超声表观积分背散射系数与骨矿密度的相关性分析

用超声评价骨质状况是近年来骨质疏松诊断方面的研究热点之一。介绍了超声背散射法及其参量表观积分背散射系数(Apparent Integral Backscatter coefficient,AIB)的测量及与骨矿密度(Bone Mineral Density,BMD)的相关性研究。在体采集了1087位志愿者跟骨的超声背散射信号,并用双能X射线骨密度仪(Dual X-ray Absorptiometry,DXA)测得腰椎和髋骨的BMD值,然后对AIB与BMD进行相关性分析。实验结果表明,参数AIB与BMD显著相关(R=0.58～0.64,n=1087,p<0.05),可被应用于松质骨状况评价。     

超声背散射信息熵成像评价脂肪肝的新方法

提出超声背散射Tsallis信息熵成像评价脂肪肝的新方法。利用滑动窗口法,估算窗口内局部背散射包络信号的Tsallis信息熵参数值,对信息熵参数值矩阵进行扫描变换、颜色映射及感兴趣区域设置,叠加到超声B模式图像,实现Tsallis信息熵成像。分析72名肝脏捐献者和204名患者的超声背散射信号,参考标准分别为磁共振波谱测得的肝脏脂肪分数(Hepatic Fat Fraction, HFF)和肝活检组织学检查测得的脂肪肝程度。对于72名肝脏捐献者,Tsallis信息熵与lg(HFF)的相关系数r=0.67(P<0.000 1)。对于204名患者,受试者工作特征曲线下面积分别为0.82、0.88、0.89(≥轻度、≥中度、≥重度),而超声背散射零差K成像分别为0.76、0.82、0.82。超声背散射Tsallis信息熵成像可以直观定征并定量评价脂肪肝的严重程度,其诊断性能优于超声背散射零差K成像,可作为一种超声评价脂肪肝的新方法。     

超声背散射信号评价皮肤烧伤程度的可行性研究

烧伤后的皮肤可分为烧伤层和健康组织层,两层间的阻抗差异将使超声脉冲在界面处发生散射,从而影响超声背散射信号及相关的参数。利用超声背散射技术,研究了新鲜带皮猪肉(皮肤+脂肪层+瘦肉层)烧伤程度与表观背散射系数(Apparent Backscatter Coefficient,ABC)、表观积分背散射系数(Apparent Integral Backscatter Coefficient,AIB)和频谱质心偏移量(Spectral Centroid Shift,SCS)的相关性。研究结果表明,烧伤级数和ABC、AIB参数都有很高的正相关性,说明将ABC和AIB用于评价烧伤程度是可行的。     

松质骨组织的若干超声参量成像方法

介绍了两种松质骨组织超声参量成像方法,即宽带超声衰减成像和超声传导速度成像,概述了这两种基于透射法的成像方法的基本原理以及应用情况．并指出了采用超声透射法参量成像时存在的问题。然后对基于背散射法的超声背散射系数成像方法的可行性进行了分析和讨论,最后对进一步的研究工作进行了展望。     

跟骨超声背散射系数与新生儿相关参数的相关性

采用超声背散射法检测新生儿跟骨的超声背散射系数(Ultrasonic Backscatter Coefficient,BSC),并分析BSC与出生胎龄、体重、身长和头围等因素之间的关系,从而评估BSC在评价新生儿松质骨状况中的作用。对122例新生儿的临床测试分析结果表明新生儿跟骨中的BSC与出生时的胎龄、体重和身长有良好的相关性。说明超声背散射信号及其BSC可用于评价新生儿的骨质量。     

一种无需乘法器的光斑质心定位方法

光斑质心定位在光学精密跟踪和精密测量中是一项关键技术,其精度和速度直接影响了光学测量的精度和响应速度.在实际应用中,往往把灰度重心法与图像预处理方法结合起来,以提高光斑质心计算的可靠性.运用图像预处理技术有效地抑制了噪声的影响,同时也会消耗大量的逻辑资源.针对在资源受限的条件下采用灰度重心法计算光斑质心的问题,本文提出了一种无需乘法器的光斑质心计算方法,用加法运算代替乘法运算,使用递推方法完成质心计算所需的低阶矩的运算.该方法的硬件仅为5个累加器,结构简单,能够以更低的资源消耗实现光斑质心定位.通过并行技术和流水线技术,其工作频率达到515 MHz.实验证明:本文的结构在FPGA内实现,在100 MHz的工作频率下,完成一帧质心计算的延时为0.35μs,误差与传统质心方法一致,占用214个Slices,其资源消耗仅为常规灰度重心法的50%.     

