Diffraction Characteristics of Small Fault ahead of tunnel face in coal roadway

Small fault ahead of the tunnel face in coal roadway is the important hidden hazard factor of coal and gas outburst accidents. The study of small fault prediction has important practical significance, which is the urgent demand of coal mine safety production. The diffraction of breakpoint can be used to identify the fault. However, unlike surface seismic exploration, the diffraction is with approximately horizontal incidence when the advanced detection is carried out in the roadway. The common advanced detection system is mainly as the reference of traffic tunnel, without considering the influence of low-velocity coal seam. Considering the influence of an acoustic wave of the roadway cavity and channel wave of the coal seam, the advanced detection model of small fault ahead of tunnel face is established. Diffraction advanced observation system in which sources located in front of tunnel face is constructed, and the numerical calculation of the high-order staggered-grid finite difference is carried out. The simulation results show that: Compared with the data collected by reflection observation system, in seismic records acquired by diffraction observation system, the suppression effect of acoustic wave is appeared. The diffracted P-wave of the breakpoint of component X is clear with strong energy and short-wave group. Multiple diffractions of the breakpoint are not found, but the multiple diffraction of tunnel face endpoint is obvious. The difference between breakpoint diffraction and multiple diffractions of the endpoint is clear, and diffracted P-wave of the breakpoint is easy to identify. The multiple reflected channel wave between the fault and the tunnel face is very obvious, and the reflected channel wave of small fault is so hard to identify. Migration results show that the imaging resolution of diffracted P-wave of small fault is higher than the reflected channel wave, and breakpoint location of imaging is consistent with the actual model.El frente de una falla pequeña sobre un manto de carbón en el socavón de un túnel es un factor importante no visible debido a los accidentes por explosión en minas de gas y carbón. El estudio de la predicción de falla pequeña tiene un importante sentido práctico: la demanda urgente de seguridad en la producción carbonífera. El punto de quiebre de la difracción puede utilizarse para identificar la falla. Sin embargo, al contrario que la exploración sísmica superficial, la difracción se acerca a la prevalencia horizontal cuando se realiza la detección avanzada en el socavón. El sistema común de detección avanzada se usa principalmente para referenciar el tráfico del túnel, sin considerar la influencia de la baja velocidad en la veta de carbón. Al valorar la respuesta de la onda acústica en la cavidad del socavón y la onda de canal de la veta de carbón se establece el modelo de detección avanzada de pequeña falla para el socavón del túnel. Se construyó el sistema de observación avanzada de difracción en el cual las fuentes se localizan en frente de la cara del túnel y se realizó el cálculo de diferencia finita en una red escalonada de orden alto. Los resultados del modelo muestran que a diferencia de la información recolectada con el sistema de observación de reflexión, en los registros sísmicos adquiridos con el sistema de observación de difracción se puede ver el efecto de supresión de la onda acústica. El punto de quiebre de la onda P difractada para el componente X es claro, con energía fuerte y en el grupo de onda corta. No se encontró el punto de quiebre para difracciones múltiples pero es evidente la difracción múltiple para el punto final de la cara del túnel. Es clara la diferencia entre el punto de ruptura de la difracción y las difracciones múltiples del punto final, mientras el punto de ruptura de la onda P difractada es fácil de identificar. Los resultados de migración muestran que la resolución de imágenes de la onda P difractada de falla pequeña es mayor que la onda de canal reflejada y la ubicación del punto de quiebre de la imagen es consistente con el modelo actual

Development of a miner personal dust continuous monitor based on the principle of oscillating balance

