Simulating semi-solid metal forming requires modelling semi-solid behaviour.However, such modelling is difficult because semi-solid behavior is thixotropic and depends on the liquid-solid spatial distribution within t...Simulating semi-solid metal forming requires modelling semi-solid behaviour.However, such modelling is difficult because semi-solid behavior is thixotropic and depends on the liquid-solid spatial distribution within the material.In order to better understand and model relationships between microstructure and behavior, a model based on micromechanical approaches and homogenisation techniques is presented.This model is an extension of a previous model established in a pure viscoplastic framework to account for elasticity.Indeed, experimental load-displacement signals reveal the presence of an elastic-type response in the earlier stages of deformation when semi-solids are loaded under rapid compression.This elastic feature of the behaviour is attributed to the response of the porous solid skeleton saturated by incompressible liquid.A good quantitative agreement is found between the elastic-viscoplastic predicted response and the experimental data.More precisely, the strong initial rising part of the load-displacement curve, the peak load and the subsequent fall in load are well captured.The effect of solid fraction on mechanical response is in qualitative agreement with experiments.展开更多
The speed of frequency response of all published carbon nanotube （CNT） integrated circuits （ICs） is far from that predicted. The transient response of CNT ICs is explored systematically through the combination of ...The speed of frequency response of all published carbon nanotube （CNT） integrated circuits （ICs） is far from that predicted. The transient response of CNT ICs is explored systematically through the combination of experimental and simulation methods. Complementary field-effect-transistor （FET） based inverters were fabricated on a single semiconducting CNT, and the dynamic response measurement indicates that it can only work at an unexpectedly low speed, i.e. with a large propagation delay of 30 }_ts. Owing to the larger output resistance of CNT FETs, the existence of parasitic capacitances should induce much larger resistive-capacitive （RC） delay than that in Si ICs. Through detailed analysis combining simulation and experimental measurements, several kinds of parasitic capacitances dragging down the actual speed of CNT FET ICs are identified one by one, and each of them limits the speed at different levels through RC delay. It is found that the parasitic capacitance from the measurement system is the dominant one, and the large RC delay lowers the speed of CNT FETs logic circuits to only several kHz which is similar to the experimental results. Various optimized schemes are suggested and demonstrated to minimize the effect of parasitic capacitances, and thus improve the speed of CNT ICs.展开更多
In this paper, we describe the basic principles and system design of continuous wave cavity ring-down spectroscopy （CWCRDS）. We also particularly study the nature and the behavior of a novel method to detune a laser...In this paper, we describe the basic principles and system design of continuous wave cavity ring-down spectroscopy （CWCRDS）. We also particularly study the nature and the behavior of a novel method to detune a laser and apply it to a cavity ring-down spectroscopy experiment. Both simulations and experiments are completed on the relation between the transmission characteristic and different refiectivities, as well as scanning speed. Output electric field equation is deduced. It has been investigated that how photons are coupled to the cavity and how to accumulate the intensity and leak out of the cavity as a function of time. It is noted that both accumulation of intensity and decay times decrease, and the oscillation amplitude increases as the reflectivity increases. Relative intensity increases with decreasing scanning velocity. Additionally, the simulations show that a non-detuned cavity displays the transmitted signals which are highly dependent on the mirror reflectivity and piezoelectric translator （PZT） modulation speed. Simulations also display that the laser switching off is different from dettming.展开更多
文摘Simulating semi-solid metal forming requires modelling semi-solid behaviour.However, such modelling is difficult because semi-solid behavior is thixotropic and depends on the liquid-solid spatial distribution within the material.In order to better understand and model relationships between microstructure and behavior, a model based on micromechanical approaches and homogenisation techniques is presented.This model is an extension of a previous model established in a pure viscoplastic framework to account for elasticity.Indeed, experimental load-displacement signals reveal the presence of an elastic-type response in the earlier stages of deformation when semi-solids are loaded under rapid compression.This elastic feature of the behaviour is attributed to the response of the porous solid skeleton saturated by incompressible liquid.A good quantitative agreement is found between the elastic-viscoplastic predicted response and the experimental data.More precisely, the strong initial rising part of the load-displacement curve, the peak load and the subsequent fall in load are well captured.The effect of solid fraction on mechanical response is in qualitative agreement with experiments.
基金This work was supported by the National Basic Research Program of China （Nos. 2011CB933001 and 2011CB933002）, the National Natural Science Foundation of China （Nos. 61322105, 61271051, 61376126, 61321001 and 61390504）, and the Beijing Municipal Science and Technology Commission （Nos. Z131100003213021 and 20121000102）.
文摘The speed of frequency response of all published carbon nanotube （CNT） integrated circuits （ICs） is far from that predicted. The transient response of CNT ICs is explored systematically through the combination of experimental and simulation methods. Complementary field-effect-transistor （FET） based inverters were fabricated on a single semiconducting CNT, and the dynamic response measurement indicates that it can only work at an unexpectedly low speed, i.e. with a large propagation delay of 30 }_ts. Owing to the larger output resistance of CNT FETs, the existence of parasitic capacitances should induce much larger resistive-capacitive （RC） delay than that in Si ICs. Through detailed analysis combining simulation and experimental measurements, several kinds of parasitic capacitances dragging down the actual speed of CNT FET ICs are identified one by one, and each of them limits the speed at different levels through RC delay. It is found that the parasitic capacitance from the measurement system is the dominant one, and the large RC delay lowers the speed of CNT FETs logic circuits to only several kHz which is similar to the experimental results. Various optimized schemes are suggested and demonstrated to minimize the effect of parasitic capacitances, and thus improve the speed of CNT ICs.
基金supported by the National Natural Science Foundation of China (No.60877047)the Natural Science Foundation of Hebei Province (No.F2008000873)the Research Fund for the Doctoral Program of Higher Education (No.20070216004)
文摘In this paper, we describe the basic principles and system design of continuous wave cavity ring-down spectroscopy （CWCRDS）. We also particularly study the nature and the behavior of a novel method to detune a laser and apply it to a cavity ring-down spectroscopy experiment. Both simulations and experiments are completed on the relation between the transmission characteristic and different refiectivities, as well as scanning speed. Output electric field equation is deduced. It has been investigated that how photons are coupled to the cavity and how to accumulate the intensity and leak out of the cavity as a function of time. It is noted that both accumulation of intensity and decay times decrease, and the oscillation amplitude increases as the reflectivity increases. Relative intensity increases with decreasing scanning velocity. Additionally, the simulations show that a non-detuned cavity displays the transmitted signals which are highly dependent on the mirror reflectivity and piezoelectric translator （PZT） modulation speed. Simulations also display that the laser switching off is different from dettming.
