A new polycrystal model was presented from the viewpoint of polycrystal structure of the billets considering free surface effects.In the model,the billet was divided into three portions,such as free surface portion,tr...A new polycrystal model was presented from the viewpoint of polycrystal structure of the billets considering free surface effects.In the model,the billet was divided into three portions,such as free surface portion,transition portion and internal portion.The grains in free surface portion were considered the single grains,and the anisotropy of the grains was taken into account by introducing grain orientation to explain the inhomogeneous deformation.In the transition portion,the effects of the neighbouring grains were adopted in the model.The grains in the internal portion were considered the polycrystalline material.With the developed model,the upsetting deformation process was simulated by the MSC Superform software.The scatter of the flow stress and inhomogeneous deformation was observed by analysis of the model.The comparisons show that the computational results are good agreed with the experimental results.This means that the presented model is effective.展开更多
A monolithic microwave integrated circuit （MMIC） power amplifier （PA） is proposed. It adopts a new on-chip bias circuit, which not only avoids the instability of the direct current bias caused by the change in the...A monolithic microwave integrated circuit （MMIC） power amplifier （PA） is proposed. It adopts a new on-chip bias circuit, which not only avoids the instability of the direct current bias caused by the change in the power supply and temperature, but also compensates deviations caused by the increase in input power. The bias circuit is a current-mirror configuration, and the feedback circuit helps to maintain bias voltage at a constant level. The gain of the feedback circuit is improved by the addition of a non-inverting amplifier within the feedback circuit. A shunt capacitor at the base node of the active bias transistor enhances the linearity of the PA. The chip is fabricated in an InGaP/GaAs heterojunction bipolar transistor （HBT） process. Measured results exhibit a 26. 6-dBm output compression point, 33.6% power-added efficiency （PAE） and - 40.2 dBc adjacent channel power ratio （ACPR） for wide-band code division multiple access （W-CDMA） applications.展开更多
Colloid-colloid interactions in charge-stabilized dispersions can to The crystallization process and polymorph selection of hard-core some extent be represented by the hard-core Yukawa model. Yukawa model are studied ...Colloid-colloid interactions in charge-stabilized dispersions can to The crystallization process and polymorph selection of hard-core some extent be represented by the hard-core Yukawa model. Yukawa model are studied by means of smart Monte Carlo simulations in the region of face-centered-cubic （fcc） phase. The contact value of bard-core Yukawa potential and the volume fraction of the colloids are fixed, while the Debye screening length can be varied. In the early stage of the crystallization, the precursors with relatively ordered liquid structure have been observed. Although the crystal structure of thermodynamically stable phase is fcc, the system crystallizes into a mixture of fcc and hexagonal close-packed （hcp） structures under small Debye screening length since the colloidal particles act as effective hard spheres. In the intermediate range of Debye screening length, the system crystallizes into a mixture of fcc, hcp, and body-centered-cubic （bcc）. The existence of metastable hcp and bcc structures can be interpreted as a manifestation of the Ostwald＇s step rule. Until the Debye screening length is large enough, the crystal structure obtained is almost a complete fcc suggesting the system eventually reaches to a thermodynamically stable state.展开更多
We apply polyelectrolyte multilayer films by consecutive alternate adsorption of positively charged polyallylamine hydrochloride and negatively charged sodium polystyrene sulfonate to the surface of graphene field eff...We apply polyelectrolyte multilayer films by consecutive alternate adsorption of positively charged polyallylamine hydrochloride and negatively charged sodium polystyrene sulfonate to the surface of graphene field effect transistors. Oscillations in the Dirac voltage shift with alternating positive and negative layers clearly demonstrate the electrostatic gating effect in this simple model system. A simple electrostatic model accounts well for the sign and magnitude of the Dirac voltage shift. Using this system, we are able to create p-type or n-type graphene at will. This model serves as the basis for understanding the mechanism of charged polymer sensing using graphene devices, a potentially technologically important application of graphene in areas such as DNA sequencing, biomarker assays for cancer detection, and other protein sensing applications.展开更多
基金Projects(50835002,50805035)support by the National Natural Science Foundation of ChinaProject(QC08C55)supported by the Natural Science Foundation of Heilongjiang Province,ChinaProject(200802131031)supported by the PhD Programs Foundation of Ministry of Education of China for Young Scholars
文摘A new polycrystal model was presented from the viewpoint of polycrystal structure of the billets considering free surface effects.In the model,the billet was divided into three portions,such as free surface portion,transition portion and internal portion.The grains in free surface portion were considered the single grains,and the anisotropy of the grains was taken into account by introducing grain orientation to explain the inhomogeneous deformation.In the transition portion,the effects of the neighbouring grains were adopted in the model.The grains in the internal portion were considered the polycrystalline material.With the developed model,the upsetting deformation process was simulated by the MSC Superform software.The scatter of the flow stress and inhomogeneous deformation was observed by analysis of the model.The comparisons show that the computational results are good agreed with the experimental results.This means that the presented model is effective.
