergence between Polyomaviruses and Their Hosts ». Journal of Virology 80, no 12 (15 juin 2006) : 5663–69. http://dx.doi.org/10.1128/jvi.00056-06.
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ABSTRACT Seventy-two full genomes corresponding to nine mammalian (67 strains) and two avian (5 strains) polyomavirus species were analyzed using maximum likelihood and Bayesian methods of phylogenetic inference. Our fully resolved and well-supported (bootstrap proportions > 90%; posterior probabilities = 1.0) trees separate the bird polyomaviruses (avian polyomavirus and goose hemorrhagic polyomavirus) from the mammalian polyomaviruses, which supports the idea of spitting the genus into two subgenera. Such a split is also consistent with the different viral life strategies of each group. Simian (simian virus 40, simian agent 12 [Sa12], and lymphotropic polyomavirus) and rodent (hamster polyomavirus, mouse polyomavirus, and murine pneumotropic polyomavirus [MPtV]) polyomaviruses did not form monophyletic groups. Using our best hypothesis of polyomavirus evolutionary relationships and established host phylogenies, we performed a cophylogenetic reconciliation analysis of codivergence. Our analyses generated six optimal cophylogenetic scenarios of coevolution, including 12 codivergence events (P< 0.01), suggesting that Polyomaviridae coevolved with their avian and mammal hosts. As individual lineages, our analyses showed evidence of host switching in four terminal branches leading to MPtV, bovine polyomavirus, Sa12, and BK virus, suggesting a combination of vertical and horizontal transfer in the evolutionary history of the polyomaviruses.
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Nichols, James D., James E. Hines, John R. Sauer, Frederick W. Fallon, Jane E. Fallon et Patricia J. Heglund. « A Double-Observer Approach for Estimating Detection Probability and Abundance From Point Counts ». Auk 117, no 2 (1 avril 2000) : 393–408. http://dx.doi.org/10.1093/auk/117.2.393.
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Abstract Although point counts are frequently used in ornithological studies, basic assumptions about detection probabilities often are untested. We apply a double-observer approach developed to estimate detection probabilities for aerial surveys (Cook and Jacobson 1979) to avian point counts. At each point count, a designated “primary” observer indicates to another (“secondary”) observer all birds detected. The secondary observer records all detections of the primary observer as well as any birds not detected by the primary observer. Observers alternate primary and secondary roles during the course of the survey. The approach permits estimation of observer-specific detection probabilities and bird abundance. We developed a set of models that incorporate different assumptions about sources of variation (e.g. observer, bird species) in detection probability. Seventeen field trials were conducted, and models were fit to the resulting data using program SURVIV. Single-observer point counts generally miss varying proportions of the birds actually present, and observer and bird species were found to be relevant sources of variation in detection probabilities. Overall detection probabilities (probability of being detected by at least one of the two observers) estimated using the double-observer approach were very high (>0.95), yielding precise estimates of avian abundance. We consider problems with the approach and recommend possible solutions, including restriction of the approach to fixed-radius counts to reduce the effect of variation in the effective radius of detection among various observers and to provide a basis for using spatial sampling to estimate bird abundance on large areas of interest. We believe that most questions meriting the effort required to carry out point counts also merit serious attempts to estimate detection probabilities associated with the counts. The double-observer approach is a method that can be used for this purpose.
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Saracco, James F., J. Andrew Royle, David F. DeSante et Beth Gardner. « Modeling spatial variation in avian survival and residency probabilities ». Ecology 91, no 7 (juillet 2010) : 1885–91. http://dx.doi.org/10.1890/09-0705.1.
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Applegate, Roger D., Robert E. Kissell, E. Daniel Moss, Edward L. Warr et Michael L. Kennedy. « Problems with Avian Point Counts for Estimating Density of Northern Bobwhite—A Case Study ». Journal of Fish and Wildlife Management 2, no 1 (1 juin 2011) : 117–21. http://dx.doi.org/10.3996/092010-jfwm-033.
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Abstract Point count data are used increasingly to provide density estimates of bird species. A favored approach to analyze point count data uses distance sampling theory where model selection and model fit are important considerations. We used uniform and half normal models and assessed model fit using χ2 analysis. We were unsuccessful in fitting models to 635 northern bobwhite Colinus virginianus observations from 85 avian point locations spanning 6 y (P ≤ 0.05). Most observations (74%) occurred in the outermost (>100-m) distance radius. Our results violated the assumptions that all observations at the point are detected. The assumption that birds were assigned to the correct distance interval also was probably violated. We caution managers in implementing avian point counts with distance sampling when estimating northern bobwhite population density. We recommend exploring other approaches such as occupancy-estimation and modeling for estimating detection probabilities.
