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Articles de revues sur le sujet "Fluctuations collectives"
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MATHAI, NEBU JOHN, et TAKIS ZOURNTOS. « EMERGENT FLUCTUATIONS IN THE TRAJECTORIES OF AGENT COLLECTIVES ». Fluctuation and Noise Letters 07, no 04 (décembre 2007) : L429—L437. http://dx.doi.org/10.1142/s0219477507004057.
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Characteristics of the collective behavior of groups have been studied in diverse disciplines; in this work, we present an approach grounded in robotics. We first specify a model for collective behavior based on a formulation of a multi-agent robotic system. In contrast to some models found in the literature, we do not use stochastic mechanisms to introduce fluctuations. Rather, we present a fully deterministic model where fluctuations emerge due to the complex dynamics of a high-dimensional coupling of dynamical systems. We investigate the emergence of fluctuations in the trajectories of individual agents about the group average trajectory, and present an illustration of the onset of these fluctuations as inter-agent coupling is increased. A selection of behavioral modes are also provided, illustrating the nature of these fluctuations.
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Balázs, Boldizsár, Gábor Vásárhelyi et Tamás Vicsek. « Adaptive leadership overcomes persistence–responsivity trade-off in flocking ». Journal of The Royal Society Interface 17, no 167 (juin 2020) : 20190853. http://dx.doi.org/10.1098/rsif.2019.0853.
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The living world is full of cohesive collectives that have evolved to move together with high efficiency. Schools of fish or flocks of birds maintain their global direction despite significant noise perturbing the individuals, yet they are capable of performing abrupt collective turns when relevant agitation alters the state of a few members. Ruling local fluctuations out of global movement leads to persistence and requires overdamped interaction dynamics, while propagating swift turns throughout the group leads to responsivity and requires underdamped interaction dynamics. In this paper we show a way to avoid this conflict by introducing a time-dependent leadership hierarchy that adapts locally to will : agents’ intention of changing direction. Integrating our new concept of will -based inter-agent behaviour highly enhances the responsivity of standard collective motion models, thus enables breaking out of their former limit, the persistence-responsivity trade-off. We also show that the increased responsivity to environmental cues scales well with growing flock size. Our solution relies on active communication or advanced cognition for the perception of will . The incorporation of these into collective motion is a plausible hypothesis in higher order species, while it is a realizable feature for artificial robots, as demonstrated by our swarm of 52 drones.
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van honacker, Karin. « Résistance locale et émeutes dans les chef-villes brabançonnes aux XVIIe et XVIIIe siècles ». Revue d’histoire moderne & ; contemporaine 47-1, no 1 (1 février 2000) : 37–68. http://dx.doi.org/10.3917/rhmc.g2000.47n1.0037.
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Résumé Les actions collectives dans les chefs-villes du Brabant doivent plutôt être étudiées en relation avec la politique de centralisation des souverains qu'avec les oscillations de la conjoncture et les années de crise. Bien qu'elles se manifestassent sous une variété de formes et qu'elles fassent leur apparition à la suite d'occasions diverses, elles parurent souvent avoir les mêmes mobiles, à savoir la lutte pour le maintien des zones d'influence. Le plus souvent, les chefs des métiers (ou corporations), faisant partie de l'administration de la ville, dirigeaient la résistance. Collective actions in the Brabant capital cities should rather be studied in relation to the policy of centralization of the princes than to cyclical fluctuations and years of crisis. Even though they manifested themselves in a variety of forms and originated as a resuit of divergent causes, they often appeared to hâve the same motives, to wit, the struggle for the préservation of sphères of influence. Usually, it were the guild leaders, being part of the city administration, who directed the résistance.
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Breinbjerg, Morten, et Jonas Fritsch. « Deltagelsens æstetik – om at tale, lytte og adlyde ». K&K - Kultur og Klasse 42, no 118 (30 décembre 2014) : 87–100. http://dx.doi.org/10.7146/kok.v42i118.19837.
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In this article we discuss aesthetics of participation as a sensory, affective and reflective engagement with the world and the historical, physical, material, political and cultural relations that form our world. We develop a theoretical understanding building on the work of Michel Serres and Jacques Rancière to unfold participation as continuous fluctuations between individual/collective, signal/noise, order/chaos in a distribution of the sensible, following a politics of aesthetics. Through the analysis of two auditory, interactive installations – BUG and Ekkomaten – we show how the aesthetics of participation arises from- and modulates complex communicative and affective relations between individuals, collectives and places. Through their crafting and design, both BUG and Ekkomaten effect a transformation of the distributions of the sensible through digital sonifications, giving its users the possibility to redefine their relational engagement with issues of surveillance in the former DDR (BUG) and the community of the residential area Møllevangen in Aarhus, Denmark (Ekkomaten). Following this, we discuss how future (participatory) design projects can benefit from cultivating an aesthetics participation where aesthetics describes the relation between forms of experience, the distribution of the sensible and the potential for participation.
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Thomas, Swapna, et M. J. Mercykutty. « Challenges Faced by Women Collectives in Lease Land Farming in Thrissur District, Kerala State ». Asian Journal of Agricultural Extension, Economics & ; Sociology 41, no 2 (10 février 2023) : 13–18. http://dx.doi.org/10.9734/ajaees/2023/v41i21842.
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Lease land farming by women collectives is an initiative introduced by Kudumbashree to encourage cultivation among self - help groups. It not only contributes to significant changes in the lives of women farmers but also helps to increase agricultural production by bringing the fallow and cultivable waste- land into agricultural use. The present study was conducted in Thrissur district from June to August 2022. An ex-post- facto research design was used. Two blocks, Kodakara and Ollukkara, representing more area of banana and vegetable respectively under leased land farming were selected. From these blocks, two panchayats each, were randomly selected. From Kodakara, Mattathur and Kodakara and from Ollukkara, Nadathara and Puthur panchayats were selected for the purpose. From these two panchayats, fifteen women joint liability groups were selected randomly, comprising 60 women farmers each who cultivate vegetables and banana under leased land. Thus, the total sample comprised of 120 women farmers. The data were collected with the help of a semi - structured pre - tested interview schedule. Garrett ranking was employed to explore the challenges faced by women collective farmers. The challenges were categorised under four categories i,e., lease land related, group related, technical and supplies, and services. Among land related challenges, the non - legalized status of leasing was ranked as the most serious one where the mean score was 63.10. Absenteeism of members was ranked first, accounting for a mean score of 61.29, with respect to group related challenges. Improper maintenance of records on farm expenses (68.63) and price fluctuations (78.7) were ranked first in technical and supply challenges respectively.
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D’Souza, Glen G., Vanessa R. Povolo, Johannes M. Keegstra, Roman Stocker et Martin Ackermann. « Nutrient complexity triggers transitions between solitary and colonial growth in bacterial populations ». ISME Journal 15, no 9 (17 mars 2021) : 2614–26. http://dx.doi.org/10.1038/s41396-021-00953-7.
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AbstractMicrobial populations often experience fluctuations in nutrient complexity in their natural environment such as between high molecular weight polysaccharides and simple monosaccharides. However, it is unclear if cells can adopt growth behaviors that allow individuals to optimally respond to differences in nutrient complexity. Here, we directly control nutrient complexity and use quantitative single-cell analysis to study the growth dynamics of individuals within populations of the aquatic bacterium Caulobacter crescentus. We show that cells form clonal microcolonies when growing on the polysaccharide xylan, which is abundant in nature and degraded using extracellular cell-linked enzymes; and disperse to solitary growth modes when the corresponding monosaccharide xylose becomes available or nutrients are exhausted. We find that the cellular density required to achieve maximal growth rates is four-fold higher on xylan than on xylose, indicating that aggregating is advantageous on polysaccharides. When collectives on xylan are transitioned to xylose, cells start dispersing, indicating that colony formation is no longer beneficial and solitary behaviors might serve to reduce intercellular competition. Our study demonstrates that cells can dynamically tune their behaviors when nutrient complexity fluctuates, elucidates the quantitative advantages of distinct growth behaviors for individual cells and indicates why collective growth modes are prevalent in microbial populations.
