An electromechanical liquid crystal theory will be presented for modeling the morphology evolution of a lipid vesicle under mechanical and electrical fields.Firstly,a general equation that governs the vesicle shape is...An electromechanical liquid crystal theory will be presented for modeling the morphology evolution of a lipid vesicle under mechanical and electrical fields.Firstly,a general equation that governs the vesicle shape is established by considering the effects of展开更多
The Ti-Supported MnO_2 electrode was modified by introducing SnO_2+RuO_2+MnO_2 as an intermediate layer into the Ti/MnO_2 interface. The anodic polarization curves were measured at various temperatures ranging from 30...The Ti-Supported MnO_2 electrode was modified by introducing SnO_2+RuO_2+MnO_2 as an intermediate layer into the Ti/MnO_2 interface. The anodic polarization curves were measured at various temperatures ranging from 30 to 80℃ and the activation energy for the oxygen evolution reaction was evaluated. The experimental activation energy increased linearly with increasing the overpotential. The activation energy at the equilibrium potential was linearly correlated with the difference between the crystal field stabilization energies of Mn^(4+) at initial state and Mn^(4+) at transition state. The electrocatalysis characteristics of the anode were discussed by means of the mechanism of the substitution reaction of the ligand(S_N1 and S_N2) and molecular orbital theory. The results show that the anode has better electrocatalystic characteristics.展开更多
Rare earth doped orthovanadate crystal LuVO4∶Yb3+ shows high power laser applications because of the low quantum defect and the high thermal conductivity. Since electronic paramagnetic resonance (EPR) is a powerful t...Rare earth doped orthovanadate crystal LuVO4∶Yb3+ shows high power laser applications because of the low quantum defect and the high thermal conductivity. Since electronic paramagnetic resonance (EPR) is a powerful tool to analyze the electronic properties and the local structures of paramagnetic impurity centers in crystals, the EPR spectra of the Yb3+ centers in LuVO4 crystal were measured recently. However, the above experimental results have not been theoretically interpreted. In this work, The EPR g factors and the hyperfine structure constants of 171Yb3+ and 173Yb3+ isotopes in LuVO4 crystal were theoretically studied from the perturbation formulae of the spin Hamiltonian parameters for 4f13 ion in tetragonal symmetry. The needed crystal parameters were obtained from the superposition model and the local structure of the studied system. The calculated results were in reasonable agreement with the observed values.展开更多
1 Introduction Snow salt is one of the multi-salt with highly added value,in named for its snowflakes structure appearance.In the present situation,the stacking density gap between different commercial snow salt is bi...1 Introduction Snow salt is one of the multi-salt with highly added value,in named for its snowflakes structure appearance.In the present situation,the stacking density gap between different commercial snow salt is big,mainly ranged from700 kg/m3to 800 kg/m3.The competition in the market展开更多
Electromagnetic wave(EMW)absorbing materials play a vital role in modern communication and information processing technologies to inhibit information leakage and prevent possible damages to environment and human bodie...Electromagnetic wave(EMW)absorbing materials play a vital role in modern communication and information processing technologies to inhibit information leakage and prevent possible damages to environment and human bodies.Currently,most of EMW absorbing materials are either composites of two or more phases or in the form of nanosheets,nanowires or nanofibers in order to enhance the EMW absorption performance through dielectric loss,magnetic loss and dielectric/magnetic loss coupling.However,the combination of complex shapes/multi phases and nanosizes may compound the difficulties of materials processing,composition and interfaces control as well as performance maintenance during service.Thus,searching for single phase materials with good stability and superior EMW absorbing properties is appealing.To achieve this goal,the EMW absorbing properties of transition metal carbides TMCs(TM=Ti,Zr,Hf,Nb and Ta)and high entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C which belong to ultrahigh temperature ceramics,were investigated in this work.Due to the good electrical conductivity and splitting of d orbitals into lower energy t2glevel and higher energy eglevel in TMC6octahedral arrangement,TMCs(TM=Ti,Zr,Hf,Nb and Ta)exhibit good EMW absorbing properties.Especially,Hf C and Ta C exhibit superior EMW absorbing properties.The minimum reflection loss(RLmin)value of Hf C is-55.8 d B at 6.0 GHz with the thickness of 3.8 mm and the effective absorption bandwidth(E_(AB))is 6.0 GHz from 12.0 to 18.0 GHz at thickness of 1.9 mm;the RL_(minvalue)of Ta C reaches-41.1 d B at 16.2 GHz with a thickness of 2.0 mm and the EABis 6.1 GHz with a thickness of 2.2 mm.Intriguingly,the electromagnetic parameters,i.e.,complex permittivity and permeability are tunable by forming single phase solid solution or high entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C.The R_(Lminvalue)of high entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C is-38.5 d B at 9.5 GHz with the thickness of 1.9 mm,and the EABis 2.3 GHz(from 11.3 to 13.6 GHz)at thickness of 1.5 mm.The significance of this work is that it opens a new window to design single phase high performance EMW absorbing materials by dielectric/magnetic loss coupling through tuning the conductivity and crystal field splitting energy of d orbitals of transition metals in carbides,nitrides and possibly borides.展开更多
