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Coal refuse pile fires are a serious health, safety, and environment hazard. The fires in Guoshan Coal Refuse Pile affect daily life of the local residents. Although conventional fire control methods (water injection, grouting and surface sealing) were used to control the fires, they rekindled soon after the fire-fighting engineering was quitted. Thus, effective methods need to be applied to extinguish the fires completely without reignition. In this paper, the environmental impact of the fire on the local land, water and air is illustrated by sample analysis and photos. The self-potential method, which achieves remote detection from the ground surface, is adopted to delineate the scope of the fires to give support for the efficient and economical extinguishment of them. The three-phase foam containing water, gas and loess is proposed to control and extinguish the fires. The corresponding fire-fighting system is also invented to fit the field work and put out the fires more efficiently and conveniently. The temperature monitoring result shows that the fires are extinguished successfully with no sign of reignition.

Summary Since the Late Paleozoic, forests have become distributed worldwide and significantly changed the Earth’s climate and landscapes, but the record of forests is rare in the Devonian (419–359 Ma in age) when they first appeared. From the Upper Devonian (Famennian with the age of 372–359 Ma) of Xinhang, Anhui, China, we report a very large in situ forest, which includes locally dense stands of lycopsid plants. The Xinhang forest is monospecific with a small tree lycopsid Guangdedendron gen. nov., probably dioecious with monocarpic reproduction. The plant shows the earliest stigmarian rooting system typical of giant tree lycopsids dominating Carboniferous forests. It colonizes coastal clastic wetlands that were influenced by floods. This significantly increases the paleogeographical coverage of in situ Devonian forests, and contributes to our understanding of atmospheric CO2 decline and coastal consolidation.

Electric effects are generated during the deformation and fracture of coal mine roof sandstones. Previous research has mostly focused on the mechanism of electric effect generation and the electromagnetic radiation released. However, few studies have investigated the hazard characteristics of the high-energy electrons released. This study explores the discharge and ignition characteristics of roof indentation fracture to identify the real ignition source of a gas explosion in a coal mine goaf. Theoretical and experimental analyses conclude that the charge of the coal mine roof sandstone will gradually escape from the surface during the loading process. The charge release process of the rock before fracture is related to the loading rate, and an instantaneous high voltage will be formed during fracture of the rock. The compressive strength of the rock plays a key role in this type of instantaneous discharge process. An electric spark can be generated at the moment of rock fracture under loading. The high-energy electrons released by rock deformation and rupture can ionise the air. Moreover, the electric spark can persist for more than 20 ms, which considerably exceeds the induction period for gas ignition. When the quartz content of the roof rock is high and reaches a certain compressive strength, stress mutations can cause the roof to undergo instantaneous rupture and generate electric sparks. The premixed gas air gathered in the area is thus broken down and ionised, igniting the gas and producing a gas explosion.

To investigate the characteristics of methane-air explosions in large-scale tunnels with different structures, the CFD code for gas explosion modelling of FLACS was validated and used to model the explosions in tunnelling faces, coalfaces and crosscuts, where explosions mostly occurred in coalmines. The maximum overpressures were obtained as about 150–1400 kPa but varied for places with different cross-sections. The confinement degree and combustible mixture volume compete for controlling the overpressures, the space congestion degree influences the competition. For the tunnelling faces and crosscuts with low congestions, the increase of confinement degree caused by reducing cross-sections takes the dominant effect, which makes the overpressure in 3 m × 2 m cross-section tunnels higher. However, the 6 m × 4 m coalface produces the largest overpressure as the highly congested coalface strengthens the effect of increasing the mixture volume on pressure rise. Since the pressure reflection results from space constraints, a higher confinement degree causes a greater reflection. In crosscuts with both ends closed, the delayed combustion of the unburnt rich mixture after the seal’s failure generates a high pressure than assumed. Because of containing the same volume combustible mixtures in the crosscut modelling with the same cross-section, little difference exists in the overpressure regardless of sealing conditions. The flame is more inclined to propagate towards free spaces, and the flame of a larger volume combustible mixture fills a longer tunnel more comprehensively. In straight tunnelling faces, the flame length can be calculated as the product of the equivalent side length of the cross-section and its corresponding simulated constant.

Surface fluorination of polyimide films was conducted for different durations (30, 60, and 90 min) in a laboratory vessel using an F2/N2 gas mixture containing 12.5 % F2 by volume. The differences in the structural, morphology, wettability, surface free energy, and electrical properties of the fluorinated polyimide films were systematically studied to assess the effects of fluorination and fluorination time, and to investigate the relationship between the surface electrical properties and surface physicochemical properties. The obtained results indicated that fluorination cracked the film surface, with the number of cracks increasing with increasing fluorination time. Fluorination also enhanced the surface wettability and polarity. Surface conductivity and surface potential decay measurements consistently showed that the surface-fluorinated samples had a higher surface conductivity than unfluorinated samples, and that the surface potential rapidly decayed because the surface conductivity increased with enhanced water adsorption on the surface. The increased occurrence of surface cracks, as well as enhanced polarity and surface conductivity of the films, were mainly attributed to the increase in the degree of chain scission that occurred with increasing fluorination time.

Improving the foamability of anionic surfactants in hard water is essential to reduce the adding concentration and economic cost of foaming agents for dust control. In this work, sodium dodecyl sulfate (SDS) and sodium dodecyl ether sulfate (SDES) were selected to explore the mechanism of polyethylene oxide (EO) groups improving the foamability of anionic surfactants in hard water by experiments and molecular dynamics simulations. The experimental results show that SDES containing EO groups has better foaming performance in hard water compared with SDS. The simulation results indicate that the presence of EO groups can inhibit the combination of SO4− groups and Ca2+ ions at the air/water interface, which makes part of Ca2+ ions migrate from the interface layer to the bulk water. In addition, EO groups attract some Ca2+ ions to distribute around them, thereby further reducing the number of Ca2+ ions combined with SO4− groups, which helps to improve the surface activity and foamability of anionic surfactants in hard water. An increase in the number of EO groups can enlarge the interfacial thickness and the number of hydrogen bonds between surfactants and water molecules, enhancing the strength of bubble film. Moreover, the farther the EO group is from the SO4− group, the smaller the contribution to the hydration of anionic surfactants.

