Highway tunnel traffic safety is an important part of traffic safety.With the aging of tunnels,increase in traffic flow,changes in the operating environment and traffic accidents,the many problems started to occur in ...Highway tunnel traffic safety is an important part of traffic safety.With the aging of tunnels,increase in traffic flow,changes in the operating environment and traffic accidents,the many problems started to occur in tunnels,affecting the operational and structural safety.In this paper,we summarize and analyze the types and causes of defects found in the process of tunnel maintenance at home and abroad,and propose corresponding suggestions for the current maintenance of the main structure of highway tunnels.展开更多
Rock load on lining structures increases over time for tunnels buried in rheological rock,and in addition deterioration of primary lining is common due to its structural characteristics and service environment attack,...Rock load on lining structures increases over time for tunnels buried in rheological rock,and in addition deterioration of primary lining is common due to its structural characteristics and service environment attack,where these delayed features affect the mechanical response of tunnels.However,accounting for these delayed features in long-term stability assessment of tunnel structures is complex and has not attracted enough attention.In this paper,an analytical approach is proposed for investigating long-term mechanical response of tunnel structures in rheological rock influenced by degradation of primary lining.For this purpose,degradation of primary lining,char-acterized by decreasing concrete stiffness over time,is quantitatively described by an exponential model.The rheological characteristic of surrounding rock is simulated by the Burgers model.The time-varying solutions for rock deformation and support pressure are obtained by considering the coordinated interaction between surrounding rock and linings,and their correctness is verified by comparing them with numerical results.The results revealed that the pressure imposed on linings due to the rheological behavior of surrounding rock increases over time.As the primary lining degrades,the rheological load is transferred from primary lining to secondary lining,leading to increasing pressure on secondary lining;and a faster degradation rate of primary lining leads to greater pressure on secondary lining.Therefore,the primary lining should not be overlooked in long-term safety assessment of operation tunnels because of its role in bearing and transmitting load.Finally,the tunnel’s design and operational maintenance strategy are discussed when the delay effects of surround-ing rock and lining are taken into account.展开更多
Air pollution from particulate matter produced by incomplete combustion of diesel fuel has become a serious environmental pollution problem,which can be addressed by catalytic combustion.In this work,a series of K-mod...Air pollution from particulate matter produced by incomplete combustion of diesel fuel has become a serious environmental pollution problem,which can be addressed by catalytic combustion.In this work,a series of K-modified MnO_(δ)catalysts with different microstructures were synthesized by the hydrothermal method,the relationship between structure of the catalysts and their catalytic performance for soot combustion was studied by characterization techniques and density functional theory(DFT)calculations.Results showed that the prepared catalysts had good catalytic performance for soot combustion and could completely oxidize soot at temperatures below 400℃.The cryptomelane-type K_(2−x)Mn_(8)O_(16)(K-OMS-2)with tunnel structure had excellent NO oxidation capacity and abundance of Mn^(4+)ions(Mn^(4+)/Mn^(3+)=1.24)with good redox ability,it demonstrated better soot combustion performance than layered birnessite-type K_(2)Mn_(4)O_(8)(K-OL-1).The T_(10),T_(50),T_(90)temperatures of KOMS-2 were 269,314,346℃,respectively.The K-OMS-2 catalyst also showed excellent stability after five catalytic cycles,with T_(10),T_(50),T_(90)values holding in the ranges of 270±2,316±2,348±3℃,respectively.展开更多
The number of urban underground road tunnels in China is increasing year by year,and health monitoring of tunnels is an effective management method to ensure their structural integrity.However,for shorter underground ...The number of urban underground road tunnels in China is increasing year by year,and health monitoring of tunnels is an effective management method to ensure their structural integrity.However,for shorter underground road tunnel projects,insufficient investment often leads to less frequent application of health monitoring systems.The application of intelligent structural health monitoring means can not only reduce the project cost but also help workers fully understand the actual situation of the tunnel structure.Therefore,this paper analyzes the characteristics,problems,and design of the urban underground road tunnel structural health monitoring system,and discusses the implementation of the urban underground road tunnel structural health monitoring system.展开更多
