3D weak-dispersion reverse time migration using a stereo-modeling operator

Reliable 3D imaging is a required tool for developing models of complex geologic structures. Reverse time migration (RTM), as the most powerful depth imaging method, has become the preferred imaging tool because of its ability to handle complex velocity models including steeply dipping interfaces and large velocity contrasts. Finite-difference methods are among the most popular numerical approaches used for RTM. However, these methods often encounter a serious issue of numerical dispersion, which is typically suppressed by reducing the grid interval of the propagation model, resulting in large computation and memory requirements. In addition, even with small grid spacing, numerical anisotropy may degrade images or, worse, provide images that appear to be focused but position events incorrectly. Recently, stereo-operators have been developed to approximate the partial differential operator in space. These operators have been used to develop several weak-dispersion and efficient stereo-modeling methods that have been found to be superior to conventional algorithms in suppressing numerical dispersion and numerical anisotropy. We generalized one stereo-modeling method, fourth-order nearly analytic central difference (NACD), from 2D to 3D and applied it to 3D RTM. The RTM results for the 3D SEG/EAGE phase A classic data set 1 and the SEG Advanced Modeling project model demonstrated that, even when using a large grid size, the NACD method can handle very complex velocity models and produced better images than can be obtained using the fourth-order and eighth-order Lax-Wendroff correction (LWC) schemes. We also applied 3D NACD and fourth-order LWC to a field data set and illustrated significant improvements in terms of structure imaging, horizon/layer continuity and positioning. We also investigated numerical dispersion and found that not only does the NACD method have superior dispersion characteristics but also that the angular variation of dispersion is significantly less than for LWC. Read More: http://library.seg.org/doi/abs/10.1190/geo2013-0472.1National Natural Science Foundation (China) (Grant 41230210)Massachusetts Institute of Technology. Earth Resources Laboratory (Founding Members Consortium

3D Weak-Dispersion Reverse-Time Migration with a StereoModeling Method

The finite difference method has been widely used in seismic modeling and reverse time migration. However, it generally has two issues: large computational cost and numerical dispersion. Recently, a nearly-analytic discrete operator was developed to approximate the partial differential operators. Based on this spatial discretization, many weak-dispersion and efficient StereoModeling methods have been developed, which are found to be superior to conventional algorithms in suppressing numerical dispersion. In this paper, we generalize one StereoModeling method, the nearly-analytic central difference method (NACD), from 2D to 3D and apply it to 3D reverse-time migration. Numerical results show that the NACD can be used effectively as a new tool for seismic modeling and migration. The reverse time migration (RTM) results for the 3D SEG/EAGE Phase A classic dataset 1 show that the NACD can get a much better image than the Lax-Wendroff correction (LWC) method particularly when using a coarse grid size.Massachusetts Institute of Technology. Earth Resources Laboratory (Founding Members Consortium

Influence of diameter of empty hole on the fragmentation effect of parallel cut blasting under confining pressure

Cut blasting is the key technology for roadway blasting excavation. High confining pressure has obvious inhibition effect on cut blasting effect, while empty hole is of great significance to improve cut blasting efficiency, but the relevant research is not sufficient so far. To study the crushing effect of the cut blasting with different empty hole diameters under the confining pressure, cubic cement mortar test blocks whose side length was 600 mm were made with sand cement ratio of 2:1. The test blocks were subjected to equal bi-axial confining pressure through an electro-hydraulic servo loading system, and the parallel cut blasting cement mortar physical model test was carried out. After the blasting fragmentation was screened and statistically analyzed, the fragmentation distribution and average particle size of model fragments under different empty hole diameters were analyzed and investigated. With fractal features of fragments characterized by fractal dimension, the fragmentation degree was quantitatively analyzed. ANSYS/LS–DYNA software was used to establish numerical models based on the parameters of the test model, and the stress contour at different times with different hole diameters was analyzed. The research result shows that, when two empty holes are charged with different charge of 2 g and 3 g, respectively, the maximum fractal dimension of the model fragment can be attained with empty holes in diameter of 24 mm and 16 mm, respectively, with the particle size of the fragment mainly concentrated in the middle segment between 19 to 75 mm, and the largest total mass of the fragment is 3.128 kg and 3.615 kg, respectively; When the sizes of empty holes are different, the stress concentration effect and the reflected tensile wave produced near the empty hole are also different, which brings the difference of cut blasting fragmentation effect and can effectively benefit from the empty hole effect. The peak value and action range of stress wave near the empty hole are bigger, with a long action time, suggesting a better crushing effect; the diameter of the empty hole is too small, the stress around the empty hole is small. An oversized empty hole will lead to the overflow of the stress wave from the hole. The compressive stress is small after the superposition of stress concentration, and the action area of tensile stress is also small. The proportion of large rock pieces will be high with extremely large or small empty hole. When charged with 3 g, the fractal dimension difference between empty hole model fragments of 32 mm and 16 mm is greater than the difference of model fragments between 16 mm and without empty hole, indicating that the influence on the fragmentation of rock is greater when the empty hole diameter is too large. When the empty hole diameter is the same as 16 mm, the average particle size of the fragments in the model charged with 3 g is less than that in the model charged with 2 g, with the greater fractal dimension and total mass of the fragments than that in the test model charged with 2 g. This shows that an increased charge can contribute to rock fragmentation and the volume of the cut cavity with the same diameter of empty holes

