Articles de revues : « 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, n^o 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, n^o 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, n^o 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, n^o 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, n^o 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, n^o 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, n^o 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, n^o 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, n^o 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, n^o 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.

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Shiratani, Masaharu, Masahiro Soejima, Hyun Woong Seo, Naho Itagaki et Kazunori Koga. « Fluctuation of Position and Energy of a Fine Particle in Plasma Nanofabrication ». Materials Science Forum 879 (novembre 2016) : 1772–77. http://dx.doi.org/10.4028/www.scientific.net/msf.879.1772.

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We are developing plasma nanofabrication, namely, nanoand micro scale guided assembly using plasmas. We manipulate nanoand micro objects using electrostatic, electromagnetic, ion drag, neutral drag, and optical forces. The accuracy of positioning the objects depends on fluctuation of position and energy of a fine particle (= each object) in plasmas. Here we evaluate such fluctuations and discuss the mechanism behind them. In the first experiment, we grabbed a fine particle in plasma using an optical tweezers. The fine particle moves in a potential well made by the optical tweezers. This is a kind of Brownian motion and the position fluctuation can be caused by neutral molecule collisions, ion collisions, and fluctuation of electrostatic force. Among theses possible causes, fluctuation of electrostatic force may be main one. In the second experiment, we deduced interaction potential between two fine particles during their Coulomb collision. We found that there exist repulsive and attractive forces between them. The repulsive force is a screened Coulomb one, whereas the attractive force is likely a force due to a shadow effect, a non-collective attractive force. Moreover, we noted that there is a fluctuation of the potential, probably due to fluctuation of electrostatic force. These position and potential energy fluctuations may limit the accuracy of guided assembly using plasmas.

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Khudaiberdiev, Daniiar, Ze Don Kvon, Matvey V. Entin, Dmitriy A. Kozlov, Nikolay N. Mikhailov et Maxim Ryzhkov. « Mesoscopic Conductance Fluctuations in 2D HgTe Semimetal ». Nanomaterials 13, n^o 21 (31 octobre 2023) : 2882. http://dx.doi.org/10.3390/nano13212882.

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Mesoscopic conductance fluctuations were discovered in a weak localization regime of a strongly disordered two-dimensional HgTe-based semimetal. These fluctuations exist in macroscopic samples with characteristic sizes of 100 μm and exhibit anomalous dependences on the gate voltage, magnetic field, and temperature. They are absent in the regime of electron metal (at positive gate voltages) and strongly depend on the level of disorder in the system. All the experimental facts lead us to the conclusion that the origin of the fluctuations is a special collective state in which the current is conducted through the percolation network of electron resistances. We suppose that the network is formed by fluctuation potential whose amplitude is higher than the Fermi level of electrons due to their very low density.

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Tsytovich, V. N., R. Bingham, U. de Angelis et A. Forlani. « Collective effects in bremsstrahlung in plasmas ». Journal of Plasma Physics 56, n^o 1 (août 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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Mendels, Dan, GiovanniMaria Piccini et Michele Parrinello. « Collective Variables from Local Fluctuations ». Journal of Physical Chemistry Letters 9, n^o 11 (7 mai 2018) : 2776–81. http://dx.doi.org/10.1021/acs.jpclett.8b00733.

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Vidal, F., M. V. Ramallo, J. Mosqueira et C. Carballeira. « Superconducting Fluctuations Above TC and the Uncertainty Principle : How Small may the Coherence Length be ? » International Journal of Modern Physics B 17, n^o 18n20 (10 août 2003) : 3470–72. http://dx.doi.org/10.1142/s0217979203021228.

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We summarize here some of our recent results on the superconducting fluctuation effects above TC in different low- and high-TC superconductors, at high reduced-temperatures and magnetic fields. These results confirm our proposal that the collective behaviour of the fluctuating Cooper pairs in the short-wavelength fluctuation regime is dominated by the uncertainty principle, which imposes a limit to the shrinkage of the superconducting wave function when T increases well above TC or H becomes of the order of Hc2(0), the upper critical magnetic field amplitude extrapolated to T = 0 K .

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Hofmann, H., et D. Kiderlen. « A Self-Consistent Treatment of Damped Motion for Stable and Unstable Collective Modes ». International Journal of Modern Physics E 07, n^o 02 (avril 1998) : 243–74. http://dx.doi.org/10.1142/s0218301398000105.

