Track irregularity from rail alternate side wear is manifested as uneven rail wear waveforms alternating in the left and right rails with equal intervals,which will cause carbody sway behaviour of railway vehicles and...Track irregularity from rail alternate side wear is manifested as uneven rail wear waveforms alternating in the left and right rails with equal intervals,which will cause carbody sway behaviour of railway vehicles and greatly influences the passenger comfort.In this work,the carbody sway behaviour and mechanism due to track irregularity from rail alternate side wear and possible solutions to this issue were studied by the field testing and numerical calculation approaches.First,the carbody sway of an urban rail transit train is introduced with full-scale field tests,through which the rail alternate side wear is characterized and the formatted track irregularity are presented.Then,multibody vehicle dynamic models are developed to reproduce the carbody sway behaviour induced by the track irregularity from the rail alternate side wear.The creep forces acting on the wheel and rail are preliminarily discussed to study the influence of the carbody sway on the wear of the wheel flange and the rail corner.Finally,some potential solutions,e.g.improving the damping ratio of carbody rigid mode and rail grinding,are proposed to relieve this issue.It is concluded that an increased damping ratio of the carbody mode can alleviate the carbody sway and wheel–rail interactions,while properly maintaining track conditions can improve the vehicle performance.展开更多
The evolution of cracks in shale directly affects the efficient production of shale gas.However,there is a lack of research on the characteristics of crack initiation in deep dense shale under different stress conditi...The evolution of cracks in shale directly affects the efficient production of shale gas.However,there is a lack of research on the characteristics of crack initiation in deep dense shale under different stress conditions.In this work,considering the different combinations of confining pressure and bedding plane inclination angle(α),biaxial mechanical loading experiments were conducted on shale containing circular holes.The research results indicate that the confining pressure and inclination angle of the bedding planes significantly influence the failure patterns of shale containing circular holes.The instability of shale containing circular holes can be classified into five types:tensile failure along the bedding planes,tensile failure through the bedding planes,shear slip along the bedding planes,shear failure through the bedding planes,and block instability failure.Furthermore,the evolution of strain and stress fields around the circular holes was found to be the fundamental cause of variations in the initiation characteristics and locations of shale cracks.The crack initiation criterion for shale containing circular hole was established,providing a new method for evaluating the trajectory of shale hole wall fractures.This study holds significant importance for evaluating the evolution and stability of fracture networks within shale reservoirs.展开更多
An effective design strategy for preparing highly transparent polyimide film with low dielectric constant is presented.The key to the strategy is to simultaneously introduce meta-substituted structure and trifluoromet...An effective design strategy for preparing highly transparent polyimide film with low dielectric constant is presented.The key to the strategy is to simultaneously introduce meta-substituted structure and trifluoromethyl in polymer chains.By using this design strategy,a highly transparent polyimide film with low-k was synthesized from 3,5-diaminobenzotrifluoride(m-TFPDA)and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride(6FDA)through a two-step method.The obtained m-TFPDA/6FDA(CPI)film(~30 pm)possesses high optical transparency(λ_(cutoff)=334 nm,T_(450nm)=85.26%,Haze=0.31)and is close to colorless(L^(*)=96.03,a^(*)=-0.34,b^(*)=2.12,yellow index=3.96).The intrinsic k and dielectric loss value of the film are 2.27 and 0.0013 at 10 kHz,respectively.More importantly,such low dielectric performance could remain stable up to 280℃,and the film shows a low moisture rate(~0.51%),which helps to maintain the low-k property stability in different humid environments.Meanwhile,the film also shows good thermal stability and mechanical properties,with a glass transition temperature(T_(g))of 296℃and the 5 wt%decomposition temperature(T_(d,s%))of 522℃under N_(2).The tensile strength and tensile modulus of the film are 85.1 MPa and 1.96 GPa,respectively.In addition,the film is soluble in common solvents,which allows simple solution processing and low-cost,continuous roll-to-roll processes.This design strategy is beneficial to improving the transparency,lightening yellow color,lowering the dielectric constant and meanwhile maintaining the comprehensive properties of polyimide films,which is mainly due to the introduced meta-substituted and trifluoromethyl structures effectively inhibiting the transfer of charge transfer complex(CTC)effects and increasing the free volume of film.This design strategy could also be extended to other high-performance polymer systems.展开更多