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Thongchaichirapha, Natawan. « The Use of a Delphi Survey to Create a Forecasting Model Regarding the Impact of Fluctuations of the Baht on Tourism in Thailand ». International Journal of System Modeling and Simulation 2, no 3 (30 septembre 2017) : 19. http://dx.doi.org/10.24178/ijsms.2017.2.3.19.
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Despite the vast research by inbound and outbound tourists does impact of Thai currency, little is known about the perspective of Thai baht fluctuation, officially that relate to Banks, tourists company and Thailand economics. The overall image that emerges from literature is directly result effects. This study recover the data of semi-structure questionnaire for create a forecasting model through Delphi survey. This survey method will useful to justify the main factors that refer to the objective of this research. To create forecasting model for tourists was based on Thai baht fluctuation demanded on two examine impacts from inbound and outbound tourists. In additional methodology, data collectives is another method that ensure to support research more reliable enough on forecasting model. In seven panelists of participant contributed knowledge and expertise in the subject of government, tourism and financial, For Delphi survey methods were conducted in three round of Delphi survey panel, in each round have different questions depends on previous round result. Which mean, on first round is important to start to vary connected the final round of questions adjust. Even though, the result might have lack of consensus result because the participants had a different ideas to investigate answered questions but look forward on percentage result significantly that for economics change were main factor that impact also contribute to baht fluctuation on tourism in Thailand.
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Qian, Wei-Liang, Kai Lin, Chong Ye, Jin Li, Yu Pan et Rui-Hong Yue. « On Statistical Fluctuations in Collective Flows ». Universe 9, no 2 (27 janvier 2023) : 67. http://dx.doi.org/10.3390/universe9020067.
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In relativistic heavy-ion collisions, event-by-event fluctuations are known to have non-trivial implications. Even though the probability distribution is geometrically isotropic for the initial conditions, the anisotropic εn still differs from zero owing to the statistical fluctuations in the energy profile. On the other hand, the flow harmonics extracted from the hadron spectrum using the multi-particle correlators are inevitably subjected to non-vanishing variance due to the finite number of hadrons emitted in individual events. As one aims to extract information on the fluctuations in the initial conditions via flow harmonics and their fluctuations, finite multiplicity may play a role in interfering with such an effort. In this study, we explore the properties and impacts of such fluctuations in the initial and final states, which both notably appear to be statistical ones originating from the finite number of quanta of the underlying system. We elaborate on the properties of the initial-state eccentricities for the smooth and event-by-event fluctuating initial conditions and their distinct impacts on the resulting flow harmonics. Numerical simulations are performed. The possible implications of the present study are also addressed.
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Klimin, Serghei, Jacques Tempere et Hadrien Kurkjian. « Low-Lying Collective Excitations of Superconductors and Charged Superfluids ». Condensed Matter 8, no 2 (3 mai 2023) : 42. http://dx.doi.org/10.3390/condmat8020042.
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We investigate theoretically the momentum-dependent frequency and damping of low-lying collective excitations of superconductors and charged superfluids in the BCS–BEC crossover regime. The study is based on the Gaussian pair-and-density fluctuation method for the propagator of Gaussian fluctuations of the pair and density fields. Eigenfrequencies and damping rates are determined in a mutually consistent nonperturbative way as complex poles of the fluctuation propagator. Particular attention is paid to new features with respect to preceding theoretical studies, which were devoted to collective excitations of superconductors in the far BCS regime. We find that at a sufficiently strong coupling, new branches of collective excitations appear, which manifest different behavior as functions of the momentum and the temperature.
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Schlickeiser, R., et P. H. Yoon. « Quasilinear theory of general electromagnetic fluctuations including discrete particle effects for magnetized plasmas : General analysis ». Physics of Plasmas 29, no 9 (septembre 2022) : 092105. http://dx.doi.org/10.1063/5.0104709.
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The general quasilinear Fokker–Planck kinetic equation for the gyrophase-averaged plasma particle distribution functions in magnetized plasmas is derived, making no restrictions on the energy of the particles and on the frequency of the electromagnetic fluctuations and avoiding the often made Coulomb approximation of the electromagnetic interactions. The inclusion of discrete particle effects breaks the dichotomy of nonlinear kinetic plasma theory divided into the test particle and the test fluctuation approximation because it provides expression of both the non-collective and collective electromagnetic fluctuation spectra in terms of the plasma particle distribution functions. Within the validity of the quasilinear approach, the resulting full quasilinear transport equation can be regarded as a determining nonlinear equation for the time evolution of the plasma particle distribution functions.
Thèses sur le sujet "Fluctuations collectives"
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Linnér, Erik. « Interplay of collective fluctuations in strongly correlated fermionic systems ». Electronic Thesis or Diss., Institut polytechnique de Paris, 2023. http://www.theses.fr/2023IPPAX090.
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Les systèmes fortement corrélés présentent souvent des diagrammes de phase riches avec différentes phases ordonnées impliquant des degrés de liberté de spin, de charge, d'appariement ou d'orbitale. La description théorique de la compétition entre les différentes instabilités dans les systèmes fortement corrélés, qui donne lieu à cette phénoménologie, reste l'un des Saint-Graal de la théorie moderne de la matière condensée. Elle pose un énorme défi de complexité à la fois conceptuelle et numérique, et l'interaction des fluctuations électroniques concurrentes constitue donc un obstacle à la compréhension des diagrammes de phase complexes d'une large gamme de matériaux quantiques corrélés. Cela motive la recherche de méthodes simplifiées pour étudier l'interaction des fluctuations collectives.Nous présentons une extension multicanal de l'approche du champ fluctuant récemment développée pour les fluctuations collectives concurrentes dans les systèmes électroniques corrélés. La méthode est basée sur une optimisation variationnelle d'une action d'essai qui contient explicitement les paramètres d'ordre des principaux canaux de fluctuation. Elle donne un accès direct à l'énergie libre du système, facilitant la distinction entre les phases stables et métastables du système. Nous appliquons notre approche au modèle de Hubbard étendu, un modèle de fermions sur réseau paradigmatique, qui occupe une place de choix dans la théorie de la matière condensée en raison de la pertinence potentielle de ses versions répulsives et attractives pour les matériaux électroniques et les systèmes artificiels. En utilisant notre technique pour étudier le régime de couplage faible à intermédiaire de l'interaction répulsive, nous constatons qu'elle capture la compétition entre les fluctuations d'onde de densité de charge et des fluctuations antiferromagnétiques en accord qualitatif avec des méthodes numériquement plus coûteuses. En outre, cette méthode permet d'accéder aux propriétés des états excités et aux effets de corrélation à plusieurs corps, directement sur l'axe des fréquences réelles sans utiliser de techniques de continuation analytique numériques. L'approche du champ fluctuant multicanal offre donc une voie prometteuse pour un traitement numériquement peu coûteux de l'interaction entre les fluctuations collectives dans les systèmes de petite et grande taille.En utilisant l'approche introduite du champ fluctuant multicanal, nous explorons le diagramme de phase du modèle de Hubbard étendu dans les régimes répulsif et attractif, en abordant l'interaction des fluctuations dans les canaux antiferromagnétiques, de l'onde de densité de charge, de l'onde s supraconductrice et de la séparation de phases. Bien que ce modèle ait été étudié de manière intensive depuis des décennies, notre nouvelle approche nous permet d'identifier une nouvelle phase caractérisée par la coexistence de fluctuations collectives de l'onde s supraconductrice et de la séparation de phases. Ces résultats sont en accord avec les observations précédentes de phases supraconductrices et de séparation de phases dans les systèmes électroniques, notamment dans les supraconducteurs à haute température critique. En outre, la méthode des champs fluctuants multicanaux permet de mettre en évidence la quintessence du modèle de Hubbard étendu grâce