The effects of strain rate on microstructure and formability of AZ31B magnesium alloy sheets were investigated through uniaxial tensile tests and hemispherical punch tests with strain rates of 10^-4, 10^-3, 10^-2, 10^...The effects of strain rate on microstructure and formability of AZ31B magnesium alloy sheets were investigated through uniaxial tensile tests and hemispherical punch tests with strain rates of 10^-4, 10^-3, 10^-2, 10^-1 s^-1 at 200℃. The results show that the volume fraction of dynamic recrystallization grains increases and the original grains are gradually replaced by recrystallization grains with the strain rate decreasing. A larger elongation and a smaller r-value are obtained at a lower strain rate, moreover the erichsen values become larger with the strain rate reducing, so the formability improves. This problem arises in part from the enhanced softening and the coordination of recrystallization grains during deformation.展开更多
The glass forming ability, thermal and mechanical properties of some Zr Cu Al Ni bulk metallic glasses were analyzed. The compositions of the alloys were theoretically determined with the dense packing and kinetic fra...The glass forming ability, thermal and mechanical properties of some Zr Cu Al Ni bulk metallic glasses were analyzed. The compositions of the alloys were theoretically determined with the dense packing and kinetic fragility index models. Cylindrical and conical ingots were produced by copper mould suction-casting under Ar atmosphere. The conical ingots were characterized by means of X-ray diffraction in order to determine the glassy structure. It was found that both alloys have a critical glassy diameter, Dc, of 3 mm. Thermal behaviours were investigated by differential scanning calorimetry at heating rates of 0.5, 0.67 and 0.83 K/s. The gamma parameter γ, supercooled liquid region ΔTx, and reduced glass transition temperature Trg, of the experimentally obtained glasses indicated high glass forming ability. The glassy compositions showed a fragility index of ~40 GPa. The compression test of the investigated alloys was carried out at a strain rate of 0.016 s^-1, obtaining a elastic modulus of ~83 GPa, total deformation of ~5%, yield strength of 1.6 GPa and hardness of 4 GPa. It was concluded that the use of the dense packing and kinetic fragility index models helped to predict glass-forming compositions in the family alloy investigated.展开更多
The development status of the variable speed system of large power AC(alternating current)motor drive in China is introduced.The large power AC drive fed by AC-AC converters(cycloconverters)has developed greatly,and s...The development status of the variable speed system of large power AC(alternating current)motor drive in China is introduced.The large power AC drive fed by AC-AC converters(cycloconverters)has developed greatly,and some innovations on the theory and engineering technique have been realized.They have been applied to rolling mills,mine hoists,and so on,and remarkable economic and social benefit has been achieved.The development of AC drive fed by large power IGCT(integrated gate commutated thyristors)AC-DC-AC converter is also introduced.It has excellent performance and reliable operation,and has been used in traction.展开更多
Monolithic integration of resonant tunneling diodes (RTDs) and high electron mobility transistors (HEMTs) is an important development direction of ultra-high speed integrated circuit. A kind of top-RTD and bottom-HEMT...Monolithic integration of resonant tunneling diodes (RTDs) and high electron mobility transistors (HEMTs) is an important development direction of ultra-high speed integrated circuit. A kind of top-RTD and bottom-HEMT material structure is epitaxied on InP substrate through molecular beam epitaxy. Based on wet chemical etching, metal lift-off and air bridge interconnection technology, RTD and HEMT are fabricated simultaneously. The peak-to-valley current ratio of RTD is 7.7 and the peak voltage is 0.33 V at room temperature. The pinch-off voltage is -0.5 V and the current gain cut-frequency is 30 GHz for a 1.0 μm gate length depletion mode HEMT. The two devices are conformable in current magnitude, which is suitable for the construction of various RTD/HEMT monolithic integration logic circuits.展开更多
A Monolithic integrated phase locked-loop （PLL） with a low phase noise is proposed in this paper. Several techniques are utilized to improve the performance of the PLL which works at the milli- meter-wave band. The ...A Monolithic integrated phase locked-loop （PLL） with a low phase noise is proposed in this paper. Several techniques are utilized to improve the performance of the PLL which works at the milli- meter-wave band. The on-chip high-Q eoplanar waveguides （CPWs） are utilized in the resonant tank and the differential current amplifier with a resonator is used to realize the VCO. In the output buffer circuit, several stages of cascaded source-followers connect and differential amplifiers are adopted to improve the driving capability of the PLL＇ s output signals. An improved analog multiplier topology is also used in the PD circuit to improve the gain of the PD. The proposed PLL is realized with a 0.2p, m GaAs pseudomorphie high electron mobility transistor （PHEMT） process. At 10 kHz offset from the center frequency, the measured output phase noise of the PLL output is only -88.83dBc/Hz. The circuit exhibits a low root mean sauare （RMS） litter of 1.68Ds.展开更多
