基于辐射传输优化模型的二类水体大气校正

遥感影像的大气校正是水色参数反演的前提。以太湖为研究区,采用6S大气辐射传输模型以及近红外波段离水反射率模型相结合的方法。通过神经网络模拟大气辐射传输过程,并利用中分辨率成像光谱仪(MERIS)754、779、865、885nm 4个近红外波段进行光谱优化,求算550nm处气溶胶光学厚度等变量。通过外推,实现可见光波段的大气校正。将2007年11月11日、20日、21日,2008年11月20日MERIS Level 1p影像以及野外实测水体遥感反射率数据集用于精度验证,结果表明,该方法能够较好地反演水体遥感反射率光谱,校正后的13个波段的平均相对误差大多分布在20%~40%之间。与6S以及Beam 4.9软件自带的大气校正方法相比,具有较高的校正精度和较强的稳定性,在太湖有较好的适用性。     

An idealized radiative transfer scheme for use in a mechanistic general circulation model from the surface up to the mesopause region

A new and numerically efficient method to compute radiative flux densities and heating rates in a general atmospheric circulation model is presented. Our method accommodates the fundamental differences between the troposphere and middle atmosphere in the long-wave regime within a single parameterization that extends continuously from the surface up to the mesopause region and takes the deviations from the gray limit and from the local thermodynamic equilibrium into account. For this purpose, frequency-averaged Eddington-type transfer equations are derived for four broad absorber bands. The frequency variation inside each band is parameterized by application of the Elsasser band model extended by a slowly varying envelope function. This yields additional transfer equations for the perturbation amplitudes that are solved numerically along with the mean transfer equations. Deviations from local thermodynamic equilibrium are included in terms of isotropic scattering, calculating the single scattering albedo from the two-level model for each band. Solar radiative flux densities are computed for four energetically defined bands using the simple Beer-Bougert-Lambert relation for absorption within the atmosphere. The new scheme is implemented in a mechanistic general circulation model from the surface up to the mesopause region. A test simulation with prescribed concentrations of the radiatively active constituents shows quite reasonable results. In particular, since we take the full surface energy budget into account by means of a swamp ocean, and since the internal dynamics and turbulent diffusion of the model are formulated in accordance with the conservation laws, an equilibrated climatological radiation budget is obtained both at the top of the atmosphere and at the surface.     

Optimized implementations of rational approximations for the Voigt and complex error function

Rational functions are frequently used as efficient yet accurate numerical approximations for real and complex valued functions. For the complex error function w(x+iy), whose real part is the Voigt function K(x,y), code optimizations of rational approximations are investigated. An assessment of requirements for atmospheric radiative transfer modeling indicates a y range over many orders of magnitude and accuracy better than 10⁻⁴. Following a brief survey of complex error function algorithms in general and rational function approximations in particular the problems associated with subdivisions of the x, y plane (i.e., conditional branches in the code) are discussed and practical aspects of Fortran and Python implementations are considered. Benchmark tests of a variety of algorithms demonstrate that programming language, compiler choice, and implementation details influence computational speed and there is no unique ranking of algorithms. A new implementation, based on subdivision of the upper half-plane in only two regions, combining Weideman's rational approximation for small |x|+y<15 and Humlicek's rational approximation otherwise is shown to be efficient and accurate for all x, y.     

Understanding the radiative decays of vector charmonia to light pseudoscalar mesons

We show that the newly measured branching ratios of vector charmonia (J/ψ$J/\psi$, ψ^′${\psi }^{\prime }$ and ψ(3770)$\psi (3770)$) into γP, where P   stands for light pseudoscalar mesons π⁰${\pi }^0$, η  , and η^′${\eta }^{\prime }$, can be well understood in the framework of vector meson dominance (VMD) in association with the ηc–η(η^′)${\eta }_c\text{–}\eta ({\eta }^{\prime })$ mixings due to the axial gluonic anomaly. These two mechanisms behave differently in J/ψ$J/\psi$ and ψ^′→γP${\psi }^{\prime }\to \gamma P$. A coherent understanding of the branching ratio patterns observed in J/ψ(ψ^′)→γP$J/\psi ({\psi }^{\prime })\to \gamma P$ can be achieved by self-consistently including those transition mechanisms at hadronic level. The branching ratios for ψ(3770)→γP$\psi (3770)\to \gamma P$ are predicted to be rather small.     