à la grande variété de types de compétitions qui émergent des différentes instabilités. La nature générale de la théorie proposée, qui permet d'incorporer une grande variété de modes collectifs, en fait un outil prometteur pour l'étude de l'interaction des fluctuations collectives dans les systèmes fermioniques fortement corrélésStrongly correlated systems often display rich phase diagrams exhibiting different ordered phases involving spin, charge, pairing, or orbital degrees of freedom. The theoretical description of the competition between different instabilities in strongly correlated systems giving rise to this phenomenology, remains one of the holy grails of modern condensed matter theory. It poses a tremendous challenge of both conceptual and computational complexity, and thus the interplay of competing electronic fluctuations constitutes a roadblock to the understanding of the complex phase diagrams of a wide range of correlated quantum materials. This motivates the search for constructing simplified methods to study interplaying collective fluctuations.We introduce a multichannel extension of the recently developed fluctuating field approach to competing collective fluctuations in correlated electron systems. The method is based on a variational optimization of a trial action that explicitly contains the order parameters of the leading fluctuation channels. It gives direct access to the free energy of the system, facilitating the distinction between stable and metastable phases of the system.We apply our approach to the extended Hubbard model, a paradigmatic fermionic lattice model, occupying a prime place in condensed matter theory due to the potential relevance of its repulsive and attractive versions for both electronic materials and artificial systems.Utilising the technique to study the weak to intermediate coupling regime of the repulsive interaction, we find it to capture the interplay of competing charge density wave and antiferromagnetic fluctuations with qualitative agreement with more computationally expensive methods. In addition, the method allows access to excited-state properties, through the one-particle excitation spectrum, and many-body correlation effects, through the self-energy, directly on the real-frequency axis without using numerical analytic continuation techniques. The multichannel fluctuating field approach thus offers a promising route for a numerically low-cost treatment of the interplay between collective fluctuations in small to large systems.Using the introduced multichannel fluctuating field approach, we explore the phase diagram of the extended Hubbard model in both repulsive and attractive regimes, addressing the interplay of fluctuations in the antiferromagnetic, charge density wave, s-wave superconducting, and phase separation channels. Despite the fact that this model has been intensively studied for decades, our novel approach allows us to identify a novel phase that is characterised by the coexistence of collective s-wave superconducting and phase separation fluctuations. These findings resonate with previous observations of interplaying phase separation and superconducting phases in electronic systems, most importantly in high-temperature superconductors. In addition, the multichannel fluctuating field method allows to display the quintessential nature of the extended Hubbard model through the large variety of types of competitions which emerges from the interplaying instabilities. The general nature of the proposed theory, allowing to incorporate a variety of collective modes, makes it a promising tool for studying the interplay of collective fluctuations in strongly correlated fermionic systems
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COLOMBO, EDUARDO HENRIQUE FILIZZOLA. « COLLECTIVE BEHAVIOR OF LIVING BEINGS UNDER SPATIOTEMPORAL ENVIRONMENT FLUCTUATIONS ». PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2018. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=36051@1.
Texte intégralRésumé :
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
FUNDAÇÃO DE APOIO À PESQUISA DO ESTADO DO RIO DE JANEIRO
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
BOLSA NOTA 10
PROGRAMA DE DOUTORADO SANDUÍCHE NO EXTERIOR
Organismos vivos têm seus próprios meios de locomoção e são capazes de se reproduzir. Além disto, o habitat no qual os organismos estão inseridos é tipicamente heterogêneo, de modo que as condições ambientais variam no tempo e no espaço. Nesta tese, são propostos e investigados modelos teóricos para compreender o comportamento coletivo de organismos vivos, visando responder questões relevantes sobre a organização e preservação da população utilizando técnicas analíticas e numéricas. Inicialmente, considerando um habitat homogêneo, em que as propriedades estatísticas das condições ambientais são independentes do tempo e do espaço, estudamos como padrões espaço-temporais podem emergir na distribuição da população devido a interações não-locais e investigamos o papel das flutuações ambientais neste processo. Em seguida, assumindo um meio ambiente heterogêneo, analisamos o caso de um único domínio de habitat. Considerando uma classe de equações não lineares, introduzindo flutuações temporais e interações entre os organismos, fornecemos uma perspectiva geral da estabilidade de populações neste caso, desafiando os conceitos ecológicos anteriores. Em um segundo passo, assumindo uma paisagem complexa fragmentada, consideramos que os indivíduos têm acesso a informações sobre a estrutura espacial do meio. Mostramos que os indivíduos sobrevivem quando as regiões espaciais viáveis estão suficientemente aglomeradas e observamos que o tamanho da população é maximizado quando os indivíduos utilizam parcialmente a informação do meio ambiente. Finalmente, como resultados exatos analíticos não são factíveis em muitas situações importantes, propomos uma abordagem efetiva para interpretar os dados experimentais. Assim, somos capazes de conectar a heterogeneidade do ambiente e a persistência da população, caracterizada pela distribuição de probabilidade para os tempos de vida.
Living entities have their own means of locomotion and are capable of reproduction. Furthermore, the habitat in which organisms are embedded is typically heterogeneous, such that environment conditions vary in time and space. In this thesis, theoretical models to understand the collective dynamics of living beings have been proposed and investigated aiming to address relevant questions such as population organization and persistence in the environment, using analytical and numerical techniques. Initially, considering an homogeneous habitat, in which the statistical properties of the environmental conditions are time and space independent, we study how spatiotemporal order can emerge in the population distribution due to nonlocal interactions and investigate the role of environment fluctuations in the self-organization process. Further, we continue our investigation assuming an heterogeneous environment, starting with the simplest case of a single habitat domain, and we obtain the critical conditions for population survival for different population dynamics. Considering a class of nonlinear equations, introducing temporal oscillations and interactions among the organisms, we are able to provide a general picture of population stability in a single habitat domain, challenging previous ecological concepts. At last, assuming a fragmented complex landscape, resembling realistic properties observed in nature, we additionally assume that individuals have access to information about the spatial structure. We show that individuals survive when patches of viable regions are clustered enough and, counter-intuitively, observe that population size is maximized when individuals have partial information about the habitat. Finally, since, analytical exact results are not feasible in many important situations, we propose an effective approach to interpret experimental data. This way we are able to connect environment heterogeneity and population persistence.
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Falcon, Claudio. « Quelques effets des fluctuations sur les systèmes collectifs ». Paris 6, 2008. http://www.theses.fr/2008PA066435.
Texte intégral
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Luo, Yu, et 罗郁. « Suppression of collective fluctuations and generation of entanglement in a spin ensemble ». Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B48329794.
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Spin degrees of freedom have been extensively explored in the context of quantum information processing. Many proposals of quantum computation architectures use spins as carriers of quantum of information. A central problem is to efficiently generate quantum entanglement between spin qubits which proves to be a crucial resource for quantum information tasks. On the other hand, uncontrollable spin degrees of freedom in the environment of spin qubits are the major causes of errors at low temperature, for example, the lattice nuclear spins hyperfine coupled to single electron spin qubit localized in semiconductor nano-structures. An outstanding problem for scalable quantum computation is to suppress the collective fluctuations from such spin baths so that the coherence time of the spin qubit can be improved. With these two motivations, the problems of suppressing collective spin fluctuations and generating entanglement in various spin ensembles are addressed in this thesis.
