Ultra fine carbon nitride nanocrystals synthesized by laser ablation in liquid solution

Crystalline carbon nitride nanopowders and nanorods have been successfully synthesized at room temperature and pressure using the novel technique of pulsed laser ablation of a graphite target in liquid ammonia solution. High-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and Fourier transform infrared spectroscopy (FTIR) were used to systematically study the morphology, nanostructure and chemical bonding. The experimental composition and structure of the nanoparticles are consistent with the theoretical calculations for α-C₃N₄. After 2 h ablation the particles had a size distribution ∼8–12 nm, whereas after 5 h ablation the particles had grown into nanorod-like structures with a crystalline C₃N₄ tip. A formation mechanism for these nanorods is proposed whereby nanoparticles are first synthesized via rapid formation of an embryonic particle, followed by a slow growth, eventually leading to a one-dimensional nanorod structure.     

Tm-Doped Fibre Laser Pumped Cr^2＋：ZnSe Poly-Crystal Laser

Demonstrations of cw lasing in Cr^2＋：ZnSe poly-crystal are reported. The laser consists of a 1.7-mm-thick Cr^2＋ ：ZnSe poly-crystal disc pumped by a Tin-silica double-clad fibre laser at 2050nm. Using a concave high- reflection mirror with a radius of curvature of 500mm as the rear mirror, the laser delivers up to 1030mW of radiation around 2.367μm.     

Guided surface modes in a hollow slab waveguide with a left-handed material substrate or cover

The structural dispersion characteristics of guided surface modes in a hollow slab waveguide with a left-handed material substrate or cover are investigated. Dispersion relation is derived by using normalized parameters, and universal dispersion curves have been obtained analytically, by solving transcendental dispersion equations in a reverse way. Existence condition, mode degeneracy and other dispersion properties of guided surface modes have been discussed for different ? or μ of three layers for this substrate or cover layer.     

Time correlation functions in classical dense fluids

The velocity autocorrelation functions and memory functions of dense classical fluids may be directly obtained from the static radial distribution function g(r) in an approximate way. Following the Mori projection operator formalism, the memory functions may be related to the fluctuating force correlation. At low densities, these functions may be evaluated by following the trajectories of particle pairs in the interatomic potential. At higher densities, the force correlation functions can be evaluated approximately from particle pair trajectories via the potential of the mean force. The contributions to the memory function come mainly from particle pairs with rather specific and rather short interatomic distances. At higher temperatures, this specific distance is even shorter, hence the memory function decays quickly with time. At lower temperatures, a negative region of the memory function may develop. On the other hand, there is relatively little density dependence of the normalized memory function. The results for argon fluids at various densities and temperatures agree satisfactorily with the molecular dynamics and the Enskog values. The decrease of the diffusion coefficient with density is partly due to the nature of g(r) which reflects the stronger clustering of atoms at higher densities.     

火焰原子吸收光谱法测定粮食中的铜

碳化酸溶消解试样,用火焰原子吸收光谱法测定三种粮食作物中的铜.回收率:99.5%-107.0%.方法快速、简便、准确度高.     

Facile fabrication and optical properties of novel Pb(OH)Cl nanotubes

Uniform Pb(OH)Cl nanotubes were synthesized for the first time through a reverse micelles system. The system was consisting of C₁₂E₉ as a surfactant, n-pentanol as a cosurfactant, hexamethylene as the continuous oil phase and lead acetate or sodium chloride solution as the dispersed aqueous phase. The obtained Pb(OH)Cl nanotubes have an average outer diameter of 60 nm, inner diameter of about 40 nm, and an length up to 3 μm as TEM picture showed. And the range of the nanotube diameter is from 50 nm to 70 nm. XRD result indicated that Pb(OH)Cl crystallized in an orthorhombic phase. Photoluminescent (PL) spectrum showed that the product emit in near ultraviolet region and visible region at 335 nm and 439 nm respectively. The experimental results show that reaction temperature have effect on the shape of Pb(OH)Cl nanotubes. A possible formation mechanism was also discussed.     

改性乙醇胺富集烟道气中CO2的FTIR研究

以四(3,5-二叔丁基-4-羟基苯基丙酸)季戊四醇酯(抗氧剂1010)、Na2SO3作为乙醇胺(MEA)的氧化降解的改性剂,考察改性MEA富集模拟烟道气中CO2的效果,利用气相色谱、红外光谱分析抗氧剂1010与Na2SO3的适宜用量、比较两种抗氧剂的抗氧化性能.结果表明,抗氧剂1010和亚硫酸钠的添加量在0.15%时效...     

Photonic bandgap properties of 8-fold symmetric photonic quasicrystals

The bandgap properties of 2D 8-fold symmetric photonic quasicrystals (PQCs) composed of a set of rods are numerically investigated for various fill factors, dielectric constants and propagation angles using the finite difference time domain (FDTD) method. Some interesting properties are found besides the known results: (i) the central frequency of the bandgap shifts to low frequency as r/a increases; (ii) an optimum fill factor to obtain the largest gap width exists, which decreases with increasing dielectric constant; (iii) compared with the behavior for a given fill factor, the variation of bandgap width for the optimum fill factor increases much more significantly with the dielectric constant. Selection guidelines for 8-fold symmetric PQC designs are provided for optimum fill factors and variation of the relative bandgap width at different dielectric constants.     

Anisotropy of sound velocity for a new PbB4O7 crystal as determined by the laser ultrasonic technique

4 O₇ crystal is a new nonlinear optical crystal. For the first time the anisotropy of the velocities of its longitudinal and surface acoustic waves (SAWs) are determined by laser ultrasonic technique. The velocities of surface waves for X-, Y-, and Z-cut crystals are also calculated. The theoretical calculations of slowness curves are in good agreement with experimental results. The SAW slowness curve is elliptical for Y- or Z-cut crystal wafers, and circular for an X-cut wafer. Received: 27 January 1997/Accepted: 30 July 1997