Journal articles on the topic 'Fluctuation de densité'
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1
Artemenko, S. N. "Modification of charge density wave fluctuations by charge perturbations." Journal de Physique IV 12, no. 9 (November 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., and Rizwan U. Haq. ""Universality" of Gaussian orthogonal ensemble fluctuations: the two-body random ensemble and shell model spectra." Canadian Journal of Physics 68, no. 3 (March 1, 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, no. 12 (December 5, 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, no. 01n02 (June 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, and JOE SATO. "EFFECTS OF MATTER DENSITY FLUCTUATION IN LONG BASELINE NEUTRINO OSCILLATION EXPERIMENTS." Modern Physics Letters A 14, no. 19 (June 21, 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, and M. Moncuquet. "Density fluctuations measured by ISEE 1-2 in the Earth's magnetosheath and the resultant scattering of radio waves." Annales Geophysicae 15, no. 4 (April 30, 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, and AJIT M. SRIVASTAVA. "BARYOGENESIS VIA DENSITY FLUCTUATIONS WITH A SECOND ORDER ELECTROWEAK PHASE TRANSITION." International Journal of Modern Physics A 18, no. 26 (October 20, 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, and Xu-Qu Hu. "Two-Dimensional Simulations of Turbulent Flow Past a Row of Cylinders using Lattice Boltzmann Method." International Journal of Computational Methods 14, no. 01 (January 11, 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, and Y. Naka. "Pressure Fluctuations on the Surface of a Hemisphere Immersed in a Thick Turbulent Boundary Layer." Journal of Fluids Engineering 109, no. 2 (June 1, 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., and C. R. Sovinec. "Pressure-driven tearing and thermal transport in finite-beta reversed field pinch computations." Physics of Plasmas 30, no. 1 (January 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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Mehay, T. P., R. Warmbier, and A. Quandt. "Investigation of density fluctuations in graphene using the fluctuation-dissipation relations." Computational Condensed Matter 13 (December 2017): 1–5. http://dx.doi.org/10.1016/j.cocom.2017.08.008.
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Singh, Rajeev. "Quantum fluctuations of baryon number density." Journal of Physics: Conference Series 2105, no. 1 (November 1, 2021): 012006. http://dx.doi.org/10.1088/1742-6596/2105/1/012006.
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Abstract Quantum fluctuation expression of the baryon number for a subsystem consisting of hot relativistic spin− 1 2 particles are derived. These fluctuations seems to diverge in the limit where system size goes to zero. For a broad range of thermodynamic parameters numerical solutions are obtained which might be helpful to interpret the heavy-ion experimental data.
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Kellogg, P. J., and T. S. Horbury. "Rapid density fluctuations in the solar wind." Annales Geophysicae 23, no. 12 (December 23, 2005): 3765–73. http://dx.doi.org/10.5194/angeo-23-3765-2005.
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Abstract. Electron density fluctuations (up to 2.5 Hz) in the solar wind have been studied, using the EFW experiment on the Cluster spacecraft, which measures density through measurements of the biased probe potentials relative to the spacecraft. The density fluctuation spectra obtained from the EFW probe potential variations are compared to earlier, OGO 5, measurements of ion density fluctuations and ISEE measurements of electron density fluctuations, and are consistent with them. The electric fields corresponding to the electron density fluctuations are extremely small compared with what would be obtained if the electron fluctuations were not cancelled out by nearly equal ion density fluctuations. This is consistent with the nature of ion acoustic waves. In agreement with ISEE work, the fluctuations are proportional to the ambient density. Correlation with magnetic fluctuations is weak, essentially nonexistent during part of the period studied. This might be expected as magnetic fluctuations are known to be nearly incompressible, but even the correlation with fluctuations in the magnitude of B is very small. However, many structures which apparently are pressure balance structures are found. Pressure balance structures are the nearly perpendicular propagation limit of ion acoustic waves. As ion acoustic waves are strongly damped in plasmas like the solar wind at least if the plasma is taken as Maxwellian, it has always been a puzzle as to why they are found there. We speculate that these waves are created by mode conversion from magnetic fluctuations, and may represent part of the dissipation process for these.
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Ma, Hua, Li-Juan Cui, Wei Li, Yu Ning, Yin-Ru Lei, Xu Pan, Yi-Fei Wang, and Man-Yin Zhang. "Effect of daily salinity fluctuation on the intraspecific interactions of a euhalophyte (Suaeda salsa) along a salinity gradient." Journal of Plant Ecology 15, no. 1 (January 11, 2022): 208–21. http://dx.doi.org/10.1093/jpe/rtac002.
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Abstract Heterogeneity of soil salinity is a prominent environmental characteristic in the intertidal zone of estuaries, affecting the plant growth and the shift of biotic interactions in the salt marsh. This study aims to examine the interactive effects of a salinity gradient and salinity fluctuations on intraspecific interactions of a euhalophyte. We assessed the impact of daily fluctuating salinity on the outcome of intraspecific interactions by cultivating seeds of Suaeda salsa (Chenopodiaceae) in river sand. The experiment was conducted in a greenhouse with three treatments: daily salinity fluctuations (static and fluctuating salinity), a salinity gradient (200 and 400 mmol L−1) and three planting densities (1, 2 and 4 plants/pot). First, height and biomass of plants were measured at both the start and end of the experiment. Then, the growth indexes and log response ratio of S. salsa were analyzed. The outcome of intraspecific interactions of S. salsa shifted from competition in low salinity to facilitation in high salinity, and high conspecific density strengthened the competition and facilitation intensities. Daily salinity fluctuation did not significantly affect the plant growth and the outcome of intraspecific interactions, but did have a significant influence on belowground biomass. Our results suggest that the stress-gradient hypothesis may apply to predicting the variation of the intraspecific relationship of a salt-tolerant species along a salinity gradient, and the magnitude of this variation is density dependent. These findings help us understand how individuals and populations of a euhalophyte species respond to the natural variation or human modification of salinity conditions.
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Lin, L., W. X. Ding, D. L. Brower, W. F. Bergerson, and T. F. Yates. "Differential interferometry for measurement of density fluctuations and fluctuation-induced transport (invited)." Review of Scientific Instruments 81, no. 10 (October 2010): 10D509. http://dx.doi.org/10.1063/1.3464480.
