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Adsorption characteristics of CO2 by coal are an important reservoir parameter to determine the CO2 storage capacity of the coal seam. The Langmuir isotherm adsorption model is commonly used to describe the isothermal adsorption line of coal. However, we cannot predict the CO2 adsorption capacity at other temperatures by using the Langmuir model based on the experimental data at a fixed temperature. This paper analyzes the ε–Vad adsorption characteristic curves of three coal samples over a range of temperatures and pressures. The study demonstrates that the adsorption characteristic curves of CO2 gas are independent of temperature and depend mainly on the dispersion force between coal and the CO2 molecules. In addition, the adsorption potential of CO2 gas has a negative correlation with the volume of the adsorbed phase. Hence, the CO2 adsorption characteristic curve of coal conforms to the logarithmic function. Based on the adsorption potential theory, the prediction model of CO2 adsorption by coal is derived. The deviation analysis from measured data shows that the average relative deviation of the three coal samples is ∼5%, and the prediction results are accurate and reliable. Under different temperature and pressure conditions of the three coal samples, the results from the prediction model of CO2 adsorption by coal and the Langmuir model have a strong correlation with the experimental results. In comparison with the Langmuir model, the prediction model of CO2 adsorption by coal can predict the adsorption capacity under different temperature and pressure conditions. Hence, it has a wide range of applications when compared to that of the Langmuir model. In practical applications, better results are achieved with a significant reduction in experimental time and labor.

Over the past few decades, the spontaneous combustion of large-scale coal stockpile is frequent due to natural airflow contacted the surface and entered in the voids of coal stockpile, coal is oxid...

Enhanced and efficient recovery of coalbed methane (CBM) is essential to prevent mine disasters and utilize unconventional gas resources. In this study, hydraulic slotting (HS) combined with liquid CO2 (LCO2) injection was employed to enhance coalbed permeability and the efficiency of methane recovery from a high-gas and low-permeability coalbed. First, mercury intrusion porosimetry and scanning electron microscopy experiments were conducted to analyze the variations in the coal microstructure and the permeability after HS combined and LCO2 freezing–thawing was conducted under laboratory conditions. The results indicated that the basic parameters of pore structures increased significantly for the treated coal; for instance, porosity and permeability increased by 47.65 % and 65.31 %, respectively. This indicated that coal permeability increased significantly under multiple stresses induced via HS and LCO2 freezing–thawing. Subsequently, a simulated experiment of LCO2 injection to enhance CH4 recovery from coal was performed; the results thus obtained revealed that LCO2 injection into a high-gas-content coalbed can enhance CBM recovery with an average efficiency of >90 %. Furthermore, an in-situ test indicated that the effective radii for HS and LCO2 injection were 2.5 m and 10 m, respectively. The results of a 90-d-long methane extraction revealed that the efficiency of CBM recovery increased by a factor of >2.2 and that the residual gas content in the test coalbed was

To address the problems of edge blur and weak detail resolution when fusing infrared and visible images with traditional methods, a novel image fusion approach based on fast super-resolution convolutional neural network and anisotropic diffusion is proposed. The proposed method first employs super-resolution reconstruction based on fast convolutional neural networks to get high-resolution infrared images. Second, the visible and high-resolution infrared images are anisotropically diffused to obtain the corresponding base layers and detail layers. Next, the fusion of the detail layer is performed through Karhunen-Loeve transform, and an adaptive saliency module is constructed to fuse the base layer. Finally, the fusion result is obtained by applying linear reconstruction on the fused detail layer and base layer. Compared with other algorithms, the experimental results show that the proposed algorithm not only has better objective evaluation indexes but also can better retain the details of the original image.

To mitigate coal spontaneous combustion in the fully mechanized caving face at the boundary of Jining No. 2 coal mine, the accurate prediction of the location and degree of coal spontaneous combust...

To achieve fast and effective control of complex coalfield fire areas in close-distance coal seams, proposals regarding “blocking air leakage, reducing oxygen, eliminating high temperature, and preventing re-ignition” were put forward. Combined with isotope radon measurement, infrared thermal imaging and ground drilling construction technology, the exact location of coalfield fire source was outlined. According to the characteristics of coalfield fire areas in Liujiamao and Qian’an mines, a set of economical and efficient coalfield fire control and extinguishing plans have been developed, which include the isolation of the production system, treatment of slope, injection of fly ash composite colloid, and excavation. The results show that the combined application of multiple detection technologies can accurately determine the location of fire source and divide three regions according to the temperature distribution. In addition, we developed a set of coalfield fire detection, fire-fighting equipment, fire-fighting materials and data monitoring as one of the coalfield fire control and extinguishing technology. Through the implementation of the plan, the coalfield fire disaster of Liujiamao and Qian’an mines was successfully solved. The successful application of this technology provides theoretical and technical support for similar coalfield fire control and extinguishing.

To prevent coal fire disaster, a precision grading warning method was previously proposed for coal seams that are susceptible to spontaneous combustion. The uncertainty in the reaction mechanism of...

