银纳米粒子/碳纳米管阵列SERS基底增强因子分析和实验

为了直观、准确地定量分析表面拉曼增强散射基底结构的拉曼增强,利用磁控溅射和高温退火的方法制备了银纳米粒子修饰垂直排列的碳纳米管阵列三维复合结构样品;实验采用罗丹明6G(R6G)溶剂作为探针分子,结合共聚焦显微拉曼系统,开展了表面增强拉曼增强因子(EF)分析计算的相关实验。SEM结果表明：在有序碳纳米管阵列的表面和外壁均匀地负载了大量银纳米粒子。对退火温度为450 ℃,退火时间为30 min的样品进行了EF计算,得到其增强因子约为2.2×103,并分析了EF值低的原因主要是：在碳纳米管上溅射的银膜膜厚不均匀,导致退火后银颗粒分布不均,使得样品粗糙度值偏大,EF值较低;实验中所用的激励光源并非银纳米颗粒的优化光源。     

The determination of concentrations of radioisotopes in some granite samples in Turkey and their radiation hazards

The primordial radionuclides activity concentrations (²²⁶Ra, ⁴⁰K and ²³²Th) are measured in some granite samples in this study. The collected granite materials are analyzed with NaI(Tl) gamma-ray spectrometry. The specific activity of ²²⁶Ra, ²³²Th and ⁴⁰K values are in range 2.60?±?0.10 to 178.9?±?0.6?Bq?kg^?1, 1.46?±?0.10 to 162.50?±?0.75?Bq?kg^?1 and 19.8?±?0.3 to 579.7?±?2.8?Bq?kg^?1 respectively. The radium’s equivalent activity, annual effective dose, absorbed dose rate, hazard index, radioactivity level index, activity utilization’s index and exposure rate are calculated for determination of radiological risk. The concentration of ²²⁶Ra (in the 71.4% of samples), ²³²Th (in the 71.4% of samples) and ⁴⁰K (in the 14.3% of samples) in the granite samples are higher than average radioactivity concentrations of this radio-isotopes defined by ICRP (35.0, 30.0 and 400.0?Bq?kg^?1, respectively).     

Variation of gamma radiation shielding properties with incident photon energy and penetration depth for WC/Al composites

In this work, we examined the usefulness of the WC_x/Al_100?x composites (x?=?10, 20, 50, 80 wt. %) for gamma-ray shielding materials. The mass attenuation coefficient (μ/ρ), effective atomic number (Z_eff), electron density (N_e) and energy absorption buildup factor (EABF) and exposure buildup factor (EBF) for WC_x/Al_100?x composites have been calculated by theoretical approach using XCOM program within the energy range 1?keV–100?GeV, 10 keV–1?GeV, 10 keV–1?GeV and 0.015?MeV–15?MeV, respectively. The results showed that both the values of mass attenuation coefficient and Z_eff of the WC_x/Al_100?x composites tend to increase with the increase of the WC concentration. For the energy region below 3?MeV, the WC₈₀/Al₂₀ composite was found to possess superior gamma-ray shielding effectiveness due to its higher values of both mass attenuation coefficient and effective atomic number, and lower values of both EABF and EBF values. However, for the energy region above 3?MeV, the EBF and EABF values of the WC/Al composites are directly proportional to their Z_eff values, leading to the lowest EBF and EABF values of the WC₁₀/Al₉₀ composites.     

Optimize the thermoelectric performance of CdO ceramics by doping Zn

The thermoelectric performance of CdO ceramics was enhanced by simultaneously optimizing the electrical and thermal transport properties via a small amount of Zn doping(≤3%). The introduction of Zn can obviously increase the electrical conductivity of CdO due to the simultaneous increase of carrier concentration and mobility, and eventually results in an improvement in power factor. Zn doping is also effective in suppressing the thermal conductivity of CdO because of stronger phonon scatterings from point defects, Zn-riched second phase, and grain boundaries. A best ZT of about 0.45 has been achieved in the Cd_(1-x)Zn_xO systems at about 1000 K, which is comparable to the highest values reported for other n-type oxide TE materials.     

Meson electro-magnetic form factors in an extended Nambu–Jona-Lasinio model including heavy quark flavors

Based on an extended NJL model including heavy quark flavors, we calculate the form factors of pseudoscalar and vector mesons. After taking into account the vector-meson-dominance effect, which introduces a form factor correction to the quark vector coupling vertices, the form factors and electric radii of π+and K+pseudo-scalar mesons in the light flavor sector fit the experimental data well. The magnetic moments of the light vector mesonsρ+and K*+are comparable with other theoretical calculations. The form factors in the light-heavy flavor sector are presented to compare with future experiments or other theoretical calculations.     

SiC电子霍耳迁移率的计算

基于对自身能带结构的分析以及各向同性弛豫时间近似法,采用三椭球等能面、抛物线性简化,建立了适于模拟n型6H-SiC电子霍耳迁移率和霍耳散射因子的解析模型,精确描述了不同散射机制对于6H-SiC低场电子输运特性的影响.计算结果与实测值有很好的一致性.     

超导质子直线加速器的分段研究

对超导直线加速器的分段进行了详细的研究.包括超导加速器的分段原则的讨论,对称性分段和非对称性分段的讨论.超导加速腔的加速单元数及设计值β_G的确定,加速器的能量增益的确定.     

非傍轴平顶高斯光束M2因子两种定义的比较研究

基于功率密度的二阶矩方法，推导出了非傍轴平顶高斯(FG)光束束宽和远场发散角的解析表达式.研究表明，当w0/λ→0时，远场发散角趋于渐近值θmax=63.435°，与阶数无关.使用非傍轴高斯光束代替傍轴高斯光束作为理想光束，研究了非傍轴FG光束的M2因子，并与传统定义的M2因子作了比较.在非傍轴范畴，非傍轴FG光束的M2因子不仅与阶数N有关，而且与w0/λ有关.按照定义，当w0/λ→0时，非傍轴FG光束的M2因子不等于0，对阶数N=1, 2, 3时，M2因子分别趋于0.913,0.882和0.886.当N→∞时，M2因子取最小值M2min=0.816.     

Integrating factors and conservation theorems of constrained Birkhoffian systems

In this paper the conservation theorems of the constrained Birkhoffian systems are studied by using the method of integrating factors. The differential equations of motion of the system are written. The definition of integrating factors is given for the system. The necessary conditions for the existence of the conserved quantity for the system are studied. The conservation theorem and its inverse for the system are established. Finally, an example is given to illustrate the application of the results.     

一种改进的计算探测器校正因子的相关抽样方法

对于小尺寸探测器处于大块介质的情形, 在探测器的校正因子的Monte Carlo模拟中, 存在两个难题: 一是由于探测器尺寸很小粒子难以到达探测器并发生碰撞; 二是两个随机变量比值难以达到要求精度. 本文使用经过改进的粒子碰撞自动重要抽样方法, 再结合相关抽样方法, 解决了这两个难题, 并在MCNP-4C程序平台上加以实现. 除了粒子碰撞自动重要抽样以外, 还选用了其他3种方法: 直接模拟、区域分裂、强迫碰撞+Dxtran球分别与相关抽样方法结合, 对一个简化的探测器校正因子计算模型进行了计算. 实际计算结果表明, 相关抽样方法无论与哪种方法结合, 都起到了提高相关量计算效率的作用; 而它与粒子碰撞自动重要抽样结合, 比其他方法具有明显的优越性.