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Littérature scientifique sur le sujet « Fluctuation de densité »

Auteur : Grafiati

Publié le 21 avril 2023

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Articles de revues sur le sujet "Fluctuation de densité"

Artemenko, S. N. « Modification of charge density wave fluctuations by charge perturbations ». Journal de Physique IV 12, n^o 9 (novembre 2002) : 77–78. http://dx.doi.org/10.1051/jp4:20020359.

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Spectral density of fluctuations of the CDW phase are calculated taking into account electric field induced by phase fluctuations. The approach based upon the fluctuation-dissipation theorem (FDT) combined with equations of linear response of the CDW conductor is used. Fluctuating electric field is found to suppress fluctuations of the phase, while fluctuations of the electric potential are sizeable. This suggests that transition from the CDW to the normal state (which is usually observed well below the mean-field transition temperature) may he provoked by fluctuations of the chemical potential, rather than by destruction of the CDW coherence between conducting chains due to phase fluctuations.

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Laberge, Gaetan J. H., et Rizwan U. Haq. « "Universality" of Gaussian orthogonal ensemble fluctuations : the two-body random ensemble and shell model spectra ». Canadian Journal of Physics 68, n^o 3 (1 mars 1990) : 301–12. http://dx.doi.org/10.1139/p90-048.

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Starting from an appropriate decomposition of the level density into an average and fluctuating part, we studied the energy level fluctuations of an ensemble defined by two-body random Hamiltonians. A detailed analysis of several spectrally averaged fluctuation measures shows close agreement with the predictions of the Gaussian orthogonal ensemble (GOE). This confirms earlier indications that, except for noninteracting particles, fluctuation measures are insensitive to the rank of the interaction. Further, analysis of spectra obtained from realistic nuclear interactions agrees well with the GOE indicating that specific properties of the Hamiltonian have little or no influence on fluctuations. These results, therefore, strengthen our belief in the "universality" of GOE fluctuations.

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Koga, Y. « Fluctuations in aqueous methanol, ethanol, and propan-1-ol : amplitude and wavelength of fluctuation ». Canadian Journal of Chemistry 77, n^o 12 (5 décembre 1999) : 2039–45. http://dx.doi.org/10.1139/v99-213.

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Density, heat capacity, and isentropic compressibility data for aqueous methanol, ethanol, and propan-1-ol by Benson's group were used to evaluate two kinds of fluctuations; mean-square fluctuation densities; and (mean-square) normalized fluctuations, respectively, in volume, entropy, and cross (entropy/volume) effect. The mean-square fluctuation densitiesprovide measures for the amplitude (intensity) of the fluctuation, while the normalized fluctuations contain information regarding the wavelength (extensity) of the fluctuation. Furthermore, their composition derivatives, the partial molar fluctuationsof alcohols were calculated. These quantities signify the effect of additional solute on the respective fluctuations. These data were interpreted in terms of mixing schemes learned earlier in this laboratory by using the data of excess partial molar enthalpy, entropy, and volume, and the respective alcohol-alcohol interaction functions, i.e., the composition derivatives of partial molar quantities. Key words: aqueous methanol, ethanol, and propan-1-ol;fluctuation density; normalized fluctuation; partial molar fluctuations of alcohol.

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SCHMID, FRIEDERIKE. « FLUCTUATIONS IN LIPID BILAYERS : ARE THEY UNDERSTOOD ? » Biophysical Reviews and Letters 08, n^o 01n02 (juin 2013) : 1–20. http://dx.doi.org/10.1142/s1793048012300113.

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We review recent computer simulation studies of undulating lipid bilayers. Theoretical interpretations of such fluctuating membranes are most commonly based on generalized Helfrich-type elastic models, with additional contributions of local "protrusions" and/or density fluctuations. Such models provide an excellent basis for describing the fluctuations of tensionless bilayers in the fluid Lαphase at a quantitative level.However, this description is found to fail for membranes in the gel phase and for membranes subject to high tensions. The fluctuations of tilted gel membranes (Lβ′phase) show a signature of the modulated ripple structure Pβ′, which is a nearby phase observed in the pretransition regime between the Lαand Lβ′state. This complicates a quantitative analysis on mesoscopic length scales. In the case of fluid membranes under tension, the large-wavelength fluctuation modes are found to be significantly softer than predicted by theory.In the latter context, we also address the general problem of the relation between frame tension and the fluctuation tension, which has been discussed somewhat controversially in recent years. Simulations of very simple model membranes with fixed area show that the fluctuations should be controlled by the frame tension, and not by the internal tension.

