Long-term effects of dissolved carbonate species on the degradation of trichloroethylene by zerovalent iron

The effect of different concentrations of total inorganic carbon (TIC) and flow rates on the reactivity of iron metal with trichloroethylene (TCE) was studied in column experiments to verify whether concentration or mass flux of TIC is the major key parameter for barrier performance. First-order rate coefficients (kobs) for TCE degradation vary initially between 0.15 and 0.32 h-' and are positively related to TIC influent concentration. Maximal kobs were reached after 164 and 591 PV, varied between 0.55 and 1.1 h(-1), and were positively correlated to the TIC mass flux, followed by a decrease resulting in values similar to the reference system at the end of the experiments. Enhancement of iron corrosion (0.7 to 3.5 mmol kgFe(-1) d(-1) and formation of gas bubbles during the initial experimental phase were observed and were also positively correlated to TIC mass flux. The higher gas bubble formation probably has a more significant effect on porosity than mineral precipitations in Fe0-systems. The results suggest that higher TIC mass fluxes cause a more pronounced acceleration in CHC degradation, but also a faster inhibition in the longer-term. This faster inhibition has serious implication for the design of funnel and gate systems.     

Quantitative read-across for predicting the acute fish toxicity of organic compounds

Read-across enables the interpolation of a property for a target chemical from respective experimental data of sufficiently similar compounds. Employing a set of 692 organic compounds with experimental values for the 96 h fish toxicity toward the fathead minnow in terms of LC(50) (lethal concentration 50%) values, a read-across method has been developed that is based on atom-centered fragments (ACFs) for evaluating chemical similarity. Prediction of log LC(50) proceeds through reading across the toxicity enhancement over predicted narcosis-level toxicity in terms of the respective logarithmic ratio, log T(e), and adding the respective baseline narcosis LC(50) estimated from log K(ow) (octanol/water partition coefficient). Depending on the minimum similarity imposed on a compound to serve as read-across basis for the target chemical, three different standard settings have been introduced, allowing one to perform screening-level estimations as well as predictions with intermediate and good confidence. The respective squared correlation coefficients (r(2)) are 0.73, 0.78, and 0.87, with root-mean square errors (rms) of 0.73, 0.60, and 0.39 log units, respectively. As a general trend, increasing the ACF minimum similarity increases the prediction quality at the cost of decreasing the application range. The method has the potential to assist in the predictive evaluation of fish toxicity for regulatory purposes such as under the REACH legislation.     

Trilobal Polyimide Fiber Insulation for Cryogenic Applications

Recent measurements have shown a record-breaking low thermal conductivity λ_total of less than 0.25 × 10⁻³ W·m⁻¹·K⁻¹ at temperatures of 120 K for an evacuated sample consisting of polyimide fibers with a trilobal fiber cross section. Existing models for the heat transport in fiber insulations cannot sufficiently describe fiber insulations consisting of fibers with non-cylindrical cross sections. In this article, a modification for the model for cylindrical fibers will be presented. The modifications for the trilobal cross section of the fiber will be explained and compared to the original cylindrical model. The results of the theoretical calculations will be discussed in comparison to experimental results of measurements performed with a guarded hot-plate apparatus at temperatures in the range from 120 K to 420 K.     

Improving reliability of large software systems

Improving field performance of telecommunication systems is the key objective of both telecom suppliers and operators, as an increasing amount of business critical systems worldwide are relying on dependable telecommunication. Early defect detection improves field performance in terms of reduced field failure rates and reduced intrinsic downtime. This paper describes an integrated approach to improve early defect detection and thus field reliability of telecommunication switching systems. The assumptions at the start of the projects discussed in this paper are: Wide application of code inspections and thorough module testing must lead to a lower fault detection density in subsequent phases. At the same time criteria for selecting the most critical components for code reviews, code inspections and module test are provided in order to optimize efficiency. The primary goal is to identify critical components and to make failure predictions as early as possible during the life cycle and hence reduce managerial risk combined with too early or too late release of such a system to the field. During test release time prediction and field performance prediction are both based on tailored and superposed ENHPP reliability models. Experiences from projects of Alcatel’s Switching and Routing Division are included to show practical impacts. This revised version was published online in June 2006 with corrections to the Cover Date.