A multi-purpose prototype test system is developed to study the mechanical behavior of tunnel sup-porting structure,including a modular counterforce device,a powerful loading equipment,an advanced intelligent manageme...A multi-purpose prototype test system is developed to study the mechanical behavior of tunnel sup-porting structure,including a modular counterforce device,a powerful loading equipment,an advanced intelligent management system and an efficient noncontact deformation measurement system.The functions of the prototype test system are adjustable size and shape of the modular counterforce structure,sufficient load reserve and accurate loading,multi-connection linkage intelligent management,and high-precision and continuously positioned noncontact deformation measurement.The modular counterforce structure is currently the largest in the world,with an outer diameter of 20.5 m,an inner diameter of 16.5 m and a height of 6 m.The case application proves that the prototype test system can reproduce the mechanical behavior of the tunnel lining during load-bearing,deformation and failure processes in detail.展开更多
To date,with the increasing attention of countries to urban drainage system,more and more regions around the world have begun to build water conveyance tunnels,sewage pressure deep tunnels and so on.However,the suffic...To date,with the increasing attention of countries to urban drainage system,more and more regions around the world have begun to build water conveyance tunnels,sewage pressure deep tunnels and so on.However,the sufficient bearing capacity and corrosion resistance of the structure,which can ensure the actual service life and safety of the tunnel,remain to be further improved.Glass Fiber Reinforced Plastics(GFRP)pipe,with light weight,high strength and corrosion resistance,has the potential to be applied to the deep tunnel structure.This paper proposed a new composite structure of deep tunnel lined with GFRP pipe,which consisted of three layers of concrete segment,cement paste and GFRP pipe.A new pipe-soil spring element model was proposed for the pipesoil interaction with gaps.Based on the C3D8R solid model and the Combin39 spring model,the finite element numerical analysis of the internal pressure status and external pressure stability of the structure was carried out.Combined with the checking calculation of the theoretical formula,the reliability of the two finite element models was confirmed.A set of numerical analysis methods for the design and optimization of the three-layer structure was established.The results showed that from the internal GFRP pipe to the outer concrete pipe,the pressure decreased from 0.5 to 0.32 MPa,due to the internal pressure was mainly undertaken by the inner GFRP pipe.The allowable buckling pressure of GFRP pipe under the cover of 5 GPa high modulus cement paste was 2.66 MPa.The application of GFRP pipe not only improves the overall performance of the deep tunnel structure but also improves the construction quality and safety.The three-layer structure built in this work is safe and economical.展开更多
A linear full 3D finite element method (FEM) was performed in order to present the key design parameters of highway tunnel asphalt pavement under double-wheel load on rectangular loaded area considering horizontal con...A linear full 3D finite element method (FEM) was performed in order to present the key design parameters of highway tunnel asphalt pavement under double-wheel load on rectangular loaded area considering horizontal contact stress induced by the acceleration/deceleration of vehicles.The key design parameters are the maximum horizontal tensile stresses at the surface of the asphalt layer,the maximum horizontal tensile stresses at the bottom of the asphalt layer and the maximum vertical shear stresses at the surface of the as- phalt layer were calculated.The influencing factors such as double-wheel weight;asphalt layer thickness;base course stiffness modulus and thickness;and the contact conditions among the structure layers on these key design parameters were also examined separately to propose construction procedures of highway tunnel asphalt pavement.展开更多
Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) were performed on monolayer film of NiTPP supported on Au(111) under ultrahigh vacuum (UHV) conditions. The constant current STM im...Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) were performed on monolayer film of NiTPP supported on Au(111) under ultrahigh vacuum (UHV) conditions. The constant current STM images show remarkable bias dependence. High resolution STM data clearly show the individual NiTPP molecules and allow easy differentiation between NiTPP and CoTPP reported before. Scanning tunneling spectra, as a function of molecule-tip separation, were acquired over a range of tip motion of 0.42 nm. Spectra do not show the variation in band splitting with tip distance. It appears for molecules such as NiTPP that the average potential at the molecule is essentially the same at the same metal substrate. For molecules of the height of NiTPP, the scanning tunneling spectra should give reliable occupied and unoccupied orbital energies over a wide range of tip-molecule distances.展开更多
This paper discusses the I-V property of the GaAs-based resonant tunnelling structure (RTS) under external uniaxial pressure by photoluminescence studies. Compressive pressure parallel to the [110] direction, whose ...This paper discusses the I-V property of the GaAs-based resonant tunnelling structure (RTS) under external uniaxial pressure by photoluminescence studies. Compressive pressure parallel to the [110] direction, whose value is determined by Hooke's law, is imposed on the sample by a helix micrometer. With the increase of the applied external uniaxial compressive pressure, the blue shift and splitting of the luminescence peaks were observed, which have some influence on the I-V curve of RTS from the point of view of the energy gap, and the splitting became more apparent with applied pressure. Full width at half maximum broadening could also be observed.展开更多
