scholarly journals Linear traveltime perturbation interpolation: a novel method to compute 3-D traveltimes

2015 ◽  
Vol 203 (1) ◽  
pp. 548-552 ◽  
Author(s):  
Jianzhong Zhang ◽  
Junjie Shi ◽  
Lin-Ping Song ◽  
Hua-wei Zhou
Keyword(s):  
Seismic Waves ◽  
Homogeneous Medium ◽  
Cell Boundary ◽  
Routine Method ◽  
Bilinear Interpolation ◽  
Linear Distribution ◽  
Heterogeneous Model ◽  
Computational Errors ◽  
Novel Method ◽  
The Difference

Abstract The linear traveltime interpolation has been a routine method to compute first arrivals of seismic waves and trace rays in complex media. The method assumes that traveltimes follow a linear distribution on each boundary of cells. The linearity assumption of traveltimes facilitates the numerical implementation but its violation may result in large computational errors. In this paper, we propose a new way to mitigate the potential shortcoming hidden in the linear traveltime interpolation. We use the vertex traveltimes in a calculated cell to introduce an equivalent homogeneous medium that is specific to the cell boundary from a source. Therefore, we can decompose the traveltime at a point on the cell boundary into two parts: (1) a reference traveltime propagating in the equivalent homogeneous medium and (2) a perturbation traveltime that is defined as the difference between the original and reference traveltimes. We now treat that the traveltime perturbation is linear along each boundary of cells instead of the traveltime. With the new assumption, we carry out the bilinear interpolation over traveltime perturbation to complete traveltime computation in a 3-D heterogeneous model. The numerical experiments show that the new method, the linear traveltime perturbation interpolation, is able to achieve much higher accuracy than that based on the linear traveltime interpolation.

The Nature of Intrinsic Attenuation

2020 ◽  
Author(s):  
Yu-Chang Wu ◽  
Cheng-Ju Wu
Keyword(s):  
Seismic Waves ◽  
Body Waves ◽  
Northwestern Pacific ◽  
The Novel ◽  
Low Velocity ◽  
High Attenuation ◽  
Intrinsic Attenuation ◽  
Novel Method ◽  
The Difference ◽  
The Relationship

<p>Intrinsic attenuation plays an important role in investigating the interior structure of Earth, especially for the Lithosphere-asthenosphere system, the best place to understand the physical mechanics of plate tectonic. The dissipation, the high attenuation of seismic waves in the low-velocity zones, and the frequency dependence are the characteristic of intrinsic attenuation. However, N. Takeuchi, et al. measured the Northwestern Pacific Ocean’s lithosphere-asthenosphere system, and state the attenuation of the asthenosphere is 50 times larger than the attenuation of lithosphere attenuation. The attenuation of the lithosphere shows strong frequency dependency, but the attenuation of the asthenosphere does not. Previous theories of attenuation failed to explain this phenomenon. Here we demonstrate an explicit attenuation formulation to explain the high attenuation of seismic waves in the low-velocity zones and to show the mechanisms of spectral of teleseismic body waves rapidly fall off as frequency bigger than 1 Hz by perturbing the wave equation with the novel method we proposed. The result also indicates that the difference between the attenuation of the lithosphere and asthenosphere is because their attenuation governs by different physics mechanisms and mathematical models. Moreover, we illustrate the explicit formulation of the relationship between apparent t*, wave velocity, and frequency.</p>

A 3D reflection ray-tracing method based on linear traveltime perturbation interpolation

Geophysics ◽  
2019 ◽  
Vol 84 (4) ◽  
pp. T181-T191 ◽  
Author(s):  
Tongyu Li ◽  
Jie Liu ◽  
Jianzhong Zhang
Keyword(s):  
Ray Tracing ◽  
Homogeneous Medium ◽  
Cell Boundary ◽  
Complex Media ◽  
Ray Tracing Method ◽  
Accuracy Requirement ◽  
The Common ◽  
The Difference ◽  
Marching Method ◽  
Tracing Method