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Zhang, Kerong, et Wuyi Liu. « Preliminary Exploration and Management Analysis of the Impact of the Avian Influenza Epidemics from the Point View of Chinese Animal Farmers ». Global Journal of Health Science 9, no 1 (14 juin 2016) : 233. http://dx.doi.org/10.5539/gjhs.v9n1p233.
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<p>In the study, the outbreak of avian influenza was explored analyzed in depth with all the data resources available. It was found that behavior choices and motivations of the animal producers fundamentally depended on their interests and accessing means in the process of animal epidemic disease prevention and control. It was suggested that the government and its sectors should formulate and execute an appropriate compensation system and make compensation timely when there appears an economic impact of major epidemic animal diseases on the producers and the producers’ economic losses are found. Furthermore, the government should take any effective measures to guide and promote the transformation of the conventional modes of livestock production, and lead those farmers and producers to the changed ways of conventional livestock production activities and modes to reduce the probabilities of animal diseases spread and outbreak, especially the infectious diseases like avian influenza.</p>
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Kang, Ting, Qimin Zhang et Libin Rong. « A delayed avian influenza model with avian slaughter : Stability analysis and optimal control ». Physica A : Statistical Mechanics and its Applications 529 (septembre 2019) : 121544. http://dx.doi.org/10.1016/j.physa.2019.121544.
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Thompson, Sarah J., Colleen M. Handel et Lance B. Mcnew. « Autonomous acoustic recorders reveal complex patterns in avian detection probability ». Journal of Wildlife Management 81, no 7 (7 juin 2017) : 1228–41. http://dx.doi.org/10.1002/jwmg.21285.
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Liu, Jia, Qunyu Xu, Min Su et Weishi Chen. « Activity Modeling and Characterization for Airport Bird Situation Awareness Using Avian Radar Datasets ». Aerospace 11, no 6 (30 mai 2024) : 442. http://dx.doi.org/10.3390/aerospace11060442.
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Birds in airport airspaces are critical threats to aviation safety. Avian radar systems are effective for long-range bird monitoring and hazard warning, but their functionalities are confined to a short-term temporal scale. Spatial–temporal activity modeling and characterization for birds are not studied comprehensively from historical radar datasets. This paper proposes a radar data analysis framework to characterize bird activities as a long-term functionality complement. Spatial domain modeling initializes data mining by extracting reference spots for data filtering. Bird activities are quantified in the temporal domain. Activity degrees are utilized for periodicity extraction with the daily segment random permutation strategy. Categorical probabilities are calculated to interpret bird activity periodicity characters. Historical radar datasets collected from an avian radar system are adopted for validation. The extracted activity periodicity trends for diurnal birds present prominent consistency with artificial observation records. Migratory bird periodicity trends present a good match with ornithology understandings. A preliminary experiment is presented to indicate the possibility of predicting bird activity levels, especially for migratory birds.
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Medina, Iliana, et Naomi E. Langmore. « Host density predicts the probability of parasitism by avian brood parasites ». Philosophical Transactions of the Royal Society B : Biological Sciences 374, no 1769 (11 février 2019) : 20180204. http://dx.doi.org/10.1098/rstb.2018.0204.
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The spatial distribution of hosts can be a determining factor in the reproductive success of parasites. Highly aggregated hosts may offer more opportunities for reproduction but can have better defences than isolated hosts. Here we connect macro- and micro-evolutionary processes to understand the link between host density and parasitism, using avian brood parasites as a model system. We analyse data across more than 200 host species using phylogenetic comparative analyses and quantify parasitism rate and host reproductive success in relation to spatial distribution using field data collected on one host species over 6 years. Our comparative analysis reveals that hosts occurring at intermediate densities are more likely to be parasitized than colonial or widely dispersed hosts. Correspondingly, our intraspecific field data show that individuals living at moderate densities experience higher parasitism rates than individuals at either low or high densities. Moreover, we show for the first time that the effect of host density on host reproductive success varies according to the intensity of parasitism; hosts have greater reproductive success when living at high densities if parasitism rates are high, but fare better at low densities when parasitism rates are low. We provide the first evidence of the trade-off between host density and parasitism at both macro- and micro-evolutionary scales in brood parasites. This article is part of the theme issue ‘The coevolutionary biology of brood parasitism: from mechanism to pattern’.
