Littérature scientifique sur le sujet « Weakly dependent process »
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Articles de revues sur le sujet "Weakly dependent process"
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Bertin, Karine, et Nicolas Klutchnikoff. « Pointwise adaptive estimation of the marginal density of a weakly dependent process ». Journal of Statistical Planning and Inference 187 (août 2017) : 115–29. http://dx.doi.org/10.1016/j.jspi.2017.03.003.
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Pang, Guodong, et Yuhang Zhou. « Functional Limit Theorems for Shot Noise Processes with Weakly Dependent Noises ». Stochastic Systems 10, no 2 (juin 2020) : 99–123. http://dx.doi.org/10.1287/stsy.2019.0051.
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We study shot noise processes when the shot noises are weakly dependent, satisfying the ρ-mixing condition. We prove a functional weak law of large numbers and a functional central limit theorem for this shot noise process in an asymptotic regime with a high intensity of shots. The deterministic fluid limit is unaffected by the presence of weak dependence. The limit in the diffusion scale is a continuous Gaussian process whose covariance function explicitly captures the dependence among the noises. The model and results can be applied in financial and insurance risks with dependent claims as well as queueing systems with dependent service times. To prove the existence of the limit process, we employ the existence criterion that uses a maximal inequality requiring a set function with a superadditivity property. We identify such a set function for the limit process by exploiting the ρ-mixing condition. To prove the weak convergence, we establish the tightness property and the convergence of finite dimensional distributions. To prove tightness, we construct two auxiliary processes and apply an Ottaviani-type inequality for weakly dependent sequences.
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Chahad, Abdelkader, et Mohammed Bassoudi. « Nonparametric estimation of P(X<Y) using local linear methods for weakly dependent data ». STUDIES IN ENGINEERING AND EXACT SCIENCES 5, no 2 (16 octobre 2024) : e9282. http://dx.doi.org/10.54021/seesv5n2-348.
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This study addresses the problem of accurately estimating P(X<Y), particularly in the presence of weakly dependent data. Traditional nonparametric methods often assume independence between observations, which can lead to biased results in dependent settings. To overcome this limitation, we propose the use of local linear methods for the nonparametric estimation of P(X<Y), focusing on weakly dependent data modeled using an autoregressive (AR(1)) process. The primary objective is to assess the performance of the local linear estimator under both independent and weakly dependent conditions, comparing bias, variance, and mean squared error (MSE). A Monte Carlo simulation with 1000 repetitions was conducted, utilizing large sample sizes to ensure robust asymptotic properties. Results show that while the estimator performs well for independent data, with low bias and variance, its accuracy decreases significantly in the presence of weak dependence, leading to increased prejudice and MSE. These findings highlight the need for adjustments in nonparametric methods when dealing with dependent data. In conclusion, while effective for independent cases, the local linear method demonstrates limitations when applied to weakly dependent data, emphasizing the importance of considering dependence structures in future nonparametric estimations.
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Künsch, H. « Discrimination between monotonic trends and long-range dependence ». Journal of Applied Probability 23, no 4 (décembre 1986) : 1025–30. http://dx.doi.org/10.2307/3214476.
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We show that the periodogram behaves differently for a weakly dependent process with a small monotonic trend and a stationary strongly dependent process. In the former case it has a non-central -distribution with noncentrality parameter tending to 0 uniformly outside intervals . In the latter case it has λα −1 times a central -distribution, 0 < α < 1.
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Künsch, H. « Discrimination between monotonic trends and long-range dependence ». Journal of Applied Probability 23, no 04 (décembre 1986) : 1025–30. http://dx.doi.org/10.1017/s0021900200115955.
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We show that the periodogram behaves differently for a weakly dependent process with a small monotonic trend and a stationary strongly dependent process. In the former case it has a non-central-distribution with noncentrality parameter tending to 0 uniformly outside intervals. In the latter case it has λα−1times a central-distribution, 0 <α< 1.
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Künsch, H. « Discrimination between monotonic trends and long-range dependence ». Journal of Applied Probability 23, no 04 (décembre 1986) : 1025–30. http://dx.doi.org/10.1017/s0021900200118819.
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We show that the periodogram behaves differently for a weakly dependent process with a small monotonic trend and a stationary strongly dependent process. In the former case it has a non-central -distribution with noncentrality parameter tending to 0 uniformly outside intervals . In the latter case it has λ α −1 times a central -distribution, 0 < α < 1.
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Davis, Richard A., et Tailen Hsing. « Point Process and Partial Sum Convergence for Weakly Dependent Random Variables with Infinite Variance ». Annals of Probability 23, no 2 (avril 1995) : 879–917. http://dx.doi.org/10.1214/aop/1176988294.
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Wieczorek, Barbara. « Blockwise bootstrap of the estimated empirical process based on $$\psi $$ ψ -weakly dependent observations ». Statistical Inference for Stochastic Processes 19, no 1 (13 juin 2015) : 111–29. http://dx.doi.org/10.1007/s11203-015-9120-2.
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KO, MI-HWA, HYUN-CHULL KIM et TAE-SUNG KIM. « ON FUNCTIONAL CENTRAL LIMIT THEOREMS FOR LINEAR RANDOM FIELDS WITH DEPENDENT INNOVATIONS ». ANZIAM Journal 49, no 4 (avril 2008) : 533–41. http://dx.doi.org/10.1017/s1446181108000217.
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AbstractFor a linear random field (linear p-parameter stochastic process) generated by a dependent random field with zero mean and finite qth moments (q>2p), we give sufficient conditions that the linear random field converges weakly to a multiparameter standard Brownian motion if the corresponding dependent random field does so.
