Structural and lattice dynamical properties of ReB2,RuB2,and OsB2 in the ReB2 structure are studied in the framework of density functional theory within the generalized gradient approximation.The present results show ...Structural and lattice dynamical properties of ReB2,RuB2,and OsB2 in the ReB2 structure are studied in the framework of density functional theory within the generalized gradient approximation.The present results show that these compounds are dynamically stable for the considered structure.The temperature-dependent behaviors of thermodynamical properties such as internal energy,free energy,entropy,and heat capacity are also presented.The obtained results are in good agreement with the available experimental and theoretical data.展开更多
The dynamical properties of a tumor cell growth system described by the logistic system with coupling between non- Gaussian and Gaussian noise terms are investigated. The effects of the nonextensive index q on the sta...The dynamical properties of a tumor cell growth system described by the logistic system with coupling between non- Gaussian and Gaussian noise terms are investigated. The effects of the nonextensive index q on the stationary properties and the transient properties are discussed, respectively. The results show that the nonextensive index q can induce the tumor cell numbers to decrease greatly in the case of q 〉 1. Moreover, the switch from the steady stable state to the extinct state is speeded up as the increases of q, and the tumor cell numbers can be more obviously restrained for a large value of q. The numerical results are found to be in basic agreement with the theoretical predictions.展开更多
The U-Nb alloy,as a kind of nuclear material with good corrosion resistance and mechanical properties,plays an important role in the nuclear industry.However,the experimental measurements and theoretical calculations ...The U-Nb alloy,as a kind of nuclear material with good corrosion resistance and mechanical properties,plays an important role in the nuclear industry.However,the experimental measurements and theoretical calculations of many parameters which are essential in describing the dynamical properties of this alloy melt,including density,diffusivity,and viscosity,have not been carried out yet.The lack of data on the dynamical properties of nuclear materials seriously hinders the high-performance nuclear materials from being developed and applied.In this work,the dynamical properties of the U-Nb alloy melt are systematically studied by means of ab initio molecular dynamics simulations and their corresponding mathematical models are established,thereby being able to rapidly calculate the densities,diffusion coefficients,viscosities,and their activation energies in the whole U-Nb liquid region.This work provides a new idea for investigating the dynamical properties of binary alloy melts,thereby promoting the development of melt research.展开更多
Two finite-element models of the CRTS II slab track are presented to simulate temperature-induced deformations of the concrete track slab with no deterioration or with a deteriorated cement asphalt mortar(CAM).One mod...Two finite-element models of the CRTS II slab track are presented to simulate temperature-induced deformations of the concrete track slab with no deterioration or with a deteriorated cement asphalt mortar(CAM).One model,which considers the fully bonding interface between the slab and the CAM layer,could applied to a track that is in good condition;the other model uses cohesive zone elements to simulate the deteriorated CAM with some possible interfacial separation and slip.Utilizing both of the models,temperature-induced warp deformations of track under various temperature loads are investigated.The influence of temperature deformation on the dynamic properties of the track is analyzed based on the train-track coupled dynamics.Numerical results show that the deteriorated CAM layer can significantly increase temperature deformations of a CRTS II track slab,which would produce tiny rail irregularities.There are clear differences between the deformation shapes of the track slabs that have an inseparable mortar layer and those have a separable mortar layer.The track slab with a deteriorated mortar layer showed more open curl distortion than the track slab in good condition.The dynamical response index of the slab track is intensified to a certain level due to the temperature deformation;with an increase of the train speed,the track dynamical responses increased linearly.However,rail irregularities due to the temperature deformations are very tiny.Even if a track is exposed to extreme temperature loads and the mortar layer is deteriorated,temperature deformation can have a negligible effect on the track’s dynamical properties.展开更多
As the typical systems of nano structures, nanotubes can be widely applied in mechanical electronics, mechanical manufacture and other fields at nano scales. The superior dynamical properties of nanotubes have become ...As the typical systems of nano structures, nanotubes can be widely applied in mechanical electronics, mechanical manufacture and other fields at nano scales. The superior dynamical properties of nanotubes have become a hot topic. Furthermore, there are always complicated conditions for practical engineering (e.g. initial stress/strain, temperature change for external environment and the interaction between the structure and elastic matrix). Then, it is important to establish the proper model and apply the effective analysis method. By using the nonlocal continuum method, this paper reviews the recent progress of dynamical properties of micro structures at nano scales. The discussion is focused on dynamical behaviors of nanotubes, including vibration, wave propagation and fluid-structure interaction, etc. At last, conclusions and prospects in future studies are discussed.展开更多
