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There are four sets of source rocks from Carboniferous (C) to Permian in Mahu Sag, and the paleoenvironment is the decisive factor for the differences of source rocks. In order to study the control...

Packing densification of mono-sized regular dodecahedral particles subjected to 3D vibrations was studied through systematical physical experiments. The influences of various vibration conditions and container size on the packing density were analyzed and the operating parameters were optimized. The obtained microstructures of different packings were characterized through 3D CT non-destructive inspection. The results show that by properly controlling the vibration conditions, the transition from initial loose to final dense packing structure of mono-sized regular dodecahedral particles can be reproduced. A maximum packing density of 0.709, which is the currently obtainable densest random packing structure of mono-sized regular dodecahedral particles in physical experiments, can be realized by extrapolating the packing densities obtained in different sized containers. Microscopic analyses on the 3D computer re-constructed packing structures from experiments clearly demonstrate the specific characteristics of the generated initial loose and final dense packings. The obtained results can enhance the deep understanding of packing behavior of dodecahedral particles and provide researchers with valuable reference to the design and fabrication of some new materials.

The random packings of binary tetrahedron-sphere mixtures were numerically reproduced by DEM simulations. The influences of particle shape (characterized by eccentricity ζ and height ratio η), particle size, and composition on the packing density of binary tetrahedron-sphere mixtures were systematically investigated. The properties of equivalent packing diameter are identified by both macroscopic and microscopic parameters. The results show that the equivalent packing diameter of tetrahedra is independent of the particle shape (ζ and η) deviation. The minimal specific volume variations ΔV are negative for each case with the size ratio ranging from 0.5 to 1 caused by the shape particularity of tetrahedra. The overall mean coordination number (CN) obtained at r = 1 (here, r = ds/dte, ds and dte are respectively sphere diameter and equivalent volume sphere diameter of tetrahedral particles) is almost identical and does not change with the variation of composition. The mean stress analysis shows that the equivalent packing diameter is not only universal for the microstructure parameters, but also for the mechanical properties of tetrahedron-sphere binary packings.

Packings of different mono-sized tetrahedral particles under 3D vibrations were studied by physical experiments and DEM simulations. The effects of vibration conditions and particle shape on the packing densification were comprehensively investigated and optimized. Corresponding characteristic microscopic properties such as coordination number (CN), particle contact type, radial distribution function (RDF), and particle orientations were numerically characterized and analyzed. The results show that the DEM model can be well validated by physical experiments. Microscopic analysis indicates that the minimum mean CN appears for tetrahedral particles with regular shape. The RDF shows that as the shape deviates from regular tetrahedral particles, the frequency of face-face, vertex-face and edge-edge contacts all decreases while that of edge-face contact increases. The cluster evolutions demonstrate that the reduction or disappearance of two important local clusters (dimer and wagon wheel structures) is one of the main reasons for the decrease of packing density of irregular tetrahedral particles.

Acid fracturing is a key measure to increase production of fracture-cavity reservoirs. Affected by the fracture-cavity system, hydraulic fractures will not propagate in a plane, and the mechanism of hydraulic fracture propagation is complicated. Therefore, considering the characteristics of hydraulic fracture propagation in fracture-cavity reservoirs, we established an extended finite element (XTEM) model for hydraulic fractures in fracture-cavity reservoirs. The simulation discussed hydraulic fracture extension in cases of a single cave and a single natural fracture and revealed the mechanism of dynamic propagation and extension of hydraulic fractures. The results indicated severe stress concentrations near caves, resulting in deflections of the fracture propagation direction. In the case of a single cave, upon shifts of shafts from the central line of the cave, the conditions of penetration of the cave by hydraulic fractures were investigated. It was shown that in the case of small approaching angles, the hydraulic fractures tend to deflect and join natural fractures; also, the hydraulic fractures can deflect and join natural fractures with large approaching angles and weak cementation. Generally small approaching angles and long natural fractures tend to induce hydraulic fractures and assist propagation towards the caves, thus increasing the probability of cave penetration.

Photogenerated electron–hole recombination significantly restricts the catalytic efficiency of titanium dioxide (TiO2). Various approaches have been developed to overcome this problem, yet it remains challenging. Recently, graphene modification of TiO2 has been considered as an effective alternative to prevent electron–hole recombination and consequently enhance the photocatalytic performance of TiO2. This study reports an efficient but simple hydrothermal method utilizing titanium (IV) butoxide (TBT) and graphene oxide (GO) to prepare TiO2-reduced graphene oxide (RGO) nanocomposites under mild reaction conditions. This method possesses several advantageous features, including no requirement of high temperature for TiO2 crystallization and a one-step hydrothermal reaction for mild reduction of GO without a reducing agent, which consequently makes the production of TiO2-RGO nanocomposites possible in a green and an efficient synthetic route. Moreover, the as-synthesized nanocomposites were characterized by numerous advanced techniques (SEM, TEM, BET, XRD, XPS, and UV-vis spectroscopy). In particular, the photocatalytic activities of the synthesized TiO2-RGO nanocomposites were evaluated by degrading the organic molecules (methylene blue, MB), and it was found that the photocatalytic activity of TiO2-RGO nanocomposites is ~4.5 times higher compared to that of pure TiO2. These findings would be useful for designing reduced graphene oxide-metal oxide hybrids with desirable functionalities in various applications for energy storage devices and environmental remediation.