The strategy of N-doping in carbon materials could provide additional Li-ion storage sites to improve their electrochemical properties. Heteroatom-containing polymers could serve as good precursors to fabricate doped ...The strategy of N-doping in carbon materials could provide additional Li-ion storage sites to improve their electrochemical properties. Heteroatom-containing polymers could serve as good precursors to fabricate doped carbons due to the capability to in situ dope heteroatoms into the structures, In this work, electrospun heterocyclic polyimide （PI） nanofiber membranes containing biphenyl and pyrimidine rings were carbonized to fabricate freestanding and flexible heteroatoms-containing carbon membranes. When the polymer membranes were subjected to various calcination temperatures （from 550℃ to 950 ℃） and durations （0.5-10 h）, the structural evolutions strongly affect their electrochemical properties as anodes for lithium ion batteries. It demonstrated that the reversible specific capacity of obtained sample treated at 650 ℃ for 3 h could achieve 695 mAh/g at 0.1 A/g and retain 245 mAh/g at 1.5 A/g after 300 cycles. Furthermore, the electrospun membrane maintains a good electrochemical performance at bending state as a flexible electrode.展开更多
A 44-year-old woman was transferred to the ICU of the First Affiliated Hospital of Jinan University for 2 days of persistent epigastric pain and 7 hours of unconsciousness.Her admission diagnosis was severe acute necr...A 44-year-old woman was transferred to the ICU of the First Affiliated Hospital of Jinan University for 2 days of persistent epigastric pain and 7 hours of unconsciousness.Her admission diagnosis was severe acute necrotizing pancreatitis(hypertriglyceridemia type)with multiple organ dysfunctions.The results of CT revealed a small area of necrotizing pancreatitis,which was not consistent with the severe clinical manifestations.Considering lack of hair and history of postpartum hemorrhage,hormone examination was carried out.According to the results of the examination,she was further diagnosed as Sheehan's syndrome and pituitary crisis.After hormone replacement therapy,her condition improved rapidly.展开更多
In this work, a fully rigid coplanar symmetric heterocyclic unit was introduced into the rigid polyimide macromolecular backbone structure to prepare high-performance polyimide fibers. The novel co-polyimide(co-PI) fi...In this work, a fully rigid coplanar symmetric heterocyclic unit was introduced into the rigid polyimide macromolecular backbone structure to prepare high-performance polyimide fibers. The novel co-polyimide(co-PI) fibers based on 3,3',4,4'-biphenyltetracarboxylic anhydride(BPDA), p-phenylenediamine(PDA) and 2,6-(4,4'-diaminodiphenyl) benzo[1,2-d:5,4-d'] bisoxazole(PBOA) were fabricated via a twostep wet-spinning method. The effects of benzobisoxazole moiety on spinnability, aggregation structure, and mechanical properties of fibers were systematically discussed. The detailed structural analysis revealed that the well-defined aggregation structures of co-PI fibers were obtained from initial amorphous structure when post hot-drawing temperature was higher than 460 ℃ under proper drawing ratio, and the incorporation PBOA into BPDA-PDA structures produced more compact structural co-PI fiber than homo BPDA-PDA fiber. The BPDA-PDA/PBOA co-PI fibers exhibited optimum tensile strength and modulus of 2.65 and 103 GPa, which increased by 182% and 84% compared to the homo BPDA-PDA fiber, respectively.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.52002344,U2034210,and 61960206010)the Development Project of State Key Laboratory of Rail Transit Vehicle System(Grant No.2022TPL_T09)。
文摘Track irregularity from rail alternate side wear is manifested as uneven rail wear waveforms alternating in the left and right rails with equal intervals,which will cause carbody sway behaviour of railway vehicles and greatly influences the passenger comfort.In this work,the carbody sway behaviour and mechanism due to track irregularity from rail alternate side wear and possible solutions to this issue were studied by the field testing and numerical calculation approaches.First,the carbody sway of an urban rail transit train is introduced with full-scale field tests,through which the rail alternate side wear is characterized and the formatted track irregularity are presented.Then,multibody vehicle dynamic models are developed to reproduce the carbody sway behaviour induced by the track irregularity from the rail alternate side wear.The creep forces acting on the wheel and rail are preliminarily discussed to study the influence of the carbody sway on the wear of the wheel flange and the rail corner.Finally,some potential solutions,e.g.improving the damping ratio of carbody rigid mode and rail grinding,are proposed to relieve this issue.It is concluded that an increased damping ratio of the carbody mode can alleviate the carbody sway and wheel–rail interactions,while properly maintaining track conditions can improve the vehicle performance.
