Search

Extraction of molybdenum (Mo) from jordisite is difficult due to the amorphous state of MoS2. In this study, mechanical activation was employed to pretreat this type of ore with a low Mo content of 0.26%, and then molybdenum and uranium were both extracted from the milled ore using sulfuric acid. The effects of milling time, oxidant, and optimal leaching conditions were investigated in the laboratory. The results show that the mechanical activation will reduce the particle size and increase the specific surface area of the ore under certain milling conditions. Mechanical activation without oxidants in a hypoxia environment is not conductive to the recovery of molybdenum. When the oxidant of MnO2 is added during the milling process, the Mo recovery will increase greatly. The effect of mechanical activation on U recovery is not so obvious. The phenomenon of agglomerate will occur during the milling process, which will reduce Mo recovery seriously, especially when the milling time is more than 120 min. The Mo and U recovery can reach 84.52% and 61.39%, respectively, after optimization of sulfuric acid leaching process conditions. [ABSTRACT FROM AUTHOR]

Space-borne synthetic aperture radar (SAR), as an all-weather observation sensor, is an important means in modern information electronic warfare. Since SAR is a broadband active radar system, radio frequency interference (RFI) in the same frequency band will affect the normal observation of the SAR system. Untangling the above problem, this research explores a quick and accurate method for detecting and segmenting RFI-contaminated images. The purpose of the current method is to quickly detect the existence of RFI and to locate it in massive SAR data. Based on deep learning, the method shown in this paper realizes the existence of RFI by determining the presence or absence of interference in the image domain and then performs pixel-level image segmentation on Sentinel-1 RFI-affected quick-look images to locate RFI. Considering the need to quickly detect RFI in massive SAR data, an improved network based on MobileNet is proposed, which replaces some inverted residual blocks in the network with ghost blocks, reducing the number of network parameters and the inference time to 6.1 ms per image. Further, this paper also proposes an improved network called the Smart Interference Segmentation Network (SISNet), which is based on U2Net and replaces the convolution of the VGG blocks in U2Net with a residual convolution and introduces attention mechanisms and a modified RFB module to improve the segmentation mIoU to 87.46% on average. Experiment results and statistical analysis based on the MID dataset and PAIS dataset show that the proposed methods can achieve quicker detection than other CNNs while ensuring a certain accuracy and can significantly improve segmentation performance under the same conditions compared to the original U2Net and other semantic segmentation networks. [ABSTRACT FROM AUTHOR]

Sandstones are enriched in deep energy reservoirs and also exist as outcrop rocks, where the pore characteristics of sandstone are influenced by hydration absorption and thermal effects. To study the influence of the initial temperature on the hydration absorption characteristics of outcrop porous sandstone in the Mogao Grottoes, China, an intelligent experimental device for rock hydration was used. The hydration absorption characteristics and temperature effects of sandstone were analyzed by using infrared thermography techniques to monitor the infrared radiation characteristics of the sandstone's surface during hydration absorption. The experimental results show that the higher the initial temperature of the rock samples, the shorter the time it takes for the sandstone to absorb enough water to reach saturation. The temperature variation of sandstone with different initial temperatures was also determined; the variation in the hydration absorption of sandstone conforms to certain rules, which can be expressed by formulae containing certain parameters. The changing trend of hydration absorption in outcrop porous sandstone shows that the hydration absorption increases rapidly at first, and then the rate of increase slows down until the hydration absorption remains unchanged after saturation. The experimental technique and method provide feasible means and techniques to evaluate the hydration absorption and thermal effects of outcrop porous sandstone, for further detecting the weathering degree of rock grottoes and revealing the damage mechanisms. [ABSTRACT FROM AUTHOR]

Purpose: Multi-well hydrofracturing is an important technology to create new fractures and expand existing fractures to increase reservoir permeability. The propagation morphology of the fracture network is affected by the disturbance between the fractures initiation sequences and spacings between adjacent wells. However, it remains unclear how well spacing and initiation sequences lead to fracture propagation, deflection and connection. Design/methodology/approach: In this study, the thermal-hydro-mechanical coupling effect in the hydrofracturing process was considered, to establish a finite element-discrete element model of multistage hydrofracturing in a horizontal well. Using typical cases, the unstable propagation of hydraulic fractures in multiple horizontal wells was investigated under varying well spacing and initiation sequences. Combined with the shear stress shadow caused by in situ stress disturbed by fracture tip propagation, the quantitative indexes of fracture propagation such as length, volume, displacement vector, deflection and unstable propagation behavior of the hydrofracturing fracture network were analyzed. Findings: The results show that the shear stress disturbance caused by multiple hydraulic fractures is a significant factor in multi-well hydrofracturing. Reducing the spacing between multiple wells increases the stress shadow area and aggravates the mutual disturbance and deflection between the fractures. The quantitative analysis results show that a decrease of well spacing reduces the total length of hydraulic fractures but increases the total volume of the fracture; compared with sequential and simultaneous fracturing, alternate fracturing can effectively reduce stress shadow area, alleviate fracture disturbance and generate larger fracture propagation length and volume. Originality/value: The numerical models and results of the unstable propagation and stress evolution of the hydraulic fracture network under thermal-hydro-mechanical coupling obtained in this study can provide useful guidance for the evaluation and design of rock mass fracture networks in deep unconventional oil and gas reservoirs. [ABSTRACT FROM AUTHOR]

Purpose: The induction of geological disasters is predominantly influenced by the dynamic evolution of the stress and plastic zones of the multilayer rock formations surrounding deep-rock roadways, and the behaviours and mechanisms of high in situ stress are key scientific issues related to deep-resource exploitation. The stress environment of deep resources is more complex owing to the influence of several geological factors, such as tectonic movements and landforms. Therefore, in practical engineering, the in situ stress field is in a complex anisotropic three-dimensional state, which may change the deformation and failure law of the surrounding rock. The purpose of this study is to investigate the tunnelling-induced stress and plastic evolution causing instability of multilayered surrounding rock by varying three-dimensional in situ stresses. Design/methodology/approach: Based on data from the Yangquan Coal Mine, China, a finite difference model was established, and the elastic-plastic constitutive model and element deletion technology designed in the study were analysed. Gradual tunnelling along the roof and floor of the coal seam was used in the model, which predicted the impact tendency, and compared the results with the impact tendency report to verify the validity of the model. The evolutions of the stress field and plastic zone of the coal roadway in different stress fields were studied by modifying the maximum horizontal in situ stress, minimum horizontal in situ stress and lateral pressure coefficient. Findings: The results shown that the in situ stress influenced the stress distribution and plastic zone of the surrounding rock. With an increase in the minimum horizontal in situ stress, the vertical in situ stress release area of the roof surrounding rock slowly decreased; the area of vertical in situ stress concentration area of the deep surrounding rock on roadway sides decreased, increased and decreased by turn; the area of roof now-shear failure area first increased and then decreased. With an increase in the lateral pressure coefficient, the area of the horizontal in situ stress release area of the surrounding rock increased; the area of vertical in situ stress release area of the roof and floor surrounding rock first decreased and then increased; the area of deep stress concentration area of roadway sides decreased; and the plastic area of the surrounding rock and the area of now-shear failure first decreased and then increased. Originality/value: The results obtained in this study are based on actual cases and reveal the evolution law of the disturbing stress and plastic zone of multilayer surrounding rock caused by three-dimensional in situ stress during the excavation of deep rock roadways, which can provide a practical reference for the extraction of deep resources. [ABSTRACT FROM AUTHOR]

