No description available.

A wide range of ecological communities ranging from polar terrestrial to tropical marine environments are affectedby global climate change. Over the last century, atmospheric temperature has increased by an average of 0. 60 C andis expected to rise by 1.1- 6.40C over the next 100 years. This rising temperature has increased the intensity andfrequency of weather extremes due to which a large number of species are facing risk of extinction. Studies haveshown that species existing on lower latitude are more sensitive to temperature variability compared to speciesexisting on higher latitude but temperature is increasing rapidly in higher latitude compare to lower latitude. Thisuneven distribution of temperature sensitive species and warming rate has highlighted the need for combined studiesof temperature variability and sensitiveness of species to predict how the ecosystems will respond to increasinglyvariable climate. Using a generalized Rosenzweig-MacArthur model, I explored how temperature variability andsensitivity of species will affect the extinction risks of species and how the connectance and species-richness ofecological communities will govern this response. This study showed that the risk of extinction of species mostlydepends on their sensitivity to temperature deviation from the optimum value and level of temperature variability.Among these two, sensitivity of species to temperature deviation was most prominent factor affecting extinction risk.In this study, connectance did not show any effect on mean extinction risk and time taken by a certain proportion ofspecies to reach pre-defined extinction thresholds. But, species-richness showed some effect on mean extinction riskof species. It was found that risk of extinction of species in species-rich communities was higher compared tospecies-poor communities. Species-rich communities also took shorter time before they lost 1/6 of the species. Thepresent study also suggests a possible tipping point due to increasing temperature variability in near future. In furtherstudies, different sensitivity of species at different trophic levels and the possible evolution of sensitivity of speciesshould also be consider while predicting how ecological communities will respond to changing climate in the longrun.

With the economic development, the high quality has become a critical issue for service continuous of power companies. To ensure the stable power supply, the asset management of power equipments is applied to prevent the system outage. With voluminous distribution transformers over very wide area, the real time monitoring of temperature has been included in the scope of smart grid. During recent years, the service outage due to transformer overloading has caused customer panic as well as deterioration of service quality. This thesis develops the Transformer Terminal Unit (TTU) by integration of computer chip for power consumption, DSP and sampling circuit of temperature measurement to achieve the functions of real time monitoring of transformer operation condition. When an abnormal operation condition such as overloading or high oil temperature occurs, the TTU can report the contingency back to the control station via the hybrid communication system so that the distribution system operators can take remedy action to prevent the contingency. The actual loading and temperature of transforms are also measured and collected in this study to develop the relationship of temperature and loading levels. By collecting transformer temperature, the power demand of a transformer can be estimated and the load shedding can then be activated to prevent the problem of overloading when the temperature exceeds the operation constraint.

As a result of concern about the effects of CO2 emssions on the global warming, there is increasing pressure to reduce such emissions from power generation systems. The use of biomass co-firing with coal in conventional pulverised fuel power plants has provided the most immediate route to introduce a class of fuel that is regarded as both sustainable and carbon neutral as it produces less net CO2 emissions. In the future it is anticipated that increased levels of biomass will be required to use in such systems to accomplish the desired CO2 emissions targets. The use of biomass, however, is believed to result in severe fireside corrosion of superheater and reheater tubing and cause unexpected early failures of tubes, which can lead to significant economic penalties. Moreover, future pulverised fuel power systems will need to use much higher steam temeptures and pressures to increase the boiler efficiency. Higher operating temperatures and pressures will also increase the risk of fireside corrosion damage to the boiler tubing and lead to shorter component life. Predicting the remaining service life of superheater and reheater tubes in coal-biomass fired power plants is therefore an important aspect of managing such power plants. The path to this type of failure of heat exchangers involves five processes: combustion, deposition, fireside corrosion, steam-side oxidation, and creep. Various models or partial models each of these processes are available from existing research, but to fully understand the impact of new fuel mixtures (i.e. biomass and coal) and changing operating conditions on such failures, an integrated model of all of these processes is required. This work has produced an integrated set of models and so predicted the remaining service life of superheater/reheater tubes based on the three frameworks which have been developed by analysing those models used in depicting the five processes: one was conceptual and the other two were based on mathematical model. In addition, the outputs of the integrated mathematical models were compared with the laboratory generated data from Cranfield University as well as historical data from Central Electricity Research Laboratories. Furthermore, alternative models for each process were applied in the model and the results were compared with other models results as well as with the experimental data. Based on these comparisons and the availability of models constants the best models were chosen in the integrated model. Finally, a sensitivity analysis was performed to assess the effect of different model input values on the residual life superheater and reheater tubing. Mid-wall metal temperature of tubes was found to be the most important factor affecting the remaining service life of boiler tubing. Tubing wall thickness and outer diameter were another critical input in the model. Significant differences were observed between the residual life of thin-walled and thick-walled tubes.

