Influence of texture and grain misorientation on the ionic conduction in multilayered solid electrolytes - interface strain effects in competition with blocking grain boundaries.

Interface strain and its influence on the ionic transport along hetero-interfaces has gained a lot of attention over the last decade and is controversially discussed. We investigate the relaxation of mismatch induced interfacial strain as a function of the degree of orientation/texture of the columnar crystallites and assess the impact on the oxygen ion conductivity in Er2O3/YSZ multilayer systems. Results from X-ray diffraction clearly show, that the width of the strained hetero-interface region increases with an increasing degree of orientation of the crystallites. The combined impact of film texture and strain at the hetero-interfaces of the film on the ionic conductivity however is not easily deduced from these measurements. The samples with the highest degree of orientation, i.e. with only one azimuthal variant, show strong anisotropic electrical properties. In samples with a lower degree of orientation, i.e. samples with a fiber texture, anisotropic properties cannot be detected, possibly due to a geometrical averaging of the electrical properties. The expected strain induced monotonic increase of the ionic conductivity with decreasing layer thickness and thus increasing interfacial influence could only be detected for samples with a fiber texture and a considerable degree of crystallite misorientation. This leads to the important conclusion that the texture and therefore the nature of the grain boundaries and their network influence the ionic conductivity of the multilayer thin films in the same order of magnitude as the misfit induced interface strain. Thus, the potential design of strain-controlled ionic conductors requires additionally the control of the microstructure in terms of grain orientation.

The alanine detector in BNCT dosimetry: dose response in thermal and epithermal neutron fields.

PURPOSE: The response of alanine solid state dosimeters to ionizing radiation strongly depends on particle type and energy. Due to nuclear interactions, neutron fields usually also consist of secondary particles such as photons and protons of diverse energies. Various experiments have been carried out in three different neutron beams to explore the alanine dose response behavior and to validate model predictions. Additionally, application in medical neutron fields for boron neutron capture therapy is discussed. METHODS: Alanine detectors have been irradiated in the thermal neutron field of the research reactor TRIGA Mainz, Germany, in five experimental conditions, generating different secondary particle spectra. Further irradiations have been made in the epithermal neutron beams at the research reactors FiR 1 in Helsinki, Finland, and Tsing Hua open pool reactor in HsinChu, Taiwan ROC. Readout has been performed with electron spin resonance spectrometry with reference to an absorbed dose standard in a (60)Co gamma ray beam. Absorbed doses and dose components have been calculated using the Monte Carlo codes fluka and mcnp. The relative effectiveness (RE), linking absorbed dose and detector response, has been calculated using the Hansen & Olsen alanine response model. RESULTS: The measured dose response of the alanine detector in the different experiments has been evaluated and compared to model predictions. Therefore, a relative effectiveness has been calculated for each dose component, accounting for its dependence on particle type and energy. Agreement within 5% between model and measurement has been achieved for most irradiated detectors. Significant differences have been observed in response behavior between thermal and epithermal neutron fields, especially regarding dose composition and depth dose curves. The calculated dose components could be verified with the experimental results in the different primary and secondary particle fields. CONCLUSIONS: The alanine detector can be used without difficulty in neutron fields. The response has been understood with the model used which includes the relative effectiveness. Results and the corresponding discussion lead to the conclusion that application in neutron fields for medical purpose is limited by its sensitivity but that it is a useful tool as supplement to other detectors and verification of neutron source descriptions.

Mucin gene (MUC1) transfer into human dendritic cells by cationic liposomes and recombinant adenovirus.

BACKGROUND: Dendritic cells (DC) as antigen presenting cells play an important role in immunotherapy of cancer. Mucin, encoded by the gene MUC1, is a human tumor antigen expressed in breast, pancreatic and ovarian cancers. Therefore, MUC1-transfected DC would be an attractive tool in constructing cancer vaccines. MATERIALS AND METHODS: Using two different cationic liposome preparations and, for comparison, a recombinant adenovirus expressing mucin, we tested the efficiency of mucin gene transfer into DC by flow cytometry. We investigated if these transfected DC were able to specifically stimulate autologous peripheral blood lymphocytes (PBL) from healthy donors. RESULTS: Flow cytometry revealed that 5-20% of DC transfected with liposomes Lipofectin and 20-40% of DC transduced with adenovirus expressed the relevant mucin epitopes. The expression of mucin on DC was similar to the expression of mucin found on carcinoma cells. After antigen uptake, DC specifically stimulated autologous PBL. CONCLUSION: We have shown that cationic liposomal gene transfer into human DC was feasible. We could obtain antigen specific stimulation of PBL at a similar rate as with adenoviral MUC1-transduced DC.

Development of antibody diversity in single germinal centers: selective expansion of high-affinity variants.

In a T cell-dependent immune response the microenvironment of the germinal center plays a crucial role in the affinity maturation of the antigen-specific, immunoglobulins. In order to look at the development of antibody diversity we have isolated single germinal centers and sequenced light chains characteristic of 2-phenyl-oxazolone (phOx)-specific antibodies. Fourteen days after immunization we can demonstrate various stages of intraclonal diversity. There are germinal centers where B cells are practically unmutated, suggesting that in these cases a substantial clonal expansion has taken place prior to the activation of the hypermutation mechanism. In other germinal centers, sequences with a low number of randomly distributed somatic mutations were observed, indicating that these changes have been introduced recently and/or that they fail to generate high-affinity variants and hence provide no basis for affinity selection. Finally, germinal centers are found in which practically all sequences carry the amino acid substitutions characteristic of the high affinity phOx antibodies. In these latter cases the high-affinity variants have been preferentially expanded. We conclude that affinity selection is a process that operates right from the beginning of germinal center development. Those B cells with a relative high affinity for the antigen gain a proliferative advantage over other cells and will dominate the response and these are the cells which will be selected to differentiate into memory cells.

The maturation of the immune response.

In a T-cell dependent immune response, the repertoire of antigen-activated B cells is diversified by a hypermutation mechanism. Only high-affinity variants are selected into the pool of memory cells. This maturation process takes place in a special micro-environment, the germinal centre. Here, Claudia Berek and Mike Ziegner discuss the mechanisms underlying these processes.

Immunoglobulin VH and VK genes of the BALB/c anti-foot-and-mouth disease virus (O1) VP1 response: cloning, characterization and transgenic mice.

Hybridomas producing monoclonal antibodies of different isotypes were isolated from BALB/c antibody responses to the capsid protein VP1 of the foot-and-mouth disease virus (FMDV) strain O1. According to antigen binding measured by ELISA a weak-binding (81D10, IgM) and a strong-binding antibody (113C12, IgG2a) were selected. As RNA sequencing of productive immunoglobulin VH and VK genes turned out, both chains of the weak-binding antibody (81D10) are encoded by germline (i.e. not mutated) genes whereas the gene encoding the strong-binding antibody (113C12) k chain is mutated at several sites. Therefore, rearranged VH and VK genes of 81D10 were cloned, expressed in immunoglobulin non-producing plasmacytoma cells, and mice transgenic for the 81D10 k gene were produced. These mice provide a first step in the development of a transgenic mouse model for genetical investigations in the affinity maturation of anti-viral immunoglobulin variable genes.