The cast preformed forming process(CPFP) is increasingly considered and applied in the metal forming industries due to its short process, low cost, and environmental friendliness, especially in the aerospace field. Ho...The cast preformed forming process(CPFP) is increasingly considered and applied in the metal forming industries due to its short process, low cost, and environmental friendliness, especially in the aerospace field. However, how to establish a unified model of a non-uniform as-cast billet depicting the flow stress and microstructure evolution behaviors during hot working is the key to microstructure prediction and parameter optimization of the CPFP. In this work, hot compression tests are performed using a non-uniform as-cast 42 CrMo billet at 1123–1423 K and 0.01–1sà1. The effect laws of the non-uniform state of the as-cast billet with different initial grain sizes on the flow stress and microstructure are revealed deeply. Based on experimental results, a unified model of flow stress and grain size evolutions is developed by the internal variable modeling method. Verified results show that the model can well describe the responses of the flow stress and microstructure to deformation conditions and initial grain sizes. To further evaluate its reliability, the unified model is applied to FE simulation of the cast preformed ring rolling process.The predictions of the rolling force and grain size indicate that it could well describe the flow stress and microstructure evolutions during the process.展开更多
Semiconductor optical amplifier-based ring cavity laser (SOA-RL), which has been widely used in optical communications, optical fiber sensing, and biophotonics fields, can be tuned at an ultra high speed up to Mega He...Semiconductor optical amplifier-based ring cavity laser (SOA-RL), which has been widely used in optical communications, optical fiber sensing, and biophotonics fields, can be tuned at an ultra high speed up to Mega Hertz over 100 nm bandwidth range with high SNR and flatness output. A steady-state model and segmentation algorithms are employed to investigate the gain spectra of four kinds of non-uniform SOA and the lasing wavelength of the SOA-RL. It shows that the dependence of the lasing wavelength on the average width is stronger when the light propagates from narrower to wider end than conversely, and there are some particular structures to show ultra high stability lasing wavelength. It is supposed that the main reason could be the carrier density distribution along the propagation.展开更多
The electron states in a two-dimensional GaAs/AlGaAs quantum ring are theoretically studied in effective mass approximation. On-centre donor impurity and uniform magnetic field perpendicular to the ring plane are take...The electron states in a two-dimensional GaAs/AlGaAs quantum ring are theoretically studied in effective mass approximation. On-centre donor impurity and uniform magnetic field perpendicular to the ring plane are taken into account. The energy spectrum with different angular momentum changes dramatically with the geometry of the ring. The donor impurity reduces the energies with an almost fixed value; however, the magnetic field alters energies in a more complex way. For example, energy levels under magnetic field will cross each other when increasing the inner radius and outer radius of the ring, leading to the fact that the arrangement of energy levels is distinct in certain geometry of the ring. Moreover, energy levels with negative angular momentum exhibit the non-monotonous dependence on the increasing magnetic field.展开更多
Polymer thin film with uniform thickness and flat surface profile is the key point for polymer light emitting diodes(PLEDs) by inkjet printing. However, the coffee ring effect is usually observed due to the mismatch b...Polymer thin film with uniform thickness and flat surface profile is the key point for polymer light emitting diodes(PLEDs) by inkjet printing. However, the coffee ring effect is usually observed due to the mismatch between the evaporation of the solvent and the decrease of solution volume, which promotes the formation of radial flow from the interior of the drop to the edge. In this paper, coffee ring effects of inkjet printed poly(spirobifluorene) films were proposed to be restrained by decreasing capillary force by adding co-solvent with high boiling point and high viscosity to the main solvent. The low evaporation rate of the co-solvent can reduce the driving force of the radial flow; meanwhile the high viscosity of the co-solvent can increase the resistance of the radial flow. Thus, polymer films with improve uniformity can be obtained due to the suppression of the radial flow. The device performance was greatly improved under the condition of proper film thickness and film uniformity and the maximum luminous efficiency of devices with inkjet printed poly(spirobifluorene) can reach 80% of the spin-coated devices.展开更多
