Das Verhalten des Benzininhaltsstoffes Methylterti?rbutylether (MTBE) in Grundwasser

Das überwachte Selbstreinigungsverm?gen (monitored natural attenuation) des Untergrundes wird seit einigen Jahren als m?gliche und kostengünstige L?sung bei Schadensf?llen mit Benzin angesehen. Methylterti?rbutylether (MTBE) wird in Nordamerika seit den 70er Jahren dem Benzin zugesetzt, um die Oktanzahl zu erh?hen und die Luftverschmutzung zu senken. MTBE ist wasserl?slich (ca. 50 g/l), wird mit Grundwasserflie?geschwindigkeit transportiert, ist schwer biologisch abbaubar und hat einen unangenehmen Geruch und Geschmack, sogar bei Konzentrationen von weniger als 100 μg/l. Die toxische Wirkung von MTBE ist nur unzureichend untersucht, und es existieren nur wenige Daten über die potentielle Gefahr, die dieser Stoff für die Grundwasserressourcen darstellt. In Europa existieren fast keine Daten zu MTBE-Konzentrationen in der Umwelt. Der weitverbreitete Einsatz von MTBE, seine physikalisch-chemischen Eigenschaften und die unzureichende biologische Abbaubarkeit machen diesen Stoff zu einem problematischen Grundwasserkontaminanten. Aus diesen Gründen wird es schwierig sein, das Selbstreinigungsverm?gen des Untergrundes als Sanierungsstrategie einzusetzen, wenn MTBE als Schadstoff auftritt.     

Grundwasser – Online-Submission

Ohne Zusammenfassung     

Wie Flussbett-Temperaturdaten zur Ermittlung der Aquifer-Heterogenität beitragen können

Groundwater discharge to a stream may show small-scale heterogeneities caused by the structure of the connected aquifer. The spatial pattern of the groundwater discharge can be investigated by temperature measurements in the streambed. Thus, the heterogeneity of the hydraulic conductivity (K) of an aquifer can be inferred from measured streambed temperatures. A flow and heat transport model of a stream-aquifer system was set up including stochastic K fields generated from the mean and variance of K data obtained from direct-push measurements. However, the simulated streambed temperatures did not cover the range of measured temperatures. Therefore, the relation between the distribution of streambed temperatures and the variance of K was used to calibrate the variance of K such that the distribution of measured temperatures could be reproduced in the model. This study showed that methods based on heat as a parameter for measuring and calibration constitute a valuable supplement to traditional investigation techniques.     

An ant colony optimisation algorithm for balancing two-sided U-type assembly lines with sequence-dependent set-up times

Some practical arrangements in assembly lines necessitate set-up times between consecutive tasks. To create more realistic models of operations, set-up times must be considered. In this study, a sequence-dependent set-up times approach for two-sided u-type assembly line (TUAL) structures is proposed for the first time. Previous studies on TUAL have not included set-up times in their analyses. Furthermore, an algorithm based on the Ant Colony Optimization (ACO) algorithm, which is using a heuristic priority rule based procedure has been proposed in order to solve this new approach. In this paper, we look at the sequence-dependent set-up times between consecutive tasks and consecutive cycles, called the “forward set-up time” and the “backward set-up time”, respectively. Additionally, we examine the “crossover set-up time”, which arises from a new sequence of tasks in a crossover station. In order to model more realistic assembly line configurations, it is necessary to include sequence-dependent set-up times when computing all of the operational times such as task starting times and finishing times as well as the total workstation time. In this study, the proposed approach aims to minimize the number of mated-stations as the primary objective and to minimize the number of total workstations as a secondary objective. In order to evaluate the efficiency of the proposed algorithm, a computational study is performed. As can be seen from the experimental results the proposed approach finds promising results for all literature-test problems.     

Effect of human pancreastatin peptide (hP-16) on oral glucose tolerance in man

Thallium-201 (201Tl) late reinjection after stress-redistribution imaging improves the detection of viable myocardium. Recently, early reinjection of 201Tl immediately after stress imaging was proposed as a new method for distinguishing ischemic myocardium, hibernating myocardium, and myocardial scar. However, there are no data on the influence of the timing of reinjection on "fill-in." This study was designed to assess whether the reinjection time influences "fill-in" in chronic coronary artery disease. Thirty-three patients with chronic coronary artery disease were studied. All patients underwent exercise 201Tl tomography. Immediately after stress imaging, 37 MBq of thallium was reinjected earlier than usual and early reinjection delayed image (ERDI) was acquired 3 h later. With the same protocol, all patients also underwent a second study involving late reinjection of 201Tl within 1 week. An additional 37 MBq of thallium was reinjected 3 h after stress imaging, and late reinjection delayed image (LRDI) was obtained 10 min later. All images were analyzed qualitatively using a 4-point grading uptake score. Of the 72 hypoperfused segments on stress images, 66 segments showed fill-in and 6 showed persistent defects on ERDI, and of the same 72 segments 55 segments displayed fill-in and the remaining 17 showed persistent defects on LRDI (p<0.05). The delta uptake score (the uptake score of the delayed image minus that of stress image) in early reinjection was 1.60+/-0.80, which was significantly higher than that in late reinjection (1.24+/-0.94, p<0.01). A small dose of thallium reinjected immediately after stress imaging with delayed images obtained 3 h later is convenient and might provide another technique for determining myocardial viability.     

TClouds

Das von der Europ?ischen Kommission gef:orderte Projekt „TClouds“ hat die Entwicklung einer sicheren und datenschutzkonformen Cloud-Infrastruktur zum Ziel. Dieser Beitrag beschreibt die Herausforderungen und die ersten L?sungsideen.     

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