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Stéphane Randoux, François Gustave, Pierre Suret, Gennady El
We examine integrable turbulence (IT) in the framework of the defocusing cubic one-dimensional nonlinear Schrödinger equation. This is done theoretically and experimentally, by realizing an optical fiber experiment in which the defocusing Kerr nonlinearity strongly dominates linear dispersive effects. Using a dispersive-hydrodynamic approach, we show that the development of IT can be divided into two distinct stages, the initial, prebreaking stage being described by a system of interacting random Riemann waves...
June 9, 2017: Physical Review Letters
Prahit Dubey, Urmila Ghia, Leonid A Turkevich
Dustiness quantifies the propensity of a finely divided solid to be aerosolized by a prescribed mechanical stimulus. Dustiness is relevant wherever powders are mixed, transferred or handled, and is important in the control of hazardous exposures and the prevention of dust explosions and product loss. Limited quantities of active pharmaceutical powders available for testing led to the development (at University of North Carolina) of a Venturi-driven dustiness tester. The powder is turbulently injected at high speed (Re ~ 2 × 10(4)) into a glass chamber; the aerosol is then gently sampled (Re ~ 2 × 10(3)) through two filters located at the top of the chamber; the dustiness index is the ratio of sampled to injected mass of powder...
May 2017: Powder Technology
Alberto Amato, Gianluca Dell'Aquila, Francesco Musacchia, Rossella Annunziata, Ari Ugarte, Nicolas Maillet, Alessandra Carbone, Maurizio Ribera d'Alcalà, Remo Sanges, Daniele Iudicone, Maria I Ferrante
Diatoms are a fundamental microalgal phylum that thrives in turbulent environments. Despite several experimental and numerical studies, if and how diatoms may profit from turbulence is still an open question. One of the leading arguments is that turbulence favours nutrient uptake. Morphological features, such as the absence of flagella, the presence of a rigid exoskeleton and the micrometre size would support the possible passive but beneficial role of turbulence on diatoms. We demonstrate that in fact diatoms actively respond to turbulence in non-limiting nutrient conditions...
June 19, 2017: Scientific Reports
Xiaohua Wu, Parviz Moin, James M Wallace, Jinhie Skarda, Adrián Lozano-Durán, Jean-Pierre Hickey
Two observations drawn from a thoroughly validated direct numerical simulation of the canonical spatially developing, zero-pressure gradient, smooth, flat-plate boundary layer are presented here. The first is that, for bypass transition in the narrow sense defined herein, we found that the transitional-turbulent spot inception mechanism is analogous to the secondary instability of boundary-layer natural transition, namely a spanwise vortex filament becomes a [Formula: see text] vortex and then, a hairpin packet...
June 19, 2017: Proceedings of the National Academy of Sciences of the United States of America
Paolo Luchini
For nearly a century, the universal logarithmic law of the mean velocity profile has been a mainstay of turbulent fluid mechanics and its teaching. Yet many experiments and numerical simulations are not fit exceedingly well by it, and the question whether the logarithmic law is indeed universal keeps turning up in discussion and in writing. Large experiments have been set up in various parts of the world to confirm or deny the logarithmic law and accurately estimate von Kármán's constant, the coefficient that governs it...
June 2, 2017: Physical Review Letters
Lipo Wang, Yongxiang Huang
The active interaction between the bacteria and fluid generates turbulent structures even at zero Reynolds number. The velocity of such a flow obtained experimentally has been quantitatively investigated based on streamline segment analysis. There is a clear transition at about 16 times the organism body length separating two different scale regimes, which may be attributed to the different influence of the viscous effect. Surprisingly the scaling extracted from the streamline segment indicates the existence of scale similarity even at the zero Reynolds number limit...
May 2017: Physical Review. E
Adam W DeMarco, Sukanta Basu
Utilizing synthetically generated random variates and laboratory measurements, we document the inherent limitations of the conventional structure function approach in limited sample size settings. We demonstrate that an alternative approach, based on the principle of maximum likelihood, can provide nearly unbiased structure function estimates with far less uncertainty under such unfavorable conditions. The superiority of this approach over the conventional approach does not diminish even in the case of strongly correlated samples...