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KOIKE, MASAFUMI, et JOE SATO. « EFFECTS OF MATTER DENSITY FLUCTUATION IN LONG BASELINE NEUTRINO OSCILLATION EXPERIMENTS ». Modern Physics Letters A 14, n^o 19 (21 juin 1999) : 1297–302. http://dx.doi.org/10.1142/s0217732399001383.

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The effects of matter density fluctuation in long baseline neutrino oscillation experiments are studied. Effects of short wavelength fluctuations are irrelevant. Effects of long wavelength fluctuations must be checked on a case-by-case basis. As an example we checked the fluctuation effects and showed its irrelevance in a case of K2K experiments.

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Lacombe, C., J. L. Steinberg, C. C. Harvey, D. Hubert, A. Mangeney et M. Moncuquet. « Density fluctuations measured by ISEE 1-2 in the Earth's magnetosheath and the resultant scattering of radio waves ». Annales Geophysicae 15, n^o 4 (30 avril 1997) : 387–96. http://dx.doi.org/10.1007/s00585-997-0387-5.

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Abstract. Radio waves undergo angular scattering when they propagate through a plasma with fluctuating density. We show how the angular scattering coefficient can be calculated as a function of the frequency spectrum of the local density fluctuations. In the Earth's magnetosheath, the ISEE 1-2 propagation experiment measured the spectral power of the density fluctuations for periods in the range 300 to 1 s, which produce most of the scattering. The resultant local angular scattering coefficient can then be calculated for the first time with realistic density fluctuation spectra, which are neither Gaussian nor power laws. We present results on the variation of the local angular scattering coefficient during two crossings of the dayside magnetosheath, from the quasi-perpendicular bow shock to the magnetopause. For a radio wave at twice the local electron plasma frequency, the scattering coefficient in the major part of the magnetosheath is b(2fp) ≃ 0.5 – 4 × 10–9 rad2/m. The scattering coefficient is about ten times stronger in a thin sheet (0.1 to1RE) just downstream of the shock ramp, and close to the magnetopause.

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LAYEK, BISWANATH, SOMA SANYAL et AJIT M. SRIVASTAVA. « BARYOGENESIS VIA DENSITY FLUCTUATIONS WITH A SECOND ORDER ELECTROWEAK PHASE TRANSITION ». International Journal of Modern Physics A 18, n^o 26 (20 octobre 2003) : 4851–68. http://dx.doi.org/10.1142/s0217751x03015799.

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We consider the presence of cosmic string induced density fluctuations in the universe at temperatures below the electroweak phase transition temperature. Resulting temperature fluctuations can restore the electroweak symmetry locally, depending on the amplitude of fluctuations and the background temperature. The symmetry will be spontaneously broken again in a given fluctuation region as the temperature drops there (for fluctuations with length scales smaller than the horizon), resulting in the production of baryon asymmetry. The time scale of the transition will be governed by the wavelength of fluctuation and, hence, can be much smaller than the Hubble time. This leads to strong enhancement in the production of baryon asymmetry for a second order electroweak phase transition as compared to the case when transition happens due to the cooling of the universe via expansion. For a two-Higgs extension of the Standard Model (with appropriate CP violation), we show that one can get the required baryon to entropy ratio if fluctuations propagate without getting significantly damped. If fluctuations are damped rapidly, then a volume factor suppresses the baryon production. Still, the short scale of the fluctuation leads to enhancement of the baryon to entropy ratio by at least 3–4 orders of magnitude compared to the conventional case of second order transition where the cooling happens due to expansion of the universe.

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Wei, Yi-Kun, et Xu-Qu Hu. « Two-Dimensional Simulations of Turbulent Flow Past a Row of Cylinders using Lattice Boltzmann Method ». International Journal of Computational Methods 14, n^o 01 (11 janvier 2017) : 1750002. http://dx.doi.org/10.1142/s0219876217500025.

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Two-dimensional simulations of channel flow past an array of cylinders are carried out at high Reynolds numbers. Considering the thickness fluctuating effect on the equation of motion, a modified lattice Boltzmann method (LBM) is proposed. Special attention is paid to investigate the thickness fluctuations and vortex shedding mechanisms between 11 cylinders. Results for the velocity and vorticity differences are provided, as well as for the energy density and enstrophy spectra. The numerical results coincide very well with some published experimental data that was obtained by turbulent soap films. The spectra extracted from the velocity and vorticity fields are displayed from simulations, along with the thickness fluctuation spectrum H(k). Our results show that the statistics of thickness fluctuations resemble closely those of a passive scalar in turbulent flows.

