•A method is proposed for image graying based on thresholding segmentation.•The navigation line is extracted based on SUSAN corner.•The system is designed and realized in simulative paddy field ...environment.
Navigation system and its navigation algorithm are the crucial parts for intelligent paddy field weeding robot. The environments of paddy fields are complicated in South China. The colors of weed, duckweed and cyanobacteria, which grow in paddy fields, are very similar with rice seedlings. Moreover, the rice seedlings present various morphological features during the growth progress. Therefore, how to extract the guidance lines for navigation system and weeding robot presents various challenges. In order to deal with the above mentioned problems, a navigation method for weeding robot based on SUSAN (smallest univalue segment assimilating nucleus) corner and improved sequential clustering algorithm is proposed in this paper. Firstly, gray feature in paddy field image is extracted by using the adaptive graying algorithm. Secondly, the SUSAN corners are extracted as characteristic points. Thirdly, the seedling navigation line is detected by applying the improved sequential clustering algorithm and Hough Transform. Finally, the position error and angle error are calculated, and a fuzzy controller is designed to control the robot. Experimental results show desirable performances of the proposed method. The proposed segmentation method is effective in complicated environment.
This study aimed to evaluate the hydrochemistry of the water resources of the Weibei Plain, Northern China, as well as the risks posed by high groundwater nitrate concentrations to human health. ...Groundwater and surface water samples numbering 168 and 14, respectively, were collected during the dry and wet seasons. Water in the study area was weakly alkaline, falling into a hard-fresh or hard-brackish category. The groundwater chemical types were mainly SO4·Cl–Ca·Mg (59.5%) and HCO3–Ca·Mg (28.6%), whereas the dominant chemistry type of surface water was SO4·Cl–Na (78.6%). Groundwater showed relatively high concentrations of NO3−, with average dry and wet season concentrations of 212 mg·L−1 and 223 mg·L−1, respectively, whereas surface water had a low NO3− content. The major processes affecting water chemistry were determined to be rock weathering, such as silicate weathering and evaporative dissolution, as well as cation exchange. NO3− in groundwater was found to mainly originate from anthropogenic inputs such as agricultural production and domestic sewage. The entropy-weight water quality index (EWQI) assessment showed that although the quality of surface water was generally good, more than half of the groundwater samples failed drinking water standards, with NO3− identified as being the most problematic parameter affecting the water quality evaluation. Risk assessment of high groundwater nitrate concentrations indicated that long-term domestic use of groundwater in the study area can put the health of residents at great risk. Totals of 81% and 75% of the groundwater samples exceeded the acceptable limit for non-carcinogenic risk (HI = 1) to infants during the dry and wet seasons, respectively, whereas 75% and 71.3% of samples exceeded the acceptable limit for children, respectively. Future management of water in the Weibei Plain should prioritize the control groundwater nitrate pollution.
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•Hydrochemistry of the water resources of Weibei Plain in different seasons was characterized.•Over 45% of groundwater samples had nitrate concentrations exceeding 200 mg L−1.•Nitrate was the main factor affecting water quality and mainly originated from agriculture.•Groundwater samples showed a high NO3− risk to human health (infants > children > adults).
Hydrochemical genesis, water quality and risk of high nitrate levels to human health in Weibei Plain, northern China were determined.
Surface subsidence induced by mineral extraction from underground mines can significantly affect the ecological environment and human life. Surface collapse is extremely hazardous and typically ...occurs without warning. In China, numerous surface collapses have occurred during mining operations in coal mines located under thick unconsolidated layers. Via analysis of the stability of the bearing structure (arch structure in unconsolidated layers and key strata in rock strata) based on their effects on strata movement, our study reveals the formation mechanism of surface collapses and the roles played by two critical parameters: mining length and mining height. It is speculated that the bearing structure cannot be self-stable and will collapse during longwall mining with increasing mining length and mining height. As a result, the ground surface will collapse on the longwall face gob accompanied by the failure of the bearing structure. With these risks in mind, this study proposes a backfilling strip mining method via determination of the appropriate longwall face length and mining height to guard against bearing structure failure and thus avoid surface collapse. A field trial of the technique was conducted at a suitable Chinese coal mine located under thick unconsolidated layers. The maximum surface subsidence observed was only 0.369 m, which is 92% less than the subsidence in longwall face (LW) 3A04. No surface collapse occurred during the mining process. Thus, our results indicate that the proposed technique can successfully prevent surface collapse during longwall mining under thick unconsolidated layers.
