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Abstract The characteristics and heterogeneity of coal pores are crucial for understanding the production mechanism of coalbed methane (CBM). In this study, coal samples with varying degrees of metamorphism (0.58% ≤ R O, max ≤ 3.44%) were collected. The characteristics of pore development and the heterogeneous properties of pores were revealed through low-temperature nitrogen adsorption (LTNA) and low-field nuclear magnetic resonance (NMR) experiments. The results indicate that pores with varying diameters exhibit favorable development in low-rank coals, along with favorable pores connectivity. The micropores composition of middle-rank coals was found to be 73.56%, however, the connectivity among transitional, meso, and macropores was observed to be poor. In high-rank coals, the proportion of micropores was 92.74%, with numerous micropores being closed or semi-closed. This resulted in inferior connectivity between micropores and transitional pores. As coal metamorphism progressed, the D L1 (characterizing the roughness of adsorption pores (AP) surface, ranging from 2.13 to 2.45) and D L2 (characterizing the complexity of AP structure, ranging from 2.56 to 2.77) initially decreased and then increased, whereas the D N (characterizing the heterogeneity of seepage pores (SP), ranging from 2.92 to 2.95) consistently improved. Furthermore, the roughness of pore surface and the complexity of pore structure in AP increased as the specific surface area and volume of pores increased. On the contrary, as the SP content increased, the uniformity of the pore structure improved. When the volume of SP remained constant, the complexity of the pore structure decreased due to increased pore connectivity.

In the process of coal mining, small faults can lead to the accumulation of gas in the goaf, forming a gas enrichment zone, which poses a great threat to production safety. Therefore, it is necessary to study the gas migration law in the goaf under the influence of small faults. By using UDEC software to numerically simulate the failure process of the overlying strata in the goaf, the porosity of the overlying strata under the influence of small faults is calculated, and FLUENT software is used to numerically simulate the gas migration law in the goaf considering the influence of small faults during the mining process. Research has shown that: ① the working face is 20 m away from the small fault, and the sliding phenomenon first appears from the top of the small fault, and the displacement of the overlying rock layer in the goaf begins to be affected by the fault; When the working face reaches the fault, due to the sliding of the fault, the hanging wall rock mass undergoes a rotation phenomenon on the fault surface, supporting the rock strata in the goaf. The displacement of the overlying rock collapses significantly, and the rock strata collapse lags behind; The influence range of small faults is limited, and after the working face passes through the small fault for 60 m, the displacement law of the overlying strata in the goaf gradually returns to normal. ② By analyzing the displacement characteristics of the overlying strata in the goaf containing small faults, the displacement of the overlying strata in the goaf and its fitting formula were obtained. The three-dimensional porosity distribution law was calculated: within the range of the caving zone, the porosity of the overlying strata is the highest at four corner positions, and there is also an increase in porosity near the inlet and outlet air tunnels of the faults; Within the fracture zone, except for the position where the fault is close to the inlet and return air roadway, the porosity is relatively low and the change is not significant in other positions. ③ Obtained the gas migration law in the goaf under the influence of small faults: At a distance of 50 m from the fault in the working face, the gas migration in the goaf is almost not affected by the fault; When the working face advances to the fault, the gas migrates along the advantageous escape channel generated by the high porosity overlying rock near the fault towards the deep part of the goaf. At the same time, the gas in the hanging wall also transfers towards the deep part, causing a large amount of gas to accumulate in the lower wall of the fault, which may cause the gas to flow into the working face and return air roadway with the leakage air; When the working face passes through a fault of 50 m, the gas in the goaf continues to transfer towards the vicinity of the upper corner; When the working face passes through a fault of 100 m, the gas migration in the overlying strata of the goaf shows a turning phenomenon, and the gas concentration in the upper corner and lower wall caving zones is high.

Promoting the high-quality development of urbanization is a crucial way to achieve sustainable development goals. Water resources are a rigid constraint for such development. However, There is still room for improvement in the research on the spatio-temporal pattern and key driving factors of high-quality urbanization development under the constraint of water resources. Aiming at the problem that the high-quality development of urbanization in the Yellow River Basin (YRB) is facing water resources constraints, this paper discussed the spatial–temporal pattern and key drivers of the high-quality development of urbanization in the YRB under water resource constraints by using the Analytic Hierarchy Process model reformed by entropy technology, multi-objective fuzzy membership function, spatial autocorrelation analysis and obstacle model. The results revealed that, first, we found the High-Quality Urbanization Development Index (UQDI) exhibited steady growth, while both the Water Resources Index (WRI) and the Water Resources Constraint Intensity (WRCI) initially increased and then decreased during the study period. Second, the UQDI displayed a dual-core pattern, with the Shandong Peninsula urban agglomeration and the Central Plains urban agglomeration serving as the cores. WRI exhibited relatively stable spatial distribution, with the southeast region outperforming the northwest. WRCI also demonstrated a relatively stable spatial distribution, resulting in two weak-constraint areas, represented by Shandong and Henan, and a strong-constraint area centered around Ningxia. Third, the UQDI, WRI, and WRCI exhibited spatial interdependence. The spatial interdependence of UQDI and WRI increased, while that of WRCI decreased during the study period. The three indexes also displayed a clear pattern of local clustering in space. Two low-value aggregation areas, namely Shandong and Henan, and a high-value aggregation area located in Ningxia, emerged during the study period. Last, the WRCI was primarily influenced by the fundamental conditions of water resources. The main influencing factors included per capita water resources, mean annual precipitation, total water resources, water resources modulus, and the total amount of foreign investment utilization. In light of the research findings, the paper proposes policy recommendations for promoting high-quality urbanization development in the YRB. This study provides decision-making guidance for countries and regions in arid areas to solve the water resources constraints on the high-quality development of urbanization.

