The excavation of foundation pit generates soil deformation around existing metro tunnel with shield driving method,which may lead to the deformation of tunnel lining.It is a challenge to evaluate the deformation of s...The excavation of foundation pit generates soil deformation around existing metro tunnel with shield driving method,which may lead to the deformation of tunnel lining.It is a challenge to evaluate the deformation of shield tunnel accurately and take measures to reduce the tunnel upward displacement as much as possible for geotechnical engineers.A new simplified analytical method is proposed to predict the longitudinal deformation of existing metro tunnel due to excavation unloading of adjacent foundation pit in this paper.Firstly,the additional stress of soils under vertical axisymmetric load in layered soil is obtained by using elastic multi-layer theory.Secondly,the metro tunnel is regarded as a Timoshenko beam supported by Winkler foundation so that the shear effect of tunnels can be taken into account.The additional stress acting on the tunnel due to excavation unloading in layered soil are compared with that in homogeneous soil.Additionally,the effectiveness of the analytical solution is verified via two actual cases.Moreover,parametric analysis is conducted to investigate the responses of the metro tunnel by considering such factors as the variation of subgrade coefficient,offset distance from the excavation center to tunnel longitudinal axis as well as equivalent shear stiffness.The proposed method can be used to provide theoretical basis for similar engineering project.展开更多
Background:Previous studies of foot strike patterns of distance runners in road races have typically found that the overwhelming majority of shod runners initially contact the ground on the rearfoot.However,none of th...Background:Previous studies of foot strike patterns of distance runners in road races have typically found that the overwhelming majority of shod runners initially contact the ground on the rearfoot.However,none of these studies has attempted to quantify foot strike patterns of barefoot or minimally shod runners.This study classifies foot strike patterns of barefoot and minimally shod runners in a recreational road race.Methods:High-speed video footage was obtained of 169 barefoot and 42 minimally shod distance runners at the 2011 New York City Barefoot Run.Foot strike patterns were classified for each runner,and frequencies of forefoot,midfoot,and rearfoot striking were compared between the barefoot and minimally shod groups.Results:A total of 59.2%of barefoot runners were forefoot strikers,20.1%were midfoot strikers,and 20.7%were rearfoot strikers.For minimally shod runners,33.3%were forefoot strikers,19.1%were midfoot strikers,and 47.6%were rearfoot strikers.Foot strike distributions for barefoot and minimally shod runners were significantly different both from one another and from previously reported foot strike distributions of shod road racers.Conclusion:Foot strike patterns differ between barefoot and minimally shod runners,with forefoot striking being more common,and rearfoot striking less common in the barefoot group.展开更多
Purpose:This study examined variation in foot strike types,lower extremity kinematics,and arch height and stiffness among Tarahumara Indians from the Sierra Tarahumara.Mexico.Methods:High speed video was used to study...Purpose:This study examined variation in foot strike types,lower extremity kinematics,and arch height and stiffness among Tarahumara Indians from the Sierra Tarahumara.Mexico.Methods:High speed video was used to study the kinematics of 23 individuals.13 who habitually wear traditional minimal running sandals(huaraches).and 10 who habitually wear modern,conventional running shoes with elevated,cushioned heels and arch support.Measurements of foot shape and arch stiffness were taken on these individuals plus an additional sample of 12 individuals.Results:Minimally shod Tarahumara exhibit much variation with 40%primarily using midfoot strikes,30%primarily using forefoot strikes,and30%primarily using rearfoot strikes.In contrast,75%of the conventionally shod Tarahumara primarily used rearfoot strikes,and 25%primarily used midfoot strikes.Individuals who used forefoot or midfoot strikes landed with significantly more plantarflexed ankles,flexed knees,and flexed hips than runners who used rearfoot strikes.Foot measurements indicate that conventionally shod Tarahumara also have significantly less stiff arches than those wearing minimal shoes.Conclusion:These data reinforce earlier studies that there is variation among foot strike patterns among minimally shod runners,but also support the hypothesis that foot stiffness and important aspects of running form,including foot strike,differ between runners who grow up using minimal versus modem,conventional footwear.展开更多
