The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Alexandre Aubry - One of the best experts on this subject based on the ideXlab platform.
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Reflection Matrix Approach for quantitative imaging of scattering media
Physical Review X, 2020Co-Authors: William Lambert, Laura Cobus, Mathieu Couade, Mathias Fink, Alexandre AubryAbstract:We present a physically intuitive Matrix Approach for wave imaging and characterization in scattering media. The experimental proof-of-concept is performed with ultrasonic waves, but this Approach can be applied to any field of wave physics for which multi-element technology is available. The concept is that focused beamforming enables the synthesis, in transmit and receive, of an array of virtual transducers which map the entire medium to be imaged. The inter-element responses of this virtual array form a focused reflection Matrix from which spatial maps of various characteristics of the propagating wave can be retrieved. Here we demonstrate: (i) a local focusing criterion that enables the image quality and the wave velocity to be evaluated everywhere inside the medium, including in random speckle, and (ii) an highly resolved spatial mapping of the prevalence of multiple scattering, which constitutes a new and unique contrast for ultrasonic imaging. The Approach is demonstrated for a controllable phantom system, and for in vivo imaging of the human abdomen. More generally, this Matrix Approach opens an original and powerful route for quantitative imaging in wave physics.
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Reflection Matrix Approach for quantitative imaging of scattering media
Physical Review X, 2020Co-Authors: William Lambert, Laura Cobus, Mathieu Couade, Mathias Fink, Alexandre AubryAbstract:We present a physically intuitive Matrix Approach for wave imaging and characterization in scattering media. The experimental proof-of-concept is performed with ultrasonic waves, but this Approach can be applied to any field of wave physics for which multi-element technology is available. The concept is that focused beamforming enables the synthesis, in transmit and receive, of an array of virtual transducers which map the entire medium to be imaged. The inter-element responses of this virtual array form a focused reflection Matrix from which spatial maps of various characteristics of the propagating wave can be retrieved. Here we demonstrate: (i) a local focusing criterion that enables the imaging quality to be evaluated everywhere inside the medium, including in random speckle; (ii) a tomographic measurement of wave velocity, which allows for aberration corrections in the original image; (iii) an highly resolved spatial mapping of the prevalence of multiple scattering, which constitutes a new and unique contrast for ultrasonic imaging. More generally, this Matrix Approach opens an original and powerful route for quantitative imaging in wave physics.
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Matrix Approach of Seismic Imaging: Application to the Erebus Volcano, Antarctica
Journal of Geophysical Research : Solid Earth, 2018Co-Authors: Thibaud Blondel, Julien Chaput, Arnaud Derode, Michel Campillo, Alexandre AubryAbstract:Multiple scattering of seismic waves is often seen as a nightmare for conventional migration techniques that generally rely on a ballistic or a single-scattering assumption. In heterogeneous areas such as volcanoes, the multiple-scattering contribution limits the imaging-depth to one scattering mean free path, the mean distance between two successive scattering events for body waves. In this Letter, we propose a Matrix Approach of passive seismic imaging that pushes back this fundamental limit by making an efficient use of scattered body waves drowned into a noisy seismic coda. As a proof of concept, the case of the Erebus volcano in Antarctica is considered. The Green's functions between a set of geophones placed on top of the volcano are first retrieved by the cross correlation of coda waves induced by multiple icequakes. This set of impulse responses forms a reflection Matrix. By combining a Matrix discrimination of singly scattered waves with iterative time reversal, we are able to push back the multiple scattering limit beyond 10 scattering mean free paths. The Matrix Approach reveals the internal structure of the Erebus volcano: A chimney-shaped structure at shallow depths, a magma reservoir at 2,500 m and several cavities at sea level and below it. The Matrix Approach paves the way toward a greatly improved monitoring of volcanic structures at depth. Beyond this specific case, the Matrix Approach of seismic imaging can generally be applied to all scales and areas where multiple scattering events undergone by body waves prevent in-depth imaging of the Earth's crust.
Peter Davis - One of the best experts on this subject based on the ideXlab platform.
