A variety of epistatic interactions can occur between partially homologous transgene loci brought together by sexual crossing

Epistatic interactions between unlinked transgene loci in tobacco plants were studied following sexual crosses between different transgenic lines. Three potential "modifier" transgene loci, which were structurally similar but integrated at different chromosomal locations, were tested for their ability to influence the expression of a partially homologous "target" transgene locus. After introduction of an individual modifier locus, the target locus could be either unaffected, completely inactivated and methylated or differentially sensitive, showing more complete inactivation and methylation when homozygous than when hemizygous. The implications of these results for inbreeding depression in plants are discussed.     

The evaluation of cell nuclei staining parameters regarding the reproducibility of fluorescence measurements.

The present methodological study is an attempt to optimize the staining parameters for a quantitative DNA determination of fluorescent cells. The application of pure dyes and a precise control of the staining procedure are preliminary conditions which have to be fulfilled, because the reproducibility of measurements is in this connection the most important criterion for a quantitative DNA related analysis of cell population. Chicken erythrocytes and isolated nuclei were applied as biological test objects. The staining procedure with acridine derivatives (acriflavine, proflavine, rivanol) was performed in accordance with the fluorescence-Feulgen reaction. The influence of staining parameters, such as (1) pH and (2) dye concentration of the staining solution, were evaluated regarding the spectral behaviour, the total fluorescence intensity, and the reproducibility of results.     

Evaluation of tribological behavior of silicon carbide and silicon nitride ceramics under different conditions

A comparative analysis of the tribological behavior of commercially available sintered silicon carbide (SiC) and three different types of silicon nitride (Si₃N₄) ceramics have been carried out using the ball-on-disk method in dry and lubrication (deionized [DI] water and ethanol) environment. Scanning electron microscopy (SEM) was used to understand the morphology and chemical composition of the tribo-surfaces. Sintered SiC (Hexoloy-SA) had the highest friction coefficient during dry sliding with an average of ∼0.34. Deionized water showed a minor improvement in friction (∼0.27) while ethanol reduced the friction greatly to ∼0.18 compared to dry sliding. During dry sliding, the presence of an abrasive third body was responsible for the high wear rates (WRs) in these compositions. Hexoloy-SA showed a lower WR during ethanol and DI water lubrication due to the formation of stable tribofilms as well as higher hardness which resisted the formation of third bodies. In comparison, Si₃N₄ samples showed a lower WR in DI water and ethanol. The samples also showed composition-dependent behavior which indicates that grain structure and grain boundary chemistry are playing a vital role in the tribological process.     

Fluorine self-diffusion in CaF2 and BaF2

The self-diffusion of F-18 in single crystals of BaF₂ and CaF₂ was measured between 350 and 940°C. The results were in agreement with diffusion coefficients deduced from ionic conductivity studies, and yieldedH's of 1,6 eV for BaF₂ and of 2.0 eV for CaF₂ for intrinsic diffusion. Below 700°C, extrinsic diffusion behaviour was observed in CaF₂ withH=0.9 eV. The formation energy for anion Frenkel defects was estimated to be in the range 2.2 to 3.1 eV. Both anion and cation diffusion rates were increased in CaF₂ doped with SmF₃ as compared with pure CaF₂, indicating an interrelation between anion and cation defects, as observed previously in the related substances, UO₂ and UO_2+x , The migration energy of cations was estimated to be roughly in the range 1.5±0.6 eV. The implications of the results in terms of diffusion mechanisms are discussed and the remaining uncertainties are indicated.Experiments performed in 1968 at CCR Euratom, Ispra, Italy. The present study constitutes part II of a study of fluorine self-diffusion. Part I is concerned with LiF and NaF (see ref. [6]).     

The effect of Fe,Ni and W impurities on uranium diffusion in uranium monocarbide

The self-diffusion of uranium with U-233 as tracer was measured in stoichiometric UC which was doped with Fe, Ni or W impurities. The impurities were added by flash evaporation on the UC and subsequent diffusion into the UC. Uranium diffusion was increased in the doped samples as compared to undoped UC at all temperatures studied (1380 to 2200°C). The increase was most pronounced (more than a factor of 100) at low temperatures. Simultaneously, pronounced grain-boundary penetration was observed at low temperatures, possibly due to eutectic formation at the grain boundaries. The ratio of grain boundary to lattice diffusion coefficients at 1380°C was of the order of 3 × 10⁴. The present data serve to explain some of the scatter of the literature data and correlate well with the known increased rate of sintering of Ni-doped UC.     

