In cold regions,rock structures will be weakened by freeze-thaw cycles under various water immersion conditions.Determining how water immersion conditions impact rock deterioration under freeze-thaw cycles is critical...In cold regions,rock structures will be weakened by freeze-thaw cycles under various water immersion conditions.Determining how water immersion conditions impact rock deterioration under freeze-thaw cycles is critical to assess accurately the frost resistance of engineered rock.In this paper,freeze-thaw cycles(temperature range of-20℃-20℃)were performed on the sandstones in different water immersion conditions(fully,partially and non-immersed in water).Then,computed tomography(CT)tests were conducted on the sandstones when the freeze-thaw number reached 0,5,10,15,20 and 30.Next,the effects of water immersion conditions on the microstructure deterioration of sandstone under freezethaw cycles were evaluated using CT spatial imaging,porosity and damage factor.Finally,focusing on the partially immersed condition,the immersion volume rate was defined to understand the effects of immersion degree on the freeze-thaw damage of sandstone and to propose a damage model considering the freeze-thaw number and immersion degree.The results show that with increasing freeze-thaw number,the porosities and damage factors under fully and partially immersed conditions increase continuously,while those under non-immersed condition first increase and then remain approximately constant.The most severe freeze-thaw damage occurs in fully immersed condition,followed by partially immersed condition and finally non-immersed condition.Interestingly,the freeze-thaw number and the immersion volume rate both impact the microstructure deterioration of the partially immersed sandstone.For the same freeze-thaw number,the damage factor increases approximately linearly with increasing immersion volume rate,and the increasing immersion degree exacerbates the microstructure deterioration of sandstone.Moreover,the proposed model can effectively estimate the freeze-thaw damage of partially immersed sandstone with different immersion volume rates.展开更多
Clean and efficient recycling of spent lithium-ion batteries(LIBs)has become an urgent need to promote sustainable and rapid development of human society.Therefore,we provide a critical and comprehensive overview of th...Clean and efficient recycling of spent lithium-ion batteries(LIBs)has become an urgent need to promote sustainable and rapid development of human society.Therefore,we provide a critical and comprehensive overview of the various technologies for recycling spent LIBs,starting with lithium-ion power batteries.Recent research on raw material collection,metallurgical recovery,separation and purification is highlighted,particularly in terms of all aspects of economic efficiency,energy consumption,technology transformation and policy management.Mechanisms and pathways for transformative full-component recovery of spent LIBs are explored,revealing a clean and efficient closed-loop recovery mechanism.Optimization methods are proposed for future recycling technologies,with a focus on how future research directions can be industrialized.Ultimately,based on life-cycle assessment,the challenges of future recycling are revealed from the LIBs supply chain and stability of the supply chain of the new energy battery industry to provide an outlook on clean and efficient short process recycling technologies.This work is designed to support the sustainable development of the new energy power industry,to help meet the needs of global decarbonization strategies and to respond to the major needs of industrialized recycling.展开更多
The mechanical properties and failure mechanism of lightweight aggregate concrete(LWAC)is a hot topic in the engineering field,and the relationship between its microstructure and macroscopic mechanical properties is a...The mechanical properties and failure mechanism of lightweight aggregate concrete(LWAC)is a hot topic in the engineering field,and the relationship between its microstructure and macroscopic mechanical properties is also a frontier research topic in the academic field.In this study,the image processing technology is used to establish a micro-structure model of lightweight aggregate concrete.Through the information extraction and processing of the section image of actual light aggregate concrete specimens,the mesostructural model of light aggregate concrete with real aggregate characteristics is established.The numerical simulation of uniaxial tensile test,uniaxial compression test and three-point bending test of lightweight aggregate concrete are carried out using a new finite element method-the base force element method respectively.Firstly,the image processing technology is used to produce beam specimens,uniaxial compression specimens and uniaxial tensile specimens of light aggregate concrete,which can better simulate the aggregate shape and random distribution of real light aggregate concrete.Secondly,the three-point bending test is numerically simulated.Thirdly,the uniaxial compression specimen generated by image processing technology is numerically simulated.Fourth,the uniaxial tensile specimen generated by image processing technology is numerically simulated.The mechanical behavior and damage mode of the specimen during loading were analyzed.The results of numerical simulation are compared and analyzed with those of relevant experiments.The feasibility and correctness of the micromodel established in this study for analyzing the micromechanics of lightweight aggregate concrete materials are verified.Image processing technology has a broad application prospect in the field of concrete mesoscopic damage analysis.展开更多
Due to the rapid advancement of the transportation industry and the continual increase in pavement infrastructure,it is difficult to keep up with the huge road maintenance task by relying only on the traditional manua...Due to the rapid advancement of the transportation industry and the continual increase in pavement infrastructure,it is difficult to keep up with the huge road maintenance task by relying only on the traditional manual detection method.Intelligent pavement detection technology with deep learning techniques is available for the research and industry areas by the gradual development of computer vision technology.Due to the different characteristics of pavement distress and the uncertainty of the external environment,this kind of object detection technology for distress classification and location still faces great challenges.This paper discusses the development of object detection technology and analyzes classical convolutional neural network(CNN)architecture.In addition to the one-stage and two-stage object detection frameworks,object detection without anchor frames is introduced,which is divided according to whether the anchor box is used or not.This paper also introduces attention mechanisms based on convolutional neural networks and emphasizes the performance of these mechanisms to further enhance the accuracy of object recognition.Lightweight network architecture is introduced for mobile and industrial deployment.Since stereo cameras and sensors are rapidly developed,a detailed summary of three-dimensional object detection algorithms is also provided.While reviewing the history of the development of object detection,the scope of this review is not only limited to the area of pavement crack detection but also guidance for researchers in related fields is shared.展开更多
