基于B样条插值的局部均值分解方法研究

局部均值分解(Local Mean Decomposition,LMD)方法是一种较新的自适应信号分析方法。LMD算法的核心思想是将原始信号分解为多个乘积函数(Production Function,PF),其中每个PF都是一个包络函数和一个纯调频函数的乘积。在LMD算法中需要提取信号的局部均值函数和包络估计,然而常规的提取方法会带来局部误差且分解速度慢。为了解决此问题,提出了利用三次B样条对信号上、下极值点进行插值得到上、下包络线,进而获取信号局部均值和包络估计的新方法。对仿真信号和机械振动信号的对比实验验证了该方法的优越性。     

NURBS curve interpolation algorithm based on tool radius compensation method

This paper focuses on developing an algorithm that can generate toolpaths in NURBS form for smooth, high speed and accurate machining. The initial toolpaths are obtained by tool radius compensation method which is based on the workpiece boundary offsetting. According to different lengths and the continuous short block (CSB) criterion, these offset linear segments can be regarded as CSBs or long straight segments. Junctions are located where the curvature value is greater than the preset curvature threshold value or where it changes abruptly, or at the two end points of any long straight segment. During machining, the NURBS fitting module first looks ahead several CSBs and converts them into parametric curves in real time. During the conversion, continuities of the position, slope or even curvature at the transition of the parametric curves and unfitted line segments can be guaranteed. Then the acceleration/deceleration feedrate-planning scheme is proposed to determine the transition feedrate at the junction between the fitted curves and unfitted long straight segments, and the corner feedrate within the fitted curve. Simulations and experiments show that the proposed algorithm can significantly improve machining accuracy and reduce cutting time to satisfy today’s high-speed and high-accurate machining requirements.     

Geometrical analysis of woven fabric microstructure based on micron-resolution computed tomography data

The global mechanical properties of textiles such as elasticity and strength, as well as transport properties such as permeability depend strongly on the microstructure of the textile. Textiles are heterogeneous structures with highly anisotropic material properties, including local fiber orientation and local fiber volume fraction. In this paper, an algorithm is presented to generate a virtual 3D–model of a woven fabric architecture with information about the local fiber orientation and the local fiber volume fraction. The geometric data of the woven fabric impregnated with resin was obtained by micron-resolution computed tomography (μCT). The volumetric μCT-scan was discretized into cells and the microstructure of each cell was analyzed and homogenized. Furthermore, the discretized data was used to calculate the local permeability tensors of each cell. An example application of the analyzed data is the simulation of the resin flow through a woven fabric based on the determined local permeability tensors and on Darcy’s law. The presented algorithm is an automated and robust method of going from μCT-scans to structural or flow models.     

Relation between computed tomography and diffraction tomography

The relationship between computed tomography (CAT) and diffraction tomography (DT) is investigated. A simple condition with a clear physical meaning is derived for the applicability of CAT. Corrections due to scattering are incorporated into CAT, and it is shown that the effect of scattering may be characterized by a two-dimensional fractional Fourier transform. The implications of these results for the three-dimensional imaging of weakly scattering objects are also discussed.     

An X-ray computed tomography imaging agent based on long-circulating bismuth sulphide nanoparticles

Nanomaterials have become increasingly important in the development of new molecular probes for in vivo imaging, both experimentally and clinically. Nanoparticulate imaging probes have included semiconductor quantum dots, magnetic and magnetofluorescent nanoparticles, gold nanoparticles and nanoshells, among others. However, the use of nanomaterials for one of the most common imaging techniques, computed tomography (CT), has remained unexplored. Current CT contrast agents are based on small iodinated molecules. They are effective in absorbing X-rays, but non-specific distribution and rapid pharmacokinetics have rather limited their microvascular and targeting performance. Here we propose the use of a polymer-coated Bi(2)S(3) nanoparticle preparation as an injectable CT imaging agent. This preparation demonstrates excellent stability at high concentrations (0.25 M Bi(3+)), high X-ray absorption (fivefold better than iodine), very long circulation times (>2 h) in vivo and an efficacy/safety profile comparable to or better than iodinated imaging agents. We show the utility of these polymer-coated Bi(2)S(3) nanoparticles for enhanced in vivo imaging of the vasculature, the liver and lymph nodes in mice. These nanoparticles and their bioconjugates are expected to become an important adjunct to in vivo imaging of molecular targets and pathological conditions.     

