A thorough understanding of the deformation behavior, damage accumulation, and progressive failure of heterogeneous coal is a prerequisite for effective control of the surrounding rock and efficient ...exploitation of resources in underground coal mines. Such understanding can be obtained by analyzing both the macro- and meso-responses of coal to loading. Accordingly, a coupled macro- and meso-mechanical model for heterogeneous coal is developed and implemented in FLAC3D in the present study. The model is based on elasto-plastic mechanics and the energy dissipation and release principle, and heterogeneity is incorporated by the combination of a statistical approach and the discrete fracture network method. The model is calibrated by experimental data and is used to simulate stress-strain responses, the evolution of acoustic emission (AE) events, and energy conversion in compressed coal. The results reveal that: (1) the model can efficiently capture the dependency of the deformability, compressive strength and AE characteristics on the confining pressure; (2) the anisotropic behavior of heterogeneous coal is realistically realized, and the initiation, propagation and coalescence of micro-cracks can be located and tracked; and (3) stress paths, the degree of heterogeneity, and the unloading rate of confining pressure significantly influence the axial stress-strain response and AE event evolution in the stressed coal. The proposed model produces reasonable values for the roof weighting interval and expansion of the excavation-damaged zone around the gate when compared to the field data measured at the Dongzhouyao mine of China.
•A coupled macro- and meso-mechanical model is established for coal.•Anisotropy is incorporated by combining a statistical approach and the DFN method.•Uniaxial and triaxial compression tests are performed.•Numerical results correlate well with experimental data.•A practical application shows that the introduced model produces realistic results.
The study of top-coal drawing characteristics is key to improving the top-coal recovery ratio and to reducing the waste of coal resources in longwall top-coal caving (LTCC) mining. This paper ...introduces a Boundary-Body-Ratio (BBR) based research system established by the authors following a long-term detailed study of the top-coal drawing mechanism. For BBR system, a simplified parabolic model is proposed to describe the development process of the boundary of top-coal in normal top-coal drawing cycles, where the drawing body is a cut variant ellipsoid (CVE) that can be described by the modified Bergmark-Ross model. A method for improving the recovery ratio and reducing the rock mixed ratio of top-coal by selecting reasonable drawing technique parameters and controlling the shape of the boundary of the top-coal is given for the BBR system. Based on the BBR research system, the drawing mechanism for loose top-coal in sublevel top-coal caving (SLTCC) in steeply inclined coal seams is studied for different sublevel heights and drawing direction conditions using distinct element numerical calculations and loose top-coal drawing experiments. The results show that the boundary curve of top-coal can be fitted by a parabola and that the drawing body remains as a cut variation ellipsoid in SLTCC, as is the case for a flat coal seam. The convex point of the boundary of the top-coal moves toward the goaf with increasing sublevel height, which would result in the incomplete development of the top-coal drawing body. The drawing extent index decreases linearly with increasing sublevel height, and the top-coal recovery ratio decreases after an initial increasing phase. Approximately 90% of the residual coal in the current sublevel will not be extracted during the drawing process of the next sublevel. Drawing from the floor to the roof expands the overlap area between the drawing body and the boundary of the top-coal, improving the recovery of the top part of the top-coal. Such a drawing sequence decreases the coal loss near the floor by 38.2% compared to drawing from the roof to the floor and greatly increases the resource recovery ratio.
•BBR system was established following a long-term detailed study of the top-coal drawing mechanism.•In SLTCC, the drawing extent index decreases linearly with increasing sublevel height (Hs).•With the increasing of Hs, the top-coal recovery ratio decreases after an initial increasing phase.•Most of the residual coal in the current sublevel will not be recovered in the next sublevel.•Drawing from the floor to the roof decreases the coal loss near the floor greatly in SLTCC.
Effective surrounding rock control is a prerequisite for realizing safe mining in underground coal mines. In the past three decades, longwall top-coal caving mining (LTCC) and single pass large ...height longwall mining (SPLL) found expanded usage in extracting thick coal seams in China. The two mining methods lead to large void space left behind the working face, which increases the difficulty in ground control. Longwall face failure is a common problem in both LTCC and SPLL mining. Such failure is conventionally attributed to low strength and high fracture intensity of the coal seam. However, the stiffness of main components included in the surrounding rock system also greatly influences longwall face stability. Correspondingly, surrounding rock system is developed for LTCC and SPLL faces in this paper. The conditions for simultaneous balance of roof structure and longwall face are put forward by taking the stiffness of coal seam, roof strata and hydraulic support into account. The safety factor of the longwall face is defined as the ratio between the ultimate bearing capacity and actual load imposed on the coal wall. The influences provided by coal strength, coal stiffness, roof stiffness, and hydraulic support stiffness, as well as the movement of roof structure are analyzed. Finally, the key elements dominating longwall face stability are identified for improving surrounding rock control effectiveness in LTCC and SPLL faces.
