On the determination of sound speeds in cubic crystals and isotropic media using a broadband ultrasonic point‐source/point‐receiver method

1993 ◽  
Vol 93 (3) ◽  
pp. 1393-1406 ◽  
Author(s):  
Kwang Yul Kim ◽  
Wolfgang Sachse ◽  
A. G. Every
Keyword(s):  
Point Source ◽  
Cubic Crystals ◽  
Sound Speeds ◽  
Source Point ◽  
Isotropic Media

Determination of point source mechanisms

2014 ◽  
pp. 108-134 ◽  
Author(s):  
Agustin Udias ◽  
Raul Madariaga ◽  
Elisa Buforn
Keyword(s):  
Point Source ◽  
Source Mechanisms

scholarly journals A complex point-source solution of the acoustic eikonal equation for Gaussian beams in transversely isotropic media

Geophysics ◽  
2020 ◽  
Vol 85 (3) ◽  
pp. T191-T207
Author(s):  
Xingguo Huang ◽  
Hui Sun ◽  
Zhangqing Sun ◽  
Nuno Vieira da Silva
Keyword(s):  
Point Source ◽  
Eikonal Equation ◽  
Taylor Series Expansion ◽  
Transversely Isotropic ◽  
Complex Point ◽  
Transversely Isotropic Media ◽  
Isotropic Media ◽  
Anisotropy Parameters ◽  
Complex Point Source ◽  
Complex Eikonal

The complex traveltime solutions of the complex eikonal equation are the basis of inhomogeneous plane-wave seismic imaging methods, such as Gaussian beam migration and tomography. We have developed analytic approximations for the complex traveltime in transversely isotropic media with a titled symmetry axis, which is defined by a Taylor series expansion over the anisotropy parameters. The formulation for the complex traveltime is developed using perturbation theory and the complex point-source method. The real part of the complex traveltime describes the wavefront, and the imaginary part of the complex traveltime describes the decay of the amplitude of waves away from the central ray. We derive the linearized ordinary differential equations for the coefficients of the Taylor-series expansion using perturbation theory. The analytical solutions for the complex traveltimes are determined by applying the complex point-source method to the background traveltime formula and subsequently obtaining the coefficients from the linearized ordinary differential equations. We investigate the influence of the anisotropy parameters and of the initial width of the ray tube on the accuracy of the computed traveltimes. The analytical formulas, as outlined, are efficient methods for the computation of complex traveltimes from the complex eikonal equation. In addition, those formulas are also effective methods for benchmarking approximated solutions.

scholarly journals Real-Time Detection Of Gravitational Microlensing

1996 ◽  
Vol 173 ◽  
pp. 221-226 ◽  
Author(s):  
M.R. Pratt ◽  
C. Alcock ◽  
R.A. Allsman ◽  
D. Alves ◽  
T.S. Axelrod ◽  
...  
Keyword(s):  
Point Source ◽  
Real Time ◽  
Temporal Resolution ◽  
Proof Of Concept ◽  
Inertial Motion ◽  
Source Point ◽  
Gravitational Microlensing ◽  
Real Time Detection ◽  
Mass Position

Real-time detection of microlensing has moved from proof of concept in 1994 (Udalski et al. 1994a, Alcock et al. 1994) to a steady stream of events this year. Global dissemination of these events by the MACHO and OGLE collaborations has made possible intensive photometric and spectroscopic follow up from widely dispersed sites confirming the microlensing hypothesis (Benetti 1995). Improved photometry and increased temporal resolution from follow up observations greatly increases the possibility of detecting deviations from the standard point-source, point-lens, inertial motion microlensing model. These deviations are crucial in understanding individual lensing systems by breaking the degeneracy between lens mass, position and velocity. We report here on GMAN (Global Microlensing Alert Network), the coordinated follow up of MACHO alerts.

scholarly journals Image Reconstruction from VLBI Amplitude and Phase Closure Data

1979 ◽  
Vol 49 ◽  
pp. 93-93
Author(s):  
William D. Cotton ◽  
Jill J. Wittels
Keyword(s):  
Point Source ◽  
Direct Synthesis ◽  
Angular Structure ◽  
Long Baseline ◽  
Test Models ◽  
Step Procedure ◽  
Source Convergence ◽  
Using Data ◽  
Starting Model

AbstractA two step procedure is developed for the determination of the angular structure of the compact components of radio sources from observations made with very long baseline interferometry (VLBI). The first step is to fit a model composed of circularly symmetric Gaussian components to the observations. Then this, or any other, model and closure phase information is used to predict visibility phases which, when paired with the corresponding visibility amplitude observation, are combined in a direct synthesis; the resulting map is deconvolved from the point source response by means of the “CLEAN” procedure. If necessary, the “cleaned” components can be used as a starting model to predict visibility phases and the process iterated. The initial model in many cases may be as simple as a point source. Convergence of this process appears to be quite rapid, requiring only a few iterations when the source is simple or the starting model is good. These two steps for source mapping can be used either together or separately. Examples are given using data generated from test models.

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