In nature, all organisms face the daily challenges created by a fluctuating environment. Circadian clocks synchronize behaviour and physiology allowing an organism to adapt to and predict daily changes to environmental conditions. In the fruit fly, Drosophila melanogaster, circadian clocks reside in a set of ~150 neurons in the brain, collectively referred to as the central clock, and in the cells of many peripheral tissues. The central clock regulates daily behavioural rhythms, whereas peripheral clocks are thought to regulate the local metabolic activities of the cells in which they reside. In this thesis, I demonstrate that a peripheral clock resides in the abdominal fat body, a tissue analogous to the mammalian liver and adipocytes. Moreover, I show that flies display a temporal feeding pattern that is partly regulated by a peripheral clock. I propose that the central clock and peripheral clocks coordinate to regulate the timing of fly feeding behaviour.

In nature, all organisms face the daily challenges created by a fluctuating environment. Circadian clocks synchronize behaviour and physiology allowing an organism to adapt to and predict daily changes to environmental conditions. In the fruit fly, Drosophila melanogaster, circadian clocks reside in a set of ~150 neurons in the brain, collectively referred to as the central clock, and in the cells of many peripheral tissues. The central clock regulates daily behavioural rhythms, whereas peripheral clocks are thought to regulate the local metabolic activities of the cells in which they reside. In this thesis, I demonstrate that a peripheral clock resides in the abdominal fat body, a tissue analogous to the mammalian liver and adipocytes. Moreover, I show that flies display a temporal feeding pattern that is partly regulated by a peripheral clock. I propose that the central clock and peripheral clocks coordinate to regulate the timing of fly feeding behaviour.

Thesis (M.S.)--Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

published_or_final_version / Fine Arts / Master / Master of Philosophy

Despite teleosts being the largest and most diverse group of vertebrates, fish models currently used to study photoperiodic effects on fish physiology have been limited to a few species, most of which are temperate seasonal breeders. The overall aim of this work was to expand our knowledge on circadian biology and environmental physiological effects in Nile tilapia (Oreochromis niloticus niloticus), a continuous breeding species of tropical-subtropical origin. The circadian light axis of Nile tilapia is described with regards to melatonin production. Circadian melatonin profiles of fish under 12L:12D photoperiods were observed to be low at day and high at night, suggesting melatonin to be an entraining signal as observed in all other vertebrates. When constant light (LL) was used, such day and night fluctuations where abolished. However when fish where exposed to constant darkness (DD) a strong robust endogenous melatonin rhythm was found, suggesting the presence of circadian oscillators in this species. Importantly, this endogenous rhythm was observed to be maintained for at least three weeks under darkness and proved to be circadian in nature. Moreover, although the melatonin system was able to produce day and night melatonin rhythms when exposed to a different (6L:6D) photocycle, the oscillator appeared to not be entrainable to such a short photo cycle when exposed to DD, as melatonin levels remained high. When comparing the circadian organization of different teleost species including Nile tilapia, preliminary studies showed at least three divergent circadian light organizations in teleosts. Nile tilapia was characterised by a pineal gland far less sensitive than in other fish species as demonstrated through in vitro studies. Furthermore, pineal melatonin production was clearly dependent on the light perceived by the eyes as ophthalmectomy resulted in basal plasma melatonin levels during the dark period. These findings are the first to be reported in a teleost and could be comparable to the circadian light organization of higher vertebrates such as mammals. The onset of puberty of Nile tilapia was studied with regards to the newly discovered Kiss1/GPR54 system. Such a system has recently been discovered in mammals and found to be the primary switch of the brain-pituitary-gonadal (BPG) axis. The results of this study not only suggest a link between the Kiss1/GPR54 system and the onset of III puberty in this tropical batch spawning teleost, that would be a highly conserved feature across vertebrates, but also that the transcriptional mechanisms regulating GPR54 expression could be directly or indirectly influenced by light. Finally, a study was conducted on the effects of different intensities of continuous light (LL) on the growth and sexual development of Nile tilapia up to first maturation. The results showed a significant growth response of fish in all LL treatments compared to control fish. Importantly, this confirmed that LL enhances growth in this species and suggests that it is the light regime more than the intensity which is having an effect. This work thus provides important basic knowledge of the light entrainment pathway and circadian melatonin rhythms in Nile tilapia. Of special importance is the discovery of a strong endogenous melatonin oscillator and a novel circadian organization in fish which would seem to be homologous to that observed in higher vertebrates. Moreover, this work provides evidence that the newly discovered Kiss1/GPR54 system has a similar role in fish as has been found in mammals and that such a system could be directly or indirectly regulated by light. If so, Nile tilapia and other fish species could become important models in the chronobiology and reproduction fields. Finally, this work not only increases our basic and applied knowledge of this species, but also broadens our understanding of the circadian light axis in teleosts and its mediatory effects on reproduction.

The concept of time in physics underwent significant changes in the decades following World War II. This dissertation considers several ways in which American physicists grappled with these changes, analyzing the extent to which philosophical methods and questions played a role in physicists' engagement with time. Two lines of questioning run through the dissertation. The first asks about the professional identities of postwar American physicists in relation to philosophy, as exemplified by their engagement with the concept of time. The second analyzes the heterogeneous nature of time in physics, and the range of presuppositions and assumptions that have constituted this "fundamental" physical concept. The first chapter looks to the development of atomic clocks and atomic time standards from 1948-1958, and the ways in which new timekeeping technologies placed concepts such as “clock”, “second,” and “measure of time” in a state of flux. The second chapter looks to the experimental discovery of CP violation by particle physicists in the early 1960s, raising questions about nature of time understood as the variable “t” in the equations of quantum mechanics. The third chapter considers attempts to unify quantum mechanics and general relativity in the late 1960s, which prompted physicists to question the “existence” of time in relation to the universe as a whole. In each episode considered, physicists engaged with the concept of time in a variety of ways, revealing a multiplicity of relationships between physics, philosophy, and time. Further, in each case physicists brought a unique set of assumptions to their concepts of time, revealing the variety ways in which fundamental conceptsfunctioned and changed in late twentieth century physics. The result is a heterogeneous picture of the practice of physics, as well as one of physics’ most basic concepts. / History of Science

Thesis (Ph. D.)--University of Virginia, 2008. / Includes bibliographical references. Also available online through Digital Dissertations.

