Active control and a simple estimation method for the onset of Rayleigh-Bénard convection in temperature-dependent-viscosity liquids

Active feedback control for the onset of Rayleigh-Bénard Convection in temperature-dependent-viscosity liquids is investigated. In this paper, three major problems are addressed: (1) The results of Tang-Bau control are improved by considering the effects of temperature-dependent viscosity; (2) A more efficient two-plate control strategy is presented. A phenomenon of coalescence of the unstable modes is observed as the controller gain is large enough; (3) A simple way to estimate the critical Rayleigh number under the effects of temperature-dependent viscosity is described. Numerical results show that the effects of temperature-dependent viscosity on the critical Rayleigh number should be taken into account in some cases and the onset of Rayleigh-Bénard convection can be effectively delayed or advanced by the active feedback control strategies studied here.     

激光沉积超导薄膜过程中出射粒子速度的飞行时间谱分析

采用飞行时间谱技术,测量了准分子激光烧蚀沉积高温超导薄膜过程中,由靶面出射粒子的飞行速度。研究了粒子速度与充氧压及其激光能量密度的关系。讨论了高能粒子在薄膜原位低温外延生长中的作用。     

Transport efficiency in femtosecond laser ablation inductively coupled plasma mass spectrometry applying ablation cells with short and long washout times

Relative mass transport efficiencies of near infrared (λ = 795 nm) femtosecond laser generated brass aerosols in helium were measured by ICP-MS applying different ablation cells with short and long washout times. It was found that the transport efficiencies are independent of the cell used within the mutual experimental uncertainties. This finding was confirmed by additional measurements providing the absolute particle mass transport efficiencies of femtosecond laser ablation in He. Here, the transport efficiencies were determined by weighing the samples before and after ablation with a micro-balance, collecting the particles by low-pressure impaction, and evaluating the impacted masses quantitatively by total reflection X-ray fluorescence. Within the experimental uncertainties (± 9–19%) the same absolute transport efficiency (about 77%) was found for all cells applied. This efficiency value can be regarded as a lower limit of the absolute mass transport efficiency since mass losses in the impactor are difficult to quantify.     

气相[（SiO2）nX]^—团簇产生机理

利用ＸｅＣｌ准分子激光烧蚀多种硅氧多孔结构材料，在负离子通道测得丰富的「（ＳｉＯ２）ｎＸ」＾－负离子团簇，并讨论了多孔网结构和表面活性基团的分布对激光能量的吸收，传输及团簇产生的重要作用。     

Determination of long-lived radionuclides in concrete matrix by laser ablation inductively coupled plasma mass spectrometry

A laser ablation system using a Nd:YAG laser was coupled both to a quadrupole inductively coupled plasma (ICP) mass spectrometer and to a double-focusing sector field ICP mass spectrometer. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was applied for the determination of long-lived radionuclides in a concrete matrix. The investigated samples were two laboratory standards with a concrete matrix, which we doped with different long-lived radionuclides (e.g. ⁹⁹Tc, ²³²Th, ²³³U, ²³⁷Np) from the ng g⁻¹ to μ g⁻¹ concentration range and an undoped concrete material (blank). Detection limits for long-lived radionuclides in the 10 ng g⁻¹ range are reached for LA-ICP-MS using the quadrupole mass spectrometer. With double-focusing sector field ICP-MS, the limits of detection are in general one order of magnitude lower and reach the sub ng g⁻¹ range for ²³³U and ²³⁷Np. A comparison of mass spectrometric results with those of neutron activation analysis on undoped concrete sample indicates that a semiquantitative determination of the concentrations of the minor and trace elements in the concrete matrix is possible with LA-ICP-MS without using a standard reference material.     

Topical Problems in Elemental Analysis of Advanced Ceramic Materials

Selected prominent problems in the analysis of advanced ceramic materials are surveyed. The importance of reliability of results is discussed in the field of elemental trace- and microanalysis in view of its interaction with economy, power of detection, local resolution and speciation selectivity. Particular problems in the analysis of major constituents, trace components and microlocal distributions are based on the striking propertics of ceramics; they are exemplified. Analytical assistance must start from the beginning of the production processing, in the preparation of the powdered base materials. Determination of the stoichiometry requires high accuracy and differentiation of chemical species in bulk and surface analysis of ceramic base powders. Element trace determination by direct instrumental methods requires standard reference materials for calibration; these are currently inavailable in a sufficient variety. For optimum reliability and power of detection, element traces must be prepared in isolated form in a small excitation volume for analysis. A review on the state-of-the-art of wet-chemical combined procedures is presented. Decomposition position procedures are emphasized, due to their risk of contributing severe systematic error. Combustion in elementary fluorine is presented for decomposition of refractory materials. The performance of some direct procedures is discussed. Very efficient methods are available for element trace determinations in ceramic materials, offering high detection power. Several approaches for high-resolution local microanalysis in non-conductive ceramic materials are identified as the most promising development in the analysis of sintered compact ceramic products and devices.     