Sandpiles are ubiquitous in nature and engineering applications but still not fully understood due to the complexity of structures and materials properties. This work presents a systematic study on the piles of Platonic solids using the discrete element method (DEM), mainly focusing on the effect of particle shape on the repose angles and bottom pressure distributions of the piles. Five Platonic particles (tetrahedron, cube, octahedron, dodecahedron, and icosahedron) were discharged to form wedge-shaped piles. It was found that the repose angle did not increase with the decrease of particle sphericity. The pile formed by the cubes had the maximum repose angle and its bottom stress dip phenomena were more significant in terms of dip width and depth than that of other particle piles. The pressure distributions at different heights of the piles were quite similar to those of the whole piles, while the shear stress distributions near the boundaries exhibited different characteristics for the cube piles. The analyses of packing structures in terms of coordination number, radial distribution function, as well as contact types inside the piles were discussed to understand the change of pressure dips. The influence of static friction on the repose angle was more significant and it enhanced the stress dip phenomenon.

A novel joining method called friction spot riveting (FSR) was proposed to improve mechanical properties between AA6061-T6 and polypropylene (PP) joints via improving mechanical interlocking. Under the synergistic effect of frictional heat and forging force, the plastic was heated and softened, which further flowed into the pre-fabricated holes in the metal. Sound metal/plastic joints were obtained via a rivet composed of PP plastics, while an intimate joining interface formed between AA6061-T6 and PP. The joining mechanism contained the mechanical interlocking induced by the rivet and the adhesion bonding. The tensile shear load was significant improved and the maximum value was 266 N. The tensile shear fracture were characterized by the fracture of the rivet and the failure of adhesive joining.

In this paper, the transition from random to ordered packings of mono-sized cylindrical particles under 3D mechanical vibration was simulated by discrete element method (DEM). The effects of particle aspect ratio, size of the particulate system and container wall on the granular crystallization were investigated. And the mechanisms were analyzed through the characterization of the order transition process in terms of packing density, coordination number (CN), orientational ordering parameter (O), nucleation and growth of cluster and granular temperature (θ). The results show that nearly perfect crystallization of mono-sized cylindrical particles can be achieved with specific aspect ratio and proper vibration conditions in a cylindrical container. The orientational ordering parameter demonstrates that the crystallization firstly starts from the container wall and then propagates inward gradually. The lower granular temperature in a cuboid container indicates less vibration energy transferred to the granular assembly compared with that in a cylindrical container, illustrating the critical role of container shape in crystallization. The vibrated crystallization of mono-sized cylindrical particles is analogous to entropy-driven process, which can be gradually achieved by the self-assembly of particles with parallel alignments along the already formed ordered clusters (nuclei) or the container wall. These results can help design complex and ordered granular structures.

Packing densification of monosized regular icosahedral particles under three-dimensional mechanical vibration has been simulated by the discrete element method (DEM). The effects of the vibration conditions and container size on packing densification were systematically investigated. In addition to the macroscale properties (packing density and porosity), the microscale properties, such as the coordination number (CN), radial distribution function (RDF), particle contact type, particle orientation distribution, and stresses/forces, in random loose packing (RLP) and random close packing (RCP) were also characterized and analyzed. The results show that transformation of icosahedral particle packing from RLP to RCP can be realized by properly controlling the vibration conditions. The maximum random packing density without the wall effect reaches 0.7078. Microscale property analysis shows that the average CN increases after vibration. The RDF curves contain two clear peaks for RLP and three for RCP. From RLP to RCP, the probability of face to face contact between two particles increases, while the probabilities of edge to edge, edge to face, and face to vertex contact decrease. The orientation correlation functions indicate the randomness of the vibrated packing structure. In addition, more uniform force and stress distributions are observed within the dense packing structure.

This paper describes a new two-dimensional (2-D) control volume finite element method (CV-FEM) for transient heat conduction in multilayer functionally graded materials (FGMs). To deal with the mixed-grid problem, 9-node quadrilateral grids and 6-node triangular grids are used. The unknown temperature and material properties are stored at the node. By using quadratic triangular grids and quadratic quadrilateral grids, the present method offers greater geometric flexibility and the potential for higher accuracy than the linear CV-FEM. The properties of the FGMs are described by exponential, quadratic and trigonometric grading functions. Some numerical tests are studied to demonstrate the performance of the developed method. First, the present CV-FEM with mixed high-order girds provides a higher accuracy than the linear CV-FEM based on the same grid size. Second, the material properties defined location is proved to have a significant effect on the accuracy of the numerical results. Third, the present method provides better numerical solutions than the conventional FEM for the FGMs in conjunction with course high-order grids. Finally, the present method is also capable of analysis of transient heat conduction in multilayer FGM.

