1,721,004 research outputs found
2D acoustic wavefield simulation by improved stiffness and mass matrices of bilinear square element
No full textIn the frequency domain, we optimize the entries of the element stiffness matrix computed on a square element with the purpose of approximating the 2D acoustic wave equation with the second spatial order. The optimized matrices are computed from the minimization of the normalized phase velocity as a function of propagation angle and the number of grid points per wavelength, leading to a remarkable reduction in the numerical error. The optimized number of 4.1 sample points in a wavelength, with a maximum error in velocities <0.3%, offering the simulation of large-scale realistic models. The superior performance of the optimized matrices to those from the lumped, consistent and eclectic matrices, is evident from the numerical examples presented, with consequent reduction not only in the numerical dispersion/anisotropy but also in an improved resolution. It is noteworthy that optimized matrices give modeling results with better accuracy than models from the high-order spectral element method. Our methodology is easily extendable to the accurate discretizing of the general 3D elastic wave equation that optimizes the bandwidth of the impedance matrix, availing computational resources for accurately modeling the compressional and shear wave velocities, density, as well as multi-parameter inversion.N
Recursive Heaviside step functions and beginning of the universe
No full textThis article introduces recursive Heaviside step functions, as a potential of the known universe, for the first time in the history of mathematics, science, and engineering. In modern cosmology, various bouncing models have been suggested based on the postulation that the current universe is the result of the collapse of a previous universe. However, all Big Bounce models leave unanswered the question of what powered inflation. Recursive Heaviside step functions are analyzed to represent the warpage of space-time during the crunch-bounce transition. In particular, the time shift appeared during the transition is modeled in the form of recursive Heaviside step functions and suggested as a possible answer for the immeasurable energy appeared for the Big Bounce. (C) 2016 Elsevier B.V. All rights reserved.OAIID:RECH_ACHV_DSTSH_NO:T201720663RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A002505CITE_RATE:.92DEPT_NM:에너지시스템공학부EMAIL:[email protected]_YN:NN
Application of efficient frequency-domain full waveform inversion using time-domain encoded simultaneous sources
No full textFull waveform inversion (FWI) is used to determine accurate subsurface velocities through recursive calculation. FWI needs extensive computation; therefore, reducing the computational cost while inverting for an acceptable result is important for the practical application of FWI. Frequency-domain FWI has the advantages of selection of certain frequency components and reduced computational time because of the use of a matrix solver, which solves many sources simultaneously through one matrix factorization. However, the size of the matrix increases exponentially with the size of the computational domain and the number of parameters. The efficiency of frequency-domain FWI decreases in 3D FWI because of limited computational memory. To enhance the efficiency of frequency-domain FWI, time-domain modeling with a simultaneous source was exploited in this study. Although the time-domain modeling scheme is one of the most efficient methods for performing 3D frequency-domain FWI, it still requires time-marching for every source. However, the efficiency can be greatly improved by using the simultaneous source method. Moreover, this method is not limited by the amount of memory required because the time-domain modeling scheme is a matrix-free method. To suppress the crosstalk noise in the simultaneous source method, we use random phase (RP) encoding, random time delay (RTD), and the partial-source assembling method. The nonlinear conjugate gradient method (NLCG) is also used to accelerate the convergence speed. To validate the efficiency of the proposed algorithm, a numerical test is conducted using the 2D SEG/EAGE overthrust model and shows that determining the appropriate balance between the computational cost and the quality of the result can improve the efficiency of the encoded simultaneous source FWI (ESSFWI). The 3D numerical test also verified that the proposed algorithm enhances the computational efficiency and guarantees the quality of the inverted result.OAIID:RECH_ACHV_DSTSH_NO:T201720681RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A002505CITE_RATE:1.828DEPT_NM:에너지시스템공학부EMAIL:[email protected]_YN:YN
Interrelation between Laplace constants and the gradient distortion effect in Laplace-domain waveform inversion
No full textLaplace-domain waveform inversion (WI) is generally used to generate smooth initial velocity models for frequency-or time-domain full-waveform inversion. However, in the inversion results of Laplace-domain WI, anomalies such as salt domes are sometimes shifted. We evaluate the "gradient-distortion effect" that causes undesirable changes in parameter updates and found that this is caused by the relationship between the partial derivatives of Laplace wavefields with respect to two different parameters. By analyzing the gradient of the Laplace-domain misfit function, we found that the gradient distortion effect increases as the Laplace constants used in the Laplace-domain WI decrease. The velocity model inverted in the Laplace domain is generally blurred from shallower parameters to deeper parameters because the partial derivatives of the Laplace wavefields