Previous reports about the growth of large graphene single crystals on polycrystalline metal substrates usually adopted the strategy of suppressing the nucleation by lowering the concentration of the feedstock, which ...Previous reports about the growth of large graphene single crystals on polycrystalline metal substrates usually adopted the strategy of suppressing the nucleation by lowering the concentration of the feedstock, which greatly limited the rate of the nucleation and the sequent growth. The emerging liquid metal catalyst possesses the characteristic of quasi-atomically smooth surface with high diffusion rate. In principle, it should be a naturally ideal platform for the lowdensity nucleation and the fast growth of graphene. However,the rapid growth of large graphene single crystals on liquid metals has not received the due attention. In this paper, we firstly purposed the insight into the rapid growth of large graphene single crystals on liquid metals. We obtained the millimeter-size graphene single crystals on liquid Cu. The rich free-electrons in liquid Cu accelerate the nucleation, and the isotropic smooth surface greatly suppresses the nucleation.Moreover, the fast mass-transfer of carbon atoms due to the excellent fluidity of liquid Cu promotes the fast growth with a rate up to 79 μm s^-1. We hope the research on the growth speed of graphene on liquid Cu can enrich the recognition of the growth behavior of two-dimensional(2 D) materials on the liquid metal. We also believe that the liquid metal strategy for the rapid growth of graphene can be extended to various 2 D materials and thus promote their future applications in the photonics and electronics.展开更多
The crystallization behavior of polyethylene (PE) and polypropylene (PP), including the neat ones and the ones nucleated with the same nucleating agent (NA), was studied by DSC. It was found that the nucleating agent ...The crystallization behavior of polyethylene (PE) and polypropylene (PP), including the neat ones and the ones nucleated with the same nucleating agent (NA), was studied by DSC. It was found that the nucleating agent decelerated the PE nonisothermal crystallization process. NA did enhance the nucleating rates for both PE and PP, but the linear growth rate dominated the volumetric growth rate for PE, and the volumetric growth rate dominated the overall crystallization rate. That is why PE nucleated with NA had a slower overall crystallization rate than the neat one.展开更多
We present an analytical analysis of the spatial resolution of quantum ghost imaging implemented by entangled photons from a general, spontaneously parametric, down-conversion process. We find that the resolution is a...We present an analytical analysis of the spatial resolution of quantum ghost imaging implemented by entangled photons from a general, spontaneously parametric, down-conversion process. We find that the resolution is affected by both the pump beam waist and the nonlinear crystal length. Hence, we determined a method to improve the resolution for a certain imaging setup. It should be noted that the resolution is not uniquely related to the degree of entanglement of the photon pair since the resolution can be optimized for a certain degree of entanglement. For certain types of Einstein-Podolsky-Rosen(EPR) states——namely the momentum-correlated or momentum-positively correlated states——the resolution exhibits a simpler relationship with the pump beam waist and crystal length. Further, a vivid numerical simulation of ghost imaging is presented for different types of EPR states,which supports our analysis. This work discusses applicable references to the applications of quantum ghost imaging.展开更多
基金Project(CSTC2010AA4035) supported by Scientific and Technological Project of Chongqing Science and Technology Commission, ChinaProject(CDJZR11130008) supported by the Fundamental Research Funds for the Central Universities,ChinaProject (2008DFR50040) supported by the Ministry of Science and Technology of China
文摘The effects of strain rate on microstructure and formability of AZ31B magnesium alloy sheets were investigated through uniaxial tensile tests and hemispherical punch tests with strain rates of 10^-4, 10^-3, 10^-2, 10^-1 s^-1 at 200℃. The results show that the volume fraction of dynamic recrystallization grains increases and the original grains are gradually replaced by recrystallization grains with the strain rate decreasing. A larger elongation and a smaller r-value are obtained at a lower strain rate, moreover the erichsen values become larger with the strain rate reducing, so the formability improves. This problem arises in part from the enhanced softening and the coordination of recrystallization grains during deformation.
