As coal mining is extended from shallow to deep areas along the western coalfield, it is of great significance to study weakly cemented sandstone at different depths for underground mining ...engineering. Sandstones from depths of 101.5, 203.2, 317.3, 406.9, 509.9 and 589.8 m at the Buertai Coal Mine were collected. The characteristic strength, acoustic emission (AE), and energy evolution of sandstone during uniaxial compression tests were analyzed. The results show that the intermediate frequency (125–275 kHz) of shallow rock mainly occurs in the postpeak stage, while deep rock occurs in the prepeak stage. The initiation strength and damage strength of the sandstone at different depths range from 0.23 to 0.50 and 0.63 to 0.84 of peak strength (
σ
c
), respectively, decrease exponentially and are a power function with depth. The precursor strength ranges from 0.88
σ
c
to 0.99
σ
c
, increases with depth before reaching a depth of 300 m, and tends to stabilize after 300 m. The ratio of the initiation strength to the damage strength (
k
) ranges from 0.25 to 0.62 and decreases exponentially with depth. The failure modes of sandstone at different depths are tension-dominated mixed tensile-shear failure. Shear failure mainly occurs at the unstable crack propagation stage. The count of the shear failure bands before the peak strength increases gradually, and increases first and then decreases after the peak strength with burial depth. The cumulative input energy, released elastic energy and dissipated energy increase with depth. The elastic release rate ranges from 0.46 × 10
–3
to 198.57 × 10
–3
J/(cm
3
s) and increases exponentially with depth.
Filling of gangue formed in coal mining is an effective means to realize green mining in coal mine. The key of gangue filling mining is to accurately understand the breaking mechanism and pore ...evolution of gangue under load. Therefore, in this paper, firstly, the yield criterion of granular materials based on radius of curvature and contact stress is built, which concluded that the change of grain size during the process of gangue compression is the main factor affecting the crushing characteristics of gangue. Secondly, the numerical simulation method which can simulate the loading of gangue is put forward, and realize the re-crushing of gangue under compression and the influence of particle shape on the compression and crushing of gangue. Finally, the calculation method of breaking rate based on single particle is given, and the influence of the location of gangue particle on the breaking rate of rock sample is analyzed.
In order to reveal the distribution characteristics and formation mechanism of groundwater salinization in the plain area of the Kashgar River Basin in Xinjiang of China, 398 groups of groundwater ...samples were collected in 2017. Hydrogeochemical methods coupling with stable isotope technology were used for sample analysis. Results showed that groundwater was weakly alkaline in general (pH ranged between 6.68 and 8.52), with total dissolved solids (TDS) ranging from 246.5 to 44,130.4 mg/L. The main groundwater hydrochemical types included SO
4
·Cl, SO
4
and HCO
3
·SO
4
. Along groundwater flow direction, increased TDS and obvious salinization were observed with hydrochemical type change from HCO
3
·SO
4
to SO
4
and to SO
4
·Cl, respectively. Groundwater was mainly recharged by river infiltration in the piedmont. Groundwater salinization was affected by lixiviation, evaporation concentration and cation exchange. Continuous weathering and dissolution of evaporative rock minerals, such as gypsum and halite, were the main factors leading to the continuous salinization of groundwater. Regional deuterium surplus calculation results showed that lixiviation was the main cause of groundwater salinization in recharge areas in the piedmont, and controlled the whole runoff process. Meanwhile, the strongest evaporation concentration mainly occurred in discharge areas of the groundwater flow system. It was concluded that groundwater salinization mainly depended on lixiviation degree.
