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The Archean-Proterozoic transition is characterized by the widespread deposition of organic-rich shale, sedimentary iron formation, glacial diamictite, and marine carbonates recording profound carbon isotope anomalies, but notably lacks bedded evaporites. All deposits reflect environmental changes in oceanic and atmospheric redox states, in part associated with Earth's earliest ice ages. Time-series data for multiple sulfur isotopes from carbonate-associated sulfate as well as sulfides in sediments of the Transvaal Supergroup, South Africa, capture the concomitant buildup of sulfate in the ocean and the loss of atmospheric mass-independent sulfur isotope fractionation. In phase with sulfur is the earliest recorded positive carbon isotope anomaly, convincingly linking these environmental perturbations to the Great Oxidation Event (ca. 2.3 Ga).

Due to the increasing importance of power electronic components in automobiles, it becomes necessary to consider their reliability. This applies especially to hybrid electrical vehicles (HEV) where a malfunction of the power electronics may prevent the vehicle to operate. Of paramount importance for the reliability of power electronics is the component operating temperature and temperature cycling. This paper deals with the development of an advanced simulation tool which is capable of determining the component temperature of a three-phase converter over long mission profiles. In addition, the expected converter reliability is calculated. To accomplish this, losses in the semiconductors and dc-link capacitors are determined first. Next, this loss data is fed into a thermal model to compute the component temperatures, for the whole mission profile. As basis for the reliability computation, failure-rate catalogs, such as Military Handbook 217F or RDF 2000, are used. Also an approach using simple formulas for lifetime prediction is presented. According to failure-rate catalogs, temperature cycles are of particular importance for the reliability of power semiconductors. A novel algorithm, detecting all relevant temperature cycles within the computed temperature curve is developed. Finally, the applicability and significance of the presented reliability prediction methods is assessed. Index Terms--Failure-rate catalogs, hybrid electrical vehicles (HEV), reliability, temperature cycles.

In modern high-power medium voltage drives, multilevel converters are increasingly used. Employing slight topological modifications, soft-switching technology can be applied to multilevel converters to reduce the switching losses. As a result, the switching frequency can be increased, thereby reducing the output filter size. However, common converter controls have to be modified. In this paper, a flexible control platform is presented that allows rapid prototyping of soft-switching topologies. An analysis of different auxiliary resonant commutated pole (ARCP) topologies shows that all switching commands can be synthesized with synchronized signals of two-level ARCP converters. Therefore, a flexible state-machine for two-level converters was developed first, which can also be used to build controls for multilevel topologies. It supports drivers with built-in intelligence as well as the control of additional switches that are required in some ARCP neutral-point-clamped (NPC) topologies. The switching commands for the state machines can be generated by standard multilevel modulation methods. Illegal switching states are filtered and multiple simultaneous commutations per phase are prevented for ARCP NPC converters. To verify the functionality, the control scheme was realized in a field programmable gate array and a completely modular test converter was developed. This test converter can be used to quickly implement all common multilevel topologies and test different modulation strategies. Experimental results are presented in this paper. Index Terms--Auxiliary resonant commutated pole (ARCP) topologies, diode-clamped-multilevel (DCML) inverter, field programmable gate array (FPGA), neutral-point-clamped (NPC) topologies, pulsewidth modulation (PWM) inverter.

State-of-the-art mechanical circuit breakers in medium-voltage systems allow a safe handling of short-circuits if the short circuit power of the grid is limited. Using delayed turn-off times, the circuit breakers can be coordinated with lower level protection gear. Hence, a high availability of the grid can be guaranteed. However, during a short-circuit a significant voltage sag can be noticed locally in the medium-voltage grid. Sensitive loads such as computers will fail even if the voltage returns within a few seconds. A semiconductor circuit breaker, however, is able to switch fast enough to keep voltage disturbance within acceptable limits. The optimization and selection of power electronic switch topologies is critical. In this paper, different semiconductors are briefly compared considering the requirements of a solid-state switch integrated into a 20-kV medium-voltage grid. Based on these semiconductor characteristics, various switch topologies are developed, which are compared under technical and economical aspects. It is shown that solid-state circuit breakers offer significant advantages when compared to present solutions and can be used in today's medium-voltage power systems. Index Terms--Current limiters, semiconductors, solid-state circuit breakers.

