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1
Humphrey, Tammy Ellen Physics Faculty of Science UNSW. "Mesoscopic quantum ratchets and the thermodynamics of energy selective electron heat engines." Awarded by:University of New South Wales. Physics, 2003. http://handle.unsw.edu.au/1959.4/19186.
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A ratchet is an asymmetric, non-equilibrated system that can produce a directed current of particles without the need for macroscopic potential gradients. In rocked quantum electron ratchets, tunnelling and wave-reflection can induce reversals in the direction of the net current as a function of system parameters. An asymmetric quantum point contact in a GaAs/GaAlAs heterostructure has been studied experimentally as a realisation of a quantum electron ratchet. A Landauer model predicts reversals in the direction of the net current as a function of temperature, amplitude of the rocking voltage, and Fermi energy. Artifacts such as circuit-induced asymmetry, also known as self-gating, were carefully removed from the experimental data, which showed net current and net differential conductance reversals, as predicted by the model. The model also predicts the existence of a heat current where the net electron current changes sign, as equal numbers of high and low energy electrons are pumped in opposite directions. An idealised quantum electron ratchet is studied analytically as an energy selective electron heat engine and refrigerator. The hypothetical device considered consists of two electron reservoirs with different temperatures and Fermi energies. The reservoirs are linked via a resonant state in a quantum dot, which functions as an idealised energy filter for electrons. The efficiency of the device approaches the Carnot value when the energy transmitted by the filter is tuned to that where the Fermi distributions in the reservoirs are equal. The maximum power regime, where the filter transmits all electrons that contribute positively to the power, is also examined. Analytic expressions are obtained for the power and efficiency of the idealised device as both a heat engine and as a refrigerator in this regime of operation. The expressions depend on the ratio of the voltage to the difference in temperature of the reservoirs, and on the ratio of the reservoir temperatures. The energy selective electron heat engine is shown to be non-endoreversible, and to operate in an analogous manner to the three-level amplifier, a laser based quantum heat engine. Implications for improving the efficiency of thermionic refrigerators and power generators are discussed.
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Třináctý, Jiří. "Parní turbína pro fosilní elektrárnu." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231811.
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This thesis deals with design is condensing steam turbines burning fossil fuels with nominal capacity of the generator of 250 MW with steam reheating and regenerative eight uncontrolled extraction points. The turbine consists of two bodies: a combined high-intermediate pressure section and low pressure parts with dual way outlet down into the water-cooled condenser. Work includes calculating thermal scheme for 100% and 75% capacity, specific heat consumption calculation and design of the flow HP-MP body. Further strength control and basic engineering design of high-medium- work completed by longitudinal section. Achievements are at the end of work compared with work 3a and the conclusion summarizes the advantages and disadvantages of the concept.
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Craig, Anthony (Anthony J. ). "Measuring supply chain carbon efficiency : a carbon label framework." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/78481.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Engineering Systems Division, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 273-293).
In the near term, efficiency improvements represent a key option for reducing the impacts of climate change. The growing awareness of climate change has increased the attention regarding the carbon emissions "embedded" in the products we consume. This increased attention creates a need to measure and improve the carbon efficiency of the supply chains that produce those goods. In this thesis we present a method for measuring the carbon efficiency of a supply chain that recognizes the decentralized nature of supply chains. First, drawing from concepts in supply chain performance measurement and eco-efficiency we propose a definition of supply chain carbon efficiency that is consistent with the idea of a product's carbon footprint. We present Life Cycle Assessment (LCA), a method for quantifying the environmental impact of a product or service, as the appropriate method of measuring a product's carbon footprint and demonstrate the use of LCA through a case study involving the supply chain of bananas. Next, we characterize the difficulty and uncertainty in performing an LCA of a supply chain through an analysis of our case study of bananas. We present a framework to reduce the uncertainty though the concept of a carbon label. The carbon label provides a system where firms can measure the carbon footprint of their activities and share this information with their supply chain partners. We identify the role of third parties in facilitating information sharing and define the characteristics that describe the carbon label. Finally, we demonstrate how the carbon label works in the context of the supply chain. Through an analysis of the mode and carrier assignment steps in an integrated supply chain we develop new metrics that show how sharing information can increase the accuracy of the measured carbon footprint and improve decision-making. We provide incentive for firms to share information through the development of a vertical differentiation model of product carbon labels. Our model shows how consumer demand for lower carbon products drives reductions in the carbon footprint throughout the supply chain and induces firms to voluntarily disclose their carbon footprint.
by Anthony J. Craig.
Ph.D.
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Roberts, Michael Adrian. "Addressing efficiency in enzyme biofuel cells." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/addressing-efficiency-in-enzyme-biofuel-cells(91027198-5ed8-4f27-9366-e69c44d39eb9).html.
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Biofuel cells (BFCs) use either enzymes or bacteria to catalyse a fuel to generate power. Their advantages over conventional fuels is that they do not use precious metals and the high selectivity of biocatalysts mean that no separation membranes are required between the electrodes. However, the application of BFCs is limited by their low power output and poor enzyme lifetimes. This thesis addresses these limitations by investigating aligned carbon nanotubes (aCNTs) as potential electrode materials. These aCNT electrodes offer high surface areas to increase enzyme coverage and hence power output and their surface topology can stabilise the enzymes to ensure maximum lifetime and current density.A novel BFC half cell was developed using aCNTs and the fungal enzyme, Trametes versicolor laccase which catalyses the four-electron reduction of oxygen to water. Laccase was shown to communicate directly with the nanotubes enabling the oxidant reduction reaction to be monitored without the need for mediators. Initial investigations compared aCNTs with other commonly reported carbon electrodes and found that the current densities were ~30-fold higher on the aCNTs than at pyrolytic graphite edge electrodes. The high surface area of these electrodes contributed to greater electroactive coverage of enzyme and minimal loss of enzyme upon deposition. Cathodic currents increased linearly with geometric electrode area; however they did not scale with actual electrode surface area and the current density was limited to the order of μA cm-2 due to O2-transport limitations. It was also discovered that the porous contribution of these aCNT electrodes could lead to misleading interpretations on nanotube electrochemistry. This effect was observed when increments in electrode area resulted in apparently significantly faster kinetics. This improvement in catalytic behaviour was proposed to be due to a transition from mass diffusion limited to thin layer cell behaviour exhibited by porous materials. Thermal pretreatment of the aCNT electrodes in oxidative and reductive atmospheres were found to improve their performance. These treatments worked by changing the nanotube surface chemistry and purifying the nanotubes, as evidenced by various physical characterisation methods. Furthermore, laccase activity was enhanced significantly after electrodes had been treated under both atmospheres, where it was believed that the removal of contaminant material and higher defect densities increased electrochemical performance.Finally, mass transport limitations were addressed by developing micro-patterned aCNT electrodes which possessed channels in the arrays, allowing better oxygen diffusion. Fundamental studies showed higher current densities per surface area and thus represent a promising electrode for future BFC research.
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Viteva, Svetlana. "The informational efficiency of the European carbon market." Thesis, University of Stirling, 2012. http://hdl.handle.net/1893/11204.
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This thesis examines the informational efficiency of the European carbon market based on the European Union Emissions Trading Scheme (EU ETS). The issue is approached from three different perspectives. I explore whether the volatility embedded in carbon options is a rational forecast of subsequently realized volatility. Then, I investigate if, and to what extent, new information about the structural and institutional set-up of the market impacts the carbon price dynamics. Lastly, I examine whether the European carbon market is relevant for the firm valuations of covered companies. First, perhaps because the market is new and derivatives’ trading on emission allowances has only started recently, carbon options have not yet been extensively studied. By using data on options traded on the European Climate Exchange, this thesis examines an aspect of market efficiency which has been previously overlooked. Market efficiency suggests that, conditional upon the accuracy of the option pricing model, implied volatility should be an unbiased and efficient forecast of future realized volatility (Campbell et al., 1997). Black (1976) implied volatility and implied volatility estimates directly surveyed from market participants are used in this thesis to study the information content of carbon options. Implied volatility is found to be highly informative and directionally accurate in forecasting future volatility. There is no evidence, however, that volatility embedded in carbon options is an unbiased and efficient forecast of future realized volatility. Instead, historical volatility-based forecasts are shown to contain incremental information to implied volatility, particularly for short-term forecasts. In addition, this thesis finds no evidence that directly surveyed implied volatility estimates perform better as a forecast of future volatility relative to Black’s (1976) estimates. Second, the market sensitivity to announcements about the organizational and institutional set-up of the EU ETS is re-examined. Despite their importance for the carbon price formation, demand-side announcements and announcements about the post-2012 framework have not yet been researched. By examining a very comprehensive and updated dataset of announcements, this thesis adds to the earlier works of Miclaus et al. (2008), Mansanet-Bataller and Pardo (2009) and Lepone et al. (2011). Market participants are found to rationally incorporate new information about the institutional and regulatory framework of the emissions trading scheme into the carbon price dynamics. However, they seem to be unable to accurately assess the implications of inter-temporal banking and borrowing on pricing futures contracts with different maturities. The impact of macroeconomic conditions on the market responsiveness is investigated by splitting the dataset into subsamples according to two alternative methods: 1) a simple split into pre-crisis and full-crisis time periods, and 2) according to a Bai-Perron structural break test. Evidence is found that in the context of economic slowdown and known allowances oversupply, the relationship between the carbon price and its fundamentals (institutional announcements, energy prices and extreme weather) breaks down. These findings are consistent with the arguments in Hintermann (2010), Keppler and Mansanet-Bataller (2010) and Koop and Tole (2011) that carbon price drivers change in response to the differing context of the individual trading periods. Third, the role of carbon performance in firm valuation is understudied. Since companies were not obliged to disclose their carbon emissions prior to the launch of the EU ETS, there exists little empirical evidence of the effect of carbon performance on market value. Earlier studies of the European carbon market have only focused on the impact of ETS compliance on the profitability and competitiveness of covered companies (e.g. Anger and Oberndorfer, 2008). There is also little research on how the newly available emissions data has altered the carbon performance of companies. This thesis addresses these gaps in the literature by examining the stock price reactions of British and German firms on the day of verified emissions release under the EU ETS over the period 2006 – 2011. An event study is conducted using a Seemingly Unrelated Regressions model to deal with the event clustering present in the dataset. Limited evidence is found that investors use information about the carbon performance of companies in their valuations. The information contained in the carbon emissions reports is shown to be somewhat more important for companies with high carbon-intensive operations. This thesis finds no conclusive evidence that the cap-and-trade programme has been able to provide regulated companies with enough incentives to de-carbonize their operations. The market does not punish companies which continue to emit carbon at increasing rates or reward companies which improve their carbon performance. In brief, the results of the thesis suggest that the market is not fully efficient yet. Inefficiently priced carbon options may allow for arbitrage trades in the market. The inability of investors to incorporate rules on inter-temporal banking and borrowing of allowances across the different trading periods leads to significant price reactions when there should be none. A recessionary economic environment and a known oversupply of emission allowances have led to a disconnect between the carbon price and its fundamental drivers. And, lastly, the signal embedded in the carbon price is not strong enough to invoke investor action and turn carbon performance into a standard component of investment analysis.