Image inpainting algorithm based on partial differential equation technique

Abstract

Image inpainting is the process of filling in missing parts of damaged images based on information gleaned from surrounding areas. In this paper, we present two variational models for image inpainting. Combining two models, we can simultaneously fill in missing, corrupted or undesirable information, while remove noise. We explain that diffusion performance of the proposed models is essentially superior to that of TV inpainting model by analysing the physical characteristics in local coordinates, and investigate the existence of minimising functionals in BV space. The experimental results show the effective performance of the proposed models in restoring scratched photos, text removal, and even removal of entire objects from images.     

A test device for damage characterisation of composites based on in situ computed tomography

For engineering design of composites, suitable damage models are required which have to predict the onset of damage, the successive failure and the subsequent reduction of the mechanical properties. To verify existing modelling approaches, the clear experimental identification of the particular damage entities is an essential condition. However, due to the complexity of the failure mechanisms of novel materials like heterogeneous textile composites, a comprehensive damage analysis is still a challenging problem. Recent progress in the field of computed tomography enables in situ measurements to detect damage phenomena in composites under loading. The article describes such a novel test device that combines an integrated testing machine with a high precision computer tomograph. The in situ method was used to study the damage evolution in carbon fibre reinforced plastics (CFRPs) made of weft knitted and woven preforms. A special focus was set to damage processes under loading in thickness direction. For this purpose, cylindrical tensile specimens according to ASTM D 7291 were manufactured and tested. Compression specimens with different aspect ratios have been used to study the compressive failure of CFRP woven composites. The experimental results are discussed with respect to the possibilities and limitations of the in situ based test method.     

A study on optimal scan conditions of Big Bore multi-slice computed tomography based on radiation dose and image noise

The newly introduced Big Bore computed tomography (CT) has a possibility to increase the tube current product scan time (mA s) for compensation of image degradation due to larger gentry opening without sound guideline. The objective of this paper is to derive optimal scan conditions for Big Bore CT scanner, mainly relating to the dose of diagnostic CT. The weighted CT dose index (CTDI(w)) was estimated at five typical protocols, such as head and neck, brain, paediatric, chest and abdomen. Noises were analysed in a circle of 1 or 2 cm of diameter in CT image slice. The results showed that measured CTDI(w) values generally follow the theoretical rule at all scanning conditions of every protocol. Although image noises decrease with increment of mA s, analysed image noises do follow the theoretical rule, but only in specific protocols. This phenomenon is presumed to result from the photon energy spectra arriving at the detection system of the Big Bore scanner.     

Damage tolerant design of cast components based on defects detected by 3D X-ray computed tomography

This paper presents the application of 3D X-ray computed tomography (XCT) in deterministic fatigue strength analysis of relatively large cast components and also probabilistic fatigue design of heavy-section castings. To this end, more than 100 fatigue specimens were cut from a rejected wind turbine hub casting. XCT was used to find the 3D map of defects in selected fatigue specimens. All fatigue specimens were axially tested at R = −1 at room temperature and fatigue life scatter was established. Fractography analysis of broken specimens was performed. For CT scanned specimens, the defect sizes and positions obtained by XCT, in conjunction with the (nearly homogeneous) stress distribution of the specimens were used to predict the fatigue life and also the position of the fatigue crack initiation site. The predicted fatigue life and crack initiation position for CT scanned specimens were compared with experimental results. The obtained defect distribution by XCT was used in a random defect analysis to establish the scatter of fatigue life for the analyzed specimens. The predicted fatigue life scatter was compared with experimental results. The comparison showed that random defect analysis can successfully predict the scatter of fatigue life and may be used to find the probability of failure of cast components, based on the given defect distribution.     

Dual-reciprocity BEM based on global interpolation functions

Several global shape functions are introduced to interpolate the body-force term in the dual-reciprocity boundary-element method. These global-interpolation functions, which include polynomial, trigonometric, and hyperbolic series, can be used in place of the locally based radial shape function. For the several examples presented, the global functions have demonstrated superior convergence properties.     

