脉图与脉象的生物力学描述

一、前言脉诊是中医获得病理、生理信息的一种重要手段。所谓脉诊,实际上是医生用手指在受检者桡动脉的寸、关、尺三个部位,感受桡动脉脉搏波的各种信息(即所谓脉象)然后经过医生大脑的综合、分析,从而得到有关病理、生理变化的资料,以达到通过脉象对疾病进行诊断的目的。在中医临床中,可通过脉象所反映的浮、沉、迟、数、虚、实、滑、涩等信息,来对疾病的表里、寒热、虚实、气盛与血淤等症状作一个大略的判断。长期实践表明,脉象是客观存在的,脉诊是行之有效的。      

分枝动脉脉搏流的数值模拟

本文考虑到血液粘度与动脉管壁的非线性特性,利用特征线法数值求解了主动脉和一根分枝动脉(桡动脉)中的脉搏流。得到的桡动脉压力波形与实测波形相似,而且改变某些生理参数能得到平缓脉、弦脉和滑脉所对应的波形,从而为解释中医脉象机理提供了一种方法,或许有可能通过脉搏波的分析求研究动脉系统的病变。     

磨损磨粒的主成分聚类方法分析

采用主成分聚类分析理论对正常磨粒、滑动磨粒、切削磨粒和疲劳磨粒等4种不同磨粒表面纹理灰度共生矩阵进行分析,得到4个不同纹理方向的能量、熵、惯性矩、局部平稳性、相关、最大概率和方差7个参量.利用主成分理论求解,构造主成分方程,得到磨粒纹理参量主成分的二维分布,最后,通过聚类分析,将4种磨粒纹理参量的主成分划分为不同的聚类区域.结果表明:主成分聚类分类方法可以对磨粒的多参量进行聚类分析;主成分聚类分类方法对冗余数据具有较强地处理能力;多组主成分聚类分析方法具有互补性,特别适合多参量磨粒分类的信息融合处理.     

桡动脉脉搏波的分析(Ⅱ)——与实测波形的比较

在前文~[1]基础上,本文分析了桡动脉压力脉搏波变化的基本特征,以无最纲参量ξ=(ι_0C_0)/L为依据,区分出五类常见的压力脉搏波,并对其所对应的生理、病理学含义做出说明。文章将理论波形与在人体桡动脉处无创伤描记到的实测波形作了比较,结果表明,两种波形的基本特征是相当一致的。 本文为中医弦、滑脉的分辨以及为某些心血管参数的无创伤检测提供了一种方法。     

基于变形场测量数据主元压缩的模型参量反求方法

利用主元分析法对数字图像相关技术所测结构变形信息进行数据压缩,并进一步用于力学模型未知参量的反求计算。首先,为降低数字图像相关技术所测庞大数据的应用成本,提出利用主元分析法对结构表面变形场数据进行压缩,实现在保留结构表面变形信息主要特征的前提下显著降低数据量的目的;其次,针对压缩后的数据建立了基于最小二乘法的力学模型参量反求模型,并利用高斯牛顿法进行求解;最后,以具体算例从计算精度、收敛速度和抗噪性等方面验证了数据压缩对模型参量反求的效果。研究结果表明,所提方法在显著降低使用数据量的前提下,能够有效提高力学模型参量反求计算的收敛速度,特别是对于包含多个模型参数的反求问题,具有较高的精度和较好的稳定性。     

