Schnelle Lochkorrosion durch ungewöhnliche Anodenstabilisierung in einem Stahl/Wasser-System

Fast pitting corrosion in a steel/water system as a result of unusual stabilization of anodes Corrosion damage as a result of fast pitting was observed in industrial equipment made of unalloyed steel. The rate of formation and the manifestation of the pits are similar to pitting corrosion of stainless steels. Estimation of the kinetics of the localized corrosion in terms of differential aeration cells led to a model which indicates the stabilization of small anodic regions. The stabilization was caused by precipitation of the products of reaction between ferrous ions and polymeric silicate. The high rate of pitting also suggests that the oxygen entering the system during service periods involving the exposure of the system to air has enhanced the corrosion. These ideas could be substantiated by experiments, which also revealed particularly the effect of the concentration of NaCl. Anodic passivation by the addition of Na₂CO₃ or perhaps inhibition may be considered as candidate protective measures.     

Runoff and infiltration characteristics of pavement structures--review of an extensive monitoring program.

The stormwater runoff and infiltration performance of permeable pavements has been systematically evaluated within an intensive monitoring program. The primary objective of the investigation was to generate a broad database, which enables the development of an advanced simulation module for urban drainage modelling. Over 160 field and lab scale experiments have been completed and analyzed for surface runoff and infiltration characteristics. The test series include several pavement types under various boundary conditions such as diverse precipitation impacts, varying surface slope and layer construction as well as different stages of surface clogging and several base and subgrade layer characteristics. The results represent a reliable and comprehensive database that allows profound conclusions and substantial recommendations.     

Estimating the load line displacement of cracked laboratory specimens using the engineering treatment model (ETM)

The Engineering Treatment Model (ETM) provides a means for estimating the load line displacement of a cracked body. Under contained yielding conditions the model uses available linear elastic solutions with an Irwin-type plasticity correction of the crack length. The magnification factor (F/F_y)^1/n describing the material's strain hardening behaviour is applied for extrapolation into the regime of net section yielding. Comparison of ETM estimates with finite element and experimental results shows that the assumptions of the model are realistic.     

The stability of duplexes involving AT and/or G4EtC base pairs is not dependent on their AT/G4EtC ratio content. Implication for DNA sequencing by hybridization

Sequencing by the recently reported hybridization technique requires the formation of DNA duplexes with similar stabilities. In this paper we describe a new strategy to obtain DNA duplexes with a thermal stability independent of their AT/GC ratio content. Melting data were acquired on 35 natural and 27 modified duplexes of a given length and of varying base compositions. Duplexes built with AT and/or G4EtC base pairs exhibit a thermal stability restrained to a lower range of temperature than that of the corresponding natural compounds (16 instead of 51 degrees C). The 16 degrees C difference in thermal stability observed between the least stable and the most stable duplex built with AT and/or G4EtC base pairs is mainly due to the sequence effect and not to their AT/G4EtC ratio content. Thus N -4-ethyl-2'-deoxycytidine (d4EtC) hybridizes specifically with natural deoxyguanosine leading to a G4EtC base pair whose stability is very close to that of the natural AT base pair. Oligonucleotide probes involving d4EtC can be easily prepared by chemical synthesis with phosphoramidite chemistry. Modified DNA targets were successfully amplified by random priming or PCR techniques using d4EtCTP, dATP, dGTP and dTTP in the presence of DNA polymerase. This new system might be very useful for DNA sequencing by hybridization.     

Fracture toughness evaluation by tensile and charpy-type tests based on micromechanical models of materials

With the aim of applying micromechanical approaches to fracture mechanics, we carried out dynamic tensile tests and instrumented impact tests with Charpy-type specimens both with a V-shaped notch and with a crack. We compared two micromechanical strain-rate-dependent models based on a modified Gurson flow function by simulating various dynamically loaded specimens. The results of the tests indicate that the critical void volume fractionf _c and the characteristic lengthl _c are practically independent of the strain rate and the geometry of the specimen. The behavior of the specimens subjected to strains and fracture can be characterized by the parameters determined in tensile tests and impact tests with the Charpy-type specimens. By the three-dimensional analysis based on the strain-rate-dependent Gurson model, we predict the onset of crack growth inside the Charpy specimen.Fraunhofer Institut für Werkstoffmechanic, Freiburg, Deutschland. Published in Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 2, pp. 77–84, March–April, 1994.     

Fast point spread function computation from aperture functions in high-resolution positron emission tomography

The problem of extracting point spread functions from detector aperture functions in high-resolution PET is addressed. In the limit of very small size detectors relative to the ring dimensions, assumptions are made that lead to a fast and simple computation model yielding point spread functions with negligible errors due to the reconstruction algorithm. The methods allows one to assess accurately the intrinsic performance of a PET tomograph, and it appears to be adequate to relate the imaging capabilities in every point of the camera reconstruction field to the geometric and physical characteristics of the detection system. The method was developed as an investigation tool to help design the next generation of very-high-resolution PET tomographs.