Shougangia bella from the Late Devonian (Famennian) of South China is a fern-like plant known for its morphology and now provided with anatomy and a reconstruction. Its stems contain a dissected stele with a four-ribbed and an elongate-curved primary xylem segments changing to three elongate and slightly curved segments. Primary branches have a dissected stele with three similar primary xylem segments as in stems. The primary xylem of the stems and primary branches is mesarch, and individual primary xylem segments bear peripheral protoxylem strands and are surrounded by secondary xylem. Shougangia is anatomically compared with fern-like plants, zygopterid ferns and early seed plants, verifying its uncertain affinity at class and order levels as suggested by morphology, or representing a new order within the Cladoxylopsida. On the basis of anatomy and branching pattern, it is emphasized that most fern-like plants appear evolutionarily closely related to iridopteridaleans. Secondary xylem is involved not on...

An experimental platform was built to investigate how aqueous foam extinguishes fire in the upper area of a goaf. A temperature-programmed oxidation testing method was used to illustrate the inhibitory effect of foam. The results showed that foam has good accumulation characteristics, cooling performance, blocking effect, and inhibition. Foam extinguishes the fire in the upper area of a goaf and cools the entire goaf from bottom to top; it even diffuses into the interior of the high-temperature zone and extinguishes any hidden fire in the porous medium. In addition, foam blocks all the cracks in the goaf, thus blocking the air supply and maintaining a constant negative pressure in the goaf. By restricting chemical reactions between coal and oxygen, foam increases the crossing point temperature and reduces CO generation and thus prevents the further oxidation of coal.

Composites of physical (superabsorbent hydrogel) and chemical (ascorbic acid) inhibitors were investigated to ascertain their ability to prevent the spontaneous combustion of coal. CO emissions from the oxidation of the composite inhibitor-treated coal were markedly lower than those for tests with raw coal. Less oxygen was also consumed during low-temperature oxidation, while the crossing point temperature of the inhibitor-treated coals was higher than that of raw coal. Together, these results demonstrate that the composite inhibitors can effectively mitigate coal oxidation. However, variation in the effectiveness was observed depending on the inhibitor-loading and the blend of the individual inhibitors in the composite. The composite inhibitor was shown to more effectively prevent oxidation than use of an individual inhibitor. The network structure of the composite inhibitor, revealed by SEM analysis, was suggested to explain the suppression of the coal oxidation.

The built-in Electro-Static discharge (ESD) protection circuits for Radio frequency identification (RFID) tag ICs are proposed. The ESD protection function is built into the rectifier and amplitude limiter. The rectifier and limiter are connected directly to the RF interface, and some transistors can discharge the larger current. These transistors can be used to build ESD protection circuits, through the redesign and optimization. The built-in ESD protection circuits can improve the ESD protection level and reduce the layout area. The circuits have been fabricated in 0.18μm CMOS process. The test results show that the built-in ESD protection circuits work well under 4kV ESD pressure and save as much as 72% of the layout area compare with foundry standard ESD protection cells.

A sustained release type of inhibitor (PS-C) prepared with poly(acrylic acid)/sodium alginate super absorbent (PS), ascorbic acid (VC), and water was developed, which exhibited a not only highly efficient but also sustained inhibition performance on the spontaneous combustion of coal. The impact of PS hydrogel on coal oxidation was examined thermodynamically by TGA–DSC tests, and the variations of functional groups on coal surface under the influence of VC were in situ monitored by an FT-IR technique. The inhibition performance was evaluated with a parameter defined as the emitted carbon monoxide concentration decay rate during coal oxidation. The results show that the PS hydrogel and VC perform distinctive inhibition characteristics by physically removing the accumulated heat and chemically interrupting the free radical chain reaction of coal oxidation, respectively. The composite PS-C is capable of combining the inhibition characteristics of PS hydrogel and VC as well as further realizing a dramatic syn...

Foam technology utilizes the good coverage of foam to form a closed space around dust sources. The foam then wets the dust particles, causing them to adhere before they spread into the air, resulting in better dust control than with water sprays. In the process of foam dust control at a heading face, the foam spray trajectory is highly influenced by the wind, making it difficult to focus foam on the dust sources, which wastes the foam and reduces dust control efficiency. To resolve this problem, the idea of transporting foam to the cutting head through the roadheader’s inner pipeline is proposed. To adapt to the high resistance of foam delivery in the roadheader’s inner pipeline, according to the water and air supply of the heading face, a table water-jet suction device and porous spiral coupling foaming device were designed, and the working conditions were tested using a self-designed experiment system in the laboratory. The results showed that the foaming agent could be automatically added into the device at a working water flow rate of 1–1.6 m3/h at a ratio of 1%. The optimum air flow was 45–50 m3/h, in which range the foam expansion ratio reached the maximum and the outlet pressure demand was satisfied. Field application showed that the new foam method had a better dust control efficiencies than traditional foam methods.

Here a new automated and inexpensive atomic simulation approach including sequential oxygen diffusion and simplified reaction was created to explore the char reactivity and combustion behavior during oxy-fuel combustion. Two large-scale (>40,000 carbon atoms) coal chars (higher- and lower-porosity chars) that differ primarily in pore volume and pore size distribution were evaluated against graphite with similar number of carbon atoms. The structural transformations, total atoms, reactive atoms, their location, conversion, rate (number of atoms reacting), size of the char, and apparent density were captured. Post analysis evaluated the total porosity, micro/mesoporosity volume, and atomic surface area. The higher porosity char burn-off was ∼38% more rapid than the graphite (number of steps), similar to the lower porosity char (∼33% faster). The peak reactivity followed the maximum atomic surface area (with a delay of 5–10% conversion) than decreased—as there were fewer reactive carbons. Porosity volume increases with conversion until 50–70% where the porosity declines. For both chars the microporosity contribution increased until 30–35% conversion then the pores either grow or coalesce into the mesoporous classification. The chars burning modes are initially changing density (pore growth accompany mass loss) until ∼50% conversion when the mode became a combination of changing density and shrinking core. Graphite was less reactive and followed a shrinking core consistent with the simulation restrictions. This approach is likely to aid in the exploration of the influence of char structure and conversion conditions upon reactivity and char behavior in combustion and gasification.

