Thesis. 1977. Ocean E.--Massachusetts Institute of Technology. Dept. of Ocean Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 93-95. / by Osie "V". Combs, Jr. / Ocean E.

by Angela Mara Bentes de Souza. / "June 2003." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (p. 176-200). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

A utilização de dióxido de carbono em condições sub e supercríticas (em associação com co-solventes) em processos de deslignificação/polpação já se encontra descrito na literatura especializada. Esta técnica se beneficia da elevada difusibilidade apresentada por fluidos no estado sub/supercrítico. Quando aplicada em processos de polpação, a utilização destes fluidos nestas condições pode proporcionar vantagens nas etapas de impregnação e de processamento dos efluentes gerados no processo. Visando aplicar o potencial da elevada difusibilidade apresentada pelo dióxido de carbono supercrítico, realizou-se o estudo comparativo do desempenho dos processos kraft, organossolve convencional e supercrítico frente à deslignificação de diferentes espécies (Eucalyptus grandis e Pinus taeda), empregando-se amostras de diferentes dimensões. O processo kraft se mostrou mais eficiente com o emprego de cavacos, enquanto que a utilização de dióxido de carbono supercrítico, com o uso de co-solvente etanol/água (processo SFE), foi mais eficiente com amostras de maiores dimensões (cubos de 3,5 x 3,5 x 4,0cm). Dentro dos intervalos considerados para as variáveis utilizadas nos diferentes processos de polpação, as polpas obtidas pelo processo SFE a partir de amostras de seção quadrada 3,5 x 3,5cm apresentaram maior conteúdo de holocelulose e maior alvura, evidenciando um elevado rendimento livre de lignina. Estudou-se também o uso de acetona/água e de dioxano/água como co-solventes em processos realizados com dióxido de carbono no estado supercrítico. Os resultados obtidos foram comparados com estudos anteriores realizados com álcoois alifáticos e indicaram a maior efetividade do uso de dioxano/água e 1-propanol/água. Foram realizados também estudos empregando amônia como fluido supercrítico no tratamento de cavacos de Pinus taeda, com o intuito de verificar a capacidade nucleofílica da amônia frente às reações de deslignificação. As reações foram realizadas com o uso exclusivo de amônia e na presença de etanol, água e misturas etanol/água como cosolventes. A análise dos resultados obtidos evidenciou a ocorrência pouco significativa de remoção de lignina, com migração desta para a periferia dos cavacos. As ligninas obtidas nos diferentes estudos foram caracterizadas por diferentes técnicas analíticas e não apresentaram diferenças significativas entre as amostras obtidas nos diferentes processos estudados. / The utilization of carbon dioxide under sub/supercritical conditions (in association with co-solvents) in delignification/pulping reactions has already been reported in the literature. This technique takes advantage of the high diffusivity presented by fluids at the supercritical state. When applied to pulping processes the utilization of these fluids can lead to advantages mainly in the impregnation and effluent treatment steps. In an attempt to apply the high diffusivity exhibited by supercritical carbon dioxide, this work presents the results obtained in the comparative study of the performance of the kraft, organosolv and supercritical processes in the delignification of different species (Eucalyptus grandis and Pinus taeda), employing samples with different dimensions. The kraft process presented a higher efficiency in the treatment of wood chips while the supercritical carbon dioxide, with ethanol/water as co-solvent, (SFE process) was more efficient in the treatment of high dimension samples (3.5 x 3.5 x 4.0 cm). In the experimental conditions applied in this study, the pulps obtained in the SFE treatment of samples with square section 3.5 x 3.5 cm showed higher holocellulose content and higher brightness which corresponds to high free of lignin pulp yield. It was also studied the utilization of acetone/water and dioxane/water as co-solvents in the carbon dioxide supercritical pulping process. The results were compared with previous studies performed with aliphatic alcohols and indicated a higher efficiency of the dioxane/water and 1-propanol/water mixtures. The utilization of supercritical ammonia in the treatment of Pinus taeda wood chips was also studied in order to verify the nucleophilic capability of this fluid in the delignification reactions. The reactions were performed with ammonia, exclusively, and in the presence of different co-solvents (ethanol, water and ethanol/water mixtures). The results of the delignifications showed the occurrence of low amount of lignin removal, with migration of lignin to the periphery of the wood chips. The lignins isolated from the reactions performed in this work were characterized by different analytical techniques. The results indicated no significant differences among the samples obtained in the different delignification processes.