The linear traveltime interpolation (LTI) method, one of the common methods to calculate the wavefront traveltimes and the raypaths in complex media, is based on the assumption that the traveltime varies linearly along each cell boundary of a discrete model. The linear assumption may result in large calculation errors when the cell size is large. To solve this problem, we have adopted a linear traveltime perturbation interpolation (LTPI) method. In LTPI, the original traveltime is decomposed into two parts: a reference traveltime and a traveltime perturbation. The reference traveltime, being one propagating in the equivalent homogeneous medium, varies nonlinearly. The traveltime perturbation, defined as the difference between the original and reference traveltimes, is assumed to be linear along each cell boundary. The traveltime perturbation is much less than the reference traveltime; therefore, the original traveltime keeps its nonlinearity. We modify LTPI to suit to irregular hexahedral cells for simulating the undulating interfaces more precisely. By combining the modified LTPI with the wavefront group-marching method, we have developed a reflection ray-tracing method in 3D complex media. Numerical experiments indicate that the modified LTPI is more accurate than LTI in computing wavefront traveltimes and raypaths. Besides, the modified LTPI performs more consistently than LTI in different grid spacing. Therefore, under a certain accuracy requirement, the modified LTPI is more efficient than LTI.

Capillary network structure does not affect theoretical analysis of glomerular size selectivity

1995 ◽  
Vol 268 (5) ◽  
pp. F972-F979
Author(s):  
A. Remuzzi ◽  
B. Ene-Iordache
Keyword(s):  
Pressure Drop ◽  
Homogeneous Model ◽  
Wistar Rat ◽  
Size Selectivity ◽  
Membrane Pore ◽  
Heterogeneous Model ◽  
Glomerular Size ◽  
The Difference ◽  
Membrane Pore Size ◽  
Log Normal

Anatomical studies have demonstrated that the glomerular capillaries are complex and heterogeneous networks. Conventional models of glomerular size selectivity, however, are based on the assumption of simplified geometries. We developed a theoretical model of glomerular size-selective function based on the geometric data obtained in a previous reconstruction of a glomerular network from a normal Munich-Wistar rat. This heterogeneous model was compared with the homogeneous model conventionally used to calculate membrane selective parameters from the fractional clearance of two test solutes, neutral dextran and Ficoll. For both models we assumed a hypothetical log-normal distribution of pore sizes and calculated optimal membrane pore-size parameters using previously published values of fractional clearances. The difference between the sieving coefficients calculated with the two models was negligible, never exceeding 5.5%. Since the homogeneous model does not consider the pressure drop along the glomerular capillary, we also computed fractional clearances with the homogeneous model, assuming the same pressure drop as in the heterogeneous one. The differences in computed fractional clearances using the homogeneous model with and without a pressure drop were less than 1.2%. We concluded that models based on identical capillary networks can therefore be used for interpreting sieving coefficients for macromolecules.

scholarly journals Image Anomaly Detection Using Normal Data Only by Latent Space Resampling

2020 ◽  
Vol 10 (23) ◽  
pp. 8660
Author(s):  
Lu Wang ◽  
Dongkai Zhang ◽  
Jiahao Guo ◽  
Yuexing Han
Keyword(s):  
Anomaly Detection ◽  
Normal Distribution ◽  
Autoregressive Model ◽  
Probability Model ◽  
Latent Space ◽  
Industrial Inspection ◽  
Detection Stage ◽  
Novel Method ◽  
The Difference ◽  
Reconstruction Model

Detecting image anomalies automatically in industrial scenarios can improve economic efficiency, but the scarcity of anomalous samples increases the challenge of the task. Recently, autoencoder has been widely used in image anomaly detection without using anomalous images during training. However, it is hard to determine the proper dimensionality of the latent space, and it often leads to unwanted reconstructions of the anomalous parts. To solve this problem, we propose a novel method based on the autoencoder. In this method, the latent space of the autoencoder is estimated using a discrete probability model. With the estimated probability model, the anomalous components in the latent space can be well excluded and undesirable reconstruction of the anomalous parts can be avoided. Specifically, we first adopt VQ-VAE as the reconstruction model to get a discrete latent space of normal samples. Then, PixelSail, a deep autoregressive model, is used to estimate the probability model of the discrete latent space. In the detection stage, the autoregressive model will determine the parts that deviate from the normal distribution in the input latent space. Then, the deviation code will be resampled from the normal distribution and decoded to yield a restored image, which is closest to the anomaly input. The anomaly is then detected by comparing the difference between the restored image and the anomaly image. Our proposed method is evaluated on the high-resolution industrial inspection image datasets MVTec AD which consist of 15 categories. The results show that the AUROC of the model improves by 15% over autoencoder and also yields competitive performance compared with state-of-the-art methods.