Purpose: Multi-well hydrofracturing is a key technology in engineering, and the evaluation, control and optimization of the fracturing network determine the recovery rate of unconventional oil and gas production. In engineering terms, altering well spacing and perforation initiation sequences changes fracture propagation behavior. Fracture propagation can result in fracture-to-fracture and well-to-well interactions. This may be attributed to the interference between fractures caused by squeezing of the reservoir strata. Meanwhile, the stratal movement caused by the propagation of the fractures may lead to either the secondary fracturing of wells with primary fractures or perforation to begin fracturing. Besides, the stratal compression and squeeze of multi-well hydrofracturing will cause earthquakes; the fracture size is different owing to the different fracturing scenarios, and the occurrence of induced microseismic events is still unknown; microseismic events also affect fracture orientation and deflection. If the mechanism of the above mechanical behavior cannot be clarified, optimizing the fracture network and reduce the induced microseismic disaster becomes difficult. Design/methodology/approach: In this study, combined finite element-discrete element models were used to simulate the multi-well hydrofracturing. Numerical cases compared the fracture network, dynamic stratal movement and microseismic events at 50, 75 and 100 m well spacings, respectively, and varying initiation sequence of multiple horizontal wells. Findings: From the results, fracture propagation in multi-well hydrofracturing may simulate the propagation and deflection of adjacent fractures and induce fracture-to-fracture and well-to-well interactions. As the well spacing increases, the effect of fracturing-induced stratal movement and squeezing deformation decrease. In alternate fracturing, starting from a well located in the middle can effectively reduce the influence of stratal movement on fracturing, and the fracturing scenario with cross-perforation can minimize the influence of stratal movement. The stratal movement between multiple wells is positively correlated to microseismic events, which behaviors can be effectively weakened by reducing the strata movement. Originality/value: The fracture network, thermal-hydro-mechanical coupling, fracturing-induced stratal movement and microseismic events were analyzed. This study analyzed the intersection and propagation behavior of fractures in multi-well hydrofracturing, which can be used to evaluate and study the mechanism of hydrofracturing fracture network propagation in multiple horizontal wells and conduct fracture optimization research to form an optimized hydrofracturing scheme by reasonably arranging the spacing between wells and initiation sequences of perforation clusters. [ABSTRACT FROM AUTHOR]

In this paper, the effects of initial electrons generation approaches on nanosecond pulsed breakdown characteristics are analyzed. Based on the numerical simulations with a 3D PIC-MCC model, the impacts of field-enhancement factor and initial electron concentration on nanosecond pulsed breakdown characteristics are investigated. Three types of switches are designed and subjected to testing under pulse voltages with rise times of 40, 70, and 120 ns, respectively. The results can be summarized as follows. First, the field-enhancement factor and initial electron concentration have significant influences on the development of the discharge channel. Second, the cathode-grooved self-triggered switch exhibits lower breakdown time delay jitter than the hemispherical self-breakdown switch at low pressure, while the differences in jitter between the two switches become negligible at high pressure. Third, the cathode-grooved self-triggered switch shows a lower breakdown time delay jitter compared to the pre-ionization self-triggered switch for pulse voltages with rise times of 40 and 70 ns. Conversely, this trend reverses for pulse voltage with a rise time of 120 ns. Finally, the breakdown time delay jitter for both the cathode-grooved self-triggered switch and the pre-ionization self-triggered switch has been reduced, and both switches are suitable for different operating requirements and conditions. [ABSTRACT FROM AUTHOR]

Teaching is deemed a taxing enterprise, especially as far as higher education is concerned. As a result, much research attention has been showered upon exploring the correlates of engagement for instructors. To contribute to this research direction, the present researchers carried out this survey to test a model of work engagement in a Chinese higher education context. Teacher self-efficacy and resilience were added as predictors of the hypothesized model. A number of 372 Chinese English as a foreign language (EFL) instructors in higher education contexts were selected through convenience sampling. The measurement models of the latent variables (i.e., self-efficacy, resilience, and work engagement) were confirmed via running Confirmatory Factor Analysis (CFA). Afterward, Structural Equation Modeling (SEM) was used to test the structural model. The results obtained from the analyses showed that both teacher self-efficacy and resilience could significantly predict EFL teachers' work engagement, with self-efficacy serving as a stronger predictor than resilience. The outcomes suggest some implications for EFL stakeholders such as teachers, teacher trainers, policy makers, and officials. Plain Language Summary: This new article bridges the identified gaps in the literature, and the current research intends to examine the predictability of EFL teachers work engagement level in terms of their self-efficacy beliefs and resilience tendencies. Based on our observation, there is a paucity in the literature examining the causal relationship between teacher self-efficacy and teacher work engagement in HE, and to our knowledge, this is the first study to consider teacher self-efficacy as a potential predictive variable of work engagement of EFL teachers in HE. [ABSTRACT FROM AUTHOR]

Lysin-Motif receptor-like kinase (LysM-RLK) proteins are widely distributed in plants and serve a critical role in defending against pathogens and establishing symbiotic relationships. However, there is a lack of comprehensive identification and analysis of LysM-RLK family members in the soybean genome. In this study, we discovered and named 27 LysM-RLK genes in soybean. The majority of LysM-RLKs were highly conserved in Arabidopsis and soybean, while certain members of subclades III, VI, and VII are unique to soybean. The promoters of these LysM-RLKs contain specific cis-elements associated with plant development and responses to environmental factors. Notably, all LysM-RLK gene promoters feature nodule specificity elements, while 51.86% of them also possess NBS sites (NIN/NLP binding site). The expression profiles revealed that genes from subclade V in soybean roots were regulated by both rhizobia and nitrogen treatment. The expression levels of subclade V genes were then validated by real-time quantitative PCR, and it was observed that the level of GmLYK4a and GmLYK4c in roots was inhibited by rhizobia but induced via varying concentrations of nitrate. Consequently, our findings provide a comprehensive understanding of the soybean LysM-RLK gene family and emphasize the role of subclade V in coupling soybean symbiotic nitrogen fixation and nitrogen response. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to investigate the unstable propagation of parallel hydraulic fractures induced by interferences of adjacent perforation clusters and thermal diffusion. Fracture propagation in the process of multistage fracturing of a rock mass is deflected owing to various factors. Hydrofracturing of rock masses in deep tight reservoirs involves thermal diffusion, fluid flow and deformation of rock between the rock matrix and fluid in pores and fractures. Design/methodology/approach: To study the unstable propagation behaviours of three-dimensional (3D) parallel hydraulic fractures induced by the interferences of adjacent perforation clusters and thermal diffusion, a 3D engineering-scale numerical model is established under different fracturing scenarios (sequential, simultaneous and alternate fracturing) and different perforation cluster spacings while considering the thermal-hydro-mechanical coupling effect. Stress disturbance region caused by fracture propagation in a deep tight rock mass is superimposed and overlaid with multiple fractures, resulting in a stress shadow effect and fracture deflection. Findings: The results show that the size of the stress shadow areas and the interaction between fractures increase with decreasing multiple perforation cluster spacing in horizontal wells. Alternate fracturing can produce more fracture areas and improve the fracturing effect compared with those of sequential and simultaneous fracturing. The larger the temperature gradient between the fracturing fluid and rock matrix, the stronger the thermal diffusion effect, and the effect of thermal diffusion on the fracture propagation is significant. Originality/value: This study focuses on the behaviours of the unstable dynamic propagation of 3D parallel hydraulic fractures induced by the interferences of adjacent perforation clusters and thermal diffusion. Further, the temperature field affects the fracture deflection requires could be investigated from the mechanisms; this paper is to study the unstable propagation of fractures in single horizontal well, which can provide a basis for fracture propagation and stress field disturbance in multiple horizontal wells. [ABSTRACT FROM AUTHOR]