Telogenetic epikarst carbon sourcing and transport processes and the associated hydrogeochemical responses are often complex and dynamic. Among the processes involved in epikarst development is a highly variable storage and flow relationship that is often influenced by the type, rate, and amount of dissolution kinetics involved. Diffusion rates of CO2 in the epikarst zone may drive hydrogeochemical changes that influence carbonate dissolution processes and conduit formation. Most epikarst examinations of these defining factors ignore regional-scale investigations in favor of characterizing more localized processes. This study aims to address that discrepancy through a comparative analysis of two telogenetic epikarst systems under various land uses to delineate regional epikarst behavior characteristics and mechanisms that influence carbon flux and dissolution processes in south-central Kentucky. High-resolution hydrogeochemical and discharge data from multiple data loggers and collected water samples serve to provide a more holistic picture of the processes at work within these epikarst aquifers, which are estimated to contribute significantly to carbonate rock dissolution processes and storage of recharging groundwater reservoirs on the scale of regional aquifer rates. Data indicate that, in agricultural settings, long-term variability is governed by seasonal availability of CO2, while in urban environments extensive impermeable surfaces trap CO2 in the soil, governing increased dissolution and conduit development in a heterogonous sense, which is often observed in eogenetic karst development, as opposed to bedding plane derived hydraulic conductivity usually observed in telogenetic settings. These results suggest unique, site-specific responses, despite regional geologic similarities. Further, the results suggest the necessity for additional comparative analyses between agricultural settings and urban landscapes, as well as a focus on carbon sourcing in urban environments, where increased urban sprawl could influence karst development

Exposed weathering profiles of a series of Pololu lava flows in Kohala, Hawaii are ideal for investigating the sequence of reactions/reaction pathways of weathered basalt. Weathering reactions for saprolites show mineral sequences that include feldspar → halloysite ± gibbsite + solutes; clinopyroxene → hematite + minor halloysite + solutes; olivine → hematite + solutes; magnetite → hematite or other Fe-oxides/hydroxides. However, the presence of smectite in four samples suggests that smectite-group clays may form as short lived intermediates at the base of the weathering profile. Regionally, on Kohala, soils and saprolites are dominated by halloysite with small quantities of other clays such as kaolinite, gibbsite, and smectite. However, one horizon in the weathering profile at the study site in Kohala is dominated by gibbsite. Smectite is found at the base of the profile above impermeable areas where mass leaching has left increased alkaline and alkaline earth elemental (Mg, Ca, Na, and K) abundances relative to the parent rock. The amount of elemental gain varies from -5% to +75% for samples with smectite. Different climates generate different weathering profile depths. MASW (multi-channel analysis of surface waves) shows that the depth of the weathering profile is 15 meters. Seismic profiles correlate the depth of the weathering profile inland (~15 meters), with cliff face (~13 meters). Other than the gibbsite horizon, most mineral zones are too thin to be resolved through second-order velocity variations. P-wave reflection surveys are unsuitable for imaging the base of the weathering front because the transition to fresh rock may be gradational. However, within the saprolite section, boundaries between relict lava flow textures produce reflections that mimic expected stratigraphic patterns. Perpendicular to the shoreline, reflectors dip gently seaward, whereas parallel to the shoreline, lenticular packages of relict lava flows are observed.

No description available.

Laser cutting is one of the most important applications of laser in manufacturing industry; it is mainly used for sheet metal cutting. In laser cutting, performing real-time evaluation of laser cut quality is very important to the advancement of this process in industry. However, due to the dynamic nature of the laser cutting process specially when cutting ferrous alloys using oxygen as an assist gas, laser cut quality cannot be easily predicted; therefore, the quality inspection of the laser cut is performed by off line inspections of the edges of the metal by skilled operators. This methodology is carried out after the process and thus cannot maintain a good quality if the process performance is out of control. Therefore, the objective of the research project is to qualify and develop a sensor system that ensure fault recognition online and can automatically control the laser metal cutting process to achieve good quality cut. For the realization of this objective the following has been done: - study the relationship between process parameters and cut quality characteristics; - identify the best sensors that can be used to monitor the process; - design and develop an experimental setup to test the proposed sensors; - collect and analyze data from the proposed sensors and correlate them to specific cut quality characteristics (process state variables); - develop direct relationships between the process signals and cut quality; - develop appropriate strategy for process control; - design and develop an integrated monitoring and control system; - test and evaluate the proposed system using simulation. In this study, a new technique for the determination of cut quality of sheet steels under the CO2 laser cutting process has been established. It is based on on-line detection and post-processing analysis of light radiation and acoustic emissions from the cut kerf. Determination of machining quality during cutting is best done through the measurement of surface roughness and kerf widths, as these are the two parameters that vary in successful through cuts. These two quality parameters can further be correlated to the two dominant process parameters of laser power and cutting speed. This study presents an analysis of acoustic emissions and reflected light for CO2 laser cutting of steel plates, and discusses their use for the estimation of cut quality parameters of kerf width and striation frequency for mild steel plates of 3mm, 5mm, 8mm, and 10mm thicknesses. Airborne acoustic and light signals are acquired with a microphone and a photodiode respectively, and recorded with a PC based data acquisition system in real time. The signals are then analyzed to establish a correlation between the signals obtained and the cut quality achieved. Experimental evidence shows that the energy levels of acoustic emission signals (RMS analysis) can be used to maintain the cutting process under steady state condition. On the other hand, the light intensity signal fluctuates with a frequency that corresponds to the frequency of striations formed on the cut surface; therefore it can be used to regulate cutting speed and laser power to obtain an optimum cutting condition and best cut quality. The validity of the proposed control strategy was tested experimentally by simulating the variations of cutting speed and examining their effect on the signals. So far, the prototype used for experimentation has been successful in providing correct information about cut quality in terms of striation frequency, and also about the state of the process where the microphone signal was successful in determining system failure or improper cutting conditions. A microprocessor based control system utilizing the PID control algorithm is recommended for the implementation of the control strategy. The implementation requirements of the proposed system for industrial use are then discussed. A new setup for the coaxial monitoring of CO2 laser cutting using a photodiode is proposed to enhance the quality of the signal and also to protect the photodiode from the harsh cutting environment. It is also proposed that an open control architecture platform is needed to enhance the integration of the proposed process control functions. Conclusions and future research directions towards the achievement of Autonomous Production Cell (APC) for the laser cutting process are then given.