Underwater imaging is often affected by light attenuation and scattering in water, leading to degraded visual quality, such as color distortion, reduced contrast, and noise. Existing underwater image enhancement (UIE) methods often lack generalization capabilities, making them unable to adapt to various underwater images captured in different aquatic environments and lighting conditions. To address these challenges, a UIE method based on the conditional denoising diffusion probabilistic model (DDPM) is proposed (DiffWater), which leverages the advantages of DDPM and trains a stable and well-converged model capable of generating high-quality and diverse samples. Considering the multiple distortion issues in underwater imaging, unconditional DDPM may not achieve satisfactory enhancement and restoration results. Therefore, DiffWater utilizes the degraded underwater image with added color compensation as a conditional guide, through which the DiffWater achieves high-quality restoration of degraded underwater images. Particularly, the proposed DiffWater introduces a color compensation method that performs channelwise color compensation in the RGB color space, tailored to different water conditions and lighting scenarios, and utilizes this condition to guide the denoising process. In the experimental section, the proposed DiffWater method is tested on four real underwater image datasets and compared against existing methods. Experimental results demonstrate that DiffWater outperforms existing comparison methods in terms of enhancement quality and effectiveness, exhibiting stronger generalization capabilities and robustness.

High-order coal has the characteristics of weak water absorption due to the development of micropores. From the perspective of micropores, it is of great significance to study the improvement effect of different types of surfactants on the wettability of high-end coal, which is of great significance for dust prevention and dust reduction of high-end coal. Taking the high-order coal of Zhaozhuang Mine in Shanxi Province and Nuodong Mine in Guizhou as the research object, the low-field nuclear magnetic resonance (LNMR) measurement system was used to carry out the coal sample sedimentation experiment and the coal sample-solution permeation pore water distribution determination experiment, and analyze the improvement law of micropore wettability of surfactant solution on high-order coal samples under different compound ratios. The results show that: In the sedimentation of eight surfactant monomer solutions, the sedimentation rate of coal samples in surfactant solution gradually increased with the increase of mass fraction, and the sedimentation rate of coal samples in each solution tended to balance at 0.5% mass fraction, among which the sedimentation effect of Trolatong X-100 (X-100), fatty alcohol polyoxyethylene ether (JFC-U) and sodium dodecyl benzene sulfonate (SDBS) was faster than that of other surfactant solutions. Based on the low-field NMR experiment T2 spectroscopy, a dual quantitative evaluation method was established, and it was found that when the three preferred surfactant solutions were compounded with volume ratios of 1∶1, 1∶2 and 2∶1 under the condition that the mass fraction was 0.5%, the compound solution played a synergistic role in the wettability of the micropores of high-order coal, and the wetting improvement effect of the compound surfactant solution was higher than that of the surfactant monomer solution. When the volume ratio of the nonionic surfactant JFC-U solution and the anionic surfactant SDBS solution were compounded 2∶1, the effect on improving the wetting of high-order coal was obvious. In the compound solution of nonionic and nonionic surfactants, the wetting improvement effect of compound surfactant solution on coal samples was positively correlated with the content of JFC-U. The research results can provide a reference for the selection of surfactant types and the research methods of coal sample wettability during wet dust control in coal mines.

More recently, the ability of the coprime array to yield large array apertures and high degrees of freedom in comparison with the uniform linear array (ULA) has drawn an enormous amount of attention. In light of this, we propose a low-rank matrix completion algorithm via minimization of the ratio of the nuclear norm and the Frobenius norm (N/F) to solve the two-dimensional (2D) direction finding problem for the L-shaped coprime array (LsCA). Specifically, we first interpolate the virtual co-array signal related to the cross-correlation matrix (CCM) and utilize the interpolated virtual signal for Toeplitz matrix reconstruction. Then, the N/F method is employed to perform low-rank matrix completion on the reconstructed matrix. Finally, exploiting the conjugate symmetry characteristics of the completed matrix, we further develop a direction-finding algorithm that enables 2D angle estimation. Remarkably, the 2D angles are able to be automatically paired by the proposed algorithm. Numerical simulation findings demonstrate that the proposed N/F algorithm generates excellent angular resolution and computational complexity. Furthermore, this algorithm yields better estimation accuracy compared to the competing algorithms.

