组织多普勒研究左室壁节段性运动速度——应用新型的左心室模型体外试验

组织多普勒(TDI)可用于测量左室壁节段性运动速度。为检测其准确性,以往多与M型曲线相对照。但报道结果不甚一致。McDicken和Miyatake等曾报告应用一旋转的圆形海绵模型验证TDI测速的准确性,但该模型不能全面反映心脏的运动状况。在本研究中,我们应用一种仿左室形态的气球模型,将TDI测速与高速摄相机录像结果相对照,以达到检验TDI准确性的目的。

维生素与运动

维生素是维持人体生命和正常机能不可缺少的一种营养素，它的种类很多，按其溶解性质分为脂。溶性与水溶性两大类。脂溶性维生素主要有维生素A、D、E；水溶性维生素主要有维生素B1、B2及C等。

多普勒组织成像研究左室壁节段性运动速度──应用新型的左心室模型体外试验

目的 应用自制的左室模型研究组织多普勒成像 (TDI)测定左室壁节段性运动速度的可靠性和准确性。方法 自制一个左室模型来验证TDI的准确性。该模型以双层气球制作 ,连接一脉冲流量泵 ,分设 8种泵出量 (5 0～ 85ml/每搏 )。将模型浸入水槽后 ,以摄像机与TDI同时记录球壁的运动位移和速度。采用GE系统 5超声诊断仪 ,探头频率 5MHz。结果 M型与二维图像显示气球模型形状和壁运动与左心室十分相似。由TDI测得的球壁运动距离与摄像机同步测量距离相关密切 [前壁 :r =0 .97,sx =0 .2 4mm ,平均差±s =(0 .0 4± 0 .2 4)mm ;后壁r =0 .95 ,sx =0 .2 2mm ,平均差±s =(0 .0 3± 0 .2 4)mm]。球壁特定测量点的TDI运动速度亦与摄像所得结果相关密切 [前壁 :r =0 .97,sx =0 .30mm ,平均差±s =- (0 .0 4+0 .2 8)mm ;后壁 :r =0 .97,sx =0 .30mm ,平均差±s =(0 .0 4+0 .2 8)mm]。结论 球体模型提供了一种检测TDI准确性的新方法 ,证明所用TDI系统在测量壁运动距离和速度方面是准确可靠的。

A simplified model for extreme-wave kinematics in deep sea

Based on the fifth-order Stokes regular wave theory, a simplified model for extreme-wave kinematics in deep sea was developed. In this model, from the wave records the average of two neighboring wave periods for the extreme crest or trough was defined as the period of the Stokes wave by the up and down zero-crossing methods. Then the input wave amplitude was deduced by substituting the wave period and extreme crest or trough into the expression for the fifth-order Stokes wave elevation. Thus the corresponding formula for the wave velocity can be used to describe kinematics beneath the extreme wave. By comparison with the published numerical models and experimental data, the proposed model is validated to be able to calculate the extreme wave velocity rather easily and accurately.

Is there an acute exercise-induced physiological/biochemical threshold which triggers increased speed of cognitive functioning? A meta-analytic investigation

Purpose： The purpose of this study was to examine, using meta-analytic measures, the evidence regarding the optimal exercise intensity at which improvements in speed of cognitive function are triggered. Specifically, it was hypothesized that the catecholamine, lactate, and ventilatory thresholds is the point at which significant improvements in speed of cognitive function are observed. Methods： We compared mean effect sizes for threshold studies and for those studies where exercise intensity was classed as moderate （40%-- 79% VO2 or equivalent） but in which the thresholds were not measured. Results： Random effects meta-analysis showed significant, moderate, mean effect sizes for studies at the threshold （g = 0.58, Z = 2.98, p 〈 0.003） and for those during moderate intensity exercise but in which the threshold was not measured （ g = 0.54, Z = 5.0l, p 〈 0.001）. There was no significant difference between mean effect sizes, which suggests that the thresholds are unlikely to represent a trigger point. Conclusion： Moderate intensity exercise, even below the thresholds, can induce improved speed of cognition, possibly due to a combination of increased peripheral catecholamine concentrations inducing vagal/nucleus tractus solitarii pathway activation and central increases due to perceptions of stress.

