光学合成孔径复原图像的振铃探测与消除

针对相位平移误差使光学合成孔径图像的复原出现的振铃效应,提出了一种结合视觉感知的振铃探测与消除方法。首先,提出并利用梯度方向随机度和局部方差值两项指标计算得到图像纹理区;然后,根据不同阈值的Canny算子检测出全边缘与主边缘,并将主边缘邻域内的全边缘作为待筛选的边缘振铃;最后,结合人类视觉系统的纹理掩盖效应分别得到振铃区与平坦区。此外,在图像分区基础上,选择亮度相似度因子作为自适应参数,利用双边滤波进行图像处理。实验显示:处理后Lena图像的峰值信噪比提高了10.8%,分辨率板的结构相似度提高了0.057。结果表明:该方法能够对图像以像素精度分区,可以在保持边缘与纹理的同时,有效消除振铃效应,提高图像复原质量。     

橡胶缓冲器接触碰撞有限元分析

利用ANSYS/LS-DYNA有限元软件对电梯对重碰撞橡胶缓冲器过程进行模拟,分析碰撞过程中不同时刻橡胶缓冲器及电梯对重的动态响应.结果表明该模拟能为研究电梯缓冲器的性能和设计,以及改善结构提供依据,以保证缓冲器在工作中满足技术要求.     

应变式称重传感器弹性体线性度的有限元分析

弹性体是应变式称重传感器的关键元件。采用有限元法对应变式称重传感器弹性体进行分析。用此方法首先要得到弹性体的应变分布特性,确定考察应力线。然后分级加载,得到载荷与考察应力线之间的一元线性回归方程,分析得出弹性体的线性度。分析结果表明,此弹性体的线性度很好,能满足使用要求。     

利用自适应纹理分布的活动形状分割前列腺磁共振图像

基于前列腺磁共振图像性质,提出利用自适应纹理分布的活动形状图像分割方法来自动分割前列腺磁共振图像.该方法首先通过图像的分类与拟合确定感兴趣的腺体区域,同时估计若干形状参数用于分割过程中调整形状;然后融人多重纹理信息,建立纹理一致测度,将传统的活动形状按照自适应的纹理判别步骤细分为纹理分布形状与补充形状,提高活动形状的搜索匹配能力.在搜索匹配部分,利用已估计参数优化活动形状搜索的初始估计,并根据纹理分布形状和补充形状调整迭代过程.实验结果表明,该方法分割出来的前列腺轮廓与金标准的Hausdorff距离为6.00 pixel,分割精度为93％.该方法对活动形状的改进是有效的,利用自适应纹理分布的活动形状能够自动、准确地将前列腺从磁共振图像中分割出来.     

Nuclear magnetic resonance apparatus for pulsed high magnetic fields

A nuclear magnetic resonance apparatus for experiments in pulsed high magnetic fields is described. The magnetic field pulses created together with various magnet coils determine the requirements such an apparatus has to fulfill to be operated successfully in pulsed fields. Independent of the chosen coil it is desirable to operate the entire experiment at the highest possible bandwidth such that a correspondingly large temporal fraction of the magnetic field pulse can be used to probe a given sample. Our apparatus offers a bandwidth of up to 20 MHz and has been tested successfully at the Hochfeld-Magnetlabor Dresden, even in a very fast dual coil magnet that has produced a peak field of 94.2 T. Using a medium-sized single coil with a significantly slower dependence, it is possible to perform advanced multi-pulse nuclear magnetic resonance experiments. As an example we discuss a Carr-Purcell spin echo sequence at a field of 62 T.     

Finite-element analysis of a five-stage cold-heading process

An elastic—plastic finite-element analysis of a five-stage cold-heading operation is presented. This gives accurate prediction of the external shapes produced, and of the internal distortion. The method can be used to optimise preform routes with respect to maximum forces, homogeneity of the product and process costs in terms of number of stages and inter-annealing requirements.     

基于水平集的前列腺磁共振图像分割方法研究

基于前列腺磁共振图像(MRI)特征信息及其病变好发特定区域等先验知识,针对前列腺内外轮廓全分割问题,提出基于边缘距离调整水平集演化(DRLSE)的前列腺MRI两步分割方法。在构建统一水平集能量函数的基础上,第1步基于前列腺MR的T1(纵向弛豫时间)图像实现其外轮廓分割,第2步在外轮廓约束限定条件下,基于前列腺MR的T2(横向弛豫时间)图像实现前列腺的内部轮廓分割,进而完成前列腺内外轮廓的全面有效分割。设计了前列腺分割的人机交互界面,对10个前列腺病例MR图像(含正常、增生和癌变共30幅)进行了分割实验研究,并采用Dice相似性系数(DSC)对分割结果进行评价分析,DSC值达到90%以上。实验结果表明,所提出的基于边缘DRLSE的前列腺MRI两步分割方法能够有效地实现前列腺内外轮廓的全面分割,非常接近于临床专家手动分割的理想结果,对前列腺疾病的临床诊断和治疗有较好的参考价值。     

