Visualization of turbulence and internal waves in a stratified fluid

A new method for measuring the density, temperature and velocity of N2 gas flow by laser induced biacetyl phosphorescence is proposed. The characteristics of the laser induced phosphorescence of biacetyl mixed with N2 are investigated both in static gas and in one-dimensional flow along a pipe with constant cross section. The theoretical and experimental investigations show that the temperature and density of N2 gas flow could be measured by observing the phosphorescence lifetime and initial intensity of biacetyl triplet (3Au) respectively. The velocity could be measured by observing the time-of-flight of the phosphorescent gas after pulsed laser excitation. The prospect of this method is also discussed.

A model of an isolated magnetic-flux tube in a stratified atmosphere

A two-dimensional model of a magnetic flux tube confined in a gravitational stratified atmosphere is discussed. The magnetic field in the flux tube is assumed to be force-free. By using the approximation of large scale height, the problem of a free boundary with nonlinear conditions may be reduced to one involving a fixed boundary. The two-dimensional features are obtained by applying the perturbation method and adopting the Luest-Schlueter model as the basic state. The results show that the configuration of a flux tube confined in a gravitational stratified atmosphere is divergent, and the more twisted the magnetic field, the more divergent is the flux tube.

微重力下环境压力和辐射再吸收对火焰沿薄燃料表面传播的影响

当环境气体不具备辐射特性时(例如环境气体为O2-N2),在较小的环境压力下,火焰向燃料表面的热传导是火焰传播的主要驱动力.但随着环境压力的增大,火焰传播速度越来越大,火焰对燃料表面的热辐射逐渐成为火焰传播的主要驱动力之一.当环境气体具有较强的辐射特性时(例如环境气体为O2-CO2),在较小的环境压力下,火焰前沿环境气体的辐射再吸收将强化火焰对燃料表面的传热、热辐射和热传导在火焰传播机理中均起重要作用.随着环境压力的增大,氧气向火焰的扩散加强,燃烧反应加剧,火焰传播加速.当环境压力大于一定值时,进一步增大环境压力,环境气体的辐射再吸收使火焰对燃料表面的热辐射减弱.因此,火焰传播速度反而随着环境压力的增大而减小,火焰向燃料表面的热传导逐渐成为火焰传播的主要驱动力.

Measurement and Calculation of Vibrational Temperature behind Strong Shock Waves

In the present paper the measured values of vibrational temperature behind strong shock waves are compared with theoretical ones. The histories of vibrational temperature behind strong shock waves in a shock tube were measured using two monochromators. The test gas was pure nitrogen at 100-300Pa, and the speeds of shock waves were 5.0-6.0km/s. The electronic temperature of N-2(+) was also approximately determined from experiment and compared with the experimental vibrational temperature. The results show that the presented calculational method is effective, and the electronic energy of N2+ is excited much faster than its vibrational energy. One Langmuir probe was used to determine the effective time of region 2. The influence of viscosity in the shock tube is also analyzed.

Plume Parameters and Thruster Properties of a Low Power Arcjet

Abstract. A low power arcjet-thruster of 1 kW-class with gas mixture of H2-N2 or pure argon as the propellant is fired at a chamber pressure about 10 Pa. The nozzle temperature is detected with an infrared pyrometer; a plate set perpendicular to the plume axis and connected to a force sensor is used to measure the thrust; a probe with a tapered head is used for measuring the impact pressure in the plume flow; and a double-electrostatic probe system is applied to evaluate the electron temperature. Results indicate that the high nozzle temperature could adversely affect the conversion from enthalpy to kinetic energy. The plume flow deviates evidently from the LTE condition, and the rarefied-gas dynamic effect should be considered under the high temperature and low-pressure condition in analyzing the experimental phenomena.

