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The coal and gas outburst process is frequently accompanied by strong dynamic effects, and the generating outburst shock wave will cause certain casualties, even damage ventilation facilities such as air doors, thus expanding the scope of accidents. In order to be close to the actual situation, a dynamic model of coal and gas outburst is established according to the phenomenon of on-site outburst process; Based on the theory of aerodynamics, the formation mechanism of one-dimensional shock wave in confined space is discussed. On this basis, the formation mechanism of outburst shock wave in the simulated roadway is clarified. It is pointed out that the high-speed gas flow sprayed into the roadway at the moment of outburst compresses air to form outburst shock wave, and the strength of outburst shock wave is determined by the gas expansion energy released during the acceleration phase of outburst gas flow; The prediction model of overpressure peak value of outburst shock wave based on gas pressure of outburst hole and diameter of outburst mouth is established. Using the simulation experiment system of coal and gas outburst impact dynamic effect and disaster characteristics, the simulation experiments of outburst dynamic effect under different gas pressure and coal loading were carried out. The experimental results show that the measured value of shock wave overpressure in the process of outburst simulation experiment is consistent with the theoretical value, which verifies the correctness of the theoretical model. When the coal loading is the same, the overpressure of outburst shock wave increases with the gas pressure; When the gas pressure is the same, with the increase of coal loading, the shock wave overpressure changes little. Under the same gas pressure, the diameter of outburst mouth will affect the magnitude of shock wave overpressure. When the diameter of outburst is small, the gas expansion energy released at the moment of outburst is small, resulting in small overpressure value of shock wave. Outburst shock wave strength \begin{document}$p'_2 $\end{document} and shock wave overpressure \begin{document}$\varDelta p' $\end{document} has a linear relationship with the ratio s1/s2 of the diameter of the outburst and the roadway. Therefore, gas pressure and outburst diameter are the main factors affecting the intensity of outburst shock wave. In addition, in the process of outburst simulation experiment, the overpressure of outburst shock wave in the simulated roadway is attenuated with the propagation distance. By analyzing the peak value data of shock wave overpressure in the roadway, it is found that the formula y=aΔPmaxx−1/2 can better describe the attenuation law of shock wave overpressure in the roadway. The outburst shock wave propagates to the end of the roadway and forms a secondary shock wave due to the reflection of obstacles. This study can provide guidance for scientific and rational design and arrangement of safety protection measures in outburst mines.

NASICON-structured Na3Zr2Si2PO12 (NZSP) has been considered as one of the ideal electrolytes for all-solid-state sodium metal batteries (ASSSB). However, the practical application of NZSP-based ASSSB is hindered by the low ionic conductivity and large interfacial resistance caused by the poor contact between NZSP and Na metal. Herein, the introduction of Fe2O3 not only improves ionic conductivity and reduces activation energy by the doping of Fe3+ in the crystal structure of NZSP, but also reduces the interfacial resistance and enhances interface stability between NZSP and Na metal anode. The synergistic effects significantly enhance the cycling stability, rate capability, and critical current density of the symmetrical solid-state cells. The interfacial reaction mechanism indicates that Fe3+ in the interface is reduced Fe2+ by Na anode, which effectively even the electric-filed distribution and suppresses the dendrite growth. Consequently, the symmetric solid-state cells exhibit stable cycling performance for 1,500 h at 0.1 mA·cm−1/0.1 mA·h·cm−1 and over 900 h at 0.2 mA·cm−1/0.2 mA·h·cm−1. The Na|NZSP-0.075%Fe2O3|Na2FePO4F solid-state full cells display high capacity retention of 94.2% after 100 cycles at 0.5 C. The stable interface of NZSP/Na and improved ionic conductivity contribute to excellent electrochemical performance, which accelerates the practical application of ASSSB.

Abstract A ground-breaking roadmap of III-nitride solid-state deep-ultraviolet light emitters is demonstrated to realize the wafer-scale fabrication of devices in vertical injection configuration, from 2 to 4 inches. The epitaxial device structure is stacked on a GaN template instead of conventionally adopted AlN, where the primary concern of the tensile strain for Al-rich AlGaN on GaN is addressed via an innovative decoupling strategy, making the device structure decoupled from the underlying GaN template. Moreover, the strategy provides a protection cushion against the stress mutation during the removal of substrates. As such, large-sized wafers can be obtained without surface cracks, even after the removal of the sapphire substrates by laser lift-off. Wafer-scale fabrication of 280 nm vertical injection deep-ultraviolet light-emitting diodes is eventually demonstrated, where a light output power of 65.2 mW is achieved at a current of 200 mA, largely thanks to the significant improvement of light extraction. This work will definitely speed up the application of III-nitride solid-state deep-ultraviolet light emitters featuring high performance and scalability.

Abstract AlGaN‐based ultraviolet light‐emitting diodes (UV‐LEDs) have the advantages of mercury (Hg) pollution free, small size, high efficiency, and so on, and are widely used in military, medical, and industrial fields, which are considered to be the most promising alternative to the traditional Hg lamps. Great efforts are made over the past few decades to improve the device performance, thereby meeting the commercial production and application requirements of UV‐LEDs, which is always accompanied by a series of interesting physical topics. In this review, the recent research progress in performance of AlGaN‐based UV‐LEDs is summarized from the perspectives of electrical injection, electro‐optical conversion, and light extraction, which are responsible for the operation of devices. The detailed discussions include the major challenges, the corresponding technological breakthroughs, and also the outlook of material growth, energy band modulation, as well as device fabrication involved in UV‐LEDs, which are expected to be helpful for the thorough comprehension of device physics and further development of AlGaN‐based UV‐LEDs.

Objective To evaluate correlations between ultrasonographic pupillary assessment (UPA) and automated UPA in neurocritical patients. Methods This was a prospective, observational study of 20 adult patients admitted to the intensive care unit with neurological pathology. Between UPA and automated UPA, 40 pupillary measurements were made. The time required to conduct UPA and automated UPA on a single patient was consistently

Abstract Aqueous zinc‐ion batteries (AZIBs) are highly promising for grid‐scale energy storage due to their high‐safety and low‐cost characteristics. Nevertheless, the progress in AZIBs has been impeded due to challenges encompassing corrosion, hydrogen evolution reaction, and the formation of dendrites on Zn anodes. These issues arise from the decomposition of active water molecules in the Zn2+ solvation structure in the electrolyte. Various strategies have been proposed to regulate the electrode/electrolyte interface to effectively address these problems. In spite of remarkable headway, an inadequacy of comprehensive studies addressing the mechanisms and evolutionary dynamics of the electrode/electrolyte interface is evident within scientific literature. This overview aims to provide a comprehensive overview of the strategies for regulating the electrode/electrolyte interface, focusing on dendrite‐free and side reactions‐suppressed AZIBs. These strategies include the introduction of metal ion additives, inorganic additives, surfactant additives, polymer additives and organic additives. Furthermore, a detailed examination is made on the effects and underlying mechanisms associated with modifying the electrolyte at the interface between the electrode and electrolyte. Moreover, an appraisal is provided on the performance metrics of diverse strategies and prospective research directions are recommended as well.