核磁共振兼容手术机器人的驱动方式分析

核磁共振兼容手术机器人的驱动问题是研究图像导航手术机器人的一个重要内容。首先分析了核磁共振兼容手术机器人存在的问题,介绍了国内外研究者关于核磁共振兼容手术机器人驱动方式的使用情况,探讨了各种驱动方式的特点,得出了各项驱动方式在核磁共振环境下的使用性能,并对其发展方向作出了展望。     

Versatile pulse programmer for nuclear magnetic resonance

A microprocessor-based pulse programmer for pulsed NMR applications employing digital integrated circuit and microprocessor techniques is described. The pulse programmer was designed to be completely general with the capability to quickly and easily program any desired pulse sequence. Pulse sequenching and timing information is entered through any standard ASCII terminal using a programming language developed specifically for NMR. A resident text editor provides for easy pulse sequence modifications as well as a program library feature. A language translator and run-time monitor transform this general hardware system into a 'smart' pulse programmer capable of extended programming functions.     

用于多传感器坐标测量机探测误差评价的薄环规标准器

设计了一种薄环规标准器,用于配有光学影像测头和接触式测头的多传感器坐标测量机的探测误差评价。该标准器兼有环规和二维平面标准圆的特征,孔的有效部分厚度为0.1 mm,圆度为0.5μm,可以满足大多数坐标测量机的校准需求,避免了普通标准器如标准球、环规对影像测头测量成像的影响。该标准器同时适用于接触式测头测量,锥孔结构保证了标准器的稳定性,用于接触式测量时,不会引起变形。利用设计的薄环规标准器实现了配有光学影像测头和接触式测头组合测量系统的探测误差评价,结果表明该标准器有效解决了上述组合系统探测误差的校准问题。参照ISO10360-9标准,给出了多传感器组合测量系统的探测误差、尺寸测量误差以及位置误差,并利用坐标变换方法修正了位置误差,优化了系统参数。     

A versatile pulse programmer for magnetic resonance imaging

Hardware and software solutions for a versatile pulse programmer have been presented. The core of the pulse programmer is an FPGA device that provides flexibility to the design and reduces the number of electronics elements needed. The event of the pulse programmer consists of 16 bits. The main feature of the proposed pulse programmer is that the 16 outputs can be independently delayed. This is important for correcting delays of the RF channels or the gradient channels due to various causes. The proposed pulse programmer is integrated into an MRI scanner, and the correction of the gradient system delay is taken as an example to experimentally demonstrate its performance.     

Lock-in detection for pulsed electrically detected magnetic resonance

We show that in pulsed electrically detected magnetic resonance (pEDMR) signal modulation in combination with a lock-in detection scheme can reduce the low-frequency noise level by one order of magnitude and in addition removes the microwave-induced non-resonant background. This is exemplarily demonstrated for spin-echo measurements in phosphorus-doped silicon. The modulation of the signal is achieved by cycling the phase of the projection pulse used in pEDMR for the readout of the spin state.     

Design of an active-passive device for human ankle movement during functional magnetic resonance imaging analysis

Functional magnetic resonance imaging analysis has made major strides in recent years, both because of the development of new scanners and owing to magnetic resonance compatible systems that make it possible to stimulate parts of the human body during analysis. The significant gains in our knowledge of the brain that can thus be achieved justify efforts to construct machines with control circuits suitable for this purpose. This paper presents a magnetic resonance compatible mechatronic device with electropneumatic control that can be used to move one or both feet during functional magnetic resonance imaging analysis of the cerebral motor zones. The system is innovative and original. The results obtained at the end of the investigation were good, and demonstrated that the design is feasible.     

Development of a miniature permanent magnetic circuit for nuclear magnetic resonance chip

The existing researches of miniature magnetic circuits focus on the single-sided permanent magnetic circuits and the Halbach permanent magnetic circuits. In the single-sided permanent magnetic circuits, the magnetic flux density is always very low in the work region. In the Halbach permanent magnetic circuits, there are always great difficulties in the manufacturing and assembly process. The static magnetic flux density required for nuclear magnetic resonance(NMR) chip is analyzed based on the signal noise ratio(SNR) calculation model, and then a miniature C-shaped permanent magnetic circuit is designed as the required magnetic flux density. Based on Kirchhoff’s law and magnetic flux refraction principle, the concept of a single shimming ring is proposed to improve the performance of the designed magnetic circuit. Using the finite element method, a comparative calculation is conducted. The calculation results demonstrate that the magnetic circuit improved with a single shimming has higher magnetic flux density and better magnetic field homogeneity than the one improved with no shimming ring or double shimming rings. The proposed magnetic circuit is manufactured and its experimental test platform is also built. The magnetic flux density measured in the work region is 0.7 T, which is well coincided with the theoretical design. The spatial variation of the magnetic field is within the range of the instrument error. At last, the temperature dependence of the magnetic flux density produced by the proposed magnetic circuit is investigated through both theoretical analysis and experimental study, and a linear functional model is obtained. The proposed research is crucial for solving the problem in the application of NMR-chip under different environmental temperatures.     