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Binkley, Aaron G. "Real estate opportunities in energy efficiency and carbon markets." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/42034.
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Thesis (S.M. in Real Estate Development)--Massachusetts Institute of Technology, Dept. of Architecture, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (leaves 67-69).
Global interest in the effects of climate change has grown rapidly in recent years. The US federal government mulls a cap and trade system for large carbon emitters while states implement their own greenhouse gas schemes. Private industries are beginning to see the need to address their greenhouse gas footprints and are increasingly offsetting their carbon emissions. The real estate industry has been under little scrutiny in spite of being responsible for over 40% of all US greenhouse gas emissions. The real estate industry is in the unique position of being able to reduce greenhouse gas emissions through energy efficiency improvements that are low cost and that create value within the underlying asset. The objective of this research is two-fold: First, to examine the potential value and feasibility of energy efficiency improvements, and second to determine if there is sufficient value creation from abatement of greenhouse gas emissions, called offsets, to subsidize further energy efficiency measures. Through a case study example I examine energy efficiency improvements at two levels and determine the resulting greenhouse gas offsets on a state-by-state basis. Then I evaluate energy savings and greenhouse gas offsets across a low and high price range. Once the case study analysis is complete, I examine the magnitude of economic value resulting from energy efficiency improvements and the sale of greenhouse gas emissions offsets for the entire real estate industry. My analysis indicates that there is potential for significant value creation. Opportunities are focused in states where energy prices are higher and where greenhouse gas emissions from power generation are greatest. In the case study, capital investment in energy efficiency has an IRR range from 26.4% to over 125%.
(cont.) Greenhouse gas offset value increases IRR further; providing an additional 26% increase in the original available energy retrofit funding. Net asset value increases from 1.1% in a low carbon price scenario to 5.5% in a high carbon price scenario. At the market level, efficiency improvements are worth between $40.3 and $201 billion annually. Greenhouse gas emissions are worth an additional $1.46 to $48.8 billion. The sum of energy efficiency and greenhouse gas emissions offsets have the potential to add between 1.0% and 6.1% to the value of the $4.03 trillion US commercial real estate market. I conclude that there is significant potential for value creation resulting from rigorous energy efficiency improvements and the sale of offsets in emerging greenhouse gas markets.
by Aaron G. Binkley.
S.M.in Real Estate Development
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Stephens, Amanda C. "Carbon Neutral Building: Architectural Manifestation of Carbon Efficient Design." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1554210795873197.
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Wang, Zhujuan. "Reinforcing Efficiency of Carbon Nanotubes in Poly (Vinyl Alcohol) Composites." Thesis, Queen Mary, University of London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.498926.
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Zheng, Zhanghua. "Overall CO2 efficiency assessment for a low carbon energy system." Thesis, University of Bath, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619233.
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Decarbonization of the power sector is of great importance for the transition to a sustainable and low-carbon world economy. Estimating carbon efficiency in the power sector is a key step to grasp the impact of demand-side usage changes and evaluate their potential environmental benefits. In order to quantify the environmental benefits of demand-side usage changes, Average Emission Factor (AEF) and Marginal Emission Factor (MEF) have been proposed in the electrical power sector. AEF is defined as the ratio of the total CO2 emitted in the system to the total electricity generated. It is an effective factor for reporting on CO2 emissions at system level and on an average basis, but the current AEF model lacks clarity on the factors actually affecting the estimation. MEF is defined as the incremental change in carbon emissions as a result of a change in demand. However, previous MEF assessments did not consider key technical limitations, such as ramp-rate constraint for generators and network constraints, and carbon trading mechanisms. This thesis improves the estimation for both AEF and MEF and key achievements can be summarized as: 1). A novel model of estimating AEF, with its application to GB, US and China’s electricity system. 2). Improvement on conventional MEF model by considering ramp-rate constraint in dispatch order. 3). Sensitivity studies on MEF using current fuel prices and future fuel prices. 4). A new model of estimating MEF considering both the utilization level of generators and the carbon costs when determining the dispatch order. 5). The effect of power network on MEF estimation, with a comparison of congested scenarios and non-congested scenario.
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Van, den Tempel Almaas Amanda, and Gustav Hillgren. "Carbon tax efficiency : What elevates it, and what undermines it?" Thesis, Uppsala universitet, Nationalekonomiska institutionen, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-449069.
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The radical rise of global temperatures has put high pressure on the environment, leading to societal pressure towards politicians to reverse the trend. In light of this environmental crisis, economists all over the world agree that carbon taxes are the most cost-effective instrument for reducing carbon emissions. This study uses difference-in-differences analysis to examine the treatment effect of a carbon tax implementation in Denmark, Finland, Norway, and Sweden. Panel data from 24 OECD countries, between 1978 and 2004, is used throughout this study. This study has not found support that different levels of democracy and GDP per capita affect tax efficiency. Moreover, higher levels of urbanisation are seen to undermine the efficiency of a carbon tax, however, the result may be affected by confounding bias. Lastly, tax rate and tax coverage are both factors that seem to affect carbon tax efficiency.
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Hurwitz, Zach Lawrence. "Economic Efficiency and Carbon Emissions in MES with Flexible Buildings." ScholarWorks @ UVM, 2020. https://scholarworks.uvm.edu/graddis/1171.
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Multi-energy systems offer an opportunity to leverage energy conversion processes and temporary energy storage mechanisms to reduce costs and emissions during operation of campuses, cities, and buildings. With increasing options for flexibility in demand-side resources it is possible to meet demand without sacrificing comfort and convenience of MES occupants.
This Thesis develops a multi-period, linear optimization model of an MES with flexible buildings that captures nonlinearities in the efficiency of energy conversion processes. The flexible buildings are parametrized, in part, based on historical data from a college campus in Vermont, USA. The idea of the MES model is to investigate the role that flexibility plays in reducing costs and emissions for a small campus relative to that of a possible carbon tax. The operation of the MES is optimized to reduce costs based on representative seasons. Interestingly, it is found that when utilized optimally, flexible buildings allows for a more cost and energy effective method of not only meeting demand but also reducing carbon emissions in the process.
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Pointeau, Virginie M. "Water-use efficiency and productivity in native Canadian populations of Populus trichocarpa and Populus balsamifera." Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/587.
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Afforestation and reforestation programs utilizing available fields for biofuel production, carbon sequestration, and other uses linked to climate change are looking to tree physiologists to identify species and genotypes best-suited to their purposes. The ideal poplar genotype for use in Canadian programs would be drought-resistant, cold-climate adapted, and fast-growing, thus requiring an understanding of links between a variety of physiological traits linked to growth and productivity. This study examined the basis for variations in water-use efficiency within four selected populations of Populus trichocarpa and Populus balsamifera (2 provenances each). Each species included both a northern and a southern provenance. Correlations between water-use efficiency, nitrogen-use efficiency, ¹³C/¹²C isotope ratio, stomatal conductance, and overall productivity were evaluated. Gas exchange variables measured included net photosynthesis, transpiration rate, stomatal conductance, and intercellular CO₂ content. Water-use efficiency and ¹³C content across all genotypes were highly correlated. Results suggested that variation in water-use efficiency was primarily related to variation in stomatal conductance across all genotypes. Whereas differences in net photosynthesis in this study were not significant between species, P. balsamifera did reveal a higher average stem volume overall. Although variation in stomatal conductance was the major determinant of differences in water-use efficiency, positive correlations were found between ¹³C isotope abundance and net photosynthesis in both P. balsamifera provenances. In this regard, results for the northern P. balsamifera provenance are the most consistent across all gas-exchange and growth trait correlations, in terms of meeting expectations for sink-driven water-use efficiency. The findings in this study suggest the possibility of identifying poplar genotypes with an absence of trade-off between water-use efficiency and nitrogen-use efficiency, notably among genotypes from the northern P. balsamifera provenance, near Gillam.
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Atherton, Jon Mark. "Multiscale remote sensing of plant physiology and carbon uptake." Thesis, University of Edinburgh, 2012. http://hdl.handle.net/1842/6219.
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This study investigated the use of optical remote sensing for estimating leaf and canopy scale light use efficiency (LUE) and carbon exchange. In addition, a new leaf level model capable of predicting dynamic changes in apparent reflectance due to chlorophyll fluorescence was developed. A leaf level study was conducted to assess the applicability of passive remote sensing as a tool to measure the reduction, and the subsequent recovery, of photosynthetic efficiency during the weeks following transplantation. Spectral data were collected on newly planted saplings for a period of 8 weeks, as well as gas exchange measurements of LUE and PAM fluorescence measurements. A set of spectral indices, including the Photochemical Reflectance Index (PRI), were calculated from the reflectance measurements. A marked depression in photosynthetic rate occurred in the weeks after outplanting followed by a gradual increase, with recovery occurring in the later stages of the experimental period. As with photosynthetic rate, there was a marked trend in PRI values over the study period but no trend was observed in chlorophyll based indices. The study demonstrated that hyperspectral remote sensing has the potential to be a useful tool in the detection and monitoring of the dynamic effects of transplant shock. Relationships between hyperspectral reflectance indices, airborne carbon exchange measurements and satellite observations of ground cover were then explored across a heterogeneous Arctic landscape. Measurements were collected during August 2008, using the University of Edinburgh’s research aircraft, from an Arctic forest tundra zone in northern Finland as part of the Arctic Biosphere Atmosphere Coupling at Multiple Scales (ABACUS) study. Surface fluxes of CO2 were calculated using the eddy covariance method from airborne data that were collected from the same platform as hyperspectral reflectance measurements. Airborne CO2 fluxes were compared to MODIS vegetation indices. In addition, LUE was estimated from airborne flux data and compared to airborne measurements of PRI. There were no significant relationships between MODIS vegetation indices and airborne flux observations. There were weak to moderate (R2 = 0.4 in both cases) correlations between PRI and LUE and between PRI and incident radiation. A new coupled physiological radiative transfer model that predicts changes in the apparent reflectance of a leaf, due to chlorophyll fluorescence, was developed. The model relates a physically observable quantity, chlorophyll fluorescence, to the sub leaf level processes that cause the emission. An understanding of the dynamics of the processes that control fluorescence emission on multiple timescales should aid in the interpretation of this complex signal. A Markov Chain Monte Carlo (MCMC) algorithm was used to optimise biochemical model parameters by fitting model simulations of transient chlorophyll fluorescence to measured reflectance spectra. The model was then validated against an independent data set. The model was developed as a precursor to a full canopy scheme. To scale to the canopy and to use the model on trans-seasonal time scales, the effects of temperature and photoinhibition on the model biochemistry needs to be taken into account, and a full canopy radiative transfer scheme, such as FluorMOD, must be developed.
