Boundary normal pressure-based electrical conductivity reconstruction for magneto–acoustic tomography with magnetic induction

As a kind of multi-physics imaging approach integrating the advantages of electrical impedance tomography and ultrasound imaging with the improved spatial resolution and image contrast, magneto–acoustic tomography with magnetic induction(MAT-MI) is demonstrated to have the capability of electrical impedance contrast imaging for biological tissues with conductivity differences. By being detected with a strong directional transducer, abrupt pressure change is proved to be generated by the gradient of the induced Lorentz force along the force direction at conductivity boundary. A simplified boundary normal pressure(BNP)-based conductivity reconstruction algorithm is proposed and the formula for conductivity distribution inside the object with the clear physical meaning of pressure derivative, is derived. Numerical simulations of acoustic pressure and conductivity reconstruction are conducted based on a 2-layer eccentric cylindrical phantom model using Hilbert transform. The reconstructed two-dimensional conductivity images accord well with the model, thus successfully making up the deficiency of only imaging conductivity boundary in traditional MAT-MI. The proposed method is also demonstrated to have a spatial resolution of one wavelength. This study provides a new method of reconstructing accurate electrical conductivity and suggests the potential applications of MAT-MI in imaging biological tissues with conductivity difference.     

基于p-6P异质诱导生长酞菁铜薄膜的NO2传感器

为实现室温下低浓度NO₂气体检测,制作了p-六联苯(p-6P)诱导层的酞菁铜有机薄膜传感器。利用原子力显微镜(AFM)研究了不同沉积速率下p-6P薄膜的生长规律,慢速沉积提供足够的分子扩散时间,利于薄膜横向生长,形成高度低、尺寸大的晶畴。在p-6P薄膜上生长了酞菁铜薄膜,可以清晰看到晶畴上酞菁铜薄膜的有序排列。利用X射线衍射(XRD)仪,阐明了p-6P对酞菁铜薄膜具有很好的诱导效应。通过对比不同沉积速率p-6P薄膜诱导的酞菁铜传感器性能,发现慢速沉积诱导层的酞菁铜器件有高的响应强度和低的回复时间。异质诱导生长的酞菁铜传感器响应强度是直接生长在二氧化硅上的酞菁铜传感器的2倍,回复时间是3.2 min,对浓度为1.0 × 10^-5的NO₂气体灵敏。     

Induction time of silver nanoparticles precipitation: Experiment and modeling

This paper describes the measurement of induction time in precipitation of silver nanoparticles at different temperatures and supersaturations, and models it with Smoluchowski's coagulation theory. Silver nanoparticles are synthesized by reaction of silver nitrate with hydrazine in the presence of sodium citrate as stabilizer. The rate of association between clusters is found to depend on temperature and their sizes. The activation energy for the association between two clusters and interfacial tension of silver nanoparticles were also estimated. The results also show that induction time decreases with increasing supersaturation and temperature. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Backward uniqueness and the existence of the spectral limit for linear parabolic SPDEs

The aim of this article is to study the asymptotic behavior for large times of solutions of linear stochastic partial differential equations of parabolic type. In particular, we will prove the backward uniqueness result and the existence of the spectral limit for abstract SPDEs and then show how these results can be applied to linear SPDEs.     

Acceleration modules in linear induction accelerators

The Linear Induction Accelerator （LIA） is a unique type of accelerator that is capable of accelerating kilo-Ampere charged particle current to tens of MeV energy. The present development of LIA in MHz bursting mode and the successful application into a synchrotron have broadened LIA＇s usage scope. Although the transformer model is widely used to explain the acceleration mechanism of LIAs, it is not appropriate to consider the induction electric field as the field which accelerates charged particles for many modern LIAs. We have examined the transition of the magnetic cores＇ functions during the LIA acceleration modules＇ evolution, distinguished transformer type and transmission line type LIA acceleration modules, and re-considered several related issues based on transmission line type LIA acceleration module. This clarified understanding should help in the further development and design of LIA acceleration modules.     