The effects of different simple cultivation facilities on yield and quality of Brassica campestris L. were compared to explore the optimal facility type for pro- duction of B. campestris, thereby providing a technical...The effects of different simple cultivation facilities on yield and quality of Brassica campestris L. were compared to explore the optimal facility type for pro- duction of B. campestris, thereby providing a technical reference for efficient cultiva- tion of B. campestris during hot season. A total of four treatments were designed, open field cultivation （CK）, ordinary anti-insect net shed cultivation, ordinary plastic film greenhouse cultivation and Japanese translucent anti-insect net shed cultivation. The results showed that compared with those in open field cultivation, the plant height, leaf area, yield, Vc content, soluble sugar content and soluble protein con- tent of B. campestris in Japanese translucent anti-insect net shed cultivation were increased by 22%, 63%, 49%, 14%, 13% and 10%, respectively, and Japanese translucent anti-insect net shed was the optimal facility type for cultivation of B. campestris in hot season.展开更多
Background:This prospective study explored the effects of endurance running(ER) in minimal versus standard running shoes on the foot’s superficial layer intrinsic muscles and the function of the longitudinal arch.Our...Background:This prospective study explored the effects of endurance running(ER) in minimal versus standard running shoes on the foot’s superficial layer intrinsic muscles and the function of the longitudinal arch.Our hypothesis was that running in minimal shoes would cause hypertrophy in these muscles and lead to higher,stronger,stiffer arches.Methods:The hypothesis was tested using a sample of 33 healthy runners randomized into two groups,a control group shod in traditional running footwear and an experimental group shod in minimal support footwear,whose feet were scanned in an MRI before and after a 12-week training regime.Running kinematics as well as arch stiffness and height were also assessed before and after the treatment period.Results:Analysis of anatomical cross-sectional areas and muscle volumes indicate that the flexor digitomm brevis muscle became larger in both groups by 11%and 21%,respectively,but only the minimally shod runners had significant areal and volumetric increases of the abductor digiti minimi of 18%and 22%,respectively,and significantly increased longitudinal arch stiffness(60%).Conclusion:These results suggest that endurance running in minimal support footwear with 4 mm offset or less makes greater use of the springlike function of the longitudinal arch,thus leading to greater demands on the intrinsic muscles that support the arch,thereby strengthening the foot.展开更多
Based on the heterogeneity of fault plane strength,the macro rupture process of a fault plane can be treated as the rupture accumulation process of local micro-elements in the fault surface.Assuming that the strength ...Based on the heterogeneity of fault plane strength,the macro rupture process of a fault plane can be treated as the rupture accumulation process of local micro-elements in the fault surface.Assuming that the strength of the local micro-elements follows the Weibull probability distribution,the macro-fault constitutive relationship of the complete load-deformation process is derived from a statistical mechanics viewpoint.Applying a one-dimensional earthquake mechanics model and using far-field displacement a as the control variable,the problem of earthquake instability is investigated by employing the stability theory.The results show that the system stiffness ratio(stiffness ratio of fault to surroun-ding rock) β is the important parameter that affects the occurrence of earthquakes.Earthquake instability occurs only when β < 1,and the sudden stress jump appears at the displacement turning point of the equilibrium path curve.The expression of three important parameters for earthquakes(fault half-dislocation distance after earthquake,earthquake stress drop and elastic energy release) is also given.When β≥1,the earthquake does not occur and the fault only slips slowly without an earthquake.展开更多
The time-history response of a structure-pile system during soil liquefaction is highly complicated and several analytical methods have been proposed through the accuracy verification based on the comparison with the ...The time-history response of a structure-pile system during soil liquefaction is highly complicated and several analytical methods have been proposed through the accuracy verification based on the comparison with the experimental works. However, the analytical methods with higher accuracy often require large computational loads and are not necessarily preferred in the actual design practice. On the other hand, while the response spectrum method is not accurate compared to the aforementioned methods, it can provide useful design guidelines in the preliminary stage for structure-pile systems under soil liquefaction with acceptable accuracy. In this paper, the previously proposed response spectrum method for a structure-pile-soil system is used where the effect of soil liquefaction is taken into account by introducing the so-called p-multiplier method. It is shown that, while in the case of inner partial liquefaction with a non-liquefied layer at the top, the demand on the pile moment is large due to the inertial effect of that non-liquefied layer at the top, in the case of overall liquefaction near the ground surface, the demand is smaller than the case of inner partial liquefaction.展开更多
