In order to improve the accuracy of wind speed forecasting in wind farms, an ensemble-enhanced combined forecasting model is proposed considering error correction. First establish five independent ...base learners, build a two-layer Stacking ensemble model to fuse the prediction results of each base learner, and divide the input data by cross-validation to improve the generalization ability of the model. Then use the model-free learning framework Q learning selects the optimal model in the base learner to correct the preliminary prediction error and obtain the final prediction result. Select the actual wind farm measured data in different seasons to simulate the prediction effect of the model, and verify the prediction ability of the proposed model through comparative analysis. The results show that the model has high prediction accuracy with ε = 0.093.
The surface-wave analysis method is widely adopted to build near-surface shear-wave velocity structure. Automatic picking of surface-wave dispersion curves is a problem that needs to be solved, ...especially when dealing with a large amount of data. In this paper, we proposed an automatic picking method of multi-mode surface-wave dispersion curves based on unsupervised machine learning methods. Firstly, seismic data is transformed to two-dimensional dispersion image by dispersion imaging method. The discrete dispersion image points are separated into two clusters: dispersion energy and background noise by Gaussian mixture model clustering method. Then the dispersion energy points are projected into frequency-velocity domain, and are distinguished as different surface-wave modes by the density-based spatial clustering of applications with noise algorithm. Finally, multi-mode dispersion curves are obtained by searching for the local peaks in different mode areas of surface waves. Particle filter is used to smooth the picked dispersion curves to eliminate the influence of noise. The synthetic tests show that the automatically picked dispersion curves can match the theoretical dispersion curves well. We also applied the proposed method to the picking of dispersion curves of two field data. The automatically picked dispersion curves are applied to the subsequent inversion. In the second field data, the one-dimensional inversion results are interpolated to obtain the near-surface three-dimensional velocity model of the work area. The inversion results are in good agreement with borehole data, which further proves the accuracy and efficiency of the automatic picking method for multi-mode dispersion curves.
•3D GMM clustering method is used to separate the dispersion energy and background noise.•The different modes of dispersion energy are distinguished by DBSCAN algorithm.•Particle filter is used to eliminate the interference of noise.•The automatic picking of the field data dispersion curves proves the efficiency of the proposed method.
Near-surface site characterization is of great significance in the fields of geotechnical engineering and resource exploration. In this paper, we propose a near-surface site characterization method ...based on the joint iterative analysis of first-arrival and surface-wave data (JIAFS). The proposed method combines the advantages of first-arrival traveltime tomography (FATT) and multichannel analysis of surface waves (MASW). First, the 1D S-wave velocity (
v
S
) models obtained by MASW are interpolated to construct the pseudo-2D
v
S
model. According to the available geological survey information and borehole data, the initial Poisson’s ratio (
σ
) model is estimated. Based on the estimated
σ
model, the pseudo-2D
v
S
model is converted to a referenced P-wave velocity (
v
P
) model which is utilized to constrain the progress of FATT. This helps FATT overcome the inherent defect that it cannot effectively identify velocity-inversion interfaces and low-velocity zones. On the other hand, the
v
P
model obtained by FATT can provide a favorable priori information to improve the reliability of the results of MASW. Then, the
v
P
and
v
S
models obtained by constrained FATT and MASW are used to update the
σ
model. In addition, the
v
P
and
v
S
models are also used as initial models in the next iterative analysis. Finally, through the iteration of this process, the two inversion methods can make use of their own advantages to improve each other, so we can establish accurate near-surface
v
P
,
v
S
and
σ
models under complex geological conditions. A velocity model including low-velocity zone is established for synthetic model test to analyze and verify the advantage of JIAFS. The
v
P
,
v
S
and
σ
models obtained by JIAFS can accurately identify the low-velocity zone and match the true models well. In addition, the proposed method is applied to the field seismic data acquired for oil and gas exploration in Northwest China. Compared with the results of individual inversions and borehole data, JIAFS can establish more reliable 3D
v
P
,
v
S
and
σ
models by interpolating the 2D inversion results, which reveals further details and enhances the geological interpretation significantly.
SUMMARY
We derive two sets of new wave equations involving the fractional time derivatives or fractional Laplacians for simulating seismic wave propagation in viscoelastic anisotropic (VA) media ...based on the Kjartansson's constant-Q model. The approximate fractional Laplacian wave equation is developed under the assumptions of the small velocity anisotropy parameter $\delta$ and attenuation anisotropy parameter ${\delta _Q}$ (or weak velocity and attenuation anisotropy). Both the formulas have the advantages of simple form and can accurately describe the constant-Q (i.e. frequency-independent quality factor) attenuation and arbitrary attenuation anisotropy behaviours compared to the widely used VA theory based on the generalized standard linear solids (GSLS) model and memory variables. Under the assumption of homogeneous plane wave and the constant-Q attenuation mechanism, we further derive exact analytical expressions for the phase velocities, attenuation coefficients, quality factors of the P- and SV-waves, and analyse their direction dependence in different attenuation anisotropy cases. For numerical modelling, we implement the fractional finite-difference (FD) method with the Grünwald–Letnikov (GL) approximation to solve the fractional time wave equation, and the generalized Fourier pseudospectral (PS) method to solve the fractional Laplacian wave equation, respectively. The PS method is highly efficient compared with the fractional FD method since it avoids additional memory to store the past wavefields. Numerical results of the homogeneous VTI (transversely isotropic with a vertical symmetry axis) model validate the accuracy of the two proposed schemes and illustrate the influence of attenuation and attenuation anisotropy on seismic wavefields, which are consistent with theoretical analysis. Finally, the modelling of the Hess VTI model shows the applicability of our formulations and algorithms in heterogeneous media.
