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Ultra-wide band (UWB) radar can penetrate non-magnetic media such as coal and rock to detect life information of personnel after collapse. Due to the complex mining environment, UWB radar loaded with vital sign signals is prone to interference from environmental noise and clutter signals. It is difficult to recognize human subject information. This paper introduces the principle of UWB radar life detection system and its application in mine rescue. This paper summarizes the current research status of UWB radar life information recognition from three aspects: UWB radar life information extraction, dynamic and static human object recognition, and life quantification. This paper points out the current issues with the application of UWB radar life detection technology in the field of mine rescue. ① There is limited research on filtering methods for non-stationary signals and environmental noise in underground collapse environments. ② The extraction and representation methods for posture, behavior, life status, and other information of moving (or micro moving) objects need to be improved. The human life information recognition model is not yet perfect and the feature correlation between models is low. ③ There is a lack of solutions to the 'overlapping' problem caused by multiple objects. This paper proposes the prospects for the research direction of UWB radar life information recognition for mine rescue. ① It is suggested to continuously optimize noise and clutter adaptive filtering methods for multiple types of mine disaster environments. ② It is suggested to construct a human life information recognition model suitable for the field of mine rescue. ③ It is suggested to further improve the quantification capability of multi-object after mine shelter. ④ It is suggested to conduct depth exploration of the method for determining the optimal detection frequency band for UWB radar.

Deep well rescue technology refers to the key technologies involved in various aspects of rescuing trapped personnel during the process of deep well accident rescue. It mainly includes environmental detection technology, life detection technology, deep well rapid demolition technology, emergency communication network construction technology, and other auxiliary technologies to ensure the smooth progress of deep well accident rescue. Deep well rescue equipment refers to necessary hardware equipment and software platforms during the implementation of deep well rescue technology. Studying deep well rescue technology and equipment is crucial for ensuring the safety of trapped personnel and reducing accident losses. The current research status of deep well rescue equipment and key technologies is analyzed. It is pointed out that existing rescue technologies and equipment cannot fully meet the complex and changing environmental requirements. There are problems such as insufficient research on the universality and specificity of rescue equipment, the need to improve the intelligence level of rescue equipment, difficulty in meeting the needs of complex rescue environments with network collaboration capabilities, and insufficient innovation research on rescue equipment. In order to solve the above issues, the development trend of deep well rescue equipment and technology is discussed. ① Deep well rescue equipment should be divided into specialized and universal categories based on different rescue scenarios. A single equipment should develop towards multifunctionality, high reliability, and high mobility. ② Rescue equipment is intelligent, precise, and self decision-making, achieving a rescue mode of intelligent equipment as the main focus and personnel as the auxiliary. ③ It is suggested to build a rapid networking, multi-mode networking, and integrated rescue network platform. ④ Although TDLAS integration does not currently meet rescue standards, its high resolution, high sensitivity, and integrability will play an important role in the future, achieving high integration, lightweight, and efficiency of environmental monitoring equipment.

As a device for timely rescue after disasters, life detectors play an irreplaceable role in locating, exploring, and searching for living organisms. This paper analyzes the working principles, technical features, usage scenarios, advantages and disadvantages of the currently used life detectors. The detectors include radar life detectors, audio life detectors, infrared life detectors, and other types of life detectors. Combined with practical applications, this paper points out the problems of the above life detectors. ① The detection technology is single and the comprehensive integration is low. ② The detection methods are traditional and equipment intelligence is insufficient. ③ The parts of the detector are not standardized, making equipment maintenance difficult. ④ Some life detectors have a relatively large structure and are inconvenient to carry, which affects rescue efficiency. In response to the existing shortcomings and problems, the development trends of life detectors are proposed. ① It is suggested to improve the integration level of life detectors. It is suggested to design life detection devices that use multi-source fusion to collect information, and use multiple information sources to obtain and detect life information. ② It is suggested to improve the intelligence level of life detectors, give them partial autonomy in decision-making, and reduce errors in life detection caused by improper operation by operators. ③ It is suggested to design modular life detectors and develop relevant standard procedures to standardize the components of the same type of life detector. It will reduce the difficulty of repair and maintenance of life detectors. ④ It is suggested to improve the circuit board design precision of the life detector, fully utilize spatial structure, reduce volume and improve portability without reducing the functionality of the life detector.

