O nitrato é uma das principais fontes de nitrogênio disponível para as plantas, sendo a nitrato redutase (NR) a enzima responsável pela sua redução a nitrito. O nitrito é considerado tóxico em altas concentrações e, por esse motivo, a atividade da NR possui uma regulação complexa, principalmente em nível transcricional e pós-traducional. Trabalhos anteriores do nosso grupo, utilizando plantas de abacaxizeiro cultivadas in vitro, demonstraram que, em condições de termoperíodo de 28ºC dia/15ºC noite, as raízes apresentaram um estímulo positivo de atividade da NR na ausência de luz quando comparado às plantas crescidas em temperatura constante de 28ºC, associado posteriormente à atividade da NR de membrana plasmática (NRPM). Baseado nesses resultados questionou-se qual seria a influência da aplicação do estímulo de frio associado ou não à presença de luz na atividade da NR em folhas e raízes de abacaxizeiro. Este trabalho teve como objetivos investigar os efeitos do frio na atividade da NR em folhas e raízes de abacaxizeiro em diferentes tempos de exposição, na presença ou ausência da luz e em diferentes fases do ciclo de 24 horas (claro/escuro). Buscou-se averiguar qual NR estaria envolvida nessas respostas: a NR citossólica (NRc) ou de membrana plasmática (NRPM), assim como verificar o envolvimento do NO na sinalização pela baixa temperatura. O ritmo diário de atividade da NR também foi avaliado, logo após a exposição ao frio, em diferentes fases do ciclo de claro/escuro. As plantas foram expostas a 1, 3, 6 ou 9 horas a 10ºC ou 25ºC (controle) na luz ou no escuro. A NR foi avaliada pelo método in vitro. O estímulo positivo na atividade da NR pelo frio ocorreu principalmente após 6 horas no claro, para as folhas, e após 6 horas no escuro, para as raízes. Novas plantas foram submetidas às mesmas condições para o fracionamento celular, mostrando que, tanto em folhas como em raízes, o incremento de atividade da NR observado a 10ºC foi associado à NR citossólica (NRc). Em ambos os casos, o estímulo ocorreu utilizando-se o NADPH como doador de elétrons, sugerindo o possível envolvimento de uma isoforma NAD(P)H biespecífica. A quantificação do NO foi realizada por leitura em espectrofluorímetro, apontando uma maior emissão induzida pelo frio para as folhas tanto na presença da luz (após 1 e 3 horas) como em sua ausência (1 e 9 horas) e em raízes apenas no escuro (9 horas), sugerindo o envolvimento do NO na sinalização da baixa temperatura. Para verificar a influência do frio em diferentes fases do dia, 4 horários foram selecionados (início da fase clara, meio da fase clara, início da fase escura, meio da fase escura) para início de cada experimento. A NR foi medida logo após a exposição ao frio (6 horas a 10ºC), pelo método in vitro e durante 24 horas em reaquecimento (25ºC), quantificada a cada 3 horas pelo método in vivo. As raízes apresentaram aumento da atividade da NR apenas quando o estímulo da baixa temperatura foi aplicado na fase escura, enquanto as folhas sofreram incremento da atividade da NR independente da condição luminosa. Em reaquecimento, a NR das folhas teve seu ritmo atrasado em todas as situações, com exceção quando o frio foi aplicado no início da fase escura, na qual houve perda quase completa de variação ao longo do dia. As raízes não mostraram grandes alterações no ritmo diário da NR. Este trabalho mostrou que a temperatura de 10ºC tem efeitos diferentes sobre folhas e raízes, sendo que as modificações na atividade da NR, em curto prazo, parecem ocorrer por alterações na NRc. O NO parece estar envolvido na sinalização do frio, mas não se determinou sua origem biossintética. As raízes tiveram um aumento da atividade