The atmospheric (CO2) partial pressure is expected to continue to increase and the scenario is that the CO2 partial pressure will reach 50-70 Pa during the 21st century.The rise in CO2 will have a direct influence on plant growth and development because CO2 is the primary substrate for photosynthesis.The aim of the studies described in this thesis was to investigate the response of grasses belonging to two subtypes to a range of CO2 partial pressures under conditions where light intensity, water and N supplies were varied.Two species which are naturalized in Australia, Panicum coloratum (NAD-ME) and Cenchrus ciliaris (NADP-ME) were chosen for a series of experiments conducted in matched growth chambers. The response of C4 plants is particularly important for Australia because they dominate the tropical grasslands that occupy 75% of the continent and form the basis for the pasture industry. Following the extensive research conducted in this study, it can be concluded that the inevitable rise in atmospheric CO2 partial pressure will increase the growth of C4 grasses when other resources are not limiting.Growth of C4 grasses will be stimulated to a greater extent under conditions of drought. / Doctor of Philsophy (PhD)

Soil carbon (C) is important because even small changes in soil C can affect atmospheric concentrations of CO₂, which in turn can influence global climate. Adequate soil carbon is also required to maintain soil quality, which is important to if agricultural production is to be sustained. The soil carbon balance of New Zealand's pastoral soils is poorly understood, with recent research showing that soils under dairy pasture have lost large amounts of C during the past few decades. The main objective of this research was to determine an annual farm scale C budget for an intensively grazed dairy farm, with a second objective being to determine the amount of CO₂-C lost following cultivation for pasture renewal, and soil pugging by dairy cattle. A third objective was to investigate the environmental controls of CO₂ exchange in a dairy farm pasture system. Net ecosystem exchange (NEE) of CO₂ was measured using an eddy covariance (EC) system from 15 December 2007 to 14 December 2008. Closed chamber techniques were used to measure CO₂ emissions from three cultivated paddocks and three adjacent pasture paddocks between 26 January 2008 and 5 March 2008. CO₂ emissions were also measured using chambers from pugged and control plots between 25 June and 5 August. Coincidentally this research was carried out in a year with a severe summer/autumn drought and a wetter than usual winter. Annual NEE measured with the eddy covariance system was -1,843 kg C ha⁻¹ (a C gain by the land surface). Accounting for C in supplement import, milk export, pasture export and losses in methane, the dairy pasture system was a net sink of -880±500 kg C ha⁻¹. This C sequestration occurred despite severe drought during the study, which was in contrast to other studies of grasslands during drought. Cultivation under dry conditions did not increase cumulative CO₂-C emissions compared to adjacent pasture paddocks. However, when C inputs to pasture paddocks via photosynthesis were included in calculations, net C loss from the cultivated paddocks (during the 39 day study) was estimated to be 622 kg C ha⁻¹ more than the pasture paddocks. CO₂ emissions were lower from pugged plots compared to control plots, probably caused by decreased microbial and root respiration due to wetter soil conditions, and lowered root respiration as a result of lower pasture production. Volumetric soil moisture content (soil moisture) had a dominant effect on CO₂ exchange at a range of temporal scales. Respiration and photosynthesis were both reduced when soil moisture was below 43% (~the lower limit of readily available water) and photosynthesis virtually ceased when soil moisture declined below 24% (~wilting point). Soil moisture also influenced the relationship between temperature and respiration and photosynthetic flux density (PPFD) and NEE. These results suggest that management related soil disturbances of occasional cultivation for pasture renewal and soil pugging, are unlikely to cause large losses of soil C. Further, a severe drought also did not cause CO₂-C losses from the land surface to the atmosphere on an annual scale, in contrast to previous studies.