Abstract In recent years, coal and gas outburst disasters are still occurring and difficult to prevent, seriously endangering the safety of coal mine production. It is well known that the transporting and crushing of outburst coal is the main pathway of energy dissipation during the coal and gas outburst process. However, a consensus regarding how much gas involves in outburst and affects energy dissipation is still lacking. Quantitative study on the gas effect on migration and fragmentation characteristics of outburst coal in restricted roadway space can improve the energy model and guide the prevention and control of gas outburst. In this paper, an improved visual coal and gas outburst dynamic effect simulation experiment system was used to conduct outburst simulation experiments at different gas pressure conditions. The results showed that the movement of outburst coal in the roadway has experienced various flow patterns. In the initial stage of the outburst, under low gas pressure condition, the motion of the outburst coal was dominated by stratified flow. However, as the gas pressure increases, the initial acceleration increases, and the outburst coal mainly move forward rapidly in the form of plug flow. The average velocity at 0.3, 0.5, and 0.8 MPa gas pressure condition were 6.75, 22.22 and 35.81 m/s, respectively. Gas also has a crushing effect on outburst coal. With increasing gas pressure, the number of coal powder particles of the same mass increased significantly, and the range of the particle size distribution of the particles decreaed, and the median particle size decreased. As the gas pressure increases, the outburst intensity gradually increases, and the total energy involved in the outburst work also increases. However, the energy dissipation pathways are different. At 0.3 MPa, the energy dissipation is dominated by crushing energy, which is about six times the ejection energy. As the gas pressure increased to 0.8 MPa, the proportion of the ejection energy gradually increases to about twice that of the crushing energy. Under the experimental conditions, 2.71–13.43% of the adsorbed gas involves in the outburst (AGIO) through rapid desorption, and the proportion increases with increasing gas pressure. This paper improves the energy model of coal and gas outburst, which is applicable to risk assessment and prevention of outburst disasters.

As the disaster-causing characteristics of coal and gas outburst and the mechanism of induced mine airflow disaster are not clear, the facilities such as air door and self-rescue system are often arranged on site according to miner’s experience, thus it is difficult to take safety protection measures and formulate scientific and reasonable emergency plan. In order to accurately grasp the impact dynamic effect and disaster-causing characteristics of coal and gas outburst, based on the similarity theory, a set of physical simulation experimental system considering the disaster-causing strengthening effect caused by gas in the pressure relief area around the outburst hole was developed. And the key parameters of the gas supplement device were determined through strict calculation based on the outburst model and gas seepage theory. The experimental system mainly includes outburst hole dynamic system, outburst excitation device, roadway simulation system and data acquisition and control center, which can simulate outburst dynamic phenomena such as the formation and propagation of outburst shock wave, the migration of outburst coal-gas two-phase flow and gas countercurrent in the simulated roadway. The simulation experiment of outburst disaster with a gas pressure of 0.8 MPa was carried out. And the forming process of outburst shock wave was directly observed with a high-speed camera. The results show that the outburst shock wave is formed instantly in the pipeline at the moment of outburst, followed by impact flow, outburst gas flow and coal-gas two-phase flow. The comparable velocities of each parameter are in the order: the air shock wave velocity > impact flow velocity > outburst gas-flow velocity > outburst coal-gas two-phase flow front velocity. The maximum velocities of each parameter are 546.5, 496.7, 112.6 and 51.5 m/s respectively, and gradually decay along the pipeline. At the moment of outburst, high-pressure gas poured into the roadway space from the outburst hole, resulting in gas reflux. During the outburst process, the gas pressure inside the outburst hole decreases exponentially. After the outburst occurs, the gas concentration in the roadway changes with time in “sudden rise stage” and “slow decline stage”, and the migration mode of the gas outburst in the roadway mainly includes “displacement" and “diffusion”. The accumulation height and quality of outburst coal along the main roadway are consistent. The difference of grain size distribution between outburst coal and raw coal is mainly concentrated in 0−500 μm, while the difference of maximum grain size distribution is mainly concentrated in 150−200 μm. In addition, the proportion of coal powder with particle size distribution in the range of 150−200 μm increases with the increase of the distance from the outburst mouth, showing a strong sorting ability.

Abstract Background As a chronic mountain sickness(CMS) with the highest incidence and the greatest harm, the pathogenesis of high altitude polycythemia (HAPC) is still not fully understood. Methods 37 HAPC patients and 42 healthy subjects were selected from plateau, and peripheral venous blood samples were collected for transcriptome sequencing on Illumina NovaSeq platform. The sequenced data were analyzed by bioinformatics and phenotypic association analysis. Results The results showed significant differences in multiple clinical indicators including RBC and HGB et al. existed between HAPC and control. Based on the RNA-seq data, 550 genes with significant differential expression were identified in HAPC patients. GO and KEGG pathway enrichment analysis showed that the up-regulated genes were mainly enriched in processes such as erythrocyte differentiation and development and homeostasis of number of cells, while the down-regulated genes were mainly enriched in categories such as immunoglobulin production, classical pathway of complement activation and other biological processes. The coupling analysis of differential expression genes(DEGs) and pathological phenotypes revealed that 91 DEGs were in close correlation with in the phenotype of red blood cell volume distribution (width-CV and width-SD), and they were all up-regulated in HAPC and involved in the process of erythrocyte metabolism. Combined with the functional annotation of DEGs and literature survey, we found that the expression of several potential genes might be responsible for pathogenesis of HAPC. Besides, cell type deconvolution analysis result suggested that the changes in the number of some immune cell types was significantly lower in HAPC patients than control, implying the autoimmune level of HAPC patients was affected to a certain extent. Conclusion This study provides an important data source for understanding the pathogenesis and screening pathogenic genes of HAPC. We found for the first time that there was a significant correlation between HAPC and the pathological phenotype of width-CV and width-SD, wherein the enriched genes were all up-regulated expressed and involved in the process of erythrocyte metabolism. Although the role of these genes needs to be further studied, the candidate genes can provide a starting point for functionally pinning down the underlying mechanism of HAPC.