At present,the emerging solid-phase friction-based additive manufacturing technology,including friction rolling additive man-ufacturing(FRAM),can only manufacture simple single-pass components.In this study,multi-laye...At present,the emerging solid-phase friction-based additive manufacturing technology,including friction rolling additive man-ufacturing(FRAM),can only manufacture simple single-pass components.In this study,multi-layer multi-pass FRAM-deposited alumin-um alloy samples were successfully prepared using a non-shoulder tool head.The material flow behavior and microstructure of the over-lapped zone between adjacent layers and passes during multi-layer multi-pass FRAM deposition were studied using the hybrid 6061 and 5052 aluminum alloys.The results showed that a mechanical interlocking structure was formed between the adjacent layers and the adja-cent passes in the overlapped center area.Repeated friction and rolling of the tool head led to different degrees of lateral flow and plastic deformation of the materials in the overlapped zone,which made the recrystallization degree in the left and right edge zones of the over-lapped zone the highest,followed by the overlapped center zone and the non-overlapped zone.The tensile strength of the overlapped zone exceeded 90%of that of the single-pass deposition sample.It is proved that although there are uneven grooves on the surface of the over-lapping area during multi-layer and multi-pass deposition,they can be filled by the flow of materials during the deposition of the next lay-er,thus ensuring the dense microstructure and excellent mechanical properties of the overlapping area.The multi-layer multi-pass FRAM deposition overcomes the limitation of deposition width and lays the foundation for the future deposition of large-scale high-performance components.展开更多
The high porosity and tunable chemical functionality of metal-organic frameworks(MOFs)make it a promising catalyst design platform.High-throughput screening of catalytic performance is feasible since the large MOF str...The high porosity and tunable chemical functionality of metal-organic frameworks(MOFs)make it a promising catalyst design platform.High-throughput screening of catalytic performance is feasible since the large MOF structure database is available.In this study,we report a machine learning model for high-throughput screening of MOF catalysts for the CO_(2) cycloaddition reaction.The descriptors for model training were judiciously chosen according to the reaction mechanism,which leads to high accuracy up to 97%for the 75%quantile of the training set as the classification criterion.The feature contribution was further evaluated with SHAP and PDP analysis to provide a certain physical understanding.12,415 hypothetical MOF structures and 100 reported MOFs were evaluated under 100℃ and 1 bar within one day using the model,and 239 potentially efficient catalysts were discovered.Among them,MOF-76(Y)achieved the top performance experimentally among reported MOFs,in good agreement with the prediction.展开更多
Graphene platelets(GPLs)-reinforced metal foam structures enhance the mechanical properties while maintaining the lightweight characteristics of metal foams.Further bonding piezoelectric actuator and sensor layers on ...Graphene platelets(GPLs)-reinforced metal foam structures enhance the mechanical properties while maintaining the lightweight characteristics of metal foams.Further bonding piezoelectric actuator and sensor layers on the surfaces of GPLs-reinforced metal foam beams enables active vibration control,greatly expanding their applications in the aerospace industry.For the first time,this paper investigates the vibration characteristics and active vibration control of GPLs-reinforced metal foam beams with surfacebonded piezoelectric layers.The constant velocity feedback scheme is used to design the closed-loop controller including piezoelectric actuators and sensors.The effects of the GPLs on the linear and nonlinear free vibrations of the beams are numerically studied.The Newmark-βmethod combined with Newton's iteration technique is used to calculate the nonlinear responses of the beams under different load forms including harmonic loads,impact loads,and moving loads.Additionally,special attention is given to the vibration reduction performance of the velocity feedback control on the responses of the beam.展开更多
Gradient coil is an essential component of a magnetic resonance imaging(MRI)scanner.To achieve high spatial resolution and imaging speed,a high-efficiency gradient coil with high slew rate is required.In consideration...Gradient coil is an essential component of a magnetic resonance imaging(MRI)scanner.To achieve high spatial resolution and imaging speed,a high-efficiency gradient coil with high slew rate is required.In consideration of the safety and comfort of the patient,the mechanical stability,acoustic noise and peripheral nerve stimulation(PNS)are also need to be concerned for practical use.In our previous work,a high-efficiency whole-body gradient coil set with a hybrid cylindrical-planar structure has been presented,which offers significantly improved coil performances.In this work,we propose to design this transverse gradient coil system with transformed magnetic gradient fields.By shifting up the zero point of gradient fields,the designed new Y-gradient coil could provide enhanced electromagnetic performances.With more uniform coil winding arrangement,the net torque of the new coil is significantly reduced and the generated sound pressure level(SPL)is lower at most tested frequency bands.On the other hand,the new transverse gradient coil designed with rotated magnetic gradient fields produces considerably reduced electric field in the human body,which is important for the use of rapid MR sequences.It's demonstrated that a safer and patient-friendly design could be obtained by using transformed magnetic gradient fields,which is critical for practical use.展开更多
Inefficient photo-carrier separation and sluggish photoreaction dynamics appreciably undermine the photocatalytic decontamination efficacy of photocatalysts.Herein,an S-scheme Mn_(0.5)Cd_(0.5)S/Bi_(2)MoO_(6)heterojunc...Inefficient photo-carrier separation and sluggish photoreaction dynamics appreciably undermine the photocatalytic decontamination efficacy of photocatalysts.Herein,an S-scheme Mn_(0.5)Cd_(0.5)S/Bi_(2)MoO_(6)heterojunction with interfacial Mo-S chemical bond is designed as an efficient photocatalyst.In this integrated photosystem,Bi2MoO6 and Mn_(0.5)Cd_(0.5)S function as oxidation and reduction centers of Mn_(0.5)Cd_(0.5)S/Bi_(2)MoO_(6)microspheres,respectively.Importantly,the unique charge transfer mechanism in the chemically bonded S-scheme heterojunction with Mo-S bond as atom-scale charge transport highway effectively inhibits the photocorrosion of Mn_(0.5)Cd_(0.5)S and the recombination of photo-generated electron-hole pairs,endowing Mn_(0.5)Cd_(0.5)S/Bi_(2)MoO_(6)photocatalyst with excellent photocatalytic decontamination performance and stability.Besides,integration of Mn_(0.5)Cd_(0.5)S nanocrystals into Bi2MoO6 improves hydrophilicity,conducive to the photoreactions.Strikingly,compared with Mn_(0.5)Cd_(0.5)S and Bi2MoO6,the Mn_(0.5)Cd_(0.5)S/Bi_(2)MoO_(6)unveils much augmented photoactivity in tetracycline eradication,among which Mn_(0.5)Cd_(0.5)S/Bi_(2)MoO_(6)-2 possesses the highest activity with the rate constant up to 0.0323 min-1,prominently outperforming other counterparts.This research offers a chemical bonding engineering combining with S-scheme heterojunction strategy for constructing extraordinary photocatalysts for environmental purification.展开更多