Scanning tunnel microscopy (STM) is performed to verify if an Rh 'nails' structure is formed accompanying the graphene growing during chemical vapor deposition. A structure of a graphene island in an Rh vacancy is...Scanning tunnel microscopy (STM) is performed to verify if an Rh 'nails' structure is formed accompanying the graphene growing during chemical vapor deposition. A structure of a graphene island in an Rh vacancy island is used as the start. While the graphene island is removed by oxygenation, the variations of the Rh vacancy island are imaged with an in-situ high-temperature STM. By fitting with our model and calculations, we conclude that the best fit is obtained for 0% Rh, i.e., for the complete absence of nails below graphene on Rh(111). That is, when graphene is formed on Rh(111), the substrate remains fiat and does not develop a SUPPorting nail structure.展开更多
The wind tunnel simulations of wind loading on a solid structure of revolution with one smooth and five rough surfaces were conducted using wind tunnel tests. Timemean and fluctuating pressure distributions on the sur...The wind tunnel simulations of wind loading on a solid structure of revolution with one smooth and five rough surfaces were conducted using wind tunnel tests. Timemean and fluctuating pressure distributions on the surface were obtained, and the relationships between the roughness Reynolds number and pressure distributions were analyzed and discussed. The results show that increasing the surface roughness can significantly affect the pressure distribution, and the roughness Reynolds numbers play an important role in the change of flow patterns. The three flow patterns of subcritical, critical and supercritical flows can be classified based on the changing patterns of both the mean and the fluctuating pressure distributions. The present study suggests that the wind tunnel results obtained in the supercritical pattern reflect more closely those of full-scale solid structure of revolution at the designed wind speed.展开更多
The method to calculate rock pressure to which the lining structure of tunnel with shallow depth is subjected in geologically inclined bedding strata is analyzed and put forward. Both the inclination angle of bedding ...The method to calculate rock pressure to which the lining structure of tunnel with shallow depth is subjected in geologically inclined bedding strata is analyzed and put forward. Both the inclination angle of bedding strata as well as the internal friction angle of bedding plane and its cohesion all exert an influence upon the magnitude of the asymmetric rock pressure applied to tunnel. The feature that rock pressure applied to tunnel structure varies with the incUnation angle of bedding strata is discussed, At last, the safety factor, which is utilized to evaluate the working state of tunnel lining structure, is calculated for both symmetric and asymmetric lining structures. The calculation results elucidate that the asymmetric tunnel structure can be more superior to bear rock pressure in comparison with the symmetric one and should be adopted in engineering as far as possible.展开更多
The blast-induced vibration during excavation by drilling and blasting method has an important impact on thesurrounding structures. In particular, with the development of tunnel engineering, the impact of blasting vib...The blast-induced vibration during excavation by drilling and blasting method has an important impact on thesurrounding structures. In particular, with the development of tunnel engineering, the impact of blasting vibrationon tunnel construction has attracted extensive attention. In this paper, the propagation attenuation characteristicsof blast-induced vibration (PPV, peak particle velocity) on different tunnel structures were systematically studiedbased on the field monitoring data. Initially, the attenuation characteristics of blasting vibration PPV on the lowerbench surface, the side wall of the excavated tunnel and the closely spaced adjacent tunnel were investigated.Subsequently, the capacity of several widely utilized empirical prediction equations to estimate the PPV on tunnelstructures was examined, along with a comparative analysis of their prediction accuracy. The research findingsindicate that it is feasible to predict the PPV on the tunnel structures using empirical equations. The attenuationcharacteristics of blasting vibration PPV are different in different structures and directions. The prediction accuracy of the empirical equations varies, while the discrepancies are minimal. The principal variation amongthese equations lies in the site-specific coefficients k, β, λ, highlighting the differential impact of structural anddirectional considerations on the predictive efficacy. Based on the empirical equation and safe PPV provided bythe blasting vibration safe standards on tunnels of China (GB6722-2014), and considering the influence of allstructures and directions, it is determined that the safe distance of blasting vibration in the tested tunnel projectshould be larger than 20.28–18.31 m, 18.31–16.16 m, and 16.16–13.75 m for blasting vibration frequency locatedin 10 Hz, 10–50 Hz, and >50 Hz.展开更多