According to the nonlinearity and nonstationarity characteristics of reciprocating compressor vibration signal, a fault feature extraction method of reciprocating compressor based on the empirical wavelet transform (EWT) and state-adaptive morphological filtering (SMF) is proposed. Firstly, an adaptive empirical wavelet transform was used to divide the Fourier spectrum by constructing a scale-space curve, and an appropriate orthogonal wavelet filter bank was constructed to extract the AM-FM component with a tightly-supported Fourier spectrum. Then according to the impact characteristic of the reciprocating compressor vibration signal, the morphological structural elements were constructed with the characteristics of the signal to perform state-adaptive morphological filtering on the partitioned modal functions. Finally, the MF-DFA method of the modal function was quantitatively analyzed and the fault identification was performed. By analyzing the experimental data, it can be shown that the method can effectively identify the fault type of reciprocating compressor valve.

Random close packings (RCP) of different shaped cylindrical particles under optimal vibration conditions were numerically reproduced using discrete element method. Corresponding characteristic macro and micro properties such as packing density, coordination number (CN), radial distribution function (RDF), particle orientation, orientation randomness and forces/stresses as a function of particle aspect ratio (AR) were systematically characterized and analyzed. And the container wall effects on the packing were also comprehensively considered. The results show that with the increase of AR, the packing density of each RCP structure first increases to a maximum (0.70 with AR = 1) and then decreases. The RDF analysis shows the particle arrangement of local structure varies with AR. The container wall is only in effect within three layers for equiaxed cylinders (AR = 1) near the boundary and just one layer for other shaped cylinders. The non-equiaxed cylinders especially elongated ones exhibit a strong tendency to horizontal alignment. With the growth of AR, the nematic order parameter of the packings first decreases to a minimum and then increases. Both particle position and orientation distributions demonstrate that the obtained packing structures are random. Force analyses indicate that the strong forces follow an exponential distribution, while those weak forces follow a power-law distribution, which is comparable to the force distributions of spherical particles. Compared with other cylindrical particles, the force orientation distribution in the packing of equiaxed cylinders is more homogenous. The peak position of the hydrostatic stress distribution is the same for different shaped cylinders. Moreover, with the increase of the packing density, the percentage of strong stresses increases. With the AR deviating from 1, the static vertical stresses present a gradually larger saturation stress in the same depth.

The formation and growth of local order clusters in a tetrahedral granular assembly driven by 3D mechanical vibration were captured in DEM (discrete element method) dynamic simulation using a multi-sphere model. Two important kinds of clusters, dimer and wagon wheel structures, were observed based on which the growth behavior and mechanism of each local cluster with different orientations/structures were investigated. The results show that during vibration, dimer clusters are formed first and then most of them grow into linear trimers and tetramers. Wagon wheel clusters are also frequently observed that grow into hexamers and, further, octamer and nonamer local clusters. Coordination number (CN) evolution indicates that the decrease of local mean CN can be regarded as the signal for the formation of local clusters in the tetrahedral particle packing system. Nematic order metric analysis shows that although the two basic structures (dimer and wagon wheel structures) grow into complex local clusters during packing densification, these local clusters are randomly distributed in the tetrahedral particle packing system. Stress analysis indicates that the dimer-based local clusters are mostly formed in the compaction state of the tetrahedral particle packing system during the vibrated packing densification process. In comparison, the wagon wheel-based local clusters need much stronger interaction forces from tetrahedral particles during vibrated packing densification.

Reciprocating compressors are widely used in petroleum and chemical industries, excessive clearance caused by bearing wear is the main form of failure. The fault vibration signal of reciprocating compressor bearing has strong non-stationary characteristics, aiming at the deficiency of adaptive algorithm in smoothing process, this paper presents an optimize local mean decomposition (OLMD) method. In interpolation calculation, interpolation points such as extreme value and eigenvalue are added, the optimized local mean function and envelope estimation function were obtained by using monotone cubic Hermite interpolation method, thus the interpolation fitting accuracy is improved. Through analog signal analysis and field test signal analysis, different LMD methods were used to resolve the large fault signal of large axle bushing clearance of type 2D12 reciprocating compressor, quantitative comparative analysis with the help of relevant evaluation indicators, through the above research, it is proved that the mono-mite interpolation LMD algorithm can be used to accurately extract and diagnoses the bearing clearance fault characteristics of reciprocating compressor.

