In this paper,we compare the differences in the charge accumulation for two different models about conductivity:one in which the conductivity value of the spacer is invariant with time(steady-state conductivity,Model...In this paper,we compare the differences in the charge accumulation for two different models about conductivity:one in which the conductivity value of the spacer is invariant with time(steady-state conductivity,ModelⅠ)and one in which the conductivity value can vary dynamically with time(dynamic conductivity,ModelⅡ).The time for the potential distribution to reach a stable state is 8078 s in ModelⅠand 7932 s in ModelⅡ.After the charge accumulation reaches saturation,the charges migrate to the middle of the spacer under the applied electric field.Maximum tangential field strength is 2.56×10^(6)V/m in ModelⅠand 2.84×5 C/m^(3),which is much smaller than the charge density in the spacer.The mechanism underlying the charge accumulation phenomenon is the differences in the conductivity value distribution caused by a time-varying temperature gradient field.This paper can provide a more precise theoretical basis for the selection and modification of HVDC-GIL spacer.展开更多
Due to its excellent insulation and mechanical properties,cross-linked polyethylene(XLPE)is widely used as the insulation candidate of power cables in power transmission and distribution systems.However,its performanc...Due to its excellent insulation and mechanical properties,cross-linked polyethylene(XLPE)is widely used as the insulation candidate of power cables in power transmission and distribution systems.However,its performance can be affected due to various stresses,which endangers safe operation of the power system in service.In this paper,dielectric and insulation properties of XLPE materials of 110 kV cables with the service lives of 0,15,and 30 years were tested and evaluated.Results show that with increase of service life,dielectric loss caused by the polarization process increases significantly,and dielectric strength decreases as well.Power frequency breakdown field strength and crystallinity decrease significantly,and carbonyl index increases.The degradation process of XLPE can be divided into two stages:the structure of the crystalline region of the original sample is relatively complete,and loss can be almost ignored.After long-term service,the crystallization region is destroyed,and thermal oxygen reaction occurs.Intermolecular force is weakened,which makes breakdown easier to occur.However,there is no direct relation between the carbonyl index and macroscopic characteristics.This paper reveals the deterioration law of the XLPE cable insulation,which provides a theoretical basis for evaluating cable aging condition and is of great significance to improve cable operation safety and maintenance quality.展开更多
Although dielectric elastomer(DE)with substantial actuated strain(AS)has been reported 20 years ago,its scientific understanding remains unclear.The most accepted theory of DE,which is proposed in 2000,holds the view ...Although dielectric elastomer(DE)with substantial actuated strain(AS)has been reported 20 years ago,its scientific understanding remains unclear.The most accepted theory of DE,which is proposed in 2000,holds the view that AS of DE is induced by the Maxwell stress.According to this theory,materials have similar ratios of permittivity and Young’s modulus should have similar AS,while the experimental results are on contrary to this theory,and the experimental AS has no relationship with ideal AS.Here,a new dipole-conformation-actuated strain cross-scale model is proposed,which can be generally applied to explain the AS of DE without pre-strain.According to this model,several characteristics of an ideal DE are listed in this work and a new DE based on polyphosphazene(PPZ)is synthesized.The AS of PPZ can reach 84%without any pre-strain.At last,a PPZ-based all soft artificial heart(ASAH)is built,which works in the similar way with natural myocardium,indicating that this material has great application potential and possibility in the construction of an ASAH for heart failure(HF)patients.展开更多
The emergence of low-dimensional nanomaterials has brought revolutionized development of magnetism,as the size effect can significantly influence the spin arrangement.Since the first demonstration of truly two-dimensi...The emergence of low-dimensional nanomaterials has brought revolutionized development of magnetism,as the size effect can significantly influence the spin arrangement.Since the first demonstration of truly two-dimensional magnetic materials(2DMMs)in 2017,a wide variety of magnetic phases and associated properties have been exhibited in these 2DMMs,which offer a new opportunity to manipulate the spin-based devices efficiently in the future.Herein,we focus on the recent progress of 2DMMs and heterostructures in the aspects of their structural characteristics,physical properties,and spintronic applications.Firstly,the microscopy characterization of the spatial arrangement of spins in 2D lattices is reviewed.Afterwards,the optical probes in the light-matter-spin interactions at the 2D scale are discussed.Then,particularly,we systematically summarize the recent work on the electronic and spintronic devices of 2DMMs.In the section of electronic properties,we raise several exciting phenomena in 2DMMs,i.e.,long-distance magnon transport,field-effect transistors,varying magnetoresistance behavior,and(quantum)anomalous Hall effect.In the section of spintronic applications,we highlight spintronic devices based on 2DMMs,e.g.,spin valves,spin-orbit torque,spin field-effect transistors,spin tunneling field-effect transistors,and spin-filter magnetic tunnel junctions.At last,we also provide our perspectives on the current challenges and future expectations in this field,which may be a helpful guide for theorists and experimentalists who are exploring the optical,electronic,and spintronic properties of 2DMMs.展开更多
基金supported by National Natural Science Foundation of China(No.52107029)China Postdoctoral Science Foundation(No.2021M692599)the Shaanxi Provincial Department of Education Youth Innovation Team Research Plan Project(No.23JP102).