scholarly journals Deceptive Jamming Detection for SAR Based on Cross-Track Interferometry

Sensors ◽  
2018 ◽  
Vol 18 (7) ◽  
pp. 2265 ◽  
Author(s):  
Qingqing Feng ◽  
Huaping Xu ◽  
Zhefeng Wu ◽  
Wei Liu
Keyword(s):  
Sar Interferometry ◽  
Synthetic Aperture ◽  
Sar Image ◽  
Frequency Detection ◽  
Interferometric Phase ◽  
Deceptive Jamming ◽  
Jamming Detection ◽  
Novel Method ◽  
The Difference ◽  
Cross Track

Deceptive jamming against synthetic aperture radar (SAR) can create false targets or deceptive scenes in the image effectively. Based on the difference in interferometric phase between the target and deceptive jamming signals, a novel method for detecting deceptive jamming using cross-track interferometry is proposed, where the echoes with deceptive jamming are received by two SAR antennas simultaneously and the false targets are identified through SAR interferometry. Since the derived false phase is close to a constant in interferogram, it is extracted through phase filtering and frequency detection. Finally, the false targets in the SAR image are obtained according to the detected false part in the interferogram. The effectiveness of the proposed method is validated by simulation results based on the TanDEM-X system.

scholarly journals A NOVEL METHOD OF CLOUD AND SHADOW EXTRACTION WITH MULTI-TEMPORAL LANDSAT8 OLI IMAGES

2017 ◽  
Vol XLII-2/W7 ◽  
pp. 1301-1305
Author(s):  
Y. Ni ◽  
G. He ◽  
W. Jiang
Keyword(s):  
Remote Sensing ◽  
Large Change ◽  
Remote Sensing Image ◽  
Image Process ◽  
Actual Application ◽  
Significant Step ◽  
Multi Temporal ◽  
Ground Object ◽  
Novel Method ◽  
The Difference

Cloud and Shadow removal is a significant step in remote sensing image process. As we all know, the ground object coverage type of the same area of the remote sensing image has little change in the short term. But for cloud and shadow coverage areas, the ground object coverage type has large change. Therefore, according to the difference between the two Landsat / OLI images caused by changes in the cover, this paper presents a method of extracting clouds and shadows based on differences in luminance values. This method selects two thresholds for the difference of brightness values, and extracts the clouds and shadows respectively, and validates them with random point method, which can obtain high precision of extracting cloud and shadow and satisfy the actual application needs.

Novel Method of Assessing Practical Intelligence Acquired in Mechatronics Laboratory Classes

2015 ◽  
pp. 895-928
Author(s):  
Zol Bahri Razali
Keyword(s):  
Engineering Education ◽  
Engineering Students ◽  
Explicit Knowledge ◽  
Assessment Instruments ◽  
Practical Intelligence ◽  
Work Related ◽  
Novel Method ◽  
The Difference ◽  
Representative Work ◽  
Method Of Assessment

Practical intelligence is often referred to as the ability of a person to solve practical challenges in a given domain. The lack of practical intelligence may be due to the way in which explicit knowledge is valued and subsequently assessed in engineering education, namely via examinations, tests, laboratory reports, and tutorial exercises. The lack of effective assessments on practical intelligence indicates implicit devaluation, which can significantly impair engineering students' ability to acquire practical intelligence. To solve this problem, the authors propose a new method of assessment for measuring practical intelligence acquired by engineering students after performing engineering laboratory classes. The novices-experts approach is used in designing the assessment instruments, based on the behaviors' of novices/experts observed and novices/experts representative work-related situations. The practical intelligence can be measured by calculating the difference between participants' and the experts' ratings; the closer the novices to experts, the higher the practical intelligence acquired.

A prediction model for amplitude-frequency characteristics of blast-induced seismic waves

Geophysics ◽  
2018 ◽  
Vol 83 (3) ◽  
pp. T159-T173 ◽  
Author(s):  
Chenglong Yu ◽  
Zhongqi Wang ◽  
Wengong Han
Keyword(s):  
Prediction Model ◽  
Field Experiment ◽  
Seismic Waves ◽  
Initial Pressure ◽  
Dominant Frequency ◽  
Frequency Characteristics ◽  
Adiabatic Exponent ◽  
The Difference ◽  
Explosive Properties