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Lee, J. S., and L. P. Lee. "Ventilatory changes of pulmonary capillary blood volume assessed by arterial density." Journal of Applied Physiology 61, no. 5 (November 1, 1986): 1724–31. http://dx.doi.org/10.1152/jappl.1986.61.5.1724.
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By use of an improved density measuring system, we found that the gravimetric density of arterial blood of dogs fluctuates at the same frequency as the spontaneous or mechanical ventilation. Similar density fluctuations were observed in the blood leaving isolated, perfused lobes of dogs that were ventilated cyclicly. Employing an analysis that balanced the erythrocyte and plasma flows through distensible capillaries containing blood with a tube hematocrit lower than the hematocrit in large blood vessels, we derived a relationship to estimate from the density fluctuation the change in pulmonary capillary blood volume (Vc). For mechanical ventilation, the maximum change in density over one ventilation cycle increased from 0.084 +/- 0.01 to 0.47 +/- 0.05 (SE) g/l as the frequency decreased from 29 to 6 cycles/min. These density changes were estimated to be the result of an 1–16% change in Vc. A larger tidal volume for the mechanical ventilation led to a larger density fluctuation. The maximum density change of spontaneous respiration of 6 cycles/min was one-sixth of the mechanical case, indicating a much smaller change in Vc during spontaneous respiration. When the airway flow resistance was increased for spontaneous respiration, larger density fluctuations were observed.
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Mingesz, R., G. Vadai, and Z. Gingl. "Power Spectral Density Estimation for Wireless Fluctuation Enhanced Gas Sensor Nodes." Fluctuation and Noise Letters 13, no. 02 (June 2014): 1450011. http://dx.doi.org/10.1142/s0219477514500114.
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Fluctuation enhanced sensing (FES) is a promising method to improve the selectivity and sensitivity of semiconductor and nanotechnology gas sensors. Most measurement setups include high cost signal conditioning and data acquisition units as well as intensive data processing. However, there are attempts to reduce the cost and energy consumption of the hardware and to find efficient processing methods for low cost wireless solutions. In this paper, we propose highly efficient signal processing methods to analyze the power spectral density of fluctuations. These support the development of ultra-low-power intelligent fluctuation enhanced wireless sensor nodes while several further applications are also possible.
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Dastgeer, S., and G. P. Zank. "Turbulence in nearly incompressible fluids: density spectrum, flows, correlations and implication to the interstellar medium." Nonlinear Processes in Geophysics 12, no. 1 (January 28, 2005): 139–48. http://dx.doi.org/10.5194/npg-12-139-2005.
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Abstract. Interstellar scintillation and angular radio wave broadening measurements show that interstellar and solar wind (electron) density fluctuations exhibit a Kolmogorov-like k-5/3 power spectrum extending over many decades in wavenumber space. The ubiquity of the Kolmogorov-like interstellar medium (ISM) density spectrum led to an explanation based on coupling incompressible magnetohydrodynamic (MHD) fluctuations to density fluctuations through a "pseudosound" relation within the context of "nearly incompressible" (NI) hydrodynamics (HD) and MHD models. The NI theory provides a fundamentally different explanation for the observed ISM density spectrum in that the density fluctuations can be a consequence of passive scalar convection due to background incompressible fluctuations. The theory further predicts generation of long-scale structures and various correlations between the density, temperature and the (magneto) acoustic as well as convective pressure fluctuations in the compressible ISM fluids in different thermal regimes that are determined purely by the thermal fluctuation level. In this paper, we present the results of our two dimensional nonlinear fluid simulations, exploring various nonlinear aspects that lead to inertial range ISM turbulence within the context of a NI hydrodymanics model. In qualitative agreement with the NI predictions and the in-situ observations, we find that i) the density fluctuations exhibit a Kolmogorov-like spectrum via a passive convection in the field of the background incompressible fluctuations, ii) the compressible ISM fluctuations form long scale flows and structures, and iii) the density and the temperature fluctuations are anti-correlated.
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Spangler, S. R. "The small amplitude of density turbulence in the inner solar wind." Nonlinear Processes in Geophysics 10, no. 1/2 (April 30, 2003): 113–20. http://dx.doi.org/10.5194/npg-10-113-2003.
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Abstract. Very Long Baseline Interferometer (VLBI) observations were made of radio sources close to the Sun, whose lines of sight pass through the inner solar wind (impact parameters 16-26 RE). Power spectra were analyzed of the interferometer phase fluctuations due to the solar wind plasma. These power spectra provide information on the level of plasma density fluctuations on spatial scales of roughly one hundred to several thousand kilometers. By specifying an outer scale to the turbulence spectrum, we can estimate the root-mean-square (rms) amplitude of the density fluctuations. The data indicate that the rms fluctuation in density is only about 10% of the mean density. This value is low, and consistent with extrapolated estimates from more distant parts of the solar wind. Physical speculations based on this result are presented.
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MOSTOVOY, MAXIM, and JASPER KNOESTER. "INSTANTON CALCULATION OF THE DENSITY OF STATES OF DISORDERED PEIERLS CHAINS." International Journal of Modern Physics B 13, no. 13 (May 30, 1999): 1601–18. http://dx.doi.org/10.1142/s0217979299001594.
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We use the optimal fluctuation method to find the density of electron states inside the pseudogap in disordered Peierls chains. The electrons are described by the one-dimensional Dirac Hamiltonian with randomly varying mass (the Fluctuating Gap Model). We establish a relation between the disorder average in this model and the quantum-mechanical average for a certain double-well problem. We show that the optimal disorder fluctuation, which has the form of a soliton–antisoliton pair, corresponds to the instanton trajectory in the double-well problem. We use the instanton method developed for the double-well problem to find the contribution to the density of states from disorder realizations close to the optimal fluctuation.
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Padmaja, S., M. Ramakrishna Nanchara Rao, P. V. Datta Prasad, and V. G. K. M. Pisipati. "Studies of the Orientational Disorder at the Isotropic to Smectic-F Interface." Zeitschrift für Naturforschung A 60, no. 4 (April 1, 2005): 296–300. http://dx.doi.org/10.1515/zna-2005-0414.
