基于传统的分离式霍普金森拉杆系统,设计了应变控制的冲击疲劳寿命测试实验,研究了冲击疲劳加载下纯钛的微观演化机制及冲击疲劳对材料宏观力学行为的影响。通过对不同冲击疲劳试验阶段的试样开展准静态力学性能测试,借助扫描电子显微镜...基于传统的分离式霍普金森拉杆系统,设计了应变控制的冲击疲劳寿命测试实验,研究了冲击疲劳加载下纯钛的微观演化机制及冲击疲劳对材料宏观力学行为的影响。通过对不同冲击疲劳试验阶段的试样开展准静态力学性能测试,借助扫描电子显微镜(scanning electron microscope,SEM)和电子背散射衍射(electron backscatter diffraction,EBSD)技术表征试样在不同阶段的微观组织以及冲击疲劳失效后的断口形貌,研究纯钛在冲击疲劳失效过程中的循环硬化/软化规律及其微观演化机制。结果表明:通过改变子弹长度可以实现应变控制的冲击疲劳寿命测试;Manson-Coffin疲劳寿命模型可以较好地反映纯钛的冲击疲劳寿命与应变幅值之间的关系;纯钛在冲击疲劳失效过程中表现出循环硬化的现象,这主要是疲劳过程中孪生变形引起的细晶强化和塑性变形引起的应变硬化共同作用的结果,纯钛的冲击疲劳损伤主要表现为变形能力的损失。展开更多
A local and global context representation learning model for Chinese characters is designed and a Chinese word segmentation method based on character representations is proposed in this paper. First, the proposed Chin...A local and global context representation learning model for Chinese characters is designed and a Chinese word segmentation method based on character representations is proposed in this paper. First, the proposed Chinese character learning model uses the semanties of loeal context and global context to learn the representation of Chinese characters. Then, Chinese word segmentation model is built by a neural network, while the segmentation model is trained with the eharaeter representations as its input features. Finally, experimental results show that Chinese charaeter representations can effectively learn the semantic information. Characters with similar semantics cluster together in the visualize space. Moreover, the proposed Chinese word segmentation model also achieves a pretty good improvement on precision, recall and f-measure.展开更多
Astronaut's body mass is an essential factor of health monitoring in space.The latest mass measurement device for the International Space Station (ISS) has employed a linear acceleration method.The principle of th...Astronaut's body mass is an essential factor of health monitoring in space.The latest mass measurement device for the International Space Station (ISS) has employed a linear acceleration method.The principle of this method is that the device generates a constant pulling force,and the astronaut is accelerated on a parallelogram motion guide which rotates at a large radius to achieve a nearly linear trajectory.The acceleration is calculated by regression analysis of the displacement versus time trajectory and the body mass is calculated by using the formula m=F/a.However,in actual flight,the device is instable that the deviation between runs could be 6-7 kg.This paper considers the body non-rigidity as the major cause of error and instability and analyzes the effects of body non-rigidity from different aspects.Body non-rigidity makes the acceleration of the center of mass (C.M.) oscillate and fall behind the point where force is applied.Actual acceleration curves showed that the overall effect of body non-rigidity is an oscillation at about 7 Hz and a deviation of about 25%.To enhance body rigidity,better body restraints were introduced and a prototype based on linear acceleration method was built.Measurement experiment was carried out on ground on an air table.Three human subjects weighing 60-70 kg were measured.The average variance was 0.04 kg and the average measurement error was 0.4%.This study will provide reference for future development of China's own mass measurement device.展开更多
The combination of deep brain stimulation(DBS) and transcranial magnetic stimulation(TMS) is expected to provide additional insights into the pathophysiology of some brain diseases. However, when using TMS in patients...The combination of deep brain stimulation(DBS) and transcranial magnetic stimulation(TMS) is expected to provide additional insights into the pathophysiology of some brain diseases. However, when using TMS in patients with DBS implants, the induced voltage between DBS electrodes presents the greatest risk of brain damage. This paper describes the characteristics of the induced DBS electrode voltage due to TMS. We first examined the TMS stimulus signal and the DBS output impedance characteristics, and then experimentally investigated the induced DBS electrode voltage for various DBS and TMS conditions. The results show that many factors impact the induced electrode voltage. The induced electrode voltage with DBS device working in the unipolar mode is greater than that with DBS device working in the bipolar mode. No matter DBS device is turned on or turned off, the induced electrode voltage is almost the same, but it can provide a significant addition to the original stimulus waveform. There are no significant differences in the induced DBS electrode voltage when the DBS system is working at different stimulus intensities. Lowering the TMS stimulus intensity could effectively reduce the induced DBS electrode voltage. The induced electrode voltage is also strongly related to the position of the TMS coil relative to the DBS lead. This study provides further information about the characteristics of the induced DBS electrode voltage in TMS applications and a reference for the combined use of DBS and TMS.展开更多
