Generation of Synthetic Turbulence in Arbitrary Domains
DEFF Research Database (Denmark)
Gilling, Lasse; Nielsen, Søren R.K.; Sørensen, Niels
2009-01-01
A new method for generating synthetic turbulence is presented. The method is intended for generating a turbulent velocity field with a fine spatial resolution but only covering a small moving part of the rotor area of a wind turbine. For this application the Mann and Sandia methods cannot be used...... because of the very high requirements for computer memory. In the present method the auto- and cross-correlation in all three directions is computed from analytical or empirical expressions and the auto- and cross-spectra are determined by using the Wiener-Khinchin relation. From the auto- and cross...
Spectrum of weak magnetohydrodynamic turbulence.
Boldyrev, Stanislav; Perez, Jean Carlos
2009-11-27
Turbulence of magnetohydrodynamic waves in nature and in the laboratory is generally cross-helical or nonbalanced, in that the energies of Alfvén waves moving in opposite directions along the guide magnetic field are unequal. Based on high-resolution numerical simulations it is proposed that such turbulence spontaneously generates a condensate of the residual energy E(v) - E(b) at small field-parallel wave numbers. As a result, the energy spectra of Alfvén waves are generally not scale invariant in an inertial interval of limited extent. In the limit of an infinite Reynolds number, the universality is asymptotically restored at large wave numbers, and both spectra attain the scaling E(k) proportional to k(perpendicular)(-2). The generation of a condensate is apparently related to the breakdown of mirror symmetry in nonbalanced turbulence.
Generating Polarization-Entangled Photon Pairs with Arbitrary Joint Spectrum
Walton, Z D; Saleh, B E A; Teich, M C; Walton, Zachary D.; Sergienko, Alexander V.; Saleh, Bahaa E. A.; Teich, Malvin C.
2004-01-01
We present a scheme for generating polarization-entangled photons pairs with arbitrary joint spectrum. Specifically, we describe a technique for spontaneous parametric down-conversion in which both the center frequencies and the bandwidths of the down-converted photons may be controlled by appropriate manipulation of the pump pulse. The spectral control offered by this technique permits one to choose the operating wavelengths for each photon of a pair based on optimizations of other system parameters (loss in optical fiber, photon counter performance, etc.). The combination of spectral control, polarization control, and lack of group-velocity matching conditions makes this technique particularly well-suited for a distributed quantum information processing architecture in which integrated optical circuits are connected by spans of optical fiber.
The spatio-temporal spectrum of turbulent flows
di Leoni, P Clark; Mininni, P D
2015-01-01
Identification and extraction of vortical structures and of waves in a disorganized flow is a mayor challegen in the study of turbulence. We present a study of the spatio-temporal behavior of turbulent flows in the presence of different restitutive forces. We show how to compute and analyze the spatio-temporal spectrum from data stemming from numerical simulations and from laboratory experiments. Four cases are considered: homogeneous and isotropic turbulence, rotating turbulence, stratified turbulence, and water wave turbulence. For homogeneous and isotropic turbulence, the spectrum allows identification of random sweeping. For rotating and for stratified turbulence, the spectrum allows identification of the waves, quantification of the energy in the waves and in the turbulent eddies, and identification of physical mechanisms such as Doppler shift and wave absorption in critical layers. Finally, in water wave turbulence the spectrum shows a transition from gravity-capillary waves to bound waves as the amplit...
Inertial-range spectrum of whistler turbulence
Directory of Open Access Journals (Sweden)
Y. Narita
2010-02-01
Full Text Available We develop a theoretical model of an inertial-range energy spectrum for homogeneous whistler turbulence. The theory is a generalization of the Iroshnikov-Kraichnan concept of the inertial-range magnetohydrodynamic turbulence. In the model the dispersion relation is used to derive scaling laws for whistler waves at highly oblique propagation with respect to the mean magnetic field. The model predicts an energy spectrum for such whistler waves with a spectral index −2.5 in the perpendicular component of the wave vector and thus provides an interpretation about recent discoveries of the second inertial-range of magnetic energy spectra at high frequencies in the solar wind.
Energy spectrum of buoyancy-driven turbulence
Kumar, Abhishek
2014-08-25
Using high-resolution direct numerical simulation and arguments based on the kinetic energy flux Πu, we demonstrate that, for stably stratified flows, the kinetic energy spectrum Eu(k)∼k-11/5, the potential energy spectrum Eθ(k)∼k-7/5, and Πu(k)∼k-4/5 are consistent with the Bolgiano-Obukhov scaling. This scaling arises due to the conversion of kinetic energy to the potential energy by buoyancy. For weaker buoyancy, this conversion is weak, hence Eu(k) follows Kolmogorov\\'s spectrum with a constant energy flux. For Rayleigh-Bénard convection, we show that the energy supply rate by buoyancy is positive, which leads to an increasing Πu(k) with k, thus ruling out Bolgiano-Obukhov scaling for the convective turbulence. Our numerical results show that convective turbulence for unit Prandt number exhibits a constant Πu(k) and Eu(k)∼k-5/3 for a narrow band of wave numbers. © 2014 American Physical Society.
The spatio-temporal spectrum of turbulent flows.
Clark di Leoni, P; Cobelli, P J; Mininni, P D
2015-12-01
Identification and extraction of vortical structures and of waves in a disorganised flow is a mayor challenge in the study of turbulence. We present a study of the spatio-temporal behavior of turbulent flows in the presence of different restitutive forces. We show how to compute and analyse the spatio-temporal spectrum from data stemming from numerical simulations and from laboratory experiments. Four cases are considered: homogeneous and isotropic turbulence, rotating turbulence, stratified turbulence, and water wave turbulence. For homogeneous and isotropic turbulence, the spectrum allows identification of sweeping by the large-scale flow. For rotating and for stratified turbulence, the spectrum allows identification of the waves, precise quantification of the energy in the waves and in the turbulent eddies, and identification of physical mechanisms such as Doppler shift and wave absorption in critical layers. Finally, in water wave turbulence the spectrum shows a transition from gravity-capillary waves to bound waves as the amplitude of the forcing is increased. PMID:26701711
Lagrangian frequency spectrum as a diagnostic for magnetohydrodynamic turbulence dynamics.
Busse, Angela; Müller, Wolf-Christian; Gogoberidze, Grigol
2010-12-01
For the phenomenological description of magnetohydrodynamic turbulence competing models exist, e.g., Boldyrev [Phys. Rev. Lett. 96, 115002 (2006)] and Gogoberidze [Phys. Plasmas 14, 022304 (2007)], which predict the same Eulerian inertial-range scaling of the turbulent energy spectrum although they employ fundamentally different basic interaction mechanisms. A relation is found that links the Lagrangian frequency spectrum with the autocorrelation time scale of the turbulent fluctuations τ(ac) and the associated cascade time scale τ(cas). Thus, the Lagrangian energy spectrum can serve to identify weak (τ(ac) ≪ τ(cas)) and strong (τ(ac) ∼ τ(cas)) interaction mechanisms providing insight into the turbulent energy cascade. The new approach is illustrated by results from direct numerical simulations of two- and three-dimensional incompressible MHD turbulence.
Pump–probe spectrum of molecular assemblies of arbitrary structure and dimension
Juzeliūnas, Gediminas; Knoester, Jasper
2000-01-01
Using the hard-core boson approach, we study the pump-probe spectrum of molecular assemblies carrying Frenkel excitons of arbitrary structure and dimension. We present a rigorous justification of the hard-core boson approach by using the Agranovich–Toshich transformation from paulions to bosons. The
The temperature spectrum generated by frictional heating in isotropic turbulence
Bos, Wouter
2014-01-01
In every turbulent flow with non-zero viscosity, heat is generated by viscous friction. This heat is then mixed by the velocity field. We consider how heat fluctuations generated this way are injected and distributed over length scales in isotropic turbulence. A triadic closure is derived and numerically integrated. It is shown how the heat fluctuation spectrum depends on the Reynolds and Prandtl numbers.
Time frequency spectrum of atmospheric turbulence and sweeping hypothesis
Institute of Scientific and Technical Information of China (English)
无
2011-01-01
The present study is focused on the structure of time frequency spectrum.A scaling law for Eulerian time frequency spectrum and the corresponding temporal structure function are calculated from the sweeping hypothesis and Kolmogorov's similarity law regarding spatial structure function.An experiment is designed to study this scaling law in the atmospheric turbulent boundary layer.The results well support the conclusion derived from relevant theoretical analysis.
Energy Spectrum of Buoyancy-Driven Turbulence
Kumar, Abhishek; Chatterjee, Anando G.; Verma, Mahendra K.
2014-01-01
Using high-resolution direct numerical simulation and arguments based on the kinetic energy flux $\\Pi_u$, we demonstrate that for stably stratified flows, the kinetic energy spectrum $E_u(k) \\sim k^{-11/5}$, the entropy spectrum $E_\\theta(k) \\sim k^{-7/5}$, and $\\Pi_u(k) \\sim k^{-4/5}$, consistent with the Bolgiano-Obukhov scaling. This scaling arises due to the conversion of kinetic energy to the potential energy by buoyancy. For weaker buoyancy, this conversion is weak, hence $E_u(k)$ follo...
Energy spectrum of stably-stratified and convective turbulent flows
Verma, Mahendra; Kumar, Abhishek
2015-11-01
In the inertial range of fluid turbulence, the energy flux is constant, while the energy spectrum scales as k - 5 / 3 (k=wavenumber). The buoyancy however could change the phenomenology dramatically. Bolgiano and Obukhov (1959) had conjectured that stably stratified flows (as in atmosphere) exhibits a decrease in the energy flux as k - 4 / 5 due to the conversion of kinetic energy to the potential energy, consequently, the energy spectrum scales as k - 11 / 5. We show using detailed numerical analysis that the stably stratified flows indeed exhibit k - 11 / 5 energy spectrum for Froude numbers Fr near unity. The flow becomes anisotropic for small Froude numbers. For weaker buoyancy (large Fr), the kinetic energy follows Kolmogorov's spectrum with a constant energy flux. However, in convective turbulence, the energy flux is a nondecreasing function of wavenumber since the buoyancy feeds positively into the kinetic energy. Hence, the kinetic energy spectrum is Kolmogorov-like (k - 5 / 3) or shallower. We also demonstrate the above scaling using a shell model of buoyancy-driven turbulence.
Anomalous k⊥(-8/3) spectrum in electron magnetohydrodynamic turbulence.
Meyrand, Romain; Galtier, Sébastien
2013-12-27
Electron magnetohydrodynamic turbulence is investigated under the presence of a relatively strong external magnetic field b0e∥ and through three-dimensional direct numerical simulations. Our study reveals the emergence of a k⊥(-8/3) scaling for the magnetic energy spectrum at scales k∥(D)≤k⊥≤k⊥(D), where k∥(D) and k⊥(D) are, respectively, the typical largest dissipative scales along and transverse to the b0 direction. Unlike standard magnetohydrodynamic, this turbulence regime is characterized by filaments of electric currents parallel to b0. The anomalous scaling is in agreement with a heuristic model in which the transfer in the parallel direction is negligible. Implications for solar wind turbulence are discussed.
Compressive sampling for energy spectrum estimation of turbulent flows
Adalsteinsson, Gudmundur F
2014-01-01
Recent results from compressive sampling (CS) have demonstrated that accurate reconstruction of sparse signals often requires far fewer samples than suggested by the classical Nyquist--Shannon sampling theorem. Typically, signal reconstruction errors are measured in the $\\ell^2$ norm and the signal is assumed to be sparse, compressible or having a prior distribution. Our spectrum estimation by sparse optimization (SpESO) method uses prior information about isotropic homogeneous turbulent flows with power law energy spectra and applies the methods of CS to 1-D and 2-D turbulence signals to estimate their energy spectra with small logarithmic errors. SpESO is distinct from existing energy spectrum estimation methods which are based on sparse support of the signal in Fourier space. SpESO approximates energy spectra with an order of magnitude fewer samples than needed with Shannon sampling. Our results demonstrate that SpESO performs much better than lumped orthogonal matching pursuit (LOMP), and as well or bette...
The Turbulence Power Spectrum in Optically Thick Interstellar Clouds
Burkhart, Blakesley; Ossenkopf, V; Stutzki, J
2013-01-01
The Fourier power spectrum is one of the most widely used statistical tools to analyze the nature of magnetohydrodynamic turbulence in the interstellar medium. Lazarian & Pogosyan (2004) predicted that the spectral slope should saturate to -3 for an optically thick medium and many observations exist in support of their prediction. However, there have not been any numerical studies to-date testing these results. We analyze the spatial power spectrum of MHD simulations with a wide range of sonic and Alfv\\'enic Mach numbers, which include radiative transfer effects of the $^{13}$CO transition. We confirm numerically the predictions of Lazarian & Pogosyan (2004) that the spectral slope of line intensity maps of an optically thick medium saturates to -3. Furthermore, for very optically thin supersonic CO gas, where the density or CO abundance values are too low to excite emission in all but the densest shock compressed gas, we find that the spectral slope is shallower than expected from the column density....
Zamek, Steve; Yitzhaky, Yitzhak
2006-08-01
In remote sensing, atmospheric turbulence and aerosols limit the image quality. For many practical cases turbulence is shown to be dominant, especially for horizontal close-to-earth imaging in hot environments. In a horizontal long-range imaging it is usually impractical to measure path-averaged refractive index structure constant C n2 (which characterizes the turbulence strength) with conventional equipment. In this paper we propose a method for estimation of C n2 based just on the available recorded turbulence-degraded image sequence. The method exploits the turbulence-induced image "dancing". C n2 is extracted from the estimated image shifts variance. Experimental comparison with C n2 measurements using a scintillometer shows reliable estimation results. We also estimate image motion with sub-pixel accuracy for the purpose of obtaining a high-resolution image by applying a simple super-resolution procedure. Results of super-resolution for real imagery are presented.
Savane, Y S; Faza-Barry, M; Lomonossov, V
2002-01-01
We study the acceleration of charged particles by the variable magnetic field. The study is based on the determination of spectrum of accelerated particles and the spectrum of hydro magnetic turbulence. We plan the self-consistent system of equation and we also find out the solution of the system for the spectrum of particles and hydro magnetic turbulence with the conditions of effective acceleration in the cosmic space of solar system.
Miquel, Benjamin; Alexakis, Alexandros; Mordant, Nicolas
2014-06-01
The weak turbulence theory has been applied to waves in thin elastic plates obeying the Föppl-Von Kármán dynamical equations. Subsequent experiments have shown a strong discrepancy between the theoretical predictions and the measurements. Both the dynamical equations and the weak turbulence theory treatment require some restrictive hypotheses. Here a direct numerical simulation of the Föppl-Von Kármán equations is performed and reproduces qualitatively and quantitatively the experimental results when the experimentally measured damping rate of waves γ_{k}=a+bk{2} is used. This confirms that the Föppl-Von Kármán equations are a valid theoretical framework to describe our experiments. When we progressively tune the dissipation so that to localize it at the smallest scales, we observe a gradual transition between the experimental spectrum and the Kolmogorov-Zakharov prediction. Thus, it is shown that dissipation has a major influence on the scaling properties of stationary solutions of weakly nonlinear wave turbulence.
Sharp vorticity gradients in two-dimensional turbulence and the energy spectrum
DEFF Research Database (Denmark)
Kuznetsov, E.A.; Naulin, Volker; Nielsen, Anders Henry;
2010-01-01
Formation of sharp vorticity gradients in two-dimensional (2D) hydrodynamic turbulence and their influence on the turbulent spectra are considered. The analog of the vortex line representation as a transformation to the curvilinear system of coordinates moving together with the di-vorticity lines...... is developed and compressibility of this mapping appears as the main reason for the formation of the sharp vorticity gradients at high Reynolds numbers. In the case of strong anisotropy the sharp vorticity gradients can generate spectra which fall off as k −3 at large k, which appear to take the same form...... as the Kraichnan spectrum for the enstrophy cascade. For turbulence with weak anisotropy the k dependence of the spectrum due to the sharp gradients coincides with the Saffman spectrum: E(k) ~ k −4. Numerical investigations of decaying turbulence reveal exponential growth of di-vorticity with a spatial distributed...
Transition from thermal to turbulent equilibrium with a resulting electromagnetic spectrum
International Nuclear Information System (INIS)
A recent paper [Ziebell et al., Phys. Plasmas 21, 010701 (2014)] discusses a new type of radiation emission process for plasmas in a state of quasi-equilibrium between the particles and enhanced Langmuir turbulence. Such a system may be an example of the so-called “turbulent quasi-equilibrium.” In the present paper, it is shown on the basis of electromagnetic weak turbulence theory that an initial thermal equilibrium state (i.e., only electrostatic fluctuations and Maxwellian particle distributions) transitions toward the turbulent quasi-equilibrium state with enhanced electromagnetic radiation spectrum, thus demonstrating that the turbulent quasi-equilibrium discussed in the above paper correctly describes the weakly turbulent plasma dynamically interacting with electromagnetic fluctuations, while maintaining a dynamical steady-state in the average sense
Institute of Scientific and Technical Information of China (English)
GE Huiliang; HE Zuoyong; BAO Xuemei
2001-01-01
The point power spectrum density and the wavenumber frequency spectrum density of turbulent-boundary-layer fluctuation pressure were measured in water-tunnel by use of a φ8 mm hydrophone and a 20-element array, respectively. The non-dimensional representation of measured point power spectrum coincides with the measured results by Bull M. K. et. al. in wind tunnel. The convection peak can be seen clearly in the measured wavenumber frequencyspectrum and the convection velocity can be calculated from the location of the convection peak.The response spectrum of a polyvinylidence fluoride (PVDF) hydrophone, which receiving area is 100 mm × 60 mm, was also measured. By comparing it with the response spectrum of the φ8 mm hydrophone, it is shown that the PVDF hyrdophone has a strong wavenumber filtering effect on turbulent-boundary-layer pressure fluctuation.
Phase noise effects on turbulent weather radar spectrum parameter estimation
Lee, Jonggil; Baxa, Ernest G., Jr.
1990-01-01
Accurate weather spectrum moment estimation is important in the use of weather radar for hazardous windshear detection. The effect of the stable local oscillator (STALO) instability (jitter) on the spectrum moment estimation algorithm is investigated. Uncertainty in the stable local oscillator will affect both the transmitted signal and the received signal since the STALO provides transmitted and reference carriers. The proposed approach models STALO phase jitter as it affects the complex autocorrelation of the radar return. The results can therefore by interpreted in terms of any source of system phase jitter for which the model is appropriate and, in particular, may be considered as a cumulative effect of all radar system sources.
Spectrum and Anisotropy of Turbulence from Multi-Frequency Measurement of Synchrotron Polarization
Lazarian, Alex
2015-01-01
We consider turbulent synchrotron emitting media that also exhibits Faraday rotation and provide a statistical description of synchrotron polarization fluctuations. In particular, we consider these fluctuations as a function of the spatial separation of the direction of measurements and as a function of wavelength for the same line-of-sight. On the basis of our general analytical approach, we introduce several measures that can be used to obtain the spectral slopes and correlation scales of both the underlying magnetic turbulence responsible for emission and the spectrum of the Faraday rotation fluctuations. We show the synergetic nature of these measures and discuss how the study can be performed using sparsely sampled interferometric data. We also discuss how additional characteristics of turbulence can be obtained, including the turbulence anisotropy, the three dimensional direction of the mean magnetic field. We consider both cases when the synchrotron emission and Faraday rotation regions coincide and wh...
Gaston, Laurence; Kamara, Alima; Bellet, Michel
2000-01-01
This is the pre-peer reviewed version of the following article : An arbitrary Lagrangian-Eulerian finite element approach to non-steady state turbulent fluid flow with application to mould filling in casting, Gaston L., Kamara A., Bellet M. International Journal for Numerical Methods in Fluids 34, 4 (2000) pages 341-369, which has been published in final form at http://dx.doi.org/10.1002/1097-0363(20001030)34:4%3C341::AID-FLD64%3E3.0.CO;2-K International audience This paper presents a t...
Coherent structures and turbulent spectrum in solar wind plasmas
Energy Technology Data Exchange (ETDEWEB)
Sharma, R. P.; Yadav, N.; Kumari, Anju [Centre for Energy Studies, Indian Institute of Technology Delhi, New Delhi-110016 (India)
2013-08-15
The present paper investigates the localization of a uniform plane kinetic Alfvén wave (KAW) due to the coupling with the density/magnetic field fluctuations associated with a magnetosonic wave propagating in the transverse direction, i.e., perpendicular to the background magnetic field. To gain the physical insight into this evolution, a simplified analytical model based on the Mathieu equation has also been studied. Numerical method has also been used to analyse the evolution of KAW. The magnetic fluctuation spectrum follows Kolmogorovian scaling above the proton gyroradius scalelength, which is regarded as the inertial range. Below this scale, a steepened spectrum has been obtained in the dispersive range with power law index ∼−2.5, which continues up to the dissipation range. Our results reveal that the proposed mechanism may be an interesting physical mechanism for transferring the energy from larger lengthscales to smaller lengthscales in the solar wind plasmas. Relevance of the present study with Cluster spacecraft observations has also been discussed.
International Nuclear Information System (INIS)
For the temperature fields in rod clads of experimental assemblies a good agreement have been got with use of prior calculations by subchannel code COBRA-IV-I, from results of which an additional information about δt/δX3 distribution was taken. The method of definition the local fields of velocity, turbulent kinetic energy, temperature and eddy diffusivities for one-phase axial stabilized fluids in arbitrary formed rod bundle assemblies with invariable upward geometry was developed. According to this model the AGURA code was worked out to calculate local thermal hydraulic problems in combination with temperature fields in fuel rods and constructive elements of fuel assemblies. The method does not use any prior geometric scales and is based only on invariant local flow parameters: turbulent kinetic energy, velocity field deformation tensor and specific work of inner friction. Verification of this method by available experimental data showed a good agreement of calculation data and findings of velocity and t.k.e. fields, when the secondary flows have not a substantial influence to a balance of axial momentum and turbulent kinetic energy. (author)
Chandran
2000-11-27
Scattering rates for a Goldreich-Sridhar (GS) spectrum of anisotropic, incompressible, magnetohydrodynamic turbulence are calculated in the quasilinear approximation. Because the small-scale fluctuations are constrained to have wave vectors nearly perpendicular to the background magnetic field, scattering is too weak to provide either the mean-free paths commonly used in Galactic cosmic-ray propagation models or the mean-free paths required for acceleration of cosmic rays at quasiparallel shocks. Where strong pitch-angle scattering occurs, it is due to fluctuations not described by the GS spectrum, such as fluctuations generated by streaming cosmic rays. PMID:11082620
Gotoh, Toshiyuki
2012-11-01
Spectrum of passive scalar variance at very high Schmidt number up to 1000 in isotropic steady turbulence has been studied by using very high resolution DNS. Gaussian random force and scalar source which are isotropic and white in time are applied at low wavenumber band. Since the Schmidt number is very large, the system was integrated for 72 large eddy turn over time for the system to forgot the initial state. It is found that the scalar spectrum attains the asymptotic k-1 spectrum in the viscous-convective range and the constant CB is found to be 5.7 which is larger than 4.9 obtained by DNS under the uniform mean scalar gradient. Reasons for the difference are inferred as the Reynolds number effect, anisotropy, difference in the scalar injection, duration of time average, and the universality of the constant is discussed. The constant CB is also compared with the prediction by the Lagrangian statistical theory for the passive scalar. The scalar spectrum in the far diffusive range is found to be exponential, which is consistent with the Kraichnan's spectrum. However, the Kraichnan spectrum was derived under the assumption that the velocity field is white in time, therefore theoretical explanation of the agreement needs to be explored. Grant-in-Aid for Scientific Research No. 21360082, Ministry of Education, Culture, Sports, Science and Technology of Japan.
S-process nucleosynthesis in AGB stars with the full spectrum of turbulence scheme for convection.
Yagüe, A.; García-Hernández, D. A.; Ventura, P.; Lugaro, M.
2016-07-01
The chemical evolution of asymptotic giant branch (AGB) stars models depends greatly on the input physics (e.g. convective model, mass loss recipe). Variations of hot bottom burning (HBB) strength, or third dredge-up (TDU) efficiency are among the main consequences of adopting different input physics in the AGB models. The ATON evolutionary code stands apart from others in that it uses the Full Spectrum of Turbulence convective model. Here we present the first results of a newly developed s-process nucleosynthesis module for ATON AGB models. Our results are compared also with observations and theoretical predictions of present AGB nucleosynthesis models using different input physics.
Origins of the k(-2) spectrum in decaying Taylor-Green magnetohydrodynamic turbulent flows.
Dallas, V; Alexakis, A
2013-11-01
We investigate the origins of k(-2) spectrum in a decaying Taylor-Green magnetohydrodynamic flow with zero large scale magnetic flux that was reported by Lee et al. [Phys. Rev. E 81, 016318 (2010)]. So far, a possible candidate for this scaling exponent has been the weak turbulence phenomenology. From our numerical simulations, we observe that current sheets in the magnetic Taylor-Green flow are formed in regions of magnetic discontinuities. Based on this observation and by studying the influence of the current sheets on the energy spectrum, using a filtering technique, we argue that the discontinuities are responsible for the -2 power law scaling of the energy spectra of this flow.
Rica, Sergio
2016-01-01
The recent observation of gravitational waves, stimulates the question of the longtime evolution of the space-time fluctuations. Gravitational waves interact themselves through the nonlinear character of Einstein's equations of general relativity. This nonlinear wave interaction allows the spectral energy transfer from mode to mode. According to the wave turbulence theory, the weakly nonlinear interaction of gravitational waves leads to the existence of an irreversible kinetic regime that dominates the longtime evolution. The resulting kinetic equation suggests the existence of an equilibrium wave spectrum and the existence of a non-equilibrium Kolmogorov-Zakharov spectrum for spatio-temporal fluctuations. Evidence of these solutions extracted in the fluctuating signal of the recent observations will be discussed in the paper. Probably, the present results would be pertinent in the new age of development of gravitational astronomy, as well as, in new tests of General Relativity.
Directory of Open Access Journals (Sweden)
S. Dastgeer
2005-01-01
Full Text Available 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.
Bailly, Christophe
2015-01-01
This book covers the major problems of turbulence and turbulent processes, including physical phenomena, their modeling and their simulation. After a general introduction in Chapter 1 illustrating many aspects dealing with turbulent flows, averaged equations and kinetic energy budgets are provided in Chapter 2. The concept of turbulent viscosity as a closure of the Reynolds stress is also introduced. Wall-bounded flows are presented in Chapter 3, and aspects specific to boundary layers and channel or pipe flows are also pointed out. Free shear flows, namely free jets and wakes, are considered in Chapter 4. Chapter 5 deals with vortex dynamics. Homogeneous turbulence, isotropy, and dynamics of isotropic turbulence are presented in Chapters 6 and 7. Turbulence is then described both in the physical space and in the wave number space. Time dependent numerical simulations are presented in Chapter 8, where an introduction to large eddy simulation is offered. The last three chapters of the book summarize remarka...
Localization of Dispersive Alfvén Wave in Solar wind plasmas and Turbulent Spectrum
Sharma, Swati; Sharma, R. P.
2016-07-01
Solar wind turbulence at large inertial scales is well known for decades and believed to consist of Alfvén cascade. The inertial range of Solar wind turbulence can be described by a magnetohydrodynamic model. But at small scales the MHD description is not valid. At scales of the order of proton inertial length, Alfvén cascade excites kinetic Alfvén wave or fast wave or whistler wave that carries wave energy to smaller scales. On the other hand, parallel propagating right(R) and left(L) circularly polarized Alfvén/ ion cyclotron wave in the framework of Hall MHD are also thought to be essential ingredients of the solar wind turbulence. Recently, He et.al[1] have used the magnetic field data from the STEREO spacecraft to calculate the magnetic helicities in the solar wind turbulence and reported the possible existence of Alfvén -cyclotron waves and their coexistence with the right handed polarized fluctuations. In the present article we intend to study the right circularly polarized dispersive Alfvén wave (DAW) and their role in the solar wind turbulence. The inclusion of the Hall term causes the dispersion of the AW which, in the present study, is considered on account of the finite frequency (frequency comparable to ion gyro frequency) of the pump wave. Filamentation instability has been reported to occur for the case of circularly polarized dispersive Alfvén wave (DAW) propagating parallel to ambient magnetic field. In the present study, the instability arises on account of the transverse density perturbations of the acoustic wave that may couple nonlinearly with the Alfvén wave and the driven ponderomotive force sequentially leads to growth of density perturbations. Numerical simulation involves finite difference method for the time domain and pseudo spectral method for the spatial domain. The power spectrum is investigated which shows a steepening for scales larger than the proton inertial length. These findings have been reported by Alexandrova et al
Institute of Scientific and Technical Information of China (English)
Z. Lin; R.E. Waltz
2007-01-01
@@ Turbulent transport driven by plasma pressure gradients [Tangl978] is one of the most important scientific challenges in burning plasma experiments since the balance between turbulent transport and the self-heating by the fusion products (a-particles) determines the performance of a fusion reactor like ITER.
Shaping the X-ray spectrum of galaxy clusters with AGN feedback and turbulence
Gaspari, M; Ruszkowski, M
2014-01-01
The hot plasma filling galaxy clusters emits copious radiation in the X-ray band. The classic unheated and unperturbed cooling flow model predicts dramatic cooling rates and an isobaric X-ray spectrum with constant differential luminosity distribution, $dL_{\\rm x}/dT \\propto (T/T_{\\rm hot})^0$. Combining past observations, it is however clear that the cores of clusters (and groups) show a strong deficit of emission increasing toward the soft X-ray band: $dL_{\\rm x}/dT \\propto (T/T_{\\rm hot})^{\\alpha=2\\pm1}$. Using 3D hydrodynamic simulations, we show that the deficit arises from the competition of thermal instability condensation and AGN outflow injection. During tight self-regulated feedback, the average luminosity distribution slope is $\\alpha\\approx2$, oscillating within the observed $18$), while pure cooling drives a too shallow slope, $\\alpha<1$. We disentangle the role of heating and turbulence via controlled experiments. Distributed heating alone induces a declining X-ray spectrum with $1<\\alpha&...
Tan, Liying; Zhai, Chao; Yu, Siyuan; Ma, Jing; Lu, Gaoyuan
2015-05-01
In the past decades, both the increasing experimental evidence and some results of theoretical investigation on non-Kolmogorov turbulence have been reported. This has prompted the study of optical propagation in non-Kolmogorov atmospheric turbulence. In this paper, based on the thin phase screen model and a non-Kolmogorov power spectrum which owns a generalized power law instead of standard Kolmogorov power law value 11/3 and a generalized amplitude factor instead of constant value 0.033, the temporal power spectrum of irradiance fluctuations for a Gaussian-beam wave is derived in the weak fluctuation regime for a horizontal path. The analytic expressions are obtained and then used to analyze the influence of spectral power law variations on the temporal power spectrum of irradiance fluctuations.
International Nuclear Information System (INIS)
An evaluation method of the neutron fluence and mean spectrum with which samples have been irradiated is proposed. The principle is based on measuring the change of the isotopic abundance ratios of arbitrary pairs of nuclides having different neutron absorption cross sections for both thermal and intermediate neutrons. Advantages of the method are as follows, although sensitivity is lower than that of the ordinary activation method in a short irradiation period. i) Any sample can be used irrespective of irradiation history. ii) Nuclides present as impurities in samples can be used as detectors. iii) Neutron fluences and mean spectra with which samples have been heavily irradiated can be measured with reasonable accuracy, thus making it possible to offer the direct information to radiation damage studies. The present study deals with the principle and applicability of the method. (author)
Full spectrum of turbulence convective mixing. II. Lithium production in AGB stars
Mazzitelli, I.; D'Antona, F.; Ventura, P.
1999-08-01
We present results from new, detailed computations of lithium production by hot bottom burning (HBB) in asymptotic giant branch (AGB) stars of intermediate mass (3.5 mass, metallicity, mass loss rate, convection and overshooting are discussed. In particular, nuclear burning, turbulent mixing and convective overshooting (if any) are self-consistently coupled by a diffusive algorithm, and the Full Spectrum of Turbulence (FST) model of convection is adopted, with test comparisons to Mixing Length Theory (MLT) stellar models. All the evolutions are followed from pre-main sequence down to late AGB, when stars do not appear any longer lithium rich. A ``reference mass" of 6 M_sun has been chosen since, although relatively close to the upper limit for which degenerate (12) C ignition occurs, all the studied mechanisms show up more clearly. HBB is always found above ~ log L/L_sun = 4.4, but the range of (initial) masses reaching HBB is largely dependent on convection model, overshooting and metallicity. For solar chemistry, masses >= 4M_sun evolve through HBB in the FST case and including core overshooting whereas, with solarly tuned MLT models and no overshooting, only masses >= 6M_sun can reach HBB. These constraints can give feedbacks about the more correct convection model and/or the extent of overshooting, thanks to the signatures of HBB in AGB stars in clusters of known turnoff masses and metallicity. Overshooting (when included) is addressed as an exponentially decreasing diffusion above formally convective regions. It makes convective cores during the main sequence to grow larger, and also starting masses and luminosities in AGB are then larger. However, also preliminary results obtained when allowing displacement of convective elements below convective regions in AGB are shown. In the ``reference" case (6M_sun), we find that overshooting from below the convective envelope totally suppresses thermal pulses and ultimately leads to the formation of massive ( ~ 1M
Density Fluctuation Spectrum of Solar Wind Turbulence between Ion and Electron Scales
Chen, C H K; Bonnell, J W; Mozer, F S; Bale, S D
2012-01-01
We present a measurement of the spectral index of density fluctuations between ion and electron scales in solar wind turbulence using the EFI instrument on the ARTEMIS spacecraft. The mean spectral index at 1 AU was found to be -2.75 +/- 0.06, steeper than predictions for pure whistler or kinetic Alfven wave turbulence, but consistent with previous magnetic field measurements. The steep spectra are also consistent with expectations of increased intermittency or damping of some of the turbulent energy over this range of scales. Neither the spectral index nor the flattening of the density spectra before ion scales were found to depend on the proximity to the pressure anisotropy instability thresholds, suggesting that they are features inherent to the turbulent cascade.
Engelbrecht, N. E.; Burger, R. A.
2015-12-01
In this study, a novel ab initio cosmic ray (CR) modulation code that solves a set of stochastic transport equations equivalent to the Parker transport equation, and that uses output from a turbulence transport code as input for the diffusion tensor, is introduced. This code is benchmarked with a previous approach to ab initio modulation. The sensitivity of computed galactic CR proton spectra at Earth to assumptions made as to the low-wavenumber behavior of the two-dimensional (2D) turbulence power spectrum is investigated using perpendicular mean free path expressions derived from two different scattering theories. Constraints on the low-wavenumber behavior of the 2D power spectrum are inferred from the qualitative comparison of computed CR spectra with spacecraft observations at Earth. Another key difference from previous studies is that observed and inferred CR intensity spectra at 73 AU are used as boundary spectra instead of the usual local interstellar spectrum. Furthermore, the results presented here provide a tentative explanation as to the reason behind the unusually high galactic proton intensity spectra observed in 2009 during the recent unusual solar minimum.
Turbulent Friction in Rough Pipes and the Energy Spectrum of the Phenomenological Theory
Gioia, G; Chakraborty, Pinaki
2005-01-01
The classical experiments on turbulent friction in rough pipes were performed by J. Nikuradse in the 1930's. Seventy years later, they continue to defy theory. Here we model Nikuradse's experiments using the phenomenological theory of Kolmogorov, a theory that is widely thought to be applicable only to highly idealized flows. Our results include both the empirical scalings of Blasius and Strickler, and are otherwise in minute qualitative agreement with the experiments; they suggest that the phenomenological theory may be relevant to other flows of practical interest; and they unveil the existence of close ties between two milestones of experimental and theoretical turbulence.
Fujita, Yutaka; Akamatsu, Hiroki; Kimura, Shigeo S.
2016-06-01
It has often been thought that the northern radio relic in the galaxy cluster CIZA J2242.8+5301 (the "Sausage" Cluster) is associated with cosmic ray (CR) electrons that are accelerated at a shock through the diffusive shock acceleration (DSA) mechanism. However, recent radio observations have shown that the radio spectrum is curved, which is inconsistent with the prediction of a simple DSA model. Moreover, the CR electron spectrum before being affected by radiative cooling seems to be too hard for DSA. In this study, we show that these facts are natural consequences if the electrons are reaccelerated in turbulence downstream of the shock. In this model, DSA is not the main mechanism for generating high-energy electrons. We find that the mean free path of the electrons should be much shorter than the Coulomb mean free path for efficient reacceleration. The scale of the turbulent eddies must be smaller than the width of the relic. We also predict hard X-ray spectra of inverse Compton scattering of photons.
Fujita, Yutaka; Kimura, Shigeo S
2016-01-01
It has often been thought that the northern radio relic in the galaxy cluster CIZA J2242.8+5301 (the "Sausage" Cluster) is associated with cosmic-ray (CR) electrons that are accelerated at a shock through diffusive shock acceleration (DSA) mechanism. However, recent radio observations have shown that the radio spectrum is curved, which is inconsistent with the prediction of a simple DSA model. Moreover, the CR electron spectrum before being affected by radiative cooling seems to be too hard for the DSA. In this study, we show that these facts are natural consequences if the electrons are reaccelerated in turbulence in the downstream of the shock. In this model, the DSA is not the main mechanism to generate high-energy electrons. We find that the mean free path of the electrons should be much shorter than the Coulomb mean free path for efficient reacceleration. The scale of the turbulent eddies must be smaller than the width of the relic. We also predict hard X-ray spectra of inverse Compton scattering of phot...
Institute of Scientific and Technical Information of China (English)
Zhou Qi
2012-01-01
To a large degree,language is arbitrary. But there are exceptions to prove that language is not always arbitrary. However,non-arbitrariness is itself inevitably arbitrary. In fact,arbitrariness and non-arbitrariness work together to complete a language. It seems that they contradict to each other, but they actually coexist as a whole in the same unity.
Globus, N; Parizot, E
2007-01-01
We extend previous studies of mixed-composition extragalactic cosmic-ray source models, by investigating the influence of a non-negligible extragalactic magnetic field on the propagated cosmic-ray spectrum and composition. We study the transport of charged particles in turbulent fields and the transition from a ballistic to a diffusive propagation regime. We introduce a method allowing a fast integration of the particle trajectories, which allows us to calculate extragalactic cosmic-ray spectra in the general case, without using either the diffusive or the rectilinear approximation. We find that the main features of the mixed-composition models -- regarding the interpretation of the ankle and the non-monotonous evolution of the average cosmic-ray mass -- remain essentially unchanged as long as the magnetic field intensity does not exceed a few nG.
Transition from geostrophic turbulence to inertia-gravity waves in the atmospheric energy spectrum.
Callies, Jörn; Ferrari, Raffaele; Bühler, Oliver
2014-12-01
Midlatitude fluctuations of the atmospheric winds on scales of thousands of kilometers, the most energetic of such fluctuations, are strongly constrained by the Earth's rotation and the atmosphere's stratification. As a result of these constraints, the flow is quasi-2D and energy is trapped at large scales—nonlinear turbulent interactions transfer energy to larger scales, but not to smaller scales. Aircraft observations of wind and temperature near the tropopause indicate that fluctuations at horizontal scales smaller than about 500 km are more energetic than expected from these quasi-2D dynamics. We present an analysis of the observations that indicates that these smaller-scale motions are due to approximately linear inertia-gravity waves, contrary to recent claims that these scales are strongly turbulent. Specifically, the aircraft velocity and temperature measurements are separated into two components: one due to the quasi-2D dynamics and one due to linear inertia-gravity waves. Quasi-2D dynamics dominate at scales larger than 500 km; inertia-gravity waves dominate at scales smaller than 500 km. PMID:25404349
Quenching the X-ray spectrum of hot halos with AGN outflows and turbulence
Gaspari, M.
2016-06-01
I highlight recent advancements in the astrophysics of AGN outflow feedback and diffuse hot gas. Thanks to XMM RGS resolution, we know that the X-ray cores of clusters, groups, and massive galaxies have a strong deficit of soft X-ray emission compared with the classic cooling flow prediction: dL_{x}/dT ∝ (T/T_{hot})^{2±1}. Using 3D hydrodynamic simulations, I show that such deficit arises from the tight self-regulation between thermal instability condensation and AGN outflow feedback. Multiphase filaments condense out of the hot plasma, they rain onto the central SMBH, and boost the AGN outflows via chaotic cold accretion. The sub-relativistic outflows thermalize in the core via shocks and turbulence, releasing more heat in the inner cooler phase, thus inducing the observed soft X-ray decline. I discuss how we can leverage XMM capabilities in the next decade by probing turbulence, conduction, AGN accretion and outflows via the information contained in X-ray spectra and surface brightness. I focus on the importance of selecting a few objects with Ms exposure and how we can unveil multiphase halos through the synergy between simulations and multiwavelength observations.
Solar-cycle dependence of a model turbulence spectrum using IMP and ACE observations over 38 years
Burger, R. A.; Nel, A. E.; Engelbrecht, N. E.
2014-12-01
Ab initio modulation models require a number of turbulence quantities as input for any reasonable diffusion tensor. While turbulence transport models describe the radial evolution of such quantities, they in turn require observations in the inner heliosphere as input values. So far we have concentrated on solar minimum conditions (e.g. Engelbrecht and Burger 2013, ApJ), but are now looking at long-term modulation which requires turbulence data over at a least a solar magnetic cycle. As a start we analyzed 1-minute resolution data for the N-component of the magnetic field, from 1974 to 2012, covering about two solar magnetic cycles (initially using IMP and then ACE data). We assume a very simple three-stage power-law frequency spectrum, calculate the integral from the highest to the lowest frequency, and fit it to variances calculated with lags from 5 minutes to 80 hours. From the fit we then obtain not only the asymptotic variance at large lags, but also the spectral index of the inertial and the energy, as well as the breakpoint between the inertial and energy range (bendover scale) and between the energy and cutoff range (cutoff scale). All values given here are preliminary. The cutoff range is a constraint imposed in order to ensure a finite energy density; the spectrum is forced to be either flat or to decrease with decreasing frequency in this range. Given that cosmic rays sample magnetic fluctuations over long periods in their transport through the heliosphere, we average the spectra over at least 27 days. We find that the variance of the N-component has a clear solar cycle dependence, with smaller values (~6 nT2) during solar minimum and larger during solar maximum periods (~17 nT2), well correlated with the magnetic field magnitude (e.g. Smith et al. 2006, ApJ). Whereas the inertial range spectral index (-1.65 ± 0.06) does not show a significant solar cycle variation, the energy range index (-1.1 ± 0.3) seems to be anti-correlated with the variance
Effects of non-Kolmogorov turbulence on the spiral spectrum of Hypergeometric-Gaussian laser beams.
Zhu, Yun; Zhang, Licheng; Hu, Zhengda; Zhang, Yixin
2015-04-01
We study the effects of non-Kolmogorov turbulence on the orbital angular momentum (OAM) of Hypergeometric-Gaussian (HyGG) beams in a paraxial atmospheric link. The received power and crosstalk power of OAM states of the HyGG beams are established. It is found that the hollowness parameter of the HyGG beams plays an important role in the received power and crosstalk power. The larger values of hollowness parameter give rise to the higher received power and lower crosstalk power. The results also show that the smaller OAM quantum number and longer wavelength of the launch beam may lead to the higher received power and lower crosstalk power.
The infrared properties of the energy spectrum in freely decaying isotropic turbulence
McComb, W D
2014-01-01
The low wavenumber expansion of the energy spectrum takes the well known form: $ E(k,t) = E_2(t) k^2 + E_4(t) k^4 + ... $, where the coefficients are weighted integrals against the correlation function $C(r,t)$. We show that expressing $E(k,t)$ in terms of the longitudinal correlation function $f(r,t)$ immediately yields $E_2(t)=0$ by cancellation. We verify that the same result is obtained using the correlation function $C(r,t)$, provided only that $f(r,t)$ falls off faster than $r^{-3}$ at large values of $r$. As power-law forms are widely studied for the purpose of establishing bounds, we consider the family of model correlations $f(r,t)=\\alpha_n(t)r^{-n}$, for positive integer $n$, at large values of the separation $r$. We find that for the special case $n=3$, the relationship connecting $f(r,t)$ and $C(r,t)$ becomes indeterminate, and (exceptionally) $E_2 \
Dimotakis, Paul E.
2005-01-01
The ability of turbulent flows to effectively mix entrained fluids to a molecular scale is a vital part of the dynamics of such flows, with wide-ranging consequences in nature and engineering. It is a considerable experimental, theoretical, modeling, and computational challenge to capture and represent turbulent mixing which, for high Reynolds number (Re) flows, occurs across a spectrum of scales of considerable span. This consideration alone places high-Re mixing phenomena beyond the reach o...
Energy Technology Data Exchange (ETDEWEB)
Nazarenko, Sergey [Warwick Univ., Coventry (United Kingdom). Mathematics Inst.
2011-07-01
Wave Turbulence refers to the statistical theory of weakly nonlinear dispersive waves. There is a wide and growing spectrum of physical applications, ranging from sea waves, to plasma waves, to superfluid turbulence, to nonlinear optics and Bose-Einstein condensates. Beyond the fundamentals the book thus also covers new developments such as the interaction of random waves with coherent structures (vortices, solitons, wave breaks), inverse cascades leading to condensation and the transitions between weak and strong turbulence, turbulence intermittency as well as finite system size effects, such as ''frozen'' turbulence, discrete wave resonances and avalanche-type energy cascades. This book is an outgrow of several lectures courses held by the author and, as a result, written and structured rather as a graduate text than a monograph, with many exercises and solutions offered along the way. The present compact description primarily addresses students and non-specialist researchers wishing to enter and work in this field. (orig.)
International Nuclear Information System (INIS)
FIV(fluid-induced vibration) is an important concern in power and process plants especially in nuclear industry subject to high axial and cross flow causing serious problems. This study addresses the effects of random pressures due to turbulent flows upon the vibrational responses to PSD(power spectrum density) in one dimensional rod supported simply at both ends. Though TIV(turbulenceinduced vibration) takes place under parallel flows where axial flow-induced vibration is a much smaller problem than cross-flow vibration, FIV in axial flow generates random pressure fluctuations due to turbulence mainly around the rod surfaces forcing them vibrate randomly. Dynamic forces produced by the total pressure fluctuating on the rod surface are calculated by the 3 dimensional LES (large eddy simulation) turbulent model in FLUENT 6 to simulate the flow field in CFD code. To acquire response to fluctuating pressure, the response equation of vibration is used in case of a cylindrical rod in one dimensional case. The first modal longitudinal joint acceptance integral including coherence function is an important parameter affecting the vibrational responses in the form of root mean square modal response along with the damping ratio. And the fluctuating stagnation pressure PSD at the wall via FFT transformation in turbulent boundary layer is a key to increasing CHF(critical heat flux). The main goal is not only to enhance the CHF but also to reduce FIV simultaneously, and to apply to designing fuel rods and spacer grid assembly including mixing vanes
Energy Technology Data Exchange (ETDEWEB)
Palistrant, M. E., E-mail: mepalistrant@yandex.com; Ursu, V. A. [Academy of Sciences of Moldova, Institute of Applied Physics (Moldova, Republic of)
2013-04-15
A theory of thermodynamic properties of a spin density wave (SDW) in a quasi-two-dimensional system (with a preset impurity concentration x) is constructed. We choose an anisotropic dispersion relation for the electron energy and assume that external magnetic field H has an arbitrary direction relative to magnetic moment M{sub Q}. The system of equations defining order parameters M{sub Q}{sup z}, M{sub Q}{sup {sigma}}, M{sub z}, and M{sup {sigma}} is constructed and transformed with allowance for the Umklapp processes. Special cases when H Double-Vertical-Line M{sub Q} and H Up-Tack M{sub Q} (H{sub Z}H{sup {sigma}} = 0) are considered in detail as well as cases of weak fields H of arbitrary direction. The condition for the transition of the system to the commensurate and incommensurate states of the SDW is analyzed. The concentration dependence of magnetic transition temperature T{sub M} is calculated, and the components of the order parameter for the incommensurate phase are determined. The phase diagram (T,{approx}x) is constructed. The effect of the magnetic field on magnetic transition temperature T{sub M} is analyzed for H{sub Z}H{sup {sigma}} = 0, and longitudinal magnetic susceptibility {chi} Double-Vertical-Line is calculated; this quantity demonstrates the temperature dependence corresponding to a system with a gap for x < x{sub c} and to a gapless state for x > x{sub c}. In the immediate vicinity of the critical impurity concentration (x {approx} x{sub c}), the temperature dependence of the magnetic susceptibility acquires a local maximum. The effect of anisotropy of the electron energy spectrum on the investigated physical quantities is also analyzed.
Turbulent thermal diffusion in strongly stratified turbulence: theory and experiments
Amir, G; Eidelman, A; Elperin, T; Kleeorin, N; Rogachevskii, I
2016-01-01
Turbulent thermal diffusion is a combined effect of the temperature stratified turbulence and inertia of small particles. It causes the appearance of a non-diffusive turbulent flux of particles in the direction of the turbulent heat flux. This non-diffusive turbulent flux of particles is proportional to the product of the mean particle number density and the effective velocity of inertial particles. The theory of this effect has been previously developed only for small temperature gradients and small Stokes numbers (Phys. Rev. Lett. {\\bf 76}, 224, 1996). In this study a generalized theory of turbulent thermal diffusion for arbitrary temperature gradients and Stokes numbers has been developed. The laboratory experiments in the oscillating grid turbulence and in the multi-fan produced turbulence have been performed to validate the theory of turbulent thermal diffusion in strongly stratified turbulent flows. It has been shown that the ratio of the effective velocity of inertial particles to the characteristic ve...
Molodij, Guillaume
2011-08-01
A general expression of the spatial correlation functions of quantities related to the phase fluctuations of a wave that have propagated through the atmospheric turbulence are derived. A generalization of the method to integrand containing the product of an arbitrary number of hypergeometric functions is presented. The formalism is able to give the coefficients of phase-expansion functions orthogonal over an arbitrary circularly symmetric weighting function for an isotropic turbulence spectrum, as well as to describe the effect of the finite outer and inner scales of the turbulence and to describe the spherical propagation or to derive the effects of the analytical operators acting on the phase such as the derivatives of any order. The derivation of the generalized integrals with multiparameters is based on the Mellin transforms integration method. PMID:21811336
Nazarenko, Sergey
2015-07-01
Wave turbulence is the statistical mechanics of random waves with a broadband spectrum interacting via non-linearity. To understand its difference from non-random well-tuned coherent waves, one could compare the sound of thunder to a piece of classical music. Wave turbulence is surprisingly common and important in a great variety of physical settings, starting with the most familiar ocean waves to waves at quantum scales or to much longer waves in astrophysics. We will provide a basic overview of the wave turbulence ideas, approaches and main results emphasising the physics of the phenomena and using qualitative descriptions avoiding, whenever possible, involved mathematical derivations. In particular, dimensional analysis will be used for obtaining the key scaling solutions in wave turbulence - Kolmogorov-Zakharov (KZ) spectra.
International Nuclear Information System (INIS)
A generalization of a transformation due to Kurskov and Ozernoi is used to rewrite the usual equations governing subsonic turbulence in Robertson-Walker cosmological models as Navier-Stokes equations with a time-dependent viscosity. This paper first rederives some well-known results in a very simple way by means of this transformation. The main result however is that the establishment of a Kolmogorov spectrum at recombination appears to be incompatible with subsonic turbulence. The conditions after recombination are also discussed briefly. (author)
International Nuclear Information System (INIS)
Solar conjunction of Mars on 1976 November 25 occurred very near the beginning of solar cycle 21, about 4 months after the first Viking spacecraft arrived at the planet. Radio wave scattering data were collected at 3.6 and 13 cm wavelengths, using the radio link between the Viking orbiters and the Earth. These data allow measurements of solar wind properties over a range of heliocentric radial distance from approx.6 to 44 R/sub sun/ with solar latitudes ranging from -170 to +70. Observations with Mariner 10 during a period of moderate solar activity in 1974 cover from 6 to 24 R/sub sun/ and from approx.200 to near 900. We have found that the temporal frequency variance spectrum of amplitude fluctuations is useful for characterizing the bulk motion of the plasma. This spectrum has an approximately constant low frequency plateau and a power-law high frequency asymptote; the plateau-asymptote intersection frequency provides a measure of the solar wind velocity V. We also obtain the spectral index p of electron density turbulence, Phi/sub N/approx.kappa/sup -p/, where kappa is spatial wavenumber. These results apply to a cylindrical region oriented with its axis along the radio ray path and its center at the point of closest approach to the Sun. The measurements of V and p cover some 78/sup d/ for Viking and 492 for Mariner 10 and show the combined effects of changing heliocentric distance rho, solar latitude theta, and solar longitude Psi, as well as solar activity. The Viking results can be regarded as a function primary of rho and Psi since the observations are concentrated in the equatorial regions when solar activity was near minimum. For Mariner 10, rho, theta, and Psi variations were important. The Viking results show an abrupt change in V(rho) and the turbulence spectral index at approx.15 R/sub sun/
Currents for Arbitrary Helicity
Dragon, Norbert
2016-01-01
Using Mackey's classification of unitary representations of the Poincar\\'e group on massles states of arbitrary helicity we disprove the claim that states with helicity |h|>=1 cannot couple to a conserved current by constructing such a current.
