Object-oriented implementation of 3D DC adaptive finite-element method

In this paper, we introduced a clear object-oriented framework to implement the complicated adaptive procedure with C ++ programming language. In this framework, it consisted of the unstructured mesh generation, a-posterior error estimating, adaptive strategy, and the postprocessing. Unlike the procedure-oriented framework, which is commonly used in DC resistivity modeling with FORTRAN language, the object-oriented one, which is famous for its characteristic of encapsulation, could be used for a class of problems that would be executed by only making some changes on the user interface. To validate its flexibility, two synthetic DC examples were tested her

Magnetotelluric Noise Attenuation Using a Deep Residual Shrinkage Network

Magnetotelluric (MT) surveying is an essential geophysical method for mapping subsurface electrical conductivity structures. The MT signal is susceptible to cultural noise, and the intensity of noise is growing with urbanization. Cultural noise is increasingly difficult to be removed by conventional data processing methods. We propose a novel time-series editing method based on the deep residual shrinkage network (DRSN) to address this issue. Firstly, the MT data are divided into small segments to form a dataset system. Secondly, we use the dataset system to train the denoising model. Finally, the trained model is used for MT data denoising. The experiments using synthetic data and actual field data collected in Qinghai and Luzong, China, show that the DRSN can effectively remove the cultural noise and has better adaptability and efficiency than traditional MT signal processing methods

Improved shift-invariant sparse coding for noise attenuation of magnetotelluric data

Magnetotelluric (MT) method is widely used for revealing deep electrical structure. However, natural MT signals are susceptible to cultural noises. In particular, the existing data-processing methods usually fail to work when MT data are contaminated by persistent or coherent noises. To improve the quality of MT data collected with strong ambient noises, we propose a novel time-series editing method based on the improved shift-invariant sparse coding (ISISC), a data-driven machine learning algorithm. First, a redundant dictionary is learned autonomously from the raw MT data. Second, cultural noises are reconstructed using the learned dictionary and the orthogonal matching pursuit (OMP) algorithm. Finally, the de-noised MT data are obtained by subtracting the reconstructed cultural noises from the raw MT data. The synthetic data, field experimental data and measured data are tested to verify the effectiveness of the newly proposed method. The results show that our new scheme can effectively remove strong cultural noises and has better adaptability and efficiency than the predefined dictionary-based methods. The method can be used as an alternative when a remote reference station is not available.ISSN:1343-8832ISSN:1880-598

Gravity Gradient Tensor of Arbitrary 3D Polyhedral Bodies with up to Third-Order Polynomial Horizontal and Vertical Mass Contrasts

During the last 20 years, geophysicists have developed great interest in using gravity gradient tensor signals to study bodies of anomalous density in the Earth. Deriving exact solutions of the gravity gradient tensor signals has become a dominating task in exploration geophysics or geodetic fields. In this study, we developed a compact and simple framework to derive exact solutions of gravity gradient tensor measurements for polyhedral bodies, in which the density contrast is represented by a general polynomial function. The polynomial mass contrast can continuously vary in both horizontal and vertical directions. In our framework, the original three-dimensional volume integral of gravity gradient tensor signals is transformed into a set of one-dimensional line integrals along edges of the polyhedral body by sequentially invoking the volume and surface gradient (divergence) theorems. In terms of an orthogonal local coordinate system defined on these edges, exact solutions are derived for these line integrals. We successfully derived a set of unified exact solutions of gravity gradient tensors for constant, linear, quadratic and cubic polynomial orders. The exact solutions for constant and linear cases cover all previously published vertex-type exact solutions of the gravity gradient tensor for a polygonal body, though the associated algorithms may differ in numerical stability. In addition, to our best knowledge, it is the first time that exact solutions of gravity gradient tensor signals are derived for a polyhedral body with a polynomial mass contrast of order higher than one (that is quadratic and cubic orders). Three synthetic models (a prismatic body with depth-dependent density contrasts, an irregular polyhedron with linear density contrast and a tetrahedral body with horizontally and vertically varying density contrasts) are used to verify the correctness and the efficiency of our newly developed closed-form solutions. Excellent agreements are obtained between our solutions and other published exact solutions. In addition, stability tests are performed to demonstrate that our exact solutions can safely be used to detect shallow subsurface targets

