Berechnung des Kriechverhaltens zylindrischer Hohlkörper mit radialem Temperaturgradienten

Theoretical Investigation of the Creep Behaviour of a Tube Subjected to Thermal and Mechanical Loading A tube specimen, in which a constant temperature distribution of axial symmetry is maintained and which is subjected to a constant axial tensile stress is considered. Calculation of the thermal stress and creep strain distribution requires detailed knowledge of the physical properties of the material. A stress analysis, based on successive approximations, is given, which has been extended into the plastic deformation range. As a result, it can be shown that the initial stress pattern is redistributed by time-dependent creep, yielding in a more homogeneous uniaxial stress distribution. From these results a simple formula is derived which gives the steady state stress distribution as well as a characteristic mean or “effective” value of the temperature within the tube wall.     

Failure to demonstrate degradation of [4-14C] cholesterol to volatile hydrocarbons in rats and in human fecal homogenates

The inability of previous workers to recover completely the radioactivity from ingested [4-14C] cholesterol has led to the hypothesis that the colonic flora of some individuals degrade the sterol nucleus to volatile hydrocarbons, particularly CH4. In the present investigation, the production of radioactive volatiles was measured following incubation of [4-14C] cholesterol with 8 human fecal homogenates or after instillation of the labeled sterol into the cecum of 3 rats housed in a closed rebreathing system. Three of the 8 homogenates and each of the 3 rats produced copious CH4. However, analysis by combustion demonstrated no radioactivity above background in the volatile headspace of the homogenates or the gas space of the closed system housing the rats, indicating that less than 0.001% of the number 4 carbon of [4-14C] cholesterol could have been converted to volatile hydrocarbons. This study, therefore, provides no support for the concept that volatile products account for the incomplete recovery of ingested sterols observed in certain subjects. However, this hypothesis can not be excluded entirely until similar results are obtained with subjects who can be shown to degrade cholesterol.     

Percussive impact wear: A study of repetitively impacting solid components in engineering

Repetitive impacting of solid components in many industries poses severe wear problems limiting service life. This paper first describes the principal variables, testing methods, testing equipment and material dependencies. Subsequently, a general engineering impact wear theory is outlined based on experimental results of the initiation and progress of wear, and the relationship between impact loads and wear scar geometry. Both the impact pulse and wear mechanism are modelled for general applications     

Cysteine protease inhibitors cure an experimental Trypanosoma cruzi infection

Trypanosoma cruzi is the causative agent of Chagas' disease. The major protease, cruzain, is a target for the development of new chemotherapy. We report the first successful treatment of an animal model of Chagas' disease with inhibitors designed to inactivate cruzain. Treatment with fluoromethyl ketone-derivatized pseudopeptides rescued mice from lethal infection. The optimal pseudopeptide scaffold was phenylalanine-homophenylalanine. To achieve cure of infection, this pseudopeptide scaffold was incorporated in a less toxic vinyl sulfone derivative. N-methyl piperazine-Phe-homoPhe-vinyl sulfone phenyl also rescued mice from a lethal infection. Six of the treated mice survived over nine months, three without further treatment. Three mice that had entered the chronic stage of infection were retreated with a 20-d regimen. At the conclusion of the experiments, five of the six mice had repeated negative hemacultures, indicative of parasitological cure. Studies of the effect of inhibitors on the intracellular amastigote form suggest that the life cycle is interrupted because of inhibitor arrest of normal autoproteolytic cruzain processing at the level of the Golgi complex. Parasites recovered from the hearts of treated mice showed the same abnormalities as those treated in vitro. No abnormalities were noted in the Golgi complex of host cells. This study provides proof of concept that cysteine protease inhibitors can be given at therapeutic doses to animals to selectively arrest a parasitic infection.     

Theoretische und experimentelle Untersuchungen zum Kriechverhalten thermisch inhomogen belasteter hohlzylindrischer Prüfkörper

Theoretical and Experimental Investigations of the Creep Behaviour of a Tube Subjected to Thermal and Mechanical Loading The inhmogeneous temperature distribution for a tubular specimen, cooled from the axial bore, has been calculated. Application of the reference value concept leads to a good approximation for the axial creep strain of the specimen. The calculations apply to steady-state as well as to transient deformations and temperature distributions. A sharp creep rate increase following abrupt changes of the temperature field is predicted; this may lead to a lifetime reduction. – The theoretical results have been checked using specimens of the alloy NiCr 80 20 in a specially designed creep machine for tubular, cooled specimens, capable of producing temperature gradients up to 50 K/mm. The agreement between theoretical and experimental results is very satisfactory, both for stationary and for transient situations.     

Ultra-thin TaN Films for Superconducting Nanowire Single-Photon Detectors

Ultra-thin films of superconducting tantalum nitride are deposited by reactive magnetron sputtering on heated sapphire substrates. The critical temperature T _C=10.25 K is reached for films thicker than 10 nm. A superconducting nanowire single-photon detector in the form of a meander line with a width of 110 nm was made from 5 nm thick TaN film. The detector had a transition temperature of 8.3 K and a critical current density of 4 MA/cm² at 4.2 K. A photon detection efficiency of 20% has been obtained for the detector with a filling factor of 0.55 at wavelengths up to 700 nm.