粉末微波滤波器的制备和特性

利用通电导线的电磁感应和铜粉的趋肤效应,试制了在超导量子计算实验系统中使用的粉末微波滤波器.滤波器的频率响应随频率升高而平缓下降,在1GHz左右衰减至-80dB.我们分析了滤波器的原理,并通过改变参数对滤波器性能的变化进行了详细的研究.     

电子性作用对MgB2超导体同位素效应的影响

通过引入电子性作用V_c,在弱耦合条件下导出了两带模型的T_c公式和同位素效应指数公式,计算了超导体MgB_2的超导转变温度和同位素效应,得到了与实验相符的结果。结果表明,带内电子性作用比带间电子性作用对同位素效应指数的影响要大。     

一类稀疏效应下食饵-捕食系统的极限环的存在唯一性

研究如下一类具稀疏效应的食饵-捕食模型dxdt=x2(e-bx)-dxy,dydt=-cy+(βx2-ry)y.应用常微分方程定性理论,对该系统的平衡点进行分析,得到了极限环存在唯一性及不存在的参数范围.     

Poole-Frenkel effect in amorphous poly(p-phenylene sulfide)

The conductivity of poly(p-phenylene sulfide) (PPS) amorphous samples sandwiched between metallic electrodes has been studied as a function of applied voltage, temperature, and electrode material. The voltage (U) dependence of the currents for electric fields within the range 10³–10⁶ V/cm exhibits exp βU^1/2 behavior with β = β_Schottky below the glass transition temperature (T_g ≊ 90°C), and β = β_{Poole-Frenkel} above T_g. Coordinated temperature measurements of dc currents with different metallic contacts and thermally stimulated currents (TSC) indicate, however, that the conductivity at T < T_g is consistent with the so-called “anomalous” Poole-Frenkel effect rather than the Schottky effect. Consequently, the p-type conductivity in amorphous PPS is proposed to be a bulk-limited process due to ionization of two different types of acceptor centers in the presence of neutral hole traps. © 1996 John Wiley & Sons, Inc.     

考虑时滞效应与均值-方差效用的非零和投资与再保险博弈

在考虑时滞效应的影响下研究了非零和随机微分投资与再保险博弈问题.以最大化终端绝对财富和相对财富的均值-方差效用为目标,构建了两个相互竞争的保险公司之间的非零和投资与再保险博弈模型,分别在经典风险模型和近似扩散风险模型下探讨了博弈的Nash均衡策略.借助随机控制理论以及相应的广义Hamilton-Jacobi-Bellm...     

The Impact of Foaming Effect on the Physical and Mechanical Properties of Foam Glasses with Molecular-Level Insights

Foaming effect strongly impacts the physical and mechanical properties of foam glass materials, but an understanding of its mechanism especially at the molecular level is still limited. In this study, the foaming effects of dextrin, a mixture of dextrin and carbon, and different carbon allotropes are investigated with respect to surface morphology as well as physical and mechanical properties, in which 1 wt.% carbon black is identified as an optimal choice for a well-balanced material property. More importantly, the different foaming effects are elucidated by all-atomistic molecular dynamics simulations with molecular-level insights into the structure–property relationships. The results show that smaller pores and more uniform pore structure benefit the mechanical properties of the foam glass samples. The foam glass samples show excellent chemical and thermal stability with 1 wt.% carbon as the foaming agent. Furthermore, the foaming effects of CaSO₄ and Na₂HPO₄ are investigated, which both create more uniform pore structures. This work may inspire more systematic approaches to control foaming effect for customized engineering needs by establishing molecular-level structure–property–process relationships, thereby, leading to efficient production of foam glass materials with desired foaming effects.     