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Das, Santanu. "Carbon Nanostructure Based Electrodes for High Efficiency Dye Sensitize Solar Cell." FIU Digital Commons, 2012. http://digitalcommons.fiu.edu/etd/678.
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Synthesis and functionalization of large-area graphene and its structural, electrical and electrochemical properties has been investigated. First, the graphene films, grown by thermal chemical vapor deposition (CVD), contain three to five atomic layers of graphene, as confirmed by Raman spectroscopy and high-resolution transmission electron microscopy. Furthermore, the graphene film is treated with CF4 reactive-ion plasma to dope fluorine ions into graphene lattice as confirmed by X-ray photoelectron spectroscopy (XPS) and UV-photoemission spectroscopy (UPS). Electrochemical characterization reveals that the catalytic activity of graphene for iodine reduction enhanced with increasing plasma treatment time, which is attributed to increase in catalytic sites of graphene for charge transfer. The fluorinated graphene is characterized as a counter-electrode (CE) in a dye-sensitized solar cell (DSSC) which shows ~ 2.56% photon to electron conversion efficiency with ~11 mAcm−2 current density. Second, the large scale graphene film is covalently functionalized with HNO3 for high efficiency electro-catalytic electrode for DSSC. The XPS and UPS confirm the covalent attachment of C-OH, C(O)OH and NO3- moieties with carbon atoms through sp2-sp3 hybridization and Fermi level shift of graphene occurs under different doping concentrations, respectively. Finally, CoS-implanted graphene (G-CoS) film was prepared using CVD followed by SILAR method. The G-CoS electro-catalytic electrodes are characterized in a DSSC CE and is found to be highly electro-catalytic towards iodine reduction with low charge transfer resistance (Rct ~5.05 Wcm2) and high exchange current density (J0~2.50 mAcm-2). The improved performance compared to the pristine graphene is attributed to the increased number of active catalytic sites of G-CoS and highly conducting path of graphene.
We also studied the synthesis and characterization of graphene-carbon nanotube (CNT) hybrid film consisting of graphene supported by vertical CNTs on a Si substrate. The hybrid film is inverted and transferred to flexible substrates for its application in flexible electronics, demonstrating a distinguishable variation of electrical conductivity for both tension and compression. Furthermore, both turn-on field and total emission current was found to depend strongly on the bending radius of the film and were found to vary in ranges of 0.8 – 3.1 V/μm and 4.2 – 0.4 mA, respectively.
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Metcalf, Steven John. "Compact, efficient carbon-ammonia adsorption heat pump." Thesis, University of Warwick, 2009. http://wrap.warwick.ac.uk/2777/.
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The modelling, design, construction and experimental testing of a carbon-ammonia adsorption heat pump is presented. The main objective of the research was to design, manufacture and test an adsorption generator with low thermal mass and high power density. The adsorption generator developed was a stainless steel, nickel brazed plate heat exchanger. Computational modelling of the generator with thermal wave and multiplebed cycles revealed that multiple-bed cycles give a superior trade-off between efficiency and power density. Further modelling was carried out to evaluate the performance of the adsorption generator in a four-bed gas-fired domestic heat pump system. The proposed system is air-source and could deliver a nominal heating power of 7 kW and a seasonal heating COP of 1.35, equivalent to a one third reduction in gas consumption in comparison to a condensing boiler. The systems performance was compared to a vapour compression heat pump on running costs and CO2 emissions and was found to be similar or better in all cases. The adsorption generator was tested in a two-bed air-source heat pump system and achieved heating powers from 7 to 11 kW and a heating COP of between 1.4 and 1.6. Specific heating power ranged from 3.9 kW kg-1 to 6.1 kW kg-1, equivalent to specific cooling powers of between 1.1 kW kg-1 and 2 kW kg-1, which is a significant increase in power density compared to the state of the art.
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Mohammed, Kasim. "Microalgal photobioreactors for carbon-efficient wastewater treatment." Thesis, University of Newcastle upon Tyne, 2013. http://hdl.handle.net/10443/2318.
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Algae-based wastewater treatment technologies are gaining popularity because of their sustainable treatment capabilities, coupled with their ability to capture carbon and consequently reduce the carbon footprint of the overall treatment process. Research was undertaken to develop a low-cost hybrid mixed microalgae-activated sludge municipal wastewater treatment system coupled with CO2 sequestration. Red light-emitting diodes were used as light source to illuminate 1 L and 21 L microalgal photobioreactors. Three phases of laboratory experiments (I, II and III) were conducted to treat real or synthetic municipal wastewater using batch and continuous modes of operation, either with or without CO2 addition. Phases I and II experiments were conducted in batch mode using a mixed microalgae-bacteria culture as inoculum, while Phase III was conducted in continuous mode using a mixture of microalgae and activated sludge as inoculum. The added gas in Phases I and II had O2 supplementation whereas the gas in Phase III had no O2 but a substantial amount of CO2. Average ‘optimal’ irradiance (582.7 μmol.s-1.m-2) was used in Phases II and III, while Phase I investigated a range of lower light regimes (i.e. 25.3 to 234.3 μmol.s-1.m-2). Results showed high wastewater treatment efficiency, in terms of soluble chemical oxygen demand (SCOD) and ammonium-nitrogen (NH4-N) removal. SCOD removal efficiency greater than 70% was achieved in all the three experimental phases. Furthermore, NH4-N removal efficiencies greater than 90, 70 and 40%, were achieved in Phases I, II and III, respectively. However, nitrite accumulation was observed in Phases I and II, indicating that NH4-N removal was due to partial nitrification. Furthermore, low phosphate removal efficiencies were achieved in Phase III. Results confirmed that considerable reduction of operational costs could be achieved by satisfying bacterial oxygen requirement through photosynthetic oxygenation in the hybrid microalgae-activated sludge (HMAS) photobioreactors, with considerable energy savings possible whilst maintaining high levels of SCOD removal. Typically, a dissolved oxygen concentration > 2 mg.L-1 could be maintained in the HMAS photobioreactors without external aeration. Microbial analyses of samples collected from Phase II and III photobioreactors revealed a dominance of bacteria over microalgae. In order to prevent system failure, it was recommended that HMAS photobioreactors be set-up with an initial microalgae-bacteria ratio of at least 90:10, as determined by flow cytometry. Overall, this study demonstrated the potential for achieving high treatment efficiency by coupling wastewater treatment with carbon capture in HMAS photobioreactors. The potential for realising cost savings in wastewater treatment through use of HMAS photobioreactors at full-scale are discussed.
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Altan, Hasim. "Energy efficiency in housing : drivers and barriers to improving energy efficiency and reducing carbon dioxide emissions in private sector housing." Thesis, University of Sheffield, 2004. http://etheses.whiterose.ac.uk/14479/.
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Global environmental degradation is one of the most serious threats facing humankind as a result of the expansion of its activities around the globe. Scientific evidence is growing that greenhouse gas emissions are having a noticeable effect on the earth's climate. Sustainable development has become a global issue and its life cycle influences the life cycles of the whole planet dramatically. As widely accepted, CO2 emissions are the most significant impact on global climate caused by the amount of energy consumed (Kyoto Protocol, 1997). The UK Government has signed the United Nations Framework Convention on Climate Change in 1992 and is therefore committed to reducing the emission of six greenhouse gases with carbon dioxide being the most significant to 12.5% lower than the 1990 levels (DEFRA, 2000). The Government has also indicated that it has an aim of further reducing the emissions with an eventual target of 20% below the 1990 levels by 20 10. Energy consumed by the UK building stock approaches 50% of the total while transport is responsible for 28% (DETR, 2000). Accordingly the energy used in housing stock is responsible for about 30% of overall emissions (Shorrock and Walters, 1998), which is a major contributor to global warming and therefore, improving energy efficiency and reducing carbon dioxide emission within housing stock is a key factor for long term sustainability in the built environment. This research aims to study the energy efficiency standards, CO2 emissions and energy ratings of privately rented, university controlled and approved properties within Sheffield. In general, properties in this particular sector account for about 15% of the total housing stock and demonstrate one of the worst conditions of housing standards in the UK (Revell and Leather, 2000). In this research however, properties analysed have shown better characteristics regarding energy efficiency standards especially when compared to the worst housing examples in the country. This is mainly due to properties being controlled and approved by the university standards/requirements, and resulted in achieving higher energy efficiency standards within the privately rented sector. Case study analysis carried out includes over 200 privately rented properties, showing dwelling conditions and examining efficiency of both water and space heating systems. iii Abstract As a global matter, environmental issues and good building design have also been increasingly important in the UK. For that reason, energy and environmental assessment methods for buildings have been developed in order to accomplish good building design, which could contribute considerably to reducing pollution and improving the environment. These assessment methods identify criteria for a range of issues also concerning the global, national and indoor environments. Due to the importance of building energy and environmental assessment methods, many components have to be discussed for the future of buildings and more emphasis should be paid to encouraging property developers to utilise the appropriate methods in order to design energy conscious buildings. Some of the existing methods concerning 'Environment and Healthy Building' developed and used in the country have been reviewed and discussed in the perspective of global effects. In this study, having chosen university-controlled properties would therefore help to utilise the university authority to take action effectively and play a key role in guiding energy efficiency improvements within privately rented properties. With university authority, potential improvements in these properties can be encouraged and implemented much effectively, whilst existing legislation and policies are inoperative to enforce retrospective energy standards in existing housing. Furthermore, this has a negative impact on private rented sector and comes into being a major barrier for this particular sector. Therefore, this is an opportunity that will not only increase energy standards of the housing stock in Sheffield, but also help to achieve the rate of improvement required by the Home Energy Conservation Act 1995 and reduce the overall energy consumption caused by the existing housing stock in the country.
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Du, Toit Petrus Gerhardus. "The effect of partial rootzone drying on the partitioning of dry matter, carbon, nitrogen and inorganic ions of grapevines." Title page, summary and table of contents only, 2005. http://hdl.handle.net/2440/37954.