In the first half of the thesis, two approaches are introduced for suppressing the collective fluctuations in the nuclear spin bath so that the quantum coherence time of electron spin qubit in semiconductor quantum dots can be improved. The first approach works for a coupled double dot system. A theory for the interaction with the nuclear spins is developed when the two-electron singlet state is in resonance with one of the triplet state in moderate external magnetic field. At this resonance condition, the nuclear-electron flip-flop process caused by the hyperfine interaction can lead to a feedback mechanism, which can be used to suppress the nuclear hyperfine field. The second approach works for a single dot system. It is shown that strong pumping of the nuclear spins in dynamic nuclear polarization processes can saturate the nuclear spin bath towards the collective “dark states”. In such dark states, the transverse nuclear field fluctuation can be substantially suppressed compared to the value at thermal equilibrium. Two physical schemes are proposed to realize the nuclear dark states for suppression of the nuclear field fluctuations.
In the second half of the thesis, schemes are presented for generating large scale quantum entanglement in two types of spin qubit systems. For atomic spin qubits in optical lattices, schemes are proposed on how to prepare pure spin coherent state (SCS) with low collective spin by incoherent pumping with collective spin raising and lowering operations. Such SCS realize networks of mutually entangled spins which can be idea resources for the quantum telecloning algorithm. For donor nuclear spin qubits in silicon architecture, proposals are shown on how to deterministic prepare Dicke states which constitute an important class of multipartite entangled states. Our scheme is capable of preparing both symmetric and asymmetric Dicke states which form a complete basis set of the spin Hilbert space. The required controls are in situ to the prototype Kane’s quantum computer. The preparation is robust because each desired Dicke state is the steady state under designed pumping process. The schemes presented here also make possible the construction of decoherence free subspaces where quantum information is protected from collective noises.published_or_final_version
Physics
Doctoral
Doctor of Philosophy
5
Moran, José. « Statistical physics and anomalous macroeconomic fluctuations ». Thesis, Paris, EHESS, 2020. http://www.theses.fr/2020EHES0106.
Texte intégralRésumé :
Comment des perturbations à l'échelle de l'individu peuvent-elle devenir des grandes fluctuations à l'échelle de l'économie? Cette question, malgré son étude depuis des décennies, est encore ouverte. Dans cet ouvrage, j'étudie cette énigme à l'aide de méthodes issues de la physique statistique. En partant d'une analyse approfondie des distributions en loi de puissance, je montre qu'une compréhension claire de leur origine et de leurs propriétés permet de mieux appréhender leurs conséquences socioéconomiques. Je propose ensuite un modèle d'économie en réseau, où les entreprises dépendent les unes des autres pour produire, de sorte que la nature même de leurs interactions peut les rendre susceptibles d'amplifier des fluctuations. Ensuite, je soumets au lecteur une étude empirique des propriétés statistiques des taux de croissance et fournis un cadre permettant d'étudier leur dynamique. Dans la partie finale je m'intéresse à des modèles qui exhibent des phénomènes collectifs non-triviaux parce qu'ils considèrent des effets d'imitation ou de mémoire dans les décisions prises par les individus, montrant bien la nécessité de tenir compte de la possible complexité des différentes parties constitutives des modèles économiquesHow do microscopic perturbations at the level of an individual grow to become macroscopic fluctuations of the whole economy? Despite decades of effort, this puzzle remains open. In this work, I tackle this problem using methods and techniques from statistical physics. Beginning with a thorough analysis of power law distributions, I argue that understanding their origin and properties helps in elucidating their socio-economic consequences. I then explore a model of an economy where firms interact through a {\em production network} in a way that causes them to be intrinsically prone to amplify fluctuations. Later on, I conduct an empirical survey of the statistical properties of firm growth rates and provide a framework to study their dynamics. I finally move onto models where non-trivial collective phenomena arise from imitation and memory effects at the level of the individual, highlighting the need of accounting for complexity in economic modelling
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Tsikata, Sedina. « Small-scale electron density fluctuations in the hall thruster, investigated by collective light scattering ». Palaiseau, Ecole polytechnique, 2009. http://tel.archives-ouvertes.fr/docs/00/48/40/27/PDF/thesis.pdf.
Texte intégralRésumé :
Les oscillations dans le plasma d'un propulseur à effet Hall sont susceptibles de provoquer le transport anormal à travers des lignes du champ magnétique. La théorie cinétique linéaire montre qu'en particulier certaines oscillations, de fréquence de l'ordre du mégahertz et de longueur d'onde millimétrique, peuvent jouer un rôle important dans le transport anormal. Les échelles caractéristiques de ces fluctuations ne sont pas détectables par des outils standards comme les sondes. Ce travail décrit pour la première fois l'utilisation d'un diagnostic de diffusion collective (PRAXIS) conçu pour l'étude du plasma du propulseur, qui a mené à l'identification des modes instables dans le plasma. Deux modes hautes fréquences ont été identifiés, se propageant dans les directions azimutale et axiale, avec des longueurs d'onde millimétriques et des fréquences de l'ordre du mégahertz. Les directions de propagation et les ouvertures angulaires de ces modes ont été déterminées. Le mode azimutal, identifié dans la théorie comme agent principal du transport, possède des composantes anti-parallèles au champ magnétique et parallèles au champ électrique et se propage dans une ouverture angulaire très restreinte. Le mode axial montre des caractéristiques liées à la vitesse et la divergence du faisceau d'ions. Le niveau de fluctuation de la densité est associé à une grande amplitude du champ électrique fluctuant. Les résultats des expériences sont en accord avec les prévisions théoriques et apportent de nouvelles informations, permettant ainsi d'améliorer et de développer des modèles pour les deux modesAnomalous electron transport across magnetic field lines in the Hall thruster plasma is believed to be due in part to plasma oscillations. Oscillations of frequencies on the order of a few megahertz and of wavelengths on the order of a millimeter have been shown to be likely to lead to transport. Measurements of fluctuations at these length scales is, however, beyond the reach of conventional thruster diagnostics such as probes. This work describes the first application of a specially-designed collective light scattering diagnostic (PRAXIS) to the measurement of electron density fluctuations and the subsequent identification of unstable modes in the thruster plasma. Two main high frequency modes are identified, propagating azimuthally and axially, of millimetric length scales and megahertz frequencies. The propagation directions and angular openings of the modes are determined. The azimuthallypropagating mode, believed to be responsible for transport, is shown to have wave vector components antiparallel to the magnetic field and parallel to the electric field, and to propagate within an extremely limited region. The axially-propagating mode is shown to have features closely related to the ion beam velocity and divergence. The electron density fluctuation level is calculated and is associated with a high electric field amplitude. The experiments, confirming a number of predictions arising from linear kinetic theory, also provide much additional information permitting the improvement and development of models for both modes
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Mirebrahimi, Seyedmeghdad. « Interacting stochastic systems with individual and collective reinforcement ». Thesis, Poitiers, 2019. http://www.theses.fr/2019POIT2274/document.