Extensive true-triaxial unloading tests are conducted on rectangular Miluo granite specimens to investigate their crack propagation behavior and peak unloading strength properties. Experimental ...results demonstrate that their failure mode transforms from shear to slabbing with the increase in intermediate principal stresses σ2. Under a lower value of σ2, the dominant failure mode represented by the macro shear band is composed of several meso-extensional cracks parallel to the maximum principal stress σ1, and the fracturing process indicates intensive dislocation and slide owing to the normal force acting on extensional cracks. However, the increase in σ2 exacerbates the extensional cracks and further propagates them toward the end of the specimen along the direction of σ1, if σ3 is unloaded to 0. This is primarily due to the enhanced ability to resist mutual slide and squeeze among extensional cracks in the shear band, and the promotion of crack initiation and propagation in the unloading direction (σ3) owing to the provided free surface. The transformation of the cracking mode is revealed via three-dimensional combined finite/discrete element modeling, scanning electron microscope observations, and acoustic emission signal feature (average frequency, rise angle, Acoustic emission (AE) counts, and accumulated AE energy) analysis. The peak unloading strength exhibits an initial increase followed by a decrease as a function of σ2. Four rock-strength criteria are employed to evaluate the true-triaxial data with emphasis on predictability in practical applications and accuracy between best-fitting functions (experimental data) and theoretical (predicted) solutions. It is demonstrated that modified the Wiebols–Cook criterion and modified Lade criterion cannot accurately estimate the unloading strength throughout the true-triaxial data. Although the Mogi 1971 criterion fits the experimental data (higher correlation coefficients) well, it cannot be correlated to strength parameters (cohesion and internal frictional angle). Hence, it fails to predict the real strength values if complex true-triaxial unloading tests are not performed. The linear Mogi criterion is recommended for predicting the true-triaxial unloading strength of granite.
Four types of Li1.5Al0.5Ge1.5(PO4)3 (LAGP) with different particle sizes are selected as active fillers incorporated into polyethylene oxide (PEO) matrix to fabricate PEO/LAGP hybrid electrolytes at ...drying room. The results show that LAGP particles have a positive effect on the ionic conductivity, lithium ion transference number, electrochemical stabilities and mechanical properties. Among the PEO/LAGP hybrid electrolytes, the PEO-20%LAGP-I hybrid electrolyte exhibits a maximum ionic conductivity of 6.76×10−4Scm−1 and an electrochemical window of 0–5.3V at 60°C. The possible reasons for conductivities improving are discussed through characterizing the phase transition behaviors of electrolytes. All-solid-state battery LiFePO4/Li is fabricated and presents fascinating electrochemical performance with high capacity retention (close to 90% after 50cycles at 60°C) and attractive capacities of 166, 155, 143 and 108mAhg−1 at current rates of 0.1, 0.2, 0.5 and 1 C, respectively. This work provides a promising PEO/LAGP hybrid electrolyte prepared by a simple method which can be manufactured easily in industry scale.
•A promising PEO/LAGP hybrid electrolyte prepared by a simple method which can be manufactured easily in industry scale.•The electrolyte exhibits an ionic conductivity of 6.76×10−4Scm−1 and an electrochemical window of 0-5.3V at 60°C.•The hybrid electrolyte has improved electrochemical and mechanical properties.•All-solid-state battery exhibits high capacity retention and attractive capacities.
A new solid polymer electrolyte (SPE) PEO-LiTFSI-1%LGPS-10%SN is successfully prepared via a convenient method with low cost. The effect of SN on the ionic conductivity of PEO-based electrolyte is ...systematically investigated. It presents a maximum conductivity of 9.10×10−5S·cm−1 at 25°C, and a 15-fold ion conductivity enhancement in PEO-LiTFSI. It exhibits wide electrochemical window (0–5.5V) and excellent compatibility with metallic Li. The LiFePO4/Li batteries exhibit a good cycling and rate performance under 40°C, whose maximum discharge specific capacity at 0.1 C is 160.6mAh·g−1, and 94.7% can be retained after 60 cycles. At 0.5C, the maximum discharge specific capacity is 138.4mAh·g−1, and capacity retention close to 90% even after 100 cycles. The reasons of activation process are discussed. This new SPE with outstanding electrochemical performance is a promising solid electrolyte candidate for applications in all-solid-state lithium battery.
This study investigated 324 groundwater samples collected from the southwest plain of Shandong Province during the dry and wet seasons. Groundwater fluoride in the study area and the influencing ...factors were characterized and discussed using statistical analysis, ion ratios, Piper diagrams, the saturation index (SI) and ArcGIS software. In addition, the risk posed by groundwater fluoride to human health was assessed. The results showed that groundwater in the study area had elevated fluoride concentrations, with average dry and wet season concentrations of 1.15 mg·L−1 and 1.08 mg·L−1, respectively. Groundwater fluoride showed consistent spatial variations during the dry and wet seasons, with a significant regionalization pattern of low concentrations in the east and high concentrations in the west. Groundwater F− was significantly negatively correlated with Ca2+ and positively correlated with pH, HCO3− and Na+. Important factors identified as having an effect on groundwater F− in the study area included the balance of dissolution of fluorite and calcite, the weakly alkaline environment and cation exchange. In addition, hydrochemical types of high-fluoride groundwater in the study area were identified as mainly HCO3-Na and SO4·Cl-Na. The assessment of the risk of high groundwater fluoride to human health showed that children are more at risk compared to adults, with the risk during the dry season exceeding that over the wet season. It is recommended that water quality management in the study area prioritize the formulation of measures to mitigate high concentrations of fluoride in groundwater .