Magnetotelluric Signal-Noise Identification and Separation Based on ApEn-MSE and StOMP

Natural magnetotelluric signals are extremely weak and susceptible to various types of noise pollution. To obtain more useful magnetotelluric data for further analysis and research, effective signal-noise identification and separation is critical. To this end, we propose a novel method of magnetotelluric signal-noise identification and separation based on ApEn-MSE and Stagewise orthogonal matching pursuit (StOMP). Parameters with good irregularity metrics are introduced: Approximate entropy (ApEn) and multiscale entropy (MSE), in combination with k-means clustering, can be used to accurately identify the data segments that are disturbed by noise. Stagewise orthogonal matching pursuit (StOMP) is used for noise suppression only in data segments identified as containing strong interference. Finally, we reconstructed the signal. The results show that the proposed method can better preserve the low-frequency slow-change information of the magnetotelluric signal compared with just using StOMP, thus avoiding the loss of useful information due to over-processing, while producing a smoother and more continuous apparent resistivity curve. Moreover, the results more accurately reflect the inherent electrical structure information of the measured site itself

Surgical treatment of benign osteolytic lesions in the femoral head and neck: a systematic review

Abstract Background and objectives Treatment of benign osteolytic lesions in the femoral head and neck can be extremely challenging, particularly in children with open physis or for aggressive tumors with pathological fracture. There remains the difficult management decision as to whether to perform complete excision of the involved area or only curettage. Moreover, there is no agreed consensus on the optimal approach to lesion access when performing curettage, which included the transcervical, open and direct approach. The current systematic review aims to provide guidance for selection of surgical methods in clinical practice by comparing the advantages and drawbacks of different procedures. Methods A comprehensive literature search of PubMed, Embase and Web of Science databases were executed for human studies restricted to the English language. The search was filtered to include studies published from January 1980 to January 2020. Results A total of 33 articles including 274 patients were enrolled in the final analysis. The most common diagnosis was chondroblastoma (CBT) (104, 38.0%), followed by giant cell tumor (GCT) (56, 20.4%). There were 57 (20.8%) patients with pathological fracture. Intralesional curettage was performed in 257 (93.8%) patients with the local recurrence of 12.5% at the mean follow-up of 51.5 months. The patients who were presented with open physis or curetted via transcervical approach developed higher local recurrence in patients with CBT (P < 0.001). The local recurrence rate of GCT is 33.3% after curettage, while 8 of 9 (88.9%) patients with fracture were treated successfully with joint preservation. Two of 45 (4.4%) patients developed avascular necrosis (AVN) of femoral head after surgical hip dislocation. The reported Musculoskeletal Tumor Society (MSTS) Score was comparable among patients with different approaches to curettage. Conclusion The majority of benign osteolytic lesions in the femoral head and neck can be treated with intralesional curettage with acceptable local tumor control and satisfactory function. The incidence of local recurrence might be decreased dramatically for lesion access under direct visualization. The native joint maintenance could be achieved even in patients with aggressive lesions presenting pathological fracture

Exact solutions of the vertical gravitational anomaly for a polyhedral prism with vertical polynomial density contrast of arbitrary orders

We present general closed-form solutions for the vertical gravitational anomaly caused by a polyhedral prism with mass density contrast varying with depth. Our equations are the first ones to implement a polynomial vertical mass density contrast of arbitrary order. Singularities in the gravity field which arise when the observation site is close to or in the anomalous polyhedral prism are removed in our analytic expressions. Therefore, the observation site can be located outside, on the faces of or inside the anomalous mass bodies. A simple prismatic body of anomalous density is adopted to test the accuracy of our newly developed closed-form solution. Cases of constant, linear, quadratic, cubic and quartic polynomial orders of mass density contrast are tested. For cases of constant, linear, quadratic and cubic polynomial orders, the relative errors between our results and other published exact solutions are less than 10⁻¹¹%. For the case of quartic polynomial order, relative errors less than 10⁻¹⁰% are obtained between our solutions and those computed by a high-order Gaussian quadrature rule (512 × 512 ×512=134217728 quadrature points), where our new analytic solution needs significantly less computational time (0.0009  versus 31.106 s). These numerical experiments not only verified the accuracy of our new formula but also demonstrated their potential in computing exact gravity anomalies for complicated mass density distributions in the Earth.ISSN:0956-540XISSN:1365-246