Calculation of the reactor neutron time of flight spectrum by convolution technique

It is a very complex and time-consuming process to simulate the nuclear reactor neutron spectrum from the reactor core to the export channel by applying a Monte Carlo program. This paper presents a new method to calculate the neutron spectrum by using the convolution technique which considers the channel transportation as a linear system and the transportation scattering as the response function. It also applies Monte Carlo Neutron and Photon Transport Code （MCNP） to simulate the response function numerically. With the application of convolution technique to calculate the spectrum distribution from the core to the channel, the process is then much more convenient only with the simple numerical integral numeration. This saves computer time and reduces some trouble in re-writing of the MCNP program.     

变组分AlGaAs/GaAs透射式光电阴极分辨力特性分析

建立了变组分AlGaAs/GaAs光电阴极二维载流子输运连续性方程.在一定的边界条件下,利用数值计算方法对此方程进行求解,得到了变组分AlGaAs/GaAs光电阴极调制传递函数(MTF)理论计算模型.利用该模型计算了透射式变组分和均匀组分阴极的理论MTF,分析了分辨力与Al组分变化范围、入射光子波长、AlGaAs和GaAs层厚度的关系.计算结果表明,变组分阴极与均匀组分阴极相比,阴极分辨力显著提高.当空间频率f在100—500 lp·mm-1区间时,分辨力的提高最为明显,如当f=200 lp·mm-1时,一般可提高150%—260%.变组分阴极分辨力的提高是内建电场作用的结果,但内建电场太大时,也会由于Al组分含量过高而影响阴极的长波响应.     

一维指数形变截面有限周期声子晶体的研究

本文利用集中质量法对弹性纵波在一维指数形截面有限周期声子晶体中的传播进行了研究, 得到了频率响应函数的表达式. 与一维等截面的声子晶体相比, 指数形变截面声子晶体带隙内的衰减值随着输出端截面积的增大而减小, 同时带隙的起始频率降低而截止频率升高, 也即带隙的宽度会得到拓展. 晶格常数和材料组份比变化时, 变截面声子晶体带隙的起始频率和截止频率的变化趋势与等截面时的声子晶体相同. 希望本文的研究能够推动声子晶体在减振降噪等领域中的应用.     

基于时空混沌系统的单向Hash函数构造

提出了一种基于时空混沌系统的Hash函数构造方法.以线性变换后的消息数作为一组初值来驱动单向耦合映像格子的时空混沌系统，产生时空混沌序列，取其空间最后一组混沌序列的适当项，线性映射为Hash值要求的128bit值.研究结果表明，这种基于时空混沌系统的Hash函数具有很好的单向性、弱碰撞性、初值敏感性，较基于低维混沌映射的Hash函数具有更强的保密性能，且实现简单. 关键词： 时空混沌 Hash函数 单向耦合映像格子     

分离作用RFQ加速器物理特性的研究

RFQ加速器中加速效率随加速能量的增高而下降,为克服由此导致的RFQ能量局限而提出的分离作用RFQ加速结构,在仍保持采用射频四极场聚焦的同时,将加速与聚焦作用相分离. 综述了对它的加速效率、反场问题、腔体及束流特性研究 的结果,初步证实了其可行性及在较高能量区加速效率得到提高,并对正在研制的一台采用了这种分离作用RFQ的1.5MeV组合加速器做了介绍.     

Full-wave modeling of piezoelectric transducers for SAW acousto-optical interactions

In this paper we present an accurate and efficient numerical method for a rigorous full-wave analysis of interdigital transducers (IDT) for the excitation of surface acoustic waves on the piezoelectric substrate of acousto-optical devices. The problem is formulated in terms of an integral equation that is solved by the method of moments. The transducer input admittance and the power coupling factors to both surface and bulk waves are computed. Numerical results for some configurations of X-Y LiNbO₃ IDT for acousto-optic applications are in very good agreement with measured data. It is pointed out that bulk wave excitation may be a serious limitation in the design of efficient, wide band transducers for acousto-optical devices.     