The location pattern of different commercial stores in Shichahai, a historic conservation area in Beijing, was investigated from a street centrality perspective. Many previous studies have investigated the relationshi...The location pattern of different commercial stores in Shichahai, a historic conservation area in Beijing, was investigated from a street centrality perspective. Many previous studies have investigated the relationship between street centrality and land use patterns or commercial activities at interurban or intraurban scales. We considered Shichahai in this study to determine if street centrality applied at the street scale and if the street network was the only factor influencing the selection of store location. First, the nearest neighbor index, nearest neighbor hierarchical spatial cluster(NNHSC), and kernel density estimation(KDE) methods were used to provide baseline spatial distributions of commercial stores. Second, urban network analysis(UNA) tools were used to measure the street centrality indices under two conditions, with and without the weighting of cultural relics calculated by a principal component analysis(PCA). Finally, both store locations and centrality values at nodes were transformed to one unit(raster pixel) for a correlation analysis.The results showed that three of the four store types were clustered and had their own hotspots that were mostly located in the eastern and central parts of city blocks. The most momentous findings were determined from the street centrality indices. Among the three store types with correlation coefficients above 0.5, all centrality indices with landmark weighting, except straightness, had higher correlations,with closeness with landmark weighting having the highest correlation, followed by betweenness with landmark weighting. Therefore,we statistically concluded that street centrality could apply at the street scale and that the street network was not the only factor that influenced store location pattern, with landmarks also playing a significant role. The results provide guidance in determining the selection strategy for stores in a historic conservation area.展开更多
An electromagnetic anti-fouling technology(EAFT) was developed further. The operating principle of the EAFT was presented using fundamental physics laws. To validate the effect of EAFT and identify the mechanism, a ci...An electromagnetic anti-fouling technology(EAFT) was developed further. The operating principle of the EAFT was presented using fundamental physics laws. To validate the effect of EAFT and identify the mechanism, a circulating flow setup was built. A series of fouling tests were carried out with and without EAFT, measuring fouling thermal resistance as function of time, making scanning electron microscope images and analyzing the particles size distribution in solution by dynamics light scattering technology. The main results were as follows: 1) All the precipitated crystals in solution were calcite and there were little differences between with EAFT and without EAFT in the experimental range. 2) The number of precipitate nucleation in solution was small and the particle growth was slow without EAFT. In opposition to the case untreated, a rapid particle growth was observed and the number of nucleation was expected to be large, due to the fact that the EAFT effectively increases the ions and crystals collision frequency and effectiveness by utilizing the induced electric field. It is indicated that the particle growth is promoted mainly by coagulation process but not nucleation growth. 3) The EAFT could prolong the delay time of fouling greatly, and after the delay time, the thermal resistance quickly increased. Therefore, in order to mitigate scale significantly, the floccules in solution should be deposited beforehand in a low-lying area of the exchangers and let off in time.展开更多
The characteristics of temperatures, stresses and strains fields have been studied numerically for a titanium alloy sheet welded with an improved gas tungsten arc welding method, in which a trailing spot heat sink is ...The characteristics of temperatures, stresses and strains fields have been studied numerically for a titanium alloy sheet welded with an improved gas tungsten arc welding method, in which a trailing spot heat sink is introduced to control the welding stress and distortion. The impinging jet model is employed to describe the internee heat transfer between the cooling media and the top suufuce of the workpiece. The influcnee of the distance between arc and heat sink is investigated. Results show that there is an ideal range of distance. Using the ideal distance, a low stress and no distortion welding structure can be derived.展开更多
Purpose:This study aims to provide a new framework for analyzing the path of technology diffusion in the innovation network at the regional level and industrial level respectively,which is conducive to the integration...Purpose:This study aims to provide a new framework for analyzing the path of technology diffusion in the innovation network at the regional level and industrial level respectively,which is conducive to the integration of innovation resources,the coordinated development of innovative subjects,and the improvement of innovation abilities.Design/methodology/approach:Based on the Z-Park patent cooperation data,we establish Inter-Enterprise Technology Transfer Network model and apply the concept of Pivotability to describe the key links of technology diffusion and quantify the importance of innovative partnerships.By measuring the topologically structural characteristics in the levels of branch park and the technosphere,this paper demonstrates how technology spreads and promotes overall innovation activities within the innovation network.Findings:The results indicate that:(1)Patent cooperation network of the Z-Park displays heterogeneity and the connections between the innovative subjects distribute extremely uneven.(2)Haidian park owns the highest pivotability in the IETTN model,yet the related inter-enterprise patent cooperation is mainly concentrated in its internal,failing to facilitate the technology diffusion across multiple branch parks.(3)Such fields as“electronics and information”and“advanced manufacturing”are prominent in the cross-technosphere cooperation,while fields such as“new energy”and“environmental protection technology”can better promote industrial integration.Research limitations:Only the part of the joint patent application is taken into account while establishing the patent cooperation network.The other factors that influence the mechanism of technology diffusion in the innovation network need to be further studied,such as financial capital,market competition,and personnel mobility,etc.Practical implications:The findings of this paper will provide useful information and suggestions for the administration and policy-making of high-tech parks.Originality/value:The value of this paper is to build a bridge between the massive amount of patent data and the nature of technology diffusion,and to develop a set of tools to analyze the nonlinear relations between innovative subjects.展开更多
Firstly,time and space characteristics of haze in Beijing-Tianjin-Hebei( B-T-H) region are revealed; results of haze source apportionment in the area are analyzed. Secondly,the influencing factors of haze are explored...Firstly,time and space characteristics of haze in Beijing-Tianjin-Hebei( B-T-H) region are revealed; results of haze source apportionment in the area are analyzed. Secondly,the influencing factors of haze are explored from the aspects of economic development,energy structure,industrial structure,transportation,etc. The internal driving forces of haze are also researched based on the DPSIR model. Finally some feasible and comprehensive control countermeasures against haze are suggested.展开更多