At present, surgical suture treatment can be performed for spinal patients after nerve injury, but nerve regeneration and functional recovery require comprehensive treatment including drug treatment. However, there is still a lack of adjuvant therapeutic drugs that can effectively promote nerve regeneration and functional recovery. Drug treatment after nerve injury is the basis of nerve injury treatment and an important supplement to surgical treatment. Finding an effective method for treating spinal nerve injury and studying its mechanism of action may have important basic and clinical significance. The nanofiber catheter material simulates the nano/sub-micron level collagen fiber bundle structure of cells in the body, so it has been more and more widely used in the field of tissue engineering. Therefore, in this study, PHBV nanofiber catheter was successfully prepared by electrostatic spinning method, and the nanofiber catheter was characterized by SEM and DSC tests. The PHBV nanofiber catheter prepared by this research method has excellent characteristics such as porosity, large specific surface area, stable structure, thermal stability, and good mechanical properties. At the same time, adult male SD rats were selected to establish an animal model of cervical spine injury in this experiment. The expressions of three inflammation-related factors (IL-1α, IL-10 and TNF-1) were analyzed by ELISA. The results showed that in the spinal injury group, the expression of the three inflammatory factors all showed a significant increase over time and then reached a peak, then decreased and stabilized. This showed that the PHBV nanofiber catheter repairs cervical spine injury by affecting the inflammatory response, which is conducive to repairing cervical spine injury. RT-PCR was used to detect the expression of CNTF, GAP-43, and Tubulin-related proteins. During the neural regeneration process in rats, the expressions of both backbone proteins continued to be expressed, and they were first up-regulated and then flattened. This indicated that in the early stage of neural regeneration, a large number of skeletal proteins are synthesized, and they continue to be expressed at low levels over time, laying a foundation for the axon skeleton reconstruction.

High-speed surface-mounted permanent magnet synchronous machine is often used in micro gas turbine generation system due to its high rotor strength and high efficiency. The electrical machine in this kind of generation system needs to integrate two functions of starter and generator. Therefore, its comprehensive performance, including starting performance and generating performance, has become a comprehensive standard to measure machine performance. In this paper, a 40 kW, 20,000 r/min high-speed machine is taken as an example, the influence of magnets magnetization direction on the machine comprehensive performance is studied. The machine models with different magnets magnetization directions are established by using finite element method and the correctness of the models is verified by comparing the experimental data with the finite element calculation data. On this basis, the influence of different magnetization directions on the performance of the machine, such as generation loss, torque ripple, output voltage, start-up time and maximum starting ability, is analyzed. Furthermore, based on the Fourier decomposition of air gap flux density and the decoupling analysis of starting torque, the influence mechanism of magnetization direction on the performance of the machine is revealed. The presented results provide a reference for the selection of a suitable magnetization direction for high-speed surface-mounted permanent magnet machines.

The uniaxial die compaction and solid-state sintering of different sized tungsten powders in powder metallurgy (PM) process was numerically reproduced in multi-particle FEM (MPFEM) modeling from particulate scale. The effects of particle size, initial packing structure, compaction pressure and sintering temperature on the relative density of the tungsten powder component were systematically studied and discussed. Various macroscopic and microscopic properties of the powder mass with different initial packing structures during compaction and sintering were characterized and analyzed. These properties include the overall relative density, local stress distributions, force structure and transmission, particle rearrangement and deformation, void filling behavior, as well as the densification dynamics and mechanism. The results show that by properly controlling the operating conditions such as initial packing structure, compaction pressure and sintering temperature, high performance PM component with high relative density, uniform density, stress, and void distributions can be obtained. Meanwhile, physical experiments were implemented to verify the simulation results. It is indicated that MPFEM modeling used in current work can provide the researchers with an effective method to simulate the whole PM process for refractory tungsten powders from particulate scale, especially the coupling of different stages can reduce the assumptions in the modeling and make the simulation results more accurate and much closer to the actual process.

This paper presents a numerical study on the packing densification process of binary sphere mixtures under air impact using a combined computational fluid dynamics and discrete element method (CFD-DEM) scheme. The effects of particle size ratio (PSR) on the force and stress characteristics including the depth-averaged normal force, probability density function (PDF) of normal forces, distributions of strong forces, mean stress distribution in the axial cross-section, and depth-averaged mean stress for various contact types, are comprehensively analyzed. In addition, the distribution of fluid-particle interaction forces is also discussed to explain the densification mechanism during air impact. The results reveal that the force and stress characteristics are significantly affected by both PSR and air impact. For each PSR, the packing density increases with the gas inlet velocity to a maximum and then decreases. Meanwhile, both the depth-averaged normal force and the mean stress in initial packing increase linearly with the depth, while the relationship between the depth-averaged normal force or mean stress and the depth is in power law growth in the final packing after air impact. The contact type of L-S (L-large sphere, S-small sphere) plays a leading role in the PDF of normal forces, while the effects of S-S contact type on the packing system is weak. Furthermore, apart from the L-L contact, the strong force percentage of other contacts increases after air impact densification. The air impact can effectively improve the uniformity of the normalized mean stress distribution for the packing of binary mixtures. Finally, the distribution of fluid-particle interaction forces demonstrates that the packing can be densified by obvious rearrangement of small particles for adjacent pore filling, and this trend will become more apparent with the increase of PSR.