Multi-scale theory of rotating turbulence
Leprovost, Nicolas; Kim, Eun-Jin
2007-01-01
We consider turbulence induced by an arbitrary forcing and derive turbulence amplitude and turbulent transport coefficients, first by using a quasi-linear theory and then by using a multi-scale renormalisation analysis. With an isotropic forcing, the quasi-linear theory gives that the turbulent transport coefficients, both parallel and perpendicular to the rotation vector, have the asymptotic scaling $\\Omega^{-1}$ for rapid rotation (i.e. when the rotation rate $\\Omega$ is larger than the inv...
Institute of Scientific and Technical Information of China (English)
刘哲
2014-01-01
The emergence of large‐span bridge and extreme weather attract much more attention of researchers on the bridge buffeting problem .One of the most important factors that affect bridge buffeting response is wind velocity spectrum .In the precious investigations ,wind velocity of various frequency has impact on the bridge buffeting response . While Proper Orthogonal Decomposition (POD ) method is proposed to decompose the wind velocity to solve the above problem and a cable‐stayed bridge was used to investigate the contribution of effective model to bridge buffeting response .The result showed that not all frequency ranges of wind velocity spectrum contributed to the response which had relationship with both structural self‐vibration mode and turbulence effective mode coefficient .%大跨度桥梁和极端天气的出现，使得桥梁的抖振问题备受关注。然而抖振分析的最重要参数之一是风速谱，传统的抖振分析方法认为所有频率的风速会激发桥梁的抖振响应，针对此问题本文提出了基于本征正交分解（Proper Orthogonal Decomposition ）方法对风速谱分解。以某斜拉桥为算例通过对风速谱的分解研究了其有效参与模态对桥梁抖振的贡献。研究发现并不是所有频率的风速谱会激发桥梁的抖振响应，其响应与结构的自振模态和风速谱的有效湍流参与系数有关。
A Simple Theory of Capillary-Gravity Wave Turbulence
Glazman, Roman E.
1995-01-01
Employing a recently proposed 'multi-wave interaction' theory, inertial spectra of capillary gravity waves are derived. This case is characterized by a rather high degree of nonlinearity and a complicated dispersion law. The absence of scale invariance makes this and some other problems of wave turbulence (e.g., nonlinear inertia gravity waves) intractable by small-perturbation techniques, even in the weak-turbulence limit. The analytical solution obtained in the present work for an arbitrary degree of nonlinearity is shown to be in reasonable agreement with experimental data. The theory explains the dependence of the wave spectrum on wind input and describes the accelerated roll-off of the spectral density function in the narrow sub-range separating scale-invariant regimes of purely gravity and capillary waves, while the appropriate (long- and short-wave) limits yield power laws corresponding to the Zakharov-Filonenko and Phillips spectra.
Universal statistics of density of inertial particles sedimenting in turbulence
Fouxon, Itzhak; Lee, Changhoon
2014-01-01
We solve the problem of spatial distribution of inertial particles that sediment in Navier-Stokes turbulence with small ratio $Fr$ of acceleration of fluid particles to acceleration of gravity $g$. The particles are driven by linear drag and have arbitrary inertia. We demonstrate that independently of the particles' size or density the particles distribute over fractal set with log-normal statistics determined completely by the Kaplan-Yorke dimension $D_{KY}$. When inertia is not small $D_{KY}$ is proportional to the ratio of integral of spectrum of turbulence multiplied by wave-number and $g$. This ratio is independent of properties of particles so that the particles concentrate on fractal with universal, particles-independent statistics. We find Lyapunov exponents and confirm predictions numerically. The considered case includes typical situation of water droplets in clouds.
Arbitrary Spin Galilean Oscillator
Hagen, C R
2014-01-01
The so-called Dirac oscillator was proposed as a modification of the free Dirac equation which reproduces many of the properties of the simple harmonic oscillator but accompanied by a strong spin-orbit coupling term. It has yet to be extended successfully to the arbitrary spin S case primarily because of the unwieldiness of general spin Lorentz invariant wave equations. It is shown here using the formalism of totally symmetric multispinors that the Dirac oscillator can, however, be made to accommodate spin by incorporating it into the framework of Galilean relativity. This is done explicitly for spin zero and spin one as special cases of the arbitrary spin result. For the general case it is shown that the coefficient of the spin-orbit term has a 1/S behavior by techniques which are virtually identical to those employed in the derivation of the g-factor carried out over four decades ago.
Dissipation in unsteady turbulence
Bos, Wouter
2016-01-01
Recent experiments and simulations have shown that unsteady turbulent flows, before reaching a dynamic equilibrium state, display a universal behaviour. We show that the observed universal non-equilibrium scaling can be explained using a non-equilibrium correction of Kolmogorov's energy spectrum. Given the universality of the experimental and numerical observations, the ideas presented here lay the foundation for the modeling of a wide class of unsteady turbulent flows.
Invariants of free turbulent decay
Llor, Antoine
2006-01-01
In practically all turbulent flows, turbulent energy decay is present and competes with numerous other phenomena. In Kolmogorov's theory, decay proceeds by transfer from large energy-containing scales towards small viscous scales through the "inertial cascade." Yet, this description cannot predict an actual decay rate, even in the simplest case of homogeneous isotropic turbulence (HIT). As empirically observed over 50 years, the steepness of the "infrared" spectrum - at scales larger than ene...
Incorporating Turbulence into Dimensionless Measures of Magnetohydrodynamic Dissipation Rates
Blackman, Eric G
2008-01-01
The magnetic Reynolds number R_M, is defined as the product of a characteristic scale and associated flow speed divided by the microphysical magnetic diffusivity. For laminar flows, R_M also approximates the ratio of advective to dissipative terms in the total magnetic energy equation. However, for turbulent flows this latter ratio depends on the energy spectra and approaches unity in a steady state. The physical implication of R_M>>1 for laminar flows (i.e. negligible magnetic dissipation of magnetic energy on dynamical times) is therefore incorrect for turbulent flows. To correctly capture the importance of dissipation for flows of arbitrary spectra we define an effective magnetic dissipation number, R_{M,e}, as the ratio of the advection to microphysical dissipation terms in the total magnetic energy equation, incorporating the full spectrum of scales, arbitrary magnetic Prandtl numbers, and distinct pairs of inner and outer scales for magnetic and kinetic spectra. For a substantial parameter range, R_{M,e...
MHD turbulence and distributed chaos
Bershadskii, A
2016-01-01
It is shown, using results of recent direct numerical simulations, that spectral properties of distributed chaos in MHD turbulence with zero mean magnetic field are similar to those of hydrodynamic turbulence. An exception is MHD spontaneous breaking of space translational symmetry, when the stretched exponential spectrum $\\exp(-k/k_{\\beta})^{\\beta}$ has $\\beta=4/7$.
Stecker, F. W.; Puget, J. L.
1972-01-01
Following the big-bang baryon symmetric cosmology of Omnes, the redshift was calculated to be on the order of 500-600. It is show that, at these redshifts, annihilation pressure at the boundaries between regions of matter and antimatter drives large scale supersonic turbulence which can trigger galaxy formation. This picture is consistent with the gamma-ray background observations discussed previously. Gravitational binding of galaxies then occurs at a redshift of about 70, at which time vortical turbulent velocities of about 3 x 10 to the 7th power cm/s lead to angular momenta for galaxies comparable with measured values.
Mixing in manipulated turbulence
Kuczaj, A.K.; Geurts, B.J.
2006-01-01
A numerical investigation of turbulent flow, subject to deterministic broad-band forcing, is presented. Explicit forcing procedures are included that represent the simultaneous agitation of a wide spectrum of length-scales, including both large scales as well as a band of much smaller scales. Such f
Wave turbulence buildup in a vibrating plate
Auliel, Maria Ines; Mordant, Nicolas
2015-01-01
We report experimental and numerical results on the buildup of the energy spectrum in wave turbulence of a vibrating thin elastic plate. Three steps are observed: first a short linear stage, then the turbulent spectrum is constructed by the propagation of a front in wave number space and finally a long time saturation due to the action of dissipation. The propagation of a front at the second step is compatible with scaling predictions from the Weak Turbulence Theory.
Generalised turbulence spectra for broadband noise predictions with the Random Particle Mesh method
Wohlbrandt, Attila; Guerin, Sebastien; Ewert, Roland
2015-01-01
For better comparison to fan broadband noise experiments the Random Particle Mesh (RPM) method is extended to generalised turbulence spectra. The RPM method synthesises turbulent fluctuations by filtering white noise with a Gaussian filter kernel, which in turn gives a Gaussian spectrum. The Gaussian function is smooth and its derivatives and antiderivatives are again Gaussian functions; the Gaussian filter is efficient and finds wide-spread applications in stochastic signal processing. However in many applications Gaussian spectra are not matching physical spectra. E.g. in turbo-machines, the von Karman, Liepmann, and modified von Karman spectra are the most relevant model spectra. In the current paper we show how to analytically derive weighting functions to realise arbitrary spectra which are isotropic and solenoidal using a superposition of weighted Gaussian spectra of differing length scales. The analytic weighting functions for the von Karman , the Liepmann , and the modified von Karman spectra are deri...
Magnetohydrodynamic turbulence
Biskamp, Dieter
2003-01-01
This book presents an introduction to, and modern account of, magnetohydrodynamic (MHD) turbulence, an active field both in general turbulence theory and in various areas of astrophysics. The book starts by introducing the MHD equations, certain useful approximations and the transition to turbulence. The second part of the book covers incompressible MHD turbulence, the macroscopic aspects connected with the different self-organization processes, the phenomenology of the turbulence spectra, two-point closure theory, and intermittency. The third considers two-dimensional turbulence and compressi
Energy Technology Data Exchange (ETDEWEB)
Klein, Kristopher G.; Howes, Gregory G. [Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242 (United States); TenBarge, Jason M. [IREAP, University of Maryland, College Park, MD 20742 (United States); Podesta, John J., E-mail: kristopher-klein@uiowa.edu [Center for Space Plasma Physics, Space Science Institute, Boulder, CO 80301 (United States)
2014-04-20
Motivated by recent observations of distinct parallel and perpendicular signatures in magnetic helicity measurements segregated by wave period and angle between the local magnetic field and the solar wind velocity, this paper undertakes a comparison of three intervals of Ulysses data with synthetic time series generated from a physically motivated turbulence model. From these comparisons, it is hypothesized that the observed signatures result from a perpendicular cascade of Alfvénic fluctuations and a local, non-turbulent population of ion-cyclotron or whistler waves generated by temperature anisotropy instabilities. By constraining the model's free parameters through comparison to in situ data, it is found that, on average, ∼95% of the power near dissipative scales is contained in a perpendicular Alfvénic cascade and that the parallel fluctuations are propagating nearly unidirectionally. The effects of aliasing on magnetic helicity measurements are considered and shown to be significant near the Nyquist frequency.
Klein, Kristopher G; TenBarge, Jason M; Podesta, John J
2014-01-01
Motivated by recent observations of distinct parallel and perpendicular signatures in magnetic helicity measurements segregated by wave period and angle between the local magnetic field and the solar wind velocity, this paper undertakes a comparison of three intervals of \\emph{Ulysses} data with synthetic time series generated from a physically motivated turbulence model. From these comparisons, it is hypothesized that the observed signatures result from a perpendicular cascade of \\Alfvenic fluctuations and a local, non-turbulent population of ion cyclotron or whistler waves generated by temperature anisotropy instabilities. By constraining the model's free parameters through comparison to \\emph{in situ} data, it is found that, on average, $ \\sim 95\\%$ of the power near dissipative scales is contained in a perpendicular \\Alfvenic cascade and that the parallel fluctuations are propagating nearly unidirectionally. The effects of aliasing on magnetic helicity measurements are considered and shown to be significa...
Non-linear diffusion of charged particles in a turbulent magnetoplasma
International Nuclear Information System (INIS)
A unified theory is presented which describes non-linear effects on relative and absolute diffusion of charged particles in a magnetoplasma, in analogy with analogous methods used for diffusion studies of pollutants in the environment. Explicit results are obtained for non-linear diffusion of test particles represented by their guiding centers in a turbulent energy spectrum in K-1 and K-3, which corresponds to recent measurements in the T.F.R. Tokamak. As expected, a BOHM scaling of the absolute diffusion coefficient is obtained for frozen turbulence. The growth of an initially small cloud of particles in an arbitrary turbulent medium corresponds to the process of relative diffusion. It is described by a generalization of the Brownian motion, including a first stage of very slow initial relative diffusion, followed by a stage of rapid expansion of the cloud up to the final stage in which particles become uncorrelated, and Brownian diffusion is reached asymptotically. The stage of exponential growth, observed in fluid turbulence corresponds to the clump effect in plasma turbulence. It is entirely due to the effect of trajectory correlations. The LJAPUNOV exponent of this exponential separation is obtained analytically. Numerical solutions of the diffusion equation are presented for the effective radius of the cloud as function of time in the case of a model spectrum of drift-wave turbulence. When compared with classical Brownian diffusion of uncorrelated particles, the effective ''diffusion coefficient'' for correlated particles is found to be reduced by orders of magnitude for rather long times. Practical implications for experimental situations are also discussed (Barium clouds released in the ionosphere, pellet injection in e.g. Tokamaks)
Classifying Serre subcategories via atom spectrum
Kanda, Ryo
2011-01-01
In this paper, we introduce the atom spectrum of an abelian category as a topological space consisting of all the equivalence classes of monoform objects. In terms of the atom spectrum, we give a classification of Serre subcategories of an arbitrary noetherian abelian category. Moreover we show that the atom spectrum of a locally noetherian Grothendieck category is homeomorphic to its Ziegler spectrum.
The Interpretation of Saussure’s Arbitrariness
Institute of Scientific and Technical Information of China (English)
王艳
2015-01-01
According to Saussure,The arbitrary nature of language is"first principle of linguistic".With the development of cognitive science,some exaggerate the importance of iconicity;some even suggest iconicity should replace arbitrariness.What leads to this extreme view is the misunderstanding of arbitrariness.The paper aims at advocating an overall and objective view towards the arbitrary nature of language,putting forward that arbitrariness and iconicity are not incompatible but complementary.
Derrida model for arbitrary spin
Energy Technology Data Exchange (ETDEWEB)
Saakyan, D.B.
1988-04-01
The variant of the Kirkpatrick-Sherrington model generalized by Derrida for the case of arbitrary spin is considered. When the number of simultaneously interacting neighbors tends to infinity, a solution to the model is obtained not only by reduction to the random-energy model but also by means of the replica method with the Parisi ansatz.
Representing Arbitrary Boosts for Undergraduates.
Frahm, Charles P.
1979-01-01
Presented is a derivation for the matrix representation of an arbitrary boost, a Lorentz transformation without rotation, suitable for undergraduate students with modest backgrounds in mathematics and relativity. The derivation uses standard vector and matrix techniques along with the well-known form for a special Lorentz transformation. (BT)
Bulk Comptonization by Turbulence in Accretion Disks
Kaufman, J
2016-01-01
Radiation pressure dominated accretion discs around compact objects may have turbulent velocities that greatly exceed the electron thermal velocities within the disc. Bulk Comptonization by the turbulence may therefore dominate over thermal Comptonization in determining the emergent spectrum. Bulk Comptonization by divergenceless turbulence is due to radiation viscous dissipation only. It can be treated as thermal Comptonization by solving the Kompaneets equation with an equivalent "wave" temperature, which is a weighted sum over the power present at each scale in the turbulent cascade. Bulk Comptonization by turbulence with non-zero divergence is due to both pressure work and radiation viscous dissipation. Pressure work has negligible effect on photon spectra in the limit of optically thin turbulence, and in this limit radiation viscous dissipation alone can be treated as thermal Comptonization with a temperature equivalent to the full turbulent power. In the limit of extremely optically thick turbulence, ra...
Spectrum Analysis of Wind Profiling Radar Measurements
Institute of Scientific and Technical Information of China (English)
阮征; 慕瑞琪; 魏鸣; 葛润生
2014-01-01
Unlike previous studies on wind turbulence spectrum in the planetary boundary layer, this investigation focuses on high-altitude (1-5 km) wind energy spectrum and turbulence spectrum under various weather conditions. A fast Fourier transform (FFT) is used to calculate the wind energy and turbulence spectrum density at high altitudes (1-5 km) based on wind profiling radar (WPR) measurements. The turbulence spectrum under stable weather conditions at high altitudes is expressed in powers within a frequency range of 2 × 10-5-10-3 s-1, and the slope b is between -0.82 and -1.04, indicating that the turbulence is in the transition from the energetic area to the inertial sub-range. The features of strong weather are reflected less obviously in the wind energy spectrum than in the turbulence spectrum, with peaks showing up at different heights in the latter spectrum. Cold windy weather appears over a period of 1.5 days in the turbulence spectrum. Wide-range rainstorms exhibit two or three peaks in the spectrum over a period of 15-20 h, while in severe convective weather conditions, there are two peaks at 13 and 9 h. The results indicate that spectrum analysis of wind profiling radar measurements can be used as a supplemental and helpful method for weather analysis.
Scintillation index in strong oceanic turbulence
Baykal, Yahya
2016-09-01
Scintillation index of spherical wave in strongly turbulent oceanic medium is evaluated. In the evaluation, modified Rytov solution and our recent formulation that expresses the oceanic turbulence parameters by the atmospheric turbulence structure constant, are employed. Variations of the scintillation index in strong oceanic turbulence are examined versus the oceanic turbulence parameters such as the rate of dissipation of kinetic energy per unit mass of fluid, the rate of dissipation of mean-squared temperature, viscosity, wavelength, the link length, and the ratio of temperature to salinity contributions to the refractive index spectrum.
Forced fluid dynamics from gravity in arbitrary dimensions
International Nuclear Information System (INIS)
We consider long wavelength solutions to the Einstein-dilaton system with negative cosmological constant which are dual, under the AdS/CFT correspondence, to solutions of the conformal relativistic Navier-Stokes equations with a dilaton-dependent forcing term. Certain forced fluid flows are known to exhibit turbulence; holographic duals of forced fluid dynamics are therefore of particular interest as they may aid efforts towards an explicit model of holographic steady state turbulence. In recent work, Bhattacharyya et al. have constructed long wavelength asymptotically locally AdS5 bulk spacetimes with a slowly varying boundary dilaton field which are dual to forced fluid flows on the 4−dimensional boundary. In this paper, we generalise their work to arbitrary spacetime dimensions; we explicitly compute the dual bulk metric, the fluid dynamical stress tensor and Lagrangian to second order in a boundary derivative expansion
Turbulence patterns and neutrino flavor transitions in high-resolution supernova models
International Nuclear Information System (INIS)
During the shock-wave propagation in a core-collapse supernova (SN), matter turbulence may affect neutrino flavor conversion probabilities. Such effects have been usually studied by adding parametrized small-scale random fluctuations (with arbitrary amplitude) on top of coarse, spherically symmetric matter density profiles. Recently, however, two-dimensional (2D) SN models have reached a space resolution high enough to directly trace anisotropic density profiles, down to scales smaller than the typical neutrino oscillation length. In this context, we analyze the statistical properties of a large set of SN matter density profiles obtained in a high-resolution 2D simulation, focusing on a post-bounce time (2 s) suited to study shock-wave effects on neutrino propagation on scales as small as O(100) km and possibly below. We clearly find the imprint of a broken (Kolmogorov-Kraichnan) power-law structure, as generically expected in 2D turbulence spectra. We then compute the flavor evolution of SN neutrinos along representative realizations of the turbulent matter density profiles, and observe no or modest damping of the neutrino crossing probabilities on their way through the shock wave. In order to check the effect of possibly unresolved fluctuations at scales below O(100) km, we also apply a randomization procedure anchored to the power spectrum calculated from the simulation, and find consistent results within ± 1σ fluctuations. These results show the importance of anchoring turbulence effects on SN neutrinos to realistic, fine-grained SN models
Elastic wave turbulence and intermittency
Chibbaro, Sergio; Josserand, Christophe
2016-07-01
We investigate the onset of intermittency for vibrating elastic plate turbulence in the framework of the weak wave turbulence theory using a numerical approach. The spectrum of the displacement field and the structure functions of the fluctuations are computed for different forcing amplitudes. At low forcing, the spectrum predicted by the theory is observed, while the fluctuations are consistent with Gaussian statistics. When the forcing is increased, the spectrum varies at large scales, corresponding to the oscillations of nonlinear structures made of ridges delimited by d cones. In this regime, the fluctuations exhibit small-scale intermittency that can be fitted via a multifractal model. The analysis of the nonlinear frequency shows that the intermittency is linked to the breakdown of the weak turbulence at large scales only.
Two-dimensional elastic turbulence
Berti, S; Boffetta, G; Celani, A; Musacchio, S; 10.1103/PhysRevE.77.055306
2010-01-01
We investigate the effect of polymer additives on a two-dimensional Kolmogorov flow at very low Reynolds numbers by direct numerical simulations of the Oldroyd-B viscoelastic model. We find that above the elastic instability threshold the flow develops the elastic turbulence regime recently observed in experiments. We observe that both the turbulent drag and the Lyapunov exponent increase with Weissenberg, indicating the presence of a disordered, turbulent-like mixing flow. The energy spectrum develops a power-law scaling range with an exponent close to the experimental and theoretical expectations.
Fragmentation in turbulent primordial gas
Glover, S C O; Klessen, R S; Bromm, V
2010-01-01
We report results from numerical simulations of star formation in the early universe that focus on the role of subsonic turbulence, and investigate whether it can induce fragmentation of the gas. We find that dense primordial gas is highly susceptible to fragmentation, even for rms turbulent velocity dispersions as low as 20% of the initial sound speed. The resulting fragments cover over two orders of magnitude in mass, ranging from 0.1 to 40 solar masses. However, our results suggest that the details of the fragmentation depend on the local properties of the turbulent velocity field and hence we expect considerable variations in the resulting stellar mass spectrum in different halos.
Arbitrary Bending Plasmonic Light Waves
Epstein, Itai
2013-01-01
We demonstrate the generation of self-accelerating surface plasmon beams along arbitrary caustic curvatures. These plasmonic beams are excited by free-space beams through a two-dimensional binary plasmonic phase mask, which provides the missing momentum between the two beams in the direction of propagation, and sets the required phase for the plasmonic beam in the transverse direction. We examine the cases of paraxial and non-paraxial curvatures and show that this highly versatile scheme can be designed to produce arbitrary plasmonic self-accelerating beams. Several different plasmonic beams, which accelerate along polynomial and exponential trajectories, are demonstrated both numerically and experimentally, with a direct measurement of the plasmonic light intensity using a near-field-scanning-optical-microscope.
Arbitrary bending plasmonic light waves.
Epstein, Itai; Arie, Ady
2014-01-17
We demonstrate the generation of self-accelerating surface plasmon beams along arbitrary caustic curvatures. These plasmonic beams are excited by free-space beams through a two-dimensional binary plasmonic phase mask, which provides the missing momentum between the two beams in the direction of propagation and sets the required phase for the plasmonic beam in the transverse direction. We examine the cases of paraxial and nonparaxial curvatures and show that this highly versatile scheme can be designed to produce arbitrary plasmonic self-accelerating beams. Several different plasmonic beams, which accelerate along polynomial and exponential trajectories, are demonstrated both numerically and experimentally, with a direct measurement of the plasmonic light intensity using a near-field scanning optical microscope.
Polarimetric studies of magnetic turbulence with interferometer
Lee, Hyeseung; Cho, Jungyeon
2016-01-01
We study statistical properties of synchrotron polarization emitted from media with magnetohydrodynamic (MHD) turbulence. We use both synthetic and MHD turbulence simulation data for our studies. We obtain the spatial spectrum and its derivative with respect to wavelength of synchrotron polarization arising from both synchrotron radiation and Faraday rotation fluctuations. In particular, we investigate how the spectrum changes with frequency. We find that our simulations agree with the theoretical predication in Lazarian \\& Pogosyan (2016). We conclude that the spectrum of synchrotron polarization and it derivative can be very informative tools to get detailed information about the statistical properties of MHD turbulence from radio observations of diffuse synchrotron polarization. Especially, they are useful to recover the statistics of turbulent magnetic field as well as turbulent density of electrons. We also simulate interferometric observations that incorporate the effects of noise and finite telesco...
EuHIT, Collaboration
2015-01-01
As a member of the EuHIT (European High-Performance Infrastructures in Turbulence - see here) consortium, CERN is participating in fundamental research on turbulence phenomena. To this end, the Laboratory provides European researchers with a cryogenic research infrastructure (see here), where the first tests have just been performed.
Energy Technology Data Exchange (ETDEWEB)
Horton, W. [Univ. of Texas, Austin, TX (United States). Inst. for Fusion Studies; Hu, G. [Globalstar LP, San Jose, CA (United States)
1998-07-01
The origin of plasma turbulence from currents and spatial gradients in plasmas is described and shown to lead to the dominant transport mechanism in many plasma regimes. A wide variety of turbulent transport mechanism exists in plasmas. In this survey the authors summarize some of the universally observed plasma transport rates.
Directory of Open Access Journals (Sweden)
D. Falceta-Gonçalves
2011-01-01
Full Text Available The Interstellar Medium (ISM is a complex, multi-phase system, where the history of the stars occurs. The processes of birth and death of stars are strongly coupled to the dynamics of the ISM. The observed chaotic and diffusive motions of the gas characterize its turbulent nature. Understanding turbulence is crucial for understanding the star-formation process and the energy-mass feedback from evolved stars. Magnetic fields, threading the ISM, are also observed, making this effort even more difficult. In this work, I briefly review the main observations and the characterization of turbulence from these observable quantities. Following on, I provide a review of the physics of magnetized turbulence. Finally, I will show the main results from theoretical and numerical simulations, which can be used to reconstruct observable quantities, and compare these predictions to the observations.
Anisotropic scaling of magnetohydrodynamic turbulence
Horbury, T S; Oughton, S
2008-01-01
We present a quantitative estimate of the anisotropic power and scaling of magnetic field fluctuations in inertial range magnetohydrodynamic turbulence, using a novel wavelet technique applied to spacecraft measurements in the solar wind. We show for the first time that, when the local magnetic field direction is parallel to the flow, the spacecraft-frame spectrum has a spectral index near 2. This can be interpreted as the signature of a population of fluctuations in field-parallel wavenumbers with a $k_{\\parallel}^{-2}$ spectrum but is also consistent with the presence of a "critical balance" style turbulent cascade. We also find, in common with previous studies, that most of the power is contained in wavevectors at large angles to the local magnetic field and that this component of the turbulence has a spectral index of 5/3.
Magnetohydrodynamic turbulence: Observation and experiment
Energy Technology Data Exchange (ETDEWEB)
Brown, M. R.; Schaffner, D. A.; Weck, P. J. [Department of Physics and Astronomy, Swarthmore College, 500 College Avenue, Swarthmore, Pennsylvania 19081 (United States)
2015-05-15
We provide a tutorial on the paradigms and tools of magnetohydrodynamic (MHD) turbulence. The principal paradigm is that of a turbulent cascade from large scales to small, resulting in power law behavior for the frequency power spectrum for magnetic fluctuations E{sub B}(f). We will describe five useful statistical tools for MHD turbulence in the time domain: the temporal autocorrelation function, the frequency power spectrum, the probability distribution function of temporal increments, the temporal structure function, and the permutation entropy. Each of these tools will be illustrated with an example taken from MHD fluctuations in the solar wind. A single dataset from the Wind satellite will be used to illustrate all five temporal statistical tools.
Magnetohydrodynamics turbulence: An astronomical perspective
Indian Academy of Sciences (India)
S Sridhar
2011-07-01
Early work on magnetohydrodynamic (MHD) turbulence in the 1960s due, independently, to Iroshnikov and Kraichnan (IK) considered isotropic inertial-range spectra. Whereas laboratory experiments were not in a position to measure the spectral index, they showed that the turbulence was strongly anisotropic. Theoretical horizons correspondingly expanded in the 1980s, to accommodate both the isotropy of the IK theory and the anisotropy suggested by the experiments. Since the discovery of pulsars in 1967, many years of work on interstellar scintillation suggested that small-scale interstellar turbulence must have a hydromagnetic origin; but the IK spectrum was too ﬂat and the ideas on anisotropic spectra too qualitative to explain the observations. In response, new theories of balanced MHD turbulence were proposed in the 1990s, which argued that the IK theory was incorrect, and made quantitative predictions of anisotropic inertial-range spectra; these theories have since found applications in many areas of astrophysics. Spacecraft measurements of solar-wind turbulence show that there is more power in Alfvén waves that travel away from the Sun than towards it. Theories of imbalanced MHD turbulence have now been proposed to address interplanetary turbulence. This very active area of research continues to be driven by astronomy.
Transition to turbulence, intermittence, and vortex fluctuations
Energy Technology Data Exchange (ETDEWEB)
Bershadskii, A.G.
1985-09-01
A model is developed which describes the fluctuation coalescence of vortices at moderately high Reynolds numbers. The model is found to be in good agreement with experimental data on (1) flow intermittence in a boundary layer, a round jet, and a plane wake; (2) the effect of a magnetic field on the formation of a turbulent energy spectrum behind a grid and on turbulent fluctuations and friction in ducts; (3) formation of a turbulent energy spectrum in a boundary layer and in ducts. 12 references.
Quantitative photography of intermittency in surface wave turbulence
Energy Technology Data Exchange (ETDEWEB)
Wright, W.; Budakian, R.; Putterman, S.J. [Univ. of California, Los Angeles, CA (United States)
1997-12-31
At high amplitudes of excitation surface waves on water distribute their energy according to a Kolmogorov type of turbulent power spectrum. We have used diffusing light photography to measure the power spectrum and to quantify the presence of large structures in the turbulent state.
Generalization of the electronic susceptibility for arbitrary molecular geometries
Scherrer, Arne; Dreßler, Christian; Ahlert, Paul; Sebastiani, Daniel
2016-04-01
We generalize the explicit representation of the electronic susceptibility χ[R](r, r') for arbitrary molecular geometries R. The electronic susceptibility is a response function that yields the response of the molecular electronic charge density at linear order to an arbitrary external perturbation. We address the dependence of this response function on the molecular geometry. The explicit representation of the molecular geometry dependence is achieved by means of a Taylor expansion in the nuclear coordinates. Our approach relies on a recently developed low-rank representation of the response function χ[R](r, r') which allows a highly condensed storage of the expansion and an efficient application within dynamical chemical environments. We illustrate the performance and accuracy of our scheme by computing the vibrationally induced variations of the response function of a water molecule and its resulting Raman spectrum.
Simulation of atmospheric turbulence layers with phase screens by JAVA
Zhang, Xiaofang; Chen, Wenqin; Yu, Xin; Yan, Jixiang
2008-03-01
In multiconjugate Adaptive Optics (MCAO), the phase screens are used to simulate atmospheric turbulence layers to study the optimal turbulence delamination and the determination of layer boundary position. In this paper, the method of power spectrum inversion and sub-harmonic compensation were used to simulate atmospheric turbulence layers and results can be shown by grey map. The simulation results showed that, with the increase of turbulence layers, the RMS of adaptive system decreased, but the amplitude diminished. So the atmospheric turbulence can be split into 2-3 layers and be modeled by phase screens. Otherwise, a small simulation atmospheric turbulence delamination system was realized by JAVA.
Turbulence: large-scale sweeping and the emergence of small-scale Kolmogorov spectra.
Dekker, H
2011-08-01
The dynamics of fully developed hydrodynamic turbulence still is a basically unsolved theoretical problem, due to the strong-coupling long-range nonlinearities in the Navier-Stokes equations. The present analysis focuses on the small-scale fluctuations in a turbulent boundary layer with one external length scale y(o). After taking a (2+1)D spatiotemporal spectral transform of the fluctuating vorticity fields, care is taken of large-scale sweeping which arises as a collective zero mode from the nonlinear flow terms. The "unswept" small-scale nonlinearities are then shown to be asymptotically locally isotropic (i.e., for wave numbers k→∞) by internal consistency, which allows to close the nonlinear hierarchy. The Navier-Stokes equations (without external forcing) are integrated to give the spectral response of the fluctuating small-scale velocity fields on the presence of a locally isotropic blob of turbulence while it is being swept around over an arbitrary steady state mean velocity profile, using viscous boundary conditions at y=0. Averaging the response spectrum over all possible orientational configurations and sweep velocities results in a novel self-consistency integral for the 4D energy spectrum function. The distribution of turbulence sweep velocities is modeled by means of Lévy-type densities, having an algebraic tail with power p>1. The generic case (which includes Von Kármán's logarithmic mean velocity profile) is found to correspond to 1Kolmogorov scaling, that is, μ=-7/3 and λ=2/3. Anomalous scaling is possible for one special mean profile.
electrode of an arbitrary shape
Directory of Open Access Journals (Sweden)
P. A. Krutitskii
1999-01-01
Full Text Available A problem on electric current in a semiconductor film from an electrode of an arbitrary shape is studied in the presence of a magnetic field. This situation describes the Hall effect, which indicates the deflection of electric, current from electric field in a semiconductor. From mathematical standpoint we consider the skew derivative problem for harmonic functions in the exterior of an open arc in a plane. By means of potential theory the problem is reduced to the Cauchy singular integral equation and next to the Fredholm equation of the 2nd kind which is uniquely solvable. The solution of the integral equation can be computed by standard codes by discretization and inversion of the matrix. The uniqueness and existence theorems are formulated.
Nonlocal bottleneck effect in two-dimensional turbulence
Biskamp, D.; Celani, A; E. Schwarz
1998-01-01
The bottleneck pileup in the energy spectrum is investigated for several two-dimensional (2D) turbulence systems by numerical simulation using high-order diffusion terms to amplify the effect, which is weak for normal diffusion. For 2D magnetohydrodynamic (MHD) turbulence, 2D electron MHD (EMHD) turbulence and 2D thermal convection, which all exhibit direct energy cascades, a nonlocal behavior is found resulting in a logarithmic enhancement of the spectrum.
Regimes of turbulence without an energy cascade
Barenghi, C F; Baggaley, A W
2016-01-01
Experiments and numerical simulations of turbulent $^4$He and $^3$He-B have established that, at hydrodynamic length scales larger than the average distance between quantum vortices, the energy spectrum obeys the same 5/3 Kolmogorov law which is observed in the homogeneous isotropic turbulence of ordinary fluids. The importance of the 5/3 law is that it points to the existence of a Richardson energy cascade from large eddies to small eddies. However, there is also evidence of quantum turbulent regimes without Kolmogorov scaling. This raises the important questions of why, in such regimes, the Kolmogorov spectrum fails to form, what is the physical nature of turbulence without energy cascade, and whether hydrodynamical models can account for the unusual behaviour of turbulent superfluid helium. In this work we describe simple physical mechanisms which prevent the formation of Kolmogorov scaling in the thermal counterflow, and analyze the conditions necessary for emergence of quasiclassical regime in quantum tu...
Influence of atmospheric turbulence on OAM-based FSO system with use of realistic link model
Li, Ming; Yu, Zhongyuan; Cvijetic, Milorad
2016-04-01
We study the influence of atmospheric turbulence on OAM-based free-space optical (FSO) communication by using the Pump turbulence spectrum model which accurately characterizes the realistic FSO link. A comprehensive comparison is made between the Pump and Kolmogorov spectrum models with respect to the turbulence impact. The calculated results show that obtained turbulence-induced crosstalk is lower, which means that a higher channel capacity is projected when the realistic Pump spectrum is used instead of the Kolmogorov spectrum. We believe that our results prove that performance of practical OAM-based FSO is better than one predicted by using the original Kolmogorov turbulence model.
Friction factor for turbulent flow in rough pipes from Heisenberg's closure hypothesis
Calzetta, Esteban
2009-01-01
We show that the main results of the analysis of the friction factor for turbulent pipe flow reported in G. Gioia and P. Chakraborty (GC), Phys. Rev. Lett. 96, 044502 (1996) can be recovered by assuming the Heisenberg closure hypothesis for the turbulent spectrum. This highlights the structural features of the turbulent spectrum underlying GC's analysis.
Friction factor for turbulent flow in rough pipes from Heisenberg's closure hypothesis.
Calzetta, Esteban
2009-05-01
We show that the main results of the analysis of the friction factor for turbulent pipe flow reported by Gioia and Chakraborty [Phys. Rev. Lett. 96, 044502 (2006)] can be recovered by assuming the Heisenberg closure hypothesis for the turbulent spectrum. This highlights the structural features of the turbulent spectrum underlying the analysis of Gioia and Chakraborty.
In situ measurements of wind and current speed and relationship between output power and turbulence
Duran Medina, Olmo; Schmitt, François G.; Sentchev, Alexei; Calif, Rudy
2015-04-01
In a context of energy transition, wind and tidal energy are sources of clean energy with the potential of partially satisfying the growing demand. The main problem of this type of energy, and other types of renewable energy remains the discontinuity of the electric power produced in different scales, inducing large fluctuations also called intermittency. This intermittency of wind and tidal energy is inherent to the turbulent nature of wind and marine currents. We consider this intermittent power production in strong relation with the turbulent intermittency of the resource. The turbulence theory is multifractal energy cascades models, a classic in physics of turbulence. From earlier studies in atmospheric sciences, we learn that wind speed and the aggregate power output are intermittent and multifractal over a wide range of scales [Calif and Schmitt 2014]. We want to extend this study to a marine current turbine and compare the scaling properties for those renewable energy sources. We consider here coupling between simultaneous velocity time series and output power from a wind turbine and a marine current turbine. Wind turbine data were obtained from Denmark and marine current data from Western Scheldt, Belgium where a prototype of a vertical and horizontal marine current turbines are tested. After an estimation of their Fourier density power spectra, we study their scaling properties in Kolmogorov's theory and the framework of fully developed turbulence. Hence, we employ a Hilbert-based methodology, namely arbitrary-order Hilbert spectral analysis [Calif et al. 2013a, 2013b] to characterize the intermittent property of the wind and marine current velocity in order to characterize the intermittent nature of the fluid. This method is used in order to obtain the spectrum and the corresponding power law for non-linear and non-stationary time series. The goal is to study the non-linear transfer characteristics in a multi-scale and multi-intensity framework.
Saturation of the turbulent dynamo.
Schober, J; Schleicher, D R G; Federrath, C; Bovino, S; Klessen, R S
2015-08-01
The origin of strong magnetic fields in the Universe can be explained by amplifying weak seed fields via turbulent motions on small spatial scales and subsequently transporting the magnetic energy to larger scales. This process is known as the turbulent dynamo and depends on the properties of turbulence, i.e., on the hydrodynamical Reynolds number and the compressibility of the gas, and on the magnetic diffusivity. While we know the growth rate of the magnetic energy in the linear regime, the saturation level, i.e., the ratio of magnetic energy to turbulent kinetic energy that can be reached, is not known from analytical calculations. In this paper we present a scale-dependent saturation model based on an effective turbulent resistivity which is determined by the turnover time scale of turbulent eddies and the magnetic energy density. The magnetic resistivity increases compared to the Spitzer value and the effective scale on which the magnetic energy spectrum is at its maximum moves to larger spatial scales. This process ends when the peak reaches a characteristic wave number k☆ which is determined by the critical magnetic Reynolds number. The saturation level of the dynamo also depends on the type of turbulence and differs for the limits of large and small magnetic Prandtl numbers Pm. With our model we find saturation levels between 43.8% and 1.3% for Pm≫1 and between 2.43% and 0.135% for Pm≪1, where the higher values refer to incompressible turbulence and the lower ones to highly compressible turbulence. PMID:26382506
A Model for Jet-Surface Interaction Noise Using Physically Realizable Upstream Turbulence Conditions
Afsar, Mohammed Z.; Leib, Stewart J.; Bozak, Richard F.
2016-01-01
This paper is a continuation of previous work in which a generalized Rapid Distortion Theory (RDT) formulation was used to model low-frequency trailing-edge noise. The research was motivated by proposed next-generation aircraft configurations where the exhaust system is tightly integrated with the airframe. Data from recent experiments at NASA on the interaction between high-Reynolds-number subsonic jet flows and an external flat plate showed that the power spectral density (PSD) of the far-field pressure underwent considerable amplification at low frequencies. For example, at the 90deg observation angle, the low-frequency noise could be as much as 10 dB greater than the jet noise itself. In this paper, we present predictions of the noise generated by the interaction of a rectangular jet with the trailing edge of a semi-infinite flat plate. The calculations are based on a formula for the acoustic spectrum of this noise source derived from an exact formal solution of the linearized Euler equations involving (in this case) one arbitrary convected scalar quantity and a Rayleigh equation Green's function. A low-frequency asymptotic approximation for the Green's function based on a two-dimensional mean flow is used in the calculations along with a physically realizable upstream turbulence spectrum, which includes a finite decorrelation region. Numerical predictions of the sound field, based on three-dimensional RANS solutions to determine the mean flow, turbulent kinetic energy and turbulence length and time scales, for a range of subsonic acoustic Mach number jets and nozzle aspect ratios are compared with experimental data. Comparisons of the RANS results with flow data are also presented for selected cases. We find that a finite decorrelation region in the turbulence spectrum increases the low-frequency algebraic decay (the low frequency "roll-off") of the acoustic spectrum with angular frequency thereby producing much closer agreement with noise data for Strouhal
International Nuclear Information System (INIS)
This paper is an introduction course in modelling turbulent thermohydraulics, aimed at computational fluid dynamics users. No specific knowledge other than the Navier Stokes equations is required beforehand. Chapter I (which those who are not beginners can skip) provides basic ideas on turbulence physics and is taken up in a textbook prepared by the teaching team of the ENPC (Benque, Viollet). Chapter II describes turbulent viscosity type modelling and the 2k-ε two equations model. It provides details of the channel flow case and the boundary conditions. Chapter III describes the 'standard' (Rij-ε) Reynolds tensions transport model and introduces more recent models called 'feasible'. A second paper deals with heat transfer and the effects of gravity, and returns to the Reynolds stress transport model. (author)
General optical scintillation in turbulent atmosphere
Institute of Scientific and Technical Information of China (English)
Ruizhong Rao
2008-01-01
A general expression of the scintillation index is proposed for optical wave propagating in turbulent atmosphere under arbitrary fluctuation conditions. The expression depends on extreme behaviors of the scintillation indices under both weak and strong fluctuations. The maximum scintillation index in the onset region and the corresponding Rytov index can be evaluated from the general expression. Plane and spherical waves in the cases of zero and non-zero turbulence inner scale are given as examples for illustration of the general behaviors of scintillation indices.
Coherence in Turbulence: New Perspective
Levich, Eugene
2009-07-01
It is claimed that turbulence in fluids is inherently coherent phenomenon. The coherence shows up clearly as strongly correlated helicity fluctuations of opposite sign. The helicity fluctuations have cellular structure forming clusters that are actually observed as vorticity bands and coherent structures in laboratory turbulence, direct numerical simulations and most obviously in atmospheric turbulence. The clusters are named BCC - Beltrami Cellular Clusters - because of the observed nearly total alignment of the velocity and vorticity fields in each particular cell, and hence nearly maximal possible helicity in each cell; although when averaged over all the cells the residual mean helicity in general is small and does not play active dynamical role. The Beltrami like fluctuations are short-lived and stabilize only in small and generally contiguous sub-domains that are tending to a (multi)fractal in the asymptotic limit of large Reynolds numbers, Re → ∞. For the model of homogeneous isotropic turbulence the theory predicts the leading fractal dimension of BCC to be: DF = 2.5. This particular BCC is responsible for generating the Kolmogorov -5/3 power law energy spectrum. The most obvious role that BCC play dynamically is that the nonlinear interactions in them are relatively reduced, due to strong spatial alignment between the velocity field v(r, t) and the vorticity field ω(r, t) = curlv(r, t), while the physical quantities typically best characterizing turbulence intermittency, such as entrophy, vorticity stretching and generation, and energy dissipation are maximized in and near them. The theory quantitatively relates the reduction of nonlinear inter-actions to the BCC fractal dimension DF and subsequent turbulence intermittency. It is further asserted that BCC is a fundamental feature of all turbulent flows, e.g., wall bounded turbulent flows, atmospheric and oceanic flows, and their leading fractal dimension remains invariant and universal in these flows
Optical arbitrary waveform characterization using linear spectrograms.
Jiang, Zhi; Leaird, Daniel E; Long, Christopher M; Boppart, Stephen A; Weiner, Andrew M
2010-08-01
We demonstrate the first application of linear spectrogram methods based on electro-optic phase modulation to characterize optical arbitrary waveforms generated under spectral line-by-line control. This approach offers both superior sensitivity and self-referencing capability for retrieval of periodic high repetition rate optical arbitrary waveforms.
Mixing in manipulated turbulence
Kuczaj, A K; Geurts, Bernard J.; Kuczaj, Arkadiusz K.
2006-01-01
A new computational framework for the simulation of turbulent flow through complex objects and along irregular boundaries is presented. This is motivated by the application of metal foams in compact heat-transfer devices, or as catalyst substrates in process-engineering. The flow-consequences of such complicated objects are incorporated by adding explicit multiscale forcing to the Navier-Stokes equations. The forcing represents the simultaneous agitation of a wide spectrum of length-scales when flow passes through the complex object. It is found that a considerable modulation of the traditional energy cascading can be introduced with a specific forcing strategy. In spectral space, forcing yields strongly localized deviations from the common Kolmogorov scaling law, directly associated with the explicitly forced scales. In addition, the accumulated effect of forcing induces a significant non-local alteration of the kinetic energy including the spectrum for the large scales. Consequently, a manipulation of turbu...
Energy Technology Data Exchange (ETDEWEB)
Talbot, L.; Cheng, R.K. [Lawrence Berkeley Laboratory, CA (United States)
1993-12-01
Turbulent combustion is the dominant process in heat and power generating systems. Its most significant aspect is to enhance the burning rate and volumetric power density. Turbulent mixing, however, also influences the chemical rates and has a direct effect on the formation of pollutants, flame ignition and extinction. Therefore, research and development of modern combustion systems for power generation, waste incineration and material synthesis must rely on a fundamental understanding of the physical effect of turbulence on combustion to develop theoretical models that can be used as design tools. The overall objective of this program is to investigate, primarily experimentally, the interaction and coupling between turbulence and combustion. These processes are complex and are characterized by scalar and velocity fluctuations with time and length scales spanning several orders of magnitude. They are also influenced by the so-called {open_quotes}field{close_quotes} effects associated with the characteristics of the flow and burner geometries. The authors` approach is to gain a fundamental understanding by investigating idealized laboratory flames. Laboratory flames are amenable to detailed interrogation by laser diagnostics and their flow geometries are chosen to simplify numerical modeling and simulations and to facilitate comparison between experiments and theory.
DEFF Research Database (Denmark)
Nielsen, Mogens Peter; Shui, Wan; Johansson, Jens
2011-01-01
term with stresses depending linearly on the strain rates. This term takes into account the transfer of linear momentum from one part of the fluid to another. Besides there is another term, which takes into account the transfer of angular momentum. Thus the model implies a new definition of turbulence...
On turbulence in dilatant dispersions
Baumert, Helmut Z.; Wessling, Bernhard
2016-07-01
This paper presents a new theory on the behaviour of shear-thickening (dilatant) fluids under turbulent conditions. The structure of a dilatant colloidal fluid in turbulent motion may be characterized by (at least) four characteristic length scales: (i) the ‘statistically largest’ turbulent scale, {λ }0, labeling the begin of the inertial part of the wavenumber spectrum; (ii) the energy-containing scale, { L }; (iii) Kolmogorov’s micro-scale, {λ }{ K }, related with the size of the smallest vortices existing for a given kinematic viscosity and forcing; (iv) the inner (‘colloidal’) micro-scale, {λ }i, typically representing a major stable material property of the colloidal fluid. In particular, for small ratios r={λ }i/{λ }{ K }∼ { O }(1), various interactions between colloidal structures and smallest turbulent eddies can be expected. In the present paper we discuss particularly that for ρ ={λ }0/{λ }{ K }\\to { O }(1) turbulence (in the narrow, inertial sense) is strangled and chaotic but less mixing fluid motions remain. We start from a new stochastic, micro-mechanical turbulence theory without empirical parameters valid for inviscid fluids as seen in publications by Baumert in 2013 and 2015. It predicts e.g. von Karman’s constant correctly as 1/\\sqrt{2 π }=0.399. In its generalized version for non-zero viscosity and shear-thickening behavior presented in this contribution, it predicts two solution branches for the steady state: The first characterizes a family of states with swift (inertial) turbulent mixing and small {λ }{ K }, potentially approaching {λ }i. The second branch characterizes a state family with ρ \\to { O }(1) and thus strangled turbulence, ρ ≈ { O }(1). Stability properties and a potential dynamic commuting between the two solution branches had to be left for future research.
Calculating fusion neutron energy spectra from arbitrary reactant distributions
Eriksson, J.; Conroy, S.; Andersson Sundén, E.; Hellesen, C.
2016-02-01
The Directional Relativistic Spectrum Simulator (DRESS) code can perform Monte-Carlo calculations of reaction product spectra from arbitrary reactant distributions, using fully relativistic kinematics. The code is set up to calculate energy spectra from neutrons and alpha particles produced in the D(d, n)3He and T(d, n)4He fusion reactions, but any two-body reaction can be simulated by including the corresponding cross section. The code has been thoroughly tested. The kinematics calculations have been benchmarked against the kinematics module of the ROOT Data Analysis Framework. Calculated neutron energy spectra have been validated against tabulated fusion reactivities and against an exact analytical expression for the thermonuclear fusion neutron spectrum, with good agreement. The DRESS code will be used as the core of a detailed synthetic diagnostic framework for neutron measurements at the JET and MAST tokamaks.
Bec, Jeremie; Khanin, Konstantin
2007-01-01
The last decades witnessed a renewal of interest in the Burgers equation. Much activities focused on extensions of the original one-dimensional pressureless model introduced in the thirties by the Dutch scientist J.M. Burgers, and more precisely on the problem of Burgers turbulence, that is the study of the solutions to the one- or multi-dimensional Burgers equation with random initial conditions or random forcing. Such work was frequently motivated by new emerging applications of Burgers mod...
Bulk Comptonization by turbulence in accretion discs
Kaufman, J.; Blaes, O. M.
2016-06-01
Radiation pressure dominated accretion discs around compact objects may have turbulent velocities that greatly exceed the electron thermal velocities within the disc. Bulk Comptonization by the turbulence may therefore dominate over thermal Comptonization in determining the emergent spectrum. Bulk Comptonization by divergenceless turbulence is due to radiation viscous dissipation only. It can be treated as thermal Comptonization by solving the Kompaneets equation with an equivalent `wave' temperature, which is a weighted sum over the power present at each scale in the turbulent cascade. Bulk Comptonization by turbulence with non-zero divergence is due to both pressure work and radiation viscous dissipation. Pressure work has negligible effect on photon spectra in the limit of optically thin turbulence, and in this limit radiation viscous dissipation alone can be treated as thermal Comptonization with a temperature equivalent to the full turbulent power. In the limit of extremely optically thick turbulence, radiation viscous dissipation is suppressed, and the evolution of local photon spectra can be understood in terms of compression and expansion of the strongly coupled photon and gas fluids. We discuss the consequences of these effects for self-consistently resolving and interpreting turbulent Comptonization in spectral calculations in radiation magnetohydrodynamic simulations of high luminosity accretion flows.
Kühnen, Jakob; Hof, Björn
2015-11-01
We show that a simple modification of the velocity profile in a pipe can lead to a complete collapse of turbulence and the flow fully relaminarises. The annihilation of turbulence is achieved by a steady manipulation of the streamwise velocity component alone, greatly reducing control efforts. Several different control techniques are presented: one with a local modification of the flow profile by means of a stationary obstacle, one employing a nozzle injecting fluid through a small gap at the pipe wall and one with a moving wall, where a part of the pipe is shifted in the streamwise direction. All control techniques act on the flow such that the streamwise velocity profile becomes more flat and turbulence gradually grows faint and disappears. In a smooth straight pipe the flow remains laminar downstream of the control. Hence a reduction in skin friction by a factor of 8 and more can be accomplished. Stereoscopic PIV-measurements and movies of the development of the flow during relaminarisation are presented.
