Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references (p. 253-274). Also available in print.

The açaí berry has grown in popularity for dieters and the health conscious. The berry contains high levels of antioxidants. The main anthocyanins are cyanidin-3-rutinoside and cyanidin-3-glucoside. The berries also contain vitamins and nutrients that help boost energy and alertness, and fatty acids that help maintain normal cholesterol levels. As a result of the health benefits of the constituents, the berries are chosen for obtaining the active ingredients by extraction. The solids left over after extraction still contain nutrients and useful components. There is a possibility of fermenting this residual and creating an açaí berry wine. Açaí berry wine is another new product on the market. The extracts and the wine are analyzed using Fourier transform infrared spectroscopy (FTIR). In an effort to utilize every part of the berry, the residual from the extract is also successfully fermented. Pilot plant studies are conducted utilizing supercritical carbon dioxide, an ethanol entrainer to increase its solubility, and subcritical water to extract components from freeze dried açaí berry. There is much potential and flexibility in the process, which effectively extracted lipids from the berry leaving behind anthocyanins without solvent residue.

January of 2010 brought record-breaking cold temperatures to Florida. Such freeze events can upset vulnerable populations of marine life and other species that rely on stable water temperatures. Sea turtles are one group of species that are particularly susceptible to abrupt drops in water temperature. When water temperatures drop below 10°C, a mass hypothermic stunning, or cold-stunning, event for sea turtles can be expected, with many debilitated turtles washing onshore with a very limited time window to be rehabilitated (Foley et al. 2007). The species of sea turtle that appears to cold-stun with the most frequency is the green turtle, especially juveniles. The green turtle represented the vast majority of marine turtles that were rescued during the 2010 cold-stun event. Therefore, accurate weather pattern recognition of marine cold snaps, or freezes, can alert sea turtle rescue groups and rehabilitation facilities in advance of any event, improving their readiness and response times, and ultimately preventing population declines. The proposed research fills this need by providing a qualitative analysis of select years for comparable atmospheric processes that could result in moderate to severe hypothermic stunning events. The 2010 event, along with other significant events, were examined using in situ air temperature, water temperature and wind data near two locations in Florida where hypothermic stunning events occurred: St. Joseph Bay and Mosquito Lagoon. These atmospheric parameters were represented graphically, depicting how each variable contributed to shaping an event. Cold stunning events were found to be primarily driven by frigid air temperatures and a subsequent decrease in water temperatures. Differences between the two event classifications, moderate and severe, are contingent upon the duration of the cold spell, not necessarily how quickly the water temperature dropped below the 10°C threshold value. Results suggest that repeated, quick exposure to cold air temperatures may influence the severity of a hypothermic stunning event. This research could be utilized in the formation of a forecasting model or strategy to efficiently alert the Florida Sea Turtle Stranding and Salvage Network (STSSN) to a potential sharp drop in water temperatures and, consequently, many debilitated sea turtles.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

No description available.

Concrete marine structures are typically exposed to harsh marine environments where the ingress of chloride ions can lead to corrosion of steel reinforcing bars, reducing both strength and service life; therefore, concrete must be proportioned to resist these environments. Current recommendations for concrete mixtures and plastic shrinkage cracking both reduce the resistance to chloride ingress. The main objective of this thesis was to understand the benefits of fiber addition to concrete exposed to chlorides and quantify those benefits, which would lead to a concrete mixture suitable for marine structures in freeze thaw environments. The research program tested two different fibers in a total of nine concrete mixtures. The results demonstrated that fiber addition at dosages up to 0.33 % by volume resulted in significant reduction or elimination of plastic shrinkage cracking and the chloride tests determined that the ternary FRC mixtures had the best resistance to chloride diffusion.