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Bondarenko, S., et K. Komoshvili. « Transverse transport properties of a charged drop in an electric field ». International Journal of Modern Physics E 24, no 05 (mai 2015) : 1550034. http://dx.doi.org/10.1142/s0218301315500342.
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Transport properties of a charged droplet of weakly interacting particles in transverse electric field are investigated. Nonequilibrium, time-dependent distribution function which describes a process of the droplet transverse evolution with constant entropy in the field is calculated. With the help of this distribution function, shear viscosity coefficients in the transverse plane are calculated as well. They are found to be dependent on the ratio of the potential energy of the droplet in the electric field to the kinetic energy of the droplet; for weakly interacting particles, this parameter is small. Additionally, these coefficients are time-dependent and change during the hydrodynamical state of the droplet's expansion. Applicability of the results to the description of initial states of quark–gluon plasma (QGP) obtained in high-energy interactions of nuclei is also discussed.
Thèses sur le sujet "Weakly dependent process"
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Boulin, Alexis. « Partitionnement des variables de séries temporelles multivariées selon la dépendance de leurs extrêmes ». Electronic Thesis or Diss., Université Côte d'Azur, 2024. http://www.theses.fr/2024COAZ5039.
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Dans un grand éventail d'applications allant des sciences du climat à la finance, des événements extrêmes avec une probabilité loin d'être négligeable peuvent se produire, entraînant des conséquences désastreuses. Les extrêmes d'évènements climatiques tels que le vent, la température et les précipitations peuvent profondément affecter les êtres humains et les écosystèmes, entraînant des événements tels que des inondations, des glissements de terrain ou des vagues de chaleur. Lorsque l'emphase est mise sur l'étude de variables mesurées dans le temps sur un grand nombre de stations ayant une localisation spécifique, comme les variables mentionnées précédemment, le partitionnement de variables devient essentiel pour résumer et visualiser des tendances spatiales, ce qui est crucial dans l'étude des événements extrêmes. Cette thèse explore plusieurs modèles et méthodes pour partitionner les variables d'un processus stationnaire multivarié, en se concentrant sur les dépendances extrémales.Le chapitre 1 présente les concepts de modélisation de la dépendance via les copules, fondamentales pour la dépendance extrême. La notion de variation régulière est introduite, essentielle pour l'étude des extrêmes, et les processus faiblement dépendants sont abordés. Le partitionnement est discuté à travers les paradigmes de séparation-proximité et de partitionnement basé sur un modèle. Nous abordons aussi l'analyse non-asymptotique pour évaluer nos méthodes dans des dimensions fixes.Le chapitre 2 est à propos de la dépendance entre valeurs maximales est cruciale pour l'analyse des risques. Utilisant la fonction de copule de valeur extrême et le madogramme, ce chapitre se concentre sur l'estimation non paramétrique avec des données manquantes. Un théorème central limite fonctionnel est établi, démontrant la convergence du madogramme vers un processus Gaussien tendu. Des formules pour la variance asymptotique sont présentées, illustrées par une étude numérique.Le chapitre 3 propose les modèles asymptotiquement indépendants par blocs (AI-blocs) pour le partitionnement de variables, définissant des clusters basés sur l'indépendance des maxima. Un algorithme est introduit pour récupérer les clusters sans spécifier leur nombre à l'avance. L'efficacité théorique de l'algorithme est démontrée, et une méthode de sélection de paramètre basée sur les données est proposée. La méthode est appliquée à des données de neurosciences et environnementales, démontrant son potentiel.Le chapitre 4 adapte des techniques de partitionnement pour analyser des événements extrêmes composites sur des données climatiques européennes. Les sous-régions présentant une dépendance des extrêmes de précipitations et de vitesse du vent sont identifiées en utilisant des données ERA5 de 1979 à 2022. Les clusters obtenus sont spatialement concentrés, offrant une compréhension approfondie de la distribution régionale des extrêmes. Les méthodes proposées réduisent efficacement la taille des données tout en extrayant des informations cruciales sur les événements extrêmes.Le chapitre 5 propose une nouvelle méthode d'estimation pour les matrices dans un modèle linéaire à facteurs latents, où chaque composante d'un vecteur aléatoire est exprimée par une équation linéaire avec des facteurs et du bruit. Contrairement aux approches classiques basées sur la normalité conjointe, nous supposons que les facteurs sont distribués selon des distributions de Fréchet standards, ce qui permet une meilleure description de la dépendance extrémale. Une méthode d'estimation est proposée garantissant une solution unique sous certaines conditions. Une borne supérieure adaptative pour l'estimateur est fournie, adaptable à la dimension et au nombre de facteursIn a wide range of applications, from climate science to finance, extreme events with a non-negligible probability can occur, leading to disastrous consequences. Extremes in climatic events such as wind, temperature, and precipitation can profoundly impact humans and ecosystems, resulting in events like floods, landslides, or heatwaves. When the focus is on studying variables measured over time at numerous specific locations, such as the previously mentioned variables, partitioning these variables becomes essential to summarize and visualize spatial trends, which is crucial in the study of extreme events. This thesis explores several models and methods for partitioning the variables of a multivariate stationary process, focusing on extreme dependencies.Chapter 1 introduces the concepts of modeling dependence through copulas, which are fundamental for extreme dependence. The notion of regular variation, essential for studying extremes, is introduced, and weakly dependent processes are discussed. Partitioning is examined through the paradigms of separation-proximity and model-based clustering. Non-asymptotic analysis is also addressed to evaluate our methods in fixed dimensions.Chapter 2 study the dependence between maximum values is crucial for risk analysis. Using the extreme value copula function and the madogram, this chapter focuses on non-parametric estimation with missing data. A functional central limit theorem is established, demonstrating the convergence of the madogram to a tight Gaussian process. Formulas for asymptotic variance are presented, illustrated by a numerical study.Chapter 3 proposes asymptotically independent block (AI-block) models for partitioning variables, defining clusters based on the independence of maxima. An algorithm is introduced to recover clusters without specifying their number in advance. Theoretical efficiency of the algorithm is demonstrated, and a data-driven parameter selection method is proposed. The method is applied to neuroscience and environmental data, showcasing its potential.Chapter 4 adapts partitioning techniques to analyze composite extreme events in European climate data. Sub-regions with dependencies in extreme precipitation and wind speed are identified using ERA5 data from 1979 to 2022. The obtained clusters are spatially concentrated, offering a deep understanding of the regional distribution of extremes. The proposed methods efficiently reduce data size while extracting critical information on extreme events.Chapter 5 proposes a new estimation method for matrices in a latent factor linear model, where each component of a random vector is expressed by a linear equation with factors and noise. Unlike classical approaches based on joint normality, we assume factors are distributed according to standard Fréchet distributions, allowing a better description of extreme dependence. An estimation method is proposed, ensuring a unique solution under certain conditions. An adaptive upper bound for the estimator is provided, adaptable to dimension and the number of factors
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Gaigalas, Raimundas. « A Non-Gaussian Limit Process with Long-Range Dependence ». Doctoral thesis, Uppsala : Matematiska institutionen, Univ. [distributör], 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-3993.