基金Projects(52104143,52109135,52374099)supported by the National Natural Science Foundation of ChinaProject(2025YFHZ0323)supported by the Natural Science Foundation of Sichuan Province,China。
文摘The evolution of cracks in shale directly affects the efficient production of shale gas.However,there is a lack of research on the characteristics of crack initiation in deep dense shale under different stress conditions.In this work,considering the different combinations of confining pressure and bedding plane inclination angle(α),biaxial mechanical loading experiments were conducted on shale containing circular holes.The research results indicate that the confining pressure and inclination angle of the bedding planes significantly influence the failure patterns of shale containing circular holes.The instability of shale containing circular holes can be classified into five types:tensile failure along the bedding planes,tensile failure through the bedding planes,shear slip along the bedding planes,shear failure through the bedding planes,and block instability failure.Furthermore,the evolution of strain and stress fields around the circular holes was found to be the fundamental cause of variations in the initiation characteristics and locations of shale cracks.The crack initiation criterion for shale containing circular hole was established,providing a new method for evaluating the trajectory of shale hole wall fractures.This study holds significant importance for evaluating the evolution and stability of fracture networks within shale reservoirs.
基金supported by the Scientific Research Inn ovation Plan of Sha nghai Education Commission(No.2019-01-07-00-03-E0001)the National Natural Science Foundation of China(Nos.21774019,21975040,51903038)+2 种基金the Program of Shanghai Academic Research Leader(No.18XD1400100)the Natural Science Foundation of Shanghai(No.18ZR1400600)the DHU Distinguished Young Professor Program.
文摘An effective design strategy for preparing highly transparent polyimide film with low dielectric constant is presented.The key to the strategy is to simultaneously introduce meta-substituted structure and trifluoromethyl in polymer chains.By using this design strategy,a highly transparent polyimide film with low-k was synthesized from 3,5-diaminobenzotrifluoride(m-TFPDA)and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride(6FDA)through a two-step method.The obtained m-TFPDA/6FDA(CPI)film(~30 pm)possesses high optical transparency(λ_(cutoff)=334 nm,T_(450nm)=85.26%,Haze=0.31)and is close to colorless(L^(*)=96.03,a^(*)=-0.34,b^(*)=2.12,yellow index=3.96).The intrinsic k and dielectric loss value of the film are 2.27 and 0.0013 at 10 kHz,respectively.More importantly,such low dielectric performance could remain stable up to 280℃,and the film shows a low moisture rate(~0.51%),which helps to maintain the low-k property stability in different humid environments.Meanwhile,the film also shows good thermal stability and mechanical properties,with a glass transition temperature(T_(g))of 296℃and the 5 wt%decomposition temperature(T_(d,s%))of 522℃under N_(2).The tensile strength and tensile modulus of the film are 85.1 MPa and 1.96 GPa,respectively.In addition,the film is soluble in common solvents,which allows simple solution processing and low-cost,continuous roll-to-roll processes.This design strategy is beneficial to improving the transparency,lightening yellow color,lowering the dielectric constant and meanwhile maintaining the comprehensive properties of polyimide films,which is mainly due to the introduced meta-substituted and trifluoromethyl structures effectively inhibiting the transfer of charge transfer complex(CTC)effects and increasing the free volume of film.This design strategy could also be extended to other high-performance polymer systems.