Mercury (Hg) is a potent human toxin and a persistent global pollutant with unique properties and environmental behaviours which make it difficult to model and understand. While anthropogenic mercury sources are well understood along with the impacts on ecosystems and human populations, the processes and transformations which govern environmental cycling lack the same level of understanding. Concentrations in Arctic environments are a specific concern, along with cycling behaviours in regions spanning from temperate to Arctic climates. The objective of this experiment was the investigation and characterization of the mechanisms which promote elemental mercury (Hg^0) flux from soils in these environments during simulated seasonal cycling. A laboratory scale experiment was conducted which used a Dynamic Flux Chamber (DFC) to monitor Hg^0 flux from a naturally Hg enriched soil during temperature cycling relevant to cold environments. The results, which were split into freeze-thaw (FT) and sub-zero (SZ) cycles, showed that Hg^0 flux from frozen soils remains active during temperature cycling. During FT cycles, Hg^0 flux is controlled by soil temperature and energy entering the system, with a linear increase in flux for increases in energy. This response is produced from the entire soil column. During SZ cycles, Hg^0 flux is produced only in the thin soil surface layer and is controlled by the air temperature at the soil-air interface. A decrease in the DFC air temperature was observed to produce an increase in flux, with an inverse relationship controlled by a separate mechanism than the FT cycle response. Recommendations for modifications to the experimental set-up and methodology have been made to improve the accuracy of the results and confirm the behaviours characterized during this study. / Natural Sciences and Engineering Research Council of Canada (NSERC)

The seasonal cycle of snow and sea ice is a fundamental feature of the Arctic climate system. In the Northern Hemisphere, about 55 million km2 of sea ice and snow undergo complete melt and freeze processes every year. Because snow and sea ice are much brighter (higher albedo) than the underlying surface, their presence reduces absorption of incoming solar energy at high latitudes. Therefore, changes of the sea-ice and snow cover have a large impact on the Arctic climate and possibly at lower latitudes. One of the most important determining factors of the seasonal snow and sea-ice cover is the timing of the seasonal melt-freeze transitions. Hence, in order to better understand Arctic climate variability, it is key to continuously monitor these transitions. This thesis presents an algorithm for obtaining melt-freeze transitions using scatterometers over both the land and sea-ice domains. These satellite-borne instruments emit radiation at microwave wavelengths and measure the returned signal. Several scatterometers are employed: QuikSCAT (1999–2009), ASCAT (2009–present), and OSCAT (2009–present). QuikSCAT and OSCAT operate at Ku-band (λ=2.2 cm) and ASCAT at C-band (λ=5.7 cm), resulting in slightly different surface interactions. This thesis discusses these dissimilarities over the Arctic sea-ice domain, and juxtaposes the time series of seasonal melt-freeze transitions from the three scatterometers and compares them with other, independent datasets. The interactions of snow and sea ice with other components of the Arctic climate system are complex. Models are commonly employed to disentangle these interactions. But this hinges upon robust and well-formulated models, reached by perpetual testing against observations. This thesis also presents an evaluation of how well eleven state-of-the-art global climate models reproduce the Arctic sea-ice cover and the summer length—given by the melt-freeze transitions—using surface observations of air temperature. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: In press. Paper 4: Submitted.</p>

The objective of the present study was to synthesize porous, biodegradable poly (D, l- lactide-co-glycolide) PLGA-B-HA (Bovine hydroxyapatite) composite and evaluate the effect of ceramic content on bone marrow cell differentiation in vitro. A macroporous biodegradable PLGA-B-HA composite with the pore size varying from 0.1 to 1000?? and a highly interconnected structure was fabricated using the freeze-drying/lyophilization technique. A pilot study was done to determine the effects of B-HA on to the osteoblast function. The main study was done to determine the effect of the increase in B-HA concentration on to the mesenchymal stem cell differentiation. Morphological characteristics of the composites were analyzed using FTIR and SEM/EDX analysis. The composites were seeded with neonatal rat calvarial osteoblasts (NRCO). The polymer: ceramic ratio in this study was 35%:65%. For comparison parallel experiments involving pure HA-200 discs were performed. SEM results indicated a higher proliferation and mineralization on PLGA-B-HA composites than pure HA discs. In addition, we evaluated the in vitro characteristics of PLGA-B-HA composites with varying ratios, i.e., 1:1, 1:2 and 1:3, seeded with rat marrow cells. FTIR indicated an increase in the area under the ceramic peak as ceramic concentration was increased. In addition, the average roughness values increased in the order of 1:3 andgt; 1:2 andgt; 1:1. Both compressive strength and modulus of 1:1 were significantly higher than 1:2 and 1:3 PLGA-B-HA composites. No significant difference in compressive modulli and strengths could be observed for 1:2 and 1:3 PLGA-B-HA composites. Cellular activity was determined by measuring AP activity, total protein analysis and osteocalcin concentration. Evaluation of alkaline phosphatase activity showed bone cells attached to 1:3 (PLGA-B-HA) expressed significantly higher alkaline phosphatase as compared to 1:1 and 1:2 PLGA-B-HA composites. In addition, cells seeded on to 1:3 composites secreted significantly higher osteocalcin and at a relatively short time period as compared to the other samples. Corrosion studies (ICP) and pH values indicate minimal difference in the concentration of Ca and P and pH in tissue culture media for all the samples at the end of all time periods. Hence we conclude that an increase in the ceramic concentration stimulated mesenchymal stem cell differentiation thereby promoting osteogenesis.

