Vertical Stress and Deformation Characteristics of Roadside Backfilling Body in Gob-Side Entry for Thick Coal Seams with Different Pre-Split Angles

Retained gob-side entry (RGE) is a significant improvement for fully-mechanized longwall mining. The environment of surrounding rock directly affects its stability. Roadside backfilling body (RBB), a man-made structure in RGE plays the most important role in successful application of the technology. In the field, however, the vertical deformation of RBB is large during the panel extraction, which leads to malfunction of the RGE. In order to solve the problem, roof pre-split is employed. According to geological conditions as well as the physical modeling of roof behavior and deformation of surrounding rock, the support resistance of RBB is calculated. The environment of surrounding rock, vertical stress and vertical deformation of the RBB in the RGE with different roof pre-split angles are analyzed using FLAC3D software. With the increase of roof pre-split angle, the vertical stresses both in the coal wall and RBB are minimum, and the vertical deformation of RBB also decreases from 110.51 mm to 6.1 mm. Therefore, based on the results of numerical modeling and field observation, roof pre-split angle of 90° is more beneficial to the maintenance of the RGE

Direct in situ NMR observation of lithium plating, corrosion, nitridation and protonolysis for ammonia synthesis

As a low-carbon and decentralized ammonia synthetic method, lithium-mediated electrochemical synthesis has shown promising efficiencies and reaction rates. Nevertheless, many mechanistic questions need to be addressed to optimize the process and in situ characterizations are in great need. Here we develop in situ NMR methodology that allows us to directly observe each reaction step of the catalytic cycle, including plating of metallic lithium and the concurrent corrosion, nitrogen splitting on lithium metal and protonolysis of lithium nitride. The in situ NMR methods are general and can be broadly applied for screening and understanding Li and beyond-Li catalysts for nitrogen splitting, accelerating the materials discovery for ammonia synthesis

Fast γ Photon Imaging for Inner Surface Defects Detecting

Only a few effective methods can detect internal defects and monitor the internal state of complex structural parts. On the basis of the principle of PET (positron emission computed tomography), a new measurement method, using γ photon to detect defects of an inner surface, is proposed. This method has the characteristics of strong penetration, anti-corrosion and anti-interference. With the aim of improving detection accuracy and imaging speed, this study also proposes image reconstruction algorithms, combining the classic FBP (filtered back projection) with MLEM (maximum likelihood expectation Maximization) algorithm. The proposed scheme can reduce the number of iterations required, when imaging, to achieve the same image quality. According to the operational demands of FPGAs (field-programmable gate array), a BPML (back projection maximum likelihood) algorithm is adapted to the structural characteristics of an FPGA, which makes it feasible to test the proposed algorithms therein. Furthermore, edge detection and defect recognition are conducted after reconstructing the inner image. The effectiveness and superiority of the algorithm are verified, and the performance of the FPGA is evaluated by the experiments

Mathematical and Mechanical Analysis of the Effect of Detonator Location and Its Improvement in Bench Blasting

The outcome of bench blasting significantly affects the downstream operations in mining. In bench blasting, the explosives charged in blastholes are generally cylindrically shaped and fired by the in-hole detonator. As the detonator determines the propagation of the detonation wave in the cylindrical charge, the effect of detonator location can never be ignored. In this paper, the mathematics and mechanics of the effect of detonator location was analyzed from the view of the distribution of explosion energy and blast stress field of a cylindrical charge. Then, a field blasting experiment and two numerical simulations were conducted to further display its effect on blasting outcomes. At last, the appearance of oversize boulders and rock toes in bench blasting was discussed, and an improved scheme of the detonator location was proposed to cope with these problems. Results indicate that the in-hole detonator has the capacity of adjusting the spatial distribution of explosion energy and blast stress field in the surrounding rock mass. The traditional recommendation of the bottom detonator is not always right. The optimized detonator location in bench blasting is available by properly combining the merits of traditional detonator locations. This study is of interest to improve the efficiency and reduce the cost of mining

Modeling and experimental analysis of U-shaped segmented unidirectional heat pipe array cogeneration unit

The Solar collectors and cogeneration units have gained increasing attention in research recently, while being developed and deployed rapidly. However, due to the instability of the solar energy, the heat flux input of solar collectors is unstable potentially causing an adverse effect on the cogeneration unit. This paper presents the mathematical models for two cogeneration units: (a) the thermal series U-shaped segmented unidirectional heat pipe array cogeneration unit with thermoelectric generator (TEG-TSUSUHP) and (b) the thermal parallel U-shaped segmented unidirectional heat pipe array cogeneration unit with thermoelectric generator (TEG-TPUSUHP). The proposed models have been validated by a series of experiments. Further, the cogeneration unit is then optimized using the proposed models. The results show that the heat loss rate of the TEG-TSUSUHP cogeneration unit is lower than that of the TEG-TPUSUHP cogeneration unit, and the lowest heat loss rate is 15.56%. Moreover, the cogeneration unit designed in this work has good thermal insulation performance with a high thermal storage efficiency of up to 80.53%. Therefore, the U-shape segmented unidirectional heat pipe array cogeneration units with thermoelectric generator (TEG-USUHP) proposed in this paper can promote the development of solar cogeneration units significantly