Background The purpose of this study was to evaluate the safety and efficacy of direct intralesional ethanol sclerotherapy for venous malformations (VMs) with oropharyngeal involvement after a temporary tracheotomy. Methods A retrospective assessment was carried out to evaluate the efficacy of direct intralesional ethanol sclerotherapy on 21 consecutive patients presenting with extensive VMs involving the oropharynx in the head and neck and who had undergone tracheotomy. Results Of the 21 patients, 4 were treated once and 17 were treated from 2 to 5 times. The duration of follow-up was, on average, 9.1 months. Of the 21 patients, 7 (33.3%) had complete palliation, whereas the rest (66.7%) achieved partial palliation. Minor complications occurred in 12 of the 21 patients. Conclusion Direct intralesional ethanol sclerotherapy after a temporary tracheotomy is a safe and effective treatment for extensive VMs involving oropharyngeal areas of the head and neck. © 2016 Wiley Periodicals, Inc. Head Neck, 2016

The colonization of terrestrial environments by rooted vascular plants had far-reaching impacts on the Earth system. However, the belowground structures of early vascular plants are rarely documented, and thus the plant−soil interactions in early terrestrial ecosystems are poorly understood. Here we report the earliest rooted paleosols (fossil soils) in Asia from Early Devonian deposits of Yunnan, China. Plant traces are extensive within the soil and occur as complex network-like structures, which are interpreted as representing long-lived, belowground rhizomes of the basal lycopsid Drepanophycus. The rhizomes produced large clones and helped the plant survive frequent sediment burial in well-drained soils within a seasonal wet−dry climate zone. Rhizome networks contributed to the accumulation and pedogenesis of floodplain sediments and increased the soil stabilizing effects of early plants. Predating the appearance of trees with deep roots in the Middle Devonian, plant rhizomes have long functioned in the belowground soil ecosystem. This study presents strong, direct evidence for plant−soil interactions at an early stage of vascular plant radiation. Soil stabilization by complex rhizome systems was apparently widespread, and contributed to landscape modification at an earlier time than had been appreciated.

Foamability, foam initial liquid volume, and bubble size of fatty alcohol sodium polyoxyethylene ether sulfate (AES) surfactant solution were studied with and without the addition of sodium carboxymethylcellulose (CMC) at different gas flow rates, using a sparging method. The generation time decreased with increasing gas flow rate. At low gas flow rates, the added CMC greatly enhanced the foamability by preventing bubble collapse. The initial liquid volume of the foam first increased rapidly, and then gradually decreased. Increasing the CMC concentration increased the initial liquid volume of the foam. The mean bubble diameter first clearly decreased, then increased slowly with increasing gas flow rate. CMC showed different effects on bubble size at high and low gas flow rates. Adsorption of CMC on AES molecules forms a network structure and improves bubble film stability, which can explain the above results. These findings provide guidelines for generating foam with excellent properties suitable ...

Mining-induced voids are a necessary factor triggering underground coal fires that endanger the underground and atmospheric environment. On the other hand, voids provide channels for underground fluid and fire-fighting material migration. A series of void rate models were proposed to determine the three-dimensional heterogeneous distribution of the mining-induced voids in the disturbed strata. The void rate distribution map of horizontal voids presents a reversed “quadripod-type” shape in the strata plane, the void rate of vertical voids has a shape similar to two “basins” of different sizes and contrasting opening directions nested together, and the void rate of isotropic pores presents a “basin-type”. It can be deduced from the distribution maps that were calculated by theoretical and numerical models that the voids present a “fractured dome” distribution and that the void rate gradually decreases from foot to crown of the dome. It was ascertained from the application of void rate models in the hydro-thermal investigation of an underground coal fire that the correlation between heat production and ground surface temperature presents a linear function, while that between outflow velocity and fire source temperature has a negative-exponential-power relationship. Additionally, a new Plan-Do-Check-Adjust cycle was established for the management of fire-fighting engineering, which includes the delineation of fire zones, the evaluation of fire behavior, the optimization of fire-fighting measures, the performance of the fire-fighting plan, and the assessment of control results to determine whether the fire-fighting plan should be reformulated or improved. After five control cycles lasting nine months, an approximately 115,200 m 2 fire zone was controlled.

Simultaneous thermal analysis was used to study the influence of Vitamin C as possible chemical additive inhibiting coal oxidation process at low temperature. Some oxidation characteristics of Vitamin C affecting the coal oxidation were investigated at different heating rates. The TG-DSC data show that the impact of Vitamin C on coal oxidation process can be directly evaluated using ignition temperature and critical temperature. Comparison with the effect of water on coal oxidation shows that Vitamin C is more efficient than water. However, the blank experiment conducted with inert α-Al2O3 also suggests that Vitamin C can decompose at about 200 °C, which limits the usage of Vitamin C on inhibiting coal oxidation.

This paper deals with the permanent magnet synchronous motor (PMSM) speed estimation and parameters identification problems. It proposes a solution to estimate speed and identify stator resistance, d-axis and q-axis inductance simultaneously. In fact, there are a lot of methods for estimating the speed, for example high-frequency injection, Kalman filter, and model reference adaptive system (MRAS). However, with the PMSM running, some parameters will change such as the stator resistance will change with the increase in temperature. These parameters are useful for estimating the speed. So, it is necessary to identify parameters simultaneously to adapt to the changes of these parameters. In this paper, MRAS is the theoretical basis. First, the adaptive law of speed observer is constructed through Popov stability. Then, the adaptive laws of stator resistance, d-axis, and q-axis inductance are constructed through Lyapunov stability. The stability of the proposed observers is also discussed. Last, this paper uses field-oriented control strategy and illustrates the obtained results through simulation and experiment.

