Relevant bibliographies by topics / Collective fluctuations

Academic literature on the topic 'Collective fluctuations'

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Published: 4 May 2024

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Journal articles on the topic "Collective fluctuations"

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Qian, Wei-Liang, Kai Lin, Chong Ye, Jin Li, Yu Pan, and Rui-Hong Yue. "On Statistical Fluctuations in Collective Flows." Universe 9, no. 2 (January 27, 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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Mendels, Dan, GiovanniMaria Piccini, and Michele Parrinello. "Collective Variables from Local Fluctuations." Journal of Physical Chemistry Letters 9, no. 11 (May 7, 2018): 2776–81. http://dx.doi.org/10.1021/acs.jpclett.8b00733.

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Benhassine, B., M. Farine, E. S. Hernandez, D. Idier, B. Remaud, and F. Sebille. "Phase space fluctuations and dynamics of fluctuations of collective variables." Nuclear Physics A 545, no. 1-2 (August 1992): 81–86. http://dx.doi.org/10.1016/0375-9474(92)90448-s.

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Klimin, Serghei, Jacques Tempere, and Hadrien Kurkjian. "Low-Lying Collective Excitations of Superconductors and Charged Superfluids." Condensed Matter 8, no. 2 (May 3, 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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Masuda, Naoki, Yoji Kawamura, and Hiroshi Kori. "Collective fluctuations in networks of noisy components." New Journal of Physics 12, no. 9 (September 6, 2010): 093007. http://dx.doi.org/10.1088/1367-2630/12/9/093007.

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Perarnau-Llobet, Martí, and Raam Uzdin. "Collective operations can extremely reduce work fluctuations." New Journal of Physics 21, no. 8 (August 12, 2019): 083023. http://dx.doi.org/10.1088/1367-2630/ab36a9.

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König, Jürgen, John Schliemann, T. Jungwirth, and A. H. MacDonald. "Collective spin fluctuations in diluted magnetic semiconductors." Physica E: Low-dimensional Systems and Nanostructures 12, no. 1-4 (January 2002): 379–82. http://dx.doi.org/10.1016/s1386-9477(01)00308-3.

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Wan, Yi, and Richard M. Stratt. "Collective fluctuations of conserved variables in liquids." Journal of Chemical Physics 98, no. 4 (February 15, 1993): 3224–39. http://dx.doi.org/10.1063/1.464095.

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Pfitzner, A., L. M�nchow, and P. M�dler. "One-body dynamics modified by collective fluctuations." Zeitschrift f�r Physik A Atomic Nuclei 331, no. 1 (March 1988): 43–51. http://dx.doi.org/10.1007/bf01289429.

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Tsytovich, V. N., R. Bingham, U. de Angelis, and A. Forlani. "Collective effects in bremsstrahlung in plasmas." Journal of Plasma Physics 56, no. 1 (August 1996): 127–47. http://dx.doi.org/10.1017/s0022377800019140.

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The results of recent developments in the theory of fluctuations in plasmas show that the previously used theory of bremsstrahlung is incomplete and the exact expressions for bremsstrahlung should include transition bremsstrahlung. The collective effects in bremsstrahlung known previously as Debye screening are changed to a qualitatively different structure, which removes the effect of ion polarization in bremsstrahlung and introduces a new effective polarization which depends on an effective ion charge and electron velocity. The results may be relevant for applications in plasmas when the wavelength is greater than the Debye length. It is shown that for the problem of photon transport in the solar interior the correct collective corrections to the bremsstrahlung change the opacity by only about −0·35%, which is less than was calculated previously when collective effects in bremsstrahlung where estimated without taking recent results of plasma fluctuation theory into account.
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Dissertations / Theses on the topic "Collective fluctuations"

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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.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
COORDENAÇÃO 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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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 corrélés
Strongly 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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Luo, Yu, and 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.
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Physics
Doctoral
Doctor of Philosophy
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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.

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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
Anomalous 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.

