scholarly journals On the Monotonicity and Log-Convexity of a Four-Parameter Homogeneous Mean

2008 ◽  
Vol 2008 (1) ◽  
pp. 149286 ◽  
Author(s):  
Zhen-Hang Yang
Keyword(s):  
Homogeneous Mean

Analytical theory of homogeneous mean shear turbulence

2013 ◽  
Vol 727 ◽  
pp. 256-281 ◽  
Author(s):  
Jerome Weinstock
Keyword(s):  
Shear Flow ◽  
Exact Expression ◽  
Turbulence Energy ◽  
Velocity Spectrum ◽  
Nonlinear Behaviour ◽  
Local Isotropy ◽  
Characteristic Energy ◽  
Nonlinear Growth ◽  
Homogeneous Mean ◽  
Dominant Characteristic

AbstractA compact nonlinear expression for the velocity spectra of homogeneous mean shear flow is derived by means of a simplified two-point closure. It applies to all scales and times. The derived equation can be viewed as a nonlinear extension of the linear, rapid-distortion-theory (RDT) equation. The principal simplification is to model the nonlinear pressure–strain rate as first-order in the spectral anisotropy: a spectral Rotta-equation. This simplified equation and its solution are expressed in terms of the RDT solution. That solution helps reveal the role of nonlinearity. An equation for the velocity spectrum is then obtained at all scales and times. A dominant characteristic predicted for nonlinear behaviour is that the turbulence energy grows exponentially with time, with the spectrum simultaneously moving to smaller and smaller wavenumbers. The nonlinear growth rate is determined. Other analytical predictions of the derived equation include: the conditions for self-similarity; local isotropy; various properties of mean shear flow, including characteristic energy, length and temporal growth scales; and a critique of perturbation theory. Comparisons are made with laboratory experiments and direct numerical simulations. Although the theory applies to all scales and times, including an exact expression for RDT, the calculations are focused on nonlinear behaviour at large times. Several approximations used in this work are examined.

scholarly journals Soil characterization using patterns of magnetic susceptibility versus effective radium concentration

2011 ◽  
Vol 11 (8) ◽  
pp. 2285-2293 ◽  
Author(s):  
F. Girault ◽  
C. Poitou ◽  
F. Perrier ◽  
B. P. Koirala ◽  
M. Bhattarai
Keyword(s):  
Magnetic Susceptibility ◽  
Radon Emanation ◽  
Residual Soils ◽  
Mean Values ◽  
River Terraces ◽  
Low Field ◽  
Homogeneous Mean ◽  
Clay Layers ◽  
Sample Set ◽  
Soil Groups

Abstract. Low-field magnetic susceptibility χm and effective radium concentration ECRa, obtained from radon emanation, have been measured in the laboratory with 129 soil samples from Nepal. Samples along horizontal profiles in slope debris or terrace scarps showed rather homogeneous values of both χm and ECRa. One sample set, collected vertically on a lateritic terrace scarp, had homogeneous values of ECRa while χm increased by a factor of 1 to 10 for residual soils and topsoils. However, for a set of samples collected on three imbricated river terraces, values of ECRa, homogeneous over a given terrace, displayed a gradual increase from younger to older terraces. By contrast, χm showed more homogeneous mean values over the three terraces, with a larger dispersion, however, for the younger one. Similarly, Kathmandu sediments exhibited a large increase in ECRa from sand to clay layers, while χm increased moderately. The combination of χm and ECRa, thus, provides a novel tool to characterize quantitatively various soil groups and may be of interest to distinguish modes of alteration or deposition histories.

scholarly journals Analytical Solutions of the Balance Equation for the Scalar Variance in One-Dimensional Turbulent Flows under Stationary Conditions

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
Andrea Amicarelli ◽  
Annalisa Di Bernardino ◽  
Franco Catalano ◽  
Giovanni Leuzzi ◽  
Paolo Monti
Keyword(s):  
Turbulent Flows ◽  
Analytical Solutions ◽  
Dirichlet Boundary Conditions ◽  
Navier Stokes ◽  
One Dimensional ◽  
Concentration Variance ◽  
Scalar Variance ◽  
Homogeneous Mean ◽  
Stationary Conditions ◽  
Reactive Scalars

This study presents 1D analytical solutions for the ensemble variance of reactive scalars in one-dimensional turbulent flows, in case of stationary conditions, homogeneous mean scalar gradient and turbulence, Dirichlet boundary conditions, and first order kinetics reactions. Simplified solutions and sensitivity analysis are also discussed. These solutions represent both analytical tools for preliminary estimations of the concentration variance and upwind spatial reconstruction schemes for CFD (Computational Fluid Dynamics)—RANS (Reynolds-Averaged Navier-Stokes) codes, which estimate the turbulent fluctuations of reactive scalars.

scholarly journals Non-homogeneous mean field picture for spin-glasses

1981 ◽  
Vol 42 (4) ◽  
pp. 73-77 ◽  
Author(s):  
H. Orland ◽  
C. de Dominicis ◽  
T. Garel
Keyword(s):  
Spin Glasses ◽  
Mean Field ◽  
Homogeneous Mean

The Turbulent Schmidt Number

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Diego A. Donzis ◽  
Konduri Aditya ◽  
K. R. Sreenivasan ◽  
P. K. Yeung
Keyword(s):  
Schmidt Number ◽  
Isotropic Turbulence ◽  
Functional Dependence ◽  
Three Dimensional ◽  
Passive Scalars ◽  
Turbulent Schmidt Number ◽  
Schmidt Numbers ◽  
Homogeneous And Isotropic Turbulence ◽  
Homogeneous Mean ◽  
Parameter Ranges

We analyze a large database generated from recent direct numerical simulations (DNS) of passive scalars sustained by a homogeneous mean gradient and mixed by homogeneous and isotropic turbulence on grid resolutions of up to 40963 and extract the turbulent Schmidt number over large parameter ranges: the Taylor microscale Reynolds number between 8 and 650 and the molecular Schmidt number between 1/2048 and 1024. While the turbulent Schmidt number shows considerable scatter with respect to the Reynolds and molecular Schmidt numbers separately, it exhibits a sensibly unique functional dependence with respect to the molecular Péclet number. The observed functional dependence is motivated by a scaling argument that is standard in the phenomenology of three-dimensional turbulence.

The Contrast Contrast Illusion

2017 ◽  
Author(s):  
Charles Chubb ◽  
Joshua A. Solomon ◽  
George Sperling
Keyword(s):  
Individual Differences ◽  
Spatial Frequency ◽  
High Contrast ◽  
Gray Background ◽  
Contrast Polarity ◽  
Homogeneous Mean ◽  
Texture Contrast

To most observers, a patch of medium-contrast texture viewed against a background of high-contrast texture appears lower in contrast than an identical patch viewed against a homogeneous, mean gray background. This is the contrast contrast illusion. This chapter reviews basic findings concerning this illusion; for example, the contrast contrast illusion is selective for texture spatial frequency as well as for texture contrast polarity. Several theories to account for the illusion are discussed. Related concepts such as texture contrast, textual granularity, individual differences, contrast polarity, color and the contrast contrast illusion, and ecological accounts of the contrast contrast illusion are explored.

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