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Suzuki, Y., M. Kiya, T. Sampo et Y. Naka. « Pressure Fluctuations on the Surface of a Hemisphere Immersed in a Thick Turbulent Boundary Layer ». Journal of Fluids Engineering 109, n^o 2 (1 juin 1987) : 130–35. http://dx.doi.org/10.1115/1.3242632.

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Statistical properties of pressure fluctuations on the surface of a hemisphere immersed in a thick turbulent boundary layer are described. The height of the hemisphere tested was 0.275 thicknesses of the boundary layer. Reynolds number based on the model diameter D and the time-mean approaching flow velocity at the level of the top Ur was 3.0 × 105. Time-mean and root-mean-square (rms) values, probability density and power spectra of the pressure fluctuations are presented and discussed. The pressure fluctuations are related to the fluctuating approaching-flow velocity in terms of the pressure-velocity admittance and the cross correlation. Main results are that the time-mean and rms pressures attained a primary maximum at the front stagnation point; that the pressure-velocity admittance near the front stagnation point was approximately unity at frequencies less than about 0.4 Ur/D; that the pressure fluctuation in front of the hemisphere is positively correlated with that in the rear side and negatively correlated with that in the middle.

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Gupta, U., et C. R. Sovinec. « Pressure-driven tearing and thermal transport in finite-beta reversed field pinch computations ». Physics of Plasmas 30, n^o 1 (janvier 2023) : 013901. http://dx.doi.org/10.1063/5.0124281.

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Nonlinear resistive-magnetohydrodynamics (MHD) computation with heating and anisotropic transport is applied to examine the interaction between thermal energy and magnetic fluctuations in inductively driven reversed-field pinches (RFPs). The magnetic fluctuations underlie magnetic field reversal through dynamo-like correlations, and they enhance thermal energy transport through fluctuations of parallel heat flux density. With the unfavorable magnetic curvature that exists across the RFP profile, thermal energy also affects the magnetic fluctuations. Computations with the NIMROD code [Sovinec et al., J. Comput. Phys. 195, 355–386 (2004)] integrate nonlinear MHD dynamics with energy transport and reproduce an RFP state with experimentally relevant values of plasma- β. Equilibria constructed from results of the 3D computations are analyzed to assess the sources of free energy in the saturated nonlinear state. Linear computations for these profiles show unstable modes of tearing parity. Their eigenfunctions are used to evaluate and compare stabilizing and destabilizing contributions to the kinetic energy integral. An assessment of the drives in the integral reveals that the pressure gradient drive is of comparable magnitude to the parallel current drive, and only the sum of the two surpasses the stabilizing contributions. Correlation of magnetic and parallel heat flux density fluctuations in the nonlinear computations shows that fluctuation-induced thermal conduction is the dominant mode of energy loss, as expected from experimental evidence. Decomposition of the fluctuating heat flux density shows that second-order correlations, alone, do not explain the total energy transport. Higher-order correlations are also important.

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Thèses sur le sujet "Fluctuation de densité"

El, Dib Georges. « Fibres optiques en verre de borophosphate de niobium pour des applications en optique non linéaire ». Electronic Thesis or Diss., Limoges, 2023. http://www.theses.fr/2023LIMO0004.

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Les principaux objectifs de cette thèse étaient de développer des fibres optiques de borophosphate riche en niobium avec une qualité optique améliorée ainsi que de tirer profit de leur haute non linéarité pour des applications comme dispositifs de guides d'ondes dans le proche infrarouge. Les travaux exposés dans cette thèse traitent d’aspects théoriques et pratiques en science des verres. Ils s’articulent autour du système vitreux borophosphate riche en niobium : (100-x) [(0,95 NaPO3 + 0,05 Na2B4O7)] - x Nb2O5 ; avec x le taux (mol %) de Nb2O5 dans le verre. Dans un premier temps, une étude détaillée portant sur les propriétés thermiques, rhéologiques et sur l’étirage des préformes a été réalisée. Grâce à cette étude une corrélation entre la composition et la capacité de fibrage des verres a pu être mise en évidence. La relation entre la méthode de synthèse du verre et les pertes optiques a ensuite été étudiée. Nous avons montré qu’une approche ne nécessitant pas la coulée du verre permet l’obtention de fibres avec des pertes significativement plus faibles. Dans un second temps, nous nous sommes intéressés à la haute non linéarité de ces verres. Nous avons démontré la faisabilité du traitement de polarisation thermique (poling) sur des fibres de sections rectangulaires pour la génération de seconde harmonique. D’autre part, les effets de propagation des impulsions laser intenses dans des fibres d’architectures cœur/gaine rectangulaire ont été explorés, montrant à terme la capacité de ces verres à générer des sources supercontinuum allant jusqu’a 2.5 µm
The main objectives of this thesis were to develop niobium-rich borophosphate optical glass fibers with improved optical quality and to take advantage of their high nonlinearity for their potential use as waveguide devices in the near infrared. The work presented in this thesis deals with theoretical and practical aspects of glass science. It is based on the niobium-rich borophosphate glass matrix : (100-x) [(0,95 NaPO3 + 0,05 Na2B4O7)] - x Nb2O5 ; where x is the Nb2O5 content (mol%) in the glass. First, a detailed study of the thermal/rheological properties and the drawing of the preforms has been performed. Thanks to this study, a correlation between the composition and the drawing ability of the glasses could be demonstrated. Then the relationship between the glass synthesis method and the optical losses has been studied. We have shown that a new approach eliminating the casting step allows to obtain fibers with significantly lower losses. In a second step, one is interested in exploiting the high nonlinearity of these glasses. We have demonstrated the feasibility of thermal poling treatment on fibers with rectangular cross sections for second harmonic generation. On the other hand, the effects of intense laser pulses propagation in fibers of rectangular core/cladding architectures were investigated, leading to show the ability of these glasses to generate supercontinuum sources up to 2.5 µm