Instantaneous electron beam emittance measurement system based on the optical transition radiation principle

One kind of instantaneous electron beam emittance measurement system based on the optical transition radiation principle and double imaging optical method has been set up. It is mainly adopted in the test for the intense electron-beam produced by a linear induction accelerator. The system features two characteristics. The first one concerns the system synchronization signal triggered by the following edge of the main output waveform from a Blumlein switch. The synchronous precision of about 1 ns between the electron beam and the image capture time can be reached in this way so that the electron beam emittance at the desired time point can be obtained. The other advantage of the system is the ability to obtain the beam spot and beam divergence in one measurement so that the calculated result is the true beam emittance at that time, which can explain the electron beam condition. It provides to be a powerful beam diagnostic method for a 2.5 kA, 18.5 MeV, 90 ns (FWHM) electron beam pulse produced by Dragon I. The ability of the instantaneous measurement is about 3 ns and it can measure the beam emittance at any time point during one beam pulse. A series of beam emittances have been obtained for Dragon I. The typical beam spot is 9.0 mm (FWHM) in diameter and the corresponding beam divergence is about 10.5 mrad.     

射频感应等离子体制备球形氧化铝的工艺研究

采用射频(RF)感应等离子体对颗粒形状不规则的氧化铝粉作球化处理,当氧化铝以极短暂时间快速穿越射频等离子体炬时,颗粒因受热而熔化成液滴,快速冷却,形成球形固态颗粒。应用单因素法讨论射频等离子体制备球形氧化铝的工艺参数,研究了制备过程中相关的中气流量、抽风负压、送粉速度和分散方式等主要工艺参数对球形氧化铝粉的影响。用电子扫描显微镜(SEM)观测评估球化效果,测定松装密度和振实密度。     

多级感应线圈炮最优发射控制策略

基于电路理论,建立了多级感应线圈炮数学机电控制模型;分析了电枢受力的影响因素,结果表明,电枢受力决定于驱动线圈和电枢的电流大小和它们之间的互感梯度。总结了多级同步感应线圈炮设计原则,根据设计原则,提出了感应线圈炮的最优发射控制策略,并从理论上证明其可行性,最后以10级线圈炮为例,归纳了多级感应线圈炮的触发公式,并进行了实验验证,其结果表明,通过修正触发公式,仿真结果与测量值吻合较好。     

多脉冲直线感应加速器外接复位系统

基于硅堆隔离网络的多脉冲直线感应加速器(LIA)需要外接独立的复位系统,以满足其加速腔磁芯在主脉冲励磁前的复位需求。介绍了猝发三脉冲LIA外接复位系统的工作原理、电路参数以及具体的电路设计,并针对大型LIA感应腔数量众多、运行时电磁环境复杂的特点,介绍了复位系统在工程实施中的主要技术难点和最终布局。该复位系统解决了磁芯在励磁和复位这两种高压模式间的切换问题,实现了10~20kV可调复位电压的稳定输出,建立了在复杂电磁环境下可稳定运行的远程监控系统,确保了三脉冲LIA的92个加速腔能够在主脉冲励磁前稳定、快速、充分的复位。     

基于遗传算法的同步感应线圈发射装置参数优化

发射速度和能量转换效率是同步感应线圈型电磁发射装置(SICEML)最重要的两项指标。驱动线圈和电枢的结构参数、驱动线圈匝数以及电枢初始触发位置都会对这两项指标产生影响。以上述参数为变量,以发射速度和能量转换效率之积为目标函数,引入遗传算法对单级SICEML参数进行了优化设计,并利用有限元软件进行了仿真验证。结果表明:在储能与发射装置总体体积不变的前提下,优化后的系统效率由5.38%提高到13.6%,出口速度由38m/s提高到61m/s,系统性能得到明显改善。利用单级SICEML样机进行了堵驻试验,结果与仿真结果吻合较好,验证了本文提出的遗传算法的可行性。