The instability and collapse of drainage boreholes is one of the key problems that hinder the efficient extraction of coal-bed methane (CBM). In order to solve the problem of instability and collapse of extraction boreholes in soft coal seams, based on the laboratory tests and theoretical analysis of variable mass flow pressure drop, a coupled mathematical model is established, which comprehensively considers borehole deformation and instability, coal bed gas migration and dynamic attenuation of borehole negative pressure along the borehole length. The influence mechanism of instability and collapse of extraction boreholes on gas extraction is numerically analyzed, and the detection technology of instability and collapse characteristics of extraction boreholes based on the distribution test of extraction negative pressure is proposed. Research shows: ① The gas drainage effect of the complete borehole is very good, and the negative pressure loss of the borehole is very small. The total negative pressure loss of the100 m long borehole for one day only accounts for 0.04% of the negative pressure of the orifice. The gas distribution and effective drainage radius of the coal seam at the orifice and the bottom of the hole are basically the same. ② The influence of borehole bottom collapse on the gas drainage effect is limited, but the influence of borehole collapse near the hole opening on the gas drainage effect is significant. When 90% of the borehole is collapsed at the borehole bottom and near the borehole opening, the gas extraction volume after 90 days of extraction is 38.7% and 69.6% lower than that of the complete borehole. After 180 days of extraction, the effective extraction radius at the borehole bottom is 88.7% and 75.0% of the effective extraction radius of the borehole opening. The total negative pressure loss in the first day of extraction accounts for 5.1% and 28.4% of the negative pressure of the borehole opening. ③ Borehole plugging seriously affects the gas extraction effect. The blocked coal body in the hole forms a continuous medium with the surrounding coal body. The pressure in the borehole becomes the gas pressure of the coal seam, and the unstable section cannot extract gas. After 90 days of drainage, the gas drainage volume of the blocked hole at the bottom of the hole only accounts for 17.6% of the gas drainage volume of the complete borehole. ④ The negative pressure distribution of extraction drilling is sensitive to the instability and collapse characteristics of extraction drilling. A detection technology for the instability and collapse characteristics of extraction drilling based on the negative pressure distribution test of extraction drilling is proposed. Through the application in the 25030 working face of a mine, the instability and collapse area (65−80 m) and collapse degree (serious collapse borehole) of extraction drilling are determined. It is suggested that the mine should carry out a targeted grouting protection for the instability and collapse area of boreholes.

In recent years, with the continuous development and popularization of unmanned aerial vehicle (UAVs) technology, the surge in the number of UAVs has led to an increasingly serious problem of illegal flights. Traditional acoustic-based UAV localization techniques have limited ability to extract short-time and long-time signal features, and have poor localization performance in low signal-to-noise ratio environments. For this reason, in this paper, we propose a deep learning-based UAV localization technique in low signal-to-noise ratio environments. Specifically, on the one hand, we propose a multiple signal classification (MUSIC) pseudo-spectral normalized mean processing technique to improve the direction of arrival (DOA) performance of a traditional broadband MUSIC algorithm. On the other hand, we design a DOA estimation algorithm for UAV sound sources based on a time delay estimation neural network, which solves the problem of limited DOA resolution and the poor performance of traditional time delay estimation algorithms under low signal-to-noise ratio conditions. We verify the feasibility of the proposed method through simulation experiments and experiments in real scenarios. The experimental results show that our proposed method can locate the approximate flight path of a UAV within 20 m in a real scenario with a signal-to-noise ratio of −8 dB.

In order to accurately determine the location of fracture zone, optimize the design parameters of high-level boreholes, and improve the effect of gas drainage, take the No. 25030 working face of Xuehu Coal Mine, Henan Shenhuo Coal & Power Co., Ltd. as the research object to study the movement law of overburden strata in the working face. To determine the height of ‘vertical three zones’ of overburden strata by combining theoretical calculation, numerical simulation and field test. Through theoretical calculation, the maximum vertical height range of caving zone from coal seam roof is 5.5–9.2 m, and the maximum vertical height range of water flowing fractured zone from coal seam roof is 26.0–37.2 m. Through numerical simulation, the maximum height of the caving zone is 8.0 m from the roof, and the maximum height of the fracture zone is 27.0 m from the roof. Through field test, when the vertical height of the final borehole from the roof of the coal seam is 18.4–30.0 m, the gas concentration extracted by the borehole is generally high. When the vertical height of the borehole is 24.6–28.4 m from the coal seam roof, the gas concentration is in the peak area. The height distribution range of rock “vertical three zones” in Xuehu Mine No. 25030 working face obtained by three methods is roughly similar, and it is suggested to refer to the measured value in the design of goaf gas drainage. The test results show that the gas drainage effect is the best when the vertical distance from the coal seam roof is 24.6–28.4 m, and it is suggested that the high level boreholes should be arranged in this area.

Abstract Based on Chebyshev polynomials, the two‐way slant range is first approximated by the fourth‐order polynomial approximation. With the series reversion method, the point target reference spectrum (PTRS) which is further used for the development of imaging algorithm in this letter is obtained. The presented method processes the echoed signal corresponding to each transmitter/receiver pair. And then a high‐resolution synthetic aperture sonar (SAS) image is obtained by coherently superposing all coarse‐resolution images. Comparing the peak sidelobe ratio (PSLR) and integration sidelobe ratio (ISLR), the performance of the presented method is superior to that of the traditional method. Simulations are further validated by the presented method.

Abstract In this Letter, the authors present a novel imaging algorithm for multireceiver synthetic aperture sonar (SAS). The Loffeld's bistatic formula (LBF) including quasi‐monostatic (QM) and multireceiver deformation (MD) phases is first reformulated into range‐variant and range‐invariant phases. After compensating the range‐invariant phase, the subsequent steps are the extended Stolt mapping for each bistatic SAS. Based on simulations, the presented method can also provide high‐resolution result which is similar to that of back projection (BP) algorithm.