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We address the dynamics of damped collective modes in terms of first and second moments. The modes are introduced in a self-consistent fashion with the help of a suitable application of linear response theory. Quantum effects in the fluctuations are governed by diffusion coefficients Dμν. The latter are obtained through a fluctuation dissipation theorem generalized to allow for a treatment of unstable modes. Numerical evaluations of the Dμν are presented. We discuss briefly how this picture may be used to describe global motion within a locally harmonic approximation. Relations to other methods are discussed, like "dissipative tunneling", RPA at finite temperature and generalizations of the "Static Path Approximation".

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Hamann, Heiko, Thomas Schmickl et Karl Crailsheim. « Analysis of Swarm Behaviors Based on an Inversion of the Fluctuation Theorem ». Artificial Life 20, n^o 1 (janvier 2014) : 77–93. http://dx.doi.org/10.1162/artl_a_00097.

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A grand challenge in the field of artificial life is to find a general theory of emergent self-organizing systems. In swarm systems most of the observed complexity is based on motion of simple entities. Similarly, statistical mechanics focuses on collective properties induced by the motion of many interacting particles. In this article we apply methods from statistical mechanics to swarm systems. We try to explain the emergent behavior of a simulated swarm by applying methods based on the fluctuation theorem. Empirical results indicate that swarms are able to produce negative entropy within an isolated subsystem due to frozen accidents. Individuals of a swarm are able to locally detect fluctuations of the global entropy measure and store them, if they are negative entropy productions. By accumulating these stored fluctuations over time the swarm as a whole is producing negative entropy and the system ends up in an ordered state. We claim that this indicates the existence of an inverted fluctuation theorem for emergent self-organizing dissipative systems. This approach bears the potential of general applicability.

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Viebach, M., C. Lange, M. Seidl, Y. Bilodid et A. Hurtado. « NEUTRON NOISE PATTERNS FROM COUPLED FUEL-ASSEMBLY VIBRATIONS ». EPJ Web of Conferences 247 (2021) : 02015. http://dx.doi.org/10.1051/epjconf/202124702015.

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The neutron flux fluctuation magnitude of KWU-built PWRs shows a hitherto unexplained correlation with the types of loaded fuel assemblies. Also, certain measured long-range neutron flux fluctuation patterns in neighboring core quadrants still lack a closed understanding of their origin. The explanation of these phenomena has recently revived a new interest in neutron noise research. The contribution at hand investigates the idea that a synchronized coolant-driven vibration of major parts of the fuel-assembly ensemble leads to these phenomena. Starting with an assumed mode of such collective vibration, the resulting effects on the time-dependent neutron-flux distribution are analyzed via a DYN3D simulation. A three-dimensional representation of the time-dependent bow of all fuel assemblies is taken into account as a nodal DYN3D feedback parameter by time-dependent variations of the fuel-assembly pitch. The impact of its variation on the cross sections is quantiﬁed using a cross-section library that is generated from the output of corresponding CASMO5 calculations. The DYN3D simulation qualitatively reproduces the measured neutron-flux fluctuation patterns. The magnitude of the fluctuations and its radial dependence are comparable to the measured details. The results imply that collective fuel-assembly vibrations are a promising candidate for being the key to understand long-known fluctuation patterns in KWU built PWRs. Further research should elaborate on possible excitation mechanisms of the assumed vibration modes.

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Zverevich, Dmitry, et Alex Levchenko. « Transport signatures of plasmon fluctuations in electron hydrodynamics ». Low Temperature Physics 49, n^o 12 (1 décembre 2023) : 1376–84. http://dx.doi.org/10.1063/10.0022363.

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In two-dimensional electron systems, plasmons are gapless and long-lived collective excitations of propagating charge density oscillations. We study the fluctuation mechanism of plasmon-assisted transport in the regime of electron hydrodynamics. We consider pristine electron liquids where charge fluctuations are thermally induced by viscous stresses and intrinsic currents, while attenuation of plasmons is determined by the Maxwell mechanism of charge relaxation. It is shown that, while the contribution of plasmons to the shear viscosity and thermal conductivity of a Fermi liquid is small, plasmon resonances in the bilayer devices enhance the drag resistance. In systems without Galilean invariance, fluctuation-driven contributions to dissipative coefficients can be described only in terms of hydrodynamic quantities: intrinsic conductivity, viscosity, and plasmon dispersion relation.

