Lead magnesium niobate-lead titanate(PMN-PT)piezoelectric single crystals are widely utilized due to their outstanding performance,with varying compositions significantly impacting their properties.While application o...Lead magnesium niobate-lead titanate(PMN-PT)piezoelectric single crystals are widely utilized due to their outstanding performance,with varying compositions significantly impacting their properties.While application of PMN-PT in high-power settings is rapidly evolving,material parameters are typically tested under low signal conditions(1 V),and effects of different PT(PbTiO_(3))contents on the performance of PMN-PT single crystals under high-power conditions remain unclear.This study developed a comprehensive high-power testing platform using the constant voltage method to evaluate performance of PMN-PT single crystals with different PT contents under high-power voltage stimulation.Using crystals sized at 10 mm×3 mm×0.5 mm as an example,this research explored changes in material parameters.The results exhibit that while trend of the parameter changes under high-power excitation was consistent across different PT contents,degree of the change varied significantly.For instance,a PMN-PT single crystal with 26%(in mol)PT content exhibited a 25%increase in the piezoelectric coefficient d_(31),a 13%increase in the elastic compliance coefficient s_(11)^(E),a 17%increase in the electromechanical coupling coefficient k_(31),and a 73%decrease in the mechanical quality factor Q_(m) when the power reached 7.90 W.As the PT content increased,the PMN-PT materials became more susceptible to temperature influences,significantly reducing the power tolerance and more readily reaching the depolarization temperatures.This led to loss of piezoelectric performance.Based on these findings,a clearer understanding of impact of PT content on performance of PMN-PT single crystals under high-power applications has been established,providing reliable data to support design of sensors or transducers using PMN-PT as the sensitive element.展开更多
This work aims to reveal the mechanical responses and energy evolution characteristics of skarn rock under constant amplitude-varied frequency loading paths.Testing results show that the fatigue lifetime,stress−strain...This work aims to reveal the mechanical responses and energy evolution characteristics of skarn rock under constant amplitude-varied frequency loading paths.Testing results show that the fatigue lifetime,stress−strain responses,deformation,energy dissipation and fracture morphology are all impacted by the loading rate.A pronounced influence of the loading rate on rock deformation is found,with slower loading rate eliciting enhanced strain development,alongside augmented energy absorption and dissipation.In addition,it is revealed that the loading rate and cyclic loading amplitude jointly influence the phase shift distribution,with accelerated rates leading to a narrower phase shift duration.It is suggested that lower loading rate leads to more significant energy dissipation.Finally,the tensile or shear failure modes were intrinsically linked to loading strategy,with cyclic loading predominantly instigating shear damage,as manifest in the increased presence of pulverized grain particles.This work would give new insights into the fortification of mining structures and the optimization of mining methodologies.展开更多
This study investigates the corrosion-assisted fatigue crack growth rate(FCGR)of 16 mm thick AA 7075-T651 friction stir welded(FSW)joints.Compact tension(CT)specimens were extracted from both the base material and FSW...This study investigates the corrosion-assisted fatigue crack growth rate(FCGR)of 16 mm thick AA 7075-T651 friction stir welded(FSW)joints.Compact tension(CT)specimens were extracted from both the base material and FSW joints to evaluate FCGR under varying corrosion exposure durations(0,7,30,60,and 90 days)at a constant stress ratio of 0.5.Microstructural analysis of the welds was conducted using optical and transmission electron microscopy(TEM).Results indicate that the critical