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Nguyen, Van Thinh. « Contribution à l'étude de la structure de la turbulence près d'une paroi lisse ». Paris 6, 1987. http://www.theses.fr/1987PA066553.

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Etude théorique des champs turbulents non homogènes. Etude de l'écoulement turbulent établi dans une conduite rectangulaire très allongée. Etude de la région au voisinage proche de la paroi. Etude expérimentale par anémométrie à fil chaud. Détermination des vitesses moyennes, fluctuations longitudinales de vitesse, densités spectrales et corrélations, densités de probabilité.

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Moon, Hee-Jang. « Modèles de combustion turbulente appliqués à l'autoinflammation. Comparaison avec la simulation numérique directe ». Rouen, 1991. http://www.theses.fr/1991ROUES010.

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Cette étude a pour but de contribuer à une meilleure approximation du comportement d'une flamme turbulente par des modélisations numériques utilisant la fonction densité de probabilité (P. D. F. ). Trois différents types d'approches ont été étudiés et comparés à la simulation directe: 1) les modèles de P. D. F. Présumée; 2) un modèle eulérien-lagrangien P. E. U. L. ; 3) les modèles à équation de P. D. F. L'étude montre la sensibilité et la capacité à la prédiction de tous ces modèles de P. D. F. En les testant par rapport aux résultats obtenus par la simulation numérique directe. Le phénomène physique qui a servi de base à ces comparaisons est celui de l'autoinflammation d'un prémélange combustible-comburant dans un milieu infini comportant initialement des fluctuations statistiquement homogènes et isotropes. L'étude a été étendue à des cas où la richesse et l'enthalpie peut fluctuer dans le mélange. Les modèles à équation de P. D. F. Sont plus précis que les deux autres catégories, et le coût en temps de calcul est beaucoup plus grand. On a montré que, l'effet du nombre de Damkohler dans les hypothèses de fermeture est actuellement mal pris en compte et reste un problème à résoudre

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Côté, Alain C. « Density fluctuation measurements with laser scattering ». Thesis, University of Oxford, 1989. http://ora.ox.ac.uk/objects/uuid:2580d8c1-32f7-40c6-afe1-14ebde9641f3.

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-2 power law. The average phase velocities are around 4.5 km/sec and are slightly larger than the electron diamagnetic drift velocity. The waves are tentatively identified with the electron drift mode. Coherent signals due to long wavelength MHD modes are detected. Results from a Langmuir probe corroborate most of these data.

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Jain, Bhuvnesh. « The evolution of cosmological density fluctuations ». Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/28060.

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Lumsden, Stuart Leonard. « The statistics and evolution of cosmological density fluctuations ». Thesis, University of Edinburgh, 1990. http://hdl.handle.net/1842/28460.

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Canavezes, Alexandre Gonzalez da Rocha Silva. « The topology of the density of the universe using PSCz ». Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314346.

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Soula, Serge. « Influence de l'effet couronne sur le champ electrique mesure au voisinage du sol sous orage ». Toulouse 3, 1986. http://www.theses.fr/1986TOU30213.

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Generalites sur l'electricite des orages. Mise au point d'un appareil de type gardien pour mesurer la densite ionique. Resultats experimentaux obtenus durant deux campagnes: ils concernent d'une part les mesures de champ electrique a plusieurs hauteurs dans les domaines des variations lentes et rapides, d'autre part celles de la densite ionique. Theorie du courant de maxwell sour l'orage. Simulation de l'evolution des divers parametres electriques venant confirmer les resultats experimentaux.

