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The fracture complexity of tight sandstone could work to improve the efficiency of tight gas reservoir fracturing.In this paper, three-point bending loading tests was used to characterize the fracture behavior, mechanical properties, fracture path and fracture energy characteristics of tight sandstone at room temperature(RT)and low temperature(LT)of liquid nitrogen(LN2), and to interpret the pre-fracture mechanism of tight sandstone at LN2.The results show that: 1)The fracture load and fracture toughness of the tight sandstone treated with LN2 are significantly lower than those at RT, while the parameters of the samples under parallel bedding slightly increased, which may be related to the enhancement of the bedding plane by LN2.2)After low temperature treatment with LN2, the complexity of fracture propagation paths increases, the number of fracture increases, and the fracture bifurcation and convergence occurs.The fracture complexity of sandstone is low at RT, and the effect of LN2 precracking on the fracture complexity of tight sandstone is significant.3)After LN2 pre-splitting, the fracture energy of tight sandstone decreases significantly, with a maximum decrease of 46.98 %.4)It is found that the fracture paths of tight sandstone mainly develops along the mineral grain boundary and forms intergranular fracture at RT, and the rock transformation degree is low.However, the complex fracture forms are formed by intergranular fracture, transgranular fracture and intergranular fracture, and the formation of transgranular fracture and complex fracture network are promoted under low temperature.The results of this study suggest that low-temperature during fracturing of tight sandstone reservoir can effectively reduce the fracturing pressure, realize the toughening-brittle transformation of rock and improve fracture complexity.

In this paper, through the secondary development of ProCAST&CAFE software, the dynamic boundary conditions of solidification process were established, the temperature field and solid fraction in the directional solidification process of low nickel austenitic stainless steel were simulated, and the effect of the pull rate on solidification microstructure was discussed. The results shows that the withdrawal rate is in the range of 15~200 μm/s, as the solidification speed increases, the isotherm becomes dense, gummy zone narrowing. And as the solidification rate increases, the primary dendrite arm gradually refines and the secondary dendrite arm becomes dense and coarse. In addition, as the withdrawal rate increases in the range of 15 to 200 μm/s, the lateral heat dissipation of the edge of the casting is gradually smaller than that of the central longitudinal heat dissipation, and the axial deviation of the dendrites is reduced from 27.66 ° to 25.964 °. At the same time, the comparative analysis simulation results are in good agreement with the experimental results, and the simulation calculation process is more reasonable.

For poor images captured by coal mine video monitoring system with low contrast, uneven illumination and a lot of noise, a single scale Retinex algorithm based on simultaneous denoising of weighted guided filtering was proposed for underground image enhancement. Firstly, low-frequency components of an image are estimated by the weighted guided filter, which replaces Gaussian filter in single scale Retinex algorithm. Secondly, high-frequency components of the image are denoised by the weighted guided filter. Finally, an enhanced image is obtained through conversion from log domain to real field. The subjective visual effect and objective evaluation results show the algorithm has better visual effect and higher image processing speed than traditional image enhancement algorithms.

In view of problem of time-consuming and subjective dependence of traditional ontology construction method, an ontology construction method of coal mining face based on formal concept analysis was proposed. The method can discover concepts implied in domain data and relationship between the concepts effectively, use concept lattice to visualize ontology and add new information to ontology automatically, and realize semi-automatically update of ontology. Experiment proved effectiveness of the proposed method.

The paper pointed out that building ontology model of heading face was an important step towards the construction of intelligent decision-making system based on deep analysis of production model of the heading face, obtained relationship between the staff, devices and environment of underground heading face by analyzing factors of mine production safety, and built safety production ontology model of the heading face. Hazardous workplace was taken as an example to simply verify the validity of construction method of the ontology model of heading face.

In view of shortcomings of low recognition rate and even unable to identify coal mine personnel existed in traditional face recognition algorithm, the paper proposed a face recognition algorithm based on SURF and FLANN. Firstly, the algorithm uses fast-Hessian detection matrix of SURF algorithm to find features, and generates feature vector of SURF descriptor. Then it adoptes search algorithm of positive and negative characteristics of Hessian detection matrix and bothway FLANN matching algorithm to match SURF descriptor, so as to realize face recognition and check on worker attendance．The experimental result shows that the algorithm can not only exclude mistake matching points，but also improve recognition speed and correct rate of SURF algorithm ,and ensure the real-time performance of the algorithm in the attendance system.

