Geometrooptical Representation of the Field Produced by an Extended Source in a Two-Dimensional Inhomogeneous Medium

2002 ◽  
Vol 48 (6) ◽  
pp. 735
Author(s):  
B. P. Sharfarets
Keyword(s):  
Inhomogeneous Medium ◽  
Two Dimensional ◽  
Extended Source

MAGNETIC FIELD AMPLIFICATION BY RELATIVISTIC SHOCKS IN AN INHOMOGENEOUS MEDIUM

2012 ◽  
Vol 08 ◽  
pp. 364-367
Author(s):  
YOSUKE MIZUNO ◽  
MARTIN POHL ◽  
JACEK NIEMIEC ◽  
BING ZHANG ◽  
KEN-ICHI NISHIKAWA ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Inhomogeneous Medium ◽  
Magnetic Energy ◽  
Small Scale ◽  
Two Dimensional ◽  
Filamentary Structure ◽  
Field Amplification ◽  
Relativistic Shocks ◽  
Field Lines ◽  
Magnetohydrodynamic Simulations

We perform two-dimensional relativistic magnetohydrodynamic simulations of a mildly relativistic shock propagating through an inhomogeneous medium. We show that the postshock region becomes turbulent owing to preshock density inhomogeneity, and the magnetic field is strongly amplified due to the stretching and folding of field lines in the turbulent velocity field. The amplified magnetic field evolves into a filamentary structure in two-dimensional simulations. The magnetic energy spectrum is flatter than the Kolmogorov spectrum and indicates that the so-called small-scale dynamo is occurring in the postshock region. We also find that the amplitude of magnetic-field amplification depends on the direction of the mean preshock magnetic field.

Two‐dimensional acoustic modeling by a hybrid method

Geophysics ◽  
1985 ◽  
Vol 50 (8) ◽  
pp. 1273-1284 ◽  
Author(s):  
V. Shtivelman
Keyword(s):  
Wave Propagation ◽  
Wave Field ◽  
Inhomogeneous Medium ◽  
Hybrid Method ◽  
Wave Scattering ◽  
Acoustic Modeling ◽  
Two Dimensional ◽  
Numerical Techniques ◽  
Numerical Examples ◽  
Field Computation

This paper follows previous work (Shtivelman, 1984) in which a hybrid method for wave‐field computation was developed. The method combines analytical and numerical techniques and is based upon separation of the processes of wave scattering and wave propagation. The method is further developed and improved; particularly, it is generalized for the case of an inhomogeneous medium above scattering objects (provided the inhomogeneity is weak, i.e., the effects of scattering can be neglected) and is represented by a simpler and more convenient form. Several numerical examples illustrating application of the method to the problems of two‐dimensional acoustic modeling are considered.

scholarly journals Image Reconstruction of Two-Dimensional Highly Scattering Inhomogeneous Medium Using MAP-Based Estimation

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Hong Qi ◽  
Yaobin Qiao ◽  
Shuangcheng Sun ◽  
Yuchen Yao ◽  
Liming Ruan
Keyword(s):  
Image Reconstruction ◽  
Inhomogeneous Medium ◽  
Measurement Errors ◽  
Field Model ◽  
Test Cases ◽  
Two Dimensional ◽  
Map Estimation ◽  
A Posteriori ◽  
Markov Random ◽  
Initial Distributions

A maximum a posteriori (MAP) estimation based on Bayesian framework is applied to image reconstruction of two-dimensional highly scattering inhomogeneous medium. The finite difference method (FDM) and conjugate gradient (CG) algorithm serve as the forward and inverse solving models, respectively. The generalized Gaussian Markov random field model (GGMRF) is treated as the regularization, and finally the influence of the measurement errors and initial distributions is investigated. Through the test cases, the MAP estimate algorithm is demonstrated to greatly improve the reconstruction results of the optical coefficients.

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