Study of MHD boundary layer flow over a heated stretching sheet with variable viscosity: A numerical reinvestigation

This work is a critique to a paper published in the International Journal of Heat and Mass Transfer 48 (2005) 4460–4466, which concerns the boundary layer flow of an electrically conducting incompressible fluid over a heated stretching sheet. The flow is permeated by a uniform transverse magnetic field and the fluid viscosity is assumed to vary as a linear function of temperature. In the published paper the calculation domain was small and the temperature profiles are truncated. Although the dynamic viscosity has been considered a function of temperature and consequently variable inside the boundary layer the Prandtl number, which depends on viscosity, has been considered constant inside the boundary layer. The results of the present work are obtained with the direct numerical solution of the boundary layer equations taking into account both viscosity and Prandtl number variation across the boundary layer. The temperature profiles of the present work are quite different from those of the above work.     

Structural and rheological investigation of low density polyethylenes

Some low density polyethylenes (LDPE) with different melt flow index (MFI) or produced by different producers have been examined in detail by solvent gradient fractionation, ¹³C NMR analysis, FTIR spectroscopy and melt rheological measurements. It was found that the distribution curves of the samples resemble Wesslau's logarithmic-normal model. From branching analyses it can be concluded that the branching content in the analyzed LDPEs is independent from the molecular weight. Relations between viscosity curve parameters and molecular structure have been investigated. It has been found that the dependence of the first normal stress difference on the shear stress is influenced by polydispersity as well as by the character of samples branching.     

Einheit von Wissenschaft und Kunst im Brückenbau: Hellmut Homberg (1909–1990) – Leben und Wirken (Teil I)

Am 5. September 2009 wäre Hellmut Homberg einhundert Jahre alt geworden. Dies ist Anlass, an sein vor allem den Brückenbau bereicherndes Wirken zu erinnern und ein, wenn auch nicht vollständiges, Werkverzeichnis zu erstellen. Das gilt sowohl für die unter seiner maßgebenden Mitwirkung entworfenen Brücken als auch für seine völlig neuartigen, die statischen Berechnungen in der Praxis erleichternden, streng theoretisch hergeleiteten und eine zutreffende Bemessung der Kreuzwerke und orthotropen Fahrbahnplatten ermöglichenden Tafel‐ und Tabellenwerke. Teil I schildert Homberg s beruflichen Weg und versucht, ein Porträt zu zeichnen; Teil II ist seinen theoretischen Untersuchungen gewidmet, und Teil III geht auf besondere Brücken ein, und. Harmony between science and art in bridge‐building: Hellmut Homberg (1909–90) – life and work (part I). Hellmut Homberg would have been 100 years old on 5 September 2009. This is an opportunity to look back on his work which so enriched the world of bridge‐building in particular, and also a chance to compile a catalogue of his work, albeit incomplete. This applies to the bridges in which he played an influential role in their design and also to his books of mathematical and design tables that enabled the accurate design of beam grids and orthotropic bridge decks. The tables with their rigorous theoretical background were at the time quite new and eased structural calculations in everyday practice. Part I describes Homberg's professional career and attempts to draw a portrait of the man; part II is devoted to his theoretical studies, and part III deals with particular bridges.     

Comment on microsystem= technologies,= https:= doi.org= 10.1007= s00542-018-3895-1”=

Microsystem Technologies - Some errors exist in the above paper.     

Comment on the paper “Change in internal energy of thermal diffusion stagnation point Maxwell nanofluid flow along with solar radiation and thermal conductivity,Mair Khan,T. Salahuddin,A. Tanveer,M.Y. Malik,Arif Hussain,Chinese Journal of Chemical Engineering,doi:10.1016/j. cjche.2018.12.023”

Some errors exist in the above paper.     

Periodic autoregressive model identification using genetic algorithms

Periodic autoregressive (PAR) models extend the classical autoregressive models by allowing the parameters to vary with seasons. Selecting PAR time‐series models can be computationally expensive, and the results are not always satisfactory. In this article, we propose a new automatic procedure to the model selection problem by using the genetic algorithm. The Bayesian information criterion is used as a tool to identify the order of the PAR model. The success of the proposed procedure is illustrated in a small simulation study, and an application with monthly data is presented.     

Characterization of the ozone zero phenomenon by infrared spectroscopy

The presence of a small amount of nitrogen in the feed gas is necessary to generate ozone efficiently out of oxygen. Operating an ozone generator with ultra-pure oxygen for extended periods results in highly deteriorated ozone generation efficiency. In extreme cases, when the nitrogen levels in the feed gas are in the lower ppm range, the efficiency of the ozone generation process even drops to zero. In this article, we present our results concerning the correlation between the N₂O₅ concentration in the off-gas and the ozone generation efficiency. After the ozone generator is run for a well-defined amount of time with an oxygen–nitrogen mixture, the N₂ supply is shut off, and the behavior of the system is monitored by near-infrared spectroscopy. Different surface materials lead to different temporal behavior of both the nitrogen oxide levels and the ozone concentration after shutting down the nitrogen supply. The measurements show a good correlation between the evolution of ozone generation efficiency and the changes of the N₂O₅ concentration in the off-gas.