3D-FE-Analysis of CT-specimens including viscoplastic material behavior and nonlocal damage

In order to describe the time-dependent inelastic behavior of steel structures up to failure, a material model is developed within the framework of thermodynamics considering viscoplastic material behavior, isotropic hardening, softening, and isotropic ductile damage. Since softening and damage lead to localization of deformations, the model is extended by a non-local implicit gradient formulation. An additional gradient equation is formulated for the local damage variable in order to achieve results independent of the finite-element discretization. The approach is verified by 3D-structural analysis of CT-specimens.     

采用新型焊接电弧提高焊接生产的经济效益和焊缝质量

通过在传统的短路过渡电弧和射流过渡电弧的基础上进行创新,发展新型的焊接电弧,可以显著地提高电弧焊接在金属连接中的优越性。两种新的焊接电弧,forceArc~杂志焊接电弧和coldArc~焊接电弧可以在一个焊接电源上实现,对焊接生产具有现实意义。了解和掌握这些新型电弧的工艺特点,可以有效地将其应用到生产中,以此提高焊接产品的质量和焊接生产的经济效益。新型焊接电弧的出现使现有的有关焊前焊接接头准备的标准和规定,特别是有关坡口角度和焊接位置,需要重新考虑。新型焊接电弧可以应用于各种金属加工工业中的焊接生产,是对弧焊工艺的一个创新。     

Association between palladium urinary concentrations and diseases of the thyroid and the immune system

The German Environmental Specimen Bank found that students suffering from diseases of the thyroid or the immune system had increased palladium urinary values compared to healthy individuals. Since the immunotoxic features of palladium are well known, there may be a causal relationship. Sources of palladium were identified as dental alloys, the chemical industry, oil- or coal-driven power plants and the consumption of meat products.     

Dislocation processes in the deformation of nanocrystalline aluminium by molecular-dynamics simulation

The mechanical behaviour of nanocrystalline materials (that is, polycrystals with a grain size of less than 100 nm) remains controversial. Although it is commonly accepted that the intrinsic deformation behaviour of these materials arises from the interplay between dislocation and grain-boundary processes, little is known about the specific deformation mechanisms. Here we use large-scale molecular-dynamics simulations to elucidate this intricate interplay during room-temperature plastic deformation of model nanocrystalline Al microstructures. We demonstrate that, in contrast to coarse-grained Al, mechanical twinning may play an important role in the deformation behaviour of nanocrystalline Al. Our results illustrate that this type of simulation has now advanced to a level where it provides a powerful new tool for elucidating and quantifying--in a degree of detail not possible experimentally--the atomic-level mechanisms controlling the complex dislocation and grain-boundary processes in heavily deformed materials with a submicrometre grain size.     

Remodeling of fibrinogen by endothelial cells in dependence on fibronectin matrix assembly. Effect of substratum wettability

The endothelization of cardiovascular implants is desirable to improve their blood compatibility. The capacity of the endothelial cells to attach, migrate, proliferate and function on the implant surface depends on the presence of matrix proteins such as fibronectin (FN) and fibrinogen (FNG). In this study, we show that the deposition of fibrinogen into extracellular matrix-like structures by human umbilical vein endothelial cells (HUVEC) is dependent on FN matrix formation. We found further that the process of organization of both adsorbed and soluble FN and FNG is dependent on the wettability of materials since it was observed only on a hydrophilic and not on a hydrophobic model surface. ₃ integrin was involved in the process of cell attachment to adsorbed FNG, while the mechanism of FNG fibrillogenesis required the activity of the ₁ integrin. Studies of EC morphology showed the predominant peripheral organization of actin filaments and the formation of distinct leading and trailing cell edges suggesting a motile phenotype of cells when they are seeded on FNG. In summary, we concluded that adsorbed fibrinogen may enhance the motility of HUVEC and that soluble FNG requires FN matrix assembly to be organized in fibrilar structures.     

Characterization of silica-based monoliths with bimodal pore size distribution

Band dispersion was studied and the retention thermodynamics addressed for insulin and angiotensin II on C18 silica monoliths with a bimodal pore size distribution, covering linear mobile-phase velocities up to 1 cm/s and different temperatures. These data suggest that the influence of average column pressure on retention (between 0 and 10 MPa) is not negligible. Plate height curves were interpreted with the van Deemter equation by assuming an independent contribution from mechanical and non-mechanical dispersion mechanisms. This analysis revealed diffusion-limited mass transfer in the mesoporous silica skeleton which, in turn, allowed us to calculate an equivalent dispersion particle diameter (d(disp) = 3 microm) using the C-term parameter of the van Deemter equation. The resulting superposition of reduced plate height curves for monolithic and particulate beds confirmed that this view presents an adequate analogy. The macroporous interskeleton network responsible for the hydraulic permeability of a monolith was translated to the interparticle pore space of particulate beds, and an equivalent permeability particle diameter (d(perm) = 15 microm) was obtained by scaling based on the Kozeny-Carman equation.