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Benhassine, B., M. Farine, E. S. Hernandez, D. Idier, B. Remaud et F. Sebille. « Phase space fluctuations and dynamics of fluctuations of collective variables ». Nuclear Physics A 545, n^o 1-2 (août 1992) : 81–86. http://dx.doi.org/10.1016/0375-9474(92)90448-s.

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RISEBOROUGH, P. S. « INELASTIC NEUTRON SCATTERING FROM ANISOTROPIC SUPERCONDUCTORS ». International Journal of Modern Physics B 16, n^o 20n22 (30 août 2002) : 3062–65. http://dx.doi.org/10.1142/s0217979202013572.

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The magnetic fluctuation spectra are calculated for various phases of anisotropic superconductors. Both singlet and triplet superconducting phases can support antiferromagnetic fluctuations for small values of the Coulomb repulsion, the spectra show power law frequency dependencies due to the nodes in the superconducting order parameter. For larger strengths of the Coulomb interaction, low energy critically damped collective excitations develop from the quasi-particle density of states in the gap. The q and ω dependence of the spectra can be used to deduce the character of the superconducting order parameter.

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LESHANSKY, ALEXANDER M., JEFFREY F. MORRIS et JOHN F. BRADY. « Collective diffusion in sheared colloidal suspensions ». Journal of Fluid Mechanics 597 (1 février 2008) : 305–41. http://dx.doi.org/10.1017/s0022112007009834.

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Collective diffusivity in a suspension of rigid particles in steady linear viscous flows is evaluated by investigating the dynamics of the time correlation of long-wavelength density fluctuations. In the absence of hydrodynamic interactions between suspended particles in a dilute suspension of identical hard spheres, closed-form asymptotic expressions for the collective diffusivity are derived in the limits of low and high Péclet numbers, where the Péclet number ${\it Pe}\,{=}\,\gamdot a^2/D_0$ with $\gamdot$ being the shear rate and D0 = kBT/6πη a is the Stokes–Einstein diffusion coefficient of an isolated sphere of radius a in a fluid of viscosity η. The effect of hydrodynamic interactions is studied in the analytically tractable case of weakly sheared (Pe ≪ 1) suspensions.For strongly sheared suspensions, i.e. at high Pe, in the absence of hydrodynamics the collective diffusivity Dc = 6 Ds∞, where Ds∞ is the long-time self-diffusivity and both scale as $\phi \gamdot a^2$, where φ is the particle volume fraction. For weakly sheared suspensions it is shown that the leading dependence of collective diffusivity on the imposed flow is proportional to D0 φPeÊ, where Ê is the rate-of-strain tensor scaled by $\gamdot$, regardless of whether particles interact hydrodynamically. When hydrodynamic interactions are considered, however, correlations of hydrodynamic velocity fluctuations yield a weakly singular logarithmic dependence of the cross-gradient-diffusivity on k at leading order as ak → 0 with k being the wavenumber of the density fluctuation. The diagonal components of the collective diffusivity tensor, both with and without hydrodynamic interactions, are of O(φPe2), quadratic in the imposed flow, and finite at k = 0.At moderate particle volume fractions, 0.10 ≤ φ ≤ 0.35, Brownian Dynamics (BD) numerical simulations in which there are no hydrodynamic interactions are performed and the transverse collective diffusivity in simple shear flow is determined via time evolution of the dynamic structure factor. The BD simulation results compare well with the derived asymptotic estimates. A comparison of the high-Pe BD simulation results with available experimental data on collective diffusivity in non-Brownian sheared suspensions shows a good qualitative agreement, though hydrodynamic interactions prove to be important at moderate concentrations.

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Wiechen, H. « New aspects of plasma sheet dynamics - MHD and kinetic theory ». Annales Geophysicae 17, n^o 5 (31 mai 1999) : 595–603. http://dx.doi.org/10.1007/s00585-999-0595-2.