The top-coal caving mining method, developed steadily in the past two decades, has become the main method for thick seam coal mining in China. In recent years, the core research areas in the top-coal ...caving mining are the mechanisms of top-coal caving and the improvement of top-coal recovery ratio. In this paper, the mechanisms of the top-coal caving are illustrated by a large number of physical simulation experiments and numerical modelings of actual cases. The marker method, which has sufficient accuracy to calculate the top-coal recovery ratio, is also described in detail.
Layered double oxides are widely employed in catalyzing the aldol condensation for producing biofuels, but its selectivity and stability need to be further improved. Herein, a novel MCM-41-supported ...Mg-Al-layered double oxide (LDO/MCM-41) was prepared via the in situ integration of a sol-gel process and coprecipitation, followed by calcination. This composite was first employed to catalyze the self-condensation of cyclopentanone for producing high-density cycloalkane precursors. LDO/MCM-41 possessed large specific surface area, uniform pore size distribution, abundant medium basic sites and Bronsted acid sites. Compared with the bulk LDO, LDO/MCM-41 exhibited a higher selectivity for C10 and C15 oxygenates at 150 °C (93.4% vs. 84.6%). The selectivity for C15 was especially enhanced on LDO/MCM-41, which was three times greater than that on LDO. The stability test showed that naked LDO with stronger basic strength had a rapid initial activity, while it suffered an obvious deactivation due to its poor carbon balance. LDO/MCM-41 with lower basic strength had an enhanced stability even with a lower initial activity. Under the optimum conditions (50% LDO loading, 170 °C, 7 h), the cyclopentanone conversion on LDO/MCM-41 reached 77.8%, with a 60% yield of C10 and 15.2% yield of C15.
Longwall top-coal caving (LTCC) is widely employed in the underground mining of thick coal seams. The technique divides a thick coal seam into a lower and an upper section. The bottom coal is sheared ...by a cutting head and transported by a conveyor in front of the support while the top coal fails and caves under mining pressure, transported by a conveyor at the rear of the support. In an LTCC panel, accurate assessment of top-coal cavability is critical to the design of mining parameters required to achieve continuous caving of top coal. In the present paper, an integrated detection system in which fracture development and ultrasonic wave velocity are used to characterize top-coal cavability is introduced. The cavability is predicted conveniently due to ease of access of the ultrasonic wave velocity in the top coal. Accordingly, an ultrasonic model is established and coupled to the mechanical model previously proposed by the authors to simulate the evolution of the wave velocity in stressed coal. The mechanical-ultrasonic coupling model is validated by comparison against experimental data and further extended to evaluate top-coal cavability in Dongzhouyao mine with a finite difference type code. The predictions, including the excavation-damaged zone, roof weighting interval, stress distribution, stress rotation and ultrasonic wave velocity evolution, are consistent with the field measurements. With the proposed model, the influence provided by hydraulic fracturing on top-coal cavability is investigated by conducting the finite difference type modeling.
•A field investigation based system for top-coal cavability assessment is introduced.•Ultrasonic wave velocity is utilized to characterize and predict top-coal cavability.•A mechanical-ultrasonic coupling model is established and calibrated.•The top-coal cavability predicted by the model agrees well with field measurements.
Understanding the characteristics of drawing body shape is essential for optimization of drawing parameters in longwall top coal caving mining. In this study, both physical experiments and ...theoretical analysis are employed to investigate these characteristics and derive a theoretical equation for the drawing body shape along the working face in an inclined seam. By analyzing the initial positions of drawn marked particles, the characteristics of the drawing body shape for different seam dip angles are obtained. It is shown that the drawing body of the top coal exhibits a shape-difference and volume-symmetry characteristic, on taking a vertical line through the center of support opening as the axis of symmetry, the shapes of the drawing body on the two sides of this axis are clearly different, but their volumes are equal. By establishing theoretical models of the drawing body in the initial drawing stage and the normal drawing stage, a theoretical equation for the drawing body in an inclined seam is proposed, which can accurately describe the characteristics of the drawing body shape. The shape characteristics and volume symmetry of the drawing body are further analyzed by comparing the results of theoretical calculations and numerical simulations. It is shown that one side of the drawing body is divided into two parts by an inflection point, with the lower part being a variation development area. This variation development area increases gradually with increasing seam dip angle, resulting in an asymmetry of the drawing body shape. However, the volume symmetry coefficient fluctuates around 1 for all values of the seam dip angle variation, and the volumes of the drawing body on the two sides are more or less equal as the variation development volume is more or less equal to the cut volume. Both theoretical calculations and numerical simulations confirm that the drawing body of the top coal exhibits the shape-difference and volume-symmetry characteristic.
