No description available.

The steady coflow diffusion flame is a widely used configuration for studying combustion kinetics, flame dynamics, and pollutant formation. In the current work, a set of diluted ethylene-air coflow flames are simulated to study the formation, growth, and oxidation of soot, with a focus on the effects of pressure on soot yield. Firstly, we assess the ability of a high performance CFD solver, coupled with detailed transport and kinetic models, to reproduce experimental measurements, like the temperature field, the species’ concentrations and the soot volume fraction. Fully coupled conservation equations for mass, momentum, energy, and species mass fractions are solved using a low Mach number formulation. Detailed finite rate chemistry describing the formation of Polycyclic Aromatic Hydrocarbons up to cyclopenta[cd]pyrene is used. Soot is modeled using a moment method and the resulting moment transport equations are solved with a Lagrangian numerical scheme. Numerical and experimental results are compared for various pressures. Reasonable agreement is observed for the flame height, temperature, and the concentrations of various species. In each case, the peak soot volume fraction is predicted along the centerline as observed in the experiments. The predicted integrated soot mass at pressures ranging from 4-8 atm, scales as P2.1, in satisfactory agreement with the measured integrated soot pressure scaling (P2.27). Significant differences in the mole fractions of benzene and PAHs, and the predicted soot volume fractions are found, using two well-validated chemical kinetic mechanisms. At 4 atm, one mechanism over-predicts the peak soot volume fraction by a factor of 5, while the other under-predicts it by a factor of 5. A detailed analysis shows that the fuel tube wall temperature has an effect on flame stabilization.

Bananas are climacteric fruits and show climacteric patterns with respect to both their ethylene production and respiration rates during the ripening process. Treatment with ethylene accelerated the ripening process, evidenced by colour changes. Chlorophyllase apparently synthesised chlorophyll in the 0.2 kGy irradiated fruit during the post-climacteric period. Gamma irradiation of green bananas with doses of 0.4 kGy or greater resulted in extensive tissue damage, undesirable colour development, and drastic changes in respiration and ethylene production. Irradiation at 0.2 kGy, did however, effectively delay ripening (without causing any phytotoxicity) of the fruit apparently by decreasing its sensitivity to its own endogenous ethylene for a period up to 28 days when kept at room temperature, provided that the relative humidity was maintained at 75 % to prevent desiccation. Irradiation at this dose did not prevent the onset of ripening when subjected to high concentrations of exogenous ethylene. Ultrastructurally total cell collapse due to cell wall, middle lamella and membrane damage was evident at doses of 0.4, 0.6 and 1.0 kGy. Irradiation with a dose of 0.2 kGy did not cause cell wall softening and membrane breakdown and thus provided a banana fruit of excellent postharvest quality with respect to ultrastructural features. Glucose and fructose occurred probably directly from sucrose that may not accumulate because it is transient after the banana fruit is harvested. The accumulation of sucrose glucose and fructose was not stimulated by ethylene in non-irradiated and irradiated fruit. These results indicate a clear temporal separation between those biochemical processes that appear to be stimulated by ethylene (respiration, fruit softening and colour change) from those that are not (sugars). Pectin methyl esterase resulted in the demethylation of pectin-like material in the cell walls of ripening bananas. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1991.

