scholarly journals Constrained Power Focusing in Inhomogeneous Media as a Polarization Optimization

2015 ◽  
Vol 2015 ◽  
pp. 1-7 ◽  
Author(s):  
Domenica Anna Maria Iero
Keyword(s):  
Parallel Programming ◽  
Open Problem ◽  
Time Reversal ◽  
Vector Fields ◽  
Search Algorithm ◽  
Scalar Fields ◽  
Inhomogeneous Media ◽  
Target Point ◽  
Inverse Filter ◽  
Global Search Algorithm

The problem of focusing a field into inhomogeneous media is a canonic open problem relevant in many engineering areas. Several approaches have been developed, for example, Time Reversal, Inverse Filter, and Eigenvalues approach, but they suffer from several drawbacks which are counteracted by Optimal Constrained Power Focusing (OCPF) technique. OCPF was first introduced to deal with scalar fields and, recently, it has been extended to tackle the problem of focusing vector fields. In particular, the proposed approach allows reducing the focusing problem, which is NP-hard in case of vector fields, to a series of convex programming (CP) ones. In this paper, an alternative OCPF formulation is presented, which consists in the research of the most suitable polarization of the field into the target point and relies on the convexity of the problem when fixing this polarization. Such a result allows the development of two different solution procedures: an enumerative one that can take advantage of parallel programming in order to explore all possible polarizations and hybrid one which relies on the exploitation of global search algorithm just to solve the nonconvex part of the problem at hand.

Classical fields in curved spacetime

2021 ◽  
pp. 294-313
Author(s):  
Iosif L. Buchbinder ◽  
Ilya L. Shapiro
Keyword(s):  
Vector Fields ◽  
Lorentz Invariance ◽  
Conformal Symmetry ◽  
Scalar Fields ◽  
Gauge Fields ◽  
Curved Spacetime ◽  
Curved Space ◽  
Spinor Fields ◽  
Vector Gauge ◽  
Classical Fields

This chapter discusses classical fields in an arbitrary Riemann spacetime. General considerations are followed by the formulation of scalar fields with non-minimal coupling. Spontaneous symmetry breaking in curved space is shown to provide the induced gravity action with a cosmological constant. The construction of spinor fields in curved spacetime is based on the notions of group theory from Part I and on the local Lorentz invariance. Massless vector fields (massless vector gauge fields) are described and the interactions between scalar, fermion and gauge fields formulated. A detailed discussion of classical conformal transformations and conformal symmetry for both matter fields and vacuum action is also provided.

scholarly journals Application of focal-time analysis for improved induced seismicity depth control: A case study from the Montney Formation, British Columbia, Canada

Geophysics ◽  
2020 ◽  
Vol 85 (6) ◽  
pp. KS185-KS196 ◽  
Author(s):  
Naimeh Riazi ◽  
David W. Eaton ◽  
Alemayehu Aklilu ◽  
Andrew Poulin
Keyword(s):  
British Columbia ◽  
Seismic Data ◽  
Induced Seismicity ◽  
Search Algorithm ◽  
Focal Depth ◽  
Global Search ◽  
3D Seismic ◽  
Global Search Algorithm ◽  
Montney Formation ◽  
3D Seismic Data

Characterization of induced seismicity and associated microseismicity is an important challenge for enhanced oil recovery and development of tight hydrocarbon reservoirs. In particular, accurately correlating hypocenters of induced events to stratigraphic layers plays an important role in understanding the mechanisms of fault activation. Existing methods for estimating focal depth, however, are prone to a high degree of uncertainty. A comprehensive analysis of inferred focal depths is applied to induced events that occurred during completions of horizontal wells targeting the Montney Formation in British Columbia, Canada. Our workflow includes a probabilistic, nonlinear global-search algorithm (NonLinLoc), a hierarchical clustering algorithm for relative relocation (GrowClust), and depth refinement using the recently developed focal-time method. The focal-time method leverages stratigraphic correlations between P-P and P-S reflections to eliminate the need for an explicit velocity model developed specifically for hypocenter depth estimation. We find that this approach is robust in the presence of noisy picks and location errors from epicenters obtained using a global-search algorithm, but it is limited to areas where multicomponent 3D seismic data are available. We have developed a novel method to determine statics corrections to ensure that the passive seismic observations and 3D seismic data share a common datum in areas of moderate to high topography. Our results highlight the importance of transverse faults, which appear to provide permeable pathways for activation of other faults at distances of up to 2 km from hydraulic fracturing operations.