Nowadays, with more and more physical education curriculum resources, schools or teachers have more and more choices for physical education curriculum resources. However, because some teachers need a deep understanding of curriculum training programs and standards, the selected curriculum resources cannot promote their curriculum development. This paper puts forward the research on the intelligent recognition and game model of physical education curriculum resources based on neural networks. The specific research conclusions are as follows: The intelligent consciousness and movement model of physical education curriculum resources based entirely on the technical knowledge of the BP neural community and deep neural community are proposed. With the help of MATLAB7.1 neural network toolbox to implement the specific recommendation system, a three-layer BP network is established, and the NEWFF function is used to create the neural network. Useful resources in each direction generate a direction recognition vector according to the route guidance standard, calculate the course recommendation degree according to selection statistics and scoring, and input the course resource recognition vector and recommendation degree into the neural network. When the number of hidden layer nodes is 10, and the learning training algorithm selects the L-M optimization algorithm, the error between the actual output and the expected output of the network meets the requirements. It shows that the accuracy of the recommendation model meets the requirements; that is, the relationship between the recognition vector of physical education course resources and the recommendation degree of course resources reflected by the neural network basically reflects the functional relationship between them and the model can be used to make corresponding recommendations.

Improving light extraction efficiency (LEE) of AlGaN-based deep-ultraviolet (DUV) light emitting diodes (LEDs) has been attempted by thinning the p-AlGaN/p-GaN layer and adopting Ni/Au/Al composite electrodes. It is found that the thin p-AlGaN/p-GaN layer can reduce the light absorption and the Ni/Au/Al electrodes achieve high reflectivity and Ohmic contact to ensure the enhancement of the light extraction and maintain fine electrical properties. By this approach, the maximum external quantum efficiency of the DUV-LEDs with optimized Ni/Au/Al reflective electrodes is increased by 40%, compared to that with conventional Ni/Au electrodes over the whole current range.

In this letter, a high performance quasi-vertical GaN-on-Si Schottky barrier diode (SBD) was fabricated by combing in-situ p-GaN layer with hydrogen plasma treatment and controlled diffusion as edge terminations (ETs), where the main junction region of Schottky contact is emerged by pattern etching the top p-GaN layer. The p-n junction with higher barrier height can screen the Schottky contact from high electric field induced by field crowding effect. The hydrogen plasma treatment and controlled diffusion applied to the p-GaN layer further reduces the electric field crowding effect near the p-n junction edge via a gradient junction termination extension structure. As a result, the breakdown voltage of the edge p-GaN terminated SBD with H treatment and diffusion is significantly boosted from 140 V in conventional SBD to 500 V with optimized fabrication process. The on/off current ratio of the diode is as high as 1011@±3 V. The forward current density is 1.45 kA/cm2@3 V and the specific on-resistance is 1.57 $\text{m}\Omega \cdot $ cm2.

Near-infrared stimulated emission from a high-quality InN layer under optical pumping was observed with a threshold excitation power density of 0.3 and 4 kW cm−2 at T = 8 and 77 K, respectively. To achieve such a low threshold power density, vicinal GaN substrates were used to reduce the edge-component threading dislocation (ETD) density of the InN film. Cross-sectional transmission electron microscopy images reveal that the annihilation of ETDs can be divided into two steps, and the ETD density can be reduced to approximately 5 × 108 cm−2 near the surface of the 5-µm-thick film. The well-resolved phonon replica of the band-to-band emission in the photoluminescence spectra at 9 K confirm the high quality of the InN film. As a result, the feasibility of InN-based photonic structures and the underlying physics of their growth and emission properties are demonstrated.

Abstract Vertical GaN‐on‐Si devices are promising for the next‐generation high‐voltage power electronics with low cost and high efficiency. However, their applications are impeded by the limited thickness of crack‐free GaN layers and high threading dislocation density (TDD) in the layer. Buffer layers are crucial for stress control while they usually behave with poor surface morphology, which causes early stress relaxation in GaN and limited thickness. Hereby, a terrace engineering approach for the buffer layers is proposed. Through tuning the supersaturation ratio, the terrace width can be manipulated and an atomically smooth AlGaN buffer layer can be realized, which effectively reduces the compressive stress relaxation and provides a firm foundation for thick GaN growth. As a result, a 7.5 µm thick GaN drift layer with TDD as low as 8.6 × 107 cm−2 is achieved on Si substrates. The room temperature electron mobility of the GaN drift layer can be raised up to 1210 cm2 V−1 s−1. The fabricated PiN diode shows a high breakdown voltage of 1058 V as well as a high on/off ratio of 1012. This work thus truly demonstrates the potential of high‐performance and low‐cost GaN‐based electronic as well as optoelectronic devices on Si platforms.

The past decades have witnessed a tremendous development of GaN-based power electronic devices grown on Si substrate. This article provides a concise introduction, review, and outlook of the research developments of GaN-on-Si power device technology. The comprehensive review has discussed the crucial issues in the state-of-the-art device technology based on both GaN materials epitaxy including stress control and point defects study, and device fabrication including normally off solutions like Cascode, trench MIS-gate, and p-GaN gate. Device reliability and other common fabrication issues in GaN high electron mobility transistors (HEMTs) are also discussed. Lastly, we give an outlook on the GaN-on-Si power devices from two aspects, namely high frequency, and high power GaN ICs, and GaN vertical power devices.

A desorption-tailoring strategy is demonstrated to steadily prepare self-assembled p-AlGaN superlattices with sub-nanometer ultrathin barriers by MOCVD, which juggle the hole concentration and transport.

Heavy carbon (C) doping is of great significance for semi-insulating GaN in power electronics. However, the doping behaviors, especially the atomic configurations and related self-compensation mechanisms, are still under debate. Here, with the formation energy as the input parameter, the concentrations of C defects with different atomic configurations are calculated by taking the configurational entropy into account. The result shows that the concentrations of tri-carbon complexes (CNCiCN, where Ci refers to interstitial carbon) and dicarbon complexes (CNCGa) cannot be neglected under heavy doping conditions. The concentration of CNCiCN can even exceed that of CN at sufficiently high doping levels. Especially, we suggest that it is the tri-carbon complex CNCiCN, instead of the commonly expected CGa, that acts as the self-compensation centers in semi-insulating GaN under heavy C doping conditions. The results provide a fresh look on the long-standing problem about the self-compensation mechanisms in C doped GaN.

We present how the interaction between Al dopants and threading dislocations affects dislocation inclinations and then plays an important role in controlling residual strain in GaN-on-Si epitaxial films. When the Al concentration in the GaN epitaxial film is increased to 0.85%, the dislocations extend almost in the growth direction, contributing to a strain-free epitaxial film. We suggest that the Al atoms could substitute for Ga vacancies at the dislocation cores on the growth surface and then inhibit the dislocation inclinations. The suppressed dislocation inclinations lead to a reduced relaxation of compressive strain. The results pave a new way to control dislocation movements and strain in GaN epitaxial films on Si substrates.