May 2017: Physical Review. E
Audun Skaugen, Luiza Angheluta
We establish a statistical relationship between the inverse energy cascade and the spatial correlations of clustered vortices in two-dimensional quantum turbulence. The Kolmogorov spectrum k^{-5/3} on inertial scales r corresponds to a pair correlation function between the vortices with different signs that decays as a power law with the pair distance given as r^{-4/3}. To test these scaling relations, we propose a forced and dissipative point vortex model that captures the turbulent dynamics of quantized vortices by the emergent clustering of same-sign vortices...
May 2017: Physical Review. E
E Jurčišinová, M Jurčišin
The influence of the uniaxial small-scale anisotropy on the kinematic magnetohydrodynamic turbulence is investigated by using the field theoretic renormalization group technique in the one-loop approximation of a perturbation theory. The infrared stable fixed point of the renormalization group equations, which drives the scaling properties of the model in the inertial range, is investigated as the function of the anisotropy parameters and it is shown that, at least at the one-loop level of approximation, the diffusion processes of the weak passive magnetic field in the anisotropically driven kinematic magnetohydrodynamic turbulence are completely equivalent to the corresponding diffusion processes of passively advected scalar fields in the anisotropic Navier-Stokes turbulent environments...
May 2017: Physical Review. E
Thomas Köllner, Thomas Boeck, Jörg Schumacher
The combined effects of buoyancy-driven Rayleigh-Bénard convection (RC) and surface tension-driven Marangoni convection (MC) are studied in a triple-layer configuration which serves as a simplified model for a liquid metal battery (LMB). The three-layer model consists of a liquid metal alloy cathode, a molten salt separation layer, and a liquid metal anode at the top. Convection is triggered by the temperature gradient between the hot electrolyte and the colder electrodes, which is a consequence of the release of resistive heat during operation...
May 2017: Physical Review. E
Michael Liberman, Nathan Kleeorin, Igor Rogachevskii, Nils Erland L Haugen
It is known that unconfined dust explosions typically start off with a relatively weak primary flame followed by a severe secondary explosion. We show that clustering of dust particles in a temperature stratified turbulent flow ahead of the primary flame may give rise to a significant increase in the radiation penetration length. These particle clusters, even far ahead of the flame, are sufficiently exposed and heated by the radiation from the flame to become ignition kernels capable to ignite a large volume of fuel-air mixtures...
May 2017: Physical Review. E
Taketo Ariki
Mean-field-based Lagrangian framework is developed for the fluid turbulence theory, which enables physically objective discussions, especially, of the history effect. Mean flow serves as a purely geometrical object of Lie group theory, providing useful operations to measure the objective rate and history integration of the general tensor field. The proposed framework is applied, on the one hand, to one-point closure model, yielding an objective expression of the turbulence viscoelastic effect. Application to two-point closure, on the other hand, is also discussed, where natural extension of known Lagrangian correlation is discovered on the basis of an extended covariance group...
May 2017: Physical Review. E
E Jurčišinová, M Jurčišin, M Menkyna
Using the field theoretic renormalization group technique and the operator product expansion, the systematic investigation of the influence of the spatial parity violation on the anomalous scaling behavior of correlation functions of the weak passive magnetic field in the framework of the compressible Kazantsev-Kraichnan model with the presence of a large-scale anisotropy is performed up to the second order of the perturbation theory (two-loop approximation). The renormalization group analysis of the model is done and the two-loop explicit expressions for the anomalous and critical dimensions of the leading composite operators are found as functions of the helicity and compressibility parameters and their anisotropic hierarchies are discussed...
May 2017: Physical Review. E
Ji Li, Chengwen Zhong, Yong Wang, Congshan Zhuo
In our study, the dual time-stepping strategy of the gas-kinetic scheme is constructed and used for the simulation of unsteady flows. In comparison to the previous implicit gas-kinetic scheme, both the inviscid and viscous flux Jacobian are considered in our work, and the linear system of the pseudo-steady-state is solved by applying generalized minimal residual algorithm. The accuracy is validated by several numerical cases, the incompressible flow around blunt bodies (stationary circular cylinder and square cylinder), and the transonic buffet on the NACA0012 airfoil under hybrid mesh...
