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The precise positioning of personnel and vehicles in coal mines is an important guarantee for safe and efficient production in coal mines. Currently, ultra-wideband (UWB) wireless communication technology is mainly used for the precise positioning of personnel and vehicles in coal mines. The positioning method that only uses the time of flight (TOF) requires two positioning substations or antennas for joint ranging and direction. It has problems such as large antenna spacing, inconvenience in installation and maintenance, and large positioning errors. In order to solve the above problems, a joint positioning method based on UWB phase difference of arrival (PDOA) and TOF is proposed for one-dimensional positioning scenarios in coal mines. This method measures the distance between the positioning card and the positioning substation through TOF, and judges the direction of the positioning card through PDOA. The method locates the positioning card based on the measured distance and direction between the positioning card and the positioning substation. This method determines the angle of arrival (AOA) of the positioning card based on the phase difference between the radio signals transmitted from the positioning card and the two antennas of the positioning substation. It does not require a large antenna spacing to determine the direction of the positioning card. It shortens the distance between the two antennas of the positioning substation. It integrates the two antennas to facilitate installation and maintenance, improving positioning precision. The underground testing results of coal mines show that the positioning precision of this method is within 15 cm. Within the test distance range of 200 m, the positioning precision is not affected by the distance. The TOF ranging value is stable within a range of ± 10 cm relative to its mean value, with good stability.

Multi-rotor aircraft has a good application prospect in coal mine production inspection because of its advantages of simple structure, hovering and multi-directional flight. However, multi-rotor aircraft moves at a high speed, and the aircraft is easily influenced by various external factors during flying. It is difficult to establish a precise mathematical model. The design of a flight control algorithm is complicated. The existing synchronous positioning and map construction method based on laser radar is difficult to meet the real-time requirement of rapid flying of the multi-rotor aircraft. In view of the above problems, an obstacle avoidance control method of multi-rotor aircraft in coal mine by using remote virtual control technology is studied. The virtual remote control system of the multi-rotor aircraft in coal mine underground roadway is constructed. The virtual roadway model and the global navigation map are established in the virtual remote control system according to the initial information of the coal mine roadway. The known static obstacle information in the moving process of the aircraft is obtained, and the known static environment model is established. The task quantity of environment perception modeling in the moving process of the multi-rotor aircraft is reduced, and the operation efficiency of virtual remote control can be improved. In the inspection process, the multi-rotor aircraft detects dynamic obstacle information in the moving direction through sensing equipment carried by the multi-rotor aircraft. The remote control system reconstructs the dynamic obstacle information in an initial virtual roadway model in real-time according to obstacle data. The virtual environment state is updated in real-time to provide a reliable environment basis for local obstacle avoidance control of the aircraft. The remote control system uses the compound virtual force field (CVFF) obstacle avoidance control algorithm to plan the obstacle avoidance path by reading the positioning data and moving speed information of obstacles and aircraft. If the obstacle in front is detected to pose a great threat to the movement of the aircraft, the remote controller can implement remote intervention on the aircraft according to the planned obstacle avoidance path. The system realizes autonomous obstacle avoidance flight and human remote intervention control. In order to improve the perception efficiency and accuracy of aircraft to dynamic obstacles, a CVFF obstacle avoidance control algorithm is studied based on virtual force field (VFF) algorithm by introducing the influence of relative velocity between aircraft and obstacles and target points. The CVFF obstacle avoidance control algorithm is verified by simulation from two aspects of static and dynamic obstacle avoidance paths. The results show that under static conditions, compared with the VFF algorithm, the CVFF algorithm reduces the number of iterations and also shortens the trajectory length of the aircraft. Under dynamic conditions, the aircraft successfully avoids the two dynamic obstacles set in advance and successfully reaches the set target point. The effectiveness of the obstacle avoidance control method of multi-rotor aircraft using the CVFF algorithm is verified.

The occurrence of coal-bearing strata in China is characterized by the variety of coal-bearing basins，the remarkable spatial and temporal differences of late tectonic deformations.The main controlling factors，which determine the tectonic framework of coalfields，include geodynamic environment，tectonic evolution，deep structures，tectonic stress，and lithologic combination features of coal measures.The continent of China has experienced multi-stage tectonic movements since the late Paleozoic，and due to the spatio-temporal heterogeneity of continental tectonic evolution and the complexity of basement properties，the coalfield structures present complex and ordered patterns.The coalfield tectonic framework of China can be divided into two major coalfield regions，three coal deformation zones，and five coal occurrence structural areas.Taking coal occurrence structural sub-areas as basic units，the tectonic characteristics of five coal occurrence structural areas in China were summarized in this paper.