Room temperature ionic liquids(RTILs) with dispersed carbon pieces exhibit distinctive physiochemical properties. To explore the molecular mechanism, RTILs/carbon pieces mixture was investigated by molecular dynamics(...Room temperature ionic liquids(RTILs) with dispersed carbon pieces exhibit distinctive physiochemical properties. To explore the molecular mechanism, RTILs/carbon pieces mixture was investigated by molecular dynamics(MD) simulation in this work. Rigid and flexible carbon pieces in the form of graphene with different thicknesses and carbon nanotubes in different sizes were dispersed in a representative RTIL 1-butyl-3-methyl-imidazolium dicyanamide([Bmim][DCA]). This study demonstrated that the diffusion coefficients of RTILs in the presence of flexible carbons are similar to those of bulk RTILs at varying temperatures, which is in contrast to the decreased diffusion of RTILs in the presence of rigid carbons. In addition, interfacial ion number density at rigid carbon surfaces was higher than that at flexible ones, which is correlated with the accessible external surface area of carbon pieces. The life time of cation-anion pair in the presence of carbon pieces also exhibited a dependence on carbon flexibility. RTILs with dispersed rigid carbon pieces showed longer ion pair life time than those with flexible ones, in consistence with the observation in diffusion coefficients. This work highlights the necessity of including the carbon flexibility when performing MD simulation of RTILs in the presence of dispersed carbon pieces in order to obtain the reliable dynamical and interfacial structural properties.展开更多
The structural, dielectric, lattice dynamical and thermodynamic properties of zinc-blende CdX （X=S, Se, Te） are studied by using a plane-wave pseudopotential method within the density-functional theory. Our calculat...The structural, dielectric, lattice dynamical and thermodynamic properties of zinc-blende CdX （X=S, Se, Te） are studied by using a plane-wave pseudopotential method within the density-functional theory. Our calculated lattice constants and bulk modulus are compared with the pubfished experimental and theoretical data. In addition, the Born effective charges, electronic dielectric tensors, phonon frequencies, and longitudinal opticaltransverse optical splitting are calculated by the linear-response approach. Some of the characteristics of the phonon-dispersion curves for zinc-blende CdX （X= S, Se, Te） are summarized. What is more, based on the lattice dynamical properties, we investigate the thermodynamic properties of CdX （X= S, Se, Te） and analyze the temperature dependences of the Helmholtz free energy F, the internal energy E, the entropy S and the constant-volume specific heat Cv. The results show that the heat capacities for CdTe, CdSe, and CdS approach approximately to the Petit-Dulong limit 6R.展开更多
A plasma screening model that accounts for electronic exchange-correlation effects and ionic nonideality in dense quantum plasmas is proposed.This model can be used as an input in various plasma interaction models to ...A plasma screening model that accounts for electronic exchange-correlation effects and ionic nonideality in dense quantum plasmas is proposed.This model can be used as an input in various plasma interaction models to calculate scattering cross-sections and transport properties.The applicability of the proposed plasma screening model is demonstrated using the example of the temperature relaxation rate in dense hydrogen and warm dense aluminum.Additionally,the conductivity of warm dense aluminum is computed in the regime where collisions are dominated by electron-ion scattering.The results obtained are compared with available theoretical results and simulation data.展开更多
Red clay,widely used as a subgrade material in southern China,requires a reliable evaluation of its dynamic behavior to ensure infrastructure safety.Long-term cyclic triaxial tests were conducted on red clay from typi...Red clay,widely used as a subgrade material in southern China,requires a reliable evaluation of its dynamic behavior to ensure infrastructure safety.Long-term cyclic triaxial tests were conducted on red clay from typical,complex subway subgrades to investigate its dynamic properties and shakedown behavior under intermittent cyclic loading.Results show that intermittent cyclic loading,especially with multiple amplitudes,causes greater axial plastic strain and lower post-cyclic strength than continuous loading.These effects diminish with increasing confining pressure.Notably,axial strain partially recovers during loading intervals,with recovery ratios depending on the number and sequence of pauses.Based on the rules of cumulative plastic strain rates and cumulative plastic strain increments,shakedown behavior for red clay under intermittent cyclic loading is divided into three categories:plastic shakedown,critical shakedown,and plastic creep.A quantitative shakedown limit criterion is proposed using the Boltzmann function.Shakedown behavior significantly influences the post-cyclic strengths,and the influence diminishes as confining pressure increases.Samples exhibiting plastic creep and plastic shakedown behavior have the lowest and highest strengths,and those with critical shakedown behaviors have medium strengths.Cyclic loading with relatively low-stress amplitude causes a hardening effect,while cyclic loading intermittence or cyclic loading with relatively high-stress amplitude causes a degradation effect,and both effects are mitigated by higher confining pressures.展开更多
Liquid-liquid phase separation(LLPS)of proteins and nucleic acids is a common phenomenon in cells that underlies the formation of membraneless organelles.Although the macroscopic behavior of biomolecular coacervates h...Liquid-liquid phase separation(LLPS)of proteins and nucleic acids is a common phenomenon in cells that underlies the formation of membraneless organelles.Although the macroscopic behavior of biomolecular coacervates has been elucidated by microscopy,the detailed dynamic properties of proteins/peptides during the LLPS process remain poorly characterized.Here,site-directed spin labeling-electron paramagnetic resonance(SDSL-EPR)spectroscopy was employed to characterize the dynamic properties of a minimal model LLPS system consisting of positively charged peptides and RNA.The degree of phase separation,indicated by broadening of the EPR spectrum of the spin-labeled peptide due to slow molecular tumbling,was monitored by EPR.In addition,three distinct populations with varying molecular motion during LLPS,featuring different spectral lineshapes,were identified.These populations included a fast motion component(Ⅰ),a slower motion component(Ⅱ)associated with peptides in the dispersed phase and an immobile component(Ⅲ)observed in the dense phase.With gradual titration of the peptides to RNA,the EPR spectrum gradually shifted,refiecting changes in the populations of the components.Together,SDSL-EPR method not only provides new insights into the dynamic behavior of biomolecules during LLPS,but also offers a sensitive method for biomolecular phase separation processes at the molecular level.展开更多