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Partial rootzone drying (PRD) is an irrigation management technique designed to reduce water use in grapevines without a decline in yield, thereby increasing water–use efficiency (measured as t/ML) (WUE). The principle of PRD is to keep part of the root system at a constant drying rate to produce soil-derived signals to above–ground plant organs to induce a physiological response. Major PRD effects include a reduced canopy size and greatly increased WUE with possible improvements in fruit quality. Although we have a good understanding of the hormonal physiology of PRD, little is known on the effect of PRD on partitioning of C, N and inorganic ions such as K. This thesis broadens our knowledge on the effects of PRD on grapevine field performance, growth and dry matter accumulation as well as its effects on physiology and biochemistry. In field experiments over 3 seasons, PRD reduced water use in grapevines without a significant decline in yield. PRD effects included reduced shoot growth and greatly increased WUE. Field–grown Cabernet Sauvignon, where the PRD grapevines were irrigated at half the control rate, and Shiraz where the PRD grapevines were irrigated at same rate as controls, confirmed that PRD is not simply an irrigation strategy that applies less water, rather it alters the way in which the plant responds to its environment, e.g. PRD alters the sensitivity of the stomatal response to atmospheric conditions and significantly influence enzymes that regulate nutrient accumulation and partitioning. PRD did not change the total amount of carbon and nitrogen on a whole plant basis. However, it caused a significant partitioning of carbon and nitrogen towards trunk, roots and fruit at the expense of shoot growth. This change in partitioning occurred as a result of altered activity of the enzymes controlling the assimilation of carbon and nitrogen. PRD significantly reduced nitrate reductase (NR) activity in grapevine leaves, which catalyses the first step in the assimilation of nitrate irrespective of the amount of water applied. The reduction in NR activity is correlated with the development of the PRD cycle and the associated reduction in stomatal conductance. PRD also significantly altered grapevine sucrolytic enzyme activity that regulate source:sink relationships. PRD showed transient increases in leaf sucrose phosphate synthase (SPS) activity (formation of sucrose) compared to control, but significantly reduced leaf neutral invertase (sucrose cleavage) and leaf starch content in both field and potted experiments. This may indicate an increased photosynthetic capacity and a reduction in its sink strength for sucrose in favor of organs such as fruit and roots. This hypothesis was reinforced by the fact that berries showed significantly higher levels in glucose and fructose early in the season. Berry sugar content and Brix at harvest however was unaffected. Although PRD had no significant effect on berry characteristics at harvest such as Brix and pH, it occasionally reduced per berry K+ content and increased total amino acid concentration that may lead to positive outcomes for wine quality. PRD–treated grapevine roots on the 'wet'– and 'drying'–sides differed greatly in enzyme activity and osmolality. PRD significantly increased osmolality in both wet and drying roots by increasing total osmolyte concentration that may facilitate the movement of water from wet to dry roots. The increases in osmolality were also associated with increased free polyamine production (spermidine and spermine) in PRD roots that may be related to increased root growth and density.Thesis (Ph.D.)--School of Agriculture and Wine, 2005.
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Dahlgren, Kristin. "Food web structures and carbon transfer efficiencies in a brackish water ecosystem." Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-38014.
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Two differently structured food webs can be distinguished in the pelagic habitat of aquatic systems; the classical one (autotrophic) with phytoplankton as a base and the microbial food web (heterotrophic) with bacteria as a base. Energy (produced at the basal trophic level) reaches higher trophic levels, i.e. zooplankton, directly in the classical food web in contrast to the microbial food web where it passes through additional trophic levels before reaching zooplankton. Energy is lost between each trophic level and therefore less energy should reach higher trophic levels in the microbial food web than in the classical food web. However, factors such as edibility of prey, temperature and properties of the predator, might also influence the food web structures and functions. In this thesis I studied which factors are important for an efficient carbon transfer and how a potential climate change might alter the food web efficiency in pelagic and pelagic-benthic food webs in the Baltic Sea. Furthermore, one of the most dominant zooplankton in the northern Baltic Sea, Limnocalanus macrurus, was studied in order to establish the seasonal pattern of lipid reserves in relation to food consumption. My studies showed that the carbon transfer efficiency during summer was not directly connected to the basal production, but factors such as the ratio between heterotrophs and autotrophs, the relationship between cladocerans and calanoid copepods and the size and community structure of both phytoplankton and zooplankton were important for the carbon transfer efficiency. In a climate change perspective, the temperature as well as the relative importance of the microbial food web is likely to increase. A temperature increase may have a positive effect on the pelagic food web efficiency, whereas increasing heterotrophy will have a negative effect on the pelagic and pelagic-benthic food web efficiency, reduce the fatty acid content of zooplankton and reduce the individual weight of both zooplankton and the benthic amphipod Monoporeia affinis. During the seasonal study on the calanoid copepod L. macrurus, I found that this species is mainly a carnivore, feeding on mesozooplankton during most of the year but switches to feeding on phytoplankton when these are abundant. Furthermore, when food is scarce, it utilizes lipids that are built up during the course of the year. From these studies I can draw some major conclusions; there are many factors that influence how efficient carbon is transferred in the food web and different factors are probably of various importance in different areas. In order to determine the carbon transfer efficiency, the various strategies exerted by different organism groups have to be considered, as for example that some zooplankton utilize lipid reserves instead of feeding all year around. Also, in a climate change perspective, the pelagic-benthic food web efficiency will decrease, as will the quality of zooplankton and M. affinis, possibly having implications for higher trophic levels such as fish.
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Tan, Kwan Chong. "Stimulating carbon efficient supply chains : carbon labels and voluntary public private partnerships." Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/52752.
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Thesis (S.M. in Technology and Policy)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (p. 151-163).
This thesis looks at the potential of labeling products with life cycle greenhouse gas emission information as a bottom-up, complementary alternative to carbon cap and trade systems. By improving the transparency of product carbon footprint information, a market for low carbon intensity products can be created. The conduct of such product life cycle assessments often allows companies to uncover cost effective emission reduction opportunities typically in the order of 10%-20%. Society benefits both from the increased supply chain efficiency of these companies as well as the heightened awareness of climate change among consumers as companies communicate these information to them. An examination of the history of the development of the nutritional label and various eco-labels in the U.S. highlights the importance of timely government intervention in setting guidelines and standards to prevent companies from misleading consumers with unsubstantiated product health or environmental claims. Case studies of current carbon labeling initiatives worldwide demonstrate the benefits of government affiliation in building credibility during their early stages. This affiliation helps in attracting the participation of large established companies who provide strong reinforcing effects that are crucial to the growth and success of new initiatives. There is still lack of consensus about the ideal format for a carbon label. A seal of approval type label could be ideal to attract companies in the initial stages which can later be succeeded by an information disclosure based format as more consumers start to understand the meaning of product carbon footprints in the future.
(cont.) Voluntary public private partnerships have been used extensively by the U.S. Environmental Protection Agency to reduce greenhouse gas emissions. These partnerships can serve as a potential model for a future carbon labeling initiative in the U.S. The SmartWay Transport Partnership is highlighted as a successful program both in terms of membership growth and emissions saved. System Dynamics modeling is applied as a tool to aid in understanding how the structure of such programs is critical to their success and is demonstrated as a method to potentially quantify the benefits of these programs prior to their actual implementation.
by Kwan Chong Tan.
S.M.in Technology and Policy
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Thyberg, Viktor. "Numerical Energy Modeling to Increase Fuel Efficiency of An Activated Carbon Production." Thesis, Karlstads universitet, Avdelningen för energi-, miljö- och byggteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-33272.
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Feaver, Aaron. "Carbon cryogel based nanomaterials for efficient energy storage /." Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/10575.
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CARVALHO, FILIPE POLLIS DE. "BE CARBON EFFICIENT IMPLIES GREATER PROFITABILITY IN BRAZIL?" PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2015. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=26641@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE SUPORTE À PÓS-GRADUAÇÃO DE INSTS. DE ENSINO
Esta pesquisa analisou os possíveis impactos na rentabilidade de empresas que ingressaram ou saíram do Índice de Carbono Eficiente (ICO2). Buscou-se compreender se a participação de uma empresa nesta carteira beneficiaria o seu acionista com ganhos de rentabilidade e, caso contrário, se a saída implicaria em queda na rentabilidade. Até então, o único estudo com tal propósito realizado para o ICO2 foi baseado na primeira carteira formada e verificou apenas o movimento de entrada. Assim, este trabalho procurou analisar este índice sob uma ótica mais dinâmica e atualizada, a partir de mudanças na sua composição ao longo do tempo. Para alcançar este objetivo, realizou-se um estudo de eventos a fim de identificar a existência de retornos anormais em empresas que entraram e saíram do ICO2. A amostra analisada compreendeu doze empresas que realizaram o movimento de entrada ou saída ao longo do período de 2012 a 2015. Os resultados proporcionaram um avanço no entendimento acerca de investimentos sustentáveis no Brasil, uma vez que foram detectados casos de retornos anormais positivos e significantes ao ingressar no ICO2. Ademais, houve caso de retorno anormal negativo e significantes ao deixar o ICO2. Logo, levanta-se a possibilidade de investidores brasileiros valorizarem mais determinadas ações de empresas que adotam práticas carbono eficientes em seu modelo de negócios.
This research examined the possible impact on the profitability of companies who entered or left the Carbon Efficient Index (ICO2). It sought to understand whether the participation of a company in this portfolio would benefit its shareholders with profitability gains and otherwise, if the output would fall in profitability. Until then, the only study for that purpose held for ICO2 was formed based on the first book and only checked the input movement. This work tried to analyze this index in a more dynamic optics and updated from changes in its composition over time. To accomplish this, there was an event study to identify the existence of abnormal returns in companies in and out of ICO2. The sample comprised twelve companies that made the entry or exit of movement throughout the period 2012 to 2015. The results provide a breakthrough in the understanding of sustainable investments in Brazil, as they have been detected cases of positive abnormal returns and significant at joining ICO2. Moreover, there was the case of negative abnormal return and significant to leave the ICO2. Hence arises the possibility of Brazilian investors to value more certain stocks of companies that adopt efficient carbon practices in their business model.
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Adiredjo, Afifuddin Latif. "Water use efficiency in sunflower : Ecophysiological and genetic approaches." Phd thesis, Toulouse, INPT, 2014. http://oatao.univ-toulouse.fr/20177/1/adiredjo.pdf.