Texte intégralRésumé :
L'urne de Polya est l'exemple typique de processus stochastique avec renforcement. La limite presque sûre (p.s.) en temps existe, est aléatoire et non dégénérée. L'urne de Friedman est une généralisation naturelle dont la limite (proportion asymptotique en temps) n'est plus aléatoire. De nombreux modèles aléatoires sont fondés sur des processus de renforcement comme pour la conception d'essais cliniques au design adaptatif, en économie, ou pour des algorithmes stochastiques à des fins d'optimisation ou d'estimation non paramétrique. Dans ce mémoire, inspirés par de nombreux articles récents, nous introduisons une nouvelle famille de systèmes (finis) de processus de renforcement où l'interaction se traduit par un phénomène de renforcement collectif additif, de type champ moyen. Les deux taux de renforcement (l'un spécifique à chaque composante, l'autre collectif et commun à toutes les composantes) sont possiblement différents. Nous prouvons deux types de résultats mathématiques. Différents régimes de paramètres doivent être considérés : type de la règle (brièvement, Polya/Friedman), taux du renforcement. Nous prouvons l'existence d'une limite p.s. coommune à toutes les composantes du système (synchronisation). La nature de la limite (aléatoire/déterministe) est étudiée en fonction du régime de paramètres. Nous étudions également les fluctuations en prouvant des théorèmes centraux de la limite. Les changements d'échelle varient en fonction du régime considéré. Différentes vitesses de convergence sont ainsi établiesThe Polya urn is the paradigmatic example of a reinforced stochastic process. It leads to a random (non degenerated) almost sure (a.s.) time-limit.The Friedman urn is a natural generalization whose a.s. time-limit is not random anymore. Many stochastic models for applications are based on reinforced processes, like urns with their use in adaptive design for clinical trials or economy, stochastic algorithms with their use in non parametric estimation or optimisation. In this work, in the stream of previous recent works, we introduce a new family of (finite) systems of reinforced stochastic processes, interacting through an additional collective reinforcement of mean field type. The two reinforcement rules strengths (one componentwise, one collective) are tuned through (possibly) different rates. In the case the reinforcement rates are like 1/n, these reinforcements are of Polya or Friedman type as in urn contexts and may thus lead to limits which may be random or not. We state two kind of mathematical results. Different parameter regimes needs to be considered: type of reinforcement rule (Polya/Friedman), strength of the reinforcement. We study the time-asymptotics and prove that a.s. convergence always holds. Moreover all the components share the same time-limit (synchronization). The nature of the limit (random/deterministic) according to the parameters' regime is considered. We then study fluctuations by proving central limit theorems. Scaling coefficients vary according to the regime considered. This gives insights into the different rates of convergence
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Tovazzi, Daniele. « Self-sustained periodic behaviors in interacting systems : macroscopic limits and fluctuations ». Doctoral thesis, Università degli studi di Padova, 2018. http://hdl.handle.net/11577/3425244.
Texte intégralRésumé :
In this thesis we study the appearance of self-sustained periodic behavior in the macroscopic dynamics of some interacting systems and related critical phenomena. The thesis is organized as follows. In Chapter 1 we focus on the emergence of periodicity in cooperative mean field models whose interaction potential undergoes a dissipative evolution. We define a generalized Curie-Weiss model with dissipation and we analyse its macroscopic dynamics: we show that not only a periodic behavior is present at sufficiently low temperature, but also that, in certain regimes, any (finite) number of stable limit cycles can coexist. Chapter 2 is concerned with a two-population Curie-Weiss model: we define two types of microscopic dynamics, one with delay and the other without. We identify configurations of the interaction network which can enhance macroscopic oscillations in the case without delay; we also show that delay allows the appearance of a collective periodic behavior in configurations in which periodicity was otherwise absent. In Chapter 3 we consider again the mechanism of dissipation, this time dropping the mean field hypothesis. We study a short-range interacting system obtained introducing dissipation in a 1-dimensional Ising model. We prove that, in a suitable zero-temperature infinite-volume limit, the total magnetization of the system displays regular oscillations between polarized phases. Finally, Chapter 4 is dedicated to the analysis of critical fluctuations for systems exhibiting a Hopf bifurcation in the dynamics of the macroscopic law. The behavior of critical fluctuations around the macroscopic limit reflects the type of bifurcation and the observables display fluctuations evolving at different time scales. We identify the slow and the fast variable and we obtain the convergence of the slow variable to its limiting dynamics via an averaging principle.In questa tesi studiamo comportamenti periodici auto-sostenuti che appaiono nella dinamica macroscopica di certi sistemi interagenti e alcuni fenomeni critici collegati a questo comportamento. La tesi è organizzata come segue. Nel primo capitolo ci concentriamo sulla comparsa di periodicità in modelli cooperativi a campo medio il cui potenziale di interazione è soggetto a una dissipazione. Definiamo un modello di Curie-Weiss generalizzato con dissipazione ed analizziamo la sua dinamica limite: mostriamo che non solo il comportamento periodico è presente a temperature sufficientemente basse, ma anche che, in certi regimi, diversi cicli limite stabili possono coesistere, purché in numero finito. Nel secondo capitolo ci occupiamo di un modello di Curie-Weiss bipopolato: definiamo due tipi di dinamiche microscopiche, una con ritardo e l'altra senza. Identifichiamo le configurazioni della rete di interazione che possono dare luogo ad oscillazioni macroscopiche nel caso senza ritardo; mostriamo inoltre che il ritardo permette la comparsa di periodicità in configurazioni nelle quali sarebbe altrimenti assente. Nel terzo capitolo consideriamo nuovamente il meccanismo della dissipazione, questa volta lasciando cadere l'ipotesi di interazione a campo medio. Studiamo un sistema di particelle con interazione a corto raggio ottenuto introducendo la dissipazione in un modello di Ising 1-dimensionale. Mostriamo che, in un opportuno limite di temperatura zero e volume infinito, la magnetizzazione totale del sistema presenta oscillazioni regolari tra fasi polarizzate. Infine, il quarto capitolo è dedicato all'analisi delle fluttuazioni critiche di sistemi che esibiscono una biforcazione di Hopf nella dinamica della legge macroscopica. Il comportamento delle fluttuazioni critiche attorno al limite macroscopico riflette il tipo di biforcazione e gli osservabili mostrano fluttuazioni che evolvono su scale temporali differenti. Identifichiamo la variable lenta e quella veloce ed otteniamo la convergenza della variabile lenta alla sua dinamica limite tramite un averaging principle.
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Bonamy, Daniel. « Phénomènes collectifs dans les matériaux granulaires : écoulements de surface et réarrangements internes dans des empilements modèles ». Paris 11, 2001. https://tel.archives-ouvertes.fr/tel-00003916.
Texte intégralRésumé :
Les matériaux granulaires possèdent des propriétés rhéologiques et mécaniques peu communes. Ils peuvent en effet s'écouler comme des liquides mais, sous certaines conditions, se bloquer et résister à des contraintes extérieures sans se déformer. Dans ce mémoire, nous étudions cette dualité solide/liquide à travers deux expériences permettant de faire le lien entre le comportement individuel des grains et celui de l'empilement. Tout d'abord on considère les écoulements à la surface d'un empilement incliné. Nous dérivons tout d'abord une description continue de leur dynamique à partir des équations de conservation intégrées sur l'épaisseur (approche de Saint-Venant) en étudiant les écoulements stationnaires dans un tambour tournant. Nous nous intéressons ensuite à la rhéologie du matériau et analysons les corrélations spatiales du champ de vitesse et les fluctuations de compacité. Nous montrons l'existence d'une forte concentration d'agrégats de grains trop denses pour pouvoir se déformer. Leur taille est distribuée en loi de puissance, sans échelle caractéristique. Nous discutons les implications de ces observations sur les approches théoriques proposées pour décrire les écoulements denses. La deuxième partie porte sur les réarrangements internes engendrés par une petite sollicitation extérieure dans un empilement apparemment statique. Une petite dilatation thermique engendre des fluctuations de conductance géantes dans un empilement de grains conducteurs. L'analyse statistique de ces fluctuations nous permet de relier cette sensibilité électrique à des fluctuations tribologiques locales et non à des réorganisations collectives du réseau des contacts comme cela a pu être suggéré par le passé. Nous visualisons dans un deuxième temps les micro-déplacements des grains engendrés par l'ajout d'une petite surcharge en surface. Cela nous permet de discuter la validité des différents modèles décrivant la répartition des contraintes dans un empilement statiqueGranular media exhibit non-intuitive rheological and mechanical properties. They can flow as liquids but, under specific conditions, they can jam and resist to external stress without being sheared. In this thesis, the solid/liquid duality is investigated through two experiments whose main features are to allow to study the relationships between the individual behavior of beads and the one of the packing. In the first part, we consider the surface flows in an inclined packing. A continuous description based on depth averaged conservation equations (Saint-Venant approach) is first derived from the study of steady surface flows in a rotating drum. We then focus on the internal rheology of these flows and investigate the spatial correlation of the instantaneous velocity field and the fluctuations of the volume fraction. We demonstrate the existence of rigid clusters of grains embedded in the flows. Their size is power-law distributed from the grain size scale up to the thickness of the flowing layer. The implications of the absence of a characteristic length scale on available theoretical models of dense granular flows are discussed. The second part of the thesis deals with internal rearrangements in a packing submitted to a small perturbation. A small thermal dilation leads to giant electrical fluctuations in a pile of metallic beads. The statistical analysis of these fluctuations allows us to relate this electrical sensitivity to local tribological fluctuations rather than collective reorganizations of the contacts network as proposed in the past. We then visualize the grains micro-displacements entailed by adding a small overload to the surface. This experiment allows us to discuss the validity of the different approaches proposed to describe stress distribution in static packing
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Tsikata, Sedina. « Fluctuations de densité électronique à petite échelle dans un propulseur à effet Hall, investigué par la méthode de diffusion collective ». Phd thesis, Ecole Polytechnique X, 2009. http://tel.archives-ouvertes.fr/tel-00484027.
