Exergy based fluid selection for a geothermal Organic Rankine Cycle for combined heat and power generation

In this study the option of combined heat and power generation was considered for geothermal resources at a temperature level below 450 K. Series and parallel circuits of an Organic Rankine Cycle (ORC) and an additional heat generation were compared by second law analysis. Depending on operating parameters criteria for the choice of the working fluid were identified. The results show that due to a combined heat and power generation, the second law efficiency of a geothermal power plant can be significantly increased in comparison to a power generation. The most efficient concept is a series circuit with an organic working fluid that shows high critical temperatures like isopentane. For parallel circuits and for power generation, fluids like R227ea with low critical temperatures are to be preferred.     

Lake George as a Sink for Contaminants Derived from the Kilembe Copper Mining Area, Western Uganda

Abstract  The copper mine at Kilembe in the Ruwenzori Mountains in western Uganda ceased to operate in 1978 but a steady flow of contaminants, including Cu, Co, Ni, Zn, Cd, and sulphate, continues to enter the Nyamwamba-Rukoki River, which passes through Queen Elizabeth National Park, and finally flows into Lake George. Lake George is quite shallow, alkaline, and highly eutrophic. Measuring mass-flow of contaminants, water, and suspended solids in the Rukoki River near Kasese allowed us to estimate their input into Lake George. Grid sampling of lake sediments indicated that the contaminants settle near the two mouths of the river; low concentrations in a drill core in the centre of Lake George indicate that further dispersion within the lake is small. Sequential extraction experiments on lake sediments and lake water analyses suggest low bioavailability of the heavy metals. We conclude that Lake George is a highly resilient system that efficiently immobilises contaminants. Though there is no health risk for the population under present environmental conditions, a reduction of the contaminant load is desirable.     

Termination Proofs for Ground Rewrite Systems – Interpretations and Derivational Complexity

It is shown that finite terminating ground term rewrite systems have linearly bounded derivational complexity. This is proven via some suitable interpretation into the natural numbers. Terminating ground systems are not necessarily totally terminating, i.e., a strictly monotone interpretation into a well-order might not exist. We show, however, that those systems are almostω-terminating in the sense that such an interpretation into the sum of a finite partial order and the natural numbers always effectively exists. Finally, we show that for ground systems total termination is equivalent to ω-termination, and that this is a decidable property. Received: December 8, 1999     

Persönliches

Ohne Zusammenfassung     

Properties of melt and thermal processes during solidification in jewellery casting

A survey is made of the significant thermal properties pertaining to liquid and solidifying jewellery alloys, and some properties of the investment are also considered. Values found in the literature, or measured in our own investigations are used together with estimates. A relatively simple model for solidification is presented. Some parameters such as volume/surface area ratio, superheat and solidification temperature are discussed. The solidification behaviour of a simplified ring is investigated in more detail using the model. In addition, some observations were made whilst casting spirals.     

Umgang mit Medizinethik in den Medien

Ohne Zusammenfassung     

Vergleichende h?matologische Untersuchungen an wildlebenden Wiederk?uern (Rehe, Rotwild, Gemsen, Rentiere)

Zusammenfassung In dieser zweiten Mitteilung wird über das weiße Blutbild von 11 Stück Rotwild, 13 Rehen, 34 Gemsen und 10 Rentieren berichtet. Rot-, Reh- und Gamswild besitzen ein lymphozytäres Blutbild; bei Rentieren überwiegt dagegen der Anteil granulozytärer neutrophiler Leucozyten. Es wurden Unterschiede in der Leucozytenzahl, dem Differentialblutbild gefunden, die auf die Tierspecies, den Parasitenbefall, das Alter der Tiere sowie die Begleitumstände der Blutentnahme zurückzuführen sind.

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Summary This second communication deals with the total leucozyte count and differentiation of leucocytes from red deer (n=11), roe deer (n-13), reindeer (n-10) and chamois (n=34). In red deer, roe deer and chamois but in contrast to reindeer, lymphocytes are the predominating white blood cells.There were differences due to the animal species, parasitic infestations, age of the animal and the circumstance of the blood sampling procedure.

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Résumé Dans cette deuxième communication sur les critères hématologiques des Ruminants sauvages, il est fait état du nombre des leucocytes et de la formule sanguine des globules blancs. Les lymphocytes sont en nombre plus élevé que les granulocytes chez le Cerf (n=11), le Chevreuil (n-13), le Chamois (n=34), mais chez le Renne d'Europe (n=10).Des différences sont observées, dépendantes de l'espèce, de l'âge, de la condition physique et des circonstances de la prise de sang. Les résultats sont discutés et comparés aux données hématologiques de ruminants domestiques et de quelques autres ruminants sauvages.