da NR pela baixa temperatura, que foi dependente do escuro, enquanto as respostas das folhas dependeram da fase do ciclo na qual foram submetidas a 10ºC / Nitrate is the main nitrogen source available to plants, and nitrate reductase (NR) is the enzyme responsible for its reduction to nitrite. Because of its toxicity in high concentrations, nitrite production by NR has a complex regulation, especially at transcriptional and post-translational level. A previous work from our group, using pineapple plants cultivated in vitro, showed that, under thermoperiod of 28ºC day/15ºC night, NR activity increased in roots during absence of light compared to activity in plants grown under constant temperature of 28ºC. Based on these results it was questioned what would be the effect of cold stimulus application with or without light on NR activity in leaves and roots of pineapple plants. This study aimed to investigate the effects of low temperature on NR activity in leaves and roots of pineapple plants at different exposure times in the presence or absence of light and at different phases of a 24 hour cycle (light/darkness). We also investigated which NR was involved in these responses: cytosolic (cNR) or plasma membrane NR (PMNR), as well as verifying the role of nitric oxide (NO) signaling at low temperature. Furthermore, the NR daily rhythm activity was measured after cold exposure, in different phases of the light/dark cycle. Plants were exposed to 10ºC or 25ºC (control group) during 1, 3, 6 or 9 hours. NR was quantified by in vitro method. In the leaves, the increase of NR activity by low temperature (10ºC) occurred mainly after 6 hours in the presence of light, while in the roots the highest NR activity occurred after 6 hours at 10ºC in darkness. Based on these results, other groups of plants were subjected to the same conditions for cell partitioning, showing that in both leaves and roots the increase of NR activity by cold was associated with cytosolic NR (NRc). In both cases, the positive stimulation occurred with NADPH as the electron donor, suggesting the possible involvement of a NAD(P)H bispecific isoform. NO quantification, measured by spectrofluorimetry, indicated a greater emission induced by cold in the leaves both in the presence (after 1 and 3 hours) and absence (1 and 9 hours) of light and in roots only in darkness (9 hours), suggesting an involvement of NO in low temperature signaling. To evaluate the influence of cold at different day phases, we performed 4 experiments beginning at different times of the 24-hour cycle (beginning of light phase, middle of light phase, beginning of dark phase, middle of dark phase). NR activity was measured immediately after cold exposure (6 hours at 10°C) by in vitro method and after rewarming at 25°C during 24 hours, quantified by in vivo method every 3 hours. In roots, NR activity showed an increase only when the cold stimulus was applied at dark phase, while in leaves, NR was independent of the light condition. Upon rewarming, leaves presented a delay in NR daily behavior in all situations, except when low temperature was applied at the beginning of dark phase, showing almost no variation throughout the day. This study demonstrated that the temperature of 10ºC affected leaves and roots differently, and the changes in NR activity after short exposure time could be associated with NRc. NO seemed to be involved in cold signaling, but its biosynthetic origin has not been determined yet. Roots showed an increment of NR activity by low temperature dependent of the dark condition, while the responses of leaves depended on the phase of the 24-hour cycle in which they were subjected to 10ºC