Silica nanoparticles (nano-silica) were used as synergistic agents with ammonium polyphosphate (APP) and pentaerythritol (PER) to enhance flame retardancy of polypropylene (PP) in this research. The composites were prepared using a melt-mixing method. The influences of nano-silica on the fire performance of composites were thoroughly discussed, which promotes understanding of nano-silica on the flame-retardant performance of polypropylene composite. Scanning electron microscope (SEM) and energy-dispersive spectrometer (EDS) results indicated that the nano-silica with a diameter of about 95 ± 3.9 nm were dispersed favorably in the composite matrix, which might elevate its synergistic effect with intumescent flame retardant and improve the flame retardancy of polypropylene composite. The synergistic effects between nano-silica and intumescent flame retardant on PP composites were studied using the limiting oxygen index (LOI), UL-94 test, and cone calorimeter test (CCT). The total amount of flame retardant was maintained at 30%. When the dosage of nano-silica was 1 wt.%, the LOI value of PP/IFR/Si1.0 composite reached 27.3% and its UL-94 classification reached V-1. Based on the parameters of the CCT, the introduction of nano-silica induced composites with depressed heat release rate (HRR) and peak heat release rate (PHRR). The PHRR of PP/IFR/Si0.5 was only 295.8 kW/m2, which was 17% lower than that of PP/IFR. Moreover, the time to PHRR of PP/IFR/Si0.5 was delayed to 396 s, which was about 36 s later than that without nano-silica. EDS was used to quantitatively analyze the distribution of silica in charred residue. The EDS results indicated that the silica tended to accumulate on the surface during the fire. The surface accumulation characteristic of silica endows it with the enhanced flame-retardant properties of polypropylene composite at a very small dosage (as low as 1 wt.%). [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to solve the engineering problem of free vibration disturbance and local mesh refinement induced by microcrack damage in circularly curved beams. The accurate identification of the crack damage depth, number and location depends on high-precision frequency and vibration mode solutions; therefore, it is critical to obtain these reliable solutions. The high-precision finite element method for the free vibration of cracked beams needs to be developed to grasp and control error information in the conventional solutions and the non-uniform mesh generation near the cracks. Moreover, the influence of multi-crack damage on the natural frequency and vibration mode of a circularly curved beam needs to be detected. Design/methodology/approach: A scheme for cross-sectional damage defects in a circularly curved beam was established to simulate the depth, location and the number of multiple cracks by implementing cross-section reduction induced by microcrack damage. In addition, the h-version finite element mesh adaptive analysis method of the Timoshenko beam was developed. The superconvergent solution of the vibration mode of the cracked curved beam was obtained using the superconvergent patch recovery displacement method to determine the finite element solution. The superconvergent solution of the frequency was obtained by computing the Rayleigh quotient. The superconvergent solution of the eigenfunction was used to estimate the error of the finite element solution in the energy norm. The mesh was then subdivided to generate an improved mesh based on the error. Accordingly, the final optimised meshes and high-precision solution of natural frequency and mode shape satisfying the preset error tolerance can be obtained. Lastly, the disturbance behaviour of multi-crack damage on the vibration mode of a circularly curved beam was also studied. Findings: Numerical results of the free vibration and damage disturbance of cracked curved beams with cracks were obtained. The influences of crack damage depth, crack damage number and crack damage distribution on the natural frequency and mode of vibration of a circularly curved beam were quantitatively analysed. Numerical examples indicate that the vibration mode and frequency of the beam would be disturbed in the region close to the crack damage, and a greater crack depth translates to a larger frequency change. For multi-crack beams, the number and distribution of cracks also affect the vibration mode and natural frequency. The adaptive method can use a relatively dense mesh near the crack to adapt to the change in the vibration mode near the crack, thus verifying the efficacy, accuracy and reliability of the method. Originality/value: The proposed combination of methodologies provides an extremely robust approach for free vibration of beams with cracks. The non-uniform mesh refinement in the adaptive method can adapt to changes in the vibration mode caused by crack damage. Moreover, the proposed method can adaptively divide a relatively fine mesh at the crack, which is applied to investigating free vibration under various curved beam angles and crack damage distribution conditions. The proposed method can be extended to crack damage detection of 2D plate and shell structures and three-dimensional structures with cracks. [ABSTRACT FROM AUTHOR]

In this paper, the effects of pulse voltage rise time on the nanosecond pulsed breakdown of the nitrogen spark switch at atmospheric pressure are analyzed. Based on the assumption of initial electrons generation due to the field emission, the simulations are performed using a three-dimensional particle-in-cell, Monte Carlo-collision model for the pulse voltage with a rise time of 40, 60, and 100 ns, respectively. The breakdown experiments of the nitrogen spark switch are carried out for three different rise times. The results obtained are as follows. First, the nanosecond pulsed breakdown of the switch includes the formation and fast propagation of the streamer, which depend on the multiplication of the electron avalanche, and the intense ionization due to photoelectrons and energetic electrons, respectively. Second, with the rise time of pulse voltage increasing, the generation of runaway electrons becomes more difficult and the streamer branches, which are mainly caused by photoionization and captured energetic electrons, become more obvious. Finally, the breakdown time delay of the switch becomes shorter and the breakdown voltage becomes higher at the same pressure for the decreasing rise time of pulse voltage, which is consistent with the measurement results. [ABSTRACT FROM AUTHOR]

Recently, researchers have focused on various factors influencing work engagement, particularly in the EFL context. In this vein, this study was carried out to investigate the relationship among proactive personality, flow, and work engagement in China. In so doing, three instruments including Proactive Personality Scale, Work-Related Flow Inventory (WOLF), and Work and Well-Being Survey (UWES) were used. Employing a convenience sampling method, 350 English teachers were selected from 20 provinces in China. Structural equation modeling (SEM) was utilized to analyze the obtained data. The findings demonstrated a positive correlation among EFL teachers’ flow, proactive personality, and work engagement. The results of SEM also indicated that work engagement could be predicted by both flow and proactive personality; however, flow had more predictive power. The findings from this study have both theoretical and practical implications for second/foreign language researchers and different stakeholders. [ABSTRACT FROM AUTHOR]

Purpose: The unstable dynamic propagation of multistage hydrofracturing fractures leads to uneven development of the fracture network and research on the mechanism controlling this phenomenon indicates that the stress shadow effects around the fractures are the main mechanism causing this behaviour. Further studies and simulations of the stress shadow effects are necessary to understand the controlling mechanism and evaluate the fracturing effect. Design/methodology/approach: In the process of stress-dependent unstable dynamic propagation of fractures, there are both continuous stress fields and discontinuous fractures; therefore, in order to study the stress-dependent unstable dynamic propagation of multistage fracture networks, a series of continuum-discontinuum numerical methods and models are reviewed, including the well-developed extended finite element method, displacement discontinuity method, boundary element method and finite element-discrete element method. Findings: The superposition of the surrounding stress field during fracture propagation causes different degrees of stress shadow effects between fractures and the main controlling factors of stress shadow effects are fracture initiation sequence, perforation cluster spacing and well spacing. The perforation cluster spacing varies with the initiation sequence, resulting in different stress shadow effects between fractures; for example, the smaller the perforation cluster spacing and well spacing are, the stronger the stress shadow effects are and the more seriously the fracture propagation inhibition arises. Moreover, as the spacing of perforation clusters and well spacing increases, the stress shadow effects decrease and the fracture propagation follows an almost straight pattern. In addition, the computed results of the dynamic distribution of stress-dependent unstable dynamic propagation of fractures under different stress fields are summarised. Originality/value: A state-of-art review of stress shadow effects and continuum-discontinuum methods for stress-dependent unstable dynamic propagation of multiple hydraulic fractures are well summarized and analysed. This paper can provide a reference for those engaged in the research of unstable dynamic propagation of multiple hydraulic structures and have a comprehensive grasp of the research in this field. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to provide a reliable and effective algorithm that is suitable for addressing the problems of continuous orders of frequencies and modes under different boundary conditions, circumferential wave numbers and thickness-to-length ratios of moderately thick circular cylindrical shells. The theory of free vibration of rotating cylindrical shells is of utmost importance in fields such as structural engineering, rock engineering and aerospace engineering. The finite element method is commonly used to study the theory of free vibration of rotating cylindrical shells. The proposed adaptive finite element method can achieve a considerably more reliable high-precision solution than the conventional finite element method. Design/methodology/approach: On a given finite element mesh, the solutions of the frequency mode of the moderately thick circular cylindrical shell were obtained using the conventional finite element method. Subsequently, the superconvergent patch recovery displacement method and high-order shape function interpolation techniques were introduced to obtain the superconvergent solution of the mode (displacement), while the superconvergent solution of the frequency was obtained using the Rayleigh quotient computation. Finally, the superconvergent solution of the mode was used to estimate the errors of the finite element solutions in the energy norm, and the mesh was subdivided to generate a new mesh in accordance with the errors. Findings: In this study, a high-precision and reliable superconvergent patch recovery solution for the vibration modes of variable geometrical rotating cylindrical shells was developed. Compared with conventional finite element method, under the challenging varying geometrical circumferential wave numbers, and thickness–length ratios, the optimised finite element meshes and high-precision solutions satisfying the preset error limits were obtained successfully to solve the frequency and mode of continuous orders of rotating cylindrical shells with multiple boundary conditions such as simple and fixed supports, demonstrating good solution efficiency. The existing problem on the difficulty of adapting a set of meshes to the changes in vibration modes of different orders is finally overcome by applying the adaptive optimisation. Originality/value: The approach developed in this study can accurately obtain the superconvergent patch recovery solution of the vibration mode of rotating cylindrical shells. It can potentially be extended to fine numerical models and high-precision computations of vibration modes (displacement field) and solid stress (displacement derivative field) for general structural special value problems, which can be extensively applied in the field of engineering computations in the future. Furthermore, the proposed method has the potential for adaptive analyses of shell structures and three-dimensional structures with crack damage. Compared with conventional finite element methods, significant advantages can be achieved by solving the eigenvalues of structures with high precision and stability. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to overcome the challenging issues involved in providing high-precision eigensolutions. The accurate prediction of the buckling load bearing capacity under different crack damage locations, sizes and numbers, and analysing the influence mechanism of crack damage on buckling instability have become the needs of theoretical research and engineering practice. Accordingly, a finite element method was developed and applied to solve the elastic buckling load and buckling mode of curved beams with crack damage. However, the accuracy of the solution depends on the quality of mesh, and the solution inevitably introduces errors due to mesh. Therefore, the adaptive mesh refinement method can effectively optimise the mesh distribution and obtain high-precision solutions. Design/methodology/approach: For the elastic buckling of circular curved beams with cracks, the section damage defect analogy scheme of a circular arc curved beam crack was established to simulate the crack size (depth), position and number. The h-version finite element mesh adaptive analysis method of the variable section Euler–Bernoulli beam was introduced to solve the elastic buckling problem of circular arc curved beams with crack damage. The optimised mesh and high-precision buckling load and buckling mode solutions satisfying the preset error tolerance were obtained. Findings: The results of testing typical examples show that (1) the established section damage defect analogy scheme of circular arc curved beam crack can effectively realise the simulation of crack size (depth), position and number. The solution strictly satisfies the preset error tolerance; (2) the non-uniform mesh refinement in the algorithm can be adapted to solve the arbitrary order frequencies and modes of cracked cylindrical shells under the conditions of different ring wave numbers, crack positions and crack depths; and (3) the change in the buckling mode caused by crack damage is applicable to the study of elastic buckling under various curved beam angles and crack damage distribution conditions. Originality/value: This study can provide a novel strategy for the adaptive mesh refinement for finite element analysis of elastic buckling of circular arc curved beams with crack damage. The adaptive mesh refinement method established in this study is fundamentally different from the conventional finite element method which employs the user experience to densify the meshes near the crack. It can automatically and flexibly generate a set of optimised local meshes by iteratively dividing the fine mesh near the crack, which can ensure the high accuracy of the buckling loads and modes. The micro-crack in curved beams is also characterised by weakening the cross-sectional stiffness to realise the characterisation of locations, depths and distributions of multiple crack damage, which can effectively analyse the disturbance behaviour of different forms of micro-cracks on the dynamic behaviour of beams. [ABSTRACT FROM AUTHOR]