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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 établies
The 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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Moran, José. "Statistical physics and anomalous macroeconomic fluctuations." Thesis, Paris, EHESS, 2020. http://www.theses.fr/2020EHES0106.

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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 économiques
How 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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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.

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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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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.

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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.
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Cavalier, Jordan. "Modèles cinétiques et caractérisation expérimentale des fluctuations électrostatiques dans un propulseur à effet Hall." Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0130/document.

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L'étude des phénomènes turbulents se développant en sortie du propulseur de Hall est nécessaire pour pouvoir modéliser le transport anormal (par opposition au transport diffusif) des électrons à travers les lignes de champ magnétique. Les relations de dispersion de deux instabilités pouvant être responsables de ce transport ont été mesurées à des échelles millimétriques à l'aide du diagnostic de diffusion collective de la lumière. Ce travail de thèse s'attache à en donner une description aussi bien théorique qu'expérimentale, pierre à l'édifice de la compréhension du transport dans le propulseur. Une instabilité se propageant majoritairement dans la direction azimutale du propulseur y est caractérisée comme étant l'instabilité de dérive électronique ExB et un modèle analytique décrivant la fréquence expérimentale y est dérivé et validé. De plus, le manuscrit présente une méthode de déconvolution du signal de la diffusion collective de la fonction d'appareil pour ce mode. Une fois déconvoluées, les relations de dispersion expérimentales peuvent être ajustées par la fréquence du modèle analytique, ce qui permet de mesurer expérimentalement et de manière originale la température et la densité électronique dans le jet d'ions énergétiques du plasma du propulseur. Enfin, la seconde instabilité, se développant autour de la direction axiale du propulseur, est caractérisée comme l'instabilité double faisceau entre les ions simplement et doublement chargés du plasma
The study of turbulent phenomena that grow at the exit plane of the Hall thruster is required to modelize the anomalous transport (in contrast to the diffusion transport) of electrons across the magnetic field lines. The dispersion relations of two instabilities that can be responsible for this transport have been mesured at millimetric scales by mean of the collective light scattering diagnostic. The aim of the thesis is to describe them theoretically as well as experimentally, improving the understanding of the Hall thruster transport. In the thesis, an instability that propagates principally azimuthally is caracterized as the ExB electron drift instability and an analytical model that describes the experimental frequency is derived and validated. In addition, the manuscript presents an original method to unfold the signal of the collective scattering diagnostic from the instrumental function of this mode. Once corrected, the experimental dispersion relations can be adjusted by the frequency given by the analytical model, allowing to measure experimentally and in an original way the electron temperature and density in the energetic ion jet of the Hall thruster plasma. The second instability that is mainly propagating in the axial direction is caracterized as the two-stream instability between the simply and doubly charged ions of the plasma
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Delmotte, Blaise. "Modeling and Simulation of Individual and Collective Swimming Mechanisms in Active Suspensions." Phd thesis, Toulouse, INPT, 2015. http://oatao.univ-toulouse.fr/14354/1/delmotte_partie_1_sur_2_2.pdf.

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We have all witnessed the flocking of starlings in the sky and the schools of fish that form in the ocean. This kind of organization of living creatures is not limited to those that we see, but also occurs for those that we don’t : swimming microorganisms. Suspen- sions of micro-swimmers exhibit a rich dynamics. Their behaviors can play an important role in the survival of the group, its development, the balance between species, their trophic strategies and even animal fertility. They can form coherent structures due to collective motion, mix the surrounding fluid or modify its rheological properties. Such diversity results from the complex interplay between swimming strategies, physiological processes, chemical reactions and hydrodynamic interactions. Fluid Mechanics is there- fore essential to understand and master the mechanisms involved in these phenomena. While experimental studies bring out new findings and, sometimes, provide physical ex- planations, modeling remains essential. Yet, including an accurate description of the micro-swimmers in a suspension containing thousands (nay millions) individuals, requires considering a wide range of coupled scales (from one micron 10^−6m to several millimeters 10^−3m). What happens on large scales depends on sophisticated mechanisms occurring two or three orders of magnitude below. Therefore, the multiscale modeling of such phenomena is still a major challenge for the state-of-the-art numerical methods. This thesis aims at providing a contribution in that direction. In a first part, we will show that reproducing swimming mechanisms at the scale of the micro-swimmer can be achieved with various models spanning different levels of complexity. We will then present our developments to incorporate these models in an efficient framework for large scale simulations. We will show how to simultaneously account for the Brownian motion of the smallest particles (10^−6m). Our code reproduces known results from the literature with the same accuracy, but at lower cost and at larger scales, thus bridging a gap between particle-based models, experiments and continuum formulations from kinetic theory. Using the capabilities afforded by our method, we eventually address two open problems in the experimental literature : the origins of orientational correla- tions between interacting self-propelled micro-droplets and the mechanisms at play in the nonlinear enhancement of Brownian particle diffusion in active suspensions.
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Books on the topic "Collective fluctuations"