In order to improve the strength and stiffness of shield cutterhead, the method of fuzzy mathematics theory in combination with the finite element analysis is adopted. An optimal design model of structural parameters ...In order to improve the strength and stiffness of shield cutterhead, the method of fuzzy mathematics theory in combination with the finite element analysis is adopted. An optimal design model of structural parameters for shield cutterhead is formulated,based on the complex engineering technical requirements. In the model, as the objective function of the model is a composite function of the strength and stiffness, the response surface method is applied to formulate the approximate function of objective function in order to reduce the solution scale of optimal problem. A multi-objective genetic algorithm is used to solve the cutterhead structure design problem and the change rule of the stress-strain with various structural parameters as well as their optimal values were researched under specific geological conditions. The results show that compared with original cutterhead structure scheme, the obtained optimal scheme of the cutterhead structure can greatly improve the strength and stiffness of the cutterhead, which can be seen from the reduction of its maximum equivalent stress by 21.2%, that of its maximum deformation by 0.75%, and that of its mass by 1.04%.展开更多
Seismic analysis of long tunnels is important for safety evaluation of the tunnel structure during earthquakes.Simplified models of long tunnels are commonly adopted in seismic design by practitioners,in which the tun...Seismic analysis of long tunnels is important for safety evaluation of the tunnel structure during earthquakes.Simplified models of long tunnels are commonly adopted in seismic design by practitioners,in which the tunnel is usually assumed as a beam supported by the ground.These models can be conveniently used to obtain the overall response of the tunnel structure subjected to seismic loading.However,simplified methods are limited due to the assumptions that need to be made to reach the solution,e.g.shield tunnels are assembled with segments and bolts to form a lining ring and such structural details may not be included in the simplified model.In most cases,the design will require a numerical method that does not have the shortcomings of the analytical solutions,as it can consider the structural details,non-linear behavior,etc.Furthermore,long tunnels have significant length and pass through different strata.All of these would require large-scale seismic analysis of long tunnels with three-dimensional models,which is difficult due to the lack of available computing power.This paper introduces two types of methods for seismic analysis of long tunnels,namely simplified and unified methods.Several models,including the mass-spring-beam model,and the beam-spring model and its analytical solution are presented as examples of the simplified method.The unified method is based on a multiscale framework for long tunnels,with coarse and refined finite element meshes,or with the discrete element method and the finite difference method to compute the overall seismic response of the tunnel while including detailed dynamic response at positions of potential damage or of interest.A bridging scale term is introduced in the framework so that compatibility of dynamic behavior between the macro-and meso-scale subdomains is enforced.Examples are presented to demonstrate the applicability of the simplified and the unified methods.展开更多
Cobalt (Co) exists in significant quantities in naturally occurring manganese (Mn) oxides and alters the growth of Mn oxide crystals. Four-layered Mn oxides, Na-buserite (Na-bus) and three Co-doped Na-buserite s...Cobalt (Co) exists in significant quantities in naturally occurring manganese (Mn) oxides and alters the growth of Mn oxide crystals. Four-layered Mn oxides, Na-buserite (Na-bus) and three Co-doped Na-buserite samples prepared from oxidation of Mn(OH)2 with 5%, 10%, and 20% Co/(Mn + Co) molar ratios (5Co-Na-bus, 10Co-Na-bus, and 20Co-Na-bus), were used to prepare todorokite, a common Mn oxide on the Earth's surface, using Mg2+/Co2+ ions as a template. The results showed that todorokites could be obtained by reflux treatment of Mg2+-exchanged non-doped Na-buserite and three Co-doped Na-buserites at atmospheric pressure. However, the formation of todorokites was prohibited by reflux treatment of Co2+-exchanged Na-bus, 5Co-Na-bus, and 10Co-Na-bus samples. Instead, todorokite was obtained by the reflux treatment of Co2+-exchanged 20Co-Na-bus samples under atmospheric pressure. X-ray photoelectron spectroscopy analysis showed that doped Co existed as Co3+ in the MnOs layers of doped Na-buserites. The amount of substituted Co3+ in the MnO6 layers may play a key role in the conversion of buserite to todorokite using Co2+ ions as a template.展开更多
文摘Highway tunnel traffic safety is an important part of traffic safety.With the aging of tunnels,increase in traffic flow,changes in the operating environment and traffic accidents,the many problems started to occur in tunnels,affecting the operational and structural safety.In this paper,we summarize and analyze the types and causes of defects found in the process of tunnel maintenance at home and abroad,and propose corresponding suggestions for the current maintenance of the main structure of highway tunnels.