The effects of crude oil on the microstructure and spontaneous combustion characteristics of coal were assessed, using raw coal sample and coal samples containing 5%, 10% and 15% oil. The pore structures, oxygen adsorption capacity, surface functional groups and spontaneous combustion characteristics were characterized by the LP-N2A, TG, FTIR and temperature-programmed experiments. The LP-N2A and TG tests revealed that the presence of crude oil reduced the porosity, specific surface area and pore volume in the coal sample containing crude oil, which would suppress the transport capacity of oxygen in mesopores and micropores not to adsorb on the specific active sites of coal surfaces. FTIR analysis indicated that the amount of oxygen-containing functional groups and –OH groups decreased tremendously in the coals containing crude oil, but the content of aliphatic C–H groups showed an increasing trend. Moreover, the values of A(CH2)/A(CH3), Ahy/Aar, Aoxygen/Aar all decrease gradually with the rising crude oil contents, indicating that the crude oil reduced the average alkyl chain length and compressed the space between aromatic clusters. The results of temperature-programmed experiments showed that O2 consumption and CO production rates decreased gradually with the increase in crude oil content. The results were in agreement with the varying trend of characterization of microstructure and function groups obtained by LP-N2A, TG and FTIR tests. Furthermore, the Pearson correlation coefficient cleared that the breaking of long aliphatic chains of aromatic rings and reduction of hydrogen bonds content have a greater contribution to the suppression of spontaneous combustion than the attenuation of physical adsorption. This study concluded that crude oil lowers down the spontaneous combustion properties of coal, which could provide a reference for the prevention of spontaneous combustion of coal seam containing crude oil.

The extraction efficiency of high-gas coal seams is low in China with a large number of pre-drainage boreholes. In this study, we analyze the coal seam gas displacement mechanism using liquid carbon dioxide by combining theoretical analysis, experiments, and field tests. Changes of gas displacement efficiency with time under different displacement flow and pressure conditions are determined. We propose a coalbed methane displacement method using liquid carbon dioxide and apply the model in a field test carried out in well No. 2 of the Sangshuping coal mine. The results show that the injection of liquid carbon dioxide in coal seams is a pressure swing adsorption process. The effective displacement radius from the in-situ tests reaches 20 m. The maximum CH4 extraction concentration in the test area is 65%, which is 2.41 times higher than that of the original coal seam (27%). The maximum methane extraction flux rate is 0.884 m3/min, which is 2.34 times that of original coal seam (0.377). Implementation of liquid carbon dioxide displacement coalbed methane technology optimizes borehole arrangement and enhances coalbed methane extraction.

Direct stenting (DS) without pre-dilatation of the culprit lesion might improve myocardial perfusion and prognosis in patients undergoing percutaneous coronary intervention for ST-elevation myocardial infarction (STEMI); however, some studies report conflicting results. We investigated whether DS provides incremental myocardial benefits over conventional stenting (CS) in STEMI patients based on cardiac magnetic resonance imaging (CMR) measures. Reperfused patients who underwent CMR examinations within 1 week of STEMI onset were selected from a multicenter CMR registry of STEMI (NCT: 03768453). Patients were stratified into either a DS or CS group. Each group comprised 137 patients after 1:1 propensity score matching. Major adverse events (MACEs), including death, myocardial re-infarction, re-admission for heart failure, and stroke were noted during a median period of 44 months (interquartile range 32-58 months). DS was associated with larger (p = 0.007) and shorter (p = 0.005) stent sizes than CS. DS and CS achieved comparable angiographic TIMI-3 flow grades (p = 0.86) and myocardial blush grades (p = 0.70). There were no group differences regarding the incidence of CMR manifestations of microvascular dysfunction, including microvascular obstruction (MVO) (p = 0.89) and intramyocardial hemorrhage (p = 0.47), the extent of MVO (p = 0.21), infarction size (p = 0.83), or left ventricular ejection fraction (p = 0.57). Kaplan-Meier analysis revealed similar risks of MACEs (log rank p = 0.909), which occurred in 23.4% of DS and 26.3% of CS patients (p = 0.576). DS did not show any incremental benefits over CS on myocardial impairments as evaluated using CMR.Clinical Trial Registration: Clinicaltrials.gov, NCT: 03768453.

Study design A retrospective study of 257 normal children at a single center from July 2016 to November 2018 was performed. Objective To evaluate the spinopelvic parameters in a population of normal children and adolescents in mainland China. Summary of background data Values for sagittal parameters of the spine vary significantly by ages and different population. No study has yet quantified the normal measures for children and adolescents in China, or how these measures compare with other populations. Methods Pelvic incidence (PI), sacral slope, pelvic tilt, thoracic kyphosis (TK, T5-T12), lumbar lordosis (LL, L1-S1), and sagittal vertical axis were measured and evaluated by whole spine AP&lateral X-ray images. Results A total of 257 subjects, including 116 boys (45%) and 141 girls (55%) aged 3 to 12 years, were enrolled. Correlation matrix analysis demonstrated that sagittal balance is strongly correlated with age and Risser sign, including PI, a reported fixed parameter. Further investigation showed that PI could be expressed by the equation PI = 26.243+1.153×age. Conclusion PI was not a fixed but a dynamic parameter in the population under 12-year old. Indeed, PI increases with age and bone maturity in childhood. We also found lower PI, pelvic tilt, and sacral slope compared with published studies of adolescents in other countries. These results may aid in the treatment of patients with spinal deformity, to help them achieve a certain degree of sagittal spinopelvic balance. Level of evidence 2.