Thèses sur le sujet "Avion (avion) – Probabilités"
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Perrichon, Rémi. « Modélisation statistique de trajectoires d'aéronefs ». Electronic Thesis or Diss., Toulouse, École nationale de l’aviation civile, 2024. https://enac.hal.science.
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Cette thèse porte sur l’étude statistique des trajectoires d’aéronefs.Dans un premier temps, nous proposons une revue de la littérature qui permet d’identifierles approches statistiques pertinentes dans l’analyse de données de trajectoires. Le cadrede l’analyse statistique des données fonctionnelles est particulièrement instructif car ilmet en lumière deux défis majeurs dans le traitement de telles données : la nécessité dereconstruire les trajectoires pour les évaluer à différentes résolutions temporelles, ainsi quel’existence de variations de phase qu’il est important de corriger sur le plan statistique. Lareconstruction de données de trajectoires présente des spécificités. Nous nous intéressonsnotamment à la prise en compte d’une contrainte de positivité pour l’altitude et à lareconstruction des composantes angulaires du vol (longitude, latitude, direction du vent).Plusieurs méthodes de correction des variations de phase sont par ailleurs comparées. Nousappliquons un alignement élastique à des trajectoires de drone et d’avion commercial avecde très bons résultats. De plus, nous suggérons une distance judicieusement choisie dansl’espace des amplitudes permettant de faire un clustering de trajectoires en présence devariations de phase.Un deuxième volet de la thèse est consacré à la comparaison de méthodes d’interpolationspatiale pour des données météorologiques utilisées dans l’aviation. Nous développonsun cadre géostatistique adapté à deux cas d’étude en particulier. Notre modèle permetd’associer des conditions météorologiques à des données de trajectoires avec une grandefiabilité, notamment pour les valeurs de température.Enfin, nous développons un modèle deMarkov caché pour la segmentation de phases de vol,dont la nature, le nombre et l’enchaînement peuvent être connus ou non. Nous appliquonsce modèle à la segmentation de vols de l’aviation commerciale et d’un vol d’hélicoptère.Notre méthode produit des résultats de qualité similaire à ceux des approches existantestout en fournissant une estimation de l’incertitude liée à la segmentationThis thesis focuses on the statistical study of aircraft trajectories.First, we propose a literature review that identifies relevant statistical approaches in theanalysis of trajectory data. The framework of Functional Data Analysis (FDA) is partic-ularly instructive as it highlights two major challenges in processing such data: the needto reconstruct trajectories to evaluate them at different temporal resolutions and the exis-tence of phase variations that are important to correct statistically. The reconstruction oftrajectory data has specific features. We are particularly interested in taking into accounta positivity constraint for altitude and the reconstruction of the angular components of theflight (longitude, latitude, wind direction). Furthermore, several methods for correctingphase variations are compared. We apply elastic registration to drone and commercialaircraft trajectories with very good results. Moreover, we suggest a judiciously chosendistance in the amplitude space, allowing for the clustering of trajectories in the presenceof phase variations.The second part of the thesis is devoted to the comparison of spatial interpolation methodsfor meteorological data used in aviation. We develop a geostatistical framework adaptedto two specific case studies. Our model reliably associates meteorological conditions withtrajectory data, particularly for temperature values.Finally, we develop a Hidden Markov Model (HMM) for the segmentation of flight phases,whose nature, number, and sequence may or may not be known. We apply this modelto the segmentation of commercial aviation flights and a helicopter flight. Our methodproduces results of similar quality to existing approaches while providing an estimate ofthe uncertainty associated with the segmentation
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Prigent, Sylvain. « Approche novatrice pour la conception et l’exploitation d’avions écologiques ». Thesis, Toulouse, ISAE, 2015. http://www.theses.fr/2015ESAE0014/document.
