In this paper a novel log-domain current-mode integrator based on MOS transistors in subthreshold is proposed. The integrator's time-constant is tunable by varying a reference bias current. By use of the integrato...In this paper a novel log-domain current-mode integrator based on MOS transistors in subthreshold is proposed. The integrator's time-constant is tunable by varying a reference bias current. By use of the integrator, a fifth-order Chebyshev lowpass filter with 0.1dB ripples is designed. The simulation results demonstrate that the proposed filter has such advantages as low power supply(1.5V), very low power dissipation (μW level), nearly ideal frequency response, very small sensitivity to components in passband, and adjustable cut-off frequency over a wide range.The circuit is composed of NMOS transistors and grounded capacitors which make it suitable for fully integrated circuit implementation.展开更多
The relation between domain wall motion and intensity of driven current is examined in a phenomenological theory where the kinetic energy is expanded as a series of polynomial function of current density just as the L...The relation between domain wall motion and intensity of driven current is examined in a phenomenological theory where the kinetic energy is expanded as a series of polynomial function of current density just as the Landau phase transition theory. The dependency of velocity on current density is square root which degenerates into linear if the current is much higher than the critical value. The theory result is consistent with several previous experiments and also can explain the change of critical current in the presence of temperature. The role of temperature playing in the dynamics of domain wall motion is also discussed. The phase transition theory in terms of current density is employed to explain the critical behavior of domain wall motion.展开更多
探讨了不同极化方式下Pb(Mg_(1/3)Nb_(2/3))O_(3)–0.3Pb Ti O_(3)(PMN-0.3PT)单晶的压电性能的变化。实验结果表明,相比于直流电极化,交流电极化后PMN-0.3PT单晶的压电系数d33从1421 pC/N提升至1857 pC/N,相对介电系数εr从4800提升至6...探讨了不同极化方式下Pb(Mg_(1/3)Nb_(2/3))O_(3)–0.3Pb Ti O_(3)(PMN-0.3PT)单晶的压电性能的变化。实验结果表明,相比于直流电极化,交流电极化后PMN-0.3PT单晶的压电系数d33从1421 pC/N提升至1857 pC/N,相对介电系数εr从4800提升至6650,压电系数与相对介电系数分别提升了30.7%和38.5%。为探究交流电优化机理,采用了实验和模拟相结合的方法,从极化畴结构演化的角度给出了解释。用压电力显微镜对PMN-0.3PT的畴结构进行了扫描,并利用相场模型对PMN-0.3PT的畴结构演化进行了表征,实验和模拟结果展现出相同的演化趋势;同时建立了相应的晶格演化模型进行解释。对于未极化的PMN-0.3PT单晶,畴结构呈现随机分布的状态;经过直流电极化后,电畴沿偏向电场的方向翻转,畴结构形貌呈现树枝状;在交流电极化后,PMN-0.3PT内部只存在两个不同极化方向,畴结构形貌呈现条带状。数值计算的结果表明,随着极化方式由无极化到直流极化再到交流极化,PMN-0.3PT的畴壁能从727.578变化到160.060再到57.910,伴随着畴壁能的减小,畴壁密度逐渐降低,这是导致压电性能提升的主要原因。该研究成果对深入理解弛豫铁电材料电畴结构与压电性能的内在联系及作用机理有非常重要的意义,并为优化铁电材料的压电性能给出了可行方案。展开更多
In a magnetic nanostripe, the effects of perpendicular magnetic anisotropy（PMA） on the current-driven horizontal motion of vortex wall along the stripe and the vertical motion of the vortex core are studied by micro...In a magnetic nanostripe, the effects of perpendicular magnetic anisotropy（PMA） on the current-driven horizontal motion of vortex wall along the stripe and the vertical motion of the vortex core are studied by micromagnetic simulations.The results show that the horizontal and vertical motion can generally be monotonously enhanced by PMA. However, when the current is small, a nonmonotonic phenomenon for the horizontal motion is found. Namely, the velocity of the horizontal motion firstly decreases and then increases with the increase of the PMA. We find that the reason for this is that the PMA can firstly increase and then decrease the confining force induced by the confining potential energy. In addition, the PMA always enhances the driving force induced by the current.展开更多
Eddy-current inverse technique is a very important method to reconstruct the shape of flaws or cracks. Using the domain derivative of the far-field pattern for eddy- current inverse problem with Dirichlet boundary con...Eddy-current inverse technique is a very important method to reconstruct the shape of flaws or cracks. Using the domain derivative of the far-field pattern for eddy- current inverse problem with Dirichlet boundary condition, a new algorithm to recover the shape of cracks was constructed and some numerical examples were given. The algorithm demonstrates that the algorithm is feasible and correct for obtaining a reasonable reconstruction of a shape of flaws or cracks from the far-field measurements even though using less data of directions of incidence and observations for fewer wave numbers are gived.展开更多
The wave-current forces on vertical piles in side-by-side arrangement induced by irregular waves with opposing current are investigated experimentally in this paper. The characteristics in both time and frequency doma...The wave-current forces on vertical piles in side-by-side arrangement induced by irregular waves with opposing current are investigated experimentally in this paper. The characteristics in both time and frequency domain of in-line, lift and resultant forces are analyzed. The grouping effect coefficients of inline, lift and resultant forces on piles related to KC number and relative spacing parameters are given. These results are compared with those in the case of irregular waves combined with following currents. It is found that the results in these two cases are quite different. The range of KC number tested is 10approx.60, the range of Reynolds number is (0.55approx.3.43) × 104.展开更多
A dynamic response analysis in the frequency domain is presented for risers subjected to combined wave and current loading. Considering the effects of current, a modified wave spectrum is adopted to compute the linear...A dynamic response analysis in the frequency domain is presented for risers subjected to combined wave and current loading. Considering the effects of current, a modified wave spectrum is adopted to compute the linearized drag force. An additional drag force convolution term is added to the linearized drag force spectrum, therefore the error is reduced which arises from the truncation of higher order terms in the drag force auto-correlation function. An expression of linearized drag force spectrum is given taking the relative velocity into account. It is found that the additional term is a fold convolution integral. In this paper dynamic responses of risers are investigated, while the influence of floater motion on risers is considered. The results demonstrate that the accuracy of the present method reaches the degree required in time domain analysis.展开更多
文摘In this paper a novel log-domain current-mode integrator based on MOS transistors in subthreshold is proposed. The integrator's time-constant is tunable by varying a reference bias current. By use of the integrator, a fifth-order Chebyshev lowpass filter with 0.1dB ripples is designed. The simulation results demonstrate that the proposed filter has such advantages as low power supply(1.5V), very low power dissipation (μW level), nearly ideal frequency response, very small sensitivity to components in passband, and adjustable cut-off frequency over a wide range.The circuit is composed of NMOS transistors and grounded capacitors which make it suitable for fully integrated circuit implementation.