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Abstract Density studies on the isotropic to smectic-F transition in higher homologues of N-(p-nalkoxybenzylidene)- p-n-decylanilines (nO.10) mesomorphic compounds with n = 13, 14 and 15 and corresponding studies on thermal expansion coefficient maxima confirm the first order nature of this transition. The density shows strong pretransitional fluctuations, which are estimated by αeff in the vicinity of the mesomorphic fluctuation dominated non-linear region (FDNLR) of this phase transition. The growth of the density fluctuations across this transition is discussed in the light of data on the same transition in other compounds.
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Yang, Yang, Xionghuan Chen, Ling Bai, Yulong Yao, Hui Wang, Leilei Ji, Zhaoming He, Xiangyu Song, and Ling Zhou. "Quantification and investigation of pressure fluctuation intensity in a multistage electric submersible pump." Physics of Fluids 35, no. 3 (March 2023): 035122. http://dx.doi.org/10.1063/5.0136664.
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Pressure fluctuation is an important factor affecting the stability of rotating machinery. Electric submersible pumps (ESPs) are generally arranged in a multistage series structure, and its internal unsteady flow is extremely easy to propagate and develop in the lengthy flow passage, which brings about differences in the characteristics of pressure fluctuations in each stage. In contrast to the conventional method of processing pressure fluctuation signals, we propose a parameter called “energy flow density (EFD)” of pressure pulsation by analogy with the definition of wave intensity, in order to directly quantify the intensity of pressure fluctuations. Here, we study these pressure fluctuation characteristics using a typical three-stage ESP as the research object. We apply theoretical analysis, numerical simulation, and test verification. First, in comparisons between numerical predictions of pressure fluctuation and test results, the period, amplitude, and phase of pulsation curves are highly consistent, verifying the accuracy of the numerical method employed in this paper. Next, the mechanism underlying the pressure fluctuations and the characteristics of inter-stage interference are investigated through flow field analysis. Subsequently, the results of the evaluation of the pressure fluctuations based on EFD processing are compared with those obtained in the conventional way. The results are consistent in terms of characterizing the multistage ESP pressure fluctuation characteristics, but the conventional method does not reflect subtle differences due to inter-stage propagation and coupling. However, the EFD method combines the amplitudes of all signals and provides the intensity of pressure fluctuations directly, which reflects inter-stage differences. Our results provide a theoretical basis for improving the operational stability of ESPs connected in a multistage series and have practical engineering significance.
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SURESH, P. K. "THERMAL SQUEEZING AND DENSITY FLUCTUATIONS IN SEMICLASSICAL THEORY OF GRAVITY." Modern Physics Letters A 16, no. 11 (April 10, 2001): 707–17. http://dx.doi.org/10.1142/s0217732301003802.
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A thermal squeezed state representation is constructed for each mode of a quantized scalar field in a spatially homogeneous and flat Robertson–Walker metric and the validity of semiclassical Einstein equation by analyzing the density fluctuation is examined. The density fluctuation in thermal squeezed state is very large and therefore the semiclassical theory may not be valid for squeezing parameter more than unity, however the theory holds when the associated squeezing parameter is much less than the unity. Further noted that the semiclassical theory is consistent in thermal coherent state formalism. The present study can account for the density fluctuations due to the thermal and quantum effects in semiclassical theory of gravity.
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Słodkowski, Marcin, Patryk Gawryszewski, and Dominik Setniewski. "Study of the influence of initial-state fluctuations on hydrodynamic simulations." EPJ Web of Conferences 245 (2020): 06005. http://dx.doi.org/10.1051/epjconf/202024506005.
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In this work, we are focusing on assessing the contribution of the initial-state fluctuations of heavy ion collision in the hydrodynamic simulations. We are trying to answer the question of whether the hydrodynamic simulation retains the same level of fluctuation in the final-state as for the initial stage. In another scenario, the hydrodynamic simulations of the fluctuation drowns in the final distribution of expanding matter. For this purpose, we prepared sufficient relativistic hydrodynamic program to study A+A interaction which allows analysing initial-state fluctuations in the bulk nuclear matter. For such an assumption, it is better to use high spatial resolution. Therefore, we applied the (3+1) dimensional Cartesian coordinate system. We implemented our program using parallel computing on graphics cards processors - Graphics Processing Unit (GPU). Simulations were carried out with various levels of fluctuation in initial conditions using the average method of events coming from UrQMD models. Energy density distributions were analysed and the contribution of fluctuations in initial conditions was assessed in the hydrodynamic simulation.
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Min, He Qun, Xiao Yang Huang, and Qi De Zhang. "Pressure Fluctuations and Flow-Induced Vibration Measurements in a Hard Disk Drive under Different Rotation Speeds." Applied Mechanics and Materials 197 (September 2012): 292–96. http://dx.doi.org/10.4028/www.scientific.net/amm.197.292.
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Flow-induced vibration (FIV) of a head gimbals assembly (HGA) in hard disk drives (HDDs) limits the positioning accuracy of magnetic head in the HGA for higher HDD magnetic recording density. The pressure fluctuations characterize turbulent fluctuations exciting the HGA off-track vibration (HGA-OTV). In this paper, experimental studies have been carried out to investigate the spectrum characteristics correspondence between pressure fluctuations around an HGA and the simultaneous HGA-OTV under different HDD rotation speeds. A practical and effective experimental setup has been implemented to enable the simultaneous measurements on both the pressure fluctuation and HGA-OTV signals, where pressure fluctuations are measured with a pressure transducer through a small hole on the HDD top cover and the direct HGA-OTV signals are detected through a laser Doppler vibrometer. Results under conditions of three different HDD rotation speeds of 7200, 9000, 10800 rpm have been investigated and compared. It is shown that the HGA off-track vibration spectra are highly associated with those of the pressure fluctuations in terms of principal peaks in four frequency bands around 1.8 kHz, 2.5-3.5 kHz, 7-7.5 kHz and 11.5-12.5 kHz. With increasing HDD rotation speed, it is shown that the spectrum magnitudes of both the pressure fluctuation and the HGA off-track vibration increase correspondingly, while the principal peak positions in spectra of either pressure fluctuation or the HGA off-track vibration always hold the line. This study demonstrates a causal nexus from the pressure fluctuation to the HGA off-track vibration and suggests the feasibility of controlling the HGA-OTV through suppression of pressure fluctuations around the HGA.