一种改进的扬声器Volterra模型研究

在研究扬声器振膜的非线性振动时,通常使用Volterra模型进行建模分析。然而受到误差的影响,该模型仅适用于微弱的非线性现象。增大激励电压,频响预测结果的误差逐渐增大。针对这一问题,一种改进的扬声器Volterra模型被提出。该模型引入了振膜平衡位置偏移量对非线性参数的影响,并且在计算位移响应时引入高阶核函数的互调项,使位移响应预测结果更为精确。为了验证模型,搭建了一套可以测量振膜瞬时位移的激光测量系统。实验中测量并计算了振膜平衡位置偏移量和位移的基频响应。结果表明,改进的扬声器Volterra模型与实验结果的一致性较传统模型更好。     

超声被动定位的一种新滤波方法

本文以距离几何学为基础，对超声被动定位提出了一种新的滤波方法，理论分析证明，利用这种方法，可以提高定位精度，本文还给出了数值的例子，说明如何使用这种新的滤波方法。     

一种测量粘度标准液密度值的方法

本介绍了用二等标准密度计测量粘度标准液密度值的方法，该测量方法简便，准确度高，满足粘度计量中对粘度标准液密值的要求。     

一种密度精密测量方法研究

采用数学推导和次级参量近似相结合的方法,提出了一种玻璃浮计高准确度测量方法.将浮计主体浸入液体至干管待测刻线,利用刻线对准比位置估读更易于实现的特点,避免了干管读数误差,实现了利用一种介质即可进行全量程测量,实现了密度测量全自动功能.提高了测量准确度及工作效率,降低了测量成本.     

A spectral stochastic element free Galerkin method for the problems with random material parameter

This paper presents a spectral stochastic element free Galerkin method (SSEFGM) for the problems involving a random material property. The random material property and resulting system response quantity are represented by a probabilistic spectral expansion techniques (Karhunen–Loeve expansion and Polynomical Chaos series, respectively) and implemented into the element free Galerkin (EFG) analysis. Numerical solutions in 1D linear elastic problem with random elastic modulus are introduced, and compared with those of Monte Carlo simulation (MCS) so as to provide the validation of the proposed approach. The present SSEFGM approach can produce a probabilistic density distribution as well as a first‐ and second‐order statistical moments (mean and variance) of response quantity by a single calculation, which is distinguished from an iterative MCS. Moreover, the method is based on an element free analysis so that there is no need of nodal connectivities, which usually require more time and labourious task than main calculations. Thus the proposed SSEFGM approach can provide an alternative analysis tool for the problems contains a stochastic material property, and demands complex mesh structures. Copyright © 2004 John Wiley & Sons, Ltd.     

一种估计船舶线谱的联合分析法

线谱是船舶辐射噪声中重要的特征信息，线谱提取是水中目标识别的关键技术。文章简述了船舶辐射噪声的物理成因和频谱特征，利用经典谱估计法与现代谱估计法在短时序列谱估计中的特点，结合Matlab仿真试验的结果，提出了一种对船舶辐射噪声0．100Hz低频段线谱估计的联合分析法。并用该方法对两艘实船噪声进行了谱分析，提取了A型船在中速航行时5．25Hz的特征线谱，B型船存在65．5Hz和69．2Hz两条特征线谱。实验结果表明该方法对低频段的线谱特征提取有明显的实用效果。     

基于全聚焦算法的混凝土超声阵列探测成像方法

混凝土结构内含有大量的砂石、骨料以及钢筋,形成多样性的声学界面,超声在混凝土结构中的信号成分复杂,且超声能量易衰减.为了提高混凝土检测分辨率与信噪比,提出基于全聚焦算法的混凝土超声阵列检测方法.首先通过建立混凝土有限元模型,开展混凝土超声阵列仿真研究,模拟一发多收方式依次激励阵列探头,并获得检测信号;然后,为了避免噪声...     

A fast method for the generation of boundary conditions for thermal autoclave simulation

Manufacturing process simulation enables the evaluation and improvement of autoclave mold concepts early in the design phase. To achieve a high part quality at low cycle times, the thermal behavior of the autoclave mold can be investigated by means of simulations. Most challenging for such a simulation is the generation of necessary boundary conditions. Heat-up and temperature distribution in an autoclave mold are governed by flow phenomena, tooling material and shape, position within the autoclave, and the chosen autoclave cycle. This paper identifies and summarizes the most important factors influencing mold heat-up and how they can be introduced into a thermal simulation. Thermal measurements are used to quantify the impact of the various parameters. Finally, the gained knowledge is applied to develop a semi-empirical approach for boundary condition estimation that enables a simple and fast thermal simulation of the autoclave curing process with reasonably high accuracy for tooling optimization.     