Texte intégralRésumé :
Les oscillations dans le plasma d'un propulseur à effet Hall sont susceptibles de provoquer le transport anormal à travers des lignes du champ magnétique. La théorie cinétique linéaire montre qu'en particulier certaines oscillations, de fréquence de l'ordre du mégahertz et de longueur d'onde millimétrique, peuvent jouer un rôle important dans le transport anormal. Les échelles caractéristiques de ces fluctuations ne sont pas détectables par des outils standards comme les sondes. Ce travail décrit pour la première fois l'utilisation d'un diagnostic de diffusion collective (PRAXIS) conçu pour l'étude du plasma du propulseur, qui a mené à l'identification des modes instables dans le plasma. Deux modes hautes fréquences ont été identifiés, se propageant dans les directions azimutale et axiale, avec des longueurs d'onde millimétriques et des fréquences de l'ordre du mégahertz. Les directions de propagation et les ouvertures angulaires de ces modes ont été déterminées. Le mode azimutal, identifié dans la théorie comme agent principal du transport, possède des composantes anti-parallèles au champ magnétique et parallèles au champ électrique et se propage dans une ouverture angulaire très restreinte. Le mode axial montre des caractéristiques liées à la vitesse et la divergence du faisceau d'ions. Le niveau de fluctuation de la densité est associé à une grande amplitude du champ électrique fluctuant. Les résultats des expériences sont en accord avec les prévisions théoriques et apportent de nouvelles informations, permettant ainsi d'améliorer et de développer des modèles pour les deux modes.
Livres sur le sujet "Fluctuations collectives"
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Nishiguchi, Daiki. Order and Fluctuations in Collective Dynamics of Swimming Bacteria. Singapore : Springer Singapore, 2020. http://dx.doi.org/10.1007/978-981-32-9998-6.
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Eric, Smith. Symmetry and Collective Fluctuations in Evolutionary Games. IOP Publishing, 2015.
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Nishiguchi, Daiki. Order and Fluctuations in Collective Dynamics of Swimming Bacteria : Experimental Exploration of Active Matter Physics. Springer, 2020.
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Nishiguchi, Daiki. Order and Fluctuations in Collective Dynamics of Swimming Bacteria : Experimental Exploration of Active Matter Physics. Springer Singapore Pte. Limited, 2021.
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Nishiguchi, Daiki. Order and Fluctuations in Collective Dynamics of Swimming Bacteria : Experimental Exploration of Active Matter Physics. Springer, 2020.
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Pelkmans, Mathijs. Conclusion. Cornell University Press, 2017. http://dx.doi.org/10.7591/cornell/9781501705137.003.0008.
Texte intégralRésumé :
This book has studied the relationship between sociopolitical instability and conviction by focusing on how secular and religious collective ideas fared in conditions of existential uncertainty in Kokjangak. It has also examined the precarious attempts of “secularists” to position themselves between fading Soviet atheism and assertions of new forms of religiosity and how spiritual practitioners who were sometimes labeled “shamans” operated in unpredictable spiritual fields. This conclusion considers the pulsation and dynamics of conviction and introduces a conceptual framework to show how collective ideas gain and lose force. The term “pulsation” emphasizes impermanence and fluctuation as key characteristics of ideational power. Three aspects of pulsation are discussed involving hope, tension, and effervescence: voicing, responding, and reverberating, respectively.
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Sutton, Adrian P. Concepts of Materials Science. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780192846839.001.0001.
Texte intégralRésumé :
This short book describes ten fundamental concepts – big ideas – of materials science. Some of them come from mainstream physics and chemistry, including thermodynamic stability and phase diagrams, symmetry, and quantum behaviour. Others are about restless atomic motion and thermal fluctuations, defects in crystalline materials as the agents of change in materials, nanoscience and nanotechnology, materials design and materials discovery, metamaterials, and biological matter as a material. A cornerstone of materials science is the idea that materials are complex systems that interact with their environments and display the emergence of new science from the collective behaviour of atoms and defects. Great attention is paid to the clarity of explanations using only high school algebra and quoting the occasional useful formula. Exceptionally, elementary calculus is used in the chapter on metamaterials. It is not a text-book, but it offers undergraduates and their teachers a unique overview and insight into materials science. It may also help graduates of other subjects to decide whether to study materials science at postgraduate level.
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Pelkmans, Mathijs. Introduction. Cornell University Press, 2017. http://dx.doi.org/10.7591/cornell/9781501705137.003.0001.
Texte intégralRésumé :
This book examines ideational power by focusing on the energy and momentum that are built into “flashes of conviction.” The discussion centers on the affective dimension of collective ideas and on how ideology comes to matter in the lives of people. Using the concept of conviction, the book analyzes the fluctuating intensity and quality of attitudes, motivations, and beliefs. It looks at different examples of conviction with particular emphasis on the impulses and resonances generated by assertions of truth. These topics are explored in the context of post-Soviet Kyrgyzstan, and particularly in the mining town of Kokjangak, at a time of economic collapse and political turmoil. This introduction explains how the concepts of conviction and ideology are employed in order to lay the foundations for the conceptual framework developed in this book.
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Hartrich, Eliza. Politics and the Urban Sector in Fifteenth-Century England, 1413-1471. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780198844426.001.0001.
Texte intégralRésumé :
Since the work of K.B. McFarlane in the mid-twentieth century, political histories of late medieval England have focused almost exclusively on the relationship between the Crown and aristocratic landholders. Such studies, however, neglect to consider that England after the Black Death was an urbanizing society. Towns not only were the residence of a rising proportion of the population, but were also the stages on which power was asserted and the places where financial and military resources were concentrated. Outside London, however, most English towns were small compared to those found in medieval Italy or Flanders, and it has been easy for historians to under-estimate their ability to influence English politics. Politics and the Urban Sector in Fifteenth-Century England, 1413–1471 offers a new approach for evaluating the role of urban society inthe political culture of late medieval England. Rather than focusing on English towns individually, it creates a model for assessing the political might that could be exerted by towns collectively as an ‘urban sector’. Based on primary sources from twenty-two towns (ranging from metropolis of London to the tiny Kentish town of Lydd), Politics and the Urban Sector demonstrates how fluctuations in inter-urban relationships affected the content, pace, and language of English politics during the tumultuous fifteenth century. Chapter 1 identifies the different types of links that towns formed with one another and with other members of political society. Chapters 2–5 are arranged chronologically, demonstrating the ways in which the frequent twists and turns of fifteenth-century ‘high politics’—from the reign of Henry V to the Wars of the Roses—were a reflection of the ever-shifting relationships between towns.