The European herb garlic mustard (Alliaria petiolata) is a serious invader of North American deciduous forests. One explanation for its success could be that in the absence of specialized herbivores, selection has favored less defended but more vigorous genotypes. This idea was addressed by comparing offspring from several native and introduced Alliaria populations with respect to their palatability to insect herbivores and their tolerance to simulated herbivory. Feeding rates of a specialist weevil from the native range were significantly greater on American plants, suggesting a loss of resistance in the introduced range. In contrast, there was significant population variation but no continent effect in the feeding rates of a generalist caterpillar. After simulated herbivory, A. petiolata showed a substantial regrowth capacity that involved changes in plant growth, architecture, and allocation. Removal of 75% leaf area or of all bolting stems reduced plant fitness to 81% and 58%, respectively, of the fitness of controls. There was no indication of a difference in tolerance between native and introduced Alliaria populations or of a trade-off between tolerance and resistance. Key words: biological invasions; Ceutorhynchus scrobicollis; compensatory regrowth; EICA hypothesis; microevolution; plant-herbivore interactions; plant resistance; Spodoptera littoralis.

Terminal Neoproterozoic and Cambrian evaporite rocks worldwide record a marked sulphur isotope excursion to very heavy [delta][sup.34]S isotopes that reflect a period of significant burial of reduced sulphur. New [delta][sup.34]S data from anhydrite and pyrite of the Ara Group in Oman extend this record to Arabia. Depositional history of the Ara Group spans c. 8 Ma across the terminal Neoproterozoic-Cambrian boundary. Therefore, these rocks provide a detailed record of sulphur isotopic evolution in this important time interval. Ara Group sulphur isotope values include a mean [delta][sup.34][S.sub.anhydrite] of 39.4 [per thousand] [+ or -] 2.6 [per thousand] (1 [sigma]; range 32.4-46.4 [per thousand]; n = 61), and a mean [delta][sup.34][S.sub.pynte] of 1.4 [per thousand] [+ or -] 7.3 [per thousand] (1 [sigma]; range -10.8 [per thousand] to 11.4 [per thousand]; n = 12). The isotope signatures were not altered significantly during diagenesis and are representative of the isotopic composition of parent waters in the basin. Marine bromine concentrations in halite and marine fossils in associated carbonate rocks indicate that these waters had a marine origin. Bacterial sulphate reduction was the dominant process leading to the segregation between isotopically heavy sulphur incorporated in evaporite rocks and isotopically light sulphur buried in pyrite and organic matter. Strong sulphate reduction operated in a hypersaline and partly anoxic basin; these environmental conditions were also conducive to the preservation of organic material and make the Ara Group a prolific hydrocarbon province. Significant variation of the observed values is attributed to the inherent variability of bacterial sulphate reduction, including partially closed-system behaviour, disproportionation processes, limited diagenesis, and possibly secular variation of sulphur isotopes within the basin. Ara Group [delta][sup.34][S.sub.anhydrite] values overlap with data from other terminal Neoproterozoic to Cambrian basins, but the mean [delta][sup.34][S.sub.anhydrite] is highest in Oman. This observation cannot be attributed solely to the specific anoxic conditions and strong bacterial sulphate reduction in Oman, because such conditions were widespread in most evaporite basins of the terminal Neoproterozoic--Cambrian Periods. Instead, slight age differences between these basins can introduce a bias in the sulphur isotope curve. Excellent preservation of Ara Group deposits and in particular the precise age constraints make the Ara Group representative for the seawater sulphur isotopic composition at the terminal Neoproterozoic--Cambrian boundary. As a result of the inherent variability of bacterial sulphate reduction, [delta][sup.34]S values at the lower end of the spectrum should be most representative for the global signal. Based on results of this study, the global signal is estimated to be approximately 35-40 [per thousand]. Keywords: Neoproterozoic, Cambrian, Oman, sulphur, isotope geochemistry.