Compressible Turbulence: The Cascade and its Locality
Aluie, Hussein
2011-01-01
We prove that inter-scale transfer of kinetic energy in compressible turbulence is dominated by local interactions. In particular, our results preclude direct transfer of kinetic energy from large-scales directly to dissipation scales, such as into shocks, in high Reynolds number turbulence as is commonly believed. Our assumptions on the scaling of structure functions are weak and enjoy compelling empirical support. Under a stronger assumption on pressure dilatation co-spectrum, we show that ...
Positive Gravitattional Energy in Arbitrary Dimensions
Choquet-Bruhat, Yvonne
2011-01-01
We present a streamlined, complete proof, valid in arbitrary space dimension $n$, and using only spinors on the oriented Riemannian space $(M^{n};g),$ of the positive energy theorem in General Relativity.
Arbitrary orbital angular momentum of photons
Pan, Yue; Ren, Zhi-Cheng; Wang, Xi-Lin; Tu, Chenghou; Li, Yongnan; Wang, Hui-Tian
2015-01-01
Orbital angular momentum (OAM) of photons, as a new fundamental degree of freedom, has excited a great diversity of interest, because of a variety of emerging applications. Arbitrarily tunable OAM has gained much attention, but its creation remains still a tremendous challenge. We demonstrate the realization of well-controlled arbitrary OAM in both theory and experiment. We present the concept of general OAM, which extends the OAM carried by the scalar vortex field to the OAM carried by the azimuthally varying polarized vector field. The arbitrary OAM has the same characteristics as the well-defined integer OAM: intrinsic OAM, uniform local OAM and intensity ring, and propagation stability. The arbitrary OAM has unique natures: it is allowed to be flexibly tailored and the radius of the focusing ring can have various choices for a desired OAM, which are of great significance to the benefit of surprising applications of the arbitrary OAM.
THE EIGENVALUE PERTURBATION BOUND FOR ARBITRARY MATRICES
Institute of Scientific and Technical Information of China (English)
Wen Li; Jian-xin Chen
2006-01-01
In this paper we present some new absolute and relative perturbation bounds for the eigenvalue for arbitrary matrices, which improves some recent results. The eigenvalue inclusion region is also discussed.
Acceleration of particles in imbalanced magnetohydrodynamic turbulence.
Teaca, Bogdan; Weidl, Martin S; Jenko, Frank; Schlickeiser, Reinhard
2014-08-01
The present work investigates the acceleration of test particles, relevant to the solar-wind problem, in balanced and imbalanced magnetohydrodynamic turbulence (terms referring here to turbulent states possessing zero and nonzero cross helicity, respectively). These turbulent states, obtained numerically by prescribing the injection rates for the ideal invariants, are evolved dynamically with the particles. While the energy spectrum for balanced and imbalanced states is known, the impact made on particle heating is a matter of debate, with different considerations giving different results. By performing direct numerical simulations, resonant and nonresonant particle accelerations are automatically considered and the correct turbulent phases are taken into account. For imbalanced turbulence, it is found that the acceleration rate of charged particles is reduced and the heating rate diminished. This behavior is independent of the particle gyroradius, although particles that have a stronger adiabatic motion (smaller gyroradius) tend to experience a larger heating.
International Nuclear Information System (INIS)
Full text: Excitation of Geodesic Acoustic Modes (GAMs) by both energetic particles (EPs) and drift wave (DW) turbulences taking into account plasma nonuniformities are investigated in this work. The global radial mode structures of EP induced GAM (EGAM) are systematically studied and their properties are found to depend on the nonuniformities of both the GAM continuous spectrum and EP radial profile. For a radially broad EP drive, the eigenmode equation valid for arbitrary EP drift orbit width is derived, and then solved using a Fourier transformation technique. The excited EGAM is shown to strongly couple to the GAM continuous spectrum; resulting in a finite drive threshold in EP density. The cross-scale couplings between micro-, meso- and macro-scales, discussed in this work, are mediated by the EP dynamics and have many interesting similarities with complex behaviors, expected in burning plasmas of fusion interest. The excitation of GAM by DW turbulence accounting for various kinetic dispersiveness and nonuniformities is also investigated, with the paradigm of three-wave resonant parametric decay instability. Considering the scale length of linear DW eigenmode envelope is much smaller than that of particle diamagnetic drift frequency L*, in the linear growth phase, the parametric instability is convective for typical tokamak parameters, when the finite group velocities of GAM and DW sideband are taken into account. This is a case of less practical interest. However, if we look at longer time scales, and finite L* effects are taken into account, the convectively amplified GAM-DW wave-packet pair is reflected at the DW linear turning points, resulting in a quasi-exponentially growing absolute instability. DW turbulence spreading with the excitation of GAM is also investigated, with emphasis on quantitative understanding of the dispersiveness associated with kinetic GAM. (author)
Phytoplankton's motion in turbulent ocean.
Fouxon, Itzhak; Leshansky, Alexander
2015-07-01
We study the influence of turbulence on upward motion of phytoplankton. Interaction with the flow is described by the Pedley-Kessler model considering spherical microorganisms. We find a range of parameters when the upward drift is only weakly perturbed or when turbulence completely randomizes the drift direction. When the perturbation is small, the drift is either determined by the local vorticity or is Gaussian. We find a range of parameters where the phytoplankton interaction with the flow can be described consistently as diffusion of orientation in effective potential. By solving the corresponding Fokker-Planck equation we find exponential steady-state distribution of phytoplankton's propulsion orientation. We further identify the range of parameters where phytoplankton's drift velocity with respect to the flow is determined uniquely by its position. In this case, one can describe phytoplankton's motion by a smooth flow and phytoplankton concentrates on fractal. We find fractal dimensions and demonstrate that phytoplankton forms vertical stripes in space with a nonisotropic pair-correlation function of concentration increased in the vertical direction. The probability density function of the distance between two particles obeys power law with the negative exponent given by the ratio of integrals of the turbulent energy spectrum. We find the regime of strong clustering where the exponent is of order one so that turbulence increases the rate of collisions by a large factor. The predictions hold for Navier-Stokes turbulence and stand for testing. PMID:26274279
Turbulence: mechanics and structure of anomalous scaling
Directory of Open Access Journals (Sweden)
S. N. Gordienko
2001-01-01
Full Text Available As the finite correlation time of a force driving turbulence is taken into account, a new, dimensionless parameter occurs in the theory of turbulence. This new parameter is responsible for two different mechanisms of formation of anomalous spectra. The first mechanism is related to the change of a governing parameter, which defines the spectrum of turbulent fluctuation. The second mechanism is associated with spontaneous formation of characteristic scales that differ parametrically from the scale of the external force. The last mechanism can explain the intermittent structure of turbulent flows. The appropriate discrete set of the possible characteristic scales and anomalous spectra has been calculated. The results give a new insight into the concept of universality: there is a set of universal power laws, although occurrence in the spectrum segments described by one or another power law from this set depends on the dimensionless parameter mentioned above. It is noted that for the broad class of geophysical flows, the new dimensionless parameter is connected with the so-called degree of turbulence, which guarantees that the smallness of this parameter, as the degree of turbulence is usually small enough. That explains the important role of the Kolmogorov spectrum in geophysical applications.
Graphical Turbulence Guidance - Composite
National Oceanic and Atmospheric Administration, Department of Commerce — Forecast turbulence hazards identified by the Graphical Turbulence Guidance algorithm. The Graphical Turbulence Guidance product depicts mid-level and upper-level...
Magnetohydrodynamic Turbulence
Montgomery, David C.
2004-01-01
Magnetohydrodynamic (MHD) turbulence theory is modeled on neutral fluid (Navier-Stokes) turbulence theory, but with some important differences. There have been essentially no repeatable laboratory MHD experiments wherein the boundary conditions could be controlled or varied and a full set of diagnostics implemented. The equations of MHD are convincingly derivable only in the limit of small ratio of collision mean-free-paths to macroscopic length scales, an inequality that often goes the other way for magnetofluids of interest. Finally, accurate information on the MHD transport coefficients-and thus, the Reynolds-like numbers that order magnetofluid behavior-is largely lacking; indeed, the algebraic expressions used for such ingredients as the viscous stress tensor are often little more than wishful borrowing from fluid mechanics. The one accurate thing that has been done extensively and well is to solve the (strongly nonlinear) MHD equations numerically, usually in the presence of rectangular periodic boundary conditions, and then hope for the best when drawing inferences from the computations for those astrophysical and geophysical MHD systems for which some indisputably turbulent detailed data are available, such as the solar wind or solar prominences. This has led to what is perhaps the first field of physics for which computer simulations are regarded as more central to validating conclusions than is any kind of measurement. Things have evolved in this way due to a mixture of the inevitable and the bureaucratic, but that is the way it is, and those of us who want to work on the subject have to live with it. It is the only game in town, and theories that have promised more-often on the basis of some alleged ``instability''-have turned out to be illusory.
Venaille, Antoine; Vallis, Geoffrey K
2014-01-01
We investigate the non-linear equilibration of a two-layer quasi-geostrophic flow in a channel forced by an imposed unstable zonal mean flow, paying particular attention to the role of bottom friction. In the limit of low bottom friction, classical theory of geostrophic turbulence predicts an inverse cascade of kinetic energy in the horizontal with condensation at the domain scale and barotropization on the vertical. By contrast, in the limit of large bottom friction, the flow is dominated by ribbons of high kinetic energy in the upper layer. These ribbons correspond to meandering jets separating regions of homogenized potential vorticity. We interpret these result by taking advantage of the peculiar conservation laws satisfied by this system: the dynamics can be recast in such a way that the imposed mean flow appears as an initial source of potential vorticity levels in the upper layer. The initial baroclinic instability leads to a turbulent flow that stirs this potential vorticity field while conserving the...
Experiments in turbulent pipe flow
Energy Technology Data Exchange (ETDEWEB)
Torbergsen, Lars Even
1998-12-31
This thesis reports experimental results for the mean velocity and turbulence statistics in two straight pipe sections for bulk Reynolds numbers in the range 22000 to 75000. The flow was found consistent with a fully developed state. Detailed turbulence spectra were obtained for low and moderate turbulent Reynolds number. For the pipe centre line location at R{sub {lambda}} = 112, a narrow range in the streamwise power spectrum applied to the -5/3 inertial subrange. However this range was influenced both by turbulence production and viscous dissipation, and therefore did not reflect a true inertial range. The result indicates how the intermediate range between the production and dissipative scales can be misinterpreted as an inertial range for low and moderate R{sub {lambda}}. To examine the universal behaviour of the inertial range, the inertial scaling of the streamwise power spectrum is compared to the inertial scaling of the second order longitudinal velocity structure function, which relate directly by a Fourier transform. Increasing agreement between the Kolmogorov constant C{sub K} and the second order structure function scaling constant C{sub 2} was observed with increasing R{sub {lambda}}. The result indicates that a true inertial range requires several decades of separation between the energy containing and dissipative scales. A method for examining spectral anisotropy is reported and applied to turbulence spectra in fully developed pipe flow. It is found that the spectral redistribution from the streamwise to the two lateral spectra goes primarily to the circumferential component. Experimental results are reported for an axisymmetric contraction of a fully developed pipe flow. 67 refs., 75 figs., 9 tabs.
Perturbation Theory for Arbitrary Coupling Strength ?
Mahapatra, B P
2016-01-01
We demonstrate Borel summability for arbitrary coupling strength in a new formulation of perturbation theory (designated here as "Mean Field Perturbation Theory (MFPT)") by applying it to one dimensional anharmonic-interactions, which includes the case of the quartic and sextic anharmonic oscillators(AHO) and the quartic double-well-oscillator (QDWO).It is well known that the perturbation-series is not Borel-summable for the QDWO in the standard formulation of perturbation theory(SFPT). In contrast, MFPT leads to a Borel-summable perturbation series and accurate values for the energy-spectra for arbitrary (physical) value of the coupling strength in each case as stated above. The general nature and the simplicity of the formulation underlying MFPT leads us to conjecture that this scheme may be applicable to arbitrary interactions in quantum theory.
Stochastic ion heating by lower hybrid turbulence
International Nuclear Information System (INIS)
The motion of an ion in a spectrum of lower hybrid waves propagating across a constant magnetic field is examined. In particular, numerical simulation is used to determine the extent to which a turbulent spectrum of these electrostatic waves may accelerate thermal ions (T < 1 eV). The significance of stochastic web development in this heating process is also discussed. 20 refs., 31 figs
MAGNETIC TURBULENCE IN CLUSTERS OF GALAXIES
Directory of Open Access Journals (Sweden)
T. A. EnBlin
2009-01-01
Full Text Available Galaxy clusters are large laboratories for magnetic plasma turbulence which permit us to confront our theoretical concepts of magnetogenesis with detailed observations. Magnetic turbulence in clusters can be studied via the radio-synchrotron emission from the intra-cluster medium in the form of cluster radio relics and halos. The power spectrum of turbulent magnetic elds can be examined via Faraday rotation analysis of extended radio sources. In case of the Hydra A cool core, the observed magnetic spectrum can be understood in terms of a turbulence-mediated feedback loop between gas cooling and the jet activity of the central galaxy. Finally, methods to measure higher-order statistics of the magnetic eld using Stokes-parameter correlations are discussed, which permit us to determine the power spectrum of the magnetic tension force. This fourth-order statistical quantity o ers a way to discriminate between di erent magnetic turbulence scenarios and di erent eld structures using radio polarimetric observations.
Introduction to quantum turbulence
Barenghi, Carlo F.; Skrbek, Ladislav; Sreenivasan, Katepalli R.
2014-01-01
The term quantum turbulence denotes the turbulent motion of quantum fluids, systems such as superfluid helium and atomic Bose–Einstein condensates, which are characterized by quantized vorticity, superfluidity, and, at finite temperatures, two-fluid behavior. This article introduces their basic properties, describes types and regimes of turbulence that have been observed, and highlights similarities and differences between quantum turbulence and classical turbulence in ordinary fluids. Our ai...
Vacuum Birefringence Caused by Arbitrary Spin Particles
Kruglov, S. I.
2007-01-01
We study the propagation of a linearly polarized laser beam in the external transverse magnetic field taking into consideration the vacuum polarization by arbitrary spin particles. Induced ellipticity of the beam are evaluated using the effective Lagrangian. With the help of the PVLAS experimental data, we obtain bounds on masses of charged higher spin particles contributed to ellipticity.
Kraus representation for arbitrary open qubit system
Tong, D M; Kwek, L C; Oh, C H; Chen, Jing-Ling
2003-01-01
We show that the time evolution of an arbitrary open qubit system can always be described in terms of the Kraus representation irrespective of the presence of initial correlations between the open system and its environment. A general scheme on how to construct the Kraus operators for an open qubit system is proposed, which can be generalized to open higher dimensional quantum systems.
Acceleration of Particles in Imbalanced Magnetohydrodynamic Turbulence
Teaca, Bogdan; Jenko, Frank; Schlickeiser, Reinhard
2014-01-01
The present work investigates the acceleration of test particles in balanced and imbalanced Alfv\\'{e}nic turbulence, relevant to the solar-wind problem. These turbulent states, obtained numerically by prescribing the injection rates for the ideal invariants, are evolved dynamically with the particles. While the energy spectrum for balanced and imbalanced states is known, the impact made on particle heating is a matter of debate, with different considerations giving different results. By performing direct numerical simulations, resonant and non-resonant particle accelerations are automatically considered and the correct turbulent phases are taken into account. For imbalanced turbulence, it is found that the acceleration rate of charged particles is reduced and the heating rate diminished. This behaviour is independent of the particle gyroradius, although particles that have a stronger adiabatic motion (smaller gyroradius) tend to experience a larger heating.
Photon Bubble Turbulence in Cold Atomic Gases
Rodrigues, João D; Ferreira, António V; Terças, Hugo; Kaiser, Robin; Mendonça, José T
2016-01-01
Turbulent radiation flow is ubiquitous in many physical systems where light-matter interaction becomes relevant. Photon bubbling, in particular, has been identified as the main source of turbulent radiation transport in many astrophysical objects, such as stars and accretion disks. This mechanism takes place when radiation trapping in optically dense media becomes unstable, leading to the energy dissipation from the larger to the smaller bubbles. Here, we report on the observation of photon bubble turbulence in cold atomic gases in the presence of multiple scattering of light. The instability is theoretically explained by a fluid description for the atom density coupled to a diffusive transport equation for the photons, which is known to be accurate in the multiple scattering regime investigated here. We determine the power spectrum of the atom density fluctuations, which displays an unusual $\\sim k^{-4}$ scaling, and entails a complex underlying turbulent dynamics resulting from the formation of dynamical bu...
DEFF Research Database (Denmark)
D'Angelo, N.; Pécseli, Hans; Petersen, P. I.
1974-01-01
Spectral measurements are reported of plasma turbulence in the Cs plasma of a Q device, modified to a magnetic cusp geometry. The excitation mechanism for the fluctuations appears to be the centrifugal instability discussed by Chen. A transition from an f−5 to an f−3 power spectrum is observed as...
Signal modeling of turbulence-distorted imagery
Young, S. Susan; Driggers, Ronald G.; Krapels, Keith; Espinola, Richard L.; Reynolds, Joseph P.; Cha, Jae
2009-05-01
Understanding turbulence effects on wave propagation and imaging systems has been an active research area for more than 50 years. Conventional atmospheric optics methods use statistical models to analyze image degradation effects that are caused by turbulence. In this paper, we intend to understand atmospheric turbulence effects using a deterministic signal processing and imaging theory point of view and modeling. The model simulates the formed imagery by a lens by tracing the optical rays from the target through a band of turbulence. We examine the nature of the turbulence-degraded image, and identify its characteristics as the parameters of the band of turbulence, e.g., its width, angle, and index of refraction, are varied. Image degradation effects due to turbulence, such as image blurring and image dancing, are revealed by this signal modeling. We show that in fact these phenomena can be related not only to phase errors in the frequency domain of the image but also a 2D modulation effect in the image spectrum. Results with simulated and realistic data are provided.
Gibson, C H
1999-01-01
A theory of fossil turbulence presented in the 11th Liege Colloquium on Marine turbulence is "revisited" in the 29th Liege Colloquium "Marine Turbulence Revisited". The Gibson (1980) theory applied universal similarity theories of turbulence and turbulent mixing to the vertical evolution of an isolated patch of turbulence in a stratified fluid as it is constrained and fossilized by buoyancy forces. Towed oceanic microstructure measurements of Schedvin (1979) confirmed the predicted universal constants. Universal constants, spectra, hydrodynamic phase diagrams (HPDs) and other predictions of the theory have been reconfirmed by a wide variety of field and laboratory observations. Fossil turbulence theory has many applications; for example, in marine biology, laboratory and field measurements suggest phytoplankton species with different swimming abilities adjust their growth strategies differently by pattern recognition of several days of turbulence-fossil-turbulence dissipation and persistence times above thres...
Reynolds-number dependence of the longitudinal dispersion in turbulent pipe flow.
Hawkins, Christopher; Angheluta, Luiza; Krotkiewski, Marcin; Jamtveit, Bjørn
2016-04-01
In Taylor's theory, the longitudinal dispersion in turbulent pipe flows approaches, on long time scales, a diffusive behavior with a constant diffusivity K_{L}, which depends empirically on the Reynolds number Re. We show that the dependence on Re can be determined from the turbulent energy spectrum. By using the intimate connection between the friction factor and the longitudinal dispersion in wall-bounded turbulence, we predict different asymptotic scaling laws of K_{L}(Re) depending on the different turbulent cascades in two-dimensional turbulence. We also explore numerically the K_{L}(Re) dependence in turbulent channel flows with smooth and rough walls using a lattice Boltzmann method.
The $Re$-number dependence of the longitudinal dispersion in a turbulent channel flow
Hawkins, Christopher; Krotkiewski, Marcin; Jamtveit, Bjørn
2016-01-01
In Taylor's theory, the longitudinal dispersion in turbulent pipe flows approaches, on long timescales, a diffusive behavior with a constant diffusivity $K_L$, that depends \\emph{empirically} on the Reynolds number $Re$. We show that the dependence on $Re$ can be determined from the turbulent energy spectrum. By using the intimate connection between the friction factor and longitudinal dispersion in wall-bounded turbulence, we predict different asymptotic scaling laws of $K_L(Re)$ depending on the different turbulent cascades in two-dimensional turbulence. We also explore numerically the $K_L(Re)$ dependence in turbulent channel flows with smooth and rough walls using a lattice Boltzmann method.
Cheng, Mingjian; Guo, Lixin; Li, Jiangting; Huang, Qingqing
2016-08-01
Rytov theory was employed to establish the transmission model for the optical vortices carried by Bessel-Gaussian (BG) beams in weak anisotropic turbulence based on the generalized anisotropic von Karman spectrum. The influences of asymmetry anisotropic turbulence eddies and source parameters on the signal orbital angular momentum (OAM) mode detection probability of partially coherent BG beams in anisotropic turbulence were discussed. Anisotropic characteristics of the turbulence could enhance the OAM mode transmission performance. The spatial partially coherence of the beam source would increase turbulent aberration's effect on the optical vortices. BG beams could dampen the influences of the turbulence because of their nondiffraction and self-healing characteristics. PMID:27505641
All-Optical Temporal Differentiator Using a High Resolution Optical Arbitrary Waveform Shaper
Institute of Scientific and Technical Information of China (English)
DONG Jian-Ji; LUO Bo-Wen; ZHANG Yin; LEI Lei; HUANG De-Xiu; ZHANG Xin-Liang
2012-01-01
We experimentally demonstrate an all-optical temporal differentiator using a high resolution optical arbitrary waveform shaper, which is based on liquid crystal on silicon switching elements, and both amplitude and phase of the spectrum are programmable. By designing specific transfer functions with the optical waveform shaper, we obtain first-, second-, and third-order differentiators for periodic pulses with small average errors. We also theoretically analyze the bandwidth limitation of optical waveform shaper on the differentiator.%We experimentally demonstrate an all-optical temporal differentiator using a high resolution optical arbitrary waveform shaper,which is based on liquid crystal on silicon switching elements,and both amplitude and phase of the spectrum are programmable.By designing specific transfer functions with the optical waveform shaper,we obtain first-,second-,and third-order differentiators for periodic pulses with small average errors.We also theoretically analyze the bandwidth limitation of optical waveform shaper on the differentiator.
Turbulence distance for laser beams propagating through non-Kolmogorov turbulence.
Huang, Yongping; Zhang, Bin
2013-11-01
Based on the second-order moments and the non-Kolmogorov turbulence spectrum, the general analytical expression for the turbulence distance of laser beams propagating through non-Kolmogorov turbulence is derived, which depends on the non-Kolmogorov turbulence parameters including the generalized exponent parameter α, inner scale l(0), and outer scale L(0) and the initial second-order moments of the beams at the plane of z=0. Taking the partially coherent Hermite-Gaussian linear array (PCHGLA) beam as an illustrative example, the effects of non-Kolmogorov turbulence and array parameters on the turbulence distance are discussed in detail. The results show that the turbulence distance z(Mx)(α) of PCHGLA beams through non-Kolmogorov turbulence first decreases to a dip and then increases with increasing α, and the value of z(Mx)(α) increases with increasing beam number and beam order and decreasing coherence parameter, meaning less influence of non-Kolmogorov turbulence on partially coherent array beams than that of fully coherent array beams and a single partially coherent beam. However, the value of z(Mx)(α) for PCHGLA beams first increases nonmonotonically with the increasing of the relative beam separation x0' for x0'≤1 and increases monotonically as x0' increases for x0'>1. Moreover, the variation behavior of the turbulence distance with the generalized exponent parameter, inner scale, and outer scale of the turbulence and the beam number is similar, but different with the relative beam separation for coherent and incoherent combination cases.
Spinor structure and matter spectrum
Varlamov, V V
2016-01-01
Classification of relativistic wave equations is given on the ground of interlocking representations of the Lorentz group. A system of interlocking representations is associated with a system of eigenvector subspaces of the energy operator. Such a correspondence allows one to define matter spectrum, where the each level of this spectrum presents a some state of elementary particle. An elementary particle is understood as a superposition of state vectors in nonseparable Hilbert space. Classification of indecomposable systems of relativistic wave equations is produced for bosonic and fermionic fields on an equal footing (including Dirac and Maxwell equations), since all these fields are equivalent levels of matter spectrum, which differ from each other by the value of mass and spin. It is shown that a spectrum of the energy operator, corresponding to a given matter level, is non-degenerate for the fields of type $(l,0)\\oplus(0,l)$, where $l$ is a spin value, whereas for arbitrary spin chains we have degenerate ...
Gaussian entanglement in the turbulent atmosphere
Bohmann, M.; Semenov, A. A.; Sperling, J.; Vogel, W.
2016-07-01
We provide a rigorous treatment of the entanglement properties of two-mode Gaussian states in atmospheric channels by deriving and analyzing the input-output relations for the corresponding entanglement test. A key feature of such turbulent channels is a nontrivial dependence of the transmitted continuous-variable entanglement on coherent displacements of the quantum state of the input field. Remarkably, this allows one to optimize the entanglement certification by modifying local coherent amplitudes using a finite, but optimal amount of squeezing. In addition, we propose a protocol which, in principle, renders it possible to transfer the Gaussian entanglement through any turbulent channel over arbitrary distances. Therefore, our approach provides the theoretical foundation for advanced applications of Gaussian entanglement in free-space quantum communication.
Large eddy simulation of stably stratified turbulence
Institute of Scientific and Technical Information of China (English)
无
2010-01-01
Stable stratification turbulence, as a common phenomenon in atmospheric and oceanic flows, is an important mechanism for numerical prediction of such flows. In this paper the large eddy simulation is utilized for investigating stable stratification turbulence numerically. The paper is expected to provide correct statistical results in agreement with those measured in the atmosphere or ocean. The fully developed turbulence is obtained in the stable stratification fluid by large eddy simulation with different initial velocity field and characteristic parameters, i.e. Reynolds number Re and Froude number Fr. The evolution of turbulent kinetic energy, characteristic length scales and parameters is analyzed for investigating the development of turbulence in stable stratification fluid. The three-dimensional energy spectra, horizontal and vertical energy spectrum, are compared between numerical simulation and real observation in the atmosphere and ocean in order to test the reliability of the numerical simulation. The results of numerical cases show that the large eddy simulation is capable of predicting the properties of stable stratification turbulence in consistence with real measurements at less computational cost. It has been found in this paper that the turbulence can be developed under different initial velocity conditions and the internal wave energy is dominant in the developed stable stratification turbulence. It is also found that the characteristic parameters must satisfy certain conditions in order to have correct statistical property of stable stratification turbulence in the atmosphere and ocean. The Reynolds number and Froude number are unnecessarily equal to those in atmosphere or ocean, but the Reynolds number must be large enough, say, greater than 10 2 , and Froude number must be less than 0.1. The most important parameter is ReFr 2 which must be greater than 10.
Efficient Spectral Power Estimation on an Arbitrary Frequency Scale
Directory of Open Access Journals (Sweden)
F. Zaplata
2015-04-01
Full Text Available The Fast Fourier Transform is a very efficient algorithm for the Fourier spectrum estimation, but has the limitation of a linear frequency scale spectrum, which may not be suitable for every system. For example, audio and speech analysis needs a logarithmic frequency scale due to the characteristic of a human’s ear. The Fast Fourier Transform algorithms are not able to efficiently give the desired results and modified techniques have to be used in this case. In the following text a simple technique using the Goertzel algorithm allowing the evaluation of the power spectra on an arbitrary frequency scale will be introduced. Due to its simplicity the algorithm suffers from imperfections which will be discussed and partially solved in this paper. The implementation into real systems and the impact of quantization errors appeared to be critical and have to be dealt with in special cases. The simple method dealing with the quantization error will also be introduced. Finally, the proposed method will be compared to other methods based on its computational demands and its potential speed.
Quantum Fidelity for Arbitrary Gaussian States
Banchi, Leonardo; Braunstein, Samuel L.; Pirandola, Stefano
2015-12-01
We derive a computable analytical formula for the quantum fidelity between two arbitrary multimode Gaussian states which is simply expressed in terms of their first- and second-order statistical moments. We also show how such a formula can be written in terms of symplectic invariants and used to derive closed forms for a variety of basic quantities and tools, such as the Bures metric, the quantum Fisher information, and various fidelity-based bounds. Our result can be used to extend the study of continuous-variable protocols, such as quantum teleportation and cloning, beyond the current one-mode or two-mode analyses, and paves the way to solve general problems in quantum metrology and quantum hypothesis testing with arbitrary multimode Gaussian resources.
Quantum fidelity for arbitrary Gaussian states
Banchi, Leonardo; Pirandola, Stefano
2015-01-01
We derive a computable analytical formula for the quantum fidelity between two arbitrary multimode Gaussian states which is simply expressed in terms of their first- and second-order statistical moments. We also show how such a formula can be written in terms of symplectic invariants and used to derive closed forms for a variety of basic quantities and tools, such as the Bures metric, the quantum Fisher information and various fidelity-based bounds. Our result can be used to extend the study of continuous-variable protocols, such as quantum teleportation and cloning, beyond the current one-mode or two-mode analyses, and paves the way to solve general problems in quantum metrology and quantum hypothesis testing with arbitrary multimode Gaussian resources.
On Arbitrary Phases in Quantum Amplitude Amplification
Hoyer, P
2000-01-01
We consider the use of arbitrary phases in quantum amplitude amplification which is a generalization of quantum searching. We prove that the phase condition in amplitude amplification is given by $\\tan(\\phi/2)=\\tan(\\phi/2)(1-2a)$, where $\\phi$ and $\\phi$ are the phases used and where $a$ is the success probability of the given algorithm. Thus the choice of phases depends nontrivially and nonlinearly on the success probability. Utilizing this condition, we give methods for constructing quantum algorithms that succeed with certainty and for implementing arbitrary rotations. We also conclude that phase errors of order up to $\\frac{1}{\\sqrt{a}}$ can be tolerated in amplitude amplification.
Potential flow about arbitrary biplane wing sections
Garrick, I E
1937-01-01
A rigorous treatment is given of the problem of determining the two-dimensional potential flow around arbitrary biplane cellules. The analysis involves the use of elliptic functions and is sufficiently general to include the effects of such elements as the section shapes, the chord ratio, gap, stagger, and decalage, which elements may be specified arbitrarily. The flow problem is resolved by making use of the methods of conformal representation. Thus the solution of the problem of transforming conformally two arbitrary contours into two circles is expressed by a pair of simultaneous integral equations, for which a method of numerical solution is outlined. As an example of the numerical process, the pressure distribution over certain arrangements of the NACA 4412 airfoil in biplane combinations is presented and compared with the monoplane pressure distribution.
Strong field ionization in arbitrary laser polarizations
Protopapas, M.; Lappas, D. G.; Knight, P. L.
1997-01-01
We present a new method for investigating the nonperturbative quantum mechanical interaction of light with atoms in two dimensions, without a basis expansion. This enables us to investigate intense laser-atom interactions with light of arbitrary polarization without approximation, within the model restrictions. Results are presented for the dependence of ionization and high harmonic generation on ellipticity seen in recent experiments. Strong evidence of stabilization in circular polarization...
Arbitrary orbital angular momentum of photons
Pan, Yue; Gao, Xu-Zhen; Ren, Zhi-Cheng; Wang, Xi-Lin; Tu, Chenghou; Li, Yongnan; Wang, Hui-Tian
2015-01-01
Orbital angular momentum (OAM) of photons, as a new fundamental degree of freedom, has excited a great diversity of interest, because of a variety of emerging applications. Arbitrarily tunable OAM has gained much attention, but its creation remains still a tremendous challenge. We demonstrate the realization of well-controlled arbitrary OAM in both theory and experiment. We present the concept of general OAM, which extends the OAM carried by the scalar vortex field to the OAM carried by the a...
Solar Wind Turbulence and the Role of Ion Instabilities
Alexandrova, Olga; Sorriso-Valvo, Luca; Horbury, Timothy S; Bale, Stuart D
2013-01-01
Solar wind is probably the best laboratory to study turbulence in astrophysical plasmas. In addition to the presence of magnetic field, the differences with neutral fluid isotropic turbulence are: weakness of collisional dissipation and presence of several characteristic space and time scales. In this paper we discuss observational properties of solar wind turbulence in a large range from the MHD to the electron scales. At MHD scales, within the inertial range, turbulence cascade of magnetic fluctuations develops mostly in the plane perpendicular to the mean field. Solar wind turbulence is compressible in nature. The spectrum of velocity fluctuations do not follow magnetic field one. Probability distribution functions of different plasma parameters are not Gaussian, indicating presence of intermittency. At the moment there is no global model taking into account all these observed properties of the inertial range. At ion scales, turbulent spectra have a break, compressibility increases and the density fluctuat...
DEFF Research Database (Denmark)
Brand, Arno J.; Peinke, Joachim; Mann, Jakob
2011-01-01
The nature of turbulent flow towards, near and behind a wind turbine, the effect of turbulence on the electricity production and the mechanical loading of individual and clustered wind turbines, and some future issues are discussed....
Kinetic equation and clipping - two limits of wave turbulence theory
E. Kartashova
2005-01-01
Different dynamics, described by kinetic equation and clipping method is shown as well as a role of approximate resonances in wave turbulence theory. Applications of clipping method are sketched for gravity-capillary and drift waves. Brief discussion of possible transition from continuous spectrum (= kinetic equation) to discrete spectrum (= clipping) is given at the end.
Polarization Mode Dispersion Probability Distribution for Arbitrary Mode Coupling
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
The probability distribution of the differential group delay for arbitrary mode coupling is simulated with Monte-Carlo method. Fitting the simulation results, we obtain probability distribution function for arbitrary mode coupling.
Scintillation index of optical wave propagating in turbulent atmosphere
Institute of Scientific and Technical Information of China (English)
Rao Rui-Zhong
2009-01-01
A concise expression of the scintillation index is proposed for a plane optical wave and a spherical optical wave both propagating in a turbulent atmosphere with a zero inner scale and a finite inner scale under an arbitrary fluc- tuation condition. The expression is based on both the results in the Rytov approximation under a weak fluctuation condition and the numerical results in a strong fluctuation regime. The maximum value of the scintillation index and its corresponding Rytov index axe evaluated. These quantities are affected by the ratio of the turbulence inner scale to the Frcsnel size.
Statistical theory of turbulent incompressible multimaterial flow
Energy Technology Data Exchange (ETDEWEB)
Kashiwa, B.
1987-10-01
Interpenetrating motion of incompressible materials is considered. ''Turbulence'' is defined as any deviation from the mean motion. Accordingly a nominally stationary fluid will exhibit turbulent fluctuations due to a single, slowly moving sphere. Mean conservation equations for interpenetrating materials in arbitrary proportions are derived using an ensemble averaging procedure, beginning with the exact equations of motion. The result is a set of conservation equations for the mean mass, momentum and fluctuational kinetic energy of each material. The equation system is at first unclosed due to integral terms involving unknown one-point and two-point probability distribution functions. In the mean momentum equation, the unclosed terms are clearly identified as representing two physical processes. One is transport of momentum by multimaterial Reynolds stresses, and the other is momentum exchange due to pressure fluctuations and viscous stress at material interfaces. Closure is approached by combining careful examination of multipoint statistical correlations with the traditional physical technique of kappa-epsilon modeling for single-material turbulence. This involves representing the multimaterial Reynolds stress for each material as a turbulent viscosity times the rate of strain based on the mean velocity of that material. The multimaterial turbulent viscosity is related to the fluctuational kinetic energy kappa, and the rate of fluctuational energy dissipation epsilon, for each material. Hence a set of kappa and epsilon equations must be solved, together with mean mass and momentum conservation equations, for each material. Both kappa and the turbulent viscosities enter into the momentum exchange force. The theory is applied to (a) calculation of the drag force on a sphere fixed in a uniform flow, (b) calculation of the settling rate in a suspension and (c) calculation of velocity profiles in the pneumatic transport of solid particles in a
Power spectra of outflow-driven turbulence
Moraghan, Anthony; Yoon, Suk-Jin
2015-01-01
We investigate the power spectra of outflow-driven turbulence through high-resolution three-dimensional isothermal numerical simulations where the turbulence is driven locally in real-space by a simple spherical outflow model. The resulting turbulent flow saturates at an average Mach number of ~2.5 and is analysed through density and velocity power spectra, including an investigation of the evolution of the solenoidal and compressional components. We obtain a shallow density power spectrum with a slope of ~-1.2 attributed to the presence of a network of localised dense filamentary structures formed by strong shock interactions. The total velocity power spectrum slope is found to be ~-2.0, representative of Burgers shock dominated turbulence model. The density weighted velocity power spectrum slope is measured as ~-1.6, slightly less than the expected Kolmogorov scaling value (slope of -5/3) found in previous works. The discrepancy may be caused by the nature of our real space driving model and we suggest ther...
Statistical features of freely decaying two-dimensional hydrodynamic turbulence
Kudryavtsev, A N; Sereshchenko, E V
2013-01-01
Statistical characteristics of freely decaying two-dimensional hydrodynamic turbulence at high Reynolds numbers are numerically studied. In particular, numerical experiments (with resolution up to $8192\\times 8192$) provide a Kraichnan-type turbulence spectrum $E_k\\sim k^{-3}$. By means of spatial filtration, it is found that the main contribution to the spectrum comes from the sharp vorticity gradients in the form of quasi-shocks. Such quasi-singularities are responsible for a strong angular dependence of the spectrum owing to well-localized (in terms of the angle) jets with minor and/or large overlapping. In each jet, the spectrum decreases as $k^{-3}$. The behavior of the third-order structure function accurately agrees with Kraichnan direct cascade concept corresponding to a constant enstrophy flux. It is shown that the power law exponents $\\zeta_n$ for higher structure functions grow more slowly than the linear dependence of $n$, which testifies to turbulence intermittency.
Distributed chaos and inertial ranges in turbulence
Bershadskii, A
2016-01-01
It is shown that appearance of inertial range of scales, adjacent to distributed chaos range, results in adiabatic invariance of an energy correlation integral for isotropic homogeneous turbulence and for buoyancy driven turbulence (with stable or unstable stratification, including Rayleigh-Taylor mixing zone). Power spectrum of velocity field for distributed chaos dominated by this adiabatic invariant has a stretched exponential form $\\propto \\exp(-k/k_{\\beta})^{3/5}$. Results of recent direct numerical simulations have been used in order to support these conclusions.
Carroll, Jonathan J; Blackman, Eric G
2010-01-01
Feedback from protostellar outflows can influence the nature of turbulence in star forming regions even if they are not the primary source of velocity dispersion for all scales of molecular clouds. For the rate and power expected in star forming regions, we previously (Carroll et al. 2009) demonstrated that outflows could drive supersonic turbulence at levels consistent with the scaling relations from Matzner 2007 although with a steeper velocity power spectrum than expected for an isotropically driven supersonic turbulent cascade. Here we perform higher resolution simulations and combine simulations of outflow driven turbulence with those of isotropically forced turbulence. We find that the presence of outflows within an ambient isotropically driven turbulent environment produces a knee in the velocity power spectrum at the outflow scale and a steeper slope at sub-outflow scales than for a purely isotropically forced case. We also find that the presence of outflows flattens the density spectrum at large scal...
Introduction to quantum turbulence.
Barenghi, Carlo F; Skrbek, Ladislav; Sreenivasan, Katepalli R
2014-03-25
The term quantum turbulence denotes the turbulent motion of quantum fluids, systems such as superfluid helium and atomic Bose-Einstein condensates, which are characterized by quantized vorticity, superfluidity, and, at finite temperatures, two-fluid behavior. This article introduces their basic properties, describes types and regimes of turbulence that have been observed, and highlights similarities and differences between quantum turbulence and classical turbulence in ordinary fluids. Our aim is also to link together the articles of this special issue and to provide a perspective of the future development of a subject that contains aspects of fluid mechanics, atomic physics, condensed matter, and low-temperature physics. PMID:24704870
Mitra, Dhrubaditya; Rogachevskii, Igor
2016-01-01
We show, by direct numerical simulations, that heavy inertial particles (with Stokes number ${\\rm St}$) in inhomogeneously forced statistically stationary turbulent flows cluster at the minima of turbulent kinetic energy. We further show that two turbulent transport processes, turbophoresis and turbulent diffusion together determine the spatial distribution of the particles. The ratio of the corresponding transport coefficient -- the turbulent Soret coefficient -- increases with ${\\rm St}$ for small ${\\rm St}$, reaches a maxima for ${\\rm St}\\approx 10$ and decreases as $\\sim {\\rm St}^{-0.33}$ for large ${\\rm St}$.
Radio Halo Formation through Magneto-turbulent Particle Acceleration in Clusters of Galaxies
Ohno, Hiroshi; Takizawa, Motokazu; Shibata, Shinpei
2002-01-01
We developed a magneto-turbulent model for the cosmic ray (CR) electrons seen in the radio halo clusters of galaxies. Steady state momentum distribution functions of the CR electrons are calculated for given spectra of the turbulent Alfven waves. The radio spectrum produced by the obtained CR electron distribution is compared to the observed radio spectrum of the Coma radio halo. We find that the observed radio spectrum of the Coma cluster is well reproduced when the spectral index of the tur...
PROPAGATION OF ADAPTIVELY CORRECTED LASER BEAMS THROUGH A TURBULENT ATMOSPHERE
Bissonnette, L
1980-01-01
This paper describes a mathematical model for solving the propagation problem of laser beams travelling in atmospheric turbulence and corrected by adaptive optics. The modeling of the adaptive optics is mathematically simple but sufficiently general to encompass the majority of the existing systems. The method allows the prediction of the average irradiance and the irradiance variance beam profiles for arbitrary scintillation levels. Typical solutions are presented for 3.8 and 10.6 µm laser b...
On the Nature of Magnetic Turbulence in Rotating, Shearing Flows
Walker, Justin; Boldyrev, Stanislav
2015-01-01
The local properties of turbulence driven by the magnetorotational instability (MRI) in rotating, shearing flows are studied in the framework of a shearing-box model. Based on numerical simulations, we propose that the MRI-driven turbulence comprises two components: the large-scale shear-aligned strong magnetic field and the small-scale fluctuations resembling magnetohydrodynamic (MHD) turbulence. The energy spectrum of the large-scale component is close to $k^{-2}$, whereas the spectrum of the small-scale component agrees with the spectrum of strong MHD turbulence $k^{-3/2}$. While the spectrum of the fluctuations is universal, the outer-scale characteristics of the turbulence are not; they depend on the parameters of the system, such as the net magnetic flux. However, there is remarkable universality among the allowed turbulent states -- their intensity $v_0$ and their outer scale $\\lambda_0$ satisfy the balance condition $v_0/\\lambda_0\\sim \\mathrm d\\Omega/\\mathrm d\\ln r$, where $\\mathrm d\\Omega/\\mathrm d\\l...
Avila, Marc; Roland, Nicolas; Hof, Bjoern
2013-01-01
Turbulence is ubiquitous in nature and although the equations governing fluid flow are well known, there are no analytical expressions that describe the complexity of turbulent motion. The nonlinear nature and the large number of spatial and temporal degrees of freedom turn this into one of the most challenging problems in mathematics and the physical sciences alike. We here report the discovery of unstable localised solutions for pipe flow that share key spatial characteristics of turbulence in the intermittent regime. While their temporal dynamics are very simple, much of the spatial complexity found in low Reynolds number turbulence is already encoded in them. We furthermore demonstrate how turbulent transients arise from one such solution branch. Our observations shed light on the origin of turbulence and link the localised structures commonly observed in turbulent flows to invariant solutions of the Navier-Stokes equations.
DEFF Research Database (Denmark)
Gilling, Lasse
Wind turbines operate in inflow turbulence whether it originates from the shear in the atmospheric boundary layer or from the wake of other wind turbines. Consequently, the airfoils of the wings experience turbulence in the inflow. The main topic of this thesis is to investigate the effect...... of resolved inflow turbulence on airfoil simulations in CFD. The detached-eddy simulation technique is used because it can resolve the inflow turbulence without becoming too computationally expensive due to its limited requirements for mesh resolution in the boundary layer. It cannot resolve the turbulence...... that is formed in attached boundary layers, but the freestream turbulence can penetrate the boundary layer. The idea is that the resolved turbulence from the freestream should mix high momentum flow into the boundary layer and thereby increase the resistance against separation and increase the maximum lift...
Sampling to estimate arbitrary subset sums
Duffield, Nick; Lund, Carsten; Thorup, Mikkel
2005-01-01
Starting with a set of weighted items, we want to create a generic sample of a certain size that we can later use to estimate the total weight of arbitrary subsets. For this purpose, we propose priority sampling which tested on Internet data performed better than previous methods by orders of magnitude. Priority sampling is simple to define and implement: we consider a steam of items i=0,...,n-1 with weights w_i. For each item i, we generate a random number r_i in (0,1) and create a priority ...
Circuits with arbitrary gates for random operators
Jukna, S.; Schnitger, G.
2010-01-01
We consider boolean circuits computing n-operators f:{0,1}^n --> {0,1}^n. As gates we allow arbitrary boolean functions; neither fanin nor fanout of gates is restricted. An operator is linear if it computes n linear forms, that is, computes a matrix-vector product y=Ax over GF(2). We prove the existence of n-operators requiring about n^2 wires in any circuit, and linear n-operators requiring about n^2/\\log n wires in depth-2 circuits, if either all output gates or all gates on the middle laye...
THE VIOLATION OF THE TAYLOR HYPOTHESIS IN MEASUREMENTS OF SOLAR WIND TURBULENCE
Energy Technology Data Exchange (ETDEWEB)
Klein, K. G. [Space Science Center, University of New Hampshire, Durham, NH 03824 (United States); Howes, G. G. [Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242 (United States); TenBarge, J. M. [IREAP, University of Maryland, College Park, MD 20742 (United States)
2014-08-01
Motivated by the upcoming Solar Orbiter and Solar Probe Plus missions, qualitative and quantitative predictions are made for the effects of the violation of the Taylor hypothesis on the magnetic energy frequency spectrum measured in the near-Sun environment. The synthetic spacecraft data method is used to predict observational signatures of the violation for critically balanced Alfvénic turbulence or parallel fast/whistler turbulence. The violation of the Taylor hypothesis can occur in the slow flow regime, leading to a shift of the entire spectrum to higher frequencies, or in the dispersive regime, in which the dissipation range spectrum flattens at high frequencies. It is found that Alfvénic turbulence will not significantly violate the Taylor hypothesis, but whistler turbulence will. The flattening of the frequency spectrum is therefore a key observational signature for fast/whistler turbulence.
DEFF Research Database (Denmark)
Xu, G. S.; Wan, B. N.; Wang, H. Q.;
2016-01-01
number spectrum of turbulence, as evidenced here, for the first time, by the direct observation of a turbulence radial wave number spectral shift and turbulence structure tilting prior to the L-H transition at tokamak edge by direct probing. This new mechanism does not require a pretransition overshoot...
New trends in turbulence; Turbulence: nouveaux aspects
Energy Technology Data Exchange (ETDEWEB)
Lesieur, M. [Institut National Polytechnique, LEGI/INPG, Institut de Mecanique, UMR 101, 38 - Grenoble (France); Yaglom, A. [Institut of Atmospheric Physics, Russian Academy of Sciences, Moscow (Russian Federation)]|[MIT, Dept. of Aeronautics and Astronautics, Cambridge, MA (United States); David, F. [CEA Saclay, SPhT, 91 - Gif-sur-Yvette (France)
2001-07-01
According to a Russian scientist, the flow of fluids actually met both in nature and engineering practice are turbulent in the overwhelmingly majority of cases. This document that reviews all the progress made recently in the understanding of turbulence, is made up of 10 courses. Course 1 ''a century of turbulence'' deals with the linear and non-linear points of views. In course 2 ''measures of anisotropy and the universal properties of turbulence'' the author gives a very complete account of fully developed turbulence experimental data both in the laboratory and in the atmosphere. Course 3 ''large-eddy simulations of turbulence (LES)'', LES are powerful tools to simulate the coherent vortices formation and evolution in a deterministic way. In Course 4 ''statistical turbulence modelling for the computation of physically complex flows'' the author describes methods used for predicting statistical industrial flows, where the geometry is right now too complex to allow the use of LES. In course 5 ''computational aero-acoustics'' an informative review of computational aero-acoustics with many applications to aircraft noise, is made. In course 6 ''the topology of turbulence'' the author presents the basis of topological fluid dynamics and stresses the importance of helicity in neutral and in magnetohydrodynamics (MHD) flows. In course 7 ''burgulence'' the authors deal with finite-time singularities, but mostly on the basis of Burger equations in one or several dimensions with the formation of multiple shocks. In course 8 ''2-dimensional turbulence'' the author presents numerous examples of 2D turbulence in the laboratory (rotating or MHD flows, plasmas), in the ocean and in the planetary atmosphere. Course 9 ''analysing and computing turbulent flows using wavelets'' is a useful presentation of
Gauthier, Serge; Keane, Christopher J.; Niemela, Joseph J.; Abarzhi, Snezhana I.
2013-07-01
companion paper Rooker et al provide a very interesting study on the generation and detection of 'whistler waves' induced space plasma turbulence at Gakona (Alaska). Physics of atmosphere. Five papers are devoted to the physics of atmosphere. Byalko presents the first experimental observation of a new hydrodynamic phenomenon, the underwater tornado. Herring and Kimura provide a review on recent results on homogeneous stably stratified turbulence. Pouquet et al use a high-resolution direct numerical simulation of rotating helical turbulence to obtain new numerical results on the inverse energy cascade in rotating flows. Tailleux discusses energy conversion and dissipation in depth in mixing flows. Zagumennyi and Chashechkin study the structure of convective flows driven by density variations in a stratified fluid by means of experiments and numerical simulations. Geophysics and Earth science. Three papers are dedicated to geophysics and Earth science. Jinadasa et al investigate small-scale and lateral intermittency of oceanic microstructure in the pycnocline. Shrira and Townsend review on a plausible mechanism of deep-ocean mixing caused by near-inertial waves in the abyssal ocean. Using numerical simulations, Imazio and Mininni study how helicity affects the spectrum of a passive scalar in rotating turbulent flows. Combustion. Two papers deal with flows with chemical reactions. Meshram used the Lewis-Kraichnan space-time version of Hopf's functional formalism to investigate turbulence with chemical reaction. Watanabe et al carry out experiments on a turbulent plane liquid jet with a second-order chemical reaction. Theoretical aspects of non-equilibrium dynamics. Six papers are devoted to fundamental aspects of non-equilibrium dynamics. Chen et al present state-of-the-art work on exact and direct derivation of macroscopic theoretical description for a flow at arbitrary Knudsen number from the Boltzmann-Bhatnagar-Gross-Krook kinetic theory with constant relaxation time
Electron magnetohydrodynamics: dynamics and turbulence.
Lyutikov, Maxim
2013-11-01
We consider dynamics and turbulent interaction of whistler modes within the framework of inertialess electron magnetohydrodynamics (EMHD). We argue that there is no energy principle in EMHD: any stationary closed configuration is neutrally stable. On the other hand, the relaxation principle, the long term evolution of a weakly dissipative system towards Taylor-Beltrami state, remains valid in EMHD. We consider the turbulent cascade of whistler modes. We show that (i) harmonic whistlers are exact nonlinear solutions; (ii) collinear whistlers do not interact (including counterpropagating); (iii) waves with the same value of the wave vector k(1)=k(2) do not interact; (iv) whistler modes have a dispersion that allows a three-wave decay, including into a zero frequency mode; (v) the three-wave interaction effectively couples modes with highly different wave numbers and propagation angles. In addition, linear interaction of a whistler with a single zero mode can lead to spatially divergent structures via parametric instability. All these properties are drastically different from MHD, so that the qualitative properties of the Alfvén turbulence can not be transferred to the EMHD turbulence. We derive the Hamiltonian formulation of EMHD, and using Bogoliubov transformation reduce it to the canonical form; we calculate the matrix elements for the three-wave interaction of whistlers. We solve numerically the kinetic equation and show that, generally, the EMHD cascade develops within a broad range of angles, while transiently it may show anisotropic, nearly two-dimensional structures. Development of a cascade depends on the forcing (nonuniversal) and often fails to reach a steady state. Analytical estimates predict the spectrum of magnetic fluctuations for the quasi-isotropic cascade [proportionality]k(-2). The cascade remains weak (not critically balanced). The cascade is UV local, while the infrared locality is weakly (logarithmically) violated. PMID:24329368
*-Regular Leavitt Path Algebras of Arbitrary Graphs
Institute of Scientific and Technical Information of China (English)
Gonzalo ARANDA PINO; Kulumani RANGASWAMY; Lia VA(S)
2012-01-01
If K is a field with involution and E an arbitrary graph,the involution from K naturally induces an involution of the Leavitt path algebra LK(E).We show that the involution on LK(E) is proper if the involution on K is positive-definite,even in the case when the graph E is not necessarily finite or row-finite.It has been shown that the Leavitt path algebra LK(E) is regular if and only if E is acyclic.We give necessary and sufficient conditions for LK(E) to be *-regular (i.e.,regular with proper involution).This characterization of *-regularity of a Leavitt path algebra is given in terms of an algebraic property of K,not just a graph-theoretic property of E.This differs from the.known characterizations of various other algebraic properties of a Leavitt path algebra in terms of graphtheoretic properties of E alone.As a corollary,we show that Handelman's conjecture (stating that every *-regular ring is unit-regular) holds for Leavitt path algebras.Moreover,its generalized version for rings with local units also continues to hold for Leavitt path algebras over arbitrary graphs.