Pion radiative weak decays in nonlocal chiral quark models

We analyze the radiative pion decay π⁺→e⁺νeγ${\pi }^{+}\to e^{+}{\nu }_e\gamma$ within nonlocal chiral quark models that include wave function renormalization. In this framework we calculate the vector and axial-vector form factors FV$F_V$ and FA$F_A$ at q²=0$q^2=0$ — where q²$q^2$ is the e⁺νe$e^{+}{\nu }_e$ squared invariant mass — and the slope a   of FV(q²)$F_V(q^2)$ at q²→0$q^2\to 0$. The calculations are carried out considering different nonlocal form factors, in particular those taken from lattice QCD evaluations, showing a reasonable agreement with the corresponding experimental data. The comparison of our results with those obtained in the (local) NJL model and the relation of FV$F_V$ and a   with the form factor in π⁰→γ^?γ${\pi }^0\to {\gamma }^{?}\gamma$ decays are discussed.     

On the equations of thermally radiative magnetohydrodynamics

An initial–boundary value problem is considered for the viscous compressible thermally radiative magnetohydrodynamic (MHD) flows coupled to self-gravitation describing the dynamics of gaseous stars in a bounded domain of R³${\mathbb{R}}^3$. The conservative boundary conditions are prescribed. Compared to Ducomet–Feireisl [13] (also see, for instance, Feireisl [18], Feireisl–Novotný [20]), a rather more general constitutive relationship is given in this paper. The analysis allows for the initial density with vacuum. Every transport coefficient admits a certain temperature scaling. The global existence of a variational (weak) solution with any finite energy and finite entropy data is established through a three-level approximation and methods of weak convergence.     

AlK壳层等离子体辐射谱模型的比对

碰撞辐射模型的比对研究对校验发展等离子体辐射谱模型、提高等离子体参数的诊断精度具有重要意义. 基于Al等离子体, 对常用的辐射模型代码FAC和FLYCHK K壳层辐射谱模型开展了比对研究, 详细比较了它们的离子丰度、特征线强度、谱发射率曲线和吸收系数曲线等特征, 并根据各能态的速率方程, 从FAC和FLYCHK模型的结构特点出发, 分析了造成这些差异的原因. FAC 和FLYCHK计算得到的类H、类He离子n=2, n=3激发态数密度有显著差异, 进而引起特征线发射率及其比值(He-IC/He-αup, He-βup/H-βup)的差异, 从而对等离子体参数的诊断结果产生影响. 除了模型中采用的能级结构和碰撞辐射过程速率外, 计算结果显著地受到FAC 和FLYCHK 模型结构的影响. n=2激发态数密度的差异是由FAC和FLYCHK分别采用能级和超组态(组态)的方式构建n=2激发态的速率方程而引起的, 而FAC代码忽略了n=3与更高激发态之间的碰撞耦合过程, 是引起n=3激发态数密度差异的原因. 主要特征线的吸收系数与基态能级的数密度相关, 受到激发态数密度的影响较小, 因此与谱发射率曲线相比, FAC和FLYCHK计算结果的差异更小.     

