Microstructure and alloy element distribution in the welded joint between austenitic stainless steel (1Cr18Ni9Ti) and pearlitic heat-resistant steel (1Cr5Mo) were researched by means of light microscopy, scanning elec...Microstructure and alloy element distribution in the welded joint between austenitic stainless steel (1Cr18Ni9Ti) and pearlitic heat-resistant steel (1Cr5Mo) were researched by means of light microscopy, scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Microstructure, divisions of the fusion zone and elemental diffusion distributions in the welded joints were investigated. Furthermore, solidification microstructure and S-ferrite distribution in the weld metal of these steels are also discussed.展开更多
Few biomechanical data exist regarding whether the polyetheretherketone (PEEK) spacer or titanium spacer is better for posterior lumbar interbody fusion (PLIF). This study evaluated the biomechanical influence that th...Few biomechanical data exist regarding whether the polyetheretherketone (PEEK) spacer or titanium spacer is better for posterior lumbar interbody fusion (PLIF). This study evaluated the biomechanical influence that these types of spacers with different levels of hardness exert on the vertebra by using finite element analysis including bone strength distribution. To evaluate the risk of spacer subsidence for PLIF, we built a finite element model of the lumbar spine using computed tomography data of osteoporosis patients. Then, we simulated PLIF in L3/4 and built models with the hardness of the interbody spacer set as PEEK and titanium. Bones around the spacer were subjected to different load conditions. Then, fracture elements and some stress states of the two modalities were compared. In both models of PLIF simulation, fracture elements and stress were concentrated in the bones around the spacer. Fracture elements and stress values of the model simulating the PEEK spacer were significantly smaller compared to those of the titanium simulation model. For PLIF of osteoporotic vertebrae, this suggested that the PEEK spacer is in a mechanical environment less susceptible to subsidence caused by microfractures of bone tissue and bone remodeling-related fusion aspects. Therefore, PEEK spacers are bio-mechanically more useful.展开更多
Preventing subsidence of intervertebral cages in posterior lumbar interbody fusion (PLIF) requires understanding its mechanism, which is yet to be done. We aimed to describe the mechanism of intervertebral cage subsid...Preventing subsidence of intervertebral cages in posterior lumbar interbody fusion (PLIF) requires understanding its mechanism, which is yet to be done. We aimed to describe the mechanism of intervertebral cage subsidence by using finite element analysis through simulation of the osteoporotic vertebral bodies of an elderly woman. The data from computed tomography scans of L2-L5 vertebrae in a 72-year-old woman with osteoporosis were used to create 2 FE models: one not simulating implant placement (LS-INT) and one simulating L3/4 PLIF using polyetheretherketone (PEEK) cages (LS-PEEK). Loads and moments simulating the living body were applied to these models, and the following analyses were performed: 1) Drucker-Prager equivalent stress distribution at the cage contact surfaces;2) the distribution of damage elements in L2-L5 during incremental loading;and 3) the distribution of equivalent plastic strain at the cage contact surfaces. In analysis 1, the Drucker-Prager equivalent stress on the L3 and L4 vertebral endplates was greater for LS-PEEK than for LS-INT under all loading conditions and tended to be particularly concentrated at the contact surfaces. In analysis 2, compared with LS-INT, LS-PEEK showed more damage elements along the bone around the cages in the L3 vertebral body posterior to the cage contact surfaces, followed by the area of the L4 vertebral body posterior to the cage contact surfaces. In analysis 3, in the L3 inferior surface in LS-PEEK the distribution of equivalent plastic strain was visualized as gradually expanding along the cages from the area posterior to the cages to the area anterior to them with increased loading. These analyses suggested that in PLIF for osteoporotic vertebral bodies, the localized stress concentration generated by the use of PEEK cages may cause accumulation of microscopic damage in the fragile osteoporotic vertebral bodies around the cages, which may result in cage subsidence.展开更多
地震是极具破坏性与不确定性的自然现象,在人们毫无察觉的情况下地震发生在人口稠密区时,将严重危害人们生命财产安全。人们不断努力了解地震的物理特征和物理危害与环境之间的相互作用,以便在地震发生前发出适当的警报。可靠的地震预...地震是极具破坏性与不确定性的自然现象,在人们毫无察觉的情况下地震发生在人口稠密区时,将严重危害人们生命财产安全。人们不断努力了解地震的物理特征和物理危害与环境之间的相互作用,以便在地震发生前发出适当的警报。可靠的地震预测应包含对地震信号的分析,但是这些信号在地震发生前不明显;因此使用数据驱动机器学习的方法来分析这些信号与地震的联系并预测地震。通过建立观测台网连续监测与地震发生相关的各种物理量或化学量,据此获取的地震前兆信息是地震预测的研究基础。地震发生前,地球物理场发生显著变化,伴随电磁和地声等多种前兆信号,其中电磁和地声信号具有临震特性,是开展地震临震观测预测研究的重要数据来源;因此对地下的电磁扰动和地声信号进行实时监测,获取长期观测数据用于数据驱动机器学习方法预测地震。该文基于AETA数据的临震模型预报,针对多分量地震监测预测系统(Acoustic and Electromagnetic Testing All in one system,AETA)在川滇地区记录的电磁和地声数据,提取时域和频域特征,采用基于随机森林算法、轻量级梯度提升决策树和极度随机树的集成学习方法共同预测该区域的发震情况,选取发震概率最大的子区域中心位置作为震中预测结果,进一步训练LightGBM回归模型以预测此子区域的震级,按周对地震三要素进行预测。实验结果表明,该方法在川滇地区地震风险预测上,准确率可达0.64,震级预测的平均误差为0.38,最小误差为0.00,具有良好的预测效果。展开更多
基金The work was supported by the Foundation of KeyLaboratory of Liquid Structure and Heredity of Materi-als, Ministry of Educat
文摘Microstructure and alloy element distribution in the welded joint between austenitic stainless steel (1Cr18Ni9Ti) and pearlitic heat-resistant steel (1Cr5Mo) were researched by means of light microscopy, scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Microstructure, divisions of the fusion zone and elemental diffusion distributions in the welded joints were investigated. Furthermore, solidification microstructure and S-ferrite distribution in the weld metal of these steels are also discussed.