The as-cast microstructures of high carbon high speed steels （HC-HSS） made by sand casting, centrifugal casting and electromagnetic centrifugal casting, respectively, were studied by using of optical microscopy （OM...The as-cast microstructures of high carbon high speed steels （HC-HSS） made by sand casting, centrifugal casting and electromagnetic centrifugal casting, respectively, were studied by using of optical microscopy （OM） and D/max2200pc X-ray diffraction. The results show that the microstructure of as-cast HC- HSS is dominated by alloy carbides （W2C, VC, Cr7C3）, martensite and austenite. The centrifugal casting and electromagnetic centrifugal casting apparently improve the solidification structure of HCoHSS. With the increase of magnetic intensity （B）, the volume fraction of austenite in the HC-HSS solidification structure increases significantly while the eutectic ledeburite decreases. Moreover, the secondary carbides precipitated from the austenite are finer with more homogeneous distribution in the electromagnetic centrifugal castings. It has also been found that the lath of eutectic carbide in ledeburite becomes finer and carbide phase spacing in eutectic ledeburite increases along with the higher magnetic field strength.展开更多
By establishing emission inventory of air pollution sources in Beijing,and classifying and compiling the pollutant types and corresponding pollution source data in more detail,it could provide the reference for studyi...By establishing emission inventory of air pollution sources in Beijing,and classifying and compiling the pollutant types and corresponding pollution source data in more detail,it could provide the reference for studying causes of haze and related policy impact assessment in Beijing.In this paper,selecting relevant data published in the Beijing Statistical Yearbook,referring to emission coefficients in the technical guidelines for the preparation of various pollution sources,and combining characteristics of energy consumption in Beijing,emission inventory of air pollution sources in six parts is established:thermal power plant,industrial combustion source(by industry),technological process source(by product variety),motor vehicle,building construction and residents life,and the contribution rate of each part to air pollutants is given.Finally,policy suggestions for haze control in Beijing are put forward.展开更多
This study focuses on the analytical prediction of subsurface settlement induced by shield tunnelling in sandy cobble stratum considering the volumetric deformation modes of the soil above the tunnel crown.A series of...This study focuses on the analytical prediction of subsurface settlement induced by shield tunnelling in sandy cobble stratum considering the volumetric deformation modes of the soil above the tunnel crown.A series of numerical analyses is performed to examine the effects of cover depth ratio(C/D),tunnel volume loss rate(h t)and volumetric block proportion(VBP)on the characteristics of subsurface settle-ment trough and soil volume loss.Considering the ground loss variation with depth,three modes are deduced from the volumetric deformation responses of the soil above the tunnel crown.Then,analytical solutions to predict subsurface settlement for each mode are presented using stochastic medium theory.The influences of C/D,h t and VBP on the key parameters(i.e.B and N)in the analytical expressions are discussed to determine the fitting formulae of B and N.Finally,the proposed analytical solutions are validated by the comparisons with the results of model test and numerical simulation.Results show that the fitting formulae provide a convenient and reliable way to evaluate the key parameters.Besides,the analytical solutions are reasonable and available in predicting the subsurface settlement induced by shield tunnelling in sandy cobble stratum.展开更多
In this investigation,a high-strength Mg-12Gd-1.0Er-0.5Zr(wt.%)alloy sheet was produced by hot extrusion(HE)and subsequent hard-plate rolling(HPR)at different temperatures.The results indicate that the microstructures...In this investigation,a high-strength Mg-12Gd-1.0Er-0.5Zr(wt.%)alloy sheet was produced by hot extrusion(HE)and subsequent hard-plate rolling(HPR)at different temperatures.The results indicate that the microstructures of these final-rolled sheets are inhomogeneous,mainly including coarse deformed grains and dynamic recrystallized(DRXed)grains,and the volume fraction of these coarse deformed grains increases as the rolling temperature increases.Thus,more DRXed grains can be found in R-385℃sheet,resulting in a smaller average grain size and weaker basal texture,while the biggest grains and the highest strong basal texture are present in R-450℃sheet.Amounts of dynamic precipitation ofβphases which are mainly determined by the rolling temperature are present in these sheets,and its precipitation can consume the content of Gd solutes in the matrix.As a result,the lowest number density ofβphase in R-450℃sheet is beneficial to modify the age hardening response.Thus,the R-450℃sheet displays the best age hardening response because of a severe traditional precipitation ofβ’(more)andβH/βM(less)precipitates,resulting in a sharp improvement in strength,i.e.ultimate tensile strength(UTS)of∼518±17 MPa and yield strength(YS)of∼438±18 MPa.However,the elongation(EL)of this sheet reduces greatly,and its value is∼2.7±0.3%.By contrasting,the EL of the peak-aging R-385℃sheet keeps better,changing from∼4.9±1.2%to∼4.8±1.4%due to a novel dislocation-induced chain-like precipitate which is helpful to keep good balance between strength and ductility.展开更多
To promote the production and application of artificial aggregates,save natural sand resources and protect the ecological environment,we evaluated the feasibility of using spherical porous functional aggregates(SPFAs)...To promote the production and application of artificial aggregates,save natural sand resources and protect the ecological environment,we evaluated the feasibility of using spherical porous functional aggregates(SPFAs) formed by basalt saw mud under autoclave curing in ordinary structural concrete.In our work,two types of prewetted functional aggregates were taken as replacements for natural aggregates with different volume substitution rates(0%,5%,10%,15%,20%,25%,and 30%) in the preparation of ordinary structural concrete with water-to-binder ratios(W/B) of 0.48 and 0.33.The effects of the functional aggregate properties and content,W/B,and curing age on the fluidity,density,mechanical properties and autogenous shrinkage of ordinary concrete were analyzed.The experimental results showed that the density of concrete declined at a rate of not more than 5%,and the 28 d compressive strength could reach 31.0-68.2 MPa.Low W/B,long curing age and high-quality functional aggregates were conducive to enhancing the mechanical properties of SPFAs concrete.Through the rolling effects,SPFAs can optimize the particle gradation of aggregate systems and improve the fluidity of concrete,and the water stored inside SPFAs provides an internal curing effect,which prolongs the cement hydration process and considerably reduces the autogenous shrinkage of concrete.SPFAs exhibits high strength and high density,as well as being more cost-effective and ecological,and is expected to be widely employed in ordinary structural concrete.展开更多
Motivation, one element of the learner characteristics, has risen in the popularity polls in recent literature as a facilitator in the learning process. It is claimed that students＇ motivation needs to be taken into ...Motivation, one element of the learner characteristics, has risen in the popularity polls in recent literature as a facilitator in the learning process. It is claimed that students＇ motivation needs to be taken into account for input to become intake and therefore is the key learner variable. During this process, authentic materials can be used to spark learners＇ motivation and interest. This article begins with different perspectives of motivation before it comes to the relationship between authentic materials and motivation.展开更多
基金funding support from the National Natural Science Foundation of China(Grant No.12172019).