stress intensity factor range(ΔK_(cr))of FSW joints is lower than that of the base material,primarily due to precipitate dissolution in the weld zone during the FSW process,as confirmed by TEM analysis.The fatigue life of FSW joints was significantly lower than that of the base material,but with prolonged exposure to seawater corrosion,the gap in fatigue life narrowed.Specimens exposed to seawater for more than 60days exhibited minimal differences in fatigue life between the base material and the FSW joints.This was attributed to the higher corrosion rate of the base material compared to the weld nugget,resulting in the formation of deeper pits that facilitated crack initiation and accelerated fatigue failure.The findings conclude that extended corrosion exposure leads to similar fatigue life and crack growth behaviour in both the base material and FSW joints.SEM and EDX analysis of AA7075-T651 revealed corrosion pits and rust products in initiation zones,ductile striations in growth regions,and secondary cracks with micro voids in fracture zones.FSW joints exhibited ultra-fine grains,smooth ductile fracture in initiation and growth regions,and brittle fracture in the fracture zones under both corroded and uncorroded conditions.展开更多
Adaptive detection of range-spread targets is considered in the presence of subspace interference plus Gaussian clutter with unknown covariance matrix.The target signal and interference are supposed to lie in two line...Adaptive detection of range-spread targets is considered in the presence of subspace interference plus Gaussian clutter with unknown covariance matrix.The target signal and interference are supposed to lie in two linearly independent subspaces with deterministic but unknown coordinates.Relying on the two-step criteria,two adaptive detectors based on Gradient tests are proposed,in homogeneous and partially homogeneous clutter plus subspace interference,respectively.Both of the proposed detectors exhibit theoretically constant false alarm rate property against unknown clutter covariance matrix as well as the power level.Numerical results show that,the proposed detectors have better performance than their existing counterparts,especially for mismatches in the signal steering vectors.展开更多
高频地波雷达的"距离-多普勒"(Range-Doppler,R-D)数据与"恒虚警率"(Constant False-AlarmRate,CFAR)检测结果数据存在非直观性的问题,本文针对此问题,分析了地波雷达回波数据特点以及结果形式,研究了采用地理信息...高频地波雷达的"距离-多普勒"(Range-Doppler,R-D)数据与"恒虚警率"(Constant False-AlarmRate,CFAR)检测结果数据存在非直观性的问题,本文针对此问题,分析了地波雷达回波数据特点以及结果形式,研究了采用地理信息系统(Geographic Information System,GIS)技术对回波数据进行显示分析,对R-D与CFAR检测结果进行表达,实现高频数据在GIS环境下的表达处理与显示。本文采用GIS的栅格表达"距离-多普勒"数据,采用矢量数据结构表达CFAR检测结果,实现了地波雷达检测信息的直观显示;研究了高频地波雷达数据中特定距离一维谱信号的提取,实现了基于距离值的目标CFAR检测查询;针对雷达数据量大、处理时间长的问题,采用多线程处理机制实现了高效实时显示和分析。展开更多
目的探讨采用PHILOS锁定钢板治疗肱骨近端粉碎性骨折的临床疗效。方法收集2010年1月至2012年6月应用PHILOS锁定钢板治疗16例肱骨近端骨折患者，通过影像学资料、Constant-Murley评分（Constant-Murley score，CMS）及美国肩肘外科医师（...目的探讨采用PHILOS锁定钢板治疗肱骨近端粉碎性骨折的临床疗效。方法收集2010年1月至2012年6月应用PHILOS锁定钢板治疗16例肱骨近端骨折患者，通过影像学资料、Constant-Murley评分（Constant-Murley score，CMS）及美国肩肘外科医师（ American shoulder and elbow surgeons, ASES） 评分对患者骨折愈合情况、肩关节功能及并发症等进行评估。结果16例患者均获随访，平均随访时间17（6～25）个月。16例（100％）患者获得骨性愈合，14例患者基本获得解剖复位（87．5％），1例（6．2％）患者术后肩关节轻度疼痛，1例（6．2％）患者术后肩关节功能严重障碍。所有病例无钢板螺钉断裂、肱骨头缺血性坏死发生；平均ASES评分为80．5（40～96）分，平均Constant评分为72．4（32-93）分；其中患肢肩关节功能优12例（75．0％）、良3例（18．8％）、差1例（6．2％）。结论采用PHILOS锁定钢板治疗肱骨近端粉碎型骨折，尤其对老年性骨质疏松患者，不仅可提供稳定的骨折固定，而且能进行早期功能锻炼，从而取得较好的疗效。展开更多
通过单二极管五参数模型太阳电池的电流方程一阶导数,推导出光生电流变化而温度不变时的最大功率方程,并绘制最大功率曲线。太阳电池恒压跟踪(constant voltage tracking,CVT)的数学表述为dVm/dIm?0,即CVT仅是最大功率跟踪的特殊情况,...通过单二极管五参数模型太阳电池的电流方程一阶导数,推导出光生电流变化而温度不变时的最大功率方程,并绘制最大功率曲线。太阳电池恒压跟踪(constant voltage tracking,CVT)的数学表述为dVm/dIm?0,即CVT仅是最大功率跟踪的特殊情况,通常情况下在最大功率曲线上仅是两个点。在CVT的点沿电流轴向两侧延伸,太阳电池最大功率点的电压变化不大而电流变化较大,就有了适用CVT的区间,其数学表述为dUm/dIm?0。该文给出了适用CVT的负载电流、光生电流区间,建议在不同的电流区间采用不同的恒定跟踪电压。从特性参数角度进行数值模拟指出,串联内阻越小、并联内阻越大、二极管反向饱和电流越小或二极管理想因子越大,适用CVT的区间就越宽。展开更多