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Water use efficiency (WUE), measured as the ratio of plant biomass to water consumption, is an essential agronomical trait for enhancing crop production under drought. Measuring water consumption is logistically difficult, especially in field conditions. The general objective of the present Thesis is to respond to three main questions: (i) can WUE be determined by using carbon isotope discrimination (CID), easy to measure?, (ii) how WUE and CID variation analysis can contribute to the genotypic selection of sunflower subjected to drought?, and (iii) can WUE variation be revealed by the variation of plant-water relation traits. Four experiments were carried out in greenhouse across two different years: (i) on two drought scenarios, progressive soil drying and stable water-stress, and (ii) on five levels of soil water content. The main traits that have been measured include WUE, CID, as well as plant-water relation traits, i.e. control of transpiration (FTSWt), water extraction capacity (TTSW), and dehydration tolerance (OA). A highly significant negative correlation was observed between WUE and CID, and a wide phenotypic variability was observed for both WUE and CID. A wide variability was also observed for FTSWt, TTSW and OA. The results provide new insight into the genetic control of WUE and CID related-traits, which, unlike to other crops, genetic control of WUE, CID, and TTSW in sunflower have never been reported in the literature. Further, quantitative trait loci (QTL) mapping for FTSWt was never reported in any plant species. The QTL for WUE and CID were identified across different drought scenarios. The QTL for CID is considered as a ‘‘constitutive’’ QTL, because it is consistently detected across different drought scenarios. The QTL for CID co-localized with the QTL for WUE, biomass and cumulative water transpired. Co-localization was also observed between the QTL for FTSWt and TTSW, between the QTL for TTSW and WUE-CID-biomass, as well as between the QTL for FTSWt-TTSW and biomass. This study highlights that WUE is physiologically and genetically associated with CID. CID is an excellent surrogate for WUE measurement, and can be used to improve WUE by using marker-assisted selection (MAS) to achieve the ultimate goal of plant breeding at genomic level.
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Jimoh, Bukola S. "Energy Efficiency Technologies for Buildings: Potential for Energy, Cost, and Carbon Emission Savings." Scholarship @ Claremont, 2011. http://scholarship.claremont.edu/cmc_theses/180.
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Buildings are a significant energy consumer and are responsible for an increasingly large percent of worldwide greenhouse gas emissions, currently between 30 and 40 percent. Energy efficiency presents unique opportunities for building owners to reduce their environmental footprint and add value through cost savings, tax deductions, and increased market value. An analysis of 183 samples of efficiency measures in seven technology categories found that 74% of efficiency investments had a positive net present value. Building automation system and chiller plant improvements had the highest mean energy and carbon dioxide savings per square foot. Additionally, building automation systems had, on average the highest return on investment, approximately $800 above the cost of implementation per one thousand square feet. Only building envelope modifications had a negative mean return on investment. Building automation system upgrades avoided an average of 350 pounds of CO2e for every dollar spent, reducing a building’s total carbon footprint by as much as 28%. The results suggest that a significant opportunity for cost, energy, and emission savings is available across all technology categories.
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Frantz, Jonathan M. "Determining the Factors That Control Respiration and Carbon Use Efficiency in Crop Plants." DigitalCommons@USU, 2003. https://digitalcommons.usu.edu/etd/6600.
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In the literature on plant respiration, there are two viewpoints concerning the source of respiratory control: supply (photosynthate availability) or demand (temperature dependent) limitations. While different studies indicate the primary dependency for respiration is either the supply or demand side, the two paradigms cannot both be true. The relative importance of each paradigm may depend on a number of factors including period of time during which respiration is measured, phase of plant development, environmental conditions, and species.
Studies were performed using continuous CO2 gas-exchange instrumentation to monitor short- and long-term changes in whole canopies of lettuce, tomato, soybean, and rice in response to changes in light and temperature during vegetative growth. Respiration in all crops was less sensitive to temperature than previously reported. This is likely due to large amounts of temperature-insensitive growth respiration as a fraction of total respiration during early growth. Carbon use efficiency (CUE) decreased with warm night temperatures, but the change was too small to decrease the final dry mass or carbon gain after night temperatures decreased. Canopies with constant day/night temperature had the same CUE, in elevated CO2 (1,200 μmol moJ- 1), regardless of temperature. In ambient CO2 (400 μmol mol-1), CUE decreased significantly when temperatures were above 32C.
Applying shade initially decreased CUE because of low photosynthesis and high respiration. After about 12 days, canopies acclimated, based on recovery of CUE. Different species acclimated to shade to different extents, but no interaction was evident between light and shade stress. These data were used to predict changes in photosynthesis, respiration, and carbon use efficiency given light, temperature, and CO2 concentrations.
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Le, Roux Debbie Jeanette. "Growth, water use efficiency and stable carbon isotopes in commercial clones of Eucalyptus." Master's thesis, University of Cape Town, 1993. http://hdl.handle.net/11427/18327.
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The expansion of Eucalyptus plantations to supply timber for an increasing population in South Africa will result in a great reduction in the country's run-off water. If Eucalyptus continues to be the source of timber in South Africa, the selection of more water use efficient species for planting in existing and new areas has to be implemented. An understanding of the physiological factors ruling growth and water use efficiency in Eucalyptus is needed to develop selection criteria for improved water use efficiency and harvestable stem production under a limited water supply. This study investigated the effects of soil moisture availability on the growth and water use efficiency of 6 commercial clones of Eucalyptus commonly grown in South Africa with the aim of determining the following: (i) The extent of clonal variation in growth, dry mass allocation patterns, water use efficiency and the water cost of wood production at 16 months after planting. (ii) The influence of plant physiological traits such as patterns of dry mass allocation, canopy leaf area, leaf canopy density, specific leaf area, foliar nitrogen concentration and instantaneous rates of photosynthesis and transpiration, on growth, water use efficiency and the water cost of wood production. (iii) The complications associated with sampling for stable carbon isotope ratios (δ¹³C) within a eucalypt canopy and the potential use of δ¹³C in plant tissues as a tool for ranking clonal water use efficiencies.
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Searle, Andrew. "Application of nanostructured emitters for high efficiency lighting." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:81731b64-c40b-4c76-9c90-dae7c956e29f.
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This is the first study comparing morphologies of CNT films on Kanthal wire, with their field emission properties, and as such offers ways to design better cylindrical emitter devices. A low turn-on field was achieved (0.35 V/µm), the field emission results have been explained using a simple model, and a fluorescent lamp was fabricated. Whilst previous work has been done on the link between “as grown” CNT films and their respective field emission properties on flat substrates, very little work has been done on linking morphology to emission performance on wire substrates, where the morphology can be very different. Microscopic structures such as towers, ridges and clumps consisting of many aligned or entangled CNTs were grown using an aerosol chemical vapour deposition (a-CVD) technique. Hydrogen added to the carrier gas resulted in a decrease in defect density in the growth of undoped CNTs, and an increase in defect density in the growth of nitrogen doped CNTs (N-CNTs) and boron doped CNTs (BCNTs). In-situ transmission electron microscopy (TEM) studies show that damage to CNT tips results in a significantly higher turn-on field compared to undamaged tips. This can be recovered by making the CNT emit current for several minutes which makes the tip recrystallize due to heat caused by the Nottingham effect. The field emission properties of the “as grown” CNT films are dominated by protruding CNTs found at the edges of ridge and tower microscopic structures. The field emission properties are also related to the dimensions of these structures with the longest ridges (hence those with the longest protruding CNTs) resulting in the lowest turn-on electric field. The ridge and tower structures act to accommodate protruding CNTs at their edges and their physical dimensions (mainly width) act to separate these emitters so that screening is minimised. This work shows that efficient emitters can be fabricated effectively from simple a-CVD techniques and microscopic structures act to improve, not degrade, field emission properties.
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Holmes, Richard James. "Chemical modification of activated carbon adsorbents." Thesis, Brunel University, 1991. http://bura.brunel.ac.uk/handle/2438/5378.
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Activated carbons have been modif fed using reactive chemicals to produce adsorbents of enhanced hydrophobic character which will also be resistant to surface oxidation that results from exposure to humid air ("ageing"). The intention was that modification would not disrupt the carbon pore structure. The adsorptive properties of the modified carbons have been investigated using probe molecules Including nitrogen, water, hexane, and chloropicrin, and the ageing characteristics of the carbons, and the factors controlling the adsorption of a model hydrophobic vapour from high humidity air have been studied. Directly fluorinated carbons were unstable, probably due to weakly adsorbed fluorine. Treatment of these adsorbents with other chemicals indicated the potential of the technique for Introducing specific functional groups onto the carbon surface. Carbons modified using selective fluorinating reagents (hexafluoropropene and 1,1-difluoroethene) were more hydrophobic, and adsorbed hydrophobic vapours more efficiently from humid air in comparison to controls. These adsorbents aged, but at a reduced rate in comparison to control carbon. Carbons modified using chlorinating reagents (carbonyl chloride and chlorine) and treated with solvents to remove adsorbed reagent and/or reaction products were of improved hydrophobic character, and adsorbed hydrophobic vapours from humid air at least as efficiently as the control samples. More importantly, these carbons offered resistance to ageing effects. A study of the factors controlling the efficiency with which hydrophobic vapours; are adsorbed from humid air revealed that the surface chemistry of the carbon is important, but that under typical conditions of use, filter performance was limited by the rate at which water displaced by the organic vapour could be carried away by the airstream. The results illustrate that filters containing chemically modified activated carbon offer advantages when volatile hydrophobic contaminant vapours are present, and where ageing effects are an important mechanism by which filtration efficiency is degraded.
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Lahiri, Indranil. "Carbon Nanotube Based Systems for High Energy Efficient Applications." FIU Digital Commons, 2011. http://digitalcommons.fiu.edu/etd/508.
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In the current age of fast-depleting conventional energy sources, top priority is given to exploring non-conventional energy sources, designing highly efficient energy storage systems and converting existing machines/instruments/devices into energy-efficient ones. ‘Energy efficiency’ is one of the important challenges for today’s scientific and research community, worldwide.
In line with this demand, the current research was focused on developing two highly energy-efficient devices – field emitters and Li-ion batteries, using beneficial properties of carbon nanotubes (CNT). Interface-engineered, directly grown CNTs were used as cathode in field emitters, while similar structure was applied as anode in Li-ion batteries. Interface engineering was found to offer minimum resistance to electron flow and strong bonding with the substrate. Both field emitters and Li-ion battery anodes were benefitted from these advantages, demonstrating high energy efficiency. Field emitter, developed during this research, could be characterized by low turn-on field, high emission current, very high field enhancement factor and extremely good stability during long-run. Further, application of 3-dimensional design to these field emitters resulted in achieving one of the highest emission current densities reported so far. The 3-D field emitter registered 27 times increase in current density, as compared to their 2-D counterparts. These achievements were further followed by adding new functionalities, transparency and flexibility, to field emitters, keeping in view of current demand for flexible displays. A CNT-graphene hybrid structure showed appreciable emission, along with very good transparency and flexibility.