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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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Sutton, Adrian P. Concepts of Materials Science. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780192846839.001.0001.

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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. Conclusion. Cornell University Press, 2017. http://dx.doi.org/10.7591/cornell/9781501705137.003.0008.

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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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Warren, Diane, and Laura Peters, eds. Rereading Orphanhood. Edinburgh University Press, 2020. http://dx.doi.org/10.3366/edinburgh/9781474464369.001.0001.

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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’.
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Pelkmans, Mathijs. Introduction. Cornell University Press, 2017. http://dx.doi.org/10.7591/cornell/9781501705137.003.0001.

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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.

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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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Book chapters on the topic "Collective fluctuations"

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Leibler, S. "Collective Phenomena in Mitosis: A Physicist’s Perspective." In 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, and H. E. Stanley. "A Random Matrix Theory Approach to Quantifying Collective Behavior of Stock Price Fluctuations." In 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., and H. Tanaka. "Dynamics of Liquid Water: Fluctuations and Collective Motions." In 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., and John C. Ham. "The Collective Impact of Sectoral Shocks on Aggregate Employment Fluctuations." In 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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Tsytovich, Vadim N. "Non-linear Interactions of Collective Oscillations and Waves with Particle Fluctuations." In 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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Behera, S. N., and S. G. Mishra. "Collective Modes of the Superconducting State in Coexistence with Other Ordered States." In 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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Simonova, Olga A. "Can Nostalgia Be Dangerous? Post-Soviet Nostalgia as Retrotopia: The Emotional Dynamic and Fluctuations of the Social Order." In 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, and G. Kothe. "Collective Order Fluctuations in Liquid Crystals Studied by Transverse Nuclear Spin Relaxation." In 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.

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Bai, Y. L., M. F. Xia, Y. J. Wei, and F. J. Ke. "Non-Equilibrium Evolution of Collective Microdamage and Its Coupling with Mesoscopic Heterogeneities and Stress Fluctuations." In High-Pressure Shock Compression of Solids VI, 255–78. New York, NY: Springer New York, 2003. http://dx.doi.org/10.1007/978-1-4613-0013-7_7.

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Huberman, Bernardo A. "Fluctuating Benefits and Collective Action." In 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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Conference papers on the topic "Collective fluctuations"

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Parrondo, Juan M. R. "Control and Rectification in Collective Stochastic Systems." In 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." In 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., and Igor V. Pimenov. "Quantum Description of Collective Excitations and Fluctuations in Layered High Temperature Superconductors." In 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, and Howard J. Carmichael. "Collective spontaneous emission from small assemblies of atoms." In SPIE's First International Symposium on Fluctuations and Noise, edited by Derek Abbott, Jeffrey H. Shapiro, and Yoshihisa Yamamoto. SPIE, 2003. http://dx.doi.org/10.1117/12.490148.

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Ordemann, Anke, Gabor Balazsi, Elizabeth Caspari, and Frank Moss. "Daphnia swarms: from single agent dynamics to collective vortex formation." In SPIE's First International Symposium on Fluctuations and Noise, edited by Sergey M. Bezrukov, Hans Frauenfelder, and Frank Moss. SPIE, 2003. http://dx.doi.org/10.1117/12.489033.