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Abstract. Magnetic reconnection is a process of fundamental importance for the dynamics of the Earth's plasma sheet. In this context, the development of thin current sheets in the near-Earth plasma sheet is a topic of special interest because they could be a possible cause of microscopic fluctuations acting as collective non-idealness from a macroscopic point of view. Simulations of the near-Earth plasma sheet including boundary perturbations due to localized inflow through the northern (or southern) plasma sheet boundary show developing thin current sheets in the near-Earth plasma sheet about 810 RE tailwards of the Earth. This location is largely independent from the localization of the perturbation. The second part of the paper deals with the problem of the macroscopic non-ideal consequences of microscopic fluctuations. A new model is presented that allows the quantitative calculation of macroscopic non-idealness without considering details of microscopic instabilities or turbulence. This model is only based on the assumption of a strongly fluctuating, mixing dynamics on microscopic scales in phase space. The result of this approach is an expression for anomalous non-idealness formally similar to the Krook resistivity but now describing the macroscopic consequences of collective microscopic fluctuations, not of collisions.Key words. Magnetospheric physics (plasma sheet) · Space plasma physics (kinetic and MHD theory; magnetic reconnection)

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Liu, Haoming, Suxiang Yang, Wei Tian, Min Zhao, Xiaoling Yuan et Bofeng Xu. « Vibration Reduction Strategy for Offshore Wind Turbines ». Applied Sciences 10, n^o 17 (2 septembre 2020) : 6091. http://dx.doi.org/10.3390/app10176091.

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The operational environment of offshore wind turbines is much more complex than that of onshore wind turbines. Facing the persistent wind and wave forces, offshore wind turbines are prone to vibration problems, which are not conducive to their long-term operation. Under this background, first, how the wave affects the vibration characteristics of offshore wind turbines is analyzed. Based on the existing wave and wave load models, we analytically show that there exist fluctuating components related to the hydrodynamic frequency in the aerodynamic load and aerodynamic torque of offshore wind turbines. Simulation results based on a GH Bladed platform further validates the analysis. Second, in order to reduce the joint impacts of the wave, wind shear and tower shadow on the wind turbine, a variable pitch control method is proposed. The integrated tower top vibration acceleration signal is superimposed on the collective pitch reference signal, then the triple frequency (3P) fluctuating component of the wind turbine output power and the azimuth angle of each blade are converted into the pitch angle adjustment signal of each blade, which is superimposed on the collective pitch signal for individual pitch control. The simulation results show that the proposed pitch control strategy can effectively smooth the fluctuation of blade root flap-wise load caused by wind and wave, and significantly reduce the fluctuation of aerodynamic torque and output power of offshore wind turbines.

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CHOU, MING JU, et HERNG ER HORNG. « EFFECTS OF QUANTUM AND THERMAL FLUCTUATIONS ON COLLECTIVE PINNING AND CRITICAL CURRENT DENSITY IN TYPE-II SUPERCONDUCTING BULK MATERIALS ». International Journal of Modern Physics B 25, n^o 04 (10 février 2011) : 609–18. http://dx.doi.org/10.1142/s0217979211058110.

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The effects of quantum and thermal fluctuations on collective pinning and critical current density Jc are investigated for bulk type-II superconductors by utilizing quantum statistics. It is shown that for a constant magnetic field, Jc is nearly independent of temperature in the quantum limit; however, in the classical limit, Jc decreases weakly with increasing temperature when T < Tdp (depinning temperature); when Tdp < T < Tf (boundary fluctuation temperature), Jc is power-law-decaying, and when T > Tf, Jc decays exponentially. For constant temperature, Jc first decreases, then increases after reaching a maximum, and finally decreases again. These results are in agreement with the experiments.

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Hwang, E. H., et S. Das Sarma. « Collective Charge Density Fluctuations in Superconducting Layered Systems with Bilayer Unit Cells ». International Journal of Modern Physics B 12, n^o 27n28 (10 novembre 1998) : 2769–83. http://dx.doi.org/10.1142/s0217979298001617.

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Collective modes of bilayered superconducting superlattices (e.g., YBCO) are investigated within the conserving gauge-invariant ladder diagram approximation including both the nearest interlayer single electron tunneling and the Josephson-type Cooper pair tunneling. By calculating the density–density response function including Coulomb and pairing interactions, we examine the two collective mode branches corresponding to the in-phase and out-of-phase charge fluctuations between the two layers in the unit cell. The out-of-phase collective mode develops a long wavelength plasmon gap whose magnitude depends on the tunneling strength with the mode dispersions being insensitive to the specific tunneling mechanism (i.e., single electron or Josephson). We also show that in the presence of tunneling the oscillator strength of the out-of-phase mode overwhelms that of the in-phase-mode at k‖ = 0 and finite kz, where kz and k‖ are respectively the mode wave vectors perpendicular and along the layer. We discuss the possible experimental observability of the phase fluctuation modes in the context of our theoretical results for the mode dispersion and spectral weight.