Coal can maintain smoldering combustion for a long time in the gob (mined-out) area which is a serious threat to the safety mining of a coal mine. However, few literatures can be obtained to well understand the smoldering phenomena of coal. To obtain the coal smoldering characteristics, vertical forward and reverse smoldering tests under different air flow rate were performed, and the smoldering combustion process, speed, and temperature were analyzed. It is found that although the combustion process of forward and reverse smoldering is significantly different, their smoldering speeds are the same and both increase monotonically with air flow rate as the higher the air flow rate is, the greater the oxygen consumption rate can reach. Even when the air flow rate is 0.074 m/min in that the wind speed belongs to the suffocation zone of the gob, the coal can still undergo smoldering until complete combustion. This indicates that the smoldering fire cannot be effectively extinguished by only accelerating the stoping speed of the working face to create fire in the suffocation zone during the mining process. And for a sealed fire zone, it is also difficult for the smoldering fire to be completely extinguished as the fire zone cannot be absolutely sealed. Meanwhile, the risk of reverse smoldering is greater than forward smoldering due to its larger smoldering temperature.

Numerous plant cuticles were collected from five sections in the Lower–Middle Devonian of Yunnan and Sichuan provinces, China. Based on these cuticles and published data, we recognize five types of stomata or stoma-like pores in Devonian plants, i.e., anomocytic, rosette and complex types of stomata, pores like in Nematothallus , and pores within thick cuticle. Anomocytic and/or rosette types of stomata are more common in some horneophytopsids, rhyniopsids, renalioids, zosterophyllopsids, lycopsids and a progymnosperm. Complex type found only in the Middle Devonian likely occurred in Orestovia and Schuguria . Pores like in Nematothallus and pores within thick cuticle are documented in both the Lower and Middle Devonian and are usually observed on dispersed cuticles which have relationship with non-vascular plants. The various plant species share only five types of stomata and stoma-like pores. It is difficult to understand the exact affinities of epidermises without other macrofossil information.

This paper presents a backstepping control method with speed estimation of permanent magnet synchronous motor (PMSM) based on model reference adaptive system (MRAS). First, a comprehensive dynamical model of PMSM in d–q axis and its space state equations are established. Next, using Lyapunov stability theorem, based on the backstepping control theory, the PMSM rotor speed and current backstepping controllers are designed. Furthermore, using Popov stability theory, based on MRAS, the PMSM rotor speed observer is designed. Finally, Matlab/Simulink simulation results show that the backstepping control and speed observer are effective and feasible.

To overcome the drawbacks of the conventional foam technology used for dust suppression, including large pressure loss, high water pressure and low driving pressure, a new pneumatic foaming system is introduced. Then an original design of foaming agent mixing device is proposed, and its performance is investigated and evaluated under different pressure compensations. Experimental results show that the maximum absorption amount increases by 2.9–6.7 times at a pressure compensation of 0.04–0.2 MPa compared with no pressure compensation. The pressure loss and pressure fluctuation both reduce significantly with increasing pressure compensation. The critical outlet pressure increases by 30.4–240%. Field application indicates that the proposed mixing device ensures the reliable addition of foaming agent used for foam dust suppression. The effect of foam on dust suppression is remarkable, and the economic cost of foam is low. Therefore, there is reason to believe that the new mixing device will greatly promote foam technology to be widely used for suppressing dust in underground coal mines. Keywords: Compressed air, Jet, Pressure compensation, Foam, Dust suppression

In this study, orthogonal experiments were conducted to investigate the influence of expandable graphite (EG), dimethyl methylphosphonate (DMMP), triethanolamine (TEA), and isocyanate content on the compressive and bonding strengths, oxygen index, and fluidity of rigid polyurethane foam (RPUF). The results revealed that EG significantly increased the oxygen index of RPUF, enlarged the diameter of foam cells, and decreased the cell-closed content in foam; thus, leading to a pressure drop in RPUF. However, excessive EG was capable of reducing the fluidity of polyurethane slurry. TEA exhibited significant influence on the compressive strength of RPUF, which dropped initially, and then increased. DMMP had a remarkable effect on the flame retardant property and compressive strength of RPUF. Compressive strength of RPUF initially displayed an increase followed by a decrease with increasing dosage of DMMP, and achieved the maximum value at DMMP dosage of 4%. DMMP could effectively reduce the diameter of RPUF cells leading to an increase in the percentage of close area in foam. DMMP displayed the flame-retardation effects mainly in the gas phase leading to a significant enhancement in the oxygen index of RPUF. Moreover, the compressive strength and bonding strength of RPUF decrease significantly with the increase of isocyanate content due to the increased blowing efficiency by the CO2. The oxygen index and flowing length of foam increased with the increase in isocyanate dosage. Keywords: Rigid polyurethane foam, Expandable graphite, Compressive strength, Flame retardant, Scanning electron microscopy (SEM), Microstructure

In order to improve the utilization rate of foam, an arc jet nozzle was designed for precise dust control. Through theoretical analysis, the different demands of foam were compared amongst arc jets, flat jets and full cone jets when the dust source was covered identically by foam. It is proved that foam consumption was least when an arc jet was used. Foam production capability of an arc jet nozzle under different conditions was investigated through experiments. The results show that with the gas liquid ratio (GLR) increasing, the spray state of an arc jet nozzle presents successively water jet, foam jet and mist. Under a reasonable working condition range of foam production and a fixed GLR, foam production quantity increases at first, and then decreases with the increase of liquid supply quantity. When the inner diameter of the nozzle is 14 mm, the best GLR is 30 and the optimum liquid supply quantity is 0.375 m3/h. The results of field experiments show that the total dust and respirable dust suppression efficiency of arc jet nozzles is 85.8% and 82.6% respectively, which are 1.39 and 1.37 times higher than the full cone nozzles and 1.20 and 1.19 times higher than the flat nozzles. Keywords: Dust control, Precise spray, Arc jet, Gas liquid ratio (GLR), Dust suppression efficiency

To mitigate the effect of the distributed generation (DG) connection on the voltage profile and power loss, the DG optimal configuration and network reconfiguration are used in distribution automation. In this paper, a new optimization method named Archimedes Optimization Algorithm (AOA) is proposed, unifying the DG optimal configuration and network reconfiguration. The DG locations and capacities are coded by integral and real numbers simultaneously in the proposed method. The integer mesh-network coding method is integrated into the new method to solve the network reconfiguration problem. The new method is compared with the Improved Genetic Algorithm (IGA) as well as the Particle Swarm Optimization (PSO). Results demonstrate that the proposed method has advantages in improving the voltage profile and reducing the power loss.