Experimental studies were conducted on two high-strength steel plate-frame structures with different truss spacings under various impact velocities to investigate the dynamic mechanical properties of hull plate-frame ...Experimental studies were conducted on two high-strength steel plate-frame structures with different truss spacings under various impact velocities to investigate the dynamic mechanical properties of hull plate-frame structures under drop weight impact.The results showed that decreasing the main beam spacing can effectively increase the structural stiffness,reduce the maximum deformation,and increase the damage range.Furthermore,to simulate the impact tests accurately,static and dynamic tensile tests at different strain rates were carried out,and the Cowper-Symonds model parameters were fitted via experimental data.The material properties obtained from the tensile tests were used as inputs for numerical simulations with the numerical results coincide with the experimental results.A systematic analysis and discussion were conducted on the effects of truss spacing and truss width on the dynamic response of the reinforced plates,and an optimal range for the ratio of truss spacing to truss width was proposed.In addition,a mesh size sensitivity analysis for ship hull plate frame collision simulations was performed.The applicability of the EPS,MMC,and RTCL failure criteria in the simulation of plate-frame structures was investigated via finite element simulations of falling weight impact tests.The research findings provide a reference for ship hull structure design and resilience assessment.展开更多
Controllable shock wave fracturing is an innovative engineering technique used for shale reservoir fracturing and reformation.Understanding the anisotropic fracture mechanism of shale under impact loading is vital for...Controllable shock wave fracturing is an innovative engineering technique used for shale reservoir fracturing and reformation.Understanding the anisotropic fracture mechanism of shale under impact loading is vital for optimizing shock wave fracturing equipment and enhancing shale oil production.In this study,using the well-known notched semi-circular bend(NSCB)sample and the novel double-edge notched flattened Brazilian disc(DNFBD)sample combined with a split Hopkinson pressure bar(SHPB),various dynamic anisotropic fracture properties of Lushan shale,including failure characteristics,fracture toughness,energy dissipation and crack propagation velocity,are comprehensively compared and discussed under mode Ⅰ and mode Ⅱ fracture scenarios.First,using a newly modified fracture criterion considering the strength anisotropy of shale,the DNFBD specimen is predicted to be a robust method for true mode Ⅱ fracture of anisotropic shale rocks.Our experimental results show that the dynamic mode Ⅱ fracture of shale induces a rougher and more complex fracture morphology and performs a higher fracture toughness or fracture energy compared to dynamic mode Ⅰ fracture.The minimal fracture toughness or fracture energy occurs in the Short-transverse orientation,while the maximal ones occur in the Divider orientation.In addition,it is interesting to find that the mode Ⅱ fracture toughness anisotropy index decreases more slowly than that in the mode Ⅰ fracture scenario.These results provide significant insights for understanding the different dynamic fracture mechanisms of anisotropic shale rocks under impact loading and have some beneficial implications for the controllable shock wave fracturing technique.展开更多
For understanding the rock microscopic damage and dynamic mechanical properties subjected to recurrent freeze-thaw cycles, experiments for five groups of homogeneous sandstone under different freeze-thaw cycles were c...For understanding the rock microscopic damage and dynamic mechanical properties subjected to recurrent freeze-thaw cycles, experiments for five groups of homogeneous sandstone under different freeze-thaw cycles were conducted. After freezethaw, nuclear magnetic resonance(NMR) tests and impact loading tests were carried out, from which microscopic damage characteristics of sandstone and dynamic mechanical parameters were obtained. The results indicate that the porosity increases with the increase of cycle number, the rate of porosity growth descends at the beginning of freeze-thaw, yet accelerates after a certain number of cycles. The proportion of pores with different sizes changes dynamically and the multi-scale distribution of pores tends to develop on pore structure with the continuing impact of freeze-thaw and thawing. Dynamic compressive stress-strain curve of sandstone undergoing freeze-thaw can be divided into four phases, and the phase of compaction is inconspicuous compared with the static curve. Elastic modulus and dynamic peak intensity of sandstone gradually decrease with freeze-thaw cycles, while peak strain increases. The higher the porosity is, the more serious the degradation of dynamic intensity is. The porosity is of a polynomial relationship with the dynamic peak intensity.展开更多
To analyze the effects of strain rate and temperature on the flow stress of 2519A aluminum alloy, the dynamic mechanical properties of 2519A aluminum alloy were measured by dynamic impact tests and quasi-static tensil...To analyze the effects of strain rate and temperature on the flow stress of 2519A aluminum alloy, the dynamic mechanical properties of 2519A aluminum alloy were measured by dynamic impact tests and quasi-static tensile tests. The effects of strain rate and temperature on the microstructure evolution were investigated by optical microscopy （OM） and transmission electron microscopy （TEM）. The experimental results indicate that 2519A aluminum alloy exhibits strain-rate dependence and temperature susceptibility under dynamic impact. The constitutive constants for Johnson--Cook material model were determined by the quasi-static tests and Hopkinson bar experiments using the methods of variable separation and nonlinear fitting. The constitutive equation seems to be consistent with the experimental results, which provides reference for mechanical characteristics and numerical simulation of ballistic performance.展开更多
This paper reports a new three-dimensional autonomous chaotic system. It contains six control parameters and three nonlinear terms. Two cross-product terms are respectively in two equations. And one square term is in ...This paper reports a new three-dimensional autonomous chaotic system. It contains six control parameters and three nonlinear terms. Two cross-product terms are respectively in two equations. And one square term is in the third equation. Basic dynamic properties of the new system are investigated by means of theoretical analysis, numerical simulation, sensitivity to initial, power spectrum, Lyapunov exponent, and Poincar~ diagrams. The dynamic properties affected by variable parameters are also analysed. Finally, the chaotic system is simulated by circuit. The results verify the existence and implementation of the system.展开更多