High temperature (HT) has recently become one of the most important abiotic stresses restricting crop production worldwide. MicroRNAs (miRNAs) are important regulators in plant development and stress ...responses. However, knowledge of miRNAs of maize in response to HT is limited. In this study, we simultaneously adopted miRNA sequencing and transcriptome profiling to analyze the differential expression of miRNAs and mRNAs in maize during exposure to HT stress. Our analysis revealed 61 known miRNAs belonging to 26 miRNA families and 42 novel miRNAs showing significant differential expression, with the majority being downregulated. Meanwhile, the expression of 5450 mRNAs was significantly altered in the same stressed tissues. Differentially expressed transcripts were most significantly associated with response to stress, photosynthesis, biosynthesis of secondary metabolites, and signal transduction pathways. In addition, we discovered 129 miRNA–mRNA pairs that were regulated antagonistically, and further depiction of the targeted mRNAs indicated that several transcription factors, protein kinases, and receptor-like-protein-related transmembrane transport and signaling transduction were profoundly affected. This study has identified potential key regulators of HT-stress response in maize and the subset of genes that are likely to be post-transcriptionally regulated by miRNAs under HT stress.
Vibrations impose negative impacts on the effectiveness and public acceptance of helicopters. Active rotors with trailing-edge flaps have been proved to be an effective way to actively eliminate ...helicopter vibrations. For the existing control algorithm based on offline system identification, the transfer functions of an active rotor under different flight conditions are pre-requisites to implement closed-loop vibration control. In this study, a three-bladed active rotor with improved trailing-edge flaps is designed, and wind-tunnel tests are conducted to identify the transfer functions of this active rotor using frequency sweep and phase sweep methods. The experimental results demonstrate that these transfer functions are insensitive to the variation of flight speeds: the amplitude of the transfer function varies slightly, while the phase delay almost remains unchanged. In addition, this finding is validated through closed-loop vibration control tests with the active rotor. The transfer function obtained from the hover test results is also applicable to closed-loop vibration control tests under the forward flight conditions. This will dramatically simplify the implementation and operation of an active rotor.
In order to solve tiny defect detection for solder balls in high-density flip-chip, this paper proposed feasibility study on the effect of detectability as well as classification based on eddy ...current pulsed thermography (ECPT). Specifically, numerical analysis of 3D finite element inductive heat model is generated to investigate disturbance on the temperature field for different kind of defects such as cracks, voids, etc. The temperature variation between defective and non-defective solder balls is monitored for defects identification and classification. Finally, experimental study is carried on the diameter 1mm tiny solder balls by using ECPT and verify the efficacy of the technique.
The fully mechanized mining with large mining height is the main method for high yield and efficient coal mining in China. The key stratum structure (KSS) is the basis of revealing the mechanism of ...roof weighting and determination of support working resistance of the longwall face with large mining height (LFLMH) in the shallow coal seam. The height of the caving zone at LFLMH is large, the thick immediate roof forms the “short cantilever beam” structure commonly, and the hinge layer of the overlying key stratum will move upward to the higher position. The “high position oblique step voussoir beam” structure of single-key stratum (SKS) and “oblique step voussoir beam and voussoir beam” structure of double-key stratum (DKS) in the shallow coal seam were proposed with physical simulation and Universal Distinct Element Code (UDEC). The analysis of the KSS and numerical simulation reveals the mechanism of strong roof weighting at the SKS longwall face and large-small alternate periodic weighting at the DKS longwall. It is concluded that the large static load caused by the “equivalent immediate roof (EIR)” is the basic load, and the instability load of the KSS is the additional dynamic load of support. Besides, the calculation methods of the reasonable support working resistance at LFLMH were obtained and verified with engineering applications.