•Over 30% of the groundwater samples have fluoride >1.0 mg L−1.•Cation exchange was an important factor affecting the fluoride concentration of groundwater in the study area.•Distributions of fluoride concentration and hazard quotient for children and adults were obtained.•Fluoride concentration was the most influential variable in the risk assessment.
In this paper, we performed uniaxial compression tests on fine sandstone–coal, coarse sandstone–coal, and oil shale–coal bi-material samples to investigate the lithology effects on their strength, ...macro-failure initiation (MFI), energy evolution, and failure characteristics, respectively. Uniaxial stress–strain characteristics of the samples primarily depended on the coal and were affected by coal–rock interactions. These interactions involved the following aspects: (1) The differences in the mechanical properties of rock and coal affected their stress states near the interface. They were in triaxial compression state with strength increasing or in triaxial compression-tension state with strength decreasing. (2) During the pre-peak stage, the rock deformation affected the values of input energy, elastic energy, and dissipated energy. Damage and energy accumulation in coal were also limited by rock deformation, resulting in higher strengths for the bi-material samples compared to pure coal samples. (3) During the post-peak stage, the rebound deformation of rock was accompanied by the elastic energy release, which promoted the failure of coal. MFI of the samples occurred within the coal. MFI models mainly included the tensile fracture of coal near the interface, the initiation and propagation of macro-cracks, and the development and evolution of micro-defects, accompanied by varying degrees of surface spalling or ejection failure. The coal showed the splitting ejection failure. The oil shale and coarse sandstone exhibited tensile failure or tensile–shear composite failure due to crack propagation in coal. Failure was not evident in the fine sandstone. The coal in the oil shale-coal bi-material samples became more broken due to the most serious rebound deformation of oil shale.
The variation of the in situ stress state is closely related to various factors. In situ stress state is also an important indicator to guide mining production. The study of in situ stress ...measurement and its distribution characteristics has always been a basic and very important work in mine production. In this study, the deep mines of Linyi Mining Area were considered as the research object. In this regard, the stress distribution law of each mine was studied. We found that the relationship between principal stresses was σH > σv > σh, which belongs to the strike-slip stress regime. In this stress regime, the lateral Earth pressure coefficient was greater than one, and the magnitude of the three principal stresses all showed an increasing trend with the increase of depth. The maximum horizontal stress direction of the Gucheng Coal Mine, Guotun Coal Mine, and Pengzhuang Coal Mine was NW-SE under the influence of regional geological structure, while the maximum horizontal stress direction of Wanglou Coal Mine was NE-SW under the influence of local geological structure. Besides, the relationship between mine in situ stress and mine geological structure, the impact of original rock stress on stope stability, and the effect of original rock stress on floor water inrushing were also investigated. We believe that the research results are beneficial to mine disaster prevention and safety production.
Long-term freeze-thaw (F-T) action causes the expansion of the fracture network in rock mass with ice-filled joints, triggering more serious engineering geological disasters. This study explores F-T ...damage effects and loading failure in double-fractured white sandstones with different saturation types (saturated and ice-filled). Saturated intact, saturated fractured, and ice-filled fractured sandstones were subjected to F-T cycle tests and uniaxial compression tests. Three-dimensional images of the specimens under various F-T cycles and stress states were obtained using computed tomography. The evolution in fracture morphology was evaluated visually, with pore network model parameters used for quantitative characterisation. Sandstone fractures evolved according to four main processes: frost-heave cracking, progressive expansion of damage, rock bridge penetration under load, and shear failure. The proportion of connected pores was used to estimate the influences of F-T cycling on pore-structure connectivity and fracture expansion in different specimen layers. During F-T cycling, pore characteristics vary according to size: micropores (equivalent radius < 100 μm) account for >60% of pores and increase in number more than pores of other sizes. Mesopores (100–500 μm) gradually decrease in number but their volume fraction remains >70%. Macropores (500–1000 μm) have the greatest increase in volume fraction. Early F-T cycling induces the connection of pore throats, while later cycling accelerates their expansion. Hydrostatic pressure increases are the leading cause of damage in ice-filled fractured sandstone, which exhibits greater variations in porosity, heterogeneity coefficient, and pore-throat parameters under F-T cycling than saturated fractured sandstone. The results provide insight into fracture evolution and failure characteristics in fractured rock masses with different saturation types (saturated and ice-filled) in cold regions.
•Fracture evolution in sandstone under freeze-thaw cycling was investigated.•Variations in pore-throat parameters were comprehensively evaluated by μCT.•The effects of different saturation methods on freeze-thaw damage are discussed.•Hydrostatic pressure is the main cause of damage in rock with ice-filled fractures.
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