辐射传输中的一个伪极限问题及其数学物理原理

当太阳入射角度和观测角都趋向于水平时,由平面平行大气辐射传输方程计算得到的大气顶的反射辐射值不唯一,其值依赖于太阳和观测角的趋近于水平方向的路径曲线,即从数学角度称为出现极限的不唯一或极限不连续.事实上这违背了辐射场物理原理,这种不连续是由于常规算法中忽略了大气辐射传输中一个隐含的物理原理而导出的.在极限条件下必须引入满足Snell光学定律的界面边界条件,否则会导致错误的结论. 关键词： 辐射传输 局地热力学平衡 大气光学 Snell定律     

970 nm抽运下Tm3+/Yb3+共掺氧氟玻璃的频率上转换发光

稀土离子掺杂的氧氟玻璃是一种新型上转换发光材料。制备了Tm^3／Yb^3＋单掺、共掺的摩尔分数为n（SiO2）-0．30,n（PbF2）-0．50,n=（Al2O3）=0．15,n（AlF3）=（0．049-x）,n（TmF3）=y,n（YbF3）=x（x=0,0．001,0．010,0．015,0．020,y=0,0．001）系统氧氟玻璃,研究了其上转换发光特性、分析了其上转换发光机理。研究发现,在970nm抽运光源激发下,Tm^3＋单掺时没有可见光上转换发射;而加入Yb^3＋后产生了强的蓝光（452nm,476nm）、红光（647nm）及近红外光（791nm）发射,分别对应如下辐射跃迁：^1D2→^3F4、^1G4→^3H6、^1G4→^3F4和^3H4→^3H6;且随着Yb^3＋离子浓度的增加上转换发光增强。在970nm光源抽运下用Yb^3＋敏化Tm^3＋可以显著提高其上转换发光强度,且随着Yb^3＋离子浓度的增加,增强了对抽运光源的吸收并提高了Yb^3＋到T^3＋”的能量转移几率,从而增强了上转换发光强度。     

一种改进的光学层析图像重建方法

Alexander D．Klose将联合差分方法用于光学层析图像重建的梯度计算中,但给出的对光学参量的求导算法有局限,他的算法只能实现对边界点光学参量的导数计算,而无法实现对内部点光学参量导数的计算,会导致图像重建失败。在联合差分算法的基础上,研究了针对内部点光学参量的求导方法,给出了一种基于树形结构的对内部点光学参量求导的策略。具体实现时,为了降低计算复杂度,采用近似梯度计算方法。算法的仿真实验结果表明：该方法可以有效地实现对内部点光学参量的导数计算,提出的近似计算方法可降低梯度计算复杂度,提高运算速度,并可得到良好的图像重建质量。     

Extreme ultraviolet and soft x-ray spectral lines in Rb XXIX

An extensive theoretical set of atomic data for Rb XXIX in a wide range with L-shell electron excitations to the M-shell has been reported. We have computed energy levels for the lowest 113 fine structure levels of Rb XXIX. The fully relativistic multiconfigurational Dirac-Fock method (MCDF) within the framework of Dirac-Coulomb Hamiltonian taking quantum electrodynamics (QED) and Breit corrections into account has been adopted for calculations. Radiative data are reported for electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions from the ground level, although calculations have been performed for a much larger number of levels. To assess the accuracy of results, we performed analogous calculations using flexible atomic code (FAC). Comparisons are made with existing available results and a good agreement has been achieved. Most of the wavelengths calculated lie in the soft x-ray (SXR) region. Lifetimes for all 113 levels have also been provided for the first time. Additionally, we have provided the spectra for allowed transitions from n=2 to n= 3 within the x-ray region and also compared our SXR photon wavelengths with experimentally recognized wavelengths. We hope that our results will be beneficial in fusion plasma research and astrophysical applications.     

Comment on “Atomic structure calculations for F-like tungsten” by S. Aggarwal [Chin. Phys B 23(2014) 093203]

Recently, S. Aggarwal [Chin. Phys. B 23 (2014) 093203] reported energy levels, radiative rates, and the lifetimes for the lowest 60 levels belonging to the 2s²2p⁵, 2s2p⁶, and 2s²2p⁴3l configurations of F-like tungsten. There is no discrepancy for his calculated energies for the levels and the radiative rates for the limited number of E1 transitions, but the reported results for the lifetimes are highly inaccurate. According to our calculations, errors in his reported lifetimes are up to 6 orders of magnitude for several levels. Here we report the correct lifetimes for future comparisons and applications, and also explain the reason for the discrepancies.     