SUMMARY
Compared with surface waves, guided waves are rarely applied in near-surface investigation. The main reason may lie in the complexity of their dispersion curves. Besides, the study and ...understanding of guided wave dispersion characteristics are now also inadequate and not deep enough. In this paper, we derived the complete theoretical dispersion curves of P–SV-wave and pure P-wave systems in layered media based on the transmission matrix method and obtained the relative displacement amplitude coefficients at the free surface as a function of frequency and phase velocity for both surface and guided waves. By assigning the value of relative displacement amplitude coefficient to the corresponding point (f,v) on dispersion curve, we got a multi-information diagram called relative amplitude dispersion map (RADM). As a unified description of surface and guided waves, RADM not only shows the velocity–frequency relationship but also represents the polarized energy ratio at the free surface by display colours. The accuracy of RADM was proved by synthetic seismic records, in which RADMs fit well with the corresponding dispersion energy of surface and guided waves. In addition, we designed six models with different Poisson's ratio (PR) and different layer numbers for comparison. It shows that the dispersive vertical-to-horizontal amplitude ratio of guided waves is complex and discontinuous in RADM, which brings great difficulty for mode identification and even affects the subsequent inversion. Tests also show that for high PR layers, the trends of guided P–SV-wave dispersion curves are basically consistent with those of pure P wave. With the decrease of PR, dispersion curves of guided P–SV wave gradually deviate from those of pure P wave. However, RADMs can be greatly consistent with the dispersion energy in either case. This is of great significance for the inversion of near-surface P and S velocities by using dispersion relationships of multimode surface and guided waves.
The absorption (anelastic attenuation) and anisotropy properties of subsurface media jointly affect the seismic wave propagation and the quality of migration imaging. Anisotropic viscoelastic model ...can effectively describe seismic velocity and attenuation anisotropy effects. To reduce the computational cost and complexity of elastic wave modes decoupling for seismic imaging in anisotropic attenuating media, we have developed a pure-viscoacoustic transversely isotropic (TI) wave equation starting from the complex-valued velocity dispersion relation of quasi-compressional (qP) wave. The wave equation involving fractional Laplacians has advantages of being able to describe the constant-
Q
(frequency-independent quality factor) attenuation, arbitrary TI velocity and attenuation, decoupled amplitude loss and velocity dispersion effects. Numerical analyses showed that the simplified equation can accurately hold the velocity and attenuation anisotropy of qP-wave in viscoelastic anisotropic media in the range of moderate anisotropy. Compared to previous pseudo-viscoacoustic equations, the pure-viscoacoustic equation can be completely free from undesirable S-wave artifacts and behaves good numerical stability in tilted transversely isotropic (TTI) attenuating media. There are obvious wavefield differences between isotropic attenuation and anisotropic attenuation cases especially in the direction perpendicular to the axis of symmetry. Furthermore, to mitigate the influences of velocity and attenuation anisotropy on migrated seismic images, we have developed an anisotropic attenuation (
Q
) compensated reverse time migration (AQ-RTM) approach based on the new propagator. The compensation can be implemented by reversing the sign of the dissipation terms and keeping the dispersion terms unchanged during wavefields extrapolation. Synthetic example from a Graben model illustrated that the anisotropic
Q
-compensated RTM scheme can produce images with more balanced amplitude and accurate position of reflecters compared with conventional RTM methods under assumptions of acoustic anisotropic (uncompensated) and isotropic attenuating media. Results from a Marmousi-II model demonstrated that the new methodology is applicable for complicated geological model to significantly improve imaging resolution of the target area and deep layers.
