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On Nonreflecting Boundary Conditions
 J. COMPUT. PHYS
, 1995
"... Improvements are made in nonreflecting boundary conditions at artificial boundaries for use with the Helmholtz equation. First, it is shown how to remove the difficulties that arise when the exact DtN (DirichlettoNeumann) condition is truncated for use in computation, by modifying the truncated ..."
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Cited by 219 (4 self)
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Improvements are made in nonreflecting boundary conditions at artificial boundaries for use with the Helmholtz equation. First, it is shown how to remove the difficulties that arise when the exact DtN (DirichlettoNeumann) condition is truncated for use in computation, by modifying the truncated condition. Second, the exact DtN boundary condition is derived for elliptic and spheroidal coordinates. Third, approximate local boundary conditions are derived for these coordinates. Fourth, the truncated DtN condition in elliptic and spheroidal coordinates is modified to remove difficulties. Fifth, a sequence of new and more accurate local boundary conditions is derived for polar coordinates in two dimensions. Numerical results are presented to demonstrate the usefulness of these improvements.
Migration velocity analysis and waveform inversion:
 Geophysical Prospecting,
, 2008
"... SUMMARY Leastsquares inversion of seismic reflection waveform data can reconstruct remarkably detailed models of subsurface structure, and take into account essentially any physics of seismic wave propagation that can be modeled. However the waveform inversion objective has many spurious local min ..."
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Cited by 35 (3 self)
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SUMMARY Leastsquares inversion of seismic reflection waveform data can reconstruct remarkably detailed models of subsurface structure, and take into account essentially any physics of seismic wave propagation that can be modeled. However the waveform inversion objective has many spurious local minima, hence convergence of descent methods (mandatory because of problem size) to useful Earth models requires accurate initial estimates of longscale velocity structure. Migration velocity analysis, on the other hand, is capable of correcting substantially erroneous initial estimates of velocity at long scales. Migration velocity analysis is based on prestack depth migration, which is in turn based on linearized acoustic modeling (Born or singlescattering approximation). Two major variants of prestack depth migration, using binning of surface data and Claerbout's surveysinking concept respectively, are in widespread use. Each type of prestack migration produces an image volume depending on redundant parameters, and supplies a condition on the image volume which expresses consistency between data and velocity model, hence a basis for velocity analysis. The surveysinking (depthoriented) approach to prestack migration is less subject to kinematic artifacts than is the binningbased (surfaceoriented) approach. Because kinematic artifacts strongly violate the consistency or semblance conditions, this observation suggests that velocity analysis based on depthoriented prestack migration may be more appropriate in kinematically complex areas. Appropriate choice of objective (differential semblance) turns either form of migration velocity analysis into an optimization problem, for which Newtonlike methods exhibit little tendency to stagnate at nonglobal minima. The extended modeling concept links migration velocity analysis to the apparently unrelated waveform inversion approach to estimation of Earth structure: from this point of view, migration velocity analysis is a solution method for the linearized waveform inversion problem. Extended modeling also provides a basis for a nonlinear generalization of migration velocity analysis. Preliminary numerical evidence suggests a new approach to nonlinear waveform inversion which may combine the global convergence of velocity analysis with the physical fidelity of modelbased data fitting.
On the logic of Quantum Physics and the concept of the time
 Los Alamos Archives Preprint, quantph/9804040
"... The logic–linguistic structure of quantum physics is analysed. The role of formal systems and interpretations in the representation of nature is investigated. The problems of decidability, completeness, and consistency can affect quantum physics in different ways. Bohr’s complementarity is of great ..."
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The logic–linguistic structure of quantum physics is analysed. The role of formal systems and interpretations in the representation of nature is investigated. The problems of decidability, completeness, and consistency can affect quantum physics in different ways. Bohr’s complementarity is of great interest, because it is a contradictory proposition. We shall see that the flowing of time prevents the birth of contradictions in nature, because it makes a cut between two different, but complementary aspects of the reality. PACS: 03.65.w Quantum mechanics; 03.65.Bz Foundations, theory of measurement, miscellaneous theories; 02.10.By Logic and foundations.