The packing densification of mono-sized equilateral cylindrical particles under mechanical vibration is numerically reproduced using discrete element method (DEM). The influences of vibration frequency, amplitude and container size on the macro property (e.g. packing density) of each packing are studied. Meanwhile, various micro-properties including coordination number (CN), radial distribution function (RDF), local structures, contact types, particle position/orientation distributions, forces/stresses of the vibrated dense packing are characterized and compared with those of the loose initial poured packing. The results show that properly controlling vibration conditions can realize the transition of equilateral cylindrical particles from random loose packing (RLP) to random close packing (RCP). The maximum packing density without wall effects can reach about 0.7166, which agrees with experimental and numerical results in literature. Micro property analyses demonstrate that the average CN increases slightly after vibration. The RDF curves indicate three obvious peaks for both poured and vibrated packings. The distributions of intersection angles imply that the perpendicular arrangements of the cylindrical particles are common in both packing structures. From RLP to RCP, the probability of side-edge, bottom-edge and edge-edge contacts between two particles decreases, while that of side-side, side-bottom and bottom-bottom contacts increases. Both particle position and orientation distributions illustrate that the structure in the center of the vibrated packing is disordered. The distribution of strong forces follows the exponential law, while that of weak forces follows the power law. The static vertical stresses in both packings can be predicted by Janssen model. After vibration, a much denser and more stable structure with a larger saturation stress is obtained due to the reducing inter-particle friction effects.

To identify the dense packing of cylinder–sphere binary mixtures (spheres as filling objects), the densification process of such binary mixtures subjected to three-dimensional (3D) mechanical vibra...

We demonstrate an optical filter using multistage of second-order microring resonators (2nd-order MRRs) for a box-like filter response. All stages have identical structure parameters elaborately designed to obtain a flat-top spectrum. The maximally flat condition is deduced in consideration of loss and compared with those reported in literature. We present the insertion loss, extinction ratio, bandwidth, and roll-off rate of the maximally flat response. We find that for the flat response of a 2nd-order MRR, the product of bandwidth and roll-off rate is constant. We compare the cascading 2nd-order MRRs with single-stage high-order filters with the same number of ring cavities. We find that the cascading structure has comparable performances in the aspects of insertion loss and roll-off rate for small radius. This cascading structure relaxes the fabrication tolerance and mitigates the difficulty of electrical wiring difficulty since there are only two ring cavities in each stage. As a proof of concept, we fabricate this kind of optical filter with ten stages on silicon-on-insulator platform, with each ring cavity tunable and each stage measurable. We obtain five flat-top responses corresponding to one to five cascading stages. The five-stage filter response has a 3 dB bandwidth of ∼17 GHz, a roll-off rate of ∼−5 dB/GHz at −3 dB point, and an on-chip insertion loss of ∼−6 dB.

Aiming at the nonlinearity, nonstationarity and multi-component coupling characteristics of reciprocating compressor vibration signals, an integrated feature extraction method based on the variational mode decomposition (VMD) and multi-fractal detrended fluctuation analysis (MFDFA) is proposed for a fault diagnosis for a reciprocating compressor valve. Firstly, to eliminate the noise interference, a novel VMD method with superior anti-interference performance was utilized to obtain several components of the quasi-orthogonal band-limited intrinsic mode function (BLIMF) from a strong non-stationarity vibration signal, and a consistent number K of BLIMFs was selected based on a novel criterion for all fault states. Secondly, the MFDFA method, which can describe the multi-fractal structure feature of non-stationary time series, was applied to analyze each BLIMF component, and the parameters of MFDFA were employed as the eigenvectors to reflect the structure characteristics and local scale behavior of the vibration signal. Then, the principal component analysis (PCA) was introduced to refine the eigenvectors for a higher recognition efficiency and accuracy. Finally, the vibration signals of four types of reciprocating compressor valve faults were analyzed by this method, and the faults were identified correctly by pattern classifiers of BTSVM and CNN. Further results comparison with other feature extraction methods verifies the superiority of the proposed method.

Natural fractures have a significant influence on the propagation geometry of hydraulic fractures in fractured reservoirs. True triaxial volumetric fracturing experiments, in which random natural fractures are created by placing cement blocks of different dimensions in a cuboid mold and filling the mold with additional cement to create the final test specimen, were used to study the factors that influence the hydraulic fracture propagation geometry. These factors include the presence of natural fractures around the wellbore, the dimension and volumetric density of random natural fractures and the horizontal differential stress. The results show that volumetric fractures preferentially formed when natural fractures occurred around the wellbore, the natural fractures are medium to long and have a volumetric density of 6–9%, and the stress difference is less than 11 MPa. The volumetric fracture geometries are mainly major multi-branch fractures with fracture networks or major multi-branch fractures (2–4 fractures). The angles between the major fractures and the maximum horizontal in situ stress are 30°–45°, and fracture networks are located at the intersections of major multi-branch fractures. Short natural fractures rarely led to the formation of fracture networks. Thus, the interaction between hydraulic fractures and short natural fractures has little engineering significance. The conclusions are important for field applications and for gaining a deeper understanding of the formation process of volumetric fractures.