设计了一种多环形结构超高频射频识别(RFID,radio frequency identification)阅读器近场天线。天线整体结构呈圆形,由8个扇形辐射贴片旋转分布组成,通过扇形辐射贴片间的紧耦合和加载寄生弧形贴片,实现了天线表面电流旋向相同,能够在识...设计了一种多环形结构超高频射频识别(RFID,radio frequency identification)阅读器近场天线。天线整体结构呈圆形,由8个扇形辐射贴片旋转分布组成,通过扇形辐射贴片间的紧耦合和加载寄生弧形贴片,实现了天线表面电流旋向相同,能够在识别区域内产生较均匀的磁场和多极化的电场。天线直径为130 mm,印制在厚度为1.6mm的阻燃4级(FR-4,flameretardant4)介质基板上。测试结果表明,端口反射系数|S11|<-10dB的频带宽度为904~932 MHz,在天线上方直径为130 mm的圆形区域内可产生较均匀的磁场;采用Impinj E710阅读器进行标签测试,在30dBm的输出功率下,磁耦合环形标签J41的最远100%读取距离为16cm;所提天线能产生多极化电场,对于不同方向摆放的电极化标签具备相近的读取能力。展开更多
基金supported by the National Natural Science Foundation of China (No’s. 51575448 and 51135007)
文摘The cast preformed forming process(CPFP) is increasingly considered and applied in the metal forming industries due to its short process, low cost, and environmental friendliness, especially in the aerospace field. However, how to establish a unified model of a non-uniform as-cast billet depicting the flow stress and microstructure evolution behaviors during hot working is the key to microstructure prediction and parameter optimization of the CPFP. In this work, hot compression tests are performed using a non-uniform as-cast 42 CrMo billet at 1123–1423 K and 0.01–1sà1. The effect laws of the non-uniform state of the as-cast billet with different initial grain sizes on the flow stress and microstructure are revealed deeply. Based on experimental results, a unified model of flow stress and grain size evolutions is developed by the internal variable modeling method. Verified results show that the model can well describe the responses of the flow stress and microstructure to deformation conditions and initial grain sizes. To further evaluate its reliability, the unified model is applied to FE simulation of the cast preformed ring rolling process.The predictions of the rolling force and grain size indicate that it could well describe the flow stress and microstructure evolutions during the process.
文摘Semiconductor optical amplifier-based ring cavity laser (SOA-RL), which has been widely used in optical communications, optical fiber sensing, and biophotonics fields, can be tuned at an ultra high speed up to Mega Hertz over 100 nm bandwidth range with high SNR and flatness output. A steady-state model and segmentation algorithms are employed to investigate the gain spectra of four kinds of non-uniform SOA and the lasing wavelength of the SOA-RL. It shows that the dependence of the lasing wavelength on the average width is stronger when the light propagates from narrower to wider end than conversely, and there are some particular structures to show ultra high stability lasing wavelength. It is supposed that the main reason could be the carrier density distribution along the propagation.
基金Project supported by the National High Technology Research and Development Program of China (Grant No. 2009AA03Z405)the National Natural Science Foundation of China (Grant Nos. 60908028 and 60971068)the Fundamental Research Funds for the Central Universities (Grant No. BUPT2009RC0411)
文摘The electron states in a two-dimensional GaAs/AlGaAs quantum ring are theoretically studied in effective mass approximation. On-centre donor impurity and uniform magnetic field perpendicular to the ring plane are taken into account. The energy spectrum with different angular momentum changes dramatically with the geometry of the ring. The donor impurity reduces the energies with an almost fixed value; however, the magnetic field alters energies in a more complex way. For example, energy levels under magnetic field will cross each other when increasing the inner radius and outer radius of the ring, leading to the fact that the arrangement of energy levels is distinct in certain geometry of the ring. Moreover, energy levels with negative angular momentum exhibit the non-monotonous dependence on the increasing magnetic field.
基金financially supported by the National Natural Science Foundation of China (Nos. 21574130, 51473161, 51873212)the Ministry of Science and Technology of China (No. 2015CB655001)National Key R&D Program of "Strategic Advanced Electronic Materials" (Nos. 2016YFB0401301, 2016YFB04011001)
文摘Polymer thin film with uniform thickness and flat surface profile is the key point for polymer light emitting diodes(PLEDs) by inkjet printing. However, the coffee ring effect is usually observed due to the mismatch between the evaporation of the solvent and the decrease of solution volume, which promotes the formation of radial flow from the interior of the drop to the edge. In this paper, coffee ring effects of inkjet printed poly(spirobifluorene) films were proposed to be restrained by decreasing capillary force by adding co-solvent with high boiling point and high viscosity to the main solvent. The low evaporation rate of the co-solvent can reduce the driving force of the radial flow; meanwhile the high viscosity of the co-solvent can increase the resistance of the radial flow. Thus, polymer films with improve uniformity can be obtained due to the suppression of the radial flow. The device performance was greatly improved under the condition of proper film thickness and film uniformity and the maximum luminous efficiency of devices with inkjet printed poly(spirobifluorene) can reach 80% of the spin-coated devices.