Effect of hormone replacement therapy on epidermal barrier lipids

Current evidence of the effect of hormone replacement therapy (HRT) on skin lipids, of postmenopausal women is scanty and indirect. Here, we report the ultrastructural differences in epidermal lipids between postmenopausal subjects who were and were not on HRT and a comparison is made with younger subjects. Biopsies were obtained from arms and legs, in a blinded, no-treatment, study conducted on postmenopausal subjects who were and were not on HRT and younger subjects. The ultrastructure of skin lipids and the lipid coverage of underlying corneocytes were compared for biopsies obtained from different subjects. Qualitative assessment as well as quantitative estimation of lipid-covered regions of corneocytes shows that skin lipids do not cover corneocytes effectively in postmenopausal women who are not on HRT. However, women who are on HRT show significantly improved lipid coverage of corneocytes, which is comparable with the younger subjects. This implies that HRT should improve the lipid coverage and skin condition of postmenopausal women.     

Entwicklung und Validierung eines Kühlmittelsensors zur Bewertung der Korrosionsschutzwirkung

A sophisticated thermal management is one of the main subsystems that enables combustion engines with high power density. In this context the demands on coolants are also increasing. There has to be a certain level of corrosion protection to ensure the functionality of the cooling system. Hereafter the result of an electrochemical sensor development is presented. With the knowledge of analytical and electrochemical results a quick test for characterizing coolants corrosion protection has been developed and validated.     

Molecular and cytogenetic analyses of stably and unstably expressed transgene loci in tobacco

To study the influence of genomic context on transgene expression, we have determined the T-DNA structure, flanking DNA sequences, and chromosomal location of four independent transgene loci in tobacco. Two of these loci were stably expressed in the homozygous condition over many generations, whereas the other two loci became unstable after several generations of homozygosity. The stably expressed loci comprised relatively simple T-DNA arrangements that were flanked on at least one side by plant DNA containing AT-rich regions that bind to nuclear matrices in vitro. Of the unstably expressed loci, one consisted of multiple incomplete T-DNA copies, and the second contained a single intact T-DNA; in both cases, however, binary vector sequences were directly contiguous to a right T-DNA border. Fluorescence in situ hybridization demonstrated that the two stably expressed inserts were present in the vicinity of telomeres. The two unstably expressed inserts occupied intercalary and paracentromeric locations, respectively. Results on the stability of transgene expression in F1 progeny obtained by intercrossing the four lines and the sensitivity of the four transgene loci to inactivation in the presence of an unlinked "trans-silencing" locus are also presented. The findings are discussed in the context of repetitive DNA sequences and the allotetraploid nature of the tobacco genome.     

Damage produced in magnesium aluminate spinel by high energy heavy ions including fission products of fission energy: microstructure modifications

The radiation stability of spinel MgAl₂O₄ against the impact of beams of a fission product at fission energy (70 MeV iodine) and at different fluences was investigated using Transmission Electron Microscopy (TEM). Specimens prethinned before irradiation were analysed by TEM and irradiated bulk specimens were investigated using cross-sectional TEM. Tracks were observed in pre-thinned specimens. Partial amorphisation was observed for the irradiation at the highest fluence. Recrystalization of the amorphous region, induced by the microscope electron beam was observed. A threshold value of 6 keV nm⁻¹ was determined for the amorphization of spinel under the above mentioned irradiation conditions. Moreover, profile measurements of the irradiated areas confirmed the large swelling values for this material when irradiated with fission products of fission energy. A thermal spike model was used to calculate the damage threshold for spinel using experimentally measured heavy-ion track radii, including results for other ions of up to very high energies. These accelerator-based fission product irradiations revealed an unexpected poor radiation stability, in contrast to the known good behaviour of the spinel against neutron or alpha particle damage.