The major reasons that cause the damage of damper bars in the leeward side are found in this paper. It provides a route for the structure optimization design of a hydro generator. Firstly, capacity of a 24 MW bulb tubular turbine generator is taken as an example in this paper. The transient electromagnetic field model is established, and the correctness of the model is verified by the comparison of experimental results and simulation data. Secondly, when the generator is operated at rated condition, the eddy current density distributions of damper bars are studied. And the asymmetric phenomenon of the eddy current density on damper bars is discovered. The change laws of the eddy currents in damper bars are determined through further analysis. Thirdly, through the study of eddy current distributions under different conditions, it is confirmed that the stator slots and armature reaction are the main factors to affect the asymmetric distribution of the eddy current in damper bars. Finally, the studies of the magnetic density distribution and theoretical analysis revealed the asymmetric distribution mechanism of eddy current density.

In the hydrothermal carbonization of carbohydrates, such as sucrose as raw material in this study, activated carbon microspheres were synthesized by two steps of hydrothermal carbonization (180 °C) and further heat treatment in nitrogen (1000 °C). The main purpose of this study was to investigate the effects of additives, such as H3PO4, ZnCl2, SnCl2, and CaCl2, on the surface characteristics and toluene adsorption ability by adding them into the two processes. The structural, chemical, and adsorption properties of sucrose-derived activated carbon microspheres were characterized using nitrogen adsorption, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, water contact angles, and dynamic adsorption of toluene. Results showed that additives played important roles in the synthesis process. The addition of CaCl2 in the hydrothermal process, the specific surface area of activated carbon spheres increased up to 1180 m2 g−1 compared with that of the blank sample (i.e., 724 m2 g−1). By contrast, the addition of H3PO4 in the heat treatment process increased the specific surface area to 1529 m2 g−1. Moreover, the micromorphology of activated carbon microspheres was more homogeneous when additives were added in the heat treatment process, but the activated carbon microspheres were more hydrophobic when additives were added in the hydrothermal process. These findings may help researchers to understand the influence of additives on the preparation of hydrochar-derived activated carbon.

The green retrofitting of existing residential buildings is an important approach to realise the sustainable development of stock buildings. In addition to the new technologies and materials related to green retrofitting, the intention of residents toward the green retrofitting of existing residential buildings must be understood. However, the factors affecting such intentions are still unclear. Hence, this study refers to the extended theory of planed behaviour and constructs a theoretical model of the intention toward the green retrofitting of existing residential buildings. On the basis of the data from 507 questionnaires collected from eastern and western China, the theoretical model is tested via structural equation modelling (SEM). Multigroup SEM is used to analyse the differences in population characteristics and the intention of residents toward the green retrofitting of existing residential buildings in residential areas. Research results reveal the following: (1) the most important factors affecting residents&rsquo, intention toward green retrofitting are policy factors, followed by cognition of green retrofitting, behaviour, subjective norms, and perceived behavioural control, (2) policy factors not only directly affect residents&rsquo, intention toward green retrofitting but also indirectly affect their intention toward existing residential green retrofitting through perceived behavioural control, (3) residents&rsquo, cognition of green retrofitting exerts no significant direct impact on their intention toward green retrofitting, but it does indirectly affect their intention toward green retrofitting through behaviour and subjective norms, (4) behaviour, subjective norms, and perceived behavioural control have direct and significant influences on intention toward green retrofitting, (5) demographic characteristics (gender, age, monthly family income, education level, and occupation) and regional variables (east and west) present significant differences in different influence paths. The conclusion of the study provides a targeted path reference for the promotion of the green retrofitting of existing residential buildings.

With the rapid development of nanotechnology, engineered nanomaterials (ENMs) have been applied in many fields, such as food industry, biomedicine, and so on. However, the study on the health and safety implications of ENMs is still insufficient. Previous studies have shown that nanoparticles under acute or chronic exposure could be transported and accumulated in various organs and tissues, resulting in adverse effects or systemic toxicity. Among these, the kidney is one of the main organs that exposed ENMs will target through different routes. One of the important functions of the kidney is to discharge metabolic wastes and exogenous substances from the blood circulation of the whole body. During ENM exposure, the kidney may become vulnerable to toxicity. Studies have suggested that nanoparticles exposed to the kidney could provoke glomerular swelling, basilar membrane thickening, degeneration, and necrosis of renal tubular cells. These adverse effects of nanoparticles on the kidney may be related to their induced oxidative stress, inflammation, autophagy, DNA damage, and ER stress. This review aims to examine current studies on ENM-induced nephrotoxicity, with the focus on elucidating the potential molecular mechanisms of nanoparticle-induced toxicity on the kidney, which will further facilitate the safer design of ENMs and their applications.

Insufficient clean freshwater has exacerbated water scarcity in China, especially in southern coastal regions where the economy is active and highly populated. Seawater is an important supplement of water source in China, and seawater desalination has been developed as a strategic and influential industry. This review systematically analyzed the status quo of industrialized desalination technology, and evaluated the trend of seawater desalination industry in China. We first presented a statistical analysis and roadmap of the whole development course of seawater desalination industry, and the contemporary industrial practice of desalination technology was summarized, including reverse osmosis, electrodialysis, forward osmosis, multiple-effect distillation and multi-stage flash, along with their relevant engineering installation as milestones. The matrix comparison of their scale, quantity and integration was specifically highlighted. Factors leading to the historical development of these desalination technologies in China were critically analyzed. Current trend of integrating the renewable energy was described. Finally, the constraints for further development of desalination production scale were explored and the potential countermeasures were proposed. This review presents a detailed database for Chinese seawater desalination industry and serves as a comprehensive and critical analysis for unique status of desalination in regions where water is abundant, but clean water is scarce.