Soil organic matter (SOM) decomposition and formation is an important climate feedback, with the potential to amplify or offset climate forcing. To understand the fate of soil carbon (C) stores and fluxes (i.e., soil respiration) under future climate it is necessary to investigate responses across spatial and temporal scales, from the ecosystem to the molecular level, from diurnal to decadal trends. Moreover, it is important to question the assumptions and paradigms that underlie apparently paradoxical evidence to reveal the true nature of soil-climate feedbacks. My dissertation includes research into the response of soil respiration in Pacific Northwest prairies to warming and wetting along a natural regional climate gradient (Chapter II), and then delves deeper into the mechanisms underlying SOM decomposition and formation, examining the temperature sensitivity of SOM decomposition of prairie soils that were experimentally warmed for ~2 yr, and a forest soil in which litter-inputs were manipulation for 20 yr (Chapter III), and finally testing soil C cycling dynamics, including mineral-associated C pools, decomposition dynamics, and the molecular nature of SOM itself, under litter-manipulation in order to understand the controls on SOM formation and mineralization (Chapter IV). This dissertation includes previously published and unpublished coauthored material; see the individual chapters for a list of co-authors, and description of contributions.

Comprendre le devenir du carbone organique stable du sol (COS) dans un environnement globalement plus chaud est un défi majeur pour prévoir sur le long terme la concentration en CO2 atmosphérique. Pour cela il apparaît nécessaire de mieux comprendre ce qu'est ce COS stable à l'échelle pluri-décennale et comment sa cinétique de minéralisation est modulée par la température. C'est avec cette ambition que cette thèse se propose (1) d'étudier la sensibilité à la température de la minéralisation du COS stable; (2) d'étudier la réponse à la température de la communauté microbienne qui minéralise le COS et (3) d'établir un lien entre âge et décomposabilité du COSLes échantillons issus de 4 essais de jachère nue ont été utilisés dans cette thèse. Des échantillons prélevés en début de chacun de ces essais et après plusieurs décennies de jachère nue ont été incubés à différentes températures pendant 427 jours. La respiration de ces échantillons a été suivie régulièrement. En fin d'incubation, la structure des communautés microbiennes a été déterminée par pyroséquençage. D'autre part, une datation du COS contenu dans les échantillons de la chrono-séquence de l'essai de jachère nue de Versailles a été réalisée.Les résultats obtenus mettent en évidence une relation générale entre vitesse de décomposition du carbone et sensibilité à la température. Ces travaux ont également mis en lumière une plus grande diversité et une plus grande sensibilité à la température des communautés microbiennes associées au carbone stable. Enfin, cette thèse met en lumière les difficultés rencontrées lors de l'utilisation de la technique de datation de la matière organique du sol par le 14C. / To understand the fate of stable soil organic carbon (SOC) in a warmer world is a major challenge to be able to predict future atmospheric CO2 concentrations. To do so, it is of prime importance to understand what the stable SOC is exactly and how its mineralization rate is modulated by temperature. This thesis proposed to study (1) the temperature sensitivity of stable SOC mineralization; (2) the response of soil microbial communities to temperature and (3) to establish a link between SOC decomposability and its age. Soil samples from four long term bare fallow experiments were used for work. We incubated soils sampled at the beggining of each experiment and after several decades of bare fallow at different temperatures for 427 days and we regularly monitored soil respiration. At the end of the incubation, soil microbial communities were assessed using pyrosequencing techniques. Finally, we determined the age of soil organic carbon by radiocarbon dating in soil samples from the chrono-sequence located at Versailles, France. The results obtained brought evidence for a general relationship between the mineralization rate of soil organic carbon and its temperature sensitivity. We also found that microbial communities linked to stable organic carbon are more diverse but also more sensitive to a temperature increase. Some bacterial phyla were particularly impacted by the temperature increase and the organic resource rarefaction. Finally, this thesis highlighted the difficulties met with the radiocarbon dating technique.