A DYNAMICAL INTERPRETATION OF THE WIND FIELD IN TROPICAL CYCLONES

Based on the primitive equations in polar coordinates and with the supposition that parcel velocity in tropical cyclones is in linear variation and that the distribution of surface pressure agrees with the Fujita formula, a set of equations are derived, which describe the impact of perturbations of central pressure, position of tropical cyclones, direction and velocity of movement of tropical cyclones on the wind field. It is proved that the second order approximation of the kinetic energy of tropical cyclones can be described by the equations under linear approximation. Typhoon Wipha (2007) is selected to verify the above interpretation method, and the results show that the interpretation method of the wind field could give very good results before the landfall of tropical cyclones, while making no apparent improvement after the landfall. The dynamical interpretation method in this paper is applicable to improving the forecasts of the wind field of tropical cyclones close to the coast.

Research on suppress vibration of rotor misalignment with shear viscous damper

A new type of shear viscous damper for rotating machinery is designed. The new damper with good stability and reliability can inhibit all kinds of frequency multiplication vibration caused by misalignment in the condition of nonstop machine. It analyzes and discusses the use of the shear viscous damper for misalignment vibration response inhibition with a finite element method, and experi ments are extensively carried out with a laboratory test rig. Both the simulation and experimental re suits basically agree well in that, the damper can effectively control the misalignment vibration of the rotor system and improves the stability of the plitude of one time running speed component bration has been basically eliminated. entire rotor system. Experimental results show the am decreases by 30% , and the two time running speed vibration has been basically eliminated.

Resultant linear acceleration of an instrumented head form does not differ between junior and collegiate taekwondo athletes' kicks

Objective： The purpose of this study was to compare the effects of various taekwondo kicks and age （school level） in absolute terms and relative body mass on the resultant linear acceleration （RLA） of an instrumented head form. Methods： Forty-eight male （middle school： 16; high school： 16; university： 16） taekwondo athletes were recruited for this study. Subjects performed 10 turning, 10 jump spinning hook, and 10 jump back kicks on a Hybrid II head mounted on a height-adjustable frame. Results： A 2-way （School x Kick） MANOVA was used to determine the differences in RLA between schools （age groups） by type of kick. There was no univariate School main effect for absolute RLA （η2 = 0.06） and RLA relative to body mass （η2 = 0.06）. No univariate Kick main effects were found for absolute （η2 = 0.06） and relative RLA （η2 = 0.06）. Conclusion： It is of concern that RLA did not significantly differ between school levels, implying that young taekwondo athletes generate similar forces to their adult counterparts, possibly exposing young athletes to an increased risk for head ir^iuries.

Kinetic Behaviors of a Competitive Population and Fitness System in Exchange-Driven Growth

We proposed an aggregation model of two species aggregates of fitness and population to study the interaction between the two species in their exchange-driven processes of the same species by introducing the monomer birth of fitness catalyzed by the population, where the fitness aggregates perform self-death process and the population aggregates perform self-birth process. The kinetic behaviors of the aggregate size distributions of the fitness and population were analyzed by the rate equation approach with their exchange rate kernel K1（k,j） = K1kj and K2（k,j） = K2kj, the fitness aggregate＇s self-death rate kernel J1 （ k ） = J1 k, population aggregate＇s self-birth rate kernel J2（ k ） = J2k and population-catalyzed fitness birth rate kernel I（k,j） = Ikj＇. The kinetic behavior of the fitness was found depending crucially on the parameter v, which reflects the dependence of the population-catalyzed fitness birth rate on the size of the catalyst （population） aggregate. （i） In the v ≤ 0 case, the effect of catalyzed-birth of fitness is rather weak and the exchange-driven aggregation and self-death of the fitness dominate the process, and the fitness aggregate size distribution αk（t） does not have scale form. （ii） When v ≥0, the effect of the population-catalyzed birth of fitness gets strong enough, and the catalyzed-birth and self-death of the fitness aggregates, together with the self-birth of the population aggregates dominate the evolution process of the fitness aggregates. The aggregate size distribution αk （t） approaches a generalized scaling form.