血液-血管耦合特性与脉搏波传播特性的关系

脉搏波既不可简单地理解为可压缩血液流体中的压力纵波，也不可简单地理解为沿固体血管传播的涨缩位移横波，而是超乎普通想象的流-固耦合和纵波-横波耦合的复杂波。从分析耦合本构关系的新途径出发，本文中提出了一个流-固耦合/纵波-横波耦合的串联模型，可为解读“位数形势”中医脉诊提供更丰富的信息。结果表明，脉搏波耦合系统的等效体积压缩模量K_s以及相应的耦合系统脉搏波传播速度c_s主要依赖于两个无量纲参数:血液-血管模量比K_b(p)/E(p)和薄壁血管径厚比D(p)/h₀，它们因人而异、因人的不同脉搏位置而异。文中定量分析了它们对c_s的影响，显示人体的K_b/E值在103数量级，从而c_s值在100～101 m/s数量级，以适应人体生理生化反应。由临床有创测量，证实脉搏体积横波与脉搏压力纵波是相耦合地以相同速度传播；还显示脉搏波是在其波阵面上具有氧合生化反应的“生物波”。此外，还讨论了“脉压放大”现象与非线性本构关系和与血管分叉处加载增强反射之间的关系，并讨论了Lewis关于重搏波形成的假设。     

非牛顿流体的一些本构方程

非牛顿流体可分成四类:(1)无弹性流体,其粘度不是常量的流体;(2)具有屈服应力的流体;(3)具有各种弹性特性的流体;(4)触变流体。本文讨论了上面四类流体的一些本构方程,并且论述了这些本构方程的适用性及其应用条件,还给出了出现在这些本构方程里的一些参量的数值。     

铝合金蚀坑损伤参量评述

将蚀坑损伤参量分成4 类:尺寸、形状、统计和试验参数,回顾了蚀坑深度、投影面积、长宽比、矩形比、表面腐蚀率、分形维数、预腐蚀系数等影响剩余寿命的主要损伤参量,总结了蚀坑等效成初始裂纹的方法.     

三点弯曲正长花岗岩的多参量信号特征试验研究

采用多参量(电荷感应、微震和声发射)同步综合监测系统，开展完整和预制裂纹正长花岗岩的三点弯曲试验，对其变形破裂过程的多参量信号特征进行研究。试验结果表明：完整和预制裂纹正长花岗岩在失稳破坏阶段有最强的多参量信号，在失稳破坏阶段产生的多参量信号的主频比较接近，但完整正长花岗岩多参量信号主频幅值是预制裂纹正长花岗岩多参量信号主频幅值的2倍左右。完整正长花岗岩从线弹性变形阶段、裂纹快速发展阶段到岩石失稳破坏阶段产生应力降时应力降的速度是快速增大的，裂纹快速发展阶段和岩石失稳破坏阶段声发射的最大震级和事件数远大于线弹性变形阶段的最大震级和事件数。正长花岗岩失稳破坏阶段多参量信号同步产生，产生的多参量信号与其他阶段相比主频最小，主频幅值最大；在试样失稳破坏阶段声发射信号早于电荷感应信号产生；电荷感应信号早于微震信号产生，声发射信号持续时间最短，微震信号持续时间最长，多参量信号都在试样产生应力降或失稳前产生。     

聊聊动态强度和损伤演化

材料强度在传统上常理解为材料在外载荷下抵抗流动/变形和破断的能力。由流变阶段到貌似突发的破断,其实源于一个隐含的应变率/时间相关的损伤演化过程。动态损伤演化研究的难点在于损伤与流变总是耦合在一起发展的。研究发现,热激活损伤演化模型可成功描述材料宏观损伤的动态演化。在此基础上,从实测的含损伤演化的表观应力应变曲线,可将两者解耦分开,并可确定各自相关的材料参数。这一思路可推广到中医脉诊的客观化研究,通过脉搏波信息定量反演脉搏波系统的正常及病态本构关系,可诊断生命体偏离正常状态的程度(病情),这可视为一种广义的损伤演化和强度问题。上述思路还可推广到地震预报研究,即“对地球把脉”。与加卸载响应比理论相结合,通过相邻3处的地震波信息来反演地球相关板块含损伤演化的非线性载荷-响应曲线,再区分出损伤演化程度,将有利于改进地震预报,这可视为另一种广义的损伤演化和强度问题。     

One-dimensional pulse propagation in composite materials modelled as interpenetrating solid continua

Modulated simple wave theory is used to study the propagation of one dimensional, finite amplitude, high frequency pulses in composites which are modelled as interpenetrating solid continua with two identifiable constituents. The equations which govern the propagation of high frequency pulses are derived and their properties are studied in detail. Particular attention is paid to small amplitude high frequency pulses and results for pulses propagating into composites of a rather general nature are presented. The special results which hold for pulses which propagate into uniform regions are discussed in detail. The influence of the structure of the composite on pulse propagation is also assessed by examining pulse propagation in a number of different types of composite.     