Using liquid carbon dioxide (LCO2) as a medium for underground coal fires prevention and control, while reducing the emissions of CO2, is a promising option for CO2 utilization worldwide. However, the mechanism of LCO2 flow with phase transition on coal temperature is still not clear. In this work, an experimental system was designed and fabricated to investigate the phase transition behavior and temperature variation during injecting LCO2 into pulverized coal and the impact of mass flow rate, nozzle diameter, and injection pressure on cooling effect. The results indicate that when LCO2 was injected into the pulverized coal, the instantaneous phase change into solid and vapor occurred just after leaving the release port. An intensive heat transfer process occurred because of the throttling effect, flashing effect, and sublimation and thereby formed a cooling area (

A computational fluid dynamics model is established to investigate the behavior of fire smoke spreading in L-shaped utility tunnels with small curvature radii (R). The fire evolution process for tunnels with R = 0–25 m and critical ventilation velocities (V) of 0.5–3.0 m/s is analyzed, and the Richardson number (Ri) is introduced to determine the critical value for the development of fire smoke back-layering. The results show that R and V strongly influence the fire-induced spatiotemporal evolution characteristics in such utility tunnels. Smaller R or higher V are associated with stronger centrifugal forces, which causes the smoke to move downstream of the fire source and increases the instability and risk. The non-dimensional smoke back-layering length shows a linear relationship with ln(Q*/V*3), where Q* is the dimensionless fire source power. Integrated with the V and smoke force in a curved tunnel, the critical Ri value is found to be 6.34 for R = 10 m. This means that smoke back-layering will appear when Ri > 6.34 and disappear when Ri

Enhanced coalbed methane (ECBM) recovery is significantly affected by the pore structure and cleat network of coal during liquid CO2 (LCO2) injection into unmineable coal seams. However, the changes in the microstructure after coal samples are treated with LCO2 freezing-thawing are poorly understood. Therefore, a combination of mercury intrusion porosimetry (MIP) and X-ray micro-computed tomography (micro-CT) methods was employed to investigate the evolution of the pore structure and cleat network in coal samples treated with LCO2 under reservoir conditions (0.5 MPa, −50 °C, for 6 h). The results indicated that average increase rates of the total pore volume, total pore area, and average pore diameter are 18.60, 3.24, and 29.90%, respectively, for the treated coal specimens. The increase rates of the specific surface area and incremental pore volume were higher for seepage pores than for adsorption pores after the coal samples were treated with LCO2. Numerous new pores are generated and the seepage capacity of the pores is increased as a result of LCO2 injection for ECBM processes. Comparison of the fractal dimension D 1 ′ of the treated specimens (average value of 2.82) with that of raw coal samples (D1, average value of 2.71) revealed that the treated specimens had more evident fractal characteristics, indicating their more complex morphology and stronger seepage capacity. Micro-CT analyses indicated a significant amount of newly generated fractures and showed that many original cleats expanded after the coal samples underwent LCO2 freezing-thawing. The connectivity of the cleat network in the coal slices was poor, resulting in slightly increased permeability of the treated specimens, which indicateds that the degree of LCO2-induced damage to the coal pore structure was greater than that to the cleat network under the laboratory conditions.

Coal spontaneous combustion has always been a worldwide problem, which causes waste of coal resources, greenhouse gas emissions and other atmospheric environmental pollution problems. Although coal temperature monitoring is the most direct and accurate means of predicting the spontaneous combustion of coal, the coal temperature often cannot be directly measured owing to various physical restrictions. As an alternative, the present study assessed the qualitative and quantitative analysis of the CO and C2H4 formation rates, as well as various gas ratios such as the CO/CO2 ratio and fire coefficient R2 (R2 = 100×ΔCO/ΔO2), to predict spontaneous combustion. This method was established based on the temperature-programmed experiments of three different coal rank (including lignite, bituminous coal and anthracite), and was verified using data obtained from on-site monitoring at an actual mine. The results show that the method accuracy is as high as 97% when predicting the coal temperature to within 15 °C (allowable error range of the predicted value). This degree of accuracy should be sufficient for on-site fire prevention and control. This new technique is not only accurate and reliable but also has theoretical significance with regard to the identification of coal spontaneous combustion in goaf and for the development of fire prevention and suppression technologies.

As to the continuous consumption of limited high-rank coal resources, low-rank bituminous coal is gradually grabbing more attention to the utilization for power resources and industrial production. However, the high risk of spontaneous combustion of low-rank coal has gradually become one of the most critical hazards worldwide during coal mining, storage, and applications. Thermogravimetry coupled with Fourier transform infrared spectrometry using a nonisothermal program method was employed to investigate the oxidized features of two low-rank coals from Jurassic strata. According to initial, first- and second-derivative thermogravimetric curves, an improved quantitative method for determining the eight characteristic temperatures of the coal oxidation process was proposed. The indexes and implications for the thermal hazard of spontaneous coal combustion during stages I–IV, based on the characteristic temperatures, were analyzed. By examining the functional groups, microcharacterization at each characteristic temperature of the coal was obtained. Three kinetic methods were used to calculate the apparent activation energy ( $$E_{\text{a}}$$ ). The evolution of $$E_{\text{a}}$$ was stage III > stage IV > stage II > stage I. The results demonstrated that the integral mechanism in the four stages described a second-order chemical reaction. Moreover, the pre-exponential factor and $$E_{\text{a}}$$ were positively correlated.

Air leakage to the gob is an indispensable factor in spontaneous combustion in underground coal mine. Foam cement is used as an effective means to overcome this problem. To obtain high-quality foam, a novel foaming device was designed. The performance of the device was tested under different working conditions. The test results demonstrate that reasonable operating conditions of the device are: a gas pressure of 0.4–0.6 MPa, foaming agent flow rate of 0.006–0.012 m3/h, and gas-water flow ratio of 14–17. Comparing the filling effect of the foam cement produced by the novel foaming device to a traditional filling material, loess, it is found that the oxygen and carbon monoxide concentrations in the gob are greatly reduced; in other words, the foam cement showed an outstanding effect of plugging air leakage. The proposed novel foaming device could greatly promote the large-scale application of foam cement filling technology used to suppress air leakage in underground coal mines to prevent spontaneous combustion.