Optical properties of transparent alkali gallium silicate glass-ceramics containing Ni2+-doped beta-Ga2O3 nanocrystals

Broadband near-infrared (IR) luminescence in transparent alkali gallium silicate glass-ceramics containing N2+-doped beta-Ga2O3 nanocrystals was observed. This broadband emission could be attributed to the T-3(2g) (F-3) -> (3)A(2g) (F-3) transition of octahedral Ni2+ ions in glass-ceramics. The full width at half-maximum (FWHM) of the near-IR luminescence and fluorescent lifetime of the glass-ceramic doped with 0.10 mol% NiO were 260 nm and similar to 1220 mu s, respectively. It is expected that transparent Ni2+-doped beta-Ga2O3 glass-ceramics with this broad near-IR emission and long fluorescent lifetime have potential applications as super-broadband optical amplification media.

高硅氧发光玻璃的制备及其荧光性能

abstract {Silica glass is an attractive host matrix for the emission ions of rare earth and transition metal ions because it has small thermal expansion coefficient, strong thermal resistance, large fracture strength and good chemical durability and so on. However, a major obstacle to using it as the host matrix is a phenomenon of concentration quenching. In this paper, we introduces a novel method to restrain the concentration quenching by using a porous glass with SiO₂ content > 95% (in mass) and prepare intense fluorescence high-SiO₂ glasses and high-SiO₂ laser glass. The porous glass with high-SiO₂ content was impregnated with rare-earth and transition metal ions, and consequently sintered into a compact non-porous glass in reduction or oxidization atmospheres. Various intense fluorescence glasses with high emission yields, a vacuum ultraviolet-excited intensely luminescent glass, high silica glass containing high concentration of Er³⁺ ion, ultrabroad infrared luminescent Bi-doped high silica glass and Nd³⁺-doped silica microchip laser glass were obtained by this method. The porous glass is also favorable for co-impregnating multi-active-ions. It can bring effective energy transferring between various active ions in the glass and increases luminescent intensity and extend range of excitation spectrum. The luminescent active ions-doped high-SiO₂ glasses are potential host materials for high power solid-state lasers and new transparent fluorescence materials.}

Fluorescence properties and laser demonstrations of Nd-doped high silica glasses prepared by sintering nanoporous glass

Porous glass with high-SiO2 content was impregnated with Nd ions, and subsequently sintered at 1100 degrees C into a compact non-porous glass in air or reducing atmosphere. Sintering in a reducing atmosphere produced an intense violet-blue fluorescence at 394 nm. However, the sintering atmospheres almost did not affect the fluorescence properties in the infrared range. A good performance Nd3+-doped silica microchip laser operating at 1064 nm was demonstrated. The Nd-doped sintering glasses with high-SiO2 content are potential host materials for high power solid-state lasers and new transparent fluorescence materials. (c) 2007 Elsevier B.V. All rights reserved.

不同退火气氛下γ-LiAlO2形貌和结构研究

研究了温度梯度法生长的γ-LiAlO2晶体在1100℃下富Li气氛和空气中退火处理后的表面形貌、表面结构以及吸收光谱。发现γ-LiAlO2晶体的抛光面在1100℃空气中退火后变为粗糙面，X射线衍射(XRD)分析表明此粗糙面为单相的LiAl5O8。而γ-LiAlO2晶体的抛光面在1100℃富Li气氛中处理后几乎没有变化。同时对不同气氛下热处理的γ-LiAlO2晶体进行了光谱分析，确认了晶片中196nm的吸收峰是由Li空位引起的。

Characteristics and optical spectra of V : YAG crystal grown in reducing atmosphere