The microstructure of nickel-based single-crystal(SC) superalloys has a pivotal influence on their creep properties. The addition of the Re element not only enhances the long-term creep properties of nickel-based SC s...The microstructure of nickel-based single-crystal(SC) superalloys has a pivotal influence on their creep properties. The addition of the Re element not only enhances the long-term creep properties of nickel-based SC superalloys, but also results in the formation of a topologically close-packed(TCP) phase which is a harmful and brittle hard phase. Here, high-temperature creep interruption tests of a nickel-based SC superalloy that contains4.8 wt% Re were performed under various temperatures and stress conditions, and the evolution of microstructure during creep was observed by scanning electron microscopy(SEM). The volume fraction of the TCP phase was also extracted to explore the mechanism that controls the impacts of the TCP phase on the creep properties.According to the microstructure evolution mechanism, the influence of the TCP phase was attributed to the initial damage and critical shear stress of the material. A creep performance prediction model for nickel-based SC superalloys considering the precipitation of the TCP phase that is based on the crystal plasticity theory and a modified creep damage model was established. The simulation curves fit well with the experimental results and the errors between prediction creep life with test results are within 5%.展开更多
A meshless radial basis function (RBF) collocation method based on the Eringen nonlocal elasticity theory is developed to calculate the band structures of ternary and quaternary nanoscale multi-layered phononic crys...A meshless radial basis function (RBF) collocation method based on the Eringen nonlocal elasticity theory is developed to calculate the band structures of ternary and quaternary nanoscale multi-layered phononic crystals (PNCs) with functionally graded (FG) interlayers. Detailed calculations are performed for anti-plane transverse waves propagating in such PNCs. The influences of FG and homogeneous interlayers, component number, nonlocal interface imperfections and nanoscale size on cut-off frequency and band structures are investigated in detail. Numerical results show that these factors have significant effects on band structures at the macroscopic and microscopic scales.展开更多
基金the National Natural Science Foundation of China,Nos.10525210 and 10722050
文摘An electromechanical liquid crystal theory will be presented for modeling the morphology evolution of a lipid vesicle under mechanical and electrical fields.Firstly,a general equation that governs the vesicle shape is established by considering the effects of
基金Supported by the National Natural Science Foundation of China.
文摘The Ti-Supported MnO_2 electrode was modified by introducing SnO_2+RuO_2+MnO_2 as an intermediate layer into the Ti/MnO_2 interface. The anodic polarization curves were measured at various temperatures ranging from 30 to 80℃ and the activation energy for the oxygen evolution reaction was evaluated. The experimental activation energy increased linearly with increasing the overpotential. The activation energy at the equilibrium potential was linearly correlated with the difference between the crystal field stabilization energies of Mn^(4+) at initial state and Mn^(4+) at transition state. The electrocatalysis characteristics of the anode were discussed by means of the mechanism of the substitution reaction of the ligand(S_N1 and S_N2) and molecular orbital theory. The results show that the anode has better electrocatalystic characteristics.
基金the Science Foundations of CSTC (2007BB4385 , 2007BB4391)Education Committee of Chongqing (KJ060515 , KJ050502)
文摘Rare earth doped orthovanadate crystal LuVO4∶Yb3+ shows high power laser applications because of the low quantum defect and the high thermal conductivity. Since electronic paramagnetic resonance (EPR) is a powerful tool to analyze the electronic properties and the local structures of paramagnetic impurity centers in crystals, the EPR spectra of the Yb3+ centers in LuVO4 crystal were measured recently. However, the above experimental results have not been theoretically interpreted. In this work, The EPR g factors and the hyperfine structure constants of 171Yb3+ and 173Yb3+ isotopes in LuVO4 crystal were theoretically studied from the perturbation formulae of the spin Hamiltonian parameters for 4f13 ion in tetragonal symmetry. The needed crystal parameters were obtained from the superposition model and the local structure of the studied system. The calculated results were in reasonable agreement with the observed values.
