Long distance time reversal and imaging in random media: Numerical simulations

2001 ◽  
Vol 110 (5) ◽  
pp. 2633-2633 ◽  
Author(s):  
Peter Blomgren ◽  
George Papanicolaou ◽  
Hongkai Zhao
Keyword(s):  
Numerical Simulations ◽  
Time Reversal ◽  
Random Media ◽  
Long Distance

Backscattering time‐reversal of acoustic waves in random media

1999 ◽  
Vol 105 (2) ◽  
pp. 956-956
Author(s):  
Arnaud Tourin ◽  
Arnaud Derode ◽  
Mathias Fink
Keyword(s):  
Time Reversal ◽  
Acoustic Waves ◽  
Random Media

The Computational Study of Microwave-Induced Thermo-Acoustic Tomography for Biologic Tissue Imaging Based on Pseudo-Spectrum Time Domain and Time Reversal Mirror Technique

2012 ◽  
Vol 195-196 ◽  
pp. 353-359 ◽  
Author(s):  
Guo Ping Chen ◽  
Zhi Qin Zhao ◽  
Qing H. Liu
Keyword(s):  
Time Domain ◽  
Time Reversal ◽  
Random Media ◽  
Imaging System ◽  
Malignant Tumors ◽  
Computational Study ◽  
Initial Pressure ◽  
Acoustic Tomography ◽  
Model Parameters ◽  
Time Reversal Mirror

Microwave-Induced Thermo-Acoustic Tomography (MITAT) own much concerns in recent years in biomedical imaging field. High contrast and resolution compared with conventional microwave or ultrasound imaging system especially for malignant tumors are outstanding characters of it. In this paper, the induced thermo-acoustic wave propagating in a mimic biologic tissue is simulated by numeric method Pseudo-Spectrum Time Domain (PSTD). Due to the excellent performance in noise-depress and the stability for the fluctuation of the model parameters, Time Reversal Mirror (TRM) imaging technique is studied computationally for the simulative received thermo-acoustic signals. Some thermo-acoustic objects with different initial pressure distribution are designed and imaged by TRM technique to represent the complex biologic tissue case in a random media. The quality of images generated by TRM technique based on PSTD method hints the potential of the MITAT technique.

scholarly journals The color phi phenomenon: Not so special, after all?

2021 ◽  
Vol 17 (9) ◽  
pp. e1009344
Author(s):  
Lars Keuninckx ◽  
Axel Cleeremans
Keyword(s):  
Neural Network ◽  
Recurrent Neural Network ◽  
Sensory Processing ◽  
Time Reversal ◽  
Echo State Network ◽  
Connectionist Models ◽  
Long Distance ◽  
Minimal Set ◽  
The Brain

We show how anomalous time reversal of stimuli and their associated responses can exist in very small connectionist models. These networks are built from dynamical toy model neurons which adhere to a minimal set of biologically plausible properties. The appearance of a “ghost” response, temporally and spatially located in between responses caused by actual stimuli, as in the phi phenomenon, is demonstrated in a similar small network, where it is caused by priming and long-distance feedforward paths. We then demonstrate that the color phi phenomenon can be present in an echo state network, a recurrent neural network, without explicitly training for the presence of the effect, such that it emerges as an artifact of the dynamical processing. Our results suggest that the color phi phenomenon might simply be a feature of the inherent dynamical and nonlinear sensory processing in the brain and in and of itself is not related to consciousness.