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Kabui, Ali. « Value at risk et expected shortfall pour des données faiblement dépendantes : estimations non-paramétriques et théorèmes de convergences ». Phd thesis, Université du Maine, 2012. http://tel.archives-ouvertes.fr/tel-00743159.
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Quantifier et mesurer le risque dans un environnement partiellement ou totalement incertain est probablement l'un des enjeux majeurs de la recherche appliquée en mathématiques financières. Cela concerne l'économie, la finance, mais d'autres domaines comme la santé via les assurances par exemple. L'une des difficultés fondamentales de ce processus de gestion des risques est de modéliser les actifs sous-jacents, puis d'approcher le risque à partir des observations ou des simulations. Comme dans ce domaine, l'aléa ou l'incertitude joue un rôle fondamental dans l'évolution des actifs, le recours aux processus stochastiques et aux méthodes statistiques devient crucial. Dans la pratique l'approche paramétrique est largement utilisée. Elle consiste à choisir le modèle dans une famille paramétrique, de quantifier le risque en fonction des paramètres, et d'estimer le risque en remplaçant les paramètres par leurs estimations. Cette approche présente un risque majeur, celui de mal spécifier le modèle, et donc de sous-estimer ou sur-estimer le risque. Partant de ce constat et dans une perspective de minimiser le risque de modèle, nous avons choisi d'aborder la question de la quantification du risque avec une approche non-paramétrique qui s'applique à des modèles aussi généraux que possible. Nous nous sommes concentrés sur deux mesures de risque largement utilisées dans la pratique et qui sont parfois imposées par les réglementations nationales ou internationales. Il s'agit de la Value at Risk (VaR) qui quantifie le niveau de perte maximum avec un niveau de confiance élevé (95% ou 99%). La seconde mesure est l'Expected Shortfall (ES) qui nous renseigne sur la perte moyenne au delà de la VaR.
Livres sur le sujet "Weakly dependent process"
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Jérôme, Dedecker, dir. Weak dependence : With examples and applications. New York : Springer, 2007.
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Rio, Emmanuel. Asymptotic Theory of Weakly Dependent Random Processes. Springer, 2017.
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Rio, Emmanuel. Asymptotic Theory of Weakly Dependent Random Processes. Springer, 2018.
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Merlevède, Florence, Magda Peligrad et Sergey Utev. Functional Gaussian Approximation for Dependent Structures. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780198826941.001.0001.
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This book has its origin in the need for developing and analyzing mathematical models for phenomena that evolve in time and influence each another, and aims at a better understanding of the structure and asymptotic behavior of stochastic processes. This monograph has double scope. First, to present tools for dealing with dependent structures directed toward obtaining normal approximations. Second, to apply the normal approximations presented in the book to various examples. The main tools consist of inequalities for dependent sequences of random variables, leading to limit theorems, including the functional central limit theorem (CLT) and functional moderate deviation principle (MDP). The results will point out large classes of dependent random variables which satisfy invariance principles, making possible the statistical study of data coming from stochastic processes both with short and long memory. Over the course of the book different types of dependence structures are considered, ranging from the traditional mixing structures to martingale-like structures and to weakly negatively dependent structures, which link the notion of mixing to the notions of association and negative dependence. Several applications have been carefully selected to exhibit the importance of the theoretical results. They include random walks in random scenery and determinantal processes. In addition, due to their importance in analyzing new data in economics, linear processes with dependent innovations will also be considered and analyzed.
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Alston, Philip, dir. The Complexity of Human Rights. Hart Publishing, 2024. http://dx.doi.org/10.5040/9781509972890.
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This book provides the first systematic assessment from a human rights law perspective of the landmark contributions of the renowned legal anthropologist, Sally Engle Merry. What impact does over-simplification have on human rights debates? The understandable tendency to present them as a single, universal, and immutable concept ignores their complexity and by extension only serves to weaken them. Merry and her colleagues transformed human rights thinking by highlighting the process of ‘vernacularization’, which sees rights discourse as being unavoidably dependent upon translation and interpretation. She also warned of the pitfalls of excessive reliance upon statistical and other indicators, through the process of quantification. Here the leading voices in the field assess the significance of these contributions. The cover shows Judith Mason’s painting The Man Who Sang and the Woman Who Kept Silent (known as ‘the Blue Dress’), part of a triptych which hangs in the South African Constitutional Court. The work symbolizes accounts of the killings of two freedom fighters under the apartheid system that emerged in the hearings of the Truth and Reconciliation Commission.
