Fast maximum intensity projections of large medical data sets by exploiting hierarchical memory architectures.

Maximum intensity projections (MIPs) are an important visualization technique for angiographic data sets. Efficient data inspection requires frame rates of at least five frames per second at preserved image quality. Despite the advances in computer technology, this task remains a challenge. On the one hand, the sizes of computed tomography and magnetic resonance images are increasing rapidly. On the other hand, rendering algorithms do not automatically benefit from the advances in processor technology, especially for large data sets. This is due to the faster evolving processing power and the slower evolving memory access speed, which is bridged by hierarchical cache memory architectures. In this paper, we investigate memory access optimization methods and use them for generating MIPs on general-purpose central processing units (CPUs) and graphics processing units (GPUs), respectively. These methods can work on any level of the memory hierarchy, and we show that properly combined methods can optimize memory access on multiple levels of the hierarchy at the same time. We present performance measurements to compare different algorithm variants and illustrate the influence of the respective techniques. On current hardware, the efficient handling of the memory hierarchy for CPUs improves the rendering performance by a factor of 3 to 4. On GPUs, we observed that the effect is even larger, especially for large data sets. The methods can easily be adjusted to different hardware specifics, although their impact can vary considerably. They can also be used for other rendering techniques than MIPs, and their use for more general image processing task could be investigated in the future.     

International comparison of quantum AC voltage standards for frequencies up to 100 kHz

This paper presents results of an international comparison of two quantum AC voltage standards based on pulse-driven Josephson arrays. The two systems differ in several hardware and software characteristics as well as in the level of automation, features which can influence the accuracy of transferring the quantum-standard voltage value to a calibrated instrument. The comparison was performed at 100 mV, 20 mV and 12 mV, at frequencies between 2.5 kHz and 100 kHz. An electronically-aided thermal transfer standard was used as a travelling standard. At the most accurate voltage and frequency point, 100 mV at 2.5 kHz, both laboratories agreed to better than 1 part in 10⁶.     

Katalytische Dechlorierung von Chlorkohlenwasserstoffen aus kontaminierten Grundwässern

In the framework of the joint research project SAFIRA, two novel catalysts were developed and examined in groundwater flow-through reactors at the Bitterfeld test-site. The catalytic active component Pd ought to be protected from deactivating ionic compounds by embedding Pd into hydrophobic polymer membranes on the one hand, and on the other hand by generating Pd clusters in the pores of hydrophobic zeolites. Both catalysts reached only short life times, caused by the formation of H2S and possibly other sulfur compounds by microbiological sulfate reduction. Though the catalysts could be regenerated by treatment with hypochlorite, poisoning occurred after short periods of operation. In conclusion, we assess the utilization of noble-metal catalysts directly in the water phase of the Bitterfeld groundwater as problematic. However, the transfer of the catalytic reaction to the gas phase yielded encouraging results. A multi-stage process, including different pretreatment techniques in the water phase, vacuum stripping of contaminants, and their catalytic hydrodechlorination over Pd catalysts in the gas phase allow the complete conversion of contaminants. The utilization of modern membrane technology and the possibility to heat the strip gas stream in a wide temperature range, provides the process a high potential concerning contaminant spectrum and concentration.     

Performance evaluation using a three compartment mass balance for the removal of volatile organic compounds in pilot scale constructed wetlands

To perform a general assessment of treatment efficiency, a mass balance study was undertaken for two types of constructed wetlands (CWs), planted gravel filters and plant root mat systems, for treating VOC (benzene; MTBE) polluted groundwater under field conditions. Contaminant fate was investigated in the respective water, plant, and atmosphere compartments by determining water and atmospheric contaminant loads and calculating contaminant plant uptake, thereby allowing for an extended efficiency assessment of CWs. Highest total VOC removal was achieved during summer, being pronounced for benzene compared to MTBE. According to the experimental results and the calculations generated by the balancing model, degradation in the rhizosphere and plant uptake accounted for the main benzene removal processes, of 76% and 13% for the gravel bed CW and 83% and 11% for the root mat system. Volatilization flux of benzene and MTBE was low (<5%) for the gravel bed CW, while in the root mat system direct contact of aqueous and gaseous phases favored total MTBE volatilization (24%). With this applied approach, we present detailed contaminant mass balances that allow for conclusive quantitative estimation of contaminant elimination and distribution processes (e.g., total, surface, and phytovolatilization, plant uptake, rhizodegradation) in CWs under field conditions.     

Katalytische Dechlorierung von Chlorkohlenwasserstoffen aus kontaminierten Grundw?ssern

Im Rahmen des Forschungsverbundes SAFIRA wurden zwei neue Katalysatorsysteme zur reduktiven Dehalogenierung von CKW mit H2 entwickelt und am Standort Bitterfeld in Grundwasser-Durchflussreaktoren untersucht. Die katalytisch aktive Komponente Pd wurde zum Schutz vor Vergiftung durch ionische Verbindungen zum einen in hydrophobe Polymermembranen eingebettet, zum anderen wurden Pd-Cluster in den Poren hydrophober Zeolithe erzeugt. Die erreichten Standzeiten beider Katalysatoren waren trotzdem bedingt durch die Bildung von H ₂ S und organischen Schwefelverbindungen durch mikrobiologische Sulfatreduktion gering. Die Katalysatoren waren zwar durch eine Spülung mit Hypochlorit regenerierbar, unterlagen aber nach wenigen Tagen erneuter Vergiftung. Der Einsatz von Pd-Katalysatoren unter Bitterfelder Grundwasserbedingungen wird deshalb als problematisch eingesch?tzt.