Analogous to the extracellular matrix (ECM) of natural tissues, properties of a tissue engineering scaffold direct cell behavior and thus regenerated tissue properties. These include both physical properties (e.g. morphology and modulus) and chemical properties (e.g. hydrophobicity, hydration and bioactivity). Notably, recent studies suggest that scaffold properties (e.g. modulus) may be as potent as growth factors in terms of directing stem cell fate. Thus, 3D scaffolds possessing specific properties modified for optimal cell regeneration have the potential to regenerate native-like tissues. Photopolymerizable poly(ethylene glycol) diacrylate (PEG-DA)-based hydrogels are frequently used as scaffolds for tissue engineering. They are ideal for controlled studies of cell-material interactions due to their poor protein adsorption in the absence of adhesive ligands thereby making them “biological blank slates”. However, their range of physical and chemical properties is limited. Thus, hydrogel scaffolds which maintain the benefits of PEG-DA but possess a broader set of tunable properties would allow the establishment of predictive relationships between scaffold properties, cell behavior and regenerated tissue properties. Towards this goal, this work describes a series of unique hybrid inorganic-organic hydrogel scaffolds prepared using different solvents and also in the form of continuous gradients. Properties relevant to tissue regeneration were investigated including: swelling, morphology, modulus, degradation rates, bioactivity, cytocompatibility, and protein adhesion. These scaffolds were based on the incorporation of hydrophobic, bioactive and osteoinductive methacrylated star polydimethylsiloxane (PDMSstar-MA) [“inorganic component”] into hydrophilic PEG-DA [“organic component”]. The following parameters were varied: molecular weight (Mn) of PEG-DA (Mn = 3k & 6k g/mol) and PDMSstar-MA (Mn = 1.8k, 7k, 14k), ratio of PDMSstar-MA to PEG-DA (0:100 to 20:80), total macromer concentration (5 to 20 wt%) and utilizing either water or dichloromethane (DCM) fabrication solvent. The use of DCM produced solvent induced phase separation (SIPS) resulting in scaffolds with macroporous morphologies, enhanced modulus and a more homogenous distribution of the PDMSstar-MA component throughout. These hybrid hydrogel scaffolds were prepared in the form of continuous gradients such that a single scaffold contains spatially varied chemical and physical properties. Thus, cell-material interaction studies may be conducted more rapidly at different “zones” defined along the gradient. These gradients are also expected to benefit the regeneration of the osteochondral interface, an interfacial tissue that gradually transitions in tissue type. The final aspect of this work was focused on enhancing the osteogenic potential of PDMS via functionalization with amine and phosphonate. Both amine and phosphonate moieties have demonstrated bioactivity. Thus, it was expected that these properties will be enhanced for amine and phosphonate functionalized PDMS. The subsequent incorporation of these PDMS-based macromers into the previously described PEG-DA scaffold system is expected to be valuable for osteochondral tissue regeneration.

Current synthetic vascular grafts have high failure rates in small-diameter (<6 mm) applications due to inadequate cell-material interactions and poor matching of arterial biomechanical properties. To address this, we have developed a multilayer vascular graft design with a non-thrombogenic inner layer that promotes endothelial cell (EC) interactions and a reinforcing layer with tunable biomechanical properties. The blood-contacting layer of the graft is based on a Streptococcal collagen-like protein (Scl2-1). Scl2-1 has the triple helical structure of collagen, but it is a non-thrombogenic protein that can be modified to have selective cell adhesion. For this application, Scl2-2 has been modified from Scl2-1 to contain integrin binding sites that promote EC adhesion. We have developed the methodology to incorporate Scl2 proteins into a poly(ethylene glycol) (PEG) hydrogel matrix. PEG-Scl2 hydrogels facilitate optimization of both bioactivity and substrate modulus to offer unique control over graft endothelialization. However, scaffold properties that promote endothelialization may not be consistent with the mechanical properties necessary to withstand physiological loading. To address this issue, we have reinforced PEG-Scl2-2 hydrogels with an electrospun polyurethane mesh. This multilayer vascular graft design decouples requisite mechanical properties from endothelialization processes and permits optimization of both design goals. We have confirmed the thromboresistance of PEG-Scl2-2 hydrogels in a series of whole blood tests in vitro as well as in a porcine carotid artery model. Additionally, we have shown that the electrospun mesh biomechanical properties can be tuned over a wide range to achieve comparable properties to current autologous grafts. Traditional acrylate-derivatized PEG (PEGDA) hydrogels were replaced with PEG diacrylamide hydrogels with similar properties to increase biostability for long-term implantation. These findings indicate that this multilayer design shows promise for vascular graft applications. As vascular graft endothelialization can significantly improve success rates, the ability to alter cell-material interactions through manipulations in PEG-Scl2-2 hydrogel properties was studied extensively. By reducing Scl2-2 functionalization density and utilizing a biostable PEG functionalization linker, Acrylamide-PEG-I, significantly improved initial EC adhesion was achieved that was maintained over 6 weeks of swelling in vitro. Additionally, increases in Scl2-2 concentration and in hydrogel modulus provided increased EC interactions. It was found that PEG-Scl2-2 hydrogels promoted enhanced EC proliferation over 1 week compared to PEG-collagen gels. In summary, we have developed a vascular graft with a biostable, non-thrombogenic intimal layer that promotes EC adhesion and migration while providing biomechanical properties comparable to current autologous grafts. This design demonstrates great potential as an off-the-shelf graft for small diameter arterial prostheses that improves upon current clinically available options.