Due to its low cost and privacy protection, Channel-State-Information (CSI)-based activity detection has gained interest recently. However, to achieve high accuracy, which is challenging in practice, a significant number of training samples are required. To address the issues of the small sample size and cross-scenario in neural network training, this paper proposes a WiFi human activity-recognition system based on transfer learning using an antenna array: Wi-AR. First, the Intel5300 network card collects CSI signal measurements through an antenna array and processes them with a low-pass filter to reduce noise. Then, a threshold-based sliding window method is applied to extract the signal of independent activities, which is further transformed into time–frequency diagrams. Finally, the produced diagrams are used as input to a pretrained ResNet18 to recognize human activities. The proposed Wi-AR was evaluated using a dataset collected in three different room layouts. The testing results showed that the suggested Wi-AR recognizes human activities with a consistent accuracy of about 94%, outperforming the other conventional convolutional neural network approach.

Abstract With the Loffeld's bistatic formula, the point target reference spectrum (PTRS) of multireceiver synthetic aperture sonar (SAS) can be decomposed into the quasi monostatic term and bistatic deformation (BD) term. The former term is analogous to the monostatic SAS PTRS while the latter one describes the bistatic phase introduced by the bistatic displacement between the transmitter and receiver. The multireceiver SAS echo signal can be transformed into monostatic SAS equivalent data after correcting the BD term. Based on the range sub‐block processing method, this data transformation is conducted by using the preprocessing step. Then, fast imaging processors based on monostatic SAS system can be directly exploited to process the monostatic SAS equivalent data. In this paper, the authors mainly focus on the application of non‐linear chirp scaling algorithm. At last, the simulations and real data are used to validate the presented method. The processing results show that the imaging performance of presented method is nearly close to that of traditional method. Besides, the imaging efficiency is highly improved compared to the phase centre approximation (PCA) method.

Abstract The shallow water noise shows obvious impulsive property, which greatly degrades the direction of arrival (DOA) performance due to the conventional design concept based on the Gaussian assumption. In this paper, DOA estimator in presence of impulsive noise utilising variational Bayesian inference is proposed. The Middleton's Class A noise model is considered as a typical underwater noise model to analyse the performance of DOA estimation. The DOA estimation problem is modelled as the sparse signal recovery problem, and the hierarchical Bayesian learning framework is formulated by considering the common sparsity of signal and the element‐wise sparsity of the impulsive noise. The variational Bayesian inference realises the posterior estimation of signal and impulsive noise components. To mitigate the basis mismatches, the root sparse Bayesian learning method is applied to refine the steering vectors. Simulations verify the advantages of the proposed DOA method in terms of spatial resolution, root mean square error, accuracy, and robustness compared with the state‐of‐the‐art benchmarks in the presence of Middleton's Class A noise.

Abstract Tieguanyin is one of the most consumed oolong teas because of its distinctive flavor. The brewing process is crucial for the flavor performance of traditional teas, thus the effects of brewing conditions, including water/tea ratio (R), brewing temperature (T), and time (S) on the sensory traits, chemical composition, and antioxidant activity of Tieguanyin tea infusion were investigated using quadratic orthogonal regression design. Results showed that R affected all the quality variables most, its reduction could lead to the promotion of tea infusion concentration, antioxidant activity, and taste intensity, which was favored by the tea consumers drinking tea almost daily (DTD) but unacceptable for those drinking tea hardly (DTH). Based on the optimization of brewing conditions in response surface methodology (RSM), we recommended several brewing schemes for diverse consume goals: R = 34 mL/g, T = 80 °C, S = 80 s for DTH; R = 39 mL/g, T = 100 °C, S = 127 s for DTO (the consumers drinking tea occasionally); R = 20 mL/g, T = 100 °C, S = 100 s for DTD; R = 26 mL/g, T = 100 °C and S = 127 s for the common consumers seeking for flavor and health benefits. These results would be helpful for tea consumers with multiple demands.

Abstract Traditional chirp scaling algorithm is often developed based on the quadratic approximation of point target reference spectrum, which neglects the higher‐order coupling between range and azimuth dimensions. Besides, the scaling operation is conducted based on quadratic term of reference range, and the residual quadratic error increases with target range far away from reference range. The analysis of phase error shows that both errors are noticeable under the case of wide‐bandwidth signal, and the imaging performance would be seriously distorted. To solve this problem, the higher‐order coupling and quadratic error are compensated by exploiting sub‐block processing method in the range dimension when the chirp scaling algorithm is exploited to reconstruct targets. Compared to traditional methods, the presented method significantly improves the focussing performance based on the simulation results. The processing of real data further shows that the performance of presented method is superior to that of traditional method.

Borehole leakage is an important cause of gas extraction failure. In order to study the influence mechanism of borehole leakage on gas extraction, the borehole air leakage mode was studied, and a mathematical model was established to describe the borehole air leakage of the gas extraction. In addition, this paper also analyzed the change rules of borehole air leakage and gas extraction effect at different borehole sealing depth, negative extraction pressure, degree of fracture development and borehole sealing quality. Research shows that: (1) The hole sealing depth has a certain influence on the borehole air leakage and the gas extraction effect. As the hole sealing depth increased, the borehole air leakage gradually decreased. Moreover, the net amount of gas extraction gradually decreased, but the gas extraction concentration increased to some extent, and the increasing range gradually decreased. The reasonable sealing depth of this coal seam was 9∼10 m. (2) The negative pressure of borehole extraction has little influence on borehole air leakage and gas extraction. With the increase of the negative extraction pressure, the gas extraction net amount and borehole air leakage both increased, but the gas extraction concentration decreased. In the later stage of the gas extraction, the negative pressure can be properly reduced to improve the gas extraction effect. (3) The borehole sealing quality has a great influence on the borehole air leakage and gas extraction effect. With the improvement of the sealing quality, the coal-rock permeability gradually decreased. Moreover, the borehole air leakage significantly reduced, and the gas extraction concentration increased significantly. Therefore, attention should be paid to the selection and improvement of sealing materials and sealing techniques in the actual production so that the airtightness and sealing quality of the hole sealing section can be improved.