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PANDA, J., and R. G. SEASHOLTZ. "Experimental investigation of density fluctuations in high-speed jets and correlation with generated noise." Journal of Fluid Mechanics 450 (January 9, 2002): 97–130. http://dx.doi.org/10.1017/s002211200100622x.
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The air density fluctuations in the plumes of fully expanded, unheated free jets were investigated experimentally using a Rayleigh-scattering-based technique. The point measuring technique used a continuous-wave laser, fibre-optic transmission and photon counting electronics. The radial and centreline profiles of time-averaged density and root-mean-square density fluctuation provided a comparative description of jet growth. To measure density fluctuation spectra a two-photomultiplier-tube (PMT) technique was used. Cross-correlation between the two PMT signals significantly reduced the electronic shot noise contribution. The density fluctuation spectra were found to be remarkably similar for all Mach number jets. A detailed survey in fully expanded Mach 0.95, 1.4 and 1.8 jets further confirmed that the distribution of various Strouhal frequency fluctuations remained similar, except for a spatial stretching with increased Mach number. In spite of this similarity in flow fluctuations the noise sources in these three jets were found to be significantly different. Spark schlieren photographs and near-field microphone measurements confirmed that Mach wave radiation was present in the Mach 1.8 jet, and was absent in the Mach 0.95 jet. Direct correlation measurement between the flow density fluctuation (cause) and far-field sound pressure fluctuation (effect) shed further light on the sound generation process. For this purpose a microphone was kept fixed at a far-field point, mostly at a distance of 50 diameters and 30° to the flow direction, and the laser probe volume was moved from point to point in the flow. In the Mach 1.8 jet, where the convective velocity of Kelvin–Helmholtz instability waves exceeded the ambient sound speed, significant correlation was measured from the peripheral shear layer, while in the Mach 0.95 jet, where the instability waves had subsonic convective speed, no correlation could be measured. Although the same instability waves were present in both Mach 1.8 and 0.95 jets, the peripheral shear layer of the former was found to be an obvious noise source, while that of the latter was not. Further correlation studies along the jet centreline showed that behaviour in the region downstream of the potential core was similar in all Mach number jets tested, 0:6[les ]M[les ]1:8. Good correlation at low Strouhal frequencies was measured from this region, which started from downstream of the potential core and extended many diameters from there.
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Gruenwald, Ruth, and Sueli M. Viegas. "Temperature Fluctuations in PN." Symposium - International Astronomical Union 155 (1993): 188. http://dx.doi.org/10.1017/s0074180900170500.
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For planetary nebulae, empirical abundances can be obtained from the observed emission-lines as long as the electron density, the electron temperature, and the ionization corrections factor are determined. However, due to temperature fluctuations in the emitting gas, the evaluation of the temperature from the observational data is strongly dependent on the method used. The temperature fluctuation is usually characterized by the mean square temperature fluctuation, t2 (Peimbert and Costero, 1969 — PC).
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Šolc, M., and J. Hostomský. "Amplitudes of Composition Fluctuations in the Simplest Chemical Reaction Equilibrium." Zeitschrift für Physikalische Chemie 218, no. 9 (September 1, 2004): 1033–40. http://dx.doi.org/10.1524/zpch.218.9.1033.41674.
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AbstractWe present a numerical study of equilibrium composition fluctuations in a system where the reaction X1 ⇔ X2 having the equilibrium constant equal to 1 takes place. The total number of reacting particles is N. On a discrete time scale, the amplitude of a fluctuation having the lifetime 2r reaction events is defined as the difference between the number of particles X1 in the microstate most distant from the microstate N/2 visited at least once during the fluctuation lifetime, and the equilibrium number of particles X1, N/2. On the discrete time scale, the mean value of this amplitude, m̅(r̅), is calculated in the random walk approximation. On a continuous time scale, the average amplitude of fluctuations chosen randomly and regardless of their lifetime from an ensemble of fluctuations occurring within the time interval (0,z), z → ∞, tends with increasing N to ~1.243 N0.25. Introducing a fraction of fluctuation lifetime during which the composition of the system spends below the mean amplitude m̅(r̅), we obtain a value of the mean amplitude of equilibrium fluctuations on the continuous time scale equal to ~1.19√N. The results suggest that using the random walk value m̅(r̅) and taking into account a) the exponential density of fluctuations lifetimes and b) the fact that the time sequence of reaction events represents the Poisson process, we obtain values of fluctuations amplitudes which differ only slightly from those derived for the Ehrenfest model.
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Mali, P., S. Sarkar, S. Ghosh, A. Mukhopadhyay, and G. Singh. "Multifractal detrended fluctuation analysis of particle density fluctuations in high-energy nuclear collisions." Physica A: Statistical Mechanics and its Applications 424 (April 2015): 25–33. http://dx.doi.org/10.1016/j.physa.2014.12.037.
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Taye, Jyotismita, Jyotirmoy Barman, Bimlesh Kumar, and Giuseppe Oliveto. "Deciphering Morphological Changes in a Sinuous River System by Higher-Order Velocity Moments." Water 12, no. 3 (March 11, 2020): 772. http://dx.doi.org/10.3390/w12030772.
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Bank erosion in a sinuous alluvial channel is a continuous phenomenon resulting in bank instability and migration of sediment. In this study, flume experiments were conducted in a sinuous channel to investigate its morphological changes and hydrodynamics. High-order velocity fluctuation moments are analyzed at outer and inner banks to explain the morphological variation in a sinuous river channel. The variance of streamwise velocity fluctuations on both banks of the sinuous channel follows a logarithmic law from a particular depth. In the outer bend region, the magnitude of velocity fluctuation moment is significant, indicating erosion. The trend of velocity fluctuation at higher even-order moments is similar to the variance of streamwise velocity fluctuations where the outer bend magnitude is greater than the inner bend. The premultiplied probability density functions (PDFs) and the flatness factor show greater magnitude in the outer bend of the channel as compared to the inner bend.
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Nie, Deming, and Jianzhong Lin. "A Lattice Boltzmann-Direct Forcing/Fictitious Domain Model for Brownian Particles in Fluctuating Fluids." Communications in Computational Physics 9, no. 4 (April 2011): 959–73. http://dx.doi.org/10.4208/cicp.181109.300610a.