We have developed a prediction model for dominant frequency and amplitude of blast-induced seismic waves. A blast expansion cavity is used to establish a relationship between the explosive properties and amplitude frequency of blast-induced seismic waves. In this model, the dominant frequency and amplitude of blast-induced seismic waves are mainly influenced by the initial pressure and the adiabatic exponent of explosives in the same medium. The dominant frequency increases with the decreasing initial pressure or the increasing adiabatic exponent. This prediction model is compared with the experiments. The difference in the blast cavity between the prediction model and the field experiment is in the range of 5%–9%, and the difference in the dominant frequency is within 18.8%–46.0%. The comparison indicates that the model can reasonably predict the frequency and amplitude of blast-induced seismic waves.

scholarly journals Separation of diffracted waves via SVD filter

2020 ◽  
Vol 17 (5) ◽  
pp. 1259-1271
Author(s):  
Hong-Yan Shen ◽  
Qin Li ◽  
Yue-Ying Yan ◽  
Xin-Xin Li ◽  
Jing Zhao
Keyword(s):  
Seismic Waves ◽  
Original Data ◽  
Identification Accuracy ◽  
Reflected Waves ◽  
Wave Separation ◽  
Imaging Results ◽  
Diffracted Waves ◽  
Fast Processing ◽  
The Difference ◽  
Value Decomposition

Abstract Diffracted seismic waves may be used to help identify and track geologically heterogeneous bodies or zones. However, the energy of diffracted waves is weaker than that of reflections. Therefore, the extraction of diffracted waves is the basis for the effective utilization of diffracted waves. Based on the difference in travel times between diffracted and reflected waves, we developed a method for separating the diffracted waves via singular value decomposition filters and presented an effective processing flowchart for diffracted wave separation and imaging. The research results show that the horizontally coherent difference between the reflected and diffracted waves can be further improved using normal move-out (NMO) correction. Then, a band-rank or high-rank approximation is used to suppress the reflected waves with better transverse coherence. Following, separation of reflected and diffracted waves is achieved after the filtered data are transformed into the original data domain by inverse NMO. Synthetic and field examples show that our proposed method has the advantages of fewer constraints, fast processing speed and complete extraction of diffracted waves. And the diffracted wave imaging results can effectively improve the identification accuracy of geological heterogeneous bodies or zones.

scholarly journals Comparison of hypertonic saline-sodium hydroxide method with modified Petroff’s method for the decontamination and concentration of sputum samples

2013 ◽  
Vol 2 (3) ◽  
pp. 78-81 ◽  
Author(s):  
SK Chaudhary ◽  
B Mishra
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Sodium Hydroxide ◽  
Hypertonic Saline ◽  
P Value ◽  
Chi Square ◽  
Major Health ◽  
Medical College ◽  
Lowenstein Jensen ◽  
Novel Method ◽  
The Difference

INTRODUCTION: Tuberculosis is one of the major health problems particularly in developing countries. For definitive diagnosis of pulmonary tuberculosis identification of tubercle bacilli in sputum by microscopy and culture is essential. For decontamination and concentration of sputum, the commonly used method in the laboratory is Modified Petroff’s method but the Hypertonic saline–sodium hydroxide (HS-SH) method is known to be better for detection of Mycobacterium tuberculosis by culture. This study was aimed to compare a novel method for the improvement of decontamination and concentration of sputum samples. MATERIALS AND METHODS: A total of 50 confirmed smear positive sputum samples from pulmonary TB patients who visited at St. John’s Medical College and Hospital during 2009 to 2010, were processed for the decontamination process. Each sample was decontaminated by Modified Petroff’s and HS-SH method separately. Treated samples were cultured in Lowenstein-Jensen media in microbiology laboratory. RESULTS: The culture positive percents of Mycobacterium tuberculosis in the L-J medium treated with HS-SH and Modified Petroff’s method were 84.0% and 70.0%, respectively. A notable feature is that by HS-SH method more samples were positive by 4th week, statistically significant (Chi- square value-11.26 with p-value < 0.05) compare to Modified Petroff’s method. The difference for 3+ grades of L-J growths found slightly higher by Modified Petroff’s method but at lower grades of growths HS-SH method performed better. CONCLUSIONS: HS-SH method is better for the detection of Mycobacterium tuberculosis by culture when compared with the Modified Petroff’s method. DOI: http://dx.doi.org/10.3126/ijim.v2i3.8664   Int J Infect Microbiol 2013;2(3):78-81

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