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L'objectif de ce travail de thèse est de poser, d'analyser et de résoudre le problème multidisciplinaire et multi-objectif de la conception d'avions plus écologiques et plus économiques. Dans ce but, les principaux drivers de l'optimisation des performances d'un avion seront: la géométrie de l'avion, son moteur ainsi que son profil de mission, autrement dit sa trajectoire. Les objectifs à minimiser considérés sont la consommation de carburant, l'impact climatique et le coût d'opération de l'avion. L'étude sera axée sur la stratégie de recherche de compromis entre ces objectifs, afin d'identifier les configurations d'avions optimales selon le critère sélectionné et de proposer une analyse de ces résultats. L'incertitude présente au niveau des modèles utilisés sera prise en compte par des méthodes rigoureusement sélectionnées. Une configuration d'avion hybride est proposée pour atteindre l'objectif de réduction d'impact climatiqueThe objective of this PhD work is to pose, investigate, and solve the highly multidisciplinary and multiobjective problem of environmentally efficient aircraft design and operation. In this purpose, the main three drivers for optimizing the environmental performance of an aircraft are the airframe, the engine, and the mission profiles. The figures of merit, which will be considered for optimization, are fuel burn, local emissions, global emissions, and climate impact (noise excluded). The study will be focused on finding efficient compromise strategies and identifying the most powerful design architectures and design driver combinations for improvement of environmental performances. The modeling uncertainty will be considered thanks to rigorously selected methods. A hybrid aircraft configuration is proposed to reach the climatic impact reduction objective
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Birman, Jessie. « Quantification et propagation d'incertitude dans les phases amont de projets de conception d'avions : de l'optimisation déterministe à l'optimisation sous contraintes probabilistes ». Toulouse 3, 2013. http://thesesups.ups-tlse.fr/2269/.
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Le " Conceptual Design " est la première étape d'un projet d'avion de transport de passagers. Classiquement, au cours de ce processus, un grand nombre de configurations possibles sont comparées après avoir été dimensionnées sur la base d'un processus d'optimisation déterministe, multidisciplinaire sous contraintes. L'objectif est de définir les paramètres principaux de l'avion qui répondent à un cahier des charges donné de haut niveau. A ce stade du projet, les ingénieurs doivent résoudre le problème en ayant très peu de connaissances sur le produit final et donc beaucoup d'incertitude. La gestion de l'incertitude est un point crucial : réussir à comprendre au plus tôt l'impact qu'elle aura sur la configuration et les performances de l'avion peut permettre de choisir les configurations qui présentent le meilleur rapport bénéfice sur risque ainsi que de réduire le temps de conception ultérieur et donc les coûts. Cette thèse introduit une nouvelle méthodologie pour la résolution d'un problème d'optimisation de configuration avion affecté par de l'incertitude. Dans un premier temps, la source principale d'incertitude présente à ce stade du projet est identifiée comme étant de l'incertitude de prédiction des modèles de simulation. Cette incertitude est de type épistémique. Elle est quantifiée à l'aide d'outils probabilistes. Pour ce faire, et en nous inspirant de la loi Béta, nous avons créé une nouvelle loi de probabilité générique, capable de s'ajuster à des distributions de formes très différentes, intitulée distribution Beta-Mystique. Dans un second temps, nous réalisons des études de propagation d'incertitudes à l'aide des méthodes de Monte Carlo et de propagation des moments, afin d'analyser la robustesse d'une configuration avion par rapport à une quantité d'incertitude donnée. Enfin, une optimisation sous contraintes probabilistes est résolue afin de générer des configurations avions robustes. Deux stratégies sont mises en place : l'approximation des contraintes probabilistes à l'aide de surfaces de réponses et la résolution du problème à l'aide de la méthode de propagation des momentsConceptual aircraft sizing is the first step in the development project of a passenger transport aircraft. Classically, in this phase, a lot of aircraft configurations are compared after having been globally sized thanks to a deterministic, multidisciplinary and constrained optimisation problem. The purpose is to determine the main characteristics of the airplane according to a set of Top Level Requirements. At preliminary stage, designers have to deal with limited knowledge and high uncertainty when solving this problem. Managing that uncertainty is a major issue: assessing its impact on the design in the early stage allows to save time and cost. This PhD thesis introduces a new methodology to solve the aircraft design optimisation affected by uncertainty. First of all, the main source of uncertainty involved at this stage is identified as predictive model uncertainty, which is part of epistemic uncertainty. This uncertainty is quantified within a probabilistic framework. For that purpose, based on the Beta distribution, we create a new generic distribution function able to assume a wide range of distribution shapes: it is called Beta-Mystique distribution. Second of all, we realise uncertainty propagation studies with Monte Carlo and moment propagation methods, in order to analyse the robustness of aircraft configuration according to a set of uncertainties. Finally, a chance constrained optimisation is solved to produce a robust aircraft configuration. Two strategies are considered: the use of Surrogate models to approximate the probabilities and the resolution of the optimisation problem thanks to the moment propagation method
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Jacob, Christelle. « Management de l'incertitude pour les systèmes booléens complexes - Application à la maintenance préventive des avions ». Thesis, Toulouse, ISAE, 2014. http://www.theses.fr/2014ESAE0010/document.
