An investigation of the structure and bond rotational potential of some fluorinated ethanes by NMR spectroscopy of solutions in nematic liquid crystalline solvents

NMR spectra of 1,2-dibromo-1,1-difluoroethane and 1-bromo-2-iodo-tetrafluoroethane dissolved in nematic liquid crystalline solvents have been analysed to yield the magnitudes and signs of the scalar couplings, J(ij), and total anisotropic couplings, T(ij), between all the (1)H, (19)F, and (13)C nuclei, except for those between two (13)C nuclei. The values obtained for T(ij) in principle contain a contribution from J(ij)(aniso), the component along the static applied magnetic field of the anisotropic part of the electron-mediated spin-spin coupling. Neglecting this contribution allows partially averaged dipolar couplings, D(ij), to be extracted from the T(ij), and these were used to determine the structure, orientational order, and the conformational distribution generated by rotation about the C-C bond. The values obtained are compared with the results of calculations by ab initio and density functional methods. The differences found are no greater than those obtained for similar compounds which do not contain fluorine, so that there is no definitive evidence for significant contributions from J(CF)(aniso) or J(FF)(aniso) in the two compounds studied.     

非线性耗散对亚稳态系统量子衰变速率的影响

发展了一种快速傅里叶变换路径积分方法，研究非线性耗散系统的量子衰变速率，得到了Bounce轨道的作用量S_B，即衰变速率的指数因子.在系统与环境存在非线性耦合f(x)=tanh［λ(x-x_b)］的情形下，发现其对衰变速率具有抑制作用.指数因子随温度T的关系不再满足S_B=a［1-b(T/T_c)²］法则；与通常的线性耗散情形相比，跨越温度T_c回升，即系统更早地进入穿透区域. 关键词： 量子衰变 非线性耦合 路径积分 快速傅里叶变换     

Beta-delayed γ-ray studies of πf7/2 - νpf shell nuclei

We have utilized the selective process of β decay to populate low-energy excited states in the neutron-rich ₂₂Ti, ₂₃V, ₂₄Cr, and ₂₅Mn nuclei. The goal was to systematically track the monopole shift of the νf_5/2 single-particle level with increased occupancy of the πf_7/2 orbital. The β-decay properties of the parent nuclides, along with the low-energy structure of the daughters, are presented and compared with the results of shell model calculations employing the GXPF1 interaction.     

Preparation of Zn(Cd)O:Ga–SiO2 composite scintillating materials

Composite material consisting of highly luminescent Zn(Cd)O:Ga powder embedded in the silica matrix was prepared. It was found out that ZnO:Ga with less developed crystals (i.e. annealed at lower temperatures) is more prone to interact with the SiO₂ matrix and form zinc silicates, which in turn resulted in the decrease in the excitonic emission. Pre-annealing of the powders at temperatures above 600 °C prevented the interaction with the SiO₂ matrix. ZnO:Ga with well-developed crystals at such a high temperatures was not affected by the matrix and retained its properties, i.e. high radioluminescence intensity and ultrafast sub nanosecond photoluminescence decay. Introducing Cd into the ZnO lattice caused observable red shift in the excitonic luminescence, without negatively affecting the total intensity or the decay.     

Intrinsic anisotropy of the effective acoustic properties in metafluids made of two-dimensional cylinder arrays

Within a unified theoretical framework, we extract the omnidirectional effective acoustic parameters for the metafluid consisting of isotropic fluid cylinders embedded in an isotropic fluid background. Besides the analytical formulas for the effective parameters reported previously, i.e., the bulk modulus and the mass density perpendicular to the cylinders, we also derive a simple expression for the effective mass density parallel to the cylinders. As expected, these two effective mass densities are not identical and constitute an anisotropic density tensor. Such intrinsic anisotropy can be engineered much stronger than the pure in-plane anisotropy induced by either anisotropic lattices or anisotropic scatterers.     

Optimizing thermography depth probing with a dynamic thermal point spread function

Derivation of two point spread functions PSFs suitable for infrared thermograms analysis is illustrated, based on two unique approaches, one based on depth decaying limit and one on diffusion limit. Experimental work using PMMA sample with back drilled holes and pulsed thermographic routine is utilized to show the effectiveness of deconvoluting pixel temperature transient history with suggested PSF’s. Synthetic second time derivative thermograms are utilized for comparison and the signal to noise ratio is used as a figure of merit for quantification.     

用声波速度确定骨组织弹性参数

本文用超声方法确定密质骨的弹性特征,其基本原理是基于弹性波理论中的Christoffel方程。本文应用液浸、声波穿透技术,对牛胫骨样品中一些特殊入射方向的声波速度进行了测试,利用固体中沿任意方向的弹性波传播速度与材料的弹性系数间的关系,通过计算机编程反演出具有六方晶体对称结构的密质骨组织的5个独立弹性常数。结果与相关文献中其它方法所得结果一致。     

Determination of the cluster spectroscopic factor of the 10.3 MeV state in 12Be

From an inelastic excitation and breakup experiment with a ¹²Be beam at 29 MeV/u, a large ⁴He+⁸He cluster decay width of 1.1(2) MeV is determined for a state at an excitation energy of 10.3 MeV and with a spin parity of 0+. By using the R-matrix analysis, a cluster spectroscopic factor of 0.53(10) is extracted from the cluster partial width, providing a strong support for the clustering structure in ¹²Be. A specially designed zero-degree telescope played an essential role in the present experiment and has been demonstrated to be a promising tool in future studies of the molecular-like resonances near the cluster separation threshold.     

Towards the decays of Nx（1625） the molecular picture

In this talk, we firstly overview the experimental status of Nx（1625）, which is an enhancement structure observed in K-3. invariant mass spectrum of J/ψ → pK-∧. process. Then we present the result of the decay of Nx（1625） under the two molecular assumptions, i.e. S-wave∧K- and S-wave ∑0K- molecular states. Several experimental suggestions for Nx （1625） are proposed.