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Masuda, Naoki, Yoji Kawamura et Hiroshi Kori. « Collective fluctuations in networks of noisy components ». New Journal of Physics 12, n^o 9 (6 septembre 2010) : 093007. http://dx.doi.org/10.1088/1367-2630/12/9/093007.

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Perarnau-Llobet, Martí, et Raam Uzdin. « Collective operations can extremely reduce work fluctuations ». New Journal of Physics 21, n^o 8 (12 août 2019) : 083023. http://dx.doi.org/10.1088/1367-2630/ab36a9.

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König, Jürgen, John Schliemann, T. Jungwirth et A. H. MacDonald. « Collective spin fluctuations in diluted magnetic semiconductors ». Physica E : Low-dimensional Systems and Nanostructures 12, n^o 1-4 (janvier 2002) : 379–82. http://dx.doi.org/10.1016/s1386-9477(01)00308-3.

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Wan, Yi, et Richard M. Stratt. « Collective fluctuations of conserved variables in liquids ». Journal of Chemical Physics 98, n^o 4 (15 février 1993) : 3224–39. http://dx.doi.org/10.1063/1.464095.

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Pfitzner, A., L. M�nchow et P. M�dler. « One-body dynamics modified by collective fluctuations ». Zeitschrift f�r Physik A Atomic Nuclei 331, n^o 1 (mars 1988) : 43–51. http://dx.doi.org/10.1007/bf01289429.

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AKPAN, JAMES ESSIEN. « ECONOMETRIC ANALYSIS OF INFLATION AND MONETARY POLICY INDICES IN NIGERIA ». GUSAU JOURNAL OF ECONOMICS AND DEVELOPMENT STUDIES 4, n^o 1 (12 janvier 2024) : 53–65. http://dx.doi.org/10.57233/gujeds.v4i1.4.

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This work studied the intricate web of economic relationships in Nigeria, exploring the interactions between exchange rates, inflation, money supply, and economic growth. The research unveiled valuable insights into the dynamics of Nigeria's economy and its implications for policymakers. The work attempts to explore the impacts of exchange rate fluctuation, increasing inflation rates increased money supply on Economic growth in Nigeria. The econometric technique of Error correction model (ECM) was relied upon as a major analytical tool to determine the relationship among the variables. Our findings unveiled a noteworthy connection between exchange rates and inflation, underlining the influence of exchange rate fluctuations on inflationary pressures. Additionally, money supply and economic growth were identified as significant factors affecting inflation rates, aligning with theoretical expectations. Notably, these variables collectively explained a substantial portion of the variation in real Gross Domestic Product (RGDP), signifying their collective influence on economic outcomes. The error correction model (ECM) underscored the statistical significance of the long-term relationships among these variables. In light of these findings, we recommend that policymakers in Nigeria pay close attention to exchange rate policies, monitor and manage money supply, and prioritize economic growth as integral elements in their efforts to control inflation and maintain economic stability. Continuous monitoring and analysis of these variables will be crucial for informed decision-making and effective economic management in Nigeria.

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Liu, Rui, Kazuyuki Aihara et Luonan Chen. « Collective fluctuation implies imminent state transition ». Physics of Life Reviews 37 (juillet 2021) : 103–7. http://dx.doi.org/10.1016/j.plrev.2021.04.002.

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Liu, Pengyu, et Jie Jian. « Effects of network topology and trait distribution on collective decision making ». AIMS Mathematics 8, n^o 5 (2023) : 12287–320. http://dx.doi.org/10.3934/math.2023619.