Circadian clocks are internal timekeepers that allow organisms to anticipate and exploit predictable daily changes in their environment, aiding survival. Clock-driven rhythms, such as asexual spore development (conidiation) in Neurospora crassa, show temperature compensated periodicity that persists in constant conditions and can be reset by environmental time cues. This ability of circadian clocks to maintain a constant period and phase of behaviour over a range of temperatures is important, and whilst much of the machinery making up the circadian clock is known, the mechanism that underpins temperature compensation is not well understood. Further, it is unknown how the clock can control conidiation in the face of changing temperatures. To investigate possible mechanisms underlying temperature compensation, I first explored how compensation may arise within the central clock machinery using a comprehensive dynamic model of the Neurospora crassa circadian clock. This clock incorporates key components of the clock, and I introduced known temperature-sensitive component changes based on experimental observations. This analysis indicated that temperature-dependent changes in the binding of CK-1a to the FRQ-FRH complex may be pivotal in the temperature compensation mechanism. Previous work has highlighted the importance of the blue-light photoreceptor VIVID (VVD), as VVD knockout strains show a temperature-dependent delay in the phase of peak conidiation. Next I explored this potential role using a theoretical output model. By incorporating regulation of this pathway by VVD, I found that VVD may contribute to phase control by increasing expression of genes or proteins that peak early on in the output pathway. RNA-Seq experiments were carried out to assess the contribution of VVD to the overall transcriptomic profile of Neurospora. The analysis highlighted several key genes through which VVD may regulate the conidiation pathway, including the clock-controlled genes eas and ccg-9, which both show temperature- and strain-dependent changes in expression patterns over the time course of conidiation. In conclusion, VVD may indeed have an important role in the temperature compensation of output pathways, though further work is needed to assess the specific
contributions of genes highlighted by my RNA-Seq analysis to the compensatory mechanism.

Na teoria quântica é usual se referir a probabilidade de encontrar uma partícula entre as posições x e x + dx no instante t, embora a teoria não forneça quando ocorre a detecção. Nos primórdios da teoria, Pauli apresentou um argumento refutando a ideia de introduzir um operador que descreva a probabilidade do instante em que ocorre a detecção. Mais tarde, Page e Wootters, motivados pelo fato de não se observar autoestados de superposição de energia, apresentaram um formalismo quântico não-relativista num espaço estendido em que espaço e tempo desempenham papéis equivalentes, sendo consistente com as indagações feitas por Pauli. Isso leva a uma descrição dada pela probabilidade condicional de encontrar uma partícula entre x e x + dx em relação ao tempo [t, t + dt] dado por outra partícula, chamada de partícula relógio. Essa dissertação consiste de uma revisão da proposta de Page e Wootters para abordar o problema do tempo na mecânica quântica bem como de uma análise detalhada desta utilizando de ferramentas recentes introduzidas na área de informação quântica para o tratamento de simetrias em física. / In quantum theory it is usual one refers to the probability of finding a particle between the positions x and x + dx at time t, although the theory does not provide when detection occurs. In the primordies of the theory, Pauli presented an argument refuting the idea of introducing an operator describing the probability of the instant in which the detection occurs. Later, Page and Wootters, motivated by the fact that one is not able to observe energy eigenstates superposition, presented a non-relativistic quantum formalism in an extended space in which space and time play equivalent roles, being consistent with Pauli´s inquiries. This leads to a description given by the conditional probability of finding a particle between x and x + dx in respect to the time [t, t + dt] given by another particle, called the clock particle. This dissertation consists in a review of the Page and Wootters proposal to address the time problem in quantum mechanics as well as a detailed analysis of this using recent tools introduced in the area of quantum information for the treatment of symmetries in physics.

My research topic concerns how learners use the analogue clock (as a human tool) to make meaning of clock time. This study is informed by a Vygotskian socio-cultural framework to learning and development based on the concept that human activities take place in cultural contexts and is mediated by tools. In this qualitative study I report on the learners meaning making of analogue clock time using the physical clock. This study was carried out at a South African primary school through an intervention programme after school. The research employed a case study method. It involved a purposeful sample of 4 learners (n=38) from the grade four class group based on their response to a baseline assessment task. The selected sample of learners included learners across the ability spectrum to gain rich insight into how learners make meaning of analogue clock time. Data collection and analysis was done through an interpretive approach. The video-taped interviews and intervention programme was my main instrument of data collection. Other research instruments included document analysis of responses to baseline assessment tasks. These research tools yielded the data collected and also allowed for triangulation. My research topic explored how the learners make meaning of analogue clock time. In particular the two-way movement of how the learners use the physical tool namely the analogue clock to develop meaning and how the clock mediates clock knowledge in return. The findings of the study suggest that learners’ find it difficult to conceptualise analogue clock symbols and signs, in particular, in Afrikaans the half hour concept, in relation to the two hands. The physical analogue clock is also important to support and extend clock knowledge in solving time-related problems. This shows the power of the analogue clock to mediate meaning making of clock time in young learners. Because of its potential to improve teaching and learning analogue clock time in primary school it is therefore recommended that the analogue clock time be further researched in South Africa.