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。     

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.     

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.     

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.     

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.     

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.     

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.     

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。     

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。     

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.     

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。     

Design and development of a novel nuclear magnetic resonance detection for the gas phase ions by magnetic resonance acceleration technique

Nuclear magnetic resonance (NMR) technique is a well-established powerful tool to study the physical and chemical properties of a wide range of materials. However, presently, NMR applications are essentially limited to materials in the condensed phase. Although magnetic resonance was originally demonstrated in gas phase molecular beam experiments, no application to gas phase molecular ions has yet been demonstrated. Here, we present a novel principle of NMR detection for gas phase ions based on a "magnetic resonance acceleration" technique and describe the design and construction of an apparatus which we are developing. We also present an experimental technique and some results on the formation and manipulation of cold ion packets in a strong magnetic field, which are the key innovations to detect NMR signal using the present method. We expect this novel method to lead new realm for the study of mass-selected gas-phase ions with interesting applications in both fundamental and applied sciences.     

A novel power amplification scheme for nuclear magnetic resonance/nuclear quadrupole resonance systems

Nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR)-based chemical analysis systems have been widely utilized in various areas such as medicine, security, and academic research. In these applications, the power amplifier stage plays a key role in generating the required oscillating magnetic fields within a radio frequency coil that serves as the probe. However, the bulky size and relatively low efficiency of the traditional power amplification schemes employed present a bottleneck for the realization of compact sized and portable NMR and NQR systems. To address this problem, this work presents a class D voltage-switching power amplification scheme with novel fast-start and fast-stop functions that are suitable for generating ideal NMR and NQR excitation signals. Compared to the traditional analog power amplifiers (PAs), the proposed switched-mode PA can achieve significant improvement on the power efficiency as well as the physical volume. A PA circuit for portable NQR-based explosive detection systems has been designed and built using the proposed scheme with 1 kW possible maximum output power and 10 MHz maximum operating frequency. Test results show that the presented PA achieves more than 60% measured efficiency within a highly compact volume while sustaining fast start and stop of excitation signals in the order of microseconds.     

In vivo evaluation of nuclear magnetic resonance flowmetry: blood flow through the normal forearm

A cylindrical crossed-coil nuclear magnetic resonance flowmeter has been developed to measure arterial blood flow through the human forearm. This paper describes the in vivo studies to evaluate the performance of the instrument. Flow rates were comparable to values reported in the literature. The NMR flowmeter is a noninvasive, contactless-type flowmeter and has the advantage of accurate measurement unimpaired by clothing, bandages, or casts. One measurement can be taken in less than 2 min.     

Environmental sustainability evaluation of additive manufacturing using the NIST test artifact

Journal of Mechanical Science and Technology - To identify which elements of 3D printers influence the environment, this paper compares four 3D printers: Material-jetting (PJ), powder-bed-fusion of...     

磁耦合共振无线能量传输系统建模与分析

为探索磁耦合共振无线能量传输机理,研究传输参数与传输性能间的关系,基于互感耦合理论,建立了磁耦合共振无线能量传输系统的电路模型,推导出系统共振角频率解析表达式,揭示了共振角频率随收发端距离由近至远过程中,由一个分裂至两个又恢复至一个的规律;指出因空心线圈的低耦合系数特性,工程中仅会观察到由两个合并为一个的过程.利用OrCAD仿真软件和实验手段对系统传输特性进行仿真分析和实验研究,结果显示系统传输特性的变化规律与理论分析相吻合,所求得的共振角频率数学公式的计算精度高,与仿真结果误差在±1％以内,能够准确描述系统的能量传输特性.所建模型为高效率磁耦合共振无线能量传输系统的设计提供了理论支持.     

A microprocessor-controlled photon counter for pulsed optically detected magnetic resonance

In pulsed optically detected magnetic resonance (ODMR) spectroscopy, a lock-in amplifier is used to monitor the signal which is phase-matched to the duty cycle of an applied sequence of pulses. However, since the desired signals reside atop a much larger amplitude-modulated signal, lock-in amplification methods are difficult to use. Commerically available photon counters are of limited use, because the pulsed ODMR method requires sequential counting over several time intervals, often with minimum time delay between the intervals. The multiaccumulator photon counter described here is capable of such sequential counting over as many as four intervals. The microprocessor which controls the counter algebraically manipulates the photon counts during each of the duty cycles. The result is an inexpensive yet versatile photon counter which is suited for pulsed ODMR and other applications in which sequential counting is necessary.