Previous studies have indicated a heightened susceptibility to cataract and glaucoma among rheumatoid arthritis (RA) patients, while it remains uncertain whether RA is causally associated with ...cataract and glaucoma. A two-sample mendelian randomization (MR) analysis was used to investigate the causal associations between RA, cataract and glaucoma in European and East Asian populations.
In the European population, genome-wide association study (GWAS) summary statistics for cataract (372,386 individuals) and glaucoma (377,277 individuals) were obtained from the FinnGen consortium (R9), while RA summary data were derived from a meta-analysis of GWAS encompassing 97173 samples. In the East Asian population, summary data for cataract (212453 individuals), glaucoma (212453 individuals), and RA (22515 individuals) were sourced from the IEU Open GWAS project. Inverse-variance weighted (IVW, random-effects) method served as the primary analysis, complemented by MR‒Egger regression, weighted median, weighted mode and simple mode methods. Additionally, various sensitivity tests, including Cochran's Q test, MR‒Egger intercept, MR pleiotropy Residual Sum and Outlier test and leave-one-out test were performed to detect the heterogeneity, horizontal pleiotropy and stability of the analysis results.
Following stringent screening, the number of selected instrumental variables ranged from 8 to 56. The IVW results revealed that RA had an increased risk of cataract (OR = 1.041, 95% CI = 1.019-1.064; P = 2.08×10-4) and glaucoma (OR = 1.029, 95% CI = 1.003-1.057; P = 2.94×10-2) in European populations, and RA displayed a positive association with cataract (OR = 1.021, 95% CI = 1.004-1.039; P = 1.64×10-2) in East Asian populations. Other methods also supported those results by IVW, and sensitivity tests showed that our analysis results were credible and stable.
This study revealed a positive causality between RA and the increased risk of cataract and glaucoma, which provides guidance for the early prevention of cataracts and glaucoma in patients with RA and furnishes evidence for the impact of RA-induced inflammation on ophthalmic diseases.
Regarded as a high-level tactic in soccer, a team formation assigns players different tasks and indicates their active regions on the pitch, thereby influencing the team performance significantly. ...Analysis of formations in soccer has become particularly indispensable for soccer analysts. However, formations of a team are intrinsically time-varying and contain inherent spatial information. The spatio-temporal nature of formations and other characteristics of soccer data, such as multivariate features, make analysis of formations in soccer a challenging problem. In this study, we closely worked with domain experts to characterize domain problems of formation analysis in soccer and formulated several design goals. We design a novel spatio-temporal visual representation of changes in team formation, allowing analysts to visually analyze the evolution of formations and track the spatial flow of players within formations over time. Based on the new design, we further design and develop ForVizor, a visual analytics system, which empowers users to track the spatio-temporal changes in formation and understand how and why such changes occur. With ForVizor, domain experts conduct formation analysis of two games. Analysis results with insights and useful feedback are summarized in two case studies.
iTTVis: Interactive Visualization of Table Tennis Data Wu, Yingcai; Lan, Ji; Shu, Xinhuan ...
IEEE transactions on visualization and computer graphics,
2018-Jan., 2018-01-00, 2018-1-00, 20180101, Letnik:
24, Številka:
1
Journal Article
Recenzirano
The rapid development of information technology paved the way for the recording of fine-grained data, such as stroke techniques and stroke placements, during a table tennis match. This data recording ...creates opportunities to analyze and evaluate matches from new perspectives. Nevertheless, the increasingly complex data poses a significant challenge to make sense of and gain insights into. Analysts usually employ tedious and cumbersome methods which are limited to watching videos and reading statistical tables. However, existing sports visualization methods cannot be applied to visualizing table tennis competitions due to different competition rules and particular data attributes. In this work, we collaborate with data analysts to understand and characterize the sophisticated domain problem of analysis of table tennis data. We propose iTTVis, a novel interactive table tennis visualization system, which to our knowledge, is the first visual analysis system for analyzing and exploring table tennis data. iTTVis provides a holistic visualization of an entire match from three main perspectives, namely, time-oriented, statistical, and tactical analyses. The proposed system with several well-coordinated views not only supports correlation identification through statistics and pattern detection of tactics with a score timeline but also allows cross analysis to gain insights. Data analysts have obtained several new insights by using iTTVis. The effectiveness and usability of the proposed system are demonstrated with four case studies.
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