A theory of pulse propagation in anisotropic elastic solids

A theory is described for the propagation of pulses in anisotropic elastic media. The pulse is initially defined by a harmonically modulated Gaussian envelope. As it propagates the pulse remains Gaussian, its spatial form characterized by a complex-valued envelope tensor. The center of the pulse follows the ray path defined by the initial velocity direction of the pulse. Relatively simple expressions are presented for the evolution of the amplitude and phase of the pulse in terms of the wave velocity, the phase slowness and unit displacement vectors. The spreading of the pulse is characterized by a spreading matrix. Explicit equations are given for this matrix in a transversely isotropic material. The rate of spreading can vary considerably, depending upon the direction of propagation. New reflected and transmitted pulses are created when a pulse strikes an interface of material discontinuity. Relations are given for the new envelope tensors in terms of the incident pulse parameters. The theory provides a convenient method to describe the evolution and change of shape of an ultrasonic pulse as it traverses a piecewise homogeneous solid. Numerical simulations are presented for pulses in a strongly anisotropic fiber reinforced composite.     

Dynamic compressive responses of intact and damaged ceramics from a single split Hopkinson pressure bar experiment

A novel dynamic compressive experimental technique has been developed based on a split Hopkinson pressure bar. This new method dynamically loads the ceramic specimen by two consecutive stress pulses. The first pulse determines the dynamic response of the intact ceramic materiaal and then crushes the specimen, and the second pulse determines the dynamic compressive constitutive behavior of the ceramic rubble. Precise pulse shaping ensures that the specimen deforms at nearly constant strain rates under dynamic stress equilibrium during the loading by both stress pulses. Pulse shaping also controls the amplitudes of loading pulses, the values of strain rates, the maximum strains in the rubble specimens, and the proper separation time between the two loading pulses. The feasibility of the new technique is demonstrated by the experimental results obtained on an AD995 alumina.     

Two systems for the synchronization of pulsed high-energy ion beams

Summary When the ion source of a high-voltage particle accelerator is modulated with pulses, e.g. for neutron time-of-flight studies, it is often necessary that synchronization should be maintained between these pulses and some electronic time-analyzing equipment. If the ion source is in a high-voltage electrode, some communication link to it must be provided. Two such links are described, one using a radio frequency system at 450 Mc/s, the other using a pulsed beam of light. Both systems provide control over pulse width as well as pulse spacing. The r.f. system will transmit pulses down to 1 microsecond and is suitable for open accelerators. The optical system will transmit pulses down to 4 microseconds and may be used with either open or pressurized accelerators.     

The dynamic behaviour of sharp V-notches under impact loading

The dynamic behaviour of sharp V-notches which are either symmetric or oblique to the longitudinal boundary of a homogeneous elastic and isotropic strip subjected to an impact plane pulse was studied by the method of caustics. The stress pulse impinging on the flanks of the notch reflects and diffracts in different ways depending on the geometry of the notch relative to the coming pulse. For compressive stress pulses a stress concentration at the bottom of the notch does not create a crack propagation phenomenon, whereas for tensile pulses there is a possibility for an incubation, nucleation and eventual propagation of a crack. A complete experimental study of the incubation nucleation and propagation of cracks from the bottoms of notches in thin strips under tensile stress pulses was undertaken, whereas for compressive stress pulses the stress concentration at the bottom of the notch was evaluated. Interesting results were disclosed concerning the reinforcement of pulses by reflection and caging in, the evolution of stress concentration at the notch and the mode of crack propagation inside the plate. Dynamic stress intensity factors were evaluated all over the paths of crack propagation indicating a close intimacy between crack velocity and values of SIFs.     