基金supported by a grant from the Tianjin Binhai New Area (TBNA) Science & Technology commission project, and grant No. 1400050006
文摘1 Introduction Snow salt is one of the multi-salt with highly added value,in named for its snowflakes structure appearance.In the present situation,the stacking density gap between different commercial snow salt is big,mainly ranged from700 kg/m3to 800 kg/m3.The competition in the market
基金the National Natural Science Foundation of China under grant No.51972089,No.51672064 and No.U1435206。
文摘Electromagnetic wave(EMW)absorbing materials play a vital role in modern communication and information processing technologies to inhibit information leakage and prevent possible damages to environment and human bodies.Currently,most of EMW absorbing materials are either composites of two or more phases or in the form of nanosheets,nanowires or nanofibers in order to enhance the EMW absorption performance through dielectric loss,magnetic loss and dielectric/magnetic loss coupling.However,the combination of complex shapes/multi phases and nanosizes may compound the difficulties of materials processing,composition and interfaces control as well as performance maintenance during service.Thus,searching for single phase materials with good stability and superior EMW absorbing properties is appealing.To achieve this goal,the EMW absorbing properties of transition metal carbides TMCs(TM=Ti,Zr,Hf,Nb and Ta)and high entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C which belong to ultrahigh temperature ceramics,were investigated in this work.Due to the good electrical conductivity and splitting of d orbitals into lower energy t2glevel and higher energy eglevel in TMC6octahedral arrangement,TMCs(TM=Ti,Zr,Hf,Nb and Ta)exhibit good EMW absorbing properties.Especially,Hf C and Ta C exhibit superior EMW absorbing properties.The minimum reflection loss(RLmin)value of Hf C is-55.8 d B at 6.0 GHz with the thickness of 3.8 mm and the effective absorption bandwidth(E_(AB))is 6.0 GHz from 12.0 to 18.0 GHz at thickness of 1.9 mm;the RL_(minvalue)of Ta C reaches-41.1 d B at 16.2 GHz with a thickness of 2.0 mm and the EABis 6.1 GHz with a thickness of 2.2 mm.Intriguingly,the electromagnetic parameters,i.e.,complex permittivity and permeability are tunable by forming single phase solid solution or high entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C.The R_(Lminvalue)of high entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C is-38.5 d B at 9.5 GHz with the thickness of 1.9 mm,and the EABis 2.3 GHz(from 11.3 to 13.6 GHz)at thickness of 1.5 mm.The significance of this work is that it opens a new window to design single phase high performance EMW absorbing materials by dielectric/magnetic loss coupling through tuning the conductivity and crystal field splitting energy of d orbitals of transition metals in carbides,nitrides and possibly borides.
基金financially supported by the National Natural Science Foundation of China(No.51875462)the Fundamental Research Funds for the Central Universities(No.3102019PY001)+1 种基金the Seed Foundation of Innovation and Creation for Graduate Students in Northwestern Polytechnical University(Nos.ZZ2019015 and ZZ2019017)the National Science and Technology Major Project(Nos.2017-IV-0003-0040 and 2017-V-00030052)。
文摘The microstructure of nickel-based single-crystal(SC) superalloys has a pivotal influence on their creep properties. The addition of the Re element not only enhances the long-term creep properties of nickel-based SC superalloys, but also results in the formation of a topologically close-packed(TCP) phase which is a harmful and brittle hard phase. Here, high-temperature creep interruption tests of a nickel-based SC superalloy that contains4.8 wt% Re were performed under various temperatures and stress conditions, and the evolution of microstructure during creep was observed by scanning electron microscopy(SEM). The volume fraction of the TCP phase was also extracted to explore the mechanism that controls the impacts of the TCP phase on the creep properties.According to the microstructure evolution mechanism, the influence of the TCP phase was attributed to the initial damage and critical shear stress of the material. A creep performance prediction model for nickel-based SC superalloys considering the precipitation of the TCP phase that is based on the crystal plasticity theory and a modified creep damage model was established. The simulation curves fit well with the experimental results and the errors between prediction creep life with test results are within 5%.
基金the supports by the National Natural Science Foundation of China (nos.11002026,11372039)Beijing Natural Science Foundation (no.3133039)the Scientific Research Foundation for the Returned (no.20121832001)
文摘A meshless radial basis function (RBF) collocation method based on the Eringen nonlocal elasticity theory is developed to calculate the band structures of ternary and quaternary nanoscale multi-layered phononic crystals (PNCs) with functionally graded (FG) interlayers. Detailed calculations are performed for anti-plane transverse waves propagating in such PNCs. The influences of FG and homogeneous interlayers, component number, nonlocal interface imperfections and nanoscale size on cut-off frequency and band structures are investigated in detail. Numerical results show that these factors have significant effects on band structures at the macroscopic and microscopic scales.