Streptococcus mutans is a member of the dental plaque and is the principal causative agent of dental caries. It can metabolize a wide array of sugars which results in the production of acid that causes demineralization of the tooth surface. S. mutans can also persist for extended periods of starvation, which may occur in different niches within the oral cavity. Previous studies have shown that mucin prolonged the survival of S. mutans in batch cultures and biofilms. Our laboratory has shown that the pyruvate dehydrogenase (pdh) operon is upregulated in stationary phase and is important for prolonged survival during nutrient starvation in chemically defined medium (CDM). In this study, I found that mucin enabled S. mutans to grow in a minimal chemically defined medium (MCDM) containing glucose and lacking all amino acids. A pdh mutant was found to be impaired in survival in CDM or MCDM supplemented with mucin. Additionally, I have shown that a galactose utilization mutant was impaired in survival in CDM with mucin and no exogenous glucose; galactose is the most abundant utilizable sugar residue in mucin. Mucin, supplemented in minimal medium with sucrose, also enabled S. mutans to form biofilms. Survival of the biofilms was pdh independent. Although biofilm formation was not seen in the absence of sucrose, cells did adhere to the glass coverslip; their survival was found to be pdh dependent. Using a previously constructed reporter strain, pdh expression was observed in a majority of cells in this condition. The expression of the pdh operon was also monitored in batch cultures. The starting inoculum size affected the percentage of fluorescent cells and the outcome of survival in media (CDM or MCDM) supplemented with mucin and no sugar. Greater than 50% of the stationary phase population expressed pdh in CDM with galactose. Less than 1% expressed pdh in CDM with glucose. However, galactose was unable to prolong survival of S. mutans in batch cultures in contrast to the effect of mucin. These results show that mucin may have a metabolic role in promoting long term survival of S. mutans. However it is possible that different components of mucin can be utilized in different conditions. / Microbiology and Immunology

<p> The selective surface oxidation of alloying elements such as Mn can cause dual phase (DP) steel wettability problems by liquid Zn during continuous galvanizing. It is well known that process parameters, such as the annealing atmosphere %H2 and dew point, can affect surface and subsurface oxidation. The purpose of this research was to study the effect of the annealing atmosphere to determine the optimum DP steel surface that would result in better reactive wetting by zinc. In particular, the evolution of the surface phases and structures during the continuous galvanizing annealing cycle were studied. It was shown that the internal I external oxidation behavior of the alloying elements of DP steel (e.g. Mn and Mo) at the surface and subsurface can be controlled by changing process parameters (dew point and H2/N2 ratio) and that some segregation of elements is unavoidable but can result in good reactive wetting by liquid galvanizing alloys. A transition from external to internal oxidation was observed when the oxidation potential (pH20ipH2) of the annealing atmosphere was increased from 0.00844 to 0.03451. Despite the presence of 9-19 wt% Mn as MnO in the pre-dipped steel surface, the coatings exhibited good adhesion and a well developed Fe2Als inhibition layer at the coating I substrate interface for all experimental annealing atmospheres as a result of reactive wetting. This is attributed to aluminothermic reduction of manganese oxide by aluminum present in the liquid galvanizing alloy. </p> / Thesis / Master of Applied Science (MASc)

<p> A unique approach for the modeling of phase noise is examined in this thesis. In previous work regarding phase noise theory, the memory property of phase is virtually ignored. The thesis introduces the Discrete Recursive Procedure (DRP): a systematic approach or methodology to predict phase noise using a discrete recursive algorithm taking into account the memory property of phase. This discrete recursive algorithm is a general extension of the Linear Time Varying (LTV) model and is referred to as the NonLinear Time Varying (NLTV) model. </p> <p> Simulations are performed using the DRP method. Phase fluctuation comparisons are made between the LTV and the NLTV models for an ideal oscillator. The simulation results show that the NLTV model taking into account the memory property of phase makes more realistic phase noise predictions than the LTV model for asymmetrical Impulse Sensitivity Function (ISF) cases. Phase noise simulation results using the NLTV model are given for a modified 810-MHz CMOS cross-coupled LC oscillator design. At 90kHz offset, the simulation prediction (-89 dBc/Hz) and the measurement readings (-93 dBc/Hz) are closely matched with a difference of approximately 4 dBc/Hz while the CAD simulation prediction ( -101. 8) has a difference of 9 dBc/Hz from the measurements. In the phase noise simulation for the 62-MHz BIT Colpitts oscillator design, the NLTV model predicts a -26 dBc/decade and -19.5 dBc/decade for the flicker noise and thermal noise regions in accordance with the theoretical -30 dBc/decade and -20 dBc/decade slopes. </p> / Thesis / Master of Applied Science (MASc)

