published_or_final_version / Physics / Master / Master of Philosophy

published_or_final_version / Radioisotope / Master / Master of Science

published_or_final_version / Microbiology / Master / Master of Medical Sciences

published_or_final_version / Education / Doctoral / Doctor of Philosophy

Dynamic logic circuits are highly suitable for high-speed applications, considering the fact that they have a smaller area and faster transition. However, their application in space or other radiation-rich environments has been significantly inhibited by their susceptibility to radiation effects. This work begins with the basic operations of dynamic logic circuits, elaborates upon the physics underlying their radiation vulnerability, and evaluates three techniques that harden dynamic logic from the layout: drain extension, pulse quenching, and a proposed method. The drain extension method adds an extra drain to the sensitive node in order to improve charge sharing, the pulse quenching scheme utilizes charge sharing by duplicating a component that offsets the transient pulse, and the proposed technique takes advantage of both. Domino buffers designed using these three techniques, along with a conventional design as reference, were modeled and simulated using a 3D TCAD tool. Simulation results confirm a significant reduction of soft error rate in the proposed technique and suggest a greater reduction with angled incidence. A 130 nm chip containing designed buffer and register chains was fabricated and tested with heavy ion irradiation. According to the experiment results, the proposed design achieved 30% soft error rate reduction, with 19%, 20%, and 10% overhead in speed, power, and area, respectively.

Coral reefs are important to sustain marine ecosystems and provide a reliable resource for studying past climate. Corals are increasingly challenged by changing environments. The marginal corals of Hong Kong provide a natural laboratory to study the combination of environmental conditions controlling coral distribution and growth. Salinity and pH were found to impact corals in studies of coral distribution, extension, and culture. Hong Kong corals have low extension rates (1.2-11.4 mm/yr) and do not colonize in areas of low in salinity and pH. Ten years of instrumental records showed extension related positively to summer salinity and dissolved oxygen. Winter seawater temperature was inversely related to extension, while chlorophyll a showed positive relationship in autumn and winter. Culture results show low salinity negatively impacted coral calcification, photosynthesis, and extension. Corals exhibited reduced growth, paling and bleached. In contrast, coral growth increased under high pCO2, but corals decalcified in dark indicating underlying mechanisms may be altering coral physiology. The boron isotope (δ11B) proxy in corals is able to reconstruct past seawater pH when the pH of the extracellular calcifying fluid (ECF) is considered. A pH offset (ΔpH) was recorded in reconstructed pHsw due to ion pumping to ensure the ECF is saturated with respect to aragonite. By incorporating carbon isotopes (δ13C) into the δ11B-ΔpH relationship, δ11B can be corrected to remove ECF processes and reconstruct seawater pH. Culture results indicated δ11Baxial from axial tip recorded pH similar to other studies while low salinity impacted δ11Bbasal at the base. The different relationship shown from the same colony within the same cultured conditions suggested vital effects with differing coral metabolisms. δ11Baxial and δ11Bbasal related to extension but insignificantly. The large isotopic offset between δ11Baxial and δ11Bbasal indicated different growth mechanisms could possibly affected boron incorporation. The δ11B variation within a coral colony suggested careful and precise sampling for pH reconstructions is important. / published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

Anthropogenically driven climate change not only results in rising of sea temperature but also leads to more frequent and longer-lasting cold and heat waves. Meanwhile, coastal marine ecosystems are constantly challenged by increasing threats of chemical pollution. Temperature and chemical stressors can jointly affect the livelihood of marine organisms, but their combined effects are still poorly understood. Therefore, this study aimed to investigate the effects of thermal stress and chemical exposure on the marine medaka Oryzias melastigma, copepod Tigriopus japonicus and rotifer Brachionus koreanus. The four selected chemical contaminants included copper sulphate pentahydrate (Cu), dichlorophenyltrichloroethane (DDT), triphenyltin chloride and copper pyrithione. It was hypothesized that marine organisms are more susceptible to chemical exposure at both cold and warm extremes. In vivo acute ecotoxicity tests were conducted over a wide temperature range to ascertain the relationship between thermal stress and chemical toxicity. For O. melastigma larvae, the lowest toxicity occurred at an optimum temperature range; the chemical toxicity further increased with temperature increase or decrease from this optimum, and exacerbated at extremely low and high temperatures. For T. japonicus and B. koreanus, the chemical toxicity generally increased with increasing temperature. Such inter-species dissimilarities were possibly due to differences in the uptake route, detoxification mechanism, avoidance behaviour and physiological response between the fish and the copepod or rotifer. Experiments were conducted to evaluate the temperature-dependent physiological and biochemical responses, and thermal tolerance of O. melastigma larvae. The growth in the fish larvae showed an inverse and negatively skewed V-shape relationship with temperature, with a significant reduction in performance at both low and high thermal extremes. A mismatch between demand and supply of oxygen and energy under extremely cold and warm conditions was probably the primary cause of growth inhibition and metabolic impairment, leading to a temporary adaptation by a shift to anaerobiosis and an induction of heat shock proteins (HSPs). Temperatures at both cold and warm extremes increased toxicities of DDT and Cu to O. melastigma larvae, resulting in restricted growth and interrupted oxygen consumption rate. The fish larvae modulated their metabolic pathway and produced stress proteins (i.e., HSPs and metallothioneins) for adaptation to the combined stress. However, such responses were disrupted by combinations of thermal extremes, in particular high temperature, and high chemical concentration. Most importantly, both DDT and Cu exposure significantly reduced the thermal tolerance of the fish larvae. The interacting effect of temperature and Cu was also investigated on T. japonicus. The results showed that their combined effect could significantly reduce the survival, lengthen the developmental time and change the sex ratio of the copepod. Transcriptions of several stress-related genes (i.e., glutathione reductase, glutathione S-transferases and HSPs) in the adult T. japonicus were significantly affected by the joint-effect of temperature and Cu exposure, implying that these genes played essential roles in protecting the cellular integrity against the stresses. This study advanced the understanding on the temperature-dependent toxicity of chemical contaminants to marine organisms, and provided valuable information and empirical models for deriving water quality criteria of chemical contaminants at various temperatures. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

<p>Denna studie har genom halvstrukturerade kvalitativa intervjuer med 13 högstadieelever undersökt hur eleverna upplever två reklamfilmer mot mobbing. Filmerna har lanserats av stiftelsen Friends och utgör en del i deras arbete mot mobbing. Resultatet sammanställdes genom induktiv tematisk analys och åtta teman framkom. Temana var: Känsloprocess, Indirekt mobbing berör mer än direkt mobbing, Kan hända vem som helst, Förståelse för mobboffret, Hjälparen väcker beundran, Medlöparens brist på ingripande, Lärarens passivitet irriterar samt Alla kan hjälpa till. Det resultat som framkom jämfördes med det som Friends önskade att åskådaren skulle uppleva. Resultatet kopplades även ihop med teorierna bystander-effect och empati. Det visade sig att intervjupersonerna i stort upplevde filmerna som Friends önskade.</p>

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