Immune algorithms can improve the self-adaptability for network traffic detection. Classical immune algorithms dynamically evolve and match the whole content of immune elements. However, most features of network traffic are isomeric to each other. The general matching and evolution for the whole immune elements slow down the process of self-adaptability to an extent and reduce the accuracy of immune elements’ evolution. In this paper, available network data features are analysed for the network traffic detection. The section simulation method in the immune system is studied by creating a math method for part matching of immune elements which can evolve in parts. The process of section evolution for immune elements is inferred. A detection method for recognizing anomaly network traffic is proposed. Simulation experiments show that the self-adaptability of the proposed method to the real network environment is superior to that of traditional immune algorithms.

Variations of the mechanical properties and the pore structures of rocks after high-temperature treatment play a significant role in ensuring the operation of underground coal gasification and prevent the pollution of groundwater. In this study, to quantitatively analyse the pore structure and mechanical properties of sandstone after treatment at different temperatures (25 °C, 100 °C, 200 °C, 300 °C, 400 °C, 500 °C, 600 °C, 700 °C, 800 °C, and 900 °C), an experiment was conducted based on nuclear magnetic resonance. The variation laws of the size and number of pores in sandstone after the high-temperature treatment were determined to investigate the development of cracks and the changes in the mechanical properties of the rock. At low temperatures, micropores account for over 90%, and the connectivity between pores and cracks is poor. In the temperature range of 200–500 °C, macropores and microcracks were found to increase the most, followed by mesopores, while micropores exhibited the smallest increase. Above 600 °C, the porosity and permeability of the sandstone improved significantly. Furthermore, the porosity and permeability increased sharply by 1.62 and 1.27 times, respectively, at 500–600 °C compared with those at room temperature. After the high-temperature treatment, the stress-strain curves of sandstone gradually became smoother, the post-peak residual stress intensified, and the brittleness weakened. The inflection point of sandstone strength occurs at 800 °C, which lags behind the porosity, permeability, and peak strain, because the trans-granular cracks penetrate the whole granule and connect with the surrounding fracture network.

The argillaceous fault fracture zone is a special area which bears the most concentrated stress when it forms and develops. Therefore, the tunnel under construction is subject to serious water and mud inrush when excavated through this area. In order to explore the destruction characteristics of mud inrush, a large-scale three-dimensional geological model test was carried out, which overcomes the “black box” problem of the traditional test, and a cone-shaped and parabolic body model were proposed to depict the shape of soil disturbance. In addition, the evolution law of displacement field inside medium was studied and the change regulation of actual disaster influence area also was been revealed. Finally, the tunnel mud inrush mechanics were revealed according to destroyed characteristics. As the results showed, the location of the initial mud inrush occurred at the spandrel of the tunnel face, the displacement of soil near the location of mud inrush increased with proceeding time, but there was a sudden saltation of the increasing rate when the disaster occurred. Besides, the shape of surface subsidence above the location of the inrush gradually transferred from “W” to “V” in the process of mud inrush. With the increase of the number of mud inrush, the soil disturbance develops from the local to the whole. When the local disturbance occurs, the soil form is cone, while when the whole disturbance occurs, the soil form is parabola. In addition, it is found that soil displacement is related to the seepage pressure under different disturbance modes. Finally, the conclusion of the model test may shed light on the catastrophic process and evolution law of the mud inrush in fault fracture zone. which has certain guidance and reference significance for the prevention of mud inrush in similar projects.

Rocks generate voltage and current when subjected to load. Hence, the study of their characteristics is critical to the prevention and management of mine dynamic disasters and their secondary impacts. To investigate the characteristics of surface potential and current induced by stress on coal mine sandstone roof, an experimental scheme for determining the mechanical–electrical characteristics of rocks is constructed. The aforementioned system tests the evolution rules of current and voltage generated by the coal mine sandstone roof at different loading rates; the formation mechanism and coupling rules with mechanical properties of sandstone are also analysed. Experimental results show that although loading rates may differ, the variations of pressure stimulated current (PSC) and pressure stimulated voltage (PSV) curves are similar. Throughout the loading process, the PSC is divided into three stages: rapid growth, slow growth, and peak; on the other hand, the PSV curve exhibits a ‘double peak’ characteristic. The loading rate changes the current and voltage growth rates and peak values. When combined with mechanical properties, it can be observed that the PSC is related to the effective elastic modulus, whereas the PSV is related to micro-crack and macro-crack events in rocks. The current and voltage generated by the coal mine sandstone roof subjected to load are consistent with stress. The mechanical–electrical properties of sandstone indicate that the change processes in the PSC and PSV result from the coupling effects of various mechanisms. In the compaction stage, these are mainly caused by the piezoelectric effect of sandstone. In the elastic–plastic deformation stage, they are primarily generated by the electric dipoles formed by micro-cracks. In the sandstone fracture deformation stage, the change processes are mainly caused by the crack tip discharge. This study provide an experimental basis and practical results that reflect the microscale process and electrical precursors of sandstone fracturing.