Buoyancy driven turbulence and distributed chaos
Bershadskii, A
2016-01-01
It is shown, using results of recent direct numerical simulations, laboratory experiments and atmospheric measurements, that buoyancy driven turbulence exhibits a broad diversity of the types of distributed chaos with its stretched exponential spectrum $\\exp(-k/k_{\\beta})^{\\beta}$. The distributed chaos with $\\beta = 1/3$ (determined by the helicity correlation integral) is the most common feature of the stably stratified turbulence (due to the strong helical waves presence). These waves mostly dominate spectral properties of the vertical component of velocity field, while the horizontal component is dominated by the diffusive processes both for the weak and strong stable stratification ($\\beta =2/3$). For the last case influence of the low boundary can overcome the wave effects and result in $\\beta =1/2$ for the vertical component of the velocity field (the spontaneous breaking of the space translational symmetry - homogeneity). For the unstably stratified turbulence in the Rayleigh-Taylor mixing zone the di...
Numerical Simulations of Driven Relativistic MHD Turbulence
Zrake, Jonathan
2011-01-01
A wide variety of astrophysical phenomena involve the flow of turbulent magnetized gas with relativistic velocity or energy density. Examples include gamma-ray bursts, active galactic nuclei, pulsars, magnetars, micro-quasars, merging neutron stars, X-ray binaries, some supernovae, and the early universe. In order to elucidate the basic properties of the relativistic magnetohydrodynamical (RMHD) turbulence present in these systems, we present results from numerical simulations of fully developed driven turbulence in a relativistically warm, weakly magnetized and mildly compressible ideal fluid. We have evolved the RMHD equations for many dynamical times on a uniform grid with 1024^3 zones using a high order Godunov code. We observe the growth of magnetic energy from a seed field through saturation at about 1% of the total fluid energy. We compute the power spectrum of velocity and density-weighted velocity and conclude that the inertial scaling is consistent with a slope of -5/3. We compute the longitudinal a...
Triad interactions in multi-scale ITG/TEM/ETG turbulence
Maeyama, Shinya; Watanabe, Tomohiko; Idomura, Yasuhiro; Nakata, Motoki; Ishizawa, Akihiro; Nunami, Masanori
2015-11-01
Most of turbulent transport studies assume scale separation between electron- and ion-scale turbulence. However, latest massively parallel simulations based on gyrokinetics reveal that multi-scale interactions between electron- and ion-scale turbulence can influence turbulent transport [S. Maeyama, Phys. Rev. Lett. 114, 255002 (2015)]. The physical mechanism is investigated by applying triad transfer analysis. It is revealed that short-wave-length ITG turbulent eddies stabilize electron-scale streamers. Additionally, it is found that electron-scale turbulence has a damping effect on zonal flows. As a result, turbulent transport spectrum obtained from the multi-scale turbulence simulation differs from the sum of ones obtained from single-scale simulations. We will discuss gyrokinetic triad transfer analysis and the applicability of its fluid approximation, and explain the physical mechanism of multi-scale interactions by means of triad transfer analysis.
Lidar sounding of the optical parameter of atmospheric turbulence
Gurvich, A. S.; Fortus, M. I.
2016-03-01
The operation of a lidar intended for clear air turbulence (CAT) positioning on the basis of the backscatter enhancement (BSE) effect is analyzed using a turbulence model with a power-law spectrum. Systematic distortions occurring due to a need to regularize the lidar positioning problem solution are estimated. It is shown that the effect of molecular viscosity of air on the positioning result can be neglected if the wave parameter, which characterizes the diffraction manifestation, is higher than 3. This corresponds to sounding ranges of more than 1 km for optical or UV lidars. The analysis results show that the BSE lidar positioning accuracy weakly depends on the exponent in the turbulence spectrum in regions of severe turbulence. The results can justify a physical experiment for the design of an aircraft system for the lidar detection of CAT regions ahead of the flight course.
Toward the Theory of Turbulence in Magnetized Plasmas
Energy Technology Data Exchange (ETDEWEB)
Boldyrev, Stanislav [University of Wisconsin - Madison
2013-07-26
The goal of the project was to develop a theory of turbulence in magnetized plasmas at large scales, that is, scales larger than the characteristic plasma microscales (ion gyroscale, ion inertial scale, etc.). Collisions of counter-propagating Alfven packets govern the turbulent cascade of energy toward small scales. It has been established that such an energy cascade is intrinsically anisotropic, in that it predominantly supplies energy to the modes with mostly field-perpendicular wave numbers. The resulting energy spectrum of MHD turbulence, and the structure of the fluctuations were studied both analytically and numerically. A new parallel numerical code was developed for simulating reduced MHD equations driven by an external force. The numerical setting was proposed, where the spectral properties of the force could be varied in order to simulate either strong or weak turbulent regimes. It has been found both analytically and numerically that weak MHD turbulence spontaneously generates a “condensate”, that is, concentration of magnetic and kinetic energy at small k{sub {parallel}}. A related topic that was addressed in the project is turbulent dynamo action, that is, generation of magnetic field in a turbulent flow. We were specifically concentrated on the generation of large-scale magnetic field compared to the scales of the turbulent velocity field. We investigate magnetic field amplification in a turbulent velocity field with nonzero helicity, in the framework of the kinematic Kazantsev-Kraichnan model.
Klumperink, Eric A.M.; Shrestha, Rameswor; Mensink, Eisse; Arkesteijn, Vincent J.; Nauta, Bram
2007-01-01
Dynamic access of unused spectrum via a cognitive radio asks for flexible radio circuits that can work at an arbitrary radio frequency. This article reviews techniques to realize radios without resorting to frequency selective dedicated filters. In particular, a recently proposed polyphase multipath technique canceling harmonics and sidebands is discussed. Using this technique, a wideband and flexible power upconverter with a clean output spectrum has been realized on a CMOS chip, aiming at f...
Spin filter for arbitrary spins by substrate engineering
Pal, Biplab; Römer, Rudolf A.; Chakrabarti, Arunava
2016-08-01
We design spin filters for particles with potentially arbitrary spin S≤ft(=1/2,1,3/2,\\ldots \\right) using a one-dimensional periodic chain of magnetic atoms as a quantum device. Describing the system within a tight-binding formalism we present an analytical method to unravel the analogy between a one-dimensional magnetic chain and a multi-strand ladder network. This analogy is crucial, and is subsequently exploited to engineer gaps in the energy spectrum by an appropriate choice of the magnetic substrate. We obtain an exact correlation between the magnitude of the spin of the incoming beam of particles and the magnetic moment of the substrate atoms in the chain desired for opening up of a spectral gap. Results of spin polarized transport, calculated within a transfer matrix formalism, are presented for particles having half-integer as well as higher spin states. We find that the chain can be made to act as a quantum device which opens a transmission window only for selected spin components over certain ranges of the Fermi energy, blocking them in the remaining part of the spectrum. The results appear to be robust even when the choice of the substrate atoms deviates substantially from the ideal situation, as verified by extending the ideas to the case of a ‘spin spiral’. Interestingly, the spin spiral geometry, apart from exhibiting the filtering effect, is also seen to act as a device flipping spins—an effect that can be monitored by an interplay of the system size and the period of the spiral. Our scheme is applicable to ultracold quantum gases, and might inspire future experiments in this direction.
General description of circularly symmetric Bessel beams of arbitrary order
Wang, Jia Jie; Wriedt, Thomas; Lock, James A.; Mädler, Lutz
2016-11-01
A general description of circularly symmetric Bessel beams of arbitrary order is derived in this paper. This is achieved by analyzing the relationship between different descriptions of polarized Bessel beams obtained using different approaches. It is shown that a class of circularly symmetric Davis Bessel beams derived using the Hertz vector potentials possesses the same general functional dependence as the aplanatic Bessel beams generated using the angular spectrum representation (ASR). This result bridges the gap between different descriptions of Bessel beams and leads to a general description of circularly symmetric Bessel beams, such that the Davis Bessel beams and the aplanatic Bessel beams are merely the two simplest cases of an infinite number of possible circularly symmetric Bessel beams. Additionally, magnitude profiles of the electric and magnetic fields, the energy density and the Poynting vector are displayed for Bessel beams in both paraxial and nonparaxial cases. The results presented in this paper provide a fresh perspective on the description of Bessel beams and cast some insights into the light scattering and light-matter interactions problems in practice.
Broadband Phase Spectroscopy over Turbulent Air Paths.
Giorgetta, Fabrizio R; Rieker, Gregory B; Baumann, Esther; Swann, William C; Sinclair, Laura C; Kofler, Jon; Coddington, Ian; Newbury, Nathan R
2015-09-01
Broadband atmospheric phase spectra are acquired with a phase-sensitive dual-frequency-comb spectrometer by implementing adaptive compensation for the strong decoherence from atmospheric turbulence. The compensation is possible due to the pistonlike behavior of turbulence across a single spatial-mode path combined with the intrinsic frequency stability and high sampling speed associated with dual-comb spectroscopy. The atmospheric phase spectrum is measured across 2 km of air at each of the 70,000 comb teeth spanning 233 cm(-1) across hundreds of near-infrared rovibrational resonances of CO(2), CH(4), and H(2)O with submilliradian uncertainty, corresponding to a 10(-13) refractive index sensitivity. Trace gas concentrations extracted directly from the phase spectrum reach 0.7 ppm uncertainty, demonstrated here for CO(2). While conventional broadband spectroscopy only measures intensity absorption, this approach enables measurement of the full complex susceptibility even in practical open path sensing.
Superfluid (quantum) turbulence and distributed chaos
Bershadskii, A
2016-01-01
Properties of distributed chaos in superfluid (quantum) turbulence have been studied using the data of recent direct numerical simulations (HVBK two-fluid model for He II, and a moving grid in the frames of Gross-Pitaevskii model of the Bose-Einstein condensates at low temperatures). It is found that for the viscous (normal) component of the velocity field in He II the viscosity dominates the distributed chaos with the stretched exponential spectrum $\\exp(-k/k_{\\beta})^{\\beta}$ and $\\beta = 2/3$. For the superfluid component the distributed chaos is dominated by the vorticity correlation integral with $\\beta =1/2$ (the soft spontaneous breaking of the space translational symmetry - homogeneity). For very low temperature the distributed chaos is tuned to the large-scale coherent motions: the viscous (normal) component is tuned to the fundamental mode, whereas the superfluid component is subharmonically tuned. For the Gross-Pitaevskii superfluid turbulence incompressible part of the energy spectrum (containing ...
Compressible turbulent mixing: Effects of Schmidt number
Ni, Qionglin
2015-01-01
We investigated the effects of Schmidt number on passive scalar transport in forced compressible turbulence. In the inertial-convective range the scalar spectrum followed the k^{-5/3} power law. For Sc >> 1, there appeared a k^{-1} power law in the viscous-convective range, while for Sc > 1, the scalar field rolled up and got mixed sufficiently. However, for Sc > 1 and Sc > 1 and Sc << 1 flows decayed faster than the theoretical prediction of k^{-2/3} for incompressible flows. Finally, the comparison with incompressible results showed that the scalar in compressible turbulence with Sc=1 lacked a conspicuous bump structure in its spectrum, but was more intermittent in the dissipative range.
Energy Technology Data Exchange (ETDEWEB)
Kerstein, A.R. [Sandia National Lab., Livermore, CA (United States)
1996-12-31
One-Dimensional Turbulence is a new turbulence modeling strategy involving an unsteady simulation implemented in one spatial dimension. In one dimension, fine scale viscous and molecular-diffusive processes can be resolved affordably in simulations at high turbulence intensity. The mechanistic distinction between advective and molecular processes is thereby preserved, in contrast to turbulence models presently employed. A stochastic process consisting of mapping {open_quote}events{close_quote} applied to a one-dimensional velocity profile represents turbulent advection. The local event rate for given eddy size is proportional to the velocity difference across the eddy. These properties cause an imposed shear to induce an eddy cascade analogous in many respects to the eddy cascade in turbulent flow. Many scaling and fluctuation properties of self-preserving flows, and of passive scalars introduced into these flows, are reproduced.
Turbulence generation by waves
Energy Technology Data Exchange (ETDEWEB)
Kaftori, D.; Nan, X.S.; Banerjee, S. [Univ. of California, Santa Barbara, CA (United States)
1995-12-31
The interaction between two-dimensional mechanically generated waves, and a turbulent stream was investigated experimentally in a horizontal channel, using a 3-D LDA synchronized with a surface position measuring device and a micro-bubble tracers flow visualization with high speed video. Results show that although the wave induced orbital motion reached all the way to the wall, the characteristics of the turbulence wall structures and the turbulence intensity close to the wall were not altered. Nor was the streaky nature of the wall layer. On the other hand, the mean velocity profile became more uniform and the mean friction velocity was increased. Close to the free surface, the turbulence intensity was substantially increased as well. Even in predominantly laminar flows, the introduction of 2-D waves causes three dimensional turbulence. The turbulence enhancement is found to be proportional to the wave strength.
Cross-field transport in Goldreich-Sridhar MHD turbulence
Fraschetti, F
2015-01-01
I derive analytically the temporal dependence of the perpendicular transport coefficient of a charged particle in the three-dimensional anisotropic turbulence conjectured by Goldreich-Sridhar by implementing multi-spacecraft constraints on the turbulence power spectrum. The particle motion away from the turbulent local field line is assessed as gradient/curvature drift of the guiding-center and compared with the magnetic field line random walk. At inertial scales much smaller than the turbulence outer scale, particles decorrelate from field lines in a free-streaming motion, with no diffusion. In the solar wind at $1$ AU, for energy sufficiently small ($< 1$ keV protons), the perpendicular average displacement due to field line tangling generally dominates over two decades of turbulent scales. However, for higher energies ($\\simeq 25$ MeV protons) within the range of multi-spacecraft measurements, the longitudinal spread originating from transport due to gradient/curvature drift reaches up to $\\simeq 10^\\ci...
Feedback Control of Turbulent Shear Flows by Genetic Programming
Duriez, Thomas; von Krbek, Kai; Bonnet, Jean-Paul; Cordier, Laurent; Noack, Bernd R; Segond, Marc; Abel, Markus; Gautier, Nicolas; Aider, Jean-Luc; Raibaudo, Cedric; Cuvier, Christophe; Stanislas, Michel; Debien, Antoine; Mazellier, Nicolas; Kourta, Azeddine; Brunton, Steven L
2015-01-01
Turbulent shear flows have triggered fundamental research in nonlinear dynamics, like transition scenarios, pattern formation and dynamical modeling. In particular, the control of nonlinear dynamics is subject of research since decades. In this publication, actuated turbulent shear flows serve as test-bed for a nonlinear feedback control strategy which can optimize an arbitrary cost function in an automatic self-learning manner. This is facilitated by genetic programming providing an analytically treatable control law. Unlike control based on PID laws or neural networks, no structure of the control law needs to be specified in advance. The strategy is first applied to low-dimensional dynamical systems featuring aspects of turbulence and for which linear control methods fail. This includes stabilizing an unstable fixed point of a nonlinearly coupled oscillator model and maximizing mixing, i.e.\\ the Lyapunov exponent, for forced Lorenz equations. For the first time, we demonstrate the applicability of genetic p...
Carroll, Jonathan J.; Frank, Adam; Blackman, Eric G.
2010-10-01
Feedback from protostellar outflows can influence the nature of turbulence in star-forming regions even if they are not the primary source of velocity dispersion for all scales of molecular clouds. For the rate and power expected in star-forming regions, we previously (Carroll et al.) demonstrated that outflows could drive supersonic turbulence at levels consistent with the scaling relations from Matzner although with a steeper velocity power spectrum than expected for an isotropically driven supersonic turbulent cascade. Here, we perform higher resolution simulations and combine simulations of outflow driven turbulence with those of isotropically forced turbulence. We find that the presence of outflows within an ambient isotropically driven turbulent environment produces a knee in the velocity power spectrum at the outflow scale and a steeper slope at sub-outflow scales than for a purely isotropically forced case. We also find that the presence of outflows flattens the density spectrum at large scales effectively reducing the formation of large-scale turbulent density structures. These effects are qualitatively independent of resolution. We have also carried out Principal Component Analysis (PCA) for synthetic data from our simulations. We find that PCA as a tool for identifying the driving scale of turbulence has a misleading bias toward low amplitude large-scale velocity structures even when they are not necessarily the dominant energy containing scales. This bias is absent for isotropically forced turbulence but manifests strongly for collimated outflow driven turbulence.
Transmission Spectrum of an Optical Cavity Containing N Atoms
Leslie, S; Brown, K R; Stamper-Kurn, D M; Whaley, K B; Leslie, Sabrina; Shenvi, Neil; Brown, Kenneth R.; Stamper-Kurn, Dan M.
2003-01-01
The transmission spectrum of a high-finesse optical cavity containing an arbitrary number of trapped atoms is presented. We take spatial and motional effects into account and show that in the limit of strong coupling, the important spectral features can be determined for an arbitrary number of atoms, N. We also show that these results have important ramifications in limiting our ability to determine the number of atoms in the cavity.
ABJM Wilson loops in arbitrary representations
Energy Technology Data Exchange (ETDEWEB)
Hatsuda, Yasuyuki [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany). Theory Group; Tokyo Institute of Technology (Japan). Dept. of Physics; Honda, Masazumi [High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki (Japan); Moriyama, Sanefumi [Nagoya Univ. (Japan). Kobayashi Maskawa Inst. and Graduate School of Mathematics; Okuyama, Kazumi [Shinshu Univ., Matsumoto, Nagano (Japan). Dept. of Physics
2013-06-15
We study vacuum expectation values (VEVs) of circular half BPS Wilson loops in arbitrary representations in ABJM theory. We find that those in hook representations are reduced to elementary integrations thanks to the Fermi gas formalism, which are accessible from the numerical studies similar to the partition function in the previous studies. For non-hook representations, we show that the VEVs in the grand canonical formalism can be exactly expressed as determinants of those in the hook representations. Using these facts, we can study the instanton effects of the VEVs in various representations. Our results are consistent with the worldsheet instanton effects studied from the topological string and a prescription to include the membrane instanton effects by shifting the chemical potential, which has been successful for the partition function.
Discrete Equilibrium Sampling with Arbitrary Nonequilibrium Processes
Hamze, Firas
2015-01-01
We present a novel framework for performing statistical sampling, expectation estimation, and partition function approximation using \\emph{arbitrary} heuristic stochastic processes defined over discrete state spaces. Using a highly parallel construction we call the \\emph{sequential constraining process}, we are able to simultaneously generate states with the heuristic process and accurately estimate their probabilities, even when they are far too small to be realistically inferred by direct counting. After showing that both theoretically correct importance sampling and Markov chain Monte Carlo are possible using the sequential constraining process, we integrate it into a methodology called \\emph{state space sampling}, extending the ideas of state space search from computer science to the sampling context. The methodology comprises a dynamic data structure that constructs a robust Bayesian model of the statistics generated by the heuristic process subject to an accuracy constraint, the posterior Kullback-Leibl...
Metamaterial Electromagnetic Superabsorber with Arbitrary Geometries
Directory of Open Access Journals (Sweden)
Jingjing Yang
2010-06-01
Full Text Available The electromagnetic superabsorber that has larger absorption cross section than its real size may be a novel photothermal device with improved solar energy conversion rates. Based on a transformation optical approach, the material parameters for a two-dimensional (2D metamaterial-assisted electromagnetic superabsorber with arbitrary geometries are derived and validated by numerical simulation. We find that for the given geometry size, the absorption cross section of the superabsorber using nonlinear transformation is larger than that using linear transformation. These transformations can also be specialized to the designing the N-sided regular polygonal superabsorber just by changing the contour equation. All theoretical and numerical results validate the material parameters for the 2D electromagnetic superabsorber we have developed.
Triggering filamentation using turbulence
Eeltink, D; Marchiando, N; Hermelin, S; Gateau, J; Brunetti, M; Wolf, J P; Kasparian, J
2016-01-01
We study the triggering of single filaments due to turbulence in the beam path for a laser of power below the filamenting threshold. Turbulence can act as a switch between the beam not filamenting and producing single filaments. This 'positive' effect of turbulence on the filament probability, combined with our observation of off-axis filaments suggests the underlying mechanism is modulation instability caused by transverse perturbations. We hereby experimentally explore the interaction of modulation instability and turbulence, commonly associated with multiple-filaments, in the single-filament regime.
Imbalanced relativistic force-free magnetohydrodynamic turbulence
International Nuclear Information System (INIS)
When magnetic energy density is much larger than that of matter, as in pulsar/black hole magnetospheres, the medium becomes force-free and we need relativity to describe it. As in non-relativistic magnetohydrodynamics (MHD), Alfvénic MHD turbulence in the relativistic limit can be described by interactions of counter-traveling wave packets. In this paper, we numerically study strong imbalanced MHD turbulence in such environments. Here, imbalanced turbulence means the waves traveling in one direction (dominant waves) have higher amplitudes than the opposite-traveling waves (sub-dominant waves). We find that (1) spectrum of the dominant waves is steeper than that of sub-dominant waves, (2) the anisotropy of the dominant waves is weaker than that of sub-dominant waves, and (3) the dependence of the ratio of magnetic energy densities of dominant and sub-dominant waves on the ratio of energy injection rates is steeper than quadratic (i.e., b+2/b−2∝(ϵ+/ϵ−)n with n > 2). These results are consistent with those obtained for imbalanced non-relativistic Alfvénic turbulence. This corresponds well to the earlier reported similarity of the relativistic and non-relativistic balanced magnetic turbulence.
Fossil turbulence and fossil turbulence waves can be dangerous
Gibson, Carl H.
2012-01-01
Turbulence is defined as an eddy-like state of fluid motion where the inertial-vortex forces of the eddies are larger than any other forces that tend to damp the eddies out. By this definition, turbulence always cascades from small scales where vorticity is created to larger scales where turbulence fossilizes. Fossil turbulence is any perturbation in a hydrophysical field produced by turbulence that persists after the fluid is no longer turbulent at the scale of the perturbation. Fossil turbu...
Spectral properties of electromagnetic turbulence in plasmas
Directory of Open Access Journals (Sweden)
D. Shaikh
2009-03-01
Full Text Available We report on the nonlinear turbulent processes associated with electromagnetic waves in plasmas. We focus on low-frequency (in comparison with the electron gyrofrequency nonlinearly interacting electron whistlers and nonlinearly interacting Hall-magnetohydrodynamic (H-MHD fluctuations in a magnetized plasma. Nonlinear whistler mode turbulence study in a magnetized plasma involves incompressible electrons and immobile ions. Two-dimensional turbulent interactions and subsequent energy cascades are critically influenced by the electron whisters that behave distinctly for scales smaller and larger than the electron skin depth. It is found that in whistler mode turbulence there results a dual cascade primarily due to the forward spectral migration of energy that coexists with a backward spectral transfer of mean squared magnetic potential. Finally, inclusion of the ion dynamics, resulting from a two fluid description of the H-MHD plasma, leads to several interesting results that are typically observed in the solar wind plasma. Particularly in the solar wind, the high-time-resolution databases identify a spectral break at the end of the MHD inertial range spectrum that corresponds to a high-frequency regime. In the latter, turbulent cascades cannot be explained by the usual MHD model and a finite frequency effect (in comparison with the ion gyrofrequency arising from the ion inertia is essentially included to discern the dynamics of the smaller length scales (in comparison with the ion skin depth. This leads to a nonlinear H-MHD model, which is presented in this paper. With the help of our 3-D H-MHD code, we find that the characteristic turbulent interactions in the high-frequency regime evolve typically on kinetic-Alfvén time-scales. The turbulent fluctuation associated with kinetic-Alfvén interactions are compressive and anisotropic and possess equipartition of the kinetic and magnetic energies.
Mutually independent cascades in anisotropic soap-film turbulence
Liu, Chien-Chia; Gioia, Gustavo; Chakraborty, Pinaki
2015-03-01
Computational, experimental and field data amassed to date indicate that in 2D turbulence the spectrum of longitudinal velocity fluctuations, E11 (k1) , and the spectrum of transverse velocity fluctuations, E22 (k1) , correspond always to the same cascade, consistent with isotropy, so that E11 (k1) ~k-α and E22 (k1) ~k-α , where the ``spectral exponent'' α is either 5/3 (for the inverse-energy cascade) or 3 (for the enstrophy cascade). Here, we carry out experiments on turbulent 2D soap-film flows in which E11 (k1) ~k - 5 / 3 and E22 (k1) ~k-3 , as if two mutually independent cascades were concurrently active within the same flow. To our knowledge, this species of spectrum has never been observed or predicted theoretically. Our finding might open up new vistas in the understanding of turbulence.
Inhomogeneous turbulence in magnetic reconnection
Yokoi, Nobumitsu
2016-07-01
Turbulence is expected to play an essential role in enhancing magnetic reconnection. Turbulence associated with magnetic reconnection is highly inhomogeneous: it is generated by inhomogeneities of the field configuration such as the velocity shear, temperature gradient, density stratification, magnetic shear, etc. This self-generated turbulence affects the reconnection through the turbulent transport. In this reconnection--turbulence interaction, localization of turbulent transport due to dynamic balance between several turbulence effects plays an essential role. For investigating inhomogeneous turbulence in a strongly nonlinear regime, closure or turbulence modeling approaches provide a powerful tool. A turbulence modeling approach for the magnetic reconnection is introduced. In the model, the mean-field equations with turbulence effects incorporated are solved simultaneously with the equations of turbulent statistical quantities that represent spatiotemporal properties of turbulence under the effect of large-scale field inhomogeneities. Numerical simulations of this Reynolds-averaged turbulence model showed that self-generated turbulence enhances magnetic reconnection. It was pointed out that reconnection states may be divided into three category depending on the turbulence level: (i) laminar reconnection; (ii) turbulent reconnection, and (iii) turbulent diffusion. Recent developments in this direction are also briefly introduced, which includes the magnetic Prandtl number dependence, spectral evolution, and guide-field effects. Also relationship of this fully nonlinear turbulence approach with other important approaches such as plasmoid instability reconnection will be discussed.
An Arbitrary Benchmark CAPM: One Additional Frontier Portfolio is Sufficient
Ekern, Steinar
2008-01-01
The benchmark CAPM linearly relates the expected returns on an arbitrary asset, an arbitrary benchmark portfolio, and an arbitrary MV frontier portfolio. The benchmark is not required to be on the frontier and may be non-perfectly correlated with the frontier portfolio. The benchmark CAPM extends and generalizes previous CAPM formulations, including the zero beta, two correlated frontier portfolios, riskless augmented frontier, and inefficient portfolio versions. The covariance between the of...
Turbulence compensation: an overview
van Eekeren, Adam W. M.; Schutte, Klamer; Dijk, Judith; Schwering, Piet B. W.; van Iersel, Miranda; Doelman, Niek J.
2012-06-01
In general, long range visual detection, recognition and identification are hampered by turbulence caused by atmospheric conditions. Much research has been devoted to the field of turbulence compensation. One of the main advantages of turbulence compensation is that it enables visual identification over larger distances. In many (military) scenarios this is of crucial importance. In this paper we give an overview of several software and hardware approaches to compensate for the visual artifacts caused by turbulence. These approaches are very diverse and range from the use of dedicated hardware, such as adaptive optics, to the use of software methods, such as deconvolution and lucky imaging. For each approach the pros and cons are given and it is indicated for which scenario this approach is useful. In more detail we describe the turbulence compensation methods TNO has developed in the last years and place them in the context of the different turbulence compensation approaches and TNO's turbulence compensation roadmap. Furthermore we look forward and indicate the upcoming challenges in the field of turbulence compensation.
Sound generation by turbulence
Energy Technology Data Exchange (ETDEWEB)
Dowling, A.P.; Hynes, T.P. [Cambridge Univ., Dept. of Engineering (United Kingdom)
2004-06-01
Sound is a weak by-product of a subsonic turbulent flow. The main convective elements of the turbulence are silent and it is only spectral components with supersonic phase speeds that couple to the far-field sound. This paper reviews recent work on sound generation by turbulence. Just as there is a hierarchy of numerical models for turbulence (scaling, RANS, LES and DNS), there are different approaches for relating the near-field turbulence to the far-field sound. Kirchhoff approaches give the far-field sound in a straightforward way, but provide little insight into the sources of sound. Acoustic analogies can be used with different base flows to describe the propagation effects and to highlight the major noise producing regions. (authors)
Origin of Perpendicular Scales in Solar Wind Turbulence
Galinsky, V. L.
2015-10-01
Results of a study of dispersive Alfvén modes propagating outward from the Sun in streaming inhomogeneous plasma are presented for the inner heliosphere (≲1 AU) region. The results clearly show that a combination of nonlinear wave-particle and wave-wave interactions of outward-only Alfvén modes initially propagating along the local background magnetic field is perfectly capable of explaining the prevalence of turbulent energy in perpendicular ({k}\\perp ) scales over energy contained in scales propagating parallel ({k}\\parallel ) to the local magnetic field perturbations observed in the solar wind. The currently agreed on explanation for this anisotropy, as well as for the scale dependence of wave energy spectra, involves various nonlinear models of imbalanced incompressible MHD turbulence that require a mixture of inward and outward propagating waves to fuel a nonlinear cascade of energy into the {k}\\perp spectrum. The presented approach, for the first time, bridges a gap between week and strong turbulence theories—the interplay of wave-particle and wave-wave processes allows us to obtain strong turbulence scalings from seemingly week turbulence wave resonances. The reported results have a major implication on the current theories of solar wind turbulence and may require a complete overhaul of the state-of-the-art turbulence paradigm, including reassessment and reevaluation of the magnitude and directions (outward \\rightleftarrows inward; {k}\\perp \\rightleftarrows {k}\\parallel ) of the turbulent cascades that are necessary to explain the observations.
Analytical reconstruction of isotropic turbulence spectra based on the Gaussian transform
Wohlbrandt, Attila; Hu, Nan; Guerin, Sebastien; Ewert, Roland
2015-01-01
The Random Particle Mesh (RPM) method used to simulate turbulence-induced broadband noise in several aeroacoustic applications is extended to realise isotropic turbulence spectra. With this method turbulent fluctuations are synthesised by filtering white noise with a Gaussian filter kernel that in turn gives a Gaussian spectrum. The Gaussian function is smooth and its derivatives and integrals are again Gaussian functions. The Gaussian filter is efficient and finds wide-spread applications in...
Modeling quasi-static magnetohydrodynamic turbulence with variable energy flux
Verma, Mahendra K
2014-01-01
In quasi-static MHD, experiments and numerical simulations reveal that the energy spectrum is steeper than Kolmogorov's $k^{-5/3}$ spectrum. To explain this observation, we construct turbulence models based on variable energy flux, which is caused by the Joule dissipation. In the first model, which is applicable to small interaction parameters, the energy spectrum is a power law, but with a spectral exponent steeper than -5/3. In the other limit of large interaction parameters, the second model predicts an exponential energy spectrum and flux. The model predictions are in good agreement with the numerical results.
Understanding rigid body motion in arbitrary dimensions
Leyvraz, Francois
2014-01-01
Why would anyone wish to generalize the already unappetizing subject of rigid body motion to an arbitrary number of dimensions? At first sight, the subject seems to be both repellent and superfluous. The author will try to argue that an approach involving no specifically three-dimensional constructs is actually easier to grasp than the traditional one and might thus be generally useful to understand rigid body motion both in three dimensions and in the general case. Specific differences between the viewpoint suggested here and the usual one include the following: here angular velocities are systematically treated as antisymmetric matrices, a symmetric tensor $I$ quite different from the moment of inertia tensor plays a central role, whereas the latter is shown to be a far more complex object, namely a tensor of rank four. A straightforward way to define it is given. The Euler equation is derived and the use of Noether's theorem to obtain conserved quantities is illustrated. Finally the equation of motion for ...
Competitive epidemic spreading over arbitrary multilayer networks
Darabi Sahneh, Faryad; Scoglio, Caterina
2014-06-01
This study extends the Susceptible-Infected-Susceptible (SIS) epidemic model for single-virus propagation over an arbitrary graph to an Susceptible-Infected by virus 1-Susceptible-Infected by virus 2-Susceptible (SI1SI2S) epidemic model of two exclusive, competitive viruses over a two-layer network with generic structure, where network layers represent the distinct transmission routes of the viruses. We find analytical expressions determining extinction, coexistence, and absolute dominance of the viruses after we introduce the concepts of survival threshold and absolute-dominance threshold. The main outcome of our analysis is the discovery and proof of a region for long-term coexistence of competitive viruses in nontrivial multilayer networks. We show coexistence is impossible if network layers are identical yet possible if network layers are distinct. Not only do we rigorously prove a region of coexistence, but we can quantitate it via interrelation of central nodes across the network layers. Little to no overlapping of the layers' central nodes is the key determinant of coexistence. For example, we show both analytically and numerically that positive correlation of network layers makes it difficult for a virus to survive, while in a network with negatively correlated layers, survival is easier, but total removal of the other virus is more difficult.
A mesh partitioning algorithm for preserving spatial locality in arbitrary geometries
Nivarti, Girish V.; Salehi, M. Mahdi; Bushe, W. Kendal
2015-01-01
A space-filling curve (SFC) is a proximity preserving linear mapping of any multi-dimensional space and is widely used as a clustering tool. Equi-sized partitioning of an SFC ignores the loss in clustering quality that occurs due to inaccuracies in the mapping. Often, this results in poor locality within partitions, especially for the conceptually simple, Morton order curves. We present a heuristic that improves partition locality in arbitrary geometries by slicing a Morton order curve at points where spatial locality is sacrificed. In addition, we develop algorithms that evenly distribute points to the extent possible while maintaining spatial locality. A metric is defined to estimate relative inter-partition contact as an indicator of communication in parallel computing architectures. Domain partitioning tests have been conducted on geometries relevant to turbulent reactive flow simulations. The results obtained highlight the performance of our method as an unsupervised and computationally inexpensive domain partitioning tool.
Universal properties of Fermi gases in arbitrary dimensions
DEFF Research Database (Denmark)
Valiente, Manuel; T. Zinner, Nikolaj; Molmer, Klaus
2012-01-01
We consider spin-1/2 Fermi gases in arbitrary, integer or non-integer spatial dimensions, interacting via a Dirac delta potential. We first generalize the method of Tan's distributions and implement short-range boundary conditions to arbitrary dimension and we obtain a set of universal relations...
Including Arbitrary Antenna Patterns in Microwave Imaging of Buried Objects
DEFF Research Database (Denmark)
Meincke, Peter; Kim, Oleksiy S.; Lenler-Eriksen, Hans-Rudolph
2004-01-01
A linear inversion scheme for microwave imaging of buried objects is presented in which arbitrary antennas are accounted for through their plane-wave transmitting and receiving spectra......A linear inversion scheme for microwave imaging of buried objects is presented in which arbitrary antennas are accounted for through their plane-wave transmitting and receiving spectra...
Inverse scattering problem in turbulent magnetic fluctuations
Treumann, Rudolf A.; Baumjohann, Wolfgang; Narita, Yasuhito
2016-08-01
We apply a particular form of the inverse scattering theory to turbulent magnetic fluctuations in a plasma. In the present note we develop the theory, formulate the magnetic fluctuation problem in terms of its electrodynamic turbulent response function, and reduce it to the solution of a special form of the famous Gelfand-Levitan-Marchenko equation of quantum mechanical scattering theory. The last of these applies to transmission and reflection in an active medium. The theory of turbulent magnetic fluctuations does not refer to such quantities. It requires a somewhat different formulation. We reduce the theory to the measurement of the low-frequency electromagnetic fluctuation spectrum, which is not the turbulent spectral energy density. The inverse theory in this form enables obtaining information about the turbulent response function of the medium. The dynamic causes of the electromagnetic fluctuations are implicit to it. Thus, it is of vital interest in low-frequency magnetic turbulence. The theory is developed until presentation of the equations in applicable form to observations of turbulent electromagnetic fluctuations as input from measurements. Solution of the final integral equation should be done by standard numerical methods based on iteration. We point to the possibility of treating power law fluctuation spectra as an example. Formulation of the problem to include observations of spectral power densities in turbulence is not attempted. This leads to severe mathematical problems and requires a reformulation of inverse scattering theory. One particular aspect of the present inverse theory of turbulent fluctuations is that its structure naturally leads to spatial information which is obtained from the temporal information that is inherent to the observation of time series. The Taylor assumption is not needed here. This is a consequence of Maxwell's equations, which couple space and time evolution. The inversion procedure takes advantage of a particular
Model of strong stationary vortex turbulence in space plasmas
Directory of Open Access Journals (Sweden)
G. D. Aburjania
2009-01-01
Full Text Available This paper investigates the macroscopic consequences of nonlinear solitary vortex structures in magnetized space plasmas by developing theoretical model of plasma turbulence. Strongly localized vortex patterns contain trapped particles and, propagating in a medium, excite substantial density fluctuations and thus, intensify the energy, heat and mass transport processes, i.e., such vortices can form strong vortex turbulence. Turbulence is represented as an ensemble of strongly localized (and therefore weakly interacting vortices. Vortices with various amplitudes are randomly distributed in space (due to collisions. For their description, a statistical approach is applied. It is supposed that a stationary turbulent state is formed by balancing competing effects: spontaneous development of vortices due to nonlinear twisting of the perturbations' fronts, cascading of perturbations into short scales (direct spectral cascade and collisional or collisionless damping of the perturbations in the short-wave domain. In the inertial range, direct spectral cascade occurs through merging structures via collisions. It is shown that in the magneto-active plasmas, strong turbulence is generally anisotropic Turbulent modes mainly develop in the direction perpendicular to the local magnetic field. It is found that it is the compressibility of the local medium which primarily determines the character of the turbulent spectra: the strong vortex turbulence forms a power spectrum in wave number space. For example, a new spectrum of turbulent fluctuations in k^{−8/3} is derived which agrees with available experimental data. Within the framework of the developed model particle diffusion processes are also investigated. It is found that the interaction of structures with each other and particles causes anomalous diffusion in the medium. The effective coefficient of diffusion has a square root dependence on the stationary level of noise.
Jeans criterion in a turbulent medium
Bonazzola, S.; Falgarone, E.; Heyvaerts, J.; Perault, M.; Puget, J. L.
1986-10-01
According to the classical Jeans analysis, all the molecular clouds of mass larger than a few 100 M(solar), size larger than about 1pc and kinetic temperature Tk less than 30K are gravitationally unstable. We have shown that in clouds supported by internal supersonic motions, local gravitational instabilities may appear within molecular clouds which are globally stable. The argument is threefold: (1) when the turbulent kinetic energy is included into the internal energy term, the virial equilibrium condition shows that molecular clouds such as those observed, which are gravitationally unstable according to the Jeans criterion, are indeed globally stable if supported by a turbulent velocity field of power spectrum steeper than 3; (2) 2D compressible hydrodynamical simulations show that a supersonic turbulent velocity field generates a turbulent pressure within clouds, the gradients of which stabilize the unstable scales (i.e., the largest scales and the cloud itself) against gravitational collapse; (3) an analysis similar to the Jeans approach but including the turbulent pressure gradient term, gives basically the same results as those given in (1). Clouds of mean density lower than a critical value are found to be stable even though more massive than their Jeans mass. In clouds of mean density larger than that critical value, the gravitational instability appears only over a range of scales smaller than the cloud size, the largest scales being stable. In practice, the observed mean densities are lower than this critical value: the observation of a small number of cores and stars of a few solar masses embedded in clouds of several hundred solar masses can only be understood in terms of small scale density fluctuations of large amplitude generated by the supersonic turbulence which would occasionally overtake the limit of gravitational stability.
Modeling turbulent flame propagation
Energy Technology Data Exchange (ETDEWEB)
Ashurst, W.T.
1994-08-01
Laser diagnostics and flow simulation techniques axe now providing information that if available fifty years ago, would have allowed Damkoehler to show how turbulence generates flame area. In the absence of this information, many turbulent flame speed models have been created, most based on Kolmogorov concepts which ignore the turbulence vortical structure, Over the last twenty years, the vorticity structure in mixing layers and jets has been shown to determine the entrainment and mixing behavior and these effects need to be duplicated by combustion models. Turbulence simulations reveal the intense vorticity structure as filaments and simulations of passive flamelet propagation show how this vorticity Creates flame area and defines the shape of the expected chemical reaction surface. Understanding how volume expansion interacts with flow structure should improve experimental methods for determining turbulent flame speed. Since the last decade has given us such powerful new tools to create and see turbulent combustion microscopic behavior, it seems that a solution of turbulent combustion within the next decade would not be surprising in the hindsight of 2004.
Nedospasov, A. V.
1992-12-01
Edge turbulence is of decisive importance for the distribution of particle and energy fluxes to the walls of tokamaks. Despite the availability of extensive experimental data on the turbulence properties, its nature still remains a subject for discussion. This paper contains a review of the most recent theoretical and experimental studies in the field, including mainly the studies to which Wootton (A.J. Wooton, J. Nucl. Mater. 176 & 177 (1990) 77) referred to most in his review at PSI-9 and those published later. The available theoretical models of edge turbulence with volume dissipation due to collisions fail to fully interpret the entire combination of experimental facts. In the scrape-off layer of a tokamak the dissipation prevails due to the flow of current through potential shifts near the surface of limiters of divertor plates. The different origins of turbulence at the edge and in the core plasma due to such dissipation are discussed in this paper. Recent data on the electron temperature fluctuations enabled one to evaluate the electric probe measurements of turbulent flows of particles and heat critically. The latest data on the suppression of turbulence in the case of L-H transitions are given. In doing so, the possibility of exciting current instabilities in biasing experiments (rather than only to the suppression of existing turbulence) is given some attention. Possible objectives of further studies are also discussed.
Limitations of estimating turbulent convection velocities from PIV
de Kat, Roeland; Dawson, James R; Ganapathisubramani, Bharathram
2013-01-01
This paper deals with determination of turbulent convection velocities from particle image velocimetry (PIV). Turbulent convection velocities are of interest because they can be used to map temporal information into space. Convection velocity can be defined in several different ways. One approach is to use the phase-spectrum of two signals with a time-separation. Obtaining convection velocity per wavenumber involves determining a spatial spectrum. PIV data is limited in spatial resolution and sample length. The influence of truncation of both spatial resolution and frequency resolution is investigated, as well as the influences of spatial filtering and measurement noise. These issues are investigated by using a synthetic data set obtained by creating velocity-time data with an imposed spectrum. Results from the validation show that, when applying a Hamming window before determining the phase spectrum, there is a usable range of wavenumbers for which convection velocities can be determined. Simulation of flow ...
Energy Technology Data Exchange (ETDEWEB)
Hoejstrup, J. [NEG Micon Project Development A/S, Randers (Denmark); Hansen, K.S. [Denmarks Technical Univ., Dept. of Energy Engineering, Lyngby (Denmark); Pedersen, B.J. [VESTAS Wind Systems A/S, Lem (Denmark); Nielsen, M. [Risoe National Lab., Wind Energy and Atmospheric Physics, Roskilde (Denmark)
1999-03-01
The pdf`s of atmospheric turbulence have somewhat wider tails than a Gaussian, especially regarding accelerations, whereas velocities are close to Gaussian. This behaviour is being investigated using data from a large WEB-database in order to quantify the amount of non-Gaussianity. Models for non-Gaussian turbulence have been developed, by which artificial turbulence can be generated with specified distributions, spectra and cross-correlations. The artificial time series will then be used in load models and the resulting loads in the Gaussian and the non-Gaussian cases will be compared. (au)
Periodically kicked turbulence
Lohse
2000-10-01
Periodically kicked turbulence is theoretically analyzed within a mean-field theory. For large enough kicking strength A and kicking frequency f the Reynolds number grows exponentially and then runs into some saturation. The saturation level Re(sat) can be calculated analytically; different regimes can be observed. For large enough Re we find Re(sat) approximately Af, but intermittency can modify this scaling law. We suggest an experimental realization of periodically kicked turbulence to study the different regimes we theoretically predict and thus to better understand the effect of forcing on fully developed turbulence. PMID:11089041
Energy Technology Data Exchange (ETDEWEB)
Bershadskii, A.G.
1985-06-01
An exact solution for the nonlinear problem of the spectral energy function of a homogeneous turbulence is derived under the assumption that energy transfer under the effect of inertial forces is determined mainly by the interactions among vortices whose wavenumbers are only slightly different from each other. The results are experimentally verified for turbulence behind grids. Similar problems are solved for MHD turbulence and for a nonstationary spectral energy function. It is shown that at the initial stage of degeneration, the spectral energy function is little influenced by the Stewart number; this agrees with experimental data for the damping of longitudinal velocity pulsations behind a grid in a longitudinal magnetic field. 15 references.
Implementation and Validation of the BHR Turbulence Model in the FLAG Hydrocode
Energy Technology Data Exchange (ETDEWEB)
Denissen, Nicholas A. [Los Alamos National Laboratory; Fung, Jimmy [Los Alamos National Laboratory; Reisner, Jon M. [Los Alamos National Laboratory; Andrews, Malcolm J. [Los Alamos National Laboratory
2012-08-29
The BHR-2 turbulence model, developed at Los Alamos National Laboratory for variable density and compressible flows, is implemented in an Arbitrary Lagrangian-Eulerian hydrocode, FLAG. The BHR-2 formulation is discussed, with emphasis on its connection to multi-component flow formulations that underlie FLAG's treatment of multi-species flow. One-dimensional and two-dimensional validation tests are performed and compared to experiment and Eulerian simulations. Turbulence is an often studied and ubiquitous phenomenon in nature, and modeling its effects is essential in many practical applications. Specifically the behavior of turbulence in the presence of strong density gradients and compressibility is of fundamental importance in applications ranging from Inertial Confinement Fusion (ICF) [1], supernovae [2], and atmospheric flows. The BHR closure approach [3] seeks to model the physical processes at work in variable density turbulence including Kelvin-Helmholtz (KH) [4], Rayleigh-Taylor (RT) [5], and Richtmyer-Meshkov (RM) [6], driven turbulence. The effectiveness of the BHR-2 implementation has been demonstrated for variable density mixing in the KH, RT, and RM cases in an Eulerian framework [7]. The primary motivation of the present work is to implement the BHR-2 turbulence model in the Arbitrary Lagrangian-Eulerian (ALE) hydrodynamics code FLAG. The goal is not only to demonstrate results in agreement with previous Eulerian calculations, but also document behavior that arises from the underlying differences in code philosophy.
Modeling of turbulent chemical reaction
Chen, J.-Y.
1995-01-01
Viewgraphs are presented on modeling turbulent reacting flows, regimes of turbulent combustion, regimes of premixed and regimes of non-premixed turbulent combustion, chemical closure models, flamelet model, conditional moment closure (CMC), NO(x) emissions from turbulent H2 jet flames, probability density function (PDF), departures from chemical equilibrium, mixing models for PDF methods, comparison of predicted and measured H2O mass fractions in turbulent nonpremixed jet flames, experimental evidence of preferential diffusion in turbulent jet flames, and computation of turbulent reacting flows.
Aviation turbulence processes, detection, prediction
Lane, Todd
2016-01-01
Anyone who has experienced turbulence in flight knows that it is usually not pleasant, and may wonder why this is so difficult to avoid. The book includes papers by various aviation turbulence researchers and provides background into the nature and causes of atmospheric turbulence that affect aircraft motion, and contains surveys of the latest techniques for remote and in situ sensing and forecasting of the turbulence phenomenon. It provides updates on the state-of-the-art research since earlier studies in the 1960s on clear-air turbulence, explains recent new understanding into turbulence generation by thunderstorms, and summarizes future challenges in turbulence prediction and avoidance.
Fourth-order mutual coherence function in oceanic turbulence.
Baykal, Yahya
2016-04-10
We have recently expressed the structure constant of atmospheric turbulence in terms of the oceanic turbulence parameters, which are the ratio of temperature to salinity contributions to the refractive index spectrum, rate of dissipation of kinetic energy per unit mass of fluid, rate of dissipation of the mean-squared temperature, wavelength, Kolmogorov microscale, and link length. In this paper, utilizing this recently found structure constant and the fourth-order mutual coherence function of atmospheric turbulence, we present the fourth-order mutual coherence function to be used in oceanic turbulence evaluations. Thus, the found fourth-order mutual coherence function of oceanic turbulence is evaluated for the special case of a point source located at the transmitter origin and at a single receiver point. The variations of this special case of the fourth-order mutual coherence function of oceanic turbulence against the changes in the ratio of temperature to salinity contributions to the refractive index spectrum, the rate of dissipation of kinetic energy per unit mass of fluid, the rate of dissipation of the mean-squared temperature, the wavelength, and the Kolmogorov microscale at various link lengths are presented. PMID:27139862
Non-locality and Intermittency in 3D Turbulence
Laval, J. -P.; B. Dubrulle; Nazarenko, S.(Russian Federal Nuclear Center (VNIIEF), Sarov, Russia)
2001-01-01
Numerical simulations are used to determine the influence of the non-local and local interactions on the intermittency corrections in the scaling properties of 3D turbulence. We show that neglect of local interactions leads to an enhanced small-scale energy spectrum and to a significantly larger number of very intense vortices (tornadoes) and stronger intermittency. On the other hand, neglect of the non-local interactions results in even stronger small-scale spectrum but significantly weaker ...
Cui, Linyan; Xue, Bindang; Cao, Xiaoguang; Zhou, Fugen
2014-04-01
Based on the generalized von Kármán spectrum and the extended Rytov theory, new analytic expressions for the variance of angle of arrival (AOA) fluctuations are derived for optical plane and spherical waves propagating through moderate-to-strong non-Kolmogorov turbulence with horizontal path. They consider finite turbulence outer scale and general spectral power law value, and cover a wide range of non-Kolmogorov turbulence strength. When the turbulence outer scale is set to infinite, the new expressions can reduce correctly to previously published analytic expressions [J. Opt. Soc. Am. A, 302188 (2013]. The final results show that the increased turbulence outer scale value enlarges the variance of AOA fluctuations greatly under moderate-to-strong (or strong) non-Kolmogorov turbulence.
Inverse turbulent cascade in swarming sperm
Creppy, Adama; Praud, Olivier; Druart, Xavier; Kohnke, Philippa; Plouraboue, Franck; Inra, Cnrs, Umr, F-37380 Nouzilly, France Team; Université de Toulouse, Inpt, Ups, Imft, Umr 5502, France Team
2014-11-01
Collective motion of self-sustained swarming flows has recently provided examples of small scale turbulence arising where viscosity effects are dominant. We report the first observation of an universal inverse enstrophy cascade in concentrated swarming sperm consistent with a body of evidence built from various independent measurements. We found a well-defined k-3 power-law decay of velocity field power-spectrum and relative dispersion of small beads consistent with theoretical predictions in two-dimensional turbulence. Concentrated living sperm displays long-range, correlated whirlpool structures the size of which provides turbulence's integral scale. We propose a consistent explanation for this quasi-two-dimensional turbulence based on self-structured laminated flow forced by steric interaction and alignment, a state of active matter that we call ``swarming liquid crystal.'' We develop scaling arguments consistent with this interpretation. The implication of multi-scale collective dynamics of sperm's collective motility for fertility assessment is discussed. This work has been supported by the French Agence Nationale pour la Recherche (ANR) in the frame of the Contract MOTIMO (ANR-11-MONU-009-01). We thank Pierre Degond, Eric Climent, Laurent Lacaze and Frédéric Moulin for interesting discussions.
Near isotropic behaviour of turbulent thermal convection
Nath, Dinesh; Kumar, Abhishek; Verma, Mahendra K
2016-01-01
We investigate the anisotropy in turbulent convection in a 3D box using direct numerical simulation. We compute the anisotropic parameter $A = u_\\perp^{2}/(2u_{\\parallel}^{2})$, where $u_{\\perp}$ and $u_{\\parallel}$ are the components of velocity perpendicular and parallel to the buoyancy direction, the shell and ring spectra, and shell-to-shell energy transfers. We observe that the flow is nearly isotropic for the Prandtl number $\\mathrm{Pr} \\approx 1$, but the anisotropy increases with the Prandtl number. For $\\mathrm{Pr}=\\infty$, $A \\approx 0.3$, thus anisotropy is not very significant even in extreme cases. We also observe that $u_{\\parallel}$ feeds energy to $u_{\\perp}$ via pressure. The computation of shell-to-shell energy transfers show that the energy transfer in turbulent convection is local and forward, similar to fluid turbulence. These results are consistent with the Kolmogorov's spectrum observed by Kumar et al.~[Phys. Rev. E {\\bf 90}, 023016 (2014)] for turbulent convection.