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AbstractThe previously developed LB-DF/FD method derived from the lattice Boltzmann method and Direct Forcing/Fictitious Domain method is extended to deal with 3D particle’s Brownian motion. In the model the thermal fluctuations are introduced as random forces and torques acting on the Brownian particle. The hydrodynamic interaction is introduced by directly resolving the fluid motions. A sphere fluctuating in a cubic box with the periodic boundary is considered to validate the present model. By examining the velocity autocorrelation function (VCF) and rotational velocity autocorrelation function (RVCF), it has been found that in addition to the two relaxation times, the mass density ratio should be taken into consideration to check the accuracy and effectiveness of the present model. Furthermore, the fluctuation-dissipation theorem and equipartition theorem have been investigated for a single spherical particle. Finally, a Brownian particle trapped in a harmonic potential has been simulated to further demonstrate the ability of the LB-DF/FD model.
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Allen, Micheal S., and Leandro E. Miranda. "Quasi-cycles in crappie populations are forced by interactions among population characteristics and environment." Canadian Journal of Fisheries and Aquatic Sciences 58, no. 3 (March 1, 2001): 594–601. http://dx.doi.org/10.1139/f01-020.
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Crappie (Pomoxis spp.) populations have been characterized as cyclic, with strong year-classes recurring at 2- to 4-year intervals. We evaluated the potential for cyclic trends in crappie populations using a population model that included a density-dependent stock recruitment function and random environmental variation. Slow, medium, and fast growth were simulated over 100 years. The model predicted highly variable recruitment that was strongly influenced by environmental fluctuation at low and intermediate stock densities. At high stock density, recruitment was low, even if environmental conditions were favorable. Significant quasi-cycles occurred, but they were not sustained throughout the time series due to random environmental fluctuation. Quasi-cycles occurred because intermediate stock density and favorable environmental conditions occasionally combined to produce a very strong year-class that greatly increased stock density in the following 13 years and produced low recruitment, even if environmental conditions were favorable. Empirical data from 32 years of sampling age-0 crappies at Ross Barnett Reservoir showed trends similar to the simulated fluctuations. We conclude that crappie populations likely do not exhibit true cycles but may show quasi-cycles as a result of the interaction between random fluctuations in environment and density-dependent mechanisms. The frequency of such quasi-cycles may be enhanced by rapid growth and high exploitation.
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Yue, Xiaoqing, Yongjia Wang, Qingfeng Li, and Fuhu Liu. "Effects of Initial Density Fluctuations on Cumulants in Au + Au Collisions at sNN = 7.7 GeV." Universe 8, no. 9 (September 18, 2022): 491. http://dx.doi.org/10.3390/universe8090491.
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Within the ultrarelativistic quantum molecular dynamics (UrQMD) model, the effect of initial density fluctuations on cumulants of the net-proton multiplicity distribution in Au + Au Collisions at sNN = 7.7 GeV was investigated by varying the minimum distance dmin between two nucleons in the initialization. It was found that the initial density fluctuations increased with the decrease of dmin from 1.6 fm to 1.0 fm, and the influence of dmin on the magnitude of the net-proton number fluctuation in a narrow pseudorapidity window (Δη≤ 4) was negligible even if it indeed affected the density evolution during the collision. At a broad pseudorapidity window (Δη≥ 4), the cumulant ratios were enlarged when the initial density fluctuations were increased with the smaller value of dmin, and this enhancement was comparable to that observed in the presence of the nuclear mean-field potential. Moreover, the enhanced cumulants were more evident in collisions with a larger impact parameter. The present work demonstrates that the fingerprint of the initial density fluctuations on the cumulants in a broad pseudorapidity window is clearly visible, while it is not obvious as the pseudorapidity window becomes narrow.
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Saito, Tatsuhiko, and Akemi Noda. "Strain energy released by earthquake faulting with random slip components." Geophysical Journal International 220, no. 3 (December 13, 2019): 2009–20. http://dx.doi.org/10.1093/gji/ggz561.
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SUMMARY This study investigates the strain energy change caused by earthquake faulting. While conventional theories often assumed uniform stress change on the fault plane, this study supposed the slip fluctuation and non-uniform stress change on the fault. By using a stochastic modelling of the slip distribution, we represent the ensemble average of the strain energy change by using the power spectral density function of the slip fluctuation. This yields the following results. (1) When the initial stress is uniform and the earthquake contains a fluctuating slip distribution, the released strain energy is less than the one by an earthquake with the uniform stress change on the fault with the same seismic moment. (2) On the other hand, when the initial stress is fluctuating, the earthquake contains a fluctuating slip distribution, and the final stress is uniform, the released strain energy is more than the one by an earthquake with the uniform stress change on the fault. (3) The stress drop becomes large due to the fluctuating slip distribution from the viewpoint of the strain energy release. We derived the analytical solution of the stress change by using the power spectral density function of the random slip fluctuation. (4) The strain energy change is proportional to the seismic moment when ${\epsilon ^2}/a \propto {( {{M_0}} )^{ - 1/3}}$ (${\epsilon ^2}$ is the variance of the fractional slip fluctuation and $a$ is the correlation distance). (5) The energy balance gives the value of initial stress that is required for the earthquake generation. In order to generate an earthquake, the initial stress needs to be larger than the sum of half of the stress drop and the apparent stress. In other words, earthquakes having rich short-wavelength components in the slip distribution are not generated under a low initial stress level.
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Hosokawa, T., and M. Yokosawa. "Pancake Collapse and Structure Formation from CDM Density Fluctuations." Symposium - International Astronomical Union 183 (1999): 250. http://dx.doi.org/10.1017/s007418090013267x.
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Several scales' density fluctuations which exist in the early universe will first gravitationally collapse along one axis and make pancake-like structures. If the collapsed baryonic pancake heats up over 104K by shock formation, radiative cooling begins to work and mass accretion toward the central region will advance. Because of this effect, mass fraction of the high density layer becomes large. Densities and widths of the layers will reflect masses of structures (e.g. galaxy) which will be formed after caustics. In this respect, we assumed an Einstein-de Sitter universe dominated by cold dark matter (ΩDM = 0.9) and investigated the evolutions of fluctuations numerically using one-dimensional hydrodynamic plus N-body codes. We applied a new method for larger fluctuation scales; it is a hybrid method of Eulerian PPM and Zeldovich approximation and it can simulate around the central pancake region with high accuracy.
