The microstructure formation and grains refinement of two Mg-based alloys,i.e.AZ31 and AZ91D,were reported using an electromagnetic vibration(EMV) technique.These two alloys were solidified at various vibration freque...The microstructure formation and grains refinement of two Mg-based alloys,i.e.AZ31 and AZ91D,were reported using an electromagnetic vibration(EMV) technique.These two alloys were solidified at various vibration frequencies and the microstructures were observed.The average size of grains was quantitatively measured as a function of vibration frequencies. Moreover,the grain size distribution was outlined versus number fraction.A novel model was proposed to account for the microstructure formation and grain refinement when considering the significant difference of the electrical resistivity properties of the solid and the liquid during EMV processing in the semisolid state.The remarkable difference originates uncoupled movement between the mobile solid and the sluggish liquid,which can activate melt flow.The microstructure evolution can be well explained when the fluid flow intensity versus vibration frequency is taken into account.Moreover,the influence of the static magnetic field on texture formation is also considered,which plays an important role at higher vibration frequencies.展开更多
By introducing Oseen's formula to describe the viscous drag force, a more complete motion equation for a charged microparticle levitated in an electrodynamic balance (EDB) has been put forward and solved numerical...By introducing Oseen's formula to describe the viscous drag force, a more complete motion equation for a charged microparticle levitated in an electrodynamic balance (EDB) has been put forward and solved numerically by the classic Runge-Kutta method in this paper. The theoretical results have firstly demonstrated the existence of the particle oscillations and their characteristics, especially of the springpoint oscillation at large amplitude. And through the comparisons of theoretical and experimental trajectories, the adopted motion equation has proved to be able to rigorously describe the particle motion in non-Stokes region-the shape of trajectory and frequency characteristics are fairly consistent and the deviations of amplitude can usually be less than 10%.展开更多
Nanoindentation tests were conducted to investigate the near-surface mechanical properties of the individual components(fiber and matrix) for three-dimensional reinforced carbon/carbon composites(3D C/C).Optical micro...Nanoindentation tests were conducted to investigate the near-surface mechanical properties of the individual components(fiber and matrix) for three-dimensional reinforced carbon/carbon composites(3D C/C).Optical microscope and polarizing light microscope were used to characterize the microstructure of 3D C/C.The microscopy results show that large number of pores and cracks exist at both bundle/matrix interface and pitch carbon matrix.These defects have important effect on the mechanical behavior of 3D C/C.The in situ properties for components of 3D C/C were acquired by nanoindentation technique.Relative to the matrix sample,the fiber samples have more larger values for modulus,stiffness and hardness.However,there is no significant difference of modulus and stiffness among fiber samples with different directions.展开更多
A theoretical model is proposed in order to study the configuration resonance in s-SNOM. The electromagnetic coupling between the sample and the probe tip is described with the quasi-electrostatic field theory. This m...A theoretical model is proposed in order to study the configuration resonance in s-SNOM. The electromagnetic coupling between the sample and the probe tip is described with the quasi-electrostatic field theory. This method permits us to analyze the confignrational resonance evoked by the interaction between the probe tip and the sample in s-SNOM intuitively. The resonant conditions for a certain system are presented in an explicit form. On the condition of considering the actual size of the sample dipoles and the probe dipole, we discuss the possibility of realizing the configurational resonance for various material samples. The numerical results indicate that the polarizability of the dielectric probe tip is too small to arouse this resonance, whereas, with the surface plasmon resonance emerging on the metallic nanoparticles, the enhanced polarizability of the metallic probe tip ensures the requirements of fulfilling the resonance.展开更多
In order to fulfil the microgravity requirements for space experiments, improved technology for the microgravity environment is proposed, including that for raising the orbital altitude, optimizing the layout of the d...In order to fulfil the microgravity requirements for space experiments, improved technology for the microgravity environment is proposed, including that for raising the orbital altitude, optimizing the layout of the disturbance source, using IN-thrusters instead of 5 N-thrusters, etc. In addition, evaluation of the microgravity environment of the recoverable satellite was also conducted using on-orbit micro-vibration measurement, on-orbit experiment and data analysis technologies. The microgravity level of the SJ-l0 recoverable satellite in China is compared with the spacecraft used for carrying out space science experiments internationally. This paper describes the microgravity environment of the SJ- 10 recoverable satellite, and its importance for analysing space experimental results.展开更多
Radiofrequency coil is one of the most important components for a nuclear magnetic resonance(NMR)instrument.In this article,some planar micro coils with an inner diameter of 2 mm and number of turns that varied from 1...Radiofrequency coil is one of the most important components for a nuclear magnetic resonance(NMR)instrument.In this article,some planar micro coils with an inner diameter of 2 mm and number of turns that varied from 1 to 11 were investigated based on the printed circuit board(PCB)technology.The electrical characterization of micro coils show that self-resonant frequencies are larger than 200 MHz.Then,an NMR measurement platform with a static magnetic field of 0.66 T was constructed and the signal to noise ratio(SNR)values of the NMR were analyzed.It was found that the SNR is optimal when the turn number of the micro coils is six and the excitation time of a 90°pulse is 0.8?s.Finally,we used the micro coil with six turns to study the transverse relaxation rate of copper sulfate pentahydrate aqueous solution with different concentrations.It was found that the transverse relaxation rate is proportional to the solution concentration.Results from the micro coil were verified by measurements using a Bruker Minispec MQ60.展开更多
文摘The microstructure formation and grains refinement of two Mg-based alloys,i.e.AZ31 and AZ91D,were reported using an electromagnetic vibration(EMV) technique.These two alloys were solidified at various vibration frequencies and the microstructures were observed.The average size of grains was quantitatively measured as a function of vibration frequencies. Moreover,the grain size distribution was outlined versus number fraction.A novel model was proposed to account for the microstructure formation and grain refinement when considering the significant difference of the electrical resistivity properties of the solid and the liquid during EMV processing in the semisolid state.The remarkable difference originates uncoupled movement between the mobile solid and the sluggish liquid,which can activate melt flow.The microstructure evolution can be well explained when the fluid flow intensity versus vibration frequency is taken into account.Moreover,the influence of the static magnetic field on texture formation is also considered,which plays an important role at higher vibration frequencies.
