Wavelength dependent neutron transmission and radiography investigations of the high temperature behaviour of materials applied in nuclear fuel and control rod claddings

Neutron radiography was used for the investigation of the nuclear fuel and control rod cladding behaviour during steam oxidation under severe nuclear accident conditions. In order to verify the hypothesis that the unexpectedly high neutron cross-section found after oxidation of Zircaloy-4 in wet air containing 10% steam is caused by a strong hydrogen uptake, the wavelength dependence of the total macroscopic neutron cross-section of the specimens was measured. The characteristic dependence for hydrogen was not found, which is a proof that hydrogen is not absorbed significantly. The data agree mostly with the behaviour expected for β-Zr.Examinations of control rod simulators annealed until the failure in single-rod tests were performed. In order to separate the effect of the neutron absorber and control rod structure materials, radiographs taken with different neutron spectra were combined. This procedure clearly showed that the local melting resulting from the eutectic reaction between the stainless steel control rod cladding and the Zircaloy-4 guide tube is the reason for the failure.     

Comparison of micropatterning methods for ceramic surfaces

The fabrication of defined ceramic micropatterns smaller than 100 μm is due to the hardness and brittleness of ceramic materials still very challenging. However, in recent years, micropatterned ceramic surfaces have become highly interesting for biomedical applications or the fabrication of energy converting devices, such as solid oxide fuel or solar cells. In this study we evaluate six modern techniques for ceramic pattern fabrication with feature sizes ranging from 5 to 100 μm. Ceramic materials such as alumina, zirconia, silica and hydroxyapatite are discussed. Advantages and disadvantages for each process are highlighted and compared to the other techniques. Three of these techniques, namely microtransfer molding, modified micromolding and Aerosol-Jet^® printing generate patterns starting with aqueous ceramic suspensions. The other three techniques, micromachining and two different types of laser treatment produce micropatterns by material removal from solid ceramic substrates. The detailed analysis yields that properties such as the desired micropatterning size, shape or the production time are strongly dependant on the chosen technique.     

Acoustic emission analysis for the quantification of autonomous crack healing in concrete

As half of the annual construction budget is spent on remediation of existing structures, self-healing of concrete, which is very sensitive to cracking, would be highly desirable. In this research, encapsulated healing agents were embedded in the concrete matrix in order to obtain self-healing properties. Upon cracking, the capsules break and the healing agent is released, resulting in crack repair. The efficiency of this crack healing technique was evaluated by means of mechanical tests and by using acoustic emission analysis. It was shown that due to autonomous crack repair, more than 80% of the original strength and stiffness can be regained. Events with an energy higher than the energy related to concrete cracking indicated breakage of the capsules. Upon reloading of beams with untreated cracks, the released energy was lower compared to beams with healed cracks. From this study it was shown that AE is a suitable technique to evaluate self-healing of cracks in concrete.     

Candida tropicalis as causative agent of septicemia (author's transl)

In connection with microbiological findings in two patients, a report on septicemia caused by C. tropicalis is given. C. tropicalis is second in frequency to C. albicans in man. Because for the different biological properties of Candida species in each case of isolation of such fungi from clinical specimens an identification of the species is obligatory, because the generalizing diagnosis of "Candida mycosis" may be insufficient for the detection of epidemiological and pathogenetic associations. The possible primary resistance of C. tropicalis against the antimycotic 5-Fluorocytosine (Ancotil) is discussed. It is shown that the antigen similarity within the most important Candida species as e.g. between C. albicans and C. tropicalis may cause a false interpretation of serological results concerning the causative agent of the infection. For a safe inactivation of C. tropicalis on human skin, cleaning with 70% isopropyl alcohol for ten seconds is proposed. Because C. tropicalis is entering the human body preferably through food it is discussed whether a microbiological control of food for patients predisposed for such infections should be performed.     

Phospholipase C beta and membrane action of calcitriol and estradiol

We have shown that estrogens and calcitriol, the hormonally active form of vitamin D, increase the concentration of intracellular calcium ([Ca2+]i) within 5 s by mobilizing calcium from the endoplasmic reticulum and the formation of inositol 1,4, 5-trisphosphate and diacylglycerol. Because the activation of effectors as phospholipase C (PLC) coupled to G-proteins is the early event in the signal transduction pathway leading to the inositol 1,4,5-trisphosphate formation and to [Ca2+]i increase, we described different PLC isoforms (beta1, beta2, gamma1, and gamma2, but not beta4) in female rat osteoblasts using Western immunoblotting. The data showed that phospholipase C beta was involved in the mobilization of Ca2+ from the endoplasmic reticulum of Fura-2-loaded confluent osteoblasts by calcitriol and 17beta estradiol, and PLC gamma was ineffective. The data also showed that only a PLC beta1 linked to a Pertussis toxin-insensitive G-protein and a PLC beta2 coupled to a Pertussis toxin-sensitive G-protein are involved in the effects of calcitriol and 17beta estradiol on the mobilization of Ca2+ from intracellular Ca2+ stores. In conclusion, these results may be an important step toward understanding membrane effects of these steroids and may be an additional argument in favor of membrane receptors to steroid hormones.