Diss.--Philosophie--Chapel Hill, N.C.--Univ., 1994. / Bibliogr. p. 264-303.

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This project's purpose was to understand the workings of a new theorem introduced in a professional paper on the cutwidth of meshes and then use this knowledge to apply it to the search for the cyclic cutwidth of the n-cube.

L'anneau de Grothendieck d'une structure a été défini par Tom Scanlon et Jan Krajicek d'une part, et François Loeser et Jan Dnf d'autre part. Il est obtenuà partir des ensembles définissables et des deux opérations d'union disjointe et de produit cartésien, en identifiant deux ensembles en bijection définissable.En nous appuyant sur des techniques mêlant topologie et combinatoire, nous montrons dans cette thèse, que les anneaux Z×Z, Z, Z[X], Z/NZ et (Z/NZ)[X] (pour N ∈ Z+) peuvent s'obtenir comme anneaux de Grothendieck de certaines structures.Dans une première partie, après avoir rappelé la construction des anneaux de Grothendieck et donné un bref aperçu de ceux déjà connus, nous préciserons le cadre d'application des techniques mises en œuvre dans les chapitres suivant.La deuxième partie est consacrée au calcul explicite de certains anneaux de Grothendieck.Nous montrons d'abord que Z×Z est l'anneau de Grothendieck des fonctions de paires sans cycles.Dans les chapitres suivants, nous proposons pour chaque anneau préalablement choisi une structure qui l'admette comme anneau de Grothendieck / The notion of Grothendieck ring of a structure has been introduced by Tom Scanlon et Jan Krajicek on the one hand. François Loeser and Jan Dnf on the other hand.This ring is obtained from the definable sets and from the operation of disjoint unions and cartesian product, by identifying the definable sets which are in definable bijection.By using thechnics involving topoligal ideas and combinatorics, we show thaht the rings Z×Z, Z, Z[X], Z/NZ et (Z/NZ)[X] (for N ∈ Z+) are the Grothendieck ring of some structures.In particular, Z×Z is the Grothendieck ring of the pairing function with no cycles.As for the other rings, we build construction specially designed to admit as Grothendick ring, the ring prealably chosen

No / There is an increasing interest in the use of Ground Source Heat Pumps (GSHPs) as a source of renewable energy in temperate countries. GSHPs coupled with buried heat collectors can harness the thermal energy from near-surface soils to provide the heating required for domestic properties. The performance of a GSHP system depends greatly on the thermal conductivity of the surrounding soils. Near-surface soils undergo cycles of drying and wetting due to, for example, the infiltration of rain water and/or fluctuations of the ground water table. Several parameters - including the properties of soil, suction head and saturation history - affect the thermal properties as well as the retention and flow of water. This paper presents results from a comprehensive laboratory investigation on sand samples with markedly different grain size distribution. Simultaneous measurements of thermal and hydraulic properties of the sands were taken under incremental increase/decrease in the suction head values to simulate cycles of drying and wetting. The results clearly suggest that the thermal conductivity is better expressed as a function of the matric suction head so as to reflect the saturation history. There has been almost five-fold increase in the measured value of thermal conductivity when the soil was wetted to a residual degree of saturation from being dry.

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It is clear that there is no long-term solution to energy supply problems other than planned and continuous conservation. The use of low-grade energy as an unlimited resource will play an important part in maintaining the balance between the future of the world for both developed and developing countries alike. A literature survey reviewing the most promising approaches to the construction of low-grade energy engines has been conducted. The validity of each feasible system has been examined and the principles of operation described. A feasibility study concerning the adoption_of the organic Rankine cycle utilizing common suitable refrigerants (e.g. halo-carbons) as working fluids has been conducted. In particular, the use of a multiple vane expander as the prime mover has been fully investigated. A suite of computer programs has been developed to: • describe working fluid properties; • optimise the geometrical and dynamical parameters of the Rankine cycle to achieve the most efficient operation in both steady and transient states; • optimise the mechanical design of the expander depending upon the mode of operation and the source and sink characteristics. A fully flexible experimental test facility was constructed so as to be capable of testing a wide variety of prime movers. This has been operated for a real time test period in excess of 300 hours. The test results are encouraging. Efficiencies were measured in accordance with the mathematical predictions and a portfolio of suggested modifications towards a high efficiency, low-cost, robust and reliable expander capable of utilising low grade thermal energy has been produced. Fruitful links with relevant British industries have been forged. Demonstrations of the system are planned within the UK and overseas.

Annual lipid cycles were determined for adult male and female Cnemidophorus tigris collected near El Paso, Texas during 1970-1971.