BACKGROUND： The detection of motor evoked potential is utilized to explore neuromuscular finger coordination. The influence of transcranial magnetic stimulation on finger force has been investigated mainly on a singl...BACKGROUND： The detection of motor evoked potential is utilized to explore neuromuscular finger coordination. The influence of transcranial magnetic stimulation on finger force has been investigated mainly on a single finger, and only time-dependent increased target finger force has been detected in the finger force task. OBJECTIVE： To explore the neural mechanism of finger force coordination in the motor cortex by observing the influence of various finger coordination patterns and patterns of transcranial magnetic stimulation （TMS）-induced finger force changes. DESIGN, TIME AND SETTING： Neurophysiological and behavioral study was performed at the Biomedical Engineering Laboratory of Chongqing University from April to June 2008. PARTICIPANTS： A total of 10 healthy, university students, comprising 5 males and 5 females, aged 21-23 years, voluntarily participated in this study. All participants were right-handed, with normal or corrected vision. Individuals with upper limb complaints or other musculoskeletal disorders were excluded. METHODS： A target force-tracking task was conducted on the index finger, the index and middle fingers, and four fingers （index, middle, ring, and little）, respectively. Target force trace in a single trial consisted of a 6-second ramp phase, a 20-second constant phase, and a 6-second drop phase. During experimentation, an unpredictable single-pulse TMS （120% motor threshold） was applied to the primary motor cortex （M1） in each phase. MAIN OUTCOME MEASURES： Changes in peak force induced by TMS were obtained for each finger pattern during each force-tracking phase. Differences in force changes were tested between different finger pattems with regard to ramp, constant, and drop phases of target force. RESULTS： Under ramp, constant, and drop phases of target force, the increase in magnetic stimulation-induced finger forces changes positively correlated with the number of fingers involved in the force tracking task. The magnetic stimulation-induced force changes from the index finger were less than the combination of the index and middle fingers or all four fingers under the corresponding target force, and the force changes from the combination of the index and middle fingers were less than all four fingers, Le., index finger 〈 index and middle fingers 〈 four fingers. CONCLUSION： Different neuromuscular mechanisms could be involved in finger force production for different finger combination patterns. Results from the present study suggested that independent motor neurons regulated individual finger force production.展开更多
Fluid percussion-induced traumatic brain injury models have been widely used in experimental research for years. In an experiment, the stability of impaction is inevitably affected by factors such as the appearance of...Fluid percussion-induced traumatic brain injury models have been widely used in experimental research for years. In an experiment, the stability of impaction is inevitably affected by factors such as the appearance of liquid spikes. Management of impact pressure is a crucial factor that determines the stability of these models, and direction of impact control is another basic element. To improve experimental stability, we calculated a pressure curve by generating repeated impacts using a fluid percussion device at different pendulum angles. A stereotactic frame was used to control the direction of impact. We produced stable and reproducible models, including mild, moderate, and severe traumatic brain injury, using the MODEL01-B device at pendulum angles of 6°, 11° and 13°, with corresponding impact force values of 1.0 ± 0.11 atm（101.32 ± 11.16 k Pa）, 2.6 ± 0.16 atm（263.44 ± 16.21 k Pa）, and 3.6 ± 0.16 atm（364.77 ± 16.21 k Pa）, respectively. Behavioral tests, hematoxylin-eosin staining, and magnetic resonance imaging revealed that models for different degrees of injury were consistent with the clinical properties of mild, moderate, and severe craniocerebral injuries. Using this method, we established fluid percussion models for different degrees of injury and stabilized pathological features based on precise power and direction control.展开更多
