强流脉冲离子束辐照靶材烧蚀效应二维数值研究

对强流脉冲离子束(IPIB)辐照Ti靶的烧蚀效应进行了二维数值研究.得到了表面烧蚀物质随脉冲时间的变化关系.得出TEMP Ⅱ 型加速器产生的脉冲束流辐照靶材时引起的汽、液化均是从表面开始、并且汽化过程中表面物质被层层烧蚀的结论.同时，得到中心区的平均烧蚀速度为10m/s 数量级，它远小于产生的烧蚀等离子体的喷发速度.得到脉冲期间靶材内部不同位置烧蚀斑痕形状的时间演化过程，以及束流中含有的离子种类分额不同时IPIB辐照过程产生的不同效果. 关键词： 强流脉冲离子束 靶 烧蚀过程 二维数值模拟     

Synthesis and luminescence of a novel conjugated europium complex with 6-parachloroaniline carbonyl 2-pyridine carboxylic acid

A novel organic ligand, 6-parachloroaniline carbonyl 2-pyridine carboxylic acid, and the corresponding europium complex, tris(6-parachloroaniline carbonyl-2-pyridine carboxylate) europium (III) have been designed and synthesized. The results showed that the synthesized product was a conjugated complex, emitting remarkable strong red luminescence, and was a good red luminescence material with good thermal stability. The ⁵D₀ lifetime of Eu³⁺ in the complex was examined using time-resolved spectroscopic analysis. The lifetime values for 1.0×10⁻⁵ mol/l ethanol solution of the complex and for the complex solid were 0.49±0.01 and 1.94±0.01 ms, respectively.     

矩形均匀电子束在激光介质中的能量沉积的模拟计算

本文主要论述了0.5MeV,单能垂直入射的电子束在三种不同密度的氟化氪准分子激光介质中的能量沉积。计算是采用Monte Carlo方法的MCSED程序,光轴方向采用周期性边界条件,因此能够给出平行于和垂直于电子束入射方向的沉积能量的空间分布。本文给出了在三种不同密度下的出射电子的角分布。用该程序对垂直入射的,初始能量为1MeV的电子在半无限大Al靶中的沉积能量的计算结果与ONETRAN程序的结果及实验结果的比较表明MCSED程序的计算结果是可靠的。     

Rational Design of Two-Dimensional Magnetic Chromium Borides Based on First-Principles Calculation

Two-dimensional(2D) magnetic materials have been experimentally recognized recently,however,the Curie temperatures(TC) of known 2D systems are quite low.Generally,magnetic systems can be seen as constituent magnetic elements providing spins and the non-magnetic elements providing frameworks to host the magnetic elements.Short bond lengths between the magnetic and non-magnetic elements would be beneficial for strong magnetic interactions and thus high TC.Based on this,we propose to combine the magnetic element Cr and the non-magnetic element boron to design novel 2D magnetic systems.Using our self-developed software package IM2 ODE,we design a series of chromium-boride based 2D magnetic materials.Nine stable magnetic systems are identified.Among them,we find that CrB4-Ⅰ,CrB4-Ⅱ and CrBs-Ⅰ with common structural units [CrB8] are ferromagnetic metals with estimated TC of 270 K,120 K and 110 K,respectively.On the other hand,five CrB3 phases with structural units [Cr2B12] are antiferromagnetic metals.Additionally,we also find one antiferromagnetic semiconductor CrB2-Ⅰ.Our work may open new directions for identifying 2D magnetic systems with high TC.     

太赫兹波段介质微腔光学特性研究

采用匀胶法制备了厚度在微米量级的 Si/[TiO₂/Al₂O₃]²TiO₂和Si/[TiO₂/MgO]²/TiO₂ 多层介质膜反射镜. 采用太赫兹(THz)时域透射光谱系统获得了多层膜的时域透射谱. 用传输矩阵法模拟了Si/[TiO₂/Al₂O₃]²TiO₂ 和Si/[TiO₂/MgO]²/TiO₂两种分布式布拉格反射镜 (DBR)的反射相移和相位穿透深度等光学特性. 设计了两种结构为 DBR/LT-GaAs/DBR的对称THz光学微腔结构并模拟了腔结构的辐射光谱. 结果表明:通过引入谐振腔, 两种DBR组成的微腔器件在谐振波长处的强度分别提高了19和14倍. 其中Si/[TiO₂/Al₂O₃]²TiO₂/LT-GaAs (12 μm)/ [TiO₂/Al₂O₃]²TiO₂腔的辐射光谱存在两个峰, 分别位于208和248 μm, 并分析了出现两个谐振峰的原因. 探讨了通过引入介质谐振腔实现对THz源的辐射特性进行调控的可行性. 关键词： 分布式布拉格反射镜 光子晶体 穿透深度 太赫兹微腔     