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Armijo, Julien. « Fluctuations de densité dans des gaz de bosons ultafroids quasi-unidimensionnels ». Phd thesis, Université Paris Sud - Paris XI, 2011. http://tel.archives-ouvertes.fr/tel-00601066.

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Cette thèse présente la conception et l'implémentation d'une nouvelle génération de puces à atomes, ouvrant de nouvelles perspectives expérimentales dans des micropièges magnétiques très anisotropes. Les propriétés thermiques des puces en nitrure d'aluminium sont étudiées en détail. Le dispositif a été optimisé pour piéger de plus grands nombres d'atomes et améliorer la qualité de l'imagerie, notamment en fabriquant un miroir de planéité sub-λ/10 à la surface de la puce.Nous étudions des gaz quasi-1D grâce à des images in situ de profils fluctuants et des méthodes précises de calibration et d'analyse statistique. Nous mesurons des fluctuations non-gaussiennes, ce qui permet de tester sensiblement la thermodynamique du gaz et donne une mesure de corrélations à trois corps. Nous étudions précisément la transition de quasicondensation et mesurons pour la première fois sa loi d'échelle. En régime 3D, c'est une condensation transverse qui déclenche la quasicondensation longitudinale, tandis qu'en régime 1D, la formation d'un quasicondensat est gouvernée par les interactions répulsives et non par la dégénérescence quantique.Obtenant des températures record pour des gaz 1D, nous observons des fluctuations subpoissoniennes lorsque les corrélations atomiques sont déterminées, au moins localement, par les fluctuations quantiques qui dominent les fluctuations thermiques. Nous discutons également la thermalisation étonnamment rapide mesurée en régime 1D profond qui suggère que des collisions effectives à 3 corps brisent l'intégrabilité du système.

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Bowles, R. J. « Density profiles and concentration fluctuations in liquid binary mixtures ». Thesis, University of East Anglia, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370382.

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Livres sur le sujet "Fluctuation de densité"

Kolb, Edward W. Origin of density fluctuations in extended inflation. Batavia, Ill : Fermi National Accelerator Laboratory, 1990.

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Bowles, R. J. Density profiles and concentration fluctuations in liquid binary mixtures. Norwich : University of East Anglia, 1986.

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Haney, Robert L. Estimating subpycnocline density fluctuations in the California Current region from upper ocean observations. Monterey, Calif : Naval Postgraduate School, 1994.

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McCann, Edward. Mesoscopic fluctuations of the electronic density of states in disordered systems. Birmingham : University of Birmingham, 1996.

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United States. National Aeronautics and Space Administration., dir. Measurement of temperature and density fluctuations in turbulence using an ultraviolet laser. San Diego, CA : San Diego State University, 1986.

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L, McKenzie Robert, et Ames Research Center, dir. Measurements of density,temperature, and their fluctuations in turbulent supersonic flow using UV laser spectroscopy. Moffett Field, Calif : National Aeronautics and Space Administration, Ames Research Center, 1992.

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United States. National Aeronautics and Space Administration., dir. Quenching of the beam-plasma instability by 3-D spectra of large scale density fluctuations. Boulder, Colo : University of Colorado, 1985.

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L, McKenzie R., et Ames Research Center, dir. Measurements of density,temperature, and their fluctuations in turbulent supersonic flow using UV laser spectroscopy. Moffett Field, Calif : National Aeronautics and Space Administration, Ames Research Center, 1992.

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Center, Langley Research, dir. A real time dynamic data acquisition and processing system for velocity, density, and total temperature fluctuation measurements. Hampton, Va : National Aeronautics and Space Administration, Langley Research Center, 1991.

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Chapitres de livres sur le sujet "Fluctuation de densité"

Niquet, Y. M., et M. Fuchs. « The Exchange-Correlation Potential in the Adiabatic-Connection Fluctuation-Dissipation Framework ». Dans Time-Dependent Density Functional Theory, 435–42. Berlin, Heidelberg : Springer Berlin Heidelberg, 2006. http://dx.doi.org/10.1007/3-540-35426-3_29.

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Gómez González, Rubén, et Vicente Garzó. « Kinetic Theory of Binary Granular Suspensions at Low Density. Thermal Diffusion Segregation ». Dans Nonequilibrium Thermodynamics and Fluctuation Kinetics, 173–89. Cham : Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-031-04458-8_9.

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Fang, Li-Zhi, et Yi-Peng Jing. « Density Fluctuations on Super-Hubble Scales ». Dans Modern Mathematical Models of Time and their Applications to Physics and Cosmology, 73–80. Dordrecht : Springer Netherlands, 1997. http://dx.doi.org/10.1007/978-94-011-5628-8_6.