Turbulence in two dimensional visco - elastic medium
Tiwari, Sanat Kumar; Das, Amita; Patel, Bhavesh G; Kaw, Predhiman
2014-01-01
The properties of decaying turbulence is studied with the help of a Generalized Hydrodynamic (GHD) fluid model in the context of two dimensional visco - elastic medium such as a strongly coupled dusty plasma system. For the incompressible case considered here however, the observations are valid for a wider class of visco - elastic systems not necessarily associated with plasmas only. Our observations show that an initial spectrum that is confined in a limited domain of wave numbers becomes broad, even when the Reynold's number is much less than the critical value required for the onset of turbulence in Newtonian fluids. This is a signature of elastic turbulence where Weissenberg's number also plays a role in the onset of turbulence. This has been reported in several experiments. It is also shown that the existence of memory relaxation time parameter and the transverse shear wave inhibit the normal process (for 2-D systems) of inverse spectral cascade in this case. A detailed simulation study has been carried ...
Turbulent buoyant jets and plumes
Rodi, Wolfgang
The Science & Applications of Heat and Mass Transfer: Reports, Reviews, & Computer Programs, Volume 6: Turbulent Buoyant Jets and Plumes focuses on the formation, properties, characteristics, and reactions of turbulent jets and plumes. The selection first offers information on the mechanics of turbulent buoyant jets and plumes and turbulent buoyant jets in shallow fluid layers. Discussions focus on submerged buoyant jets into shallow fluid, horizontal surface or interface jets into shallow layers, fundamental considerations, and turbulent buoyant jets (forced plumes). The manuscript then exami
Containerless Ripple Turbulence
Putterman, Seth; Wright, William; Duval, Walter; Panzarella, Charles
2002-11-01
One of the longest standing unsolved problems in physics relates to the behavior of fluids that are driven far from equilibrium such as occurs when they become turbulent due to fast flow through a grid or tidal motions. In turbulent flows the distribution of vortex energy as a function of the inverse length scale [or wavenumber 'k'] of motion is proportional to 1/k5/3 which is the celebrated law of Kolmogorov. Although this law gives a good description of the average motion, fluctuations around the average are huge. This stands in contrast with thermally activated motion where large fluctuations around thermal equilibrium are highly unfavorable. The problem of turbulence is the problem of understanding why large fluctuations are so prevalent which is also called the problem of 'intermittency'. Turbulence is a remarkable problem in that its solution sits simultaneously at the forefront of physics, mathematics, engineering and computer science. A recent conference [March 2002] on 'Statistical Hydrodynamics' organized by the Los Alamos Laboratory Center for Nonlinear Studies brought together researchers in all of these fields. Although turbulence is generally thought to be described by the Navier-Stokes Equations of fluid mechanics the solution as well as its existence has eluded researchers for over 100 years. In fact proof of the existence of such a solution qualifies for a 1 M millennium prize. As part of our NASA funded research we have proposed building a bridge between vortex turbulence and wave turbulence. The latter occurs when high amplitude waves of various wavelengths are allowed to mutually interact in a fluid. In particular we have proposed measuring the interaction of ripples [capillary waves] that run around on the surface of a fluid sphere suspended in a microgravity environment. The problem of ripple turbulence poses similar mathematical challenges to the problem of vortex turbulence. The waves can have a high amplitude and a strong nonlinear
Zare, Armin; Georgiou, Tryphon T
2016-01-01
Second-order statistics of turbulent flows can be obtained either experimentally or via direct numerical simulations. Statistics reflect fundamentals of flow physics and can be used to develop low-complexity turbulence models. Due to experimental or numerical limitations it is often the case that only partial flow statistics can be reliably known, i.e., only certain correlations between a limited number of flow field components are available. Thus, it is of interest to complete the statistical signature of the flow field in a way that is consistent with the known dynamics. This is an inverse problem and our approach utilizes stochastically-forced linearization around turbulent mean velocity profile. In general, white-in-time stochastic forcing is not sufficient to explain turbulent flow statistics. In contrast, colored-in-time forcing of the linearized equations allows for exact matching of available correlations. To accomplish this, we develop dynamical models that generate the required stochastic excitation...
Samanta, Devranjan; Holzner, Markus; Schäfer, Christof; Morozov, Alexander; Wagner, Christian; Hof, Björn
2013-01-01
Turbulence is ubiquitous in nature yet even for the case of ordinary Newtonian fluids like water our understanding of this phenomenon is limited. Many liquids of practical importance however are more complicated (e.g. blood, polymer melts or paints), they exhibit elastic as well as viscous characteristics and the relation between stress and strain is nonlinear. We here demonstrate for a model system of such complex fluids that at high shear rates turbulence is not simply modified as previously believed but it is suppressed and replaced by a new type of disordered motion, elasto-inertial turbulence (EIT). EIT is found to occur at much lower Reynolds numbers than Newtonian turbulence and the dynamical properties differ significantly. In particular the drag is strongly reduced and the observed friction scaling resolves a longstanding puzzle in non-Newtonian fluid mechanics regarding the nature of the so-called maximum drag reduction asymptote. Theoretical considerations imply that EIT will arise in complex fluid...
Kim, Eun-Jin; Diamond, P. H.
2001-01-01
We examine the dynamics of turbulent reconnection in 2D and 3D reduced MHD by calculating the effective dissipation due to coupling between small-scale fluctuations and large-scale magnetic fields. Sweet-Parker type balance relations are then used to calculate the global reconnection rate. Two approaches are employed -- quasi-linear closure and an eddy-damped fluid model. Results indicate that despite the presence of turbulence, the reconnection rate remains inversely proportional to $\\sqrt{R...
Stochastic tools in turbulence
Lumey, John L
2012-01-01
Stochastic Tools in Turbulence discusses the available mathematical tools to describe stochastic vector fields to solve problems related to these fields. The book deals with the needs of turbulence in relation to stochastic vector fields, particularly, on three-dimensional aspects, linear problems, and stochastic model building. The text describes probability distributions and densities, including Lebesgue integration, conditional probabilities, conditional expectations, statistical independence, lack of correlation. The book also explains the significance of the moments, the properties of the
Turbulence in magnetohydrodynamics
Beresnyak, Andrey
2016-01-01
Magnetohydrodynamics describes dynamics in electrically conductive fluids. These occur in our environment as well as in our atmosphere and magnetosphere, and play a role in the sun's interaction with our planet. This work gives the basic information on turbulence in nature, comprising the needed equations, notions and numerical simulations. The current state of our knowledge and future implications of MHD turbulence are outlined systematically. It is indispensable for all scientists engaged in research of our atmosphere and in space science.
Rossby-wave turbulence in a rapidly rotating sphere
Directory of Open Access Journals (Sweden)
N. Schaeffer
2005-01-01
Full Text Available We use a quasi-geostrophic numerical model to study the turbulence of rotating flows in a sphere, with realistic Ekman friction and bulk viscous dissipation. The forcing is caused by the destabilization of an axisymmetric Stewartson shear layer, generated by differential rotation, resulting in a forcing at rather large scales. The equilibrium regime is strongly anisotropic and inhomogeneous but exhibits a steep m-5 spectrum in the azimuthal (periodic direction, at scales smaller than the injection scale. This spectrum has been proposed by Rhines for a Rossby wave turbulence. For some parameter range, we observe a turbulent flow dominated by a large scale vortex located in the shear layer, reminding us of the Great Red Spot of Jupiter.
Aeroelectric structures and turbulence in the atmospheric boundary layer
Directory of Open Access Journals (Sweden)
S. V. Anisimov
2013-10-01
Full Text Available Complex electrical measurements with the use of sodar data show that electric field pulsation analysis is useful for electrodynamics/turbulence monitoring under different conditions. In particular, the number of aeroelectric structures (AES generated per hour is a convenient measure of the turbulence intensity. During convectively unstable periods, as many as 5–10 AES form per hour. Under stable conditions, AES occasionally form as well, indicating the appearance of occasional mixing events reflected in the electric field perturbations. AES magnitudes under stable conditions are relatively small, except in special cases such as high humidity and fog. The analysis of electric field (EF spectra gives additional useful information on the parameters of the atmospheric boundary layer and its turbulence. A rather sharp change in the spectrum slope takes place in the vicinity of 0.02 Hz under stable conditions. The characteristic slope of the spectrum and its change are reproduced in a simple model of EF formation.
RF wave propagation and scattering in turbulent tokamak plasmas
Energy Technology Data Exchange (ETDEWEB)
Horton, W., E-mail: wendell.horton@gmail.com; Michoski, C. [Institute for Fusion Studies, The University of Texas at Austin, Austin, TX 78654 (United States); Peysson, Y.; Decker, J. [CEA, IRFM, 13108, Saint-Paul, Durance Cedex (France)
2015-12-10
Drift wave turbulence driven by the steep electron and ion temperature gradients in H-mode divertor tokamaks produce scattering of the RF waves used for heating and current drive. The X-ray emission spectra produced by the fast electrons require the turbulence broaden RF wave spectrum. Both the 5 GHz Lower Hybrid waves and the 170 GHz electron cyclotron [EC] RF waves experience scattering and diffraction by the electron density fluctuations. With strong LHCD there are bifurcations in the coupled turbulent transport dynamics giving improved steady-state confinement states. The stochastic scattering of the RF rays makes the prediction of the distribution of the rays and the associated particle heating a statistical problem. Thus, we introduce a Fokker-Planck equation for the probably density of the RF rays. The general frame work of the coupled system of coupled high frequency current driving rays with the low-frequency turbulent transport determines the profiles of the plasma density and temperatures.
Role of Cross Helicity in Cascade Processes of MHD turbulence
Mizeva, Irina; Frick, Peter; 10.1134/S1028335809020128
2009-01-01
The purpose of this work is to investigate the spectral properties of the developed isotropic (non-Alfven) MHD turbulence stationary excited by an external force, which injects the cross helicity into the flow simultaneously with the energy. It is shown that the cross helicity blocks the spectral energy transfer in MHD turbulence and results in energy accumulation in the system. This accumulation proceeds until the vortex intensification compensates the decreasing efficiency of nonlinear interactions. The formula for estimating the average turbulence energy is obtained for the set ratio between the injected helicity and energy. It is remarkable that the turbulence accumulates the injected cross helicity at its low rate injection -- the integral correlation coefficient significantly exceeds the ratio between the injected helicity and the energy. It is shown that the spectrum slope gradually increases from "5/3" to "2" with the cross helicity level.
RF wave propagation and scattering in turbulent tokamak plasmas
Horton, W.; Michoski, C.; Peysson, Y.; Decker, J.
2015-12-01
Drift wave turbulence driven by the steep electron and ion temperature gradients in H-mode divertor tokamaks produce scattering of the RF waves used for heating and current drive. The X-ray emission spectra produced by the fast electrons require the turbulence broaden RF wave spectrum. Both the 5 GHz Lower Hybrid waves and the 170 GHz electron cyclotron [EC] RF waves experience scattering and diffraction by the electron density fluctuations. With strong LHCD there are bifurcations in the coupled turbulent transport dynamics giving improved steady-state confinement states. The stochastic scattering of the RF rays makes the prediction of the distribution of the rays and the associated particle heating a statistical problem. Thus, we introduce a Fokker-Planck equation for the probably density of the RF rays. The general frame work of the coupled system of coupled high frequency current driving rays with the low-frequency turbulent transport determines the profiles of the plasma density and temperatures.
Simulations of nonhelical hydromagnetic turbulence
Haugen, N E L; Dobler, W; Haugen, Nils Erland L.; Brandenburg, Axel; Dobler, Wolfgang
2003-01-01
Nonhelical hydromagnetic forced turbulence is investigated using large scale simulations on up to 256 processors and 1024^3 meshpoints. The magnetic Prandtl number is varied between 0.3 and 30, although in most cases it is unity. When the magnetic Reynolds number is based on the inverse forcing wavenumber, the critical value for dynamo action is shown to be between 25 and 35 for a range of different forcing scales and magnetic Prandtl numbers. The Kazantsev k^{3/2} spectrum for magnetic energy is confirmed for the kinematic regime, i.e. when nonlinear effects are still unimportant and when the magnetic Prandtl number is unity. In the nonlinear regime, the energy budget converges for large Reynolds numbers (around 1000) such that about 70% is in kinetic energy and about 30% is in magnetic energy. The energy dissipation rates are converged to 30% viscous dissipation and 70% resistive dissipation. Second order structure functions of the Elsasser variables give evidence for a k^{-5/3} spectrum. Nevertheless, the ...
Turbulent Plasmoid Reconnection
Widmer, Fabien; Yokoi, Nobumitsu
2016-01-01
The plasmoid instability may lead to fast magnetic reconnection through long current sheets(CS). It is well known that large-Reynolds-number plasmas easily become turbulent. We address the question whether turbulence enhances the energy conversion rate of plasmoid-unstable current sheets. We carry out appropriate numerical MHD simulations, but resolving simultaneously the relevant large-scale (mean-) fields and the corresponding small-scale, turbulent, quantities by means of direct numerical simulations (DNS) is not possible. Hence we investigate the influence of small scale turbulence on large scale MHD processes by utilizing a subgrid-scale (SGS) turbulence model. We verify the applicability of our SGS model and then use it to investigate the influence of turbulence on the plasmoid instability. We start the simulations with Harris-type and force-free CS equilibria in the presence of a finite guide field in the direction perpendicular to the reconnection plane. We use the DNS results to investigate the growt...
Conformal array design on arbitrary polygon surface with transformation optics
Deng, Li; Wu, Yongle; Hong, Weijun; Zhu, Jianfeng; Peng, Biao; Li, Shufang
2016-06-01
A transformation-optics based method to design a conformal antenna array on an arbitrary polygon surface is proposed and demonstrated in this paper. This conformal antenna array can be adjusted to behave equivalently as a uniformly spaced linear array by applying an appropriate transformation medium. An typical example of general arbitrary polygon conformal arrays, not limited to circular array, is presented, verifying the proposed approach. In summary, the novel arbitrary polygon surface conformal array can be utilized in array synthesis and beam-forming, maintaining all benefits of linear array.
Conformal array design on arbitrary polygon surface with transformation optics
Directory of Open Access Journals (Sweden)
Li Deng
2016-06-01
Full Text Available A transformation-optics based method to design a conformal antenna array on an arbitrary polygon surface is proposed and demonstrated in this paper. This conformal antenna array can be adjusted to behave equivalently as a uniformly spaced linear array by applying an appropriate transformation medium. An typical example of general arbitrary polygon conformal arrays, not limited to circular array, is presented, verifying the proposed approach. In summary, the novel arbitrary polygon surface conformal array can be utilized in array synthesis and beam-forming, maintaining all benefits of linear array.
Teleportation of an arbitrary mixture of diagonal states of multiqudit
International Nuclear Information System (INIS)
This paper proposes a scheme to teleport an arbitrary mixture of diagonal states of multiqutrit via classical correlation and classical communication. To teleport an arbitrary mixture of diagonal states of N qutrits, N classically correlated pairs of two qutrits are used as channel. The sender (Alice) makes Fourier transform and conditional gate (i.e., XOR(3) gate) on her qutrits and does measurement in appropriate computation bases. Then she sends N ctrits to the receiver (Bob). Based on the received information, Bob performs the corresponding unitary transformation on his qutrits and obtains the teleported state. Teleportation of an arbitrary mixture of diagonal states of multiqudit is also discussed
Teleportation of an arbitrary mixture of diagonal states of multiqudit
Institute of Scientific and Technical Information of China (English)
Du Qian-Hua; Lin Xiu-Min; Chen Zhi-Hua; Lin Gong-Wei; Chen Li-Bo; Gu Yong-Jian
2008-01-01
This paper proposes a scheme to teleport an arbitrary mixture of diagonal states of multiqutrit via classical correlation and classical communication. To teleport an arbitrary mixture of diagonal states of N qutrits, N classically correlated pairs of two qutrits are used as channel. The sender (Alice) makes Fourier transform and conditional gate (i.e., XOR(3) gate) on her qutrits and does measurement in appropriate computation bases. Then she sends N ctrits to the receiver (Bob). Based on the received information, Bob performs the corresponding unitary transformation on his qutrits and obtains the teleported state. Teleportation of an arbitrary mixture of diagonal states of multiqudit is also discussed.
Yang-Mills Instanton Sheaves with Arbitrary Topological Charges
Lai, Sheng-Hong; Lai, I-Hsun
2016-01-01
We use a set of ADHM 3-instanton data to systematically construct a class of SU(2) Yang-Mills instanton solutions with arbitrary topological charges. Moreover, by using the biquaternion calculation with biconjugation operation developed recently, these new ADHM data are used to construct a class of SL(2,C) Yang-Mills instanton sheaves on CP^3 with arbitrary topological charges k greater than 3. This result extends the previous construction of Yang-Mills 2-instanton sheaves to arbitrary higher k-instanton sheaves.
Feynman propagator for an arbitrary half-integral spin
Institute of Scientific and Technical Information of China (English)
黄时中; 张鹏飞; 阮图南; 祝玉灿; 郑志鹏
2003-01-01
Based on the solution to Bargmann-Wigner equation for a particle with arbitrary half-integral spin, a direct derivation of the projection operator and propagator for a particle with arbitrary half-integral spin is worked out. The projection operator constructed by Behrends and Fronsdal is re-deduced and confirmed and simplified, the general commutation rules and Feynman propagator with additional non-covariant terms for a free particle with arbitrary half-inteRzal spin are derived, and explicit expressions for the propagators for spins 3/2, 5/2 and 7/2 are provided.
Renner, Elizabeth; Price, Elizabeth E; Subiaul, Francys
2016-01-01
Do visual cues such as size, color, and number facilitate sequential recall in orangutans and human children? In Experiment 1, children and adult orangutans solved two types of sequences, arbitrary (unrelated pictures) and meaningful (pictures varied along a spectrum according to the size, color, or number of items shown), in a touchscreen paradigm. It was found that visual cues did not increase the percentage of correct responses for either children or orangutans. In order to demonstrate that the failure to spontaneously seriate along these dimensions was not due to a general inability to perceive the dimensions nor to an inability to seriate items, in Experiment 2, orangutans were trained on one type of sequence and tested on novel sequences organized according to the same rule (i.e., pictures varied on the number spectrum only). The orangutans performed significantly better on novel meaningful sequences in this task than on novel arbitrary sequences. These results indicate that, while orangutans and human children share the ability to learn how to order items according to their size, color, or number, both orangutans and humans lack a cognitive propensity to spontaneously (i.e., without prior training or enculturation) order multiple items by size, color, or number. PMID:26298671
Gravity surface wave turbulence in a laboratory flume
Denissenko, Petr; Lukaschuk, Sergei; Nazarenko, Sergey
2006-01-01
We present experimental results for water wave turbulence excited by piston-like programmed wavemakers in a water flume with horisontal dimensions 6x12x1.5 meters. Our main finding is that for a wide range of excitation amplitudes the energy spectrum has a power-law scaling, $E_\\omega \\sim \\omega^{-\
Flavor evolution of supernova neutrinos in turbulent matter
International Nuclear Information System (INIS)
The neutrino signal from the next galactic supernova carries with it an enormous amount of information on the explosion mechanism of a core-collapse supernova, as well as on the stellar progenitor and on the neutrinos themselves. In order to extract this information we need to know how the neutrino flavor evolves over time due to the interplay of neutrino self-interactions and matter effects. Additional turbulence in the supernova matter may impart its own signatures on the neutrino spectrum, and could partly obscure the imprints of collective and matter effects. We investigate the neutrino flavor evolution due to neutrino self-interactions, matter effects due to the shock wave propagation, and turbulence in three progenitors with masses of 8.8 M⊙, 10.8 M⊙ and 18.0 M⊙. In the lightest progenitor we find that the impact of moderate turbulence of the order 10% is limited and occurs only briefly early on. This makes the signatures of collective and matter interactions relatively straightforward to interpret. Similarly, with moderate turbulence the two heavier progenitors exhibit only minor changes in the neutrino spectrum, and collective and matter signatures persists. However, when the turbulence is increased to 30% and 50% the high density matter resonance features in the neutrino spectrum get obscured, while new features arise in the low density resonance channel and in the non-resonant channels. We conclude that with moderate amounts of turbulence spectral features of collective and matter interactions survive in all three progenitors. For the larger amounts of turbulence in the 10.8 M⊙ and 18.0 M⊙ progenitor new features arise, as others disappear
Arbitrary Phase Vocoders by means of Warping
Directory of Open Access Journals (Sweden)
Gianpaolo Evangelista
2013-08-01
duration and/or frequency dependent bandwidth. As an example, in a constant Q frequency band allocation, the ratios of center band frequencies over bandwidth remains constant, so that the frequency bands become wider and wider as center frequency increases, similarly to the frequency distance of 12-tone scale notes or of octaves.While time-frequency allocation can be performed in an arbitrary way, the ability to reconstruct the original signal from Vocoder analysis data is essential in sound processing and transformation applications. Moreover, even the analysis or the production of spectrograms benefits from the perfect reconstruction property if one needs to be confident that no important information is hidden, which serves to completely describe the signal.
Nonlinear Flow Generation By Electrostatic Turbulence In Tokamaks
Energy Technology Data Exchange (ETDEWEB)
Wang, W. X.; Diamond, P. H.; Hahm, T. S.; Ethier, S.; Rewoldt, G.; Tang, W. M.
2010-07-07
Global gyrokinetic simulations have revealed an important nonlinear flow generation process due to the residual stress produced by electrostatic turbulence of ion temperature gradient (ITG) modes and trapped electron modes (TEM). In collisionless TEM (CTEM) turbulence, nonlinear residual stress generation by both the fluctuation intensity and the intensity gradient in the presence of broken symmetry in the parallel wave number spectrum is identified for the first time. Concerning the origin of the symmetry breaking, turbulence self-generated low frequency zonal flow shear has been identified to be a key, universal mechanism in various turbulence regimes. Simulations reported here also indicate the existence of other mechanisms beyond E × B shear. The ITG turbulence driven “intrinsic” torque associated with residual stress is shown to increase close to linearly with the ion temperature gradient, in qualitative agreement with experimental observations in various devices. In CTEM dominated regimes, a net toroidal rotation is driven in the cocurrent direction by “intrinsic” torque, consistent with the experimental trend of observed intrinsic rotation. The finding of a “flow pinch” in CTEM turbulence may offer an interesting new insight into the underlying dynamics governing the radial penetration of modulated flows in perturbation experiments. Finally, simulations also reveal highly distinct phase space structures between CTEM and ITG turbulence driven momentum, energy and particle fluxes, elucidating the roles of resonant and non-resonant particles.
Renormalization Group Analysis of Weakly Rotating Turbulent Flows
Institute of Scientific and Technical Information of China (English)
王晓宏; 周全
2011-01-01
Dynamic renormalization group (RNG) analysis is applied to the investigation of the behavior of the infrared limits of weakly rotating turbulence. For turbulent How subject to weak rotation, the anisotropic part in the renormalized propagation is considered to be a perturbation of the isotropic part. Then, with a low-order approximation, the coarsening procedure of RNG transformation is performed. After implementing the coarsening and rescaling procedures, the RNG analysis suggests that the spherically averaged energy spectrum has the scaling behavior E(k) ∝ k11/5 for weakly rotating turbulence. It is also shown that the Coriolis force will disturb the stability of the Kolmogorov -5/3 energy spectrum and will change the scaling behavior even in the case of weak rotation.%Dynamic renormalization group(RNG)analysis is applied to the investigation of the behavior of the infrared limits of weakly rotating turbulence.For turbulent flow subject to weak rotation,the anisotropic part in the renormalized propagation is considered to be a perturbation of the isotropic part.Then,with a low-order approximation,the coarsening procedure of RNG transformation is performed.After implementing the coarsening and rescaling procedures,the RNG analysis suggests that the spherically averaged energy spectrum has the scaling behavior E(k)∝ k-11/5 for weakly rotating turbulence.It is also shown that the Coriolis force will disturb the stability of the Kolmogorov-5/3 energy spectrum and will change the scaling behavior even in the case of weak rotation.
Che, H.; Goldstein, M. L.; Vinas, A. F.
2014-01-01
The observed steep kinetic scale turbulence spectrum in the solar wind raises the question of how that turbulence originates. Observations of keV energetic electrons during solar quiet time suggest them as a possible source of free energy to drive kinetic turbulence. Using particle-in-cell simulations, we explore how the free energy released by an electron two-stream instability drives Weibel-like electromagnetic waves that excite wave-wave interactions. Consequently, both kinetic Alfvénic and whistler turbulence are excited that evolve through inverse and forward magnetic energy cascades.
Cosmic-ray pitch-angle scattering in imbalanced MHD turbulence simulations
Weidl, Martin S; Teaca, Bogdan; Schlickeiser, Reinhard
2015-01-01
Pitch-angle scattering rates for cosmic-ray particles in magnetohydrodynamic (MHD) simulations with imbalanced turbulence are calculated for fully evolving electromagnetic turbulence. We compare with theoretical predictions derived from the quasilinear theory of cosmic-ray diffusion for an idealized slab spectrum and demonstrate how cross helicity affects the shape of the pitch-angle diffusion coefficient. Additional simulations in evolving magnetic fields or static field configurations provide evidence that the scattering anisotropy in imbalanced turbulence is not primarily due to coherence with propagating Alfven waves, but an effect of the spatial structure of electric fields in cross-helical MHD turbulence.
Integrable turbulence and formation of rogue waves
Agafontsev, D S
2014-01-01
In the framework of the focusing Nonlinear Schrodinger (NLS) equation we study numerically the nonlinear stage of the modulation instability (MI) of the condensate. As expected, the development of the MI leads to formation of "integrable turbulence" [V.E. Zakharov, Turbulence in integrable systems, Stud. in Appl. Math. 122, no. 3, 219-234, (2009)]. We study the time evolution of it's major characteristics averaged across realizations of initial data - the condensate solution seeded by small random noise with fixed statistical properties. The measured quantities are: (1) wave-action spectrum and spatial correlation function, (2) the probability density function (PDF) of wave amplitudes and their momenta, and (3) kinetic and potential energies.
Imbalanced magnetohydrodynamic turbulence modified by velocity shear in the solar wind
Gogoberidze, Grigol
2016-01-01
We study incompressible imbalanced magnetohydrodynamic turbulence in the presence of background velocity shears. Using scaling arguments, we show that the turbulent cascade is significantly accelerated when the background velocity shear is stronger than the velocity shears in the subdominant Alfv% \\'{e}n waves at the injection scale. The spectral transport is then controlled by the background shear rather than the turbulent shears and the Tchen spectrum with spectral index $-1$ is formed. This spectrum extends from the injection scale to the scale of the spectral break where the subdominant wave shear becomes equal to the background shear. The estimated spectral breaks and power spectra are in good agreement with those observed in the fast solar wind. The proposed mechanism can contribute to enhanced turbulent cascades and modified $-1$ spectra observed in the fast solar wind with strong velocity shears. This mechanism can also operate in many other astrophysical environments where turbulence develops on top ...
Imbalanced magnetohydrodynamic turbulence modified by velocity shear in the solar wind
Gogoberidze, G.; Voitenko, Y. M.
2016-11-01
We study incompressible imbalanced magnetohydrodynamic turbulence in the presence of background velocity shears. Using scaling arguments, we show that the turbulent cascade is significantly accelerated when the background velocity shear is stronger than the velocity shears in the subdominant Alfvén waves at the injection scale. The spectral transport is then controlled by the background shear rather than the turbulent shears and the Tchen spectrum with spectral index -1 is formed. This spectrum extends from the injection scale to the scale of the spectral break where the subdominant wave shear becomes equal to the background shear. The estimated spectral breaks and power spectra are in good agreement with those observed in the fast solar wind. The proposed mechanism can contribute to enhanced turbulent cascades and modified -1 spectra observed in the fast solar wind with strong velocity shears. This mechanism can also operate in many other astrophysical environments where turbulence develops on top of non-uniform plasma flows.
Symmetric finite volume schemes for eigenvalue problems in arbitrary dimensions
Institute of Scientific and Technical Information of China (English)
DAI Xiaoying; YANG Zhang; ZHOU Aihui
2008-01-01
Based on a linear finite element space, two symmetric finite volume schemes for eigenvalue problems in arbitrary dimensions are constructed and analyzed. Some relationships between the finite element method and the finite difference method are addressed, too.
Symmetric finite volume schemes for eigenvalue problems in arbitrary dimensions
Institute of Scientific and Technical Information of China (English)
2008-01-01
Based on a linear finite element space,two symmetric finite volume schemes for eigenvalue problems in arbitrary dimensions are constructed and analyzed.Some relationships between the finite element method and the finite difference method are addressed,too.
ON QUADRATURE FORMULAE FOR SINGULAR INTEGRALS OF ARBITRARY ORDER
Institute of Scientific and Technical Information of China (English)
杜金元
2004-01-01
Some quadrature formulae for the numerical evaluation of singular integrals of arbitrary order are established and both the estimate of remainder and the convergence of each quadrature formula derived here are also given.
Arbitrary orbital angular momentum addition in second harmonic generation
International Nuclear Information System (INIS)
We demonstrate second harmonic generation performed with optical vortices with different topological charges imprinted on orthogonal polarizations. Besides the intuitive charge doubling, we implement arbitrary topological charge addition on the second harmonic field using polarization as an auxiliary parameter. (paper)
Novel FBG Writing System With Arbitrary Amplitude and Phase Control
Institute of Scientific and Technical Information of China (English)
J.J.; Pan; Claire; Gu; Albert; Li; Henry; He
2003-01-01
FBGs with arbitrary apodization and phase have been fabricated by constantly moving fibers with a highly precision air bearing translation stage while a CW UV laser beam is switched on/off by triggers with nanosecond accuracy.
Turbulence and Fossil Turbulence in Oceans and Lakes
Institute of Scientific and Technical Information of China (English)
Pak-Tao Leung; Carl H. Gibson
2004-01-01
Turbulence is defined as an eddy-like state of fluid motion where the inertial-vortex forces of the eddies are larger than any of the other forces that tend to damp the eddies out. Energy cascades of irrotational flows from large scales to small are non-turbulent, even if they supply energy to turbulence. Turbulent flows are rotational and cascade from small scales to large, with feedback. Viscous forces limit the smallest turbulent eddy size to the Kolmogorov scale. In stratified fluids, buoyancy forces limit large vertical overturns to the Ozmidov scale and convert the largest turbulent eddies into a unique class of saturated, non-propagating, internal waves, termed fossil-vorticity-turbulence. These waves have the same energy but different properties and spectral forms than the original turbulence patch. The Gibson (1980, 1986) theory of fossil turbulence applies universal similarity theories of turbulence and turbulent mixing to the vertical evolution of an isolated patch of turbulence in a stratified fluid as its growth is constrained and fossilized by buoyancy forces. Quantitative hydrodynamic-phase-diagrams (HPDs) from the theory are used to classify microstructure patches according to their hydrodynamic states. When analyzed in HPD space, previously published oceanic datasets showed their dominant microstructure patches are fossilized at large scales in all layers. Laboratory and field measurements suggested phytoplankton species with different swimming abilities adjust their growth strategies by pattern recognition of turbulence-fossil-turbulence dissipation and persistence times that predict survival-relevant surface layer sea changes. New data collected near a Honolulu waste-water outfall showed the small-to-large evolution of oceanic turbulence microstructure from active to fossil states, and revealed the ability of fossil-density-turbulence patches to absorb, and vertically radiate, internal wave energy, information, and enhanced turbulent
Wave turbulence in shallow water models.
Clark di Leoni, P; Cobelli, P J; Mininni, P D
2014-06-01
We study wave turbulence in shallow water flows in numerical simulations using two different approximations: the shallow water model and the Boussinesq model with weak dispersion. The equations for both models were solved using periodic grids with up to 2048{2} points. In all simulations, the Froude number varies between 0.015 and 0.05, while the Reynolds number and level of dispersion are varied in a broader range to span different regimes. In all cases, most of the energy in the system remains in the waves, even after integrating the system for very long times. For shallow flows, nonlinear waves are nondispersive and the spectrum of potential energy is compatible with ∼k{-2} scaling. For deeper (Boussinesq) flows, the nonlinear dispersion relation as directly measured from the wave and frequency spectrum (calculated independently) shows signatures of dispersion, and the spectrum of potential energy is compatible with predictions of weak turbulence theory, ∼k{-4/3}. In this latter case, the nonlinear dispersion relation differs from the linear one and has two branches, which we explain with a simple qualitative argument. Finally, we study probability density functions of the surface height and find that in all cases the distributions are asymmetric. The probability density function can be approximated by a skewed normal distribution as well as by a Tayfun distribution. PMID:25019897
Wave turbulence in shallow water models
di Leoni, P Clark; Mininni, P D
2013-01-01
We study wave turbulence in shallow water flows in numerical simulations using two different approximations: the shallow water model, and the Boussinesq model with weak dispersion. The equations for both models were solved using periodic grids up to $2048^2$ points. In all simulations, the Froude number varies between 0.05 and 0.015, while the Reynolds number and level of dispersion are varied to span different regimes. In all cases, most of the energy in the system remains in the waves, even after integrating the system for very long times. For shallow flows, non-linear waves are non-dispersive and the spectrum of potential energy is compatible with $k^{-2}$ scaling. For deeper (Boussinesq) flows, the non-linear dispersion relation as directly measured from the wave and frequency spectrum (each calculated independently) shows signatures of dispersion, and the spectrum of potential energy is compatible with predictions of weak turbulence theory, $k^{-4/3}$ In this later case, the non-linear dispersion relatio...
Directory of Open Access Journals (Sweden)
V. Carbone
Full Text Available Some signed measures in turbulence are found to be sign-singular, that is their sign reverses continuously on arbitrary finer scales with a reduction of the cancellation between positive and negative contributions. The strength of the singularity is characterized by a scaling exponent κ, the cancellation exponent. In the present study by using some turbulent samples of the velocity field obtained from spacecraft measurements in the interplanetary medium, we show that sign-singularity is present everywhere in low-frequency turbulent samples. The cancellation exponent can be related to the characteristic scaling laws of turbulence. Differences in the values of κ, calculated in both high- and low-speed streams, allow us to outline some physical differences in the samples with different velocities.
Sunrise: Polychromatic Dust Radiative Transfer in Arbitrary Geometries
Jonsson, Patrik
2006-01-01
This paper describes Sunrise, a parallel, free Monte-Carlo code for the calculation of radiation transfer through astronomical dust. Sunrise uses an adaptive-mesh refinement grid to describe arbitrary geometries of emitting and absorbing/scattering media, with spatial dynamical range exceeding 10^4, and it can efficiently generate images of the emerging radiation at arbitrary points in space. In addition to the monochromatic radiative transfer typically used by Monte-Carlo codes, Sunrise is c...
Closed description of arbitrariness in resolving quantum master equation
Batalin, Igor A.; Lavrov, Peter M.
2016-07-01
In the most general case of the Delta exact operator valued generators constructed of an arbitrary Fermion operator, we present a closed solution for the transformed master action in terms of the original master action in the closed form of the corresponding path integral. We show in detail how that path integral reduces to the known result in the case of being the Delta exact generators constructed of an arbitrary Fermion function.
Closed description of arbitrariness in resolving quantum master equation
Directory of Open Access Journals (Sweden)
Igor A. Batalin
2016-07-01
Full Text Available In the most general case of the Delta exact operator valued generators constructed of an arbitrary Fermion operator, we present a closed solution for the transformed master action in terms of the original master action in the closed form of the corresponding path integral. We show in detail how that path integral reduces to the known result in the case of being the Delta exact generators constructed of an arbitrary Fermion function.
Spread of arbitrary conventions among chimpanzees: a controlled experiment
Bonnie, Kristin E.; Horner, Victoria; Whiten, Andrew; de Waal, Frans B. M.
2006-01-01
Wild chimpanzees (Pan troglodytes) have a rich cultural repertoire—traditions common in some communities are not present in others. The majority of reports describe functional, material traditions, such as tool use. Arbitrary conventions have received far less attention. In the same way that observations of material culture in wild apes led to experiments to confirm social transmission and identify underlying learning mechanisms, experiments investigating how arbitrary habits or conventions a...
SOME SMALL DEVIATION THEOREMS FOR ARBITRARY CONTINUOUS RANDOM SEQUENCE
Institute of Scientific and Technical Information of China (English)
Wang Zhongzhi
2007-01-01
Let (Xn)n∈N be a sequence of arbitrary continuous random variables, by the notion of relative entropy h(μ)μ(ω) as a measure of dissimilarity between probability measure μ and reference measure (μ), the explicit, general bounds for the partial sums of arbitrary continuous random variables under suitable conditions are developed. The argument uses the known and elementary lemma of convergence for likelihood ratio.
CMOS circuits generating arbitrary chaos by using pulsewidthmodulation techniques
Morie, Takashi; Sakabayashi, S; Nagata, M.; Iwata, A
2000-01-01
This paper describes CMOS circuits generating arbitrary chaotic signals. The proposed circuits implement discrete-time continuous-state dynamics by means of analog processing in a time domain. Arbitrary nonlinear transformation functions can be generated by using the conversion from an analog voltage to a pulsewidth modulation (PWM) signal; for the transformation, time-domain nonlinear voltage waveforms having the same shape as the inverse function of the desired transformation function are u...
Experimental characterization of turbulent superfluid helium
Paoletti, Matthew S.
Fundamental processes in turbulent superfluid 4He are experimentally characterized by refining a visualization technique recently introduced by Bewley et al.. A mixture of hydrogen and helium gas is injected into the bulk fluid, which produces a distribution of micron-sized hydrogen tracer particles that are visualized and individually tracked allowing for local velocity measurements. Tracer trajectories are complex since some become trapped on the quantized vortices while others flow with the normal fluid. This technique is first applied to study the dynamics of a thermal counterflow. The resulting observations constitute the first direct confirmation of two-fluid motions in He II and provide a quantitative test of the expression for the dependence of the normal fluid velocity, vn, on the applied heat flux, q, derived by L. D. Landau in 1941. Nearly 20,000 individual reconnection events are identified for the first time and used to characterize the dynamics by the minimum separation distance, delta( t), between two reconnecting vortices. Dimensional arguments predict that this separation behaves asymptotically as delta(t) ≈ A(kappa∣t -- t0∣) 1/2, where kappa = h/m is the quantum of circulation. The major finding of the experiments is strong support for this asymptotic form with kappa as the dominant controlling quantity. Nevertheless there are significant event-to-event fluctuations that are equally well fit by two modified expressions: (a) an arbitrary power-law expression delta( t) = B∣t -- t0∣alpha and (b) a correction-factor expression delta(t) = A(kappa∣t -- t 0)1/2 (1 + c∣t -- t0∣). In light of various physical interpretations we regard the correction-factor expression (b), which attributes the observed deviations from the predicted asymptotic form to fluctuations in the local environment and boundary conditions, as best describing the experimental data. The observed dynamics appear statistically time-reversible, suggesting that an effective
Turbulence as a constrained system
Mendes, A C R; Takakura, F I
2000-01-01
Hydrodynamic turbulence is studied as a constrained system from the point of view of metafluid dynamics. We present a Lagrangian description for this new theory of turbulence inspired from the analogy with electromagnetism. Consequently it is a gauge theory. This new approach to the study of turbulence tends to renew the optimism to solve the difficult problem of turbulence. As a constrained system, turbulence is studied in the Dirac and Faddeev-Jackiw formalisms giving the Dirac brackets. An important result is that we show these brackets are the same in and out of the inertial range, giving the way to quantize turbulence.
The mean velocity profile of near-wall turbulent flow
Kazakov, Kirill A.
2014-01-01
The issue of analytical derivation of the mean velocity profile in a near-wall turbulent flow is revisited in the context of a two-dimensional channel flow. An approach based on the use of dispersion relations for the flow velocity is developed. It is shown that for an incompressible flow conserving vorticity, there exists a decomposition of the velocity field into rotational and potential components, such that the restriction of the former to an arbitrary cross-section of the channel is a fu...
Kakuwa, Jun
2015-01-01
Stochastic acceleration of nonthermal electrons is investigated in the context of hard photon spectra of blazars. It is well known that this acceleration mechanism can produce a hard electron spectrum of $m \\equiv \\partial \\ln n_{\\rm e}(\\gamma)/\\partial \\ln \\gamma = 2$ with the high-energy cutoff, called an ultrarelativistic Maxwellian-like distribution, where $n_{\\rm e}(\\gamma)$ is an electron energy spectrum. We revisit the formation of this characteristic spectrum, considering a particular situation where the electrons are accelerated through gyroresonant interaction with magnetohydrodynamic wave turbulence driven by the turbulent cascade. By solving kinetic equations of the turbulent fields, electrons, and photons emitted via the synchrotron self-Compton (SSC) process, we demonstrate that in the non-test-particle treatment, the formation of a Maxwellian-like distribution is prevented by the damping effect on the turbulent fields due to the electron acceleration, at least unless an extreme parameter value ...
Turbulence and Stochastic Processes
Celani, Antonio; Mazzino, Andrea; Pumir, Alain
sec:08-1In 1931 the monograph Analytical Methods in Probability Theory appeared, in which A.N. Kolmogorov laid the foundations for the modern theory of Markov processes [1]. According to Gnedenko: "In the history of probability theory it is difficult to find other works that changed the established points of view and basic trends in research work in such a decisive way". Ten years later, his article on fully developed turbulence provided the framework within which most, if not all, of the subsequent theoretical investigations have been conducted [2] (see e.g. the review by Biferale et al. in this volume [3]. Remarkably, the greatest advances made in the last few years towards a thorough understanding of turbulence developed from the successful marriage between the theory of stochastic processes and the phenomenology of turbulent transport of scalar fields. In this article we will summarize these recent developments which expose the direct link between the intermittency of transported fields and the statistical properties of particle trajectories advected by the turbulent flow (see also [4], and, for a more thorough review, [5]. We also discuss the perspectives of the Lagrangian approach beyond passive scalars, especially for the modeling of hydrodynamic turbulence.
Turbulence Visualization at the Terascale on Desktop PCs
Treib, M.
2012-12-01
Despite the ongoing efforts in turbulence research, the universal properties of the turbulence small-scale structure and the relationships between small-and large-scale turbulent motions are not yet fully understood. The visually guided exploration of turbulence features, including the interactive selection and simultaneous visualization of multiple features, can further progress our understanding of turbulence. Accomplishing this task for flow fields in which the full turbulence spectrum is well resolved is challenging on desktop computers. This is due to the extreme resolution of such fields, requiring memory and bandwidth capacities going beyond what is currently available. To overcome these limitations, we present a GPU system for feature-based turbulence visualization that works on a compressed flow field representation. We use a wavelet-based compression scheme including run-length and entropy encoding, which can be decoded on the GPU and embedded into brick-based volume ray-casting. This enables a drastic reduction of the data to be streamed from disk to GPU memory. Our system derives turbulence properties directly from the velocity gradient tensor, and it either renders these properties in turn or generates and renders scalar feature volumes. The quality and efficiency of the system is demonstrated in the visualization of two unsteady turbulence simulations, each comprising a spatio-temporal resolution of 10244. On a desktop computer, the system can visualize each time step in 5 seconds, and it achieves about three times this rate for the visualization of a scalar feature volume. © 1995-2012 IEEE.
Wind speed power spectrum analysis for Bushland, Texas
Energy Technology Data Exchange (ETDEWEB)
Eggleston, E.D. [USDA-Agricultural Research Service, Bushland, TX (United States)
1996-12-31
Numerous papers and publications on wind turbulence have referenced the wind speed spectrum presented by Isaac Van der Hoven in his article entitled Power Spectrum of Horizontal Wind Speed Spectrum in the Frequency Range from 0.0007 to 900 Cycles per Hour. Van der Hoven used data measured at different heights between 91 and 125 meters above the ground, and represented the high frequency end of the spectrum with data from the peak hour of hurricane Connie. These facts suggest we should question the use of his power spectrum in the wind industry. During the USDA - Agricultural Research Service`s investigation of wind/diesel system power storage, using the appropriate wind speed power spectrum became a significant issue. We developed a power spectrum from 13 years of hourly average data, 1 year of 5 minute average data, and 2 particularly gusty day`s 1 second average data all collected at a height of 10 meters. While the general shape is similar to the Van der Hoven spectrum, few of his peaks were found in the Bushland spectrum. While higher average wind speeds tend to suggest higher amplitudes in the high frequency end of the spectrum, this is not always true. Also, the high frequency end of the spectrum is not accurately described by simple wind statistics such as standard deviation and turbulence intensity. 2 refs., 5 figs., 1 tab.
Turbulence introduction to theory and applications of turbulent flows
Westerweel, Jerry; Nieuwstadt, Frans T M
2016-01-01
This book provides a general introduction to the topic of turbulent flows. Apart from classical topics in turbulence, attention is also paid to modern topics. After studying this work, the reader will have the basic knowledge to follow current topics on turbulence in scientific literature. The theory is illustrated with a number of examples of applications, such as closure models, numerical simulations and turbulent diffusion, and experimental findings. The work also contains a number of illustrative exercises.
Wave turbulent statistics in non-weak wave turbulence
Yokoyama, Naoto
2011-01-01
In wave turbulence, it has been believed that statistical properties are well described by the weak turbulence theory, in which nonlinear interactions among wavenumbers are assumed to be small. In the weak turbulence theory, separation of linear and nonlinear time scales derived from the weak nonlinearity is also assumed. However, the separation of the time scales is often violated even in weak turbulent systems where the nonlinear interactions are actually weak. To get rid of this inconsiste...
Spectra and structure functions in nonhelical hydromagnetic turbulence
Haugen, N E L; Dobler, W; Haugen, Nils Erland L.; Brandenburg, Axel; Dobler, Wolfgang
2003-01-01
Nonhelical hydromagnetic turbulence without imposed magnetic field is considered. The magnetic field is entirely due to dynamo action. The structure function exponents scale approximately like in nonmagnetic turbulence and follow the She-Leveque scaling for predominantly one-dimensional (tube-like) dissipative structures. Throughout the inertial range the spectral magnetic energy exceeds the kinetic energy by a factor of 2 to 3, and both spectra are approximately parallel. At first glance, the total energy spectrum seems to be close to k^{-3/2}, but there is a strong bottleneck effect and it is suggested that the asymptotic spectrum is k^{-5/3}. This is supported by the value of the second order structure function exponent that is found to be \\zeta_2=0.70, suggesting a k^{-1.70} spectrum.
Reynolds-number dependence of the longitudinal dispersion in turbulent pipe flow.
Hawkins, Christopher; Angheluta, Luiza; Krotkiewski, Marcin; Jamtveit, Bjørn
2016-04-01
In Taylor's theory, the longitudinal dispersion in turbulent pipe flows approaches, on long time scales, a diffusive behavior with a constant diffusivity K_{L}, which depends empirically on the Reynolds number Re. We show that the dependence on Re can be determined from the turbulent energy spectrum. By using the intimate connection between the friction factor and the longitudinal dispersion in wall-bounded turbulence, we predict different asymptotic scaling laws of K_{L}(Re) depending on the different turbulent cascades in two-dimensional turbulence. We also explore numerically the K_{L}(Re) dependence in turbulent channel flows with smooth and rough walls using a lattice Boltzmann method. PMID:27176402
Neutrino oscillations in a turbulent plasma
Energy Technology Data Exchange (ETDEWEB)
Mendonça, J. T. [Instituto de Física, Universidade de São Paulo, São Paulo, SP, CEP 05508-090 Brazil and IPFN, Instituto Superior Técnico, 1049-001 Lisboa (Portugal); Haas, F. [Departamento de Física, Universidade Federal do Paraná, Curitiba PR, CEP 81531-990 (Brazil)
2013-07-15
A new model for the joint neutrino flavor and plasma oscillations is introduced, in terms of the dynamics of the neutrino flavor polarization vector in a plasma background. Fundamental solutions are found for both time-invariant and time-dependent media, considering slow and fast variations of the electron plasma density. The model is shown to be described by a generalized Hamiltonian formalism. In the case of a broad spectrum of electron plasma waves, a statistical approach indicates the shift of both equilibrium value and frequency oscillation of flavor coherence, due to the existence of a turbulent plasma background.
Turbulence and Fossil Turbulence in Oceans and Lakes
Leung, P T; Leung, Pak Tao; Gibson, Carl H.
2003-01-01
Turbulence is defined as an eddy-like state of fluid motion where the inertial-vortex forces of the eddies are larger than any of the other forces that tend to damp the eddies out. Energy cascades of irrotational flows from large scales to small are non-turbulent, even if they supply energy to turbulence. Turbulent flows are rotational and cascade from small scales to large, with feedback. Viscous forces limit the smallest turbulent eddy size to the Kolmogorov scale. In stratified fluids, buoyancy forces limit large vertical overturns to the Ozmidov scale and convert the largest turbulent eddies into a unique class of saturated, non-propagating, internal waves, termed fossil-vorticity-turbulence. These waves have the same energy but different properties and spectral forms than the original turbulence patch. The Gibson (1980, 1986) theory of fossil turbulence applies universal similarity theories of turbulence and turbulent mixing to the vertical evolution of an isolated patch of turbulence in a stratified flu...
Yang, Huan; Zimmerman, Aaron; Lehner, Luis
2015-02-27
We demonstrate that rapidly spinning black holes can display a new type of nonlinear parametric instability-which is triggered above a certain perturbation amplitude threshold-akin to the onset of turbulence, with possibly observable consequences. This instability transfers from higher temporal and azimuthal spatial frequencies to lower frequencies-a phenomenon reminiscent of the inverse cascade displayed by (2+1)-dimensional fluids. Our finding provides evidence for the onset of transitory turbulence in astrophysical black holes and predicts observable signatures in black hole binaries with high spins. Furthermore, it gives a gravitational description of this behavior which, through the fluid-gravity duality, can potentially shed new light on the remarkable phenomena of turbulence in fluids.
Energy Technology Data Exchange (ETDEWEB)
Mann, Jakob [Risoe National Lab., Wind Energy and Atmosheric Physics Dept., Roskilde (Denmark)
1999-03-01
The purpose of this work is to develop a model of the spectral velocity-tensor in neutral flow over complex terrain. The resulting equations are implemented in a computer code using the mean flow generated by a linear mean flow model as input. It estimates turbulence structure over hills (except on the lee side if recirculation is present) in the so-called outer layer and also models the changes in turbulence statistics in the vicinity roughness changes. The generated turbulence fields are suitable as input for dynamic load calculations on wind turbines and other tall structures and is under implementation in the collection of programs called WA{sup s}P Engineering. (au) EFP-97; EU-JOULE-3. 15 refs.
Yang, Huan; Zimmerman, Aaron; Lehner, Luis
2015-02-27
We demonstrate that rapidly spinning black holes can display a new type of nonlinear parametric instability-which is triggered above a certain perturbation amplitude threshold-akin to the onset of turbulence, with possibly observable consequences. This instability transfers from higher temporal and azimuthal spatial frequencies to lower frequencies-a phenomenon reminiscent of the inverse cascade displayed by (2+1)-dimensional fluids. Our finding provides evidence for the onset of transitory turbulence in astrophysical black holes and predicts observable signatures in black hole binaries with high spins. Furthermore, it gives a gravitational description of this behavior which, through the fluid-gravity duality, can potentially shed new light on the remarkable phenomena of turbulence in fluids. PMID:25768746
Stochastic modelling of turbulence
DEFF Research Database (Denmark)
Sørensen, Emil Hedevang Lohse
This thesis addresses stochastic modelling of turbulence with applications to wind energy in mind. The primary tool is ambit processes, a recently developed class of computationally tractable stochastic processes based on integration with respect to Lévy bases. The subject of ambit processes...... turbine operates in the turbulent atmospheric boundary layer. In this respect, three regimes are of particular interest: modelling the turbulent wind before it interacts with the wind turbine (e.g. to be used in load simulations), modelling of the interaction of the wind with the wind turbine (e.......g. to extract information about a wind turbine's production of power), and modelling the wake generated by the wind turbine so that its influence on other wind turbines further downstream in turn can be modelled (e.g. to be used in load simulations). The thesis makes the contributions listed below. A spatial...