The Waitomo Caves attract approximately 500 000 tourists each year. A requirement of tourist cave management is that the partial pressure of carbon dioxide (PCO₂) is kept below levels that are: hazardous to the health of visitors, hazardous to the glowworms and other natural inhabitants, or potentially corrosive to speleothems. For the Glowworm Cave at Waitomo, the maximum permissible PCO₂ level is 2400 ppm. When exceeded, the tourist operators are required to close the cave. Ten years of monitoring data at the Glowworm Cave was analysed. Most of the variation in PCO₂ could be attributed to CO₂ respired by tourists, and the mixing of cave air with lower PCO₂ outside air. Occasionally, there were periods with high PCO₂ levels while the cave was closed to tourists. The main objective of this study was to investigate the potential role of the Waitomo Stream in contributing CO₂ to the Glowworm Cave atmosphere. Analysis of ten years of Glowworm Cave monitoring data showed that the 2400 ppm PCO₂ limit was, on average, exceeded five times each year, with a total of 48 events between 1998 and 2007. Of the PCO₂ limit exceedences, approximately 31% of events were largely driven by high tourist numbers; 27% of PCO₂ limit exceedences were mainly driven by increased discharge, rainfall, and/or a low temperature gradient between the cave and outside air, whilst 29% of the PCO₂ limit exceedences were due to a combination of tourists and increased discharge, rainfall, and/or a low temperature gradient. The remaining 13% of exceedences were unexplained by tourists or the factors investigated. It may be that the unexplained exceedences were due to the night time closure of the cave door, restricting air exchange. The PCO₂ of the Waitomo Stream was measured by equilibrating air with the streamwater within a closed loop. The air was passed continuously through an infrared gas analyser (IRGA). The streamwater PCO₂ typically ranged between 600 - 1200 ppm. Fluctuations in the PCO₂ of the Waitomo Stream coincided with PCO₂ fluctuations in the Glowworm Cave air, and under most conditions, the stream probably acted as a sink for cave air CO₂. However, following rainfall events, the stream PCO₂ increased, exceeding cave air PCO₂, thus acting as a source of CO₂ to the cave air. High stream PCO₂ often occurred at times when air flow through the cave was restricted, e.g. when the temperature gradient between the cave air and outside air was low, or stream levels were high, thus limiting air movement. The combination of high stream PCO₂ and a low temperature gradient increased the likelihood of high cave air PCO₂. Dripwater was measured to determine whether an increase in dripwater PCO₂ occurred in response to rainfall events. When rainfall events resulted in increased discharge, the dripwater PCO₂ sometimes increased (occasionally exceeding 5000 ppm), however the pattern was not consistent. The chemistry of the Waitomo and Okohua (Ruakuri) Streams was monitored with daily samples collected and analysed for major ions: HCO₃ -, Ca²⁺, Na⁺ and Mg²⁺, and δ¹³C stable isotope. The HCO₃ -, Ca²⁺, Na⁺ and Mg²⁺ concentrations in the streamwater decreased with increased discharge, presumably due to dilution. Increased discharge following rainfall events correlated with increasing PCO₂ in the Waitomo Stream, suggesting that soil atmosphere CO₂ dissolved in soil waters, and carried to the stream by saturated flow, was responsible for the streamwater PCO₂ increase. Ca in the stream showed both an increase and a decrease with respect to rainfall. Increased Ca in the stream occurred at times when the discharged waters were coming from the phreatic zone, and thus sufficient time had lapsed for CO₂ in the discharge waters to react with the limestone (carbonate dissolution reaction). Decreased Ca occurred when the infiltration and percolation of rainwater was rapid, and thus the streamwater was characterised by a higher PCO₂ and a lower Ca concentration, as insufficient time had lapsed for the discharge waters to equilibrate with the limestone. Increased negativity in the δ¹³C of the Waitomo and Ruakuri Streams coincided with increased discharge. During summer low flow, the δ¹³C of Waitomo Stream waters was -11.3‰, whereas during high stream discharge events, the δ¹³C dropped to -12 - -14‰. The δ¹³C of limestone is 0‰, the atmosphere is -7‰, and the soil atmosphere is reported to be about -24‰, thus the decrease in δ¹³C during high flow events supports the contention that soil atmosphere CO₂ is a likely source of the increased CO₂ in flood waters.