Both reverse osmosis (RO) and nanofiltration (NF) membranes have been increasingly used for water purification and desalination. However, the salt rejection of NF membranes is quite different from that of RO membranes, which makes a significant distinction in their process designs. This work started from the performance investigation of a single NF membrane element and then focused on the process design of the NF system for surface water treatment. In experimental tests, it was found that the observed rejection of the NF element becomes nearly constant when the concentrate flow is large enough, while the membrane flux of the NF element is quite stable regardless of the water flow across the membrane surface. These findings can be used to instruct the process design of the NF system for surface water treatment. In process design, a two-stage arrangement is sufficient for the NF system to reach the highest water recovery, while the RO system requires a three-stage arrangement.

Local mean decomposition (LMD) is a new time–frequency analysis method which can decompose a signal adaptively into a set of product function (PF) components, and the construction of local mean function and envelope function plays an important role in the accuracy of its PF components. Aiming at the strong nonstationarity, nonlinearity and multi-component coupling characteristics of reciprocating compressor vibration signals, an improved LMD was proposed by a novel construction method of local mean function and envelope function. By introducing an extreme symmetrical point between two extreme points and using the Monotone Piecewise Cubic Hermite Interpolation (MPCHI) instead of Cubic Spline Interpolation (CSI) to construct the envelopes, a novel construction method of local mean function and envelope function was proposed, and then the improved LMD algorithm was given based on this novel construction method. The improved LMD was applied to decompose the vibration signals of reciprocating compressor fault states, and the comparison of details between different LMD decomposition results verified the superiority of this improved method. The envelope frequency spectrum of PF component gives a more significant peak of fault frequency than that of original signal, which further indicates that this proposed method is competent for the diagnosis of reciprocating compressor oversized bearing clearance fault.

A novel rolling bearing fault diagnosis method based on hierarchical fuzzy entropy (HFE), Laplacian score (LS) and improved support vector machine based binary tree (ISVM-BT) is proposed in this paper. Focus on the difficulty of extracting fault feature from the non-linear and non-stationary vibration signal under complex operating conditions, HFE method is utilized for fault feature extraction. Compared with multi-scale fuzzy entropy (MFE) method, HFE method considers both the low and high frequency components of the vibration signals, which can provide a much more accurate estimation of entropy. Besides, Laplacian score (LS) method is introduced to refine the fault feature by sorting the scale factors. Subsequently, the obtained features are fed into the multi-fault classifier ISVM-BT to automatically fulfill the fault pattern identifications. The experimental results demonstrate that the proposed method is effective in recognizing the different categories and severities of rolling bearings faults.

Constructing functional filtration-membrane materials for effective oil-water separation and water further purification are of great significance not only to the environment but also to human health. In this work, we present a facile approach to fabricate TiO2-composited cotton fabrics with silanized surfaces by the immersion and spraying combination. The functionalized fabrics not merely exhibited the desirable superhydrophobic and oleophilic property towards the application of oil-water separation, but also synchronously performed the considerable photocatalytic activity for the degradation of water-soluble pollutants during the oil and water separating process. Moreover, the fabrics have the good self-cleaning ability. Importantly, the excellent performance of oil-water separation and photocatalytic degradation has been maintained through more than ten-cycles test, verifying the fabrics with the sustainability and stability. The chemical constituents, structures, morphologies, wettability and photocatalytic activity of the fabrics have been characterized by series of infrared spectrum, X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, water contact angle and ultraviolet-visible absorption spectrum measurements. Our primary results provide the facile and promising strategy to fabricate superhydrophobic TiO2-composited cotton fabrics combined oil-water separation and photocatalytic degradation functions, which show great potential in the oil-contained wastewater treatment and environmental restoration.

The discrete element method (DEM) was used to simulate the piling of rod-like (elongated sphero-cylindrical) particles, mainly focusing on the effect of particle shape on the structural and force properties of the piles. In this work, rod-like particles of different aspect ratios were discharged on a flat surface to form wedge-shaped piles. The surface properties of the piles were characterized in terms of angle of repose and stress at the bottom of the piles. The results showed that the rise of the angle of repose became slower with the increase of particle aspect ratio. The pressure dip underneath the piles reached the maximum when the particle aspect ratio was around 1.6, beyond which the pressure dip phenomenon became attenuated. Both the pressure dip and the shear stress dip were quantitatively examined. The structure and forces inside the piles were further analyzed to understand the change in pressure dip, indicating that "bridging" or "arching" structures within the piles were the cause of the pressure dip.