基金Supported by the National Natural Science Foundation of China (No. 29876022) the Doctoral Foundation of Education Ministry of China (No. 20010610027).
文摘By introducing Oseen's formula to describe the viscous drag force, a more complete motion equation for a charged microparticle levitated in an electrodynamic balance (EDB) has been put forward and solved numerically by the classic Runge-Kutta method in this paper. The theoretical results have firstly demonstrated the existence of the particle oscillations and their characteristics, especially of the springpoint oscillation at large amplitude. And through the comparisons of theoretical and experimental trajectories, the adopted motion equation has proved to be able to rigorously describe the particle motion in non-Stokes region-the shape of trajectory and frequency characteristics are fairly consistent and the deviations of amplitude can usually be less than 10%.
基金Project(61391) supported by the National Security Basic Research Program of ChinaProject (91016029) supported by the National Natural Science Foundation of China
文摘Nanoindentation tests were conducted to investigate the near-surface mechanical properties of the individual components(fiber and matrix) for three-dimensional reinforced carbon/carbon composites(3D C/C).Optical microscope and polarizing light microscope were used to characterize the microstructure of 3D C/C.The microscopy results show that large number of pores and cracks exist at both bundle/matrix interface and pitch carbon matrix.These defects have important effect on the mechanical behavior of 3D C/C.The in situ properties for components of 3D C/C were acquired by nanoindentation technique.Relative to the matrix sample,the fiber samples have more larger values for modulus,stiffness and hardness.However,there is no significant difference of modulus and stiffness among fiber samples with different directions.
基金This work was supported by the National Natural Science Founda-tion of China under grants No. 30170276.
文摘A theoretical model is proposed in order to study the configuration resonance in s-SNOM. The electromagnetic coupling between the sample and the probe tip is described with the quasi-electrostatic field theory. This method permits us to analyze the confignrational resonance evoked by the interaction between the probe tip and the sample in s-SNOM intuitively. The resonant conditions for a certain system are presented in an explicit form. On the condition of considering the actual size of the sample dipoles and the probe dipole, we discuss the possibility of realizing the configurational resonance for various material samples. The numerical results indicate that the polarizability of the dielectric probe tip is too small to arouse this resonance, whereas, with the surface plasmon resonance emerging on the metallic nanoparticles, the enhanced polarizability of the metallic probe tip ensures the requirements of fulfilling the resonance.
文摘In order to fulfil the microgravity requirements for space experiments, improved technology for the microgravity environment is proposed, including that for raising the orbital altitude, optimizing the layout of the disturbance source, using IN-thrusters instead of 5 N-thrusters, etc. In addition, evaluation of the microgravity environment of the recoverable satellite was also conducted using on-orbit micro-vibration measurement, on-orbit experiment and data analysis technologies. The microgravity level of the SJ-l0 recoverable satellite in China is compared with the spacecraft used for carrying out space science experiments internationally. This paper describes the microgravity environment of the SJ- 10 recoverable satellite, and its importance for analysing space experimental results.
基金supported by the National Natural Science Foundation of China(Grant No.51175083)the Jiangsu Province University Industry Cooperation Innovation Foundation-Prospective Study of China(Grant No.BY 2011135)
文摘Radiofrequency coil is one of the most important components for a nuclear magnetic resonance(NMR)instrument.In this article,some planar micro coils with an inner diameter of 2 mm and number of turns that varied from 1 to 11 were investigated based on the printed circuit board(PCB)technology.The electrical characterization of micro coils show that self-resonant frequencies are larger than 200 MHz.Then,an NMR measurement platform with a static magnetic field of 0.66 T was constructed and the signal to noise ratio(SNR)values of the NMR were analyzed.It was found that the SNR is optimal when the turn number of the micro coils is six and the excitation time of a 90°pulse is 0.8?s.Finally,we used the micro coil with six turns to study the transverse relaxation rate of copper sulfate pentahydrate aqueous solution with different concentrations.It was found that the transverse relaxation rate is proportional to the solution concentration.Results from the micro coil were verified by measurements using a Bruker Minispec MQ60.