基金supported by the National Natural Science Foundation of China(Grant Nos.51738002,51978356)the Key Project of Highspeed Rail Joint Fund of National Natural Science Foundation of China(Grant No.U1934210)Fundamental Research Funds for the Central Universities of China(Grant No.2021YJS112).
文摘Rock load on lining structures increases over time for tunnels buried in rheological rock,and in addition deterioration of primary lining is common due to its structural characteristics and service environment attack,where these delayed features affect the mechanical response of tunnels.However,accounting for these delayed features in long-term stability assessment of tunnel structures is complex and has not attracted enough attention.In this paper,an analytical approach is proposed for investigating long-term mechanical response of tunnel structures in rheological rock influenced by degradation of primary lining.For this purpose,degradation of primary lining,char-acterized by decreasing concrete stiffness over time,is quantitatively described by an exponential model.The rheological characteristic of surrounding rock is simulated by the Burgers model.The time-varying solutions for rock deformation and support pressure are obtained by considering the coordinated interaction between surrounding rock and linings,and their correctness is verified by comparing them with numerical results.The results revealed that the pressure imposed on linings due to the rheological behavior of surrounding rock increases over time.As the primary lining degrades,the rheological load is transferred from primary lining to secondary lining,leading to increasing pressure on secondary lining;and a faster degradation rate of primary lining leads to greater pressure on secondary lining.Therefore,the primary lining should not be overlooked in long-term safety assessment of operation tunnels because of its role in bearing and transmitting load.Finally,the tunnel’s design and operational maintenance strategy are discussed when the delay effects of surround-ing rock and lining are taken into account.
基金the Key Research and Development Program of MOST(No.2017YFE0131200)for collaboration between China and Polandthe National Natural Science Foundation of China(Nos.22072095 and U1908204)+5 种基金University Joint Education Project for China-Central and Eastern European Countries(No.2021097)National Engineering Laboratory for Mobile Source Emission Control Technology(No.NELMS2018A04)Liaoning Provincial central government guides local science and technology development funds(No.2022JH6/100100052)Major/Key Project of Graduate Education and Teaching Reform of Shenyang Normal University(No.YJSJG120210008/YJSJG220210022)University level innovation team of Shenyang Normal Universityand Major Incubation Program of Shenyang Normal University(No.ZD201901)。
文摘Air pollution from particulate matter produced by incomplete combustion of diesel fuel has become a serious environmental pollution problem,which can be addressed by catalytic combustion.In this work,a series of K-modified MnO_(δ)catalysts with different microstructures were synthesized by the hydrothermal method,the relationship between structure of the catalysts and their catalytic performance for soot combustion was studied by characterization techniques and density functional theory(DFT)calculations.Results showed that the prepared catalysts had good catalytic performance for soot combustion and could completely oxidize soot at temperatures below 400℃.The cryptomelane-type K_(2−x)Mn_(8)O_(16)(K-OMS-2)with tunnel structure had excellent NO oxidation capacity and abundance of Mn^(4+)ions(Mn^(4+)/Mn^(3+)=1.24)with good redox ability,it demonstrated better soot combustion performance than layered birnessite-type K_(2)Mn_(4)O_(8)(K-OL-1).The T_(10),T_(50),T_(90)temperatures of KOMS-2 were 269,314,346℃,respectively.The K-OMS-2 catalyst also showed excellent stability after five catalytic cycles,with T_(10),T_(50),T_(90)values holding in the ranges of 270±2,316±2,348±3℃,respectively.
文摘The number of urban underground road tunnels in China is increasing year by year,and health monitoring of tunnels is an effective management method to ensure their structural integrity.However,for shorter underground road tunnel projects,insufficient investment often leads to less frequent application of health monitoring systems.The application of intelligent structural health monitoring means can not only reduce the project cost but also help workers fully understand the actual situation of the tunnel structure.Therefore,this paper analyzes the characteristics,problems,and design of the urban underground road tunnel structural health monitoring system,and discusses the implementation of the urban underground road tunnel structural health monitoring system.