基金the financial support from UNAM-DGAPA-PAPIIT thorough the project 101016CONACYT for the 232312 Ph D scholarship grant
文摘The glass forming ability, thermal and mechanical properties of some Zr Cu Al Ni bulk metallic glasses were analyzed. The compositions of the alloys were theoretically determined with the dense packing and kinetic fragility index models. Cylindrical and conical ingots were produced by copper mould suction-casting under Ar atmosphere. The conical ingots were characterized by means of X-ray diffraction in order to determine the glassy structure. It was found that both alloys have a critical glassy diameter, Dc, of 3 mm. Thermal behaviours were investigated by differential scanning calorimetry at heating rates of 0.5, 0.67 and 0.83 K/s. The gamma parameter γ, supercooled liquid region ΔTx, and reduced glass transition temperature Trg, of the experimentally obtained glasses indicated high glass forming ability. The glassy compositions showed a fragility index of ~40 GPa. The compression test of the investigated alloys was carried out at a strain rate of 0.016 s^-1, obtaining a elastic modulus of ~83 GPa, total deformation of ~5%, yield strength of 1.6 GPa and hardness of 4 GPa. It was concluded that the use of the dense packing and kinetic fragility index models helped to predict glass-forming compositions in the family alloy investigated.
文摘The development status of the variable speed system of large power AC(alternating current)motor drive in China is introduced.The large power AC drive fed by AC-AC converters(cycloconverters)has developed greatly,and some innovations on the theory and engineering technique have been realized.They have been applied to rolling mills,mine hoists,and so on,and remarkable economic and social benefit has been achieved.The development of AC drive fed by large power IGCT(integrated gate commutated thyristors)AC-DC-AC converter is also introduced.It has excellent performance and reliable operation,and has been used in traction.
基金Supported by National Natural Science Foundation of China (No. 60876009)Tianjin Research Program of Application Foundation and Advanced Technology (No. 09JCZDJC16600)
文摘Monolithic integration of resonant tunneling diodes (RTDs) and high electron mobility transistors (HEMTs) is an important development direction of ultra-high speed integrated circuit. A kind of top-RTD and bottom-HEMT material structure is epitaxied on InP substrate through molecular beam epitaxy. Based on wet chemical etching, metal lift-off and air bridge interconnection technology, RTD and HEMT are fabricated simultaneously. The peak-to-valley current ratio of RTD is 7.7 and the peak voltage is 0.33 V at room temperature. The pinch-off voltage is -0.5 V and the current gain cut-frequency is 30 GHz for a 1.0 μm gate length depletion mode HEMT. The two devices are conformable in current magnitude, which is suitable for the construction of various RTD/HEMT monolithic integration logic circuits.
基金Supported by the National Natural Science Foundation of China （No. 61106024, 60901012, 60976029） , the National High Technology Research and Development Program of China （No. 2011AA010301 ）, and the Science and Technology Program of Southeast University （No. K J2010402 ）.
