Multi-element analysis by ArF laser excited atomic fluorescence of laser ablated plumes: Mechanism and applications

A new multi-element analysis technique based on laser-excited atomic fluorescence was reviewed. However, the one-wavelength-one-transition constraint was overcome. Numerous elements were induced to fluoresce at a single excitation wavelength of 193 nm. This was possible provided that the analytes were imbedded in dense plumes, such as those produced by pulsed laser ablation. The underlying mechanism of the technique was explained and corroborated. Analytical applications to metals, plastics, ceramics and their composites were discribed. Detection limits in the ng/g range and mass limits of atto moles were demonstrated. Several real-world problems, including the analysis of paint coating for trace lead, the non-destructive analysis of potteries and ink, the chemical profiling of electrode-plastic interfaces, and the analysis of ingestible lead colloids were discussed.     

Dynamic instability and steady-state response of an elliptical cracked shaft

An elliptical front crack has been found to be more accurate and realistic for modeling the transverse surface crack in rotating machinery compared with the widely used straight front crack. When the shaft rotates, the elliptical crack opens and closes alternatively, due to gravity, and thus, a “breathing effect” occurs. This variance in shaft stiffness is time-periodic, and hence, a parametrically excited system is expected. Therefore, the dynamic instability and steady-state response of a rotating shaft containing an elliptical front crack are studied in the paper. The local flexibility due to the crack is derived, and the governing equations of the crack shaft system are established using the assumed modes method. Utilizing the Bolotin’s method and harmonic balance method, the boundaries of two typical instability regions and maximum response amplitude of the cracked shaft could be computed numerically. The elliptical crack parameters (depth, shape factor and position) and damping are, respectively, considered and discussed for their effects on the dynamic behavior of the elliptical cracked shaft. Some research results might be helpful for the crack detection in rotating machinery.     

Lode角对应力张量的导数的基本性质

为计及岩土类材料塑性力学行为的中主应力影响或应力路径相关性,通常将应力张量Lode角/Lode数引入屈服函数与塑性势函数。由此在计算塑性应变增量时必然涉及Lode角/Lode数对应力的导数张量（记为 ）。然而,应力张量主值有重根时 的计算存在困难。本文给出了 的主值计算方法及谱分解表达式并详细讨论了张量 的基本性质。     

Complete noncompact manifolds with harmonic curvature

Let (M ⁿ , g) be an n-dimensional complete noncompact Riemannian manifold with harmonic curvature and positive Sobolev constant. In this paper, by employing an elliptic estimation method, we show that (M ⁿ , g) is a space form if it has sufficiently small L ^n/2-norms of trace-free curvature tensor and nonnegative scalar curvature. Moreover, we get a gap theorem for (M ⁿ , g) with positive scalar curvature.     

Ultrathin nanosheets of Mn<Subscript>3</Subscript>O<Subscript>4</Subscript>: A new two-dimensional ferromagnetic material with strong magnetocrystalline anisotropy

Two-dimensional (2D) materials with robust ferromagnetism have played a key role in realizing nextgeneration spin-electronic devices, but many challenges remain, especially the lack of intrinsic ferromagnetic behavior in almost all 2D materials. Here, we highlight ultrathin Mn₃O₄ nanosheets as a new 2D ferromagnetic material with strong magnetocrystalline anisotropy. Magnetic measurements along the in-plane and out-of-plane directions confirm that the out-of-plane direction is the easy axis. The 2D-confined environment and Rashba-type spin-orbit coupling are thought to be responsible for the magnetocrystalline anisotropy. The robust ferromagnetism in 2D Mn₃O₄ nanosheets with magnetocrystalline anisotropy not only paves a new way for realizing the intrinsic ferromagnetic behavior in 2D materials but also provides a novel candidate for building next-generation spin-electronic devices.     

Wideband high-efficient linear polarization rotators

We demonstrate a wideband polarization rotator with characteristics of high efficiency and large-range incidence angle by using a very simple anisotropic reflective metasurface. The calculated results show that reflection coefficient of cross polarization is larger than 71% over an octave frequency bandwidth from ~4.9 GHz to ~10.4 GHz. The proposed metasurface can still work very well even at incidence angle of 60?. The experiment at microwave frequencies is carried out and its results agree well with the simulated ones.     

Simulation of the wave-absorbing model of a carbonyl iron / silver-coated core–shell structure

The microwave-absorbing performances of carbonyl iron powder / silver core–shell composite particles are studied on the basis of the electromagnetic scattering theory and the energy conservation law. In addition, a calculation method for reflection loss of the carbonyl iron powder / silver core–shell composite particles with microwave is proposed. The calculated reflection loss of the carbonyl iron powder / silver core–shell composite particles is compared with the experimental results. The findings show that the trend of reflection loss of the carbonyl iron powder / silver composite particles can be predicted which can subsequently provide a relevant reference for future experiment and calculation of the absorbing mechanism of electromagnetic wave-microscopic carbonyl iron powder / silver core–shell composite particles.     

Metallic hollow waveguide based on GeO2–NaOH precursor solution for transmission of CO2 laser radiations

Optical and Quantum Electronics - This paper presents a highly efficient method based on finite impulse response filtering and Fourier transform techniques to solve the eigen-problems, especially...     

An experimental study of the merging probability of double buoyancy-controlled jet flame

This article presents an experimental investigation on the merging probability of buoyancy-controlled jet flames. Two rectangular jet nozzles with different aspect ratios and heat release rates were studied in the open space. The nozzles of the same area with dimensions of 1.5 × 24, 3 × 12, and 6 × 6 mm were used in this article. It is found that the merging probability increases with the heat release rate and decreases with the space between these two nozzles. A model to predict the merging probability has been developed, which is proportional to a dimensionless parameter linearly within a certain scope.     

An upgraded external beam PIXE setup for multielemental analysis of atmospheric aerosol samples

The external beam particle‐induced X‐ray emission (PIXE) setup has been upgraded by introducing a new silicon drift detector with the aim of obtaining better minimum detection limits (MDLs) at the 2 × 1.7 MV Tandetron accelerator of the Beijing Normal University in China. The upgraded external beam PIXE setup is equipped with two silicon drift detectors for PIXE analysis of low and high Z elements. A surface barrier detector for Rutherford backscattering spectrometry monitors beam and helium flow. Two kinds of aerosol filter samples (quartz fiber filters and Teflon filters) were studied. A 200‐μm thick Mylar absorber in front of the medium‐high energy X‐rays detector was adopted, and it got the best MDLs for atmospheric aerosol samples analysis. Multielemental analysis of quartz fiber filter aerosol samples was achieved. For more accurate and better MDLs of low Z elements in PIXE analysis, it is necessary to keep sufficient helium flow behind the thin samples.