Driven by the pulse pressure, fractures can branch and form a complex network, which is mostly desired in the reservoir stimulation. Thus, the pulsed fracture(PF) should be an inspiring potential technique to improve the reservoir. To explore the regulations of the pulsed fracturing process in field size, the PF is simulated by using the discretized virtual internal bond method. The normal triangular and the in-situ measured pulse are respectively taken as the pressure input in the numerical simulation. It is found that in the high in-situ stress contrast condition, the simple fracture symmetrically initiates on the wellbore wall and then propagates along the major in-situ stress direction. After the fracture advances a certain distance from the wellbore, it suddenly branches in the radial pattern, which forms a complex network. The distance of the fracture network to the wellbore is determined by the difference of the two principal in-situ stresses. The smaller the stress difference is, the closer the fracture network is to the wellbore. On the post-peak stage of pulse, the fracture network still grows self-similarly, but the growing velocity decreases with increasing the unloading rate. When the loading time is fixed, the peak pressure has significant impact on the fracture network profile. The higher peak pressure can generate a larger and more complex fracture network. It is observed that many branched fractures oblique stretch towards the minor in-situ stress direction, which is very helpful for the PF connect to the reservoir in that direction. In addition, the fracture network is generated at a certain distance to the wellbore in the larger in-situ stress difference cases, which is in favor of the wellbore stability. Besides these qualitative regulations, some quantitative conclusions are drawn in this paper. These provide valuable references for the assessment of the PF stimulation in reservoir.

Polyamide (PA) membrane-based reverse-osmosis (RO) serves as one of the most important techniques for water desalination and purification. Fundamental understanding of PA RO membranes at the atomistic level is critical to enhance their separation capabilities, leading to significant societal and commercial benefits. In this paper, a fully atomistic molecular dynamics simulation was performed to investigate PA membrane. Our simulated cross-linked membrane exhibits structural properties similar to those reported in experiments. Our results also reveal the presence of small local two-layer slip structures in PA membrane with 70% cross-linking, primarily due to short-range anisotropic interactions among aromatic benzene rings. Inside the inhomogeneous polymeric structure of the membrane, water molecules show heterogeneous diffusivities and converge adjacent to polar groups. Increased diffusion of water molecules is observed through the less cross-linked pathways. The existence of the fast pathways for water permeation has no effect on membrane's salt rejections.

We demonstrate a microwave photonic filter based on multistage high-order silicon microring resonators. The boxlike filter responses and rolloff enhancement effect are demonstrated experimentally, with a brief comparison with other schemes.

Graphene oxide (GO)-based membranes provide an encouraging opportunity to support high separation efficiency for wastewater treatment. However, due to the relatively weak interaction between GO nanosheets, it is difficult for bare GO-based membranes to survive in cross-flow filtration. In addition, the permeation flux of the bare GO membrane is not high sufficiently due to its narrow interlayer spacing. In this study, GO membranes interlinked with multi-walled carbon nanotubes (MWCNTs) via covalent bonds were fabricated on modified polyacrylonitrile (PAN) supports by vacuum filtration. Due to the strong bonds between GO, MWCNTs and the PAN membrane, the membranes could be used for the treatment of simulated nuclear wastewater containing strontium via a cross-flow process. The result showed a high flux of 210.7L/(m2h) at 0.4MPa, which was approximately 4 times higher than that of commercial nanofiltration membranes. The improved water permeation was attributed to the nanochannels created by the interlinked MWCNTs in the GO layers. In addition, the hybrid membrane exhibited a high rejection of 93.4% for EDTA-chelated Sr2+ in an alkaline solution, and could also be used to separate Na+/Sr2+ mixtures. These results indicate that the MWCNTs-interlinked GO membrane has promising prospects for application in radioactive waste treatment.

In this paper, four binary hard sphere crystals were numerically constructed by discrete element method (DEM) through different packing modes under three-dimensional (3D) mechanical vibration. For each crystal, a modified Voronoi tessellation method (called radical tessellation) was utilized to quantitatively investigate the topological and metrical properties of radical polyhedra (RPs). The topological properties such as the number of faces, edges, vertices per RP and the number of edges per RP face as well as the metrical properties such as perimeter, surface area, volume, and relative pore size per RP were systematically characterized and compared. Meanwhile, the mechanism of the binary hard sphere crystallization was also investigated. The results show that the packing sequence and pattern of the large spheres can determine the structure of the binary hard sphere crystal. The RP structures and their metrical and topological properties of the four binary hard sphere crystals (even the packing density of the two crystals is the same) are quite different. Each property can clearly reflect the specific characteristics of the corresponding binary hard sphere crystalline structure. The obtained quantitative results would be useful for the deep understanding of the structure and resultant properties of binary hard sphere crystals.

We demonstrate an optical filter based on multistage second-order microring resonators (MRs) with box-like spectral responses. Compared with single-stage high-order optical filters with the same number of MRs, the demonstrated structure has comparable performances in the aspects of passband flatness, rolling-off slope and insertion loss. Moreover, the architecture relaxes the fabrication tolerance, electrical wiring and tuning difficulty since there are only two MRs in each stage. We experimentally demonstrate this kind of optical filter with five stages, which shows a 3-dB bandwidth of ~17 GHz, a rolling-off slope of ~5 dB/GHz and an on-chip insertion loss of ~6 dB.