Background: The impact of concomitant impairments of left and right ventricular (LV and RV) strain on the long-term prognosis of acute ST-elevation myocardial infarction (STEMI) is not clear.Methods: We analyzed CMR images and followed up 420 first STEMI patients from the EARLY Assessment of MYOcardial Tissue Characteristics by CMR in STEMI (EARLY-MYO-CMR) registry (NCT03768453). These patients received timely primary percutaneous coronary intervention (PCI) within 12 h and CMR examination within 1 week (median, 5 days; range, 2–7 days) after infarction. Global longitudinal strain (GLS), global radial strain (GRS), and global circumferential strain (GCS) of both ventricles were measured based on CMR cine images. Conventional CMR indexes were also assessed. Primary clinical outcome was composite major adverse cardiac and cerebrovascular events (MACCEs) including cardiovascular death, re-infarction, re-hospitalization for heart failure and stroke. In addition, CMR data from 40 people without apparent heart disease were used as control group.Results: Compared to controls, both LV and RV strains were remarkably reduced in STEMI patients. During follow-up (median: 52 months, interquartile range: 29–68 months), 80 patients experienced major adverse cardiac and cerebrovascular events (MACCEs) including cardiovascular death, re-infarction, heart failure, and stroke. LV-GCS > −11.20% was an independent predictor of MACCEs (P < 0.001). RV-GRS was the only RV strain index that could effectively predict the risk of MACCEs (AUC = 0.604, 95% CI [0.533, 0.674], P = 0.004). Patient with RV-GRS ≤ 38.79% experienced more MACCEs than those with preserved RV-GRS (log rank P < 0.001). Moreover, patients with the concomitant decrease of LV-GCS and RV-GRS were more likely to experience MACCEs than patients with decreased LV-GCS alone (log rank P = 0.010). RV-GRS was incremental to LV-GCS for the predictive power of MACCEs (continuous NRI: 0.327; 95% CI: 0.095–0.558; P = 0.006). Finally, tobacco use (P = 0.003), right coronary artery involvement (P = 0.002), and LV-GCS > −11.20% (P = 0.012) was correlated with lower RV-GRS.Conclusions: The concomitant decrease of LV and RV strain is associated with a worse long-term prognosis than impaired LV strain alone. Combination assessment of both LV and RV strain indexes could improve risk stratification of patients with STEMI.Trial Registration:ClinicalTrials.gov, NCT03768453. Registered 7 December 2018 - Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT03768453.

High-temperature poisonous smoke produced by coal mine roadway fire seriously affects miners' lives and safety. Studying the development law of high-temperature smoke in the process of mine roadway fire and then exploring the danger of roadway are of great significance to personnel safety and post-disaster rescue. In order to study this problem, the CFD numerical simulation method is used to establish a fire calculation model based on ANSYS Fluent software in the development stage of mine fire. The high-temperature flue gas flow in the roadway during the development stage of mine fire is simulated, and the variation law of temperature field and gas concentration field with time and space position under different levels of roadway in the development stage of fire is revealed. The variation rules of environmental parameters, such as temperature, CO, and CO2, are obtained by numerical calculation. Based on these, the danger zones of smoke spread in fire development stage are divided by the critical values of high-temperature smoke and toxicity evaluation index, and the mathematical fitting analysis of the evolution of the dangerous area with time is carried out. The research results have certain theoretical guiding significance for reducing underground environmental pollution and ensuring the personal safety of workers and rescuers.

To study the behavior of gas extraction from the protected layer by surface drilling, the common characteristics of gas extraction concentration and gas extraction quantity are summarized through the collection of key parameters of surface drilling and a combination of data and figures, with the background of 11−2 coal protection 13−1 coal in the Huainan mining area. The research results show that the flow of pressure relief gas extraction of the protected layer by surface drilling has three stages: a rising period, stable period, and decay period. When the extraction processes of multiple surface wells on the same working face are coordinated, the extraction flow is superimposed, and the extraction volume of surface drilling shows an increasing trend and fluctuates with the location of the drilling. The extraction flow rate before ground drilling is relatively small, and the extraction flow rate increases after ground drilling. This behavior is further confirmed by field observation of mining changes in the protective layer and the expansion and deformation of the protected layer. The periodic variation in the surface drilling and extraction quantity is affected primarily by the mining movement of the working face of the protective layer. Specifically, it is affected by factors such as the mining progress of the working face of the protective layer, mining height, degree of compacted goaf, degree of pressure relief of the protected layer, original gas content, and other measures taken to extract the protected layer.

Advances in coal mining technology and an increase in coal output are resulting in increasingly challenging conditions being encountered at coal seams. This is particularly so at thin coal seams, where a large number of hard rock layers known as gangue are often present, which seriously affect the normal operation of the shearer and reduce coal output. Therefore, the effective weakening of hard gangue layers in a coal seam is crucial to ensure that the shearer operates effectively and that coal output is maximized. In this paper, the weakening effect of deep-hole presplitting blasting technology on the hard gangue layer in a coal seam is studied via a similar simulation. Four test schemes are designed: (1) A blasting hole spacing of 200 mm with the holes offset vertically. (2) A blast hole spacing of 300 mm with the holes offset vertically. (3) A blast hole spacing of 200 mm with the holes parallel to the gangue layer. (4) A blasting hole spacing of 200 mm with the holes offset vertically and initiation of interval blasting. The effect of the different blasting hole spacings and arrangements and different detonation methods on the weakening of coal seam clamping by gangue is studied, and the best configuration is identified. This improves the effect of weakening the coal gangue layer by deep-hole presplitting blasting.