High-Speed Ring Shear Tests to Study the Motion and Acceleration Processes of the Yingong Landslide

In this paper, the motion and acceleration process, as well as the mechanism of a high speed and long run landslide are investigated by adopting high speed ring shear test and taking the landslide occurred at Yigong River in Bomi, Tibet on April 9, 2000 as the background. According to the motion characteristics of high-speed and long distance motion landside, the mechanism is studied under different conditions such as shear speed, consolidated drained and consolidated undrained status. Results show that high speed shearing process hinders and delays the dissipation of pore pressure, and drives pore water migrating to shear zone slowly. Both of water content and fine particle content at shear zone are obviously higher than those in other layers; and soil liquefaction occurs at shear zone in the saturated consolidated undrained ring shear tests. The effective internal friction angle of the consolidated undrained soil is much lower than that of the consolidated drained soil under ring shearing. The results also indicate that the shearing speed affecting the strength of soil to some extent. The higher the ring shearing speed is, the lower the strength of soil is. This investigation provides a preliminary interpretation of the mechanism of the motion and acceleration process of the Yigong landslide, occurred in Tibet in 2000.

Modeling of Bubble Motion in Two Dimensional Space

The equations of motion of a bubble, expanding adiabatically through an incompressible viscous fluid, are deduced when the centre of the bubble moves in a vertical plane in the presence of gravitational acceleration, acting vertically downwards. The non-linear equations of motion obtained are solved numerically for different values of the various parameters of the problem. The path traced by the centre of the bubble and velocity of the centre, the change of radius R with time, and the influence of the buoyancy force, which is experienced by the expanding bubble for different values of the gravitational acceleration on these quantities, are investigated. The radius R（t） of the bubble is found to vary periodically with time when the acceleration due to gravity is small. But when the acceleration due to gravity increases, this periodicity in the value of R（t） with t is lost. The influence of viscosity in determining the periodicity of the bubble motion is also investigated.

Research on Axial Trail of High-Speed Gas Painting Automizor

The non linear dynamic model is set up of one type of high speed painting automizor with gas supporting system. The stability of motion and dynamic response of the gas painting automizor system are studied over a relatively wide range of rotating speed by numerical analytic method, the critical velocity under working condition is found, and rotate stability and critical condition are discussed in theory. Furthermore, the range of the critical parameter of the system when Hopf bifurcation occurs and the law between axis trace and bearing clearance are acquired, too.

Vibration characteristics of bogie hunting motion based on root loci curves

Vibration behaviors of bogie hunting motion contain key information that dominates the dynamic performance of rail vehicles,in which the eigenvalue of each mode reflects the damping ratio and the natural frequency.This paper focuses on the root loci curves of bogie hunting motion,starting from a rigid bogie,then to a bogie with flexible primary suspension.With regard to the rigid bogie,analytical formulas for the eigenvalues,the critical speed as well as the corresponding hunting frequency are derived and verified.While for the flexible bogie,the root loci curves are calculated numerically.The study shows that both free rigid bogie and free wheelset are dynamically unstable at any speed.The critical speed increases with diminished wheel-rail conicity,track gauge,and wheelset and bogie inertia,and with increased wheelbase and wheel radius.The dominating factors such as the stiffness of the primary suspension and the wheel-rail conicity should be optimized for a practical design.The influences of the damping coefficients and the variations of creep coefficients are negligible.The motor suspension affects the root loci curves and the critical speed significantly.Both inappropriate motor suspension design and rigidly suspended motor reduce the critical speed.The increase of critical speed by a motor suspension can only be achieved when the lower natural frequency of the motor-bogie frame-wheelsets system coincides with or is close to the hunting frequency.Special care should be taken for the design of motor suspension,the first is to avoid the decreased damping ratio in a certain speed range below the critical speed and the second is that the variations of parameters should not induce the rapid reduction of the critical speed.The main feature of the present study is that the root loci curves,which are derived as analytical formulas or calculated numerically,are used to study the vibrational behaviors of bogie hunting motion.Both the influencing laws of the dominating parameters and the principles regarding the motor suspension are significant for the stability design of modem railway vehicles which may use innovative structures/materials as well as modem control and monitoring technologies.