Magnetic turbulence in Tokamaks
International Nuclear Information System (INIS)
From a discussion of the disruption process, it is concluded that this process plausibly consists of the onset of a fine grain turbulence. This turbulence must be able to produce the large values of the inductive electric field which are associated with the reorganization of the poloidal flux and the current density on the magnetic surfaces. It is then plausible that the turbulence belongs to a class of 'rippling' modes, that may explain the experimental values for the magnetic perturbations corresponding to a substantial radial ergodicity of the flux lines. The stability of the modes in the presence of such an ergodicity is accordingly considered. It is found that the modes may be unstable even in collisionless regime, the ergodicity playing a role similar to the resistivity to partially remove the M.H.D. constraint
Non-Kolmogorov cascade of helicity driven turbulence
Kessar, Mouloud; Stepanov, Rodion; Balarac, Guillaume
2015-01-01
We solve the Navier-Stokes equations with two simultaneous forcings. One forcing is applied at a given large-scale and it injects energy. The other forcing is applied at all scales belonging to the inertial range and it injects helicity. In this way we can vary the degree of turbulence helicity from non helical to maximally helical. We find that increasing the rate of helicity injection does not change the energy flux. On the other hand the level of total energy is strongly increased and the energy spectrum gets steeper. The energy spectrum spans from a Kolmogorov scaling law $k^{-5/3}$ for a non-helical turbulence, to a non-Kolmogorov scaling law $k^{-7/3}$ for a maximally helical turbulence. In the later case we find that the characteristic time of the turbulence is not the turnover time but a time based on the helicity injection rate. We also analyse the results in terms of helical modes decomposition. For a maximally helical turbulence one type of helical mode is found to be much more energetic than the o...
Soliton turbulence in shallow water ocean surface waves.
Costa, Andrea; Osborne, Alfred R; Resio, Donald T; Alessio, Silvia; Chrivì, Elisabetta; Saggese, Enrica; Bellomo, Katinka; Long, Chuck E
2014-09-01
We analyze shallow water wind waves in Currituck Sound, North Carolina and experimentally confirm, for the first time, the presence of soliton turbulence in ocean waves. Soliton turbulence is an exotic form of nonlinear wave motion where low frequency energy may also be viewed as a dense soliton gas, described theoretically by the soliton limit of the Korteweg-deVries equation, a completely integrable soliton system: Hence the phrase "soliton turbulence" is synonymous with "integrable soliton turbulence." For periodic-quasiperiodic boundary conditions the ergodic solutions of Korteweg-deVries are exactly solvable by finite gap theory (FGT), the basis of our data analysis. We find that large amplitude measured wave trains near the energetic peak of a storm have low frequency power spectra that behave as ∼ω-1. We use the linear Fourier transform to estimate this power law from the power spectrum and to filter densely packed soliton wave trains from the data. We apply FGT to determine the soliton spectrum and find that the low frequency ∼ω-1 region is soliton dominated. The solitons have random FGT phases, a soliton random phase approximation, which supports our interpretation of the data as soliton turbulence. From the probability density of the solitons we are able to demonstrate that the solitons are dense in time and highly non-Gaussian. PMID:25238388
MODERN TURBULENCE AND NEW CHALLENGES
Institute of Scientific and Technical Information of China (English)
张兆顺; 崔桂香; 许春晓
2002-01-01
The paper briefly reviews the progress in turbulence research in the 20th century and a number of issues are addressed based on achievements. The modern theory of Navier-Stokes equation provides the theoretical basis for the development of turbulence research. The significance and bottle neck of DNS and the physical experiment in exploring turbulent flows are analyzed. The active manipulation of turbulence is directly guided by the knowledge of large-scale coherent structures. The existing problems in the large-eddy simulation are also pointed out. Scalar turbulence, which behaves quite different from fluid turbulence in many aspects, has drawn much attention in recent years. Besides the analysis of the difficulties in turbulence research, a number of examples are also presented to show how to use modern theory,computer and high technology to explore the nature of turbulence.
Turbulence in the Interstellar Medium
Falceta-Goncalves, D; Falgarone, E; Chian, A C -L
2014-01-01
Turbulence is ubiquitous in the insterstellar medium and plays a major role in several processes such as the formation of dense structures and stars, the stability of molecular clouds, the amplification of magnetic fields, and the re-acceleration and diffusion of cosmic rays. Despite its importance, interstellar turbulence, alike turbulence in general, is far from being fully understood. In this review we present the basics of turbulence physics, focusing on the statistics of its structure and energy cascade. We explore the physics of compressible and incompressible turbulent flows, as well as magnetized cases. The most relevant observational techniques that provide quantitative insights of interstellar turbulence are also presented. We also discuss the main difficulties in developing a three-dimensional view of interstellar turbulence from these observations. Finally, we briefly present what could be the the main sources of turbulence in the interstellar medium.
Bloch, F.; Staub, H.
1943-08-18
Measurements of the spectrum of the fission neutrons of 25 are described, in which the energy of the neutrons is determined from the ionization produced by individual hydrogen recoils. The slow neutrons producing fission are obtained by slowing down the fast neutrons from the Be-D reaction of the Stanford cyclotron. In order to distinguish between fission neutrons and the remaining fast cyclotron neutrons both the cyclotron current and the pusle amplifier are modulated. A hollow neutron container, in which slow neutrons have a lifetime of about 2 milliseconds, avoids the use of large distances. This method results in much higher intensities than the usual modulation arrangement. The results show a continuous distribution of neutrons with a rather wide maximum at about 0.8 MV falling off to half of its maximum value at 2.0 MV. The total number of netrons is determined by comparison with the number of fission fragments. The result seems to indicate that only about 30% of the neutrons have energies below .8 MV. Various tests are described which were performed in order to rule out modification of the spectrum by inelastic scattering. Decl. May 4, 1951
Turbulence Measurements in Swirling Flows
Directory of Open Access Journals (Sweden)
V. M. Domkundwar
1981-10-01
Full Text Available Investigation have been conducted to find out the region of high turbulent intensities in a swirling jet passing through a divergent passage. A hot wire anemometer is used to measure the turbulence intensity using a four position method. It has been concluded that the jet spreads with increasing diffuser angle and the region of high turbulent intensity also spreads. The high turbulence intensity region lies around the recirculation zone and it decays rapidly along the main flow direction.
Direct numerical simulations of gravity-capillary wave turbulence
Deike, Luc; Fuster, Daniel; Berhanu, Michael; Falcon, Eric
2012-11-01
Direct numerical simulation of the full two phase Navier-Stokes equations, including surface tension are performed, using the code Gerris (Popinet, 2009), in order to investigate gravity-capillary wave turbulence. Wave turbulence concerns the study of the statistical and dynamical properties of a set of nonlinear interacting waves (Zakharov, 1992). Waves at the air-water interface, initially at rest, are excited at low wave-numbers and a stationary wave turbulence state is obtained after a time long enough (typically 30 periods of the wave forcing period). The space-time wave height power spectrum is calculated for both capillary and gravity waves regimes. The observed dispersion relation is in agreement with the theoretical one for linear gravity-capillary wave. The wave height power spectrum in the wave-number-space or in the frequency-space exhibit a power law and will be discussed with respects of weak turbulence theory (Zakharov, 2012). Finally the scaling of the spectrum with the injected power will be compared with theoretical and experimental works.
Zilberman, Arkadi; Golbraikh, Ephim; Kopeika, Norman S
2008-12-01
Turbulence properties of communication links (optical and microwave) in terms of log-amplitude variance are studied on the basis of a three-layer model of refractive index fluctuation spectrum in the free atmosphere. We suggest a model of turbulence spectra (Kolmogorov and non-Kolmogorov) changing with altitude on the basis of obtained experimental and theoretical data for turbulence profile in the troposphere and lower stratosphere.
An overview of turbulence compensation
Schutte, K.; Eekeren, A.W.M. van; Dijk, J.; Schwering, P.B.W.; Iersel, M. van; Doelman, N.J.
2012-01-01
In general, long range visual detection, recognition and identification are hampered by turbulence caused by atmospheric conditions. Much research has been devoted to the field of turbulence compensation. One of the main advantages of turbulence compensation is that it enables visual identification
Spectral properties of decaying turbulence in electron magnetohydrodynamics
International Nuclear Information System (INIS)
The spectral properties of decaying turbulence in 2(1/2)-dimensional electron magnetohydrodynamics are studied numerically. In the range kde-7/3 and k-13/3, respectively. The self-similar decay state of the turbulence is reached after an initial phase of fast exchange between the axial and poloidal magnetic energies. The time behavior t-2/3 of the total energy is found to be consistent with that obtained from selective decay. The maximum of the energy spectrum shifts towards low mode numbers and decays in time as t-1, in agreement with the infrared scaling of the turbulence. In the large de limit, both energy and mean square generalized momentum exhibit direct cascades. No stationary turbulent state could be found as long as the axial kinetic energy is large as compared to the poloidal kinetic energy initially. The global physical quantities decay well before turbulent macroscopic quantities have established similar space-time behavior, and the turbulence is infected by the lack of stationarity. The system decouples into a Navier-Stokes equation and a passive scalar equation only if the poloidal kinetic energy is larger than or equal to the axial kinetic energy. In this limit the k-5/3 and k-3 spectra of the poloidal kinetic energy are recovered
A Model for the Saturation of the Turbulent Dynamo
Schober, Jennifer; Federrath, Christoph; Bovino, Stefano; Klessen, Ralf S
2015-01-01
The origin of strong magnetic fields in the Universe can be explained by amplifying weak seed fields via turbulent motions on small spatial scales and subsequently transporting the magnetic energy to larger scales. This process is known as the turbulent dynamo and depends on the properties of turbulence, i.e. on the hydrodynamical Reynolds number and the compressibility of the gas, and on the magnetic diffusivity. While we know the growth rate the magnetic energy in the linear regime, the saturation level, i.e. the ratio of magnetic energy to turbulent kinetic energy that can be reached, is not known from analytical calculations. In this paper we present the first scale-dependent saturation model based on an effective turbulent resistivity which is determined by the turnover timescale of turbulent eddies and the magnetic energy density. The magnetic resistivity increases compared to the Spitzer value and the effective scale on which the magnetic energy spectrum is at its maximum moves to larger spatial scales...
Freely Decaying Weak Turbulence for Sea Surface Gravity Waves
Onorato, M.; Osborne, A. R.; Serio, M.; Resio, D.; Pushkarev, A.; Zakharov, V. E.; Brandini, C.
2002-09-01
We study the long-time evolution of deep-water ocean surface waves in order to better understand the behavior of the nonlinear interaction processes that need to be accurately predicted in numerical models of wind-generated ocean surface waves. Of particular interest are those nonlinear interactions which are predicted by weak turbulence theory to result in a wave energy spectrum of the form of |k|-2.5. We numerically implement the primitive Euler equations for surface waves and demonstrate agreement between weak turbulence theory and the numerical results.
Relativistic particle acceleration in developing Alfv\\'{e}n turbulence
Matsukiyo, S; 10.1088/0004-637X/692/2/1004
2009-01-01
A new particle acceleration process in a developing Alfv\\'{e}n turbulence in the course of successive parametric instabilities of a relativistic pair plasma is investigated by utilyzing one-dimensional electromagnetic full particle code. Coherent wave-particle interactions result in efficient particle acceleration leading to a power-law like energy distribution function. In the simulation high energy particles having large relativistic masses are preferentially accelerated as the turbulence spectrum evolves in time. Main acceleration mechanism is simultaneous relativistic resonance between a particle and two different waves. An analytical expression of maximum attainable energy in such wave-particle interactions is derived.
Classes of hydrodynamic and magnetohydrodynamic turbulent decay
Brandenburg, Axel
2016-01-01
We perform numerical simulations of decaying hydrodynamic and magnetohydrodynamic turbulence. We classify our time-dependent solutions by their evolutionary tracks in parametric plots between instantaneous scaling exponents. We find distinct classes of solutions evolving along specific trajectories toward points on a line of self-similar solutions. These trajectories are determined by the underlying physics governing individual cases, and not by the initial conditions, as is widely assumed. In the helical case, even for a scale-invariant initial spectrum (inversely proportional to wavenumber k), the solution evolves along the same trajectory as for a Batchelor spectrum (proportional to k^4). All of our self-similar solutions have an intrinsic subinertial range close to k^4$.
DEFF Research Database (Denmark)
Henten, Anders; Tadayoni, Reza; Windekilde, Iwona Maria
The digital dividend discussion represents an obvious conflict of interest between on the one hand the traditional broadcasters and market players from other mobile communication sectors and on the other hand between the stake holders within the mobile communication sector. The first one being...... communications sector, including commercial mobile operators and the stake holders representing specific uses like Public Safety and Emergency (PSE), Intelligent Traffic System (ITS), etc in getting access to these resources. The paper gives an analysis of the digital dividend and discusses relevant new...... a conflict in accessing to the valuable spectrum resources allocated to TV broadcast that has been there for many years and which has been intensified in different phases of technological development and the second being an obvious conflict of interest between the different stake holders within the mobile...
Wave turbulent statistics in non-weak wave turbulence
International Nuclear Information System (INIS)
In wave turbulence, which is made by nonlinear interactions among waves, it has been believed that statistical properties are well described by the weak turbulence theory, where separation of linear and nonlinear time scales derived from weak nonlinearity is assumed. However, the separation of the time scales is often violated. To get rid of this inconsistency, closed equations are derived in wave turbulence without assuming the weak nonlinearity according to Direct-Interaction Approximation (DIA), which has been successful in Navier–Stokes turbulence. The DIA equations is a natural extension of the conventional kinetic equation to not-necessarily-weak wave turbulence. -- Highlights: ► Direct-Interaction Approximation is applied to wave turbulence. ► The DIA equations describe non-weak wave turbulent statistics. ► They can be applied to spatio-temporal intermittent structures. ► The conventional kinetic equation is recoverable in the weak nonlinear limit.
Multilevel turbulence simulations
Energy Technology Data Exchange (ETDEWEB)
Tziperman, E. [Princeton Univ., NJ (United States)
1994-12-31
The authors propose a novel method for the simulation of turbulent flows, that is motivated by and based on the Multigrid (MG) formalism. The method, called Multilevel Turbulence Simulations (MTS), is potentially more efficient and more accurate than LES. In many physical problems one is interested in the effects of the small scales on the larger ones, or in a typical realization of the flow, and not in the detailed time history of each small scale feature. MTS takes advantage of the fact that the detailed simulation of small scales is not needed at all times, in order to make the calculation significantly more efficient, while accurately accounting for the effects of the small scales on the larger scale of interest. In MTS, models of several resolutions are used to represent the turbulent flow. The model equations in each coarse level incorporate a closure term roughly corresponding to the tau correction in the MG formalism that accounts for the effects of the unresolvable scales on that grid. The finer resolution grids are used only a small portion of the simulation time in order to evaluate the closure terms for the coarser grids, while the coarse resolution grids are then used to accurately and efficiently calculate the evolution of the larger scales. The methods efficiency relative to direct simulations is of the order of the ratio of required integration time to the smallest eddies turnover time, potentially resulting in orders of magnitude improvement for a large class of turbulence problems.
Veen, van der Roeland Cornelis Adriaan
2016-01-01
In this thesis, several questions related to drop impact and Taylor-Couette turbulence are answered. The deformation of a drop just before impact can cause a bubble to be entrapped. For many applications, such as inkjet printing, it is crucial to control the size of this entrapped bubble. To study t
Spirituality in Turbulent Times.
Wheatley, Margaret J.
2002-01-01
Discusses the importance of spiritual leadership in turbulent, uncertain times. Describes several spiritual principles--for example, life is cyclical; all life is interconnected. Offers six suggestions for personal health: Start day peacefully, learn to be mindful, slow things down, create own measures, expect surprise, practice gratefulness. (PKP)
Analysis of turbulence spectrum in the TBR-1
International Nuclear Information System (INIS)
The fluctuation signals of ion saturation current in plasma edge of the TBR-1 tokamak were measured, using three Langmuir probes aligned to toroidal magnetic field direction, for detecting trapped particle modes in this region. The construction of Langmuir probes is also described. The dispersion relation and respective spectra were obtained using spectral technique developed by Powers et all. The index of spectra decay for high frequencies, as well as radial variation of these index and fluctuation levels, were also determined. (M.C.K.)
Kinematic simulation of turbulent dispersion of triangles.
Khan, M A I; Pumir, A; Vassilicos, J C
2003-08-01
As three particles are advected by a turbulent flow, they separate from each other and develop nontrivial geometries, which effectively reflect the structure of the turbulence. We investigate here the geometry, in a statistical sense, of three Lagrangian particles advected, in two dimensions, by kinematic simulation (KS). KS is a Lagrangian model of turbulent diffusion that makes no use of any delta correlation in time at any level. With this approach, situations with a very large range of inertial scales and varying persistence of spatial flow structure can be studied. We first demonstrate that the model flow reproduces recent experimental results at low Reynolds numbers. The statistical properties of the shape distribution at a much higher Reynolds number is then considered. The numerical results support the existence of nontrivial shape statistics, with a high probability of having elongated triangles. Even at the highest available inertial range of scales, corresponding to a ratio between large and small scale L/eta=17,000, a perfect self-similar regime is not found. The effects of the parameters of the synthetic flow, such as the exponent of the spectrum and the effect of the sweeping affect our results, are also discussed. Special attention is given to the effects of persistence of spatial flow structure. PMID:14525111
Imbalanced Relativistic Force-Free Magnetohydrodynamic Turbulence
Cho, Jungyeon
2013-01-01
When magnetic energy density is much larger than that of matter, as in pulsar/black hole magnetospheres, the medium becomes force-free and we need relativity to describe it. As in non-relativistic magnetohydrodynamics (MHD), Alfv\\'enic MHD turbulence in the relativistic limit can be described by interactions of counter-traveling wave packets. In this paper we numerically study strong imbalanced MHD turbulence in such environments. Here, imbalanced turbulence means the waves traveling in one direction (dominant waves) have higher amplitudes than the opposite-traveling waves (sub-dominant waves). We find that (1) spectrum of the dominant waves is steeper than that of sub-dominant waves, (2) the anisotropy of the dominant waves is weaker than that of sub-dominant waves, and (3) the dependence of the ratio of magnetic energy densities of dominant and sub-dominant waves on the ratio of energy injection rates is steeper than quadratic (i.e., \\$b_+^2/b_-^2 \\propto (\\epsilon_+/\\epsilon_-)^n \\$ with n>2). These result...
Vortex turbulence in linear Schroedinger wave mechanics
Energy Technology Data Exchange (ETDEWEB)
Chiueh, Tzihong [Department of Physics, National Taiwan University, Taipei 106, Taiwan (China); Woo, Tak-Pong [Center for Theoretical Sciences, National Taiwan University, Taipei 106, Taiwan (China); Jian, Hung-Yu [Center for Quantum Sciences and Engineering, National Taiwan University, Taipei 106, Taiwan (China); Schive, Hsi-Yu, E-mail: chiuehth@phys.ntu.edu.tw, E-mail: bonwood@scu.edu.tw, E-mail: hyj@phys.ntu.edu.tw, E-mail: b88202011@ntu.edu.tw [LeCosPa, National Taiwan University, Taipei 106, Taiwan (China)
2011-06-14
Quantum turbulence that exhibits vortex creation, annihilation and interactions is demonstrated as an exact solution of the time-dependent, free-particle Schroedinger equation evolved from a smooth random-phased initial condition. Relaxed quantum turbulence in 2D and 3D exhibits universal scaling in the steady-state energy spectrum as k{sup -1} in small scales. Due to the lack of dissipation, no evidence of the Kolmogorov-type forward energy cascade in 3D or the inverse energy cascade in 2D is found, but the rotational and potential flow components do approach equi-partition in the scaling regime. In addition, the 3D vortex line-line correlation exhibits universal behaviour, scaled as {Delta}r{sup -2}, where {Delta}r is the separation between any two vortex line elements, in fully developed turbulence. We also show that the quantum vortex is not frozen to the matter, nor is the vortex motion induced by other vortices via Biot-Savart's law. Thus, the quantum vortex is actually a nonlinear wave, propagating at a speed very different from a classical vortex.
Analytical and phenomenological studies of rotating turbulence
Mahalov, Alex; Zhou, YE
1995-01-01
A framework, which combines mathematical analysis, closure theory, and phenomenological treatment, is developed to study the spectral transfer process and reduction of dimensionality in turbulent flows that are subject to rotation. First, we outline a mathematical procedure that is particularly appropriate for problems with two disparate time scales. The approach which is based on the Green's method leads to the Poincare velocity variables and the Poincare transformation when applied to rotating turbulence. The effects of the rotation are now reflected in the modifications to the convolution of a nonlinear term. The Poincare transformed equations are used to obtain a time-dependent analog of the Taylor-Proudman theorem valid in the asymptotic limit when the non-dimensional parameter mu is identical to Omega(t) approaches infinity (Omega is the rotation rate and t is the time). The 'split' of the energy transfer in both direct and inverse directions is established. Secondly, we apply the Eddy-Damped-Quasinormal-Markovian (EDQNM) closure to the Poincare transformed Euler/Navier-Stokes equations. This closure leads to expressions for the spectral energy transfer. In particular, an unique triple velocity decorrelation time is derived with an explicit dependence on the rotation rate. This provides an important input for applying the phenomenological treatment of Zhou. In order to characterize the relative strength of rotation, another non-dimensional number, a spectral Rossby number, which is defined as the ratio of rotation and turbulence time scales, is introduced. Finally, the energy spectrum and the spectral eddy viscosity are deduced.
Slatyer, Tracy R
2015-01-01
Any injection of electromagnetically interacting particles during the cosmic dark ages will lead to increased ionization, heating, production of Lyman-alpha photons and distortions to the energy spectrum of the cosmic microwave background, with potentially observable consequences. In this note we describe numerical results for the low-energy electrons and photons produced by the cooling of particles injected at energies from keV to multi-TeV scales, at arbitrary injection redshifts (but focusing on the post-recombination epoch). We use these data, combined with existing calculations modeling the cooling of these low-energy particles, to estimate the resulting contributions to ionization, excitation and heating of the gas, and production of low-energy photons below the threshold for excitation and ionization. We compute corrected deposition-efficiency curves for annihilating dark matter, and demonstrate how to compute equivalent curves for arbitrary energy-injection histories. These calculations provide the ne...
Analysis of turbulent boundary layers
Cebeci, Tuncer
1974-01-01
Analysis of Turbulent Boundary Layers focuses on turbulent flows meeting the requirements for the boundary-layer or thin-shear-layer approximations. Its approach is devising relatively fundamental, and often subtle, empirical engineering correlations, which are then introduced into various forms of describing equations for final solution. After introducing the topic on turbulence, the book examines the conservation equations for compressible turbulent flows, boundary-layer equations, and general behavior of turbulent boundary layers. The latter chapters describe the CS method for calculati
Remarks on turbulent constitutive relations
Shih, Tsan-Hsing; Lumley, John L.
1993-01-01
The paper demonstrates that the concept of turbulent constitutive relations can be used to construct general models for various turbulent correlations. Some of the Generalized Cayley-Hamilton formulas for relating tensor products of higher extension to tensor products of lower extension are introduced. The combination of dimensional analysis and invariant theory can lead to 'turbulent constitutive relations' (or general turbulence models) for, in principle, any turbulent correlations. As examples, the constitutive relations for Reynolds stresses and scalar fluxes are derived. The results are consistent with ones from Renormalization Group (RNG) theory and two-scale Direct-Interaction Approximation (DIA) method, but with a more general form.
Renormalized perturbation theory: Vlasov-Poisson System, weak turbulence limit and gyrokinetics
International Nuclear Information System (INIS)
The Self-consistency of the renormalized perturbation theory is demonstrated by applying it to the Vlasov-Poisson System and showing that the theory has the correct weak turbulence limit. Energy conservation is proved to arbitrary high order for the electrostatic drift waves. The theory is applied to derive renormalized equations for a low-β gyrokinetic system. Comparison of our theory with other current theories is presented. 22 refs
Self-forces on static bodies in arbitrary dimensions
Harte, Abraham I; Taylor, Peter
2016-01-01
We derive exact expressions for the scalar and electromagnetic self-forces and self-torques acting on arbitrary static extended bodies in arbitrary static spacetimes with any number of dimensions. Non-perturbatively, our results are identical in all dimensions. Meaningful point particle limits are quite different in different dimensions, however. These limits are defined and evaluated, resulting in simple "regularization algorithms" which can be used in concrete calculations. In these limits, self-interaction is shown to be progressively less important in higher numbers of dimensions; it generically competes in magnitude with increasingly high-order extended-body effects. Conversely, we show that self-interaction effects can be relatively large in $1+1$ and $2+1$ dimensions. Our motivations for this work are twofold: First, no previous derivation of the self-force has been provided in arbitrary dimensions, and heuristic arguments presented by different authors have resulted in conflicting conclusions. Second,...
Surface waves on arbitrary vertically-sheared currents
Smeltzer, Benjamin K
2016-01-01
We study dispersion properties of linear surface gravity waves propagating in an arbitrary direction atop a current profile of arbitrary depth-varying magnitude using a piecewise linear approximation, and develop a robust numerical framework for practical calculation. The method has been much used in the past in 2D, and we herein extend and apply it to 3D problems. Being valid for all wavelengths without loss of accuracy, the scheme is particularly well suited to solve problems involving Fourier transformations in the horizontal plane. We examine the group and phase velocities over different wavelength regimes and current profiles, highlighting characteristics due to the depth-variable vorticity. We show an example application to ship waves on an arbitrary current profile, and demonstrate qualitative differences in the wake patterns between a concave down profile when compared to a constant shear profile with equal depth-averaged vorticity. New insight is given concerning the nature of extra spurious solution...
Radio Wave Scintillations and Models of Interstellar Turbulence
Spangler, Steven R.
1998-05-01
There are a number of well-established observational results from radio scintillations which have implications for the nature of interstellar turbulence. Among such results are evidence for anisotropy and a Kolmogorov spectrum for the density irregularities. It is probable the galactic magnetic field organizes these irregularities so that spatial gradients along the field are much less than those perpendicular to the field. Such a behavior for turbulence is predicted by theories of magnetohydrodynamic turbulence in which the amplitude is small. The turbulence is then described by a theory termed reduced magnetohydrodynamics. A limiting case of reduced magnetohydrodynamics is two dimensional magnetohydrodynamics, in which the direction of the large scale magnetic field z defines the ignorable coordinate. Two dimensional magnetohydrodynamics consists of a pair of coupled nonlinear partial differential equations for the velocity stream function psi and the z component of the magnetic vector potential A_z. A number of observed features of interstellar turbulence can be identified with solutions to the equations of two dimensional magnetohydrodynamics. Examples are the development of Kolmogorov-like spectra for the velocity and magnetic field from a wide class (although not totally general) initial conditions, a natural explanation for the formation of intermittancy in turbulence, and the rapid development of small scale, large spatial wavenumber fluctuations, in contrast to the eddy cascade of hydrodynamic turbulence. The equations of two dimensional magnetohydrodynamics may serve as a simple but tractable model of interstellar plasma turbulence that may complement and be superior to the traditional model of an ensemble of magnetohydrodynamic waves.
Static magnetic fields enhance turbulence
Pothérat, Alban
2015-01-01
More often than not, turbulence occurs under the influence of external fields, mostly rotation and magnetic fields generated either by planets, stellar objects or by an industrial environment. Their effect on the anisotropy and the dissipative behaviour of turbulence is recognised but complex, and it is still difficult to even tell whether they enhance or dampen turbulence. For example, externally imposed magnetic fields suppress free turbulence in electrically conducting fluids (Moffatt 1967), and make it two-dimensional (2D) (Sommeria & Moreau 1982); but their effect on the intensity of forced turbulence, as in pipes, convective flows or otherwise, is not clear. We shall prove that since two-dimensionalisation preferentially affects larger scales, these undergo much less dissipation and sustain intense turbulent fluctuations. When higher magnetic fields are imposed, quasi-2D structures retain more kinetic energy, so that rather than suppressing forced turbulence, external magnetic fields indirectly enha...
Laboratory Experiments on Wave Turbulence
Falcon, Eric
2010-01-01
This review paper is devoted to a presentation of recent progress in wave turbulence. I first present the context and state of the art of this field of research both experimentally and theoretically. I then focus on the case of wave turbulence on the surface of a fluid, and I discuss the main results obtained by our group: caracterization of the gravity and capillary wave turbulence regimes, the first observation of intermittency in wave turbulence, the occurrence of strong fluctuations of injected power in the fluid, the observation of a pure capillary wave turbulence in low gravity environment and the observation of magnetic wave turbulence on the surface of a ferrofluid. Finally, open questions in wave turbulence are discussed.
Bisimulation on Markov Processes over Arbitrary Measurable Spaces
DEFF Research Database (Denmark)
Bacci, Giorgio; Bacci, Giovanni; Larsen, Kim Guldstrand;
2014-01-01
We introduce a notion of bisimulation on labelled Markov Processes over generic measurable spaces in terms of arbitrary binary relations. Our notion of bisimulation is proven to coincide with the coalgebraic definition of Aczel and Mendler in terms of the Giry functor, which associates with a mea......We introduce a notion of bisimulation on labelled Markov Processes over generic measurable spaces in terms of arbitrary binary relations. Our notion of bisimulation is proven to coincide with the coalgebraic definition of Aczel and Mendler in terms of the Giry functor, which associates...
Topological flat band models with arbitrary Chern numbers
Yang, Shuo; Gu, Zheng-Cheng; Sun, Kai; Sarma, S. Das
2012-01-01
We report the theoretical discovery of a systematic scheme to produce topological flat bands (TFBs) with arbitrary Chern numbers. We find that generically a multi-orbital high Chern number TFB model can be constructed by considering multi-layer Chern number C=1 TFB models with enhanced translational symmetry. A series of models are presented as examples, including a two-band model on a triangular lattice with a Chern number C=3 and an $N$-band square lattice model with $C=N$ for an arbitrary ...
Probabilistic teleportation of an arbitrary three-particle state
Institute of Scientific and Technical Information of China (English)
Lin Xiu; Li Hong-Cai
2005-01-01
A scheme for teleporting an arbitrary and unknown three-particle state from a sender to either one of two receivers is proposed. The quantum channel is composed of a two-particle non-maximally entangled state and two three-particle non-maximally entangled W states. An arbitrary three-particle state can be perfectly teleported probabilistically if the sender performs three generalized Bell-state measurements and sends to the two receivers the classical result of these measurements, and either one of the two receivers adopts an appropriate unitary transformation conditioned on the suitable measurement outcomes of the other receiver. All kinds of unitary transformations are given in detail.
Probabilistic teleportation of an arbitrary pure state of two atoms
Institute of Scientific and Technical Information of China (English)
Yang Zhen-Biao; Wu Huai-Zhi; Su Wan-Jun
2007-01-01
In the context of microwave cavity QED, this paper proposes a new scheme for teleportation of an arbitrary pure state of two atoms. The scheme is very different from the previous ones which achieve the integrated state measurement,it deals in a probabilistic but simplified way. In the scheme, no additional atoms are involved and thus only two atoms are required to be detected. The scheme can also be used for the teleportation of arbitrary pure states of many atoms or two-mode cavities.
Feynman propagator for an arbitrary half-integral spin
Institute of Scientific and Technical Information of China (English)
黄时中; 张鹏飞; 阮图南; 祝玉灿; 郑志鹏
2003-01-01
Based on the solution to Bargmann-Wigner equation for a particle with arbitrary half-integral spin, a directderivation of the projection operator and propagator for a particle with arbitrary half-integral spin is worked out. Theprojection operator constructed by Behrends and Fronsdal is re-deduced and confirmed and simplified, the generalcommutation rules and Feynman propagator with additional non-covariant terms for a free particle with arbitraryhalf-integral spin are derived, and explicit expressions for the propagators for spins 3/2, 5/2 and 7/2 are provided.
Satellite sensing of submerged fossil turbulence and zombie turbulence
Gibson, Carl H.
2004-11-01
Surface brightness anomalies from a submerged municipal wastewater outfall trapped by buoyancy in an area 0.1 km^2 are surprisingly detected from space satellites in areas > 200 km^2. How is this possible? Microstructure measurements near the outfall diffuser reveal enhanced turbulence and temperature dissipation rates above the 50 m trapping depth. Near-vertical radiation of internal waves by fossil and zombie turbulence microstructure patches produce wind ripple smoothing with 30-50 m internal wave patterns in surface Fourier brightness anomalies near the outfall. Detections at 10-14 km distances are at 100-220 m bottom boundary layer (BBL) fossil turbulence scales. Advected outfall fossils form zombie turbulence patches in internal wave patterns as they extract energy, vorticity, turbulence and ambient vertical internal wavelength information as their density gradients are tilted by the waves. As the zombies fossilize, patterned energy radiates near-vertically to produce the detected Fourier anomalies. Zombie turbulence patches beam extracted energy in a preferred direction with a special frequency, like energized metastable molecules in a chemical maser. Thus, kilowatts to produce the submerged field of advected fossil outfall turbulence patches are amplified by beamed zombie turbulence maser action (BZTMA) into megawatts of turbulence dissipation to affect sea surface brightness on wide surface areas using gigawatts of BBL fossil turbulence wave energy available.
Epstein, Ariel
2014-01-01
We present a semi-analytical formulation of the interaction between a given source field and a scalar Huygens metasurface (HMS), a recently introduced promising concept for wavefront manipulation based on a sheet of orthogonal electric and magnetic dipoles. Utilizing the equivalent surface impedance representation of these metasurfaces, we establish that an arbitrary source field can be converted into directive radiation via a passive lossless HMS if two physical conditions are met: local power conservation and local impedance equalization. Expressing the fields via their plane-wave spectrum and harnessing the slowly-varying envelope approximation we obtain semi-analytical formulae for the scattered fields, and prescribe the surface reactance required for the metasurface implementation. The resultant design procedure indicates that the local impedance equalization induces a Fresnel-like reflection, while local power conservation forms a radiating virtual aperture which follows the total excitation field magni...
The Theory of Prime Ideals of Leavitt Path Algebras over Arbitrary Graphs
Rangaswamy, Kulumani M
2011-01-01
Given an arbitrary graph E and a field K, the prime ideals as well as the primitive ideals of the Leavitt path algebra L_K(E) are completely described in terms of their generators. The stratification of the prime spectrum of L_K(E) is indicated with information on its individual stratum. Necessary and sufficient conditions are given on the graph E under which every prime ideal of L_K(E) is primitive. Leavitt path algebras of Krull dimension zero are characterized and those with various prescribed Krull dimension are constructed. The minimal prime ideals of L_K(E) are are described in terms of the graphical properties of E and using this, complete descriptions of the height one as well as the co-height one prime ideals of L_K(E) are given.
Photonic generation of arbitrary waveforms based on incoherent wavelength-to-time mapping
Institute of Scientific and Technical Information of China (English)
Dong Jian-Ji; Luo Bo-Wen; Yu Yuan; Zhang Xin-Liang
2012-01-01
We demonstrate experimentally a radio frequency arbitrary waveform generator using the incoherent wavelengthto-time mapping technique.The system is implemented by amplitude modulation of a broadband optical resource whose spectrum is reshaped by a programmable optical pulse shaper and transmitted over a single mode fiber link.The shape of the generated waveform is controlled by the optical pulse shaper,and the fiber link introduces a certain group velocity delay to implement wavelength-to-time mapping.Assisted by the flexible optical pulse shaper,we obtain different shapes of optical waveforms,such as rectangle,triangle,and sawtooth waveforms.Furthermore,we also demonstrate ultra-wideband generation,such as Gaussian monocycle,doublet,and triplet waveforms,using the incoherent technique.
Magneto-optical response in the arbitrary-Chern number topological phase on square lattice
Wang, Yi-Xiang
2016-07-01
In this work, we investigate the magneto-optical response in the arbitrary-Chern number topological phase. Based on the Dirac theory, we derive the analytic expressions for the magneto-optical response. More importantly, we construct the model on the possible square lattice and make the numerical calculations with the exact diagonalization method. We find the analytical and numerical results are in good agreement with each other. For the optical absorption spectrum, the low-energy absorptive peaks and the corresponding hopping processes are distinct in different Chern number phases, heavily depending on the filling factor of the system. While for the optical Hall conductivities, the physical mechanisms are revealed for the dichroism of the absorption peaks in response to the right- and left-circularly polarized light. We discuss the feasibility of these results in experiment.
Fotouhi, Babak
2014-01-01
In studying network growth, the conventional approach is to devise a growth mechanism, quantify the evolution of a statistic or distribution (such as the degree distribution), and then solve the equations in the steady state (the infinite-size limit). Consequently, empirical studies also seek to verify the steady-state prediction in real data. The caveat concomitant with confining the analysis to this time regime is that no real system has infinite size; most real growing networks are far from the steady state. This underlines the importance of finite-size analysis. In this paper, we consider the shifted-linear preferential attachment as an illustrative example of arbitrary-time network growth analysis. We obtain the degree distribution for arbitrary initial conditions at arbitrary times. We corroborate our theoretical predictions with Monte Carlo simulations.
Direct numerical simulation and analysis of shock turbulence interaction
Lee, Sangsan; Lele, Sanjiva K.; Moin, Parviz
1991-01-01
Two kinds of linear analysis, rapid distortion theory (RDT) and linear interaction analysis (LIA), were used to investigate the effects of a shock wave on turbulence. Direct numerical simulations of two-dimensional isotropic turbulence interaction with a normal shock were also performed. The results from RDT and LIA are in good agreement for weak shock waves, where the effects of shock front curvature and shock front unsteadiness are not significant in producing vorticity. The linear analyses predict wavenumber-dependent amplification of the upstream one-dimensional energy spectrum, leading to turbulence scale length scale decrease through the interaction. Instantaneous vorticity fields show that vortical structures are enhanced while they are compressed in the shock normal direction. Entrophy amplfication through the shock wave compares favorably with the results of linear analyses.
Microelectrokinetic turbulence in microfluidics at low Reynolds number
Wang, Guiren; Yang, Fang; Zhao, Wei
2016-01-01
There is commonly no turbulence in microfluidics, and the flows are believed to be either laminar or chaotic, since Reynolds number (Re) in microflows is usually on the order of unity or lower. However, we recently demonstrated that it is possible to achieve turbulence with low Re (based on the measured flow velocity and the width of the channel entrance) when a pressure-driven flow is electrokinetically forced in a quasi T-microchannel. To be able to measure high frequency velocity fluctuations in microchannels, a velocimeter with submicrometer spatial resolution and microsecond temporal resolution, called a laser-induced fluorescence photobleaching anemometer, is developed. Here we characterize the microelectrokinetic turbulence and observe some typical and important features of high Re flows, such as Kolmogorov -5 /3 spectrum of velocity fluctuation, which usually can be realized only at very high Re in macroturbulent flows.
Fully Lagrangian Renormalized Approximation theory of fluid turbulence: Progress report
International Nuclear Information System (INIS)
The purpose of this paper is to discuss our refinement and extension of the work of Y. Kaneda on a Lagrangian Renormalized Approximation (LRA) for homogeneous hydrodynamic turbulence. Kaneda's results are important to the development of a consistent theory of turbulence because the LRA theory successfully overcomes the failure of other turbulence theories (namely the Direct Interaction Approximation) to predict the Kolmogorov wavenumber spectrum. It is thought that this success is due to the use of a Lagrangian rather than Eulerian description of the fluid so that convection of the small eddies by the large ones is properly treated. However, some aspects of these results are puzzling and are considered here. For example, the form of the correlation function and the value of the Kolmogorov constant, K, depend on the choice of the form of the correlation function
Space-time resolved wave turbulence in a vibrating plate.
Cobelli, Pablo; Petitjeans, Philippe; Maurel, Agnès; Pagneux, Vincent; Mordant, Nicolas
2009-11-13
Wave turbulence in a thin elastic plate is experimentally investigated. By using a Fourier transform profilometry technique, the deformation field of the plate surface is measured simultaneously in time and space. This enables us to compute the wave-vector-frequency (k, omega) Fourier spectrum of the full space-time deformation velocity. In the 3D (k, omega) space, we show that the energy of the motion is concentrated on a 2D surface that represents a nonlinear dispersion relation. This nonlinear dispersion relation is close to the linear dispersion relation. This validates the usual wave-number-frequency change of variables used in many experimental studies of wave turbulence. The deviation from the linear dispersion, which increases with the input power of the forcing, is attributed to weak nonlinear effects. Our technique opens the way for many new extensive quantitative comparisons between theory and experiments of wave turbulence. PMID:20365984
On the evolution of the primordial cosmic turbulence
International Nuclear Information System (INIS)
The evolution of the primordial cosmic turbulence in the big-bang universe is studied by numerical integration of the spectral equation derived by Nariai and closed by Heisenberg's hypothesis. In order to examine whether the turbulence can survive by the epoch of the plasma recombination, the equation is dealt with by taking full account of the viscosity effect. The main conclusion is that the resulting spectrum survived against the viscous decay depends on the initial spectral shape which is assumed at the epoch t sub(eq) when the density of matter is equal to that of radiation. The Taylor's micro-scale is also calculated which is available to determine the fate of the primordial cosmic turbulence. (author)
Turbulent transport of alpha particles in tokamak plasmas
Croitoru, A; Vlad, M; Spineanu, F
2016-01-01
We investigate the ExB diffusion of fusion born \\alpha particles in tokamak plasmas. We determine the transport regimes for a realistic model that has the characteristics of the ion temperature gradient (ITG) or of the trapped electron modes (TEM) driven turbulence. It includes a spectrum of potential fluctuations that is modeled using the results of the numerical simulations, the drift of the potential with the effective diamagnetic velocity and the parallel motion. Our semi-analytical statistical approach is based on the decorrelation trajectory method (DTM), which is adapted to the gyrokinetic approximation. We obtain the transport coefficients as a function of the parameters of the turbulence and of the energy of the \\alpha particle. According to our results, signficant turbulent transport of the \\alpha particles can appear only at energies of the order of 100KeV. We determine the corresponding conditions.
Oscillating grids turbulence generator for turbulent transport studies
Directory of Open Access Journals (Sweden)
A. Eidelman
2002-01-01
Full Text Available An oscillating grids turbulence generator was constructed for studies of two new effects associated with turbulent transport of particles, turbulent thermal diffusion and clustering instability. These effects result in formation of large-scale and small-scale inhomogeneities in the spatial distribution of particles. The advantage of this experimental set-up is the feasibility to study turbulent transport in mixtures with controllable composition and unlimited observation time. For flow measurements we used Particle Image Velocimetry with the adaptive multi-pass algorithm to determine a turbulent velocity field and its statistical characteristics. Instantaneous velocity vector maps, flow streamlines and probability density function of velocity field demonstrate properties of turbulence generated in the device.
Faeth, G. M.
1989-01-01
Measurements and predictions of the structure of several multiphase flows are considered. The properties of dense sprays near the exits of pressure-atomizing injectors and of noncombusting and combusting dilute dispersed flows in round-jet configurations are addressed. It is found that the properties of dense sprays exhibit structure and mixing properties similar to variable-density single-phase flows at high Reynolds numbers within the atomization regime. The degree of development and turbulence levels at the injector exit have a surprisingly large effect on the structure and mixing properties of pressure-atomized sprays, particularly when the phase densities are large. Contemporary stochastic analysis of dilute multiphase flows provides encouraging predictions of turbulent dispersion for a wide variety of jetlike flows, particle-laden jets in gases and liquids, noncondensing and condensing bubbly jets, and nonevaporating, evaporating, and combusting sprays.
Anaïs Schaeffer
2015-01-01
As a member of the EuHIT (European High-Performance Infrastructures in Turbulence - see here) consortium, CERN is participating in fundamental research on turbulence phenomena. To this end, the Laboratory provides European researchers with a cryogenic research infrastructure (see here), where the first tests have just been performed. The last day of data collection, tired but satisfied after seven intense days of measurements. Around the cryostat, from left to right: Philippe-E. Roche, Éléonore Rusaouen (CNRS), Olivier Pirotte, Jean-Marc Quetsch (CERN), Nicolas Friedlin (CERN), Vladislav Benda (CERN). Not in the photo: Laurent Le Mao (CERN), Jean-Marc Debernard (CERN), Jean-Paul Lamboy (CERN), Nicolas Guillotin (CERN), Benoit Chabaud (Grenoble Uni), and Gregory Garde (CNRS). CERN has a unique cryogenic facility in hall SM18, consisting of 21 liquid-helium-cooled test stations. While this equipment was, of course, designed for testing parts of CERN's acce...
Controlled-Turbulence Bioreactors
Wolf, David A.; Schwartz, Ray; Trinh, Tinh
1989-01-01
Two versions of bioreactor vessel provide steady supplies of oxygen and nutrients with little turbulence. Suspends cells in environment needed for sustenance and growth, while inflicting less damage from agitation and bubbling than do propeller-stirred reactors. Gentle environments in new reactors well suited to delicate mammalian cells. One reactor kept human kidney cells alive for as long as 11 days. Cells grow on carrier beads suspended in liquid culture medium that fills cylindrical housing. Rotating vanes - inside vessel but outside filter - gently circulates nutrient medium. Vessel stationary; magnetic clutch drives filter cylinder and vanes. Another reactor creates even less turbulence. Oxygen-permeable tubing wrapped around rod extending along central axis. Small external pump feeds oxygen to tubing through rotary coupling, and oxygen diffuses into liquid medium.
Dynamics of number systems computation with arbitrary precision
Kurka, Petr
2016-01-01
This book is a source of valuable and useful information on the topics of dynamics of number systems and scientific computation with arbitrary precision. It is addressed to scholars, scientists and engineers, and graduate students. The treatment is elementary and self-contained with relevance both for theory and applications. The basic prerequisite of the book is linear algebra and matrix calculus. .
Zero Cycles on Certain Surfaces in Arbitrary Characteristic
Indian Academy of Sciences (India)
G V Ravindra
2006-02-01
Let be a field of arbitrary characteristic. Let be a singular surface defined over with multiple rational curve singularities and suppose that the Chow group of zero cycles of its normalisation $\\overline{S}$ is finite dimensional. We give numerical conditions under which the Chow group of zero cycles of is finite dimensional.
Mathematical model of bisubject qualimetric arbitrary objects evaluation
Morozova, A.
2016-04-01
An analytical basis and the process of formalization of arbitrary objects bisubject qualimetric evaluation mathematical model information spaces are developed. The model is applicable in solving problems of control over both technical and socio-economic systems for objects evaluation using systems of parameters generated by different subjects taking into account their performance and priorities of decision-making.
Electronic interaction anisotropy between atoms in arbitrary angular momentum states
Krems, R.V.; Groenenboom, G.C.; Dalgarno, A.
2004-01-01
A general tensorial expansion for the interaction potential between two atoms in arbitrary angular momentum states is derived and the relations between the expansion coefficients and the Born-Oppenheimer potentials of the diatomic molecule are obtained. It is demonstrated that a complete expansion o
Garbage-free reversible constant multipliers for arbitrary integers
DEFF Research Database (Denmark)
Mogensen, Torben Ægidius
2013-01-01
We present a method for constructing reversible circuitry for multiplying integers by arbitrary integer constants. The method is based on Mealy machines and gives circuits whose size are (in the worst case) linear in the size of the constant. This makes the method unsuitable for large constants, ......, but gives quite compact circuits for small constants. The circuits use no garbage or ancillary lines....
Canonical Quantum Teleportation of Two-Particle Arbitrary State
Institute of Scientific and Technical Information of China (English)
HAO Xiang; ZHU Shi-Qun
2005-01-01
The canonical quantum teleportation of two-particle arbitrary state is realized by means of phase operator and number operator. The maximally entangled eigenstates between the difference of phase operators and the sum of number operators are considered as the quantum channels. In contrast to the standard quantum teleportation, the different unitary local operation of canonical teleportation can be simplified by a general expression.
Probabilistic Teleportation of an Arbitrary n-Particle Entangled State
Institute of Scientific and Technical Information of China (English)
XIYong-Jun; FANGJian-Xing; ZHUShi-Qun; GUOZhan-Ying
2005-01-01
A scheme for teleporting an arbitrary n-particle entangled state via n pairs of non-maximally entangled states is proposed. The probability of successful teleportation is determined only by the smaller coefficients of the partially entangled pairs. The method is very easy to be realized.
Quantum electrodynamics with arbitrary charge on a noncommutative space
Institute of Scientific and Technical Information of China (English)
ZHOU Wan-Ping; CAI Shao-Hong; LONG Zheng-Wen
2009-01-01
Using the Seiberg-Witten map,we obtain a quantum electrodynamics on a noncommutative space,which has arbitrary charge and keep the gauge invariance to at the leading order in theta.The one-loop divergence and Compton scattering are reinvestigated.The uoncommutative effects are larger than those in ordinary noncommutative quantum electrodynamics.
Rainbows in the grass. II. Arbitrary diagonal incidence.
Adler, Charles L; Lock, James A; Fleet, Richard W
2008-12-01
We consider external reflection rainbow caustics due to the reflection of light from a pendant droplet where the light rays are at an arbitrary angle with respect to the horizontal. We compare this theory to observation of glare spots from pendant drops on grass; we also consider the potential application of this theory to the determination of liquid surface tension. PMID:19037345
Unveiling Reality of the Mind: Cultural Arbitrary of Consumerism
Choi, Su-Jin
2012-01-01
This paper discusses the cultural arbitrary of consumerism by focusing on a personal realm. That is, I discuss what consumerism appeals to and how it flourishes in relation to our minds. I argue that we need to unveil reality of the mind, be aware of ourselves in relation to the perpetuation of consumerism, in order to critically intervene in the…
Random functions and turbulence
Panchev, S
1971-01-01
International Series of Monographs in Natural Philosophy, Volume 32: Random Functions and Turbulence focuses on the use of random functions as mathematical methods. The manuscript first offers information on the elements of the theory of random functions. Topics include determination of statistical moments by characteristic functions; functional transformations of random variables; multidimensional random variables with spherical symmetry; and random variables and distribution functions. The book then discusses random processes and random fields, including stationarity and ergodicity of random
Nihoul, J.C.J.
1980-01-01
The variability of the ocean over a wide range of scales, from the megameter to the millimeter, is examined in the light of turbulence theory.The geophysical constraints which arise from the Earth's rotation and curvature and from the stratification are discussed with emphasis on the role they can play at different scales in inducing instabilities and a transfer of energy to other scales of motion.
Turbulent General Magnetic Reconnection
Eyink, G. L.
2015-07-01
Plasma flows with a magnetohydrodynamic (MHD)-like turbulent inertial range, such as the solar wind, require a generalization of general magnetic reconnection (GMR) theory. We introduce the slip velocity source vector per unit arclength of field line, the ratio of the curl of the non-ideal electric field in the generalized Ohm’s Law and magnetic field strength. It diverges at magnetic nulls, unifying GMR with null-point reconnection. Only under restrictive assumptions is the slip velocity related to the gradient of quasi-potential (which is the integral of parallel electric field along magnetic field lines). In a turbulent inertial range, the non-ideal field becomes tiny while its curl is large, so that line slippage occurs even while ideal MHD becomes accurate. The resolution is that ideal MHD is valid for a turbulent inertial range only in a weak sense that does not imply magnetic line freezing. The notion of weak solution is explained in terms of renormalization group (RG) type theory. The weak validity of the ideal Ohm’s law in the inertial range is shown via rigorous estimates of the terms in the generalized Ohm’s Law. All non-ideal terms are irrelevant in the RG sense and large-scale reconnection is thus governed solely by ideal dynamics. We discuss the implications for heliospheric reconnection, in particular for deviations from the Parker spiral model. Solar wind observations show that reconnection in a turbulence-broadened heliospheric current sheet, which is consistent with Lazarian-Vishniac theory, leads to slip velocities that cause field lines to lag relative to the spiral model.
Rank-Ordered Multifractal Analysis (ROMA of probability distributions in fluid turbulence
Directory of Open Access Journals (Sweden)
C. C. Wu
2011-04-01
Full Text Available Rank-Ordered Multifractal Analysis (ROMA was introduced by Chang and Wu (2008 to describe the multifractal characteristic of intermittent events. The procedure provides a natural connection between the rank-ordered spectrum and the idea of one-parameter scaling for monofractals. This technique has successfully been applied to MHD turbulence simulations and turbulence data observed in various space plasmas. In this paper, the technique is applied to the probability distributions in the inertial range of the turbulent fluid flow, as given in the vast Johns Hopkins University (JHU turbulence database. In addition, a new way of finding the continuous ROMA spectrum and the scaled probability distribution function (PDF simultaneously is introduced.
Simulation model of SAR remote sensing of turbulent wake of semi-elliptical submerged body
Institute of Scientific and Technical Information of China (English)
无
2005-01-01
In terms of the 2-dimensional hydrodynamic simplified model of a semi-elliptical submerged body moving horizontally at high speed,by using the full-spectrum model of SAR(synthetic aperture radar) remote sensing and taking the effect of oceanic interior turbulence on surface gravity capillary waves into account, applying the k-ε model of turbulence with internal wave mixing, and adopting the Nasmyth spectrum of oceanic turbulence, the 2-dimensional simulation model of SAR remote sensing of this semi-elliptical submerged body is built up. Simulation by using this model at X band and C band is made in the northeastern South China Sea (21°00'N,119°00'E). Satisfactory results of the delay time and delay distance of turbulent surface wake of this semi-elliptical submerged body, as well as the minimum submerged depth at which this submerged body which cannot be discovered by SAR, are obtained through simulation.