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Wälchli, Bernhard. The rise of gender in Nalca (Mek, Tanah Papua). Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198795438.003.0004.
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This chapter reconstructs how Nalca, a Mek language of the Trans-New Guinea phylum, has acquired gender markers and describes the non-canonical properties of this highly unusual gender system. Gender in Nalca is mainly assigned by two different defaults, phonological assignment is holistic, there is a gender switch depending on the syntax of the noun phrase, controller and target are adjacent, and gender has the function of case marker hosts. Gender in Nalca is only weakly entrenched in the lexicon and predominantly phrasal. It is argued that canonical gender is an attractor (a complex, diachronically stable structure with heterogeneous origins). A model of the gender attractor based on the notion of information transfer chain is developed. The rise of Nalca gender is an instance of system emergence where several diachronic processes, such as grammaticalization, reanalysis, and analogy, interact. Chains of rapid diachronic change are triggered by anomalies that entail other anomalies.
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Wood, John. Russia, the Asymmetric Threat to the United States. ABC-CLIO, 2009. http://dx.doi.org/10.5040/9798216010333.
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Exploring themes critical to understanding the current world order, this book lays bare the reality of the new Russia that emerged under Vladimir Putin. Russia holds the world's largest natural gas reserves, the second largest coal and uranium reserves, and the eighth largest oil reserves. Europe is dependent on Russia for 25 percent of its oil and gas. Russia is also positioning itself to play a similar role with respect to China. The key to this strategy is a network of new oil and natural gas pipelines that Russia is in the process of constructing, which will by-pass the problematic Ukraine, Georgia, Poland and the Baltic States in the West, and lock-in the enormous potential of China in the East. Further, as the Western economies including the USA begin themselves to recover, their growing energy dependence will come back into the forefront, and therefore the need to ensure that Russia does not fail in its opening up of new energy resources in the Arctic and Eastern Siberia. Russia is no longer a superpower, in the Cold War sense of the word, because its military is significantly weaker, and as such is incapable of conducting a regional let alone global war against either the United States or NATO. It is precisely because of its military weakness that Putin has been forced to adopt an asymmetric approach. Thus, the pipeline spigot and the proliferation of missiles and aircraft have become Russia's weapons of choice, along with an ever growing reliance on its strategic nuclear forces to provide it with the necessary deterrent to foreign aggression. In addition, Putin and Medvedev have no interest in an arms race with the United States, it is too costly and detracts from their priority, which is economic reform. From Putin's perspective, America is in the process of imposing "absolute security" or as Joint Vision 2020 put it: "full spectrum dominance" over the world. As the sole remaining superpower, the United States enjoys a massive strategic imbalance in its favor, which it has used first to contain, but now with the intent to control the world. How? NATO expansion lays the groundwork for a U.S. global missile defense system to contain perceived adversaries, such as Russia, which in turn secures the dominance of America through its Prompt Global Strike (PGS) capability – the ability to strike anywhere on the planet with impunity within 90 minutes of the order being given by The President. Thus, PGS will be to the 21st Century, what British Gun Boat Diplomacy was to the 19th Century. In such a context, Russia is forced to respond asymmetrically.
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Dube, Opha Pauline. Climate Policy and Governance across Africa. Oxford University Press, 2016. http://dx.doi.org/10.1093/acrefore/9780190228620.013.605.
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This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Climate Science. Please check back later for the full article.Africa, a continent with the largest number of countries falling under the category of Least Developed Countries (LDCs), remains highly dependent on rain-fed agriculture that suffers from low intake of water, exacerbating the vulnerability to climate variability and anthropogenic climate change. The increasing frequency and severity of climate extremes impose major strains on the economies of these countries. The loss of livelihoods due to interaction of climate change with existing stressors is elevating internal and cross-border migration. The continent is experiencing rapid urbanization, and its cities represent the most vulnerable locations to climate change due in part to incapacitated local governance. Overall, the institutional capacity to coordinate, regulate, and facilitate development in Africa is weak. The general public is less empowered to hold government accountable. The rule of law, media, and other watchdog organizations, and systems of checks and balances are constrained in different ways, contributing to poor governance and resulting in low capacity to respond to climate risks.As a result, climate policy and governance are inseparable in Africa, and capacitating the government is as essential as establishing climate policy. With the highest level of vulnerability to climate change compared with the rest of the world, governance in Africa is pivotal in crafting and implementing viable climate policies.It is indisputable that African climate policy should focus first and foremost on adaptation to climate change. It is pertinent, therefore, to assess Africa’s governance ability to identify and address the continent’s needs for adaptation. One key aspect of effective climate policy is access to up-to-date and contextually relevant information that encompasses indigenous knowledge. African countries have endeavored to meet international requirements for reports such as the National Communications on Climate Change Impacts and Vulnerabilities and the National Adaptation Programmes of Action (NAPAs). However, the capacity to deliver on-time quality reports is lacking; also the implementation, in particular integration of adaptation plans into the overall development agenda, remains a challenge. There are a few successes, but overall adaptation operates mainly at project level. Furthermore, the capacity to access and effectively utilize availed international resources, such as extra funding or technology transfer, is limited in Africa.While the continent is an insignificant source of emissions on a global scale, a more forward looking climate policy would require integrating adaptation with mitigation to put in place a foundation for transformation of the development agenda, towards a low carbon driven economy. Such a futuristic approach calls for a comprehensive and robust climate policy governance that goes beyond climate to embrace the Sustainable Development Goals Agenda 2030. Both governance and climate policy in Africa will need to be viewed broadly, encompassing the process of globalization, which has paved the way to a new geological epoch, the Anthropocene. The question is, what should be the focus of climate policy and governance across Africa under the Anthropocene era?
