Stochastic sensitivity analysis of coupled acoustic-structural systems under non-stationary random excitations

This paper presents a new sensitivity analysis method for coupled acoustic–structural systems subjected to non-stationary random excitations. The integral of the response power spectrum density (PSD) of the coupled system is taken as the objective function. The thickness of each structural element is used as a design variable. A time-domain algorithm integrating the pseudo excitation method (PEM), direct differentiation method (DDM) and high precision direct (HPD) integration method is proposed for the sensitivity analysis of the objective function with respect to design variables. Firstly, the PEM is adopted to transform the sensitivity analysis under non-stationary random excitations into the sensitivity analysis under pseudo transient excitations. Then, the sensitivity analysis equation of the coupled system under pseudo transient excitations is derived based on the DDM. Moreover, the HPD integration method is used to efficiently solve the sensitivity analysis equation under pseudo transient excitations in a reduced-order modal space. Numerical examples are presented to demonstrate the validity of the proposed method.     

Experimental and theoretical investigations of the molecular structure,the spectroscopic properties and TD-DFT analysis of a new semiconductor hybrid based iron(III)

In this work, a new hybrid material (C₅H₆N₂Cl)₂[FeCl₄].Cl abbreviated (CAP)₂[FeCl₄].Cl was prepared using room temperature slow evaporation technique. The X-ray diffraction analysis revealed that the compound is crystallized in the centrosymmetric space group P2₁/c of the monoclinic system. The crystallographic network consists of an Fe(III) ion located on an inversion center and coordinated by four chlorine, isolated Cl^– and two (CAP)⁺ protonated cations linked by N–H...Cl and C–H...Cl hydrogen bonds to form a zero-dimensional network. Hirshfeld surface analysis was used to analyze intermolecular interactions present in the crystal structure. The vibrational properties were inspected by means of Infra-Red absorption and Raman diffusion spectroscopy techniques. In addition, theoretical calculations based on the DFT/B3LYP/LanL2DZ method and the time-dependent density functional theory (TD–DFT) were performed in order to gain more information and help in the examination of over-all properties of the title compound. Good and interesting experimental findings were presented and good consistency was found with the calculated results.     

参外联合激励下的簇发振荡及其机理

当周期激励频率远小于系统固有频率时，会存在快慢耦合效应，与单项激励不同，参外联合激励不仅会导致快子系统平衡曲线和分岔行为的复杂化，也会产生一些特殊的非线性现象，为此，本文以两耦合Hodgkin-Huxley细胞模型为例，引入周期参外联合激励，探讨在频域不同尺度耦合时该系统的簇发振荡的特点及其分岔机制．通过建立相应的快慢子系统，得到慢变参数变化下的快子系统的各种分岔模式以及相应的分岔行为，结合转换相图，揭示耦合系统随激励幅值变化时的动力学行为及其机理．研究表明，在激励幅值较小时，系统表现为概周期振荡，两频率分别近似于快子系统平衡曲线由Hopf分岔引起的两稳定极限环的振荡频率．概周期解随激励幅值的增加进入簇发振荡，导致这些簇发振荡的主要原因是在慢变参数变化的部分区间内，存在唯一稳定的平衡曲线，使得系统的轨迹逐渐趋向该平衡曲线，产生沉寂态，并随着慢变参数的变化，由分岔进入激发态．同时，快子系统中参与簇发振荡的稳定吸引子随激励幅值的变化也会不同，导致不同形式的簇发振荡．另外，与单项激励下的情形不同，联合激励时快子系统的部分稳定吸引子掩埋在其它稳定吸引子内，从而失去对簇发振荡的影响．     

Painlevé analysis,lump-kink solutions and localized excitation solutions for the (3+1)-dimensional Boiti–Leon–Manna–Pempinelli equation

In this paper the (3+1)-dimensional Boiti–Leon–Manna–Pempinelli (BLMP) equation is investigated. The integrability test is performed yielding a positive result. Through the Painlevé–Bäcklund transformation, we derive four types of lump-kink solutions composed of two quadratic functions and N exponential functions. It is shown that fission and fusion interactions occur in the lump-kink solutions. Furthermore, a new variable separation solution with two arbitrary functions is obtained, the localized excitations including lumps, dromions and periodic waves are analyzed by some graphs.     

Measurement of the surface excitation parameter of Kapton,polyethylene (PE), polymethyl methacrylate (PMMA), polystyrene (PS) and polytetrafluoroethylene (PTFE)

Reflection electron energy loss spectra (REELS) were measured for five insulating organic compounds: Kapton, polyethylene (PE), poly(methyl methacrylate) (PMMA), polystyrene (PS) and polytetrafluoroethylene (PTFE), as well as for Ni and Si, in the energy range between 200 and 1600 eV. The average number of surface excitations for a single surface crossing were determined from the experimental data and were found to be considerably smaller than for earlier studied materials, which mainly consisted of elemental metals [Surf. Sci. 486(2001)L461]. The surface excitation parameter, a material parameter used to quantify the relative intensity of surface losses in (photo)electron spectroscopy, was extracted from the data and compared with values found in the literature. The results indicate that surface excitations only have a minor influence on quantification of XPS spectra of polymers. On the other hand, a correction for surface excitations turns out to be essential for measurements of the electron inelastic mean free path of polymers when a metal is used as reference material.     

Photoluminescence of green nanophosphors Sr2MgSi2O7 doped with Tb3+ under 374-nm excitation

A series of Sr₂MgSi₂O₇:Tb³⁺ nanophosphors is prepared using a high-temperature solid-state reaction. The x-ray diffraction patterns show that the crystal structure of the sample is not significantly affected by Tb³⁺ ions. However, the images of the scanning electron microscope illustrate that the average size of nanoparticles becomes larger with the increase of Tb³⁺ concentration. Unlike earlier investigations on down-conversion emission of Tb³⁺ ion excited by deep ultraviolet light, in this work, the photoluminescence characteristics of Sr₂MgSi₂O₇ nanophosphors doped with different Tb³⁺ concentrations are analyzed under 374-nm excitations. The intense green emission at 545 nm is observed at an optimal doping concentration of 1.6 mol%. The main reason for the concentration quenching is due to the electric dipole-electric dipole interaction among Tb³⁺ ions.     

Selective Excitation with Asymmetric Adiabatic Pulses for NMR Spectroscopy

Existing selective pulses are mainly constructed in the forms of classically shaped pulses, such as the Gaussian pulses, or generated by using numerical optimization methods. However, all of these pulses are highly sensitive to radiofrequency (RF) intensity variation, which means their performance is highly dependent on the accuracy and stability of the RF intensity. Even a slight RF intensity deviation can cause severe degradation in the excitation profile. To solve this problem, we propose a method for narrow selective excitation by sequential application of a pair of phase‐opposite asymmetric adiabatic pulses, all within two scans. By retaining the adiabatic character, the new method is highly robust to RF intensity variation. Moreover, it has flexible excitation bandwidth, ranging from line‐selective to narrow‐band‐selective pulses. The method is tested both in numerical simulations and solution‐state NMR experiments.     

Uniform Reduction of Scalar Coupling by Real‐Time Homonuclear J‐Downscaled NMR

Scalar coupling in proton NMR spectra provides important information for the structural analysis. However, the low resolution due to the resulting signal splitting, together with the rather narrow spectral range of hydrogen, often prevents the extraction of J‐coupling information. Here we present a method to achieve real‐time homonuclear J‐downscaling. Thereby, all J‐values are uniformly reduced by an arbitrary scaling factor. In the resulting one‐dimensional spectra, signal overlap is reduced, while scalar coupling information is still available.