理论研究OH+离子电子态光谱及跃迁性质

采用高精度的内收缩多参考组态相互作用方法（icMRCI）计算OH⁺离子基态和低激发态的势能曲线和A³П-X³Σ^-跃迁体系的跃迁偶极矩。计算过程中考虑了能量的Davidson修正（+Q）效应和标量相对论修正。根据势能曲线,通过求解核的一维Schrödinger方程得到OH⁺的光谱参数。通过计算A³П-X³Σ^-体系的跃迁偶极矩研究这一跃迁体系的Einstein系数、F-C因子。研究了A³П（ν'=0~6）态的跃迁辐射寿命,结果显示其数量级为10^-6 s。     

Systematic measurements of M X-ray components X-ray fluorescence cross-sections for the elements with 77 ≤ Z ≤ 92 by employing laboratory source based energy dispersive X-ray fluorescence setup

The differential X-ray fluorescence (XRF) cross-sections for (Mξ₂, Mξ₁, Mδ₁), (Mδ₂, Mα_1,2 M₅-O₃), (Mβ, M₄-O_2,3), (Mγ, Mm₂, M₃-N₄, M₅-O_2,3), (Mm₁, M₃-N_6,7, M₃-O_4,5) and (Mm_2, M₂-N₆) group of M X-rays components have been measured for the elements with 77 ≤ Z ≤ 92 following photoionization by Mn K X-rays (E_Kαβ = 5.96 keV) obtained from ⁵⁵Fe radioisotope. The measurements were performed in annular source geometry at 126° emission angle using a low-energy Ge (LEGe) detector. The measured cross-section values are compared with theoretical values calculated using available sets of M_i (i = 1–5) photoionization cross-sections, radiative emission rates (F_ij), Coster-Kronig (f_ij), and fluorescence (ω_i) yields. The measured XRF cross-sections for the (Mξ₂, Mξ₁, Mδ₁), (Mm₁, M₃-N_6,7) and (Mm₂, M₂-N₆) groups of X-rays agree with the theoretical values within the experimental errors. The (Mβ, M₄-O_2,3) group of X-rays exhibit agreement with theoretical values within experimental uncertainty for all the elements under investigation except ₇₉Au and ₈₀Hg. The XRF cross-section for the (Mδ₂, Mα_1,2) group of X-rays are in general higher by ~20% for the elements with Z = 77–83 and exhibit agreement for the ₉₀Th and ₉₂U elements. For the (Mγ, Mm₂, M₃-N₄) X-ray group, the measured values are generally higher than the theoretical values, but the deviations are within experimental uncertainties. The large deviation in measured XRF cross-section for different M X-ray components from the theoretical ones are attributed to (i) poor separation of M X-ray components (ii) contribution of self-resonant Raman scattering (RRS) process and (iii) self-fluorescence of M₅ subshell by M_i subshell X-rays (i = 1–3).     

Theoretical study on the transition properties of AlF

Potential energy curves of the X$^{1}\Sigma ^{+}$ and A$^{1}\Pi $ states of the AlF molecule are studied through the combination of the multi-reference configuration interaction (MRCI) approach and Davidson corrections (MRCI$+$Q). The AWCV5Z basis set is employed in the calculations. The transition dipole moments (TDMs) of the A$^{1}\Pi \leftrightarrow {\rm X}^{1}\Sigma^{+}$ transition are explored based on the AWCV5Z basis set and (4, 2, 2, 0) active space. The Schrödinger equation is solved via the LEVEL 8.2 program, and the vibrational levels and rotational constants of the X$^{1}\Sigma^{+}$ and A$^{1}\Pi $ states are calculated. It is shown that the AlF molecule has high diagonal Franck-Condon factors ($f_{00}=0.9949$ and $f_{11}=0.9854$) and large Einstein coefficients for the transition of A$^{1}\Pi {(\nu }'=0)\leftrightarrow {\rm X}^{1}\Sigma^{+}{\rm (\nu }'=0)$. In addition, the radiative lifetimes of the vibrational levels are close to 10$^{-9}$ s for the A$^{1}\Pi $ state. The line intensities of the A$^{1}\Pi {\rm (\nu }'=4-15)\leftrightarrow {\rm X}^{1}\Sigma^{+}{\rm (\nu }'=0)$ transitions are also calculated. The calculated TDMs and transition probabilities in this work are credible and provide some guidance for the study of similar transitions, particularly for exploring interstellar space.