The effective diffusivity of ordered and freely evolving bubbly suspensions

2018 ◽  
Vol 840 ◽  
pp. 215-237 ◽  
Author(s):  
Aurore Loisy ◽  
Aurore Naso ◽  
Peter D. M. Spelt
Keyword(s):  
Numerical Simulations ◽  
Peclet Number ◽  
Random Media ◽  
Chemical Species ◽  
Effective Diffusivity ◽  
Passive Scalar ◽  
Solid Particles ◽  
Péclet Number ◽  
Mechanical Dispersion ◽  
Fixed Beds

We investigate the dispersion of a passive scalar such as the concentration of a chemical species, or temperature, in homogeneous bubbly suspensions, by determining an effective diffusivity tensor. Defining the longitudinal and transverse components of this tensor with respect to the direction of averaged bubble rise velocity in a zero mixture velocity frame of reference, we focus on the convective contribution thereof, this being expected to be dominant in commonly encountered bubbly flows. We first extend the theory of Kochet al.(J. Fluid Mech., vol. 200, 1989, pp. 173–188) (which is for dispersion in fixed beds of solid particles under Stokes flow) to account for weak inertial effects in the case of ordered suspensions. In the limits of low and of high Péclet number, including the inertial effect of the flow does not affect the scaling of the effective diffusivity with respect to the Péclet number. These results are confirmed by direct numerical simulations performed in different flow regimes, for spherical or very deformed bubbles and from vanishingly small to moderate values of the Reynolds number. Scalar transport in arrays of freely rising bubbles is considered by us subsequently, using numerical simulations. In this case, the dispersion is found to be convectively enhanced at low Péclet number, like in ordered arrays. At high Péclet number, the Taylor dispersion scaling obtained for ordered configurations is replaced by one characterizing a purely mechanical dispersion, as in random media, even if the level of disorder is very low.

scholarly journals Time Reversal for Dispersive Waves in Random Media

2004 ◽  
Vol 64 (5) ◽  
pp. 1810-1838 ◽  
Author(s):  
André Nachbin ◽  
Jean-Pierre Fouque ◽  
Josselin Garnier
Keyword(s):  
Time Reversal ◽  
Random Media ◽  
Dispersive Waves

scholarly journals Time reversal for classical waves in random media

2001 ◽  
Vol 333 (11) ◽  
pp. 1041-1046 ◽  
Author(s):  
Guillaume Bal ◽  
Leonid Ryzhik
Keyword(s):  
Time Reversal ◽  
Random Media ◽  
Classical Waves

NUMERICAL AND EXPERIMENTAL TIME-REVERSAL OF ACOUSTIC WAVES IN RANDOM MEDIA

2001 ◽  
Vol 09 (03) ◽  
pp. 993-1003 ◽  
Author(s):  
ARNAUD DERODE ◽  
MICKAËL TANTER ◽  
ARNAUD TOURIN ◽  
LAURENT SANDRIN ◽  
MATHIAS FINK
Keyword(s):  
Time Reversal ◽  
Acoustic Waves ◽  
Random Media ◽  
Initial Conditions ◽  
Classical Mechanics ◽  
High Sensitivity ◽  
Amount Of Information ◽  
Simulation Based ◽  
Initial Source ◽  
Time Invariant

In classical mechanics, a time-reversal experiment with a large number of particles is impossible. Because of the high sensitivity to initial conditions, one would need to resolve the positions and velocities of each particle with infinite accuracy. Thus, it would require an infinite amount of information, which is of course out of reach. In wave physics however, the amount of information required to describe a wave field is limited and depends on the shortest wavelength of the field. Thus we can propose an acoustic equivalent of the experiment we mentioned above. We start with a coherent transient pulse, let it propagate through a disordered highly scattering medium, then record the scattered field and time-reverse it: surprisingly, it travels back to its initial source, which is not predictable by usual theories for random media. Indeed, to study waves propagation in disordered media theoreticians, who find it difficult to deal with one realization of disorder, use concepts defined as an average over the realizations, which naturally leads to the diffusion approximation. But the corresponding equation is not time-reversal invariant and thus fails in describing our experiment. Then, to understand our experimental results and try to predict new ones, we have developed a finite elements simulation based on the real microscopic time-invariant equation of propagation. The experimental and numerical results are found to be in very good agreement.

Sign in / Sign up

Export Citation Format

Share Document