深空核爆电磁脉冲壳模型下的电子运动规律

 采用壳模型分析了深空核爆的电子运动规律,对深空核爆电磁脉冲的形成机理进行了初步研究。考虑MeV量级出射电子的相对论效应,在相对论框架下进行了电子运动过程的推导。计算了空间电荷层限制的形成时间,并提出一旦形成空间电荷限制,后续状态满足准静态近似条件。在此基础上,推导了空间电荷振荡的频率,并与半数值计算的结果进行比对,二者符合得较好。计算表明,远场达到峰值的时间与爆炸当量、电子初始动能和弹体半径等参数密切相关,电场峰值总是出现在核反应极大值之前,并且在空间电荷层限制的形成时间附近。     

Intense ultraviolet and blue upconversion emissions in Yb-Tm codoped stoichiometric Y7O6F9 powder

Stoichiometric Y₇O₆F₉ powder codoped with Yb³⁺-Tm³⁺ was synthesized via co-precipitation and subsequent calcining route. The results of X-ray diffraction and transmission electron microscopy reveal that when the calcining temperature is beyond 800 °C, orthorhombic YF₃ nanoparticles can be completely oxidized into orthorhombic Y₇O₆F₉ powder. Under the excitation of a 980 nm laser, Y₇O₆F₉ powder exhibits multicolor UC emission in regions spanning the UV to the NIR. In addition, the upconversion emission intensities of YF₃, Y₇O₆F₉ and Y₂O₃ powders were compared under the same dopant condition (Yb/Tm=5/0.5 mol%). The low phonon energy revealed by Raman spectra helped to understand the high efficient upconversion emission of Y₇O₆F₉ and the main phonon vibration of Y₇O₆F₉ lies at 472 cm⁻¹, which is far lower that of Y₂O₃ (at 708 cm⁻¹). Our results indicate that orthorhombic rare earth ions doped Y₇O₆F₉ is an efficient matrix for UV and blue UC emission, and has potential applications in color displays, anti-counterfeiting and multicolor fluorescent labels.     

Molecular dynamics simulation of thermal conductivity of Cu–Ar nanofluid using EAM potential for Cu–Cu interactions

Mechanism of heat conduction in copper-argon nanofluids is studied by molecular dynamics simulation and the thermal conductivity was obtained using the Green–Kubo method. While the interatomic potential between argon atoms is described using the well-known Lennard–Jones (L–J) potential, a more accurate embedded atom method (EAM) potential is used in describing the interatomic interaction between copper atoms. It is found that the heat current autocorrelation function obtained using L–J potential to describe the copper-copper interatomic interaction fluctuates periodically due to periodic oscillation of the instantaneous microscopic heat fluxes. Thermal conductivities of nanofluids using EAM potentials were calculated with different volume fractions but the same nanoparticle size. The results show that thermal conductivity of nanofluids are almost a linear function of the volume fraction and slightly higher than the results predicted by the conventional effective media theory for a well-dispersed solution. A solid-like base fluid liquid layer with a thickness of 0.6 nm was found in the simulation and this layer is believed to account for the small discrepancy between the results of MD simulation and the conventional effective media theory.     

银岛膜表面胸腺嘧啶吸附行为的表面增强拉曼光谱和表面增强红外光谱研究

利用激光刻蚀法制备了具有化学纯净表面的银岛膜,该岛膜有很好的表面增强特性。利用表面增强拉曼光谱和表面增强红外光谱对胸腺嘧啶分子在银岛膜表面的吸附状态进行了对比研究。表面增强拉曼光谱中CN和C—O伸缩振动模式的出现表明胸腺嘧啶分子由原来的酮式结构变成了烯醇式结构;C(4)O伸缩振动谱带明显增强和N(3)的去质子化异构体特征峰的存在证明胸腺嘧啶分子是通过O(8)和N(3)的共同作用倾斜地吸附在银岛膜表面。对10-5 mol.L-1胸腺嘧啶在银岛膜表面上的红外光谱利用欧米采样器进行了反射法测量,发现其红外吸收增强了200倍。红外信号分析的结果支持了胸腺嘧啶分子通过O(8)与银表面发生相互作用的论断,同时也可得出胸腺嘧啶倾斜地吸附在银岛膜表面的结论。     

一类扰动洛伦兹系统的解法

研究了一个大气物理中洛伦兹系统的求解问题.首先利用广义变分原理构造一组变分迭代,其次决定系统的初始近似,最后通过变分迭代方法得到了对应模型的各次近似解.广义变分迭代方法是一个解析方法,得到的解还能够继续进行解析运算. 关键词： 洛伦兹方程 变分原理 近似解     

一类非线性尘埃等离子体孤波解

研究了一类非线性尘埃等离子体孤波解. 首先构造一个变分迭代, 其次决定系统的初始近似, 最后通过变分迭代方法得到了对应模型的各次近似解. 关键词： 等离子体 变分迭代 近似解     

扰动厄尔尼诺/拉尼娜-南方涛动模型的解

厄尔尼诺/拉尼娜-南方涛动(ENSO)是一个包括在赤道太平洋中海-气交互作用的年际现象. 本文创建一个求解ENSO模型非线性方程的近似方法. 并在这基础上借助同伦映射方法研究了一类ENSO模型振子模型的近似解与精确解. 同时讨论了近似解的精度. 从得到的结果看出,同伦映射方法能够用于分析ENSO模型在赤道东太平洋中的SST异常和气-海振荡的温跃层深度异常.     

An Efficient One‐pot Synthesis of Pyrazolone Derivatives Promoted by Acidic Ionic Liquid

A new class of pyrazolone derivatives has been isolated in good to excellent yields from the 2:1 condensation reaction between 3‐methyl‐1‐phenyl‐5‐pyrazolone and arylaldehydes in the presence of ionic liquid [HMIM]HSO₄. The compounds were characterised by their IR, NMR spectra, MS and elemental analyses. The important features of the methodology are a wide application range of substrates, higher yields and shorter reaction time.     

新型异噁唑啉类化合物的合成及其抗肿瘤活性

以3,4-二氟苯甲醛为起始物,经4步反应合成了关键中间体N-[{3-[3-氟-4-(1-哌嗪基)苯基]4,5-二氢-5-异噁唑}甲基]乙酰胺(4);4与取代苯磺酰氯经亲核取代反应合成了6个新型的异噁唑啉类化合物(6a～6f),其结构经1H NMR和MS表征.采用MTT法对6a～6f进行初步生物活性测试结果表明,部分化合...     

广西建筑材料市场花岗岩放射性水平调查与评价

对广西5个城市建筑装修材料市场的各种花岗岩石材进行抽样,共抽取了128个花岗岩石材样品,用低本底多道γ能谱仪测定其放射性核素226 Ra,232 Th,40 K的放射性比活度、内照射指数和外照射指数,并据此进行分类,其中A类装饰装修材料样品为115个,占89.8%;B类装饰装修材料样品为11个,占8.6%;C类装饰装修...