In this paper, the behavior analysis of two cells chopper connected to a nonlinear load is reported. Thus, this is done in order to highlight the way to chaos. Furthermore, throughout the study of these dynamical beha...In this paper, the behavior analysis of two cells chopper connected to a nonlinear load is reported. Thus, this is done in order to highlight the way to chaos. Furthermore, throughout the study of these dynamical behaviors of this complex switched system some basic dynamical properties, such as Poincare section, first return map, bifurcation diagram, power spectrum, and strange attractor are investigated. The system examined in Matlab-Simulink. Analyses of simulation results show that this system has complex dynamics with some interesting characteristics.展开更多
To obtain dynamic mechanical properties and failure rule of layered backfill under strain rates from10to80s-1,impactloading test on layered backfill specimens(LBS)was conducted by using split Hopkinson pressure bar sy...To obtain dynamic mechanical properties and failure rule of layered backfill under strain rates from10to80s-1,impactloading test on layered backfill specimens(LBS)was conducted by using split Hopkinson pressure bar system.The results indicatethat positive correlation can be found between dynamic compressive strength and strain rate,as well as between strength increasefactor and strain rate.Dynamic compressive strength of LBS gets higher as the arithmetic average cement-sand ratio increases.Compared with static compressive strength,dynamic compressive strength of LBS is enhanced by11%to163%.In addition,theenergy dissipating rate of LBS lies between that of corresponding single specimens,and it decreases as the average cement contentincreases.Deformation of LBS shows obvious discontinuity,deformation degree of lower strength part of LBS is generally higherthan that of higher strength part.A revised brittle fracture criterion based on the Stenerding-Lehnigk criterion is applied to analyzingthe fracture status of LBS,and the average relevant errors of the3groups between the test results and calculation results are4.80%,3.89%and4.66%,respectively.展开更多
Poly(vinyl alcohol) (PVA)/hydroxyapatite (HA) composite hydrogel specimens were prepared with 15% PVA and 1%,2%, 3%, 4% and 5% HA by repeated freezing-thawing. The tests of static and dynamic mechanical properties wer...Poly(vinyl alcohol) (PVA)/hydroxyapatite (HA) composite hydrogel specimens were prepared with 15% PVA and 1%,2%, 3%, 4% and 5% HA by repeated freezing-thawing. The tests of static and dynamic mechanical properties were carried out todiscuss the influence of different contents of HA and freezing-thawing cycles on the mechanical properties of PVA/HA compositehydrogel. The results of static mechanical tests showed that the PVA/HA composite hydrogel with 3% HA and ninefreezing-thawing cycles had excellent stress relaxation properties, higher relaxation ratio, lower stress equilibrium value andpresented better properties of creep and recovery. The results of dynamic mechanical test showed that the PVA/HA compositehydrogel with nine freezing-thawing cycles had higher storage modulus and loss modulus, so was the PVA/HA compositehydrogel with 3% HA.展开更多
Aluminate-based coupling agent was added as a compatibilizer to make the chemical modification of wood powder. The mechanical properties and morphology of wood powder/polypropylene composites were studied. The results...Aluminate-based coupling agent was added as a compatibilizer to make the chemical modification of wood powder. The mechanical properties and morphology of wood powder/polypropylene composites were studied. The results showed that the compatibilizer can increase the impact strength of the wood/polypropylene composites, but it has a slightly negative effect on the tensile and flexural strength. For dynamic mechanical properties and Differential Scanning Calorimetry, Aluminate-based coupling agent can slightly increase the storage modulus and loss modulus, and decrease the melt point and the Calorie of Melt. Scanning electron microscopy showed that Aluminate-based coupling agent had a stronger affinity between the wood and polypropylene surfaces. These results suggested that Aluminate-based coupling agent may play a useful role in improving wood powder/polypropylene composites properties.展开更多
The effect of Gd content ranging from 6.5 wt.%to 8.5 wt.%on microstructure evolution and dynamic mechanical behavior of Mg−xGd−3Y−0.5Zr alloys was investigated by optical microscopy,X-ray diffraction,scanning electron...The effect of Gd content ranging from 6.5 wt.%to 8.5 wt.%on microstructure evolution and dynamic mechanical behavior of Mg−xGd−3Y−0.5Zr alloys was investigated by optical microscopy,X-ray diffraction,scanning electron microscopy and split Hopkinson pressure bar.The microstructure of as-cast Mg−xGd−3Y−0.5Zr alloys indicates that the addition of Gd can promote grain refinement in the casting.Due to the rapid cooling rate during solidification,a large amount of non-equilibrium eutectic phase Mg_(24)(Gd,Y)_(5) appears at the grain boundary of as-cast Mg−xGd−3Y−0.5Zr alloys.After solution treatment at 520℃ for 6 h,the Mg_(24)(Gd,Y)_(5) phase dissolves into the matrix,and the rare earth hydrides(REH)phase appears.The stress−strain curves validate that the solution-treated Mg−xGd−3Y−0.5Zr alloys with optimal Gd contents maintain excellent dynamic properties at different strain rates.It was concluded that the variation of Gd content and the agglomeration of residual REH particles and dynamically precipitated fine particles are key factors affecting dynamic mechanical properties of Mg−xGd−3Y−0.5Zr alloys.展开更多
文摘Structural and lattice dynamical properties of ReB2,RuB2,and OsB2 in the ReB2 structure are studied in the framework of density functional theory within the generalized gradient approximation.The present results show that these compounds are dynamically stable for the considered structure.The temperature-dependent behaviors of thermodynamical properties such as internal energy,free energy,entropy,and heat capacity are also presented.The obtained results are in good agreement with the available experimental and theoretical data.
