Highly efficient sonochemical reaction with a switched spiral focal field

This paper describes an efficient method of inducing sonochemical reactions with focussed ultrasound. A sector-vortex transducer (a phased array transducer with multiple sectors and a geometric focus) is used to produce focal ultrasound fields with spiral-shaped wavefronts. Clockwise and counter-clockwise spiral focal fields, with basically the same ultrasound power distribution but having different wavefront angles, are produced by using the same array transducer. The oxidation of the iodide ions induced from the periodic switching between such a pair of spiral focal fields is investigated at an ultrasound frequency of 750 kHz. The oxidation rate at the optimum switching period (3 ms) is about ten times higher than that at switching periods of 1 s. The optimum switching period and the sonochemical reaction rate are unchanged when the viscosity was adjusted to that of human blood.     

双螺旋叠栅条纹检测光束准直性的两种方法

介绍双螺旋叠栅条纹检测光束准直性的基本原理,进一步就双螺旋叠栅条纹的特征参量与被测光束发散角(即光束准直精度)的关系进行分析和推导。在分析双螺旋叠栅条纹进行时,首先采用频域低通滤波提取纯叠栅条纹,然后提取纯叠栅条纹的特征参量。提出两种特征参量的提取方法,一种依次进行傅里叶变换计算相位信息的傅里叶变换方法,另一种是受传统时间相移算法启发而提出的空间相移算法,讨论了在两种方法中极坐标的重采样问题和相应的计算公式,并进行了计算机模拟。结果表明,傅里叶变换方法和空间相移算法实质都是获取叠栅条纹全场趋势的平均值,使最终光束发散角的检测具有很高的精度,对自成像条纹周期的检测误差在±2.8‰以内。     

小型化第三代移动通信系统用高温超导滤波子系统的研制

本文研究了双向螺旋型谐振器的耦合特性,并采用此谐振器设计、制作了适用于第三代移动通信系统的8节高温超导滤波器.该滤波器中心频率为1950 MHz,带宽为60 MHz.滤波器完成制备后,采用集成封装方式,将其与低温低噪声放大器封装在同一金属盒内,实现了滤波器系统的小型化.文章研究了集成封装方式的尺寸、结构对滤波器性能的影响.测试结果表明,采用集成封装方式的滤波器系统具有优良性能,与独立封装方式相比,器件的总尺寸减小了20%以上.     

Evolution of Spiral Waves in Excitable Systems

Spiral waves, whose rotation center can be regarded as a point defect, widely exist in various two-dimensional excitable systems. In this paper, by making use of Duan＇s topological current theory, we obtain the charge density of spiral waves and the topological inner structure of its topological charge. The evolution of spiral wave is also studied from the topological properties of a two-dimensional vector field. The spiral waves are found generating or annihilating at the limit points and encountering, splitting, or merging at the bifurcation points of the two-dimensional vector field. Some applications of our theory are also discussed.     

Fabrication of 2D–3D photonic crystal heterostructures by glancing angle deposition

We fabricate 2D–3D photonic crystal heterostructures based on the silicon [001]-diamond:1 square spiral geometry using glancing angle deposition. We compare the normal incidence reflection properties of the fabricated 2D–3D heterostructures to simulated spectra generated using finite-difference time-domain calculations. Reflection peaks are observed, resulting from the presence of a photonic band gap, and defect modes are created by the 2D layer. Deterioration of the reflectance peaks with increased number of vertical spiral periods is observed. A series of square spiral structures are fabricated with a varying number of vertical periods to quantify the degradation of reflection peaks. At normal light incidence, a maximum reflection peak is observed from the film with three vertical periods. Beyond three spiral rotations, deterioration of the substrate-plane periodicity causes scattering losses.     

双脉冲高功率脉冲调制器的设计

采用螺旋线和折叠线技术相结合的方法,设计了一种基于水介质高功率脉冲调制器。该调制器采用了两个开关,通过控制两个开关的导通时刻,可以在两个负载上得到脉冲长度相等的两个脉冲。对该种折叠型传输线的波过程进行了详细分析,给出了过渡段部分阻抗等参数对负载电压的影响;用Pspice电路软件对脉冲形成线的充电电压和二极管电压、电流进行了模拟;最后利用高压同轴电缆,对该种类型调制器进行了低压情况下的验证实验,实验结果与理论分析、模拟研究一致。此种类型的调制器具有结构紧凑、可同时输出两个脉冲的优点。     

两层耦合可激发介质中螺旋波转变为平面波

采用Br-Eiswirth模型研究了两层耦合可激发介质中螺旋波的动力学,两层介质通过网络连接,即在每一层介质上,每一列选一个可激发单元作为中心点,在一层介质上同一列的可激发单元只与另一层介质上对应的中心点及其8个邻居有耦合.数值模拟结果表明:通过这种局部耦合,在适当小的耦合强度下两耦合螺旋波可实现同步,增大耦合强度会导致螺旋波漫游和漂移,造成螺旋波不同步,观察到螺旋波与静息态、低频平面波和不规则斑图共存现象.在适当强的耦合强度下,还观察到两螺旋波转变成同步的平面波消失现象.对产生这些现象的物理机理做了讨论.     

Multi-mode Spiral Wave in a Coupled Oscillatory Medium

Multi-mode spiral wave and its breakup in 1-d and 2-d coupled oscillatory media is studied here by theoretic analysis and numerical simulations. The analysis in 1-d system shows that the dispersion relation curve could be nonmonotonic depending on the coupling strength. It may also lead to the coexistence of different wave numbers within one system. Direct numerical observations in 1-d and 2-d systems conform to the prediction of dispersion relation analysis. Our findings indicate that the wave grouping can also be observed in oscillatory media without tip meandering and waves with negative group velocity can occur without inhomogeneity.     

麻省理工学院物理教育状况研究

通过对麻省理工学院物理教育理念、专业设置、课程体系、教材选用情况和教学方式的分析与研究,进一步了解MIT物理教育的特点以及培养拔尖创新人才的模式,可对我国大学的物理教育改革提供一些科学的参考和启示.     

Spiral and Antispiral Waves in Reaction-Diffusion Systems

Spiral waves are ubiquitous phenomena in nonlinear chemical, physical, and biological systems. But antispiral waves are infrequent to date. The transition between spiral and antispiral waves has been rarely explored. We have analyzed the extended Brusselator model and the extended Oregonator model by linear stability analysis. We have demonstrated that it is possible and plausible to realize the transition between them by control of diffusion coefficient of inactivator from theoretical analysis and numerical simulations.