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Komorowski, Tomasz, Claudio Landim et Stefano Olla. « Equilibrium Fluctuations of the Density Field ». Dans Grundlehren der mathematischen Wissenschaften, 241–74. Berlin, Heidelberg : Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-29880-6_7.

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Szalay, Alexander S. « Constraints on the Biasing of Density Fluctuations ». Dans Large Scale Structures of the Universe, 163–67. Dordrecht : Springer Netherlands, 1988. http://dx.doi.org/10.1007/978-94-009-2995-1_22.

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Weng, Z. Y., et C. S. Ting. « Doping Effects on the Spin-Density-Wave Background ». Dans Dynamics of Magnetic Fluctuations in High-Temperature Superconductors, 335–46. Boston, MA : Springer US, 1991. http://dx.doi.org/10.1007/978-1-4684-7490-9_34.

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Safonov, Vladimir L., et H. Neal Bertram. « Magnetization Dynamics and Thermal Fluctuations in Fine Grains and Films ». Dans The Physics of Ultra-High-Density Magnetic Recording, 81–109. Berlin, Heidelberg : Springer Berlin Heidelberg, 2001. http://dx.doi.org/10.1007/978-3-642-56657-8_3.

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Balestrino, G., E. Milani et A. A. Varlamov. « The Role of Density of States Fluctuations on the C-Axis Resistivity of High T c Superconductors ». Dans Fluctuation Phenomena in High Temperature Superconductors, 201–15. Dordrecht : Springer Netherlands, 1997. http://dx.doi.org/10.1007/978-94-011-5536-6_15.

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Cress, C. M. « Probing Density Fluctuations Using the First Radio Survey ». Dans Observational Cosmology, 137–42. Dordrecht : Springer Netherlands, 1998. http://dx.doi.org/10.1007/978-94-011-5238-9_24.

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Scaramella, Roberto, et Nicola Vittorio. « Constraints on the amplitude of primordial density fluctuations ». Dans The Epoch of Galaxy Formation, 401–2. Dordrecht : Springer Netherlands, 1989. http://dx.doi.org/10.1007/978-94-009-0919-9_55.

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Actes de conférences sur le sujet "Fluctuation de densité"

Hori, Yoshikazu, Yasushi Matsui, Jun Ohya, Hiroyuki Serizawa et Hisanao Sato. « Theoretical Analysis of Reflection Noise in Semiconductor Lasers ». Dans Numerical Simulation and Analysis in Guided-Wave Optics and Opto-Electronics. Washington, D.C. : Optica Publishing Group, 1989. http://dx.doi.org/10.1364/gwoe.1989.sa2.

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Intensity fluctuations of semiconductor lasers due to optical feedback were theoretically analyzed by using modified rate equations which include a refractive index fluctuation. Photon density fluctuations were simulated, and their Fourier transformed spectra were obtained and analyzed. Optical beating of the external cavity modes, which generates the fluctuation of the refractive indices of the semiconductor materials, is proved to be an origin of the reflection noise.

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Toronov, V., M. Filiaci, S. Fantini et E. Gratton. « Study of Large Scale Fluctuations in Turbid Media by Photon-Density-Wave Fluctuation Correlation Spectroscopy ». Dans Advances in Optical Imaging and Photon Migration. Washington, D.C. : OSA, 1998. http://dx.doi.org/10.1364/aoipm.1998.asub7.

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Takei, Masahiro, Hui Li, Mitsuaki Ochi, Yoshifuru Saito et Kiyoshi Horii. « 3D Wavelet Multiresolution of Multiphase Flow CT Images ». Dans ASME 2002 Joint U.S.-European Fluids Engineering Division Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/fedsm2002-31118.

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The extraction of dominant particle density fluctuation in various time-space frequency levels on a pipeline cross section was performed using capacitance-computed tomography and three-dimensional discrete wavelets transform. As a result, particle density fluctuation downstream of a bent pipe is decomposed into the time-space levels in a non-choking state and a pseudo-choking state. The proposed method enables realization of the time and position at which particle density fluctuations with respect to dominant time-space levels pass through the pipeline.

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Phillips, Ronald L., et Larry C. Andrews. « Probability density function for two-scale non-Gaussian scattering ». Dans OSA Annual Meeting. Washington, D.C. : Optica Publishing Group, 1988. http://dx.doi.org/10.1364/oam.1988.wp2.