New device models for circuit simulation are developed for high-power thyristor-type devices, such as gate-turn-off thyristors, integrated gate-commutated thyristors, and MOS turn-off thyristors. These models are based on semiconductor physics, which guarantees a wide range of validity. In particular, the proposed models are based on the lumped charge approach. Coupled electrical and thermal behavior is implemented to allow transient thermal simulations. To account for the nonuniform current distribution during turn-off, several of these single-cell models are connected in parallel to simulate a complete device. Simulation results are compared with measurements. Index Terms--Circuit simulation model, current spreading, gate-turn-off thyristor (GTO), high-power semiconductor, integrated gate-commutated thyristor (IGCT).

Biostratigraphic, carbon isotope, and U-Pb zircon geochronological data from the Ara Group of Oman indicate an abrupt last appearance of Cloudina and Namacalathus coincident with a large-magnitude, but short-lived negative excursion in the carbon isotope composition of seawater that is globally coincident with the Precambrian-Cambrian boundary. U-Pb zircon age data from an intercalated ash bed directly define this negative excursion to be at 542.0 [+ or -] 0.3 Ma, consistent with previous age constraints from Siberia and Namibia. Combined with the global biostratigraphic record, these new data strengthen hypotheses invoking mass extinction within terminal Proterozoic ecosystems at or near the Precambrian-Cambrian boundary. Keywords: extinction, Proterozoic, Cambrian, Oman, U-Pb, geochronology, carbon isotopes.

A new method is developed to embed DSP control algorithms into PSpice providing accurate time stamped simulation of real-time applications. The proposed method allows to build new PSpice models with an arbitrary number of external nodes using PSpice's Device Equation option. Sampled systems can be simulated including the effects of discrete sampling times as well as propagation delays caused by processors. Control code developed in C-language can be embedded into this PSpice control model prior to downloading into the real-time DSP environment. To verify the simulation approach, simulation results and experimntal results of a shunt active filter for harmonic current compensation in a three-phase system are presented. Index Terms--Device equation, PSpice, real-time DSP, shunt active filter, simulation.

Circuit simulation is a powerful tool for the design of high power converters, if suitable device models exist. Unfortunately, the commercially available circuit simulators do not have accurate models for high power semiconductors. Therefore, new device models are developed for power diodes and thyristor based devices, such as GTO, IGCT, and MTO. These models are based on semiconductor physics, which guarantees a wide range of validity. Electrical and thermal behavior is implemented, which allows transient temperature simulation. The models are programmed in the C++ language and are implemented in the widely used circuit simulator PSpice using the Device Equation Option. Simulation results are compared with measurements. Index Terms--Circuit simulation, GTO, high-power semiconductor, IGCT, MTO, physical model, PSpice, thermal model.

This paper evaluates the need for power-factor correction (PFC) in switched reluctance drive systems supplied from single-phase mains. The aim is to achieve interference values lower than the prescribed norms at minimal system costs and volume. It is shown that for certain applications, a PFC circuit has to be implemented, but simpler technical solutions are often possible. Finally, a suggestion is presented as to how a low-cost power-factor-corrected system should be built for high-volume production. Index Terms--Harmonics, power-factor correction, switched reluctance.