基金The National High Technology Research and Development Program of China(863 Program)(No.2009AA01Z260)
文摘A monolithic microwave integrated circuit （MMIC） power amplifier （PA） is proposed. It adopts a new on-chip bias circuit, which not only avoids the instability of the direct current bias caused by the change in the power supply and temperature, but also compensates deviations caused by the increase in input power. The bias circuit is a current-mirror configuration, and the feedback circuit helps to maintain bias voltage at a constant level. The gain of the feedback circuit is improved by the addition of a non-inverting amplifier within the feedback circuit. A shunt capacitor at the base node of the active bias transistor enhances the linearity of the PA. The chip is fabricated in an InGaP/GaAs heterojunction bipolar transistor （HBT） process. Measured results exhibit a 26. 6-dBm output compression point, 33.6% power-added efficiency （PAE） and - 40.2 dBc adjacent channel power ratio （ACPR） for wide-band code division multiple access （W-CDMA） applications.
基金the National Natural Science Foundation of China (11172302, 11302226, 10972217)the Opening Fund of State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, China (LNM201503)
文摘Colloid-colloid interactions in charge-stabilized dispersions can to The crystallization process and polymorph selection of hard-core some extent be represented by the hard-core Yukawa model. Yukawa model are studied by means of smart Monte Carlo simulations in the region of face-centered-cubic （fcc） phase. The contact value of bard-core Yukawa potential and the volume fraction of the colloids are fixed, while the Debye screening length can be varied. In the early stage of the crystallization, the precursors with relatively ordered liquid structure have been observed. Although the crystal structure of thermodynamically stable phase is fcc, the system crystallizes into a mixture of fcc and hexagonal close-packed （hcp） structures under small Debye screening length since the colloidal particles act as effective hard spheres. In the intermediate range of Debye screening length, the system crystallizes into a mixture of fcc, hcp, and body-centered-cubic （bcc）. The existence of metastable hcp and bcc structures can be interpreted as a manifestation of the Ostwald＇s step rule. Until the Debye screening length is large enough, the crystal structure obtained is almost a complete fcc suggesting the system eventually reaches to a thermodynamically stable state.
文摘We apply polyelectrolyte multilayer films by consecutive alternate adsorption of positively charged polyallylamine hydrochloride and negatively charged sodium polystyrene sulfonate to the surface of graphene field effect transistors. Oscillations in the Dirac voltage shift with alternating positive and negative layers clearly demonstrate the electrostatic gating effect in this simple model system. A simple electrostatic model accounts well for the sign and magnitude of the Dirac voltage shift. Using this system, we are able to create p-type or n-type graphene at will. This model serves as the basis for understanding the mechanism of charged polymer sensing using graphene devices, a potentially technologically important application of graphene in areas such as DNA sequencing, biomarker assays for cancer detection, and other protein sensing applications.
