Image registration using stationary velocity fields parameterized by norm-minimizing Wendland kernel

2015 ◽  
Author(s):  
Akshay Pai ◽  
Stefan Sommer ◽  
Lauge Sørensen ◽  
Sune Darkner ◽  
Jon Sporring ◽  
...  
Keyword(s):  
Image Registration ◽  
Velocity Fields ◽  
Stationary Velocity

Kernel Bundle Diffeomorphic Image Registration Using Stationary Velocity Fields and Wendland Basis Functions

2016 ◽  
Vol 35 (6) ◽  
pp. 1369-1380 ◽  
Author(s):  
Akshay Pai ◽  
Stefan Sommer ◽  
Lauge Sorensen ◽  
Sune Darkner ◽  
Jon Sporring ◽  
...  
Keyword(s):  
Image Registration ◽  
Velocity Fields ◽  
Basis Functions ◽  
Diffeomorphic Image Registration ◽  
Stationary Velocity

Symmetries in hydrodynamic turbulence and MHD dynamo theory

1996 ◽  
Vol 56 (3) ◽  
pp. 391-406 ◽  
Author(s):  
George Knorr
Keyword(s):  
Magnetic Fields ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Velocity Fields ◽  
Dynamo Theory ◽  
Hydrodynamic Turbulence ◽  
Mhd Dynamo ◽  
Ideal Mhd ◽  
Dynamo Effect ◽  
Stationary Velocity

The three-dimensional equations of ideal hydrodynamics and ideal MHD are expanded in eigenfunctions of the curl, and the resulting basic interactions of these nonlinear systems are analysed. As the equations are invariant under time and amplitude reversal, a criterion defining the arrow of time is introduced. A new parameter, the center of energy, serves to characterize a basic interaction. In the 3D Euler equations we find four different interactions and their mirror images, two of which can transport energy to smaller wavenumbers. This can lead to the appearance of structures in turbulent flow, and throws doubt on a derivation of Kolmogorov's law based on a cascading of energy to higher wavenumbers.In energy the corresponding two-dimensional equations, which are isomorphic to the guiding centre model in plasma physics, only one interaction exists, with a strong inverse cascade, which can lead to accumulation of energy in the spatially largest accessible modes. In MHD theory it is possible to separate magnetic from kinetic interactions. The former give again four basic interactions, two being regular and two being inverse cascades. One of these is quite strong, and can lead to the MHD dynamo effect. Kinetic energy can be transferred into magnetic energy. The dynamo effect is is accompanied by alignment of velocity and magnetic fields. We show that stationary velocity fields may lead to exponentially growing magnetic fields and we give an explicit criterion for this instability.

C. The Continuous Spectrum of Pulsating Variable Stars

1967 ◽  
Vol 28 ◽  
pp. 177-206
Author(s):  
J. B. Oke ◽  
C. A. Whitney
Keyword(s):  
Continuous Spectrum ◽  
Variable Stars ◽  
Velocity Fields ◽  
The Other ◽  
Line Spectrum ◽  
Direct Information ◽  
Thermodynamic Structure ◽  
Diagnostic Interpretation ◽  
Pulsating Variable Stars ◽  
The Continuum

Pecker:The topic to be considered today is the continuous spectrum of certain stars, whose variability we attribute to a pulsation of some part of their structure. Obviously, this continuous spectrum provides a test of the pulsation theory to the extent that the continuum is completely and accurately observed and that we can analyse it to infer the structure of the star producing it. The continuum is one of the two possible spectral observations; the other is the line spectrum. It is obvious that from studies of the continuum alone, we obtain no direct information on the velocity fields in the star. We obtain information only on the thermodynamic structure of the photospheric layers of these stars–the photospheric layers being defined as those from which the observed continuum directly arises. So the problems arising in a study of the continuum are of two general kinds: completeness of observation, and adequacy of diagnostic interpretation. I will make a few comments on these, then turn the meeting over to Oke and Whitney.

Sign in / Sign up

Export Citation Format

Share Document