Experiment determination of after-operating gas compositions in a transverse-flow CW high power CO2 laser

For a high-power CO₂ laser with a close-confined structure, the compositions and ratios of gas mixtures are changed due to electron impacts during the laser-operating period. As a result, the laser performance is gradually degraded, even to non-lasing output. In this paper, three different methods (a chemiluminescence, a titration analysis and a thermal conductivity measurement) are utilized to determine both the compositions and the ratios, according to different thermal and chemical characteristics of the gases. Corresponding experiments are implemented to a typical transverse-flow high-power CO₂ laser after a long-term discharge (around 15 h) with the output power decreased from an initial 3 kW to final 2 kW. There is evidence in the experiments to indicate that CO₂ decreases by 13.2% comparing with an initially optimal content. Also, the produced impurities are mostly CO and O₂ molecules with noticeable concentrations, while nitrogen–oxygen complexes are little in the gas mixtures.     

非线性晶体内腔倍频的温度模式分布

为了提高谐波转换效率和消除温升引起的晶体走离效应，对于非线性晶体温度场分布特点进行了分析与计算.同时研究了基波偏心辐射对KTP晶体温度场的影响.通过对腔内倍频KTP晶体工作特点的分析，建立了方形非线性晶体热模型并首次引入了方形晶体辐射偏心度的定义.基于热传导方程，得到了温度场分布的一般解析表达式.     

Influence of surface modification adopting thermal treatments on dispersion of detonation nanodiamond

In order to improve the dispersion of detonation nanodiamonds (ND) in aqueous and non-aqueous media, a series of thermal treatments have been conducted in air ambient to modify ND surface. Small angle X-ray scattering (SAXS) technique and high resolution transmission electron microscopy (HRTEM) were introduced to observe the primary size of ND. Differential thermal analysis (DTA), X-ray diffraction (XRD) methodology, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy were adopted to analyze the structure, bonds at surfaces of the treated ND. Malvern instrument Zetasizer3000HS was used for measuring the surface electric potential and the size distribution of ND. As thermal treatments can cause graphitization and oxidization of functional groups at the surface, ND treated at high temperature is correspondingly more negatively charged in an aqueous medium, and the increased absolute value of zeta potential ensures the electrostatic stability of ND particles. Specially, after being treated at a temperature more than 850 K, ND can be well dispersed in various media.     

Development of the Monte Carlo model CASCADE-2004 of high-energy nuclear interactions

The Monte Carlo code CASCADE for the calculation of inelastic hadron- and nucleus-nucleus interactions at energies from several tens of MeV up to several tens of GeV and for modelling of nuclear-physical processes accompanying the transport of particles and nuclei in matter is improved by considering a more detailed model of decay of highly excited residual (after-intranuclear-cascade) nuclei. Results of calculations are in good agreement with experiment. However, there are some deviations for light-isotope production, which prompt the necessity of developing more correct models of evaporation and strong asymmetric high-energy fission.     

Stability of Tokamak Equilibrium with Internal Transport Barrier against High n MHD Ballooning Mode

Internal transport barriers （ITBs） are phenomena associated with improved confinement mode of tokamak plasmas. Within the region where the ITB locates, the plasma pressure has a large gradient while the magnetic shear s has a minimum so that within and near the ITB, the absolute value of the shear is very low. Physics involved is plentiful, from the macroscopic （ MHD ） stability, to the suppression of microscopic instabilities thought to be responsible for anomalous transport. The treatment of very low shear also poses some theoretical difficulties.     

Adatom concentration on GaAs(001) during MBE annealing

We study the concentration of adatoms on GaAs(001) during annealing under MBE conditions. By rapidly cooling the sample from typical growth temperatures and typical As overpressures, the thermal concentration of adatoms can be frozen into small islands on the terraces. The area of the resulting islands is measured with STM far from terrace steps, giving an estimate of the concentration of adatoms during equilibrium. We find that a surprisingly large concentration of adatoms is present for typical growth temperatures, e.g. 0.18 monolayer at 600°C. Possible consequences for current growth models are discussed.     

Resolution of conflicting views concerning frequency-response models for conducting materials with dispersive relaxation, and isomorphism of macroscopic and microscopic models

Possible errors in the widely used 1972–1973 macroscopic original-electric-modulus formalism are identified, corrected, and their consequences considered. These errors include misidentification of the high-frequency-limiting dielectric constant arising entirely from mobile charges, ε_C1∞, and the failure to treat properly the high-frequency-limiting dielectric constant associated with bulk dipolar and vibrionic effects, ε_D∞. It is shown that the corrected modulus formalism, which describes dispersed mobile-charge effects, is isomorphic in form with the 1973 microscopic continuous-time random-walk hopping model of Scher and Lax after a minor but significant correction is made to the latter's response function. This firmly established correction, which nevertheless could not be determined by Kronig–Kramers transformation, involved inversion of synthetic frequency-response data to determine a distribution of relaxation times and led to extension of the real part of the Scher–Lax dielectric response to higher frequencies by the inclusion of a nonzero limiting value. This isomorphism, along with excellent data fitting using the corrected modulus formalism, suggests that since the Scher–Lax stochastic model involves no explicit Coulomb interactions, cation motion in glasses is dominated by short-range interactions. Finally, two very-high-frequency processes, which each lead to a limiting plateau value of the real part of the conductivity at sufficiently high frequencies, are discussed in detail.     

Processes limiting the rate of response in photorefractive composites

The processes limiting the rate of response of highly diffractive, reorientationally enhanced photorefractive polymer composite materials are identified from a series of degenerate four wave mixing and Mach–Zehnder interferometric measurements. In the regime of low intensity writing beams charge generation limits the rate of holographic grating formation, but at higher intensities charge transport or reorientation of dye molecules can restrict the rate of grating formation more strongly. A grating risetime of 540 ms is observed in a composite of high dye content with high reorientational mobility of the dye molecules. In this case it is proposed that the charge carrier mobility of the doped poly(N-vinylcarbazole):2,4,7-trinitro-9-fluorenone (PVK:TNF) matrix is the principal limiting factor in grating response rates.     

Effect of composition,thickness and temperature on non-linear I–V curves in vanadium phosphate glasses

Summary Glass layers of (V₂O₅)_1−x (P₂O₅) _x were prepared by melting appropriate mixtures of V₂O₅ and P₂O₅ powders. The measurements ofI–V characteristic curves show three regions of conduction, namely high-resistance state, turnover point with zero-differential resistance region (∂V/∂I=0) and differential negative-resistance region. The turnover point is strongly dependent on composition, sample thickness and temperature. It is found that the increase of the ratio of phosphorus/vanadium reduces conductance as well as it raises the field required to produce turnover behaviour. The data in the range up to the turnover point are discussed on the basis of an electrothermal process. Results of the negative-resistance state could be explained in terms of a hopping mechanism.     

The viscous-slip, diffusion-slip, and thermal-creep problems for a binary mixture of rigid spheres described by the linearized Boltzmann equation

An analytical version of the discrete-ordinates method (the ADO method) is used with recently established analytical expressions for the rigid-sphere scattering kernels to develop concise and particularly accurate solutions to the viscous-slip, the diffusion-slip, and the half-space thermal-creep problems for a binary gas mixture described by the linearized Boltzmann equation. In addition to a computation of the viscous-slip, the diffusion-slip, and the thermal-slip coefficients, for the case of Maxwell boundary conditions for each of the two species, the velocity, heat-flow, and shear-stress profiles are established for each species of particles. Numerical results are reported for two binary mixtures (Ne–Ar and He–Xe) with various molar concentrations.