An optimization procedure for stress concentrations by the finite element technique

Load-free notch surfaces of bodies made of a linear-elastic, homogeneous, isotropic material are optimized within given variation domains by means of an interation procedure so that the occurring maximum tangéntial stress is reduced to a minimum. The hypothesis of a constant tangential stress distribution for obtaining minimal notch stresses proposed by R. V. Baud has been confirmed by means of the Fade-away Law of the notch stress theory. The finite element method is applied for calculating the displacement and stress field of the styructure. An increment procedure is used for determing the displacement field after every iteration step, which permits the calculation of the displacement quantities with sufficient accuracy in a single step. Numerical solutions and their comparison with analytical solutions and stress results obtained with the aid of photo-elasticity confirm the usefulness of this procedure. The known optimization methods^1,2 differ from those used in the present paper.     

Modeling methods for a flexible computer-aided embodiment design system

The investigation and implementation of product modeling methods are two of the most important research objectives in the field of computer-aided engineering design. Commercial product modeling systems go beyond geometric modeling systems in that they are adapted to user requirements through the addition of systems that aid in the generation of engineering models and methods. The embodiment design of a mechanical energy storage system serves as an example of future continuous and flexible computer-aided design (CAD). This example is implemented with GEKO, a user system for the layout of design elements. GEKO is coupled with a commercial geometric modeler (CATIA) and uses several programming interfaces.     

Combination of Surface Charge and Size Controls the Cellular Uptake of Functionalized Graphene Sheets

A fundamental issue for biomedical applications of graphene is the correlation between its physicochemical properties and cellular uptake mechanism. However, such studies are challenging due to the intrinsic polydispersity of graphene. In this work, a series of water soluble graphene sheets with the same polymer coverage, density of functional groups, and fluorescence intensity but three different sizes and surface charges are produced. The effect of the latter two factors and their combination on the mechanism of cellular uptake and intracellular pathways of these defined nanosheets is investigated via confocal and Raman microscopies. While positively (? NH₃⁺) and negatively (? OSO₃^?) charged sheets show an energy dependent uptake, their neutral analogs do not show any significant uptake. The cellular uptake efficacy of positively charged graphene sheets is independent of the size and occurs both through phagocytosis and clathrin‐mediated endocytosis pathways. However, cellular uptake efficacy of graphene sheets with negative surface charge strongly depends on the size of the sheets. They cross the membrane mainly through phagocytosis and sulfate‐receptor‐mediated endocytosis. This study demonstrates that the impact of the size of graphene derivatives on their cellular uptake pathways highly depends on their surface charges and vice versa.     

Kombinierte Herkunftsbestimmung der Wässer im Jökulsáá Fjöllum-Canyon (NE-Island)

The northeastern region of Iceland is characterized by dreary stony deserts and marshland with the exception of the areas Hólmatungur and Forvö in the Jökulsáá Fjöllum-canyon. The rich vegetation and the high density of springs are exceptional in this region. Since many fissure swarms run through the catchment of the Jökulsáá Fjöllum and inside the canyon there are springs with discharges over 300 l/s, it was necessary to investigate the origin of the water in both spring areas. In a field campaign the physicochemical parameters from over hundred springs were measured, samples were taken and analyzed for their water contents and isotopical parameters. Through the combination of interpolated species distibutions with measured fissures and joints and the usage of the index-species sulphate and total-boron to detect geothermal influences and chloride and δ ¹⁸ O, which shows a dependence on the continental effect, it was possible to separate springs with geothermal influences from water of uninfluenced catchments.     

Experimental investigations for mechanical joint strength following ultrasonically welded pin osteosynthesis

The purpose of this study was to determine whether fixation of cranial bone segments using ultrasonically welded pin osteosynthesis showed differences in mechanical stability as compared to fixation of cranial bone segments using screw osteosynthesis. Right and left cranial bone segments from each of 16 young sheep were obtained by craniotomy and re-fixed: on the right with a mesh plate and pins, and on the left with a mesh plate and screws. All osteosynthesis materials consisted of PDLLA, fully amorphous polyactid. A total of 167 cranial bone / mesh plate segments from 16 animals were investigated; 84 segments were pin-fixed and 83 segments were screw-fixed. The implantation time of the re-fixed segments ranged from 1 day to 196 days. The mechanical methods chosen for simulation of stress on the bone segment bonds were two bending tests (horizontal and vertical directions) and a tensile test. The values obtained in the mechanical tests indicate differences in the bond strength between the pin- and screw- fixation methods over the length of in vivo implantation time. The mechanical stability of the ultrasonically welded pin osteosynthesis bonds over the screw osteosynthesis bonds proved to be statistically significant. The implication of these findings should also be relevant in the field of medicine.     

1D nanofabrication with a micrometer-sized laser spot

A simple laser-assisted procedure for the fabrication of functional organic nanostructures is demonstrated. Native silicon samples are coated with alkylsiloxane monolayers and patterned with a focused beam of an Ar(+) laser (lambda = 514 nm). After patterning, the coating is chemically functionalized following a robust preparation scheme. Despite a laser spot diameter of about 2.5 mum, this routine allows for the fabrication of well-confined organosiloxane stripes with widths below 100 nm. As shown, these structures provide a versatile means for building ordered surface architectures of nanoscopic components. In particular, gold nanoparticles (d = 16 nm) self-assemble into one-dimensional arrangements, such as single chains.