Ultrasound imaging through time-domain diffraction tomography

Time-domain diffraction tomography, a technique for imaging with acoustic (and other) fields in which a medium parameter, such as density, can be mapped from scatter data collected from one pulse, is discussed. When Born approximations hold, the technique provides an exact inversion of the acoustical scattering equations. Computer simulation of the time-domain diffraction tomography equations indicates that under ideal conditions, and when the Born approximation is valid, the method can reconstruct maps of parameter variations. However, when data are collected from an incident pulse whose bandwidth is limited, the reconstruction is no longer perfect. A simple question is derived that characterizes the performance of time-domain diffraction tomography, and the limitations are explained as the effect of a spatial filter that eliminates some of the spatial frequencies. Relations between the object parameters, pulse bandwidth, and reconstruction accuracy are investigated with numerical experiments.     

Risk of formation of cracks on the rolling surface of solid railroad wheels damaged during braking

Conclusion Analysis by fracture mechanics approaches of stresses on the level corresponding to the threshold range of the SIF K_th showed that the structural elements weakened by crack can operate for long periods of time under specific conditions. The methods of statistical fracture mechanics can be used to determine the permissible crack dimensions not leading to failure.The solid railroad wheels damaged by braking cannot be regarded as long-term structures. The presence of radial cracks and the possibility of their continuous formation during service must be taken into account. Therefore, the service rules of solid wheels specified by the German National Railway Board are completely justified.The article was received in the German language. Authorized translation by S. Ya. Yarema.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 26, No. 4, pp. 90–95, July–August, 1990.     

Oxygen transport in the system niobium-uranium dioxide

Luch Technological Society. Translated from Atomnaya Énergiya, Vol. 71, No. 1, pp. 62–64, July, 1991.     

无线传感器网络中基于树的动态多路径容错路由协议

多路径路由对无线传感器网络的负载均衡和容错能力等方面都有一定改善作用。在研究一些多路径路由算法的基础上,对分层的无线传感器网络路由进行探索,提出了一种基于树的动态多路径路由的生成方法,快速获得当前节点的主路径与备用路径。仿真结果表明,该方法可有效地均衡网络负载、减少时延、提高网络的可靠性。     

城市可持续发展中GDP有质量增长的绩效轨迹

我国的国内生产总值(GDP)目前已经突破48万亿。有专家预言,到2030年中国将成为世界上经济总量最大的国家。因此,我国的经济总量和发展速度成为了世界关注的热点。今年我国政府主动提出要放慢国内生产总值的增长速度,提高GDP增长的质量。那么,什么叫有质量、有效益的GDP增长呢?这是一个在科学发展的背景下,各级地方政府需要通过转型发展来深化的重大课题。     

Test of local Lorenz invariance using a double-cavity laser system

We report the results of testing the local Lorentz invariance during five-month operation of a double-cavity laser system, where one cavity operates in a free generation mode while the frequency of the second cavity is stabilized with a nonlinear ultra-narrow absorption resonance of the methane molecule. An interpretation of the experimental results is given on the basis of the Robertson-Mansouri-Sexl formalism.     

Kinematic analysis of 3SPS+1PS bionic parallel test platform for hip joint simulator based on unit quaternion

As a novel parallel hip joint simulator, the 3SPS+1PS bionic parallel test platform with 4 degrees of freedom including three rotations and one translation is proposed. SPS denotes the spherical-prismatic-spherical leg and PS denotes the prismatic-spherical leg where only the prismatic joint is actuated and hence underlined. By means of the unit quaternion method, the formulae for solving the inverse/forward displacement, the inverse/forward velocity and the inverse/forward acceleration kinematics are derived. Using the unit quaternion to represent the position and orientation of a moving platform, singularities caused by Euler angles can be avoided. Combining the topological structure characteristics of the 3SPS+1PS bionic parallel test platform and letting the three-dimensional (3-D) motion of a human hip joint as its output movement, the displacement trajectories of three active legs are constructed based on the inverse displacement kinematics. The forward kinematic tests whose data are recorded by a 3-D orientation capture system are carried out on the developed parallel hip joint simulator. Moreover, the results of the forward kinematic tests prove that the 3SPS+1PS bionic parallel test platform can approximately represent human hip joint motion and provide more reliable experimental data for hip joint prostheses in clinical application.     

Procedural models for cartoon cracks and fractures animations

We present an approach for animating cracks and fractures in cartoon style. In our method we take a 2D hand-drawn object as input and then construct a 2.5D model of the object in order to approximate the object volume. Next, we generate the Voronoi textures on the 2.5D object model for visual abstraction of cartoon cracks. Further, cracking gaps on the Voronoi textures are widened progressively until Voronoi cells split apart and finally fall onto ground according to simplified physical rules. With minimum user intervention, our model is able to generate cartoon cracks and fractures animations procedurally, as demonstrated by examples given in the paper.