Foam is used as an efficient means of dust suppression in underground coal mines. The poor performance of conventional adding device of foaming agent restricts its wide application. The objective of this study is to propose and investigate a new parallel jet adding device (PJAD). Experimental results show that PJAD requires a greater water flow to produce negative pressure than the single stage jet adding device (SJAD) and is harder to generate cavitation. PJAD consumes a less pressure loss than SJAD and realizes any adding proportion below 1%, which is especially suitable for precision addition of foaming agent. A foaming system used for dust suppression is put forward with PJAD adding foaming agent. Field application indicates that foam achieves a far better dust suppression effect than the roadheader water spraying, and the foam cost is significantly reduced due to the low adding proportion of foaming agent. The marked dust suppression effect makes us believe that the proposed PJAD will greatly promote the large-scale application of foam technology used for dust suppression in underground coal mines.

Premise of research. Rooting structures were major contributors to Devonian global change, but anatomically preserved plant roots are rare from this period. We report a new type of plant axis from the Upper Devonian strata of South China that contains a protostele, relatively extensive secondary xylem, and adventitious root traces.\ud \ud Methodology. The original specimens were fragmentary coalified axes, most of which were embedded in Epon resin, sectioned transversely and longitudinally, and ground into thin sections. The sections were observed and imaged with a light microscope. A few were observed directly with a scanning electron microscope.\ud \ud Pivotal results. The axis of this new plant, named Pleurorhizoxylon gen. nov., consists of a three-ribbed protostele and thick secondary xylem; the primary xylem is of apparent mesarch maturation, with a single protoxylem lacuna near the end of each rib. The secondary xylem has variable rays composed of parenchyma cells and has scalariform to elliptical bordered pits on both radial and tangential walls of the tracheids. The adventitious root traces are located opposite each primary xylem rib going through the wood; they are accompanied by large rays and cause significant accommodation (knotting) in the wood. Extraxylary portions are poorly preserved, and no cambium or secondary phloem has been found.\ud \ud Conclusions. The new plant has a unique combination of characters and demonstrates the anatomical basis for adventitious root growth present in a Devonian moniliform plant, other than cladoxylopsids, for the first time.

This paper deals with robust control problems for double-pendulum overhead cranes. For this reason, a linearized and decoupled double-pendulum overhead crane dynamic model is derived by adopting a disturbance observer and modal analysis technology. Next, a robust linear feedback controller, whose gains are obtained via LMI optimization method, is proposed. Finally, numerical simulations validate that the proposed method has superior control performance.

International audience; The location of buried utility pipes is often unknown. We use the time-domain induced polarization method to non-intrusively localize metallic pipes. A new approach, based on injecting a primary electrical current between a pair of electrodes and measuring the time-lapse voltage response on a set of potential electrodes after shutting down this primary current is used. The secondary voltage is measured on all the electrodes with respect to a single electrode used as a reference for the electrical potential, in a way similar to a self-potential time lapse survey. This secondary voltage is due to the formation of a secondary current density in the ground associated with the polarization of the metallic pipes. An algorithm is designed to localize the metallic object using the secondary voltage distribution by performing a tomography of the secondary source current density associated with the polarization of the pipes. This algorithm is first benchmarked on a synthetic case. Then, two laboratory sandbox experiments are performed with buried metallic pipes located in a sandbox filled with some clean sand. In Experiment #1, we use a horizontal copper pipe while in Experiment #2 we use an inclined stainless steel pipe. The result shows that the method is effective in localizing these two pipes. At the opposite, electrical resis-tivity tomography is not effective in localizing the pipes because they may appear resistive at low frequencies. This is due to the polarization of the metallic pipes which blocks the charge carriers at its external boundaries.

Coal fire is a global catastrophe. Xinjiang suffers the most severe coal fire in China and even in the world. Coal firefighting work has been being conducted for decades in Xinjiang. In this paper, coal fire detection, extinguishing, and monitoring approaches that were derived from coal firefighting experience are introduced in detail by taking the Fifth Fire Area (FFA) of the Heshituoluogai coal fire for instance. We first introduce the geology and fire situation in the FFA. Before developing efficient strategies to extinguish it, magnetic and self-potential methods are adopted to delineate the extent of the fire. A composite index is proposed to better indicate the fire. The comprehensive coal firefighting method is illustrated in detail, which consists of surface cooling, excavation and leveling, borehole drilling, borehole water injection and grouting, and loess backfill. The subsequent temperature and CO monitoring records show that the fire is extinguished successfully without burnback. The methodology presented here provides guidance and reference for putting out other coal fires around the world.

Magnetic bearings have been used in flywheel energy storage systems to improve their performance because these kinds of bearings can provide non-contact supporting so that the friction between the rotor and the bearings is reduced significantly. However, the gyroscopic coupling, parameter coupling, and imbalance force affect the operating performance and stability of a magnetic suspended flywheel energy storage system with asymmetric rotor; therefore, the main purpose of this study is to propose a control method for achieving decoupling and stable operation of the aforementioned system. To this end, after deriving the mathematical model of a radial 4-degree-of-freedom rotor–bearing system, a novel cross-feedback-based modal decoupling controller is designed for vibration suppression caused by gyroscopic coupling, parameter coupling, and imbalance force. Better performance is obtained through comparing the decoupling performance, control performance, and disturbance rejection performance with a traditional decentralized proportional–integral–derivative controller and a cross-feedback controller via ADAMS–MATLAB co-simulation technology and experimental results.

Monilistrobus Wang et Berry is a fossil lycopsid reported from the Upper Devonian Wutong Formation of Jiangsu Province, China, and includes only the type species Monilistrobus yixingensis Wang et Berry. Along a single fertile axis, Monilistrobus has cone-like structures separated by and alternated with a length of vegetative region, which is an important character here termed as periodicity of reproductive growth. The alternation of fertile and vegetative growth occurs regularly and produces repeated intercalary (non-terminal) fertile zones. New specimens, identified as Monilistrobus cf. yixingensis, from the same formation but of Zhejiang Province extend the geographic distribution of this genus. These new specimens demonstrate morphological variations within this genus, such as the lack of spiny appendages on the leaves, different measurements of leaf bases, and different shapes and positions of cone-like structures. The distribution of intercalary fertile zones, as summarized for the first time in this paper, occurs in the Drepanophycales, the Protolepidodendrales, the Isoetales, the Lycopodiales, the Selaginellales, and Wuxia Berry, Wang et Cai and Monilistrobus of uncertain affinities. Thus, this peculiar trait might have evolved in the very early evolutionary stage of the lycopsids, as indicated in the basal group Drepanophycales. However, the presence of repeated, two or more intercalary fertile zones along a single fertile axis is demonstrated only in Monilistrobus and the extant Huperzia Bernhardi.

