Machining of silica glasses using excimer laser radiation

Various silica glasses were engraved deliberately by excimer laser radiation using wavelengths of 308 and 248 nm. The ablation of different samples was investigated by systematic Variation of the processing parameters. The ablation rates were determined using profilometry and gravimetric measurements by evaluating the processing quaUty and the morphology of the processed surfaces was considered. The phenomenon of ablation is explained as a non-linear interaction of the laser beam and the glass. The experimental results show that the ablation behaviour of silica glass depends on the wavelength and the intensity of the laser radiation, on the surface quahty and the degree of purity of the glass. Although high ablation rates were obtained, the suitability of excimer lasers for micromachining is restricted due to the rough surface morphology and poorly defmed edges

Dimensional analysis of droplet size and ligament length during high-speed rotary bell atomization

Modern spray-coating processes are based on high-volume, low-pressure, airless atomization or high-speed rotary bell atomization, often assisted by electrostatic charging to increase the transfer efficiency. The process from the liquid film flow beneath the bell, through ligament formation and consecutive disintegration to droplet deposition, has been constantly explored during the evolution of automotive spray coating. This work proposes a set of dimensionless groups that fully describe the process from film flow to ligament disintegration, including shear and elongational flow effects during atomization of particle laden, shear thinning, viscoelastic fluids

Dimensional analysis of droplet size and ligament length during high-speed rotary bell atomization

Modern spray-coating processes are based on high-volume, low-pressure, airless atomization or high-speed rotary bell atomization, often assisted by electrostatic charging to increase the transfer efficiency. The process from the liquid film flow beneath the bell, through ligament formation and consecutive disintegration to droplet deposition, has been constantly explored during the evolution of automotive spray coating. This work proposes a set of dimensionless groups that fully describe the process from film flow to ligament disintegration, including shear and elongational flow effects during atomization of particle laden, shear thinning, viscoelastic fluids

Surface treatment of glass and ceramics using XeCI excimer laser radiation

A XeCl excimer laser with uniform beam profile and 308 nm wavelength was used for ablation and surface modification of technical glasses and ceramics.The ablation behaviour and the resulting surface morphology of the different materials were measured in dependence upon the energy density and the number of pulses. In contradiction to ceramics, glasses show a higher ablation threshold and considerable higher ablation rates. Due to the short wavelength of the excimer laser, microstructuring of glass and ceramic surfaces is possible. Examples are presented, like marking of glasses, microline structuring of float glass, as well as positive and negative microstructuring of ceramics

Visibly transparent & radiopaque inorganic organic composites from flame-made mixed-oxide fillers

Radiopaque composites have been produced from flame-made ytterbium/silica mixed oxide within a crosslinked methacrylate resin matrix. The refractive index of the filler powder increased with ytterbium oxide loading. A high transparency was achieved for a matching refractive index of the filler powder and the polymer in comparison to commercial materials with 52wt% ceramic filling. It was demonstrated that powder homogeneity with regard to particle morphology and distribution of the individual metal atoms is essential to obtain a highly transparent composite. In contrast, segregation of crystalline single-oxide phases drastically decreased the composite transparency despite similar specific surface areas, refractive indices and overall composition. The superior physical strength, transparency and radiopacity compared to composites made from conventional silica based-fillers makes the flame-made mixed-oxide fillers especially attractive for dental restoration material

The Shift-Share Regression: An Application to Regional Employment Development

This paper presents an outline of the so-called Shift-Share Regression and an application of this method to the analysis of employment development. The method used is not a deterministic decomposition such as the classical Shift-Share-Analysis, but a powerful, yet simple and flexible econometric tool to test theory-related hypotheses, which can be applied as a ?work-horse? in studies of many kinds. Classical deterministic Shift-Share-Analysis has often been criticised, since it does not permit a model-based analysis. The detection of causal effects is at least problematic and the inclusion of additional explanatory variables is possible only in special cases. A major problem is the nature of the method as a deterministic procedure which excludes significance tests. Shift-Share Regression is able to overcome all these critical points. In a basic version it was introduced by Patterson (1991) as a method for analysing and testing regional industrial developments. In contrary to the deterministic Shift-Share-Analysis employment development was examined in a linear model. In Patterson?s analysis the industrial sector structure was used as the sole determining factor alongside the location effects and the national trend. We extend this basic structure further: In our case, the effects of sectoral structures, establishment size, qualification structures and locational determinants on employment growth are studied. The regional units used are districts of Western Germany (?Landkreise? and ?kreisfreie Städte?), especially in the present context the districts of the federal State of Bavaria. The analysis is motivated by theoretical considerations of different sources. The most important one refers to theoretical analyses of structural change. According to a specific theorem, the employment effect of technological progress depends on the elasticity of product demand. If demand is inelastic the direct labour saving effect of technological progress is dominating and the effect is negative. Then it is profitable for a firm to reduce its labour force. If, however, demand is elastic a compensating effect dominates. In this case price decreases following higher productivity lead to an extension of product demand which (over-)com¬pensates the direct labour saving effect. Then, it is profitable for a firm to increase the size of its labour force. It can be assumed that in different industries of an economy different demand elasticities are dominating. Therefore, an empirical analysis of employment effects should focus on the industries of an economy. In the paper the sources of different regional employment development in Bavaria are presented, analysed by Shift-Share Regression

Analysis of Paint Flow Pulsations during High-Speed Rotary Bell Atomization

High-speed rotary bell atomization is the preeminent coating technique in the automotive industry. It is widely accepted that a narrow droplet size distribution and constant spray are necessary in order to guarantee uniform film thickness and high-quality appearance. This may be deteriorated by paint flow pulsations. So far, however, no studies exist regarding such fluctuations quantitatively for this type of atomizers. We fill this gap using image analysis of high-speed recordings close to the bell edge. We could show that the fundamental pulsation frequency increases linearly with rotational speed. A ratio of pulsation frequency and true rotational speed of about 3 was found, indicating that pulsations were initiated mainly by the three struts of the distributor disc. The coefficient of variation, i.e., the amplitude of fluctuation increased with decreasing liquid volume rate and rotational speed. Beyond that, we could show that the formation of droplets larger than 100 μm, which are assumed to cause paint defects, is promoted by the degree of fluctuation. These findings may stimulate development of bell cups showing less paint flow pulsations