Dielectric modeling of transmittance spectra of thin ZnO:Al films

A dielectric model comprising band gap transitions and free electron excitations (Drude model) is successfully applied to simulate transmittance spectra of ZnO films doped with 0.5%, 1% and 2% Al. The Drude formula contains a frequency-dependent damping term in order to get a good fit in the visible spectral region. Useful physical parameters obtained from the fit are electron density and mobility within the grains, film thickness, band gap and refractive index. The optically determined film thickness agrees with that obtained with the stylus method within 2%. The optically determined electronic parameters are compared with those obtained by electrical measurements. Contrary to thin In₂O₃:Sn films, the Drude mobility inside the grains is similar to the direct current Hall mobility indicating more perfect film growth without forming pronounced grain boundaries. Maximum value is 35 cm²/V s. The effective electron mass is estimated to be about 0.6 of the free electron mass. The refractive index at 550 nm decreases with increasing electron density.     

Chladnis Beiträge zur Raumakustik

A lot of publications on the acoustics of theatres and churches were published around the turn of the 18th to the 19th century.The authors were architects who were interested in acoustical problems. Chladni was the first physicist who published on the acoustics of rooms, he introduced the term “reverberation” into this field. His publications on this subject are reviewed. They have been the basis for the great progress of room acoustics since 1900.

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Zum 250. Geburtstag des Gelehrten     

Conditions of Liquid Steel Treatment for Near Net‐Shape Casting Processes

Slab casting for hot rolled steel and strip casting using the twin roll casting (TRC) method are compared in terms of inclusions evolution. There are differences of the processes, mainly the use of casting flux in CC of slabs, or pool shapes and sizes in terms of TRC, particularly when roll diameters vary. The inclusion evolution of alumina in a low carbon steel grade was estimated. By modelling particle growth rate, coagulation and deposition, an ‘agglomeration index’ was created to describe the probability of clogging in the SEN. Similarly the growth of secondary alumina precipitation during cooling of the melt in the pool by Stokes collision and turbulent collision was estimated in terms of forming large particles which are able to float‐up. Influences of melt superheat or caster size were taken into account.     

Modern Teaching and Training in Metallurgical Engineering

This contribution deals with advanced educational technologies needed to equip customers from higher education institutions, research and industry with efficient tools supporting their work and operating new skills‐training methods. The challenges are reducing the training costs, improving quality and increasing the number of graduates in engineering departments. The concept of a Virtual Lab based on the combination of various teaching methods and tools is presented. Principles of mathematisation in metallurgical education and training are discussed. An example of online course designed in the form of Virtual Lab is demonstrated.     

Influence of Threshold Stress on the Estimation of the Weibull Statistics

The influence of threshold stress on the estimation of the Weibull statistics is discussed in terms of the Akaike information criterion. Numerical simulations show that, if sample data are limited in number and threshold stress is not too large, the two-parameter Weibull distribution is still a preferred choice. For example, the fit of strength data of glass and ceramics to the two- and three-parameter Weibull distributions is compared.     

Harvesting Wiki Consensus: Using Wikipedia Entries as Vocabulary for Knowledge Management

Vocabularies that provide unique identifiers for conceptual elements of a domain can improve precision and recall in knowledge-management applications. Although creating and maintaining such vocabularies is generally hard, wiki users easily manage to develop comprehensive, informal definitions of terms, each one identified by a URI. Here, the authors show that the URIs of Wikipedia entries are reliable identifiers for conceptual entities. They also demonstrate how Wikipedia entries can be used for annotating Web resources and knowledge assets and give precise estimates of the amount of Wikipedia URIs in terms of the popular Proton ontology's top-level concepts.