文摘Few biomechanical data exist regarding whether the polyetheretherketone (PEEK) spacer or titanium spacer is better for posterior lumbar interbody fusion (PLIF). This study evaluated the biomechanical influence that these types of spacers with different levels of hardness exert on the vertebra by using finite element analysis including bone strength distribution. To evaluate the risk of spacer subsidence for PLIF, we built a finite element model of the lumbar spine using computed tomography data of osteoporosis patients. Then, we simulated PLIF in L3/4 and built models with the hardness of the interbody spacer set as PEEK and titanium. Bones around the spacer were subjected to different load conditions. Then, fracture elements and some stress states of the two modalities were compared. In both models of PLIF simulation, fracture elements and stress were concentrated in the bones around the spacer. Fracture elements and stress values of the model simulating the PEEK spacer were significantly smaller compared to those of the titanium simulation model. For PLIF of osteoporotic vertebrae, this suggested that the PEEK spacer is in a mechanical environment less susceptible to subsidence caused by microfractures of bone tissue and bone remodeling-related fusion aspects. Therefore, PEEK spacers are bio-mechanically more useful.
文摘Preventing subsidence of intervertebral cages in posterior lumbar interbody fusion (PLIF) requires understanding its mechanism, which is yet to be done. We aimed to describe the mechanism of intervertebral cage subsidence by using finite element analysis through simulation of the osteoporotic vertebral bodies of an elderly woman. The data from computed tomography scans of L2-L5 vertebrae in a 72-year-old woman with osteoporosis were used to create 2 FE models: one not simulating implant placement (LS-INT) and one simulating L3/4 PLIF using polyetheretherketone (PEEK) cages (LS-PEEK). Loads and moments simulating the living body were applied to these models, and the following analyses were performed: 1) Drucker-Prager equivalent stress distribution at the cage contact surfaces;2) the distribution of damage elements in L2-L5 during incremental loading;and 3) the distribution of equivalent plastic strain at the cage contact surfaces. In analysis 1, the Drucker-Prager equivalent stress on the L3 and L4 vertebral endplates was greater for LS-PEEK than for LS-INT under all loading conditions and tended to be particularly concentrated at the contact surfaces. In analysis 2, compared with LS-INT, LS-PEEK showed more damage elements along the bone around the cages in the L3 vertebral body posterior to the cage contact surfaces, followed by the area of the L4 vertebral body posterior to the cage contact surfaces. In analysis 3, in the L3 inferior surface in LS-PEEK the distribution of equivalent plastic strain was visualized as gradually expanding along the cages from the area posterior to the cages to the area anterior to them with increased loading. These analyses suggested that in PLIF for osteoporotic vertebral bodies, the localized stress concentration generated by the use of PEEK cages may cause accumulation of microscopic damage in the fragile osteoporotic vertebral bodies around the cages, which may result in cage subsidence.
文摘地震是极具破坏性与不确定性的自然现象,在人们毫无察觉的情况下地震发生在人口稠密区时,将严重危害人们生命财产安全。人们不断努力了解地震的物理特征和物理危害与环境之间的相互作用,以便在地震发生前发出适当的警报。可靠的地震预测应包含对地震信号的分析,但是这些信号在地震发生前不明显;因此使用数据驱动机器学习的方法来分析这些信号与地震的联系并预测地震。通过建立观测台网连续监测与地震发生相关的各种物理量或化学量,据此获取的地震前兆信息是地震预测的研究基础。地震发生前,地球物理场发生显著变化,伴随电磁和地声等多种前兆信号,其中电磁和地声信号具有临震特性,是开展地震临震观测预测研究的重要数据来源;因此对地下的电磁扰动和地声信号进行实时监测,获取长期观测数据用于数据驱动机器学习方法预测地震。该文基于AETA数据的临震模型预报,针对多分量地震监测预测系统(Acoustic and Electromagnetic Testing All in one system,AETA)在川滇地区记录的电磁和地声数据,提取时域和频域特征,采用基于随机森林算法、轻量级梯度提升决策树和极度随机树的集成学习方法共同预测该区域的发震情况,选取发震概率最大的子区域中心位置作为震中预测结果,进一步训练LightGBM回归模型以预测此子区域的震级,按周对地震三要素进行预测。实验结果表明,该方法在川滇地区地震风险预测上,准确率可达0.64,震级预测的平均误差为0.38,最小误差为0.00,具有良好的预测效果。
