双分散颗粒体系在临界堵塞态的结构特征

堵塞行为是颗粒体系中一种常见的现象,其力学性质与堆积结构的关联非常复杂.本文采用离散元法研究了由两种不同半径颗粒组成的二维双分散无摩擦球形颗粒体系在临界堵塞态所呈现的结构特征,讨论了大小颗粒粒径比与大颗粒百分比对临界堵塞态的影响.数值模拟结果表明,当粒径比小于1.4时,临界平均接触数与大颗粒百分比关系不大,当粒径比大于1.4时随着大颗粒百分比的增大临界平均接触数先减小再增大.而临界体积分数在粒径比小于1.8时随着大颗粒百分比的增加先减小后增大,大于1.8时又基本不随大颗粒百分比而变化.大颗粒百分比在接近0或1时,系统近似为单分散体系,临界平均接触数与体积分数基本不随半径比的增大而变化;在接近0.5时,临界平均接触数随着半径比的增大逐渐减小,而临界体积分数则是先减小后增大.文中对大-小颗粒这一接触类型的百分比也进行了探讨,其值随着大颗粒百分比的增大呈二次函数的变化趋势,粒径比对这一变化趋势只有较小的影响.     

X射线光栅微分相衬成像视场分析

X射线光栅微分相衬成像对由轻元素构成的物质的内部探测具有传统吸收成像无法比拟的优势, 尤其在癌症的早期诊断和轻元素材料及器件的无损检测等领域应用潜力巨大. 大视场成像是影响该技术从实验室走向实际应用的重要因素. 针对大视场成像的客观需求, 基于菲涅耳衍射原理和光栅结构特征, 建立了量化物理模型用于分析影响成像视场的因素, 提出了实现大成像视场的有效途径, 为未来大视场光栅微分相衬成像方法的设计和应用提供理论依据.     

Sn掺杂ZnO薄膜的室温气敏性能及其气敏机理

采用化学气相沉积方法在预制好电极的玻璃基底上制备出Sn掺杂ZnO薄膜和纯ZnO薄膜. 两种样品典型的形貌为四足状ZnO晶须, 其直径约为150-400 nm, 呈疏松状结构. 气敏测试结果显示Sn掺杂ZnO薄膜具有优良的室温气敏性, 并对乙醇具有良好的气敏选择性, 而纯ZnO薄膜在室温条件下对乙醇和丙酮均没有气敏响应. X射线衍射结果表明两种样品均为六方纤锌矿结构. Sn掺杂ZnO样品中没有出现Sn及其氧化物的衍射峰, 其衍射结果与纯ZnO样品对比, 衍射峰向小角度偏移. 光致发光结果表明, Sn掺杂ZnO薄膜与纯ZnO薄膜均出现紫外发光峰和缺陷发光峰, 但是Sn的掺杂使得ZnO的缺陷发光峰明显增强. 将Sn掺杂ZnO样品在空气中退火后, 其室温气敏性消失, 说明Sn掺杂ZnO样品的室温气敏性可能与其缺陷含量高有关. 采用自由电子散射模型解释了Sn掺杂ZnO薄膜的室温气敏机理.     

高功率激光终端KDP晶体非共线高效三倍频及远场色分离方案数值模拟分析

为满足高功率激光装置对终端光学系统的改进要求,控制3ω光路透射元件厚度以降低激光损伤风险,避免3ω非对称聚焦与色分离元件对靶场调靶产生不利影响,本文利用非共线相位匹配原理讨论了KDP晶体Ⅰ类和Ⅱ类两种和频产生351 nm(3ω)激光及其远场色分离过程.模拟结果表明,室温20?C环境中除目前常用的共线和频外,1053 nm(ω)与526.5 nm(2ω)激光可选择Ⅰ类或Ⅱ类两种非共线和频方式实现高效3ω激光输出并在激光远场实现色分离,且具有足够的高效转换失谐角容宽.计算表明,与Ⅰ类和频类似,Ⅱ类和频也存在一个非临界相位匹配过程,其匹配方向约为θ(3ω)=86.53?.可通过增加晶体厚度克服其有效非线性系数较低的缺点,实现3ω高效输出,失谐角容宽可达±20 mrad.为满足靶场需要,解决非共线角容宽苛刻带来的调节不便,并进一步使光路紧凑,将楔角为12?的熔石英楔板置于倍频晶体之后,ω与2ω激光在熔石英楔板后表面可产生约3.5 mrad分离角.经非共线和频,使用薄透镜即可实现聚焦及色分离.该方案完全满足终端光学系统的改进要求,可作为可靠的备选方案之一.     