This article uses semiconductor simulation software to simulate the composition and thickness of the epitaxial structure of the InGaAs near-infrared detector. By optimizing and adjusting different parameters, the surface dark current control of the detector structure is realized, making the overall performance of the infrared detector has been improved. The calculation results show that by reducing the thickness of the intrinsic layer within a certain range, the surface dark current of the device can be appropriately reduced, and the minimum dark current can be obtained under certain epitaxial doping. Under the condition of preparing the passivation layer, through a series of preparation processes such as metallization, the final InGaAs detector is obtained, and the test results of the detector are consistent with the calculation, and the dark current is controlled at the level of nA, which can be used for near infrared short-wave imaging.

Supplemental Digital Content is available in the text, Vitiligo is a chronic skin condition lack of melanocytes. However, researches on the aetiology and pathogenesis of vitiligo are still under debate. This study aimed to explore the key genes and pathways associated with occurrence and development of vitiligo. Weighted gene coexpression network analysis (WGCNA) was applied to reanalyze the gene expression dataset GSE65127 systematically. Functional enrichments of these modules were carried out at gene ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), gene set variation analysis (GSVA), and gene set enrichment analysis (GSEA). Then, a map of regulatory network was delineated according to pivot analysis and drug prediction. In addition, hub genes and crucial pathways were validated by an independent dataset GSE75819. The expressions of hub genes in modules were also tested by quantitative real-time polymerase chain reaction (qRT-PCR). Eight coexpressed modules were identified by WGCNA based on 5794 differentially expressed genes of vitiligo. Three modules were found to be significantly correlated with Lesional, Peri-Lesional, and Non-Lesional, respectively. The persistent maladjusted genes included 269 upregulated genes and 82 downregulated genes. The enrichments showed module genes were implicated in immune response, p53 signaling pathway, etc. According to GSEA and GSVA, dysregulated pathways were activated incessantly from Non-Lesional to Peri-Lesional and then to Lesional, 4 of which were verified by an independent dataset GSE75819. Finally, 42 transcription factors and 228 drugs were spotted. Focusing on the persistent maladjusted genes, a map of regulatory network was delineated. Hub genes (CACTIN, DCTN1, GPR143, HADH, MRPL47, NKTR, NUF2) and transcription factors (ITGAV, SYK, PDPK1) were validated by an independent dataset GSE75819. In addition, hub genes (CACTIN, DCTN1, GPR143, MRPL47, NKTR) were also confirmed by qRT-PCR. The present study, at least, might provide an integrated and in-depth insight for exploring the underlying mechanism of vitiligo and predicting potential diagnostic biomarkers and therapeutic targets.

While existing studies have mapped out various networks with some visualization techniques, we move one step forward by examining if city/firm performance is dependent not only on intra-city networks, as proposed by the clustering literature, but also on inter-city networks, the core concept in the world city network literature. Our second contribution is to investigate the complementarity between inter- and intra-city networks, and how it could affect the performance of firms and cities. In doing so, we provide some preliminary evidence that studies on clustering and the world city network could benefit from having more dialogues with each other.

If an airtight wall in a coal mine leaks air, it may cause spontaneous combustion of residual coal in the gob and even cause a full-blown fire or gas explosion. In this study, we developed a new type of foamed concrete, low-alkalinity sulphoaluminate cement (LASC), to control air leakage. The performance of filling materials that were prepared by adding various dosages of foam to LASC was studied. The longer the curing period for the foam filling material of LASC, the better the crystallinity of the hydrated product. With an increasing foam dosage, the initial setting time gradually extends while the fluidity of the foam slurry decreases. The bubble rate of the filling material increases and the density decreases with increasing foam dosage. The compressive strength of the LASC filling material decreases with increasing foam dosage and increases with increasing curing time. In the LASC filling materials, the optimal volume ratio of foam dosage to gel slurry is 2. The crystallinity, initial gel time, and compressive strength of the LASC foaming materials are better than those of ordinary Portland cement (OPC) foaming materials. When the crossheading is filled with LASC foam cement, the deformation of the surrounding rock is less than 19 cm, and the air leakage prevention is better than that achieved with loess and fly-ash-cement foam. Thus, the proposed LASC foam material can be applied to the filling of the crossheading to efficiently prevent leakage in underground coal mines.

Mining high-gas coal seams in China has the characteristics mining of deep, high storage and low permeability, and low drainage efficiency, which seriously restrict the efficient prevention and control of mine gas disasters. Based on the characteristics of low viscosity and permeability, phase change pressurization, and strong adsorption potential energy of liquid CO2, the technology system of liquid CO2 displacement for high-gas and low-permeability coal seam was developed, and field industrial of low-pressure (0.5~2.5 MPa) and medium-pressure (2.5~15.0 MPa) combined injection test was carried out. In this test, the mode of injection followed by drainage was adopted, and the gas drainage effect was investigated for 30 days. The test results show that the effective influence radius of CO2 in this test is 20 m, and the liquid seepage radius is 5 to 7 m. After the injection of liquid CO2 into coal seam, the average gas drainage concentration and drainage purity of all drainage holes were increased by 3.2 and 3.4 times, respectively, and the gas promotion effect was significant. Taking the liquid CO2 low-medium-pressure displacement gas test area as the calculation unit, from the comprehensive benefit analysis, compared with the original drainage mode, the liquid CO2-combined pressure injection process can save 34.7% of the engineering cost and shorten the gas drainage standard time by 45.9%. Therefore, the application of this technology has important technical support and reference significance for the efficient management of gas in the same type of mine.