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<abstract><p>Individual-level interactions shape societal or economic processes, such as infectious diseases spreading, stock prices fluctuating and public opinion shifting. Understanding how the interaction of different individuals affects collective outcomes is more important than ever, as the internet and social media develop. Social networks representing individuals' influence relations play a key role in understanding the connections between individual-level interactions and societal or economic outcomes. Recent research has revealed how the topology of a social network affects collective decision-making in a community. Furthermore, the traits of individuals that determine how they process received information for making decisions also change a community's collective decisions. In this work, we develop stochastic processes to generate networks of individuals with two simple traits: Being a conformist and being an anticonformist. We introduce a novel deterministic voter model for a trait-attributed network, where the individuals make binary choices following simple deterministic rules based on their traits. We show that the simple deterministic rules can drive unpredictable fluctuations of collective decisions which eventually become periodic. We study the effects of network topology and trait distribution on the first passage time for a sequence of collective decisions showing periodicity.</p></abstract>

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Wang, Ziqiang. « Strongly Correlated Fermi Liquid and the Normal State of High Tc Superconductors ». International Journal of Modern Physics B 06, n^o 05n06 (mars 1992) : 603–54. http://dx.doi.org/10.1142/s0217979292000384.

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New insights into the strongly correlated Fermi liquid state of the SU(N) infinite-U Hubbard and t-J models are presented in connection to the metallic state of unbroken symmetry of the copper oxide planes. The nature of single particle and collective excitations is analyzed and the Landau Fermi Liquid parameters are derived. The one-particle spectral function in the Hubbard valence band is obtained with both Hubbard and Gutzwiller-like features. A simple interpretation of the large incoherent background is given in terms of a superposition of quasiparticles and a collective mode describing the propagation of a bare hole in a large U system. The spin exchange interactions produce very low lying collective modes describing the propagation of staggered spin chirality which soften at incommensurate wavevectors. The quasiparticles are strongly scattered by the low lying chirality fluctuations resulting in deviations from canonical Fermi liquid behavior at low energy scales. Of the same origin, the quasiparticle self energy is found to be strongly k-dependent. It leads to corrections to the dispersion and enhancement of the quasiparticle lifetime in the hole-like region of the interacting Fermi surface. The combined effects are sufficient to produce a sign change in the Hall coefficient evaluated for parameters relevant to the copper oxide planes. We show that these models also exhibit a zero temperature fluctuation driven transition from Fermi liquid to non Fermi liquid phase without the onset of magnetic ordering below a critical doping δc=1/4N, whereby providing a microscopic mechanism for the destruction of the Fermi liquid coherence by strong longitudinal gauge fluctuations which represent the effects of the infinite-U constraint.

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Zhang, H. P., A. Be'er, E. L. Florin et H. L. Swinney. « Collective motion and density fluctuations in bacterial colonies ». Proceedings of the National Academy of Sciences 107, n^o 31 (19 juillet 2010) : 13626–30. http://dx.doi.org/10.1073/pnas.1001651107.

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Ziherl, P., A. Šarlah et S. Žumer. « Collective fluctuations and wetting in nematic liquid crystals ». Physical Review E 58, n^o 1 (1 juillet 1998) : 602–9. http://dx.doi.org/10.1103/physreve.58.602.

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Prakashchand, Dube Dheeraj, Navjeet Ahalawat, Satyabrata Bandyopadhyay, Surajit Sengupta et Jagannath Mondal. « Nonaffine Displacements Encode Collective Conformational Fluctuations in Proteins ». Journal of Chemical Theory and Computation 16, n^o 4 (24 mars 2020) : 2508–16. http://dx.doi.org/10.1021/acs.jctc.9b01100.

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Fulde, P., et K. W. Becker. « Collective density fluctuations in heavy‐fermion systems (invited) ». Journal of Applied Physics 63, n^o 8 (15 avril 1988) : 3673–75. http://dx.doi.org/10.1063/1.340682.

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Mädler, P., L. Münchow et A. Pfitzner. « Randomization of single-particle motion by collective fluctuations ». Physics Letters B 198, n^o 1 (novembre 1987) : 25–28. http://dx.doi.org/10.1016/0370-2693(87)90150-x.

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Feliachi, Ouassim, Marc Besse, Cesare Nardini et Julien Barré. « Fluctuating kinetic theory and fluctuating hydrodynamics of aligning active particles : the dilute limit ». Journal of Statistical Mechanics : Theory and Experiment 2022, n^o 11 (1 novembre 2022) : 113207. http://dx.doi.org/10.1088/1742-5468/ac9fc6.