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Dzogang, Fabon, Thomas Lansdall-Welfare, and Nello Cristianini. "Seasonal Fluctuations in Collective Mood Revealed by Wikipedia Searches and Twitter Posts." In 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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Ren, Y. H., G. Luepke, Y. f. Hu, Qi Li, C. S. Hong, and N. H. Hur. "Ultrafast collective dynamics of short-range charge/orbital ordering fluctuations in colossal magnetoresistive oxides." In International Quantum Electronics Conference. Washington, D.C.: OSA, 2004. http://dx.doi.org/10.1364/iqec.2004.ituf7.

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Woods, Kristina N. "Using Far-Infrared Spectroscopy as a Means of Probing Collective Fluctuations in Biological Molecules." In PORTABLE SYNCHROTRON LIGHT SOURCES AND ADVANCED APPLICATIONS: 2nd International Symposium on Portable Synchrotron Light Sources and Advanced Applications. AIP, 2007. http://dx.doi.org/10.1063/1.2723622.

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Ouzit, Zakarya, Jiawen Liu, Juan Pintor, Lilian Guillemeney, Benoît Wagnon, Benjamin Abécassis, and Laurent Coolen. "Collective Blinking in Self-Assembled Stacks of Semiconducting Nanoplatelets Enabled by FRET." In Novel Optical Materials and Applications. Washington, D.C.: Optica Publishing Group, 2022. http://dx.doi.org/10.1364/noma.2022.noth3c.3.

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We show by micro-photoluminescence collective blinking of self-assembled stacks of CdSe nanoplatelets. We highlight through a random walk model the effects of FRET and quencher emitters in the stacks on the fluorescence fluctuations.
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Junker, W., M. Saffman, and L. Lading. "Spatially resolved measurements of density fluctuations with a hybrid Doppler/time-of-flight laser anemometer." In 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.

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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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Reports on the topic "Collective fluctuations"

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Smith, D. R., E. Mazzucato, W. Lee, H. K. Park, C. W. Domier, and 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), February 2009. http://dx.doi.org/10.2172/950697.

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Torero, Máximo, and Jaime Saavedra-Chanduví. Union Density Changes and Union Effects on Firm Performance in Peru. Inter-American Development Bank, September 2002. http://dx.doi.org/10.18235/0011249.

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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, and Millena Oliveira. TUC Urban Lab Profile: Alliance for the Centre of Recife, Brazil. United Nations University - Institute for Environment and Human Security (UNU-EHS), March 2024. http://dx.doi.org/10.53324/hcyv7857.

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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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Raja, Rameez Ali, Mustafa Kilic, Monica Prezzi, Rodrigo Salgado, and Fei Han. Implementation Study: Continuous, Wireless Data Collection and Monitoring of the Sagamore Parkway Bridge. Purdue University, 2022. http://dx.doi.org/10.5703/1288284317367.

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This report presents, in detail, the development and implementation of a wireless solar powered DAQ system for continuous real-time monitoring of the Sagamore Parkway Bridge using the data collected from strain gauges installed in the bridge pier and its foundation piles. The data analysis showed that there is no significant change in the load-settlement response of the bridge pier 3 years after its construction. The pile cap contribution in carrying the total load carried by the bridge pier is significant (about 20%). The hourly ambient temperature trends match with the incremental bending moments measured on the bridge pier and the piles. The daily temperature cycles also affected the load transferred between the piles within the pile group. The water level fluctuations of the Wabash River impacted the total load carried by the pier, such that a rise in water level resulted in slight drop in the total load carried by the bridge pier due to buoyant forces. The overall results of the bridge monitoring showed that the bridge has performed well since its construction.
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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, and Ana Iris Enríquez-Alcaraz. TUC Urban Lab Profile: Naucalpan, Mexico. United Nations University - Institute for Environment and Human Security (UNU-EHS), March 2024. http://dx.doi.org/10.53324/tmew2903.

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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.
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