with respect to shallower parameters tend to be larger than those of deeper parameters. We found two solutions for suppressing the gradient distortion effect. The first one is the sequentially ordered Laplace constant approach with multiple Laplace constants. We discover that a dense, broad set of Laplace constants should be sequentially used in this approach. The second solution is the Gauss-Newton method, in which the Hessian matrix is considered. Numerical tests performed using a four-layer model and the BP benchmark model show the gradient distortion effect appeared in the inversion results and the effectiveness of the sequentially ordered Laplace constant approach. In addition, tests using an inverted BP benchmark model determine that the inversion results can be improved by applying a broad, dense set of Laplace constants to synthetic data. Finally, we verify the effectiveness of the GaussNewton method at suppressing the gradient distortion effect using the BP benchmark model.OAIID:RECH_ACHV_DSTSH_NO:T201720652RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A002505CITE_RATE:2.368DEPT_NM:에너지시스템공학부EMAIL:[email protected]_YN:YN
Regularized Laplace-Fourier-Domain Full Waveform Inversion Using a Weighted l(2) Objective Function
No full textFull waveform inversion (FWI) can be applied to obtain an accurate velocity model that contains important geophysical and geological information. FWI suffers from the local minimum problem when the starting model is not sufficiently close to the true model. Therefore, an accurate macroscale velocity model is essential for successful FWI, and Laplace-Fourier-domain FWI is appropriate for obtaining such a velocity model. However, conventional Laplace-Fourier-domain FWI remains an ill-posed and ill-conditioned problem, meaning that small errors in the data can result in large differences in the inverted model. This approach also suffers from certain limitations related to the logarithmic objective function. To overcome the limitations of conventional Laplace-Fourier-domain FWI, we introduce a weighted l2 objective function, instead of the logarithmic objective function, as the data-domain objective function, and we also introduce two different model-domain regularizations: first-order Tikhonov regularization and prior model regularization. The weighting matrix for the data-domain objective function is constructed to suitably enhance the far-offset information. Tikhonov regularization smoothes the gradient, and prior model regularization allows reliable prior information to be taken into account. Two hyperparameters are obtained through trial and error and used to control the trade-off and achieve an appropriate balance between the datadomain and model-domain gradients. The application of the proposed regularizations facilitates finding a unique solution via FWI, and the weighted l2 objective function ensures a more reasonable residual, thereby improving the stability of the gradient calculation. Numerical tests performed using the Marmousi synthetic dataset show that the use of the weighted l2 objective function and the model-domain regularizations significantly improves the LaplaceFourier- domain FWI. Because the Laplace-Fourier-domain FWI is improved, the frequency-domain FWI, in which the LaplaceFourier- domain FWI result is used as the starting model, yields inversion result much closer to the true velocity.OAIID:RECH_ACHV_DSTSH_NO:T201720691RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A002505CITE_RATE:1.591DEPT_NM:에너지시스템공학부EMAIL:[email protected]_YN:YN
Frequency domain reverse time migration for acoustic-elastic coupled media using the wavefield separation method
No full textRecent research results concerning frequency domain reverse time migration based on the adjoint-state of the acoustic wave equation have highlighted several limitations imposed by the use of an acoustic-based algorithm. In marine seismic exploration, targeted areas are located within elastic media. Elastic wave components, such as S-waves, surface waves and mode converted waves can remain obscured by reverse time migration based on the acoustic wave equation in the targeted media. Several research papers addressing the topic of acoustic-elastic coupled media with full waveform inversion have shown that this method can generate more accurate inversion results for P-wave velocity models than acoustic-based algorithms. This paper formulates the frequency domain reverse time migration for acoustic-elastic coupled media based on the adjoint-state of the wave equation. It goes on to adopt the wavefield separation method to reduce the effects of crosstalk artifacts on migrated images. The validity of the proposed algorithm is demonstrated using a synthetic dataset generated by elastic staggered grid time modeling. The image of the frequency domain reverse time migration for acoustic-elastic coupled media calculated using the wavefield separation method is then compared to the results of the acoustic reverse time migration and reverse time migration for acoustic-elastic coupled media using a conventional zero-lag cross-correlation approach. Comparison of the migration images revealed that the images of acoustic-elastic coupled media from the wavefield separation method resolved geological structures with greater accuracy and exhibited fewer noise-contaminated components than those obtained from the acoustic and conventional acoustic-elastic coupled media imaging methods. We also analyze the reverse time migration method's sensitivity to correct P- and S-wave inputs and density model assumptions.OAIID:RECH_ACHV_DSTSH_NO:T201720876RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A002505CITE_RATE:.549DEPT_NM:에너지시스템공학부EMAIL:[email protected]_YN:YN