Purpose: In this paper, a superconvergent patch recovery method is proposed for superconvergent solutions of modes in the finite element post-processing stage of variable geometrical Timoshenko beams. The proposed superconvergent patch recovery method improves the solution speed and accuracy of the finite element analysis of a curved beam. The free vibration and natural frequency of the beam were considered for studying forced vibrations and structural resonance. Beam vibration mode analysis was performed for high-precision vibration mode solutions and frequency values. The proposed method can be used to compute beam vibration modes of beams with different shapes and boundary conditions as well as variable cross sections and curvatures. The purpose of this paper is to address these issues. Design/methodology/approach: An adaptive method was proposed to analyse the in-plane and out-of-plane free vibrations of the variable geometrical Timoshenko beams. In the post-processing stage of the displacement-based finite element method, the superconvergent patch recovery method and high-order shape function interpolation technique were used to obtain the superconvergent solution of mode (displacement). The superconvergent solution of mode was used to estimate the error of the finite element solution of mode in the energy form under the current mesh. Furthermore, an adaptive mesh refinement was proposed by mesh subdivision to derive an optimised mesh and accurate finite element solution to meet the preset error tolerance. Findings: The results computed using the proposed algorithm were in good agreement with those computed using other high-precision algorithms, thus validating the accuracy of the proposed algorithm for beam analysis. The numerical analysis of parabolic curved beams, beams with variable cross sections and curvatures, elliptically curved beams and circularly curved beams helped verify that the solutions of frequencies were consistent with the results obtained using other specially developed methods. The proposed method is well suited for the mesh refinement analysis of a curved beam structure for analysing the changes in high-order vibration mode. The parts where the vibration mode changed significantly were locally densified; a relatively fine mesh division was adopted that validated the reliability of the mesh optimisation processing of the proposed algorithm. Originality/value: The proposed algorithm can obtain high-precision vibration solutions of variable geometrical Timoshenko beams based on more optimized and reasonable meshes than the conventional finite element method. Furthermore, it can be used for vibration problems of parabolic curved beams, beams with variable cross sections and curvatures, elliptically curved beams and circularly curved beams. The proposed algorithm can be extended for application in superconvergent computation and adaptive analysis of finite element solutions of general structures and solid deformation fields and used for adaptive analysis of more complex plates, shells and three-dimensional structures. Additionally, this method can analyse the vibration and stability of curved members with crack damage to obtain high-precision vibration modes and instability modes under damage defects. [ABSTRACT FROM AUTHOR]

Iron (Fe) is essential for DNA synthesis, photosynthesis and respiration of plants. The demand for Fe substantially increases during legumes‐rhizobia symbiotic nitrogen fixation because of the synthesis of leghemoglobin in the host and Fe‐containing proteins in bacteroids. However, the mechanism by which plant controls iron transport to nodules remains largely unknown. Here we demonstrate that GmYSL7 serves as a key regulator controlling Fe uptake from root to nodule and distribution in soybean nodules. GmYSL7 is Fe responsive and GmYSL7 transports iron across the membrane and into the infected cells of nodules. Alterations of GmYSL7 substantially affect iron distribution between root and nodule, resulting in defective growth of nodules and reduced nitrogenase activity. GmYSL7 knockout increases the expression of GmbHLH300, a transcription factor required for Fe response of nodules. Overexpression of GmbHLH300 decreases nodule number, nitrogenase activity and Fe content in nodules. Remarkably, GmbHLH300 directly binds to the promoters of ENOD93 and GmLbs, which regulate nodule number and nitrogenase activity, and represses their transcription. Our data reveal a new role of GmYSL7 in controlling Fe transport from host root to nodule and Fe distribution in nodule cells, and uncover a molecular mechanism by which Fe affects nodule number and nitrogenase activity. [ABSTRACT FROM AUTHOR]

Purpose: Hydrofracturing technology has been widely used in tight oil and gas reservoir exploitation, and the fracture network formed by fracturing is crucial to determining the resources recovery rate. Due to the complexity of fracture network induced by the random morphology and type of fluid-driven fractures, controlling and optimising its mechanisms is challenging. This paper aims to study the types of multiscale mode I/II fractures, the fluid-driven propagation of multiscale tensile and shear fractures need to be studied. Design/methodology/approach: A dual bilinear cohesive zone model (CZM) based on energy evolution was introduced to detect the initiation and propagation of fluid-driven tensile and shear fractures. The model overcomes the limitations of classical linear fracture mechanics, such as the stress singularity at the fracture tip, and considers the important role of fracture surface behaviour in the shear activation. The bilinear cohesive criterion based on the energy evolution criterion can reflect the formation mechanism of complex fracture networks objectively and accurately. Considering the hydro-mechanical (HM) coupling and leak-off effects, the combined finite element-discrete element-finite volume approach was introduced and implemented successfully, and the results showed that the models considering HM coupling and leak-off effects could form a more complex fracture network. The multiscale (laboratory- and engineering-scale) Mode I/II fractures can be simulated in hydrofracturing process. Findings: Based on the proposed method, the accuracy and applicability of the algorithm were verified by comparing the analytical solution of KGD and PKN models. The effects of different in situ stresses and flow rates on the dynamic propagation of hydraulic fractures at laboratory and engineering scales were investigated. when the ratio of in situ stress is small, the fracture propagation direction is not affected, and the fracture morphology is a cross-type fracture. When the ratio of in situ stress is relatively large, the propagation direction of the fracture is affected by the maximum in situ stress, and it is more inclined to propagate along the direction of the maximum in situ stress, forming double wing-type fractures. Hydrofracturing tensile and shear fractures were identified, and the distribution and number of each type were obtained. There are fewer hydraulic shear fractures than tensile fractures, and shear fractures appear in the initial stage of fracture propagation and then propagate and distribute around the perforation. Originality/value: The proposed dual bilinear CZM is effective for simulating the types of Mode I/II fractures and seizing the fluid-driven propagation of multiscale tensile and shear fractures. Practical fracturing process involves the multi-type and multiscale fluid-driven fracture propagation. This study introduces general fluid-driven fracture propagation, which can be extended to the fracture propagation analysis of potential fluid fracturing, such as other liquids or supercritical gases. [ABSTRACT FROM AUTHOR]