Wave turbulent statistics in non-weak wave turbulence
Yokoyama, Naoto
2011-01-01
In wave turbulence, which is made by nonlinear interactions among waves, it has been believed that statistical properties are well described by the weak turbulence theory, where separation of linear and nonlinear time scales derived from weak nonlinearity is assumed. However, the separation of the time scales is often violated. To get rid of this inconsistency, closed equations are derived in wave turbulence without assuming the weak nonlinearity according to Direct-Interaction Approximation ...
Suppression of turbulent resistivity in turbulent Couette flow
Energy Technology Data Exchange (ETDEWEB)
Si, Jiahe, E-mail: jsi@nmt.edu; Sonnenfeld, Richard G.; Colgate, Arthur S.; Westpfahl, David J.; Romero, Van D.; Martinic, Joe [New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801 (United States); Colgate, Stirling A.; Li, Hui [Los Alamos National Laboratory, Los Alamos, New Mexico 87544 (United States); Nornberg, Mark D. [University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)
2015-07-15
Turbulent transport in rapidly rotating shear flow very efficiently transports angular momentum, a critical feature of instabilities responsible both for the dynamics of accretion disks and the turbulent power dissipation in a centrifuge. Turbulent mixing can efficiently transport other quantities like heat and even magnetic flux by enhanced diffusion. This enhancement is particularly evident in homogeneous, isotropic turbulent flows of liquid metals. In the New Mexico dynamo experiment, the effective resistivity is measured using both differential rotation and pulsed magnetic field decay to demonstrate that at very high Reynolds number rotating shear flow can be described entirely by mean flow induction with very little contribution from correlated velocity fluctuations.
Gudimetla, V S Rao; Holmes, Richard B; Riker, Jim F
2012-12-01
An analytical expression for the log-amplitude correlation function for plane wave propagation through anisotropic non-Kolmogorov turbulent atmosphere is derived. The closed-form analytic results are based on the Rytov approximation. These results agree well with wave optics simulation based on the more general Fresnel approximation as well as with numerical evaluations, for low-to-moderate strengths of turbulence. The new expression reduces correctly to the previously published analytic expressions for the cases of plane wave propagation through both nonisotropic Kolmogorov turbulence and isotropic non-Kolmogorov turbulence cases. These results are useful for understanding the potential impact of deviations from the standard isotropic Kolmogorov spectrum.
Che, H; Goldstein, M L; Viñas, A F
2014-02-14
The observed steep kinetic scale turbulence spectrum in the solar wind raises the question of how that turbulence originates. Observations of keV energetic electrons during solar quiet time suggest them as a possible source of free energy to drive kinetic turbulence. Using particle-in-cell simulations, we explore how the free energy released by an electron two-stream instability drives Weibel-like electromagnetic waves that excite wave-wave interactions. Consequently, both kinetic Alfvénic and whistler turbulence are excited that evolve through inverse and forward magnetic energy cascades.
Statistical Properties of Turbulence: An Overview
Pandit, Rahul; Ray, Samriddhi Sankar
2009-01-01
We present an introductory overview of several challenging problems in the statistical characterisation of turbulence. We provide examples from fluid turbulence in three and two dimensions, from the turbulent advection of passive scalars, turbulence in the one-dimensional Burgers equation, and fluid turbulence in the presence of polymer additives.
Statistical properties of turbulence: An overview
Indian Academy of Sciences (India)
Rahul Pandit; Prasad Perlekar; Samriddhi Sankar Ray
2009-07-01
We present an introductory overview of several challenging problems in the statistical characterization of turbulence. We provide examples from fluid turbulence in three and two dimensions, from the turbulent advection of passive scalars, turbulence in the one-dimensional Burgers equation, and fluid turbulence in the presence of polymer additives.
International Nuclear Information System (INIS)
A new transport theory of cosmic rays in magnetized space plasmas with axisymmetric incompressible magnetic turbulence is developed extending the quasilinear approximation to the particle orbit. Arbitrary gyrophase deviations from the unperturbed spiral orbits in the uniform magnetic field are allowed. For quasi-stationary and spatially homogeneous magnetic turbulence, we derive the small Larmor radius approximation gyrophase-averaged cosmic ray Fokker-Planck coefficients. The generalized Fokker-Planck coefficients correctly reduce to their known quasilinear values in the corresponding limit. New forms of the quasilinear Fokker-Planck coefficients in axisymmetric turbulence are derived which no longer involve infinite sums of products of Bessel functions, which facilitate their numerical computation for specified turbulence field correlation tensors. The Fokker-Planck coefficients for arbitrary phase orbits of the cosmic ray particles provide strict upper limits for the perpendicular and pitch-angle Fokker-Planck coefficients, which in turn yield strict upper and lower limits for the perpendicular and parallel spatial diffusion coefficients, respectively, describing the spatial diffusion of the isotropic part of the cosmic ray phase space density. For the associated mean free paths, we find for this general case that the product of the minimum parallel mean free path with the sum of the maximum perpendicular mean free paths equals R2L, where RL denotes the cosmic ray gyroradius.
From Weakly to Strongly Magnetized Isotropic MHD Turbulence
Alexakis, Alexandros
2012-01-01
High Reynolds number isotropic magneto-hydro-dynamic turbulence in the presence of large scale magnetic fields is investigated as a function of the magnetic field strength. For a variety of flow configurations the energy dissipation rate \\epsilon, follows the Kolmogorov scaling \\epsilon ~ U^3/L even when the large scale magnetic field energy is twenty times larger than the kinetic. Further increase of the magnetic energy showed a transition to the \\epsilon ~ U^2 B / L scaling implying that magnetic shear becomes more efficient at this point at cascading the energy than the velocity fluctuations. Strongly helical configurations form helicity condensates that deviate from these scalings. Weak turbulence scaling was absent from the investigation. Finally, the magnetic energy spectra showed support for the Kolmogorov spectrum k^{-5/3} while kinetic energy spectra are closer to the Iroshnikov-Kraichnan spectrum k^{-3/2}.
Spontaneous chiral symmetry breaking of Hall magnetohydrodynamic turbulence.
Meyrand, Romain; Galtier, Sébastien
2012-11-01
Hall magnetohydrodynamics (MHD) is investigated through three-dimensional direct numerical simulations. We show that the Hall effect induces a spontaneous chiral symmetry breaking of the turbulent dynamics. The normalized magnetic polarization is introduced to separate the right- (R) and left-handed (L) fluctuations. A classical k(-7/3) spectrum is found at small scales for R magnetic fluctuations which corresponds to the electron MHD prediction. A spectrum compatible with k(-11/3) is obtained at large-scales for the L magnetic fluctuations; we call this regime the ion MHD. These results are explained heuristically by rewriting the Hall MHD equations in a succinct vortex dynamical form. Applications to solar wind turbulence are discussed.
Non-elliptic wavevector anisotropy for magnetohydrodynamic turbulence
Narita, Y.
2015-11-01
A model of non-elliptic wavevector anisotropy is developed for the inertial-range spectrum of magnetohydrodynamic turbulence and is presented in the two-dimensional wavevector domain spanning the directions parallel and perpendicular to the mean magnetic field. The non-elliptic model is a variation of the elliptic model with different scalings along the parallel and the perpendicular components of the wavevectors to the mean magnetic field. The non-elliptic anisotropy model reproduces the smooth transition of the power-law spectra from an index of -2 in the parallel projection with respect to the mean magnetic field to an index of -5/3 in the perpendicular projection observed in solar wind turbulence, and is as competitive as the critical balance model to explain the measured frequency spectra in the solar wind. The parameters in the non-elliptic spectrum model are compared with the solar wind observations.
Spontaneous chiral symmetry breaking of Hall magnetohydrodynamic turbulence.
Meyrand, Romain; Galtier, Sébastien
2012-11-01
Hall magnetohydrodynamics (MHD) is investigated through three-dimensional direct numerical simulations. We show that the Hall effect induces a spontaneous chiral symmetry breaking of the turbulent dynamics. The normalized magnetic polarization is introduced to separate the right- (R) and left-handed (L) fluctuations. A classical k(-7/3) spectrum is found at small scales for R magnetic fluctuations which corresponds to the electron MHD prediction. A spectrum compatible with k(-11/3) is obtained at large-scales for the L magnetic fluctuations; we call this regime the ion MHD. These results are explained heuristically by rewriting the Hall MHD equations in a succinct vortex dynamical form. Applications to solar wind turbulence are discussed. PMID:23215387
Institute of Scientific and Technical Information of China (English)
ShidaLIU; ZuguangZheng; 等
1996-01-01
We analyse the behavior of the nonlinear dynamical systems which are the truncated-spectrum model of the atmospheric turbulence equation.It shows that the chaos can appear in the Lorenz equation obtained by simple equations for the unstable stratification(Ri0),And the chaos can also appear in Burgers-Chao equations for the stable stratification(Ri>0,Ra<0),The atmospheric turbulence is intermittent in the stable stratified atmosphere.
Density Studies of MHD Interstellar Turbulence: Statistical Moments, Correlations and Bispectrum
Burkhart, Blakesley; Falceta-Goncalves, D.; Kowal, G.; Lazarian, A.
2008-01-01
We present a number of statistical tools for obtaining studying turbulence in molecular clouds and diffuse interstellar medium. For our tests we used of three-dimensional 512 cube compressible MHD isothermal simulations performed for different sonic and Alfvenic Mach numbers. We introduce the bispectrum, a new tool for statistical studies of the interstellar medium which, unlike an ordinary power spectrum of turbulence, preserves the phase information of the stochastic field. We show that the...
Passive scalars: mixing, diffusion and intermittency in helical and non-helical rotating turbulence
Imazio, P. Rodriguez; Mininni, P.D.
2015-01-01
We use direct numerical simulations to compute structure functions, scaling exponents, probability density functions and turbulent transport coefficients of passive scalars in turbulent rotating helical and non-helical flows. We show that helicity affects the inertial range scaling of the velocity and of the passive scalar when rotation is present, with a spectral law consistent with $\\sim k_{\\perp}^{-1.4}$ for the passive scalar variance spectrum. This scaling law is consistent with the phen...
4th European Turbulence Conference
1993-01-01
The European Turbulence Conferences have been organized under the auspices of the European Mechanics Committee (Euromech) to provide a forum for discussion and exchange of recent and new results in the field of turbulence. The first conference was organized in Lyon in 1986 with 152 participants. The second and third conferences were held in Berlin (1988) and Stockholm (1990) with 165 and 172 participants respectively. The fourth was organized in Delft from 30 June to 3 July 1992 by the J.M. Burgers Centre. There were 214 participants from 22 countries. This steadily growing number of participants demonstrates both the success and need for this type of conference. The main topics of the Fourth European Turbulence Conference were: Dynamical Systems and Transition; Statistical Physics and Turbulence; Experiments and Novel Experimental Techniques; Particles and Bubbles in Turbulence; Simulation Methods; Coherent Structures; Turbulence Modelling and Compressibility Effects. In addition a special session was held o...
Bruno, Roberto
2016-01-01
This book provides an overview of solar wind turbulence from both the theoretical and observational perspective. It argues that the interplanetary medium offers the best opportunity to directly study turbulent fluctuations in collisionless plasmas. In fact, during expansion, the solar wind evolves towards a state characterized by large-amplitude fluctuations in all observed parameters, which resembles, at least at large scales, the well-known hydrodynamic turbulence. This text starts with historical references to past observations and experiments on turbulent flows. It then introduces the Navier-Stokes equations for a magnetized plasma whose low-frequency turbulence evolution is described within the framework of the MHD approximation. It also considers the scaling of plasma and magnetic field fluctuations and the study of nonlinear energy cascades within the same framework. It reports observations of turbulence in the ecliptic and at high latitude, treating Alfvénic and compressive fluctuations separately in...
Tackling turbulent flows in engineering
Energy Technology Data Exchange (ETDEWEB)
Dewan, Anupam [Indian Institute of Technology Delhi, New Delhi (India). Dept. of Applied Mechanics
2011-07-01
The emphasis of this book is on engineering aspects of fluid turbulence. The book explains for example how to tackle turbulence in industrial applications. It is useful to several disciplines, such as, mechanical, civil, chemical, aerospace engineers and also to professors, researchers, beginners, under graduates and post graduates. The following issues are emphasized in the book: - Modeling and computations of engineering flows: The author discusses in detail the quantities of interest for engineering turbulent flows and how to select an appropriate turbulence model; Also, a treatment of the selection of appropriate boundary conditions for the CFD simulations is given. - Modeling of turbulent convective heat transfer: This is encountered in several practical situations. It basically needs discussion on issues of treatment of walls and turbulent heat fluxes. - Modeling of buoyancy driven flows, for example, smoke issuing from chimney, pollutant discharge into water bodies, etc. (orig.)
Turbulent Reconnection and Its Implications
Lazarian, Alex; Vishniac, Ethan T; Kowal, Grzegorz
2015-01-01
Magnetic reconnection is a process of magnetic field topology change, which is one of the most fundamental processes in magnetized plasmas. In most astrophysical environments the Reynolds numbers are large and therefore the transition to turbulence is inevitable. This turbulence must be taken into account for any theory of magnetic reconnection, since the initially laminar configurations can transit to the turbulence state, what is demonstrated by 3D high resolution numerical simulations. We discuss ideas of how turbulence can modify reconnection with the focus on the Lazarian & Vishniac (1999) reconnection model and present numerical evidence supporting the model and demonstrate that it is closely connected to the concept of Richardson diffusion and compatible with the Lagrangian dynamics of magnetized fluids. We point out that the Generalized Ohm's Law, that accounts for turbulent motion, predicts the subdominance of the microphysical plasma effects for a realistically turbulent media. We show that on o...
Transition to turbulence in ferrofluids
Altmeyer, Sebastian; Lai, Ying-Cheng
2015-01-01
It is known that in classical fluids turbulence typically occurs at high Reynolds numbers. But can turbulence occur at low Reynolds numbers? Here we investigate the transition to turbulence in the classic Taylor-Couette system in which the rotating fluids are manufactured ferrofluids with magnetized nanoparticles embedded in liquid carriers. We find that, in the presence of a magnetic field turbulence can occur at Reynolds numbers that are at least one order of magnitude smaller than those in conventional fluids. This is established by extensive computational ferrohydrodynamics through a detailed bifurcation analysis and characterization of behaviors of physical quantities such as the energy, the wave number, and the angular momentum through the bifurcations. A striking finding is that, as the magnetic field is increased, the onset of turbulence can be determined accurately and reliably. Our results imply that experimental investigation of turbulence can be greatly facilitated by using ferrofluids, opening up...
Cui, Linyan
2015-06-01
Analytic expressions for the temporal power spectra of irradiance fluctuations and angle of arrival (AOA) fluctuations are derived for optical waves propagating through weak anisotropic non-Kolmogorov atmospheric turbulence. In the derivation, the anisotropic non-Kolmogorov spectrum is adopted, which adopts the assumption of circular symmetry in the orthogonal plane throughout the path and the same degree of anisotropy along the propagation direction for all the turbulence cells. The final expressions consider simultaneously the anisotropic factor and general spectral power law values. When the anisotropic factor equals one (corresponding to the isotropic turbulence), the derived temporal power spectral models have good consistency with the known results for the isotropic turbulence. Numerical calculations show that the increased anisotropic factor alleviates the atmospheric turbulence's influence on the final expressions.
Energy Technology Data Exchange (ETDEWEB)
O`Hern, T.J.; Torczynski, J.R.; Shagam, R.N.; Blanchat, T.K.; Chu, T.Y.; Tassin-Leger, A.L.; Henderson, J.A.
1997-01-01
This report summarizes the work performed under the Sandia Laboratory Directed Research and Development (LDRD) project ``Optical Diagnostics for Turbulent and Multiphase Flows.`` Advanced optical diagnostics have been investigated and developed for flow field measurements, including capabilities for measurement in turbulent, multiphase, and heated flows. Particle Image Velocimetry (PIV) includes several techniques for measurement of instantaneous flow field velocities and associated turbulence quantities. Nonlinear photorefractive optical materials have been investigated for the possibility of measuring turbulence quantities (turbulent spectrum) more directly. The two-dimensional PIV techniques developed under this LDRD were shown to work well, and were compared with more traditional laser Doppler velocimetry (LDV). Three-dimensional PIV techniques were developed and tested, but due to several experimental difficulties were not as successful. The photorefractive techniques were tested, and both potential capabilities and possible problem areas were elucidated.
Line-of-sight statistical methods for turbulent medium: VCS for emission and absorption lines
Pogosyan, D
2009-01-01
We present an overview of the Velocity Coordinate Spectrum (VCS), a new technique for studying astrophysical turbulence that utilizes the line-of-sight statistics of Doppler-broadened spectral lines. We consider the retrieval of turbulence spectra from emission intensity observations of both high and low spatial resolution and find that the VCS allows one to study turbulence even when the emitting turbulent volume is not spatially resolved. This opens interesting prospects for using the technique for extragalactic research. VCS developed for spectral emission lines is applicable to absorption lines as well if the optical depth is used instead of intensity. VCS for absorption lines in point-source spectra benefit from effectively narrow beam and does not require dense sky coverage by sampling directions. Even strongly saturated absorption lines still carry the information about the small scale turbulence, albeit limited to the wings of a line. Combining different absorption lines one can develop tomography of ...
Kneller, James P
2013-01-01
(Abridged) The transition probabilities describing the evolution of a neutrino with a given energy along some ray through a turbulent supernova are random variates unique to each ray. If the source of the neutrinos were a point then all neutrinos of a given energy and emitted at the same time which were detected in some far off location would have seen the same turbulent profile therefore their transition probabilities would be exactly correlated. But if the source has a finite size then the profiles seen by neutrinos emitted from different points at the source will have seen different turbulence and the correlation of the transition probabilities will be reduced. In this paper we study the correlation of the neutrino transition probabilities through turbulent supernova profiles as a function of the separation between the emission points using an isotropic and an anisotropic power spectrum for the random field used to model the turbulence. The spectral features in the high density resonance mixing channel of ...
Lack of universal scaling in magnetohydrodynamic turbulence
Pouquet, A.; Brachet, M.; Krstulovic, G.; Lee, E.; Mininni, P.; Rosenberg, D. L.
2012-12-01
Universality is often viewed as a hallmark of turbulent flows, with a search for scaling exponents that derive from intrinsic dynamics and do not depend on initial conditions or forcing, the Kolmogorov law for the energy spectrum of an incompressible fluid being the best known case. However, in the presence of waves due to an external agent such as rotation, stratification or a strong large-scale magnetic field B0, different regimes -- such as weak or strong turbulence, may arise and thus, different scaling behavior may arise as well. This is observed for example in the ocean, and it leads to different mixing and transport properties. In this talk, we shall first review, in the context of MHD turbulence, the phenomenological models that can be constructed using the following plausible dimensionless parameters: (i) RT, the ratio of characteristic time scales (here, the wave period Tw=L_0/B_0 and the eddy-turn-over time based on large-scale length and velocity, TNL=L0/U_0; (ii) RE, the ratio of magnetic to kinetic energy EM/E_V; and (iii) RA, the degree of alignment between the velocity and the magnetic field \\cos(v,b), or between the magnetic potential and magnetic induction, \\cos(A,b). Note that these ratios can also be defined at scale ℓ of velocity uℓ (as opposed to L0, U0), and thus one can consider as well the variation of such ratios across scales. We shall then contrast these models with data stemming from (mostly) solar observations that indicate a clear lack of universal scaling behavior. Similarly, a number of direct numerical simulations (DNS) including some at high resolution, in the spin-down of forcing case, in the presence of boundaries or not, and with or without an imposed strong external magnetic field B0, all point-out to different energy spectra, although the attainable Reynolds numbers in present-day DNS are still limited when contrasted with geophysical and astrophysical flows. In particular, we shall show that, when using as initial
Power Spectrum Estimation of Randomly Sampled Signals
DEFF Research Database (Denmark)
Velte, C. M.; Buchhave, P.; K. George, W.
The random, but velocity dependent, sampling of the LDA presents non-trivial signal processing challenges due to the high velocity bias and the arbitrariness of particle path through the measuring volume, among other factors. To obtain the desired non-biased statistics, it has previously been shown...... is that if the algorithms are not able to produce correct statistics from this simple signal, then they will certainly not be able to function well for a more complex measured LDA signal. This is, of course, true also for other methods that are based on the tested algorithms. The extremes are tested by increasing, e....... Residence time weighting provides non-biased estimates regardless of setting. The free-running processor was also tested and compared to residence time weighting using actual LDA measurements in a turbulent round jet. Power spectra from measurements on the jet centerline and the outer part of the jet...
Power Spectrum Estimation of Randomly Sampled Signals
DEFF Research Database (Denmark)
Velte, Clara M.; Buchhave, Preben; K. George, William
2014-01-01
The random, but velocity dependent, sampling of the LDA presents non-trivial signal processing challengesdue to the high velocity bias and the arbitrariness of particle path through the measuring volume, among other factors.To obtain the desired non-biased statistics, it has previously been shown...... proportional to velocity magnitude that consist of well-defined frequency content, which makes bias easy to spot. The idea is that if the algorithms are not able to produce correct statistics from this simple signal, then they will certainly not be able to function well for a more complex measured LDA signal...... with high data rate and low inherent bias, respectively, while residence time weighting provides non-biased estimates regardless of setting. The free-running processor was also tested and compared to residence time weighting using actual LDA measurements in a turbulent round jet. Power spectra from...
Kakuwa, Jun
2016-01-01
Stochastic acceleration of nonthermal electrons is investigated in the context of hard photon spectra of blazars. It is well known that this acceleration mechanism can produce a hard electron spectrum of m≡ ∂ {ln}{n}{{e}}(γ )/∂ {ln}γ =2 with the high-energy cutoff, called an ultrarelativistic Maxwellian-like distribution, where {n}{{e}}(γ ) is an electron energy spectrum. We revisit the formation of this characteristic spectrum, considering a particular situation where the electrons are accelerated through gyroresonant interaction with magnetohydrodynamic wave turbulence driven by the turbulent cascade. By solving kinetic equations of the turbulent fields, electrons, and photons emitted via the synchrotron self-Compton (SSC) process, we demonstrate that in the non-test-particle treatment, the formation of a Maxwellian-like distribution is prevented by the damping effect on the turbulent fields due to the electron acceleration, at least unless an extreme parameter value is chosen. Instead, a softer electron spectrum with the index of m ≈ -1 is produced if the Kolmogorov-type cascade is assumed. The SSC spectrum that originates from the resultant softer electron spectrum is still hard, but somewhat softer and broader than the case of m = 2. This change of achievable hardness should be noted when this basic particle acceleration scenario is accurately tested with observations of hard photon spectra.
Matalon, M.; Cui, C.; Bechtold, J. K.
2003-07-01
Based on a hydrodynamic length, which is typically larger than the nominal flame thickness, a premixed flame can be viewed as a surface of density discontinuity, advected and distorted by the flow. The velocities and the pressure suffer abrupt changes across the flame front that consist of Rankine Hugoniot jump conditions, to leading order, with corrections of the order of the flame thickness that account for transverse fluxes and accumulation. To complete the formulation, expressions for the flame temperature and propagation speed, which vary along the flame as a result of local non-uniformities in the flow field and of flame front curvature, are derived. Unlike previous studies that assumed a mixture consisting of a single deficient reactant, the present study uses a two-reactant scheme and thus considers mixtures whose compositions vary from lean to rich conditions. Furthermore, non-unity and general reaction orders are considered in an attempt to mimic a wider range of reaction mechanisms and, to better represent actual experimental conditions, all transport coefficients are allowed to depend arbitrarily on temperature. The present model, expressed in a coordinate-free form, is valid for flames of arbitrary shape propagating in general fluid flows, either laminar or turbulent.
Galactic turbulence and paleoclimate variability
Bershadskii, A
2010-01-01
The wavelet regression detrended fluctuations of the reconstructed temperature for the past three ice ages: approximately 340000 years (Antarctic ice cores isotopic data), exhibit clear evidences of the galactic turbulence modulation up to 2500 years time-scales. The observed strictly Kolmogorov turbulence features indicates the Kolmogorov nature of galactic turbulence, and provide explanation to random-like fluctuations of the global temperature on the millennial time scales.
Freely decaying weak turbulence for sea surface gravity waves
Onorato, M.; Osborne, A. R.; Resio, D.; Pushkarev, A.; Zakharov, V.; Serio, M.; Brandini, C.
2002-01-01
We study numerically the generation of power laws in the framework of weak turbulence theory for surface gravity waves in deep water. Starting from a random wave field, we let the system evolve numerically according to the nonlinear Euler equations for gravity waves in infinitely deep water. In agreement with the theory of Zakharov and Filonenko, we find the formation of a power spectrum characterized by a power law of the form of $|{\\bf k}|^{-2.5}$.
A glimpse of fluid turbulence from the molecular scale
Komatsu, Teruhisa S.
2014-08-01
Large-scale molecular dynamics (MD) simulations of freely decaying turbulence in three-dimensional space are reported. Fluid components are defined from the microscopic states by eliminating thermal components from the coarse-grained fields. The energy spectrum of the fluid components is observed to scale reasonably well according to Kolmogorov scaling determined from the energy dissipation rate and the viscosity of the fluid, even though the Kolmogorov length is of the order of the molecular scale. © 2014 The Authors.
High Reynolds number magnetohydrodynamic turbulence using a Lagrangian model
Graham, J. Pietarila; P. D. Mininni; Pouquet, A.
2011-01-01
With the help of a model of magnetohydrodynamic (MHD) turbulence tested previously, we explore high Reynolds number regimes up to equivalent resolutions of 6000^3 grid points in the absence of forcing and with no imposed uniform magnetic field. For the given initial condition chosen here, with equal kinetic and magnetic energy, the flow ends up being dominated by the magnetic field, and the dynamics leads to an isotropic Iroshnikov-Kraichnan energy spectrum. However, the locally anisotropic m...
Wave turbulence in magnetized plasmas
Directory of Open Access Journals (Sweden)
S. Galtier
2009-02-01
Full Text Available The paper reviews the recent progress on wave turbulence for magnetized plasmas (MHD, Hall MHD and electron MHD in the incompressible and compressible cases. The emphasis is made on homogeneous and anisotropic turbulence which usually provides the best theoretical framework to investigate space and laboratory plasmas. The solar wind and the coronal heating problems are presented as two examples of application of anisotropic wave turbulence. The most important results of wave turbulence are reported and discussed in the context of natural and simulated magnetized plasmas. Important issues and possible spurious interpretations are also discussed.
Cross-field transport in Goldreich-Sridhar magnetohydrodynamic turbulence.
Fraschetti, F
2016-01-01
I derive analytically the temporal dependence of the perpendicular transport coefficient of a charged particle in the three-dimensional anisotropic turbulence conjectured by Goldreich-Sridhar by implementing multispacecraft constraints on the turbulence power spectrum. The particle motion away from the turbulent local field line is assessed as gradient-curvature drift of the guiding center and compared with the magnetic field line random walk. At inertial scales much smaller than the turbulence outer scale, particles decorrelate from field lines in a free-streaming motion, with no diffusion. In the solar wind at 1 AU, for energy sufficiently small (<1 keV protons), the perpendicular average displacement due to field line tangling generally dominates over two decades of turbulent scales. However, for higher energies (≃25 MeV protons) within the range of multispacecraft measurements, the longitudinal spread originating from transport due to gradient-curvature drift reaches up to ≃10^{∘}-20^{∘}. This result highlights the role of perpendicular transport in the interpretation of interplanetary and interstellar data.
Asymptotic expansion and statistical description of turbulent systems
International Nuclear Information System (INIS)
A new approach to studying turbulent systems is presented in which an asymptotic expansion of the general dynamical equations is performed prior to the application of statistical methods for describing the evolution of the system. This approach has been applied to two specific systems: anomalous drift wave turbulence in plasmas and homogeneous, isotropic turbulence in fluids. For the plasma case, the time and length scales of the turbulent state result in the asymptotic expansion of the Vlasov/Poisson equations taking the form of nonlinear gyrokinetic theory. Questions regarding this theory and modern Hamiltonian perturbation methods are discussed and resolved. A new alternative Hamiltonian method is described. The Eulerian Direct Interaction Approximation (EDIA) is slightly reformulated and applied to the equations of nonlinear gyrokinetic theory. Using a similarity transformation technique, expressions for the thermal diffusivity are derived from the EDIA equations for various geometries, including a tokamak. In particular, the unique result for generalized geometry may be of use in evaluating fusion reactor designs and theories of anomalous thermal transport in tokamaks. Finally, a new and useful property of the EDIA is pointed out. For the fluid case, an asymptotic expansion is applied to the Navier-Stokes equation and the results lead to the speculation that such an approach may resolve the problem of predicting the Kolmogorov inertial range energy spectrum for homogeneous, isotropic turbulence. 45 refs., 3 figs
A Lagrangian PDF Model for the Scalar Dissipation in Homogeneous Turbulence
Fox, Rodney O.
1996-11-01
The scalar dissipation is a key quantity in the description of turbulent mixing. The spectral relaxation model (SRM) was developed to account for the effect of the evolution of the scalar spectrum on the mean scalar dissipation , and it successfully predicts the observed (DNS, grid turbulence) dependence on Re, Sc (>= 1), and the initial scalar spectrum without recourse to fitting parameters. In this work, we present a Lagrangian PDF version (LSRM) for the PDF of ɛ_φ conditioned on the turbulent vortex stretching history of Kolmogorov-scale fluid particles. In homogeneous turbulence, the LSRM is coupled to a Lagrangian PDF model for the turbulent dissipation (ɛ) which strongly influences the statistics of ɛ_φ. Closure of scalar molecular dissipation term () is carried out using the Fokker-Planck model that was developed earlier for the joint scalar, scalar gradient PDF following fluid particles with the identical vortex stretching histories. Model predictions for inert scalar mixing in homogeneous turbulence with and without a uniform mean scalar gradient are compared to DNS data. In particular, the effect of the mean scalar gradient on the correlation between ɛ_φ and ɛ (i.e. local anisotropy) is examined, as well as the effect of the initial scalar spectrum and small-scale random vortex stretching on non-Gaussian behavior of the scalar PDF.
Effects of sharp vorticity gradients in two-dimensional hydrodynamic turbulence
DEFF Research Database (Denmark)
Kuznetsov, E.A.; Naulin, Volker; Nielsen, Anders Henry;
2007-01-01
The appearance of sharp vorticity gradients in two-dimensional hydrodynamic turbulence and their influence on the turbulent spectra are considered. We have developed the analog of the vortex line representation as a transformation to the curvilinear system of coordinates moving together with the ......The appearance of sharp vorticity gradients in two-dimensional hydrodynamic turbulence and their influence on the turbulent spectra are considered. We have developed the analog of the vortex line representation as a transformation to the curvilinear system of coordinates moving together...... with the divorticity lines. Compressibility of this mapping can be considered as the main reason for the formation of the sharp vorticity gradients at high Reynolds numbers. For two-dimensional turbulence in the case of strong anisotropy the sharp vorticity gradients can generate spectra which fall off as k−3 at large...... k, resembling the Kraichnan spectrum for the enstrophy cascade. For turbulence with weak anisotropy the k dependence of the spectrum due to the sharp gradients coincides with the Saffman spectrum, E(k)~k−4. We have compared the analytical predictions with direct numerical solutions of the two...
PLASMA TURBULENCE AND KINETIC INSTABILITIES AT ION SCALES IN THE EXPANDING SOLAR WIND
Energy Technology Data Exchange (ETDEWEB)
Hellinger, Petr; Trávnícek, Pavel M. [Astronomical Institute, CAS, Bocni II/1401, CZ-14100 Prague (Czech Republic); Matteini, Lorenzo [Department of Physics, Imperial College London, London SW7 2AZ (United Kingdom); Landi, Simone; Verdini, Andrea; Franci, Luca, E-mail: petr.hellinger@asu.cas.cz [Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze Largo E. Fermi 2, I-50125 Firenze (Italy)
2015-10-01
The relationship between a decaying strong turbulence and kinetic instabilities in a slowly expanding plasma is investigated using two-dimensional (2D) hybrid expanding box simulations. We impose an initial ambient magnetic field perpendicular to the simulation box, and we start with a spectrum of large-scale, linearly polarized, random-phase Alfvénic fluctuations that have energy equipartition between kinetic and magnetic fluctuations and vanishing correlation between the two fields. A turbulent cascade rapidly develops; magnetic field fluctuations exhibit a power-law spectrum at large scales and a steeper spectrum at ion scales. The turbulent cascade leads to an overall anisotropic proton heating, protons are heated in the perpendicular direction, and, initially, also in the parallel direction. The imposed expansion leads to generation of a large parallel proton temperature anisotropy which is at later stages partly reduced by turbulence. The turbulent heating is not sufficient to overcome the expansion-driven perpendicular cooling and the system eventually drives the oblique firehose instability in a form of localized nonlinear wave packets which efficiently reduce the parallel temperature anisotropy. This work demonstrates that kinetic instabilities may coexist with strong plasma turbulence even in a constrained 2D regime.
Spectral Properties of MHD Turbulence in 2.5-Dimensional Compressible Plasmas
Institute of Scientific and Technical Information of China (English)
DUAN Shuchao; MA Zhiwei
2009-01-01
Spectral properties of magnetohydrodynamic (MHD) turbulence with a strong back-ground mean magnetic field in 2.5-dime nsional compressible plasmas are studied by high-resolutionnumerical simulations. The spatial properties of MHD turbulences and the energy transfer pro-cess in the k-space are analyzed through angle-averaged energy spectrum. It is found that in the inertial phase, the energy spectrum index of compressible MHD turbulences during the decaying phase is evolved with time. The index varies in a quite wide regime from Kolmogorov's 5/3 to IK's 3/2 during the late simulation period. The energy spectrum index in the later nonlinear stage is also dependent on the chosen initial conditions. The spectral index increases with the increase of the initial magnetic fluctuation while the index decreases with the increase of the initial flow perturbation.
Gravity wave turbulence revealed by horizontal vibrations of the container.
Issenmann, B; Falcon, E
2013-01-01
We experimentally study the role of forcing on gravity-capillary wave turbulence. Previous laboratory experiments using spatially localized forcing (vibrating blades) have shown that the frequency power-law exponent of the gravity wave spectrum depends on the forcing parameters. By horizontally vibrating the whole container, we observe a spectrum exponent that does not depend on the forcing parameters for both gravity and capillary regimes. This spatially extended forcing leads to a gravity spectrum exponent in better agreement with the theory than by using a spatially localized forcing. The role of the vessel shape has been also studied. Finally, the wave spectrum is found to scale linearly with the injected power for both regimes whatever the forcing type used.
Brocchini, M
2006-01-01
This book contains a collection of 11 research and review papers devoted to the topic of fluid-structure interaction.The subject matter is divided into chapters covering a wide spectrum of recognized areas of research, such as: wall bounded turbulence; quasi 2-D turbulence; canopy turbulence; large eddy simulation; lake hydrodynamics; hydraulic hysteresis; liquid impacts; flow induced vibrations; sloshing flows; transient pipe flow and air entrainment in dropshaft.The purpose of each chapter is to summarize the main results obtained by the individual research unit through a year-long activity
Phase-synchronization, energy cascade, and intermittency in solar-wind turbulence.
Perri, S; Carbone, V; Vecchio, A; Bruno, R; Korth, H; Zurbuchen, T H; Sorriso-Valvo, L
2012-12-14
The energy cascade in solar wind magnetic turbulence is investigated using MESSENGER data in the inner heliosphere. The decomposition of magnetic field time series in intrinsic functions, each characterized by a typical time scale, reveals phase reorganization. This allows for the identification of structures of all sizes generated by the nonlinear turbulent cascade, covering both the inertial and the dispersive ranges of the turbulent magnetic power spectrum. We find that the correlation (or anticorrelation) of phases occurs between pairs of neighboring time scales, whenever localized peaks of magnetic energy are present at both scales, consistent with the local character of the energy transfer process.
Study of Nonlinear Interaction and Turbulence of Alfven Waves in LAPD Experiments
Energy Technology Data Exchange (ETDEWEB)
Boldyrev, Stanislav; Perez, Jean Carlos
2013-11-29
The complete project had two major goals — investigate MHD turbulence generated by counterpropagating Alfven modes, and study such processes in the LAPD device. In order to study MHD turbulence in numerical simulations, two codes have been used: full MHD, and reduced MHD developed specialy for this project. Quantitative numerical results are obtained through high-resolution simulations of strong MHD turbulence, performed through the 2010 DOE INCITE allocation. We addressed the questions of the spectrum of turbulence, its universality, and the value of the so-called Kolmogorov constant (the normalization coefficient of the spectrum). In these simulations we measured with unprecedented accuracy the energy spectra of magnetic and velocity fluctuations. We also studied the so-called residual energy, that is, the difference between kinetic and magnetic energies in turbulent fluctuations. In our analytic work we explained generation of residual energy in weak MHD turbulence, in the process of random collisions of counterpropagating Alfven waves. We then generalized these results for the case of strong MHD turbulence. The developed model explained generation of residual energy is strong MHD turbulence, and verified the results in numerical simulations. We then analyzed the imbalanced case, where more Alfven waves propagate in one direction. We found that spectral properties of the residual energy are similar for both balanced and imbalanced cases. We then compared strong MHD turbulence observed in the solar wind with turbulence generated in numerical simulations. Nonlinear interaction of Alfv´en waves has been studied in the upgraded Large Plasma Device (LAPD). We have simulated the collision of the Alfven modes in the settings close to the experiment. We have created a train of wave packets with the apltitudes closed to those observed n the experiment, and allowed them to collide. We then saw the generation of the second harmonic, resembling that observed in the
The nonlinear interaction of two-crossed focussed ultrasonic beams in the presence of turbulence
Rife, Stephen C.
1988-06-01
This paper examines the scattering of a nonlinearly generated sum frequency acoustic wave component from a region of turbulence defined by the overlap volume of two mutually perpendicular crossed focussed ultrasonic beams. The scattered sum frequency pressure amplitude is measured at different radial scan positions across the jet flow stream providing conclusions that explain some qualitative results governing the sum frequency scattering mechanism. Information about the instantaneous velocity components of the turbulent field in the sound-sound interaction volume is measured with an electronic spectrum analyzer. Average spectral shapes of the spectrum near the sum frequency represent information about the probability distribution function of the turbulent velocities. Acoustic measurements are correlated with velocity measurements of circular jets. These correlations demonstrate that the focussed crossed beam apparatus is an effective diagnostic tool for the experimental study of turbulent fluid fields in water. The results of the nonlinear crossed beam experiments indicate the apparatus can be utilized as a diagnostic tool to measure some parameters of turbulent velocity. The measured pressure of the radiated sum frequency correlates with turbulent velocities in the interaction region. Measurements of the Doppler shift and sum-frequency broadening are used to determine mean velocity and turbulent rms velocities respectively.
Directory of Open Access Journals (Sweden)
H. Z. Baumert
2009-03-01
Full Text Available This paper extends a turbulence closure-like model for stably stratified flows into a new dynamic domain in which turbulence is generated by internal gravity waves rather than mean shear. The model turbulent kinetic energy (TKE, K balance, its first equation, incorporates a term for the energy transfer from internal waves to turbulence. This energy source is in addition to the traditional shear production. The second variable of the new two-equation model is the turbulent enstrophy (Ω. Compared to the traditional shear-only case, the Ω-equation is modified to account for the effect of the waves on the turbulence time and space scales. This modification is based on the assumption of a non-zero constant flux Richardson number in the limit of vanishing mean shear when turbulence is produced exclusively by internal waves. This paper is part 1 of a continuing theoretical development. It accounts for mean shear- and internal wave-driven mixing only in the two limits of mean shear and no waves and waves but no mean shear, respectively.
The new model reproduces the wave-turbulence transition analyzed by D'Asaro and Lien (2000b. At small energy density E of the internal wave field, the turbulent dissipation rate (ε scales like ε~E^{2}. This is what is observed in the deep sea. With increasing E, after the wave-turbulence transition has been passed, the scaling changes to ε~E^{1}. This is observed, for example, in the highly energetic tidal flow near a sill in Knight Inlet. The new model further exhibits a turbulent length scale proportional to the Ozmidov scale, as observed in the ocean, and predicts the ratio between the turbulent Thorpe and Ozmidov length scales well within the range observed in the ocean.
Compressibility, turbulence and high speed flow
Gatski, Thomas B
2013-01-01
Compressibility, Turbulence and High Speed Flow introduces the reader to the field of compressible turbulence and compressible turbulent flows across a broad speed range, through a unique complimentary treatment of both the theoretical foundations and the measurement and analysis tools currently used. The book provides the reader with the necessary background and current trends in the theoretical and experimental aspects of compressible turbulent flows and compressible turbulence. Detailed derivations of the pertinent equations describing the motion of such turbulent flows is provided and
Derkachov, S E
1995-01-01
The spectrum of the anomalous dimensions of the composite operators (with arbitrary number of fields n and derivatives l) in the scalar \\phi^4 - theory in the first order of the \\epsilon -expansion is investigated. The exact solution for the operators with number of fields \\leq 4 is presented. The behaviour of the anomalous dimensions in the large l limit has been analyzed. It is given the qualitative description of the structure of the spectrum for the arbitrary n.
Global simulations of magnetorotational turbulence II: turbulent energetics
Parkin, E R
2013-01-01
Magnetorotational turbulence draws its energy from gravity and ultimately releases it via dissipation. However, the quantitative details of this energy flow have not been assessed for global disk models. In this work we examine the energetics of a well-resolved, three-dimensional, global magnetohydrodynamic accretion disk simulation by evaluating statistically-averaged mean-field equations for magnetic, kinetic, and internal energy using simulation data. The results reveal that turbulent magnetic (kinetic) energy is primarily injected by the correlation between Maxwell (Reynolds) stresses and shear in the (almost Keplerian) mean flow, and removed by dissipation. This finding differs from previous work using local (shearing-box) models, which indicated that turbulent kinetic energy was primarily sourced from the magnetic energy reservoir. Lorentz forces provide the bridge between the magnetic and kinetic energy reservoirs, converting ~ 1/5 of the total turbulent magnetic power input into turbulent kinetic ener...
Niccoli, G
2014-01-01
Generic inhomogeneous integrable XXZ chains with arbitrary spins are studied by means of the quantum separation of variables (SOV) method. Within this framework, a complete description of the spectrum (eigenvalues and eigenstates) of the antiperiodic transfer matrix is derived in terms of discrete systems of equations involving the inhomogeneity parameters of the model. We show here that one can reformulate this discrete SOV characterization of the spectrum in terms of functional T-Q equations of Baxter's type, hence proving the completeness of the solutions to the associated systems of Bethe-type equations. More precisely, we consider here two such reformulations. The first one is given in terms of Q-solutions, in the form of trigonometric polynomials of a given degree $N_s$, of a one-parameter family of T-Q functional equations with an extra inhomogeneous term. The second one is given in terms of Q-solutions, again in the form of trigonometric polynomials of degree $N_s$ but with double period, of Baxter's ...
Resonant ultrasound spectroscopy for materials with high damping and samples of arbitrary geometry
Remillieux, Marcel C.; Ulrich, T. J.; Payan, Cédric; Rivière, Jacques; Lake, Colton R.; Le Bas, Pierre-Yves
2015-07-01
Resonant ultrasound spectroscopy (RUS) is a powerful and established technique for measuring elastic constants of a material with general anisotropy. The first step of this technique consists of extracting resonance frequencies and damping from the vibrational frequency spectrum measured on a sample with free boundary conditions. An inversion technique is then used to retrieve the elastic tensor from the measured resonance frequencies. As originally developed, RUS has been mostly applicable to (i) materials with small damping such that the resonances of the sample are well separated and (ii) samples with simple geometries for which analytical solutions exist. In this paper, these limitations are addressed with a new RUS approach adapted to materials with high damping and samples of arbitrary geometry. Resonances are extracted by fitting a sum of exponentially damped sinusoids to the measured frequency spectrum. The inversion of the elastic tensor is achieved with a genetic algorithm, which allows searching for a global minimum within a discrete and relatively wide solution space. First, the accuracy of the proposed approach is evaluated against numerical data simulated for samples with isotropic symmetry and transversely isotropic symmetry. Subsequently, the applicability of the approach is demonstrated using experimental data collected on a composite structure consisting of a cylindrical sample of Berea sandstone glued to a large piezoelectric disk. In the proposed experiments, RUS is further enhanced by the use of a 3-D laser vibrometer allowing the visualization of most of the modes in the frequency band studied.
On Black-Brane Instability In an Arbitrary Dimension
Kol, B; Kol, Barak; Sorkin, Evgeny
2004-01-01
The black-hole black-string system is known to exhibit critical dimensions and therefore it is interesting to vary the spacetime dimension $D$, treating it as a parameter of the system. We derive the large $D$ asymptotics of the critical, i.e. marginally stable, string following an earlier numerical analysis. For a background with an arbitrary compactification manifold we give an expression for the critical mass of a corresponding black brane. This expression is completely explicit for ${\\bf T}^n$, the $n$ dimensional torus of an arbitrary shape. An indication is given that by employing a higher dimensional torus, rather than a single compact dimension, the total critical dimension above which the nature of the black-brane black-hole phase transition changes from sudden to smooth could be as low as $D\\leq 11$.
Sunrise: Polychromatic Dust Radiative Transfer in Arbitrary Geometries
Jonsson, P
2006-01-01
This paper describes Sunrise, a parallel, free Monte-Carlo code for the calculation of radiation transfer through astronomical dust. Sunrise uses an adaptive-mesh refinement grid to describe arbitrary geometries of emitting and absorbing/scattering media, with spatial dynamical range exceeding 10^4, and it can efficiently generate images of the emerging radiation at arbitrary points in space. In addition to the monochromatic radiative transfer typically used by Monte-Carlo codes, Sunrise is capable of propagating a range of wavelengths simultaneously. This ``polychromatic'' algorithm gives significant improvements in efficiency and accuracy when spectral features are calculated. Sunrise is used to study the effects of dust in hydrodynamic simulations of interacting galaxies, and the procedure for this is described. The code is tested against previously published results.
Topological flat band models with arbitrary Chern numbers
Yang, Shuo; Gu, Zheng-Cheng; Sun, Kai; Das Sarma, S.
2012-12-01
We report the theoretical discovery of a systematic scheme to produce topological flat bands (TFBs) with arbitrary Chern numbers. We find that generically a multiorbital high Chern number TFB model can be constructed by considering multilayer Chern number C=1 TFB models with enhanced translational symmetry. A series of models are presented as examples, including a two-band model on a triangular lattice with a Chern number C=3 and an N-band square lattice model with C=N for an arbitrary integer N. In all these models, the flatness ratio for the TFBs is larger than 30 and increases with increasing Chern number. In the presence of appropriate interparticle interactions, these models are likely to lead to the formation of Abelian and non-Abelian fractional Chern insulators. As a simple example, we test the C=2 model with hardcore bosons at 1/3 filling, and an intriguing fractional quantum Hall state is observed.
Locally indistinguishable orthogonal product bases in arbitrary bipartite quantum system
Xu, Guang-Bao; Yang, Ying-Hui; Wen, Qiao-Yan; Qin, Su-Juan; Gao, Fei
2016-08-01
As we know, unextendible product basis (UPB) is an incomplete basis whose members cannot be perfectly distinguished by local operations and classical communication. However, very little is known about those incomplete and locally indistinguishable product bases that are not UPBs. In this paper, we first construct a series of orthogonal product bases that are completable but not locally distinguishable in a general m ⊗ n (m ≥ 3 and n ≥ 3) quantum system. In particular, we give so far the smallest number of locally indistinguishable states of a completable orthogonal product basis in arbitrary quantum systems. Furthermore, we construct a series of small and locally indistinguishable orthogonal product bases in m ⊗ n (m ≥ 3 and n ≥ 3). All the results lead to a better understanding of the structures of locally indistinguishable product bases in arbitrary bipartite quantum system.
Universal properties of Fermi gases in arbitrary dimensions
Valiente, Manuel; Molmer, Klaus
2012-01-01
We consider spin-1/2 Fermi gases in arbitrary, integer or non-integer spatial dimensions, interacting via a Dirac delta potential. We first generalize the method of Tan's distributions and implement short-range boundary conditions to arbitrary dimension and we obtain a set of universal relations for the Fermi gas, which serve as dimensional interpolation/extrapolation formulae in between integer dimensions. We show that, under very general conditions, effective reduced-dimensional scattering lengths due to transversal confinement depend on the original three-dimensional scattering length in a universal way. As a direct consequence, we find that confinement-induced resonances occur in all dimensions different from D=2, without any need to solve the associated multichannel scattering problem. Finally, we show that reduced-dimensional contacts --- related to the tails of the momentum distributions --- are connected to the actual three-dimensional contact through a correction factor of purely geometric origin.
Optimizing the controllability of arbitrary networks with genetic algorithm
Li, Xin-Feng; Lu, Zhe-Ming
2016-04-01
Recently, as the controllability of complex networks attracts much attention, how to optimize networks' controllability has become a common and urgent problem. In this paper, we develop an efficient genetic algorithm oriented optimization tool to optimize the controllability of arbitrary networks consisting of both state nodes and control nodes under Popov-Belevitch-Hautus rank condition. The experimental results on a number of benchmark networks show the effectiveness of this method and the evolution of network topology is captured. Furthermore, we explore how network structure affects its controllability and find that the sparser a network is, the more control nodes are needed to control it and the larger the differences between node degrees, the more control nodes are needed to achieve the full control. Our framework provides an alternative to controllability optimization and can be applied to arbitrary networks without any limitations.
Quantum teleportation of an arbitrary superposition of atomic states
Institute of Scientific and Technical Information of China (English)
Chen Qiong; Fang Xi-Ming
2008-01-01
This paper proposes a scheme to teleport an arbitrary multi-particle two-level atomic state between two parties or an arbitrary zero- and one-photon entangled state of multi-mode between two high-Q cavities in cavity QED.This scheme is based on the resonant interaction between atom and cavity and does not involve Bell-state measurement.It investigates the fidelity of this scheme and find out the case of this unity fidelity of this teleportation.Considering the practical case of the cavity decay,this paper finds that the condition of the unity fidelity is also valid and obtains the effect of the decay of the cavity on the successful probability of the teleportation.
The arbitrary l continuum states of the hyperbolic molecular potential
Energy Technology Data Exchange (ETDEWEB)
Wei, Gao-Feng, E-mail: fgwei_2000@163.com [School of Physics and Mechatronics Engineering, Xi' an University of Arts and Science, Xi' an 710065 (China); Chen, Wen-Li, E-mail: physwlchen@163.com [Department of Basic Science, Xi' an Peihua University, Xi' an 710065 (China); Dong, Shi-Hai, E-mail: dongsh2@yahoo.com [Escuela Superior de Física y Matemáticas, Instituto Politécnico Nacional, Edificio 9, Unidad Profesional Adolfo López Mateos, Mexico D.F. 07738 (Mexico); Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803-4001 (United States)
2014-06-27
Within the framework of partial-wave method, we study in this Letter the arbitrary l continuum states of the Schrödinger equation with the hyperbolic molecular potential in terms of an improved approximation to the centrifugal term. We present the normalized radial wave functions and obtain analytical formula of phase shifts. In addition, the corresponding bound states are also discussed by studying the analytical properties of the scattering amplitude. We calculate the energy spectra and scattering phase shifts by the improved, previous approximations and the accurate methods, respectively and find that the improved approximation is better than the previous one since the present results are in better agreement with the accurate ones. - Highlights: • The hyperbolic potential with arbitrary l state is solved. • Improved approximation to centrifugal term is used. • Phase shift formula is derived analytically. • Accurate results are compared with the present results.