Alpha Decay of the Neutron-deficient Isotopes 215,216U

The most neutron-deficient isotopes 215;216U were produced in the complete-fusion reaction 180W(40Ar, 4-5n)215,216U. Evaporation residues recoiled from the target were separated in-flight from the primary beam by the gas-filled recoil separator SHANS and subsequently identified on the basis of correlated -decay chains. Two -decaying states were identified in 216U, one for the ground state and the other for the isomeric state with 8+(h9=2f7=2) configuration. The -decay properties for 215;216U and the systematics of 8+ isomeric state in N =124,126 isotones were investigated.     

铁基高温超导体电子结构的角分辨光电子能谱研究

铜氧化物超导体和铁基超导体是人类相继发现的两类高温超导家族,它们的高温超导机理是凝聚态物理领域中长期争论但悬而未决的重大问题.对铁基超导体广泛而深入的研究,以及与铜氧化物高温超导体的对比,对于发展新的量子固体理论、解决高温超导机理、探索新的超导体以及超导实际应用都具有重要意义.固体材料的宏观物性由其微观电子结构所决定,揭示高温超导材料的微观电子结构是理解高温超导电性的前提和基础.由于角分辨光电子能谱技术具有独特的同时对能量、动量甚至自旋的分辨能力,已成为探测材料微观电子结构的最直接、最有力的实验手段,在高温超导体的研究中发挥了重要作用.本文综述了在不同体系铁基超导体中费米面拓扑结构、超导能隙大小和对称性、轨道三维性和选择性、电子耦合模式等的揭示和发现,为甄别和提出铁基超导新理论、解决高温超导机理问题提供重要依据.     

浅海时变声速环境下的自适应匹配场定位算法实现*

针对浅海环境下声速剖面失配引起的匹配场处理器失配问题,提出了一种自适应匹配场定位算法在声速剖面时变环境下的实现方式。将先验声速剖面集简化为经验正交函数表示,结合蒙特卡洛方法与环境扰动约束算法对当下时刻的目标声源进行匹配场定位。本文以某次试验获取的连续20小时的声速剖面数据为研究对象,通过仿真试验对该算法进行验证,结果表明：在先验声速剖面集的半小时之后,利用自适应算法的距离和深度定位成功率较常规匹配场算法有较大提升,其中,深度正确定位概率相对较低。     

Correlation lengths in quasi-one-dimensional systems via transfer matrices

ABSTRACT

Using transfer matrices up to next-nearest-neighbour interactions, we examine the structural correlations of quasi-one-dimensional systems of hard disks confined by two parallel lines and hard spheres confined in cylinders. Simulations have shown that the non-monotonic and non-smooth growth of the correlation length in these systems accompanies structural crossovers [Fu et al., Soft Matter 13, 3296 (2017)]. Here, we identify the theoretical basis for these behaviours. In particular, we associate kinks in the growth of correlation lengths with eigenvalue crossing and splitting. Understanding the origin of such structural crossovers answers questions raised by earlier studies, and thus bridges the gap between theory and simulations for these reference models.     

Robust Preparation of Atomic Concatenated Greenberger–Horne–Zeilinger States via Shortcuts to Adiabaticity

Here, a protocol for robust preparation of an atomic concatenated Greenberger–Horne–Zeilinger (C‐GHZ) state via shortcuts to adiabaticity (STA) is proposed. The devices for implementing the protocol consist of atoms, cavities, and the optical fibers, which are feasible with current technology. The atoms are trapped in the separated cavities allowing individual control over each atom with classical fields. STA helps to design Rabi frequencies of classical fields so that the atoms can be driven from the initial states to the target states. The numerical simulations show that the protocol holds robustness against atomic spontaneous emissions and photonic leakages. Thus, the protocol may be realized by experiments in the near future.     

Microwave photonics reconfigurable mixer based on polarization modulator

A reconfigurable and stable mixer is proposed and demonstrated in this paper. It mainly consists of a dual-driven Mach–Zehnder modulator and a polarization modulator with several polarization controllers (PC) and polarizers (Pol). According to the theoretical analysis, different functions (such as single ended mixer, balanced mixer, I/Q mixer and image rejection mixer) can be realized by adjusting the PCs and Pols. The simulation results verify the possibility of multi-functions that realized by the reconfigurable mixer. In addition, another research on how the non-ideal parameters affect the image rejection ratio (ISR) and conversion efficiency of the mixer is also carried. The results show that both of them perform better as the extinction ratio gets higher. However, they are incurring a sharp decrease if the DC bias points deviate from the settled values. In the meantime, the results also indicate that the higher modulation indices lead to a better ISR. A 57.12 dB ISR can be achieved with conversion efficiency of ? 9.53 dB.