Abstract To obtain the similar materials with specific physical and mechanical parameters and adsorption and desorption indexes used in coal and gas outburst simulation tests, pulverized coal was selected as aggregate, and sodium humate was selected as cementing agent and river sand was selected as auxiliary materials. Based on this, orthogonal tests with 6 factors and 5 levels were designed, and the tests of weighing, uniaxial compression, firmness, adsorption and desorption were carried out. The parameters such as density, uniaxial compressive strength, elastic modulus, firmness coefficient and adsorption–desorption index of similar materials with different ratios were obtained, and the sensitivity of each factor was analyzed by range analysis. The influence of various factors on the similar materials was studied, and the ratio model of similar materials was obtained. The reliability of the model was verified, and a complete method for determining the ratio model of similar materials of outburst coal was put forward. The results show that the density of the similar materials increases with the river sand content, and the uniaxial compressive strength and elastic modulus increase significantly with the pulverized coal ratio and sodium humate content, and the firmness coefficient increases linearly with the pulverized coal ratio. The adsorption constant increases linearly with the sodium humate content, while the adsorption constant b decreases linearly with the sodium humate content. The initial elution rate Δp of similar materials increases at first and then decreases with the increase of sodium humate content.

In this paper, we propose a dynamic key technique based on Cellular Neural Network (CNN) for security improvement in the orthogonal frequency division multiplexing passive optical network (OFDM-PON). To enhance the encryption scheme security, a six-dimensional CNN hyperchaotic system is employed to encrypt the data. And, the keys are divided into the dynamic and static. The dynamic key is randomly extracted from a key set by incorporating the random feature of the input data. Then, the chaotic sequence generated by the dynamic key is served as the synchronous sequence for encryption. Moreover, the chaotic sequences generated by the static keys are used to resist the chosen-plaintext attacks (CPAs) and scramble the phase of QAM symbols on the frequency domain. With these processing techniques, the multi-fold data encryption can create a key space of ∼10315 to protect against the exhaustive trial. The transmission of 10-Gb/s encrypted 16-QAM-based OFDM signal is demonstrated over 20-km single mode fiber (SMF) by experiment. The results show that our proposed scheme can provide excellent confidentiality of data transmission against the CPAs and brute-force attack.

Abstract With the increase of mining depth, the occurrence mechanism of coal and gas outburst becomes more complex, and stress‐dominated outburst disaster has become one of the major safety problems in deep coal mines. Therefore, stress relief of coal seam has become an urgent technical demand for outburst prevention method in deep mines. In this study, based on zonal disintegration characteristics of deep surrounding rock, a regional strip outburst prevention method, called strip stress relief combined with gas extraction through stress‐relief floor roadway, was proposed, and relevant in‐site investigations were carried out in the Qujiang coal mine in China. Our results show that the zonal disintegration phenomenon occurs in the high‐stress surrounding rock at great depths, and induces the stress‐relief effect on the upper coal seam, in which the permeability and extraction radius of boreholes are increased greatly. The results of deformation and failure of surrounding rock of floor roadway show that from the surface to deep regions, fractured and nonfractured zones were alternatively distributed in the surrounding rock of deep floor roadways, the damage degree of surrounding rock was gradually weakened, and the width of fractured area was gradually reduced. The displacement of surrounding rock also presented the characteristics of alternative distribution of wave peak and trough. Moreover, the deformation and failure of surrounding rock presented a time‐dependent rheological behavior. In the stress‐relief zone, the coal seam permeability was enhanced significantly, with the maximum value being 43 times larger than that of the original coal seam. The effective gas extraction radius of the borehole was improved by 15%‐45%. During the driving period of coal roadways, the outburst risk prediction indexes K1 and S of the working face were lower than the critical value, and the driving speed of the coal roadway improved from 40 m per month to 100 m per month. This indicates that the proposed strip regional outburst prevention method can simultaneously reduce the ground stress and the gas content, and can effectively eliminate the outburst risk of coal roadway in deep mines.

Abstract Based on the analysis of shear movement characteristics of overlying strata under mining effect, a quantitative calculation model for shear displacement in the along‐strike and down‐dip directions of the overlying strata is established. The shear displacement at any point on the interface of overlying strata in composite rock beam under slice mining is analyzed. The evolution law of shear displacement and deformation of the overlying strata with the advancement of working face was inverted by physical simulation test. The results show that the shear movement of the overlying strata is characterized by a repeated pattern of "increase → decrease →increase → decrease.” The shear displacement of the overlying strata increases gradually after slice mining. The shear displacement of the overlying strata is in the shape of “W” after the lower seam mining, and the maximum shear displacement of the overlying strata by the lower seam mining is 1.67 times of that of the overlying strata after the upper seam mining. Field test of shear movement of the overlying strata was conducted on the panel 4308 of Chengzhuang coal mine. The results show that the shear displacement of the overlying strata above the coal seam increases with the burial depth. And the shear displacement of the overlying strata movement after mining has "time‐delay" effect. The larger the depth of the measuring point is, the larger value of the along‐strike shear displacement is. The breakage of the key strata of the overlying strata will cause the shear displacement of the overlying strata to increase rapidly. And there is a demarcation depth (127.98 m) for the shear displacement of the overlying strata. The shear movement of the overlying strata above the dividing point is not obvious, while the shear movement of the overlying strata below the dividing point is in the shape of "S" (amplitude of 50 mm). When the working face advanced beyond the test well, the overlying strata would experience multiple shear movement. When the working face advanced 34‐100 m ahead of the surface test well, the overlying strata experienced the most severe shear displacement. When the working face advanced to 74 m away from the surface test well, the shear displacement of the overlying strata between 10# (depth of 192.01 m) and 16# (depth of 300.07 m) is larger than that at the upper position, and down‐dip shear displacement is the most severe(about 315 mm). The shear displacement of the overlying strata is coincident with the along‐strike shear displacement, and the down‐dip shear displacement is smaller than the along‐strike shear displacement. This research provides theoretical guidance for the design of shale gas or coalbed methane surface wells and coal mine shaft under slice mining.

Abstract The lithium-sulfur battery is the subject of much recent attention due to the high theoretical energy density, but practical applications are challenged by fast decay owing to polysulfide shuttle and electrode architecture degradation. A comprehensive study of the sulfur host microstructure design and the cell architecture construction based on the MXene phase (Ti3C2T x nanosheets) is performed, aiming at realize stable cycling performance of Li–S battery with high sulfur areal loading. The interwoven KB@Ti3C2T x composite formed by self-assembly of MXene and Ktejen black, not only provides superior conductivity and maintains the electrode integrality bearing the volume expansion/shrinkage when used as the sulfur host, but also functions as an interlayer on separator to further retard the polysulfide cross-diffusion that possibly escaped from the cathode. The KB@Ti3C2T x interlayer is only 0.28 mg cm−2 in areal loading and 3 μm in thickness, which accounts a little contribution to the thick sulfur electrode; thus, the impacts on the energy density is minimal. By coupling the robust KB@Ti3C2T x cathode and the effective KB@Ti3C2T x modified separator, a stable Li–S battery with high sulfur areal loading (5.6 mg cm−2) and high areal capacity (6.4 mAh cm−2) at relatively lean electrolyte is achieved.