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Beattie, James R., Christoph Federrath, and Amit Seta. "Magnetic field fluctuations in anisotropic, supersonic turbulence." Monthly Notices of the Royal Astronomical Society 498, no. 2 (August 6, 2020): 1593–608. http://dx.doi.org/10.1093/mnras/staa2257.
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ABSTRACT The rich structure that we observe in molecular clouds is due to the interplay between strong magnetic fields and supersonic (turbulent) velocity fluctuations. The velocity fluctuations interact with the magnetic field, causing it too to fluctuate. Using numerical simulations, we explore the nature of such magnetic field fluctuations, $\delta \mathrm{{\boldsymbol {\mathit {B}}}}$, over a wide range of turbulent Mach numbers, $\operatorname{\mathcal {M}}= 2\!-\!20$ (i.e. from weak to strong compressibility), and Alfvén Mach numbers, $\operatorname{\mathcal {M}_{\text{A0}}}= 0.1\!-\!100$ (i.e. from strong to weak magnetic mean fields, B0). We derive a compressible quasi-static fluctuation model from the magnetohydrodynamical (MHD) equations and show that velocity gradients parallel to the mean magnetic field give rise to compressible modes in sub-Alfvénic flows, which prevents the flow from becoming two dimensional, as is the case in incompressible MHD turbulence. We then generalize an analytical model for the magnitude of the magnetic fluctuations to include $\operatorname{\mathcal {M}}$, and find $|\delta \mathrm{{\boldsymbol {\mathit {B}}}}| = \delta B = c_{\rm s}\sqrt{\pi \rho _0}\operatorname{\mathcal {M}}\operatorname{\mathcal {M}_{\text{A0}}}$, where cs is the sound speed and ρ0 is the mean density of gas. This new relation fits well in the strong B-field regime. We go on to study the anisotropy between the perpendicular (B⊥) and parallel (B∥) fluctuations and the mean-normalized fluctuations, which we find follow universal scaling relations, invariant of $\operatorname{\mathcal {M}}$. We provide a detailed analysis of the morphology for the δB⊥ and δB∥ probability density functions and find that eddies aligned with B0 cause parallel fluctuations that reduce B∥ in the most anisotropic simulations. We discuss broadly the implications of our fluctuation models for magnetized gases in the interstellar medium.
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Sobry, Roger, and Salvino Ciccariello. "Background subtraction and moments of the microscopic density fluctuation." Journal of Applied Crystallography 35, no. 2 (March 22, 2002): 220–27. http://dx.doi.org/10.1107/s0021889802000584.
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Some models of microscopic density fluctuations are numerically analysed in order to study the behaviour of the related background contribution. The results suggest that this contribution can be described by an algebraic expression depending on only the moments of the microscopic density fluctuation. In this way, the parameter values, determined by a best-fit procedure to account for background contributions in the case of real samples, acquire a definite physical meaning. The procedure is applied to the small-angle X-ray intensities of a polymer sample analysed at different temperatures and yields satisfactory results.
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DI CASTRO, D., N. L. SAINI, A. BIANCONI, and A. LANZARA. "DOPING DEPENDENT FLUCTUATIONS NEAR Tc IN THE BI2212 SUPERCONDUCTOR." International Journal of Modern Physics B 14, no. 25n27 (October 30, 2000): 2872–77. http://dx.doi.org/10.1142/s0217979200003022.
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We have measured temperature dependent complex conductivity on Bi 2 Sr 2 CaCu 2 O 8+δ (Bi2212) superconducting system at different doping using single coil technique to determine the superconducting fluctuations near the T c . The results show that the fluctuation region below T c evolves linearly with the doping and is mainly controlled by the superfluid density. On the other hand, the fluctuation region above T c shows an exponential increase with underdoping and seems to have an intimate relationship with the anomalous electronic structure in the underdoped regime.
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Wijesinghe, H. S., C. S. Tan, and E. E. Covert. "Aerodynamic Response of Turbomachinery Blade Rows to Convecting Density Wakes." Journal of Turbomachinery 124, no. 2 (April 1, 2002): 269–74. http://dx.doi.org/10.1115/1.1311287.
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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 nondimensional density parameter ρ*.
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Xu, Siyao, David H. Weinberg, and Bing Zhang. "Statistical Measurements of Dispersion Measure Fluctuations in Fast Radio Bursts." Astrophysical Journal Letters 922, no. 2 (November 26, 2021): L31. http://dx.doi.org/10.3847/2041-8213/ac399c.
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Abstract Extragalactic fast radio bursts (FRBs) have large dispersion measures (DMs) and are unique probes of intergalactic electron density fluctuations. By using the recently released First CHIME/FRB Catalog, we reexamined the structure function (SF) of DM fluctuations. It shows a large DM fluctuation similar to that previously reported in Xu & Zhang, but no clear correlation hinting toward large-scale turbulence is reproduced with this larger sample. To suppress the distortion effect from FRB distances and their host DMs, we focus on a subset of CHIME catalog with DM < 500 pc cm−3. A trend of nonconstant SF and nonzero correlation function (CF) at angular separations θ less than 10° is seen, but with large statistical uncertainties. The difference found between SF and that derived from CF at θ ≲ 10° can be ascribed to the large statistical uncertainties or the density inhomogeneities on scales on the order of 100 Mpc. The possible correlation of electron density fluctuations and inhomogeneities of density distribution should be tested when several thousands of FRBs are available.
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PISANI, FRANCESCA, THIÉRY PIERRE, and DIMITRI BATANI. "Microwave coherent backscattering from acoustic or electronic waves in a magnetized plasma." Journal of Plasma Physics 59, no. 1 (January 1998): 69–82. http://dx.doi.org/10.1017/s0022377897006260.