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Risk Matrix Approach useful in adapting agriculture to climate change
Climatic Change, 2016Co-Authors: David H. Cobon, Allyson Williams, Brendan Power, David Mcrae, Peter DavisAbstract:A risk management Approach to assessing climate change impacts was completed for grazing, wheat and sorghum production systems in eastern Australia. This ‘risk Matrix’ Approach for wheat and sorghum was compared to results from simulation modelling of the impacts of projected climate change from general circulation models (GCM’s). In the modelling we used five GCM’s, the A1FI emissions scenario and a baseline climate (historical, 1960–2010); both the ‘risk Matrix’ Approach and modelling used a time horizon of 2030. While some people find the risk Matrix process a highly effective tool for assessing climate change impacts others question its utility without the support of quantitative data such as that produced from integrated climate and agricultural models. Here we show the impacts of climate change on wheat and sorghum production systems using both Approaches, and also show the risk, adaptation responses and vulnerability of all three production systems using the ‘risk Matrix’ Approach. Advantages and disadvantages of each Approach are identified. The independent assessment showed the two Approaches produced similar results. The ‘risk Matrix’ showed little overall impact, risk or vulnerability for the central slopes from climate change using the adaptation strategies currently available for yield, protein levels, pests and disease, weeds and soil condition. The simulation modelling showed no statistically significant impact on yield, drainage, erosion and runoff, although more high-end extremes were evident. The risks to 2030 from anthropogenic climate change can largely be managed by continuing to implement best management practice and managing the risks already posed by climate variability. The ‘risk Matrix’ Approach was a useful tool under these circumstances to assess the impacts, adaptation, risk and vulnerability of climate change in the absence of local modelling information, and demonstrates the power of expert opinion to help understand and respond to climate change at the regional scale.
Venkata R Rao - One of the best experts on this subject based on the ideXlab platform.
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a material selection model using graph theory and Matrix Approach
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2006Co-Authors: Venkata R RaoAbstract:Abstract This paper presents a methodology for material selection for a given engineering component using graph theory and Matrix Approach. A ‘material suitability index’ is proposed that evaluates and ranks the materials for a given engineering component. The index is obtained from a material selection factors function, obtained from the material selection factors graph. The graph is developed considering material selection factors and their relative importance for the application considered. Two examples are included to illustrate the Approach.
A. Pascolini - One of the best experts on this subject based on the ideXlab platform.
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A scattering-Matrix Approach to the eigenenergies of quantum dots
Physica E: Low-dimensional Systems and Nanostructures, 2009Co-Authors: G. Cattapan, P. Lotti, A. PascoliniAbstract:We present a scattering-Matrix Approach for the evaluation of the eigenenergies in closed periodic systems of quantum dots. The method can be used in a pre-selected window of energies and takes naturally into account the presence of evanescent modes. Together with its counterpart for scattering boundary conditions, it allows for the treatment of closed and open systems in a unique, consistent framework.
David H. Cobon - One of the best experts on this subject based on the ideXlab platform.
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Risk Matrix Approach useful in adapting agriculture to climate change
Climatic Change, 2016Co-Authors: David H. Cobon, Allyson Williams, Brendan Power, David Mcrae, Peter DavisAbstract:A risk management Approach to assessing climate change impacts was completed for grazing, wheat and sorghum production systems in eastern Australia. This ‘risk Matrix’ Approach for wheat and sorghum was compared to results from simulation modelling of the impacts of projected climate change from general circulation models (GCM’s). In the modelling we used five GCM’s, the A1FI emissions scenario and a baseline climate (historical, 1960–2010); both the ‘risk Matrix’ Approach and modelling used a time horizon of 2030. While some people find the risk Matrix process a highly effective tool for assessing climate change impacts others question its utility without the support of quantitative data such as that produced from integrated climate and agricultural models. Here we show the impacts of climate change on wheat and sorghum production systems using both Approaches, and also show the risk, adaptation responses and vulnerability of all three production systems using the ‘risk Matrix’ Approach. Advantages and disadvantages of each Approach are identified. The independent assessment showed the two Approaches produced similar results. The ‘risk Matrix’ showed little overall impact, risk or vulnerability for the central slopes from climate change using the adaptation strategies currently available for yield, protein levels, pests and disease, weeds and soil condition. The simulation modelling showed no statistically significant impact on yield, drainage, erosion and runoff, although more high-end extremes were evident. The risks to 2030 from anthropogenic climate change can largely be managed by continuing to implement best management practice and managing the risks already posed by climate variability. The ‘risk Matrix’ Approach was a useful tool under these circumstances to assess the impacts, adaptation, risk and vulnerability of climate change in the absence of local modelling information, and demonstrates the power of expert opinion to help understand and respond to climate change at the regional scale.