Design optimization of functionally graded dental implant for bone remodeling

Despite a great success, one of the key issues facing in dental implantation clinic is a mismatch of mechanical properties between engineered and native biomaterials, which makes osseointegration and bone remodeling problematical. Functionally Graded Material (FGM) has been proposed as a potential upgrade to some conventional implant materials like titanium for selection in prosthetic dentistry. The idea of FGM dental implant is that the property would vary in a certain pattern to match the biomechanical characteristics required at different regions in the hosting bone. However, mating properties do not necessarily guarantee the best osseointegration and bone remodeling. No existing report has been available to develop an optimal design of FGM dental implant for promoting a long-term success. This paper aims to explore this critical issue by using the computational bone remodeling and design optimization. A buccal–lingual sectional model, which consists of a single unit implant and four other adjacent teeth, was constructed from computerized tomography (CT) scan images. Bone remodeling induced by use of various FGM dental implants is calculated over the period of 4 years. Based upon remodeling results, response surface method (RSM) is adopted to develop a multi-objective optimal design for FGM implantation FGM designs.     

A method for the random analysis of linear systems subjected to non-stationary multi-correlated loads

The paper shows a procedure for evaluating the correlation matrix and the evolutionary power spectral density matrix of the response of linear structural systems subjected to random non-stationary multi-correlated vector processes. The approach reduces this problem to the solution of some corresponding stationary problems. It is shown that the assumption of a modulating matrix function, whose elements are the sum of exponential functions, allows to transform the initial non-stationary problem into a stationary one. This stationary problem can be solved by well-known unconditionally stable step-by-step numerical procedures in the time domain, and, in closed form, in the frequency domain. The comparison of the results obtained using the proposed approach with those obtained by Monte Carlo Simulations (MCS) has revealed a very good level of accuracy.     

Numerical method for optimizing design variables of carbon-fiber-reinforced epoxy composite coil springs

To successfully reduce a vehicle's weight by replacing steel with composite materials, it is essential to optimize the material parameters and design variables of the structure. In this study, we investigated numerical and experimental methods for determining the ply angles and wire diameters of carbon fiber/epoxy composite coil springs to attain a spring rate equal to that of an equivalent steel component. First, the shear modulus ratio for two materials was calculated as a function of the ply angles and compared with the experimental results. Then, by using the equation of the spring rate with respect to the shear modulus and design variables, normalized spring rates were obtained for specific ply angles and wire diameters. Finally, a finite element model for an optimal composite coil spring was constructed and analyzed to obtain the static spring rate, which was then compared with the experimental results.     

改进的风力发电机组噪声音调评估方法

摘要：针对目前风力发电机组（Wind Turbine,WT）噪声音调评估方法的不足,提出了相应的改进方法。首先,采用Gabor阶比分量提取技术从WT运行状态下采集的噪声数据中,提取出与WT本身音调相关的噪声信号,消除了用停机状态下背景噪声修正开机状态下的WT噪声所造成的误差;然后,利用基于转速的最优分割法将一分钟WT噪声信号划分为尽可能平稳的子段信号,避免了由非平稳信号FFT变换引起的频率混叠现象;最后,采用基于谱平面的音调判定法代替IEC标准中基于心理声学模型的音调估计法,消除了初始音调预测的误差并简化了音调辨识的过程。新疆达坂城的试验研究表明,提出的音调改进技术能够消除IEC中音调辨识方法的不确定性和不一致性,在WT的音调噪声评估中具有良好的应用前景。     

Application of instrumented indentation technique for enhanced fitness-for-service assessment of pipeline crack

While most in-field non-destructive technologies for structural integrity diagnosis focus on precise crack detection, a novel instrumented indentation technique for non-destructively determining tensile properties in fields is introduced here. The goal of this work is to apply the newly-developed indentation technique to in-field fitness-for-service (FFS) assessment of linepipe cracks. As one step to verify its applicability, tensile properties in base metal and girth weldement of API-X65-graded linepipe were evaluated by this indentation technique and provided for construction of material-specific failure assessment diagrams (FADs). Results are discussed in terms of the accuracy of the indentation data and how the FAD assessment results are affected by the variation in local tensile properties measured by indenting small target regions such as heat-affected zones (HAZs). Based on the results, we suggest that the indentation technique may be useful for reducing possible difficulties in flaw assessment (arising from the use of incorrect tensile properties) by providing reliably practical data for FAD construction.