Development of an observation and control system for industrial laser cladding

Laser cladding has become an important surface modification technique in today’s industry. It is not only applied\ud for coating new products but also for repair and refurbishment as well as in rapid prototyping.\ud A laser clad workstation has been developed. It uses a 4 kW Nd:YAG fibre coupled laser as heat source. A\ud specially developed optical system combines the benefits from a Top-hat energy distribution with a practical\ud working distance. The clad material is supplied to the melt pool by a lateral powder nozzle.\ud A camera based monitoring system for the laser cladding process has been developed. This system determines\ud the main dimensions of the melt pool in real-time.\ud A developed FEM model of the laser cladding process accurately predicts the shape and temperature of the clad\ud layers by including the interaction between the laser beam and the powder jet. The model results are in good\ud correspondence with experimental results.\ud An extensive set of cladding experiments has been performed with variable spot size, laser power, cladding\ud speed and powder mass rate. From the experimental work, a clear correlation between the dilution and the width\ud of the melt pool was found. This correlation was found to be independent of the substrate temperature, enabling\ud real time control of the dilution by adjusting the laser power.\ud A feedback control strategy was developed and implemented based on the melt pool width information from the\ud camera. As a result, the energy input into the substrate and consequently thermal distortion of the products is\ud minimized, while a good metallurgical bonding and minimal dilution are obtained. Due to this minimal dilution,\ud the hardness of the clad layer can be controlled and maintained to be uniform.\ud High temperature gradients and different material properties may cause high residual stresses or even cracks. To\ud investigate this effect, a simple and fast method based on deflection measurements has been developed. The\ud residual stress values obtained by this procedure have been compared with stresses from X-ray measurements.\ud The results show tensile stresses of large magnitude develop in the layer, which increase with the cladding speed

Innovation and institutional change : the transition to a sustainable electricity system

The aim of this book is to specify this perspective by analysing patterns of change in the electricity system. Scientifically, the relevance of the book is in its analysis and explanation of fundamental processes of change, a topic relevant for a range of scientific disciplines, from economics, sociology, technology studies, to policy science. Its societal relevance lies mainly in its use for gaining insight in the way systems change can be directed towards the normative goal of sustainable development

Mitigating the Impact of Natural Disasters on Public Finance

Naturkatastrophe; Öffentliche Finanzwirtschaft; Versicherungstechnisches Risiko; Securitization; Rückversicherung

Marketable yield quantity and quality of leek and residual soil mineral nitrogen in relation to nitrogen fertilization

In Flanders threshold values of soil mineral nitrogen (Nmin) in the soil profile (0-90 cm) in autumn are used in legislation to judge fertilization practices and evaluate the nitrate (NO3-) leaching risk during winter. The average Nmin measured in leek fields are high compared to most arable crops. The objective of this study was to investigate if high Nmin values at harvest can be decreased without reducing yield quantity and quality. We re-analyzed Flemish leek field experiments with various nitrogen (N) fertilizer application rates (2001-2016). We examined marketable yield quantity and quality and residual soil mineral N (RSMN) to rooting depth (0-60 cm) at harvest from July till April the next year. Considering the N supply (= applied effective N + Nmin (0-60 cm) at planting), the marketable yield was on average higher in July till December than in January till April. The maximum marketable yield was obtained at ≈150-200 kg N supply ha‑1. Generally RSMN values measured in July till December were higher than those in January till April. This can be explained by higher N mineralization rates in the first case and possibly some NO3- leaching in the latter case. There was no significant difference in scores of abrasion hardness nor leaf color or uniformity at ≈150-200 kg N supply ha‑1 compared to higher N supplies. Taking into account a mean Nmin value (0-60 cm) at planting of 69±45 kg N ha‑1 (average±standard deviation), effective N application rates in the order of 80-130 kg N ha‑1 are maximum, which allows Nmin values below 50 and 70 kg N ha‑1 in the 0-60 cm and 0-90 cm layer, respectively. These results indicate that N fertilization advices of leek can be reduced without risking a decreased marketable yield quantity and quality but minimizing NO3- leaching during winter

Tightening the Complexity of Equivalence Problems for Commutative Grammars

We show that the language equivalence problem for regular and context-free commutative grammars is coNEXP-complete. In addition, our lower bound immediately yields further coNEXP-completeness results for equivalence problems for communication-free Petri nets and reversal-bounded counter automata. Moreover, we improve both lower and upper bounds for language equivalence for exponent-sensitive commutative grammars.Comment: 21 page

The protection of alloys against high temperature sulphidation by SiO2-coatings deposited by MOCVD

Silica coatings have been deposited on various alloys by MOCVD (Metal Organic Chemical Vapor Deposition) to protect them against high temperature corrosion in coal gasification environments. DiAcetoxyDitertiaryButoxySilane (DADBS) has been used as a metal organic precursor at deposition temperatures between 773 - 873 °K and amorphous layers were produced with a growth rate of about 1 μm. h-1. These coatings have been tested at 823°K in a sulphiclizing atmosphere with a low oxygen (9.3 10 -29 bar) and a high sulphur partial pressure (1.2 10 bar). In this environment the sulphidation resistance of various alloys has improved by a factor of at least 100 by the coating. The observed corrosion reaction is local and is explained by a model in which in the first stage cracks are formed due to mechanical stresses in the coating. In the second stage metal sulphides are formed by outward diffusion of metal and inward diffusion of sulphur through the cracks. When stainless steels are used as the alloy the outer layer consists of FeS and the lower one of CrS