本工作通过原位原子力显微镜Peak force tapping模式对石墨烯和迈科烯(MXene)的结构稳定性进行了比较。当原位观察二维材料还原氧化石墨烯(rGO)时,rGO形貌基本不随时间发生改变;而当原位观察二维材料迈科烯V_(2)C时,V_(2)C表面发生纳米...本工作通过原位原子力显微镜Peak force tapping模式对石墨烯和迈科烯(MXene)的结构稳定性进行了比较。当原位观察二维材料还原氧化石墨烯(rGO)时,rGO形貌基本不随时间发生改变;而当原位观察二维材料迈科烯V_(2)C时,V_(2)C表面发生纳米刻蚀现象,其形貌表面积随扫描时间逐渐减小。利用数据处理软件分析面积变化,计算出纳米刻蚀的速率,发现增大峰值力,平均纳米刻蚀速率随之增大,且在大气环境中的刻蚀速率大于在手套箱(Ar气氛围,H_(2)O和O_(2)含量小于1×10^(-6))中的速率,说明大气中的水分对材料的稳定性有影响,会加快纳米刻蚀的速率。本研究表明原子力显微镜Peak force tapping模式可以用来快速表征二维材料的稳定性。展开更多
The atomic force microscope(AFM)can measure nanoscale morphology and mechanical properties and has a wide range of applications.The traditional method for measuring the mechanical properties of a sample does so for th...The atomic force microscope(AFM)can measure nanoscale morphology and mechanical properties and has a wide range of applications.The traditional method for measuring the mechanical properties of a sample does so for the longitudinal and transverse properties separately,ignoring the coupling between them.In this paper,a data processing and multidimensional mechanical information extraction algorithm for the composite mode of peak force tapping and torsional resonance is proposed.On the basis of a tip–sample interaction model for the AFM,longitudinal peak force data are used to decouple amplitude and phase data of transverse torsional resonance,accurately identify the tip–sample longitudinal contact force in each peak force cycle,and synchronously obtain the corresponding characteristic images of the transverse amplitude and phase.Experimental results show that the measured longitudinal mechanical characteristics are consistent with the transverse amplitude and phase characteristics,which verifies the effectiveness of the method.Thus,a new method is provided for the measurement of multidimensional mechanical characteristics using the AFM.展开更多
It is extremely important to select appropriate feedrates for the stable machining of parts with ruled surface in modern aviation industrial applications.However,the current studies take too much time to achieve this ...It is extremely important to select appropriate feedrates for the stable machining of parts with ruled surface in modern aviation industrial applications.However,the current studies take too much time to achieve this goal.Therefore,this paper presents an efficient feedrate optimization method for constant peak cutting force in five-axis flank milling process.The solution method of the instantaneous undeformed chip thickness(IUCT)is proposed using least squares theory with the cutter entry angle and feedrate as variables.Based on this method,an explicit analytical expression of the peak cutting force for each cutting point is established.Furthermore,a feedrate scheduling method is developed to quickly solve the appropriate feedrate under constant peak cutting force.To verify the proposed IUCT model,the fitting IUCT is compared with the accuracy data at different feedrates.Additionally,some experiments of five-axis flank milling are conducted to demonstrate the effectiveness of the peak force model and the feedrate scheduling method.And the surface roughness before and after feedrate scheduling is detected.The results show that the proposed feedrate scheduling method can quickly adjust the feedrate and ensure constant peak force during machining.At the same time,the surface quality is kept at a high level.展开更多
Plant root system plays an important role in preventing soil erosion and improving slope stability.However,its performance is significantly affected by soil moisture content,and the role of soil moisture in root reinf...Plant root system plays an important role in preventing soil erosion and improving slope stability.However,its performance is significantly affected by soil moisture content,and the role of soil moisture in root reinforcement is not fully understood.In this study,the influence of soil moisture on root pullout properties was studied by experiments.Vertical in-situ pullout tests under four different levels of soil matric suction(12 kPa,18 kPa,24 kPa,30 kPa)were carried out on roots of sea buckthorn plants(Hippophae rhamnoides Linn.)which were artificially cultivated for 7 months.Diameter and length of the root system of sea buckthorn were investigated.The results showed that a very significant correlation was observed between root diameter(D)and root length(L)(P<0.01),and root diameter decreased with soil depth.When soil bulk density was constant,peak pullout force(F)and friction coefficient of root-soil interface(μ)decreased with increasing gravimetric soil moisture content in power functions.Soil moisture content significantly affected root pullout resistance because the increase of soil moisture content decreased the friction coefficient between the roots and soil.Root diameter at breakage point(Db)and length of root segment left in soil(Lb)were increased with soil moisture content.In addition,peak pullout force of the roots increased in a power function with root diameter at the soil surface(D0)and in a linear function with total root length(L).The results provided an experimental basis for quantifying the effects of soil moisture content on soil reinforcement by plant roots.展开更多