基金Project(51568006)supported by the National Natural Science Foundation of ChinaProject(2018JJA160134)supported by the Natural Science Foundation of Guangxi Province,China。
文摘The excavation of foundation pit generates soil deformation around existing metro tunnel with shield driving method,which may lead to the deformation of tunnel lining.It is a challenge to evaluate the deformation of shield tunnel accurately and take measures to reduce the tunnel upward displacement as much as possible for geotechnical engineers.A new simplified analytical method is proposed to predict the longitudinal deformation of existing metro tunnel due to excavation unloading of adjacent foundation pit in this paper.Firstly,the additional stress of soils under vertical axisymmetric load in layered soil is obtained by using elastic multi-layer theory.Secondly,the metro tunnel is regarded as a Timoshenko beam supported by Winkler foundation so that the shear effect of tunnels can be taken into account.The additional stress acting on the tunnel due to excavation unloading in layered soil are compared with that in homogeneous soil.Additionally,the effectiveness of the analytical solution is verified via two actual cases.Moreover,parametric analysis is conducted to investigate the responses of the metro tunnel by considering such factors as the variation of subgrade coefficient,offset distance from the excavation center to tunnel longitudinal axis as well as equivalent shear stiffness.The proposed method can be used to provide theoretical basis for similar engineering project.
文摘Background:Previous studies of foot strike patterns of distance runners in road races have typically found that the overwhelming majority of shod runners initially contact the ground on the rearfoot.However,none of these studies has attempted to quantify foot strike patterns of barefoot or minimally shod runners.This study classifies foot strike patterns of barefoot and minimally shod runners in a recreational road race.Methods:High-speed video footage was obtained of 169 barefoot and 42 minimally shod distance runners at the 2011 New York City Barefoot Run.Foot strike patterns were classified for each runner,and frequencies of forefoot,midfoot,and rearfoot striking were compared between the barefoot and minimally shod groups.Results:A total of 59.2%of barefoot runners were forefoot strikers,20.1%were midfoot strikers,and 20.7%were rearfoot strikers.For minimally shod runners,33.3%were forefoot strikers,19.1%were midfoot strikers,and 47.6%were rearfoot strikers.Foot strike distributions for barefoot and minimally shod runners were significantly different both from one another and from previously reported foot strike distributions of shod road racers.Conclusion:Foot strike patterns differ between barefoot and minimally shod runners,with forefoot striking being more common,and rearfoot striking less common in the barefoot group.
基金a grant from the American School of Prehistoric Research (Harvard University)
文摘Purpose:This study examined variation in foot strike types,lower extremity kinematics,and arch height and stiffness among Tarahumara Indians from the Sierra Tarahumara.Mexico.Methods:High speed video was used to study the kinematics of 23 individuals.13 who habitually wear traditional minimal running sandals(huaraches).and 10 who habitually wear modern,conventional running shoes with elevated,cushioned heels and arch support.Measurements of foot shape and arch stiffness were taken on these individuals plus an additional sample of 12 individuals.Results:Minimally shod Tarahumara exhibit much variation with 40%primarily using midfoot strikes,30%primarily using forefoot strikes,and30%primarily using rearfoot strikes.In contrast,75%of the conventionally shod Tarahumara primarily used rearfoot strikes,and 25%primarily used midfoot strikes.Individuals who used forefoot or midfoot strikes landed with significantly more plantarflexed ankles,flexed knees,and flexed hips than runners who used rearfoot strikes.Foot measurements indicate that conventionally shod Tarahumara also have significantly less stiff arches than those wearing minimal shoes.Conclusion:These data reinforce earlier studies that there is variation among foot strike patterns among minimally shod runners,but also support the hypothesis that foot stiffness and important aspects of running form,including foot strike,differ between runners who grow up using minimal versus modem,conventional footwear.