基于混合空穴注入层的湿法制备高效蓝光热激活延迟有机发光二极管

在溶液法制备有机电致发光器件(OLEDs)的研究中, PEDOT∶PSS由于具有较好的成膜性与高透光性而常被用作器件的空穴注入层。但相关研究表明, PEDOT∶PSS本身稳定性较差以及功函数较低,这使得溶液法制备OLEDs的性能差且不稳定。蓝色作为全彩色的三基色之一,制备高效的蓝光器件对于实现高质量显示器件和固态照明装置必不可少。而目前溶液法制备蓝光OLEDs的器件效率普遍较差,针对此问题,本文利用传统的蓝光热激活延迟荧光发光(TADF)材料DMAC-DPS作为发光层,用溶液法制备了蓝光TADF OLEDs,通过在PEDOT∶PSS中掺杂PSS-Na制备混合空穴注入层(mix-HIL)来提高空穴注入层的功函数,研究其对于蓝光TADF OLEDs器件性能的影响。首先在PEDOT∶PSS水溶液中掺入不同体积的PSS-Na溶液,在相同条件下旋涂制膜,进行器件制备。通过观测各个实验组器件的电致发光(EL)光谱,发现掺入PSS-Na后器件EL谱存在光谱蓝移的现象,这是由于掺入PSS-Na水溶液后, mix-HIL层的厚度有所降低,使得在微腔效应作用下, EL光谱发生蓝移。通过对比各组器件的电流密度-电压-亮度(J-V-L)曲线及其计算所得器件的电流效率,结果显示随着PSS-Na的掺入,器件的亮度和电流都有所增大,器件的电流效率也得到了提升,当掺杂比例为0.5∶0.5(PEDOT∶PSS/PSS-Na)时提升幅度最大(亮度提升86.7%,电流效率提升34.3%)。通过在瞬态电致发光测试过程中施加或撤去驱动电压观测了器件EL强度的变化,分析了在混合空穴注入层/发光层(mix-HIL/EML)界面处的电荷积累情况。实验证明,通过在PEDOT∶PSS中掺杂PSS-Na制备mix-HIL获得了蓝光TADF OLEDs器件性能的提升,这是一个获得高效率溶液法制备OLEDs的可行方法。     

基于自适应径向基神经网络的类星体光谱自动识别方法

通过对光谱的研究来识别和认证类星体是天文学研究中的重要方法。文章提出了一种对类星体光谱进行自动识别的自适应径向基神经网络(RBFN)方法。该方法包括以下几个步骤: (1)先将训练样本归一化,再利用PCA变换进行降维,获得样本特征向量; (2)设计出K均值聚类算法与梯度下降法相结合的径向基神经网络结构的基本模型,再用SSE(sum of squares error)误差函数进行判断,对RBFN隐含层的神经元进行自动调节,直至满足给定误差阈值; (3)用训练得到的参数对用于测试的样本中的类星体光谱进行识别。该方法不但克服了经典RBFN算法选择隐层神经元数目的困难,而且还提高了对类星体识别的稳定性和正确率。研究结果对于大型光谱巡天所产生的海量数据的自动处理具有重要意义。     

Investigation of Cr-atom clustering in Fe‒Cr model alloys under irradiation

Irradiation-induced microstructure in Fe?Cr model alloys, 0.5 MeV-He ion-irradiated at room temperature, was investigated by atom probe tomography (APT). The APT results showed the formation of Cr-atom clustering depending on the ion-penetration depth. Although the Cr-atom clustering was observed in the irradiation damaged zone, this effect was not dominant in the less-damaged zone. In addition, we performed computer simulations using the Metropolis–Monte Carlo (MMC) method for investigating the tendency to form Cr-atom clustering in binary Fe?Cr alloys. The simulation results revealed the formation of Cr-atom clustering. The degree of Cr-atom clustering for the APT analysis and the MMC simulation was verified by plotting the Cr?Cr radiation distribution function. It was found that the number of Cr atoms, located in the first and second nearest-neighboring sites, increased significantly. Both results support the formation of Cr-clustering, which is believed to be a source of radiation hardening. The application of two techniques, APT and the MMC simulation, provided complementary information on the radiation-induced microstructure.     

The work function of hydrothermally synthesized UO2 and the implications for semiconductor device fabrication

The photoelectric work function of nearly stoichiometric (111) and (100) hydrothermally grown UO₂ was measured to be 6.28 ± 0.36 eV and 5.80 ± 0.36 eV, respectively. Candidate metals for electrical contacts are identified for both rectifying and non‐rectifying contacts based on work function, lattice compatibility, and electrical conductivity.