Maximum power point tracking converter based on the open-circuit voltage method for thermoelectric generators

Thermoelectric generators (TEGs) convert heat energy into electricity in a quantity dependant on the temperature difference across them and the electrical load applied. It is critical to track the optimum electrical operating point through the use of power electronic converters controlled by a Maximum Power Point Tracking (MPPT) algorithm. The MPPT method based on the opencircuit voltage is arguably the most suitable for the linear electrical characteristic of TEGs. This paper presents an innovative way to perform the open-circuit voltage measure during the pseudo-normal operation of the interfacing power electronic converter. The proposed MPPT technique is supported by theoretical analysis and used to control a synchronous buck-boost converter. The prototype MPPT converter is controlled by an inexpensive microcontroller, and a lead-acid battery is used to accumulate the harvested energy. Experimental results using commercial TEG devices prove that the converter accurately tracks the maximum power point during thermal transients. Precise measurements in steady state show that the converter finds the maximum power point with a tracking efficiency of 99.85%

The effect of temperature mismatch on thermoelectric generators electrically connected in series and parallel

The use of thermoelectric generators (TEGs) to recover useful energy from waste heat has increased rapidly in recent years with applications ranging from microwatts to kilowatts. Several thermoelectric modules can be connected in series and/or parallel (forming an array) to provide the required voltage and/or current. In most TEG systems the individual thermoelectric modules are subject to temperature mismatch due to operating conditions. Variability of the electro-thermal performance and mechanical clamping pressure of individual TEG modules are also sufficient to cause a significant mismatch. Consequently, when in operation each TEG in the array will have a different electrical operating point at which maximum energy can be extracted and problems of decreased power output arise.<p></p> This work analyses the impact of thermal imbalance on the power produced at module and system level in a TEG array. Experimental results clearly illustrate the issue and a theoretical model is presented to quantify the impact. The authors believe the experimental results presented in this paper are the first to validate a rigorous examination of the impact of mismatched operating temperatures on the power output of an array of thermoelectric generators

Constant heat characterisation and geometrical optimisation of thermoelectric generators

It is well known that for a thermoelectric generator (TEG) in thermal steady-state with constant temperature difference across it the maximum power point is found at half of the open-circuit voltage (or half of the short-circuit current). However, the effective thermal resistance of the TEG changes depending on the current drawn by the load in accordance with the parasitic Peltier effect. This article analyses the different case in which the input thermal power is constant and the temperature difference across the TEG varies depending on its effective thermal resistance. This situation occurs in most waste heat recovery applications because the available thermal power is at any time limited. The first part of this article presents the electrical characterisation of TEGs for constant-heat and it investigates the relationship between maximum power point and open-circuit voltage. The second part studies the maximum power that can be produced by TEGs with pellets (or legs) of different size and number, i.e. with different packing factors, and of different height. This work provides advice on the optimisation of the pellets geometrical parameters in order to increase the power generated, and consequently the thermodynamic efficiency, and to minimise the quantity of thermoelectric material used, for systems with limited input thermal power.</p

Regulation of the U3 small subunit processome and associated RNA-binding proteins

PhD ThesisThe rate of ribosome biogenesis regulates the growth rate of the cell and is believed to be linked to the cell’s proliferative potential. Moreover, ribosome production is down-regulated in terminally differentiated cells and up-regulated in the majority of cancers. rRNA transcription is regulated in these processes although much remains unclear about the regulation of rRNA processing. In eukaryotes, 18S ribosomal RNA (rRNA) processing is mediated by the small subunit (SSU) processome. This is composed of the U3 small nucleolar (sno)RNP, many sub-complexes and a range of putative rRNA binding and modifying proteins. It is not clear however, which proteins bind or cleave the pre-rRNA, with the exception of NOB1. Moreover, the majority of research to date has been conducted in the yeast Saccharomyces cerevisiae whereas the human SSU processome remains largely unstudied. Here we report that U3 snoRNP accumulation and function are regulated through the U3-specific hU3-55k protein. We demonstrate that U3 snoRNP levels are specifically down-regulated during human lung (CaLu-3) and colon (CaCo-2) epithelial cell differentiation and that this is likely mediated through regulating hU3- 55k levels. Moreover, CaCO-2 adenocarcinoma cells are believed to revert to their pre-cancerous phenotype during differentiation, suggesting that U3 snoRNP levels increase during tumourogenesis. We also show that phosphorylation of hU3-55k is likely to be essential for U3 snoRNP function; being required for the initial cleavage of the pre-rRNA. We therefore demonstrate two independent mechanisms that may regulate ribosome biogenesis through hU3-55k. We also demonstrate that the human and yeast SSU processomes contain many orthologous proteins. However, components responsible for 3’ pre-18S rRNA processing may function at temporally and spatially different points to their counterparts in yeast. Nonetheless, PNO1 and NOB1 are closely associated, with their nucleocytoplasmic shuttling affected by blocking pre-rRNA transcription, CRM1 mediated export and the mTOR pathway, likely preventing pre-40S export to the cytoplasm. This suggests yet another level of regulation to ribosome biogenesis through pre-rRNA processingBBSR