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The non-Gaussian nature of optical wave scattering by a number of different mechanisms has been modeled as a compound random modulation process. The success of this modeling approach has been due to the scattering mechanisms themselves having two discernible scales of fluctuations. A small-scale fluctuation appears to have a modulation over a much larger scale. This modulated scatterer gives rise to a similar scattered optical wave. The scattered optical wave appears to have a fine structure whose strength is modulated by a more coarse structure. The probability density function (PDF) of the detected intensity can be calculated from conditional statistics. The small-scale rapid fluctuations are treated as a conditional PDF and then averaged over the PDF of the large-scale slower fluctuations. This approach has been used to describe scattering by surfaces, phase screens, and extended path turbulence. A more exact approach to this two-scale phenomenon is to express the scattered field as a sum of scattered components, i.e.,

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Montgomery, David. « Turbulent magnetohydrodynamic density fluctuations ». Dans AIP Conference Proceedings Volume 174. AIP, 1988. http://dx.doi.org/10.1063/1.37600.

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Peterleithner, Johannes, Nicolai V. Stadlmair, Jakob Woisetschläger et Thomas Sattelmayer. « Analysis of Measured Flame Transfer Functions With Locally Resolved Density Fluctuation and OH-Chemiluminescence Data ». Dans ASME Turbo Expo 2015 : Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-42745.

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The goal of the study presented in this paper is to analyze flame transfer functions with a new approach based on the combination of-line-of sight OH*-chemiluminescence and density fluctuation data. The OH*-chemiluminescence is acquired with a photomultiplier and an intensified camera, the density fluctuations are measured with a Laser vibrometer on a two axis traverse. In flames with forcing the acoustic fluctuations can be extracted from the data by discrimination of all contributions from combustion noise, because it is not correlated with the excitation device. Assuming rotational symmetry of the fluctuations originating from excitation, planar phase-resolved and pseudo-local OH*-chemiluminescence and density fluctuation data is obtained from the measured line-of-sight integrated signals. In the study this technique is applied to a swirl burner configuration with FTFs from known multi-microphone measurements (MMM). In the first step, the externally premixed mode without equivalence ratio fluctuations is studied and in the second step the fuel is injected in the swirler in order to generate equivalence ratio waves. At selected frequencies the planar fields of the OH*-chemiluminescence and density fluctuations are compared to the FTFs in order to improve the understanding regarding the specific amplitude and phase values. In addition to heat release the vibrometer data reveals the periodic oscillation of the conical annular jet of the cold reactants in the combustor filled with hot products. On the global scale the amplitudes and phases of heat release expected from the MMM are satisfactorily reproduced by both methods for the premixed cases, whereas OH*-chemiluminescence data cannot be used as indicator for heat release if equivalence ratio fluctuations are present, because the amplitude of the FTF is significantly over-predicted due to the sensitivity of OH* on the local fuel-air mixture.

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Wijesinghe, H. S., C. S. Tan et E. E. Covert. « Aerodynamic Response of Turbomachinery Blade Rows to Convecting Density Wakes ». Dans ASME Turbo Expo 2000 : Power for Land, Sea, and Air. American Society of Mechanical Engineers, 2000. http://dx.doi.org/10.1115/2000-gt-0417.

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A two–dimensional computational study was conducted to characterize the density wake induced force and moment fluctuations on a compressor blade row. The flow simulations indicate unsteady blade excitation generated by: (1) density wake fluid directed to the blade suction surface, (2) axial deflection of the blade passage shock wave position and (3) formation of a separation bubble on the blade suction surface. The blade force and moment fluctuation amplitudes are found to scale with the nondimensional density wake width w/c and a non–dimensional density parameter ρ*.

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Kasahara, Naoto, Nobuyuki Kimura et Hideki Kamide. « Thermal Fatigue Evaluation Method Based on Power Spectrum Density Functions Against Fluid Temperature Fluctuation ». Dans ASME 2005 Pressure Vessels and Piping Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/pvp2005-71307.

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Fluid temperature fluctuates at an incomplete mixing area of high and low temperature fluids in nuclear components. It induces random variations of local temperature gradients in structural walls, which lead to cyclic thermal stresses. When thermal stresses and cycle numbers are large, there are possibilities of fatigue crack initiations and propagations. It is recognized that there are attenuation factors depending on fluctuation frequency in the transfer process from fluid temperature to thermal stresses. If a frequency of fluctuation is very low, whole temperature of the wall can respond to fluid temperature, because thermal diffusivity homogenizes structural temperature. Therefore, low frequency fluctuations do not induce large thermal stress due to temperature gradients in structures. On the other hand, a wall surface cannot respond to very high frequency fluctuation, since a structure has a time constant of thermal response. High frequency fluctuations do not lead to large thermal stress. Paying attention to its attenuation mechanism, Japan Nuclear Cycle Development Institute (JNC) has proposed a fatigue evaluation method related to frequencies. The first step of this method is an evaluation of Power Spectrum Density (PSD) on fluid, from design specifications such as flow rates, diameters of pipes and materials. In the next step, the PSD of fluid is converted to PSD of thermal stress by the frequency transfer function. Finally, the PSD of thermal stress is transformed to time history of stress under an assumption of random phase. Fatigue damage factors can be evaluated from stress ranges and cycles obtained by the rain flow wave count method. Proposed method was applied to evaluate fatigue damage of piping junction model tests conducted at Oarai Engineering Center. Through comparison with direct evaluation from measurements and predictions by conventional methods, the accuracy of the proposed method was validated.