The arborescent lycopsid Sublepidodendron grabaui was widely distributed in the Late Devonian of South China. Its morphology and anatomy have been described, but the microsporangiate strobilus remains unclear. New material collected from the Guanshan Member of the Wutong Formation in Zhejiang Province allowed us to provide more details of this plant. The pseudomonopodial axis without secondary xylem bears medullated stele and branch traces arranged in irregular helices. The lateral branch possesses solid exarch primary xylem. This pseudomonopodial branching system possibly represents the crown or cauline lateral branch. The microsporangiate strobilus contains microspores belonging to the Lycospora granulata Group. The monosporangiate nature of S. grabaui is confirmed, and the classification of Sublepidodendraceae into the suborder Dichostrobiles is supported. The L. granulata Group microspores are suggested to occur not only in bisporangiate strobili but also in monosporangiate strobili.

New material collected from the Middle Devonian (Givetian) Haikou Formation of Yunnan Province, southwestern China, reveals details of anatomy of the cladoxylopsid Panxia gabata Y. Wang et Berry. The primary xylem in main axes consists of numerous primary xylem segments, most of which are radially directed and elongate. Some xylem segments are connected toward the center to form V, Y, W, or more complex-shaped configurations. One permanent protoxylem strand occurs near the outer tip of each xylem segment of the main axes. A dissected primary xylem column occurs in first-order branches, but the xylem segments are fewer in number and smaller in size than those in main axes. Most xylem segments in first-order branches are unidirectional and parallel in orientation, some are connected to form Y, twice-dichotomous, or more complex-shaped configurations, and one protoxylem strand occurs near each of the two ends of individual xylem segment or a segment group. Metaxylem tracheids are characterized by multiseriate circular bordered pits. Vascular traces depart from the tip of primary xylem segments, produced by elongation and division of protoxylem strands. These traces are of various sizes and shapes, from circular, elliptical to elongate–elliptical in transverse outline, with one or two protoxylem strands. Cortex tissues are mainly composed of thin-walled, approximately isodiametric cells. Within the Cladoxylopsida, Panxia , a plant endemic in South China, is more similar in stellar anatomy to the Laurussian Pseudosporochnales and Rotoxylon Cordi et Stein than to other plants. These shared anatomical traits seem unlikely to represent the convergent evolution of plants on different continents, but imply that Panxia , Rotoxylon , and Pseudosporochnales may have evolved from a recent common ancestor which had existed across Laurussia and South China in earlier times.

Organic chemical reactions cause the temperature rising during coal oxidation; however, because of the complex structure of coal, it is difficult to analyze and characterize the reactions involved in coal low-temperature oxidation. To date, a main reaction pathway describing the heating progress during coal oxidation has not been proposed. Here, a series of cyclic chain reactions is presented to describe the oxidation mechanism during coal spontaneous combustion using quantum chemistry calculations. Main active sites and their molecular models were built. Three interactive modes of active orbitals and detailed reaction sequences of coal oxidation are proposed. The structural parameters and thermodynamic data were calculated and the orders of reactions for transformations between functional groups were identified based on their activation energies. The reaction pathway was constructed based on functional transformation relationships and the order of reactions. The results show that main reactions occurring during coal oxidation can be defined as the reactions of oxygen and hydroxide free radicals reacting with coal active sites. Methyne and carbon free radicals reacting with oxygen is the initial reaction during coal oxidation. The decomposition of peroxides linking the reaction pathway form cyclic chain. Hydroxyl and aliphatic hydrocarbon radicals as key of chain reactions consumes coal active sites and oxygen continuously. Aliphatic hydrocarbons appear to contribute more to heat release during coal oxidation due to greater heat release and lower activation energy of their reactions. Limited spontaneous reactions maintain constant apparent activation energy for the oxidation until the chain reactions are generated; the apparent activation energy then increases. Low-ranking coals have higher apparent activation energies during oxidation due to more oxygen-containing groups and side chains contain more reactions with higher activation energy. Results from this study can improve understanding of mechanism of coal oxidation and provide a guide to forecasting and preventing spontaneous combustion of coal in underground coal mines or coal stockpiles.

Chinese lignite coal from the Beizao mine which located in Shandong Province of China was studied using a combination of ultrasonic extraction under mild conditions (which generate minimal chemical changes) in conjunction with modern analytical instrumental techniques. This procedure allowed the development of a structural model. Calculations with the Gaussian 09W package generated an optimized structural geometry and also determined the activities of various functional groups. The initial stages of oxidation were found to consist of the oxidation of hydroxyl groups, the rupture of C–O and C–C bonds, and the dehydrogenation of carboxyl groups. In contrast, both the decarboxylation and decarbonylation reactions were determined to require significant energy inputs and thus occur only at high temperatures. In situ Fourier transform infrared analyses were used to confirm the results of the theoretical calculations.

In this study, the corn straw after removing the lignin was grafted with 2-acrylamido-2-methylpropanesulfonic acid (AMPS) to prepare sulfonated cellulose. The grafting copolymerization between the sulfonated cellulose and acrylic acid (AA) was performed using potassium persulfate and N,N′-methylenebisacrylamide as the initiator and crosslinking agent, respectively, to prepare corn straw-co-AMPS-co-AA hydrogels. The structure and properties of the resulting hydrogels were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, and dynamic rheometry. The effects of initiator, crosslinker, monomer neutralization degree, and temperature on the swelling ratio of the hydrogels were studied. The water retention, salt resistance, and recyclability of the corn straw-co-AMPS-co-AA hydrogels were also investigated. The optimum water absorptivity of the corn straw hydrogels was obtained at a polymerization temperature of 50 °C with 1.2% crosslinker, 1:7 ratio of the pretreated corn straw and AA, 2% initiator, and 50% neutralized AA.