文摘The relation between domain wall motion and intensity of driven current is examined in a phenomenological theory where the kinetic energy is expanded as a series of polynomial function of current density just as the Landau phase transition theory. The dependency of velocity on current density is square root which degenerates into linear if the current is much higher than the critical value. The theory result is consistent with several previous experiments and also can explain the change of critical current in the presence of temperature. The role of temperature playing in the dynamics of domain wall motion is also discussed. The phase transition theory in terms of current density is employed to explain the critical behavior of domain wall motion.
文摘探讨了不同极化方式下Pb(Mg_(1/3)Nb_(2/3))O_(3)–0.3Pb Ti O_(3)(PMN-0.3PT)单晶的压电性能的变化。实验结果表明,相比于直流电极化,交流电极化后PMN-0.3PT单晶的压电系数d33从1421 pC/N提升至1857 pC/N,相对介电系数εr从4800提升至6650,压电系数与相对介电系数分别提升了30.7%和38.5%。为探究交流电优化机理,采用了实验和模拟相结合的方法,从极化畴结构演化的角度给出了解释。用压电力显微镜对PMN-0.3PT的畴结构进行了扫描,并利用相场模型对PMN-0.3PT的畴结构演化进行了表征,实验和模拟结果展现出相同的演化趋势;同时建立了相应的晶格演化模型进行解释。对于未极化的PMN-0.3PT单晶,畴结构呈现随机分布的状态;经过直流电极化后,电畴沿偏向电场的方向翻转,畴结构形貌呈现树枝状;在交流电极化后,PMN-0.3PT内部只存在两个不同极化方向,畴结构形貌呈现条带状。数值计算的结果表明,随着极化方式由无极化到直流极化再到交流极化,PMN-0.3PT的畴壁能从727.578变化到160.060再到57.910,伴随着畴壁能的减小,畴壁密度逐渐降低,这是导致压电性能提升的主要原因。该研究成果对深入理解弛豫铁电材料电畴结构与压电性能的内在联系及作用机理有非常重要的意义,并为优化铁电材料的压电性能给出了可行方案。
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11247026 and 11374253)
文摘In a magnetic nanostripe, the effects of perpendicular magnetic anisotropy（PMA） on the current-driven horizontal motion of vortex wall along the stripe and the vertical motion of the vortex core are studied by micromagnetic simulations.The results show that the horizontal and vertical motion can generally be monotonously enhanced by PMA. However, when the current is small, a nonmonotonic phenomenon for the horizontal motion is found. Namely, the velocity of the horizontal motion firstly decreases and then increases with the increase of the PMA. We find that the reason for this is that the PMA can firstly increase and then decrease the confining force induced by the confining potential energy. In addition, the PMA always enhances the driving force induced by the current.
文摘Eddy-current inverse technique is a very important method to reconstruct the shape of flaws or cracks. Using the domain derivative of the far-field pattern for eddy- current inverse problem with Dirichlet boundary condition, a new algorithm to recover the shape of cracks was constructed and some numerical examples were given. The algorithm demonstrates that the algorithm is feasible and correct for obtaining a reasonable reconstruction of a shape of flaws or cracks from the far-field measurements even though using less data of directions of incidence and observations for fewer wave numbers are gived.
文摘The wave-current forces on vertical piles in side-by-side arrangement induced by irregular waves with opposing current are investigated experimentally in this paper. The characteristics in both time and frequency domain of in-line, lift and resultant forces are analyzed. The grouping effect coefficients of inline, lift and resultant forces on piles related to KC number and relative spacing parameters are given. These results are compared with those in the case of irregular waves combined with following currents. It is found that the results in these two cases are quite different. The range of KC number tested is 10approx.60, the range of Reynolds number is (0.55approx.3.43) × 104.
文摘A dynamic response analysis in the frequency domain is presented for risers subjected to combined wave and current loading. Considering the effects of current, a modified wave spectrum is adopted to compute the linearized drag force. An additional drag force convolution term is added to the linearized drag force spectrum, therefore the error is reduced which arises from the truncation of higher order terms in the drag force auto-correlation function. An expression of linearized drag force spectrum is given taking the relative velocity into account. It is found that the additional term is a fold convolution integral. In this paper dynamic responses of risers are investigated, while the influence of floater motion on risers is considered. The results demonstrate that the accuracy of the present method reaches the degree required in time domain analysis.