文摘In this paper,we compare the differences in the charge accumulation for two different models about conductivity:one in which the conductivity value of the spacer is invariant with time(steady-state conductivity,ModelⅠ)and one in which the conductivity value can vary dynamically with time(dynamic conductivity,ModelⅡ).The time for the potential distribution to reach a stable state is 8078 s in ModelⅠand 7932 s in ModelⅡ.After the charge accumulation reaches saturation,the charges migrate to the middle of the spacer under the applied electric field.Maximum tangential field strength is 2.56×10^(6)V/m in ModelⅠand 2.84×5 C/m^(3),which is much smaller than the charge density in the spacer.The mechanism underlying the charge accumulation phenomenon is the differences in the conductivity value distribution caused by a time-varying temperature gradient field.This paper can provide a more precise theoretical basis for the selection and modification of HVDC-GIL spacer.
基金supported by the National Natural Science Foundation of China under Grant No.11975052,51507135,52107029supported by China Postdoctoral Science Foundation(No.2021M692599).
文摘Due to its excellent insulation and mechanical properties,cross-linked polyethylene(XLPE)is widely used as the insulation candidate of power cables in power transmission and distribution systems.However,its performance can be affected due to various stresses,which endangers safe operation of the power system in service.In this paper,dielectric and insulation properties of XLPE materials of 110 kV cables with the service lives of 0,15,and 30 years were tested and evaluated.Results show that with increase of service life,dielectric loss caused by the polarization process increases significantly,and dielectric strength decreases as well.Power frequency breakdown field strength and crystallinity decrease significantly,and carbonyl index increases.The degradation process of XLPE can be divided into two stages:the structure of the crystalline region of the original sample is relatively complete,and loss can be almost ignored.After long-term service,the crystallization region is destroyed,and thermal oxygen reaction occurs.Intermolecular force is weakened,which makes breakdown easier to occur.However,there is no direct relation between the carbonyl index and macroscopic characteristics.This paper reveals the deterioration law of the XLPE cable insulation,which provides a theoretical basis for evaluating cable aging condition and is of great significance to improve cable operation safety and maintenance quality.
基金supported by the Basic Science Center Program of the National Natural Science Foundation of China (51988102)the National Key Research and Development Program of China (2017YFB0306903)+2 种基金the Major Program of National Natural Science Foundation of China (51790501)the Innovative Research Groups (51221002 and 51521062)the National Natural Science Foundation of China (52003024)
文摘Although dielectric elastomer(DE)with substantial actuated strain(AS)has been reported 20 years ago,its scientific understanding remains unclear.The most accepted theory of DE,which is proposed in 2000,holds the view that AS of DE is induced by the Maxwell stress.According to this theory,materials have similar ratios of permittivity and Young’s modulus should have similar AS,while the experimental results are on contrary to this theory,and the experimental AS has no relationship with ideal AS.Here,a new dipole-conformation-actuated strain cross-scale model is proposed,which can be generally applied to explain the AS of DE without pre-strain.According to this model,several characteristics of an ideal DE are listed in this work and a new DE based on polyphosphazene(PPZ)is synthesized.The AS of PPZ can reach 84%without any pre-strain.At last,a PPZ-based all soft artificial heart(ASAH)is built,which works in the similar way with natural myocardium,indicating that this material has great application potential and possibility in the construction of an ASAH for heart failure(HF)patients.
基金This work was supported by the National Key Research and Development Program of China(Grant No.2017YFE0131900)the Major Program of National Natural Science Foundation of China(Grant No.91833306)+1 种基金the National Natural Science Foundation of China(Grant No.61801210,91833302,61904077,and 61904080)the Natural Science Foundation of Jiangsu Province(Grant No.BK20180686,BK20161008,and BK20190670).
文摘The emergence of low-dimensional nanomaterials has brought revolutionized development of magnetism,as the size effect can significantly influence the spin arrangement.Since the first demonstration of truly two-dimensional magnetic materials(2DMMs)in 2017,a wide variety of magnetic phases and associated properties have been exhibited in these 2DMMs,which offer a new opportunity to manipulate the spin-based devices efficiently in the future.Herein,we focus on the recent progress of 2DMMs and heterostructures in the aspects of their structural characteristics,physical properties,and spintronic applications.Firstly,the microscopy characterization of the spatial arrangement of spins in 2D lattices is reviewed.Afterwards,the optical probes in the light-matter-spin interactions at the 2D scale are discussed.Then,particularly,we systematically summarize the recent work on the electronic and spintronic devices of 2DMMs.In the section of electronic properties,we raise several exciting phenomena in 2DMMs,i.e.,long-distance magnon transport,field-effect transistors,varying magnetoresistance behavior,and(quantum)anomalous Hall effect.In the section of spintronic applications,we highlight spintronic devices based on 2DMMs,e.g.,spin valves,spin-orbit torque,spin field-effect transistors,spin tunneling field-effect transistors,and spin-filter magnetic tunnel junctions.At last,we also provide our perspectives on the current challenges and future expectations in this field,which may be a helpful guide for theorists and experimentalists who are exploring the optical,electronic,and spintronic properties of 2DMMs.