激光产生的钒硫簇离子的统计分布与结构探讨

以脉冲激光在高真空中溅射钒粉和硫粉的混合物，产生了一系列钒硫原子簇正负离子。根据对其实验记录的激光等离子体质谱进行分析，发现钒硫原子簇的化学键基本上是共价型的，对应于相同钒原子数目的正负离子的相对丰度分别符合于不同形式的对数正态分布。正离子的相对丰度随硫原子数的增加呈对数衰减，由此可以确定各种大小簇合物的簇骼与几何构型；负离子的相对丰度则基本上呈正常的正态分布，说明在簇骼上结合了不同数量硫原子的负离子之结构稳定性大致相近。在实验中还观察到一类硫原子含量较高的簇离子，其中的部分硫原子可能在本身成键形成环状的硫集团后，又与原来的簇骼结合，因而在硫原子数较多时它们的相对丰度符合另一条对数正态分布曲线。     

含氢碳原子团簇的初步研究

介绍直接用激光溅射芳香化合物固态样品产生的含氢磷原子团簇离子（C_nH~＋_m），并用飞行时间质谱仪研究了其组成和结构．实验发现，在低质量区（n＝32－56）得到了具有奇偶碳原子数的含氢磷原子簇，而在高质量区（n＞100）除了得到纯碳原子簇以外，还得到了含氢碳原子簇．根据对实验结果的分析提出了两种结构模型：对低质量区的团簇，其结构为芳香基团与富勒烯笼状框架的复合体；对高质量区的团簇，其结构为蜗牛形与圆柱形的复合体．     

Radiation exposure to operator and patients during cardiac electrophysiology study,radiofrequency catheter ablation and cardiac device implantation procedures

The purpose of this study was to measure the radiation exposure to operator and patient during cardiac electrophysiology study, radiofrequency catheter ablation and cardiac device implantation procedures and to calculate the allowable number of cases per year. We carried out 9 electrophysiology studies, 40 radiofrequency catheter ablation and 11 cardiac device implantation procedures. To measure occupational radiation dose and dose–area product (DAP), 13 photoluminescence glass dosimeters were placed at eyes (inside and outside lead glass), thyroids (inside and outside thyroid collar), chest (inside and outside lead apron), wrists, genital of the operator (inside lead apron), and 6 of photoluminescence glass dosimeters were placed at eyes, thyroids, chest and genital of the patient. Exposure time and DAP values were 11.7?±?11.8?min and 23.2?±?26.2?Gy?cm² for electrophysiology study; 36.5?±?42.1?min and 822.4?±?125.5?Gy?cm² for radiofrequency catheter ablation; 16.2?±?9.3?min and 27.8?±?16.5?Gy?cm² for cardiac device implantation procedure, prospectively. 4591 electrophysiology studies can be conducted within the occupational exposure limit for the eyes (150?mSv), and 658-electrophysiology studies with radiofrequency catheter ablation can be carried out within the occupational exposure limit for the hands (500?mSv). 1654 cardiac device implantation procedure can be conducted within the occupational exposure limit for the eyes (150?mSv). The amounts of the operator and patient's radiation exposure were comparatively small. So, electrophysiology study, radio frequency catheter ablation and cardiac device implantation procedures are safe when performed with modern equipment and optimized protective radiation protect equipment.     

How the Physicochemical Properties of the Bulk Material Affect the Ablation Crater Profile,Mass Balance,and Bubble Dynamics During Single-Pulse,Nanosecond Laser Ablation in Water

Understanding the key steps that drive the laser-based synthesis of colloids is a prerequisite for learning how to optimize the ablation process in terms of nanoparticle output and functional design of the nanomaterials. Even though many studies focus on cavitation bubble formation using single-pulse ablation conditions, the ablation efficiency and nanoparticle properties are typically investigated under prolonged ablation conditions with repetition rate lasers. Linking single-pulse and multiple-pulse ablation is difficult due to limitations induced by gas formation cross-effects, which occur on longer timescales and depend on the target materials’ oxidation-sensitivity. Therefore, this study investigates the ablation and cavitation bubble dynamics under nanosecond, single laser pulse conditions for six different bulk materials (Au, Ag, Cu, Fe, Ti, and Al). Also, the effective threshold fluences, ablation volumes, and penetration depths are quantified for these materials. The thermal and chemical properties of the corresponding bulk materials not only favor the formation of larger spot sizes but also lead to the highest molar ablation efficiencies for low melting materials such as aluminum. Furthermore, the concept of the cavitation bubble growth linked with the oxidation sensitivity of the ablated material is discussed. With this, evidence is provided that intensive chemical reactions occurring during the very early timescale of ablation are significantly enhanced by the bubble collapse.