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Les analyses de sûreté de fonctionnement standards sont basées sur la représentation des événements redoutés par des arbres de défaillances, qui les décrivent à l'aide de combinaison logiques d'événements plus basiques (formules Booléennes complexes). Les analyses quantitatives se font avec l'hypothèse que les probabilités d'occurrence de ces événements basiques sont connues. Le but de cette thèse est d'étudier l'impact de l'incertitude épistémique sur les événements élémentaires, ainsi que la propagation de cette incertitude à de plus hauts niveaux. Le problème soulevé est comment calculer l'intervalle de probabilité dans lequel se trouvera l'occurrence d'un événement redouté, lorsque les événements basiques qui le décrivent ont eux-mêmes une probabilité imprécise. Lorsque l'indépendance stochastique est supposée, on se retrouve avec un problème NP-hard. Nous avons donc développé un algorithme permettant de calculer l'intervalle exact dans lequel se trouvera la probabilité d'occurrence d'un événement redouté, grâce à des techniques d'analyse par intervalles. Cet algorithme a également été étendu dans le cas où les probabilités des événements basiques évolueraient en fonction du temps. Nous avons également utilisé une approche par fonctions de croyance pour étudier le cas où l'indépendance stochastique des événements ne peut pas être démontrée : on suppose alors que les probabilités viennent de différentes sources d'information Indépendantes. Dans ce cas, les mesures de plausibilité et de nécessité d'une formule Booléenne complexe sont difficiles à calculer, néanmoins nous avons pu dégager des situations pratiques dans le cadre de leur utilisation pour les Arbres de défaillances pour lesquelles elles se prêtent aux calculsStandard approaches to reliability analysis relies on a probabilistic analysis of critical events based on fault tree representations. However in practice, and especially for preventive maintenance tasks, the probabilities ruling the occurrence of these events are seldom precisely known. The aim of this thesis is to study the impact of epistemic uncertainty on probabilities of elementary events such as failures over the probability of some higher level critical event. The fundamental problem addressed by the thesis is thus to compute the probability interval for a Boolean proposition representing a failure condition, given the probability intervals of atomic propositions. When the stochastic independence is assumed, we face a problem of interval analysis, which is NP-hard in general. We have provided an original algorithm that computes the output probability interval exactly, taking into account the monotonicity of the obtained function in terms of some variables so as to reduce the uncertainty. We have also considered the evolution of the probability interval with time, assuming parameters of the reliability function to be imprecisely known. Besides, taking advantage of the fact that a probability interval on a binary space can be modelled by a belief function, we have solved the same problem with a different assumption, namely information source independence. While the problem of computing the belief and plausibility of a Boolean proposition are even harder to compute, we have shown that in practical situations such as usual fault-trees, the additivity condition of probability theory is still valid, which simplifies this calculation. A prototype has been developed to compute the probability interval for a complex Boolean proposition
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Mann, Richard Philip. « Prediction of homing pigeon flight paths using Gaussian processes ». Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:bf6c3fb5-5208-4dfe-aa0a-6e6da45c0d87.
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Studies of avian navigation are making increasing use of miniature Global Positioning Satellite devices, to regularly record the position of birds in flight with high spatial and temporal resolution. I suggest a novel approach to analysing the data sets pro- duced in these experiments, focussing on studies of the domesticated homing pigeon (Columba Livia) in the local, familiar area. Using Gaussian processes and Bayesian inference as a mathematical foundation I develop and apply a statistical model to make quantitative predictions of homing pigeon flight paths. Using this model I show that pigeons, when released repeatedly from the same site, learn and follow a habitual route back to their home loft. The model reveals the rate of route learning and provides a quantitative estimate of the habitual route complete with associated spatio-temporal covariance. Furthermore I show that this habitual route is best described by a sequence of isolated waypoints rather than as a continuous path, and that these waypoints are preferentially found in certain terrain types, being especially rare within urban and forested environments. As a corollary I demonstrate an extension of the flight path model to simulate ex- periments where pigeons are released in pairs, and show that this can account for observed large scale patterns in such experiments based only on the individual birds’ previous behaviour in solo flights, making a successful quantitative prediction of the critical value associated with a non-linear behavioural transition.