Unmanned aerial vehicles, with their inherent fine attributes, such as flexibility, mobility, and autonomy, play an increasingly important role in the Internet of Things (IoT). Airborne infrared and visible image fusion, which constitutes an important data basis for the perception layer of IoT, has been widely used in various fields such as electric power inspection, military reconnaissance, emergency rescue, and traffic management. However, traditional infrared and visible image fusion methods suffer from weak detail resolution. In order to better preserve useful information from source images and produce a more informative image for human observation or unmanned aerial vehicle vision tasks, a novel fusion method based on discrete cosine transform (DCT) and anisotropic diffusion is proposed. First, the infrared and visible images are denoised by using DCT. Second, anisotropic diffusion is applied to the denoised infrared and visible images to obtain the detail and base layers. Third, the base layers are fused by using weighted averaging, and the detail layers are fused by using the Karhunen–Loeve transform, respectively. Finally, the fused image is reconstructed through the linear superposition of the base layer and detail layer. Compared with six other typical fusion methods, the proposed approach shows better fusion performance in both objective and subjective evaluations.

We propose a method for measuring the thermal effect of spontaneous combustion and the adiabatic spontaneous combustion period of coal based on the coupled thermal effects of coal and oxygen. A physical similarity reference test system was established by combining the characteristics of the thermal analyses. Using this system, coal samples from the main coal seam of the Zhao Xian mine, which has high propensity for spontaneous combustion, were tested and analyzed. The adiabatic spontaneous combustion period for coal was determined by curve fitting. Based on the heat equation, the adiabatic spontaneous combustion period for coal from the Zhao Xian coal mine was determined to be 95.9 h. Mutual verification among the adiabatic spontaneous combustion periods of coal was achieved through the same fitting procedure. The error between the two experimental results was less than 0.22 % with 0.01 variance, which proves that the experimental approach is applicable for calculating the adiabatic spontaneous combustion period of the Zhao Xian coal sample. Our results should facilitate theoretical and experimental evaluations of the likelihood of spontaneous coal combustion and its associated risks.

The fire of coal pillars caused by spontaneous combustion in contiguous coal seams at the Dongrong2# colliery in China was examined. The reasons of spontaneous combustion of coal pillars in 16# coal seam were investigated. Based on testing results, the scope of high temperature was judged. To deal with the problem of significant air leakage together with a large fire area and the hidden fire source easily re-ignite, a series of key techniques for extinguishing the fire of coal pillars was put into practice. These mainly included plugging air leakage channel, high-flow injection of liquid nitrogen, and infusion of a large quantity of foam inhibitor into flame locations by drillings. The results showed that these integrated measures rapidly extinguish the fire of coal pillars, reduce carbon monoxide (CO) concentration from 1.6% to about 0.001% and temperature in the closed area of 16# coal seam from 81℃ to less than 20℃. In a word, the fire of coal pillars is successfully controlled in contiguous coal seams, which protect the safety of personnel and equipment.

Due to the huge reserves and great commercial potential of No. A group coal seam, the study on its thermal properties and combustion kinetics have attracted much attention. Via thermogravimetric (TG) analysis, the combustion characteristics and kinetics of No. A 3 coal were studied with three types of coal samples, with the grain diameter less than 200 meshes, 200~100 meshes, 100~60meshes, seperately. Under three characteristic temperatures such as T t , T p and T b , the whole combustion process could be roughly divided into 4 stages. Combined with the T max and T i , these five characteristic temperatures increase with elevating heating rates. The Kissinger-Akahira-Sunose (KAS) method and Flynn-Wall-Ozawa (FWO) method as reliable methods were used to verify the results of activation energy ( E a ) determined by of model-fitting methods. As complementary, the Coats-Redfern method was used to calculate the pre-exponential factor ( A ) and the correlation coefficient ( R 2 ). According to the evaluation criteria of E a and R 2 , D1 mechanism was the most probable model to depict the combustion kinetics.

As an effective technology for carbon utilization, enhanced coalbed methane (ECBM) with CO2 injection has great potential for reduction of CO2 emission. To better comprehend the effects of ECBM using liquid CO2, a combination of low-pressure nitrogen adsorption-desorption (LP-N2-Ad), mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM) was used to investigate the varying characteristics in coal before and after infiltration by liquid CO2. The specific surface area and volume were 5.08% and 9.82% higher on average in the treated specimens than in the untreated ones. The average pore diameter and permeability of the treated samples were higher than those of the untreated samples. The features of the pore structure after liquid CO2 immersion were found to be characterized by new pore generation and the transformation of original pores into larger ones. D1 and D2 can be used to quantitatively represent the adsorbed pore surface roughness and volumetric complexity. They were both found to be higher after liquid CO2 treatment, which indicated the treated coal samples have more rough and complex pore structure than that of the raw specimens. D4 can be used to describe characteristics of seepage pores. A positive relationship was obtained between D4 and seepage capability. The SEM images indicated a higher number of microfractures and fewer minerals filled in the coal pores with the treated specimens, representing an improvement of seepage capability with the coal samples through liquid CO2 infiltration. This study provides a theoretical basis for the understanding of its influence on liquid CO2-ECBM process.

Early prediction is one of the key technologies to the prevention and extinguishment of spontaneous combustion of coal. The aim of this study was to propose a type of scientific and convenient forecasting indicator for initial spontaneous combustion of coal in the gob area. The authors developed the calculation model of carbon monoxide (CO) concentration in the air return corner based on the generation mechanism, sources, and influencing factors of CO. The parameters obtained from both large-scale coal self-heating experiment and in-situ observation of four collieries in Yuanyang lake mine area were used to calculate the extreme value of CO concentrations on various stages of spontaneous combustion. The established indicators were applied to specific coal mine scenarios and combined with the in-situ measurements. It demonstrates that this method has provided the scientific guidance for safer exploitation on coal mines. Furthermore, the main reasons of unstable CO concentrations in the return corne...