文摘The effects of different simple cultivation facilities on yield and quality of Brassica campestris L. were compared to explore the optimal facility type for pro- duction of B. campestris, thereby providing a technical reference for efficient cultiva- tion of B. campestris during hot season. A total of four treatments were designed, open field cultivation （CK）, ordinary anti-insect net shed cultivation, ordinary plastic film greenhouse cultivation and Japanese translucent anti-insect net shed cultivation. The results showed that compared with those in open field cultivation, the plant height, leaf area, yield, Vc content, soluble sugar content and soluble protein con- tent of B. campestris in Japanese translucent anti-insect net shed cultivation were increased by 22%, 63%, 49%, 14%, 13% and 10%, respectively, and Japanese translucent anti-insect net shed was the optimal facility type for cultivation of B. campestris in hot season.
基金supported by the Charles Phelps Taft Research Center at the University of Cincinnati
文摘Background:This prospective study explored the effects of endurance running(ER) in minimal versus standard running shoes on the foot’s superficial layer intrinsic muscles and the function of the longitudinal arch.Our hypothesis was that running in minimal shoes would cause hypertrophy in these muscles and lead to higher,stronger,stiffer arches.Methods:The hypothesis was tested using a sample of 33 healthy runners randomized into two groups,a control group shod in traditional running footwear and an experimental group shod in minimal support footwear,whose feet were scanned in an MRI before and after a 12-week training regime.Running kinematics as well as arch stiffness and height were also assessed before and after the treatment period.Results:Analysis of anatomical cross-sectional areas and muscle volumes indicate that the flexor digitomm brevis muscle became larger in both groups by 11%and 21%,respectively,but only the minimally shod runners had significant areal and volumetric increases of the abductor digiti minimi of 18%and 22%,respectively,and significantly increased longitudinal arch stiffness(60%).Conclusion:These results suggest that endurance running in minimal support footwear with 4 mm offset or less makes greater use of the springlike function of the longitudinal arch,thus leading to greater demands on the intrinsic muscles that support the arch,thereby strengthening the foot.
基金supported by the Central Public-interest Scientific Institution Basal Research Fund of Institute of Geophysics,China Earthquake Administration(DQJB08B21)
文摘Based on the heterogeneity of fault plane strength,the macro rupture process of a fault plane can be treated as the rupture accumulation process of local micro-elements in the fault surface.Assuming that the strength of the local micro-elements follows the Weibull probability distribution,the macro-fault constitutive relationship of the complete load-deformation process is derived from a statistical mechanics viewpoint.Applying a one-dimensional earthquake mechanics model and using far-field displacement a as the control variable,the problem of earthquake instability is investigated by employing the stability theory.The results show that the system stiffness ratio(stiffness ratio of fault to surroun-ding rock) β is the important parameter that affects the occurrence of earthquakes.Earthquake instability occurs only when β < 1,and the sudden stress jump appears at the displacement turning point of the equilibrium path curve.The expression of three important parameters for earthquakes(fault half-dislocation distance after earthquake,earthquake stress drop and elastic energy release) is also given.When β≥1,the earthquake does not occur and the fault only slips slowly without an earthquake.
文摘The time-history response of a structure-pile system during soil liquefaction is highly complicated and several analytical methods have been proposed through the accuracy verification based on the comparison with the experimental works. However, the analytical methods with higher accuracy often require large computational loads and are not necessarily preferred in the actual design practice. On the other hand, while the response spectrum method is not accurate compared to the aforementioned methods, it can provide useful design guidelines in the preliminary stage for structure-pile systems under soil liquefaction with acceptable accuracy. In this paper, the previously proposed response spectrum method for a structure-pile-soil system is used where the effect of soil liquefaction is taken into account by introducing the so-called p-multiplier method. It is shown that, while in the case of inner partial liquefaction with a non-liquefied layer at the top, the demand on the pile moment is large due to the inertial effect of that non-liquefied layer at the top, in the case of overall liquefaction near the ground surface, the demand is smaller than the case of inner partial liquefaction.