Seven strains of Streptococcus cremoris and Streptococcus lactis were tested for temperature sensitivity on a temperature gradient bar. A temperature of 37 C was the optimum for differentiating between temperature-sensitive and insensitive strains. Temperature-insensitive strains produced cell masses with absorbance values of 0.1 or higher and activity levels of 1.0 (expressed as a decrease in pH) or above at 37 C. Temperature-sensitive strains failed to produce these cell masses and activity levels, Strain selection and resistant- mutant isolation made it possible to identify ten strains of Streptococci sufficiently free of phage sensitivity for use in a cheese plant rotation program. These resistant mutants failed after being successfully used in mixed cultures for a short period of time, They became either slow acid producers or were again attacked by new bacteriophages. More work is needed to successfully isolate phage-resistant mutants suitable for cheese starters.

No description available.

Tropical soils are a globally important store of terrestrial carbon (C) and source of atmospheric carbon dioxide (CO2), regulated by the activity of soil microorganisms, through the mineralisation of plant residues and soil organic matter (SOM). Climatic warming will influence microbial activity, and this may accelerate the rate of C release from soils as CO2, contributing to alterations in current atmospheric composition, and generating feedbacks to climate change. Yet the magnitude of C loss from tropical soils remains uncertain, partly because we do not fully understand how non-climatic factors – including the chemistry of plant inputs, the availability of soil nutrients and the composition of the decomposer community – will interact to determine the response to changes in temperature. This thesis examines how these factors together regulate the rate of C cycling in contrasting soils across a 3400 m tropical elevation gradient in the Peruvian Andes, spanning a 20 ºC range (6.5 – 26.4 ºC) in mean annual temperature. Large-scale field-based manipulation experiments, translocating leaves and soil-cores across the elevation gradient (to impose an in-situ experimental warming treatment), were combined with controlled laboratory studies to examine the microbial-scale mechanisms which underlie the processes of decomposition and soil respiration observed in-situ. Results show that, across the gradient, rates of leaf-decomposition were determined principally by temperature and foliar chemical traits, while soil fertility had no significant influence. The effect of temperature was, however, stronger across higher-elevation sites, suggesting a greater vulnerability of the C-rich soils in montane systems to increased C loss under climatic warming. In lowland forests, the presence of invertebrate macrofauna also accelerated rates of decomposition, but leaf chemistry explained the greatest proportion of the observed variance, with a strong role for leaf chemical traits also identified under controlled conditions. Despite marked differences in microbial abundance and community composition among soils, these metrics were not associated with observed rates of decomposition. These results suggest that climate-related changes to plant species distributions (with associated changes to the chemistry of leaf-inputs), and upslope extension of macrofaunal ranges, could strongly influence future rates of leaf decomposition, independently of the direct response to warming. From the soil translocation study, root-soil interactions stimulated substantial net C loss from montane soils following translocation downslope (experimental warming treatment), indicating that warming-related changes to root productivity, exudation and/or species-composition could represent an important mode of future C loss from these soils. To examine more closely how inputs of plant-derived C influence the turnover of pre-existing SOM, and whether soil nutrient availability modulates the response, soils were amended with simple and complex 13C-labelled substrates in combination with inorganic nutrient treatments. Isotopic partitioning was used to determine the degree to which C and nutrient inputs accelerated (positive priming) or retarded (negative priming) the decomposition of SOM. Amendment of upper montane forest and montane grassland soils with nitrogen (N; alone and in combination with C) substantially retarded the decomposition of SOM, suggesting that microbial demand for N strongly regulates the turnover of organic matter in these soils. In contrast, amendment of lower montane and lowland forest soils with C stimulated positive priming of SOM, which was strongest in response to the simple C substrate and was not influenced by nutrient treatments, suggesting that microorganisms in these soils are primarily constrained by availability of labile C. Functional differences among microbial groups were also evident, with gram-negative bacteria and fungi using more labile sources of C while gram-positive bacteria used more complex C. Together, results from these studies considerably advance our understanding of soil C dynamics across lowland and montane systems, painting a rich picture of interacting processes which will determine the future soil C balance in tropical ecosystems. They show that the influence of temperature on the rate of soil C cycling is strongly affected by the nature and composition of plant-derived and atmospheric inputs, the principal additional constraints varying with elevation, leading to both opposing and reinforcing effects on rates of decomposition. The greater observed temperature sensitivity of decomposition at higher elevations is coupled with high microbial demand for N which regulates the turnover of SOM, whereas at lower elevations leaf decomposition is accelerated by active macrofaunal breakdown, while microbial decomposition of SOM is constrained by the availability of labile C. Under a global change scenario of increased temperature and N deposition, results therefore suggest that: (i) modified chemistry of plant inputs will influence rates of decomposition, independently of climate; (ii) increased availability of labile C will lead to more rapid decomposition of SOM at lower elevations; (iii) greater root productivity (associated with warming and plant-community shifts) will stimulate soil C loss across montane regions; but (iv) at higher elevations, a possible countervailing effect may be imposed on rapid warming-accelerated decomposition if increased N availability reduces microbial mineralisation of SOM. The net effect on the ecosystem C budget will depend on the balance of C gain from primary productivity and C loss from soils. Overall, however, the results presented here suggest that the large soil C stores in higher-elevation montane regions are particularly vulnerable to substantial reductions under exposure to short- and medium-term climatic warming.