The ultra wideband (UWB) radar detection technology can achieve mine human target detection for drilling rescue. However, UWB electromagnetic waves are susceptible to the complex environment of catastrophic mines. The UWB radar echo signals are susceptible to the background clutter and environmental noise of catastrophic mines. It is difficult to achieve precise detection of human targets in catastrophic mines. In order to solve the above problems, the underground target detection scenarios and human target detection principles based on UWB radar are introduced. The research status of UWB electromagnetic wave characteristics and UWB echo noise filtering methods are analyzed. The existing problems are summarized as following points. ① The propagation characteristics of UWB electromagnetic waves in the complex environment of catastrophic mines require in-depth research. ② The reason for the generation of background clutter is not yet clear. There is limited research on the filtering technology of background clutter and environmental noise in catastrophic mines. ③ The UWB radar human target detection technology for drilling rescue still needs to be improved. In response to the shortcomings of existing technologies, the development trend of UWB radar underground human target detection technology for drilling rescue is prospected. ① It is suggested to do in-depth research on the sensitivity of key characterization parameters of UWB electromagnetic wave penetration transmission to complex underground environmental characteristics. ② It is suggested to construct methods for filtering background clutter and environmental noise suitable for catastrophic mines. ③ It is suggested to deeply optimize UWB radar human target detection technology for drilling rescue.

Obtaining the position of underground trapped personnel quickly and precisely is a key issue for life information detection in the early stage of borehole rescue. In the process of vertical drilling and rescue, due to the collapse of the roadway in the detection area or the displacement of the final hole position, it is impossible to obtain the position of the trapped personnel quickly and accurately. It delays the golden time of rescue and affects the safety of personnel. Through conducting a UWB radar wave transmission attenuation study, a rescue plan can be quickly formulated for on-site rescue commanders. This paper analyzes the current situation and demand of UWB radar wave application in mine borehold rescue. Combined with the background of mine borehold rescue, it is pointed out the attenuation law of UWB radar wave transmission. The study analyzes the influence of the characteristic parameters of the medium on the attenuation of radar wave transmission from the perspective of anisotropy of the medium. The influence of dielectric parameters on radar wave transmission attenuation is analyzed from four aspects: dielectric constant, conductivity, magnetic permeability and spatiotemporal variation. The influence of radar characteristic parameters on radar wave transmission attenuation is analyzed from two aspects: radar frequency and polarization. Based on the above analysis, it is pointed out that there are few studies on the simultaneous penetration of UWB radar waves through anisotropic media such as coal and rock masses and the mechanism of media propagation and attenuation. There are few theories and experiments on UWB radar wave transmission attenuation in complex and changeable underground or simulating disaster environments. And there are few summaries of relevant laws. The mapping relationship database between key parameters and influencing factors of UWB radar waves is not yet complete. The key technologies to be studied in the future are given as follows. It is suggested to conduct research on anisotropic media such as coal and rock masses at both macro and micro levels. It is suggested to establish an experimental simulation system for radar wave transmission attenuation under catastrophic environmental conditions. It is suggested to add research on UWB radar signal propagation characteristics and channel modeling numerical simulation in unstructured environments after disasters.

The existing mine moving target positioning system has the problems of serious attenuation of underground wireless signal transmission, large non-line-of-sight error, complex underground electromagnetic environment, wide sensing range of dynamic and static targets, strong linkage of multi-system information fusion, etc. At present, the research on mine moving target precise positioning technology and optimization method does not comprehensively analyze the characteristics and technical requirements of the moving target accurate positioning service. It lacks a comprehensive comparison between the mainstream and emerging positioning technologies. In order to solve the above problems, the advantages and disadvantages of the common signal transmission technology and the positioning and ranging method applied in the mine moving target precise positioning system are analyzed. The radio positioning technology is pointed out to be a more suitable and feasible mine moving target precise positioning technology. This paper analyzes the research status and existing problems of the optimization method of the mine moving target precise positioning in China from four aspects: signal anti-collision technology, error elimination method, positioning result optimization method and fusion positioning technology. ① The comprehensiveness of the signal anti-collision algorithm still needs to be improved. ② The efficiency of ranging error control means needs to be improved. ③ The application of the fusion positioning method in the production site is not yet mature. ④ The auxiliary role of the system in emergency rescue is not fully played. In view of the shortcomings of the existing technology, the development trend of the mine moving target precise positioning technology is proposed: ① It is suggested to study the signal collision mechanism and post-conflict recovery mechanism in dynamic environment, and design a comprehensive signal anti-collision scheme. ② It is suggested to research precise, efficient and economical ranging error control scheme to save communication costs. ③ It is suggested to study dynamic positioning scheme design with deep integration of multiple positioning methods to improve the reliability, flexibility and applicability of the system. ④ It is suggested to study the multi-system linkage scheme and the emergency communication and positioning recovery mechanism in extreme cases, and give full play to the role of the system in emergency rescue.