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Cook, Kerry H. Climate Change Scenarios and African Climate Change. Oxford University Press, 2018. http://dx.doi.org/10.1093/acrefore/9780190228620.013.545.
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Accurate projections of climate change under increasing atmospheric greenhouse gas levels are needed to evaluate the environmental cost of anthropogenic emissions, and to guide mitigation efforts. These projections are nowhere more important than Africa, with its high dependence on rain-fed agriculture and, in many regions, limited resources for adaptation. Climate models provide our best method for climate prediction but there are uncertainties in projections, especially on regional space scale. In Africa, limitations of observational networks add to this uncertainty since a crucial step in improving model projections is comparisons with observations. Exceeding uncertainties associated with climate model simulation are uncertainties due to projections of future emissions of CO2 and other greenhouse gases. Humanity’s choices in emissions pathways will have profound effects on climate, especially after the mid-century.The African Sahel is a transition zone characterized by strong meridional precipitation and temperature gradients. Over West Africa, the Sahel marks the northernmost extent of the West African monsoon system. The region’s climate is known to be sensitive to sea surface temperatures, both regional and global, as well as to land surface conditions. Increasing atmospheric greenhouse gases are already causing amplified warming over the Sahara Desert and, consequently, increased rainfall in parts of the Sahel. Climate model projections indicate that much of this increased rainfall will be delivered in the form of more intense storm systems.The complicated and highly regional precipitation regimes of East Africa present a challenge for climate modeling. Within roughly 5º of latitude of the equator, rainfall is delivered in two seasons—the long rains in the spring, and the short rains in the fall. Regional climate model projections suggest that the long rains will weaken under greenhouse gas forcing, and the short rains season will extend farther into the winter months. Observations indicate that the long rains are already weakening.Changes in seasonal rainfall over parts of subtropical southern Africa are observed, with repercussions and challenges for agriculture and water availability. Some elements of these observed changes are captured in model simulations of greenhouse gas-induced climate change, especially an early demise of the rainy season. The projected changes are quite regional, however, and more high-resolution study is needed. In addition, there has been very limited study of climate change in the Congo Basin and across northern Africa. Continued efforts to understand and predict climate using higher-resolution simulation must be sustained to better understand observed and projected changes in the physical processes that support African precipitation systems as well as the teleconnections that communicate remote forcings into the continent.
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Bouët, Antoine, Sunday Pierre Odjo et Chahir Zaki, dir. 2022 Africa Agriculture Trade Monitor (AATM). AKADEMIYA2063 and the International Food Policy Research Institute (IFPRI), 2022. http://dx.doi.org/10.54067/9781737916437.
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Agricultural trade and global food security have been dramatically affected by a series of events. While the global economy is recovering in 2022 from the COVID-19 pandemic, the Russian invasion of Ukraine has sparked new and challenging problems. In a context where agricultural prices were recovering from a generalized surge throughout the pandemic, the war reversed these trends and opened an new episode of rising food prices, general inflationary pressures, and increased volatility. The combination of these shocks affects agricultural trade and food security throughout Africa, especially in countries highly dependent on food imports. The role of trade in creating resilience in this volatile environment is crucial and has been much discussed. From this perspective, the 2022 Africa Agriculture Trade Monitor (AATM) contributes to our understanding of African agricultural trade and its relationship with food and nutrition security in several important ways. First, it provides a thorough analysis of regional and continental trade in agriculture and selected value chains using accurate statistics developed for this report. This year, it adds an analysis of the nutritional content of African trade and looks closely at the trade in processed products. Second, it examines the potentially transformative impact of the African Continental Free Trade Area (AfCFTA) on the region’s economies. Third, at the regional level, it analyzes the evolution of intra- as well as extra-regional trade flows, and trade policy of one of Africa’s Regional Economic Communities (RECs), namely the Economic Community of Central Africa States (ECCAS). As in prior editions, this fifth AATM provides improved trade statistics and uses consistent indicators to monitor trends in Africa’s participation in global trade as well as the status of intra-African trade. The report highlights three main findings. First, the insertion of African countries in global and regional value chains is low but has recently improved. Indeed, both forward participation in value chains (that is, provision of inputs to other countries’ processing sectors) and backward participation (incorporation of imported intermediates into African traded products) have increased, although forward links have grown faster than backward links. Second, intra-African trade increased significantly prior to the pandemic in most RECs, especially in processed products. Yet, this trend was halted by the COVID-19 shock, especially in ECCAS and the Arab Maghreb Union (AMU). Third, the nutritional content of extra-African trade is concentrated in products with a high value and a low caloric content. In comparison, intra-African flows are more intensive in calories, fat, and protein. The report also examines a number of special topics. One chapter is devoted to modeling the impacts on trade, growth, and welfare of several potential approaches to AfCFTA implementation. The results confirm that there is a high opportunity cost associated with weak AfCFTA implementation, which is why it is crucial to take a more ambitious approach that fully liberalizes tariffs and reduces nontariff measures. The 2022 AATM also conducts a detailed analysis of trends and policy issues in value chains for stimulants (cocoa, coffee, and tea), demonstrating that trade in these sectors is still concentrated in unprocessed products. Finally, the report examines in-depth the patterns of trade integration within ECCAS. One important finding is that intraregional trade is still impeded by many tariffs, nontariff measures, and poor transport infrastructure. AKADEMIYA2063 and the International Food Policy Research Institute (IFPRI) are pleased to present this collaborative report, which provides an insightful review of Africa’s progress in trade development, within and beyond the continent, and new analysis on critical topics for trade in Africa’s agrifood sector.