Li-ion battery anodes, prepared using the interface-engineered CNTs, have offered 140% increment in capacity, as compared to conventional graphite anodes. Further, it has shown very good rate capability and an exceptional ‘zero capacity degradation’ during long cycle operation. Enhanced safety and charge transfer mechanism of this novel anode structure could be explained from structural characterization. In an attempt to progress further, CNTs were coated with ultrathin alumina by atomic layer deposition technique. These alumina-coated CNT anodes offered much higher capacity and an exceptional rate capability, with very low capacity degradation in higher current densities. These highly energy efficient CNT based anodes are expected to enhance capacities of future Li-ion batteries.
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Åberg, Magnus. "System Effects of Improved Energy Efficiency in Swedish District-Heated Buildings." Doctoral thesis, Uppsala universitet, Institutionen för teknikvetenskaper, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-229477.
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To alleviate global warming, European-Union member states must reduce primary energy use, emit less carbon dioxide (CO2), and increase renewable energy use. Buildings constitute a great potential for energy savings, but saving energy in district-heated buildings influences combined heat and power (CHP) production, other electricity generation, and global CO2 emissions. This thesis investigates the system effects from Swedish district heating production caused by district heating demand changes due to energy conservation in buildings. The cost-optimising linear programming modelling tools MODEST and FMS, the latter developed in the context of this thesis, are used to describe present district heating production and to investigate the impact of heat-demand reductions in twelve Swedish district heating systems, four of them representing all Swedish district heating. Energy savings in district-heated, multi-family residential buildings yield a lower, more seasonally levelled district heating demand. These demand changes mainly reduce use of fossil-fuel and biomass for heat production. CHP production is significantly reduced if it supplies intermediate or peak district heating load. The αsystem value (ratio between generated CHP electricity and produced district heating) increases by demand reductions if CHP mainly supplies base district heating load. CO2 emissions due to district heat production depend on the approach used for CO2 assessment of electricity, and are generally reduced with heat demand reductions, unless the share of CHP production is large and the reduced fuel use yields smaller emission reductions than the emission increase from power production that replaces reduced CHP generation. In total, heat demand reductions reduce CO2 emissions due to Swedish district heating, and the district heating systems even constitute a carbon sink at certain energy conservation levels. If saved biomass replaces fossil fuels elsewhere, a lower heat demand reduces CO2 emissions for every studied district heating system.
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Fourie, Andri. "Carbon minus : a research centre for green technology : focussing on resource efficiency minus footprint." Diss., Pretoria : [s.n.], 2008. http://upetd.up.ac.za/thesis/available/etd-11212008-103255.
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Lebeau, Juliana Laurence Dominique. "Improving the carbon efficiency in the bio-production of citramalic acid in Escherichia coli." Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/49947/.
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Methacrylic acid (MAA) is a bulk chemical used in the synthesis of acrylic polymers as well as for the manufacture of many different products such as resins, and paints. However, the industrial manufacturing processes for MAA production involve toxic raw materials that are reliant on availability and economic variability of petroleum derived compounds. Global consumption and market of acrylics keep growing, rendering constant production processes as well as price stability highly desirable. To date, there is no direct bio-process available for the biosynthesis of MAA itself. Fortunately, a bio-production route of citramalic acid, which was previously demonstrated to be converted readily to MAA in a simple chemical patented hot pressurised water process, was demonstrated in Escherichia coli with promising titres of product (130 g/L). The enzyme citramalate synthase was used, and catalysed the condensation of two central cellular metabolites, pyruvate and acetyl-CoA, to (R)-citramalate in a one-step reaction. However, the biocatalytic reaction is limited by the availability of the starting materials. Acetyl-CoA is mainly produced via the decarboxylation of pyruvate, resulting in losing carbon by the formation of CO2, and is known as one of the major limitation for the development of cost-effective microbial bio-production of commodity bio-chemicals. In this thesis, E. coli strains were engineered to be able to co-consume carbohydrate and/or non-carbohydrate sources, in order to address the metabolic limitation due to pyruvate decarboxylation. In E. coli, both acetate and ethanol are directly linked to acetyl-CoA via different reversible enzyme pathways and were thus identified as potential external sources of acetyl-CoA. The introduction of either an acetate or an ethanol assimilation pathway with the appropriate co-feeding of glucose/acetate or glucose/ethanol resulted in increasing the specific productivities of (R)-citramalate in E. coli up to 50% in comparison to bio-production systems based on glucose only. Thus, acetate and ethanol co-feeding strategies provided promising outcomes for the bio-production of MAA.
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Lefébure, Robert. "Effects of temperature and terrestrial carbon on fish growth and pelagic food web efficiency." Doctoral thesis, Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-54028.
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Both temperature and terrestrial dissolved organic carbon (TDOC) have strong impacts on aquatic food web dynamics and production. Temperature affects vital rates of all organisms and terrestrial carbon has been shown to alter the dynamics of phytoplankton and bacterial production and affect the trophic structure of planktonic food webs. As climate change predictions for the Baltic Sea suggests future increases in both terrestrial carbon run-off and increases in temperature, the aim of thesis was to adopt a system-ecological approach and study effects of these abiotic variables, not only on interactions within planktonic food webs, but also on the growth and consumption rates of one of the most common zooplanktivorous fish in the Baltic Sea, the three-spined stickleback Gasterosteus aculeatus. Results showed that three-spined sticklebacks display a high degree of resilience against increasing temperatures, as both growth rates as well as consumption rates on zooplankton were high at temperatures well over 20 °C. Furthermore, it was shown that the minimal resource densities required to sustain individual and population growth, actually decreased with increasing temperatures, implying that sticklebacks around their optimum temperature for growth at 21 °C will actually have an increased scope for growth. As stickleback population densities have increased over the last decade in the Baltic Sea and are now suggested to out-compete other coastal fish species for shared zooplankton resources, the results presented in this thesis suggest that increased water temperatures would only serve to increase sticklebacks competitive advantage. As the structuring role of this small zooplanktivore on pelagic communities might be considerable, further studies investigating competitive interactions as well as patterns of population abundances are definitely warranted. TDOC was overall shown to stimulate bacterial production and the microbial food web. Because of the longer trophic pathways required to transport carbon from bacterial production to higher trophic levels, the addition of TDOC always reduced food web transfer efficiency. However, it became apparent that the full effect of TDOC additions on pelagic food webs was complex and depended heavily not only on the existing trophic structure to which the carbon was introduced, but also on ambient temperature levels. When three-spined sticklebacks were part of food webs with significant TDOC inputs, the presence of fish, indirectly, through predator release of lower trophic levels, amplified the magnitude of the effects of carbon addition on bacterial production, turning the base of the system significantly more heterotrophic, which ultimately, impacted negatively on their own production. However, when a pelagic food web containing sticklebacks was simultaneously subjected to realistic increases in temperature and TDOC concentrations, food web efficiency and fish production increased compared to present day conditions. These results were explained by a temperature dependent increased production potential of zooplankton, sustained by an increased production of heterotropic microzooplankton via TDOC additions, which lead to higher fish production. Although the increased number of trophic linkages in heterotrophic food webs should have reduced energy transfer efficiency, these negative effects seem here to have been overridden by the positive increases in zooplankton production as a result of increased temperature. These results show that heterotrophic carbon transfer can be a viable pathway to top-consumers, but also indicates that in order to understand the full effects of climate change on trophic dynamics and fish production, abiotic variables cannot be studied in isolation.
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Sharpe, Kathleen Angela. "Functionalization of single walled carbon nanotubes with proteins : a comparison of methods and efficiency." Thesis, University of Surrey, 2010. http://epubs.surrey.ac.uk/843398/.
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Before any novel biochemical device is fabricated, one needs to know that the technology and methodology being used are the most efficient. In the case of immobilised proteins, one needs to know that the method used will not harm the protein and that the conjugation technique used facilitates the highest binding efficiencies for the protein in question. Three methods from literature (non-specific binding, non-covalent binding and covalent binding) were used to conjugate bovine serum albumin (BSA) to single-walled carbon nanotubes (SWNTs). Efforts to use simple methods for protein concentration determination were hampered by the strong absorbance and interference from the nanotubes themselves. FITC tagged BSA was then used to investigate the conjugation methods. This technique was also subject to interference from the nanotubes when they were present. However, the subtraction of the amount of BSA removed from the nanotubes during washing was found to be accurate enough to compare the different conjugation techniques used. This showed that non-specific binding was the best method for conjugation, with approximately 79% of the original BSA remaining on the nanotubes after eight washes. The non-covalent and covalent method showed efficiencies of 54 and 60% respectively. A novel method for protein binding was investigated. This involved using a short DNA oligonucleotide as a tether for binding. The protein concentration was investigated as before using fluorescent BSA. This showed that approximately 88% of the BSA originally added remained on the nanotubes after washing. This value is higher than the other methods investigated and therefore this was the best technique. In addition to BSA conjugation, the enzyme urease was attached using non-specific binding and non-covalent conjugation. An attempt was made to determine the amount of urease bound through an assessment of its catalytic activity. This investigation was unable to accurately determine the amount of urease present, but did show there to be a difference in the amount of urease bound to SWNTs using either non-specific binding and non-covalent binding. The investigation of the best method for protein immobilisation in this thesis has shown that the novel DNA mediated conjugation is the most efficient, closely followed by the simplest method, non-specific binding. Both of these methods can allow the protein to remain structurally intact, an important factor to consider in the creation of novel devices.
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Policandriotes, Tod. "DESIGN OF AN EFFICIENT AND RAPID CHEMICAL VAPOR INFILTRATION (CVI) RE-CIRCULATION SYSTEM." OpenSIUC, 2013. https://opensiuc.lib.siu.edu/dissertations/721.
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Carbon-carbon (C/C, carbon fiber reinforced carbon matrix) composites are widely used in the aerospace industry because of the material's high temperature capability and structural properties. C/C maintains its mechanical and friction properties during extreme conditions so it is used extensively for high energy brakes, clutches, nosecones and leading edges of aircraft/spacecraft. Manufacturing C/C is expensive, requires high temperatures (approx. 1000°C) and typically requires rough vacuum environments (5-225 Torr). There are 5 general types of chemical vapor infiltration (CVI) systems and each type has a standard configuration in terms of a vacuum plumbing circuit. Standard CVI systems have a total carbon deposition efficiency of 5-30% using a reaction zone filled with carbon fiber preforms. Total processing time varies from 50 to 2000 hours depending on the type of system and its temperature, pressure and residence time. Unused hydrocarbon reaction exhaust (effluent) gases are either burned off or used to power something externally adding more CO2 and CO to the environment. A reduction of processing time and waste is needed to reduce the cost of production and the emissions of greenhouse gases. A new method can be added to 4 of the general types of CVI that decreases the residence time by re-circulating a controlled amount of the effluent gases through a separate in-situ isobaric semi-closed loop circuit which also allows for more carbon to be deposited per liter of virgin precursor gas in the reaction zone. An electric potential is also applied to compare the effect on carbon deposition to standard techniques. Re-circulating a portion of effluent gases through the reaction zone decreases the residence time with minimal effect on the desired matrix microstructure. Decreasing the residence time and re-circulating a portion of effluent gases increases the deposition rate and total carbon deposition efficiency. This re-circulating loop can be added to any CVI system to enhance the process, lower production costs and reduce greenhouse emissions.
