scholarly journals The role of coherent structures and inhomogeneity in near-field interscale turbulent energy transfers

2020 ◽  
Vol 896 ◽  
Author(s):  
F. Alves Portela ◽  
G. Papadakis ◽  
J. C. Vassilicos
Keyword(s):  
Coherent Structures ◽  
Near Field ◽  
Turbulent Energy ◽  
Energy Transfers ◽  
Image Position

The role of differential phase contrast in electron microscopy

1978 ◽  
Vol 36 (1) ◽  
pp. 176-177
Author(s):  
E.M. Waddell ◽  
J.N. Chapman ◽  
R.P. Ferrier
Keyword(s):  
Phase Contrast ◽  
Practical Method ◽  
Position Vector ◽  
Differential Phase ◽  
Pure Phase ◽  
Differential Phase Contrast ◽  
The Difference ◽  
Image Position ◽  
First Moment

Dekkers and de Lang (1977) have discussed a practical method of realising differential phase contrast in a STEM. The method involves taking the difference signal from two semi-circular detectors placed symmetrically about the optic axis and subtending the same angle (2α) at the specimen as that of the cone of illumination. Such a system, or an obvious generalisation of it, namely a quadrant detector, has the characteristic of responding to the gradient of the phase of the specimen transmittance. In this paper we shall compare the performance of this type of system with that of a first moment detector (Waddell et al.1977).For a first moment detector the response function R(k) is of the form R(k) = ck where c is a constant, k is a position vector in the detector plane and the vector nature of R(k)indicates that two signals are produced. This type of system would produce an image signal given bywhere the specimen transmittance is given by a (r) exp (iϕ (r), r is a position vector in object space, ro the position of the probe, ⊛ represents a convolution integral and it has been assumed that we have a coherent probe, with a complex disturbance of the form b(r-ro) exp (iζ (r-ro)). Thus the image signal for a pure phase object imaged in a STEM using a first moment detector is b2 ⊛ ▽ø. Note that this puts no restrictions on the magnitude of the variation of the phase function, but does assume an infinite detector.

scholarly journals Role of the forcing dimensionality in thin-layer turbulent energy cascades

2020 ◽  
Vol 5 (6) ◽  
Author(s):  
Basile Poujol ◽  
Adrian van Kan ◽  
Alexandros Alexakis
Keyword(s):  
Thin Layer ◽  
Turbulent Energy ◽  
Energy Cascades

On the dynamical role of coherent structures in turbulence

2012 ◽  
Vol 13 (9-10) ◽  
pp. 866-877 ◽  
Author(s):  
Nicholas T. Ouellette
Keyword(s):  
Coherent Structures
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