Background Bone is a dynamic tissue that constantly undergoes remodeling in which a coupled process of bone formation and resorption continues throughout life.This remodeling is necessary to maintain the structural in...Background Bone is a dynamic tissue that constantly undergoes remodeling in which a coupled process of bone formation and resorption continues throughout life.This remodeling is necessary to maintain the structural integrity of the skeleton under conditions of changing mechanical forces.It is important to develop bone remodeling theory in order to explain bone development and to instruct bone disease therapy and rehabilitation.However,the process and mechanism are not fully understood.Our study was carried out to investigate biomechanical mechanism of bone remodeling with the respect to bone tissue/cell mechanobiology,computational biomechanics and animal model.展开更多
Introduction The endothelial cells(ECs)lining every blood vessel wall constantly expose to the mechanical forces generated by the blood flow.The EC responses to these hemodynamic forces play a critical role in the hom...Introduction The endothelial cells(ECs)lining every blood vessel wall constantly expose to the mechanical forces generated by the blood flow.The EC responses to these hemodynamic forces play a critical role in the homeostasis of the circulatory system.In addition to forming a transport barrier between the blood and vessel wall,vascular ECs play important roles in regulating circulation functions.Besides biochemical stimuli,blood flow induced(hemodynamic)mechanical stimuli,such as shear stress,pressure and circumferential stretch,modulate EC morphology and functions by activating mechanosensors,signaling pathways,and gene and protein expressions.The EC responses to the hemodynamic forces(mechano-sensing and transduction)展开更多
Cell-matrix interaction is the key for understanding the cell behaviors,especially the mechanosensitivity of cell adhesion,cell migration and differentiation,etc.Cells are constantly probing,pushing and pulling on the...Cell-matrix interaction is the key for understanding the cell behaviors,especially the mechanosensitivity of cell adhesion,cell migration and differentiation,etc.Cells are constantly probing,pushing and pulling on the surrounding extracellular matrix.These cell-generated forces drive cell migration and tissue morphogenesis,and maintain the intrinsic mechanical tone of tissues.Therefore,knowledge of the spatial and temporal nature of these forces are essential to understanding when and where mechanical events come to play in both physiological and pathological settings.However,because of the complexity of cell geometry and insufficient展开更多
针对无源侦察系统的实时性应用需求,该文提出了一种基于功率聚焦的宽带阵列信号检测算法。利用均匀线阵接收信号的相位变化信息,通过改进的二重FFT算法将各阵元接收信号的功率聚焦到信号到达角(Direction Of Arrival,DOA)。在此基础上,...针对无源侦察系统的实时性应用需求,该文提出了一种基于功率聚焦的宽带阵列信号检测算法。利用均匀线阵接收信号的相位变化信息,通过改进的二重FFT算法将各阵元接收信号的功率聚焦到信号到达角(Direction Of Arrival,DOA)。在此基础上,推导了聚焦后各角度上噪声数据的概率密度函数,构造了具有恒虚警特性的检验统计量和相应的检测门限,并推导了不同虚警率和信噪比条件下的理论检测概率。该算法聚焦过程计算复杂度较小,检测过程不依赖于信号先验信息,检测结果还可为后续的精确角度测量提供初值。仿真实验表明,该算法对弱信号具有较好的检测效果。展开更多
Rock bolts are widely used in rock engineering projects to improve the shear capacity of the jointed rock mass.The bolt inclination angle with respect to the shear plane has a remarkable influence on the bolting perfo...Rock bolts are widely used in rock engineering projects to improve the shear capacity of the jointed rock mass.The bolt inclination angle with respect to the shear plane has a remarkable influence on the bolting performance.In this study,a new artificial molding method based on 3D scanning and printing technology was first proposed to prepare bolted joints with an inclined bolt.Then,the effects of the bolt inclination angle and boundary conditions on the shear behavior and failure characteristic of bolted joints were addressed by conducting direct shear tests under both CNL and CNS conditions.Results indicated that rock bolt could significantly improve the shear behavior of rock joints,especially in the post-yield deformation region.With the increase of bolt inclination angle,both the maximum shear stress and the maximum friction coefficient increased first and then decreased,while the maximum normal displacement decreased monotonously.Compared with CNL conditions,the maximum shear stress was larger,whereas the maximum normal displacement and friction coefficient were smaller under the CNS conditions.Furthermore,more asperity damage was observed under the CNS conditions due to the increased normal stress on the shear plane.展开更多