This paper focuses on developing improved concept models for straight thin-walled box sectional columns which can better predict the peak crushing force that occurs during crashworthiness analyses. We develop a nonlin...This paper focuses on developing improved concept models for straight thin-walled box sectional columns which can better predict the peak crushing force that occurs during crashworthiness analyses. We develop a nonlinear translational spring based on previous research and apply such a spring element to build the enhanced concept models. The work presented in this article is developed on the basis of the publication of the author (Liu and Day, 2006b) and has been applied in a crashworthiness design issue, which is presented by the author in another paper (Liu, 2008).展开更多
Purpose The aim of the study was to establish the optimum variable resistance(VR)intensity for loaded countermovement jump(LCMJ)to induce post-activation potentiation(PAP).Methods Eleven male athletes(age 23±2.3 ...Purpose The aim of the study was to establish the optimum variable resistance(VR)intensity for loaded countermovement jump(LCMJ)to induce post-activation potentiation(PAP).Methods Eleven male athletes(age 23±2.3 years,height 1.77±0.05 m,body mass 73.7±9.0 kg)attended one familiariza-tion and four testing sessions.Subjects performed their own pre-competition warm up before performing two countermove-ment jumps(CMJ)for baseline measure.Subsequently,they performed 2×3 unloaded(UCMJ)or loaded CMJ(LCMJ)with one of the three VR intensities,Orange(6.7±0.6 kg),Red(14.0±0.9 kg)and Blue(24.0±1.4 kg),in random order,before performing two more CMJ for post-test measure.Each testing session was separated by at least 48 h.Results There was significant increase in jump height in all conditions(P<0.05),but no significant difference in change in jump height between conditions(P>0.05).There were small to moderate effect when comparing Orange and the other conditions.Peak force and velocity increased in Red(P<0.05)and Orange(P<0.05),respectively.Change in jump height was significantly correlated to change in peak velocity(r=0.46,P=0.002)and peak power(r=0.46,P=0.002).Conclusion The findings of the study showed that UCMJ and LCMJ were effective in improving jump height acutely,and an intensity level of about 10%body weight contributed by VR seems to be the optimum resistance level.展开更多
Purpose Isometric strength training (IST) with rapid non-sustained contraction (RIST) is effective in improving the ability to generate force rapidly.However,the neuromuscular adaptation of IST with sustained contract...Purpose Isometric strength training (IST) with rapid non-sustained contraction (RIST) is effective in improving the ability to generate force rapidly.However,the neuromuscular adaptation of IST with sustained contraction (SIST) and RIST is not known.Therefore,the aim of the study was to compare the neuromuscular adaptations of RIST with SIST.Methods Thirty-three national floorball players (23.9 ± 3.1 years old;1.69± 0.08 m;64.6± 11.1 kg) were recruited for this study.Pre-and post-test included countermovement jump (CMJ),30-m sprint (TT30),isometric squat at 90° (ISqT90) and 120° (ISqT120) knee angles.They were randomly assigned to either control (Con) (n =9),RIST (n =12) or SIST (n =12)group and performed 12 sessions of intervention training.All groups performed the same sets of exercises,but RIST and SIST had to perform ISqT with and without sustained contraction,respectively.Results Time × group effect for CMJ height (P =0.01,η2p=0.25),peak force (PF) (P =0.03,η2p =0.22) and rate of force development (RFD) (P =0.02,η2p =0.22) obtained from ISqT 120 were noted.A main effect for time was observed in CMJ height,PF obtained from ISqT90 and ISqT120,and RFD obtained from ISqT90 (P < 0.01,0.27 < η2p < 0.57).There was greater improvement in TT30 (P =0.043,d =3.00),ISqT90 PF (P =0.034,d =3.12),ISqT 120 PF (P =0.003,d =4.54) and ISqT120 RFD (P=0.033,d=1.36) in the SIST than the Con group.Conclusion SIST was more effective in improving strength and dynamic performance as compared to RIST,making it a viable training method to enhance dynamic performances.展开更多