Rock mass has typical pore structure, and the induced coupling effects of fluid and solid matrix appear in the disaster evolution process of deep energy exploitation and overground rock hydration. As a representative case, influenced by the water absorption environment, the surrounding rock and murals of Mogao Grottoes produce hydration diseases, which may be related to unclear interaction mechanisms between the surrounding rock and water. In this study, the self-developed physical experimental system for real-time experimental monitoring was applied to test the water absorption evolution behaviors of sandstone. The experimental results showed that the water evaporation of the rock sample during the process of water absorption could be measured through this well-designed physical experimental system, and the actual water absorption of the rock sample is the difference between the decrease of water in the water storage bucket, measured by the balance and the water evaporation in the process of experiment; by drawing the actual water absorption curve of the rock sample, the time when the water absorption of the rock sample reaches saturation could be determined accurately; and the curve of water absorption with time could be expressed as an exponential function. The experimental techniques and methods in this study provide a feasible research idea for studying the water absorption evolution behaviors and mechanisms of the surrounding rock weathering when it meets water, and have significance for revealing the disease mechanisms of the surrounding sandstone in Mogao Grottoes, China. [ABSTRACT FROM AUTHOR]

Purpose: Moderately thick circular cylindrical shells are widely used as supporting structures or storage cavities in structural engineering, rock engineering, and aerospace engineering. In practical engineering, shells often work with micro-cracks or defects. The existence of micro-crack damage may result in the disturbance of dynamic behaviours and even induce accidental dynamic disasters. The free vibration frequency and mode are important parameters for the dynamic performance and damage identification analysis. In particular, stiffness weakening of the local damage region leads to significant changes in the vibration mode, which makes it difficult for the mesh generated in the conventional finite element method to capture a high-precision solution of the local oscillation. Design/methodology/approach: In response to the above problems, this study developed an adaptive finite element method and a crack damage characterisation method for moderately thick circular cylindrical shells. By introducing the inverse power iteration method, error estimation, and mesh subdivision refinement technique for the analysis of finite element eigenvalue problems, an adaptive computation scheme was constructed for the free vibration problem of moderately thick circular cylindrical shells with circumferential crack damage. Findings: Based on typical numerical examples, the established adaptive finite element solution for the free vibration of moderately thick circular cylindrical shells demonstrated its suitability for solving the high-precision free vibration frequency and mode of cylindrical shell structures. The any order frequency and mode shape of cracked cylindrical shells under the conditions of different ring wave numbers, crack locations, crack depths, and multiple cracks were successfully solved. The influences of the location, depth, and number of cracks on the disturbance of dynamic behaviours were analysed. Originality/value: This study can be used as a reference for the adaptive finite element solution of free vibration of moderately thick circular cylindrical shells with cracks and lays the foundation for further development of a high-performance computation method suitable for the dynamic disturbance and damage identification analysis of general cracked structures. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to analyse the deep resource mining that causes high in situ stress, and the disturbance of tunnelling and mining which may induce large stress concentration, plastic deformation and rock strata compression deformation. The depth of deep resources, excavation rate and multilayered heterogeneity are critical factors of excavation disturbance in deep rock. However, at present, there are few engineering practices used in deep resource mining, and it is difficult to analyse the high in situ stress and dynamic three-dimensional (3D) excavation process in laboratory experiments. As a result, an understanding of the behaviours and mechanisms of the dynamic evolution of the stress field and plastic zone in deep tunnelling and mining surrounding rock is still lacking. Design/methodology/approach: This study introduced a 3D engineering-scale finite element model and analysed the scheme involved the elastoplastic constitutive and element deletion techniques, while considering the influence of the deep rock mass of the roadway excavation, coal seam mining-induced stress, plastic zone in the process of mining disturbance of the in situ stress state, excavation rate and layered rock mass properties at the depths of 500 m, 1,500 m and 2,500 m of several typical coal seams, and the tunnelling and excavation rates of 0.5 m/step, 1 m/step and 2 m/step. An engineering-scale numerical model of the layered rock and soil body in an actual mining area were also established. Findings: The simulation results of the surrounding rock stress field, dynamic evolution and maximum value change of the plastic zone, large deformation and settlement of the layered rock mass are obtained. The numerical results indicate that the process of mining can be accelerated with the increase in the tunnelling and excavation rate, but the vertical concentrated stress induced by the surrounding rock intensifies with the increase in the excavation rate, which becomes a crucial factor affecting the instability of the surrounding rock. The deep rock mass is in the high in situ stress state, and the stress and plastic strain maxima of the surrounding rock induced by the tunnelling and mining processes increase sharply with the excavation depth. In ultra-deep conditions (depth of 2,500 m), the maximum vertical stress is quickly reached by the conventional tunnelling and mining process. Compared with the deep homogeneous rock mass model, the multilayered heterogeneous rock mass produces higher mining-induced stress and plastic strain in each layer during the entire process of tunnelling and mining, and each layer presents a squeeze and dislocation deformation. Originality/value: The results of this study can provide a valuable reference for the dynamic evolution of stress and plastic deformation in roadway tunnelling and coal seam mining to investigate the mechanisms of in situ stress at typical depths, excavation rates, stress concentrations, plastic deformations and compression behaviours of multilayered heterogeneity. [ABSTRACT FROM AUTHOR]

Background: With the continuous improvement of people's living standards, the incidence of hyperuricemia (HUA) is increasing globally. The prevalence of HUA ranged in terms of region, race, and age. This study aims to investigate the changes in the prevalence of HUA in clients of health examination in Eastern China between 2009 and 2019. Methods: Chinese men and women aged 20–79 years (n = 4847 in the 2009 group and n = 12,188 in 2019 group) who had received health examinations were enrolled. Serum uric acid (UA) levels and biochemical parameters, including fasting blood-glucose (FBG), triglyceride (TG), total cholesterol (CHOL), high-density lipoprotein (HDL), low-density lipoprotein (LDL), creatinine (Cr) and blood urea nitrogen (BUN) were evaluated. The prevalence of HUA in different age groups were measured, and the correlation of biochemical parameters with HUA were analyzed. Results: The prevalence of HUA was 18.7% in the 2019 group, which was significantly higher than that in 2009 (11.1%). In females, the prevalence of HUA was significantly higher in 2019 than 2009 for age groups of 20–29 and 30–39 years. In male population, 2019 participants had significantly higher age-specific prevalence for all age groups than 2009 participants. Young men aged 20–29 years became the main population of HUA in the 2019 participants, whereas middle-aged men aged 40–49 years had the highest prevalence of HUA in the 2009 participants. The prevalence rates of HUA in all BMI groups in 2019 participants were significantly higher than those in 2009 participants. Spearmen's correlation analysis and Logistic regression analysis indicated that BMI was positively correlated with HUA. The receiver-operating characteristic curve (ROC) analysis showed BMI > 24.48 kg/m2 and BMI > 23.84 kg/m2 displayed good capacities to discriminate the population with HUA from those without HUA in 2009 and 2019 participants, respectively. Conclusions: In recent 10 years, the prevalence of HUA was increased rapidly in Chinese adults, especially in males. In 2019, the young male group (20–29 years old) replaced the middle-aged male group (40–49 years old) in 2009 as the leading age group for male HUA. BMI was positively correlated with HUA, and might be a potential risk factors to predict HUA. [ABSTRACT FROM AUTHOR]

Pulse generators with a sub-nanosecond rise time are typically used to calibrate measurement probes in electromagnetic pulses. However, the technological dilemma between high voltage and low inductance has not been adequately addressed in this context. In this paper, the authors investigate the effects of the circuit and structural parameters on the generator. To reduce the rise time of the output voltage of the generator to a few hundred picoseconds, the inductance of its structure and the spark gap needs to be strictly controlled. We use SF6 at 1 MPa as an insulating gas for the spark gap to reduce the inductance of the capacitor and the switch to the order of several nH. The results of theoretical calculations and simulations were used to design and test two generators that used a coaxial ceramic capacitor and three plate ceramic capacitors, respectively. The experimental results showed that a double-exponential pulse voltage with a sub-nanosecond rise time could be obtained in a 50 Ω transmission line in both generators. The generator with the coaxial ceramic capacitor had better characteristics than the one that used three plate ceramic capacitors with a rise time of 630–860 ps when the peak output voltage was in the range of 5–30 kV. [ABSTRACT FROM AUTHOR]

Quantitative characterization of propagation behaviors and morphology of hydraulic fractures is crucial for controlling and optimizing hydrofracturing effects. To study the disturbance deflection behaviors of multiple hydraulic fractures, a three-dimensional field-scale numerical model for multistage fracturing is established to study the shear stress disturbance and unstable propagation behavior of hydraulic fractures under different perforation cluster spacing. In the model, the thermal diffusion, fluid flow and deformation in reservoirs are considered to describe the thermal-hydro-mechanical coupling. In the numerical case study, the derived results show that the thermal effect between fracturing fluid and rock matrix is an important factor affecting fracture propagation, and thermal effects may increase the extent of fracture propagation. The size of stress shadow areas and the deflection of hydraulic fractures will increase with a decrease in multiple perforation cluster spacing in horizontal wells. The shear stress disturbance caused by fracture propagation is superimposed in multiple fractures, resulting in the stress shadow effect and deflection of fractures. [ABSTRACT FROM AUTHOR]