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Marrero, Santiago Javier. « Expérimental study of lean aeronautical ignition : impact of critical parameters on the mechanisms acting along the different ignition phases ». Thesis, Normandie, 2018. http://www.theses.fr/2018NORMIR03/document.
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La certification des moteurs aéronautiques impose des fortes réductions des émissions polluantes. Une des solutions adoptées par les constructeurs est d'introduire la combustion pauvre dans les nouvelles chambres. Cette configuration pose des problèmes de stabilité de flamme et de ré-allumage en altitude. Le ré-allumage des moteurs doit être garanti et il y a une nécessité réelle de mieux comprendre les interactions complexes et multi-physiques guidant ce processus. Cette étude expérimentale vise les différentes phases de l'allumage aéronautique dans deux chambres swirlées, confinées diphasiques. Un foyer mono-injecteur permet d'analyser le développement du noyau de flamme dans ses premiers instants et de décrire comment les interactions avec l'écoulement local peuvent conduire à une réussite d'allumage ou à une ratée, via différents mécanismes. Une chambre multi-injecteur est dédiée à analyser la propagation de la flamme entre injecteurs pour différents espacements et carburantsJet engine certification undergoes more and more stringent controls that impose a strong reduction of pollutant emissions. As a response, designs move towards lean combustion, which raises difficulties relative to combustion stability and re-ignition capabilities in high altitude. The use of liquid fuels in real chambers introduces new variables into the ignition process, which involves complex simultaneous multi-physical interactions. The present experimental investigation addresses different phases of aeronautical ignition in two different confined, swirled, spray jet chambers. A single-injector facility is used to study the initial flame kernel development and interaction with the flow leading to successful ignition or misfire, following different mechanisms. A multi-injector facility enables the investigation of flame propagation between injectors, which is also governed by the local flow. Here, inter-injector distances are varied and fuels of different volatilities are tested
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Wu, Hung-Yi, et 吳弘毅. « Studies on the probability of coccidia carrying avian viruses ». Thesis, 1996. http://ndltd.ncl.edu.tw/handle/03076561986020785146.
Texte intégralRésumé :
碩士國立中興大學
獸醫學系
84
We investigated the probability of coccidia (Eimeria tenella and Eimeria acervulina) carrying avian viruses(Newcastle disease virus; NDV, Avian reovirus; ARV, and Avian encephalomyelitis viruas; AEV) by simultaneous infection of 10-day-old chickens with coccidia and avian viruses. Immunofluoresent assay and in situ hybridization were used to detect the presence of avian viruses in coccidia. Positive immunofluorescent reactions against NDV, ARV or AEV were observed in schizonts, gametocytes and zygotes of Eimeria tenella or E. acervulina. In situ hybridization also revealed positive signals of NDV or ARV in different life stages of Eimeria tenella or E. acervulina. Specific pathogen free (SPF) chickens repeatly inoculated with sporulated oocyst from wild strains of coccidia (Eimeria tenella or E. acervulina) or from coccidia (Eimeria tenella or E. acervulina)-avian viruses(NDV, ARV or AEV) infected chickens revealed positive antibody reaction to NDV, ARV or AEV by enzyme-linked immunosorbent assay (ELISA) or haemagglutination inhibition (HI) test. Moreover, coccidia-avian viruses infected chickens showed the changes of excreted oocyst number and sporulation rate when compared with those infected with only purified coccidia. The results indicated a probability that coccidia (Eimeria tenella or E. acervulina) can contain avian virus proteins (NDV, ARV, or AEV) and nucleic acids(NDV or ARV) and thus coccidia (Eimeria tenella or E. acervulina) might play an important role in the epizootiology.
Chapitres de livres sur le sujet "Avion (avion) – Probabilités"
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Bourouiba, Lydia, Stephen Gourley, Rongsong Liu, John Takekawa et Jianhong Wu. « Avian Influenza Spread and Transmission Dynamics ». Dans Wiley Series in Probability and Statistics, 137–59. Hoboken, NJ, USA : John Wiley & Sons, Inc., 2015. http://dx.doi.org/10.1002/9781118630013.ch7.
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Richardson, Heather, et Dongmei Chen. « Analyzing the Potential Impact of Bird Migration on the Global Spread of H5N1 Avian Influenza (2007-2011) Using Spatiotemporal Mapping Methods ». Dans Wiley Series in Probability and Statistics, 161–76. Hoboken, NJ, USA : John Wiley & Sons, Inc., 2015. http://dx.doi.org/10.1002/9781118630013.ch8.