A comprehensive understanding of the spontaneous combustion characteristics of coal in various surroundings is necessary for developing reliable test platform and predictive models. In this study, the characteristics of oxidation and self-heating combining various gas flow equations in loose coal were investigated separately and used to simulate the experimental procedure of spontaneous combustion. The main focus was to investigate the effect of thermal boundary on temperature profiles as well as spontaneous combustion period. The results showed that the numerical approach was validated by comparison with the test data. Furthermore, the model based upon Brinkman equation showed a higher accuracy, which indicated that airflow behavior influences the balances of coal oxidation and heat dissipation, thus impacts the temperature profiles of loose coal. The areas of high temperature zones would be evidently expanded and the spontaneous ignition time would be significantly accelerated if the thermal exchange between the coal and its surroundings decreased. Our results, especially for the field of engineering, have substantial effects for grasping and controlling coal spontaneous combustion disaster.

This paper reports an experimental study on the electrical properties of five coal samples taken from various Chinese coal mines. The dielectric permittivity and specific resistivity of grinded coal samples subjected to electromagnetic (EM) fields in a wide frequency spectrum were determined. Based on the experimental data, a set of approximating equations of the change in electric properties the 100-1000 MHz frequency region was obtained. These equations, along with EM equations for EM speed and attenuation, were used for modeling and studying radar-wave propagation in a coal seam and radar-wave reflection from the body of miners trapped in collapsed tunnels. The modeling concept assumes that a radar transducer with the dominating frequency of 500 MHz is lowered through a vertical or inclined rescue borehole to the depth of the coal seam. It is assumed that only the miner is present in the part of the tunnel that did not collapse. Thus, in the path of the radar wave from the transducer to the human body, only one geological interface reflecting the radar signals is present (coal-air) and one is connected with human body. The human (acting as the reflector) can be located at various distances from the tunnel face; this factor was included in the analyzed geometrical model. Based on the modeling results of different thickness coal seams (2, 3, 4, 5, 6, 7, 8m), conclude that a radar wave reflected from a human body can be reliably measured, when the distance between the human and the transducer is not exceed 8m.

Coal resources are rich in China. They are mainly concentrated in the northwest region. But these resources also make the situation of spontaneous coal combustion hazards most serious in this area. Affected by the arid and semiarid climate, the water resource in this area is relatively scarce. In order to improve the utilization rate of water, a macromolecule colloid for coal mine fire fighting was developed in this research. The main components of the macromolecule colloid and the principle of gel formation were analyzed. The physical and chemical properties of the macromolecule colloid were analyzed by the time of gelation and the water loss. The water content of the macromolecule colloid was as high as 99%. The inhibition performance of the macromolecule colloid on coal fire was studied by the programmed heating device. The experimental results show that the macromolecule colloid has a significant inhibitory effect on the heating rate, oxygen consumption rate, and gas production rate. It inhibits the coal-oxygen composite by increasing the activation energy (Ea) of coal, which also has the effect of wrapping coal to isolate oxygen. The inhibition performance of the macromolecule colloid on coal fire disasters is better than that of water, water glass, loess compound colloids, and other traditional fire-extinguishing materials.

In view of the fact that the current sequential power supply control methods can not meet the requirements of large power and small size design for the positive and negative voltage sequential power supply control circuit of the millimeter wave fuze detector power supply system at the same time, a high power miniaturization design method for the sequential power supply control circuit is proposed. The method is to design a power supply delayer in the power supply system of the millimeter wave fuze detector, so that the positive voltage can be output after a certain time delay, and the power supply system of the detector can realize the high power and miniaturization design of the sequential power supply control circuit on the basis of the negative voltage prior to the positive voltage supply. The test results show that the sequential supply of negative voltage before positive voltage can be realized effectively by using power supply delayer, and the design method of sequential supply control circuit can meet the system design requirements of high-power and small-scale.

In view of the fact that the conventional millimeter wave fuze antenna cannot meet the requirements of miniaturization, high gain and specific direction pointing in a single antenna, the microstrip beamforming array antenna of millimeter wave fuze is designed. The antenna is made of an alumina thin film dielectric plate as a substrate, and a microstrip antenna array of a specific size and shape is etched on the surface. Experimental tests show that the antenna center frequency is 34.5GHz, and the reflection parameter S11 is less than −10dB in the 1GHz bandwidth at 34.02-35.05GHz. The antenna diameter is 16mm, which is 50% smaller than the conventional array antenna size. The antenna beam width is 36°, the angle between the antenna beam angle and the normal is 35°. The vertical illumination of the main beam of the antenna to the ground target can be realized within the falling angle of the fuze range between 36° to 72°.

CO2 is both a primary greenhouse gas and an available energy source. In this study, a new type of underground coal permeability enhancement technique by liquid CO2 (L-CO2) fracturing is proposed. The key parameters that determine the feasibility of the technique are identified: L-CO2 injection pressure and flow rate. Based on the principle of stress superposition and the experiments for L-CO2 fracturing under true triaxial stress conditions, the calculation models of the initiation pressure and flow were determined. The mathematical model of the initiation pressure of the L-CO2 fracturing of coal is verified, and the quantitative relationship between the injection flow rates of L-CO2 and hydraulic fracturing is derived. Accordingly, a complete set of underground high-pressure (30 MPa) L-CO2 fracturing equipment for coal permeability enhancement is developed. A field test of the coal permeability enhancement by fracturing in an upward cross-borehole was performed. The results confirm that after the fracturing, the gas drainage mixed flow and pure flow of the observation borehole that was located 25 m distant from the fracturing borehole increased by 3.2 and 3.3 times, respectively, and the maximal CO2 concentration in the observation borehole was 40%. The influence radius of the L-CO2 fracturing was determined to be approximately 25 m. Compared with areas with no coal permeability enhancement measures, the average single-borehole gas drainage concentration increased by approximately 1.57 times, and the pure flow increased by approximately 1.82 times within a radius of 25 m after L-CO2 fracturing.