May 2017: Physical Review. E
Gaspar Cano, Rui Dilão
We show that action potentials in the Hodgkin-Huxley neuron model result from a type I intermittency phenomenon that occurs in the proximity of a saddle-node bifurcation of limit cycles. For the Hodgkin-Huxley spatially extended model, describing propagation of action potential along axons, we show the existence of type I intermittency and a new type of chaotic intermittency, as well as space propagating regular and chaotic diffusion waves. Chaotic intermittency occurs in the transition from a turbulent regime to the resting regime of the transmembrane potential and is characterised by the existence of a sequence of action potential spikes occurring at irregular time intervals...
June 14, 2017: Journal of Computational Neuroscience
Christian Binter, Alexander Gotschy, Simon H Sündermann, Michelle Frank, Felix C Tanner, Thomas F Lüscher, Robert Manka, Sebastian Kozerke
BACKGROUND: Turbulent kinetic energy (TKE), assessed by 4-dimensional (4D) flow magnetic resonance imaging, is a measure of energy loss in disturbed flow as it occurs, for instance, in aortic stenosis (AS). This work investigates the additional information provided by quantifying TKE for the assessment of AS severity in comparison to clinical echocardiographic measures. METHODS AND RESULTS: Fifty-one patients with AS (67±15 years, 20 female) and 10 healthy age-matched controls (69±5 years, 5 female) were prospectively enrolled to undergo multipoint 4D flow magnetic resonance imaging...
June 2017: Circulation. Cardiovascular Imaging
Ann Lantagne, Wyndol Furman
The present study explored how romantic relationship qualities develop with age and relationship length. Eight waves of data on romantic relationships were collected over 10.5 years during adolescence and early adulthood from a community-based sample in a Western U.S. city (100 males, 100 females; M age Wave 1 = 15.83). Measures of support, negative interactions, control, and jealousy were derived from interviews and questionnaire measures. Using multilevel modeling, main effects of age were found for jealousy, and main effects of relationship length were found for each quality...
June 12, 2017: Developmental Psychology
Anna-Maria Ciciliani, Peter Langguth, Herbert Wachtel
BACKGROUND: Combining in vitro mouth-throat deposition measurements, cascade impactor data and computational fluid dynamics (CFD) simulations, four different inhalers were compared which are indicated for chronic obstructive pulmonary disease (COPD) treatment. METHODS: The Respimat inhaler, the Breezhaler, the Genuair, and the Ellipta were coupled to the idealized Alberta throat model. The modeled dose to the lung (mDTL) was collected downstream of the Alberta throat model using either a filter or a next generation impactor (NGI)...
2017: International Journal of Chronic Obstructive Pulmonary Disease
Patricia A Dailey, Robert Harwood, Kyle Walsh, James B Fink, Tina Thayer, Greg Gagnon, Arzu Ari
BACKGROUND: Heliox (helium-oxygen mixture) has been shown to reduce turbulence and improve aerosol delivery in a range of clinical settings. We questioned whether heliox as compared with oxygen via high-flow nasal cannula (HFNC) would affect aerosol delivery. We hypothesized that heliox would have a significant effect on aerosol delivery as compared with oxygen with both quiet and distressed breathing patterns. METHODS: A vibrating mesh nebulizer was placed at the inlet of a humidifier via HFNC with small adult cannula distal to the heated-wire circuit with prongs placed into simulated nares with a T-shaped trap and absolute filter connected to a breath simulator set to adult quiet and distressed breathing parameters...
June 6, 2017: Respiratory Care
Denis Berdajs, Selim Mosbahi, Enrico Ferrari, Dominique Charbonnier, Ludwig K von Segesser
BACKGROUND: In this study, the effect of aortic valve (AV) pathology on local hemodynamic conditions was evaluated as a potential trigger for the onset of acute type A and B aortic dissection. METHODS: A time- and pressure-related four-dimensional (4-D) computed fluid dynamic model of the aorta was established. In an experimental setup, AV stenosis and AV insufficiency were created. 4-D pressure-related geometry of the aortic root (AR) with valve insufficiency and valve stenosis were determined by high-fidelity (200 Hz) microsonometric crystals...
June 3, 2017: Annals of Thoracic Surgery
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