对部分研究生跟骨骨强度状况的初步调查

本实验采用定量超声技术对首都体育学院男、女共77名研究生的跟骨骨强度进行了测定。结果表明:我院研究生骨强度男性高于女性,而与日本同性别、同龄青年相比无统计差异。     

Experimental study on centrifugal concrete-filled steel tubes under bending and torsion

INTRODUCTIONConcrete filledsteeltubesarenowwidelyusedinfactories ,powerstations,bridges ,etc .Centrifugalconcrete filledsteeltubesarehollowstructuralmemberscentrifugatedbyhigh speedcentrifuge ,andarethereforeofconsiderablylessweightthantraditionaltubes .A…     

The relationship between torque and joint angle during knee extension in boys and men

The length-tension relationship of muscle contraction is well documented in adults. However, research on this relationship in children has been limited. The aim of this study was to compare differences in the torque-joint angle relationship of the quadriceps muscle in children and adults. Eight boys aged 8-10 years and eight men aged 20-26 years performed two maximal voluntary isometric contractions at six knee joint angles (20°, 40°, 60°, 80°, 90°, 100°). The mean of the two trials was used as the performance measure. Both groups demonstrated an expected increase in relative torque as the joint angle increased (P ? 0.05). The men produced significantly greater relative torque at 20°, 40° and 60° knee flexion (P ? 0.05). The percentage of maximal torque at these angles for the men and boys respectively were: 35.2 - 4.3 vs 15.2 - 12%, 63.6 - 9.1 vs 51.8 - 16.8% and 93.6 - 6.5 vs 84.4 - 14.4%. There were no group differences at 80° or 90°. Peak torque was attained at 80° in men, but decreased significantly (P ? 0.05) at 90° and 100°. For boys, peak torque was attained at joint angles of 80° and 90°. The reduction in peak torque at 100° was not statistically significant, but the relative torque at this angle was lower in men than in boys (77.9 - 13.7 vs 87.1 - 10.4%; P ? 0.05). In conclusion, the relationship between torque and joint angle appears to be affected by age.     

轮轨垂向接触刚度分析

目前在机车／线路耦合动力学研究中,常采用赫兹非线性理论计算轮轨接触刚度,由于赫兹理论存在局限性,本文采用有限元计算方法,建立了三维轮轨接触模型,考虑了钢轨弯曲对接触区的影响,计算出合理的轮轨接触状态,考虑枕木周期变化对轮轨接触刚度的影响,考虑了道床对轮轨接触刚度的影响,计算得到轮轨接触刚度并与基于赫兹非线性理论的轮轨接触刚度进行比较。     

The time course of muscle-tendon properties and function responses of a five-minute static stretching exercise

Abstract

The purpose of this study was to investigate the time course of the changes of muscle-tendon mechanical properties and the function responses of the plantar flexor muscles following 5?×?60?s of static stretching.

Fourteen healthy volunteers were tested on four separate days in a random order with three different rest times (0, 5, 10?min) after 5?×?60?s of stretching or following a control period without stretching. During each test, the dorsiflexion range of motion (RoM), passive resistive torque (PRT), and maximum voluntary contraction (MVC) were measured with a dynamometer. Ultrasonography of the gastrocnemius medialis (GM) muscle-tendon junction displacement and motion capture allowed us to determine the length changes in the tendon and muscle, respectively, and hence to calculate their stiffness.

We observed an increase in RoM and decrease in MVC at 0, 5, and 10?min post-stretching. This could be attributed to an increase in muscle elongation which lasted at least 10?min. A decrease in muscle-tendon stiffness was observed immediately, but not 5 or 10?min after the stretching. A decrease in PRT and muscle stiffness was observed up to 5?min after the stretching. No changes were detected in tendon stiffness or in any variable in the control group.

The effects of a 5?×?60?s static stretching exercise changes the muscle-tendon functions (RoM, MVC), which are related to mechanical changes of the muscle but not the tendon structure, respectively. Although the functional changes last for at least 10?min, changes in muscle stiffness were only observed up to 5?min after the stretching exercise.     

Evolution laws of strength parameters of soft rock at the post-peak considering stiffness degradation

To evaluate the strength attenuation law of soft rock in the western mining area of China, we established an evolution model for the strength parameters of soft mudstone at the post-peak stage by employing a tri-linear strain softening model. In the model, a stiffness degradation coefficient co and a softening modulus coefficient a were introduced to take into account the stiff- ness degradation, and the subsequent yield surfaces at post-peak stage were all assumed to meet the Molar-Coulomb yield criterion. Furthermore, attenuation laws of stiffness and strength parameters of soft mudstone were analyzed according to an engineering case. Finally, the model＇s accuracy was verified by comparison of results from numerical calculation and tri-axial compression tests. Results showed that the attenuation of the friction angle was dominated mainly by the instantaneous stress states and damage features, while the attenuation law of cohesion was also related to the plastic behavior. The degradation rates of strength param- eters decreased with increasing confining pressure and the friction angle tended towards its initial value. Residual strengths were also enhanced with increasing confming pressure. The results indicate that the evolution model can accurately describe the strain softening behavior of soft rock.     

有限元线性代数方程组新的存储格式

根据有限元总刚度矩阵大型稀疏、对称正定、带状的特点,给出了一种紧致存储格式,并给出了在此格式下代数方程组的求解方法和有关的Maclab程序．     

不同跳绳频率的运动训练研究

跳绳运动是体能训练之一,但是不同跳绳运动频率在运动训练的效益与人体健康的影响仍有待探讨。利用VICON动作捕捉系统及Kistler测力板撷取受过跳绳运动训练的15位小学生选手的下肢运动学资料及地面反作用力值,并采用重复量数单因子变异数分析检定三种频率跳绳运动各组间的跳跃高度及运动学参数是否有差异,统一显著水平定为α=．05,达显著时再用杜凯氏HSD法做事后比较。在探讨在跳绳运动训练过程中,进行低频组（60±2次／分钟）、中频组（100±2次／分钟）及高频组（140±2次／分钟）跳绳运动,下肢所受到相关力学参数的差异,以及下肢关节运动学变化及下肢劲度对着地策略的影响情形。研究结果表明,不同频率跳绳运动的垂直地面反作用力的最大值、被动冲量、负荷率、下肢劲度及角劲度值以高频组较高;不同频率跳绳运动的动作时间以低频组较多;下肢各关节角度变化量方面膝关节角度变化在中频组有突增现象（p〈05）。建议进行跳绳运动运动时,仍应注意高频率跳跃时垂直地面反作用力对人体的冲击。     

Experimental study on centrifugal concrete-filled steel tubes under bending and torsion

A real-size experiment on 11 tubes was done to study the performance of centrifugal concrete-filled steel tubes under bending and torsion. This paper first introduces the relevant operating method, equipment, subjects and processes. The factors that affect deformation and stiffness and the break mechanism under different loading were studied. Experimental stress analysis showed that the values of practical critical stress of steel tubes accorded well with the MISES Yielding Rule. The correlative equation (on the bearing capacity of a structural member under bending and torsion) deduced in this study may provide valuable reference for the design of this structural member. Project supported by the Zhejiang Province Electric Power Designing Institute and the Electric Power Ministry of China     

汽车车身结构中接头的计算分析

接头是汽车车身上一种重要的结构形式,本文以B柱上部接头为例,介绍了汽车车身中接头刚度的计算方法,并进行了B柱上部接头Y向刚度关于板件厚度的灵敏度计算分析。