文摘In cold regions,rock structures will be weakened by freeze-thaw cycles under various water immersion conditions.Determining how water immersion conditions impact rock deterioration under freeze-thaw cycles is critical to assess accurately the frost resistance of engineered rock.In this paper,freeze-thaw cycles(temperature range of-20℃-20℃)were performed on the sandstones in different water immersion conditions(fully,partially and non-immersed in water).Then,computed tomography(CT)tests were conducted on the sandstones when the freeze-thaw number reached 0,5,10,15,20 and 30.Next,the effects of water immersion conditions on the microstructure deterioration of sandstone under freezethaw cycles were evaluated using CT spatial imaging,porosity and damage factor.Finally,focusing on the partially immersed condition,the immersion volume rate was defined to understand the effects of immersion degree on the freeze-thaw damage of sandstone and to propose a damage model considering the freeze-thaw number and immersion degree.The results show that with increasing freeze-thaw number,the porosities and damage factors under fully and partially immersed conditions increase continuously,while those under non-immersed condition first increase and then remain approximately constant.The most severe freeze-thaw damage occurs in fully immersed condition,followed by partially immersed condition and finally non-immersed condition.Interestingly,the freeze-thaw number and the immersion volume rate both impact the microstructure deterioration of the partially immersed sandstone.For the same freeze-thaw number,the damage factor increases approximately linearly with increasing immersion volume rate,and the increasing immersion degree exacerbates the microstructure deterioration of sandstone.Moreover,the proposed model can effectively estimate the freeze-thaw damage of partially immersed sandstone with different immersion volume rates.
基金supported by the National Key R&D Program of China,China(2022YFC3902600)CAS Project for Young Scientists in Basic Research,China(YSBR-044)+1 种基金Guangdong Basic and Applied Basic Research Foundation,China(2021B1515020068)China Postdoctoral Science Foundation,China(2023M733510).
文摘Clean and efficient recycling of spent lithium-ion batteries(LIBs)has become an urgent need to promote sustainable and rapid development of human society.Therefore,we provide a critical and comprehensive overview of the various technologies for recycling spent LIBs,starting with lithium-ion power batteries.Recent research on raw material collection,metallurgical recovery,separation and purification is highlighted,particularly in terms of all aspects of economic efficiency,energy consumption,technology transformation and policy management.Mechanisms and pathways for transformative full-component recovery of spent LIBs are explored,revealing a clean and efficient closed-loop recovery mechanism.Optimization methods are proposed for future recycling technologies,with a focus on how future research directions can be industrialized.Ultimately,based on life-cycle assessment,the challenges of future recycling are revealed from the LIBs supply chain and stability of the supply chain of the new energy battery industry to provide an outlook on clean and efficient short process recycling technologies.This work is designed to support the sustainable development of the new energy power industry,to help meet the needs of global decarbonization strategies and to respond to the major needs of industrialized recycling.
基金supported by the National Science Foundation of China(10972015,11172015)the Beijing Natural Science Foundation(8162008).
文摘The mechanical properties and failure mechanism of lightweight aggregate concrete(LWAC)is a hot topic in the engineering field,and the relationship between its microstructure and macroscopic mechanical properties is also a frontier research topic in the academic field.In this study,the image processing technology is used to establish a micro-structure model of lightweight aggregate concrete.Through the information extraction and processing of the section image of actual light aggregate concrete specimens,the mesostructural model of light aggregate concrete with real aggregate characteristics is established.The numerical simulation of uniaxial tensile test,uniaxial compression test and three-point bending test of lightweight aggregate concrete are carried out using a new finite element method-the base force element method respectively.Firstly,the image processing technology is used to produce beam specimens,uniaxial compression specimens and uniaxial tensile specimens of light aggregate concrete,which can better simulate the aggregate shape and random distribution of real light aggregate concrete.Secondly,the three-point bending test is numerically simulated.Thirdly,the uniaxial compression specimen generated by image processing technology is numerically simulated.Fourth,the uniaxial tensile specimen generated by image processing technology is numerically simulated.The mechanical behavior and damage mode of the specimen during loading were analyzed.The results of numerical simulation are compared and analyzed with those of relevant experiments.The feasibility and correctness of the micromodel established in this study for analyzing the micromechanics of lightweight aggregate concrete materials are verified.Image processing technology has a broad application prospect in the field of concrete mesoscopic damage analysis.
基金The first author appreciates the financial support from Hunan Provincial Expressway Group Co.,Ltd.and the Hunan Department of Transportation(No.202152)in ChinaThe first author also appreciates the funding support from the National Natural Science Foundation of China(No.51778038)the Beijing high-level overseas talents in China.Any opinion,finding,and conclusion expressed in this paper are those of the authors and do not necessarily represent the view of any organization.
文摘Due to the rapid advancement of the transportation industry and the continual increase in pavement infrastructure,it is difficult to keep up with the huge road maintenance task by relying only on the traditional manual detection method.Intelligent pavement detection technology with deep learning techniques is available for the research and industry areas by the gradual development of computer vision technology.Due to the different characteristics of pavement distress and the uncertainty of the external environment,this kind of object detection technology for distress classification and location still faces great challenges.This paper discusses the development of object detection technology and analyzes classical convolutional neural network(CNN)architecture.In addition to the one-stage and two-stage object detection frameworks,object detection without anchor frames is introduced,which is divided according to whether the anchor box is used or not.This paper also introduces attention mechanisms based on convolutional neural networks and emphasizes the performance of these mechanisms to further enhance the accuracy of object recognition.Lightweight network architecture is introduced for mobile and industrial deployment.Since stereo cameras and sensors are rapidly developed,a detailed summary of three-dimensional object detection algorithms is also provided.While reviewing the history of the development of object detection,the scope of this review is not only limited to the area of pavement crack detection but also guidance for researchers in related fields is shared.