基金supported by the National Natural Science Foundation of China (Grant No. 11205006)the Science Foundation of the Education Bureau of Shaanxi Province, China (Grant No. 12JK0962)the Science Foundation of Baoji University of Arts and Sciences of China (Grant No. ZK11053)
文摘The dynamical properties of a tumor cell growth system described by the logistic system with coupling between non- Gaussian and Gaussian noise terms are investigated. The effects of the nonextensive index q on the stationary properties and the transient properties are discussed, respectively. The results show that the nonextensive index q can induce the tumor cell numbers to decrease greatly in the case of q 〉 1. Moreover, the switch from the steady stable state to the extinct state is speeded up as the increases of q, and the tumor cell numbers can be more obviously restrained for a large value of q. The numerical results are found to be in basic agreement with the theoretical predictions.
基金Project supported by the Science Challenging Project,China(Grant No.TZ2016004)the National Natural Science Foundation of China(Grant No.51701193)。
文摘The U-Nb alloy,as a kind of nuclear material with good corrosion resistance and mechanical properties,plays an important role in the nuclear industry.However,the experimental measurements and theoretical calculations of many parameters which are essential in describing the dynamical properties of this alloy melt,including density,diffusivity,and viscosity,have not been carried out yet.The lack of data on the dynamical properties of nuclear materials seriously hinders the high-performance nuclear materials from being developed and applied.In this work,the dynamical properties of the U-Nb alloy melt are systematically studied by means of ab initio molecular dynamics simulations and their corresponding mathematical models are established,thereby being able to rapidly calculate the densities,diffusion coefficients,viscosities,and their activation energies in the whole U-Nb liquid region.This work provides a new idea for investigating the dynamical properties of binary alloy melts,thereby promoting the development of melt research.
基金supported by the National Basic Research Program of China("973"Project)(Grant No.2013CB036202)the National Natural Science Foundation of China(Grant Nos.51008254,51478397)the Fundamental Research Funds for Central Universities(Grant No.2682013CX029)
文摘Two finite-element models of the CRTS II slab track are presented to simulate temperature-induced deformations of the concrete track slab with no deterioration or with a deteriorated cement asphalt mortar(CAM).One model,which considers the fully bonding interface between the slab and the CAM layer,could applied to a track that is in good condition;the other model uses cohesive zone elements to simulate the deteriorated CAM with some possible interfacial separation and slip.Utilizing both of the models,temperature-induced warp deformations of track under various temperature loads are investigated.The influence of temperature deformation on the dynamic properties of the track is analyzed based on the train-track coupled dynamics.Numerical results show that the deteriorated CAM layer can significantly increase temperature deformations of a CRTS II track slab,which would produce tiny rail irregularities.There are clear differences between the deformation shapes of the track slabs that have an inseparable mortar layer and those have a separable mortar layer.The track slab with a deteriorated mortar layer showed more open curl distortion than the track slab in good condition.The dynamical response index of the slab track is intensified to a certain level due to the temperature deformation;with an increase of the train speed,the track dynamical responses increased linearly.However,rail irregularities due to the temperature deformations are very tiny.Even if a track is exposed to extreme temperature loads and the mortar layer is deteriorated,temperature deformation can have a negligible effect on the track’s dynamical properties.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11002045, 11172084, 10632020 and 10672017)
文摘As the typical systems of nano structures, nanotubes can be widely applied in mechanical electronics, mechanical manufacture and other fields at nano scales. The superior dynamical properties of nanotubes have become a hot topic. Furthermore, there are always complicated conditions for practical engineering (e.g. initial stress/strain, temperature change for external environment and the interaction between the structure and elastic matrix). Then, it is important to establish the proper model and apply the effective analysis method. By using the nonlocal continuum method, this paper reviews the recent progress of dynamical properties of micro structures at nano scales. The discussion is focused on dynamical behaviors of nanotubes, including vibration, wave propagation and fluid-structure interaction, etc. At last, conclusions and prospects in future studies are discussed.
基金supported by the National Natural Science Foundation of China (51406060)the Natural Science Foundation of Hubei Province of China (2014CFA089)+2 种基金the Fundamental Research Funds for the Central Universities (2015ZZGH008)the support from the Fluid Interface Reactions, Structures and Transport (FIRST), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciencesthe National Energy Research Scientific Computing Center, which is supported by the Office of Science of the U.S. Department of Energy under Contract DEAC02-05CH11231
文摘Room temperature ionic liquids(RTILs) with dispersed carbon pieces exhibit distinctive physiochemical properties. To explore the molecular mechanism, RTILs/carbon pieces mixture was investigated by molecular dynamics(MD) simulation in this work. Rigid and flexible carbon pieces in the form of graphene with different thicknesses and carbon nanotubes in different sizes were dispersed in a representative RTIL 1-butyl-3-methyl-imidazolium dicyanamide([Bmim][DCA]). This study demonstrated that the diffusion coefficients of RTILs in the presence of flexible carbons are similar to those of bulk RTILs at varying temperatures, which is in contrast to the decreased diffusion of RTILs in the presence of rigid carbons. In addition, interfacial ion number density at rigid carbon surfaces was higher than that at flexible ones, which is correlated with the accessible external surface area of carbon pieces. The life time of cation-anion pair in the presence of carbon pieces also exhibited a dependence on carbon flexibility. RTILs with dispersed rigid carbon pieces showed longer ion pair life time than those with flexible ones, in consistence with the observation in diffusion coefficients. This work highlights the necessity of including the carbon flexibility when performing MD simulation of RTILs in the presence of dispersed carbon pieces in order to obtain the reliable dynamical and interfacial structural properties.