文摘基于传统的分离式霍普金森拉杆系统,设计了应变控制的冲击疲劳寿命测试实验,研究了冲击疲劳加载下纯钛的微观演化机制及冲击疲劳对材料宏观力学行为的影响。通过对不同冲击疲劳试验阶段的试样开展准静态力学性能测试,借助扫描电子显微镜(scanning electron microscope,SEM)和电子背散射衍射(electron backscatter diffraction,EBSD)技术表征试样在不同阶段的微观组织以及冲击疲劳失效后的断口形貌,研究纯钛在冲击疲劳失效过程中的循环硬化/软化规律及其微观演化机制。结果表明:通过改变子弹长度可以实现应变控制的冲击疲劳寿命测试;Manson-Coffin疲劳寿命模型可以较好地反映纯钛的冲击疲劳寿命与应变幅值之间的关系;纯钛在冲击疲劳失效过程中表现出循环硬化的现象,这主要是疲劳过程中孪生变形引起的细晶强化和塑性变形引起的应变硬化共同作用的结果,纯钛的冲击疲劳损伤主要表现为变形能力的损失。
基金Supported by the National Natural Science Foundation of China(No.61303179,U1135005,61175020)
文摘A local and global context representation learning model for Chinese characters is designed and a Chinese word segmentation method based on character representations is proposed in this paper. First, the proposed Chinese character learning model uses the semanties of loeal context and global context to learn the representation of Chinese characters. Then, Chinese word segmentation model is built by a neural network, while the segmentation model is trained with the eharaeter representations as its input features. Finally, experimental results show that Chinese charaeter representations can effectively learn the semantic information. Characters with similar semantics cluster together in the visualize space. Moreover, the proposed Chinese word segmentation model also achieves a pretty good improvement on precision, recall and f-measure.
文摘Astronaut's body mass is an essential factor of health monitoring in space.The latest mass measurement device for the International Space Station (ISS) has employed a linear acceleration method.The principle of this method is that the device generates a constant pulling force,and the astronaut is accelerated on a parallelogram motion guide which rotates at a large radius to achieve a nearly linear trajectory.The acceleration is calculated by regression analysis of the displacement versus time trajectory and the body mass is calculated by using the formula m=F/a.However,in actual flight,the device is instable that the deviation between runs could be 6-7 kg.This paper considers the body non-rigidity as the major cause of error and instability and analyzes the effects of body non-rigidity from different aspects.Body non-rigidity makes the acceleration of the center of mass (C.M.) oscillate and fall behind the point where force is applied.Actual acceleration curves showed that the overall effect of body non-rigidity is an oscillation at about 7 Hz and a deviation of about 25%.To enhance body rigidity,better body restraints were introduced and a prototype based on linear acceleration method was built.Measurement experiment was carried out on ground on an air table.Three human subjects weighing 60-70 kg were measured.The average variance was 0.04 kg and the average measurement error was 0.4%.This study will provide reference for future development of China's own mass measurement device.
基金supported by the National Key Technology Research and Development Program(Grant No.2011BAI12B07)the National Natural Science Foundation of China(Grant No.51125028)
文摘The combination of deep brain stimulation(DBS) and transcranial magnetic stimulation(TMS) is expected to provide additional insights into the pathophysiology of some brain diseases. However, when using TMS in patients with DBS implants, the induced voltage between DBS electrodes presents the greatest risk of brain damage. This paper describes the characteristics of the induced DBS electrode voltage due to TMS. We first examined the TMS stimulus signal and the DBS output impedance characteristics, and then experimentally investigated the induced DBS electrode voltage for various DBS and TMS conditions. The results show that many factors impact the induced electrode voltage. The induced electrode voltage with DBS device working in the unipolar mode is greater than that with DBS device working in the bipolar mode. No matter DBS device is turned on or turned off, the induced electrode voltage is almost the same, but it can provide a significant addition to the original stimulus waveform. There are no significant differences in the induced DBS electrode voltage when the DBS system is working at different stimulus intensities. Lowering the TMS stimulus intensity could effectively reduce the induced DBS electrode voltage. The induced electrode voltage is also strongly related to the position of the TMS coil relative to the DBS lead. This study provides further information about the characteristics of the induced DBS electrode voltage in TMS applications and a reference for the combined use of DBS and TMS.