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Belzig, Wolfgang. « Density correlations in ultracold atomic Fermi gases ». Dans NOISE AND FLUCTUATIONS : 18th International Conference on Noise and Fluctuations - ICNF 2005. AIP, 2005. http://dx.doi.org/10.1063/1.2036873.

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Watanabe, K., Y. Kaiho, S. Hara, T. Tsukahara et Y. Kawaguchi. « A Study on Heat Transport Phenomena in a Developed Thermal Boundary Layer of Drag Reducing Channel Flow ». Dans ASME 2016 Fluids Engineering Division Summer Meeting collocated with the ASME 2016 Heat Transfer Summer Conference and the ASME 2016 14th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/fedsm2016-7680.

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The heat transport phenomena in a developed thermal boundary layer of surfactant solution flow were investigated experimentally. The experiment was conducted under different surfactant additive concentrations. The temperature fluctuations in a thermal boundary layer in a smooth channel flow were measured by fine-wire thermocouple probe. Heat transfer reducing rate and temperature fluctuation characteristics including mean temperature distribution, intensity, wave form, spectral density function, and skewness factor were studied. The results showed that the turbulent transport is obstructed by additives, and the temperature field shows dramatic changes. High frequency component of temperature fluctuation of surfactant solution flow was decreased due to suppression of turbulence and viscoelasticity. Large temperature fluctuations occur in the thermal boundary layer because the development of the thermal boundary layer is obstructed, and large temperature fluctuations appear to concentrate the temperature gradient in the near-wall region (10 < y+ < 60). In contrast, viscous sublayer expands due to viscoelasticity, and the temperature gradient and turbulence fluctuation are small in the near-wall region of y+ < 10. As a result, two layers having significantly different characteristics seem to coexist. The heat transfer reduction is constant with variation of additive concentration condition, but heat transport phenomena were microscopically influenced by viscoelasticity.

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Rapports d'organisations sur le sujet "Fluctuation de densité"

Shen, W., R. N. Dexter et S. C. Prager. Current density fluctuations and ambipolarity of transport. Office of Scientific and Technical Information (OSTI), octobre 1991. http://dx.doi.org/10.2172/10109823.

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Nazikian, R., et E. Mazzucato. Reflectometer measurements of density fluctuations in tokamak plasmas. Office of Scientific and Technical Information (OSTI), août 1994. http://dx.doi.org/10.2172/10172218.

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Shen, Weimin. Measurement of current density fluctuations and ambipolar particle flux due to magnetic fluctuations in MST. Office of Scientific and Technical Information (OSTI), août 1992. http://dx.doi.org/10.2172/7273865.

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Thomas, D. M. An edge density fluctuation diagnostic for DIII-D using lithium beams. Office of Scientific and Technical Information (OSTI), décembre 1991. http://dx.doi.org/10.2172/5690058.

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Gray, A. L., et K. E. Mattar. Influence of Ionospheric Electron Density Fluctuations on Satellite Radar Interferometry. Natural Resources Canada/ESS/Scientific and Technical Publishing Services, 2000. http://dx.doi.org/10.4095/219669.

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H. Park, E. Mazzucato, T. Munsat, C.W. Domier, M. Johnson, Jr N.C. Luhmann, J. Wang et al. Simultaneous Microwave Imaging System for Density and Temperature Fluctuation Measurements on TEXTOR. Office of Scientific and Technical Information (OSTI), mai 2004. http://dx.doi.org/10.2172/827935.

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Ayik, S. Dynamics of density fluctuations in a non-Markovian Boltzmann- Langevin model. Office of Scientific and Technical Information (OSTI), mars 1996. http://dx.doi.org/10.2172/224952.

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Mazzucato, E., et R. Nazikian. Microwave reflectometry for the study of density fluctuations in tokamak plasmas. Office of Scientific and Technical Information (OSTI), décembre 1990. http://dx.doi.org/10.2172/6377672.

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