In this study, we introduce a jet-type foam preparation device for use in mine dust control, which can enhance the reliability and applicability of the foam production process compared with conventional foam generators. In order to elucidate the foaming agent self-suction properties of this novel foam generator, we used a self-built experimental setup to investigate the effects of the working pressure and outlet pressure on negative pressure (vacuum degree) during foaming agent suction, as well as the functional relationship between negative pressure and the foaming agent by adding parameters. We also studied the effects of the valve opening degree on the foaming agent flow rate and addition ratio. The results showed that the working pressure and outlet pressure affected the formation of negative pressure in a positive linear manner and a negative linear manner, respectively. Thus, the negative pressure increased linearly as the working pressure increased, whereas it decreased in a linear manner as the outlet pressure increased. There was also a quadratic relationship between the vacuum degree and foaming agent quantity with the piecewise characteristics of the growth process, where they increased slowly with a lower vacuum degree but increased rapidly with a higher vacuum degree. After creating a moderate negative pressure with the water jet, the foaming agent could be added automatically at a low flow rate with a low ratio via the regulating valve on the liquid suction hose. This study provides basic information that should facilitate the application of this novel foam preparation technique.

Coal fires are a serious threat to the workers' security and safe production in open pit mines. The coal fire source is hidden and innumerable, and the large-area cavity is prevalent in the coal seam after the coal burned, causing the conventional extinguishment technology difficult to work. Foams are considered as an efficient means of fire extinguishment in these large-scale workplaces. A noble foam preparation method is introduced, and an original design of cavitation jet device is proposed to add foaming agent stably. The jet cavitation occurs when the water flow rate and pressure ratio reach specified values. Through self-building foaming system, the high performance foams are produced and then infused into the blast drilling holes at a large flow. Without complicated operation, this system is found to be very suitable for extinguishing large-scale coal fires. Field application shows that foam generation adopting the proposed key technology makes a good fire extinguishment effect. The temperature reduction using foams is 6-7 times higher than water, and CO concentration is reduced from 9.43 to 0.092‰ in the drilling hole. The coal fires are controlled successfully in open pit mines, ensuring the normal production as well as the security of personnel and equipment.

To study the flow characteristics of three-phase foam in gob area, different perfusion experiments in coal mine gob were designed and put forward in the paper. Through the observation of flow range, flow characteristics of three phase foam were analyzed with different flow rates. And, unsteady seepage process of three-phase foam was simulated with CFD software. Base on experiment and numerical simulation results, flow characteristics of three-phase foam and its major influence factors are discussed, and the optimal arrangement distribution of mine fire control drills is also determined. Research results show that the flow range and stacking height of three-phase foam in gob are significantly influenced by gravity. The vertical stacking height and horizontal diffusion distance of three-phase foam are also directly related to the flow volume of foam perfusion, the larger flow single hole perfusion volume, the higher stacking height and the longer diffusion distance could be obtained. Keywords: Three-phase foam, Gob area, Seepage, Diffusion range, Numerical simulation

In order to improve the jet pump cavitation, a new method of inhaling air into the low-pressure region was proposed, and its performance was investigated experimentally under different air suction quantity and cavitation levels. Test results show that the cavitation number increases with the air suction quantity increasing in a linear approximation fashion. Increasing air suction quantity corresponds to a sharp decrease in acoustic noise, especially for the severe cavitation. As the air suction quantity increases, the pressure fluctuation range and fluctuation variance both decrease in the downstream, which relieve the cavitation vibration damage and enhance the jet pump stability. In addition, the pressure loss ratio reduces by 0.95%–3.46% and the pressure ratio increases by 5.7%–18% due to the water–air cushion layer formed in the wall boundary. The marked effect on preventing cavitation damage and improving the pressure transmission performance of the jet pump proves that the new air suction method proposed is practical and effective. Therefore, it is believed that this study would lay an important foundation for the widespread application of jet pump in the future.

We have developed a new class of aqueous Pickering foams, which were stabilized by sodium dodecyl sulfate (SDS)-modified micro fly ash (FA) particles and exhibited excellent stability and inhibition characteristics for coal spontaneous combustion. Specifically, this study aimed to characterize the microstructure, foaming behavior, evolution process and inhibition characteristic for coal spontaneous combustion of these Pickering foams. The evolution of these Pickering foams is quantified by measuring the rate of bubble growth as well as the kinetics of liquid drainage and the two processes are correlated. These data allow us to identify a transition time, separating two distinct stages of foam evolution. An increasing FA concentration in the Pickering foams lead to an increase in foam stability, which arises from the formation of a robust FA-armoured bubble structure. In addition, the coal acceleration oxidation experimental results show that these Pickering foams can improve the coal thermal stability and effectively inhibit the coal oxidation process by increasing crossing point temperature (CPT) and reducing CO emission. The results indicate that the prepared aqueous, low-cost and nontoxic FA-stabilized Pickering foams effectively slow the oxidation of coal, thereby demonstrating its application potentials in coal spontaneous combustion prevention and control.

To realize a stable addition of foaming agent used for foam technology, a new adding method using the jet cavitation was introduced, and its performance was investigated experimentally under different operating conditions. Experimental results show that the bubble region in the jet device has a constant vapor pressure, which creates a good condition for liquid absorption, while it shrinks with increasing outlet pressure. The liquid absorption amount keeps unchanged when the outlet pressure is lower than a critical value. The critical outlet pressure increases by 40% with decreasing cavitation absorption amount, which is especially suitable for mini-flow quantitative addition of foaming agent used for foam dust suppression. Its effectiveness on suppressing mine dust was evaluated in a heading face of underground coal mines. Field application indicates that the reliable and simple foaming system adopting the new adding method makes a marked dust suppression effect. The working environment of heading face is significantly improved, ensuring the safe tunneling and personal security.