An accurate measurement of coal mine dust concentration is an important prerequisite for effective dust control. Traditional offline filter sampling gravimetric methods need a long measuring period and cumbersome operations, while direct-reading light absorption/scattering measurement methods are susceptible to environmental conditions and dust properties. To overcome the above-mentioned problems, a miner personal dust continuous monitor based on the principle of oscillating balance was developed. The finite element simulation method was used to explore the effects of different characteristics of the oscillating element on the response frequency and mass sensitivity of the oscillation system. The optimal gradient optimization algorithm was used to design the material and shape of the oscillating element. An oscillating tube with highly stable elastic modulus was fabricated. Its frequency temperature coefficient is 3×10−5 Hz/℃, which is minimally affected by temperature, ensuring the accurate measurement of the oscillation frequency when the external ambient temperature conditions vary. An oscillating balance mass sensor was developed. A digital self-excited oscillation closed-loop control circuit was designed to realize the automatic control of resonant frequency and real-time output. The oscillating balance mass sensor had a mass sensitivity of approximately 1 mg/Hz and a mass detection limit of 2 μg. Finally, a miner personal dust continuous monitor based on the principle of oscillating balance was developed for the first time in China by integrating the respiratory dust sampler, the total dust sampler, the heating tube, the mass sensor, the air pump, the flow rate controller, and the temperature, humidity and pressure sensors. The detection limit of this instrument is 0.035 mg/m3 in terms of the average dust mass concentration. The instrument can provide continuous monitoring information, including the real-time total dust or respirable dust concentration and the cumulative occupational exposure concentration of the day. This instrument was applied to dust measurement in an underground coal mine. Its measurement results were compared with those from the instrument using traditional filter sampling gravimetric method, with a relative error of approximately 5%. This instrument has the capability of rapid and accurate measurement of coal mine dust. It has the potential to be an alternative of offline filter sampling weighing methods and direct-reading dust monitors based on optical principles

Determination of six fluoroquinolones in aquatic products by QuEChERS-ultra performance liquid chromatography-tandem mass spectrometry

Objective To establish a method for the determination of norfloxacin, ciprofloxacin, lomefloxacin, enrofloxacin, ofloxacin and pefloxacin in aquatic products by QuEChERS with ultra performance liquid chromatographytandem mass spectrometry (UPLC-MS/MS). Methods Six fluoroquinolones in aquatic products were extracted by 1% formic acid acetonitrile solution, purified by QuEChERS, separated by C18 column (2.1 mm×100 mm, 1.7 μm) using 0.1% formic acid and methanol-acetonitrile (4∶6, V/V) as mobile phases, then identified and quantified by UPLC-MS/MS. Results Norfloxacin, ciprofloxacin, lomefloxacin, enrofloxacin, ofloxacin and pefloxacin had good linear relationships in a certain concentration range with correlation coefficients (r) above 0.999. The limits of detection of six fluoroquinolones were 0.30-0.80 μg/kg, and limits of quantification were 1.0-2.5 μg/kg. The average recoveries of the method were between 86.6% and 120%, and the relative standard deviations were between 0.59% and 7.6%. Conclusion The method was rapid and accurate, and was suitable for rapid screening and analysis of the six fluoroquinolones in aquatic products

Recent Advances and Applications of Semiconductor Photocatalytic Technology

Along with the development of industry and the improvement of people’s living standards, peoples’ demand on resources has greatly increased, causing energy crises and environmental pollution. In recent years, photocatalytic technology has shown great potential as a low-cost, environmentally-friendly, and sustainable technology, and it has become a hot research topic. However, current photocatalytic technology cannot meet industrial requirements. The biggest challenge in the industrialization of photocatalyst technology is the development of an ideal photocatalyst, which should possess four features, including a high photocatalytic efficiency, a large specific surface area, a full utilization of sunlight, and recyclability. In this review, starting from the photocatalytic reaction mechanism and the preparation of the photocatalyst, we review the classification of current photocatalysts and the methods for improving photocatalytic performance; we also further discuss the potential industrial usage of photocatalytic technology. This review also aims to provide basic and comprehensive information on the industrialization of photocatalysis technology

Controlling mass and energy diffusion with metamaterials

Diffusion driven by temperature or concentration gradients is a fundamental mechanism of energy and mass transport, which inherently differs from wave propagation in both physical foundations and application prospects. Compared with conventional schemes, metamaterials provide an unprecedented potential for governing diffusion processes, based on emerging theories like the transformation and the scattering cancellation theory, which enormously expanded the original concepts and suggest innovative metamaterial-based devices. We hereby use the term ``diffusionics'' to generalize these remarkable achievements in various energy (e.g., heat) and mass (e.g., particles and plasmas) diffusion systems. For clarity, we categorize the numerous studies appeared during the last decade by diffusion field (i.e., heat, particles, and plasmas) and discuss them from three different perspectives: the theoretical perspective, to detail how the transformation principle is applied to each diffusion field; the application perspective, to introduce various intriguing metamaterial-based devices, such as cloaks and radiative coolers; and the physics perspective, to connect with concepts of recent concern, such as non-Hermitian topology, nonreciprocal transport, and spatiotemporal modulation. We also discuss the possibility of controlling diffusion processes beyond metamaterials. Finally, we point out several future directions for diffusion metamaterial research, including the integration with artificial intelligence and topology concepts.Comment: This review article has been accepted for publication in Rev. Mod. Phy