Laplace–fourier-domain full waveform inversion of deep-sea seismic data acquired with limited offsets
No full textLaplace-Fourier-domain full waveform inversion is considered one of the most reliable schemes to alleviate the drawbacks of conventional frequency-domain inversion, such as local minima. Using a damped wavefield, we can reduce the possibility of converging to local minima and produce an accurate long-wavelength velocity model. Then, we can obtain final inversion results using high-frequency components and low damping coefficients. However, the imaging area is limited because this scheme uses a damped wavefield that makes the magnitudes of the gradient and residual small in deep areas. Generally, the imaging depth of Laplace-Fourier-domain full waveform inversion is half the streamer length. Thus, dealing with seismic data in the deep-sea layer is difficult. The deep-sea layer reduces the amplitude of signals and acts as an obstacle for computing an exact gradient image. To reduce the water layer's effect, we extrapolated the wavefield with a downward continuation and performed refraction tomography. Then, we performed Laplace-Fourier-domain full waveform inversion using the refraction tomography results as an initial model. After obtaining a final velocity model, we verified the inversion results using Kirchhoff migration. We presented common image gathers and a synthetic seismogram of Sumatra field data to prove the reliability of the velocity model obtained by Laplace-Fourier-domain full waveform inversion. Through the test, we concluded that Laplace-Fourier-domain full waveform inversion with refraction tomography of the downward-continued wavefield recovers the subsurface structures located at depth despite a relatively short streamer length compared to the water depth.OAIID:RECH_ACHV_DSTSH_NO:T201720865RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A002505CITE_RATE:1.591DEPT_NM:에너지시스템공학부EMAIL:[email protected]_YN:YN
Pimozide Inhibits the Human Prostate Cancer Cells Through the Generation of Reactive Oxygen Species
No full textThe United States Food and Drug Administration-approved antipsychotic drug, pimozide, has anticancer activities. However, the role of reactive oxygen species (ROS) in its effect on prostate cancer is not well-known. We examined cell proliferation, colony formation, migration, ROS production, and the expression of antioxidant-related genes after treatment of human prostate cancer PC3 and DU145 cells with pimozide. In addition, histopathology, ROS production, and superoxide dismutase (SOD) activity were analyzed after administering pimozide to TRAMP, a transgenic mouse with prostate cancer. Pimozide increased the generation of ROS in both cell lines and inhibited cell proliferation, migration, and colony formation. Oxidative stress induced by pimozide caused changes in the expression of antioxidant enzymes (SOD1, peroxiredoxin 6, and glutathione peroxidase 2) and CISD2. Co-treatment with glutathione, an antioxidant, reduced pimozide-induced ROS levels, and counteracted the inhibition of cell proliferation. Administration of pimozide to TRAMP mice reduced the progression of prostate cancer with increased ROS generation and decreased SOD activity. These results suggest that the antipsychotic drug, pimozide, has beneficial effects in prostate cancer in vivo and in vitro. The mechanism of pimozide may be related to augmenting ROS generation. We recommend pimozide as a promising anticancer agent.Y
Waveform inversion in the shifted Laplace domain
No full textLaplace domain waveform inversion (WI) is one of the most effective algorithms to generate an initial velocity model. Because of its bandwidth independence with respect to the source wavelet, this method can yield reasonable initial models without low-frequency components in the seismic data. However, the conventional Laplace domain WI algorithm has an accuracy problem from its simultaneous consideration of the first arrival traveltime and apparent amplitude in the Laplace domain wavefield. This simultaneous consideration creates undesirable cross-correlation terms between the residual of the traveltime and the partial derivatives of the apparent amplitude in the gradient directions and between the residual of the apparent amplitude and the partial derivatives of the traveltime in the gradient directions. In this paper, we introduce a new objective function that uses a shifted Laplace domain wavefield to solve the problem of Laplace domain WI. Information that is associated with the traveltime and apparent amplitude can be separately inverted by using this shifted Laplace domain WI. This separation of the information can suppress the undesirable cross-correlation terms between the residual of the traveltime and the partial derivatives of apparent amplitude and between the residual of the apparent amplitude and the partial derivatives of the traveltime in the gradient directions. We can effectively perform shifted Laplace domain modelling by using the damped monochromatic wave equation. We verify the accuracy of this shifted Laplace domain modelling scheme by comparing the shifted Laplace-transformed result from a synthetic seismogram to a wavefield that is modelled in the shifted Laplace domain. We perform a contribution analysis to demonstrate that the shifted Laplace domain wavefield is essential to improve the accuracy of the inverted results. Finally, we confirm the robustness of the shifted Laplace domain WI algorithm by testing it against a BP model.OAIID:RECH_ACHV_DSTSH_NO:T201720695RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A002505CITE_RATE:2.528DEPT_NM:에너지시스템공학부EMAIL:[email protected]_YN:YN
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