A V:YAG single crystal was grown by the temperature gradient technique (TGT) with graphite-heating elements. The as-grown crystal has different colorations of light green and yellow brown in different parts. Distribution of vanadium in three samples with different colorations was determined by inductively coupled plasma-mass spectrometry. From the absorption spectrum of the yellow-brown part with peaks at 370, 820 and 1320nm, we can deduce that the reducing atmosphere of carbon diffused from the heating elements can increase the concentration of tetrahedral V3+ ions and induce F color centers. All three samples exhibited light-green color after annealing in vacuum or H-2 atmospheres. In the vacuum annealing process, the V3+ ions in tetrahedral positions were enhanced through two methods: one method is the exchanging of octahedral V3+ and tetrahedral Al3+ ions in neighboring sites under thermal excitation, the other is that F color centers were thoroughly eliminated and the escaped free electrons could be captured by V ions with higher valance states to further improve the concentration of tetrahedral V3+ ions. Besides the two mechanisms, the H-2 annealing process greatly improved the V-tetra(3+) ions through the reduction effect of H-2. (c) 2006 Elsevier B.V. All rights reserved.

Cr4+在八面体格位中的光谱特性研究

Cr-doped and Mg, Cr-codoped Al2O3 crystals were grown by Czochralski method. The latter has a broad absorption peak in 900-1600nm region. We investigated the change of the absorption band with annealing under different atmospheres or temperatures. Through establishing a structure defect model, we successfully interpreted all the experiment results and confirmed that the extremely broad infrared absorption band belonged to Cr4+, which should occupy the octahedral sites in Al2O3.

提拉法Ti:LiAlO_2晶体的生长、缺陷及N_2退火研究

本文采用提拉法成功地生长了钛掺杂浓度为0.1%原子分数的LiAlO2单晶体,借助光学显微镜,结合化学腐蚀法,对Ti:LiAlO2晶体(100)面空气退火前后的缺陷特征进行了研究,用AFM观测了(100)面晶片在不同温度下流动N2气氛退火过的表面形貌。结果表明:Ti:LiAlO2晶体(100)面的位错腐蚀坑是底面为平行四边形的锥形坑,位错密度约为5.0×104cm-2,900℃空气退火后晶片表面的位错腐蚀坑变大;N2退火能显著影响晶片的表面形貌,当退火温度为900℃时,晶片的均方根粗糙度(RMS)达到最低值

射频磁控溅射法制备TiO2-xNX薄膜的结构性能研究

利用射频磁控溅射法室温下在Si（100）衬底上制备了N掺杂的TiO2薄膜，并且采用x射线衍射（XRD）、X射线光电子能谱（XPS）和透射光谱对薄膜进行了表征。XRD结果表明在纯Ar和N2（33．3％）／Ar气氛下制备的TiO2-xNx薄膜均为单一的金红石相，薄膜结晶性良好，呈高度（211）择优取向，而在N2（50．0％）／Ar下制备的薄膜结晶性明显变差；对于N掺杂的TiO2薄膜，XPS表明部分N原子进入TiO2晶格，并且以N—Ti—O、N—O键以及间隙式N原子形式存在；透射光谱表明掺N后的TiO2薄膜吸收边发生了红移。

非晶硅薄膜制备及其晶化特性研究

用磁控溅射法在K9玻璃上沉积了非晶硅（a—Si）膜和a—Si／Al膜，并将其在流动的N2气氛下进行退火。对退火前后的样品进行Raman光谱、XRD和SEM表征和分析。Raman光谱表明随着退火温度的升高，a-Si膜的散射峰出现了明显的蓝移，但XRD结果表明薄膜仍为非晶态；而a—Si／Al膜在温度很低时就已经开始晶化。

基底微缺陷对介质薄膜光学性能影响的理论研究

基于非均匀膜理论提出一种存在微缺陷的介质基底的折射率分层模型，将基底依次分为表面层、亚表面层和体材料层，其中表面层和亚面层分别等效为折射率服从统计分布的非均匀膜，将它们分别再次细分为N1和N2个子层，每一子层均视为均匀介质膜．应用光学薄膜特征矩阵法对其进行理论分析，并对单层介质膜的光学性能进行数值计算．研究结果表明：基底的表面和亚表面微缺陷改变了薄膜和基底的等效折射率，导致了准Brewster角和组合反射率与理想情形的偏离．同时这些微缺陷也改变了光在薄膜和基底中的传播特性，因此反射相移和相位差均偏离理想情