The accurate prediction of the degree of coal spontaneous combustion is critical for the prevention and control of spontaneous combustion in coal mines. However, the qualitative three-stage classification method is difficult to meet the demand for accurate early warning of coal spontaneous combustion. Therefore, with long-flame coal in the Tangjiahui Mine as the study object, this paper conducted the temperature-programed coal spontaneous combustion experiment and the coal spontaneous combustion experiment. The parameters that were measured were O2 concentration and gas generation volume during the process of coal spontaneous combustion under different oxygen supply conditions. Furthermore, this study analyzed the characteristics of gas and gas ratio variation with coal temperature, screened out the characteristic gas indexes of coal spontaneous combustion in Tangjiahui Mine, and defined six characteristic temperatures and their threshold values. Accordingly, the coal spontaneous combustion process was divided into seven stages, including the latent stage, recombination stage, self-heating stage, activation stage, thermal decomposition stage, fission stage, and combustion stage. We provide the early warning criteria and the threshold values of characteristic gas parameters at each stage and define the names of graded warnings, such as gray, blue, yellow, orange, red, and black. With this warning method, we successfully forecasted the degree of coal spontaneous combustion in the gob of the 61,102 working face, guaranteeing the successful withdrawal of this working face.

Spontaneous combustion period is an important characteristic parameter of coal spontaneous combustion. It must be understood to prevent and control coal fire disasters in a coal mine. Fresh coal samples were then collected from the Bulianta Coal Mine in the Shenfu-Dongsheng Coalfield for mini combustion furnace experiments. We then analyzed the changing rules of coal temperature, O2 and CO during spontaneous combustion of coal under pure oxygen adiabatic conditions. A method for calculating oxygen consumption rate during spontaneous combustion of coal under those conditions was then proposed. Based on the Arrhenius law, heat loss rate (RPD) function during coal spontaneous combustion was developed. The coal temperature and oxygen concentration during spontaneous combustion oxidation process of coal in air accurately were calculated from a pure oxygen insulation experiment. When RPDair = 0, 0.2, 0.4, 0.6, and 0.8, the coal spontaneous combustion periods of Bulianta were 15.12, 18.94, 25.25, 37.87, and 75.74 days, respectively. The spontaneous combustion period of Bulianta coal, which was measured using 2-t experimental furnace for coal spontaneous combustion, was 16.66 days. The temperature change curve for spontaneous ignition experiment is similar to the adiabatic condition (RPDair = 0). This demonstrates that the coal spontaneous combustion period calculation method in air using pure oxygen adiabatic experiment is valid.

More than 60% of China’s coal seams have the feature of low permeability, which severely restricts the gas drainage efficiency when using traditional drilling method. The development of enhanced coalbed methane (ECBM) technologies is essential to prevent coal and gas outburst (CGO) disasters caused by high levels of coal bed methane (CBM). This paper proposes an ECBM technology by liquid carbon dioxide (LCO2-ECBM), based on permeability improvement by thermal damage and CO2-CH4 displacement effect. In-situ experiment conducted in the No. 6 coal seam of Zhangji mine shows the effectiveness of LCO2-ECBM technology, which had drainage efficiency 1.9 times higher than that of the traditional drilling method. The mechanisms of LCO2-ECBM recovery were theoretically deduced and experimentally verified. The evolution of adsorbed pores (ADP) and seepage pores (SEP) in coal samples before and after LCO2 saturation were revealed. The ADP specific area, SEP volume, and permeability in the saturated coal samples were both greater than those of the raw ones. Moreover, the periodic features of binary-gas competitive adsorption in ADP and SEP were revealed by the variation of the CH4 concentration in the displacement test. The feasibility of LCO2-ECBM technology was proved by in-situ experiment and laboratory tests, and it provided a new means for preventing CGO hazards.

In recent times, enhanced deep-buried coalbed methane recovery has increased the interest in coal and unconventional natural gas exploration. This study investigated liquid CO2 (LCO2) injection to enhance coalbed methane recovery, the variation in the gas component and the sweep efficiency of CH4 recovery by LCO2 injection into coal were studied under laboratory conditions. The results demonstrated that the rate of decrease in CH4 concentration initially increased and then stabilized with the increase in the injection pressure of LCO2. This investigation revealed two factors behind the decrease in the CH4 concentration. The first was the carrying effect of CO2 airflow and the competitive adsorption between CO2 and CH4 that enhanced CH4 recovery in coal, while the second was the dilution effect of high-concentration CO2 that diluted the residual CH4 molecules and the experiment converted into an inefficient stage. Additionally, the quantitatively calculated results indicated that the average sweep efficiency of CH4 recovery was greater than 92.0%, which proves the sweep efficiency of CH4 recovery by low-pressure LCO2 injection was obvious. An in-situ test of high-gas-content coalbed in Chinese mining areas concluded that the effective migration radius of CO2 in the test coalbed was beyond 15 m when the cumulative LCO2 injection volume was approximately 5.0 m3. The amount of methane extraction was compared with that obtained by the original gas extraction for 60 consecutive days, the amount of methane extracted from the test coalbed was 2–3 times higher and the time taken for methane extraction to reach the standard was significantly reduced.