A spectroscopic study of laser-induced tin–lead plasma: Transition probabilities for spectral lines of Sn I

In this paper, we present transition probabilities for 97 spectral lines of Sn I, corresponding to transitions n(n = 6,7,8)s → 5p², n(n = 5,6,7)d → 5p², 5p³ → 5p², n(n = 7)p → 6s, determined by measuring the intensities of the emission lines of a Laser-induced breakdown (emission) spectrometry (LIBS). The optical emission spectroscopy from a laser-induced plasma generated by a 10 640 Å radiation, with an irradiance of 1.4 × 10¹⁰ Wcm^− 2 on an Sn–Pb alloy (an Sn content of approximately 20%), in vacuum, was recorded at 0.8 µs, and analysed between 1900 and 7000 Å. The population-level distribution and corresponding temperature were obtained using Boltzmann plots. The electron density of the plasma was determined using well-known Stark broadening parameters of spectral lines. The plasma under study had an electron temperature of 13,200 K and an electron number density of 2 × 10¹⁶ cm^− 3. The experimental relative transition probabilities were put on an absolute scale using the branching ratio method to calculate Sn I multiplet transition probabilities from available radiative lifetime data of their upper states and plotting the Sn I emission spectrum lines on a Boltzmann plot assuming local thermodynamic equilibrium (LTE) to be valid and following Boltzmann's law. The LTE conditions and plasma homogeneity have been checked. Special attention was paid to the possible self-absorption of the different transitions. The experimental results obtained have been compared with the experimental values given by other authors.     

Atomic transition probabilities for selected Yb II lines emitted from a ferroelectric plasma source

The relative intensities of several hundred emission lines of Yb II between 200 nm and 900 nm were obtained with the use of ferroelectric plasma source. These relative intensities obtained for lines from 21 energy levels have been used to determine the line branching fractions, which have then been combined with accurate experimental radiative lifetime measurements to give absolute transition probabilities for 111 Yb II lines. The obtained values were compared with theoretical and experimental data taken from available literature.     

The de novo design of median molecules within a property range of interest

Summary In this paper an application is presented of the median molecule workflow to the de novo design of novel molecular entities with a property profile of interest. Median molecules are structures that are optimised to be similar to a set of existing molecules of interest as an approach for lead exploration and hopping. An overview of this workflow is provided together with an example of an instance using the similarity to camphor and menthol as objectives. The methodology of the experiments is defined and the workflow is applied to designing novel molecules for two physical property datasets: mean molecular polarisability and aqueous solubility. This paper concludes with a discussion of the characteristics of this method.     

Comparison of zinc and cadmium plasma parameters produced by laser-ablation

We report the measurement of the zinc and cadmium plasma parameters produced by the fundamental, second, and third harmonics of the neodymium-doped yttrium aluminium garnet laser. The excitation temperature has been determined from the Boltzmann plot method, whereas the electron number density is estimated from the Stark broadened profile of several spectral lines. The temporal evolution of the plasma has also been investigated. Besides, we present experimental relative transition probabilities of the Zn (4s5s ³S₁ → 4s4p ³P_0,1,2) and Cd (5s6s ³S₁ → 5s5p ³P_0,1,2) triplets and compare our data with that listed in the National Institute of Standards and Technology database. The experiments have been performed in air but also in He, Ne and Ar atmosphere to study the effects of ambient gas environment on the emission intensity of the atomic and ionic lines and on the plasma parameters.     

Simultaneous kinetic determination of thiocyanate and sulfide using eigenvalue ranking and correlation ranking in principal component-wavelet neural network

In this work, two toxic compound, sulfide and thiocyanate were determined simultaneously using kinetic spectrophotometry. These anions have shown the catalytic effects on the reaction between iodine and azide. Since the system was nonlinear, a nonlinear model, principal component-wavelet neural network (PC-WNN) was used as the multivariate calibration method. The principal component analysis was used to decrease the dimension of the original matrix. In other words, the scores of the PCs, 5, instead of the original variables, 301, were used as the input for the model. Two methods were used to select the most relevant principal components: eigenvalue ranking and correlation ranking. In this work, eigenvalue and correlation ranking methods have shown better results for thiocyanate and sulfide, respectively, and it can be concluded that these methods are complementary. The WNN has several advantages relative to other types of neural network such as better convergence ability. The data set was divided to calibration, prediction and validation sets. Each set was selected so that the concentrations of the analytes were approximately covered the entire ranges of the analytes. Mean relative error for thiocyanate and sulfide in validation set were 8.5 and 10.6, respectively. Thiocyanate and sulfide can be determined in the range of 60–700 ng ml⁻¹ and 20–400 ng ml⁻¹, respectively. The proposed method was applied for the determination of sulfide and thiocyanate in real samples such as tap, waste and river waters with satisfactory results.     

离子对生成反应的LCAC-SW量子散射理论研究

离子对生成反应微观动力学的理论和实验研究有助于从本质上揭示气相、液相及上层空间大气化学反应机理.实验上已经发展到用激光-交叉分子束技术研究其态-态过程;理论上则主要是采用准经典轨迹法.     

Application of the Lie algebraic approach to diffractionally and rotationally inelastic molecule–surface scattering

The Lie algebraic approach of Alhassid and Levine [Phys. Rev. A 18 , 89 (1978)] is applied to the molecule–surface scattering. Specially, the diffractionally and rotationally inelastic scattering of a diatomic molecule from a solid surface is dealt with. Within the framework of the close-coupling method, we construct a Hamiltonian for the scattering system and use it to generate a dynamical algebra h₆. By solving equations of motion for the group parameters, the scattering wave functions near the surface are obtained. Computed transition probabilities of diffractively and rotationally inelastic scattering of H₂ from LiF(001) surface with the use of Lie algebraic method are seen to agree well with the coupled-channel calculations. The Lie algebraic method thus appears to have a wide range of validity for describing the dynamics of gas–surface scattering. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 63: 981–989, 1997     

Edge ranking and searching in partial orders

We consider a problem of searching an element in a partially ordered set (poset). The goal is to find a search strategy which minimizes the number of comparisons. Ben-Asher, Farchi and Newman considered a special case where the partial order has the maximum element and the Hasse diagram is a tree (tree-like posets) and they gave an O(n⁴log³n)-time algorithm for finding an optimal search strategy for such a partial order. We show that this problem is equivalent to finding edge ranking of a simple tree corresponding to the Hasse diagram, which implies the existence of a linear-time algorithm for this problem.Then we study a more general problem, namely searching in any partial order with maximum element. We prove that such a generalization is hard, and we give an -approximate polynomial-time algorithm for this problem.     

四川省市州经济发展差异的统计分析

采用因子分析研究四川省21市州之间的相关性,利用主因子计算出各个市州得分,以市州得分作为新变量进行集团排序,再将基于相对位置排序法引入到集团排序中,进而得到最终的市州分类结果,在统计分析的基础上对市州经济发展给出一些建议.