Zugl.: Freiburg (Breisgau), Univ., Diss., 2009

Thesis (Ph. D.)--University of Chicago, Dept. of Pharmacological and Physiological Sciences, August 1999. / Includes bibliographical references. Also available on the Internet.

Mainz, Univ., Diss., 2001.

The aim of this thesis is to study the effects of turbulent flow on a fixed pitch tidal current turbine from the perspective of turbine design and operation. A prototype turbine, Deltastream as it is known, is being developed by Tidal Energy Ltd for deployment in Ramsey Sound, Wales. It is well known that turbulence plays an important role in the fatigue life of marine turbines. Field measurements of tidal flow at the turbine site were analysed to establish the velocity spectra and turbulence intensity. This revealed a wide range of anisotropic turbulence which is dependent upon the tidal direction with intensities ranging from 5-20%. A numerical turbine model based on momentum theory was constructed in a time marching formulation that accounts for the effects of dynamic inflow and rotationally augmented airfoil stall delay properties. The turbine rotor design allows for load alleviation by regulation of the turbine tip speed ratio. At flow velocities above the rated velocity the tip speed ratio can be increased to reduce turbine loads. The model has been combined with a novel rotor speed control algorithm that estimates unsteady turbine inflow velocity from turbine loading without the requirement for external sensing of flow speed. When the turbine is subjected to three dimensional turbulent inflow the rotor speed controller has been shown to significantly reduce the fatigue effect of unsteady, turbulent flow. The turbine blade design has been developed using the model established. Experimental validation studies were carried out at 1/16th scale in turbulent conditions. Studies using the model have; identified the relationship between turbulence intensity and turbine fatigue load, established a controller schedule to significantly reduce fatigue loading and determined the blading fatigue life in realistic turbulent flows.

Made available in DSpace on 2014-12-17T14:55:07Z (GMT). No. of bitstreams: 1 ClarissaLN.pdf: 3152047 bytes, checksum: a2e14bfa9e4c314444ebb4284dc7608b (MD5) Previous issue date: 2008-10-21 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / This work presents a theoretical and experimental investigation about the properties of microstrip antennas for ultra-wideband systems. Configurations of elliptic monopoles with different eccentricities and circular monopoles are considered. Two prototypes for each antenna configuration were built, one with the typical microstrip configuration and the other is similar to the first, except for a small aperture in the ground plane. Therefore, this work proposes to modify the configuration of the ground plane of the monopoles designed adding a rectangular stub, in order to optimize and improve the performance of such structures. The obtained results show that the introduction of that rectangular aperture in the ground plane allows an improvement of the frequency response for the considered antenna propotypes. It is observed a good agreement between the measured and simulated results. Finally, some proposals for future works are presented / Este trabalho apresenta uma investiga??o te?rica e experimental sobre as propriedades de antenas de microfita para sistemas de banda ultra larga. S?o consideradas configura??es de monopolos el?pticos com excentricidades diferentes, e monopolos circulares. Foram constru?dos dois prot?tipos para cada configura??o de antena, um com a configura??o t?pica de microfita e outro similar ao primeiro, mas com uma pequena abertura no plano de terra. Assim, este trabalho objetiva modificar a configura??o do plano de terra dos monopolos projetados atrav?s da inser??o de um recorte retangular, para fins de otimiza??o e melhoria nos desempenhos das estruturas. Os resultados obtidos mostram que a introdu??o dessa abertura retangular no plano de terra permite melhorar a resposta em freq??ncia das antenas consideradas. Observa-se uma boa concord?ncia entre os resultados medidos e simulados. Algumas propostas para a realiza??o de trabalhos futuros s?o apresentadas

Abstract In dim light, reliable coding of visual information becomes compromised, unless the sensitivity of the visual system to light is improved by structural and functional adaptations. Thus far, many adaptations for night vision in the compound eyes of nocturnal insects have been described, but little is known about the mechanisms underlying the electrochemical signalling in their photoreceptors. In this thesis, whole-cell patch-clamp and mathematical modelling are utilised to study basic electrical properties and ionic currents in photoreceptors of two nocturnal insects, the American cockroach Periplaneta americana and the field cricket Gryllus bimaculatus. Photoreceptors in both species showed large input resistance, membrane capacitance and phototransduction gain (large single photon responses) compared with most studied diurnal insects, providing improved sensitivity to light. The photoreceptors also expressed two voltage-sensitive outward currents: a transient current and a sustained current. The cricket photoreceptor expressed a dominating transient current, which is a typical characteristic for insects adapted for slow vision in dim light. By contrast, in the majority of cockroach photoreceptors the sustained current dominated, which is more common among fast diurnal species. Model simulations indicated that the sustained current is necessary for improved photoreceptor dynamics. Examination of light-induced currents suggested that the functional variability in cockroach photoreceptors is in part derived from variations in the total area of the photosensitive membrane. Recordings of light-induced currents also revealed that the cockroach light-gated channels are only moderately Ca2+-selective and that the polarisation-sensitive photoreceptors of the cricket may utilise phototransduction machinery in some details different from that in regular photoreceptors. Furthermore, the dynamics and information transfer rates of polarisation-sensitive photoreceptors in the cricket were clearly inferior to their regular counterparts, suggesting that they are not necessary for image formation.