According to the dimensionless formulae of DOP(depth of penetration) of a rigid projectile into different targets,the resistive force which a target exerts on the projectile during the penetration of rigid projectile ...According to the dimensionless formulae of DOP(depth of penetration) of a rigid projectile into different targets,the resistive force which a target exerts on the projectile during the penetration of rigid projectile is theoretically analyzed.In particular,the threshold V_C of impact velocity applicable for the assumption of constant resistive force is formulated through impulse analysis.The various values of V_C corresponding to different pairs of projectile-target are calculated,and the consistency of the relative test data and numerical results is observed.展开更多
The kinetic mechanism for the preparation of silymarin from milk thistle seeds was studied during the microwave-assisted extraction （MAE） process. The results showed that the transfer rate of silymarin from milk thi...The kinetic mechanism for the preparation of silymarin from milk thistle seeds was studied during the microwave-assisted extraction （MAE） process. The results showed that the transfer rate of silymarin from milk thistle seeds increased with the microwave output power and temperature during MAE processing. The apparent extraction rate constant k （s-1） was 1.2028×10-2 , 1.2248×10-2 , and 1.2485×10-2 , and diffusion coefficient D （m2·s-1 ） was 4.21×10-10, 4.29×10-10 , and 4.37×10-10 at the microwave temperatures of 383, 393, and 403 K, respectively, in the silymarin MAE process. With the help of scanning electron microscopy （SEM）, the microstructures of the samples extracted by MAE were observed. The results revealed that the increased efficiency and rate of MAE of silymarin could be attributed mainly to the subsequent cell change resulting from superheating effects during MAE.展开更多
基金Research and Development Project on Voltage Sensors by China Southern Power Grid Digital Research Institute(210000KK52220017)。
文摘Lead magnesium niobate-lead titanate(PMN-PT)piezoelectric single crystals are widely utilized due to their outstanding performance,with varying compositions significantly impacting their properties.While application of PMN-PT in high-power settings is rapidly evolving,material parameters are typically tested under low signal conditions(1 V),and effects of different PT(PbTiO_(3))contents on the performance of PMN-PT single crystals under high-power conditions remain unclear.This study developed a comprehensive high-power testing platform using the constant voltage method to evaluate performance of PMN-PT single crystals with different PT contents under high-power voltage stimulation.Using crystals sized at 10 mm×3 mm×0.5 mm as an example,this research explored changes in material parameters.The results exhibit that while trend of the parameter changes under high-power excitation was consistent across different PT contents,degree of the change varied significantly.For instance,a PMN-PT single crystal with 26%(in mol)PT content exhibited a 25%increase in the piezoelectric coefficient d_(31),a 13%increase in the elastic compliance coefficient s_(11)^(E),a 17%increase in the electromechanical coupling coefficient k_(31),and a 73%decrease in the mechanical quality factor Q_(m) when the power reached 7.90 W.As the PT content increased,the PMN-PT materials became more susceptible to temperature influences,significantly reducing the power tolerance and more readily reaching the depolarization temperatures.This led to loss of piezoelectric performance.Based on these findings,a clearer understanding of impact of PT content on performance of PMN-PT single crystals under high-power applications has been established,providing reliable data to support design of sensors or transducers using PMN-PT as the sensitive element.