基金the National Natural Science Foundation of China, No. 3077054630970758+1 种基金Chongqing Natural Science Foundation, No. 2006BB2043 2007BB5148
文摘BACKGROUND： The detection of motor evoked potential is utilized to explore neuromuscular finger coordination. The influence of transcranial magnetic stimulation on finger force has been investigated mainly on a single finger, and only time-dependent increased target finger force has been detected in the finger force task. OBJECTIVE： To explore the neural mechanism of finger force coordination in the motor cortex by observing the influence of various finger coordination patterns and patterns of transcranial magnetic stimulation （TMS）-induced finger force changes. DESIGN, TIME AND SETTING： Neurophysiological and behavioral study was performed at the Biomedical Engineering Laboratory of Chongqing University from April to June 2008. PARTICIPANTS： A total of 10 healthy, university students, comprising 5 males and 5 females, aged 21-23 years, voluntarily participated in this study. All participants were right-handed, with normal or corrected vision. Individuals with upper limb complaints or other musculoskeletal disorders were excluded. METHODS： A target force-tracking task was conducted on the index finger, the index and middle fingers, and four fingers （index, middle, ring, and little）, respectively. Target force trace in a single trial consisted of a 6-second ramp phase, a 20-second constant phase, and a 6-second drop phase. During experimentation, an unpredictable single-pulse TMS （120% motor threshold） was applied to the primary motor cortex （M1） in each phase. MAIN OUTCOME MEASURES： Changes in peak force induced by TMS were obtained for each finger pattern during each force-tracking phase. Differences in force changes were tested between different finger pattems with regard to ramp, constant, and drop phases of target force. RESULTS： Under ramp, constant, and drop phases of target force, the increase in magnetic stimulation-induced finger forces changes positively correlated with the number of fingers involved in the force tracking task. The magnetic stimulation-induced force changes from the index finger were less than the combination of the index and middle fingers or all four fingers under the corresponding target force, and the force changes from the combination of the index and middle fingers were less than all four fingers, Le., index finger 〈 index and middle fingers 〈 four fingers. CONCLUSION： Different neuromuscular mechanisms could be involved in finger force production for different finger combination patterns. Results from the present study suggested that independent motor neurons regulated individual finger force production.
基金supported by a grant from the International S cience and Technology Cooperation Projects of China,No.2011DFG33430
文摘Fluid percussion-induced traumatic brain injury models have been widely used in experimental research for years. In an experiment, the stability of impaction is inevitably affected by factors such as the appearance of liquid spikes. Management of impact pressure is a crucial factor that determines the stability of these models, and direction of impact control is another basic element. To improve experimental stability, we calculated a pressure curve by generating repeated impacts using a fluid percussion device at different pendulum angles. A stereotactic frame was used to control the direction of impact. We produced stable and reproducible models, including mild, moderate, and severe traumatic brain injury, using the MODEL01-B device at pendulum angles of 6°, 11° and 13°, with corresponding impact force values of 1.0 ± 0.11 atm（101.32 ± 11.16 k Pa）, 2.6 ± 0.16 atm（263.44 ± 16.21 k Pa）, and 3.6 ± 0.16 atm（364.77 ± 16.21 k Pa）, respectively. Behavioral tests, hematoxylin-eosin staining, and magnetic resonance imaging revealed that models for different degrees of injury were consistent with the clinical properties of mild, moderate, and severe craniocerebral injuries. Using this method, we established fluid percussion models for different degrees of injury and stabilized pathological features based on precise power and direction control.