Ga1-xInxNyAs1-y/GaAs量子阱中电子-LO声子的散射率

在有效质量近似下利用打靶法求出Ga_1-xIn_xN_yAs_1-y/GaAs量子阱中的本征能级E_n, 并通过费米黄金规则计算电子-LO声子由第一激发态到基态的散射率和平均散射率随温度、阱宽以及氮(N)和铟(In)组分变化的规律. 计算结果表明: 在In 组分恒定的情况下, 随着N组分的增加, 散射率和平均散射率增加; 在N组分恒定的情况下, 随着In组分的增加, 散射率和平均散射率减小; 随着温度的增加, 在温度较低时散射率和平均散射率随温度的增加变化不大, 在温度较高时随温度的增加而增加; 随着阱宽的增加, 散射率和平均散射率都是先增加到一个最大值, 然后再减小, 最大值出现在阱宽200 Å附近. 计算结果对Ga_1-xIn_xN_yAs_1-y/GaAs量子阱在光电子器件应用方面有一定的指导意义. 关键词： 费米黄金规则 1-xIn_xN_yAs_1-y/GaAs量子阱')" href="#">Ga_1-xIn_xN_yAs_1-y/GaAs量子阱 LO声子 散射率     

Time-varying human mobility patterns with metapopulation epidemic dynamics

In this paper, explicitly considering the influences of an epidemic outbreak on human travel, a time-varying human mobility pattern is introduced to model the time variation of global human travel. The impacts of the pattern on epidemic dynamics in heterogeneous metapopulation networks, wherein each node represents a subpopulation with any number of individuals, are investigated by using a mean-field approach. The results show that the pattern does not alter the epidemic threshold, but can slightly lower the final average density of infected individuals as a whole. More importantly, we also find that the pattern produces different impacts on nodes with different degree, and that there exists a critical degree _kc$k_c$. For nodes with degree smaller than _kc$k_c$, the pattern produces a positive impact on epidemic mitigation; conversely, for nodes with degree larger than _kc$k_c$, the pattern produces a negative impact on epidemic mitigation.     

Crystalline Morphology and Nonisothermal Crystallization Behaviors of iPP/PcBR Blends

Isotactic polypropylene/poly(cis‐butadiene) rubber (iPP/PcBR) blends were prepared by melt mixing. The influence of PcBR content on crystalline morphology and nonisothermal crystallization behaviors of iPP was investigated by polarized optical microscopy (POM), small angle light scattering (SALS), and differential scanning calorimetry (DSC). The POM showed that an increase of PcBR ranging from 10 vol% to 40 vol% led to less perfection of spherulites, vaguer boundaries between spherulites, and smaller spherulite size, which was quantitatively validated by SALS. The presence of PcBR also remarkably affected the nonisothermal crystallization behaviors of iPP. An addition of PcBR caused higher crystallization peak temperature and a faster crystallization rate, meaning a heterogeneous nucleation effect of PcBR upon crystallization of iPP. For the same sample, the crystallization peak temperature moved to lower temperature and the crystallization rate increased as the cooling rate increased. The Ozawa and combined Avrami and Ozawa equations were used to describe the nonisothermal crystallization process of iPP and blends. The combined Avrami and Ozawa equation was more appropriate for the crystallization of the blends. Crystallization activation energy of iPP and blends was calculated by the Kissinger equation; the result showed that crystallization activation energy decreased as the content of PcBR increased from 30 vol% to 40 vol%.     

Flow Injection Kinetic Spectrophotometric Determination of Cerium Based on the Decolorization Reaction Between Arsenazo III and Cerium (IV)

ABSTRACT

Trace amounts of cerium were analyzed by flow injection kinetic spectrophotometry, based on the decolorization reaction between arsenazo III and Ce(IV) in sulfuric acid medium at room temperature. The absorbance difference (ΔA) of decolorization was linear with the concentration of Ce(IV). The flow injection technique was used to precisely control the timing. Under the optimum conditions, the determination of Ce(IV) in the range 0.0–8.0 µg mL^?1 with a correlation coefficient (r) of 0.9982, the regression equation was ΔA = 0.0014 + 0.0406c (µg mL^?1). The detection limit (3σ) of 0.2 µg mL^?1 was achieved at a sampling frequency of 60 h^?1. The proposed method was applied to the analyses of Ce in soil successfully.     

Grüneisen parameter for HCP iron at extreme compression

The Thomas–Fermi approximation gives the Grüneisen parameter γ=γ_∞=1/2 for all materials at extreme compression (P→∞ or V→0). After re-analyzing the existing experimental data of volume dependence of Grüneisen parameter γ of hexagonal close-packed (HCP) iron, we find that γ=1/2+a(V/V ₀)^1/3+b(V/V ₀) ⁿ , where a, b and n are constants. Based on this new form of γ, the second Grüneisen parameter q, the Debye temperature θ_D and the shear sound velocity v _s of HCP iron are discussed in the present work. It is found that the zero pressure second Grüneisen parameter q ₀=0.654, which is consistent with the previously determined value of HCP iron for Earth's core physics from Dubrovinsky et al. The calculations for the Debye temperature and the shear sound velocity are also found to be in good agreement with the experimental data.