Multi-well hydrofracturing is an important technology for forming complex fracture networks and increasing reservoir permeability. The distribution and design of horizontal wells affect fracture propagation; however, it is still unclear how the spacing between adjacent wells leads to fracture propagation, deflection and connection. In this study, the thermal-hydro-mechanical coupling effect in the hydrofracturing process is comprehensively considered and a multi-well hydrofracturing model based on the finite element–discrete element method is established. Using typical cases, the unstable propagation of hydraulic fractures in multiple horizontal wells under varying adjacent well spacings is studied. Combined with the shear stress shadow caused by in situ stress disturbed by fracture tip propagation, quantitative indexes (such as length, volume, deflection and unstable propagation behaviors of hydrofracturing fracture networks) are analyzed. The results show that the shear stress disturbance caused by multiple hydraulic fractures is a significant factor for multi-well hydrofracturing. Reducing well spacing will increase the stress shadow area and aggravate the mutual disturbance and deflection between fractures. The results of quantitative analysis show that the total length of hydraulic fractures decreases with the decrease of well spacing, and the total volume of hydraulic fractures increases with the decrease of well spacing. The results of unstable propagation and stress evolution of hydraulic fracture networks considering thermal-hydro-mechanical coupling obtained in this study can provide useful guidance for the valuation and design of hydrofracturing fracture networks in deep unconventional oil and gas reservoirs. [ABSTRACT FROM AUTHOR]

Online learning has become increasingly prevalent in the era of digitalization, impacted by both internet penetration and the COVID-19 pandemic. Classroom interaction, as a key factor in evaluating students' learning experience in online settings, has been identified to be associated with their academic achievement. While previous research has underscored the significance of classroom interaction in language learning settings, there is relatively limited research on its relationships with student satisfaction and learning. This research intends to explore classroom interaction and its mediating role in the correlation between student satisfaction and perceived online learning in online contexts. Given this, the paper reports a quantitative-method study that examined how Chinese EFL tertiary students perceived three types of classroom interaction (i.e., learner-learner, learner-instructor, and learner-content), their satisfaction, and its influences on their perceived online learning. Data was collected from 319 Chinese university students through convenience sampling and a self-designed questionnaire, and then analyzed with the help of SPSS. The results showed that: 1) the students had moderately positive perceptions of classroom interaction and online learning, but were neutral about their satisfaction; 2) positive correlations were observed between classroom interaction, student satisfaction, and online learning; and 3) student satisfaction predicted perceived online learning, with classroom interaction partially mediating this relationship. The findings of this research have implications for strengthening the effectiveness of online language teaching in the post-COVID-19 era. [ABSTRACT FROM AUTHOR]

Given the inherent challenges and substantial effort required in education, learners' levels of enjoyment have a fundamental value in the language acquisition process, especially in the English as a foreign language (EFL) context. This research aimed to validate a model of foreign language enjoyment (FLE) incorporating both the external factors such as classroom climate and the internal factors like trait emotional intelligence (EI) among Chinese EFL students. As a result, the study employed convenient sampling, selecting 346 Chinese EFL learners who participated by responding to valid scales for the three constructs, namely FLE, trait EI, and classroom climate. Structural equation modeling (SEM) was utilized for the data analysis, enlightening that both classroom climate and trait EI exerted a significant positive impact on FLE. Notably, trait EI exhibited a stronger influence than classroom climate. These findings underscore the significance of promoting a constructive classroom climate and cultivating trait EI to enhance EFL students' enjoyment in the process of learning. [ABSTRACT FROM AUTHOR]

The operation of separated gas foil thrust bearing (SGFTB) is generally vulnerable to the tilting angle of rotor thrust disc. The optimal structural parameters of SGFTB are obtained by L 49 (64) orthogonal design. A modified Reynolds equation is developed to investigate the bearing performances of SGFTB with/without considering the tilting angle. A test bench is designed to test the bearing performances of SGFTB. Results indicate the axial bearing forces and friction torque increase and result in an uneven distribution of gas film pressure on the surface of the fan pad when the rotor thrust disc is tilted. The optimized design of SGFTB achieves the desired bearing effect. [ABSTRACT FROM AUTHOR]

Purpose: This study presents a novel hp-version adaptive finite element method (FEM) to investigate the high-precision eigensolutions of the free vibration of moderately thick circular cylindrical shells, involving the issues of variable geometrical factors, such as the thickness, circumferential wave number, radius and length. Design/methodology/approach: An hp-version adaptive finite element (FE) algorithm is proposed for determining the eigensolutions of the free vibration of moderately thick circular cylindrical shells via error homogenisation and higher-order interpolation. This algorithm first develops the established h-version mesh refinement method for detecting the non-uniform distributed optimised meshes, where the error estimation and element subdivision approaches based on the superconvergent patch recovery displacement method are introduced to obtain high-precision solutions. The errors in the vibration mode solutions in the global space domain are homogenised and approximately the same. Subsequently, on the refined meshes, the algorithm uses higher-order shape functions for the interpolation of trial displacement functions to reduce the errors quickly, until the solution meets a pre-specified error tolerance condition. In this algorithm, the non-uniform mesh generation and higher-order interpolation of shape functions are suitable for addressing the problem of complex frequencies and modes caused by variable structural geometries. Findings: Numerical results are presented for moderately thick circular cylindrical shells with different geometrical factors (circumferential wave number, thickness-to-radius ratio, thickness-to-length ratio) to demonstrate the effectiveness, accuracy and reliability of the proposed method. The hp-version refinement uses fewer optimised meshes than h-version mesh refinement, and only one-step interpolation of the higher-order shape function yields the eigensolutions satisfying the accuracy requirement. Originality/value: The proposed combination of methodologies provides a complete hp-version adaptive FEM for analysing the free vibration of moderately thick circular cylindrical shells. This algorithm can be extended to general eigenproblems and geometric forms of structures to solve for the frequency and mode quickly and efficiently. [ABSTRACT FROM AUTHOR]

Purpose: Simultaneous hydrofracturing of multiple perforation clusters in vertical wells has been applied in the stimulation of hydrocarbon resources reservoirs. This technology is significantly impeded due to the challenges in its application to the multilayered reservoirs that comprise multiple interlayers. One of the challenges is the accurate understanding and characterization of propagation and deflection of the multiple hydraulic fractures between reservoirs and embedded interlayers. Design/methodology/approach: Numerical models of the tight multilayered reservoirs containing multiple interlayers were established to study hydrofracturing of multiple perforation clusters and its influencing factors on unstable propagation and deflection of hydraulic fractures. Brittle and plastic multilayered reservoirs fully considering the influences of different in situ stress ratio and physical attributes for reservoir and interlayer strata on propagations of hydraulic fractures were investigated. The combined finite element–discrete element method and mesh refinement strategy were adopted to guarantee the accuracy of stress solutions and reliability of fracture path in computation. Findings: Results show that the shear stress fields between adjacent multiple hydraulic fractures are superposed to cause fractures deflection. Stress shadows induce the shielding effects of hydraulic fractures and inhibit fractures growth to emerge unstable propagation behaviors, and a main single fracture and several minor fractures develop. As the in situ stress ratio increases, hydraulic fractures more easily deflect toward the direction of maximum in situ stress, and stress shadow and mutual interaction effects between them are intensified. Compared to brittle reservoir, plastic-enhanced reservoir may limit fracture growth and cannot form long fracture length; nevertheless, plastic properties of reservoir are prone to induce more microseismic events with larger magnitude. Originality/value: The obtained fracturing behaviors and mechanisms based on engineering-scale multilayered reservoir may provide effective schemes for controlling and estimating the unstable propagation of multiple hydraulic fractures. [ABSTRACT FROM AUTHOR]

With the emergence of the positive psychology trend, studying teacher resilience has gained tremendous momentum in mainstream education. Nonetheless, it has yet remained an underappreciated concept in English language education and research. The challenges that teachers experience in maintaining their resilience have also been the focus of a limited number of inquiries. To address these gaps, the present investigation set out to explore the challenges of sustaining resilience among Chinese and Iranian EFL teachers. In doing so, an open-ended questionnaire was administered to 18 Chinese and 15 Iranian EFL teachers, varying in age from 30 to 55 years old. Adopting a qualitative model of data analysis, the participants’ responses to the open-ended questionnaire were analyzed through MAXQDA software. The analysis of Chinese and Iranian EFL teachers’ answers resulted in the generation of 16 themes and 50 subthemes, demonstrating the challenges to teacher resilience. Findings indicated that both Chinese and Iranian EFL teachers perceived person-focused factors to be the major challenges of preserving teacher resilience. Other factors, including system-focused, context-focused, and process-focused factors, were conceived to be less problematic for teacher resilience. Finally, some major implications of the findings are presented and thoroughly discussed. [ABSTRACT FROM AUTHOR]