The ocean, covering 71% of the Earth’s surface, is integral to human life [...]

To use monostatic based imaging algorithms for multireceiver synthetic aperture sonar, the monostatic conversion is often carried out based on phase centre approximation, which is widely exploited by multireceiver SAS systems. This article presents a novel aspect for dealing with the multireceiver SAS imagery, which still depends on the idea of monostatic conversion. The approach in this article is based on Loffeld's bistatic formula that consists of two important terms, i.e., quasi monostatic and bistatic deformation terms. Our basic idea is to preprocess the bistatic deformation term and then incorporate the quasi monostatic term into an analogous monostatic spectrum. With this new spectrum, traditional imaging algorithms designed for monostatic synthetic aperture sonar can be easily exploited. In this article, we show that Loffeld's bistatic formula can be reduced to the same formula as spectrum based on phase centre approximation when certain conditions are met. Based on our error analysis, the maximum error magnitude of PCA method is about 1 rad, which would noticeably affect the SAS imagery. Fortunately, the error magnitude of presented method can be always kept within ${{\rm{\pi }} \mathord{/ {\vphantom {{\rm{\pi }} 4}} \kern-\nulldelimiterspace} 4}$. It means that Loffeld's bistatic formula provides a more accurate approximation of the spectrum compared to that based on phase centre approximation. After that, this article develops a new imaging scheme and presents imaging results. Based on quantitative comparisons, the presented method well focuses multireceiver SAS data, and it provides better image compared to phase centre approximation method.

To deeply study the variation characteristics of the gas content in the process of gas adsorption for coal samples under different gas pressures and confining pressures, low-field nuclear magnetic resonance technology was used to carry out experimental research on the gas adsorption of coal. The relationship between the T 2 spectrum amplitude integral and the gas quantity was analyzed. The results show the following: (1) When the samples were inflated for 11 h at each gas pressure point (0.31, 0.74, 1.11, and 1.46 MPa), after ∼5 h of adsorption, the amount of adsorbed gas exceeded 85.0% of the total adsorption capacity; additionally, as the adsorption time increased, the amount of adsorbed gas gradually tended to stabilize. When the gas pressure was >1 MPa, the amount of adsorbed gas exceeded 90.0% of the total adsorption capacity; Higher the pressure of aerated gas, greater the gas pressure gradient or concentration gradient on the surface of the coal sample and the greater the driving force for gas molecules to seep or diffuse into the coal sample. (2) When the samples were inflated for 11 h at each confining pressure point (3, 4, 5, and 7 MPa), the adsorbed gas increased by ∼85.0% of the total adsorbed gas in the first 5 h. When the pressure was

The pore characteristics of coal have an important influence on the coal adsorption of methane. The liquid nitrogen adsorption method was used to study the pore structure of low- and middle-rank coal samples from two aspects: pore specific surface area and pore shape. Low-field nuclear magnetic resonance (NMR) technology was used to study the difference in methane adsorption of coal samples under the same adsorption conditions. The influence and mechanism of the pore structure of middle- and low-rank coal samples on gas adsorption are discussed and analyzed. The results show the following: (1) There are differences in the adsorption capacity of medium- and low-rank coal samples. Within 1 h of methane inflation, the methane adsorption capacity of middle-rank coals such as Henan Pingdingshan (PDS) and Shanxi Wangzhuang (WZ) and Xinjiang low-rank coals (XJ) increases by 36.4%, 31.7%, and 35.8%, respectively, and as the inflation time is extended to the cumulative inflation of 10 h, the order of the increase in methane adsorption capacity is still PDS>XJ>WZ. (2) The pore types of the experimental coal samples are mostly wedge-shaped pores and ink bottle-shaped pores. The order of the BET specific surface area of the coal samples is in the order of WZ>PDS> XJ, which means that the WZ samples can provide more adsorption sites for gas molecule adsorption, but under the same adsorption conditions, the WZ sample has the least amount of gas adsorbed. Further analysis shows that the order of the tortuosity of the coal sample is WZ>XJ>PDS, which means that the WZ sample has a large pore tortuosity, a long channel for methane molecules to diffuse into the internal pores of the coal sample, and large diffusion resistance. It is the main reason why the methane adsorption capacity of WZ coal samples is less than that of PDS and XJ coal samples in the same adsorption conditions.