Diversity of New Zealand Deep-sea Amphipoda

Biodiversity and the ecological and evolutionary processes which influence faunal distributions are poorly understood in deep-sea habitats. This thesis assesses diversity of deep-sea amphipod crustaceans at three taxonomic levels (family, species, genetic) on continental margins of New Zealand relative to environmental variables. Sampling was undertaken at 20 stations located on Chatham Rise and Challenger Plateau, two major geomorphic features with contrasting environmental conditions. In Chapter 1, total diversity of the >12,500 amphipods assessed at the family-level revealed high abundance (range: 44 – 2074 individuals 1000 m⁻²) and taxonomic richness (27 families). Amphipod assemblages at all stations were largely dominated by the same families. Chatham Rise stations were mostly similar in family composition to one another and to the two closest Challenger Plateau stations. Overall, amphipod community composition correlated most strongly with surface chlorophyll a, suggesting strong benthic-pelagic coupling. In Chapter 2, I used molecular methods (COI DNA sequence thresholds of 6%) to estimate species diversity in the dominant amphipod family identified from Chapter 1 - the Phoxocephalidae. Analyses revealed 49 putative species-level taxa, which greatly exceeds the current number (n=17) of formally described New Zealand phoxocephalid species. A cluster of stations with highly similar taxa was identified, broadly distributed over the crest of the Chatham Rise, in association with elevated food availability. Similar to the family-level analyses of Chapter 1 multivariate analysis of phoxocephalid assemblages and environmental parameters revealed a strong correlation with measures of food supply. Analyses of inter-station assemblages revealed a major split between regions, indicating minimal overlap in taxon distributions on eastern and western continental margins. Chapter 3 examined genetic connectivity among deep-sea habitats. A phylogenetic analyses of three relatively abundant and widespread taxa; cf. Ampelisca chiltoni, cf. Oediceroides apicalis and Phoxocephalidae sp., was combined with available genetic data from a further 61 taxa collected from the same stations, to examine mean levels of inter-station genetic divergences. Nearly identical levels of genetic divergence were found between eastern and western regions for all three taxa. Furthermore, inter-station analysis of the wider amphipod community revealed similar patterns of genetic structure in most taxa. Based on molecular clock estimates, genetic divergences most likely corresponded to isolation following landmass changes during the Pleistocene. This thesis research has revealed a biodiversity hotspot on New Zealand continental margins. I conclude that Cook Strait and the subtropical front are important structures responsible for shaping benthic communities on New Zealand continental margins and that vicariance is likely to have played an important role in the evolutionary radiation of the New Zealand deep-sea fauna