In view of the low production efficiency of the esophageal stent graft and the problem of postoperative complications such as esophageal restenosis due to insufficient graft strength, an integrated esophageal stent graft was prepared at one time with nitinol alloy wire and high-strength polyester multifilament based on the integrated braiding technology. The transportability, radial support performance, graft strength and bending performance of the integrated stent graft were studied through constant elongation tensile test, radial compression and elastic recovery force tests. The results show that the outer diameter of the integrated esophageal stent graft can be compressed to 45.39% of the original; the elastic recovery rate is 96.81% and the radial compression strength is 489.42 cN; after 50 constant elongation tests, there is no wear or breakage of the membrane material; the diameter of the stent and the smoothness of the pipeline are still maintained after 180° bending. It indicates that the braided integrated esophageal stent graft has excellent transportability, stable radial support performance, excellent fatigue resistance and good flexibility. [ABSTRACT FROM AUTHOR]

Under the background of changing global environment and frequent anthropogenic activities, rainfall-runoff relationship has suffered tremendous change in many regions of China, particularly in arid and semi-arid regions. The Jinghe River basin (JRB) in the middle of the Loess Plateau, which is the major base of grain production in Shannxi Province, has experienced significant changes in hydro-climatic variables and the relationship between them during the past decades, causing many water resources problems. In this paper, we focused on analyzing the variation characteristics of rainfall-runoff relationship in JRB, and quantitatively assessing the effects of climate changes and human activities on the runoff reduction. It was of great importance for mastering the evolution of hydrological cycle, water resources planning and management, and water and soil conservation in JRB. The monthly rainfall and runoff data were used in the study and summed annually to investigate the variation characteristics in 1960-2010. To detect the change points of rainfall-runoff relationship, the sliding partial correlation coefficients method was proposed and the change points were further confirmed by the double mass curve method. On the basis of the studies, the relative changes of rainfall, runoff, and rainfall-runoff relationship were analyzed around the change points. Moreover, we also introduced the Archimedean Copula function, from the perspective of probability, to analyze the probability of synchronous-asynchronous encounter of rainfall and runoff in JRB. What caused the variation of rainfall-runoff relationship? Climate change or human activities? To figure out this, the method of slope change ratio of cumulative quantity (SCRCQ) was adopted in this paper. According to these results, we obtained the following conclusions: (i) Annual runoff and rainfall presented wavelike decrease change. Nevertheless, annual runoff declined more greatly than rainfall; especially, in some periods annual rainfall increased, however, runoff decreased. This illustrated that some non-rainfall factors caused the occurrence of phenomenon in JRB; (ii) Change points of rainfall-runoff relationship occurred in 1996 validated by the sliding partial correlation coefficients method and double mass curve method. Meanwhile, we could ascertain the conclusion by the evidence of the process of human activities in JRB, which presented the increasing industrial, agricultural and domestic water consumption and large-scale water conservancy and soil conservation projects since 1990s; (iii) To compare the magnitude of the changes of rainfall, runoff and rainfall-runoff relationship, the hydrological variables series were divided into the periods of 1960-1996 and 1997-2010. Compared to runoff and rainfall in 1960-1996, the annual mean runoff and rainfall in 1997-2010 dropped 43.47% and 6.64%, respectively. The change of monthly rainfall had no significance in different periods. On the contrary, monthly runoff decreased more greatly and the difference was smaller in each month i.e. the runoff distribution for each month was more uniform. The correlation between rainfall and runoff diminished and runoff yield decreased under the same rainfall. When precipitation was above 400 mm, the relative change rate of runoff was above 40% in 1997-2010 compared to that in 1960-1996; (iv) The joint distributions of rainfall and runoff constructed by the Archimedean Copula function were different in 1960-1996 and 1997-2010, and the distributions in the 2 periods were fitting Clayton and Gumbel-Hougaard Copula better, respectively. The probabilities of synchronous-asynchronous encounter of the same rainfall and runoff changed strikingly in different periods. For instance, when rainfall was less than 550 mm and runoff was less than 40 mm, the probability of synchronous-asynchronous encounter was 44% in 1960-1996 and 73% in 1997-2010; (v) In JRB, human activities, i.e. non-rainfall factors, have played a fundamental role in rainfall-runoff relationship change. Further compared with some research results, the irrigation, the construction of reservoirs and the water-and-soil conservation measures in the region should be responsible for the change to a large extent. Compared to the period of 1960-1996, the contribution from human activities in the period of 1997-2010 reached about 81% and climate change was merely around 19% obtained by the method of SCRCQ. The research results can provide theoretical basis for water resource management and water and soil conservation for the administrators. [ABSTRACT FROM AUTHOR]

Regenerative surgery is an emerging multidisciplinary field that has the potential to transform the surgical treatment for diseases and injuries. This article provides a brief overview of the history of surgery and regenerative medicine, introduces the new concept of regenerative surgery, describes the surgical procedures, and discusses the role of surgeons in developing and implementing these technologies. Insights gained from recent clinical research of regenerative medicine are beginning to yield three strategies for regenerative therapies for surgical diseases, and this review also provides the challenges and translational perspectives of these different strategies.