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In order to study the law of ground pressure appearance in the face with large mining height in shallow coal seam and determine its reasonable working resistance of support, the 5-2 coal 503 working face of Daliuta Coal Mine in Shendong is selected as the research object. The law of ground pressure appearance in the face with large mining height in shallow coal seam is studied through the thin plate theory and the field measured ground pressure data, and the support resistance is calculated by combining two different theoretical calculation formulas force analysis. The results show that the initial step distance of 52503 working face is 64.4 m, which is basically consistent with 61.7 m calculated based on thin plate theory; the periodic weighting step fluctuates between 7.65 m and 29.75 m during the normal mining period, with an average of 19.16 m, a dynamic load coefficient of 1.45-1.57, an average of 1.50, which shows a strong mine pressure; during the weighting period, the support resistance along the inclined direction of the working face presents a “convex” type among them, the lower support resistance of the working face is about 69.8% of the middle part, and the upper support resistance of the working face is about 66.5% of the middle part; the working resistance calculated based on the two support strength theories is 17 871 kN and 19 890 kN respectively, which is smaller than the ZY21000/36.5/70D hydraulic support with the rated working resistance of 21 000 kN, which can meet the support requirements of the roof pressure above the working face.

In order to study the influence of the aspect ratio of the short-wall filling roadway on the stability of surrounding rock, the theory of numerical analysis and numerical simulation were used to analyze the principle of cooperative roof control of the short-wall filling roadway. The change laws of the stability of surrounding rock under different aspect ratios are presented.Research indicates that: when the height of the roadway is fixed, the maximum approach of the top floor and the two sides increases slowly with the increase of the width to height ratio and then decreases slightly, and then increases rapidly after the width to height ratio is greater than 1.0. And when the width to height ratio of the roadway is 1.0, the deformation of the panel per unit area is the smallest, which is most beneficial to the stability of the surrounding rock of the panel. Combined with the specific conditions of Bailiang Xusheng Coal Mine, the reasonable width-to-height ratio of the short-wall filling roadway was determined to be 1.0, and a specific support scheme was given based on the asymmetric deformation characteristics of the roof.

The slip–stick vibration intensity of a plane gate is usually large, which often brings serious safety risks to itself and the auxiliary structure. The slip–stick vibration of a plane gate is investigated using an experimental model test. The test conditions mainly focus on the gate-closing and gate-opening processes in transient flow. Based on the results, comparison diagrams of the slip–stick vibration response versus the external fluid excitation are constructed. The intensity and period of the slip–stick vibration both gradually increase with the opening degree of the plane gate decreasing. The frequency of slip–stick vibration is consistent with the natural frequency of the equivalent system, indicating that the slip–stick vibration is a nonlinear self-excited vibration. The slip–stick vibration and fluid excitation acting on the plane gate have a significant difference in response intensity and dominant frequency. In addition, a difference in gate support material can have a significant effect on the slip–stick vibration intensity. Therefore, the friction factor between gate support and track, rather than the fluid excitation, is the direct cause of slip–stick vibration, which can further prove that the slip–stick vibration is a friction-induced vibration caused by the gate's active motion, enriching the theory of the gate's vibration. [ABSTRACT FROM AUTHOR]

We consider a two-stage submodular maximization problem subject to a cardinality constraint and k matroid constraints, where the objective function is the expected difference of a nonnegative monotone submodular function and a nonnegative monotone modular function. We give two bi-factor approximation algorithms for this problem. The first is a deterministic $\left({{1 \over {k + 1}}\left({1 - {1 \over {{e^{k + 1}}}}} \right),1} \right)$ -approximation algorithm, and the second is a randomized $\left({{1 \over {k + 1}}\left({1 - {1 \over {{e^{k + 1}}}}} \right) - \varepsilon ,1} \right)$ -approximation algorithm with improved time efficiency. [ABSTRACT FROM AUTHOR]

Light‐emitting electrochemical cells (LECs) are kind of easily fabricated and low‐cost light‐emitting devices that can efficiently convert electric power to light energy. Compared with blue and green LECs, the performance of deep‐red LECs is limited by the high non‐radiative rate of emitters in long‐wavelength region. While various organic emitters with deep‐red emission have been developed to construct high‐performance LECs, including polymers, metal complexes, and organic luminous molecules (OLMs), but this is seldom summarized. Therefore, we overview the recent advances of organic emitters with emission at the deep‐red region for LECs, and specifically highlight the molecular design approach and electrochemiluminescence performance. We hope that this review can act as a reference for further research in designing high‐performance deep‐red LECs. [ABSTRACT FROM AUTHOR]