3-D network ray tracing

Klimeš, Luděk; Kvasnička, Michal

doi:10.1111/j.1365-246x.1994.tb03293.x

Cited by 104 publications

(69 citation statements)

References 15 publications

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“…It also loses simplicity and becomes expensive (Zhang and Toksöz, 1998). Comparisons of the finite-difference method and graph theory are found in Klimeš and Kvasnička (1994) and Zhang and Toksöz (1998); they suggest the superiority of ray tracing by the graph theory. Nakanishi and Yamaguchi (1986) applied the idea of the shortest path (in the graph theory) to seismic ray tracing.…”

Section: Introductionmentioning

confidence: 98%

“…The efficiency of the hybrid scheme with the simplex method is now examined. The accuracy required for travel times in tomography is between 1% (Fischer and Lees, 1993) and 0.1% (Klimeš and Kvasnička, 1994). From the relative error in the travel time as a function of block size in Fig.…”

Section: Example 1 Constant Velocity Gradient Modelmentioning

confidence: 99%

“…When accuracy and stability are required, this method becomes similar to the method by the graph theory based on Fermat's principle (Klimeš and Kvasnička, 1994). It also loses simplicity and becomes expensive (Zhang and Toksöz, 1998).…”

Section: Introductionmentioning

confidence: 99%

“…Since the work of Nakanishi and Yamaguchi (1986), several improvements have increased the accuracy and the efficiency of the calculation (e.g., Saito, 1989Saito, , 1990Moser, 1991;Fisher and Lees, 1993;Klimeš and Kvasnička, 1994;Cheng and House, 1996;Zhang and Toksöz, 1998).…”

Section: Introductionmentioning

confidence: 99%

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A three-dimensional robust seismic ray tracer for volcanic regions

Nishi

2014

Earth Planet Sp

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Seismic velocity structure of volcanic region is highly heterogeneous so that seismic ray tracer used in this field should be robust for the velocity heterogeneity. From this view point a three-dimensional robust seismic ray tracer, effective in any complicated velocity structure, is developed by using a hybrid scheme of the shortest path calculation and the downhill simplex optimization method. The node configuration necessary for the three-dimensional shortest path calculation is newly presented. Validity and efficiency of the calculation are examined by synthetic tests. A travel time accuracy of less than 0.1%, and a rms ray path error of 0.05 km are achieved. Calculations for the synthetic velocity models and checkerboard testing show the effectiveness of this ray tracer in practical situations. The present ray tracer is recommended to be used in travel time tomography in highly heterogeneous velocity structure such as volcanic regions.

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Section: Introductionmentioning

confidence: 98%

Section: Example 1 Constant Velocity Gradient Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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A three-dimensional robust seismic ray tracer for volcanic regions

Nishi

2014

Earth Planet Sp

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“…However, for highly accurate results, this method requires vast memory and intensive calculation. Recent improvements have been made by Fischer and Lee (1993), Klimes and Kvasnicka (1993), Weber (1995), . In this study, we apply the approach developed by Zhang (1996).…”

Section: Calculating Refraction Travletimes and Raypathsmentioning

confidence: 99%

Nonlinear refraction traveltime tomography

Zhang¹,

Toksöz²

1998

GEOPHYSICS

421

150

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We identify a few unique issues that are important for performing a nonlinear refraction traveltime tomography effectively. These include accuracy of traveltime and raypath calculation for a turning ray and physical information in a refraction traveltime curve. Consequently, we develop a shortest path raytracing method with an optimized node distribution that can accurately calculate refraction traveltimes and raypaths in any velocity model. We find that minimizing misfit of refraction traveltimes with the least-squares criterion does not account for the whole physical meaning of a refraction traveltime curve. We therefore pose a different nonlinear inverse problem that explicitly minimizes misfits of both traveltimes (integrated slownesses) and traveltime gradients (apparent slownesses). As a result, we enhance the resolution of the tomographic inversion as well as the convergence speed. We regularize our inverse problem with the Tikhonov method as opposed to applying ad hoc smoothing to keep the inversion stable. The use of the Tikhonov regularization avoids solving an ill-posed problem and allows us to invert an infinite number of unknowns. We apply this tomographic technique to image the shallow velocity structure at a coastal site near Boston, Massachusetts. The results are consistent with a local boring survey.

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DDT Polymorphism and the Lethality of Crystal Forms

Yang

Zhu

et al. 2017

Angew Chem Int Ed

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DDT (1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane), a contact insecticide with a rich and controversial history since its activity was discovered in 1939, has long been thought to be monomorphic. Herein we report the discovery and characterization of a second polymorph, designated Form II, which can be isolated as single crystals, but converts very slowly at room temperature to the form reported previously, now designated as Form I. Computations based on an evolutionary algorithm for crystal structure prediction revealed that Forms I and II are among the four lowest energy crystal structures of fifty calculated. A preliminary study of the contact insecticidal activity toward fruit flies (Drosophila melanogaster) indicates that Form II is more active, suggesting opportunities for more effective solid-state formulations that would allow reduced amounts of DDT, thereby minimizing environmental impact.

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3-D network ray tracing

Cited by 104 publications

References 15 publications

A three-dimensional robust seismic ray tracer for volcanic regions

A three-dimensional robust seismic ray tracer for volcanic regions

Nonlinear refraction traveltime tomography

DDT Polymorphism and the Lethality of Crystal Forms

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