Ultracold molecules promise a revolutionary test bed for quantum science with applications ranging from experiments that probe the nature of our universe, to hosting new platforms for quantum computing. Cooling and trapping molecules in the ultracold regime is the first step to unlocking the wide array of proposed applications, and developing these techniques to control molecules is a key but challenging research field. In this thesis, we describe progress towards a new apparatus designed to cool and trap barium monohydride (BaH), a molecule that is amenable to laser cooling and has prospects as a precursor for ultracold atomic hydrogen. The same complexity that makes molecules interesting objects of study creates challenges for optical control. To mitigate some of these challenges, we first cool the molecules using cryogenic techniques and technologies. Our apparatus uses a cryogenic buffer gas to thermalize BaH within a contained cell. The molecules are extracted into a beam with millikelvin transverse temperature, and forward velocities <100 m/s. The BaH beam in this work is the brightest hydride beam to date, with molecule density and kinetic characteristics well suited for laser cooling and trapping.

This thesis presents details of the design, construction and measurements of an apparatus (Blue Elbow cryostat) for high voltage testing of a full-size cryogenic nEDM cell in liquid helium at 4.2 K SVP. The test cell is cylindrical and of 24 cm internal diameter with stainless steel electrodes and an insulating borosilicate glass spacer. The cylinder axis of the cell is vertical and the insulator is located in grooves in the electrodes. The electrode separation can be varied from 0.2 cmto 2.6 cm and a voltage of up to 260 kV can be applied across the cell. It has long been expected that a nEDM cell immersed in superfluid LHe at 0.5 K should permit E-fields much greater than room temperature experiments. Long et al. (1) showed that over 400 kV/cm was obtainable in a large cell without an insulating spacer at 4.2 K, but that this was reduced dramatically as the temperature, and hence pressure, was reduced to below 2 K in a pumped LHe bath. Subsequent work by Davidson (2) in this laboratory on small spacerless cells showed that the dielectric strength in the superfluid at 1.9 K could be restored to its 400 kV/cm value by pressurising the LHe to 1 bar. Further work in this laboratory by Davidson (2) and Hill (3) shows that the introduction of a dielectric spacer reduces the value of the breakdown field, Ebd , for a given geometry. However, measurements presented here on smaller scales than the Blue Elbow cryostat, overcame the reduced fields through careful groove optimisation and insulator material choice. Ebd data as a function of separation with the Blue Elbow cryostat in LN2 show a clear reduction compared to data from smaller scale cells, due to surface area effects. Breakdown fields in LHe at 4.2 K SVP with this apparatus indicate fields at 120 kV/cm were achievable at 6mm separation but dropped off dramatically as separation was increased to 12 mm then 16 mm. The reason for the drop off is attributed to the geometry of the electrode. This result, together with Davidson's pressure dependence data, should inform the design of a future cryogenic nEDM experiment.

Pressure and temperature are two environmental variables that are increasingly being exploited by solid-state researchers probing structure-property relationships in the crystalline state. Modern high-pressure apparatus is capable of generating many billions of Pascals in the laboratory, and therefore can produce significantly greater alterations to crystalline materials than changes in temperature, which can typically be varied by only a few thousand Kelvin. Many systems such as single-molecule magnets exhibit interesting properties under low-temperature regimes that can be substantially altered with pressure. The desire by investigators to perform analogous single-crystal X-ray diffraction studies has driven the development of new high-pressure apparatus and techniques designed to accommodate low-temperature environments. [Ni(en)3][NO3]2 undergoes a displacive phase transition from P6322 at ambient pressure to a lower symmetry P6122/P6522 structure between 0.82 and 0.87 GPa, which is characterized by a tripling of the unit cell c axis and the number of molecules per unit cell. The same transition has been previously observed at 108 K. The application of pressure leads to a general shortening of O···H hydrogen bonding interactions in the structure, with the greatest contraction (24%) occurring diagonally between stacks of Ni cation moieties and nitrate anions. A novel Turnbuckle Diamond Anvil Cell designed for high-pressure low-temperature single-crystal X-ray experiments on an open-flow cryostat has been calibrated using the previously reported phase transitions of five compounds: NH4H2PO4 (148 K), ferrocene (164 K), barbituric acid dihydrate (216 K), ammonium bromide (235 K), and potassium nitrite (264 K). From the observed thermal differentials between the reported and observed transition temperatures a linear calibration curve has been constructed that is applicable between ambient-temperature and 148 K. Low-temperature measurements using a thermocouple have been shown to vary significantly depending on the experimental setup for the insertion wire, whilst also adding undesirable thermal energy into the sample chamber which was largely independent of attachment configuration. High-pressure low-temperature single-crystal X-ray diffraction data of [Mn12O12(O2CMe)16(H2O)4] (known as Mn12OAc) reveals a pressure-induced expulsion of the crystallized acetic acid from the crystal structure and resolution of the Jahn-Teller axes disorder between ambient pressure and 0.87 GPa. These structural changes have been correlated with high-pressure magnetic data indicating the elimination of a slow-relaxing isomer over this pressure range. Further application of pressure to 2.02 GPa leads to the expansion of these Jahn-Teller axes, resulting in an enhancement of the slow-relaxing magnetic anisotropy as observed in the literature. Relaxation of pressure leads to a resolvation of the crystal structure and re-disordering of the Jahn-Teller axes, demonstrating that this structural-magnetic phenomenon is fully reversible with respect to pressure. The space group of the Prussian blue analogue Mn3[Cr(CN)6].15H2O has been re-evaluated as R-3m between ambient pressure and 2.07 GPa using high-pressure single-crystal X-ray and high-pressure neutron powder data. Reductions in metal-metal distances and gradual distortions of the Mn octahedral geometry have been correlated with previously reported increases in Tc and declines in ferrimagnetic moment in the same pressure range. Increasing the applied pressure to 2.97 GPa leads to partial amorphization and results in a loss of long-range magnetic order as shown by the literature. The application of pressure (1.8 GPa) to the structure of K2[Pt(CN)4]Br0.24.3.24H2O (KCP(Br)) causes a reduction in the Pt intra-chain and inter-chain distances, and results in an enhancement of the overall conductivity under these conditions as demonstrated in the literature. Almost no changes occur to the high-pressure crystal structure upon cooling to 4 K, except in the Pt-Pt intra-chain distances which converge and suppress the Peierls distortion known to occur at 4 K, resulting in a comparatively greater electrical conductivity under these conditions.

