力约束法在人体起跳动力学数值仿真中的应用

为描述人体步行、弹跳等运动过程中柔性鞋底和硬地面之间的接触柔性、微滑和摩擦特性,提出一个多点柔性接触模型,将鞋底与地面的单面几何约束转化为力约束。针对一个15刚体人体机构模型,得到一个不含机械回路约束方程的动力学全局仿真模型。然后,采用不同模型参数,数值仿真研究了双脚起跳过程中地面对鞋底的作用力。计算结果显示该模型能有效地揭示鞋底与地面接触的复杂作用过程,为用数值仿真方法研究人体与地面接触时的动力学提供了一个高效手段。     

典型材料点焊时表面接触规律的研究

针对低碳钢和铝合金这2种典型伯材料,采用弹塑性力学模型对其在点焊中各接触表面上的接触规律进行了定量化分析与计算。结果表明,在点焊条件下,压力、温度和材料强度及弹性模量是影响接触率的主要因素,而表面粗糙度的影响基本可以忽略,通过对这2种典型材料接触规律的研究还可以得出,点焊时采用“软电极＋硬工件”是较好的配合方式。     

在恒壁面热流条件下汽泡接触周期研究

以湍流漩涡扩散理论为根据,建立了漩涡与壁面接触时液体温度的分布方程。再根据汽泡顶点温度必须高于热力平衡温度的原则,确定了接触周期,该计算分析结果与文献所给出的实验数据吻合较好。     

测定液体表面张力系数实验中的系数误差

通过利用概率统计学方法对实验数据进行了研究,证明在表面张力系数的测量中存在系统误差．     

蜗杆副传动接触线载荷的研究

建立了蜗杆副在常规的润滑与磨损传动条件下,齿面接触线载荷的计算模型,结合蜗杆副传动的润滑与磨损规律特点,阐明了蜗杆副传动中,弹性流体动力润滑油膜和齿面磨损状态对齿面接触线载荷变化规律的影响。     

Relationship between action potential, contraction-relaxation pattern, and intracellular Ca2+ transient in cardiomyocytes of dogs with chronic heart failure

Abnormalities of contractile function have been identified in cardiomyocytes isolated from failed human hearts and from hearts of animals with experimentally induced heart failure (HF). The mechanism(s) responsible for these functional abnormalities are not fully understood. In the present study, we examined the relationship between action potential duration, pattern of contraction and relaxation, and associated intracellular Ca²⁺ transients in single cardiomyocytes isolated from the left ventricle (LV) of dogs (n = 7) with HF produced by multiple sequential intracoronary microembolizations. Comparisons were made with LV cardiomyocytes isolated from normal dogs. Action potentials were measured in isolated LV cardiomyocytes by perforated patch clamp, Ca²⁺ transients by fluo 3 probe fluorescence, and cardiomyocyte contraction and relaxation by edge movement detector. HF cardiomyocytes exhibited an abnormal pattern of contraction and relaxation characterized by an attenuated initial twitch (spike) followed by a sustained contracture ('dome') of 1 to 8 s in duration and subsequent delayed relaxation. This pattern was more prominent at low stimulation rates (58% at 0.2 Hz, n = 211, 21% at 0.5 Hz, n = 185). Measurements of Ca²⁺ transients in HF cardiomyocytes at 0.2 Hz manifested a similar spike and dome configuration. The dome phase of both the contraction/relaxation pattern and Ca²⁺ transients seen in HF cardiomyocytes coincided with a sustained plateau of the action potential. Shortening of the action potential duration by administration of saxitoxin (100 nM) or lidocaine (30 μM) reduced the duration of the dome phase of both the contraction/relaxation profile as well as that of the Ca²⁺ transient profile. An increase of stimulation rate up to 1 Hz caused shortening of the action potential and disappearance of the spike-dome profile in the majority of HF cardiomyocytes. In HF cardiomyocytes, the action potential and Ca²⁺ transient duration were not significantly different from those measured in normal cells. However, the contraction-relaxation cycle was significantly longer in HF cells (314 ± 67 ms, n = 21, vs. 221 ± 38 ms, n = 46, mean ± SD), indicating impaired excitation-contraction uncou pling in HF cardiomyocytes. The results show that, in cardiomyocytes isolated from dogs with HF, contractile abnormalities and abnormalities of intracellular Ca²⁺ transients at low stimulation rates are characterized by a spike-dome configuration. This abnormal pattern appears to result from prolongation of the action potential. Received 22 January 1998; received after revision 16 March 1998; accepted 27 March 1998     

接触问题可靠度分析的随机有限元法

首次提出接触问题可靠度分析的随机有限元法,建立了可靠度计算的基本公式,研制了电算程序。通过两子结构接触问题可靠度分析算例,验证了本文所述方法的正确性和可行性,实际计算表明,该方法具有收敛快,精度高的优点,适用于大型复杂结构的接触问题可靠度计算,并可推广到三维多子结构的接触问题可靠度分析。     

北秦岭松树沟接触变质岩的形成温度研究

本文应用氧同位素和电子探针分析方法测定了北秦岭松树沟阿尔卑斯型超镁铁岩体接触变质带内角闪岩和及其原岩秦岭群斜长角闪片岩的形成温度．角闪岩的角闪石－石榴子石Ｆｅ－Ｍｇ配分温度计给出不同期次形成温度分别是：早期８１５～８５５℃，主期７００～７７０℃．矿物对氧同位素地质测温结果得到，角闪岩的主期变质温度为７４５～７７０℃，与其电子探针结果在误差范围内一致；斜长角闪片岩为５００～６０５℃，代表了秦岭群区域变质温度     

不带凸条件双曲守恒律熵解渐近行为

讨论了非凸双曲守恒律熵解的大时间渐近问题．若初值当｜ｘ｜充分大时为接触间断的Ｒｉｅｍａｎｎ数据时，熵解逼近相应Ｒｉｅｍａｎ问题解；当初值有紧支时，熵解以代数数率收敛于零．     

微晶CuCr材料的制备及电击穿性能的研究

根据真空断路器大功率、小型化发展趋势对触头材料的要求，探索用高能球磨制粉、热压烧结的方法制备微晶ＣｕＣｒ触头材料．结果表明，高能球磨能够制备出超细晶Ｃｕ－Ｃｒ合金粉．７５０℃热压时材料仍保持合金粉形貌，颗粒内发生部分过饱和固溶Ｃｕ与Ｃｒ的时效析出过程．９２０℃热压时Ｃｕ与Ｃｒ组元重新分布并发生了再结晶过程，晶粒尺寸为２～３μｍ，远远小于常规方法生产的ＣｕＣｒ材料．由于微晶ＣｕＣｒ材料中Ｃｒ相固溶度升高，使材料电击穿机制发生变化，首次击穿相从常规材料中的Ｃｒ相转移到Ｃｕ相上．