Dynamic buckling of a simple elastic-plastic model under pulse loading

The dynamic buckling of an elastic-plastic imperfection-sensitive model subjected to rectangular- and triangular-shaped loading pulses is examined to provide some insight into the dynamic buckling behaviour of structures. The loading pulse is expressed as a function of the horizontal displacement, which allows an analytical method to be used for determining the stability domains for both pulses. The estimates obtained are compared with some previously published results on the dynamic elastic-plastic buckling of the same model under a step loading. It transpires that for the pulse loading of models with large imperfections dynamic instability occurs either elastically or plastically depending on the pulse duration, while for a step loading only an elastic instability is possible for the parameters examined.     

Amplification of longitudinal stress pulses in elastic bars with an intermediate tapered region

Experiments are performed to study the amplification of longitudinal pulses which propagate along tapered elastic bars in the direction of decreasing cross-sectional area. Each bar specimen is composed of two uniform cylindrical end sections of different radius joined by a tapered transition in the form of a cone frustrum. The amplification of a pulse which propagates from the large end to the small end in such a bar is shown to depend on the spatial pulse length (nondimensionalized with respect to the length of the transition region) for a given ratio of the terminating cross-sectional areas. The observed amplification is plotted over a wide range of nondimensionalized pulse lengths for several choices of the overall area ratio. For very short and very long pulses, the amplification approaches the limiting values given by simple equations which involve only the geometric parameters of the bar. The factors which influence the amplitude and shape of pulses which are reflected from the cone frustrum are discussed briefly.     

Properties of dynamic rupture and energy partition in a solid with a frictional interface

We study properties of dynamic ruptures and the partition of energy between radiation and dissipative mechanisms using two-dimensional in-plane calculations with the finite element method. The model consists of two identical isotropic elastic media separated by an interface governed by rate- and state-dependent friction. Rupture is initiated by gradually overstressing a localized nucleation zone. Different values of parameters controlling the velocity dependence of friction, the strength excess parameter and the length of the nucleation zone, lead to the following four rupture modes: supershear crack-like rupture, subshear crack-like rupture, subshear single pulse and supershear train of pulses. High initial shear stress and weak velocity dependence of friction favor crack-like ruptures, while the opposite conditions favor the pulse mode. The rupture mode can switch from a subshear single pulse to a supershear train of pulses when the width of the nucleation zone increases. The elastic strain energy released over the same propagation distance by the different rupture modes has the following order: supershear crack, subshear crack, supershear train of pulses and subshear single pulse. The same order applies also to the ratio of kinetic energy (radiation) to total change of elastic energy for the different rupture modes. Decreasing the dynamic coefficient of friction increases the fraction of stored energy that is converted to kinetic energy. General considerations and observations suggest that the subshear pulse and supershear crack are, respectively, the most and least common modes of earthquake ruptures.     

高g值加速度发生器中的波形整形技术

以Hopkinson压杆实验装置作为火工品抗过载实验中的高g值加速度发生器,通过数值模拟分析了子弹（形状）、波形整形器（材料、直径、厚度）对加载脉冲的影响规律,并获得了所需的加速度脉冲,实现了有效控制和改善火工品冲击实验中的加载环境。研究结果可为检验火工品在冲击环境下或经冲击后性能可靠度的实验设计、测试等提供依据。     

Dynamic stress-concentration factors

The problem of the response of structural discontinuities to short-duration stress pulses is studied experimentally. Employing explosively induced stress pulses in thin plastic plates containing central circular holes, a dynamic stress-concentration factor is determined as a function of pulse frequency. It is concluded, for the loading case, that the dynamic stress concentration is significantly lower than the static value.