基金Project(52174069) supported by the National Natural Science Foundation of ChinaProject(8202033) supported by the Beijing Natural Science Foundation,ChinaProject(KCF2203) supported by the Henan Key Laboratory for Green and Efficient Mining&Comprehensive Utilization of Mineral Resources (Henan Polytechnic University),China。
文摘This work aims to reveal the mechanical responses and energy evolution characteristics of skarn rock under constant amplitude-varied frequency loading paths.Testing results show that the fatigue lifetime,stress−strain responses,deformation,energy dissipation and fracture morphology are all impacted by the loading rate.A pronounced influence of the loading rate on rock deformation is found,with slower loading rate eliciting enhanced strain development,alongside augmented energy absorption and dissipation.In addition,it is revealed that the loading rate and cyclic loading amplitude jointly influence the phase shift distribution,with accelerated rates leading to a narrower phase shift duration.It is suggested that lower loading rate leads to more significant energy dissipation.Finally,the tensile or shear failure modes were intrinsically linked to loading strategy,with cyclic loading predominantly instigating shear damage,as manifest in the increased presence of pulverized grain particles.This work would give new insights into the fortification of mining structures and the optimization of mining methodologies.
文摘This study investigates the corrosion-assisted fatigue crack growth rate(FCGR)of 16 mm thick AA 7075-T651 friction stir welded(FSW)joints.Compact tension(CT)specimens were extracted from both the base material and FSW joints to evaluate FCGR under varying corrosion exposure durations(0,7,30,60,and 90 days)at a constant stress ratio of 0.5.Microstructural analysis of the welds was conducted using optical and transmission electron microscopy(TEM).Results indicate that the critical stress intensity factor range(ΔK_(cr))of FSW joints is lower than that of the base material,primarily due to precipitate dissolution in the weld zone during the FSW process,as confirmed by TEM analysis.The fatigue life of FSW joints was significantly lower than that of the base material,but with prolonged exposure to seawater corrosion,the gap in fatigue life narrowed.Specimens exposed to seawater for more than 60days exhibited minimal differences in fatigue life between the base material and the FSW joints.This was attributed to the higher corrosion rate of the base material compared to the weld nugget,resulting in the formation of deeper pits that facilitated crack initiation and accelerated fatigue failure.The findings conclude that extended corrosion exposure leads to similar fatigue life and crack growth behaviour in both the base material and FSW joints.SEM and EDX analysis of AA7075-T651 revealed corrosion pits and rust products in initiation zones,ductile striations in growth regions,and secondary cracks with micro voids in fracture zones.FSW joints exhibited ultra-fine grains,smooth ductile fracture in initiation and growth regions,and brittle fracture in the fracture zones under both corroded and uncorroded conditions.
基金supported by the National Natural Science Foundation of China(61971432)Taishan Scholar Project of Shandong Province(tsqn201909156)the Outstanding Youth Innovation Team Program of University in Shandong Province(2019KJN031)。
文摘Adaptive detection of range-spread targets is considered in the presence of subspace interference plus Gaussian clutter with unknown covariance matrix.The target signal and interference are supposed to lie in two linearly independent subspaces with deterministic but unknown coordinates.Relying on the two-step criteria,two adaptive detectors based on Gradient tests are proposed,in homogeneous and partially homogeneous clutter plus subspace interference,respectively.Both of the proposed detectors exhibit theoretically constant false alarm rate property against unknown clutter covariance matrix as well as the power level.Numerical results show that,the proposed detectors have better performance than their existing counterparts,especially for mismatches in the signal steering vectors.