Chapitres de livres sur le sujet "Weakly dependent process"
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Rio, Emmanuel. « The Variance of Partial Sums ». Dans Asymptotic Theory of Weakly Dependent Random Processes, 1–32. Berlin, Heidelberg : Springer Berlin Heidelberg, 2017. http://dx.doi.org/10.1007/978-3-662-54323-8_1.
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Rio, Emmanuel. « Algebraic Moments, Elementary Exponential Inequalities ». Dans Asymptotic Theory of Weakly Dependent Random Processes, 33–49. Berlin, Heidelberg : Springer Berlin Heidelberg, 2017. http://dx.doi.org/10.1007/978-3-662-54323-8_2.
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Rio, Emmanuel. « Maximal Inequalities and Strong Laws ». Dans Asymptotic Theory of Weakly Dependent Random Processes, 51–63. Berlin, Heidelberg : Springer Berlin Heidelberg, 2017. http://dx.doi.org/10.1007/978-3-662-54323-8_3.
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Rio, Emmanuel. « Central Limit Theorems ». Dans Asymptotic Theory of Weakly Dependent Random Processes, 65–87. Berlin, Heidelberg : Springer Berlin Heidelberg, 2017. http://dx.doi.org/10.1007/978-3-662-54323-8_4.
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Rio, Emmanuel. « Mixing and Coupling ». Dans Asymptotic Theory of Weakly Dependent Random Processes, 89–100. Berlin, Heidelberg : Springer Berlin Heidelberg, 2017. http://dx.doi.org/10.1007/978-3-662-54323-8_5.
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Rio, Emmanuel. « Fuk–Nagaev Inequalities, Applications ». Dans Asymptotic Theory of Weakly Dependent Random Processes, 101–11. Berlin, Heidelberg : Springer Berlin Heidelberg, 2017. http://dx.doi.org/10.1007/978-3-662-54323-8_6.
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Rio, Emmanuel. « Empirical Distribution Functions ». Dans Asymptotic Theory of Weakly Dependent Random Processes, 113–24. Berlin, Heidelberg : Springer Berlin Heidelberg, 2017. http://dx.doi.org/10.1007/978-3-662-54323-8_7.
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Rio, Emmanuel. « Empirical Processes Indexed by Classes of Functions ». Dans Asymptotic Theory of Weakly Dependent Random Processes, 125–48. Berlin, Heidelberg : Springer Berlin Heidelberg, 2017. http://dx.doi.org/10.1007/978-3-662-54323-8_8.
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Rio, Emmanuel. « Irreducible Markov Chains ». Dans Asymptotic Theory of Weakly Dependent Random Processes, 149–69. Berlin, Heidelberg : Springer Berlin Heidelberg, 2017. http://dx.doi.org/10.1007/978-3-662-54323-8_9.
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Nze, Patrick Ango, et Paul Doukhan. « Weak Dependence : Models and Applications ». Dans Empirical Process Techniques for Dependent Data, 117–36. Boston, MA : Birkhäuser Boston, 2002. http://dx.doi.org/10.1007/978-1-4612-0099-4_2.
Texte intégralActes de conférences sur le sujet "Weakly dependent process"
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Yang, G., et J. A. Liburdy. « The Effects of Driving Waveform and Frequency on the Droplet Formation Process ». Dans ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-41607.
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For a piezoelectric stack (PZT) driven droplet generator, the driving waveform and driving frequency effects on liquid filament shape and droplet characteristics have been studied. A lumped element model (LEM) is developed to study the acoustic-mechanical behavior and the volumetric rejection of the droplet generator. Based on the LEM, the PZT displacement magnitude dominates the internal pressure variation within the chamber. However due to the natural response of droplet generator, the acoustic pressure in the droplet generator decays exponentially. Experimental data show that the droplet formation process can be waveform and frequency dependent. When the droplet formation process is driven in the “low frequency” regime, the droplet formation process is weakly affected by frequency. Meniscus interaction effects, which are the interaction of a liquid filament from different droplet generation cycles, on the droplet formation process will be present when the droplet formation process is driven in the “high frequency” regime. Due to meniscus interactions, the droplet formation process at “high frequency” is waveform and frequency dependent. Results show that the droplet volume reduces with driving frequency, and droplet velocity increases with driving frequency. However the droplet break-off time is only weakly affected by the driving frequency.
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Sun, Hua, Guy Lauriat et Xavier Nicolas. « Transient Evaporation of Liquid Water Films and Condensation of Humid Air at the Isothermal Walls of a Square Cavity ». Dans 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22467.
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The aim of this paper is to present modelling and numerical simulations of heat and mass transfer by double-diffusive convection and surface condensation or evaporation in a two-dimensional square cavity subjected to a uniform, but time-dependent wall temperature. At initial state, the cavity is filled with quiescent humid air at uniform temperature and density. By decreasing the wall temperature, condensation occurs at the four wall surfaces. The walls are then heated and evaporation of the liquid water is considered. Since the mass of humid air and average pressure experience noticeable changes during the periodic process, a weakly compressible formulation has been used for the modelling of the thermosolutal flow. Local thermodynamic assumption at the liquid-vapor interface and thin liquid film approximation are introduced.