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A microwave coherent backscattering experiment has been carried out on Mirabelle, a weakly ionized plasma device, with the objective of measuring the electron-density fluctuation level. The experiment is a preliminary step in order to prepare the detection system for a microwave stimulated-backscattering experiment. The incident electromagnetic wave is focused in front of a plane grid, which excites ion acoustic or electron Bernstein waves and induces fluctuations in the plasma. The backscattering signal is collected by the launching circuit and detected by homodyne mixing. The typical ratio of the scattered power to the incident power is about 10−12 and the relative density fluctuations is of the order of δne/ne ≈10−3 against a background electron density ne=(1–5)×109 cm−3. The backscattering measurement is also compared with Langmuir-probe measurements, and gives good agreement with the relative density fluctuations. The spectral width of the backscattered signal has also been studied, by taking into account effects due to the incident-wave focusing and plasma-wave damping.
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Ye, Lyuzhou, Jérémy R. Rouxel, Daeheum Cho, and Shaul Mukamel. "Imaging electron-density fluctuations by multidimensional X-ray photon-coincidence diffraction." Proceedings of the National Academy of Sciences 116, no. 2 (December 24, 2018): 395–400. http://dx.doi.org/10.1073/pnas.1816730116.
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The ultrafast spontaneous electron-density fluctuation dynamics in molecules is studied theoretically by off-resonant multiple X-ray diffraction events. The time- and wavevector-resolved photon-coincidence signals give an image of electron-density fluctuations expressed through the four-point correlation function of the charge density in momentum space. A Fourier transform of the signal provides a real-space image of the multipoint charge-density correlation functions, which reveal snapshots of the evolving electron density in between the diffraction events. The proposed technique is illustrated by ab initio simulations of the momentum- and real-space inelastic scattering signals from a linear cyanotetracetylene molecule.
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Silk, Joseph. "Origin and evolution of the large-scale structure of the universe." Canadian Journal of Physics 68, no. 9 (September 1, 1990): 799–807. http://dx.doi.org/10.1139/p90-117.
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Ever since the epoch of the spontaneous breaking of grand unification symmetry between the nuclear and electromagnetic interactions, the universe has expanded under the imprint of a spectrum of density fluctuations that is generally considered to have originated in this phase transition. I will discuss various possibilities for the form of the primordial fluctuation spectrum, spanning the range of adiabatic fluctuations, isocurvature fluctuations, and cosmic strings. Growth of the seed fluctuations by gravitational instability generates the formation of large-scale structures, from the scale of galaxies to that of clusters and superclusters of galaxies. There are three areas of confrontation with observational cosmology that will be reviewed. The large-scale distribution of the galaxies, including the apparent voids, sheets and filaments, and the coherent peculiar velocity field on scales of several tens of megaparsecs, probe the primordial fluctuation spectrum on scales that are only mildly nonlinear. Even larger scales are probed by study of the anisotropy of the cosmic microwave background radiation, which provides a direct glimpse of the primordial fluctuations that existed about 106 years or so after the initial big bang singularity. Galaxy formation is the process by which the building blocks of the universe have formed, involving a complex interaction between hydrodynamical and dynamical processes in a collapsing gas cloud. Both by detection of forming galaxies in the most remote regions of the universe and by study of the fundamental morphological characteristics of galaxies, which provide a fossilized memory of their past, can one relate the origin of galaxies to the same primordial fluctuation spectrum that gave rise' to the large-scale structure of the universe.
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ALISSE, JEAN-RÉMI, and CLAUDE SIDI. "Experimental probability density functions of small-scale fluctuations in the stably stratified atmosphere." Journal of Fluid Mechanics 402 (January 10, 2000): 137–62. http://dx.doi.org/10.1017/s0022112099006813.
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Small-scale random fluctuations of atmospheric variables are ubiquitous dynamical components in the stable, free atmosphere. There, within the O(1–10 m) vertical wavelength band, spectra of temperature and horizontal velocity often follow either a m−5/3 or a m−3 power law, m being the vertical wavenumber. Using high-resolution vertical profiles obtained by balloon-born instrumentation in the troposphere and stratosphere, we determine experimental probability density functions (PDFs) of velocity and temperature fluctuations in the spectral band (2–20 m) within atmospheric layers which follow one or the other spectral law. PDFs of such band-filtered fluctuations of temperature and velocities (horizontal and vertical) are estimated within 101 seemingly homogeneous atmospheric layers. It appears that PDFs of horizontal velocity fluctuations, once normalized by their r.m.s. values, do collapse towards two significantly different regimes depending upon the spectral law followed in the wavelength band considered. On the other hand, temperature fluctuation PDFs are shown to be close to each other in both regimes. All these PDFs show close-to-exponential tails. Their high kurtosis appears to be mainly related to intermittency of the fluctuations fields, though marginal influence of residual inhomogeneity of the selected layers may be suspected. These results are compared with published results of laboratory and numerical experiments. We wish to emphasize the unexpected non-Gaussian character of these PDFs.
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Das, Arghya, and Mustansir Barma. "Fluctuation dominated phase ordering in coarse-grained depth models: domain wall structures, extreme values and coarsening." Journal of Statistical Mechanics: Theory and Experiment 2023, no. 4 (April 1, 2023): 043203. http://dx.doi.org/10.1088/1742-5468/acc729.
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Abstract Models of particles driven by a one-dimensional fluctuating surface are known to exhibit fluctuation dominated phase ordering (FDPO), in which both the order and fluctuations appear on macroscopic scales. Highly dynamic and macroscopically broad interfacial regions, each composed of many domain walls, appear between macroscopically ordered regions and consequently the scaled correlation function violates the Porod law. We focus on two essential quantities which together quantify the unique characteristics of FDPO, namely the total number of domain walls and the length of the largest ordered domain. We present results in the context of coarse-grained depth (CD) models, both in steady state and while coarsening. Analytic arguments supported by numerical simulations show that even though domain wall number fluctuations are very strong, the associated variance remains constant in time during coarsening. Further, the length of the largest cluster grows as a power law with significant multiplicative logarithms which involve both the time and system size. In addition, we identify corrections to the leading power law scaling in several quantities in the coarsening regime. We also study a generalisation of the CD model in which the domain wall density is controlled by a fugacity and show that it maps on to the truncated inverse distance squared Ising model. The generalised model shows a mixed order phase transition, with the regular CD model (which exhibits FDPO) corresponding to the critical point.