The molecular structure of coal is complex, and the existing research methods are limited, so it is difficult to clarify its influence mechanism on the spontaneous-combustion characteristics of coal. In this paper, the previous extraction, FTIR, TPR, TG-DSC and other experimental results are combined to analyze the extraction weakening effect and the correlation analysis of the spontaneous-combustion characteristic parameters of raffinate coal. The results show that extraction can destroy the connection bond of coal molecules, change the content of dominant active groups in the coal spontaneous-combustion reaction, increase the lower limit of the key temperature nodes of coal spontaneous-combustion or extend the temperature range, resulting in an increase in the ignition-point temperature of coal and a decrease in coal quality. This paper will provide a theoretical basis for the study of the microscopic mechanism of coal spontaneous-combustion and then provide new ideas for the development of an active prevention and control technology for coal spontaneous-combustion. [ABSTRACT FROM AUTHOR]

The acoustic temperature measurement method has a broad application prospect due to its advantages of high precision, non-contact, etc. It is expected to become a new method for hidden fire source detection in mines. The acoustic time of flight (TOF) can directly affect the accuracy of acoustic temperature measurement. We proposed a quadratic correlation-based phase transform weighting (PHAT-β) algorithm for estimating the time delay of the acoustic temperature measurement of a loose coal. Validation was performed using an independently built experimental system for acoustic temperature measurement of loose coals under multi-factor coupling. The results show that the PHAT-β algorithm estimated acoustic TOF values closest to the reference line as the sound travelling distance increased. The results of coal temperature inversion experiments show that the absolute error of the PHAT-β algorithm never exceeds 1 °C, with a maximum value of 0.862 °C. Using the ROTH weighted error maximum, when the particle of the coal samples is 3.0–5.0 cm, the absolute error maximum is 4.896 °C, which is a difference of 3.693 °C from the error minimum of 1.203 °C in this particle size interval. The accuracy of six algorithms was ranked as PHAT-β > GCC > PHAT > SCOT > HB > ROTH, further validating the accuracy and reliability of the PHAT-β algorithm. [ABSTRACT FROM AUTHOR]

As one of the five major disasters in coal mine production, coal spontaneous combustion severely restricts the safety, efficiency and eco-friendliness in the mining process. Due to the diversified characteristics of theoretical methods for the prevention mechanism and prevention technology of coal spontaneous combustion fire disaster, this paper analyzes the difficulties for the prevention and control of coal fire disaster. The advantages and disadvantages of prediction methods and disaster prevention technology for the existing coal seam fire are discussed. The development prospects of coal spontaneous combustion fire prevention technology are prospected. On this basis, the key direction of research on coal seam fire prevention in China in future includes: the formation, evolution and inhibition mechanism of coal spontaneous combustion; fine division of coal spontaneous combustion stage; dynamic monitoring and intelligent early warning of coal spontaneous combustion; active, grading and coordinated prevention and control of coal spontaneous combustion.

A gas explosion experimental system based on a piece of 15 m-long and 9I8O semi-closed wide open steel pipe was constructed. An explosion experimental study on straight pipelines and pipeline structures with different angles (45°, 90°, and 135°) was conducted. Research results demonstrated that before the turn, flame propagation speed and flame sustaining time in different pipeline structures were consistent. With the increase of the distance away from the ignition source, the flame propagation velocity increases and the flame sustaining time decreases; at the turning point, the flame velocity suddenly decreases and the flame duration increases obviously. Meanwhile, the peak value of overpressure on the lateral wall of the turning corner is greater than that on the inner wall. Among the three different angles, the peak value of overpressure on the lateral wall of 135° bend is the highest. Different pipeline structures have great influence on gas explosion overpressure and flame propagation speed. These research conclusions provide theoretical references for gas explosion resistance in coal mines. [ABSTRACT FROM AUTHOR]

"Financial Extortion" indicates the unreasonable and predatory revenue policies and measures, which was showed as notortious or exorbitant taxes and tyranny. We should not denounce all the financial policies and measures which were carried out by the late Qing Dynasty aiming at increasing revenue as "financial extortion". During the late Qing Dynasty, the main measures of "financial extortion" were as below: added levying of original taxes, levying new taxes, forcing to contribute, inflation, and so on. There was a conflict of "financial extortion" and "anti-financial extortion" between the central and the local authority, which had caused disunity of local authority with central government. "Financial extortion" had eventually transferred to the massive poor people, and the future trouble was that the late Qing government bad lost its support from people and ruined in the collapse of its sovereignty. [ABSTRACT FROM AUTHOR]