文摘高频地波雷达的"距离-多普勒"(Range-Doppler,R-D)数据与"恒虚警率"(Constant False-AlarmRate,CFAR)检测结果数据存在非直观性的问题,本文针对此问题,分析了地波雷达回波数据特点以及结果形式,研究了采用地理信息系统(Geographic Information System,GIS)技术对回波数据进行显示分析,对R-D与CFAR检测结果进行表达,实现高频数据在GIS环境下的表达处理与显示。本文采用GIS的栅格表达"距离-多普勒"数据,采用矢量数据结构表达CFAR检测结果,实现了地波雷达检测信息的直观显示;研究了高频地波雷达数据中特定距离一维谱信号的提取,实现了基于距离值的目标CFAR检测查询;针对雷达数据量大、处理时间长的问题,采用多线程处理机制实现了高效实时显示和分析。
文摘目的探讨采用PHILOS锁定钢板治疗肱骨近端粉碎性骨折的临床疗效。方法收集2010年1月至2012年6月应用PHILOS锁定钢板治疗16例肱骨近端骨折患者，通过影像学资料、Constant-Murley评分（Constant-Murley score，CMS）及美国肩肘外科医师（ American shoulder and elbow surgeons, ASES） 评分对患者骨折愈合情况、肩关节功能及并发症等进行评估。结果16例患者均获随访，平均随访时间17（6～25）个月。16例（100％）患者获得骨性愈合，14例患者基本获得解剖复位（87．5％），1例（6．2％）患者术后肩关节轻度疼痛，1例（6．2％）患者术后肩关节功能严重障碍。所有病例无钢板螺钉断裂、肱骨头缺血性坏死发生；平均ASES评分为80．5（40～96）分，平均Constant评分为72．4（32-93）分；其中患肢肩关节功能优12例（75．0％）、良3例（18．8％）、差1例（6．2％）。结论采用PHILOS锁定钢板治疗肱骨近端粉碎型骨折，尤其对老年性骨质疏松患者，不仅可提供稳定的骨折固定，而且能进行早期功能锻炼，从而取得较好的疗效。
文摘通过单二极管五参数模型太阳电池的电流方程一阶导数,推导出光生电流变化而温度不变时的最大功率方程,并绘制最大功率曲线。太阳电池恒压跟踪(constant voltage tracking,CVT)的数学表述为dVm/dIm?0,即CVT仅是最大功率跟踪的特殊情况,通常情况下在最大功率曲线上仅是两个点。在CVT的点沿电流轴向两侧延伸,太阳电池最大功率点的电压变化不大而电流变化较大,就有了适用CVT的区间,其数学表述为dUm/dIm?0。该文给出了适用CVT的负载电流、光生电流区间,建议在不同的电流区间采用不同的恒定跟踪电压。从特性参数角度进行数值模拟指出,串联内阻越小、并联内阻越大、二极管反向饱和电流越小或二极管理想因子越大,适用CVT的区间就越宽。
基金supported by the National Natural Science Foundation of China(No.10832012)
文摘Background Bone is a dynamic tissue that constantly undergoes remodeling in which a coupled process of bone formation and resorption continues throughout life.This remodeling is necessary to maintain the structural integrity of the skeleton under conditions of changing mechanical forces.It is important to develop bone remodeling theory in order to explain bone development and to instruct bone disease therapy and rehabilitation.However,the process and mechanism are not fully understood.Our study was carried out to investigate biomechanical mechanism of bone remodeling with the respect to bone tissue/cell mechanobiology,computational biomechanics and animal model.