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Russell, P. St J., et C. N. Pannell. « Forward Brillouin scattering in dual-mode optical fiber ». Dans OSA Annual Meeting. Washington, D.C. : Optica Publishing Group, 1991. http://dx.doi.org/10.1364/oam.1991.mgg1.
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Forward stimulated Brillouin scattering (FSBS) is similar in physical origin to conventional backward SBS (BSBS), except that it occurs in a forward direction between two nondegenerate copropagating optical modes of a dual-mode optical fiber.1 FSBS may, however, be the only example of a nonlinear effect where the threshold falls as the mode spot size is increased. This curious behavior is a consequence of the fact that the acoustic gain depends on an electrostrictive moment and not (as in conventional SBS) a pressure. Intermodal beating between an LP01 and a frequency shifted LP11 mode gives rise to a moving interference pattern with regions of constructive interference that alternate across the core. In the correct matching conditions, electrostriction will feed optical energy into a flexural mode of the fiber. The results of a theoretical study of FSBS are presented, including calculations of the threshold power (only weakly dependent on the laser linewidth, owing to the copropagating nature of the process) with a discussion of the novel phenomenology caused by long phonon lifetimes. We also show how the theory may be used to design special fibers in which the FSBS threshold power is many times smaller than in BSBS.
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Imane Zemoul, Sara, et Youcef Berkoun. « Linear Process With Associated Innovations Under Weak Dependence ». Dans 2021 International Conference on Recent Advances in Mathematics and Informatics (ICRAMI). IEEE, 2021. http://dx.doi.org/10.1109/icrami52622.2021.9585976.
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Bao, Hua, Xiulin Ruan, Bradley F. Habenicht et Oleg V. Prezhdo. « Temperature Dependence of Hot Carrier Relaxation in a PBSE Quantum Dot : An Ab Initio Study ». Dans ASME 2009 Heat Transfer Summer Conference collocated with the InterPACK09 and 3rd Energy Sustainability Conferences. ASMEDC, 2009. http://dx.doi.org/10.1115/ht2009-88134.
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Temperature dependent dynamics of phonon-assisted relaxation of hot carriers, both electrons and holes, is studied in a PbSe quantum dot using ab initio time-domain density functional theory. The electronic structure is first calculated, showing that the hole states are denser than the electron states. Fourier transforms of the time resolved energy levels show that the hot carriers couple to both acoustic and optical phonons. At higher temperature, more phonon modes in the high frequency range participate in the relaxation process due to their increased occupation number. The phonon-assisted hot carrier decay dynamics is predicted using non-adiabatic molecular dynamics, and the calculated relaxation rates clearly show a temperature-activation behavior. The complex temperature dependence is attributed to the combined effects of the phonon occupation number and thermal expansion. Comparing the simulation results with experiments, we suggest that the multiphonon relaxation channel is efficient at high temperature, while the Auger-like process may dominate the relaxation at low temperature. This combined mechanism can explain the weak temperature dependence at low temperature and stronger temperature dependence at higher temperature.
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LEAH, T. G. « LANDSCAPE APPROACH IN THE STUDY OF ALLUVIAL SOILS OF THE REPUBLIC MOLDOVA ». Dans Теоретические и прикладные проблемы ландшафтной географии. VII Мильковские чтения. Voronezh State University, 2023. http://dx.doi.org/10.17308/978-5-9273-3692-0-2023-286-289.
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The characteristic of alluvial soils of Lower Dniester River of Moldova is presented. These soils are characterized by high biogenicity, layering, and the presence of buried humus horizons. Depending on the process of soilformation, they are divided into the following units: weakly developed, typical, semi-swamp and swamp. The recommendations for agricultural use and improvement of alluvial soils properties, at the regional level, information on the limits of the distribution of soil properties, soil-forming species and groundwater, based on the system-landscape approach, is necessary.
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Guenadou, D., E. Meillot et A. Saget. « Particle Treatment Modeling in a Time-Dependent D.C. Plasma Flow ». Dans ITSC2005, sous la direction de E. Lugscheider. Verlag für Schweißen und verwandte Verfahren DVS-Verlag GmbH, 2005. http://dx.doi.org/10.31399/asm.cp.itsc2005p0326.
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Abstract D.C. plasma spraying process leads to coatings with high level properties. The control of these properties implies to overcome well the process and in particular the interactions between the particles and the plasma plume. This latter shows high fluctuations outside the torch due to arc root movements on the anode wall inside the torch. These movements are responsible of less or more weak plasma flow stretching outside the torch and of air engulfment. From a simple numerical model based on the gas heating by JOULE effect in the anode, the realistic flow behavior is reproduced, in particular, the mechanisms of air engulfment into the plasma plume, such as it was described by PFENDER and al. Moreover, the centerline velocities and temperatures of the gas are compared with experimental values: the comparison shows good agreement. From this realistic flow, zirconia particle treatment modeling is carried on. Depending on the plasma plume stretching outside the torch and on particle granulometry, the particle trajectories and also velocities and temperatures present high variations, leading to particle thermocinetic states at impact quite different from one particle to the other.
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Dianov, E. M., P. G. Kazansky et D. Yu Stepanov. « Simulation of the effective second-harmonic generation process in optical fibers ». Dans OSA Annual Meeting. Washington, D.C. : Optica Publishing Group, 1990. http://dx.doi.org/10.1364/oam.1990.tuu4.
