With the increasing use of metal foams in various engineering applications, investigation of their dynamic behaviour under varying strain rate is necessary. Closed cell aluminium fly ash foam developed through liquid ...With the increasing use of metal foams in various engineering applications, investigation of their dynamic behaviour under varying strain rate is necessary. Closed cell aluminium fly ash foam developed through liquid metallurgy route was investigated for its stress--strain behaviour at different strain rates ranging from 700 s^-1 to 1950 s^-1. The numerical model of split Hopkinson pressure bar （SHPB） was simulated using commercially available finite element code Abaqus/Explicit. Validation of numerical simulation was carried out using available experimental and numerical results. Full scale stress--strain curves wez＇e developed for various strain rates to study the effect of strain rate on compressive strength and energy absorption. The results showed that the closed cell aluminium fly ash foam is sensitive to strain rate.展开更多
Objective: To introduce a method to calculate cardiovascular age, a new, accurate and much simpler index for assessing cardiovascular autonomic regulatory function, based on statistical analysis of heart rate and bloo...Objective: To introduce a method to calculate cardiovascular age, a new, accurate and much simpler index for assessing cardiovascular autonomic regulatory function, based on statistical analysis of heart rate and blood pressure variability (HRV and BPV) and baroreflex sensitivity (BRS) data. Methods: Firstly, HRV and BPV of 89 healthy aviation personnel were analyzed by the conventional autoregressive (AR) spectral analysis and their spontaneous BRS was obtained by the sequence method. Secondly, principal component analysis was conducted over original and derived indices of HRV, BPV and BRS data and the relevant principal components, PCi orig and PCi deri (i=1, 2, 3,...) were obtained. Finally, the equation for calculating cardiovascular age was obtained by multiple regression with the chronological age being assigned as the dependent variable and the principal components significantly related to age as the regressors. Results: The first four principal components of original indices accounted for over 90% of total variance of the indices, so did the first three principal components of derived indices. So, these seven principal components could reflect the information of cardiovascular autonomic regulation which was embodied in the 17 indices of HRV, BPV and BRS exactly with a minimal loss of information. Of the seven principal components, PC2 orig , PC4 orig and PC2 deri were negatively correlated with the chronological age ( P <0 05), whereas the PC3 orig was positively correlated with the chronological age ( P <0 01). The cardiovascular age thus calculated from the regression equation was significantly correlated with the chronological age among the 89 aviation personnel ( r =0.73, P <0 01). Conclusion: The cardiovascular age calculated based on a multi variate analysis of HRV, BPV and BRS could be regarded as a comprehensive indicator reflecting the age dependency of autonomic regulation of cardiovascular system in healthy aviation personnel.展开更多
目的探讨盐敏感性高血压不同中医证候间血压特点及差异,并对心率变异性进行研究,以明确自主神经张力对不同中医证候盐敏感性高血压病人血压的影响。方法选择131例盐敏感性高血压病人,运用动态血压及动态心电图对不同中医证候组间血压及...目的探讨盐敏感性高血压不同中医证候间血压特点及差异,并对心率变异性进行研究,以明确自主神经张力对不同中医证候盐敏感性高血压病人血压的影响。方法选择131例盐敏感性高血压病人,运用动态血压及动态心电图对不同中医证候组间血压及心率变异性差异进行分析。结果 24 h平均收缩压(24 h ASBP)、日间平均收缩压(DASBP),脾肾阳虚、水饮内停组>阴虚阳亢组,差异有统计学意义(P<0.05);夜间平均收缩压(NASBP),脾肾阳虚、水饮内停组明显高于其他两组,差异有统计学意义(P<0.05);24 h平均舒张压(24 h ADBP),痰湿壅盛及脾肾阳虚、水饮内停组明显高于阴虚阳亢组(P<0.05);日间平均舒张压(DADBP)、夜间平均舒张压(NADBP)脾肾阳虚、水饮内停组明显高于阴虚阳亢组(P<0.05);24 h平均动脉压(24 h APP)、日间平均动脉压(DAPP),脾肾阳虚、水饮内停组明显高于阴虚阳亢组(P<0.05);24 h收缩压变异系数(24 h SBPV)、日间收缩压变异系数(DSBPV)、24 h舒张压变异系数(24 h DBPV)、日间舒张压变异系数(DDBPV)、夜间舒张压变异系数(NDBPV),脾肾阳虚、水饮内停组明显高于阴虚阳亢组(P<0.05);24 h舒张压负荷(24 h DBPL)、日间舒张压负荷(DDBPL)、夜间舒张压负荷(NDBPL),脾肾阳虚、水饮内停组明显高于阴虚阳亢组(P<0.05)。夜间收缩压下降率(NSBPRR)、夜间舒张压下降率(NDBPRR),脾肾阳虚、水饮内停组明显低于痰湿壅盛组(P<0.05)。心率变异性比较结果:脾肾阳虚、水饮内停组24 h总心搏数及平均心率均明显高于阴虚阳亢组和痰湿壅盛组(P<0.05);脾肾阳虚、水饮内停组窦性R-R间期(NN间期)(SDNN)、RR间期平均值标准差(SDANN)、相邻NN间期差的标准差(SDSD)、三角指数明显低于其他两组(P<0.05);而RR间期差值的均方根(RMSSD)、相邻NN之差>50 ms占总心搏百分比(PNN50)组间比较,差异无统计学意义(P>0.05)。结论盐敏感性高血压脾肾阳虚、水饮内停证血压程度最高,血压负荷最重,血压节律紊乱且夜间血压下降不足,相应的交感神经张力增高最明显,提示脾肾阳虚、水饮内停证交感神经张力增高可能是其血压高于其他证候的原因之一。展开更多
文摘With the increasing use of metal foams in various engineering applications, investigation of their dynamic behaviour under varying strain rate is necessary. Closed cell aluminium fly ash foam developed through liquid metallurgy route was investigated for its stress--strain behaviour at different strain rates ranging from 700 s^-1 to 1950 s^-1. The numerical model of split Hopkinson pressure bar （SHPB） was simulated using commercially available finite element code Abaqus/Explicit. Validation of numerical simulation was carried out using available experimental and numerical results. Full scale stress--strain curves wez＇e developed for various strain rates to study the effect of strain rate on compressive strength and energy absorption. The results showed that the closed cell aluminium fly ash foam is sensitive to strain rate.