For low identification ratio of attendance system of coal mine caused by difficult facial contour extraction of underground personnel, a facial contour extraction method was proposed based on active contour model (Snake model) and active shape model (ASM). Firstly, the initial contour position is estimated by ASM. Secondly, the gap between marker and real contour is narrowed after multiple iterations by Snake algorithm through defining energy function of Snake model. Finally, gray value contour of orthogonal interpolation obtained by ASM are extracted, so as to get facial contour. Experimental results show that the method can extract facial contour more accurately than traditional Snake model.

This article documents the rammed earth construction practices undertaken at the "Tiles Hill–Xiangshan Campus Reception Centre" project. Traditional rammed earth craftsmanship is a sustainable construction method, with its core rooted in the precise material ratios and building techniques. This project aimed to explore the revival of this nearly forgotten vernacular construction method by integrating modern building technologies, all while adhering to the principle of avoiding any stabilizer additives. The project utilized a total of 2200 cubic meters of rammed earth to construct 16 walls, predominantly oriented north-south, with heights ranging from 3.6 m to 9.6 m and a thickness of 0.6 m. Before the formal commencement of the project, the team conducted experiments in the laboratory, constructing test walls to determine the optimal template fabrication and installation system compatible with modern rammed earth techniques. During the construction process, the team refined the rammed earth techniques, addressing challenges such as wall tilting, horizontal cracking caused by material settlement, and the flexible connection between the earthen walls and the primary structural framework through rational structural node design. The walls also passed compressive strength tests. Furthermore, advancements in the construction process allowed for the recycling and reuse of excavated soil. The article emphasizes that the sustainability of rammed earth techniques extends beyond material reuse to encompass the material's inherent environmental friendliness and nondestructive nature. It argues that, provided there is a thorough understanding of the material properties of soil and reasonable structural and node design, coupled with the addition of necessary structural measures, it is entirely feasible to achieve ecological sustainability in rammed earth construction without the use of stabilizing additives. [ABSTRACT FROM AUTHOR]

A foundation pit's excavation area, which is determined by its radius in a circular foundation pit, exerts a considerable influence on the pit's behavior. Using a full-scale experiment on a circular foundation pit retained by a prefabricated recyclable supporting structure (PRSS), this study develops a series of axisymmetric numerical models to systematically investigate the influence of excavation radius on the pit's deformation, stress, and stability. Furthermore, simulation results from axisymmetric models are compared with those from plane strain models to illustrate the influence mechanism. The results show that at a given excavation depth, the deflection and bending moments of the supporting piles, the earth pressure on the non-excavation side, and ground surface settlement increase with the enlarged excavation radius, but the increase rate progressively decreases. However, the foundation pit's safety factor decreases with an increasing excavation radius and gradually stabilizes. When the excavation radius exceeds 50 m, its influence on the foundation pit's behavior significantly diminishes. The axisymmetric model results closely approximate those from the plane strain models, suggesting that the spatial arching effects of the circular foundation pit can be disregarded. [ABSTRACT FROM AUTHOR]

The restoration of fine motor function in the hand is crucial for stroke survivors with hemiplegia to reintegrate into daily life and presents a significant challenge in post-stroke rehabilitation. Current mirror rehabilitation systems based on wearable devices require medical professionals or caregivers to assist patients in donning sensor gloves on the healthy side, thus hindering autonomous training, increasing labor costs, and imposing psychological burdens on patients. This study developed a low-load wearable hand function mirror rehabilitation robotic system based on visual gesture recognition. The system incorporates an active visual apparatus capable of adjusting its position and viewpoint autonomously, enabling the subtle monitoring of the healthy side's gesture throughout the rehabilitation process. Consequently, patients only need to wear the device on their impaired hand to complete the mirror training, facilitating independent rehabilitation exercises. An algorithm based on hand key point gesture recognition was developed, which is capable of automatically identifying eight distinct gestures. Additionally, the system supports remote audio–video interaction during training sessions, addressing the lack of professional guidance in independent rehabilitation. A prototype of the system was constructed, a dataset for hand gesture recognition was collected, and the system's performance as well as functionality were rigorously tested. The results indicate that the gesture recognition accuracy exceeds 90% under ten-fold cross-validation. The system enables operators to independently complete hand rehabilitation training, while the active visual system accommodates a patient's rehabilitation needs across different postures. This study explores methods for autonomous hand function rehabilitation training, thereby offering valuable insights for future research on hand function recovery. [ABSTRACT FROM AUTHOR]