文摘Introduction The endothelial cells(ECs)lining every blood vessel wall constantly expose to the mechanical forces generated by the blood flow.The EC responses to these hemodynamic forces play a critical role in the homeostasis of the circulatory system.In addition to forming a transport barrier between the blood and vessel wall,vascular ECs play important roles in regulating circulation functions.Besides biochemical stimuli,blood flow induced(hemodynamic)mechanical stimuli,such as shear stress,pressure and circumferential stretch,modulate EC morphology and functions by activating mechanosensors,signaling pathways,and gene and protein expressions.The EC responses to the hemodynamic forces(mechano-sensing and transduction)
基金supported by the National Natural Science Foundation of China through grant nos.11221202 and 11025208
文摘Cell-matrix interaction is the key for understanding the cell behaviors,especially the mechanosensitivity of cell adhesion,cell migration and differentiation,etc.Cells are constantly probing,pushing and pulling on the surrounding extracellular matrix.These cell-generated forces drive cell migration and tissue morphogenesis,and maintain the intrinsic mechanical tone of tissues.Therefore,knowledge of the spatial and temporal nature of these forces are essential to understanding when and where mechanical events come to play in both physiological and pathological settings.However,because of the complexity of cell geometry and insufficient
文摘针对无源侦察系统的实时性应用需求,该文提出了一种基于功率聚焦的宽带阵列信号检测算法。利用均匀线阵接收信号的相位变化信息,通过改进的二重FFT算法将各阵元接收信号的功率聚焦到信号到达角(Direction Of Arrival,DOA)。在此基础上,推导了聚焦后各角度上噪声数据的概率密度函数,构造了具有恒虚警特性的检验统计量和相应的检测门限,并推导了不同虚警率和信噪比条件下的理论检测概率。该算法聚焦过程计算复杂度较小,检测过程不依赖于信号先验信息,检测结果还可为后续的精确角度测量提供初值。仿真实验表明,该算法对弱信号具有较好的检测效果。
基金Project(U1865203)supported by the Key Projects of the Yalong River Joint Fund of the National Natural Science Foundation of ChinaProject(51279201)supported by the National Natural Science Foundation of ChinaProjects(2019YFC0605103,2019YFC0605100)supported by the National Key R&D Program of China。
文摘Rock bolts are widely used in rock engineering projects to improve the shear capacity of the jointed rock mass.The bolt inclination angle with respect to the shear plane has a remarkable influence on the bolting performance.In this study,a new artificial molding method based on 3D scanning and printing technology was first proposed to prepare bolted joints with an inclined bolt.Then,the effects of the bolt inclination angle and boundary conditions on the shear behavior and failure characteristic of bolted joints were addressed by conducting direct shear tests under both CNL and CNS conditions.Results indicated that rock bolt could significantly improve the shear behavior of rock joints,especially in the post-yield deformation region.With the increase of bolt inclination angle,both the maximum shear stress and the maximum friction coefficient increased first and then decreased,while the maximum normal displacement decreased monotonously.Compared with CNL conditions,the maximum shear stress was larger,whereas the maximum normal displacement and friction coefficient were smaller under the CNS conditions.Furthermore,more asperity damage was observed under the CNS conditions due to the increased normal stress on the shear plane.
基金supported by the National Outstanding Young Scientist Foundation of China(11225213)Major Program of National Natural Science Foundation of China(Grant No.11390362)
文摘According to the dimensionless formulae of DOP(depth of penetration) of a rigid projectile into different targets,the resistive force which a target exerts on the projectile during the penetration of rigid projectile is theoretically analyzed.In particular,the threshold V_C of impact velocity applicable for the assumption of constant resistive force is formulated through impulse analysis.The various values of V_C corresponding to different pairs of projectile-target are calculated,and the consistency of the relative test data and numerical results is observed.
基金Supported by the National Natural Science Foundation of China(31071579)the Key Program of the Natural Science Foundation of Heilongjiang Province of China(ZD201013)the Key Project of Education Department of Heilongjiang Province of China(125212003)
文摘The kinetic mechanism for the preparation of silymarin from milk thistle seeds was studied during the microwave-assisted extraction （MAE） process. The results showed that the transfer rate of silymarin from milk thistle seeds increased with the microwave output power and temperature during MAE processing. The apparent extraction rate constant k （s-1） was 1.2028×10-2 , 1.2248×10-2 , and 1.2485×10-2 , and diffusion coefficient D （m2·s-1 ） was 4.21×10-10, 4.29×10-10 , and 4.37×10-10 at the microwave temperatures of 383, 393, and 403 K, respectively, in the silymarin MAE process. With the help of scanning electron microscopy （SEM）, the microstructures of the samples extracted by MAE were observed. The results revealed that the increased efficiency and rate of MAE of silymarin could be attributed mainly to the subsequent cell change resulting from superheating effects during MAE.