文摘Objective: To introduce a method to calculate cardiovascular age, a new, accurate and much simpler index for assessing cardiovascular autonomic regulatory function, based on statistical analysis of heart rate and blood pressure variability (HRV and BPV) and baroreflex sensitivity (BRS) data. Methods: Firstly, HRV and BPV of 89 healthy aviation personnel were analyzed by the conventional autoregressive (AR) spectral analysis and their spontaneous BRS was obtained by the sequence method. Secondly, principal component analysis was conducted over original and derived indices of HRV, BPV and BRS data and the relevant principal components, PCi orig and PCi deri (i=1, 2, 3,...) were obtained. Finally, the equation for calculating cardiovascular age was obtained by multiple regression with the chronological age being assigned as the dependent variable and the principal components significantly related to age as the regressors. Results: The first four principal components of original indices accounted for over 90% of total variance of the indices, so did the first three principal components of derived indices. So, these seven principal components could reflect the information of cardiovascular autonomic regulation which was embodied in the 17 indices of HRV, BPV and BRS exactly with a minimal loss of information. Of the seven principal components, PC2 orig , PC4 orig and PC2 deri were negatively correlated with the chronological age ( P <0 05), whereas the PC3 orig was positively correlated with the chronological age ( P <0 01). The cardiovascular age thus calculated from the regression equation was significantly correlated with the chronological age among the 89 aviation personnel ( r =0.73, P <0 01). Conclusion: The cardiovascular age calculated based on a multi variate analysis of HRV, BPV and BRS could be regarded as a comprehensive indicator reflecting the age dependency of autonomic regulation of cardiovascular system in healthy aviation personnel.
文摘目的探讨盐敏感性高血压不同中医证候间血压特点及差异,并对心率变异性进行研究,以明确自主神经张力对不同中医证候盐敏感性高血压病人血压的影响。方法选择131例盐敏感性高血压病人,运用动态血压及动态心电图对不同中医证候组间血压及心率变异性差异进行分析。结果 24 h平均收缩压(24 h ASBP)、日间平均收缩压(DASBP),脾肾阳虚、水饮内停组>阴虚阳亢组,差异有统计学意义(P<0.05);夜间平均收缩压(NASBP),脾肾阳虚、水饮内停组明显高于其他两组,差异有统计学意义(P<0.05);24 h平均舒张压(24 h ADBP),痰湿壅盛及脾肾阳虚、水饮内停组明显高于阴虚阳亢组(P<0.05);日间平均舒张压(DADBP)、夜间平均舒张压(NADBP)脾肾阳虚、水饮内停组明显高于阴虚阳亢组(P<0.05);24 h平均动脉压(24 h APP)、日间平均动脉压(DAPP),脾肾阳虚、水饮内停组明显高于阴虚阳亢组(P<0.05);24 h收缩压变异系数(24 h SBPV)、日间收缩压变异系数(DSBPV)、24 h舒张压变异系数(24 h DBPV)、日间舒张压变异系数(DDBPV)、夜间舒张压变异系数(NDBPV),脾肾阳虚、水饮内停组明显高于阴虚阳亢组(P<0.05);24 h舒张压负荷(24 h DBPL)、日间舒张压负荷(DDBPL)、夜间舒张压负荷(NDBPL),脾肾阳虚、水饮内停组明显高于阴虚阳亢组(P<0.05)。夜间收缩压下降率(NSBPRR)、夜间舒张压下降率(NDBPRR),脾肾阳虚、水饮内停组明显低于痰湿壅盛组(P<0.05)。心率变异性比较结果:脾肾阳虚、水饮内停组24 h总心搏数及平均心率均明显高于阴虚阳亢组和痰湿壅盛组(P<0.05);脾肾阳虚、水饮内停组窦性R-R间期(NN间期)(SDNN)、RR间期平均值标准差(SDANN)、相邻NN间期差的标准差(SDSD)、三角指数明显低于其他两组(P<0.05);而RR间期差值的均方根(RMSSD)、相邻NN之差>50 ms占总心搏百分比(PNN50)组间比较,差异无统计学意义(P>0.05)。结论盐敏感性高血压脾肾阳虚、水饮内停证血压程度最高,血压负荷最重,血压节律紊乱且夜间血压下降不足,相应的交感神经张力增高最明显,提示脾肾阳虚、水饮内停证交感神经张力增高可能是其血压高于其他证候的原因之一。