In this investigation an electric field was applied to a phase change thermal storage system while it was discharging energy. The phase change material used was octadecane. Octadecane is a high purity dielectric material that has a melting temperature close to room temperature. The material was forced to solidify using a heat exchanger mount below the phase change material, cold water flowed through the heat exchanger to ensure it maintained a constant temperature below the melting temperature of the phase change material. By applying -8kV to 9 electrodes – positioned in the phase change material – and by using the heat exchanger as an electrical ground – an electric field was generated in the phase change material. The electric field caused unbalanced body forces in the fluid which generated electro-convection in the fluid. The system was designed such that electro-convection is the only source of convection in the system to isolate the effects of electro-convection, allowing for the underlying physics of electro-convection to be studied easier. To understand the effects of applying electro-convection, a case where there is no applied voltage on the electrodes was compared to a case where there was -8 kV applied to the electrodes. Experiments showed that the effect of applying electro-convection depends on the initial temperature; however, it was found that the improvement after two hours was less than 10%. For a wall temperature of 8.5℃ and an initial temperature of 50℃ - the melting temperate of octadecane is 28℃- then the maximum enhancement of the energy extracted is 50%, but two hours after the start of the test the enhancement approached zero. For a wall temperature of 8.5℃ and an initial temperature of 30℃, the maximum enhancement is 10% and similarly fall to zero after a few hours of application. A simple analytical model was developed. The experimental and numerical results showed that at the early stages of energy discharge the electro-convection case had a large improvement compared to a pure conduction case, however as time progresses this improvement decreases. The explanation for the trend is that adding convection only increases the rate that energy is taken out of the liquid, thus the maximum improvement is bounded by the amount of sensible energy in the liquid phase change material, once this sensible energy is removed applying electrohydrodynamics is no longer beneficial. / Thesis / Master of Applied Science (MASc)

The purpose of this study was to examine the relationships between age, gender and fatigue resistance, and further, to determine the relative influence that estrogen status, membrane excitability, absolute force and muscle length have over the development of fatigue. A total of 48 subjects, classified by age and gender participated in this study; 12 young males (25.3 ± 2.1 yrs.), 12 young females (23.5 ± 2.1 yrs.), 12 elderly males (71.7 ± 5.6 yrs.) and 12 elderly females (69.5 ± 4.6 yrs.). The young females were all eumenorrheic, not taking oral contraceptives and tested in the mid-follicular phase of the menstral cycle. None of the elderly females were on hormone replacement therapy. A 3 minute paradigm of intermittent maximal voluntary contractions (MVC) was used to fatigue the adductor pollicis muscle, in which 5s MVC's were alternated with 2s rest periods. In addition, maximal twitches were evoked in each 2s rest period. No gender difference in fatigability was evident between young males and young females when considering the fatigue index of the evoked twitch (FI-PT) (young males: 39.8 ± 26.7%, young females: 36.6 ± 19.0%). There was also no gender difference in fatigability found between elderly males and elderly females when considering the FI-PT (elderly males: 24.9 ± 26.6%, elderly females: 16.4 ± 48.9%). However, potentiation of the evoked twitches during fatigue may have confounded these measures. When considering the changes in voluntary force during fatigue, there was a strong trend for a gender by time interaction between young males and young females.(p=0.06), which suggests that the former were more fatigable. The trend for this gender difference was also apparent in the voluntary fatigue index (FI-MVC) (young males: 44.7 ± 10.5%, young females: 37.8 ± 14.1 %; p=0.12). Similarly, young males had a significant decrease in M-wave amplitude during the fatigue protocol and a trend for a decrease in M-wave area (p=0.08), while young females showed no significant decreases in either M-wave measure during the fatigue protocol. There was no gender difference found between the elderly males and elderly females when considering the FI-MVC (elderly males: 24.2 ± 10.7%, elderly females: 26.3 ± 14.5%). Both groups also showed small but significant reductions in theM-wave amplitude during the fatigue protocol, although M-wave area was well maintained. The fact that a strong trend for a gender difference in fatigability was found in the young subjects but not the elderly subjects, suggests that estrogen may possess fatigue resisting properties, even during short duration exercise in which glycogen depletion is not a concern. With respect to the age-related differences in fatigue, elderly males were found to be significantly more fatigue resistant than young males as indicated by the FI-MVC (p<0.01), and the significant age by time interaction during the fatigue protocol (p<0.01). In contrast, only a trend was found for an age by time interaction between the young and elderly females during the fatigue protocol (p=0.06). This trend for an age-related difference in fatigue amongst women was also reflected in the FI- MVC (p=0.13). / Thesis / Master of Science (MSc)