Abstract Background Despite potential for improving patient outcomes, studies using three-dimensional measurements to quantify proximal tibial sclerotic bone and its effects on prosthesis stability after total knee arthroplasty (TKA) are lacking. Therefore, this study aimed to determine: (1) the distribution range of tibial sclerotic bone in patients with severe genu varum using three-dimensional measurements, (2) the effect of the proximal tibial sclerotic bone thickness on prosthesis stability according to finite-element modelling of TKA with kinematic alignment (KA), mechanical alignment (MA), and 3° valgus alignment, and (3) the effect of short extension stem augment utilization on prosthesis stability. Methods The sclerotic bone in the medial tibial plateau of 116 patients with severe genu varum was measured and classified according to its position and thickness. Based on these cases, finite-element models were established to simulate 3 different tibial cut alignments with 4 different thicknesses of the sclerotic bone to measure the stress distribution of the tibia and tibial prosthesis, the relative micromotion beneath the stem, and the influence of the short extension stem on stability. Results The distribution range of proximal tibial sclerotic bone was at the anteromedial tibial plateau. The models were divided into four types according to the thickness of the sclerotic bone: 15 mm, 10 mm, 5 mm, and 0 mm. The relative micromotion under maximum stress was smallest after MA with no sclerotic bone (3241 μm) and largest after KA with 15 mm sclerotic bone (4467 μm). Relative micromotion was largest with KA and smallest with MA in sclerotic models with the same thickness. Relative micromotion increased as thickness of the sclerotic bone increased with KA and MA (R = 0.937, P = 0.03 and R = 0.756, P = 0.07, respectively). Relative micromotion decreased with short extension stem augment in the KA model when there was proximal tibial sclerotic bone. Conclusions The influence of proximal tibial sclerotic bone on prosthesis’s stability is significant, especially with KA tibial cut. Tibial component’s short extension stem augment can improve stability.

Time-optimal path-constrained trajectory planning is of significant importance for enhancing the work efficiency of robotic systems. In particular, when inadmissible island constraints are considered, existing approaches are typically offline. In order to solve the problem online, this paper proposes a heuristic tree-search-based any-time time-optimal trajectory planning algorithm to achieve incremental computation of feasible trajectories. In a limited planning period, the proposed algorithm iteratively generates feasible trajectories, as optimal as possible, until the period terminates. This any-time performance of the proposed algorithm ensures that feasible trajectories can be obtained in real time and even time-optimal trajectories can be obtained if the planning period is long enough for searching. Experimental results on active-casters-based omnidirectional wheeled mobile robots demonstrate the validity of the proposed algorithm.

The back projection (BP) algorithm is characterized by its high performance for multi-receiver synthetic aperture sonar (SAS). For this reason, it is usually used to evaluate the imaging performance of Fourier-domain methods. However, this algorithm suffers from a large computation load, and the imaging efficiency is seriously lowered. In order to improve the imaging performance, this paper proposes focusing the multi-receiver SAS data using the BP algorithm based on two interpolators, including the linear interpolation and nearest-neighbor interpolation. The former interpolation is used to decrease the interpolation error based on adjacent sampled data; the latter estimates the data at the desired moment by assigning the data value of the nearest sample as estimated data. Then, the imaging performance of the presented method is discussed in detail based on simulations and real-data processing. With the presented method, the imaging performance can be improved without a loss of efficiency compared to nearest-neighbor interpolation without an upsampling operation. In comparison with the traditional BP algorithm, the presented method can be used to improve the imaging efficiency without any loss of performance.

The shock wave generated by a severe gas explosion accident can damage the main fan, and the toxic and harmful gases in the well cannot be discharged in time, leading to the expansion of disaster accidents. Therefore, it is meaningful to study impact loads of main fan blades in gas explosion. In this paper, a full-scale three-dimensional numerical simulation model has been established based on No. 2 Yangchangwan Coal Mine in China. The propagation of shock wave in shaft and air tunnel and the dynamic process of main fan blade subjected to shock load when gas explosion of different volume occurs in heading face have been simulated. The overpressure on the blade at different times, the overpressure distribution on the blade, and the relationship between the overpressure and the explosion intensity have been obtained. The results showed that the time when the explosion shock wave reached, each blade of the wind turbine was basically the same, and the time when each blade reached, the maximum overpressure was basically the same. With the increase of gas explosion volume, occurrence time of overpressure and maximum overpressure time on the fan blade were shortened, and the time interval between them was also shortened. There is a little difference in the overpressure of each blade. Fan blade directly above the hub was subject to the highest overpressure, and fan blade directly below the hub was subject to the lowest overpressure. The overpressure of the maximum overpressure blade was 5.44% to 6.77% higher than that of the minimum overpressure blade. The distribution of overpressure on each fan blade was uneven, and the overpressures on blade edges were the lowest. The overpressure on the fan blades showed a corrugated distribution along the radial direction. There was 12.06% to 15.40% difference between the maximum and minimum overpressure section on the fan blade.

When the multi-receiver synthetic aperture sonar (SAS) works with a wide-bandwidth signal, the performance of the range-Doppler (R-D) algorithm is seriously affected by two approximation errors, i.e., point target reference spectrum (PTRS) error and residual quadratic coupling error. The former is generated by approximating the PTRS with the second-order term in terms of the instantaneous frequency. The latter is caused by neglecting the cross-track variance of secondary range compression (SRC). In order to improve the imaging performance in the case of wide-bandwidth signals, an improved R-D algorithm is proposed in this paper. With our method, the multi-receiver SAS data is first preprocessed based on the phase center approximation (PCA) method, and the monostatic equivalent data are obtained. Then several sub-blocks are generated in the cross-track dimension. Within each sub-block, the PTRS error and residual quadratic coupling error based on the center range of each sub-block are compensated. After this operation, all sub-blocks are coerced into a new signal, which is free of both approximation errors. Consequently, this new data is used as the input of the traditional R-D algorithm. The processing results of simulated data and real data show that the traditional R-D algorithm is just suitable for an SAS system with a narrow-bandwidth signal. The imaging performance would be seriously distorted when it is applied to an SAS system with a wide-bandwidth signal. Based on the presented method, the SAS data in both cases can be well processed. The imaging performance of the presented method is nearly identical to that of the back-projection (BP) algorithm.