Opposition to Government in early sixteenth-century Florence, 1494-1530

This examination of opposition tries to understand the political history of an Italian city -state in a new way. The aim of this study is to gain a better understanding of the nature of political conflict in Florence, and of the reasons for the instability of Florentine political life in the early sixteenth century. The concern is with plots, the violent overthrow of governments, and those condemned for speaking against the regime, rather than with simply critical opinion. These episodes of conflict between regimes and their opponents are the events from which the historian can learn most, both about the reasons for political conflict and its outcome, and about the strengths and weaknesses of both regimes and their opponents.Some of this opposition, such as the plot of February 1527, and those condemned for outspokenness against the regime throughout the period, is completely unknown to modern historians, and none has been examined in depth. This study examines opposition systematically for the first time, from a number of perspectives that have previously been neglected. It is based on extensive research in the Florentine archives, which permit us to give a full account, presented in the Appendices, of the political and social backgrounds of more than two hundred individuals involved in plots and other acts against the regime.There are two key aspects of opposition which concern Part One of this study: the role of foreign support in plots and the way in which conspiracy was affected by the advent of the Italian Wars in 1494; and how far conspiracy was characterized by the desire to introduce an aristocratic government to Florence or to re- establish the past regime. Part Two examines contemporary definitions and conceptions of political offences; the punishment of political crime; common attitudes towards plots and the way in which conspirators sought to explain and justify their deeds.The political and social backgrounds of opponents are examined in Part Three. The following questions are considered: how far was conspiracy the work of former supporters of the regime or long- standing opponents who had always sought its overthrow, of those from inside or outside the ruling circles of government, of those in power or those they had thrown out of it; what was the relationship between plots and the way in which regimes treated their opponents and supporters; and what were the respective roles of wealth, youth and nobility in plots? By considering opposition from these perspectives, this study recovers a significant part of the political history of Florence, and forces a re- evaluation both of the nature of political conflict in the city after 1494, and of the reasons for the instability of Florentine political life in the early sixteenth century

Embedding spanning bipartite graphs of small bandwidth

Boettcher, Schacht and Taraz gave a condition on the minimum degree of a graph G on n vertices that ensures G contains every r-chromatic graph H on n vertices of bounded degree and of bandwidth o(n), thereby proving a conjecture of Bollobas and Komlos. We strengthen this result in the case when H is bipartite. Indeed, we give an essentially best-possible condition on the degree sequence of a graph G on n vertices that forces G to contain every bipartite graph H on n vertices of bounded degree and of bandwidth o(n). This also implies an Ore-type result. In fact, we prove a much stronger result where the condition on G is relaxed to a certain robust expansion property. Our result also confirms the bipartite case of a conjecture of Balogh, Kostochka and Treglown concerning the degree sequence of a graph which forces a perfect H-packing.Comment: 23 pages, file updated, to appear in Combinatorics, Probability and Computin

Moral Uncertainty and Political Philosophy

This thesis addresses a methodological tendency in political philosophy whereby philosophers develop their ethical views independently of the political realm and then import those views into political argumentation intact, without considering whether this sort of primacy of the ethical is appropriate. Observing that the political is non-accidentally typified by disagreement about all manner of things, including, importantly, the ethical, reveals this to be deeply problematic. Through a discussion of moral epistemology, the thesis aims to show that we should not be certain about our moral beliefs in the face of disagreement, which means in turn that we must alter the way in which we approach political philosophy. It considers two responses to this concern: the Unilateral Solution, which argues that if you have access to the moral facts you may ignore disagreement, and the Pluralist Solution, which argues that moral disagreement ought to be taken seriously and that it is the job of political philosophy to provide a framework in which this disagreement can play out. After arguing that neither of these solutions is satisfactory, the thesis concludes that the moral uncertainty caused by disagreement is unavoidable, and offers some suggestions for how we might practice political philosophy in light of this situation

Influências ecológicas e filogenéticas sobre a dentição maxilar das serpentes

Usamos a dentição maxilar das serpentes como um sistema para investigar a importância relativa das pressões seletivas ecológicas e das restrições filogenéticas na determinação da morfologia. Examinamos a morfologia maxilar de três grupos de serpentes com diferentes dietas, com cada grupo compreendendo duas linhagens distintas-Boidae e Colubroidea. Nossos resultados sugerem que as pressões seletivas relacionadas à dieta podem ser mais significativas que a história filogenética na conformação da morfologia maxilar.Ecological and phylogenetic influences on maxillary dentition in snakes. The maxillary dentition of snakes was used as a system with which to investigate the relative importance of the interacting forces of ecological selective pressures and phylogenetic constraints in determining morphology. The maxillary morphology of three groups of snakes having different diets, with each group comprising two distinct lineages-boids and colubroids-was examined. Our results suggest that dietary selective pressures may be more significant than phylogenetic history in shaping maxillary morphology