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Warren, Diane, et Laura Peters, dir. Rereading Orphanhood. Edinburgh University Press, 2020. http://dx.doi.org/10.3366/edinburgh/9781474464369.001.0001.
Texte intégralRésumé :
Building on the legacy of Laura Peters’ landmark work, Orphan Texts (2000), and extending its analyses to new work in family, marriage and kinship studies, Rereading Orphanhood: Texts Inheritance, Kin explores the ways in which the figure of the literary orphan can be used to illuminate our understanding of the long nineteenth century, especially in relation to family and kinship. Contributors to this highly cohesive collection examine the shifting status of orphanhood as a cultural construction and show how much those fluctuating definitions reveal about the cultural preoccupations and anxieties of their day. Correspondingly, the sense that the orphan condition inflects the individual character’s thought processes and actions, throughout their lives, is also a recurrent trope in these chapters. Some contributors also emphasise the enduring influence of nineteenth-century conceptualisations of orphanhood and kinship, seen in, but not limited to, work on the posthuman and neo-Victorian texts. Read collectively, the chapters explore how orphan characters (both child and adult) contribute to discourses of gender, home, family, law, inheritance, class, illegitimacy, charity, notions of the human and the development of the novel, across a wide range of canonical and non-canonical texts. As Talia Schaffer notes: ‘This collection is theoretically astute and usefully varied, and will reward anyone interested in family dynamics in the literature of the nineteenth century’.
Chapitres de livres sur le sujet "Fluctuations collectives"
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Huberman, Bernardo A. « Fluctuating Benefits and Collective Action ». Dans Advances in Computational Economics, 237–47. Boston, MA : Springer US, 1997. http://dx.doi.org/10.1007/978-1-4757-2644-2_16.
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Leibler, S. « Collective Phenomena in Mitosis : A Physicist’s Perspective ». Dans Physics of Biomaterials : Fluctuations, Selfassembly and Evolution, 135–51. Dordrecht : Springer Netherlands, 1996. http://dx.doi.org/10.1007/978-94-009-1722-4_5.
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Plerou, V., P. Gopikrishnan, B. Rosenow, L. A. N. Amaral et H. E. Stanley. « A Random Matrix Theory Approach to Quantifying Collective Behavior of Stock Price Fluctuations ». Dans Empirical Science of Financial Fluctuations, 35–40. Tokyo : Springer Japan, 2002. http://dx.doi.org/10.1007/978-4-431-66993-7_5.
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Ohmine, I., et H. Tanaka. « Dynamics of Liquid Water : Fluctuations and Collective Motions ». Dans Molecular Dynamics Simulations, 130–38. Berlin, Heidelberg : Springer Berlin Heidelberg, 1992. http://dx.doi.org/10.1007/978-3-642-84713-4_11.
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Altonji, Joseph G., et John C. Ham. « The Collective Impact of Sectoral Shocks on Aggregate Employment Fluctuations ». Dans Labor Market Adjustments in the Pacific Basin, 161–201. Dordrecht : Springer Netherlands, 1987. http://dx.doi.org/10.1007/978-94-009-3251-7_8.
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Behera, S. N., et S. G. Mishra. « Collective Modes of the Superconducting State in Coexistence with Other Ordered States ». Dans Theoretical and Experimental Aspects of Valence Fluctuations and Heavy Fermions, 565–68. Boston, MA : Springer US, 1987. http://dx.doi.org/10.1007/978-1-4613-0947-5_91.
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Webman, Esther. « The Evolution of a Founding Myth : The Nakba and Its Fluctuating Meaning ». Dans Palestinian Collective Memory and National Identity, 27–45. New York : Palgrave Macmillan US, 2009. http://dx.doi.org/10.1057/9780230621633_2.
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Tsytovich, Vadim N. « Non-linear Interactions of Collective Oscillations and Waves with Particle Fluctuations ». Dans Lectures on Non-linear Plasma Kinetics, 307–20. Berlin, Heidelberg : Springer Berlin Heidelberg, 1995. http://dx.doi.org/10.1007/978-3-642-78902-1_12.
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Simonova, Olga A. « Can Nostalgia Be Dangerous ? Post-Soviet Nostalgia as Retrotopia : The Emotional Dynamic and Fluctuations of the Social Order ». Dans Collective Memory Narratives in Contemporary Culture, 55–70. Cham : Springer Nature Switzerland, 2023. http://dx.doi.org/10.1007/978-3-031-41921-8_4.
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Stohrer, J., G. Gröbner, C. Mayer, K. Weisz et G. Kothe. « Collective Order Fluctuations in Liquid Crystals Studied by Transverse Nuclear Spin Relaxation ». Dans 25th Congress Ampere on Magnetic Resonance and Related Phenomena, 323–24. Berlin, Heidelberg : Springer Berlin Heidelberg, 1990. http://dx.doi.org/10.1007/978-3-642-76072-3_167.
Texte intégralActes de conférences sur le sujet "Fluctuations collectives"
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Parrondo, Juan M. R. « Control and Rectification in Collective Stochastic Systems ». Dans NOISE AND FLUCTUATIONS : 18th International Conference on Noise and Fluctuations - ICNF 2005. AIP, 2005. http://dx.doi.org/10.1063/1.2036688.
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Takayasu, Misako. « Critical fluctuations observed in collective human behaviors ». Dans 2011 21st International Conference on Noise and Fluctuations (ICNF). IEEE, 2011. http://dx.doi.org/10.1109/icnf.2011.5994340.
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Kurin, Vladislav V., et Igor V. Pimenov. « Quantum Description of Collective Excitations and Fluctuations in Layered High Temperature Superconductors ». Dans NOISE AND FLUCTUATIONS : 19th International Conference on Noise and Fluctuations ; ICNF 2007. AIP, 2007. http://dx.doi.org/10.1063/1.2759675.
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Clemens, James P., Levente Horvath, Barry C. Sanders et Howard J. Carmichael. « Collective spontaneous emission from small assemblies of atoms ». Dans SPIE's First International Symposium on Fluctuations and Noise, sous la direction de Derek Abbott, Jeffrey H. Shapiro et Yoshihisa Yamamoto. SPIE, 2003. http://dx.doi.org/10.1117/12.490148.
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Matsuo, M. « Correlation and fluctuation measures for damped collective motion ». Dans NONEQUILIBRIUM AND NONLINEAR DYNAMICS IN NUCLEAR AND OTHER FINITE SYSTEMS:International Conference. AIP, 2001. http://dx.doi.org/10.1063/1.1427472.
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Ordemann, Anke, Gabor Balazsi, Elizabeth Caspari et Frank Moss. « Daphnia swarms : from single agent dynamics to collective vortex formation ». Dans SPIE's First International Symposium on Fluctuations and Noise, sous la direction de Sergey M. Bezrukov, Hans Frauenfelder et Frank Moss. SPIE, 2003. http://dx.doi.org/10.1117/12.489033.
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Junker, W., M. Saffman et L. Lading. « Spatially resolved measurements of density fluctuations with a hybrid Doppler/time-of-flight laser anemometer ». Dans The European Conference on Lasers and Electro-Optics. Washington, D.C. : Optica Publishing Group, 1996. http://dx.doi.org/10.1364/cleo_europe.1996.cwb3.
Texte intégralRésumé :
Collective light scattering from density fluctuations is an established approach to optica! velocimetry that is applicable in flows without light scattering particles. It has traditionally been applied to plasma diagnostics [1], while recent interest has considered the use of collective scattering for velocimetry of high speed flows[2,3], where particles are either difficult to introduce, or do not accurately reflect the flow statistics. A generic limitation of this method is that the poor axial resolution results in measurements that are spatially averaged. We have introduced recently a hybrid Doppler/time-of-flight configuration [4], that provides improved axial resolution.