This paper presents a feature classification method based on vision sensor in dynamic environment. Aiming at the detected targets, a double-projection error based on orb and surf is proposed, which combines texture constraints and region constraints to achieve accurate feature classification in four different environments. For dynamic targets with different velocities, the proposed classification framework can effectively reduce the impact of large-area moving targets. The algorithm can classify static and dynamic feature objects and optimize the conversion relationship between frames only through visual sensors. The experimental results show that the proposed algorithm is superior to other algorithms in both static and dynamic environments.

The area coverage rate is dramatically improved by using the multireceiver technique. However, this configuration leads to the complexity of the synthetic aperture image formation. In order to solve this issue, the target based on the phase centre approximation (PCA) is to be reconstructed. The data related to the multireceiver SAS system is coerced into the data like traditional monostatic synthetic aperture sonar (SAS) system. Then, the data can be processed by traditional imaging methods. In this paper, the chirp scaling algorithm is exploited as an example. Moreover, the influence of some important steps with the monostatic conversion, i.e. pulse compression in the range dimension and the micro range cell migration correction (RCMC), is further discussed in detail. The simulations show that the presented method can focus the target well.

The attribution of learning success or failure is crucial for students' learning and motivation. Effective attribution of their learning success or failure in the context of a small private online course (SPOC) could generate students' motivation toward learning success while an incorrect attribution would lead to a sense of helplessness. Based on the attribution theories developed by Wiener and Kelly with learning analytics technology, this article developed a systematic framework for learning analytics in SPOC in an undergraduate course. A total of 197 undergraduates participated in the experiment and were randomly assigned to a treatment group (98 students) and a control group (99 students). The treatment group applied the learning analytics system framework in a SPOC, and the control group applied the traditional SPOC teaching method, and other conditions are consistent. Structural equation modeling is adopted to explore the correlations among attribution variables (i.e., ability, effort, difficulty of the task, and luck), motivational variables (i.e., endogenous motivation, and extrinsic motivation), and learning achievement. The results indicated that all four attribution variables have a significant correlation with both endogenous and extrinsic motivation and have a significant effect on learning achievement. Students in the experimental class exhibited better outcomes than students in the control class with respect to learning motivation and learning achievement. The findings validated the effectiveness of using the SPOC analytics system to facilitate SPOC learners making effective attributions, leading to the enhancement of learning motivation and achievement.

This article presents a novel line segment extraction algorithm using two-dimensional (2D) laser data, which is composed of four main procedures: seed-segment detection, region growing, overlap region processing, and endpoint generation. Different from existing approaches, the proposed algorithm borrows the idea of seeded region growing in the field of image processing, which is more efficient with more precise endpoints of the extracted line segments. Comparative experimental results with respect to the well-known Split-and-Merge algorithm are presented to show superior performance of the proposed approach in terms of efficiency, correctness, and precision, using real 2D data taken from our hallway and laboratory.

Motivated by achieving precise positioning of the throttle plate, an extended state observer–based intelligent double integral sliding mode control strategy is proposed for the electronic throttle control system. Specifically, an extended state observer is first designed to observe the opening angle change of the electronic throttle and compensate unexpected external disturbance. On this basis, an intelligent double integral sliding mode controller for electronic throttle valve is presented based on Lyapunov stability theory and sliding mode control theory, which includes stability analysis and parameter adaptation design. Finally, extensive simulations are conducted to demonstrate the superior performance of the proposed method.

Near infrared spectroscopy (NIRS) analysis technology, combined with chemometrics, can be effectively used in quick and nondestructive analysis of quality and category. In this paper, an effective drug identification method by using deep belief network (DBN) with dropout mechanism (dropout-DBN) to model NIRS is introduced, in which dropout is employed to overcome the overfitting problem coming from the small sample. This paper tests proposed method under datasets of different sizes with the example of near infrared diffuse reflectance spectroscopy of erythromycin ethylsuccinate drugs and other drugs, aluminum and nonaluminum packaged. Meanwhile, it gives experiments to compare the proposed method’s performance with back propagation (BP) neural network, support vector machines (SVMs) and sparse denoising auto-encoder (SDAE). The results show that for both binary classification and multi-classification, dropout mechanism can improve the classification accuracy, and dropout-DBN can achieve best classification accuracy in almost all cases. SDAE is similar to dropout-DBN in the aspects of classification accuracy and algorithm stability, which are higher than that of BP neural network and SVM methods. In terms of training time, dropout-DBN model is superior to SDAE model, but inferior to BP neural network and SVM methods. Therefore, dropout-DBN can be used as a modeling tool with effective binary and multi-class classification performance on a spectrum sample set of small size.

In this paper, we introduce a novel sub-bottom profiler, making good use of the Mills cross configuration of multibeam sonar and synthetic aperture techniques of the synthetic aperture sonar system. The receiver array is mounted along the ship keel, while the transmitter array is mounted perpendicular to the receiver array. With the synthetic aperture technique, the along-track resolution can be greatly improved. The system often suffers from motion error, which severely degrades the imaging performance. To solve this problem, the imaging algorithm with motion compensation (MC) is proposed. With the presented method, the motion error is first estimated based on overlapped elements between successive pulses. Then, the echo data is processed by using the range migration algorithm based on the phase center approximation (PCA) method, which simultaneously performs the MC with the estimated motion error. In order to validate the proposed sub-bottom profiler and data processing method, some simulations and lake trial results are discussed. The processing results of the real data further indicate that the presented configuration has great potential to find buried objects in seabed sediments.