利用二维插值核的高分辨力图像重构

利用连续图像采样及其内插公式,提出了一种基于二维插值核重建高分辨力图像的新算法。该算法先使一般低分辨力序列图像具有标准位移关系,再根据高、低分辨力图像之间的关系重构高分辨力图像。同时利用正则化技术导出了一套重复迭代算法,以提高算法的处理效果和克服病态问题。实验表明,该算法使图像的细节和清晰度大大增强,分辨力大幅度提高,明显优于零阶保持插值算法的处理结果,其峰值信噪比提高8-9dB。     

医用CT剂量指数测量结果的不确定度评定

为了使医用诊断计算机断层摄影装置（CT）X射线辐射源在模体中的剂量指数测量结果的不确定度评定合理。基于用带有100mm长杆电离室的积分剂量仪测量CT剂量指数的数学模型,对其测量不确定度来源进行分析,列出了方差、灵敏系数及标准不确定度的计算公式,从而给出了CT剂量指数测量的合成标准不确定度和扩展不确定度。     

Comparison of computed tomography dose reporting software

Computed tomography (CT) dose reporting software facilitates the estimation of doses to patients undergoing CT examinations. In this study, comparison of three software packages, i.e. CT-Expo (version 1.5, Medizinische Hochschule, Hannover, Germany), ImPACT CT Patients Dosimetry Calculator (version 0.99×, Imaging Performance Assessment on Computed Tomography, www.impactscan.org) and WinDose (version 2.1a, Wellhofer Dosimetry, Schwarzenbruck, Germany), has been made in terms of their calculation algorithm and the results of calculated doses. Estimations were performed for head, chest, abdominal and pelvic examinations based on the protocols recommended by European guidelines using single-slice CT (SSCT) (Siemens Somatom Plus 4, Erlangen, Germany) and multi-slice CT (MSCT) (Siemens Sensation 16, Erlangen, Germany) for software-based female and male phantoms. The results showed that there are some differences in final dose reporting provided by these software packages. There are deviations of effective doses produced by these software packages. Percentages of coefficient of variance range from 3.3 to 23.4 % in SSCT and from 10.6 to 43.8 % in MSCT. It is important that researchers state the name of the software that is used to estimate the various CT dose quantities. Users must also understand the equivalent terminologies between the information obtained from the CT console and the software packages in order to use the software correctly.     

Lamb波CT成像的实验研究

根据Ｘ射线ＣＴ成像原理和方法，利用Ｌａｍｂ波对薄层铝板的人工伤进行了ＣＴ成像的实验研究，得到较好的成像结果。     

利用插值法和曲线拟合法标定电涡流传感器

首先介绍了插值法和曲线拟合法的基本类型及数据模型,然后介绍了如何利用两种方法结合建立传感器输出与位移的对应关系,即传感器的标定。对两种方法的系统分析而建立的标定数据模型是一种有效的电涡流传感器标定模型,通过进一步论证得到了完整的标定流程。     

基于插补导航的全自主旋翼机设计与控制

为了解决传统旋翼无人机因手动遥操作而导致飞行不稳定的问题,研究了基于插补导航的全自主旋翼机的设计与控制方法。首先,根据导航系统和地面站,获得当前无人机与目标点之间的位置姿态关系;然后基于插补控制算法,利用机载控制器输出相应的能够控制无人机稳定飞行的脉冲宽度信号,实现脱离手动遥操作的四旋翼无人机全自主飞行控制。最后,通过全自主插补导航飞行仿真与实验,验证了该全自主无人机设计的可行性。结果表明,该全自主控制架构能够有效地模拟遥操作信号,实现无人机的全自主飞行控制,且具有更高的稳定性。     

基于B样条插值的图像边缘检测的硬件实现

为了能高速、高质量地进行图像边缘检测,提出了一种新的基于B样条插值的边缘检测方法.该方法采用了三次B样条插值原理,对图像的像素点灰度值进行插值运算,提出了基于B样条插值的一阶和二阶微分算子,并引入数字滤波技术加以实现.还利用B样条的可分离特性,实现了2维空间中基于B样条插值的连续图像的重构函数,在此基础上提出了用于边缘检测的基于3次B样条的一阶微分模板和二阶微分模板.设计出一套基于DSP FPGA的实时图像处理和显示系统.     

Quality control and patient doses in X-ray computed tomography

Results of quality control (QC) tests for a period of over a year and patient doses were analysed for several computed tomography units in our centre. The results of the QC tests were generally within limits for all of the examined scanners, proving good and stable performance of the systems. The tests were not helpful in predicting breakdowns of the systems such as tube failure. The doses for the same anatomical areas differed between scanners and in some cases exceeded the diagnostic reference levels (DRLs). DRLs are defined for typical diagnostic examinations performed in general hospitals and are not directly applicable to the examinations performed in the oncological centre.