Wavelet-Based Hydrological Time Series Forecasting

These days wavelet analysis is becoming popular for hydrological time series simulation and forecasting. There are, however, a set of key issues influencing the wavelet-aided data preprocessing and modeling practice that need further discussion. This article discusses four key issues related to wavelet analysis: discrepant use of continuous and discrete wavelet methods, choice of mother wavelet, choice of temporal scale, and uncertainty evaluation in wavelet-aided forecasting. The article concludes with a personal reflection on solving the four issues for improving and supplementing relevant wavelet studies, especially wavelet-based artificial intelligence modeling

Global Freshwater availability below normal conditions and population impact under 1.5°C and 2°C stabilization scenarios

Based on the large ensembles of the half a degree additional warming, prognosis, and projected impacts historical, +1.5 and +2 °C experiments, we quantify changes in the magnitude of water availability (i.e., precipitation minus actual evapotranspiration; a function of monthly precipitation flux, latent heat flux, and surface air temperature) below normal conditions (less than median, e.g., 20th percentile water availability). We found that, relative to the historical experiment, water availability below normal conditions of the +1.5 and +2 °C experiments would decrease in the midlatitudes and the tropics, indicating that hydrological drought is likely to increase in warmer worlds. These cause more (less) people in East Asia, Central Europe, South Asia, and Southeast Asia (West Africa and Alaska/Northwest Canada) to be exposed to water shortage. Stabilizing warming at 1.5 °C instead of 2 °C would limit population impact in most of the regions, less effective in Alaska/Northwest Canada, Southeast Asia, and Amazon. Globally, this reduced population impact is ~117 million people

Scenario set-up and forcing data for impact model evaluation and impact attribution within the third round of the Inter-Sectoral Model Intercomparison Project (ISIMIP3a)

This paper describes the rationale and the protocol of the first component of the third simulation round of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP3a, www.isimip.org) and the associated set of climate-related and direct human forcing data (CRF and DHF, respectively). The observation-based climate-related forcings for the first time include high-resolution observational climate forcings derived by orographic downscaling, monthly to hourly coastal water levels, and wind fields associated with historical tropical cyclones. The DHFs include land use patterns, population densities, information about water and agricultural management, and fishing intensities. The ISIMIP3a impact model simulations driven by these observation-based climate-related and direct human forcings are designed to test to what degree the impact models can explain observed changes in natural and human systems. In a second set of ISIMIP3a experiments the participating impact models are forced by the same DHFs but a counterfactual set of atmospheric forcings and coastal water levels where observed trends have been removed. These experiments are designed to allow for the attribution of observed changes in natural, human and managed systems to climate change, rising CH4 and CO2 concentrations, and sea level rise according to the definition of the Working Group II contribution to the IPCC AR6

WSNs Microseismic Signal Subsection Compression Algorithm Based on Compressed Sensing

For wireless network microseismic monitoring and the problems of low compression ratio and high energy consumption of communication, this paper proposes a segmentation compression algorithm according to the characteristics of the microseismic signals and the compression perception theory (CS) used in the transmission process. The algorithm will be collected as a number of nonzero elements of data segmented basis, by reducing the number of combinations of nonzero elements within the segment to improve the accuracy of signal reconstruction, while taking advantage of the characteristics of compressive sensing theory to achieve a high compression ratio of the signal. Experimental results show that, in the quantum chaos immune clone refactoring (Q-CSDR) algorithm for reconstruction algorithm, under the condition of signal sparse degree higher than 40, to be more than 0.4 of the compression ratio to compress the signal, the mean square error is less than 0.01, prolonging the network life by 2 times