For the multireceiver synthetic aperture sonar (SAS), the point target reference spectrum (PTRS) in the two-dimensional (2D) frequency domain and azimuth modulation in the range Doppler domain were first deduced based on a numerical evaluation method and accurate time delay. Then, the difference between the PTRS and azimuth modulation generated the coupling term in the 2D frequency domain. Compared with traditional methods, the PTRS, azimuth modulation and coupling term was better at avoiding approximations. Based on three functions, an imaging algorithm is presented in this paper. Considering the fact that the coupling term is characterized by range variance, the range-dependent sub-block processing method was exploited to perform the decoupling. Simulation results showed that the presented method improved the imaging performance across the whole swath in comparison with existing multireceiver SAS processor. Furthermore, real data was used to validate the presented method.

Birdsongs and the regions of their brain that control song exhibit obvious sexual differences. However, the mechanisms underlying these sexual dimorphisms remain unknown. To address this issue, we first examined apoptotic cells labeled with caspase-3 or TUNEL in Bengalese finch song control nuclei - the robust nucleus of the archopallium (RA), the lateral magnocellular nucleus of the anterior nidopallium (LMAN), the high vocal center (HVC) and Area X from post-hatch day (P) 15 to 120. Next, we investigated the expression dynamics of pro-apoptotic (Bid, Bad and Bax) and anti-apoptotic (Bcl-2 and Bcl-xL) genes in the aforementioned nuclei. Our results revealed that the female RA at P45 exhibited marked cell apoptosis, confirmed by low densities of Bcl-xL and Bcl-2. Both the male and female LMAN exhibited apoptotic peaks at P35 and P45, respectively, and the observed cell loss was more extensive in males. A corresponding sharp decrease in the density of Bcl-2 after P35 was observed in both sexes, and a greater density of Bid was noted at P45 in males. In addition, we observed that RA volume and the total number of BDNF-expressing cells decreased significantly after unilateral lesion of the LMAN or HVC (two areas that innervate the RA) and that greater numbers of RA-projecting cells were immunoreactive for BDNF in the LMAN than in the HVC. We reasoned that a decrease in the amount of BDNF transported via HVC afferent fibers might result in an increase in cell apoptosis in the female RA. Our data indicate that cell apoptosis resulting from different pro- and anti-apoptotic agents is involved in generating the differences between male and female song control nuclei.

In order to discover novel eco-friendly lead compounds for plant pathogenic fungi control, a series of benzaldehyde thiosemicarbazide derivatives with a piperidine moiety have been designed and synthesized. Fungicidal activities of all the synthesized compounds were evaluated in vitro. The results indicated that all the title compounds exhibited moderate to good fungicidal activities. Compound 3b displayed excellent activities against Pythium aphanidermatum, Rhizoctonia solani, Valsa mali, and Gaeu-mannomyces graminsis, with EC50 values lower than 10 μg/mL. Especially, in the case of Pythium aphanidermatum, its activity (EC50 = 1.6 μg/mL) is superior to the commercial azoxystrobin (EC50 = 16.9 μg/mL) and close to fluopicolide (EC50 = 1.0 μg/mL). Initial structure–activity relationship (SAR) analysis showed that the heterocyclic piperidine group can influence the biological activities of the title compounds significantly. The fungicidal activity of compounds with piperidine is better than that of compounds without piperidine. The highly-active compound 3b, with its simple structure and easy synthetic route, is worthy to be further studied as a new lead fungicide.

Samples of preparations contaminated by diethylene glycol (DEG), diethylene glycol raw materials and laboratory prepared solutions were measured to get NIR spectra. Then the identification models were developed using the collected spectra and the spectra of distilled water, propylene glycol and the preparations without diethylene glycol. Besides, the quantification model was also established for determining the concentration of diethylene glycol in the preparations. Validation results show the identification and quantification models have ideal prediction performance. The emergency NIR models are rapid, easy to use and accurate, and can be implemented for identifying diethylene glycol raw material, screening the preparations contaminated by diethylene glycol in the markets and analyzing the concentrations of DEG.

Song control nuclei have distinct sexual differences and thus are an ideal model to address how brain areas are sexually differentiated. Through a combination of histological analysis and electrical lesions, we first identified the ventricle site for HVC progenitor cells. We then found that there were significant sex differences in the cellular proliferation activity in the ventricular zone of the HVC, the number of migrating cells along the radial cells (positive immunoreactions to vimentin) and differentiation towards neurons. Through co-culturing of male and female slices containing the developing HVC in the same well, we found that the male slices could produce diffusible substances to masculinize the female HVC. By adding estrogen, an estrogen antagonist, brain-derived neurotrophic factor (BDNF) or its antibody into the culture medium, separately or in combination, we found that these diffusible substances may include estrogen and BDNF. Finally, we found that 1) estrogen-induced BDNF upregulation could be detected 48 hr after estrogen treatment and could not be blocked by a vascular endothelial growth factor (VEGF) receptor inhibitor and 2) the amount of VEGF mRNA expressed in the developing HVC and its adjacent area did not display any significant sex differences, as did the distribution of VEGF and laminin-expressing endothelial cells in the developing HVC. Because these findings are largely different from previous reports on the adult female HVC, it is suggested that our estrogen-induced BDNF up-regulation and the resultant sexual differentiation might not be mediated by VEGF and endothelial cells, but instead, may result from the direct effects of estrogen on BDNF.