文摘本工作通过原位原子力显微镜Peak force tapping模式对石墨烯和迈科烯(MXene)的结构稳定性进行了比较。当原位观察二维材料还原氧化石墨烯(rGO)时,rGO形貌基本不随时间发生改变;而当原位观察二维材料迈科烯V_(2)C时,V_(2)C表面发生纳米刻蚀现象,其形貌表面积随扫描时间逐渐减小。利用数据处理软件分析面积变化,计算出纳米刻蚀的速率,发现增大峰值力,平均纳米刻蚀速率随之增大,且在大气环境中的刻蚀速率大于在手套箱(Ar气氛围,H_(2)O和O_(2)含量小于1×10^(-6))中的速率,说明大气中的水分对材料的稳定性有影响,会加快纳米刻蚀的速率。本研究表明原子力显微镜Peak force tapping模式可以用来快速表征二维材料的稳定性。
基金This project is supported by the General Program of the National Natural Science Foundation of China(62073227)the National Natural Science Foundation of China(61927805 and 61903359).
文摘The atomic force microscope(AFM)can measure nanoscale morphology and mechanical properties and has a wide range of applications.The traditional method for measuring the mechanical properties of a sample does so for the longitudinal and transverse properties separately,ignoring the coupling between them.In this paper,a data processing and multidimensional mechanical information extraction algorithm for the composite mode of peak force tapping and torsional resonance is proposed.On the basis of a tip–sample interaction model for the AFM,longitudinal peak force data are used to decouple amplitude and phase data of transverse torsional resonance,accurately identify the tip–sample longitudinal contact force in each peak force cycle,and synchronously obtain the corresponding characteristic images of the transverse amplitude and phase.Experimental results show that the measured longitudinal mechanical characteristics are consistent with the transverse amplitude and phase characteristics,which verifies the effectiveness of the method.Thus,a new method is provided for the measurement of multidimensional mechanical characteristics using the AFM.
基金co-supported by the Major National S&T Program(2017ZX04002001)the Major National S&T Program(2016ZX04004004)。
文摘It is extremely important to select appropriate feedrates for the stable machining of parts with ruled surface in modern aviation industrial applications.However,the current studies take too much time to achieve this goal.Therefore,this paper presents an efficient feedrate optimization method for constant peak cutting force in five-axis flank milling process.The solution method of the instantaneous undeformed chip thickness(IUCT)is proposed using least squares theory with the cutter entry angle and feedrate as variables.Based on this method,an explicit analytical expression of the peak cutting force for each cutting point is established.Furthermore,a feedrate scheduling method is developed to quickly solve the appropriate feedrate under constant peak cutting force.To verify the proposed IUCT model,the fitting IUCT is compared with the accuracy data at different feedrates.Additionally,some experiments of five-axis flank milling are conducted to demonstrate the effectiveness of the peak force model and the feedrate scheduling method.And the surface roughness before and after feedrate scheduling is detected.The results show that the proposed feedrate scheduling method can quickly adjust the feedrate and ensure constant peak force during machining.At the same time,the surface quality is kept at a high level.
基金supported by the National Natural Science Foundation of China project(No.31600582)Research Project Supported by Shanxi Scholarship Council of China(2020-054)+1 种基金Program for the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi Province of China(2017)Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi(2019L0175)。
文摘Plant root system plays an important role in preventing soil erosion and improving slope stability.However,its performance is significantly affected by soil moisture content,and the role of soil moisture in root reinforcement is not fully understood.In this study,the influence of soil moisture on root pullout properties was studied by experiments.Vertical in-situ pullout tests under four different levels of soil matric suction(12 kPa,18 kPa,24 kPa,30 kPa)were carried out on roots of sea buckthorn plants(Hippophae rhamnoides Linn.)which were artificially cultivated for 7 months.Diameter and length of the root system of sea buckthorn were investigated.The results showed that a very significant correlation was observed between root diameter(D)and root length(L)(P<0.01),and root diameter decreased with soil depth.When soil bulk density was constant,peak pullout force(F)and friction coefficient of root-soil interface(μ)decreased with increasing gravimetric soil moisture content in power functions.Soil moisture content significantly affected root pullout resistance because the increase of soil moisture content decreased the friction coefficient between the roots and soil.Root diameter at breakage point(Db)and length of root segment left in soil(Lb)were increased with soil moisture content.In addition,peak pullout force of the roots increased in a power function with root diameter at the soil surface(D0)and in a linear function with total root length(L).The results provided an experimental basis for quantifying the effects of soil moisture content on soil reinforcement by plant roots.