Excavations for underground structures, such as working shafts, underground grain silos, and parking garages, are characterized by uniformity, consistent dimensions, large quantities, and strict timelines. Prefabricated recyclable supporting structures (PRSS) are gaining attention over traditional retaining structures due to their standardized design, efficient construction, and reusability, which suit such excavations better. To validate their performance, full-scale tests are conducted to analyze the deformation and stress characteristics of PRSS. The results show that the average maximum lateral displacement of supporting pile is 0.07% of the excavation depth (He), roughly half that of steel plate. Differences in ground surface settlement behind steel plates and the supporting piles are not as significant as those in their lateral displacements. While the displacement of the supporting piles is insufficient to induce soil movement into the active limit state on the non-excavation side, the circular excavation's arching effect reduces the earth pressure on this side of the supporting piles below the active earth pressure limit. Furthermore, the earth pressure acting on the steel plates is lower than that acting on the supporting piles, suggesting the presence of a soil arching effect between two adjacent piles. These findings offer valuable insights for guiding the construction of PRSS. [ABSTRACT FROM AUTHOR]

In this work, semi‐aromatic polyamide containing ether bond (PAE10T) was synthesized through nucleophilic substitution reaction using 1, 10‐N, N′‐bis(4‐fuorobenzamide) decane (BFBD) and hydroquinone (HQ) as the raw materials. And then the composites hydroxyapatite/semi‐aromatic polyamide (40%HA‐PAE10T and 60%HA‐PAE10T) were prepared by chemical precipitation method. Mechanical, SEM, FT‐IR, XRD, DSC, TGA and bioactivity tests were performed to characterize the structure, morphology, thermal and mechanical properties of PAE10T and its composites. Mechanical tests revealed that the difference of HA in weight played an important role in mechanical performance of the composites. Furthermore, in comparison with PAE10T, the 60%HA‐PAE10T showed the highest enhancement in compressive strength (133 MPa) at 75.9%, and the 40%HA‐PAE10T given expression to the best increase in bending strengths (97 MPa) at about 18.4%. The 40%HA‐PAE10T and 60% HA‐PAE10T exhibited the mechanical performances closed to the cortical bone of human. After 28 days of dip in the phosphate buffer saline (PBS), PAE10T, and its composites showed satisfactory stability. The cell culture results showed all composites gad good cytocompatibility, cells attached on the materials well with excellent morphology. All the experimental results showed that the composites were expected to have a good application in the field of compact bone repair. [ABSTRACT FROM AUTHOR]

The prefabricated recyclable supporting structure (PRSS) is an innovative support system that integrates a steel skeleton with polymer waterproof technology. Earth berms are extensively adopted to support the PRSS, but there is limited understanding on the factors influencing their behavior in circular excavations. In this paper, a numerical model is first validated with a case history in Henan, China. Afterwards, the geometric parameters of the earth berms, including the height (H), the top width (B1), and the bottom width (B2), on the behavior of the PRSS, are investigated. It is shown that, by increasing the height, top width and bottom width of earth berms, the lateral deflections, and bending moments of supporting piles, as well as the ground surface settlements, tend to decrease. However, the reduction effect of these parameters diminishes as well. Moreover, the raised effective formation level considering the effect of the earth berms on stability and deformation analyses is discussed. The factor of the safety of the excavation is almost doubled when axisymmetric conditions are considered compared to plane strain conditions. In deformation analysis, the raised effective formation level increases with the height of the earth berms until a steady value is reached. [ABSTRACT FROM AUTHOR]