Finite-element analysis of flat rolling with inclusion of anisotropy

Anisotropy is a major phenomenon which influences roll torque, roll force and distribution of pressure and shear stress on the roll—strip interface. In this paper, a model for steady-state plane strain cold rolling is presented, which takes into account anisotropic behavior of the sheet. For this purpose, a modified yield function is presented for solving plane strain problem. A parametric study has been carried out for hypothetical material parameters to study their influence on design parameters. It is established that anisotropy should be included in numerical simulation codes for getting correct estimate of design parameters.     

磁共振成像在喉癌和下咽癌放化疗评价中的应用

目的:探讨磁共振成像(MRI)在喉癌和下咽癌放化疗评价中的应用价值,为喉癌和下咽癌放化疗效果评价提供新的思路。方法:收集经病理证实的喉癌及下咽癌109例初治患者纳入此次前瞻性研究。患者均于我院接受放化疗综合治疗,分别于治疗前、治疗后行磁共振检查,记录其扩散加权成像(DWI)半定量参数,以及MR动态多期增强扫描(DCE-MRI)定量参数,比较完全缓解(CR)者与非CR者上述参数差异,运用受试者工作特征曲线(ROC),计算各项参数预测喉癌和下咽癌放化疗效果的价值。结果:109例患者均顺利完成治疗,治疗结束后,CR 48例,PR 61例,CR率为44.04%。CR组治疗前ADCmean、ADCmax低于非CR组,两组患者治疗后ADCmean均较治疗前上升,CR组治疗后ADCmean高于非CR组,差异有统计学意义(P <0.05)。CR组治疗前Kep高于非CR组,两组患者治疗后Kep均下降,Ve均上升,CR组治疗后Ktrans下降,非CR组治疗后Ktrans上升,差异有统计学意义(P <0.05)。以治疗前ADCmean≤1.06预测CR的ROC曲线下面积为0.642(灵敏度为91.57%、特异性为54.88%),以治疗前Kep≥1.105min预测CR的曲线下面积为0.581(灵敏度为93.65%、特异性为51.62%)。结论:治疗前DWI半定量参数及DCE-MRI定量参数均可为喉癌和下咽癌患者放化疗效果的预测提供一定参考,值得进一步关注。     

Finite-element vibration analysis of tapping-mode atomic force microscopy in liquid

Investigation of morphology and mechanical properties of biological specimens using atomic force microscopy (AFM) often requires its operation in liquid environment. Due to the hydrodynamic force, the vibration of AFM cantilevers in liquid shows dramatically different dynamic characteristics from that in air. A good understanding of the dynamics of AFM cantilevers vibrating in liquid is needed for the interpretation of scanning images, selection of AFM operating conditions, and evaluation of sample's mechanical properties. In this study, a finite element (FE) model is used for frequency and transient response analysis of AFM cantilevers in tapping mode (TM) operated in air or liquid. Hydrodynamic force exerted by the fluid on AFM cantilevers is approximated by additional mass and hydrodynamic damping. The additional mass and hydrodynamic damping matrices corresponding to beam elements are derived. With this model, numerical simulations are performed for an AFM cantilever to obtain the frequency and transient responses of the cantilever in air and liquid. The comparison between our simulated results and the experimentally obtained ones shows good agreement. Based on the simulations, different characteristics of cantilever dynamics in air and liquid are discussed.     

眼电伪迹自动去除方法的研究与分析

脑电信号采集时很容易受到眼电信号的干扰,从而影响脑机接口系统的性能。为此,提出一种基于离散小波变换(DWT)和典型相关分析(CCA)的眼电伪迹自动去除方法,即 DCCA 法。首先,对采集的多导脑电信号和眼电信号进行离散小波变换,获得多尺度小波系数,并利用典型相关分析去除小波系数间的相关性,得到互不相关的典型小波系数;进而,利用相关系数判别眼迹成分,将相应典型小波系数置零并依次采用 CCA逆变换和 DWT逆变换重构剔除眼电伪迹后的脑电信号。基于9位实验者的4种眼电数据进行实验研究,并从统计学的角度对实验结果进行显著性检验。结果表明, DCCA法相对其他方法在均方根误差、信噪比方面具有显著优势,且具有较好的实时性,并表现出较强的适应能力。     

双球渐开线样板的理论分析和应用

为确保齿轮测量仪器的高精度校准,国际标准ISO/TR 10064-5:2005推荐了新型的双球渐开线样板.该样板采用高精度球体的部分圆弧代替渐开线,通过误差补偿,获得高精度渐开线以实现渐开线溯源.研究了该样板相关的理论问题,为双球样板设计与应用提供了理论基础.针对数控齿轮测量仪器常采用的电子展成法,分析并给出了理想安装...     

车辆滑柱式减振器活塞杆UG/STRUCTURES有限元分析

这里借助集CAD/CAM/CAE功能于一体的软件UG(Unigraphics)对减振器各部件建模,并利用UG/scenarioforStructures分析了活塞杆的应力分布,得结论:活塞杆的基本载荷来自拉伸和压缩两工况;拉伸时,活塞杆所受阻尼力大于压缩工况,故应以拉伸工况的强度要求来设计;活塞杆两端部所受应力最大。