Abstract During the multiseam mining process, the overlying strata were damaged due to different mining disturbances, where a large number of fractures were produced which were the main seepage paths of gas and water, easy to cause gas or water inrush accidents. Thus, it is necessary to explore the development characteristics of the fractured zone in the overlying strata from multiseam mining. In this paper, laboratory triaxial compression tests were firstly conducted on the rock specimens subjected to different mining disturbances. In these tests, the specimen was loaded to different stress before a regular test to simulate the different damage effects on the rock strata caused by different mining disturbances. And the corresponding values of m and s could be obtained through a calculation based on the test results. Subsequently, the numerical simulation was conducted to simulate the field situation, in which the m and s values were used in the numerical model combined with the Hoek‐Brown–modified criterion, and the results show that the overburden failure height was increased with the mining disturbances from 48 to 120 m, and then, the effects of mining height and interval thickness on the development height of fracture zone were studied by numerical simulation. Finally, the leakage of roof drilling at different stages was tested and calculated in the field. The results showed that the loss of leakage drilling can directly reflect the development degree of roof cracks, and the detection results were close to the development height of the numerical simulation fracture zone. It is verified that the simulation method used in this paper is feasible and can be used as a reference for similar research.

We report GaN high-electron-mobility transistors (HEMTs) with a thick (7.7 µm) GaN buffer on a Czochralski low resistivity Si (LRS) substrate. The GaN HEMTs exhibit high performance for both radio-frequency (RF) amplification and power conversion. The thick GaN buffer was grown by means of vacancy engineering, delivering a low dislocation density of ∼1.6 × 108 cm−2, contributing to suppressed RF signal coupling to the lossy Si substrate and a high vertical voltage blocking capability. For RF performance, GaN HEMTs with a 650 nm gate exhibit an fT/fMAX value of 25.1/32.3 GHz and a maximum output power POUT of 2.2 W/mm at 4 GHz with a drain voltage VDS of 20 V, which is comparable with the performance of RF GaN HEMTs on a high-resistivity silicon substrate without the existence of the field plate. For power performance, the vertical breakdown voltage of the wafer is 1160 V, and the three-terminal lateral breakdown voltage is 885 V in a GaN HEMT with a gate-to-drain distance of 8 µm. The thick GaN layer on the LRS substrate scheme thus provides a compelling platform for monolithic integration of high-performance RF devices and high-voltage power devices.

ABSTRACT The objective of this research was to evaluate the correlation between inhibitory zones and MIC when testing ceftazidime-avibactam using disk diffusion, Etest, and broth microdilution method established by the Clinical and Laboratory Standards Institute (CLSI). Four-hundred and 58 isolates of Enterobacterales isolated from 54 medical centers from the China Antimicrobial Surveillance Network (CHINET) in 2016 to 2020 were collected. Antimicrobial susceptibility testing using broth microdilution, Etest, and disk diffusion were performed according to the CLSI. Of the 458 Enterobacterales, 17.2% (79/458) and 82.8%(379/458) were resistant or susceptible to ceftazidime-avibactam by broth microdilution, respectively. Compared with the broth microdilution method, the categorical agreement (CA) and essential agreement (EA) of the Etest were 99.6% (456/458) and 94.8% (434/458), respectively; the major error (ME) and very major error (VME) were both 0.2% (1/458). For disk diffusion, the CA and VME were 99.8% (457/458) and 0.2% (1/458), respectively. For Escherichia coli, the CA and EA of the Etest were 100% and 97.1% (135/139), respectively. The CA of the disk diffusion was 100%. For Klebsiella pneumoniae, the CA and EA of the Etest were 99.3% (288/290) and 93.4% (271/290), respectively, the ME and VME were both 0.3% (1/290). The CA and VME of disk diffusion were 99.7% (289/290) and 0.3% (1/290), respectively. For other Enterobacterales, the CA and EA of the Etest were 100% and 96.6% (28/29), respectively. The CA of the disk diffusion was 100%. Ceftazidime-avibactam disk diffusion (30/20-μg disks) and Etest demonstrated good performance for ceftazidime-avibactam susceptibility testing against Enterobacterales clinical isolates. IMPORTANCE Multidrug-resistant Gram-negative bacteria, especially for extended-spectrum β-lactamases-producing and carbapenemase-producing Enterobacterales, are disseminating rapidly around the world. Treatment options for these infections are limited, which prompt the development of novel or combinational therapies to combat the infections caused by multidrug-resistant pathogens. The newly available β-lactam combination agent ceftazidime-avibactam has been demonstrated good in vitro and in vivo activity against ESBL, AmpC, KPC-2, or OXA-48-like-producing isolates and has shown promise in treating carbapenem-resistant Enterobacterales infections. Concerningly, there are few available automated systems for ceftazidime-avibactam susceptibility testing, and the broth microdilution method is hard to perform in most routine laboratories. Therefore, we urgently need an economical and practical method for the accurate detection of ceftazidime-avibactam activity against Gram-negative bacilli. Here, we evaluate the performance of the disk diffusion and Etest compared with the reference broth microdilution method against Enterobacterales clinical strains.

The bearing capacity of the vertical underpinning structure system is the key index in the design of top-down construction for adding a basement layer under existing buildings. The influence of the lateral restraint is the most significant under the dynamic construction excavation. For the problem of the bearing capacity of the existing engineering pile group under the top-down construction, the linear eigenvalue stability method was used first to study the influence of the lateral restraints such as the horizontal resistance of soil, the diameter of piles body, and the bending rigidity of the temporary steel bracing on its bearing capacity. The corresponding critical stability load and the effective length coefficient were then obtained. Then, based on the nonlinear extreme point stability method with the initial geometrical imperfection, the amplification range for the effective length coefficient was studied. Finally, based on the current Chinese Code Formula (JGJ 94-2008) and considering the influence of the compression buckling effect of the high cap pile, the present solution of the bearing capacity for the pile body was obtained and compared with the code solution. It turns out that the nonlinear bearing capacity of existing engineering piles group with initial imperfection is smaller than the critical stability load of the linear eigenvalue and increases with the increase of the imperfection amplitude, and the amplification range of the effective length coefficient is 1.10∼1.20. The present solution of the bearing capacity with the compression buckling effect is 1.10∼1.30 times of the code solution, which shows that the code solution is partial to safety, and the residual bearing can be properly considered in the design.

We report on a highly sensitive gallium nitride (GaN) micro-electromechanical (MEMS) resonator with a record quality factor (Q) exceeding 105 at the high resonant frequency (f) of 911 kHz by the strain engineering for the GaN-on-Si structure. The f of the double-clamped GaN beam bridge is increased from 139 to 911 kHz when the tensile stress is increased to 640 MPa. Although it is usually regarded that the energy dissipation increases with increasing resonant frequency, an ultra-high Q-factor which is more than two orders of magnitude higher than those of the other reported GaN-based MEMS is obtained. The high Q-factor results from the large tensile stress which can be intentionally introduced and engineered in the GaN epitaxial layer by utilizing the lattice mismatch between GaN and Si, leading to the stored elastic energy and drastically decreasing the energy dissipation. The developed GaN MEMS is further demonstrated as a highly sensitive mass sensor with a resolution of 10−12 g/s through detecting the microdroplet evaporation process. This work provides an avenue to improve the f × Q product of the MEMS through an internally strained structure.