Based on the load survey study, a stratified sampling method is proposed to select the proper size of customers so that the load patterns derived can represent the load behavior of whole customer population. In this study there are 1315 customers out of Taipower customers over various service classes are selected for the installation of intelligent meters in the field to measure the power consumption within every 15 minutes. The bad data detection is performed to identify the abnormal power consumption by executing the Chi-square test. The standardized daily load pattern of each customer class has been derived with the mean per-unit method of customer load. The billing data are retrieved from the customer information system and applied to derive the customer daily load pattern by considering the customer load patterns. According to the total power consumption by all customers within the same class and considering the corresponding daily load pattern, the daily load profile of the customer class is then determined. By aggregating the load profiles of all customer classes, the daily load composition and load model of each service district can therefore be solved. By the same manner, the daily load pattern of whole Taipower system can be derived and it can be used to support the proper design of tariff structure according to the respective contribution of system power demand by each customer class. To investigate the overloading of distribution main transformers during the summer season, the correlations analysis of customer power consumption and temperature is performed. The effect of temperature change to the power consumption of each customer class is solved by multiple regression analysis with 95% confidential level. Based on the temperature sensitivity and the corresponding load composition, the load change due to temperature rise for various customer classes can be estimated. To demonstrate the impact of temperature change to distribution system operation, considering the temperature sensitivity of power consumption and load composition solves the power demand at each load bus. By updating the bus load demand due to temperature change, the feeder loading and power loss is therefore derived. To resolve the over loading problem of distribution feeders and main transformers during the summer season, a temperature adaptive switching operation has been proposed to perform the proper load transfer among the feeders/main transformers. In this dissertation, the effect of temperature change to the time varying characteristics of load buses and power transmission in Taipower is investigated. The dc circuit model of Taipower system and the temperature effect of customer power consumption are considered in the stochastic load flow analysis. With the temperature rise, the power demand of northern buses is increased dramatically and more power has to be transmitted from the southern region. The large voltage angle difference is significantly various between system buses during the summer peak period. It is suggested that the safety margin assessment of system operation has to be executed by considering the temperature effect to the bus loading of power systems.