Diagnostic workup of endocrine dysfunction in recurrent pregnancy loss: a cross-sectional study in Northeast China

ObjectiveTo evaluate the prevalence of abnormal endocrine dysfunction for recurrent pregnancy loss (RPL) amongst patients with two versus three or more pregnancy losses.MethodsThis cross-sectional study retrospectively collected pre-pregnancy data of 537 women diagnosed with RPL in Shengjing Hospital of China Medical University from 2017 to 2022, including the baseline data of patients and the test results of endocrine factors. Several endocrine dysfunction included in this study were: thyroid dysfunction, obesity, hyperprolactinemia, polycystic ovary syndrome and blood glucose abnormality. Furthermore, vitamin D level were collected to study its relationship with endocrine dysfunction. Finally, we subdivided the patients according to the number of previous pregnancy loss and compared the prevalence of endocrine dysfunction between subgroups.ResultsAmong 537 RPL patients, 278 (51.8%) patients had abnormal endocrine test results. The highest incidence of endocrine dysfunction was thyroid dysfunction (24.39%, 131/537), followed by hyperprolactinemia (17.34%, 85/490), obesity (10.8%, 58/537), polycystic ovary syndrome (10.50%, 56/533), and abnormal blood glucose (5.29%, 27/510). Only 2.47%(13/527) of patients have vitamin D level that reach the standard. After subdividing the population according to the number of pregnancy loss, we did not find that the incidence of endocrine dysfunction (P=0.813), thyroid dysfunction (P=0.905), hyperprolactinemia (P=0.265), polycystic ovary syndrome (P=0.638), blood glucose abnormality (P=0.616) and vitamin D deficiency (P=0.908) were different among patients with two versus three or more pregnancy losses. However, obesity (P=0.003) was found more frequently observed in patients with more times of pregnancy loss.ConclusionThe prevalence of endocrine dysfunction in RPL population is high. There is no difference in the prevalence of endocrine dysfunction, except for obesity, among patients with two or more pregnancy losses, which may suggest investigations of endocrine dysfunction when patients have two pregnancy losses

Controllable Load Management Approaches in Smart Grids

With rapid smart grid technology development, the customer can actively participate in demand-side management (DSM) with the mutual information communication between the distributor operation company and the smart devices in real-time. Controllable load management not only has the advantage of peak shaving, load balance, frequency regulation, and voltage stability, but is also effective at providing fast balancing services to the renewable energy grid in the distributed power system. The load management faces an enormous challenge as the customer has a large number of both small residential loads and dispersed renewable sources. In this paper, various controllable load management approaches are discussed. The traditional controllable load approaches such as the end users’ controllable appliances, storage battery, Vehicle-to-Grid (V2G), and heat storage are reviewed. The “broad controllable loads” management, such as the microgrid, Virtual Power Plant (VPP), and the load aggregator are also presented. Furthermore, the load characteristics, control strategies, and control effectiveness are analyzed

Analysis and optimization of a novel high cooling flux stacked T-shaped thermoelectric cooler