Byline: Rudolf Hering (1), Ralph Vorwerk (1), Hermann Wrigge (1), Jorg Zinserling (1), Stefan Schroder (1), Tilman von Spiegel (1), Andreas Hoeft (1), Christian Putensen (1) Keywords: Prone position Mechanical ventilation Cardiovascular function Indocyanine green clearance Gastric tonometry Intra-abdominal pressure Abstract: Objective: To investigate the effects of prone positioning on systemic hemodynamics, intra-abdominal pressure (IAP), plasma disappearance rate of indocyanine green (PDR.sub.ICG), and gastric intramucosal to arterial PCO.sub.2 difference (Pi-aCO.sub.2). Design and setting: Prospective randomized study in the intensive care unit of a university hospital. Patients: 12 mechanically ventilated, hemodynamically stable patients with acute lung injury. Intervention: Positioning supine and prone for 3 h in random order. Measurements: Systemic hemodynamics were determined by transpulmonary double-indicator dilution technique using an integrating fiberoptic monitoring system. The same monitoring system was used to measure PDR.sub.ICG. IAP was measured in the urinary bladder and gastric intramucosal PCO.sub.2 was evaluated by automated recirculation gas tonometry. Results: IAP increased from 10+-3 in the supine to 13+-4 mmHg in the prone position. Cardiac index increased from 3.8+-0.9 (supine) to 4.2+-0.6 l/m.sup.2 per minute (prone), mean arterial pressure from 75+-10 (supine) to 81+-11 mmHg (prone), PaO.sub.2/FIO.sub.2 from 194+-66 (supine) to 269+-68 mmHg (prone), and oxygen delivery from 558+-122 (supine) to 620+-74 ml/m.sup.2 per minute (prone). No other parameters, including PDR.sub.ICG and Pi-aCO.sub.2, differed between the two positions. Conclusions: Prone positioning in mechanically ventilated patients with acute lung injury, despite a small increase in IAP, does not negatively affect the hepatic capacity to eliminate ICG and gastric intramucosal energy balance when systemic blood flow and oxygenation are improved. Author Affiliation: (1) Department of Anesthesiology and Intensive Care Medicine, University of Bonn, Sigmund-Freud-Strasse 25, 53105 Bonn, Germany Article History: Received Date: 05/04/2001 Accepted Date: 30/10/2001 Article note: Electronic Publication

The phosducin-like protein (PhLP) was the resultant protein formed after cDNA isolation from rat brain with high phosducin homology. PhLP variants displayed indicated strong similarities with phosducin, although substantial differences were observed for N terminus length. PhLP showed binding capability with G-protein beta subunits through an unknown interaction process, implying a possible role in endogenous regulation of G-protein function.

The semiempirical PM3 method was used to study the type IV nucleophilic substitution reaction at the anomeric carbon of beta-nicotinamide riboside. Thestudy consisted of an investigation on the isoenergetic attacks of dimethyl ether on the trimethyloxonium cation and of trimethylamine on the tetramethylammonium cation. The findings demonstrate that the type IV nucleophilic substitution reactions investigated follow the general profile of gas-phase ion-molecule process. In particular, ion-dipole complexes exhibiting electrostatic interactions only precede the transition states.

Animal-like multicellular fossils appeared towards the end of the Precambrian, followed by a rapid increase in the abundance and diversity of fossils during the Early Cambrian period, an event also [...]

Dielectric materials are of great interest in a vast amount of applications ranging from cable insulation to advanced electronic devices. The emerging trend of device miniaturization is creating an increased demand for dielectric thin films that can be produced precisely on the nanometer scale. In addition, special mechanical properties are often required, for example in the field of flexible organic electronics. Polymers are first-choice materials for this purpose. However, it is extremely difficult to produce precise nanoscale thin films, which have a low defect density and are free of e.g. residual solvent, by wet chemistry approaches. Initiated chemical vapor deposition (iCVD) is a solvent-free polymer thin film deposition process which can be used to produce high quality dielectric thin films with nanoscale control and circumvents thus these problems. This work demonstrates the versatility of the iCVD process in the field of electrical applications by some new application examples of iCVD. By adding e.g. a hydrophobic organosiloxane thin film on columnar zinc oxide (ZnO:Fe) gas sensing structures there was a change in the selectivity from ethanol to hydrogen, as well as improved performance at high humidity level. The modified sensors can thus be used in humid ambient, especially for breathing tests, which can lead to the diagnosis of some diseases by cutting edge non-invasive approaches.