To explore the intricate connections between Chinese English as a Foreign Language (EFL) learners' classroom emotions (anxiety, boredom and enjoyment) and their engagement within the context of English as a medium of instruction (EMI) in technology-based learning environments, four modified and validated questionnaires focusing on assessing emotions, engagement levels, and comfort with technology integration were administered to university EFL learners on the Chinese mainland. A structural equation modeling (SEM) analysis was employed to discern the direct and indirect influences of EFL emotions on engagement, considering the mediating effects of EMI and technology comfort. The results indicate that the indirect impact of emotions on learners' academic engagement through technology and EMI as mediators was significant at 95% confidence level. It means that 69% of changes in learners' academic engagement can be explained by interaction among learners' emotions and their technology and EMI perceptions. These results imply that both technology-enhanced learning and EMI serve as significant mediators in the relationship between emotions and academic engagement. The positive estimates suggest that higher levels of positive emotions may lead to increased academic engagement through these mediated pathways. Our findings may have implications for pedagogical practices, curriculum development, and the design of technology-enhanced language instruction. [ABSTRACT FROM AUTHOR]

The Shaanxi-Gansu-Ningxia (SGN) region in Northwest China has been challenged by drought and water shortage for decades. Based on the precipitation data from 30 weather stations in the SGN region during 1973–2019, the Empirical Orthogonal Function (EOF) and the Wavelet analysis (WA) were applied to analyze the precipitation spatio-temporal variations at different time scales. The results showed that precipitation at annual scale had decreased significantly (P < 0.01) at the rate of 1.46 mm/10a during 1973–2019, and 56.7% of stations showed a decreasing trend, which was mainly concentrated in the Jing River basin. In terms of seasonal precipitation, more than 65% of the stations showed an increasing trend in summer and winter, with increasing at 2.06 mm/10a and 0.56 mm/10a, respectively, but most significantly, 86.7% of the stations showed a decreasing trend in the spring, and only less than 15% of the stations in the Hulu River basin showed an increasing trend. This study will help to further improve understanding of climate change, and provide reference to cope with future climate change and solve the problem of water shortage. [ABSTRACT FROM AUTHOR]

In view of the diversified demands for thermal management materials in soaring developments of electrical systems, the high thermally conductive composites often suffer from their poor mechanical properties and electrical insulation. Targeting at enhancing simultaneous thermal conductivity, dielectric and mechanical properties, the fibers reinforced gradient structured polyethylene-based composites consisting of ultrahigh molecular weight polyethylene (UHMWPE) fiber layer and hybrid-filled layer are proposed and successfully prepared by simple overlapping-hot pressing. The fibers collaborated with gradient arrangement of hybrid-filled layer in modulating the temperature, electric and stress field distribution. The resultant as-designed composites exhibit excellent thermal conductivity of 0.91 W/(m·K), ultrahigh tensile strength of 104.7 MPa and superior breakdown strength of 161.5 kV/mm, which are increased by 18%, 1374% and 37% than those of the homogeneous composites, respectively. This work provides a new strategy for manufacturing high-performance polymer-based composites. [Display omitted] • A new strategy was proposed to design PE-based composites with high thermal-dielectric-mechanical performances. • The UHMWPE fibers reinforced gradient structure was constructed through simple overlapping-hot pressing. • The structured composites have ultrahigh tensile strength, superior breakdown strength and high thermal conductivity. • The fibers collaborated with hybrid-filled layer in modulating the temperature, electric and stress field distribution. [ABSTRACT FROM AUTHOR]

While research on informal digital learning of English (IDLE) has proliferated recently, there still exists a noticeable gap in factors that influence language teachers' attitudes and intentions to incorporate IDLE into the formal curriculum context. To address this gap, this study drew on the theory of planned behavior (TPB) and collected questionnaire responses from 1008 English language teachers in the Chinese mainland context. A structural equation modeling (SEM) approach was utilized to construct a hypothesized structural model and analyze the quantitative data. By validating the TPB-supported structural model, the findings showed that language teachers' behavioral intention to embrace IDLE in the classroom was positively and strongly predicted by their Attitude , Subjective norm , and Perceived behavioral control. The SEM also revealed external variables that could account for the formulation of teachers' Attitude, Subjective norm , and Perceived behavioral control respectively. In addition, the results of two-group difference tests displayed that in-service teaching experience served as a significant moderator in the three paths from Subjective norm to Behavioral intention , Perceived behavioral control to Behavioral intention , and Control beliefs to Attitude. Finally, this study proposes implications for future research and practices based on the discussion of these results. • Attitude fosters teachers' intention to integrate IDLE into the classroom. • Subjective norm fosters teachers' intention to integrate IDLE into the classroom. • Perceived behavioral control fosters teachers' IDLE integration intention. • In-service teaching experience moderates teachers' IDLE integration intention. • External variables predict attitude, subjective norm and perceived behavioral control. [ABSTRACT FROM AUTHOR]

Hollow silica microsphere (h-SiO2) has been widely applied in the field of thermal insulation, catalyst supports and drug storage/delivery containers. In this research, h-SiO2 has been innovatively used as synergistic agent to enhance the flame retardancy of intumescent flame-retardant polystyrene. The synergistic effects of h-SiO2 on intumescent flame-retardant polystyrene have been studied by limiting oxygen index (LOI), UL-94 test and cone calorimeter test (CCT). When 0.5 mass% h-SiO2 was substituted for the intumescent flame-retardant additive, the LOI of polystyrene composite (PS/IFR/Si0.5) increased by 5 units and the composite preserved the V-0 rating. Manipulation of parameters from CCT indicated that the peak heat release rate was reduced by 27% for the PS/IFR/Si0.5 composite, whereas the total heat release decreased by 14.5% and the ratio of residue increased by 85.6% (from 13.2 to 24.5%) compared to those of the composite without h-SiO2. The synergistic effects of h-SiO2 on intumescent flame-retardant polystyrene are attributed to physical and chemical processes in the condensed phase. The morphologies of charred layer after CCT proved that h-SiO2 induced compact charred layer with enhanced thermal and gas barrier effect, which in turn protected the inner matrix from combustion and decreased specific extinction area by 24.2%. [ABSTRACT FROM AUTHOR]

There are two bias schemes, namely current-bias and voltage-bias, for the directly coupled readout circuit of direct current superconducting quantum interference device (dc SQUID). In order to find out the difference between two bias schemes, we present the theoretical analyses on their equivalent circuits, working point locations, and noise performances. The theoretical analysis and experimental validation prove that the voltage-bias scheme achieves a larger transfer coefficient and exhibits a better noise performance than the current-bias scheme in the reading of conventional dc SQUID. [ABSTRACT FROM AUTHOR]