晶化对Nd3+∶NaYF4荧光动力学的影响

采用融熔急冷法制备了前驱玻璃和与之晶化后的纳米晶结构玻璃陶瓷.利用光辐射理论,计算在两种样品中Nd3各能级的辐射跃迁几率.根据Dexter理论,得到交叉弛豫几率与Nd3+相对浓度的关系.基于速率方程,描述荧光动力学过程.结果表明:晶化作用能降低Nd3+各能级辐射跃迁几率,减小交叉弛豫几率,延缓动态系统趋于平衡的速率.同时,在较低Nd3+相对浓度掺杂时,晶化作用提高4F3/2能级的相对粒子数,减少4I9/2能级的相对粒子数,结果显示晶化作用能有效提高1.06 μm的输出.     

辐射不透明度计算中含温有界原子结构理论的不确定度量化

以交换势的泛函表达式为核心,分析产生原子结构理论不确定度的主要原因,阐述辐射不透明度计算中含温有界原子结构理论不确定度量化的具体步骤,给出能级、矩阵元的不确定度量化计算公式,以及判定理论模型优劣的判据.以汞、金、铁元素为例,通过数值计算,根据对比分析,验证该不确定度量化方法的可行性.     

高离化态金离子的辐射复合及其退激发过程的理论研究

利用基于多组态Dirac-Fock方法的程序包GRASP92和RATIP以及最新发展的RERR06程序,详细计算了高离化态金离子(类镍Au51+、类铜Au50+和类锌Au49+)俘获一个自由电子到nl(n=4—8,l=0—3)壳层的辐射复合谱以及相应的辐射退激发谱.理论计算的辐射复合谱很好地重现了实验谱.研究结果表明:对类镍Au51+、类铜Au50+和类锌Au49+而言,将一个自由电子俘获到n=4壳层的概率最大;在辐射复合过程之后,处在n=4壳层的俘获电子的辐射退激发谱线最强,并且体现了整个辐射退激发谱的主要特征.     

随机分布烟尘团簇粒子辐射特性研究

基于分形理论,采用蒙特卡罗方法对随机分布的烟尘团簇粒子结构进行了仿真模拟,利用离散偶极子近似(discrete dipole approximation, DDA)方法研究了随机分布的烟尘团簇粒子的辐射特性,分析讨论了分形维数、原始微粒粒径和数量以及复折射率对随机分布烟尘团簇粒子辐射特性的影响.研究表明,在给定分形维数的情况下,烟尘团簇粒子的辐射特性取决于原始微粒粒径、数量及复折射率;原始微粒较小的团簇粒子,当分形维数较小时,吸收截面变化不明显,但当分形维数大于2时,吸收截面骤然增大,然而,对于具有比较大的原始微粒粒径、数量及复折射率的烟尘团簇粒子,吸收截面随着分形维数的增大而单调递减;随着分形维数的增大,团簇粒子的散射截面、消光截面及单次散射反照率均单调递增;从整体上来讲,团簇粒子的辐射特性与等效球形粒子的辐射特性存在着比较大的差别,并且这种差别随着分形维数的增大而减小.该工作对研究气溶胶粒子的辐射及气候效应具有重要的科学价值. 关键词： 烟尘团簇粒子 辐射特性 离散偶极子近似方法     

Microwave-Accelerated Metal-Enhanced Fluorescence (MAMEF): Application to Ultra Fast and Sensitive Clinical Assays

In this rapid communication we describe an exciting platform technology that promises to fundamentally address two underlying constraints of modern assays and immunoassays, namely sensitivity and rapidity. By combining the use of Metal-enhanced Fluorescence (MEF) with low power microwave heating (Mw), we can significantly increase the sensitivity of surface assays as well as >95% kinetically complete the assay within a few seconds. This technology is subsequently likely to find significant importance in certain clinical assays, such as in the clinical assessment of myoglobin, where both the assay rapidity and sensitivity are paramount for the assessment and treatment of acute myocardial infarction.