Abstract Nowadays, the water jet technique has been more frequently used for coal bed methane stimulation. As the ultimate component of the water jet system, the nozzle has important influence on the rock breaking ability of water jet. To optimize the nozzle, a simplified model for impinging water jet was established. The effects of geometric structure (cylindrical, conical, and conical‐straight) and parameters (outlet diameter d, conical angle α, and length L) on the flow field of the impinging water jet are simulated through computational fluid dynamics software Fluent14.0. Besides, the effects of inlet pressure (Pin) and target distances (S) on the jet dynamics are also discussed based on the simulation results. The results show that the jet dynamic parameters including dynamic pressure, velocity, and impinging pressure vary with different nozzles. The jet dynamic parameters linearly increase with the inlet pressure, while they first increase then decrease with the increase in target distance. Additionally, the optimal nozzle designed based on the numerical simulation was used in the field test, and the results indicate that this technique can effectively improve the gas drainage efficiency.

Abstract When faced with multi‐seam mining, some coal pillars are left to support the overlying strata when mining the lower seam, where stress concentration usually occurs. When the working face in the lower seam advances to the area influenced by these coal pillars, high ground pressure behavior occurs. Furthermore, the instability of coal pillars under the participation of the roof may induce rock burst, which threaten the safe production of coal mine. To study the roof strata movement and coal pillar instability in multi‐seam mining, a coal mine in Datong was taken as an example. Firstly, the bursting liability of coal and rock stratum was tested. The test results show that the 7#, 8#, and 11# coal seams in the mining area all have strong bursting liability. And the roof was dominated by siltstone and firestone, which also have strong bursting liability. Then, based on the geological conditions of the coal mine, we investigated roof movement and instability of the coal pillar during multi‐seam mining through physical simulation. The simulation results indicate that multi‐seam mining aggravates the roof damage, which leads to the increase in the fracture range of overlying strata, and that the failure height increases from 46 to 121 m. In addition, the detailed distribution of stress on residual coal pillars and its influence on the lower working face were studied through numerical simulation. The results show that, when the working face 8707 of the 8# coal seam advances to a horizontal distance of 20 m from the coal pillar, it enters the influence zone. As the working face advances beneath the coal pillar, the stress reached to 24 MPa. Moreover, when the working face passes by the coal pillar, the coal pillar is cutoff, thus affecting the working face.

Abstract Understanding the stress‐cracks‐permeability evolution law inside coal body under cyclic loading is significant to optimize the gas extraction technology and gas disasters prevention technology. In order to explore the influence of mining cyclic stress on the mechanical behavior and permeability variation of gas‐bearing seams, the experiments on permeability evolution, deformation law, and acoustic emission (AE) characteristics of coal samples under cyclic loading with different loading stress level and different loading frequency were carried out. These results indicate that the higher loading stress level, the shorter the fatigue life of coal sample. With the increase of the loading stress level, the change rate of permeability became higher and the relation curves between permeability and loading cycles developed from “U” to “V,” which can be defined and divided into three stages, for example, decrease stage, stable stage, and increase stage. And the permeability in the decrease stage can be modeled as a power function of the loading cycles, while the permeability in the increase stage can be modeled as an exponential function of the loading cycles. Besides, the loading stress level has a significant on the permeability, while the loading frequency has little impact on the permeability evolution. In the process of coal deformation under cyclic loading, the strain development of strain coal samples was in the shape of inverted “S,” while the variation of the peak values of corresponding AE ring counts presented “U” type. In addition, there was a good correlation between the permeability and the AE parameters of coal samples, which provide a new sight into the dynamic variation process of the stress‐cracks‐permeability evolution inside coal body under cyclic loading.

Since monolithic movement is considered a promising technology to relocate historical buildings, corresponding real-time monitoring is of great interest due to the buildings’ age and poor structural integrity. However, the related paperwork and practical applications are still limited. This paper describes a wireless sensor network (WSN)-based strategy as a non-invasive approach to monitor heritage curtilage during monolithic movement. The collected data show that the inclination of the curtilage is almost negligible. With the aid of finite element simulation, it was found that the crack displacement curves changed from −0.02 to 0.07 mm, which is affected by moving direction while the value is not enough to cause structural cracks. The deformation of the steel underpinning beam, which is used to reinforce masonry walls and wooden pillars, is obviously related to the stiffness in different directions. Additionally, the strain variations of the steel chassis, which bear the vertical loads from wooden pillars and masonry walls, are less than 0.04%. This indicates that they are kept within the elastic range during monolithic movement. This work has proved that the WSN-based approach has the potential to be applied as an effective route in real-time monitoring of the monolithic movement of an historic building.

Particle size and shape distribution can be measured in great detail by dynamic image analysis (DIA). The narrow dispersion of repeated experiment results indicates that the particle size distribution can be obtained with high reliability. Particle size distribution can be better fitted to Rosin-Rammler equation than Gaudin-Schuhmann distribution and the lognormal distribution. The spread parameter (m) and the location parameters (d0) of the Rosin-Rammler equation can be calculated precisely. We analyzed the similarities and differences between the different particle shape distributions. The distributions of form factor and circularity are right-skewed distributions, while the distributions of ellipse ratio, irregularity, and aspect ratio obey a normal distribution. By studying the relation between particle size and shape, we find a linear relationship between the ellipse ratio and the Legendre ellipse diameter on the logarithmic scale.

Coal and gas outburst is still a major safety problem in the process of coal production in China. Correctly understanding of the migration law of outburst high gas and pulverized coal is an important basis for accurately predicting the occurrence time and possible scope of outburst. To reveal the airflow disturbance characteristics and coal-gas flow rule in coal and gas outburst process, outburst coal-gas migration simulations under different gas pressures were conducted using a self-developed visual outburst dynamic effect test device. The results showed that coal-gas flow state at the outburst port is divided into subcritical flow, critical flow, and supercritical flow state. The pulverized coal-gas flow migration in the roadway space can be divided into coal gas two-phase flow area, air compression area, and undisturbed area. Under the experimental conditions, the maximum propagation velocities of wave are 342.22~359.21 m/s, and the coal gas two-phase flow is far less than the propagation velocities of outburst wave, just 3.68~33.33 m/s. When the outburst energy is large, multiple compression waves can superimpose to form shock waves. The peak value of the wave does not necessarily appear in the first boosting range. The presence of pulverized coal leads to a faster attenuation of shock wave, but it makes a greater dynamic destructive force at the same speed.