基于第一性原理的单层WS2热输运特性研究

二维WS₂是一种层状过渡金属硫化物,因其具有特殊的层状结构、可调带隙及稳定的物理化学性质而备受关注。结合玻尔兹曼输运方程(BTE)和密度泛函理论(DFT),利用第一性原理研究了单层WS₂声子的输运特性,分析了声子的谐性效应和非谐性效应对WS₂晶格热导率的影响机理,计算了其声子的临界平均自由程,提出通过调整阻断频率的方法来调控WS₂的晶格热导率。研究结果表明：单层WS₂在300 K时的本征晶格热导率为149.12 W/(m·K),且随温度的升高而降低;从各声子支对总热导率的贡献来看,声学声子支起主要作用,特别是纵向声学(longitudinal acoustic, LA)声子支对单层WS₂热导率的贡献百分比最大(44.28%);单层WS₂声学声子支和光学声子支之间的较大带隙(声光学声子支之间无散射)导致其具有较高的晶格热导率。本文研究可为基于单层WS₂纳米电子器件的设计和改进提供借鉴和理论指导。     

Li原子掺杂C28单分子器件的热自旋输运性质

利用第一性原理对Li原子掺杂C₂₈的分子器件的热自旋输运性质进行了计算。在不同的温度场下,上下自旋分别为Li原子掺杂C₂₈的分子器件中的空穴和电子提供了输运通道,在MJ₁和MJ₃分子器件中,热自旋电流随着温度增加而增大,但在MJ₂分子器件中,热自旋电流先增大再减小。三种分子器件都出现了自旋塞贝克效应,MJ₂还出现了负微分电阻现象,利用费米-狄拉克分布和自旋输运谱对其物理机理进行了解释。根据Li掺杂C₂₈的单分子器件的热自旋输运性质,可设计新的自旋纳米器件。     

RIG型磁光薄膜的研究进展及应用

随着光通信技术与光子集成电路的发展,非互易性器件作为光通信系统中重要的组成部分得到了越来越广泛的研究与应用。基于磁光效应制成的磁光隔离器和环行器是目前应用最为广泛的非互易性器件,为了将非互易性器件整块集成在硅片上,需制备性能与块状磁光材料相当的磁光薄膜。在近红外通信波段(1 550 nm),以钇铁石榴石(Y₃Fe₅O₁₂,YIG)为代表的稀土铁石榴石(RIG)具备优良的磁光效应,是最具应用前景的磁光材料之一。研究发现,使用稀土离子对YIG薄膜进行掺杂可以有效改善其磁光性能,尤其是Bi³⁺和Ce³⁺掺杂的YIG表现出巨法拉第效应。本文首先介绍了法拉第效应原理,介绍了三种常见磁光薄膜的生长方法,回顾了近年来的主要研究成果,介绍了磁光薄膜在光隔离器和环行器中的应用,最后对磁光薄膜的未来发展趋势进行了展望。     

Acoustoelastic effect simulation by time–space finite element formulation based on quadratic interpolation of the acceleration

Acoustoelastic effect describes the change of ultrasound velocity due to the initial stress. Its simulation involves a numerical analysis of nonlinear elastodynamics and requires high accuracy in the time domain. A time–space finite element formulation, derived from the quadratic interpolation of the acceleration within a time segment, is proposed for an accurate simulation of the acoustoelastic effect in the present study. Ten different integration schemes are generated based on this formulation and nine of them are found to be conditionally stable. Among the nine stable schemes, one is found to obtain a spectral radius of one when the normalized step ratio is less than 5.477, indicating no numerical dissipation or numerical divergence. Compared with integration schemes from previous studies, this integration scheme demonstrates better performance in calculation accuracy and energy conservation. A two-stage approach, namely the static stage and the dynamic stage, has been employed in the simulation of the acoustoelastic effect. The former stage is adopted to obtain the initial stress and the latter stage, where the proposed integration scheme is implemented, is adopted to simulate the ultrasound propagation in an initial stress state. The simulation results of the dynamic stage show that the ultrasound velocity increases in a compression stress state and decreases in a tension stress state for aluminum alloy, which is in good agreement with previous experimental studies. Together with the simulation result of the static stage, it is conjectured that the acoustoelastic effect results from the stress-dependent elastic modulus.