The objective of this study was to compare different modifiers in two asphalt cements, namely Cold Lake 80/100 obtained from the Edmonton, Alberta refinery of Imperial Oil Limited and a PG 58-28 obtained from a now closed refinery in the Montreal, Quebec area. The modifiers investigated were polyphosphoric acid (PPA), styrene-butadiene-styrene (SBS), and reactive ethylene terpolymer (Elvaloy® RET). The comparisons were done based on both unaged and laboratory-aged materials. The investigation covers high temperature grading using a dynamic shear rheometer (DSR), low temperature grading using a bending beam rheometer (BBR), ductile strain tolerance as measured in the double-edge-notched tension (DENT) test and percentage recovered strain using multiple shear creep recovery (MSCR) test. The Superpave® performance grade span was increased for all modifiers with substantial increases in the high temperature rutting parameter G*/sin while the BBR parameters, T(S = 300 MPa) and T(m = 0.3), remained largely unchanged. In the PG 58-28 base asphalt, Elvaloy® modifiers were able to reduce the intermediate Superpave® grade temperature by significant amounts. All polymer modifiers were good at improving the ductile strain tolerance as measured in the DENT test. In contrast, PPA alone reduces the strain tolerance due to the formation of extra asphaltenes and the likely gelation of the asphaltene-rich phase. Nearly all the modified samples passed the MSCR test except those with poor compatibility (i.e. SBS blended with Cold Lake without sulfur, Elvaloy® systems without acid catalyst, and pure PPA modified systems) or no modifier, which did not reach the required elastic recovery at high levels of non-recoverable compliance. In the BBR test done at low temperatures, all modified systems showed similar elastic recovery and viscous (non-recoverable) compliance. However, in the ductile-to-brittle range the Elvaloy® RET-modified binders showed a definite advantage of a few degrees over the unmodified base asphalts. Finally, chemical aging tendencies, as measured by weight gain and carbonyl formation, turned out to be very similar for all the investigated compositions. / Thesis (Master, Chemistry) -- Queen's University, 2010-12-13 13:29:45.173

1,2-Dichloroethane (1,2-DCA), a short chain chlorinated aliphatic compound, is one of the most hazardous toxic pollutant of soil and groundwater, with an annual production in excess of 5.44 × 109 kg. The major concern over soil contamination with 1,2-DCA stems largely from health risks. Owing to their toxicity, persistence and potential for bioaccumulation, there is a growing interest in technologies for their removal. Many sites are, however, co-contaminated with a complex mixture of 1,2-DCA and heavy metal contaminants. Co-contaminated environments are considered difficult to remediate because of the mixed nature of the contaminants and the fact that the two components often must be treated differently. Therefore, the objective of this study was to evaluate the aerobic biodegradation of 1,2-DCA by autochthonous microorganisms in soil co-contaminated with 1,2-DCA and heavy metals, namely; arsenic (As3+), cadmium (Cd2+), mercury (Hg2+) and lead (Pb2+), via a direct and quantitative measurement of the inhibitory effects of heavy metals in a microcosm setting. Effects of various metal concentrations and their combinations were evaluated based on the following: (i) degradation rate constants; (ii) estimated minimal inhibitory concentrations (MICs) of metals; (iii) concentrations of heavy metals that caused biodegradation half-life doublings (HLDs); and (iv) heavy metal concentrations that caused a significant effect on biodegradation (> 10% increase in t½ of 1,2-DCA). The effects of biostimulation, bioaugmentation and the addition of treatment additives on the biodegradation process were evaluated. The presence of heavy metals was observed to have a negative impact on the biodegradation of 1,2-DCA in both clay and loam soil samples, with the toxic effect being more pronounced in loam soil for all heavy metal concentrations except for Hg2+, after 15 days. Heavy metal concentrations of 75 mg/kg As3+, 840 mg/kg Hg2+, and 420 mg/kg Pb2+, resulted in 34.24%, 40.64%, and 45.94% increases in the t½ of 1,2-DCA, respectively, in loam soil compared to clay soil. Moreover, the combination of four heavy metals in loam soil resulted in 6.26% less degradation of 1,2-DCA compared to clay soil, after 15 days. Generally, more than 127.5 mg/kg Cd2+, 840 mg/kg Hg2+ and 420 mg/kg of Pb2+ was able to cause a > 10% increase in the t½ of 1,2-DCA in clay soil, while less than 75 mg/kg was required for As3+. An increased reduction in 1,2-DCA degradation was observed with increasing concentration of the heavy metals. In clay soil, a dose-dependant relationship between k1 and metal ion concentrations in which k1 decreased with higher initial metal concentrations was observed for all the heavy metals tested except Hg2+. Ammonium nitrate-extractable fractions of bioavailable As3+ and Cd2+ concentrations varied greatly, with approximately < 2.73% and < 0.62% of the total metal added to the system being bioavailable, respectively. Although bioavailable heavy metal fractions were lower than the total metal concentration added to the system, indigenous microorganisms were sensitive to the heavy metals. Biostimulation, bioaugmentation and amendment with treatment additives were all effective in enhancing the biodegradation of 1,2-DCA in the co-contaminated soil. In particular, biostimulation with fertilizer, dual-bioaugmentation and amendment with CaCO3 were most efficient in enhancing 1,2-DCA degradation resulting in 41.93%, 59.95% and 51.32% increases in the degradation rate constant of 1,2-DCA in the As3+ co-contaminated soil, respectively, after 20 days. Among all the treatments, dualbioaugmentation produced the highest 1,2-DCA degrading population of up to 453.33 × 107 cfu/ml in the Cd2+ co-contaminated soil. On comparison of the As3+ and Cd2+ co-contaminated soil undergoing either biostimulation or dual-bioaugmentation, similarity in the denaturing gradient gel electrophoresis (DGGE) banding patterns was observed. However, the banding patterns for the different bioremediation options demonstrated a difference in bacterial diversity between the fertilized and dual-bioaugmented samples. DGGE profiles also indicate that while numerous bands were common in the fertilized co-contaminated soils, there were also changes in the presence and intensity of bands due to treatment and temporal effects. Dehydrogenase and urease activities provided a more accurate assessment of the negative impact of heavy metals on the indigenous soil microorganisms, resulting in up to 87.26% and 69.58% decreases in activities, respectively. In both the biostimulated and bioaugmented soil microcosms, dehydrogenase activity appeared biphasic with an initial decrease followed by an increase in the treated soils over time. Results from this study provide relevant information on some alterations that could be introduced to overcome a critical bottle-neck of the application of bioremediation technology. In conclusion, the bioremediation strategies adopted in this study may be used as a rational methodology for remediation of sites co-contaminated with 1,2-DCA and heavy metals, subject to a thorough understanding of the microbial ecology and physico-chemical parameters of the site. / Thesis (M.Sc.)-University of KwaZulu-Natal, 2009.