An experimental waste-rock pile (50m x 60m x 15m, 0.053 wt. % S) was constructed at the Diavik Diamond Mine, in the Northwest Territories, Canada to evaluate the generation of acid-rock drainage and the seasonal and annual release of various metals in drainage leachate. A dense internal instrumentation network enabled well resolved observations of temperature, air content, water content, fluid flow, microbiology, mineralogy and geochemistry within the waste-rock pile. Water samples were collected from soil water solution samplers (SWSSs) to measure core pore-water characteristics, from 4 m2 to 16 m2 scale basal collection lysimeters (BCLs) to measure core leachate characteristics, and from basal drains (3000 m2 basal area) to measure aggregated leachate characteristics. Monitoring of pore-water geochemistry within the core of the test pile indicated an evolving weathering front characterized by changes in predominant acid-consuming mineral-dissolution reactions. Initially, acid neutralization occurred through dissolution of carbonate minerals. A subsequent decline in pH was limited by acid neutralization through dissolution of Al- and Fe-bearing minerals. This lower pH environment was accompanied by increasing concentrations of SO4, Al, Fe, Ni, Co, Cu, Zn, Cd, Ca, Mg, K, Na and Si. Annual drainage cycles in the core of the test pile were characterized by distinct, high concentration ‘spring flushes’ followed by a steady decline of all dissolved constituents with minimums prior to freeze-up. Core trends were typical of freshets observed in polar environments and primarily explained by a combination of fluid residence time and the build-up of oxidation products over the winter. The opposite trend was observed in the aggregated pile drainage, whereby early-season low-concentration leachate was derived from snowmelt and batter flow and late-season high-concentration leachate was dominated by contributions from the core of the pile. Thermal data demonstrating the annual freeze-thaw cycle was used to delineate core and batter subsystems within the pile. Mean annual solute concentrations and geochemical speciation modelling results revealed two different environments within these subsystems. Concentrations in the core of the test pile were 2.5 to 8.5 times greater than concentrations in the batter. Dilution through snowmelt contributions and shorter flow pathways were expected to control solute concentrations in the batter subsystem. Aggregated basal leachate loading exhibited a linear annual increase for all ARD reaction products, with the maximum annual release observed in 2012. Between 2007 and 2012 core flow accounted for 13 % of the total drainage volume; whereas 35 to 51 % of major and trace metal loads were attributed to this zone. Parameter correlation analysis and core contribution estimates were used to identify common source minerals for elements and infer mechanisms controlling the mobility of dissolved metals (sorption, co-precipitation and precipitation-dissolution). By 2012, the release of pyrrhotite oxidation products from the < 5 mm reactive fraction of waste rock reached as high as 5.1 %, 9.0 %, 7.2 % and < 0.1 % for S, Ni, Co and Fe respectively. The results of this study indicate that a comprehensive understanding of thermal cycling is imperative when estimating seasonal and annual releases of weathering products from waste rock. Observations of active zone dynamics and the temporal and spatial evolution of waste rock drainage loading recognized in this study will assist in the advancement of reactive transport models describing ARD in cold climates.