Rechnerische Bestimmung der lonenbeweglichkeit in Ziegelstein unter Zuhilfenahme von Ergebnissen aus nichtstationären Diffusionsversuchen

Ion concentration profiles in sandwich-brick specimens have been determined experimentally at different degrees of water saturation. Based on the experimental data, ion diffusion coefficients were determined by inverse analysis. The diffusion equation served as a basis for an optimization technique. It has been shown that the ion diffusivity in bricks decreases markedly as the moisture content decreases. The interface between two adjacent bricks slows down the ion migration at low water content in particular. It is planed to investigate the interface between mortar and bricks in further experimental and numerical studie

Expansion behaviour of (Gd, Pr)-substituted CeO2_{2} in dependence on temperature and oxygen partial pressure

Substituted ceria is a material which has attracted great interest in solid oxide fuel cell technology [45]. Due to its chemical stability, it may also be a promising candidate as a mixed conductive membrane for oxygen separation with flue gas contact. As part of this paper, dilatometry measurements and X-ray powder diffraction experiments were carried out on ceramic materials in air and in argon with two separate series involving the substitution of ceria; cerium was substituted with different amounts of Gd and Pr. The first substitution of Gd caused an increase of the unit cell with a small rise in linear thermal expansion in relation to pure ceria. CeO2 − δ and Ce0.8Gd0.2O2 − δ showed no chemical expansion in both atmospheres. The second substitution of Gd with Pr decreased the unit cell in relation to pure ceria. It is therefore understandable that Pr is preferentially introduced and shown in this work as Pr4 + in ceria. These samples showed a remarkable chemical expansion in air and in argon. The chemical expansion displayed a clear positive correlation with increasing Pr content. The thermal expansion coefficients are comparable to the first substitution without any trend in relation to the amount of Pr. The dilatometry behaviour above 400 °C can be explained due to the release of oxygen and simultaneous reduction of Pr4 +, forming Pr3 + and oxygen vacancies. The results are in accordance with the two competing processes of forming vacancies (lattice contraction) and ionic radius change (lattice expansion) [16] and [27]. After cooling in air, the samples showed no residual expansion. In contrast, these samples displayed a remarkable residual expansion in argon of about 0.87% of the total relative expansion of 1.85% for Ce0.8Pr0.2O2 −

Articular cartilage repair by genetically modified bone marrow aspirate in sheep

Bone marrow presents an attractive option for the treatment of articular cartilage defects as it is readily accessible, it contains mesenchymal progenitor cells that can undergo chondrogenic differentiation and, once coagulated, it provides a natural scaffold that contains the cells within the defect. This study was performed to test whether an abbreviated ex vivo protocol using vector-laden, coagulated bone marrow aspirates for gene delivery to cartilage defects may be feasible for clinical application. Ovine autologous bone marrow was transduced with adenoviral vectors containing cDNA for green fluorescent protein or transforming growth factor (TGF)-beta1. The marrow was allowed to clot forming a gene plug and implanted into partial-thickness defects created on the medial condyle. At 6 months, the quality of articular cartilage repair was evaluated using histological, biochemical and biomechanical parameters. Assessment of repair showed that the groups treated with constructs transplantation contained more cartilage-like tissue than untreated controls. Improved cartilage repair was observed in groups treated with unmodified bone marrow plugs and Ad.TGF-beta1-transduced plugs, but the repaired tissue from TGF-treated defects showed significantly higher amounts of collagen II (P<0.001). The results confirmed that the proposed method is fairly straightforward technique for application in clinical settings. Genetically modified bone marrow clots are sufficient to facilitate articular cartilage repair of partial-thickness defects in vivo. Further studies should focus on selection of transgene combinations that promote more natural healing