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Valkiunas, Gediminas. « Biotic Factors Influencing the Probability of Bird Infection ». Dans Avian Malaria Parasites and other Haemosporidia, 169–72. CRC Press, 2004. http://dx.doi.org/10.1201/9780203643792.ch12.
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McCoy, Karen D. « Community-Level Interactions and Disease Dynamics ». Dans Infectious Disease Ecology of Wild Birds, 145–70. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198746249.003.0008.
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An ecological community includes all individuals of all species that interact within a single patch or local area of habitat. Understanding the outcome of host–parasite interactions and predicting disease dynamics is particularly challenging at this biological scale because the different component species interact both directly and indirectly in complex ways. Current shifts in biodiversity due to global change, and its associated modifications to biological communities, will alter these interactions, including the probability of disease emergence, its dynamics over time, and its community-level consequences. Birds are integral component species of almost all natural communities. Due to their ubiquity and specific life history traits, they are defining actors in the ecology, evolution, and epidemiology of parasitic species. To better understand this role, this chapter examines the relative importance of birds and parasites in natural communities, revisiting basic notions in community ecology. The impact of changes in diversity for disease dynamics, including the debate surrounding dilution and amplification effects are specifically addressed. By considering the intrinsic complexities of natural communities, the importance of combining data from host and parasite communities to better understand how natural systems function over time and space is highlighted. The different elements in each section of the chapter are illustrated with brief, concrete examples from avian species, with a detailed example from marine bird communities in which Lyme disease bacteria circulate.
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Dunn, Jenny C., Dana M. Hawley, Kathryn P. Huyvaert et Jennifer C. Owen. « Fitness Effects of Parasite Infection in Birds ». Dans Infectious Disease Ecology of Wild Birds, 99–120. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198746249.003.0006.
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Parasites and pathogens inherently cause harm to their hosts, but the degree to which that harm causes notable fitness costs for an individual host can be highly variable. While some effects of parasites on host fitness are drastic and immediate in nature, a growing body of evidence suggests that even parasites that cause chronic and subclinical infections can still have notable negative fitness consequences for hosts by reducing the probability of long-term survival and reproductive success. This chapter considers the ways in which fitness effects of infection are typically evaluated in birds and then examines the impacts of parasites and pathogens on diverse fitness-relevant traits in birds, including survival and components of reproductive success. Because fitness effects associated with infection can be highly variable and context-dependent, the chapter highlights some of the characteristics of parasites, hosts, or the environment likely to influence the extent of fitness effects of infection on avian hosts. The potential influence of abiotic factors such as climate and nutritional stress on the fitness impacts of parasites has not yet been well studied in birds but represent an important area for future research. Overall, understanding the individual-level fitness consequences of parasite infection is critical because these effects ultimately contribute to a population’s growth potential and determine the strength of selection that parasites place on host populations.
Actes de conférences sur le sujet "Avion (avion) – Probabilités"
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Martino, P. Di, S. Colantuoni, L. Cirillo et G. Cinque. « CFD Modelling of an Advanced 1600 K Reverse-Flow Combustor ». Dans ASME 1994 International Gas Turbine and Aeroengine Congress and Exposition. American Society of Mechanical Engineers, 1994. http://dx.doi.org/10.1115/94-gt-468.
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A fully-elliptic three dimensional computational fluid dynamic (CFD) code based on pressure-correction techniques has been used in the design of an advanced turbine single annular reverse-flow combustor (AR1600) under development at Alfa Romeo Avio (ARA). Fuel injection was handled using a Lagrangian liquid droplet spray model coupled to the gas phase equations, which are solved in an Eulerian frame of reference. Turbulent transport is described by the standard k-ε model. The combustion model utilizes a conserved scalar formulation and an assumed shape probability density function to account for chemistry-turbulence interaction. The numerical algorithm employs structured nonorthogonal curvilinear grids, node-centered variable arrangement and Cartesian velocity components. The code was validated on a similar combustor (AR318 turboprop engine of 600 SHP). The numerical results agree well with the test measurements available for this chamber. The aerothermal design of AR1600 (1600K exit temperature) has the same gemetrical constraints of AR318 (tip and root diameters for compressor outlet and turbine inlet), but the lenght is shorter to reduce surface area for less cooling and to utilize the excess air for more efficient mixing and combustion.