文摘A multi-purpose prototype test system is developed to study the mechanical behavior of tunnel sup-porting structure,including a modular counterforce device,a powerful loading equipment,an advanced intelligent management system and an efficient noncontact deformation measurement system.The functions of the prototype test system are adjustable size and shape of the modular counterforce structure,sufficient load reserve and accurate loading,multi-connection linkage intelligent management,and high-precision and continuously positioned noncontact deformation measurement.The modular counterforce structure is currently the largest in the world,with an outer diameter of 20.5 m,an inner diameter of 16.5 m and a height of 6 m.The case application proves that the prototype test system can reproduce the mechanical behavior of the tunnel lining during load-bearing,deformation and failure processes in detail.
基金This project was supported by the Fundamental Research Funds for the Central Universities(WUT:2018IB001)the Fundamental Research Funds for the Central Universities(WUT:2019III130CG).
文摘To date,with the increasing attention of countries to urban drainage system,more and more regions around the world have begun to build water conveyance tunnels,sewage pressure deep tunnels and so on.However,the sufficient bearing capacity and corrosion resistance of the structure,which can ensure the actual service life and safety of the tunnel,remain to be further improved.Glass Fiber Reinforced Plastics(GFRP)pipe,with light weight,high strength and corrosion resistance,has the potential to be applied to the deep tunnel structure.This paper proposed a new composite structure of deep tunnel lined with GFRP pipe,which consisted of three layers of concrete segment,cement paste and GFRP pipe.A new pipe-soil spring element model was proposed for the pipesoil interaction with gaps.Based on the C3D8R solid model and the Combin39 spring model,the finite element numerical analysis of the internal pressure status and external pressure stability of the structure was carried out.Combined with the checking calculation of the theoretical formula,the reliability of the two finite element models was confirmed.A set of numerical analysis methods for the design and optimization of the three-layer structure was established.The results showed that from the internal GFRP pipe to the outer concrete pipe,the pressure decreased from 0.5 to 0.32 MPa,due to the internal pressure was mainly undertaken by the inner GFRP pipe.The allowable buckling pressure of GFRP pipe under the cover of 5 GPa high modulus cement paste was 2.66 MPa.The application of GFRP pipe not only improves the overall performance of the deep tunnel structure but also improves the construction quality and safety.The three-layer structure built in this work is safe and economical.
文摘A linear full 3D finite element method (FEM) was performed in order to present the key design parameters of highway tunnel asphalt pavement under double-wheel load on rectangular loaded area considering horizontal contact stress induced by the acceleration/deceleration of vehicles.The key design parameters are the maximum horizontal tensile stresses at the surface of the asphalt layer,the maximum horizontal tensile stresses at the bottom of the asphalt layer and the maximum vertical shear stresses at the surface of the as- phalt layer were calculated.The influencing factors such as double-wheel weight;asphalt layer thickness;base course stiffness modulus and thickness;and the contact conditions among the structure layers on these key design parameters were also examined separately to propose construction procedures of highway tunnel asphalt pavement.
基金This work was supported by the Excellent Scientist Program of South China University of Technology (324-D60090), the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry and the National Natural Science Foundation of China (20643001).
文摘Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) were performed on monolayer film of NiTPP supported on Au(111) under ultrahigh vacuum (UHV) conditions. The constant current STM images show remarkable bias dependence. High resolution STM data clearly show the individual NiTPP molecules and allow easy differentiation between NiTPP and CoTPP reported before. Scanning tunneling spectra, as a function of molecule-tip separation, were acquired over a range of tip motion of 0.42 nm. Spectra do not show the variation in band splitting with tip distance. It appears for molecules such as NiTPP that the average potential at the molecule is essentially the same at the same metal substrate. For molecules of the height of NiTPP, the scanning tunneling spectra should give reliable occupied and unoccupied orbital energies over a wide range of tip-molecule distances.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 50775209 and 50730009)
文摘This paper discusses the I-V property of the GaAs-based resonant tunnelling structure (RTS) under external uniaxial pressure by photoluminescence studies. Compressive pressure parallel to the [110] direction, whose value is determined by Hooke's law, is imposed on the sample by a helix micrometer. With the increase of the applied external uniaxial compressive pressure, the blue shift and splitting of the luminescence peaks were observed, which have some influence on the I-V curve of RTS from the point of view of the energy gap, and the splitting became more apparent with applied pressure. Full width at half maximum broadening could also be observed.