基金Supported by the National Natural Science Foundation of China under Grant No 11374217
文摘The structural, dielectric, lattice dynamical and thermodynamic properties of zinc-blende CdX （X=S, Se, Te） are studied by using a plane-wave pseudopotential method within the density-functional theory. Our calculated lattice constants and bulk modulus are compared with the pubfished experimental and theoretical data. In addition, the Born effective charges, electronic dielectric tensors, phonon frequencies, and longitudinal opticaltransverse optical splitting are calculated by the linear-response approach. Some of the characteristics of the phonon-dispersion curves for zinc-blende CdX （X= S, Se, Te） are summarized. What is more, based on the lattice dynamical properties, we investigate the thermodynamic properties of CdX （X= S, Se, Te） and analyze the temperature dependences of the Helmholtz free energy F, the internal energy E, the entropy S and the constant-volume specific heat Cv. The results show that the heat capacities for CdTe, CdSe, and CdS approach approximately to the Petit-Dulong limit 6R.
基金funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan Grant No.AP19678033“The study of the transport and optical properties of hydrogen at high pressure.”。
文摘A plasma screening model that accounts for electronic exchange-correlation effects and ionic nonideality in dense quantum plasmas is proposed.This model can be used as an input in various plasma interaction models to calculate scattering cross-sections and transport properties.The applicability of the proposed plasma screening model is demonstrated using the example of the temperature relaxation rate in dense hydrogen and warm dense aluminum.Additionally,the conductivity of warm dense aluminum is computed in the regime where collisions are dominated by electron-ion scattering.The results obtained are compared with available theoretical results and simulation data.
基金the support of the National Natural Science Foundation of China(Grant No.52108319)the Natural Science Foundation of Jiangxi Province(20224BAB214069)。
文摘Red clay,widely used as a subgrade material in southern China,requires a reliable evaluation of its dynamic behavior to ensure infrastructure safety.Long-term cyclic triaxial tests were conducted on red clay from typical,complex subway subgrades to investigate its dynamic properties and shakedown behavior under intermittent cyclic loading.Results show that intermittent cyclic loading,especially with multiple amplitudes,causes greater axial plastic strain and lower post-cyclic strength than continuous loading.These effects diminish with increasing confining pressure.Notably,axial strain partially recovers during loading intervals,with recovery ratios depending on the number and sequence of pauses.Based on the rules of cumulative plastic strain rates and cumulative plastic strain increments,shakedown behavior for red clay under intermittent cyclic loading is divided into three categories:plastic shakedown,critical shakedown,and plastic creep.A quantitative shakedown limit criterion is proposed using the Boltzmann function.Shakedown behavior significantly influences the post-cyclic strengths,and the influence diminishes as confining pressure increases.Samples exhibiting plastic creep and plastic shakedown behavior have the lowest and highest strengths,and those with critical shakedown behaviors have medium strengths.Cyclic loading with relatively low-stress amplitude causes a hardening effect,while cyclic loading intermittence or cyclic loading with relatively high-stress amplitude causes a degradation effect,and both effects are mitigated by higher confining pressures.
基金supported by the National Natural Science Foundation of China(No.21927814)the National Key Research and Development Program of China(Nos.2019YFA0405600,2019YFA0706900,2021YFA1200104,2022YFC3400500)+2 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Nos.XDB0540200,XDB37040201)Plans for Major Provincial Science&Technology Projects(No.202303a07020004)the Youth Innovation Promotion Association,CAS(No.2022455)。
文摘Liquid-liquid phase separation(LLPS)of proteins and nucleic acids is a common phenomenon in cells that underlies the formation of membraneless organelles.Although the macroscopic behavior of biomolecular coacervates has been elucidated by microscopy,the detailed dynamic properties of proteins/peptides during the LLPS process remain poorly characterized.Here,site-directed spin labeling-electron paramagnetic resonance(SDSL-EPR)spectroscopy was employed to characterize the dynamic properties of a minimal model LLPS system consisting of positively charged peptides and RNA.The degree of phase separation,indicated by broadening of the EPR spectrum of the spin-labeled peptide due to slow molecular tumbling,was monitored by EPR.In addition,three distinct populations with varying molecular motion during LLPS,featuring different spectral lineshapes,were identified.These populations included a fast motion component(Ⅰ),a slower motion component(Ⅱ)associated with peptides in the dispersed phase and an immobile component(Ⅲ)observed in the dense phase.With gradual titration of the peptides to RNA,the EPR spectrum gradually shifted,refiecting changes in the populations of the components.Together,SDSL-EPR method not only provides new insights into the dynamic behavior of biomolecules during LLPS,but also offers a sensitive method for biomolecular phase separation processes at the molecular level.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52171311 and 5227127).