The seismic image produced by pre-stack depth migration is more accurate and has clearer geological significance than the time image. However, the waveform of the depth-domain seismic image is ...affected not only by depth-dependent velocity variation but also by media attenuation, resulting in strong spectral variation of depth-domain seismic data. Therefore, depth-domain seismic inversion is still challenging. We propose a wavelet extraction method of attenuation media based on the generalized seismic wavelet, to address this issue. Then, the estimated depth-domain wavelets were applied to the direct acoustic impedance inversion. First, we investigated the effect of attenuation media on depth-domain source wavelets and derived an analytical formula for the depth-domain wavelets of attenuation media. Next, the time-domain generalized seismic wavelet was extended to the depth domain, which was utilized to study the feasibility of using the generalized seismic wavelet to characterize the seismic wavelet of the depth-domain attenuation media. Based on the orthogonal matching pursuit, we propose a method to extract the depth-domain generalized seismic wavelet directly from depth-domain seismic data. Finally, we applied this method to the depth-domain direct acoustic impedance inversion of a 3D field data example. Tests on the synthetic and 3D field datasets show that the proposed method can correctly extract the depth-domain seismic wavelet of attenuation media and attain direct inversion of the depth-domain acoustic impedance with high accuracy. Therefore, our method is effective and has robust potential in reservoir characterization, fluid prediction, and attribute extraction in the depth domain.
Abstract Background Drug memories that associate drug-paired stimuli with the effects of abused drugs contribute to relapse. Exposure to drug-associated contexts causes consolidated drug memories to ...be in a labile state, during which manipulations can be given to impair drug memories. Although substantial evidence demonstrates the crucial role of neuronal signaling in addiction, little is known about the contribution of astrocyte-neuron communication. Methods Rats were trained for cocaine-induced conditioned place preference (CPP) or self-administration and microinjected with the glycogen phosphorylation inhibitor 1,4-dideoxy-1,4-imino-D-arabinitol into the basolateral amygdala (BLA) immediately after retrieval. The concentration of lactate was measured immediately after retrieval via microdialysis, and the CPP score and number of nosepokes were recorded 24 hours later. Furthermore, we used antisense oligodeoxynucleotides to disrupt the expression of astrocytic lactate transporters (monocarboxylate transporters 1 and 2) in the BLA after retrieval, tested the expression of CPP 1 day later, and injected L-lactate into the BLA 15 minutes before retrieval to rescue the effects of the oligodeoxynucleotides. Results Injection of 1,4-dideoxy-1,4-imino-D-arabinitol into the BLA immediately after retrieval prevented the subsequent expression of cocaine-induced CPP, decreased the concentration of lactate in the BLA, and reduced the number of nosepokes for cocaine self-administration. Disrupting the expression of monocarboxylate transporters 1 and 2 in the BLA also caused subsequent deficits in the expression of cocaine-induced CPP, which was rescued by pretreatment with L-lactate. Conclusions Our results suggest that astrocyte-neuron lactate transport in the BLA is critical for the reconsolidation of cocaine memory.
Display omitted
•With different UI designs, the learning performances in VR vary greatly.•In HTC Vive navigation, fishing mode is preferred rather than flying mode.•Grasp method performs better than ...proxy method in virtual construction operations.•A virtual observation scale close to body-and-mockup in real world performs best.
Virtual Reality (VR) technologies have been widely applied to the field of architecture education because of its unique immersion. There have been many researches on hardware and platform development in the world. However, there are relatively few on User Interface (UI) design. This is a study of UI design in VR applications applied in architectural education, which aims to improve users’ learning performance. Through a previous study and other scholars’ researches, four key factors have been extracted from the challenges of UI design in VR applications: navigation modes, operation methods, observation scales and background options. A set of experiments were conducted based on correlation analysis with 120 students of these four factors and learning performance. It is concluded that fishing mode with instantaneous movement is preferred rather than flying mode in HTC Vive navigation; the way of direct grasp in virtual operation performs better than the way of using an operational proxy in virtual construction process; a virtual observation scale close to body-and-mockup in real world performs best; contribution of a background environment in VR is not as significant as expected. In brief, the learning performances in a VR platform vary greatly with different UI designs.
It is a convenient and effective way to infer near-surface S-wave velocity (
) structures by using seismic surface waves. In spite of many successful applications on the geotechnical or engineering ...scale, surface-wave analysis and inversion methods are still not widely used in oil seismic exploration. Particularly, there are few researches reported on the three-dimensional (3D)
structure modelling with the surface wave methods on this exploration scale. In this paper, we proposed a seismic surface wave data processing and inversion scheme for 3D near-surface
modelling, and applied it to a field seismic data acquired for oil prospecting in Eastern China. Firstly, we analysed and adjusted the acquisition geometry to suit surface-wave analysis. Next, the interpolation and stacking processing was applied to the seismic data to eliminate spatial aliasing and improve the quality of dispersion images. In term of phase velocity dispersion imaging method, we adopted the cross-correlation and phase-shifting (CCPS) method to acquire accurate dispersion images. Simultaneous linearisation inversion of
and layer thickness was used to inverse the surface wave dispersion curves. This inversion method reduces dependence of the initial models and has ability to detect the top interface of high-velocity layer. At last, the 3D near-surface
structure was constructed by interpolating the all of 360 1D
structures. We contrasted the surface wave inversion result with the first-arrival tomography inversion result, and the geological stratification results of both were coincident. Within the near-surface range, the surface wave inversion result has a higher resolution. This confirms that 3D
modelling with surface waves in oil seismic prospecting is effective and practical.
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