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.     

The RADURA-terminology and food irradiation

The meaning of the international RADURA-logo and the terminology behind it is not clearly understood, the historical background of the RADURA-idea is no longer present in the actual interpretation by many people in the field of food irradiation. The history of this terminology is narrated here, in order that this heritage is not lost by time passing.     

Influence of the use of rice husk ash on the electrical resistivity of concrete: A technical and economic feasibility study

This study investigated the behavior of apparent electrical resistivity of concrete mixes with the addition of rice husk ash using Wenner’s four electrode method. Tests included compressive strength, porosity and electrical conductivity of the pore solution. The contents of rice husk ash tested were 10%, 20% and 30% and results were compared with a reference mix with 100% Portland cement and two other binary mixes with 35% fly ash and 50% blast furnace slag. Higher contents of rice husk ash resulted in higher electrical resistivity, which exceeded those of all other samples. However, for compressive strength levels between 40 MPa and 70 MPa, the mix with 50% blast furnace slag showed the best combination of cost and performance.     

Experimental investigation of parameters influencing the freeze start ability of a fuel cell system

To improve the freeze start ability of a fuel cell system some significant influencing parameters are defined and investigated. Experiments with a fuel cell test system are carried out in a climate chamber at various conditions. The time interval until fuel cell stack power equals 50% of its maximum power is defined as an indicator for a successful freeze start as well as a value for comparison and evaluation of the results. The target of this work is the minimization of this freeze start time by avoiding the freezing of process water on the catalyst layer of the Membrane Electrode Assembly (MEA), since this leads to temporary performance losses.The shut down strategy of the fuel cell system is identified to be one of the main parameters influencing the freeze start. It is found that a higher degree of dryness in the stack leads to a significant improvement in the freeze start performance, since the water absorbing capacity of the membrane increases and therefore also the time until its saturation. If this saturation takes place after the temperature of the MEA reached 0 °C, no significant ice-formation occurs. It is shown that by improving the shut down strategy of the fuel cell system at T_Start = −6 °C a start without performance loss can be realized. At temperatures lower than that temporary performance losses occur.Even if a lower voltage leads to a higher current and therefore to a higher water production rate, its effect on the freeze start due to the increased heat of reaction is positive. Further investigated parameters, for example the volume of the coolant loop, also affect the freeze start ability, but it can be concluded that the shut down strategy is of main importance.     

Efficient polymer solar cell modules

Polymer solar cell modules based on the standard polymer–fullerene system of to-date, P3HT–PCBM, have been prepared and characterized. We have observed a loss of only 20% when up-scaling the active area of the solar cell by a factor somewhat larger than 10. An average solar cell efficiency of 3% and a module efficiency of 1.9% for three serially interconnected solar cells of 5.4 cm² each are reported. The route for further optimization of module performance is discussed based on analyzing the existing loss factors within this design.     

Plasmaspiegel und scheinbare Verdaulichkeit von α-Tocopherol in Abhängigkeit von der Vitamin-E-Versorgung bei frühentwöhnten Ferkeln

Plasma Levels and Apparent Digestibility of α-Tocopherol as Related to Vitamin E Supplementation in Early-Weaned Piglets Piglets weaned at 21 d of age were fed a complete ration containing 16 I.U. vitamin E/kg (treatment I) according to NRC (1988) or supplemented with 45 mg or 225 mg α-tocopheryl acetate/kg (treatments II and III). Concentrations of α-tocopherol (AT) in plasma were measured until day 14. In weeks 5 and 7, the apparent digestibility of AT, total lipids and organic matter was analysed using chromic oxide as a marker. In treatment I, plasma AT concentration decreased with a mean half-life of 11.4 d. In week 5, the apparent digestibility of AT was 17.3%, 23.6% and 17.1% in treatments I to III, respectively. In week 7, it was unchanged in treatment I, while it was significantly higher (p<0.05) in treatments II and III (46.6% and 55.4%). No age-dependent differences were found in the apparent digestibility of total lipids and organic matter.     

Untersuchung des einflusses molekularer parameter auf morphologie und eigenschaften von polyethylenen niedriger dichte

Based on the example of PE-LD grades and on model substances obtained by preparative fractionation (fractions in the molecular weight range M?_w = 1.2 ? 390·10⁴ g/mol), comprehensive investigations regarding the problems of structure/properties have been carried out. The correlations of M?_w with 15 physical and application technological perameters have been investigated taking into account the reaction mechanism during the manufacturing of PE-LD in the tubular and agitated autoclave reactor, resulting in the formation of so-called primary structure perameters M?_n, M?_w, molar mass distribution, short chain branching and long chain branching. For the interpretation of the results, among other factors, also the morphological conditions have been taken into consideration, which in connection with the molecular parameters reveal — for specific M?_w-ranges — strong changes and saturation ranges, resp., for the physical and application technological properties.