基金financially supported by the DHU Distinguished Young Professor Programthe National Natural Science Foundation of China (No. 51403036)
文摘The strategy of N-doping in carbon materials could provide additional Li-ion storage sites to improve their electrochemical properties. Heteroatom-containing polymers could serve as good precursors to fabricate doped carbons due to the capability to in situ dope heteroatoms into the structures, In this work, electrospun heterocyclic polyimide （PI） nanofiber membranes containing biphenyl and pyrimidine rings were carbonized to fabricate freestanding and flexible heteroatoms-containing carbon membranes. When the polymer membranes were subjected to various calcination temperatures （from 550℃ to 950 ℃） and durations （0.5-10 h）, the structural evolutions strongly affect their electrochemical properties as anodes for lithium ion batteries. It demonstrated that the reversible specific capacity of obtained sample treated at 650 ℃ for 3 h could achieve 695 mAh/g at 0.1 A/g and retain 245 mAh/g at 1.5 A/g after 300 cycles. Furthermore, the electrospun membrane maintains a good electrochemical performance at bending state as a flexible electrode.
基金the Fundamental Research Funds for the Central Universities(No.21614306)the National Natural Science Foundation of China(No.81403302)+1 种基金Administration of Traditional Chinese Medicine of Guangdong Province,China(No.20131152)Medical Scientific Research Foundation of Guangdong Province,China(No.2011336).
文摘A 44-year-old woman was transferred to the ICU of the First Affiliated Hospital of Jinan University for 2 days of persistent epigastric pain and 7 hours of unconsciousness.Her admission diagnosis was severe acute necrotizing pancreatitis(hypertriglyceridemia type)with multiple organ dysfunctions.The results of CT revealed a small area of necrotizing pancreatitis,which was not consistent with the severe clinical manifestations.Considering lack of hair and history of postpartum hemorrhage,hormone examination was carried out.According to the results of the examination,she was further diagnosed as Sheehan's syndrome and pituitary crisis.After hormone replacement therapy,her condition improved rapidly.
基金financially supported by the National Natural Science Foundation of China (Nos. 51903038 and 21975040)Guangdong Basic and Applied Basic Research Foundation (No. 2020A1515110897)。
文摘In this work, a fully rigid coplanar symmetric heterocyclic unit was introduced into the rigid polyimide macromolecular backbone structure to prepare high-performance polyimide fibers. The novel co-polyimide(co-PI) fibers based on 3,3',4,4'-biphenyltetracarboxylic anhydride(BPDA), p-phenylenediamine(PDA) and 2,6-(4,4'-diaminodiphenyl) benzo[1,2-d:5,4-d'] bisoxazole(PBOA) were fabricated via a twostep wet-spinning method. The effects of benzobisoxazole moiety on spinnability, aggregation structure, and mechanical properties of fibers were systematically discussed. The detailed structural analysis revealed that the well-defined aggregation structures of co-PI fibers were obtained from initial amorphous structure when post hot-drawing temperature was higher than 460 ℃ under proper drawing ratio, and the incorporation PBOA into BPDA-PDA structures produced more compact structural co-PI fiber than homo BPDA-PDA fiber. The BPDA-PDA/PBOA co-PI fibers exhibited optimum tensile strength and modulus of 2.65 and 103 GPa, which increased by 182% and 84% compared to the homo BPDA-PDA fiber, respectively.