基金supported by the National Key Research and Development Program of China(No.2022YFB3404700)the National Natural Science Foundation of China(Nos.52105313 and 52275299)+2 种基金the Research and Development Program of Beijing Municipal Education Commission,China(No.KM202210005036)the Natural Science Foundation of Chongqing,China(No.CSTB2023NSCQ-MSX0701)the National Defense Basic Research Projects of China(No.JCKY2022405C002).
文摘At present,the emerging solid-phase friction-based additive manufacturing technology,including friction rolling additive man-ufacturing(FRAM),can only manufacture simple single-pass components.In this study,multi-layer multi-pass FRAM-deposited alumin-um alloy samples were successfully prepared using a non-shoulder tool head.The material flow behavior and microstructure of the over-lapped zone between adjacent layers and passes during multi-layer multi-pass FRAM deposition were studied using the hybrid 6061 and 5052 aluminum alloys.The results showed that a mechanical interlocking structure was formed between the adjacent layers and the adja-cent passes in the overlapped center area.Repeated friction and rolling of the tool head led to different degrees of lateral flow and plastic deformation of the materials in the overlapped zone,which made the recrystallization degree in the left and right edge zones of the over-lapped zone the highest,followed by the overlapped center zone and the non-overlapped zone.The tensile strength of the overlapped zone exceeded 90%of that of the single-pass deposition sample.It is proved that although there are uneven grooves on the surface of the over-lapping area during multi-layer and multi-pass deposition,they can be filled by the flow of materials during the deposition of the next lay-er,thus ensuring the dense microstructure and excellent mechanical properties of the overlapping area.The multi-layer multi-pass FRAM deposition overcomes the limitation of deposition width and lays the foundation for the future deposition of large-scale high-performance components.
基金financial support from the National Key Research and Development Program of China(2021YFB 3501501)the National Natural Science Foundation of China(No.22225803,22038001,22108007 and 22278011)+1 种基金Beijing Natural Science Foundation(No.Z230023)Beijing Science and Technology Commission(No.Z211100004321001).
文摘The high porosity and tunable chemical functionality of metal-organic frameworks(MOFs)make it a promising catalyst design platform.High-throughput screening of catalytic performance is feasible since the large MOF structure database is available.In this study,we report a machine learning model for high-throughput screening of MOF catalysts for the CO_(2) cycloaddition reaction.The descriptors for model training were judiciously chosen according to the reaction mechanism,which leads to high accuracy up to 97%for the 75%quantile of the training set as the classification criterion.The feature contribution was further evaluated with SHAP and PDP analysis to provide a certain physical understanding.12,415 hypothetical MOF structures and 100 reported MOFs were evaluated under 100℃ and 1 bar within one day using the model,and 239 potentially efficient catalysts were discovered.Among them,MOF-76(Y)achieved the top performance experimentally among reported MOFs,in good agreement with the prediction.
基金Project supported by the National Natural Science Foundation of China(Nos.12102015 and 12472003)the R&D Program of Beijing Municipal Education Commission of China(No.KM202110005030)。
文摘Graphene platelets(GPLs)-reinforced metal foam structures enhance the mechanical properties while maintaining the lightweight characteristics of metal foams.Further bonding piezoelectric actuator and sensor layers on the surfaces of GPLs-reinforced metal foam beams enables active vibration control,greatly expanding their applications in the aerospace industry.For the first time,this paper investigates the vibration characteristics and active vibration control of GPLs-reinforced metal foam beams with surfacebonded piezoelectric layers.The constant velocity feedback scheme is used to design the closed-loop controller including piezoelectric actuators and sensors.The effects of the GPLs on the linear and nonlinear free vibrations of the beams are numerically studied.The Newmark-βmethod combined with Newton's iteration technique is used to calculate the nonlinear responses of the beams under different load forms including harmonic loads,impact loads,and moving loads.Additionally,special attention is given to the vibration reduction performance of the velocity feedback control on the responses of the beam.
基金supported by the Instrument Developing Project of Magnetic Resonance Union of Chinese Academy of Sciences,Grant No.2022GZL002.
文摘Gradient coil is an essential component of a magnetic resonance imaging(MRI)scanner.To achieve high spatial resolution and imaging speed,a high-efficiency gradient coil with high slew rate is required.In consideration of the safety and comfort of the patient,the mechanical stability,acoustic noise and peripheral nerve stimulation(PNS)are also need to be concerned for practical use.In our previous work,a high-efficiency whole-body gradient coil set with a hybrid cylindrical-planar structure has been presented,which offers significantly improved coil performances.In this work,we propose to design this transverse gradient coil system with transformed magnetic gradient fields.By shifting up the zero point of gradient fields,the designed new Y-gradient coil could provide enhanced electromagnetic performances.With more uniform coil winding arrangement,the net torque of the new coil is significantly reduced and the generated sound pressure level(SPL)is lower at most tested frequency bands.On the other hand,the new transverse gradient coil designed with rotated magnetic gradient fields produces considerably reduced electric field in the human body,which is important for the use of rapid MR sequences.It's demonstrated that a safer and patient-friendly design could be obtained by using transformed magnetic gradient fields,which is critical for practical use.
文摘Inefficient photo-carrier separation and sluggish photoreaction dynamics appreciably undermine the photocatalytic decontamination efficacy of photocatalysts.Herein,an S-scheme Mn_(0.5)Cd_(0.5)S/Bi_(2)MoO_(6)heterojunction with interfacial Mo-S chemical bond is designed as an efficient photocatalyst.In this integrated photosystem,Bi2MoO6 and Mn_(0.5)Cd_(0.5)S function as oxidation and reduction centers of Mn_(0.5)Cd_(0.5)S/Bi_(2)MoO_(6)microspheres,respectively.Importantly,the unique charge transfer mechanism in the chemically bonded S-scheme heterojunction with Mo-S bond as atom-scale charge transport highway effectively inhibits the photocorrosion of Mn_(0.5)Cd_(0.5)S and the recombination of photo-generated electron-hole pairs,endowing Mn_(0.5)Cd_(0.5)S/Bi_(2)MoO_(6)photocatalyst with excellent photocatalytic decontamination performance and stability.Besides,integration of Mn_(0.5)Cd_(0.5)S nanocrystals into Bi2MoO6 improves hydrophilicity,conducive to the photoreactions.Strikingly,compared with Mn_(0.5)Cd_(0.5)S and Bi2MoO6,the Mn_(0.5)Cd_(0.5)S/Bi_(2)MoO_(6)unveils much augmented photoactivity in tetracycline eradication,among which Mn_(0.5)Cd_(0.5)S/Bi_(2)MoO_(6)-2 possesses the highest activity with the rate constant up to 0.0323 min-1,prominently outperforming other counterparts.This research offers a chemical bonding engineering combining with S-scheme heterojunction strategy for constructing extraordinary photocatalysts for environmental purification.