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Sundberg, Cecilia. "Improving compost process efficiency by controlling aeration, temperature and pH /." Uppsala : Swedish University of Agricultural Sciences, 2005. http://epsilon.slu.se/2005103.pdf.
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Soundararajan, Rengarajan. "Efficiency loss analysis for oxy-combustion CO2 capture process : Energy and Exergy analysis." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-14177.
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Natural gas combined cycles with oxy-fuel combustion is expected tobe an important component of the future carbon constrained energyscenario. An oxy-combustion power cycle enables the fuel to burn in anitrogen free environment and thereby helps separate the CO2 streamfor storage. Depending on the oxygen source and purity, the CO2stream may need further purification via a purification unit (CPU)before compressing it to a high pressure for storage. The major energy penalty in this type of power cycle is the production of oxygenand the downstream purification to remove volatiles. It is this energypenalty which results in the cost of avoiding the CO2 emissions to theatmosphere.Cryogenic Air Separation Units (ASU) for oxygen production con-tribute to approximately 20% of the total energy penalty of such powerplants. Oxygen Transport Membranes (OTM) for oxygen production offers a potential solution to reduce the energy penalty of oxy-combustion natural gas cycles. The energy penalties associated withOTMs are that membranes operate at high temperatures and requirea sweep gas to establish an oxygen partial pressure difference betweenthe feed and permeate streams. Further, while the Cryogenic ASUhas minimum integration with the power process, oxy-combustion cycles with OTMs are tightly integrated with the power plant. Thusthe contributions to efficiency penalty in an OTM-based cycles aredistributed and not easily identified.The objective of the thesis is to answer the question: "Where doesthe plant efficiency loss originate in oxy-combustion CO2 capture process using Oxygen Transport Membrane as compared to one withcryogenic ASU?" The contribution of the work will be to highlight thelosses at the sub-process and at the equipment level.This work studies three different cases of oxy-combustion naturalgas combined cycles (NGCC) with CO2 capture. The baseline scenario, modified/improved scenario and the advanced scenario. Thebaseline scenario is a simple oxy-combustion NGCC power plant withASU as the oxygen source. Various losses associated with this systemare studied in detail. The modified/improved scenario involves analysis of possible modifications to the baseline case and applying theresults in-order to improve the baseline case. The modified scenario isexpected to have a better overall plant performance. The advancedscenario involves usage of OTM for oxygen production.The power plants are simulated in Aspen HYSYS and plant massand heat balances are calculated. Using the stream enthalpy, entropyand composition, we can calculate the stream exergy values. Controlvolumes help us analyze the component and sub-system exergy lossesand arrive at the overall power plant exergetic efficiency. The base-line power plant scheme is found to have an exergetic efficiency of 47percentage points with a thermal efficiency of 49.6 percentage, withcapture.The modified power plant scheme is obtained by increasing the gasturbine pressure ratio and this has a significant impact on the over-all system design and hence the performance. The modified systemhas exergetic and thermal efficiency of 49 and 51 percentage pointsrespectively. The advanced power plant with OTM, also called as theAdvanced Zero Emissions Powerplant (AZEP) has an exergetic efficiency of 51 and a thermal efficiency of 53.4 percentage. In all the cases, the combustor where most of the fuel is burnt is responsible formajority of the exergy destruction.There is potential for improving the ASU and thereby achieving alesser specific oxygen production power and also due to system integration and other improvements, the overall oxy-combustion NGCCpower plant is expected to play an important role in 5 - 10 years. Alsoas the working fluid is different from that of a normal air based powerplant, significant work needs to be done in the gas turbine and compressor part. Also detailed cost estimations, reliability and flexibilitystudies, operability and safety related studies need to be carried outin-order to boost the confidence in oxy-fuel NGCC power plants andtake it to the next phase.
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Fremont, Thibault, and Clotilde Maurel. "The Carbon Market Efficiency : An investigation about the return correlation of financial instruments traded on an emerging market." Thesis, Umeå University, Umeå School of Business, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-25887.
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Morris, Jonathan. "Benchmarking domestic gas and electricity consumption to aid local authority carbon reduction policy." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12368.
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As part of an effort to be a world leader in international efforts in reducing atmospheric carbon dioxide levels, the UK Government has set itself ambitious targets to reduce carbon dioxide emissions by 80% relative to 1990 levels by 2050. To meet this target, there is a strong emphasis in reducing carbon emissions from the domestic sector through the reduction of energy consumption in UK households by improving the energy efficiency of the housing stock, and the behaviours of the occupants. The Department of Energy and Climate Change have indicated that Local Authorities in England are potentially to work in partnership with businesses and community organizations to facilitate delivery; and as a promoter of domestic energy efficiency policies. Consultation with 11 Local Authorities across England confirmed that they are lacking a reliable mechanism that can detect areas within their administrative boundaries that are most in need of intervention to improve the energy efficiency of the housing stock. For the year 2008 the regression models demonstrate that geographical variations in the size of the house, median household income, and air temperature account for 64% of the variation in English domestic gas consumption, and that variations in the size of the house, median household income, and proportion of households connected to the national gas grid account for 73% of the variation in domestic electricity consumption. The predicted values from these regression models serve as benchmarks of domestic gas and electricity consumption in England having accounted for household income, house size, house type, tenure, and climatic differences and could be used to identify areas within Local Authorities with higher than expected energy consumption for energy efficiency interventions. These results contribute to the wider academic debate over how best to achieve the overall aims of household CO2 reductions by moving beyond a purely technical or behavioural-based approach to reducing domestic energy consumption.
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Sathitsuksanoh, Noppadon Tatarchuk Bruce J. "Sequestration of CO₂ by chemically reactive aqueous K₂CO₃ in high efficiency adsorbents using microfibrous media entrapped support particulates." Auburn, Ala., 2007. http://repo.lib.auburn.edu/2006%20Fall/Theses/SATHITSUKSANOH_NOPPADON_5.pdf.
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Ojuva, Arto. "Processing and performance of zeolites for efficient carbon dioxide separation." Doctoral thesis, Stockholms universitet, Institutionen för material- och miljökemi (MMK), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-114160.
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We have structured zeolites from powders of zeolite 13X and 4A into hierarchically porous monoliths for efficient carbon dioxide capture by tailoring the pore dimensions to facilitate rapid gas uptake and release. Freeze-casting was used for the first time to shape adsorbents into a lamellar structure. Lamellar walls with thicknesses and spacing in the range of 10 µm were found to be the best combination between rapid gas transport and a short diffusion distance in the zeolite-containing walls for rapid carbon dioxide uptake and release. Compressive strength measurements of the freeze-cast zeolite-based monoliths showed that monoliths with small pores, thin walls and a lot of interconnectivity between the walls were stronger than monoliths with large pores and thick walls. Image analysis of the structures together with modelling of the deformation behavior suggests that the failure mechanism of freeze-cast monoliths is dominated by buckling. Binder-free zeolite Y and ZSM-5 -based monoliths were produced by pulsed current processing (PCP) into strong, hierarchically porous monoliths with minimal loss of crystallinity. Ranges for the maximum PCP processing temperatures for the zeolites with different aluminium contents were identified by powder x-ray diffraction (PXRD) with full-profile fitting analysis. Matching the thermal expansion behavior of the supports with the zeolite film is important to minimize the risk of thermally induced cracking of zeolite membranes. Zeolite supports with a macroporous structure was prepared by PCP and the thermal expansion coefficient was determined by PXRD and compared to traditional alumina substrates. It was found that the slightly negative thermal expansion coefficient of the zeolite supports matched the thermal expansion of the zeolite films very well, whereas the alumina support would induce large stresses upon fluctuating temperatures. Methylcellulose-directed synthesis of zeolite 4A produced nano-sized crystals with a narrow size distribution, which could be tuned by adjusting the methylcellulose content. The crystallinity of the synthesized 4A was controlled by PXRD and found to be very high, and the gas uptake capability performed well in comparison with available micron-sized zeolites.At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Submitted.
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Cho, Taeg Sang. "An energy efficient CMOS interface to carbon nanotube sensor arrays." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/40519.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 95-98).
A carbon nanotube is considered as a candidate for a next-generation chemical sensor. CNT sensors are attractive as they allow room-temperature sensing of chemicals. From the system perspective, this signifies that the sensor system does not require any micro hotplates, which are one of the major sources of power dissipation in other types of sensor systems. Nevertheless, a poor control of the CNT resistance poses a constraint on the attainable energy efficiency of the sensor platform. An investigation on the CNT sensors shows that the dynamic range of the interface should be 17 bits, while the resolution at each base resistance should be 7 bits. The proposed CMOS interface extends upon the previously published work to optimize the energy performance through both the architecture and circuit level innovations. The 17-bit dynamic range is attained by distributing the requirement into a 10-bit Analog-to-Digital Converter (ADC) and a 8-bit Digital-to-Analog Converter (DAC). An extra 1-bit leaves room for any unaccounted subblock performance error. Several system-level all-digital calibration schemes are proposed to account for DAC nonlinearity, ADC offset voltage, and a large variation in CNT base resistance. Circuit level techniques are employed to decrease the leakage current in the sensitive frontend node, to decrease the energy consumption of the ADC, and to efficiently control the DAC. The interface circuit is fabricated in 0.18 /m CMOS technology, and can operate at 1.83 kS/s sampling rate at 32 pW worst case power. The resistance measurement error across the whole dynamic range is less than 1.34% after calibration. A functionality of the full chemical sensor system has been demonstrated to validate the concepts introduced in this thesis.
by Taeg Sang Cho.
S.M.
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Pereira, Ryan. "Tropical lowland rainforests : rapid recyclers or efficient storers of carbon?" Thesis, University of Newcastle upon Tyne, 2013. http://hdl.handle.net/10443/2303.