文摘Experimental studies were conducted on two high-strength steel plate-frame structures with different truss spacings under various impact velocities to investigate the dynamic mechanical properties of hull plate-frame structures under drop weight impact.The results showed that decreasing the main beam spacing can effectively increase the structural stiffness,reduce the maximum deformation,and increase the damage range.Furthermore,to simulate the impact tests accurately,static and dynamic tensile tests at different strain rates were carried out,and the Cowper-Symonds model parameters were fitted via experimental data.The material properties obtained from the tensile tests were used as inputs for numerical simulations with the numerical results coincide with the experimental results.A systematic analysis and discussion were conducted on the effects of truss spacing and truss width on the dynamic response of the reinforced plates,and an optimal range for the ratio of truss spacing to truss width was proposed.In addition,a mesh size sensitivity analysis for ship hull plate frame collision simulations was performed.The applicability of the EPS,MMC,and RTCL failure criteria in the simulation of plate-frame structures was investigated via finite element simulations of falling weight impact tests.The research findings provide a reference for ship hull structure design and resilience assessment.
基金supported by the National Natural Science Foundation of China(Grant No.12302500)the National Key Research and Development Program of China(Grant No.2020YFA0710503)Postdoctoral Fellowship Program(Grade B)of China Postdoctoral Science Foundation(Grant No.GBZ20230022).
文摘Controllable shock wave fracturing is an innovative engineering technique used for shale reservoir fracturing and reformation.Understanding the anisotropic fracture mechanism of shale under impact loading is vital for optimizing shock wave fracturing equipment and enhancing shale oil production.In this study,using the well-known notched semi-circular bend(NSCB)sample and the novel double-edge notched flattened Brazilian disc(DNFBD)sample combined with a split Hopkinson pressure bar(SHPB),various dynamic anisotropic fracture properties of Lushan shale,including failure characteristics,fracture toughness,energy dissipation and crack propagation velocity,are comprehensively compared and discussed under mode Ⅰ and mode Ⅱ fracture scenarios.First,using a newly modified fracture criterion considering the strength anisotropy of shale,the DNFBD specimen is predicted to be a robust method for true mode Ⅱ fracture of anisotropic shale rocks.Our experimental results show that the dynamic mode Ⅱ fracture of shale induces a rougher and more complex fracture morphology and performs a higher fracture toughness or fracture energy compared to dynamic mode Ⅰ fracture.The minimal fracture toughness or fracture energy occurs in the Short-transverse orientation,while the maximal ones occur in the Divider orientation.In addition,it is interesting to find that the mode Ⅱ fracture toughness anisotropy index decreases more slowly than that in the mode Ⅰ fracture scenario.These results provide significant insights for understanding the different dynamic fracture mechanisms of anisotropic shale rocks under impact loading and have some beneficial implications for the controllable shock wave fracturing technique.
基金Project(2013YQ17046310)supported by the National Key Scientific Instrument and Equipment Development Project of ChinaProject(2013M542138)supported by China Postdoctoral Science FoundationProjects(20130162110010,20130162120012)supported by Specialized Research Fund for the Doctoral Program of Higher Education of China
文摘For understanding the rock microscopic damage and dynamic mechanical properties subjected to recurrent freeze-thaw cycles, experiments for five groups of homogeneous sandstone under different freeze-thaw cycles were conducted. After freezethaw, nuclear magnetic resonance(NMR) tests and impact loading tests were carried out, from which microscopic damage characteristics of sandstone and dynamic mechanical parameters were obtained. The results indicate that the porosity increases with the increase of cycle number, the rate of porosity growth descends at the beginning of freeze-thaw, yet accelerates after a certain number of cycles. The proportion of pores with different sizes changes dynamically and the multi-scale distribution of pores tends to develop on pore structure with the continuing impact of freeze-thaw and thawing. Dynamic compressive stress-strain curve of sandstone undergoing freeze-thaw can be divided into four phases, and the phase of compaction is inconspicuous compared with the static curve. Elastic modulus and dynamic peak intensity of sandstone gradually decrease with freeze-thaw cycles, while peak strain increases. The higher the porosity is, the more serious the degradation of dynamic intensity is. The porosity is of a polynomial relationship with the dynamic peak intensity.
基金Project(51105139)supported by the National Natural Science Foundation of ChinaProject(14JJ5015)supported by the Hunan Provincial Natural Science Foundation of ChinaProject(HPCM-2013-03)supported by the Open Research Fund of Key Laboratory of High Performance Complex Manufacturing,Central South University,China
文摘To analyze the effects of strain rate and temperature on the flow stress of 2519A aluminum alloy, the dynamic mechanical properties of 2519A aluminum alloy were measured by dynamic impact tests and quasi-static tensile tests. The effects of strain rate and temperature on the microstructure evolution were investigated by optical microscopy （OM） and transmission electron microscopy （TEM）. The experimental results indicate that 2519A aluminum alloy exhibits strain-rate dependence and temperature susceptibility under dynamic impact. The constitutive constants for Johnson--Cook material model were determined by the quasi-static tests and Hopkinson bar experiments using the methods of variable separation and nonlinear fitting. The constitutive equation seems to be consistent with the experimental results, which provides reference for mechanical characteristics and numerical simulation of ballistic performance.