基金Under the auspices of National Natural Science Foundation of China(No.51478007,51178016)Project of Fundamental Research of Chinese Cultural Heritage Research Institute(No.2016-JBKY-08)
文摘The location pattern of different commercial stores in Shichahai, a historic conservation area in Beijing, was investigated from a street centrality perspective. Many previous studies have investigated the relationship between street centrality and land use patterns or commercial activities at interurban or intraurban scales. We considered Shichahai in this study to determine if street centrality applied at the street scale and if the street network was the only factor influencing the selection of store location. First, the nearest neighbor index, nearest neighbor hierarchical spatial cluster(NNHSC), and kernel density estimation(KDE) methods were used to provide baseline spatial distributions of commercial stores. Second, urban network analysis(UNA) tools were used to measure the street centrality indices under two conditions, with and without the weighting of cultural relics calculated by a principal component analysis(PCA). Finally, both store locations and centrality values at nodes were transformed to one unit(raster pixel) for a correlation analysis.The results showed that three of the four store types were clustered and had their own hotspots that were mostly located in the eastern and central parts of city blocks. The most momentous findings were determined from the street centrality indices. Among the three store types with correlation coefficients above 0.5, all centrality indices with landmark weighting, except straightness, had higher correlations,with closeness with landmark weighting having the highest correlation, followed by betweenness with landmark weighting. Therefore,we statistically concluded that street centrality could apply at the street scale and that the street network was not the only factor that influenced store location pattern, with landmarks also playing a significant role. The results provide guidance in determining the selection strategy for stores in a historic conservation area.
文摘An electromagnetic anti-fouling technology(EAFT) was developed further. The operating principle of the EAFT was presented using fundamental physics laws. To validate the effect of EAFT and identify the mechanism, a circulating flow setup was built. A series of fouling tests were carried out with and without EAFT, measuring fouling thermal resistance as function of time, making scanning electron microscope images and analyzing the particles size distribution in solution by dynamics light scattering technology. The main results were as follows: 1) All the precipitated crystals in solution were calcite and there were little differences between with EAFT and without EAFT in the experimental range. 2) The number of precipitate nucleation in solution was small and the particle growth was slow without EAFT. In opposition to the case untreated, a rapid particle growth was observed and the number of nucleation was expected to be large, due to the fact that the EAFT effectively increases the ions and crystals collision frequency and effectiveness by utilizing the induced electric field. It is indicated that the particle growth is promoted mainly by coagulation process but not nucleation growth. 3) The EAFT could prolong the delay time of fouling greatly, and after the delay time, the thermal resistance quickly increased. Therefore, in order to mitigate scale significantly, the floccules in solution should be deposited beforehand in a low-lying area of the exchangers and let off in time.
基金This work is supported by The Aeronautical Funds of China
文摘The characteristics of temperatures, stresses and strains fields have been studied numerically for a titanium alloy sheet welded with an improved gas tungsten arc welding method, in which a trailing spot heat sink is introduced to control the welding stress and distortion. The impinging jet model is employed to describe the internee heat transfer between the cooling media and the top suufuce of the workpiece. The influcnee of the distance between arc and heat sink is investigated. Results show that there is an ideal range of distance. Using the ideal distance, a low stress and no distortion welding structure can be derived.
基金This work was support by the National Natural Science Foundation of China(Grant No.71971006)Beijing Natural Science Foundation(Grant No.9194024)Technology Plan Key Program of Beijing Municipal Education Commission(Grant No.KZ20181005010).
文摘Purpose:This study aims to provide a new framework for analyzing the path of technology diffusion in the innovation network at the regional level and industrial level respectively,which is conducive to the integration of innovation resources,the coordinated development of innovative subjects,and the improvement of innovation abilities.Design/methodology/approach:Based on the Z-Park patent cooperation data,we establish Inter-Enterprise Technology Transfer Network model and apply the concept of Pivotability to describe the key links of technology diffusion and quantify the importance of innovative partnerships.By measuring the topologically structural characteristics in the levels of branch park and the technosphere,this paper demonstrates how technology spreads and promotes overall innovation activities within the innovation network.Findings:The results indicate that:(1)Patent cooperation network of the Z-Park displays heterogeneity and the connections between the innovative subjects distribute extremely uneven.(2)Haidian park owns the highest pivotability in the IETTN model,yet the related inter-enterprise patent cooperation is mainly concentrated in its internal,failing to facilitate the technology diffusion across multiple branch parks.(3)Such fields as“electronics and information”and“advanced manufacturing”are prominent in the cross-technosphere cooperation,while fields such as“new energy”and“environmental protection technology”can better promote industrial integration.Research limitations:Only the part of the joint patent application is taken into account while establishing the patent cooperation network.The other factors that influence the mechanism of technology diffusion in the innovation network need to be further studied,such as financial capital,market competition,and personnel mobility,etc.Practical implications:The findings of this paper will provide useful information and suggestions for the administration and policy-making of high-tech parks.Originality/value:The value of this paper is to build a bridge between the massive amount of patent data and the nature of technology diffusion,and to develop a set of tools to analyze the nonlinear relations between innovative subjects.
基金Supported by National Social Science Foundation Item(15BJY059)Social Science Foundation Item of Beijing City(14JGB036)
文摘Firstly,time and space characteristics of haze in Beijing-Tianjin-Hebei( B-T-H) region are revealed; results of haze source apportionment in the area are analyzed. Secondly,the influencing factors of haze are explored from the aspects of economic development,energy structure,industrial structure,transportation,etc. The internal driving forces of haze are also researched based on the DPSIR model. Finally some feasible and comprehensive control countermeasures against haze are suggested.