Abstract Epitaxial growth of III‐nitrides on 2D materials enables the realization of flexible optoelectronic devices for next‐generation wearable applications. Unfortunately, it is difficult to obtain high‐quality III‐nitride epilayers on 2D materials such as hexagonal BN (h‐BN) due to different atom hybridizations. Here, the epitaxy of single‐crystalline GaN films on the chemically activated h‐BN/Al2O3 substrates is reported, paying attention to interface atomic configuration. It is found that chemical‐activated h‐BN provides BON and NO bonds, where the latter ones act as effective artificial dangling bonds for following GaN nucleation, leading to Ga‐polar GaN films with a flat surface. The h‐BN is also found to be effective in modifying the compressive strain in GaN film and thus improves indium incorporation during the growth of InGaN quantum wells, resulting in the achievement of pure green light‐emitting diodes. This work provides an effective way for III‐nitrides epitaxy on h‐BN and a possible route to overcome the epitaxial bottleneck of high indium content III‐nitride light‐emitting devices.

A floating GaN micro-ring is fabricated by standard semiconductor technology. Under pump power conditions, ultraviolet lasing with a quality factor of 3600 is obtained. Resonant mode analysis indicates that the lasing spectra contain two types of whispering gallery modes and one type of Fabry–Perót mode. With the increase in pumping power, the state filling induced Burstein–Moss effect is observed and understood through synchronous measurement of photoluminescence and time resolution photoluminescence spectra.

Grapholita molesta, the oriental fruit moth, is a serious global pest of many Rosaceae fruit trees. Gut microorganisms play important roles in host nutrition, digestion, detoxification, and resistance to pathogens. However, there are few studies on the microbiota of G. molesta, particularly during metamorphosis. Here, the diversity of gut microbiota across the holometabolous life cycle of G. molesta was investigated comprehensively by Illumina high-throughput sequencing technology. The results showed that the microbiota associated with eggs had a high number of operational taxonomic units (OTUs). OTU and species richness in early-instar larvae (first and second instars) were significantly higher than those in late-instar larvae (third to fifth instars). Species richness increased again in male pupae and adults, apparently during the process of metamorphosis, compared to late-instar larvae. Proteobacteria and Firmicutes were the dominant phyla in the gut and underwent notable changes during metamorphosis. At the genus level, gut microbial community shifts from Gluconobacter and Pantoea in early-instar larvae to Enterococcus and Enterobacter in late-instar larvae and to Serratia in pupae were apparent, in concert with host developmental changes. Principal coordinate analysis (PCoA) and linear discriminant analysis effect size (LEfSe) analyses confirmed the differences in the structure of gut microbiota across different developmental stages. In addition, sex-dependent bacterial community differences were observed. Microbial interaction network analysis showed different correlations among intestinal microbes at each developmental stage of G. molesta, which may result from the different abundance and diversity of gut microbiota at different life stages. Phylogenetic Investigation of Communities by Reconstruction of Unobserved States (PICRUSt) analysis indicated that most functional prediction categories of gut microbiota were related to membrane transport, carbohydrate and amino acid metabolism, and DNA replication and repair. Bacteria isolated by conventional culture-dependent methods belonged to Proteobacteria, Firmicutes, and Actinobacteria, which was consistent with high-throughput sequencing results. In conclusion, exploration of gut bacterial community composition in the gut of G. molesta should shed light into deeper understanding about the intricate associations between microbiota and host and might provide clues to the development of novel pest management strategies against fruit borers.

In this paper, we first experimentally demonstrate a novel cellular neural network (CNN)-based physical layer encryption scheme to achieve the capability of chosen-plaintext attacks (CPAs) resistance and time synchronization simultaneously in orthogonal frequency division multiplexing passive optical network (OFDM-PON). By utilizing the hyperchaotic phenomena within a certain parameter range characteristics of CNN, a four-dimensional (4-D) CNN-based system is constructed to strengthen the security of data transmission. And, according to CNN, the chaotic Feistel transform is executed after extracting the indexes of QAM data, in which completely dynamic encrypted data can be achieved for the CPAs resistance. Moreover, a chaotic training sequence generated by CNN used as timing sequence is added to the transmitted OFDM signals to obtain time synchronization and further increasing the confidentiality of the encryption system. A verified experimental system with 10-Gb/s 16-QAM encrypted OFDM signals through 20-km single-mode fiber (SMF) transmission is conducted. And, the results show that the Feistel and CNN-based physical-layer encryption scheme can generate completely dynamic ciphertexts for the CPAs resistance and accurately realize the time synchronization, and without apparent receiver sensitivity deterioration (~0.3dB) is introduced in comparison with other against CPAs schemes.

We propose a chaotic discrete Hartley transform (DHT) to enhance the physicallayer security and simultaneously improve the transmission performance of optical orthogonal frequency division multiplexing (OFDM) in passive optical network. The theoretical analysis and numerical simulation show that the chaotic DHT precoding matrix after independent row/column permutations can also effectively reduce the peak-to-average power ratio (PAPR) of OFDM signals, which can be generated for OFDM data encryption using digital chaos. The multifold data encryption provides a huge key space of ~10178 to ensure the physical-layer confidentiality. An encrypted data transmission of 8.9 Gb/s 16-QAM optical OFDM signals is successfully demonstrated over 20 km standard single-mode fiber. Due to the effective reduction in PAPR by the chaotic DHT precoding matrix, the receiver sensitivity is improved by ~1.4 dB (BER@10-3). Moreover, the proposed scheme has low computational complexity, which also provides high spectral efficiency since no additional sideband information is required.

This paper proposes and experimentally demonstrates a physical-layer data encryption scheme using multi-fold chaotic mapping of quadrature amplitude modulation (QAM) symbols in orthogonal frequency-division-multiplexed passive optical network (OFDM-PON). Dynamic radius and phase offsets are added in the standard QAM during QAM mapping on constellation using digital chaos. Due to the dynamic chaotic radius and phase offsets, the QAM symbols are mapped over the entire constellation plane, and thus the random, flexible QAM mapping is reconstructed to provide high-level security during data transmission. Since the chaotic offsets along with the data permutations are independently predetermined by a hyper digital chaos, the multi-fold data encryption creates an overall key space of ~10340 to enhance the physical-layer security. Successful transmission experiment of 9.4-Gb/s, 16-QAM encrypted OFDM data is demonstrated over a 22-km standard single-mode fiber in OFDM-PON. Moreover, with the use of dynamic mapping of QAM symbols, the transmission performance is not significantly degraded after implementing the proposed multi-fold secure data encryption.