There are several reasons for reducing particulate formation as a result of combustion processes and to date, a number of approaches have been proposed to numerically predict soot. There is a trade-off between accuracy and computational cost and processing time. Two equation semi-empirical models have been used, with some success, to reconcile the need for fast solution turn around and accuracy. However, these models do not account for the mass balance between the gas phase and soot. In this study, the effects of mass conservation of the soot precursors in the gas phase were investigated in an ethylene-air laminar flame simulation at atmospheric pressure. Soot formation was predicted with a two-equation model. Then the model was modified for predicting soot in a turbulent ethylene-air flame operating at 1 atm. The new model is a [2+1]-equation model which accounts for the mass conservation of soot precursors.

No description available.

Density functional theory is used to study the physico-chemical effects of two metallic thin films separated by distances in a range of 4-10 amperes. In this condition, the electrons from the metallic thin film surfaces tunnel through the energy barrier existing between the separated thin films, creating an electronic distribution in the gap between films. The characteristics and features of this electronic distribution, such as energy, momentum, and number of electrons, can be traced by quantum mechanical analyses. These same features can be tuned by varying metallic thin film properties like thickness, separation between films, and film chemical nature. The possibility to tune the physical properties of the electrons located in the gap between thin films makes the studied systems promising for applications that range from catalysis to nano-electronics. Molecular oxygen, water, and ethylene were located in the gap between thin films in order to study the physical and chemical effects of having those molecules in the gap between thin films. It was observed that the electron structure in the gap modifies the geometric and electronic structure of those molecules placed in the gap. In the case of molecular oxygen, it was found that the dissociation energy can be tuned by changing the separation between thin films and changing the chemical nature of the surface and overlayer of the thin film. For water, it was found that by tuning the chemical nature of the surface and sub-surface of both metallic thin films, molecular water dissociation can occur. When ethylene was located in the gap between Ti/Pt thin films, the molecule converts in an anion radical adopting the geometry and structure of the activated monomer necessary to initiate chain polymerization. Regarding magnetism, it was found that by the surface interaction between Ti/Pt and Pt thin films, the magnetic moment of the system decreases as the separation between thin films decreases. The phenomenon was explained by changes observed in the number of electronic states at the Fermi level and in the exchange splitting as a function of separation between films. Finally, a system that resembles a p-n junction was proposed and analyzed. The system is a junction of two metallic thin films with different electronic density in the gap between surfaces. These junctions can be the building blocks for many electronic devices.