Design and acoustic shielding prediction of hybrid wingbody aircraft
, 2009
"... Recent research and developmental efforts in aircraft design have focused on the growing concerns about the environment impact of aviation and the rising costs of fuel. Under NASA's N+2 subsonics fixedwing project, hybridwingbody (HWB) aircraft are investigated with the goal to meet the N+2 ..."
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Recent research and developmental efforts in aircraft design have focused on the growing concerns about the environment impact of aviation and the rising costs of fuel. Under NASA's N+2 subsonics fixedwing project, hybridwingbody (HWB) aircraft are investigated with the goal to meet the N+2 noise, fuel burn, and emissions requirements. As part of the N+2 program, this thesis is focused on the design and assessment of an HWB aircraft and the development of a prediction method for turbomachinery noise shielding. Based on MIT's previous experience in the Silent Aircraft Initiative, the SAX40 aircraft concept was further developed into the N+2 HWB aircraft. The design effort resulted in two aircraft configurations: the N2A aircraft with conventional podded engines, and the N2B aircraft with a distributed propulsion system embedded in the airframe. The initial performance assessment shows that the N2A and the N2B aircraft can both meet the N+2 fuel burn goal and that the N2A aircraft is 5.7 EPNdB short of the noise goal. Also, the assessment revealed that current noise prediction methods cannot model the advanced propulsion system of the N2B aircraft, requiring the development of noise assessment tools
Turbomachinery Noise Shielding Method
, 2011
"... A current research focus in subsonic aeronautics is the reduction of noise, emissions and fuel burn. The Silent Aircraft Initiative, NASA N+2 and N+3 projects are examples of recent efforts investigating innovative aircraft configurations to meet the future goals of air transportation. This requires ..."
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A current research focus in subsonic aeronautics is the reduction of noise, emissions and fuel burn. The Silent Aircraft Initiative, NASA N+2 and N+3 projects are examples of recent efforts investigating innovative aircraft configurations to meet the future goals of air transportation. This requires novel methodologies to assess unconventional aircraft designs. This thesis is part of the N+2 program and focuses on the development of a method for the assessment of turbomachinery noise shielding in hybrid wing body aircraft. The preliminary design and assessment of novel aircraft configurations require both low computational cost and versatility of the shielding method. High fidelity methods, such as for example boundary element methods, are computationally expensive and not amenable for optimization framework integration. On the other hand, low fidelity methods, such as the barrier shielding method, are limited in their source and geometry definitions. The diffraction integral method is a simplified ray tracing method capturing edge diffracted rays. Creeping rays and reflected rays are not accounted for making the method suitable for flat geometries with sharp edges. It is based on the MaggiRubinowicz formulation of
The Influence off Supersonic Airflow on Aerial Photography
, 1961
"... NOTICE: When government or other drawings, specifications or other data are used for any purpose other than in connection with a definitely related government procurement operation, the U. S. Government thereby incurs no responsibility, nor any obligation whatsoever; and the fact that the Gov ..."
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NOTICE: When government or other drawings, specifications or other data are used for any purpose other than in connection with a definitely related government procurement operation, the U. S. Government thereby incurs no responsibility, nor any obligation whatsoever; and the fact that the Government may have formulated, furnished, or in any way supplied the said drawings, specifications, or other data is not to be regarded by implication or otherwise as in any manner licensing the holder or anyother person or corporation, or conveying any rights or permission to manufacture, use or sell anypatented invention that may in any way be related thereto. o c ASD TECHNICAL NOTE 6135
Raytracing
, 2012
"... modelling of the diffraction by halfplanes and slits based on the energy flow lines concept ..."
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modelling of the diffraction by halfplanes and slits based on the energy flow lines concept
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"... Raytracing modelling of the diffraction by halfplanes and slits based on the energy flow lines concept ..."
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Raytracing modelling of the diffraction by halfplanes and slits based on the energy flow lines concept