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Amazonian rainforests are important systems that vigorously cycle carbon and water at the global and regional scale. However, despite their importance, dynamics of organic matter cycling in tropical rainforests within the global carbon cycle is poorly understood. New field-based hydrology and geochemistry data is presented from a three-year study (2009-2011) in the pristine rainforest of central Guyana at the northern rim of Amazonia. The study shows that two commonly used satellite- and interpolated-based models to estimate rainfall greatly overestimate and underestimate in the wet and dry season, respectively. This misrepresentation of hydrology at local and regional scales greatly affects our ability to understand and predict the connections and feedbacks between the hydrological and geochemical cycles. River water δ2H and δ18O isotopes from peak wet and dry seasons suggest that the majority of rainfall has a residence time of at least one month, which provides regions of water saturated zones for organic matter (OM) to be preserved in deeper rainforest soils (Δ14C ages of 360-1200 years). In contrast, Δ14C values of surface soils and dissolved organic matter (DOM) in river water recycle within ~60 years or less. Carbon normalised yields of lignin phenols, used as tracers of vascular plant material, are abundant across the terrestrial-aquatic interface. However, lignin appears to accumulate in river bed sediments. Soil leachate experiments confirm that during mobilisation from soil particulates into the dissolved phase, desorption processes change the composition of lignin biomarker ratios. Surface soil δ13C signatures show that the majority of carbon is fixed through the C3 pathway (-26.4 to -32.0‰). However, a strong variability of up to 10‰ in riverine δ13C of dissolved organic carbon suggests that changing δ13C of DOC reflects changing contributions of degraded and fresh organic compounds within the total OM pool. Superimposed on seasonal cycling, short intense rain events cause rapid mobilisation of large amounts of DOC (up to 114 mg/L) that is divided into two main fractions, humic substances and ‘invisible’ DOM, or ‘iDOM’. The latter group is characterised by non UV-absorbing organic compounds of mono- and oligosaccharides, alcohols, aldehydes, ketones and amino sugars. Importantly, iDOM contributes up to 89% to the total river OM pool during peak DOC supply.
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Zvandasara, Tendayi. "Influence of hydrodynamics on carbon steel erosion-corrosion and inhibitor efficiency in simulated oilfield brines." Thesis, University of Glasgow, 2010. http://theses.gla.ac.uk/2284/.
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Corrosion within the oil and gas sector is an ongoing concern for operators. The challenging nature of extraction and processing fluids is an unavoidable cause of severe metallic corrosion. With modern emphasis on health, safety and the environment, the case for managing corrosion has become an imperative agenda. Whilst new and more effective methods of mitigation are key, an interim solution is improving the value of current methods. A literature survey carried out within this project has revealed CO2 corrosion as contributing to most corrosion related failures within the industry. The corrosion behaviour in CO2 containing environments is complex partly due to the wide range of prevailing conditions such as temperature, CO2 concentration and flow conditions. For oil and gas transportation pipelines, internal corrosion mitigation can be achieved by the use of chemical inhibitors. Inhibitors have been established to be effective but are by no means a complete solution. Issues such as their effectiveness in high velocity and high shear flow are a main consideration for their function. The hydrodynamic nature of the flowing fluids can affect inhibitor efficiency by either slowing the rate of formation of the inhibitive layer or causing degradation of well-formed inhibitive layers. A combined effect may also be active. The corrosion behaviour of carbon steel in simulated oilfield conditions is investigated in this project with emphasis on conditions of varying velocity, impinging flow and consequently shear stress. Since inhibition is the main mitigation technique for fluid related corrosion, the efficiency of a commercially used inhibitor is, in this case assessed in the abovementioned conditions. To simulate both impingement and flow, a jet impingement apparatus is used in conjunction with a segmented-electrode specimen set up to separately study the erosion-corrosion behaviour of different hydrodynamic zones under the jet. Corrosion rates are measured by gravimetric analysis and results are also evaluated with electrochemistry. Additionally, galvanic interactions between the different hydrodynamic zones have been investigated. Visual and light-optical microscopic examinations are also used to assess variable effects within the zones. Under such conditions, the corrosion rates have been found to be significantly higher in impingement zones. Aerated conditions have shown a significant variation in corrosion behaviour between impingement and non-impingement zones. The results in CO2 saturated brines are consistent but with evidence of different relations between hydrodynamics and the corrosion rate. The inhibitor has been shown to be effective in CO2 saturated brines and significantly influenced by both inhibitor concentration and hydrodynamic conditions. Inhibitor efficiency has also shown a complex dependence on concentration and establishes a need to evaluate optimum inhibitor concentrations before field application. Evaluation of the mass loss results against electrochemistry has shown a large discrepancy between the two methods. This rather surprising result suggests solid-free flow is not entirely free of erosion and synergistic effects. This comprehensive study has not only improved current knowledge on the relation between hydrodynamics and inhibitor efficiency but also indicates a critical need to evaluate suitability of current monitoring methods. Electrochemical methods are increasingly used as a method of choice and while they contribute significant monitoring data, they are observed to be unable, alone, to monitor erosion and synergy. An industry review on their suitability to monitor solid-free flow corrosion is recommended.
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Moutaftsis, Dimitrios. "Improved structural, embodied carbon and cost efficiency of single storey industrial buildings using sandwich panels." Thesis, Oxford Brookes University, 2016. https://radar.brookes.ac.uk/radar/items/fb46ae71-4cb3-4912-9bb9-c2a37d1325b1/1/.
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Recent changes to the Building Regulations aimed at improving energy efficiency have resulted in significant increases in the amount of insulation incorporated into building envelopes. As a consequence, composite (sandwich) panels have become deeper, considerably improving their structural capability in terms of strength and stiffness. This however has largely been ignored in the design of building structures, so this study has sought to ascertain the degree to which more efficient solutions, that take advantage of the improved capabilities of panels, may reduce the embodied carbon of building structures, and indeed of whole buildings. The research focused on single-storey industrial buildings. A series of studies were undertaken to evaluate the opportunities, and to quantify the benefits and trade-offs associated with structural solutions that fully exploit panel capabilities. The studies addressed a) long span sandwich panels to reduce the number of supporting structural members, b) diaphragm action to stiffen the frame and c) frameless buildings. Results suggested that the greatest potential benefit (up to 60% steelwork saving) arises from the use of long span systems, particularly for trussed roof frames with northlight construction. The study identified that further realistically achievable improvement in the spanning capabilities of panels would provide significant additional benefits. An improved long span sandwich panel design was therefore developed using theoretical investigations, structural testing and a Pareto-optimisation process. The optimal solution in terms of embodied carbon and panel strength was defined. Optimised frame arrangements combined with enhanced long span roof sandwich panels were compared with traditional portal frame solutions. This comparison demonstrated the considerable savings in terms of both embodied carbon and cost that can be achieved over traditional construction. The study demonstrated that exploiting the increased insulation depth of composite panels can deliver solutions with greater structural efficiency and reduced environmental impact.
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Ma, Yuge. "The emergence of low carbon development in China and India : energy efficiency as a lens." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:0fdc5632-0f8c-468f-a237-9652450850d0.
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Low-carbon development (LCD) in China and India is crucial to global sustainability. As representatives of the emerging world, China and India have to tackle the LCD challenge at the same time as they address rapid urbanization, industrialization and globalization, making this process an unprecedented problem in policy and practice. My dissertation uses a comparative perspective to examine the unique institutional change processes of China and India's LCD during the period of late 1970s to the present day - through the lens of energy efficiency (EE). I argue that despite the manifold differences in political, economic and social contexts in contemporary China and India, the process of institutional development and change in EE reveals some similar mechanisms. I investigate the common mechanisms through a five-phase framework, and find: First, in both countries, EE was initially triggered by complicated interactions between international and domestic crises. Second, through processes of political negotiation led by various policy groups, EE was conceived and planned by each state to embody not one single objective but multiple political, economic and social development goals. Third, in order to realize EE, an organizational complex formed within an existing governance structure. Fourth, detailed policy processes (which both shape and are shaped by their institutional settings) emerged from the previous stages. Finally, EE institutions are stabilized jointly through legalization and the establishment of specialist technical subfields. I argue that the key mechanism of the five-phase process of institutional change is the bundling structure between EE organizations and the host governance structure. While in China the latter is the structure of economic governance, in India it is that of energy governance. These bundling structures imprinted multiple path-dependencies from the host governance structure to the newly developed EE regime, which in turn determine the long-term impact of EE on LCD in China and India. My original contributions are threefold. First, this project is one of the first scholarly attempts to systematically make sense of LCD in large and complex countries with fast economic growth by using the perspective of institutional change. Second, drawing on broad theoretical resources and through an interdisciplinary exploration, the thesis tries to construct a cause-effect, systemic, and political-economic theory of LCD in contemporary China and India. Finally, my comparative framework adds a systemic and nuanced methodological viewpoint to the emerging field of multidisciplinary China-India comparative scholarship.
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Lu, Hong. "Development of Calcium-Based Durable Sorbents with High Carbon Dioxide Uptake Efficiency at High Temperatures." University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1239116430.
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Maldei, Michael. "Quantum efficiency measurements of a-C:H based photovoltaic cells." Ohio : Ohio University, 1997. http://www.ohiolink.edu/etd/view.cgi?ohiou1177092277.
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Spargo, John T. "Continuous No-till Management: Implications for Soil Quality, Carbon Sequestration, and Nitrogen Conservation." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/26166.
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No-till management for agronomic crop production is recognized as an effective practice to regain a portion of soil organic matter lost following decades of cultivation. Increasing soil organic matter sequesters C, conserves organic N and concomitantly improves soil quality. Objectives of this research were to: i) quantify C sequestration rate and N conservation with duration of continuous no-till; ii) measure C stratification with continuous no-till as an indicator of soil quality; and iii) evaluate the Illinois soil N test (ISNT) for its value to predict fertilizer N needs of corn in Virginia.
Objectives i and ii were achieved by collecting soil samples from 63 production fields in the Virginia Coastal Plain that were managed using continuous no-till from 0 to 14 yrs. No-till management resulted in sequestration of 0.308 ± 0.280 Mg C ha-1 yr-1 and conservation of 22.2 ± 21.2 kg N ha-1 yr-1 (0-15 cm). The C stratification ratio (0-2.5 cm: 7.5-15 cm) increased with increasing duration of continuous no-till (0.133 ± 0.056 yr-1) due to the accumulation of organic matter at the soil surface indicating improved soil quality with continuous no-till management.
Objective iii was addressed by conducting 29 on-farm fertilizer N response trials in major corn producing areas of Virginia with the duration of continuous no-till management ranging from 0 to 25 yrs. The ISNT values were significantly related to yield without fertilizer N (r2 = 0.57; p<0.001) and relative yield (r2 = 0.64; p<0.0001). We also found that the ISNT extracted a relatively consistent percentage of total soil N (16.3 ± 0.73 %) suggesting it is a poor indicator of labile N. Total soil N values did almost as well as the ISNT in predicting yield without fertilizer N (r2 = 0.53; p = 0.0002), and equally well predicting relative yield (r2 = 0.64; p<0.0001). Results do not suggest the ISNT is useful for measuring mineralizalbe N or improving fertilizer N recommendations in Virginia cropping systems.Ph. D.