optimal focusing
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2020 ◽  
Author(s):  
Jean-Xavier Dessa ◽  
Marie-Odile Beslier ◽  
Laure Schenini ◽  
Serge Sambolian ◽  
Albane Canva ◽  
...  

<p>The first leg of the SEFASILS cruise took place in November 2018 onboard the RV Pourquoi-Pas ? Up-to-date multichannel and wide-angle seismic data were acquired offshore Monaco, from margin to basin, aiming at providing a renewed vision of the complex North Ligurian backarc system. The compressive and extensive tectonic phases that have closely alternated in time and space over the last 45 My have yielded fairly contrasting structures, whose understanding is rendered even more challenging by the strong overprint of the Messinian salt tectonics. There is ample evidence of a compressive reactivation of the North Ligurian margin since 5 Ma at least, especially to the East, along the Gulf of Genoa. Such deformation is associated with some notable seismicity originating from faults and mechanisms that remain poorly apprehended. Yet, this seismicity peaked at one historical Mw ~6.6-6.9 destructive event (1887 Ligurian earthquake). The main objective of the SEAFASILS effort is a better characterization of the crustal structures, and chiefly, of the active crustal faults and their potential interplay with salt tectonics beneath the margin and the northernmost part of the basin, both featuring seismicity. Linking these aspects with broader-scale lithospheric processes within the Southern Alps/Northern Apennines, addressed in the AlpArray initiative, is also of great importance. Here we present preliminary results of these seismic investigations, with time and prestack depth migrated MCS data. Emphasis was put on the construction of some suitable velocity models to get optimal focusing of structures from surface to depth. Some active crustal tomographic velocities derived from the dense OBS deployment providing complementary insight will also be presented.</p>



2019 ◽  
Vol 2019 (19) ◽  
pp. 6063-6066 ◽  
Author(s):  
Yinchuan Li ◽  
Yikun Zhao ◽  
Yin Xiang ◽  
Zegang Ding ◽  
Haibo Liu ◽  
...  


2019 ◽  
Vol 142 (3) ◽  
pp. 385-413 ◽  
Author(s):  
Alexey Slunyaev


Algorithms ◽  
2019 ◽  
Vol 12 (2) ◽  
pp. 33
Author(s):  
Yang Bi ◽  
Xi’an Feng ◽  
Yangmei Zhang

Biases of initial direction estimation and focusing frequency selection affect the final focusing effect and may even cause algorithm failure in determining the focusing matrix in the coherent signal–subspace method. An optimized sonar broadband focused beamforming algorithm is proposed to address these defects. Initially, the robust Capon beamforming algorithm was used to correct the focusing matrix, and the broadband signals were then focused on the optimal focusing frequency by the corrected focusing matrix such that the wideband beamforming was transformed into a narrowband problem. Finally, the focused narrowband signals were beamformed by the second-order cone programming algorithm. Computer simulation results and water pool experiments verified that the proposed algorithm provides a good performance.



2018 ◽  
Vol 115 (26) ◽  
pp. 6554-6559 ◽  
Author(s):  
Kai Lou ◽  
Steve Granick ◽  
François Amblard

We amend the general belief that waves with extended spherical wavefront focus at their center of curvature. Instead, when the spherical symmetry of waves is broken by propagating them through a finite aperture along an average direction, the forward/backward symmetry is broken and the focal volume shifts its center backward along that direction. The extent of this focal shift increases as smaller apertures are used, up to the point that the nominal focal plane is out of focus. Furthermore, the loss of axial symmetry with noncircular apertures causes distinct focal shifts in distinct axial planes, and the resulting astigmatism possibly degrades the axial focusing resolution. Using experiments and simulations, focal shift with noncircular apertures is described for classical and temporal focusing. The usefulness of these conclusions to improve imaging resolution is demonstrated in a high-resolution optical microscopy application, namely line-temporal focusing microscopy. These conclusions follow from fundamental symmetries of the wave geometry and matter for an increasing number of emerging optical techniques. This work offers a general framework and strategy to understand and improve virtually any wave-based application whose efficacy depends on optimal focusing and may be helpful when information is transmitted by waves in applications from electromagnetic communications, to biological and astronomical imaging, to lithography and even warfare.



2017 ◽  
Vol 849 ◽  
pp. 012039 ◽  
Author(s):  
José Avila ◽  
Antoine Boury ◽  
Borja Caja-Muñoz ◽  
Chaoyu Chen ◽  
Stephane Lorcy ◽  
...  


Author(s):  
Hulya Dogan ◽  
Elif Baykal ◽  
Murat Ekinci ◽  
Mustafa Emre Ercin ◽  
Safak Ersoz


2016 ◽  
Vol 371 ◽  
pp. 226-230 ◽  
Author(s):  
Juan Manuel Franco ◽  
Moisés Cywiak ◽  
David Cywiak ◽  
Idir Mourad


2016 ◽  
Vol 850 ◽  
pp. 148-152
Author(s):  
Xiao Long Liu ◽  
Yun Tao Liu ◽  
Song Bai Han ◽  
Dong Feng Chen ◽  
Mei Juan Li ◽  
...  

The monochromator for the new residual stress diffractometer at China Advanced Research Reactor (CARR) was simulated and optimized using SIMRES software. Objected the Fe (211) diffraction peak, the effect of horizontal and vertical curvature of Si (400) monochromator on Figure of Merit was studied to optimize the focusing parameters. With the optimal focusing condition, the influence of wafer thickness, number of wafers, packet height and gap of packets on performance of instrument was calculated consequently and the corresponding geometrical size was fixed. Finally, the design of the monochromator for the new residual stress diffractometer at CARR was completed.



2015 ◽  
Vol 356 ◽  
pp. 170-174 ◽  
Author(s):  
Victor Arrizón ◽  
Ulises Ruiz ◽  
Dilia Aguirre-Olivas ◽  
Gabriel Mellado-Villaseñor
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