scholarly journals Failure-Robot Path Complementation for Robot Swarm Mission Planning

2019 ◽  
Vol 9 (18) ◽  
pp. 3756 ◽  
Author(s):  
Meng-Tse Lee ◽  
Bo-Yu Chen ◽  
Wen-Chi Lu
Keyword(s):  
Search Algorithm ◽  
Optimal Solution ◽  
Unmanned Vehicles ◽  
Target Point ◽  
Diversification Strategy ◽  
Robot Swarm ◽  
Limited Power ◽  
Time Distance ◽  
Global Optimal ◽  
Robot Path

Currently, unmanned vehicles are widely used in different fields of exploration. Due to limited capacities, such as limited power supply, it is almost impossible for one unmanned vehicle to visit multiple wide areas. Multiple unmanned vehicles with well-planned routes are required to minimize an unnecessary consumption of time, distance, and energy waste. The aim of the present study was to develop a multiple-vehicle system that can automatically compile a set of optimum vehicle paths, complement failed assignments, and avoid passing through no-travel zones. A heuristic algorithm was used to obtain an approximate solution within a reasonable timeline. The A* Search algorithm was adopted to determine an alternative path that does not cross the no-travel zone when the distance array was set, and an improved two-phased Tabu search was applied to converge any initial solutions into a feasible solution. A diversification strategy helped identify a global optimal solution rather than a regional one. The final experiments successfully demonstrated a group of three robot cars that were simultaneously dispatched to each of their planned routes; when any car failed during the test, its path was immediately reprogrammed by the monitoring station and passed to the other cars to continue the task until each target point had been visited.

Comparison between time reversal and spatio‐temporal inverse filter application to focusing through a human skull

2001 ◽  
Vol 109 (5) ◽  
pp. 2397-2397
Author(s):  
Mickael Tanter ◽  
Jean‐Francois Aubry ◽  
Jean‐Louis Thomas ◽  
Mathias Fink
Keyword(s):  
Time Reversal ◽  
Inverse Filter ◽  
Human Skull ◽  
Spatio Temporal

scholarly journals Stability and boundedness in AdS/CFT with double trace deformations

2019 ◽  
Vol 34 (18) ◽  
pp. 1950138 ◽  
Author(s):  
Steven Casper ◽  
William Cottrell ◽  
Akikazu Hashimoto ◽  
Andrew Loveridge ◽  
Duncan Pettengill
Keyword(s):  
Renormalization Group ◽  
Boundary Conditions ◽  
Vector Fields ◽  
Scalar Fields ◽  
Legendre Transform ◽  
Renormalization Group Flow ◽  
Physical Content ◽  
Effective Masses ◽  
Group Flow

Scalar fields on the bulk side of AdS/CFT correspondence can be assigned unconventional boundary conditions related to the conventional one by Legendre transform. One can further perform double trace deformations which relate the two boundary conditions via renormalization group flow. Thinking of these operators as S and T transformations, respectively, we explore the SL(2, R) family of models which naively emerges from repeatedly applying these operations. Depending on the parameters, the effective masses vary and can render the theory unstable. However, unlike in the SL(2, Z) structure previously seen in the context of vector fields in AdS4, some of the features arising from this exercise, such as the vacuum susceptibility, turns out to be scheme dependent. We explain how scheme independent physical content can be extracted in spite of some degree of scheme dependence in certain quantities.

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