基金Supported by the National Natural Science Foundation of China under Grant No 51402026the Basic Research Program of Jiangsu Province under Grant No BK20130236the High Technology Research Key Laboratory of Changzhou under Grant No CM20133007
文摘Scanning tunnel microscopy (STM) is performed to verify if an Rh 'nails' structure is formed accompanying the graphene growing during chemical vapor deposition. A structure of a graphene island in an Rh vacancy island is used as the start. While the graphene island is removed by oxygenation, the variations of the Rh vacancy island are imaged with an in-situ high-temperature STM. By fitting with our model and calculations, we conclude that the best fit is obtained for 0% Rh, i.e., for the complete absence of nails below graphene on Rh(111). That is, when graphene is formed on Rh(111), the substrate remains fiat and does not develop a SUPPorting nail structure.
文摘The wind tunnel simulations of wind loading on a solid structure of revolution with one smooth and five rough surfaces were conducted using wind tunnel tests. Timemean and fluctuating pressure distributions on the surface were obtained, and the relationships between the roughness Reynolds number and pressure distributions were analyzed and discussed. The results show that increasing the surface roughness can significantly affect the pressure distribution, and the roughness Reynolds numbers play an important role in the change of flow patterns. The three flow patterns of subcritical, critical and supercritical flows can be classified based on the changing patterns of both the mean and the fluctuating pressure distributions. The present study suggests that the wind tunnel results obtained in the supercritical pattern reflect more closely those of full-scale solid structure of revolution at the designed wind speed.
文摘The method to calculate rock pressure to which the lining structure of tunnel with shallow depth is subjected in geologically inclined bedding strata is analyzed and put forward. Both the inclination angle of bedding strata as well as the internal friction angle of bedding plane and its cohesion all exert an influence upon the magnitude of the asymmetric rock pressure applied to tunnel. The feature that rock pressure applied to tunnel structure varies with the incUnation angle of bedding strata is discussed, At last, the safety factor, which is utilized to evaluate the working state of tunnel lining structure, is calculated for both symmetric and asymmetric lining structures. The calculation results elucidate that the asymmetric tunnel structure can be more superior to bear rock pressure in comparison with the symmetric one and should be adopted in engineering as far as possible.
基金supported by the General Project of China Postdoctoral Science Foundation(2023M742141)the Open Fund of State Key Laboratory of Mining Response and Disaster Prevention and Control in Deep Coal Mine(SKLMRDPC23KF06)the Talent Introduction Project of Shandong University of Science and Technology(0104060540171).
文摘The blast-induced vibration during excavation by drilling and blasting method has an important impact on thesurrounding structures. In particular, with the development of tunnel engineering, the impact of blasting vibrationon tunnel construction has attracted extensive attention. In this paper, the propagation attenuation characteristicsof blast-induced vibration (PPV, peak particle velocity) on different tunnel structures were systematically studiedbased on the field monitoring data. Initially, the attenuation characteristics of blasting vibration PPV on the lowerbench surface, the side wall of the excavated tunnel and the closely spaced adjacent tunnel were investigated.Subsequently, the capacity of several widely utilized empirical prediction equations to estimate the PPV on tunnelstructures was examined, along with a comparative analysis of their prediction accuracy. The research findingsindicate that it is feasible to predict the PPV on the tunnel structures using empirical equations. The attenuationcharacteristics of blasting vibration PPV are different in different structures and directions. The prediction accuracy of the empirical equations varies, while the discrepancies are minimal. The principal variation amongthese equations lies in the site-specific coefficients k, β, λ, highlighting the differential impact of structural anddirectional considerations on the predictive efficacy. Based on the empirical equation and safe PPV provided bythe blasting vibration safe standards on tunnels of China (GB6722-2014), and considering the influence of allstructures and directions, it is determined that the safe distance of blasting vibration in the tested tunnel projectshould be larger than 20.28–18.31 m, 18.31–16.16 m, and 16.16–13.75 m for blasting vibration frequency locatedin 10 Hz, 10–50 Hz, and >50 Hz.