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In this paper we propose a dynamic mechanism of efficient second-harmonic amplification in optical fibers and explain the existence of phenomenon thresholds. We start with the assumption that the second-order susceptibility grating appears in fibers because of the strong electrostatic field caused by coherent photocurrent.1 We have obtained equations for the amplitudes and phases of this grating and second harmonic that are similar to equations describing dynamic self-diffraction of light beams. We have shown that the phase shift of the grating relative to the "interference" pattern (the pattern of coherent photocurrent oscillations) leads to an amplification of weak second-harmonic seeding. Strong exponential growth takes place when this amplification is greater than the losses. We have obtained a threshold condition connecting pump power, distance from the fiber end, and time from the beginning of fiber preparation. We have shown that the value of the length threshold and the length dependence of second-harmonic intensity are different for various seed intensities because of the dependence of photoconductivity on second-harmonic intensity. The results of numerical simulation of the phenomenon are in close agreement with known experimental results.2
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Kochan, P., et H. J. Carmichael. « Photon-statistics dependence of single-atom absorption ». Dans OSA Annual Meeting. Washington, D.C. : Optica Publishing Group, 1993. http://dx.doi.org/10.1364/oam.1993.wxx.8.
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Under usual laboratory conditions the absorption of a beam of light by a dilute two-level medium depends on the intensity and spectrum of the incident light. If the incident photon flux is small compared to the decay rate of the absorber’s excited state, saturation effects can be neglected and only the spectrum of the light is important; thus, weak-field absorption depends only on the firstorder correlation function of the incident light. This result relies, however, on a requirement that the incident beam cross-section be much larger than the absorption cross-section of an atom. Then individual atoms act as low efficiency scatterers and the statistics of the scattering process is governed by the law of large numbers applied to many scattering sites. In contrast, if it is arranged that just one atom significantly absorbs (scatters) a beam of photons, correlation functions of the incident light beyond the first-order must be considered. For a beam that is focused within an absorption cross-section, we might naively predict that every photon will be scattered and none transmitted. In fact, even for a very weak beam there is a finite probability for two photons to arrive at the atom within the excited state lifetime, and in this event at least one of them will be transmitted (statistical saturation). In this paper we calculate the transmitted photon flux for a weak beam of photons focussed strongly onto a single, resonant two-state atom. We study the dependence of the transmitted flux on the statistics of the incident photons. Photon beams derived from sources of coherent, chaotic, squeezed, coherent-antibunched, and broadband-antibunched light are considered. our calculations are based on a recently developed theory of cascaded open systems,1,2 and serve to illustrate the usefulness of this theory.
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Li, Longjian, Qinghua Chen, Wenzhi Cui, Tien-Chien Jen, Yi-Hsin Yen, Quan Liao et Lin Zhu. « The Effects of the Distance Between Nozzle and Substrate on Cold Gas Dynamic Spray Process ». Dans ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-10501.
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In this paper, numerical simulations were performed for the gas-particle two phase flow in the Cold Gas Dynamic Spray (CGDS) process to investigate the acceleration of micro- and nanoparticles with diameters ranging from 100nm to 50μm. Nitrogen (N2) and Helium (He) were chosen as the carrier gas, respectively. The acceleration of carrier gas to particles in the De-Laval-Type supersonic nozzle was strongly dependent on the characteristics of flow field, as well as the densities and the size of the particles. Copper particles (Cu) were chosen as the spraying materials. The computed results showed that the flow structures of the carrier gas were very different for different gas and different spraying distance, which resulted in consequently different accelerating features. The cone-shape weak shocks (compression waves) occurred at the exit of divergent section, and the bow-shaped strong shock wave was found right before the substrate, which played a resistance role to the particles and prevented the smaller particles from approaching on the substrate.
Rapports d'organisations sur le sujet "Weakly dependent process"
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Pradelli, Juan Jose, Kimberly Waithe, Allan Wright, Dillon Clarke, Jeetendra Khadan, Juan Pedro Schmid et Mark D. Wenner. Caribbean Region Quarterly Bulletin : Volume 6 : Issue 1 : March 2017. Inter-American Development Bank, mars 2017. http://dx.doi.org/10.18235/0008149.
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This Caribbean Region Quarterly Bulletin explores constraints to private sector development in the Caribbean. With economic growth weak and dependent on only a few sectors -either tourism or commodity exports- authorities in all countries aim at diversifying the economy and boosting private sector development. While the private sector in each country faces specific issues, most share challenges resulting from red tape, complicated and tedious processes and weak environments for doing business. As usual, the Quarterly Bulletin covers the economic developments in The Bahamas, Barbados, Guyana, Jamaica, Suriname and Trinidad and Tobago, and routinely includes a section on the Organisation of Eastern Caribbean States (OECS).
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Hegazi, Farah, et Katongo Seyuba. The Social Side of Climate Change Adaptation : Reducing Conflict Risk. Stockholm International Peace Research Institute, septembre 2022. http://dx.doi.org/10.55163/seyz9437.
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In developing countries, the effects of climate change interact with factors such as underdevelopment, high dependence on natural resource-based livelihoods, inequality, weak state institutions and marginalization to increase the risk of insecurity and violent conflict. Along with sustainable development and climate change mitigation, climate change adaptation is another key entry point for addressing climate-related security risks. However, key social factors that could positively influence adaptation outcomes and ultimately mitigate climate-related security risks are often overlooked. This SIPRI Policy Brief offers insights into the importance of social capital for facilitating climate change adaptation and preventing and resolving natural resource-related communal conflict in developing countries. The policy brief recommends: (a) improving trust between communities and governments through collaborative processes for knowledge exchange, setting priorities and determining appropriate climate change adaptation practices; and (b) increasing knowledge of climate change among traditional and local leaders to strengthen local conflict resolution mechanisms.