文摘This paper reports a new three-dimensional autonomous chaotic system. It contains six control parameters and three nonlinear terms. Two cross-product terms are respectively in two equations. And one square term is in the third equation. Basic dynamic properties of the new system are investigated by means of theoretical analysis, numerical simulation, sensitivity to initial, power spectrum, Lyapunov exponent, and Poincar~ diagrams. The dynamic properties affected by variable parameters are also analysed. Finally, the chaotic system is simulated by circuit. The results verify the existence and implementation of the system.
文摘In this paper, the behavior analysis of two cells chopper connected to a nonlinear load is reported. Thus, this is done in order to highlight the way to chaos. Furthermore, throughout the study of these dynamical behaviors of this complex switched system some basic dynamical properties, such as Poincare section, first return map, bifurcation diagram, power spectrum, and strange attractor are investigated. The system examined in Matlab-Simulink. Analyses of simulation results show that this system has complex dynamics with some interesting characteristics.
基金Project(2012BAC09B02)supported by the 12th Five-Year Key Programs for Science and Technology Development of ChinaProject(2016zzts444)supported by the Financial Support from the Fundament Research Funds for the Central Universities of Central South University,China
文摘To obtain dynamic mechanical properties and failure rule of layered backfill under strain rates from10to80s-1,impactloading test on layered backfill specimens(LBS)was conducted by using split Hopkinson pressure bar system.The results indicatethat positive correlation can be found between dynamic compressive strength and strain rate,as well as between strength increasefactor and strain rate.Dynamic compressive strength of LBS gets higher as the arithmetic average cement-sand ratio increases.Compared with static compressive strength,dynamic compressive strength of LBS is enhanced by11%to163%.In addition,theenergy dissipating rate of LBS lies between that of corresponding single specimens,and it decreases as the average cement contentincreases.Deformation of LBS shows obvious discontinuity,deformation degree of lower strength part of LBS is generally higherthan that of higher strength part.A revised brittle fracture criterion based on the Stenerding-Lehnigk criterion is applied to analyzingthe fracture status of LBS,and the average relevant errors of the3groups between the test results and calculation results are4.80%,3.89%and4.66%,respectively.
基金supported by National Natural Science Foundation of China(Grant No.50875252)Program for New Century Excellent TaIents in University (Grant No.NCET-06-0479)Natural Science Foundation of Jiangsu Proyince (Grant No.BK2008005)
文摘Poly(vinyl alcohol) (PVA)/hydroxyapatite (HA) composite hydrogel specimens were prepared with 15% PVA and 1%,2%, 3%, 4% and 5% HA by repeated freezing-thawing. The tests of static and dynamic mechanical properties were carried out todiscuss the influence of different contents of HA and freezing-thawing cycles on the mechanical properties of PVA/HA compositehydrogel. The results of static mechanical tests showed that the PVA/HA composite hydrogel with 3% HA and ninefreezing-thawing cycles had excellent stress relaxation properties, higher relaxation ratio, lower stress equilibrium value andpresented better properties of creep and recovery. The results of dynamic mechanical test showed that the PVA/HA compositehydrogel with nine freezing-thawing cycles had higher storage modulus and loss modulus, so was the PVA/HA compositehydrogel with 3% HA.
基金This study was supported by Introduce Foreign Advanced Technology Project (2001-1).
文摘Aluminate-based coupling agent was added as a compatibilizer to make the chemical modification of wood powder. The mechanical properties and morphology of wood powder/polypropylene composites were studied. The results showed that the compatibilizer can increase the impact strength of the wood/polypropylene composites, but it has a slightly negative effect on the tensile and flexural strength. For dynamic mechanical properties and Differential Scanning Calorimetry, Aluminate-based coupling agent can slightly increase the storage modulus and loss modulus, and decrease the melt point and the Calorie of Melt. Scanning electron microscopy showed that Aluminate-based coupling agent had a stronger affinity between the wood and polypropylene surfaces. These results suggested that Aluminate-based coupling agent may play a useful role in improving wood powder/polypropylene composites properties.
基金supported by the National Natural Science Foundation of China (Nos.51575289,51705270)the Key Research and Development Project of Shandong Province,China (No.2019GHY112068)the Natural Science Foundation of Shandong Province,China (No.ZR2019PEE028)。
文摘The effect of Gd content ranging from 6.5 wt.%to 8.5 wt.%on microstructure evolution and dynamic mechanical behavior of Mg−xGd−3Y−0.5Zr alloys was investigated by optical microscopy,X-ray diffraction,scanning electron microscopy and split Hopkinson pressure bar.The microstructure of as-cast Mg−xGd−3Y−0.5Zr alloys indicates that the addition of Gd can promote grain refinement in the casting.Due to the rapid cooling rate during solidification,a large amount of non-equilibrium eutectic phase Mg_(24)(Gd,Y)_(5) appears at the grain boundary of as-cast Mg−xGd−3Y−0.5Zr alloys.After solution treatment at 520℃ for 6 h,the Mg_(24)(Gd,Y)_(5) phase dissolves into the matrix,and the rare earth hydrides(REH)phase appears.The stress−strain curves validate that the solution-treated Mg−xGd−3Y−0.5Zr alloys with optimal Gd contents maintain excellent dynamic properties at different strain rates.It was concluded that the variation of Gd content and the agglomeration of residual REH particles and dynamically precipitated fine particles are key factors affecting dynamic mechanical properties of Mg−xGd−3Y−0.5Zr alloys.