To meet the cooling demands of high heat flow density hotspots in scenarios such as electronic chips, a novel three-dimensional stacked T-shaped thermoelectric cooler (STTEC) is designed in this study. Under steady-state conditions, a finite element method with coupled thermal–electrical–mechanical physical fields is utilized, and the temperature dependence of thermoelectric (TE) materials is considered. First, the cooling flux, coefficient of performance (COP), and minimum cooling temperature of STTEC under different input-current and thermal boundary conditions are investigated and compared to the traditional π-shaped thermoelectric cooler (π-TEC). Second, the effects of geometrical parameter variations under optimal currents on the cooling performance and reliability of STTEC are studied. Finally, the structural parameters are optimized. The results show that the STTEC altered the path of TE conversion and transfer, which significantly improved the optimal current. The STTEC has a remarkable advantage in cooling performance under low temperature differences or high cooling loads. Compared to the π-TEC, STTEC enhances cooling flux by 101.6%, rises COP by 358.5%, and lowers the cold-end temperature by 46.6 K. At optimal current conditions, by optimizing the thickness of the T-shaped copper slice and the height difference between the TE leg and the T-shaped copper slice, the thermal stress decreased by 18.4%. The STTEC’s novel design could inspire the manufacturing and commercialization of high-performance thermoelectric coolers

Research on the area of mechanized construction of transmission lines

In order to continuously improve the construction capacity of power grid projects, improve the level of construction technology, and promote the transformation and upgrading of construction enterprises, power companies actively promote the mechanized construction of transmission lines. On the basis of summarizing the existing calculation rules of mechanized construction area, through on-site investigation and extensive collection of funds, research and excavate indicators that adapt to the new situation and new regulations. According to the actual area composition of the mechanized construction site, scientific calculation rules are formulated by modeling analysis and other methods. Compare and verify the calculated area of the new rule with the actual compensation area and the calculated area of the original rule, and propose a complete set of calculation rules for mechanized construction area, which has the conditions and value for popularization and application

Collaborative Determination Method of Metro Train Plan Adjustment and Passenger Flow Control under the Impact of COVID-19

Aiming at the problem of metro operation and passenger transport organization under the impact of the novel coronavirus (COVID-19), a collaborative determination method of train planning and passenger flow control is proposed to reduce the train load rate in each section and decrease the risk of spreading COVID-19. The Fisher optimal division method is used to determine reasonable passenger flow control periods, and based on this, different flow control rates are adopted for each control period to reduce the difficulty of implementing flow control at stations. According to the actual operation and passenger flow changes, a mathematical optimization model is established. Epidemic prevention risk values (EPRVs) are defined based on the standing density criteria for trains to measure travel safety. The optimization objectives of the model are to minimize the EPRV of trains in each interval, the passenger waiting time and the operating cost of the corporation. The decision variables are the number of running trains during the study period and the flow control rate at each station. The original model is transformed into a single-objective model by the linear weighting of the target, and the model is solved by designing a particle swarm optimization and genetic algorithm (PSO-GA). The validity of the method and the model is verified by actual metro line data. The results of the case study show that when a line is in the moderate-risk area of COVID-19, two more trains should be added to the full-length and short-turn routes after optimization. Combined with the flow control measures for large passenger flow stations, the maximum train load rate is reduced by 35.18%, and the load rate of each section of trains is less than 70%, which meets the requirements of COVID-19 prevention and control. The method can provide a theoretical basis for related research on ensuring the safety of metro operation during COVID-19

Study on the Influence of the Joint Angle between Blast Holes on Explosion Crack Propagation and Stress Variation

The joints and fissures in a natural rock mass can affect the mechanical properties of the rock mass, the propagation of a blasting stress wave, and the blasting effect of the smooth surface of roadways. In the process of roadway drilling and blasting, there will inevitably be some joints between the two blast holes. Taking the joint angle as the starting point, this paper studies the rule of rock explosion crack propagation and stress variation when there are joints with different angles between two blast holes and analyzes the influence of joints on rock mechanical properties and blasting effects. The numerical simulation method and the software ANSYS/LS-DYNA are used to establish 7 rock mass models with various joint angles. When there is no joint between two holes and joints of 15°, 30°, 45°, 60°, 75°, and 90°, the propagation of explosive cracks and stress variations in the rock mass are discussed. The results show that the joints at different angles have obvious guiding and blocking effects on the propagation of explosive cracks, and as joint angles increase, the guiding effect becomes more apparent and the blocking effect becomes weaker. The effective stress of the rock mass will vary depending on the angles of the joints between the hole and the joint. As the joint angle increases, the joint’s influence on the reflection and superposition of stress waves gradually weakens, and the peak value of the effective stress of the rock mass gradually decreases. The peak effective stress of the rock mass on the blasting side of the joint is similarly impacted by the superposition of stress waves, and the extreme value may be seen at the critical node of each change curve. The explosive crack will break through at the critical location because the maximal effective stress of the rock mass is distributed in a “W” form on the blasting side of the joint