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Abstract Kinetic and hydrodynamic theories are widely employed for describing the collective behavior of active matter systems. At the fluctuating level, these have been obtained from explicit coarse-graining procedures in the limit where each particle interacts weakly with many others, so that the total forces and torques exerted on each of them is of order unity at all times. Such limit is however not relevant for dilute systems that mostly interact via alignment; there, collisions are rare and make the self-propulsion direction to change abruptly. We derive a fluctuating kinetic theory, and the corresponding fluctuating hydrodynamics, for aligning self-propelled particles in the limit of dilute systems. We discover that fluctuations at kinetic level are not Gaussian and depend on the interactions among particles, but that only their Gaussian part survives in the hydrodynamic limit. At variance with fluctuating hydrodynamics for weakly interacting particles, we find that the noise variance at hydrodynamic level depends on the interaction rules among particles and is proportional to the square of the density, reflecting the binary nature of the aligning process. The results of this paper, which are derived for polar self-propelled particles with polar alignment, could be straightforwardly extended to polar particles with nematic alignment or to fully nematic systems.

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YAN, XIN-ZHONG. « PAIRING-FLUCTUATION EFFECT IN QUASI-TWO-DIMENSIONAL SUPERCONDUCTIVITY ». International Journal of Modern Physics B 17, n^o 03 (30 janvier 2003) : 319–36. http://dx.doi.org/10.1142/s021797920301598x.

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We present a self-consistent approach to deal with the pairing-fluctuation effects in quasi-two-dimensional superconducting systems. Besides the Cooper pairs in the Bose–Einstein condensate, there are pairs occupying the excited states, which results in the predominant fluctuations. The low-lying excited states are the collective modes. On the basis of ladder-diagram approximation, we treat the single particles and the pairs on an equal-footing manner. The Green's function of single particles is obtained as an analytic solution to a cubic equation. The bosonic degrees of freedom are relevant to the pseudogap physics in the high-T c cuprates. The superconducting order parameter and the transition temperature are substantially reduced from the values of the mean-field theory. The calculated phase boundary of superconducting state can reasonably describe the experiment data for cuprates.

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Šuvakov, Milovan, et Bosiljka Tadić. « Collective charge fluctuations in single-electron processes on nanonetworks ». Journal of Statistical Mechanics : Theory and Experiment 2009, n^o 02 (4 février 2009) : P02015. http://dx.doi.org/10.1088/1742-5468/2009/02/p02015.

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Kawaguchi, Koji, Koichi Murase et Tetsufumi Hirano. « Multiplicity fluctuations and collective flow in small colliding systems ». Nuclear Physics A 967 (novembre 2017) : 357–60. http://dx.doi.org/10.1016/j.nuclphysa.2017.07.010.

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Rozgacheva, I. K. « Collective dynamics of density fluctuations in a gravitating medium ». Astrophysics 28, n^o 3 (1988) : 368–73. http://dx.doi.org/10.1007/bf01112975.

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Zakhvataev, V. E., O. S. Volodko, L. A. Kompaniets et D. V. Zlobin. « Numerical study of a model of terahertz collective modes in DNA ». Journal of Physics : Conference Series 2094, n^o 2 (1 novembre 2021) : 022012. http://dx.doi.org/10.1088/1742-6596/2094/2/022012.

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Abstract Terahertz density fluctuations in DNA have been recognized to be associated with biological function of DNA and widely studied both experimentally and theoretically. In the present work, we investigate numerically a new model for the terahertz dynamics of density fluctuations in DNA, proposed earlier. This model considers the length scales corresponding to wave numbers up to the position of the maximum of the static structure factor and allows to reflect structural effects caused by the dependence of the static structure factor on wave number. We study the parametric dependencies of the model to elucidate the effect of dlocalization of the dynamics of density fluctuations caused by structural effects.

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Ohmine, Iwao. « Liquid Water Dynamics : Collective Motions, Fluctuation, and Relaxation ». Journal of Physical Chemistry 99, n^o 18 (mai 1995) : 6767–76. http://dx.doi.org/10.1021/j100018a004.

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Gong, M., M. Nishiura, R. Yanai et Y. Takemura. « Development of correlation ECE system for electron temperature fluctuation measurement in LHD ». Journal of Instrumentation 18, n^o 10 (1 octobre 2023) : C10007. http://dx.doi.org/10.1088/1748-0221/18/10/c10007.