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Majcherczyk, Michał, Nikolaos Zarzalis et Fabio Turrini. « Influence of the Turbulence Length Scale and Intensity on Spark Ignition of Kerosene Jet-A1–Air Mixtures at High Altitude Relight Conditions ». Dans ASME Turbo Expo 2014 : Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/gt2014-25332.
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In recent years Avio Aero and the Karlsruhe Institute of Technology (KIT) have significantly enhanced their available experimental technology level in order to consolidate and deepen the investigation of some critical phenomena in aero-engine gas turbine combustion. A key parameter in the development of a lean-burn combustor is the design of the ignition system. The increase in the amount of air that flows through the primary zone to approximately 60% of the overall air proves to be beneficial for emissions reduction. In return it causes shorter residence times in the primary zone and makes the flame kernel generation and propagation a real challenge. With the scope to enhance the fundamental understanding of the ignition process at altitude conditions, the ISCRA rig (Ignition in Subatmospheric Conditions – Rig for Altitude Relight Investigation) has been designed and manufactured at the KIT. The design of the rig allows the generation of altitude conditions at variable flow velocities and turbulence characteristics. An optical access for ignition recording by a CCD camera is also provided. The paper presents the results of a fundamental investigation at the KIT using a generic setup. It consists of a pressure atomizer with known atomization properties mounted in a test rig which allows the variation of several parameters that influence ignition, namely: air pressure; air temperature; velocity; Fuel-Air-Ratio (FAR); Sauter Mean Diameter (SMD); spark energy; turbulence intensity and length scale. Two grey spots that exist in the knowledge map of the ignition process are addressed in this paper. These are data on kerosene spray ignition at temperatures below 293 K, where data is scarce and the relationship between flame kernel generation and propagation, which has not been broadly investigated nor is well understood. The ignition probabilities of kerosene sprays as a function of ignition energy in the temperature range from 253 K to 293 K, pressure of 0.7 bar, flow velocities up to 6 m/s at different turbulence intensities and length scales are measured. Furthermore, the influence of the above mentioned parameters on the kernel generation and propagation is presented and discussed. Results show that the energy required for flame kernel propagation is higher than for flame kernel generation. This difference increases at lower temperature and higher turbulence intensity. The paper gives an insight in magnitude of this difference in energy and compares the tendencies with an earlier model. The absolute values need to and will be corrected by future in situ measurements.
Rapports d'organisations sur le sujet "Avion (avion) – Probabilités"
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Falconi, César. Potential Economic Impacts of Avian Influenza in LAC. Inter-American Development Bank, août 2006. http://dx.doi.org/10.18235/0006877.
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This presentation discuses bird flu in two different related scenarios: as a disease that could affect the Poultry Sector and as a disease that could cause a Human Pandemic. The paper includes an analysis on what's at stake, risks and probabilities, costs, impacts and ways of prevention, as well as a series of conclusions. This presentation was created for the Seminar "The Mass Media and the Threat of Avian Influenza in Latin America" held in August of 2006.
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Kintz, Erika, Elaine Pegg, Wendy Perry et Wioleta Trzaska. A Qualitative Assessment of the Risk of Acquiring Avian Influenza from Poultry and Game Bird Meat Poultry products. Food Standards Agency, juillet 2023. http://dx.doi.org/10.46756/sci.fsa.vlf743.
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Avian influenza (AI) viruses cause infections primarily in bird species, although they are capable of spill-over infections into mammalian species, including humans. Many different strains of AI viruses are found in birds, but they can be divided into two groups based on their virulence in poultry: high pathogenicity (HPAI) and low pathogenicity (LPAI); both are capable of quickly spreading through a flock. HPAI infections often lead to severe clinical signs and high mortality while LPAI infections may not present with any clinical signs. Certain strains of AI have been associated with human case fatality rates of over 50%. Since October 2021, there has been a substantial increase in the number of AI infections reported both at commercial premises and in wild birds in the UK. The last FSA assessment on the risk to consumers of exposure to AI from the food chain was in 2015. Since the increase in infections may lead to an increased likelihood that poultry products from infected birds are entering the retail market, an updated risk assessment was commissioned to ensure advice relating to the consumption of poultry products is still appropriate. This risk assessment did not focus on the currently circulating outbreak strain but considered any AI virus. This assessment considered the risk of consumers acquiring an AI infection from poultry products, including commercial poultry, game birds, and table eggs. The risk of home processing of birds was also considered. The farm to fork risk pathway spanned from the probability that products from infected poultry would reach market to the ability of AI to cause infections in humans via the gastrointestinal route.