基金Project(51074180) supported by the National Natural Science Foundation of ChinaProject(2012AA041801) supported by the National High Technology Research and Development Program of China+2 种基金Project(2007CB714002) supported by the National Basic Research Program of ChinaProject(2013GK3003) supported by the Technology Support Plan of Hunan Province,ChinaProject(2010FJ1002) supported by Hunan Science and Technology Major Program,China
文摘In order to improve the strength and stiffness of shield cutterhead, the method of fuzzy mathematics theory in combination with the finite element analysis is adopted. An optimal design model of structural parameters for shield cutterhead is formulated,based on the complex engineering technical requirements. In the model, as the objective function of the model is a composite function of the strength and stiffness, the response surface method is applied to formulate the approximate function of objective function in order to reduce the solution scale of optimal problem. A multi-objective genetic algorithm is used to solve the cutterhead structure design problem and the change rule of the stress-strain with various structural parameters as well as their optimal values were researched under specific geological conditions. The results show that compared with original cutterhead structure scheme, the obtained optimal scheme of the cutterhead structure can greatly improve the strength and stiffness of the cutterhead, which can be seen from the reduction of its maximum equivalent stress by 21.2%, that of its maximum deformation by 0.75%, and that of its mass by 1.04%.
基金The research has been supported by the National Natural Science Foundation of China(Grant No.51678438&51478343)the Shanghai Rising-Star Program(17QC1400500)+1 种基金the Shanghai Committee of Science and Technology(Grant No.16DZ1200302&16DZ1201904)The authors acknowledge the support from the Fundamental Research Funds for the State Key Laboratory for GeoMechanics and Deep Underground Engineering,China University of Mining&Technology(SKLGDUEK1723).
文摘Seismic analysis of long tunnels is important for safety evaluation of the tunnel structure during earthquakes.Simplified models of long tunnels are commonly adopted in seismic design by practitioners,in which the tunnel is usually assumed as a beam supported by the ground.These models can be conveniently used to obtain the overall response of the tunnel structure subjected to seismic loading.However,simplified methods are limited due to the assumptions that need to be made to reach the solution,e.g.shield tunnels are assembled with segments and bolts to form a lining ring and such structural details may not be included in the simplified model.In most cases,the design will require a numerical method that does not have the shortcomings of the analytical solutions,as it can consider the structural details,non-linear behavior,etc.Furthermore,long tunnels have significant length and pass through different strata.All of these would require large-scale seismic analysis of long tunnels with three-dimensional models,which is difficult due to the lack of available computing power.This paper introduces two types of methods for seismic analysis of long tunnels,namely simplified and unified methods.Several models,including the mass-spring-beam model,and the beam-spring model and its analytical solution are presented as examples of the simplified method.The unified method is based on a multiscale framework for long tunnels,with coarse and refined finite element meshes,or with the discrete element method and the finite difference method to compute the overall seismic response of the tunnel while including detailed dynamic response at positions of potential damage or of interest.A bridging scale term is introduced in the framework so that compatibility of dynamic behavior between the macro-and meso-scale subdomains is enforced.Examples are presented to demonstrate the applicability of the simplified and the unified methods.
基金Supported by the National Natural Science Foundation of China(Nos.41001139 and 40771102)
文摘Cobalt (Co) exists in significant quantities in naturally occurring manganese (Mn) oxides and alters the growth of Mn oxide crystals. Four-layered Mn oxides, Na-buserite (Na-bus) and three Co-doped Na-buserite samples prepared from oxidation of Mn(OH)2 with 5%, 10%, and 20% Co/(Mn + Co) molar ratios (5Co-Na-bus, 10Co-Na-bus, and 20Co-Na-bus), were used to prepare todorokite, a common Mn oxide on the Earth's surface, using Mg2+/Co2+ ions as a template. The results showed that todorokites could be obtained by reflux treatment of Mg2+-exchanged non-doped Na-buserite and three Co-doped Na-buserites at atmospheric pressure. However, the formation of todorokites was prohibited by reflux treatment of Co2+-exchanged Na-bus, 5Co-Na-bus, and 10Co-Na-bus samples. Instead, todorokite was obtained by the reflux treatment of Co2+-exchanged 20Co-Na-bus samples under atmospheric pressure. X-ray photoelectron spectroscopy analysis showed that doped Co existed as Co3+ in the MnOs layers of doped Na-buserites. The amount of substituted Co3+ in the MnO6 layers may play a key role in the conversion of buserite to todorokite using Co2+ ions as a template.