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Asenov, A., G. Slavcheva, S. Kaya, and R. Balasubramaniam. "Quantum Corrections to the ‘Atomistic’ MOSFET Simulations." VLSI Design 13, no. 1-4 (January 1, 2001): 15–21. http://dx.doi.org/10.1155/2001/62398.
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We have introduced in a simple and efficient manner quantum mechanical corrections in our 3D ’atomistic’ MOSFET simulator using the density gradient formalism. We have studied in comparison with classical simulations the effect of the quantum mechanical corrections on the simulation of random dopant induced threshold voltage fluctuations, the effect of the single charge trapping on interface states and the effect of the oxide thickness fluctuations in decanano MOSFETs with ultrathin gate oxides. The introduction of quantum corrections enhances the threshold voltage fluctuations but does not affect significantly the amplitude of the random telegraph noise associated with single carrier trapping. The importance of the quantum corrections for proper simulation of oxide thickness fluctuation effects has also been demonstrated.
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Hou, Yicun, Angui Li, and Ying Zhang. "Air-fluctuation nozzle and its periodic, wave-like air distribution evaluation." Indoor and Built Environment 29, no. 2 (June 25, 2019): 196–207. http://dx.doi.org/10.1177/1420326x19856677.
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In order to investigate dynamic characteristics of fluctuating air, one kind of nozzles of producing periodical fluctuating air is presented in this paper. Assume that the jet is isothermal and free, the typical parameters of the airflow characteristics, such as the maximum jet velocity decay, the non-dimensional velocity profile on different sections and the turbulence intensity have been discussed. In addition, power spectrum density of experimental data was calculated and analysed. The result shows that compared with stable air supply, the fluctuating air velocity decay is slower, thus forming a more uniform velocity field. Furthermore, turbulence intensity of the fluctuating air is larger. The power spectrum density exponent value approaches to the value of typical natural wind when the air velocity decreases to 0.6 m/s. With airflow diffusion, the fluctuation characteristic of airflow changes to that of natural wind gradually.
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Amoura, Zouhir, Cédric Besnaci, Frédéric Risso, and Véronique Roig. "Velocity fluctuations generated by the flow through a random array of spheres: a model of bubble-induced agitation." Journal of Fluid Mechanics 823 (June 22, 2017): 592–616. http://dx.doi.org/10.1017/jfm.2017.347.
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This work reports an experimental investigation of the flow through a random array of fixed solid spheres. The volume fraction of the spheres is 2 %, and the Reynolds number $Re$ based on the sphere diameter and the average flow velocity is varied from 120 to 1040. Using time and spatial averaging, the fluctuations have been decomposed into two contributions of different natures: a spatial fluctuation that accounts for the strong inhomogeneity of the flow around each sphere, and a time fluctuation that comes from the instability of the flow at large enough Reynolds numbers. The evolutions of these two contributions with the Reynolds number are different, so that their relative importance varies. However, when each is normalized by using its own variance and the integral length scales of the fluctuations, their spectra and probability density functions (PDFs) are almost independent of $Re$. The spatial fluctuation mostly comes from the velocity deficit in the wakes of the spheres, and is thus dominated by scales larger than one or two sphere diameters. It is found to be responsible for the asymmetry of the PDFs of the vertical fluctuations and of the major part of the anisotropy level between the vertical and the horizontal components of the fluctuations. The time fluctuation dominates at scales smaller than the integral length scale. It is isotropic and its PDFs, well described by an exponential distribution, are non-Gaussian. The spectra of the spatial and the time fluctuations both show an evolution as the power $-3$ of the wavenumber, but not exactly in the same subrange. All these properties are found in remarkable agreement with the results of both experimental investigations and large eddy simulations (LES) of a homogeneous bubble swarm. This confirms that the main mechanism responsible for the production of bubble-induced fluctuations is the interaction of the velocity disturbances caused by obstacles immersed in a flow and that the structure of this agitation is weakly dependent on the precise nature of the obstacles. The understanding and the modelling of the agitation generated by the motion of a dispersed phase, such as the bubble-induced agitation, therefore require one to distinguish between the roles of these two contributions.
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Zhang, Hao-Hao, Jun-Xing Wang, Shuai-Qun Du, Li Chen, and Jin-Rong Da. "Dynamic Response Simulation of the Slope Triggered by Fluctuating Pressure during High Dam Flood Discharge." Shock and Vibration 2022 (January 18, 2022): 1–13. http://dx.doi.org/10.1155/2022/1717578.
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The problem of slope vibration induced by flood discharge of high dams cannot be ignored. In this paper, this problem is simplified to be the relationship among the fluctuating pressures, the inherent properties of the slope system, and its dynamic responses. The characteristics of fluctuating pressures in the plunge pool during flood discharge are analyzed by the hydraulic model test. And a numerical slope model consisting of the finite element domain and the PML domain is established to study the inherent characteristics and vibration responses by numerical simulation. The results show that the flow fluctuation in plunge pool is a continuous and stable random vibration process. And the fluctuating pressures on the bottom area of the plunge pool are greater than that of the sidewall, but the fluctuation phenomenon at the sidewall is more intense. In addition, the slope displacement vibration intensity caused by fluctuating pressures is small, only at the micron level. The fluctuating pressures on the bottom area of the plunge pool are the dominant factor affecting the kinetic energy density distribution of the slope. This work provides a simple and efficient method for the study of slope vibration induced by high dam flood discharge.
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GAHLOT, AJAY, RITU WALIA, SURESH C. SHARMA, and R. P. SHARMA. "Distortion of an amplitude modulated electromagnetic signal with time-dependent dust charging." Journal of Plasma Physics 78, no. 1 (August 3, 2011): 33–38. http://dx.doi.org/10.1017/s002237781100033x.
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AbstractA large amplitude modulated Gaussian electromagnetic beam propagating in a dusty plasma with dust charge fluctuations has been studied. The electrons are heated non-uniformly by the electromagnetic beam. For non-steady state, we obtain nonlinear current density in the presence of dust grains. This expression has been used to study the non-stationary self-focusing and resulting self-distortion of the amplitude modulated electromagnetic beam. It has been observed that the dust charge fluctuation increases the self-focusing of electromagnetic beam. It is also found that the effect of dust charge fluctuations is significant on the modulation index.