Purpose: Optimized three-dimensional (3D) fracture networks are crucial for multistage hydrofracturing. To better understand the mechanisms controlling potential disasters as well as to predict them in 3D multistage hydrofracturing, some governing factors, such as fluid injection-induced stratal movement, compression between multiple hydraulic fractures, fracturing fluid flow, fracturing-induced microseismic damaged and contact slip events, must be properly simulated via numerical models. This study aims to analyze the stratal movement and microseismic behaviours induced by multistage propagation of 3D multiple hydraulic fractures. Design/methodology/approach: Adaptive finite element–discrete element method was used to overcome the limitations of conventional finite element methods in simulating 3D fracture propagation. This new approach uses a local remeshing and coarsening strategy to ensure the accuracy of solutions, reliability of fracture propagation path and computational efficiency. Engineering-scale numerical models were proposed that account for the hydro-mechanical coupling and fracturing fluid leak-off, to simulate multistage propagation of 3D multiple hydraulic fractures, by which the evolution of the displacement, porosity and fracture fields, as well as the fracturing-induced microseismic events were computed. Findings: Stratal movement and compression between 3D multiple hydraulic fractures intensify with increasing proximity to the propagating fractures. When the perforation cluster spaces are very narrow, alternate fracturing can improve fracturing effects over those achieved via sequential or simultaneous fracturing. Furthermore, the number and magnitude of microseismic events are directly proportional to the stratal movement and compression induced by multistage propagation of fracturing fracture networks. Originality/value: Microseismic events induced by multistage propagation of 3D multiple hydraulic fractures and perforation cluster spaces and fracturing scenarios that impact the deformation and compression among fractures in porous rock matrices are well predicted and analyzed. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to overcome the involved challenging issues and provide high-precision eigensolutions. General eigenproblems in the system of ordinary differential equations (ODEs) serve as mathematical models for vector Sturm-Liouville (SL) and free vibration problems. High-precision eigenvalue and eigenfunction solutions are crucial bases for the reliable dynamic analysis of structures. However, solutions that meet the error tolerances specified are difficult to obtain for issues such as coefficients of variable matrices, coincident and adjacent approximate eigenvalues, continuous orders of eigenpairs and varying boundary conditions. Design/methodology/approach: This study presents an h-version adaptive finite element method based on the superconvergent patch recovery displacement method for eigenproblems in system of second-order ODEs. The high-order shape function interpolation technique is further introduced to acquire superconvergent solution of eigenfunction, and superconvergent solution of eigenvalue is obtained by computing the Rayleigh quotient. Superconvergent solution of eigenfunction is used to estimate the error of finite element solution in the energy norm. The mesh is then, subdivided to generate an improved mesh, based on the error. Findings: Representative eigenproblems examples, containing typical vector SL and free vibration of beams problems involved the aforementioned challenging issues, are selected to evaluate the accuracy and reliability of the proposed method. Non-uniform refined meshes are established to suit eigenfunctions change, and numerical solutions satisfy the pre-specified error tolerance. Originality/value: The proposed combination of methodologies described in the paper, leads to a powerful h-version mesh refinement algorithm for eigenproblems in system of second-order ODEs, that can be extended to other classes of applications in damage detection of multiple cracks in structures based on the high-precision eigensolutions. [ABSTRACT FROM AUTHOR]

It has been found that when superconducting quantum interference device magnetometers operate in a geomagnetic field environment, its output will occasionally show small momentary jumps with the change of the external magnetic field, which seriously affects the measurement accuracy of the geomagnetic field and needs to be eliminated. A magnetic flux jump model called the parasitic superconducting ring model was built to explain the causes of these small jumps, and Helmholtz coils were set up to study the jump and verify this model in the laboratory. The experimental results showed that the position and amplitude of the jumps were consistent with the model. It is believed that this model can guide the design of superconducting chips in geophysical applications. [ABSTRACT FROM AUTHOR]

Optimization of complex fracture networks improves the fracturing effects and enhances production in multistage hydrofracturing technology. To understand the controlling mechanisms of multistage hydrofracturing in unconventional tight reservoirs, some governing issues, such as hydro-mechanical coupling, stress shadow effects, propagation interaction behaviours of three-dimensional (3D) multiple fractures, and 3D multistage hydrofracturing, should be addressed. However, the characterization of perforation cluster spaces and fracturing scenarios of horizontal wells, which significantly affect the evolution of the stress field and 3D morphology of the fracture network, is a challenge. In this study, to overcome the drawbacks of the traditional finite-element method in simulating 3D fracture propagation, the adaptive finite element–discrete element method is used. This method uses a local remeshing and coarsening strategy to ensure the accuracy of solutions, reliability of the fracture propagation path, and computational efficiency. The study proposes 3D engineering-scale numerical models, considering the crucial hydro-mechanical coupling and fracturing fluid leak-off, to simulate 3D multistage hydrofracturing and fracture interaction behaviours. The numerical results show that the stress shadow effects and fracture interaction behaviours become more intense once the spaces between different propagating fractures become thinner due to superposition and reduction effects in fracturing-induced shear stress variation areas. The alternate fracturing can reduce the stress shadow effects through adjusting the sequence of perforation clusters that are activated and injected with fracturing fluid. When the perforation cluster spaces become narrow, the alternate fracturing scenario can yield more fracturing fracture areas and improve the fracturing effects as compared to sequential and simultaneous fracturing. [ABSTRACT FROM AUTHOR]

The distribution structure of dielectric fillers is attracting more attention in designing composites with excellent dielectric properties and energy storage performances. Barium titanate (BT) and polyvinylidene fluoride (PVDF) were introduced to low‐density polyethylene (LDPE) to build the dielectric structure by modulating the phase structure of PVDF/LDPE and the distribution behavior of BT. The results showed that BT particles can be selectively distributed in the phase structure of PVDF/LDPE by controlling the surface modification of BT, which contributed much to the enhancement of dielectric properties and energy storage performances. The dielectric constant and discharge energy density of the composites with the selective distribution of core‐shell structured BT@PE in the LDPE phase of PVDF/LDPE blend were increased by 51% and 95% in comparison with PVDF/LDPE blend, respectively. By simulating with finite element analysis (FEA), the increased internal polarization and the decreased electric field distortion of PVDF/LDPE/BT@PE due to BT@PE distributed in the LDPE phase and the small dielectric constant difference between the LDPE/BT@PE phase and PVDF phase were the factors to enhance the dielectric constant and breakdown strength, which consequently enhance the energy storage performances of the composites. Highlights: Phase structure constructed with BT and BT@PE selectively distributed in PVDF/LDPE.Co‐enhanced dielectric constant and breakdown strength of PVDF/LDPE/BT@PE.Modulated polarization and electric field due to BT@PE in the LDPE phase of composites. [ABSTRACT FROM AUTHOR]

The objective of this article is to investigate the effect of the vibration mixing process (VMP) on the performance of cement stabilized recycled aggregate (CSRA). The ordinary mixing process (OMP) was also used for comparative analysis with the VMP. The performance of CSRA with different cement content was tested and comprehensively analyzed by the unconfined compressive strength test, dry shrinkage test, and temperature shrinkage test. The results showed that compared with OMP, VMP can greatly improve the compressive strength, dry shrinkage, and temperature shrinkage properties of CSRA. The optimum parameters of vibration time and vibration frequency in VMP were 30 s and 40 Hz, respectively. The reason why VMP can improve the performance of CSRA was that VMP strengthened the aggregate and interface transition zone and introduced microbubbles to optimize the pore structure. [ABSTRACT FROM AUTHOR]

The objective of this article is to investigate the effect of the vibration mixing process (VMP) on the performance of cement stabilized recycled aggregate (CSRA). The ordinary mixing process (OMP) was also used for comparative analysis with the VMP. The performance of CSRA with different cement content was tested and comprehensively analyzed by the unconfined compressive strength test, dry shrinkage test, and temperature shrinkage test. The results showed that compared with OMP, VMP can greatly improve the compressive strength, dry shrinkage, and temperature shrinkage properties of CSRA. The optimum parameters of vibration time and vibration frequency in VMP were 30 s and 40 Hz, respectively. The reason why VMP can improve the performance of CSRA was that VMP strengthened the aggregate and interface transition zone and introduced microbubbles to optimize the pore structure. [ABSTRACT FROM AUTHOR]

Practical superconducting quantum interference devices (SQUIDs) have been developed into multiloop hybrid electric circuits with Josephson junctions and normal elements such as resistor, inductor and capacitor. To find a common circuit analysis and simulation method for different types of SQUID hybrid circuits consist of both superconducting and normal components, we introduce a mesh-current method, which can derive both the general system model and uniform circuit equations directly from the equivalent circuit. The mesh-current method is demonstrated in the simulation of a SQUID additional positive feedback circuit. The numerical simulation results are presented and verified with the measurements. Compared with the conventional nodal analysis method, the mesh-current method is excellent in dealing with the relations including external flux, self and mutual inductances in multiloop hybrid circuit analysis; its final circuit equations directly exhibit the physical theorems; its general system model reveals the quantum interference mechanism inside SQUID circuits, and is applicable for further dynamics studies. [ABSTRACT FROM AUTHOR]

Direct current superconducting quantum interference device (dc SQUID) can be regarded as a hybrid system with two nonlinear Josephson currents driving a linear network consists of conventional resistors (R), inductors (L), and capacitors (C). There must be LC resonances inside the SQUID loop with influences on its static current-voltage characteristics. To study the working principle of the LC resonance, we build an equivalent dynamic system model transformed directly from the circuit equations of dc SQUID. With dynamic system analyses in both dc and alternating current (ac) domains, we derive the analytical expressions of the resonance point with only the RLC circuit parameters. The analytical derivation proves that the LC resonance inside a symmetrical dc SQUID with resonance frequency ω = 1/√LC results in the flux modulation suppression with I–V curves concentrated on one resonance point. Based on those mathematical expressions, the resonance point is easily indentified from the measured I–V curves, and can be utilized for practical SQUID parameters characterization. [ABSTRACT FROM AUTHOR]