Although potential contamination of groundwater As is expected to occur in Xinjiang, P.R. China, few data are available for the regional distribution of groundwater As. In this study, the spatial ...distribution of groundwater As was investigated in the Chepaizi (CPZ-N) and Shihezi (SHZ-N) areas of northern Xinjiang, the Balikun-Yiwu Basin (BY-E) in eastern Xinjiang, and the Tarim (TRM-S) and Yanqi (YQ-S) basins in southern Xinjiang. Arsenic concentrations greater than 10 μg/L were found in 12% of analyzed groundwaters. All groundwater samples collected in CPZ-N had As concentrations greater than 10 μg/L (25–185 μg/L), 30% in SHZ-N (<0.25–49 μg/L), 2.7% in BY-E, and 6.1% in TRM-S and YQ-S. No high As groundwater (As >10 μg/L) was found in the eastern and southern TRM-S and YQ-S. Distribution of groundwater As showed a tremendous spatial variability, which greatly varied over a short distance horizontally. Arsenic concentration generally increased with increasing sampling depth. The spatial distribution of groundwater As would be regulated by As source and hydrogeochemical processes. Higher pH and/or lower ORP values were generally observed in high As groundwater (>10 μg/L) in comparison with low As groundwater (<10 μg/L). Arsenic mobility in SHZ-N and CPZ-N may result from As desorption under relatively high pH conditions, and more tentatively from reductive dissolution of Fe(III) oxides in BY-E and TRM-S. However, detailed mechanisms of As mobilization in these regions need further investigation.
•Spatial distribution of groundwater As was investigated in Xinjiang.•High As groundwater was found in the north, south and east of Xinjiang.•Arsenic concentrations generally increased with the increase in well depths.•Desorption and/or reductive dissolution led to As enrichment in groundwater.•Model-based prediction of groundwater As would deviate from real data.
Active rotor with trailing-edge flaps is a promising method to alleviate vibrations and noise level of helicopters. Hysteresis of the piezoelectric actuators used to drive the flaps can degrade the ...performance of an active rotor. In this study, bench-top tests are conducted to measure the nonlinear hysteresis of a double-acting piezoelectric actuator. Based on the experimental data, a rate-dependent hysteresis model is established by combining a Bouc-Wen model and a transfer function of a second order system. Good agreement is exhibited between the model outputs and the measured results for different frequencies. A compound control regime composed of a feedforward compensator and PID (Proportional-Integral-Derivative) feedback control is developed to suppress the hysteresis of this actuator. Bench-top test results demonstrate that this compound control regime is capable to suppress hysteresis at different frequencies from 10 Hz to 60 Hz, and errors between the desired actuator outputs and the measured outputs are reduced dramatically at different frequencies, revealing that this compound control regime has the potential to be implemented in an active helicopter rotor to suppress actuator hysteresis.
The removal of arsenic contamination from the aqueous environment is of great importance in the conservation of the Earth's water resources, and surfactants are a promising material used to modify ...magnetic nanoparticles to improve adsorption properties. Therefore, it is important to develop efficient and selective adsorbents for arsenic. Surface modification of Fe
3
O
4
was carried out using anionic, cationic and zwitterionic surfactants to obtain composite Fe
3
O
4
@SDS, Fe
3
O
4
@CTAB, Fe
3
O
4
@SNC 16 and Fe
3
O
4
@NPC 16 (collectively referred to as Fe
3
O
4
@surfactants). The synthesized composite Fe
3
O
4
@surfactants magnetic nanoparticles were characterized by XRD, TEM and FTIR. The As(V) removal characteristics of the composite magnetic nanoparticles from the aqueous solution were evaluated by adsorption batch experiments which indicated the possibility of effective application of the surfactant-modified Fe
3
O
4
magnetic nanoparticles for the removal of As(V) from aqueous solution. The adsorption equilibrium of the composites was reached in 30 min and the kinetic data followed the pseudo-second-order model. Langmuir equation could represent the adsorption isotherm data very well. Moreover, under the identical conditions, Fe
3
O
4
@CTAB showed maximum capacity of adsorption for As(V) (55.671 mg g
−1
), with its removal efficiency being much higher than that of the other composites. In addition, the Fe
3
O
4
@surfactants composite magnetic nanoparticles retained 93.5% of its initial arsenic removal efficiency even after re-using it five times. The mechanism of arsenic adsorption by Fe
3
O
4
@surfactants composite magnetic nanoparticles was proved to be complexation via electrostatic attraction, which was mainly innersphere in nature.
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