Thomas Patch (1725-1782) is a relatively unknown English artist of the eighteenth century whose claim to fame so far has rested in his caricature work. He went to Rome around 1747, was banished from there in 1755 and joined the English circle in Florence where he remained until his death in 1782. Patch's work in Florence included his copying of what Vasari had said to be a fresco cycle by Giotto in the Church of the Carmine. This cycle had been damaged in a fire that broke out in the old church in 1771, and it had to be destroyed to make way for the new church that was completed in 1773. What led Patch to do this work? How successful was he? We see the influences of Hugford and Bottari and the lively interest of connoisseurship in the medieval and the Trecento. Patch's skill as a copyist is analyzed and found to be excellent. There are now only twelve fragments left of the original fresco and they have been given a variety of attributions. On the basis of dating, this paper agrees with those who reject the Giotto attribution and it is not prepared to accept the Spinello Aretino one without additional confirmation. The cycle does not appear to fit the style and character of Spinello in the period to which it is usually assigned. Recent evidence however still makes it worth while to leave the door open to Spinello though on the basis of style and spatial utilization, other artists of this period should also be considered. When compared with other Saint John the Baptist cycles, the iconography shows the master of the Manetti Chapel frescoes to have been an inventive and imaginative artist whom both Masaccio and Agnolo Gaddi thought worthy of emulating and copying. His inventiveness is seen in the fact that though he seems to have got ideas from the Peruzzi Chapel and from the doors of the Baptistery, he put his own stamp on them. His angel in flight, his headless body of Saint John, his shivering Christ and his many re-arrangements of crowd scenes give ample evidence of an innovati.ve-ness which is only surpassed by his skill at integrating his scenes. Patch's engravings therefore should form an important incentive to further assessment of the work of Spinello and his possible influence on the late Trecento and Quattrocento Italian art. They also form a pathway for the study of influences of this period on eighteenth century English art. Patch represents a whole era of connoisseurship and is a possible source of valuable character study of the English emigre community of late eighteenth century Florence. His work merits a great deal more consideration than it has so far received in the history of art. / Arts, Faculty of / Art History, Visual Art and Theory, Department of / Graduate

Research focusing on static scenes with static objects is omitting the time factor from real life examples we are trying to study. Can we say that a lifeguard looking for a drowning man is using the same brain processes that were observed in the laboratory for static scenes? We can conclude that a static scene is a big simplification of the task itself. The aim of this thesis is to prepare a tool which would allow researching dynamic scenes and thus broadening the possibilities of visual detection tasks at hand. Along the tool we also present a couple of simplified examples with which we would like to demonstrate the utilization of the tool. All concluding with a final experiment in which we will try to detect masked patterns in a noisy environment. 1

Foraging behavior has recently become a popular area of research with which ethologists, behavioral ecologists, and experimental psychologists converge their traditionally separate disciplines into a more multidisciplinary framework. Ethologists and behavioral ecologists usually study foraging as it occurs in the natural environment or the "field," while experimental psychologists contrive laboratory simulations of foraging and make the assumption, sometimes incorrectly, that generalization occurs across settings, situations, and species. Scientific advances are now beginning to occur in the ability of laboratory researchers to better simulate foraging as it occurs in the field. Field researchers are also becoming more willing to accept these findings as important. The purpose of this dissertation was to use a laboratory analogue of foraging behavior to examine the effects of prey vulnerability, density, and prey-patch replenishment on the number of prey rejections and switches between patches. This analogue may have more biological validity than previous simulations in the operant laboratory by simulating conditions of replenishing and depleting patches under adjusting (progressive and regressive) random-ratio schedules of reinforcement. Three experiments were conducted. The first examined the effects of response-cost on acceptability of prey items offered. Results indicated that as the cost of obtaining one prey item increased while the cost of another was held constant, subjects consistently pursued the lower-cost prey and rejected higher-cost prey at increasing probability ratios of 1:3, 1:10, and 1:15. The second experiment covaried response cost (vulnerability) with the probability of encounter (density) for two prey types and evaluated their effects on the acceptability of prey. This experiment showed that when the density of the low-cost prey increased (p = .66), the subjects were more selective. Subjects were less selective when the density of the low-cost prey decreased (p = .33). In the third experiment, prey patches were replenished at reinforcer-determined (regressive random ratio) baseline rates and compared to several fixed-time schedules of patch replenishment. Results of Experiment III indicated no major differences in patch use behaviors (number of switches between patches). The validity and utility of this simulation was discussed as a useful model for the experimental analysis of foraging behavior.

At the neuromuscular junction, nicotinic acetylcholine receptors (AChRs) convert chemical stimuli into electrical signals. They are heteropentameric membrane protein complexes assembled from four evolutionary related subunits (two α subunits, and one each of the β-, δ-, and ε-subunits), arranged around a central ion-conducting pore, which is regulated by the neurotransmitter acetylcholine. Understanding how the binding of acetylcholine leads to channel opening is of fundamental importance. While it is known that channel opening results from a global conformational change involving the cooperative action of all five subunits, how the subunits achieve this cooperativity is unclear. Our hypothesis is that this subunit cooperation is maintained through coevolution of the subunits, and thus studies of subunit coevolution can provide insight into subunit cooperativity. Using an ancestral reconstruction approach, combined with single-molecule patch clamp electrophysiology, we have begun dissecting the mechanistic consequences of preventing coevolution of the acetylcholine receptor β-subunit. This approach has allowed us to identify new amino acid determinants of acetylcholine receptor function.