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Abstract Correlation-ECE (C-ECE) is a standard method for investigating turbulence driven transport. This method allows electron temperature fluctuations that contain information on turbulent transport and independent thermal noise. The turbulence feature is extracted from a correlation analysis from two close locations. The A C-ECE system is utilized on the large helical device (LHD) to measure emission within the frequency range of 74–79.6 GHz. This system employs the spectral decorrelation method and serves as a collective Thomson scattering diagnostic receiver in the LHD. The C-ECE receiver system is comprised of a filter bank system with 32 band-pass filters and a fast digitizer system operating at a sampling rate of 12.5 GHz in the intermediate frequency (IF) stage. This study presents initial experimental results on temperature fluctuation spectra in the LHD, obtained through the C-ECE system using a coherency-based analysis method. An MHD mode at 5 kHz is excited from the onset of neutral beam injection in a magnetic probe, and coherence spectra are obtained from two C-ECE receiver systems. The temperature fluctuation results are derived from the coherence spectrum after bias removal and indicate a level of approximately 3% in the frequency range of 0 to 400 kHz. Further investigations will be conducted to explore drift wave turbulence activities and reconstruct the radial profile of temperature fluctuation in the LHD using the C-ECE receiver systems.

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Riboux, Guillaume, Dominique Legendre et Frédéric Risso. « A model of bubble-induced turbulence based on large-scale wake interactions ». Journal of Fluid Mechanics 719 (19 février 2013) : 362–87. http://dx.doi.org/10.1017/jfm.2013.12.

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AbstractNavier–Stokes simulations of the agitation generated by a homogeneous swarm of high-Reynolds-number rising bubbles are performed. The bubbles are modelled by fixed momentum sources of finite size randomly distributed in a uniform flow. The mesh grid is regular with a spacing close to the bubble size. This allows us to simulate a swarm of a few thousand bubbles in a computational domain of a hundred bubble diameters, which corresponds to a gas volume fraction $\alpha $ from 0.6 % to 4 %. The small-scale disturbances close to the bubbles are not resolved but the wakes are correctly described from a distance of a few diameters. This simple model reproduces well all the statistical properties of the vertical velocity fluctuations measured in previous experiments: scaling as ${\alpha }^{0. 4} $, self-similar probability density functions and power spectral density including a subrange evolving as the power $- 3$ of the wavenumber $k$. It can therefore be concluded that bubble-induced agitation mainly results from wake interactions. Considering the flow in a frame that is fixed relative to the bubbles, the combined use of both time and spatial averaging makes it possible to distinguish two contributions to the liquid fluctuations. The first is the spatial fluctuations that are the consequence of the bubble mean wakes. The second corresponds to the temporal fluctuations that are the result of the development of a flow instability. Note that the latter is not due to the destabilization of individual bubble wakes, since a computation with a single bubble leads to a steady flow. It is a collective instability of the randomly distributed bubble wakes. The spectrum of the time fluctuations shows a peak around a frequency ${f}_{cwi} $, which is independent of $\alpha $. From the present results it is possible to determine the origin of the overall properties of the total fluctuations observed in the experiments. The scaling of the velocity fluctuation as ${\alpha }^{0. 4} $ is a combination of the scalings of the spatial and temporal fluctuations, which are different from each other. As the time fluctuations are symmetric in the vertical direction, the asymmetry of the probability density function of the vertical velocity comes from that of the spatial fluctuations. Both contributions exhibit a ${k}^{- 3} $ spectral behaviour around the same range of wavenumbers, which explains why it is observed regardless of the nature of the dominant contribution.

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Llanes-Estrada, Felipe J., Belén Martínez Carmona et Jose L. Muñoz Martínez. « Velocity fluctuations of fission fragments ». International Journal of Modern Physics E 25, n^o 02 (février 2016) : 1650009. http://dx.doi.org/10.1142/s0218301316500099.

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We propose event by event velocity fluctuations of nuclear fission fragments as an additional interesting observable that gives access to the nuclear temperature in an independent way from spectral measurements and relates the diffusion and friction coefficients for the relative fragment coordinate in Kramers-like models (in which some aspects of fission can be understood as the diffusion of a collective variable through a potential barrier). We point out that neutron emission by the heavy fragments can be treated in effective theory if corrections to the velocity distribution are needed.

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