文摘This paper focuses on developing improved concept models for straight thin-walled box sectional columns which can better predict the peak crushing force that occurs during crashworthiness analyses. We develop a nonlinear translational spring based on previous research and apply such a spring element to build the enhanced concept models. The work presented in this article is developed on the basis of the publication of the author (Liu and Day, 2006b) and has been applied in a crashworthiness design issue, which is presented by the author in another paper (Liu, 2008).
文摘Purpose The aim of the study was to establish the optimum variable resistance(VR)intensity for loaded countermovement jump(LCMJ)to induce post-activation potentiation(PAP).Methods Eleven male athletes(age 23±2.3 years,height 1.77±0.05 m,body mass 73.7±9.0 kg)attended one familiariza-tion and four testing sessions.Subjects performed their own pre-competition warm up before performing two countermove-ment jumps(CMJ)for baseline measure.Subsequently,they performed 2×3 unloaded(UCMJ)or loaded CMJ(LCMJ)with one of the three VR intensities,Orange(6.7±0.6 kg),Red(14.0±0.9 kg)and Blue(24.0±1.4 kg),in random order,before performing two more CMJ for post-test measure.Each testing session was separated by at least 48 h.Results There was significant increase in jump height in all conditions(P<0.05),but no significant difference in change in jump height between conditions(P>0.05).There were small to moderate effect when comparing Orange and the other conditions.Peak force and velocity increased in Red(P<0.05)and Orange(P<0.05),respectively.Change in jump height was significantly correlated to change in peak velocity(r=0.46,P=0.002)and peak power(r=0.46,P=0.002).Conclusion The findings of the study showed that UCMJ and LCMJ were effective in improving jump height acutely,and an intensity level of about 10%body weight contributed by VR seems to be the optimum resistance level.
文摘Purpose Isometric strength training (IST) with rapid non-sustained contraction (RIST) is effective in improving the ability to generate force rapidly.However,the neuromuscular adaptation of IST with sustained contraction (SIST) and RIST is not known.Therefore,the aim of the study was to compare the neuromuscular adaptations of RIST with SIST.Methods Thirty-three national floorball players (23.9 ± 3.1 years old;1.69± 0.08 m;64.6± 11.1 kg) were recruited for this study.Pre-and post-test included countermovement jump (CMJ),30-m sprint (TT30),isometric squat at 90° (ISqT90) and 120° (ISqT120) knee angles.They were randomly assigned to either control (Con) (n =9),RIST (n =12) or SIST (n =12)group and performed 12 sessions of intervention training.All groups performed the same sets of exercises,but RIST and SIST had to perform ISqT with and without sustained contraction,respectively.Results Time × group effect for CMJ height (P =0.01,η2p=0.25),peak force (PF) (P =0.03,η2p =0.22) and rate of force development (RFD) (P =0.02,η2p =0.22) obtained from ISqT 120 were noted.A main effect for time was observed in CMJ height,PF obtained from ISqT90 and ISqT120,and RFD obtained from ISqT90 (P < 0.01,0.27 < η2p < 0.57).There was greater improvement in TT30 (P =0.043,d =3.00),ISqT90 PF (P =0.034,d =3.12),ISqT 120 PF (P =0.003,d =4.54) and ISqT120 RFD (P=0.033,d=1.36) in the SIST than the Con group.Conclusion SIST was more effective in improving strength and dynamic performance as compared to RIST,making it a viable training method to enhance dynamic performances.