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Dzogang, Fabon, Thomas Lansdall-Welfare et Nello Cristianini. « Seasonal Fluctuations in Collective Mood Revealed by Wikipedia Searches and Twitter Posts ». Dans 2016 IEEE 16th International Conference on Data Mining Workshops (ICDMW). IEEE, 2016. http://dx.doi.org/10.1109/icdmw.2016.0136.
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Mushtaq, Noraiz, et Paolo Gaetani. « The Effect of Upstream Unsteadiness on the Unstarting of a Supersonic Inlet Turbine ». Dans ASME Turbo Expo 2023 : Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/gt2023-103883.
Texte intégralRésumé :
Abstract A 15% increase in thermal efficiency at medium pressure ratios is promised by rotating detonation engine technology over conventional Joule-Bryton cycles. A supersonic inlet turbine is a viable option to extract substantial work from the highly fluctuating and supersonic flow delivered by the detonating combustor. However, an additional unstarting mechanism based on the generation of a collective shock from the coalescence of leading-edge bow-shock waves further restricts the available design space. Firstly, the effect of unsteady inlet conditions with variable frequency, amplitude, and mean value on collective shock generation is investigated. Then, a fast and cost-effective tool was developed and verified to predict bow shock wave motion from a prescribed inlet Mach trend; the parameters of the transfer function were estimated with a classical identification method based on a step-response CFD simulation. The model was employed to rapidly calculate the maximum amplitude of fluctuations accepted by the supersonic blade row for each frequency and average inlet Mach number. Finally, the influence of the inlet geometric angle, pitch to leading-edge thickness ratio, and static temperature on the model parameters is studied. The preliminary observations of the parametric analysis were confirmed by the rigorous quantitative approach of a global sensitivity analysis based on Sobol sensitivity indices.
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Koutin, S. V., et A. N. Lebedev. « Density effects on quantum fluctuation of radiation in synchrotrons ». Dans The sixteenth advanced international committee on future accelerators beam dynamics workshop on nonlinear and collective phenomena in beam physics. AIP, 1999. http://dx.doi.org/10.1063/1.58419.
Texte intégralRapports d'organisations sur le sujet "Fluctuations collectives"
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Smith, D. R., E. Mazzucato, W. Lee, H. K. Park, C. W. Domier et Luhmann, Jr., N. C. A Collective Scattering System for Measuring Electron Gyroscale Fluctuations on the National Spherical Torus Experiment. Office of Scientific and Technical Information (OSTI), février 2009. http://dx.doi.org/10.2172/950697.
Texte intégral
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Torero, Máximo, et Jaime Saavedra-Chanduví. Union Density Changes and Union Effects on Firm Performance in Peru. Inter-American Development Bank, septembre 2002. http://dx.doi.org/10.18235/0011249.
Texte intégralRésumé :
The paper documents the sharp reduction in union density in Peru between 1986 and 1998, in a context of large macroeconomic fluctuations, structural reforms and changes in the Collective Bargaining Law in 1993. The authors find that a blue-collar job, a permanent contract, higher education and working in a large firm increase the likelihood of unionization, but only before the legislative change. Using a panel of firms for the manufacturing sector for the period 1994-1996, a negative impact of unions on profits for all firm sizes is found. In the econometric analysis, a significant negative effect even after controlling for firm and sector characteristics and firm fixed effects is found. There is some evidence that this effect diminishes over time, consistent with the reduction in union density during that period, but the reduction is not robust to different specifications.
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Turmena, Lucas, Flávia Guerra, Altiere Freitas, Alejandra Ramos-Galvez, Simone Sandholz, Michael Roll, Isadora Freire et Millena Oliveira. TUC Urban Lab Profile : Alliance for the Centre of Recife, Brazil. United Nations University - Institute for Environment and Human Security (UNU-EHS), mars 2024. http://dx.doi.org/10.53324/hcyv7857.
Texte intégralRésumé :
After almost two years in operation, the challenges and key achievements of the TUC Urban Lab established in Comunidade do Pilar in Recife, Brazil, provide valuable lessons for sustaining ongoing activities, accelerating broader transformations and guiding similar efforts elsewhere: 1. DEVELOPING A PLACE-BASED APPROACH AND BUILDING MUTUAL TRUST: Meaningful participation is contingent upon establishing and maintaining trust between UL facilitators and participants. In the case of Comunidade do Pilar, overcoming initial distrust and skepticism required tailoring UL activities to residents’ needs and linking those to climate action, while increasing presence in the territory and creating safe spaces for equal participation. The strengthening of a place-based approach has been a key contributor to the UL’s achievements. 2. NAVIGATING PARTICIPATION IN REALITY: Participation is often less smooth than planned. Facilitators must consider fluctuations in the frequency and manner of participation and develop strategies to adapt the UL process accordingly. Open dialogues and clear communication are essential. The UL is not a static organization but a flexible arrangement with the potential to bridge diverse interests and aspirations, linking local needs with the climate change agenda. 3. IMPLEMENTING STRATEGIES TO WIDEN THE IMPACT: The UL in Comunidade do Pilar strives to foster long-term outcomes through small-scale experiments. Incremental changes nurture individual and collective capacities, laying the foundation for broader and deeper transformations. However, scaling up learnings depends on institutionalizing changes and garnering support from decision-makers, which can be challenging.
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Roll, Michael, Marisol Romero Magallán, Andrea Ramírez, Flávia Guerra, Alejandra Ramos-Galvez, Simone Sandholz, Mariana Campos-Sánchez, Gorka Zubicaray, Óscar Jair Villasís-Escobedo et Ana Iris Enríquez-Alcaraz. TUC Urban Lab Profile : Naucalpan, Mexico. United Nations University - Institute for Environment and Human Security (UNU-EHS), mars 2024. http://dx.doi.org/10.53324/tmew2903.
Texte intégralRésumé :
After almost two years in operation, the challenges and key achievements of the TUC Urban Lab established in Naucalpan, Mexico, provide valuable lessons for sustaining ongoing activities, accelerating broader transformations and guiding similar efforts elsewhere: 1. RECOGNIZING THE CHALLENGES AND BENEFITS OF UL MEMBERSHIP FLUCTUATION: If a core group of UL members exists, changes in UL membership are to be expected and are often beneficial. Such change can already be planned for as soon as the UL enters a new phase, for example when moving from planning to implementation of concrete action. UL facilitators should support the integration of new members to maximize the benefit of their new perspectives and contributions for ongoing UL work. 2. ADDRESSING LIMITED REPRESENTATION OF RESIDENTS AND THE PRIVATE SECTOR: Participation processes need a sound methodology and creative thinking. Even with the best of intentions and adequate facilitation, certain groups or sectors are particularly difficult to involve in the ULs. This may be because some UL members have doubts and see potential risks associated with the participation of others, or because the other actors see no benefits or are just not interested. Going forward, the UL Naucalpan will consider alternative, innovative and locally specific approaches and formats to encourage participation and meaningful engagement by these stakeholders. 3. BUILDING ON DIVERSE PERSPECTIVES TO FOSTER NEW NETWORKS AND MUTUAL TRUST: By providing a setting for the exchange and constructive discussion of diverse perspectives, knowledge, interests and opinions, the UL approach fosters the emergence of new networks as well as mutual trust and cohesion. This is particularly evident between civil society and government in an otherwise ‘low-trust in government’ environment and provides a strong basis for collective climate action. 4. NAVIGATING THE PARTICIPATION OF AND THE DEPENDENCE ON GOVERNMENT AUTHORITIES: While strong government authorities’ participation and support are critical for ULs, being too dependent on them is a risk for UL neutrality, for constructive discussions and for its potential transformative impact. As an opportunity for UL operation, sustainability and the scaling of experimental projects, government participation and support therefore must be carefully balanced with that of other sectors.