scholarly journals TRPIV investigation of space-time correlation in turbulent flows over flat and wavy walls

2014 ◽  
Vol 30 (4) ◽  
pp. 468-479 ◽  
Author(s):  
Wei Wang ◽  
Xin-Lei Guan ◽  
Nan Jiang
Keyword(s):  
Turbulent Flows ◽  
Time Correlation ◽  
Space Time

scholarly journals Spatial and space-time correlations in systems of subpopulations with genetic drift and migration.

Genetics ◽  
1993 ◽  
Vol 133 (3) ◽  
pp. 711-727
Author(s):  
B K Epperson
Keyword(s):  
Population Genetics ◽  
Time Correlation ◽  
Space Time ◽  
Spatial Correlations ◽  
Gene Frequencies ◽  
Migration Patterns ◽  
Migration Rates ◽  
Space And Time ◽  
Time Correlations ◽  
And Migration

Abstract The geographic distribution of genetic variation is an important theoretical and experimental component of population genetics. Previous characterizations of genetic structure of populations have used measures of spatial variance and spatial correlations. Yet a full understanding of the causes and consequences of spatial structure requires complete characterization of the underlying space-time system. This paper examines important interactions between processes and spatial structure in systems of subpopulations with migration and drift, by analyzing correlations of gene frequencies over space and time. We develop methods for studying important features of the complete set of space-time correlations of gene frequencies for the first time in population genetics. These methods also provide a new alternative for studying the purely spatial correlations and the variance, for models with general spatial dimensionalities and migration patterns. These results are obtained by employing theorems, previously unused in population genetics, for space-time autoregressive (STAR) stochastic spatial time series. We include results on systems with subpopulation interactions that have time delay lags (temporal orders) greater than one. We use the space-time correlation structure to develop novel estimators for migration rates that are based on space-time data (samples collected over space and time) rather than on purely spatial data, for real systems. We examine the space-time and spatial correlations for some specific stepping stone migration models. One focus is on the effects of anisotropic migration rates. Partial space-time correlation coefficients can be used for identifying migration patterns. Using STAR models, the spatial, space-time, and partial space-time correlations together provide a framework with an unprecedented level of detail for characterizing, predicting and contrasting space-time theoretical distributions of gene frequencies, and for identifying features such as the pattern of migration and estimating migration rates in experimental studies of genetic variation over space and time.

Turbulence functions useful for probes (space–time correlation) and for scattering (wave-number–frequency spectrum) analysis

1968 ◽  
Vol 46 (23) ◽  
pp. 2683-2702 ◽  
Author(s):  
I. P. Shkarofsky
Keyword(s):  
Characteristic Size ◽  
Time Correlation ◽  
Exponential Model ◽  
Time Correlation Function ◽  
Maximum Energy ◽  
Confluent Hypergeometric Function ◽  
Space Time ◽  
Wave Number ◽  
Taylor’S Hypothesis ◽  
Number Frequency

The wave-number–frequency dependent spectral function, S(k, ω), and the space–time correlation function, C(r, t), are considered in a turbulent flowing plasma. The decay mechanisms are associated with either velocity fluctuations about the mean convection velocity or diffusion effects or attachment, or combinations of these, including the Brownian motion model. The ψ(k, ω) function, which is the ratio of S(k, ω) to its frequency-integrated value, depends on the mechanism and exhibits a profile which can be Gaussian, Lorentzian, a Z function, a Hermite polynomial modification of the Gaussian, or a confluent hypergeometric function. Anisotropic forms are also considered.The function C(r, t), obtained by convolving ψ (r, t) with C(r), the space autocorrelation function, is next considered. Adopting a Gaussian or an exponential model (which may be anisotropic) for C(r), we illustrate C(r, t) forms, which can readily be manipulated. Furthermore, letting r = 0, we derive two conditions for the applicability of Taylor's hypothesis. The assumption of frozen flow is not necessary, only that the root-mean-square Lagrangian displacement in a given time, associated with the decay, be much smaller than both the flow distance and the characteristic size of blobs having maximum energy.

Space-time correlation measurements in a hypersonic transitional boundary layer

1995 ◽  
Author(s):  
Roger Kimmel ◽  
Anthony Demetriades ◽  
Joseph Donaldson
Keyword(s):  
Boundary Layer ◽  
Time Correlation ◽  
Space Time ◽  
Transitional Boundary Layer

scholarly journals Particle dispersion processes in two-dimensional turbulence: a comparison with 2-D kinematic simulation.

2007 ◽  
Vol 14 (2) ◽  
pp. 139-151 ◽  
Author(s):  
R. Castilla ◽  
J. M. Redondo ◽  
P. J. Gámez-Montero ◽  
A. Babiano
Keyword(s):  
Turbulent Flows ◽  
Particle Dispersion ◽  
Space Time ◽  
Relative Dispersion ◽  
Kinematic Simulation ◽  
Space Time Structure ◽  
Coherent Vortices ◽  
The One ◽  
Turbulent Particle Dispersion ◽  
Kinematic Simulations

Abstract. We study numerically the comparison between Lagrangian experiments on turbulent particle dispersion in 2-D turbulent flows performed, on the one hand, on the basis of direct numerical simulations (DNS) and, on the other hand, using kinematic simulations (KS). Eulerian space-time structure of both DNS and KS dynamics are not comparable, mostly due to the absence of strong coherent vortices and advection processes in the KS fields. The comparison allows to refine past studies about the contribution of non-homogeneous space-time 2-D Eulerian structure on the turbulent absolute and relative particle dispersion processes. We particularly focus our discussion on the Richardson's regime for relative dispersion.

Space-time correlation based fast regional spectrum sensing in cognitive radio

2017 ◽  
Vol 14 (5) ◽  
pp. 78-90 ◽  
Author(s):  
Sai Huang ◽  
Yuanyuan Yao ◽  
Zhiyong Feng ◽  
Ping Zhang ◽  
Yifan Zhang
Keyword(s):  
Cognitive Radio ◽  
Spectrum Sensing ◽  
Time Correlation ◽  
Space Time
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