文摘A Monolithic integrated phase locked-loop （PLL） with a low phase noise is proposed in this paper. Several techniques are utilized to improve the performance of the PLL which works at the milli- meter-wave band. The on-chip high-Q eoplanar waveguides （CPWs） are utilized in the resonant tank and the differential current amplifier with a resonator is used to realize the VCO. In the output buffer circuit, several stages of cascaded source-followers connect and differential amplifiers are adopted to improve the driving capability of the PLL＇ s output signals. An improved analog multiplier topology is also used in the PD circuit to improve the gain of the PD. The proposed PLL is realized with a 0.2p, m GaAs pseudomorphie high electron mobility transistor （PHEMT） process. At 10 kHz offset from the center frequency, the measured output phase noise of the PLL output is only -88.83dBc/Hz. The circuit exhibits a low root mean sauare （RMS） litter of 1.68Ds.
基金supported by the National Natural Science Foundation of China(21673161)the Sino-German Center for Research Promotion(1400)
文摘Previous reports about the growth of large graphene single crystals on polycrystalline metal substrates usually adopted the strategy of suppressing the nucleation by lowering the concentration of the feedstock, which greatly limited the rate of the nucleation and the sequent growth. The emerging liquid metal catalyst possesses the characteristic of quasi-atomically smooth surface with high diffusion rate. In principle, it should be a naturally ideal platform for the lowdensity nucleation and the fast growth of graphene. However,the rapid growth of large graphene single crystals on liquid metals has not received the due attention. In this paper, we firstly purposed the insight into the rapid growth of large graphene single crystals on liquid metals. We obtained the millimeter-size graphene single crystals on liquid Cu. The rich free-electrons in liquid Cu accelerate the nucleation, and the isotropic smooth surface greatly suppresses the nucleation.Moreover, the fast mass-transfer of carbon atoms due to the excellent fluidity of liquid Cu promotes the fast growth with a rate up to 79 μm s^-1. We hope the research on the growth speed of graphene on liquid Cu can enrich the recognition of the growth behavior of two-dimensional(2 D) materials on the liquid metal. We also believe that the liquid metal strategy for the rapid growth of graphene can be extended to various 2 D materials and thus promote their future applications in the photonics and electronics.
基金finically supported by the National Basic Research Program of China (973 Project, 2005CB623800)
文摘The crystallization behavior of polyethylene (PE) and polypropylene (PP), including the neat ones and the ones nucleated with the same nucleating agent (NA), was studied by DSC. It was found that the nucleating agent decelerated the PE nonisothermal crystallization process. NA did enhance the nucleating rates for both PE and PP, but the linear growth rate dominated the volumetric growth rate for PE, and the volumetric growth rate dominated the overall crystallization rate. That is why PE nucleated with NA had a slower overall crystallization rate than the neat one.
基金supported by the National Natural Science Foundation of China(Grant Nos.11174121,11321063,91121001,and 91321312)the National Program on Key Basic Research Project(Grant No.2012CB921802)
文摘We present an analytical analysis of the spatial resolution of quantum ghost imaging implemented by entangled photons from a general, spontaneously parametric, down-conversion process. We find that the resolution is affected by both the pump beam waist and the nonlinear crystal length. Hence, we determined a method to improve the resolution for a certain imaging setup. It should be noted that the resolution is not uniquely related to the degree of entanglement of the photon pair since the resolution can be optimized for a certain degree of entanglement. For certain types of Einstein-Podolsky-Rosen(EPR) states——namely the momentum-correlated or momentum-positively correlated states——the resolution exhibits a simpler relationship with the pump beam waist and crystal length. Further, a vivid numerical simulation of ghost imaging is presented for different types of EPR states,which supports our analysis. This work discusses applicable references to the applications of quantum ghost imaging.