Generation of Electromagnetic Waves with Arbitrary Orbital Angular Momentum Modes
Cheng, Li; Hong, Wei; Hao, Zhang-Cheng
2014-01-01
Recently, much attention has been focused on beams carrying orbital angular momentum (OAM) for radio communication. Here we experimentally demonstrate a planar-spiral phase plate (planar-SPP) for generating arbitrary mixed OAM beams. This proposed planar-SPP uses the concept of transmit array antenna having a perforated substrate to control the outputting phase for generating beams carrying OAM with arbitrary modes. As demonstrations, three planar-SPPs with a single OAM mode and two mixed OAM modes around 94 GHz have been investigated with design and experiments in this paper, respectively. The typical experimental intensity and phase patterns show that the proposed method of generating OAM beams really works. PMID:24770669
Experimental remote preparation of arbitrary photon polarization states
International Nuclear Information System (INIS)
We demonstrate an experiment for remote preparation of arbitrary photon polarization states. With local operations, polarization measurement, and one way classical communication, any states lying on and inside the Poincare sphere can be remotely prepared. For arbitrary pure states, the efficiency is 100% with a communication cost of one entanglement bit and two classical bits. For mixed states, polarization insensitive measurement is introduced and the classical communication cost is one bit. Spontaneous parametric down-conversion (SPDC) is employed as an entanglement source. The remotely prepared qubits are estimated via quantum tomography process and fidelity between the experimentally prepared state and the expected state is considered to test the data. We achieve remote preparation of 13 states with fidelities all above 0.994
Estimating False Discovery Proportion Under Arbitrary Covariance Dependence
Fan, Jianqing; Gu, Weijie
2011-01-01
Multiple hypothesis testing is a fundamental problem in high dimensional inference, with wide applications in many scientific fields. In genome-wide association studies, tens of thousands of tests are performed simultaneously to find if any SNPs are associated with some traits and those tests are correlated. When test statistics are correlated, false discovery control becomes very challenging under arbitrary dependence. In the current paper, we propose a novel method based on principal factor approximation, which successfully subtracts the common dependence and weakens significantly the correlation structure, to deal with an arbitrary dependence structure. We derive an approximate expression for false discovery proportion (FDP) in large scale multiple testing when a common threshold is used and provide a consistent estimate of realized FDP. This result has important applications in controlling FDR and FDP. Our estimate of realized FDP compares favorably with Efron (2007)'s approach, as demonstrated in the sim...
Fluid flow over arbitrary bottom topography in a channel
Panda, Srikumar
2016-05-01
In this paper, two-dimensional free surface potential flow over an arbitrary bottom in a channel is considered to analyze the behavior of the free surface profile using linear theory. It is assumed that the fluid is inviscid, incompressible and flow is irrotational. Perturbation analysis in conjunction with Fourier transform technique is employed to determine the first order corrections of some important physical quantities such as free surface profile, velocity potential, etc. From the practical point of view, one arbitrary bottom topography is considered to determine the free surface profile since the free surface profile depends on the bottom topography. It is found that the free surface profile is oscillatory in nature, representing a wave propagating downstream and no wave upstream.
Steady states in Leith's model of turbulence
Grebenev, V. N.; Griffin, A.; Medvedev, S. B.; Nazarenko, S. V.
2016-09-01
We present a comprehensive study and full classification of the stationary solutions in Leith’s model of turbulence with a generalised viscosity. Three typical types of boundary value problems are considered: Problems 1 and 2 with a finite positive value of the spectrum at the left (right) and zero at the right (left) boundaries of a wave number range, and Problem 3 with finite positive values of the spectrum at both boundaries. Settings of these problems and analysis of existence of their solutions are based on a phase-space analysis of orbits of the underlying dynamical system. One of the two fixed points of the underlying dynamical system is found to correspond to a ‘sharp front’ where the energy flux and the spectrum vanish at the same wave number. The other fixed point corresponds to the only exact power-law solution—the so-called dissipative scaling solution. The roles of the Kolmogorov, dissipative and thermodynamic scaling, as well as of sharp front solutions, are discussed.
Steady states in Leith's model of turbulence
Grebenev, V. N.; Griffin, A.; Medvedev, S. B.; Nazarenko, S. V.
2016-09-01
We present a comprehensive study and full classification of the stationary solutions in Leith’s model of turbulence with a generalised viscosity. Three typical types of boundary value problems are considered: Problems 1 and 2 with a finite positive value of the spectrum at the left (right) and zero at the right (left) boundaries of a wave number range, and Problem 3 with finite positive values of the spectrum at both boundaries. Settings of these problems and analysis of existence of their solutions are based on a phase–space analysis of orbits of the underlying dynamical system. One of the two fixed points of the underlying dynamical system is found to correspond to a ‘sharp front’ where the energy flux and the spectrum vanish at the same wave number. The other fixed point corresponds to the only exact power-law solution—the so-called dissipative scaling solution. The roles of the Kolmogorov, dissipative and thermodynamic scaling, as well as of sharp front solutions, are discussed.
Arbitrary-order parasupersymmetric coherent states of quantum harmonic oscillator
Energy Technology Data Exchange (ETDEWEB)
Fakhri, H. [Faculty of Physics, Tabriz University, Tabriz (Iran, Islamic Republic of) and Research Institute for Fundamental Sciences, Tabriz (Iran, Islamic Republic of)]. E-mail: Hfakhri@ark.tabrizu.ac.ir; Bahadori, M.E. [Faculty of Physics, Tabriz University, Tabriz (IR): Research Institute for Fundamental Sciences, Tabriz (Iran)]. E-mail: Msph0977@ark.tabrizu.ac.ir
2000-10-13
The eigenstates of arbitrary-order parasupersymmetric Hamiltonian p corresponding to a particle with spin p/2 in the presence of a harmonic oscillator potential and constant magnetic field directed along the z-axis are constructed in terms of eigenstates of a one-dimensional harmonic oscillator. Also, parasupersymmetric coherent states with degenerate multiplicity of an ad hoc bosonic annihilation operator of parasupersymmetric eigenstates of the Hamiltonian mentioned above are calculated. (author)
Arbitrary-order parasupersymmetric coherent states of quantum harmonic oscillator
International Nuclear Information System (INIS)
The eigenstates of arbitrary-order parasupersymmetric Hamiltonian p corresponding to a particle with spin p/2 in the presence of a harmonic oscillator potential and constant magnetic field directed along the z-axis are constructed in terms of eigenstates of a one-dimensional harmonic oscillator. Also, parasupersymmetric coherent states with degenerate multiplicity of an ad hoc bosonic annihilation operator of parasupersymmetric eigenstates of the Hamiltonian mentioned above are calculated. (author)
Arbitrary rotation and entanglement of flux SQUID qubits
Kis, Z
2003-01-01
We propose a new approach for the arbitrary rotation of a three-level SQUID qubit and describe a new strategy for the creation of coherence transfer and entangled states between two three-level SQUID qubits. The former is succeeded by exploring the coupled-uncoupled states of the system when irradiated with two microwave pulses, and the latter is succeeded by placing the SQUID qubits into a microwave cavity and used adiabatic passage methods for their manipulation.
Quantification of Entanglement of Teleportation in Arbitrary Dimensions
Sazim, Sk; Adhikari, Satyabrata; Banerjee, Subhashish; Pramanik, T.
2012-01-01
We study bipartite entangled states in arbitrary dimensions and obtain different bounds for the entanglement measures in terms of teleportation fidelity. We find that there is a simple relation between negativity and teleportation fidelity for pure states but for mixed states, an upper bound is obtained for negativity in terms of teleportation fidelity using convex-roof extension negativity (CREN). However, with this it is not clear how to distinguish betweeen states useful for teleportation ...
Consistency Conditions for Brane Worlds in Arbitrary Dimensions
Leblond, F; Winters, D J; Leblond, Frederic; Myers, Robert C.; Winters, David J.
2001-01-01
We consider ``brane world sum rules'' for compactifications involving an arbitrary number of spacetime dimensions. One of the most striking results derived from such consistency conditions is the necessity for negative tension branes to appear in five--dimensional scenarios. We show how this result is easily evaded for brane world models with more than five dimensions. As an example, we consider a novel realization of the Randall--Sundrum scenario in six dimensions involving only positive tension branes.
Self-forces on static bodies in arbitrary dimensions
Harte, Abraham I.; Flanagan, Éanna É.; Taylor, Peter
2016-06-01
We derive exact expressions for the scalar and electromagnetic self-forces and self-torques acting on arbitrary static extended bodies in arbitrary static spacetimes with any number of dimensions. Nonperturbatively, our results are identical in all dimensions. Meaningful point particle limits are quite different in different dimensions, however. These limits are defined and evaluated, resulting in simple "regularization algorithms" which can be used in concrete calculations. In these limits, self-interaction is shown to be progressively less important in higher numbers of dimensions; it generically competes in magnitude with increasingly high-order extended-body effects. Conversely, we show that self-interaction effects can be relatively large in 1 +1 and 2 +1 dimensions. Our motivations for this work are twofold: First, no previous derivation of the self-force has been provided in arbitrary dimensions, and heuristic arguments presented by different authors have resulted in conflicting conclusions. Second, the static self-force problem in arbitrary dimensions provides a valuable test bed with which to continue the development of general, nonperturbative methods in the theory of motion. Several new insights are obtained in this direction, including a significantly improved understanding of the renormalization process. We also show that there is considerable freedom to use different "effective fields" in the laws of motion—a freedom which can be exploited to optimally simplify specific problems. Different choices give rise to different inertias, gravitational forces, and electromagnetic or scalar self-forces, but there is a sense in which none of these quantities are individually accessible to experiment. Certain combinations are observable, however, and these remain invariant under all possible field redefinitions.
Universality and Borel summability of arbitrary quartic tensor models
Delepouve, Thibault; Gurau, Razvan; Rivasseau, Vincent
2016-01-01
We extend the study of \\emph{melonic} quartic tensor models to models with arbitrary quartic interactions. This extension requires a new version of the loop vertex expansion using several species of intermediate fields and iterated Cauchy-Schwarz inequalities. Borel summability is proven, uniformly as the tensor size $N$ becomes large. Every cumulant is written as a sum of explicitly calculated terms plus a remainder, suppressed in $1/N$. Together with the existence of the large $N$ limit of ...
Resonant tunneling in a Luttinger liquid for arbitrary barrier transmission
Huegle, S.; Egger, R.
2003-01-01
A numerically exact dynamical quantum Monte Carlo approach has been developed and applied to transport through a double barrier in a Luttinger liquid with arbitrary transmission. For strong transmission, we find broad Fabry-Perot Coulomb blockade peaks, with a lineshape parametrized by a single parameter, but at sufficiently low temperatures, non-Lorentzian universal lineshapes characteristic of coherent resonant tunneling emerge, even for strong interactions. For weak transmission, our data ...
Cell assemblies at multiple time scales with arbitrary lag distributions
Russo, Eleonora; Durstewitz, Daniel
2016-01-01
Hebb's idea of a cell assembly as the fundamental unit of neural information processing has dominated neuroscience like no other theoretical concept within the past 60 years. A range of different physiological phenomena, from precisely synchronized spiking to broadly simultaneous rate increases, has been subsumed under this term. Yet progress in this area is hampered by the lack of statistical tools that would enable to extract assemblies with arbitrary constellations of time lags, and at mul...
Axial Anomaly in Lattice Abelian Gauge Theory in Arbitrary Dimensions
Fujiwara, T; Wu, K; Fujiwara, Takanori; Suzuki, Hiroshi; Wu, Ke
1999-01-01
Axial anomaly of lattice abelian gauge theory in hyper-cubic regular lattice in arbitrary even dimensions is investigated by applying the method of exterior differential calculus. The topological invariance, gauge invariance and locality of the axial anomaly determine the explicit form of the topological part. The anomaly is obtained up to a multiplicative constant for finite lattice spacing and can be interpreted as the Chern character of the abelian lattice gauge theory.
Statistical Reconstruction of arbitrary spin states of particles: root approach
Bogdanov, Yu. I.
2005-01-01
A method of quantum tomography of arbitrary spin particle states is developed on the basis of the root approach. It is shown that the set of mutually complementary distributions of angular momentum projections can be naturally described by a set of basis functions based on the Kravchuk polynomials. The set of Kravchuk basis functions leads to a multi-parametric statistical distribution that generalizes the binomial distribution. In order to analyze a statistical inverse problem of quantum mec...
Entangling two oscillators with arbitrary asymmetric initial states
Yang, Chui-Ping; Su, Qi-Ping; Zheng, Shi-Biao; Nori, Franco; Han, Siyuan
2016-01-01
A Hamiltonian is presented, which can be used to convert any asymmetric state $|\\varphi \\rangle_{a}|\\phi \\rangle_{b}$ of two oscillators $a$ and $b$ into an entangled state. Furthermore, with this Hamiltonian and local operations only, two oscillators, initially in any asymmetric initial states, can be entangled with a third oscillator. The prepared entangled states can be engineered with an arbitrary degree of entanglement. A discussion on the realization of this Hamiltonian is given. Numeri...
Multilevel Polarization of Polar Codes Over Arbitrary Discrete Memoryless Channels
Sahebi, Aria G.; Pradhan, S. Sandeep
2011-01-01
It is shown that polar codes achieve the symmetric capacity of discrete memoryless channels with arbitrary input alphabet sizes. It is shown that in general, channel polarization happens in several, rather than only two levels so that the synthesized channels are either useless, perfect or "partially perfect". Any subset of the channel input alphabet which is closed under addition, induces a coset partition of the alphabet through its shifts. For any such partition of the input alphabet, ther...
A Dynamically Adaptive Arbitrary Lagrangian-Eulerian Method for Hydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Anderson, R W; Pember, R B; Elliott, N S
2002-10-19
A new method that combines staggered grid Arbitrary Lagrangian-Eulerian (ALE) techniques with structured local adaptive mesh refinement (AMR) has been developed for solution of the Euler equations. The novel components of the combined ALE-AMR method hinge upon the integration of traditional AMR techniques with both staggered grid Lagrangian operators as well as elliptic relaxation operators on moving, deforming mesh hierarchies. Numerical examples demonstrate the utility of the method in performing detailed three-dimensional shock-driven instability calculations.
A Dynamically Adaptive Arbitrary Lagrangian-Eulerian Method for Hydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Anderson, R W; Pember, R B; Elliott, N S
2004-01-28
A new method that combines staggered grid Arbitrary Lagrangian-Eulerian (ALE) techniques with structured local adaptive mesh refinement (AMR) has been developed for solution of the Euler equations. The novel components of the combined ALE-AMR method hinge upon the integration of traditional AMR techniques with both staggered grid Lagrangian operators as well as elliptic relaxation operators on moving, deforming mesh hierarchies. Numerical examples demonstrate the utility of the method in performing detailed three-dimensional shock-driven instability calculations.
ON THE SCATTERING OF ARBITRARY SHAPE MICROSTRIP PATCH
Institute of Scientific and Technical Information of China (English)
He Xiulian; Gong Shuxi; Liu Qizhong
2004-01-01
In this letter, discrete complex image method is employed to compute the Green's functions in the spatial domain, which improves the speed of evaluating the impedance matrix.The triangle vector basis function--RWG, is used to simulate the current distribution in order to compute the scattering properties of arbitrary shape microstrip patch without the staircase approximation. The numerical result shows the validity of the proposed method.
Generalized Prediction Intervals for Arbitrary Distributed High-Dimensional Data
Kuehn, Steffen
2008-01-01
This paper generalizes the traditional statistical concept of prediction intervals for arbitrary probability density functions in high-dimensional feature spaces by introducing significance level distributions, which provides interval-independent probabilities for continuous random variables. The advantage of the transformation of a probability density function into a significance level distribution is that it enables one-class classification or outlier detection in a direct manner.
Arbitrary Waveform Generator for Quantum Information Processing with Trapped Ions
R. Bowler; Warring, U.; Britton, J. W.; Sawyer, B. C.; Amini, J.
2013-01-01
Atomic ions confined in multi-electrode traps have been proposed as a basis for scalable quantum information processing. This scheme involves transporting ions between spatially distinct locations by use of time-varying electric potentials combined with laser or microwave pulses for quantum logic in specific locations. We report the development of a fast multi-channel arbitrary waveform generator for applying the time-varying electric potentials used for transport and for shaping quantum logi...
Bosonization of interacting fermions in arbitrary dimensions / Peter Kopietz
Kopietz, Peter
2006-01-01
This review is a summary of my work (partially in collaboration with Kurt Schoenhammer) on higher-dimensional bosonization during the years 1994-1996. It has been published as a book entitled "Bosonization of interacting fermions in arbitrary dimensions" by Springer Verlag (Lecture Notes in Physics m48, Springer, Berlin, 1997). I have NOT revised this review, so that there is no reference to the literature after 1996. However, the basic ideas underlying the functional bosonization approach ou...
Probabilistic Teleportation of an Arbitrary Two-particle State
Institute of Scientific and Technical Information of China (English)
顾永建; 郑亦庄; 郭光灿
2001-01-01
A scheme for the teleportation of an arbitrary two-particle state via two non-maximally entangled particle pairsis proposed. We show that teleportation can be successfully realized with a certain probability if the receiveradopts an appropriate unitary-reduction strategy. A specific strategy is provided in detail The probability of successful teleportation is determined by the smaller coefficients of the two entangled pairs.
Arbitrary Finite-time Tracking Control for Magnetic Levitation Systems
Xuan-Toa Tran; Hee-Jun Kang
2014-01-01
In this paper, an arbitrary finite-time tracking control (AFTC) method is developed for magnetic levitation systems with uncertain dynamics and external disturbances. By introducing a novel augmented sliding- mode manifold function, the proposed method can eliminate the singular problem in traditional terminal sliding-mode control, as well as the reaching-phase problem. Moreover, the tracking errors can reach the reference value with faster convergence and better tracking precision in arbitra...
Xue, Bindang; Cui, Linyan; Xue, Wenfang; Bai, Xiangzhi; Zhou, Fugen
2011-05-01
A new generalized modified atmospheric spectral model is derived theoretically for wave propagating through non-Kolmogorov turbulence, which has been reported recently by increasing experimental evidence and theoretical investigation. The generalized, modified atmospheric spectrum considers finite turbulence inner and outer scales and has a spectral power law value in the range of 3 to 5 instead of the standard power law value of 11/3. When the inner scale and outer scale are set to zero and infinity, respectively, this spectral model is reduced to the classical non-Kolmogorov spectrum.
Yokoyama, Naoto
2014-01-01
A weakly nonlinear spectrum and a strongly nonlinear spectrum coexist in a statistically steady state of elastic wave turbulence. The analytical representation of the nonlinear frequency is obtained by evaluating the extended self-nonlinear interactions. The {\\em critical\\/} wavenumbers at which the nonlinear frequencies are comparable with the linear frequencies agree with the {\\em separation\\/} wavenumbers between the weak and strong turbulence spectra. We also confirm the validity of our analytical representation of the separation wavenumbers through comparison with the results of direct numerical simulations by changing the material parameters of a vibrating plate.
Yokoyama, Naoto; Takaoka, Masanori
2014-01-01
A weakly nonlinear spectrum and a strongly nonlinear spectrum coexist in a statistically steady state of elastic wave turbulence. The analytical representation of the nonlinear frequency is obtained by evaluating the extended self-nonlinear interactions. The critical wave numbers at which the nonlinear frequencies are comparable with the linear frequencies agree with the separation wave numbers between the weak and strong turbulence spectra. We also confirm the validity of our analytical representation of the separation wave numbers through comparison with the results of direct numerical simulations by changing the material parameters of a vibrating plate. PMID:24580299
Scatter broadening of pulsars and implications on the interstellar medium turbulence
Xu, Siyao
2016-01-01
Observations reveal a uniform Kolmogorov turbulence throughout the diffuse ionized interstellar medium (ISM) and supersonic turbulence preferentially located in the Galactic plane. Correspondingly, we consider the Galactic distribution of electron density fluctuations consisting of not only a Kolmogorov density spectrum but also a short-wave-dominated density spectrum with the density structure formed at small scales due to shocks. The resulting dependence of the scatter broadening time on the dispersion measure (DM) naturally interprets the existing observational data for both low and high-DM pulsars. According to the criteria that we derive for a quantitative determination of scattering regimes over wide ranges of DMs and frequencies $\
Directory of Open Access Journals (Sweden)
V.V. Kulish
2014-06-01
Full Text Available In the paper, spin waves in an arbitrary translational-symmetry composite nanosystem containing an “easy axis” ferromagnet are studied. For such a system, equation for the magnetic potential in magnetostatic approximation is obtained taking into account the magnetic dipole-dipole interaction, the exchange interactionб and the anisotropy effects. The theory that allows to obtain the dispersion relation and the transverse wavenumber spectrum for a particular system of this type is proposed; dispersion relation for a system with small transverse size is obtained. The dispersion relation and the transverse wavenumber spectrum are written for nanotubes with round and elliptic cross-sections.
Advances in compressible turbulent mixing
International Nuclear Information System (INIS)
This volume includes some recent additions to original material prepared for the Princeton International Workshop on the Physics of Compressible Turbulent Mixing, held in 1988. Workshop participants were asked to emphasize the physics of the compressible mixing process rather than measurement techniques or computational methods. Actual experimental results and their meaning were given precedence over discussions of new diagnostic developments. Theoretical interpretations and understanding were stressed rather than the exposition of new analytical model developments or advances in numerical procedures. By design, compressibility influences on turbulent mixing were discussed--almost exclusively--from the perspective of supersonic flow field studies. The papers are arranged in three topical categories: Foundations, Vortical Domination, and Strongly Coupled Compressibility. The Foundations category is a collection of seminal studies that connect current study in compressible turbulent mixing with compressible, high-speed turbulent flow research that almost vanished about two decades ago. A number of contributions are included on flow instability initiation, evolution, and transition between the states of unstable flow onset through those descriptive of fully developed turbulence. The Vortical Domination category includes theoretical and experimental studies of coherent structures, vortex pairing, vortex-dynamics-influenced pressure focusing. In the Strongly Coupled Compressibility category the organizers included the high-speed turbulent flow investigations in which the interaction of shock waves could be considered an important source for production of new turbulence or for the enhancement of pre-existing turbulence. Individual papers are processed separately
Advances in compressible turbulent mixing
Energy Technology Data Exchange (ETDEWEB)
Dannevik, W.P.; Buckingham, A.C.; Leith, C.E. [eds.
1992-01-01
This volume includes some recent additions to original material prepared for the Princeton International Workshop on the Physics of Compressible Turbulent Mixing, held in 1988. Workshop participants were asked to emphasize the physics of the compressible mixing process rather than measurement techniques or computational methods. Actual experimental results and their meaning were given precedence over discussions of new diagnostic developments. Theoretical interpretations and understanding were stressed rather than the exposition of new analytical model developments or advances in numerical procedures. By design, compressibility influences on turbulent mixing were discussed--almost exclusively--from the perspective of supersonic flow field studies. The papers are arranged in three topical categories: Foundations, Vortical Domination, and Strongly Coupled Compressibility. The Foundations category is a collection of seminal studies that connect current study in compressible turbulent mixing with compressible, high-speed turbulent flow research that almost vanished about two decades ago. A number of contributions are included on flow instability initiation, evolution, and transition between the states of unstable flow onset through those descriptive of fully developed turbulence. The Vortical Domination category includes theoretical and experimental studies of coherent structures, vortex pairing, vortex-dynamics-influenced pressure focusing. In the Strongly Coupled Compressibility category the organizers included the high-speed turbulent flow investigations in which the interaction of shock waves could be considered an important source for production of new turbulence or for the enhancement of pre-existing turbulence. Individual papers are processed separately.
Stochastic Subspace Modelling of Turbulence
DEFF Research Database (Denmark)
Sichani, Mahdi Teimouri; Pedersen, B. J.; Nielsen, Søren R.K.
2009-01-01
Turbulence of the incoming wind field is of paramount importance to the dynamic response of civil engineering structures. Hence reliable stochastic models of the turbulence should be available from which time series can be generated for dynamic response and structural safety analysis. In the pape...
Magnetized Turbulent Dynamo in Protogalaxies
International Nuclear Information System (INIS)
The prevailing theory for the origin of cosmic magnetic fields is that they have been amplified to their present values by the turbulent dynamo inductive action in the protogalactic and galactic medium. Up to now, in calculation of the turbulent dynamo, it has been customary to assume that there is no back reaction of the magnetic field on the turbulence, as long as the magnetic energy is less than the turbulent kinetic energy. This assumption leads to the kinematic dynamo theory. However, the applicability of this theory to protogalaxies is rather limited. The reason is that in protogalaxies the temperature is very high, and the viscosity is dominated by magnetized ions. As the magnetic field strength grows in time, the ion cyclotron time becomes shorter than the ion collision time, and the plasma becomes strongly magnetized. As a result, the ion viscosity becomes the Braginskii viscosity. Thus, in protogalaxies the back reaction sets in much earlier, at field strengths much lower than those which correspond to field-turbulence energy equipartition, and the turbulent dynamo becomes what we call the magnetized turbulent dynamo. In this paper we lay the theoretical groundwork for the magnetized turbulent dynamo. In particular, we predict that the magnetic energy growth rate in the magnetized dynamo theory is up to ten times larger than that in the kinematic dynamo theory. We also briefly discuss how the Braginskii viscosity can aid the development of the inverse cascade of magnetic energy after the energy equipartition is reached
Conditional Eddies in Plasma Turbulence
DEFF Research Database (Denmark)
Johnsen, Helene; Pécseli, Hans; Trulsen, J.
1986-01-01
Conditional structures, or eddies, in turbulent flows are discussed with special attention to electrostatic turbulence in plasmas. The potential variation of these eddies is obtained by sampling the fluctuations only when a certain condition is satisfied in a reference point. The resulting...
Active turbulence in active nematics
Thampi, S. P.; Yeomans, J. M.
2016-07-01
Dense, active systems show active turbulence, a state characterised by flow fields that are chaotic, with continually changing velocity jets and swirls. Here we review our current understanding of active turbulence. The development is primarily based on the theory and simulations of active liquid crystals, but with accompanying summaries of related literature.
Magnetized Turbulent Dynamo in Protogalaxies
Energy Technology Data Exchange (ETDEWEB)
Leonid Malyshkin; Russell M. Kulsrud
2002-01-28
The prevailing theory for the origin of cosmic magnetic fields is that they have been amplified to their present values by the turbulent dynamo inductive action in the protogalactic and galactic medium. Up to now, in calculation of the turbulent dynamo, it has been customary to assume that there is no back reaction of the magnetic field on the turbulence, as long as the magnetic energy is less than the turbulent kinetic energy. This assumption leads to the kinematic dynamo theory. However, the applicability of this theory to protogalaxies is rather limited. The reason is that in protogalaxies the temperature is very high, and the viscosity is dominated by magnetized ions. As the magnetic field strength grows in time, the ion cyclotron time becomes shorter than the ion collision time, and the plasma becomes strongly magnetized. As a result, the ion viscosity becomes the Braginskii viscosity. Thus, in protogalaxies the back reaction sets in much earlier, at field strengths much lower than those which correspond to field-turbulence energy equipartition, and the turbulent dynamo becomes what we call the magnetized turbulent dynamo. In this paper we lay the theoretical groundwork for the magnetized turbulent dynamo. In particular, we predict that the magnetic energy growth rate in the magnetized dynamo theory is up to ten times larger than that in the kinematic dynamo theory. We also briefly discuss how the Braginskii viscosity can aid the development of the inverse cascade of magnetic energy after the energy equipartition is reached.
An overview of turbulence compensation
Schutte, Klamer; van Eekeren, Adam W. M.; Dijk, Judith; Schwering, Piet B. W.; van Iersel, Miranda; Doelman, Niek J.
2012-09-01
In general, long range visual detection, recognition and identification are hampered by turbulence caused by atmospheric conditions. Much research has been devoted to the field of turbulence compensation. One of the main advantages of turbulence compensation is that it enables visual identification over larger distances. In many (military) scenarios this is of crucial importance. In this paper we give an overview of several software and hardware approaches to compensate for the visual artifacts caused by turbulence. These approaches are very diverse and range from the use of dedicated hardware, such as adaptive optics, to the use of software methods, such as deconvolution and lucky imaging. For each approach the pros and cons are given and it is indicated for which type of scenario this approach is useful. In more detail we describe the turbulence compensation methods TNO has developed in the last years and place them in the context of the different turbulence compensation approaches and TNO's turbulence compensation roadmap. Furthermore we look forward and indicate the upcoming challenges in the field of turbulence compensation.
Generic Multiuser Coordinated Beamforming for Underlay Spectrum Sharing
Denkovski, Daniel; Atanasovski, Vladimir; Gavrilovska, Liljana; Mähönen, Petri
2015-01-01
The beamforming techniques have been recently studied as possible enablers for underlay spectrum sharing. The existing beamforming techniques have several common limitations: they are usually system model specific, cannot operate with arbitrary number of transmit/receive antennas, and cannot serve arbitrary number of users. Moreover, the beamforming techniques for underlay spectrum sharing do not consider the interference originating from the incumbent primary system. This work extends the common underlay sharing model by incorporating the interference originating from the incumbent system into generic combined beamforming design that can be applied on interference, broadcast or multiple access channels. The paper proposes two novel multiuser beamforming algorithms for user fairness and sum rate maximization, utilizing newly derived convex optimization problems for transmit and receive beamformers calculation in a recursive optimization. Both beamforming algorithms provide efficient operation for the interfer...
Shell Models of Magnetohydrodynamic Turbulence
Plunian, Franck; Frick, Peter
2012-01-01
Shell models of hydrodynamic turbulence originated in the seventies. Their main aim was to describe the statistics of homogeneous and isotropic turbulence in spectral space, using a simple set of ordinary differential equations. In the eighties, shell models of magnetohydrodynamic (MHD) turbulence emerged based on the same principles as their hydrodynamic counter-part but also incorporating interactions between magnetic and velocity fields. In recent years, significant improvements have been made such as the inclusion of non-local interactions and appropriate definitions for helicities. Though shell models cannot account for the spatial complexity of MHD turbulence, their dynamics are not over simplified and do reflect those of real MHD turbulence including intermittency or chaotic reversals of large-scale modes. Furthermore, these models use realistic values for dimensionless parameters (high kinetic and magnetic Reynolds numbers, low or high magnetic Prandtl number) allowing extended inertial range and accu...
Calculations of turbulent separated flows
Zhu, J.; Shih, T. H.
1993-01-01
A numerical study of incompressible turbulent separated flows is carried out by using two-equation turbulence models of the K-epsilon type. On the basis of realizability analysis, a new formulation of the eddy-viscosity is proposed which ensures the positiveness of turbulent normal stresses - a realizability condition that most existing two-equation turbulence models are unable to satisfy. The present model is applied to calculate two backward-facing step flows. Calculations with the standard K-epsilon model and a recently developed RNG-based K-epsilon model are also made for comparison. The calculations are performed with a finite-volume method. A second-order accurate differencing scheme and sufficiently fine grids are used to ensure the numerical accuracy of solutions. The calculated results are compared with the experimental data for both mean and turbulent quantities. The comparison shows that the present model performs quite well for separated flows.
Non-Kolmogorov cascade of helicity-driven turbulence.
Kessar, Mouloud; Plunian, Franck; Stepanov, Rodion; Balarac, Guillaume
2015-09-01
We solve the Navier-Stokes equations with two simultaneous forcings. One forcing is applied at a given large scale and it injects energy. The other forcing is applied at all scales belonging to the inertial range and it injects helicity. In this way we can vary the degree of turbulence helicity from nonhelical to maximally helical. We find that increasing the rate of helicity injection does not change the energy flux. On the other hand, the level of total energy is strongly increased and the energy spectrum gets steeper. The energy spectrum spans from a Kolmogorov scaling law k^{-5/3} for a nonhelical turbulence, to a non-Kolmogorov scaling law k^{-7/3} for a maximally helical turbulence. In the latter case we find that the characteristic time of the turbulence is not the turnover time but a time based on the helicity injection rate. We also analyze the results in terms of helical modes decomposition. For a maximally helical turbulence one type of helical mode is found to be much more energetic than the other one, by several orders of magnitude. The energy cascade of the most energetic type of helical mode results from the sum of two fluxes. One flux is negative and can be understood in terms of a decimated model. This negative flux, however, is not sufficient to lead an inverse energy cascade. Indeed, the other flux involving the least energetic type of helical mode is positive and the largest. The least energetic type of helical mode is then essential and cannot be neglected.
Are there two regimes in strongly rotating turbulence?
Baqui, Yasir Bin; Davidson, P. A.; Ranjan, Avishek
2016-04-01
We describe numerical experiments of freely decaying, rapidly rotating turbulence in which the Rossby number varies from Ro = O(1) down to Ro ˜ 0.02. Our central premise is that there exists two distinct dynamical regimes; one for Ro > 0.3 → 0.4, which is typical of most laboratory experiments, and another corresponding to Ro 0.3 → 0.4 is reported in Baqui and Davidson ["A phenomenological theory of rotating turbulence," Phys. Fluids 27, 025107 (2015)] and is characterised by: (i) a growth of the parallel integral scale according to l|| ˜ l⊥Ωt; (ii) a dissipation law which is quite different from that predicted by weak-turbulence theories, specifically ɛ = βu3/l|| where the pre-factor β is a constant of order unity; and (iii) an inertial-range energy spectrum for both the parallel and perpendicular wavenumbers which scales as k-5/3, a scaling that has nothing to do with Kolmogorov's law in non-rotating turbulence. (Here, l|| is the integral length-scale parallel to the rotation vector Ω, l⊥ the integral length-scale perpendicular to Ω, u the integral scale velocity, and ɛ the viscous dissipation rate per unit mass.) By contrast, in the low-Ro regime, we find that l|| ˜ l⊥Ωt is replaced by l|| ˜ ut and there is no power-law scaling of the inertial range energy spectrum. While the dissipation law ɛ = βu3/l|| continues to hold at low Ro, at least approximately, the value of β now depends on Ro. It appears, therefore, that the dynamics of these two regimes are very different, and this may help explain why experimentalists and theoreticians sometimes present rather different interpretations of rotating turbulence.
Forward and Inverse Cascades in EMHD Turbulence
Cho, Jungyeon
2016-05-01
Electron magnetohydrodynamics (EMHD) provides a simple fluid-like description of physics below the proton gyro-scale in collisionless plasmas, such as the solar wind. In this paper, we discuss forward and inverse cascades in EMHD turbulence in the presence of a strong mean magnetic field. Similar to Alfvén waves, EMHD waves, or EMHD perturbations, propagate along magnetic field lines. Therefore, two types of EMHD waves can exist: waves moving parallel to and waves moving anti-parallel to the the magnetic field lines. For energy cascade in EMHD turbulence, the relative amplitudes of opposite-traveling waves are important. When the amplitudes are balanced, we will see fully-developed forward cascade with a k -7/3 energy spectrum and a scale-dependent anisotropy. On the other hand, when the amplitudes are imbalanced, we will see inverse cascade, as well as (presumably not fully developed) forward cascade. The underlying physics for the inverse cascade is magnetic helicity conservation.
Lack of universality in decaying magnetohydrodynamic turbulence.
Lee, E; Brachet, M E; Pouquet, A; Mininni, P D; Rosenberg, D
2010-01-01
Using computations of three-dimensional magnetohydrodynamic (MHD) turbulence with a Taylor-Green flow, whose inherent time-independent symmetries are implemented numerically, and in the absence of either a forcing function or an imposed uniform magnetic field, we show that three different inertial ranges for the energy spectrum may emerge for three different initial magnetic fields, the selecting parameter being the ratio of nonlinear eddy to Alfvén time. Equivalent computational grids range from 128(3) to 2048(3) points with a unit magnetic Prandtl number and a Taylor Reynolds number of up to 1500 at the peak of dissipation. We also show a convergence of our results with Reynolds number. Our study is consistent with previous findings of a variety of energy spectra in MHD turbulence by studies performed in the presence of both a forcing term with a given correlation time and a strong, uniform magnetic field. However, in contrast to the previous studies, here the ratio of characteristic time scales can only be ascribed to the intrinsic nonlinear dynamics of the paradigmatic flows under study.
Turbulence driven particle transport in Texas Helimak
International Nuclear Information System (INIS)
We analyze the turbulence driven particle transport in Texas Helimak [K. W. Gentle and H. He, Plasma Sci. Technol. 10, 284 (2008)], a toroidal plasma device with a one-dimensional equilibrium with magnetic curvature and shear. Alterations on the radial electric field, through an external voltage bias, change the spectral plasma characteristics inducing a dominant frequency for negative bias values and a broad band frequency spectrum for positive bias values. When applying a negative bias, the transport is high where the waves propagate with phase velocities near the plasma flow velocity, an indication that the transport is strongly affected by a wave particle resonant interaction. On the other hand, for positive bias values, the plasma has a reversed shear flow, and we observe that the transport is almost zero in the shearless radial region, an evidence of a transport barrier in this region.
Spectral calculations in stably stratified turbulence.
Dutta, Kishore; Nandy, Malay K
2014-12-01
We perform a Leslie-type perturbative treatment on stably stratified turbulence with Boussinesq approximation, where the buoyancy terms in the corresponding dynamical equations are treated as perturbations against the isotropic background fields. Thus we calculate the anisotropic corrections to various correlation functions, namely, velocity-velocity, temperature-temperature, and velocity-temperature correlations, up to second order in this scheme. We find that the prefactors associated with the anisotropic corrections depend on the energy flux, scalar flux, Kolmogorov constant, Batchelor constant, and the eddy-damping amplitudes. The correlation functions further yield the anisotropic parts of the energy and mean-square temperature spectra as k(-3) and the anisotropic buoyancy spectrum as k(-7/3). The resulting angle-dependent energy density is found to be concentrated predominantly around the vertical wave vector signifying layered structures in the physical space. PMID:25615193
Ishii, Takaaki
2015-01-01
We study nonlinear dynamics of the flux tube between an external quark-antiquark pair in $\\mathcal{N}=4$ super Yang-Mills theory using the AdS/CFT duality. In the gravity side, the flux tube is realized by a fundamental string whose endpoints are attached to the AdS boundary. We perturb the endpoints in various ways and numerically compute the time evolution of the nonlinearly oscillating string. As a result, cusps can form on the string, accompanied by weak turbulence and power law behavior in the energy spectrum. When cusps traveling on the string reach the boundary, we observe the divergence of the force between the quark and antiquark. Minimal amplitude of the perturbation below which cusps do not form is also investigated. No cusp formation is found when the string moves in all four AdS space directions, and in this case an inverse energy cascade follows a direct cascade.
Turbulent premixed flames on fractal-grid-generated turbulence
International Nuclear Information System (INIS)
A space-filling, low blockage fractal grid is used as a novel turbulence generator in a premixed turbulent flame stabilized by a rod. The study compares the flame behaviour with a fractal grid to the behaviour when a standard square mesh grid with the same effective mesh size and solidity as the fractal grid is used. The isothermal gas flow turbulence characteristics, including mean flow velocity and rms of velocity fluctuations and Taylor length, were evaluated from hot-wire measurements. The behaviour of the flames was assessed with direct chemiluminescence emission from the flame and high-speed OH-laser-induced fluorescence. The characteristics of the two flames are considered in terms of turbulent flame thickness, local flame curvature and turbulent flame speed. It is found that, for the same flow rate and stoichiometry and at the same distance downstream of the location of the grid, fractal-grid-generated turbulence leads to a more turbulent flame with enhanced burning rate and increased flame surface area. (paper)
Turbulent premixed flames on fractal-grid-generated turbulence
Energy Technology Data Exchange (ETDEWEB)
Soulopoulos, N; Kerl, J; Sponfeldner, T; Beyrau, F; Hardalupas, Y; Taylor, A M K P [Mechanical Engineering Department, Imperial College London, London SW7 2AZ (United Kingdom); Vassilicos, J C, E-mail: ns6@ic.ac.uk [Department of Aeronautics, Imperial College London, London SW7 2AZ (United Kingdom)
2013-12-15
A space-filling, low blockage fractal grid is used as a novel turbulence generator in a premixed turbulent flame stabilized by a rod. The study compares the flame behaviour with a fractal grid to the behaviour when a standard square mesh grid with the same effective mesh size and solidity as the fractal grid is used. The isothermal gas flow turbulence characteristics, including mean flow velocity and rms of velocity fluctuations and Taylor length, were evaluated from hot-wire measurements. The behaviour of the flames was assessed with direct chemiluminescence emission from the flame and high-speed OH-laser-induced fluorescence. The characteristics of the two flames are considered in terms of turbulent flame thickness, local flame curvature and turbulent flame speed. It is found that, for the same flow rate and stoichiometry and at the same distance downstream of the location of the grid, fractal-grid-generated turbulence leads to a more turbulent flame with enhanced burning rate and increased flame surface area. (paper)
Dynamic Stochastic Superresolution of sparsely observed turbulent systems
International Nuclear Information System (INIS)
Real-time capture of the relevant features of the unresolved turbulent dynamics of complex natural systems from sparse noisy observations and imperfect models is a notoriously difficult problem. The resulting lack of observational resolution and statistical accuracy in estimating the important turbulent processes, which intermittently send significant energy to the large-scale fluctuations, hinders efficient parameterization and real-time prediction using discretized PDE models. This issue is particularly subtle and important when dealing with turbulent geophysical systems with an vast range of interacting spatio-temporal scales and rough energy spectra near the mesh scale of numerical models. Here, we introduce and study a suite of general Dynamic Stochastic Superresolution (DSS) algorithms and show that, by appropriately filtering sparse regular observations with the help of cheap stochastic exactly solvable models, one can derive stochastically ‘superresolved’ velocity fields and gain insight into the important characteristics of the unresolved dynamics, including the detection of the so-called black swans. The DSS algorithms operate in Fourier domain and exploit the fact that the coarse observation network aliases high-wavenumber information into the resolved waveband. It is shown that these cheap algorithms are robust and have significant skill on a test bed of turbulent solutions from realistic nonlinear turbulent spatially extended systems in the presence of a significant model error. In particular, the DSS algorithms are capable of successfully capturing time-localized extreme events in the unresolved modes, and they provide good and robust skill for recovery of the unresolved processes in terms of pattern correlation. Moreover, we show that DSS improves the skill for recovering the primary modes associated with the sparse observation mesh which is equally important in applications. The skill of the various DSS algorithms depends on the energy spectrum
Anomalous spectral laws in differential models of turbulence
International Nuclear Information System (INIS)
Differential models for hydrodynamic, passive-scalar and wave turbulence given by nonlinear first- and second-order evolution equations for the energy spectrum in the k-space were analysed. Both types of models predict formation an anomalous transient power-law spectra. The second-order models were analysed in terms of self-similar solutions of the second kind, and a phenomenological formula for the anomalous spectrum exponent was constructed using numerics for a broad range of parameters covering all known physical examples. The first-order models were examined analytically, including finding an analytical prediction for the anomalous exponent of the transient spectrum and description of formation of the Kolmogorov-type spectrum as a reflection wave from the dissipative scale back into the inertial range. The latter behaviour was linked to pre-shock/shock singularities similar to the ones arising in the Burgers equation. Existence of the transient anomalous scaling and the reflection-wave scenario are argued to be a robust feature common to the finite-capacity turbulence systems. The anomalous exponent is independent of the initial conditions but varies for for different models of the same physical system. (paper)
Two-fluid turbulence including electron inertia
Energy Technology Data Exchange (ETDEWEB)
Andrés, Nahuel, E-mail: nandres@iafe.uba.ar; Gómez, Daniel [Instituto de Astronomía y Física del Espacio, CC. 67, suc. 28, 1428 Buenos Aires (Argentina); Departamento de Física, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón I, 1428 Buenos Aires (Argentina); Gonzalez, Carlos; Martin, Luis; Dmitruk, Pablo [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and IFIBA, CONICET, 1428 Buenos Aires (Argentina)
2014-12-15
We present a full two-fluid magnetohydrodynamic (MHD) description for a completely ionized hydrogen plasma, retaining the effects of the Hall current, electron pressure, and electron inertia. According to this description, each plasma species introduces a new spatial scale: the ion inertial length λ{sub i} and the electron inertial length λ{sub e}, which are not present in the traditional MHD description. In the present paper, we seek for possible changes in the energy power spectrum in fully developed turbulent regimes, using numerical simulations of the two-fluid equations in two-and-a-half dimensions. We have been able to reproduce different scaling laws in different spectral ranges, as it has been observed in the solar wind for the magnetic energy spectrum. At the smallest wavenumbers where plain MHD is valid, we obtain an inertial range following a Kolmogorov k{sup −5∕3} law. For intermediate wavenumbers such that λ{sub i}{sup −1}≪k≪λ{sub e}{sup −1}, the spectrum is modified to a k{sup −7∕3} power-law, as has also been obtained for Hall-MHD neglecting electron inertia terms. When electron inertia is retained, a new spectral region given by k>λ{sub e}{sup −1} arises. The power spectrum for magnetic energy in this region is given by a k{sup −11∕3} power law. Finally, when the terms of electron inertia are retained, we study the self-consistent electric field. Our results are discussed and compared with those obtained in the solar wind observations and previous simulations.
Two-fluid turbulence including electron inertia
International Nuclear Information System (INIS)
We present a full two-fluid magnetohydrodynamic (MHD) description for a completely ionized hydrogen plasma, retaining the effects of the Hall current, electron pressure, and electron inertia. According to this description, each plasma species introduces a new spatial scale: the ion inertial length λi and the electron inertial length λe, which are not present in the traditional MHD description. In the present paper, we seek for possible changes in the energy power spectrum in fully developed turbulent regimes, using numerical simulations of the two-fluid equations in two-and-a-half dimensions. We have been able to reproduce different scaling laws in different spectral ranges, as it has been observed in the solar wind for the magnetic energy spectrum. At the smallest wavenumbers where plain MHD is valid, we obtain an inertial range following a Kolmogorov k−5∕3 law. For intermediate wavenumbers such that λi−1≪k≪λe−1, the spectrum is modified to a k−7∕3 power-law, as has also been obtained for Hall-MHD neglecting electron inertia terms. When electron inertia is retained, a new spectral region given by k>λe−1 arises. The power spectrum for magnetic energy in this region is given by a k−11∕3 power law. Finally, when the terms of electron inertia are retained, we study the self-consistent electric field. Our results are discussed and compared with those obtained in the solar wind observations and previous simulations
Turbulent deflagrations, autoignitions, and detonations
Bradley, Derek
2012-09-01
Measurements of turbulent burning velocities in fan-stirred explosion bombs show an initial linear increase with the fan speed and RMS turbulent velocity. The line then bends over to form a plateau of high values around the maximum attainable burning velocity. A further increase in fan speed leads to the eventual complete quenching of the flame due to increasing localised extinctions because of the flame stretch rate. The greater the Markstein number, the more readily does flame quenching occur. Flame propagation along a duct closed at one end, with and without baffles to increase the turbulence, is subjected to a one-dimensional analysis. The flame, initiated at the closed end of the long duct, accelerates by the turbulent feedback mechanism, creating a shock wave ahead of it, until the maximum turbulent burning velocity for the mixture is attained. With the confining walls, the mixture is compressed between the flame and the shock plane up to the point where it might autoignite. This can be followed by a deflagration to detonation transition. The maximum shock intensity occurs with the maximum attainable turbulent burning velocity, and this defines the limit for autoignition of the mixture. For more reactive mixtures, autoignition can occur at turbulent burning velocities that are less than the maximum attainable one. Autoignition can be followed by quasi-detonation or fully developed detonation. The stability of ensuing detonations is discussed, along with the conditions that may lead to their extinction. © 2012 by Pleiades Publishing, Ltd.
Helically Decomposed Turbulence
Alexakis, Alexandros
2016-01-01
A decomposition of the energy and helicity fluxes in a turbulent hydrodynamic flow is proposed. The decomposition is based on the projection of the flow to a helical basis that allows to investigate separately the role of interactions among modes of different helicity. The proposed formalism is then applied in large scale numerical simulations of a non-helical and a helical flow, where the decomposed fluxes are explicitly calculated. It is shown that the total energy flux can be split in to three fluxes that independently remain constant in the inertial range. One of these fluxes that corresponds to the interactions of fields with the same helicity is negative implying the presence of an inverse cascade that is `hidden' inside the forward cascade. Similar to the energy flux the helicity flux is also shown that it can be decomposed to two fluxes that remain constant in the inertial range. Implications of these results as well possible new directions for investigations are discussed.
Unsteady turbulent buoyant plumes
Woodhouse, Mark J; Hogg, Andrew J
2015-01-01
We model the unsteady evolution of turbulent buoyant plumes following temporal changes to the source conditions. The integral model is derived from radial integration of the governing equations expressing the conservation of mass, axial momentum and buoyancy. The non-uniform radial profiles of the axial velocity and density deficit in the plume are explicitly described by shape factors in the integral equations; the commonly-assumed top-hat profiles lead to shape factors equal to unity. The resultant model is hyperbolic when the momentum shape factor, determined from the radial profile of the mean axial velocity, differs from unity. The solutions of the model when source conditions are maintained at constant values retain the form of the well-established steady plume solutions. We demonstrate that the inclusion of a momentum shape factor that differs from unity leads to a well-posed integral model. Therefore, our model does not exhibit the mathematical pathologies that appear in previously proposed unsteady i...
Cheng, Mingjian; Guo, Lixin; Li, Jiangting; Huang, Qingqing; Cheng, Qi; Zhang, Dan
2016-06-10
The analytical formulas for the orbital angular momentum (OAM) mode probability density, signal OAM mode detection probability, and spiral spectrum of partially coherent Laguerre-Gaussian (LG) beams with optical vortices propagation in weak horizontal oceanic turbulent channels were developed, based on the Rytov approximation theory. The effect of oceanic turbulence and beam source parameters on the propagation behavior of the optical vortices carried by partially coherent LG beams was investigated in detail. Our results indicated that optical turbulence in an ocean environment produced a much stronger effect on the optical vortex than that in an atmosphere environment; the effective range of the signal OAM mode of LG beams with a smaller ratio of the mode crosstalk was limited to only several tens of meters in turbulent ocean. The existence of oceanic turbulence evidently induced OAM mode crosstalk and spiral spectrum spread. The effects of oceanic turbulence on the OAM mode detection probability increased with the increase of radial and azimuthal mode orders, oceanic turbulent equivalent temperature structure parameter, and temperature-salinity balance parameter. The spatial partial coherence of the beam source would enhance the effect of turbulent aberrations on the signal OAM mode detection probability, and fully coherent vortex beams provided better performance than partially coherent ones. Increasing wavelength of the vortex beams would help improve the performance of this quantum optical communication system. These results might be of interest for the potential application of optical vortices in practical underwater quantum optical communication among divers, submarines, and sensors in the ocean environment. PMID:27409021
A study on turbulence modulation via an analysis of turbulence anisotropy-invariants
Institute of Scientific and Technical Information of China (English)
Michael; MANHART
2010-01-01
We investigate the turbulence modulation by particles in a turbulent two-phase channel flow via an analysis of turbulence anisotropy-invariants. The fluid turbulence is calculated by a large eddy simulation with a point-force two-way coupling model and particles are tracked by the Lagrangian trajectory method. The channel turbulence follows the two-component turbulence state within the viscous sub-layer region and outside the region the turbulence tends to follow the right curve of the anisotropy-invariant. The channel turbulence, interacting with heavy particles, is modulated to the two-component turbulence limit state near the wall and is separate from the axisymmetric turbulence state in the turbulence anisotropy-invariants map. The fluctuations of streamwise component are transferred to the other two components and hence the anisotropy decreases due to particle modulation. The study has deepened the understanding of the turbulence modulation mechanism in two-phase turbulent flows.
Is Navier-Stokes turbulence chaotic?
Deissler, R. G.
1986-01-01
Whether turbulent solutions of the Navier-Stokes equations are chaotic is considered. Initially neighboring solutions for a low-Reynolds-number fully developed turbulence are compared. The turbulence is sustained by a nonrandom time-independent external force. The solutions separate exponentially with time, having a positive Liapunov characteristic exponent. Thus the turbulence is characterized as chaotic.
Impurity transport in plasma edge turbulence
Naulin, V; Rasmussen, J J; Naulin, Volker; Wood, Martin Priego; Rasmussen, Jens Juul
2004-01-01
The turbulent transport of minority species/impurities is investigated in 2D drift-wave turbulence as well as in 3D toroidal drift-Alfven edge turbulence. The full effects of perpendicular and -- in 3D -- parallel advection are kept for the impurity species. Anomalous pinch effects are recovered and explained in terms of Turbulent EquiPartition (TEP)
Strong Turbulence in Partially Ionized Plasmas
DEFF Research Database (Denmark)
Mikkelsen, Torben; Pécseli, Hans
1980-01-01
Experimental investigations of strong turbulence in partially ionized, low-β plasmas are reported. The observed spectra are interpreted by applying Taylor's hypothesis and related to turbulent fluctuations in the ionosphere.......Experimental investigations of strong turbulence in partially ionized, low-β plasmas are reported. The observed spectra are interpreted by applying Taylor's hypothesis and related to turbulent fluctuations in the ionosphere....
Clumps in drift wave turbulence
DEFF Research Database (Denmark)
Pecseli, H. L.; Mikkelsen, Torben
1986-01-01
, two-dimensional random flow serves as a particularly simple illustration. For this case particles can be trapped for all times in a local vortex (macro-clump). A small test-cloud of particles (micro-clump) chosen arbitrarily in a realization will on the other hand expand on average. A formulation is...... proposed in terms of conditional eddies, in order to discriminate turbulent flows where macro-clumps may be observed. The analysis is illustrated by results from experimental investigations of strongly turbulent, resistive drift-wave fluctuations. The related problem for electrostatic turbulence in...