Hydrogen production from reforming bio-fuels is considered as one of the major ways of utilizing renewable energy sources. Conventionally, most reforming catalysts are noble metal catalysts with high operation temperature above 1000 °C, which result in low thermal efficiency, long start-up time and use of high grade materials. These reasons hinder the development of hydrogen production technology. Novel self-sustained electrochemical promotion (SSEP) catalysts were developed and evaluated for heavy hydrocarbon reforming at relatively low temperatures, 450 to 650 °C. Typically, the SSEP catalysts contain NiO/Ni/CuO/Cu/CeO2 as a selective anodic phase, La0.9Sr0.1MnO3 (LSM) as a selective cathodic phase, yttria stabilized zirconia (YSZ) as an oxygen ion conduction phase, and Ni/Cu also as an electronic conduction phase. The reforming performance of the SSEP catalysts was evaluated using a fixed bed reforming reactor for n-pentadecane. A commercially available noble metal containing catalyst, 2.4 %Pt on CeO2 support, was evaluated using exactly the same method. The following conclusions can be drawn as a consequence of this study: 1) The fuel conversion for the SSEP catalyst was 10 folds of that for the noble metal catalyst and the yield of hydrogen and carbon monoxide for the SSEP catalysts was 100 folds of that for the noble metal catalyst at 450°C. 2) The mechanism of the SSEP catalysts was proved by the experimental results. 3) The study of the effect of each component and the effect of the concentration clearly reveals that the performance of the SSEP catalysts can be further improved to a higher level by many ways. In addition, all the catalysts were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), Transmission Electron Microscopy (TEM) and Accelerated Surface Area and Porosimetry Analyzer 2020 (ASAP 2020).

This thesis research aims to develop an improved, efficient, low-capacity heat engine, running on an Organic Rankine Cycle (ORC) to generate power. The ORC is driven by low or moderate temperature heat sources, such as; renewable energy in the form of a hot gas derived from biomass/biogas/biofuel combustion streams, waste heat recovery, process heat recovery, etc. The ORC is more suitable and flexible than a conventional steam Rankine cycle, especially when it is applied to low power range. In this research, an extended surface heat exchanger is used to boil the pressurised working fluid, R134a, using a hot air as heat source. The expander used is a scroll type, coupled to a generator, which is able to produce maximum 1.6 kW output. Experimental data of the heat engine are measured under different operating conditions and utilized in the analysis and comparisons. Power generation under various conditions is investigated in order to determine the optimum performance parameters for the heat engine. The isentropic efficiency of the expander is found to be over 40% and reaches 80% for the improved expansion conditions. For the boiler, it is determined that the overall heat transfer coefficient multiplied with the heat transfer area is around 150 W/K. The energy efficiency of the experimental ORC is around 3% for hot air as the low temperature heat source at about 105oC where exergy efficiency reaches 22%, respectively. / UOIT