基金supported by the special fund for basic scientifi c research of central colleges,Chang’an University (CHD2010JC015)the innovation fund of small and medium-sized enterprise of Science & Technology Ministry of China under grant no. 10C26213201139Beijing Education Committee patent outcome conversion item
文摘The as-cast microstructures of high carbon high speed steels （HC-HSS） made by sand casting, centrifugal casting and electromagnetic centrifugal casting, respectively, were studied by using of optical microscopy （OM） and D/max2200pc X-ray diffraction. The results show that the microstructure of as-cast HC- HSS is dominated by alloy carbides （W2C, VC, Cr7C3）, martensite and austenite. The centrifugal casting and electromagnetic centrifugal casting apparently improve the solidification structure of HCoHSS. With the increase of magnetic intensity （B）, the volume fraction of austenite in the HC-HSS solidification structure increases significantly while the eutectic ledeburite decreases. Moreover, the secondary carbides precipitated from the austenite are finer with more homogeneous distribution in the electromagnetic centrifugal castings. It has also been found that the lath of eutectic carbide in ledeburite becomes finer and carbide phase spacing in eutectic ledeburite increases along with the higher magnetic field strength.
基金Supported by Beijing Natural Science Foundation Project(9192002)Key Project of Beijing Social Science Foundation(19YJA002).
文摘By establishing emission inventory of air pollution sources in Beijing,and classifying and compiling the pollutant types and corresponding pollution source data in more detail,it could provide the reference for studying causes of haze and related policy impact assessment in Beijing.In this paper,selecting relevant data published in the Beijing Statistical Yearbook,referring to emission coefficients in the technical guidelines for the preparation of various pollution sources,and combining characteristics of energy consumption in Beijing,emission inventory of air pollution sources in six parts is established:thermal power plant,industrial combustion source(by industry),technological process source(by product variety),motor vehicle,building construction and residents life,and the contribution rate of each part to air pollutants is given.Finally,policy suggestions for haze control in Beijing are put forward.
基金This study was supported by the National Natural Science Foundation of China(Grant Nos.51538001 and 51978019).
文摘This study focuses on the analytical prediction of subsurface settlement induced by shield tunnelling in sandy cobble stratum considering the volumetric deformation modes of the soil above the tunnel crown.A series of numerical analyses is performed to examine the effects of cover depth ratio(C/D),tunnel volume loss rate(h t)and volumetric block proportion(VBP)on the characteristics of subsurface settle-ment trough and soil volume loss.Considering the ground loss variation with depth,three modes are deduced from the volumetric deformation responses of the soil above the tunnel crown.Then,analytical solutions to predict subsurface settlement for each mode are presented using stochastic medium theory.The influences of C/D,h t and VBP on the key parameters(i.e.B and N)in the analytical expressions are discussed to determine the fitting formulae of B and N.Finally,the proposed analytical solutions are validated by the comparisons with the results of model test and numerical simulation.Results show that the fitting formulae provide a convenient and reliable way to evaluate the key parameters.Besides,the analytical solutions are reasonable and available in predicting the subsurface settlement induced by shield tunnelling in sandy cobble stratum.
基金financially supported by National Key R&D Program of China(No.2021YFB3701100)Beijing Municipal Natural Science Foundation(No.2202004).
文摘In this investigation,a high-strength Mg-12Gd-1.0Er-0.5Zr(wt.%)alloy sheet was produced by hot extrusion(HE)and subsequent hard-plate rolling(HPR)at different temperatures.The results indicate that the microstructures of these final-rolled sheets are inhomogeneous,mainly including coarse deformed grains and dynamic recrystallized(DRXed)grains,and the volume fraction of these coarse deformed grains increases as the rolling temperature increases.Thus,more DRXed grains can be found in R-385℃sheet,resulting in a smaller average grain size and weaker basal texture,while the biggest grains and the highest strong basal texture are present in R-450℃sheet.Amounts of dynamic precipitation ofβphases which are mainly determined by the rolling temperature are present in these sheets,and its precipitation can consume the content of Gd solutes in the matrix.As a result,the lowest number density ofβphase in R-450℃sheet is beneficial to modify the age hardening response.Thus,the R-450℃sheet displays the best age hardening response because of a severe traditional precipitation ofβ’(more)andβH/βM(less)precipitates,resulting in a sharp improvement in strength,i.e.ultimate tensile strength(UTS)of∼518±17 MPa and yield strength(YS)of∼438±18 MPa.However,the elongation(EL)of this sheet reduces greatly,and its value is∼2.7±0.3%.By contrasting,the EL of the peak-aging R-385℃sheet keeps better,changing from∼4.9±1.2%to∼4.8±1.4%due to a novel dislocation-induced chain-like precipitate which is helpful to keep good balance between strength and ductility.
基金Funded by the National Natural Science Foundation of China(No.52378213)the Technology Development Project(No.20201902977180010) of CABR Technology Co.,Ltd。
文摘To promote the production and application of artificial aggregates,save natural sand resources and protect the ecological environment,we evaluated the feasibility of using spherical porous functional aggregates(SPFAs) formed by basalt saw mud under autoclave curing in ordinary structural concrete.In our work,two types of prewetted functional aggregates were taken as replacements for natural aggregates with different volume substitution rates(0%,5%,10%,15%,20%,25%,and 30%) in the preparation of ordinary structural concrete with water-to-binder ratios(W/B) of 0.48 and 0.33.The effects of the functional aggregate properties and content,W/B,and curing age on the fluidity,density,mechanical properties and autogenous shrinkage of ordinary concrete were analyzed.The experimental results showed that the density of concrete declined at a rate of not more than 5%,and the 28 d compressive strength could reach 31.0-68.2 MPa.Low W/B,long curing age and high-quality functional aggregates were conducive to enhancing the mechanical properties of SPFAs concrete.Through the rolling effects,SPFAs can optimize the particle gradation of aggregate systems and improve the fluidity of concrete,and the water stored inside SPFAs provides an internal curing effect,which prolongs the cement hydration process and considerably reduces the autogenous shrinkage of concrete.SPFAs exhibits high strength and high density,as well as being more cost-effective and ecological,and is expected to be widely employed in ordinary structural concrete.
文摘Motivation, one element of the learner characteristics, has risen in the popularity polls in recent literature as a facilitator in the learning process. It is claimed that students＇ motivation needs to be taken into account for input to become intake and therefore is the key learner variable. During this process, authentic materials can be used to spark learners＇ motivation and interest. This article begins with different perspectives of motivation before it comes to the relationship between authentic materials and motivation.