In this paper, we propose a key space enhanced chaos-based encryption scheme with no requirement of redundant sideband information in an orthogonal frequency division multiplexing passive optical network (OFDM-PON). For the first time, a simple 1-D chaotic logistic map is employed to scramble the chaotic subcarrier allocation both in time/frequency domain and logical operation, which provides a huge key space to enhance the physical layer confidentiality. Due to the dynamic chaotic permutations, the largest key space is achieved in comparison with the reported encryption schemes in OFDM-PON. In addition, a ~10-Gb/s secure transmission with encrypted OFDM data is experimentally demonstrated over 25-km standard single-mode fiber. The proposed encryption scheme demonstrates the excellent security of data transmission in OFDM-PON and the robustness against exhaustive attacks.

With mining depths increasing, coal and gas outburst disasters are becoming more and more serious and complicated, which directly restricts the production efficiency of coal mines. In order to study the rules of energy dissipation during the occurrence of a coal and gas outburst based on the occurrence mechanisms, a simulation experiment of a coal and gas outburst with a ground stress of 16 MPa and a gas pressure of 0.5 MPa was carried out using a self-developed large-scale coal and gas outburst simulation experimental system. A quantitative analysis was given based on the energy model. The results showed the following: (1) In the process of the coal and gas outburst, the main energy source originated from the elastic potential energy of the coal body and the gas internal energy. The main energy loss was used for coal crushing and throwing. (2) The outburst coal sample in this experiment had a mass of 18.094 kg, and the relative outburst intensity was 1.21%. Additionally, the farthest throwing distance of the outburst coal samples was 3.3 m away from the outburst hole wall. The distribution of the outburst coal sample decreased along the roadway, and the proportion of the coal sample grain size in each area first decreased and then increased with the decrease of the grain size. The coal samples with a grain size less than 0.2 mm after the outburst accounted for 6.34% of the mass of the total coal samples. (3) The elastic potential energy of the coal body accounted for 0.34% of the total outburst energy, while the gas internal energy accounted for 99.66%. It was verified that gas internal energy was the key energy source for the coal and gas outburst, and this internal energy was two orders of magnitude more than the elastic potential energy, playing a leading role in the outburst process. After the outburst initiation, most of the energy was consumed in coal crushing, which was in the same order of magnitude as the gas internal energy. Moreover, the energy losses due to friction, vibration, and sound during the outburst process comprised no more than 10% of the total energy. The research results can provide certain guidance for clarifying the mechanism of a coal and gas outburst and the quantitative analysis of outburst energy.

With mining technology and mechanization degree being improving, fully mechanized caving mining technology (FCM) has become a main method for thick coal seam extraction in China. However, roof-coal caving characteristics in turn restrict its recovery efficiency, especially for the coal seam with complicated structure (CCS), that is, the coal seam comprises hard or soft coal and gangue. In order to explore the key factors influencing the roof-coal caving and recovery characteristics, related research work has been conducted as follows: firstly, a mechanical model of CCS has been established, which indicates the strength of the coal and gangue will directly affect the roof-coal recovery. Meanwhile, based on the geological settings of Qinyuan coal mine, numerical simulation on roof-coal caving law under different thicknesses of hard or soft coal and gangue has been performed using UDEC software. The results show that the maximum principal stress will increase with the increase of mining depth, making the roof-coal to break easily. Furthermore, the range of the plastic zone of the top coal and the damage degree of the top coal increase with the increase of mining depth. Physical modeling results show that when an extraction-caving ratio is 1, the number of times the coal arch forms is 0.43 at every caving, up to a maximum of 3; the number of times coal arch forms with an extraction-caving ratio of 2 is 4.65 times larger than that with an extraction-caving ratio of 1. The probability of coal arch formation with an extraction-caving ratio of 3 is minimal, about 0.4, which is due to that the arch span is large and the curvature is small, so it is difficult to form a stable arch structure. According to the mechanical characteristics of roof-coal in Qinyuan coal mine, deep-hole blasting technique has been used to reduce the fragments of roof-coal crushed. The results show that this technique can effectively improve the recovery of roof-coal.

This paper proposes and demonstrates a physical layer security-enhanced transmission scheme for discrete Fourier transform spread orthogonal frequency-division multiplexing (DFT-S-OFDM) signals in a passive optical network. During the DFT-S-OFDM transmission, the reconfigurable DFT matrix, the subcarrier allocation, and the training sequence for OFDM symbol synchronization are well encrypted by digital chaotic sequences generated via a 4-D hyperdigital chaos, which provides a huge key space of ~1045. Secure transmission of 13.3-Gb/s encrypted DFT-S-OFDM signals is demonstrated over a 20-km standard single-mode fiber, which proves the excellent confidentiality of the proposed secure DFT-S-OFDM transmission. Moreover, the receiver sensitivity is improved ~2 dB (BER@10-3), which is due to the effective reduction of peak-to-average power ratio via DFT precoding. In addition, this scheme has the advantages of low computational complexity and has no requirement of redundant sideband information.

The role of low-resistivity substrate on vertical leakage current (VLC) of AlGaN/GaN-on-Si epitaxial layers has been investigated. AlGaN/GaN high-electron-mobility transistors (HEMTs) grown on both p-type and n-type Si substrates with low resistivity are applied to analyze the vertical leakage mechanisms. The activation energy (Ea) for p-type case is higher than that for n-type at 0−600 V obtained by temperature-dependent current-voltage measurements. An additional depletion region in the region of 0−400 V forms at the AlN/p-Si interface but not for AlN/n-Si. That depletion region leads to a decrease of electron injection and hence effectively reduces the VLC. While in the region of 400−600 V, the electron injection from p-Si substrate increases quickly compared to n-Si substrate, due to the occurrence of impact ionization in the p-Si substrate depletion region. The comparative results indicate that the doping type of low-resistivity substrate plays a key role for VLC.

It is a fact that surface electron accumulation layer with sheet electron density in the magnitude of ~1013 cm−2 on InN, either as-grown or Mg-doped, makes InN an excellent candidate for sensing application. In this paper, the response of hydrogen sensors based on Mg-doped InN films (InN:Mg) grown by molecular beam epitaxy has been investigated. The sensor exhibits a resistance variation ratio of 16.8% with response/recovery times of less than 2 min under exposure to 2000 ppm H2/air at 125 °C, which is 60% higher in the magnitude of response than the one based on the as-grown InN film. Hall-effect measurement shows that the InN:Mg with suitable Mg doping level exhibits larger sheet resistance, which accords with buried p-type conduction in the InN bulk. This work shows the advantage of InN:Mg and signifies its potential for sensing application.

We fabricate 2.6 μm InGaAs photodetectors by MBE technology and study its dark current mechanisms. Deep-level transient spectroscopy (DLTS) demonstrates a deep-level trap located at Ec - 0.25 eV in the absorption layer. Using the trap parameters, a dark current model is constructed and the device simulation generates the dark current characteristic which agrees well with the experimental data. The model suggests that the dark current at low reverse voltage is dominated by the Shockley-Read-Hall (SRH) and trap-assisted tunneling (TAT). Furthermore, it predicts some basic rules for suppressing the dark current in 2.6 μm InGaAs detectors.