Dry bean (Phaseolus vulgaris) is a sub-tropical crop severely affected by exposure to low temperatures during all of its growing stages. Cool spring temperatures and the risk of frost are major limiting factors for the early sowing of dry bean in Saskatchewan. Due to its economic importance; however, it has been introduced to Saskatchewan, but it needs to be made more cold tolerant to further expand acreage. The genes that can contribute some tolerance to low temperature stress in bean are not found within the primary gene pool, which limits the capability of breeders to generate a cultivar with such characteristics. Consequently studies have being done in order to find a possible source of genes that can induce tolerance to low temperature exposure. Phaseolus acutifolius is a relative of the domesticated dry bean and previous hybridizations with it have been successful. It is also known to be tolerant to abiotic stresses such as drought. For this reason the decision was taken to explore the level of resistance to low temperature stress exposure in several P. acutifolius accessions. Using whole plant freezing tests in controlled environment chambers, P. acutifolius W6 15578 was found to be more tolerant to exposure to sub-zero temperatures than were P. vulgaris genotypes. Interspecies hybrids were produced between P. vulgaris NY5-161 and W6 15578 and BC2 plants were produced using embryo rescue. The whole plant freezing test is a destructive method that cannot be used with unique F1 and BC2 genotypes, so an alternative methodology to evaluate the hybrids was explored. An electrolyte leakage test was used and showed similar results to the whole plant freezing test with the parent plant controls. The F1 hybrids had an intermediate tolerance to low temperature stress and the further generations (BC1 and BC2) had a better level of tolerance to this kind of stress than the cultivated parent (NY5-161). This suggests that the genes that confer tolerance to low temperature exposure are being maintained through several generations of backcrossing and that these interspecies hybrids may offer a chance for the development of improved dry bean cultivars for the Saskatchewan environment.

No description available.

Single crystalline silicon spheres have been used as alternative material for solar cell fabrication. This innovative technology has several advantages over traditional wafer technology. However, the material, process flow and characterization techniques are very different from the planar technology due to the spherical geometry. In material characterization, microwave photoconductivity decay is used to measure carrier lifetime. This technique is analyzed theoretically by mathematical treatment in this thesis. Furthermore, the carrier lifetime is measured in order to investigate rapid thermal grown oxide quality in the role of surface passivation of silicon sphere. A traditional way of making spherical cells is to create a p-n junction by high temperature diffusion of phosphorous dopants into p-type silicon spheres. To further reduce the fabrication cost, a low temperature epitaxial film highly doped with phosphorous is deposited on the sphere surface to form an emitter layer using Plasma Enhanced Chemical Vapour Deposition (PECVD). The process flow of device fabrication is very different from silicon wafer thus a new set of process steps are derived for silicon spheres. Two main device structures, omission of insulating layer and silicon nitride as insulating layer between emitter film and substrate, are proposed. The deposition parameters, pressure, power, and deposition time are optimized for spherical geometry. The quality of the junction is evaluated by its current-voltage characteristic and capacitance-voltage characteristic. The results are also compared to similar device structures in planar technology. To examine the photovoltaic performance, illuminated current-voltage measurement is taken to provide information on short circuit current, open circuit voltage and fill factor. Furthermore, spectral response of quantum efficiency is investigated to assess the ability of carrier collection for a spectrum of wavelength. Limitations on spherical diode performance are concluded from the measurement results.

This thesis describes trapping and evaporative cooling of ultracold 87Sr and 88Sr mixtures in an optical dipole trap to produce the first Bose-Einstein condensate (BEC) of 88Sr. Furthermore, this work presents thermalization studies that characterize the scattering properties of these ultracold strontium samples. Such ultracold atomic gases have become an important area of research because of their potential for improving optical frequency standards and for realizing quantum computation using neutral atoms. A BEC of 88Sr is particularly interesting because the small value of its background s-wave scattering length may enable the use of optical Feshbach resonances to create two-dimensional solitons. However, the small scattering length for 88Sr also hinders efficient evaporative cooling in the optical dipole trap, a necessary step to producing a BEC. Experiments with other ultracold gases have successfully overcome this hurdle by mixing in a second atomic species which, by introducing stronger interactions with the weakly interacting species, enables evaporation to colder temperatures via sympathetic cooling. For this work, we use 87Sr to sympathetically cool 88Sr during forced evaporation to quantum degeneracy. Previous experiments in the Killian Lab characterized 88Sr in detail. Here, I emphasize the new or improved aspects that have allowed trapping and cooling of the mixtures of 87Sr and 88 Sr: trapping of 87Sr by itself, spectroscopic measurements of all the stable strontium isotopes to guide the trapping of isotopic mixtures, imaging of both 87Sr and 88Sr, and the various trade-offs necessary to simultaneously trap 87Sr and 88Sr. Finally, I discuss how the thermalization studies of the scattering properties of the isotopes guide the forced evaporation of mixed isotope samples. These efforts result in the production of the BEC of 88Sr, but they also point the way to future studies of fermionic quantum degeneracy in 87Sr and to the rich physics of mixed species ultracold atomic systems.