0.35μm激光辐照下柱腔靶的等离子体状态与运动特性

 使用针孔相机配X光条纹相机、法拉第杯等观测了腔靶等离子体的运动特性、腔内壁衬CH膜对高Z高密度等离子体运动的抑制现象以及隔离膜对等离子体膨胀的影响。并用硬X光能谱法和受激喇曼散射光的短波截止推算了相应的腔内热等离子体电子温度。 这些结果有助于0.35μｍ激光辐照下腔靶辐射场特性的深入研究以及未来神光Ⅱ腔靶构型的设计。     

次协调逻辑下的自动推理

引进了一套次协调逻辑系统──注解逻辑的线性归结方法后，在探讨的过程中提出了若干命题，并用一个推理实例表明在该系统中产生次协调性后，仍然可以进行正常的推理．     

试射法在求解二阶线性微分方程边值问题中的应用

对二阶线性微分方程的边值问题(第一类、第二类及第三类边值条件),通常可利用古典的差分方法进行求解,即通过对微分方程离散化而求解线性方程组得到原微分方程的解.通过数值实验说明试射法也可作为求解二阶线性微分方程的一种有效算法且能保证具有较高的精度.     

Real-time dynamics of the acoustically driven electron–hole transport in GaAs quantum wires

We have investigated the dynamics of photogenerated carriers in GaAs quantum wires during their transport by surface acoustic waves using spatially and time-resolved photoluminescence. This technique allows us to map in real time the spatial carrier distribution during the transport as well as to study the nature of radiative defect sites in the transport path.     

Higher‐order upwind leapfrog methods for multi‐dimensional acoustic equations

A non‐dissipative and very accurate one‐dimensional upwind leapfrog method was successfully extended to higher‐order and multi‐dimensional acoustic equations. The governing equations in characteristic form and staggered grid were utilized to preserve the accuracy. Fourier analysis was performed to find the accurate scheme for acoustics and the resultant two‐dimensional methods were successfully applied to several classical test cases. Copyright © 2004 John Wiley & Sons, Ltd.     

Relationship between acoustic emission energy and the kinetics of martensite formation in plain carbon steels

The kinetics of the martensitic transformation in Fe-0.80C determined on the basis of dilatometry data is compared to the acoustic emission (AE) energy accompanying the transformation in the same steel reported in a previous study. The discrepancy between the AE energy and the volume fraction of martensite indicates that the mechanism for the generation of AE during the martensitic transformation is not solely dependent on the kinetics and the associated moving interfaces as suggested in previous studies. During the growth of martensite, slip takes place in order to relieve internal stresses, and dislocations are thought to be mainly introduced in the relatively soft austenite matrix. The quantitative analysis in this study demonstrates that the AE energy generated per unit time is a function of both the transformation kinetics and the volume fraction of remaining austenite. This strongly indicates that the moving dislocations associated with the plastic deformation of the austenite surrounding the as-formed martensite are the dominant sources of the generated acoustic waves. This improved AE source model is consistent with the well-accepted mechanism of AE during conventional plastic deformation due to an external load.     

A novel design scheme for acoustic cloaking of complex shape based on region partitioning and multi-origin coordinate transformation

Acoustic cloaking is an important application of acoustic metamaterials. This article proposes a novel design scheme for acoustic cloaking based on the region partitioning and multi-origin coordinate transformation. The cloaked region is partitioned into multiple narrow strips. For each strip, a local coordinate system is established with the local origin located at the strip center, and a coordinate transformation in the local coordinate system is conducted to squeeze the material along the strip length direction to form the cloaked region. To facilitate the implementation of the acoustic cloak, the multilayer effective medium is used to approximate the non-uniform anisotropic material parameters. The effectiveness of the proposed coordinate transformation method is verified by comparing the results from our method with those in the literature. Firstly, the results of a circular acoustic cloak in the literature are reproduced by using our finite element (FE) simulations for validation. Then, a comparison is made between the traditional coordinate transformation scheme and our new scheme for simulating an elliptical acoustic cloak. The results indicate that the proposed multi-origin coordinate transformation method has a better cloaking effect on the incident wave along the ellipse minor axis direction than the traditional method. This means that for the same object, an appropriate transformation scheme can be selected for different incident wave directions to achieve the optimal control effect. The validated scheme is further used to design an arch-shaped cloak composed of an upper semicircular area and a lower rectangular area, by combining the traditional single-centered coordinate transformation method for the semicircular area and the proposed multi-origin method for the rectangular area. The results show that the designed cloak can effectively control the wave propagation with significantly reduced acoustic pressure level. This work provides a flexible acoustic cloak design method applicable for arbitrary shapes and different wave incident directions, enriching the theory of acoustic cloaking based on coordinate transformation.     

风速对声点阵立靶系统建模及算法的影响研究

室外靶场中点阵声学立靶应用时风对报靶精度有较大影响。使用几何方法推导了激波到达时间、矢量风速、弹丸速度和入射角、着靶位置之间的模型方程,然后将激波到达时间显式表述。该显式表达式可简化非线性最小二乘法求解并加速了收敛性,可同时求得弹丸着靶位置以及速度、入射角,可适用于不同的传感器阵列样式。通过仿真给出了风速对报靶精度影响的误差图。     

Advanced vapor recognition materials for selective and fast responsive surface acoustic wave sensors: A review

The necessity of selectively detecting various organic vapors is primitive not only with respect to regular environmental and industrial hazard monitoring, but also in detecting explosives to combat terrorism and for defense applications. Today, the huge arsenal of micro-sensors has revolutionized the traditional methods of analysis by, e.g. replacing expensive laboratory equipment, and has made the remote screening of atmospheric threats possible. Surface acoustic wave (SAW) sensors – based on piezoelectric crystal resonators – are extremely sensitive to even very small perturbations in the external atmosphere, because the energy associated with the acoustic waves is confined to the crystal surface. Combined with suitably designed molecular recognition materials SAW devices could develop into highly selective and fast responsive miniaturized sensors, which are capable of continuously monitoring a specific organic gas, preferably in the sub-ppm regime. For this purpose, different types of recognition layers ranging from nanostructured metal oxides and carbons to pristine or molecularly imprinted polymers and self-assembled monolayers have been applied in the past decade. We present a critical review of the recent developments in nano- and micro-engineered synthetic recognition materials predominantly used for SAW-based organic vapor sensors. Besides highlighting their potential to realize real-time vapor sensing, their limitations and future perspectives are also discussed.     

Focusing surface acoustic waves assisted electrochemical detector in microfluidics

This article demonstrates a novel electrochemical detection device. The device is composed by two focusing interdigital transducers for exciting focused surface acoustic waves by applying an AC signal, a three-electrode system for electrochemical measurement, and a liquid pool for holding liquid on a LiNbO₃ wafer. The amperometry current of ferrocenecarboxylic acid and potassium phosphate buffer solution is used to characterize the detection sensitivity. Two experiments are carried out to optimize the device design. The result shows that the two focusing interdigital transducers with arc degree 30° and distance 5 mm can remarkably enhance the liquid mixing rate. Under this condition, the oxidation current is about 27 times larger than that without surface acoustic wave stirring.