A counter-current two-phase flow under an applied electric field has been studied theoretically using potential flow equations. A flooding correlation has been derived taking account of applied electric field on the interface for both adiabatic and condensing system. It is found that the electric field enhances flooding phenomena in case of adiabatic system. In the case with system involving condensation the electric field enhances flooding at low liquid flow rates and at high liquid flow rates the flooding point decreases under electric field depending on the rate of subcooling. / Thesis / Master of Engineering (ME)

The vapour-phase reaction of 2-methy-tetrhydropyran and 2-ethyltetralydropyran with aniline over an activated alumina catalyst has been studied. The product, in each case, consisted of a mature of an N-aryl-piperidine, an N-arylpyrrolidine formed by ring contraction, and two N-alkelnylanilines formed by ring opening. The structures of the nitrogen heterocyclic compounds were established by independent syntheses involving the reaction of the appro­priate dibromoalkane with aniline. The N-alkenylanilines were characterised by hydrogenation to known N-alkylanilines and by identification of the osonolysis products. / Thesis / Master of Science (MSc)

No description available.

A method has been developed which calculates two-dimensional, transonic, viscous flow in ducts. The finite volume, time marching formulation is used to obtain steady flow solutions of the Reynolds-averaged form of the Navier Stokes equations. The entire calculation is performed in the physical domain. The method is currently limited to the calculation of attached flows. The features of the current method can be summarized as follows. Control volumes are chosen so that smoothing of flow properties, typically required for stability, is not needed. Different time steps are used in the different governing equations to improve the convergence speed of the viscous calculations. A new pressure interpolation scheme is introduced which improves the shock capturing ability of the method. A multi-volume method for pressure changes in the boundary layer allows calculations which use very long and thin control volumes (length/height ≅ 1000). A special discretization technique is also used to stabilize these calculations which use long and thin control volumes. A special formulation of the energy equation is used to provide improved transient behavior of solutions which use the full energy equation. The method is then compared with a wide variety of test cases. The freestream Mach numbers range from 0.075 to 2.8 in the calculations. Transonic viscous flow in a converging diverging nozzle is calculated with the method; the Mach number upstream of the shock is approximately 1.25. The agreement between the calculated and measured shock strength and total pressure losses is good. Essentially incompressible turbulent boundary layer flow in an adverse pressure gradient is calculated and the computed distribution of mean velocity and shear stress are in good agreement with the measurements. At the other end of the Mach number range, a flat plate turbulent boundary layer with a freestream Mach number of 2.8 is calculated using the full energy equation; the computed total temperature distribution and recovery factor agree well with the measurements when a variable Prandtl number is used through the boundary layer. / Ph. D.

We examine a model of solid-solid phase transitions that includes thermo-elastic effects and an order parameter. The model is derived as a special case of the Gurtin-Fried model posed in one space dimension with a symmetric triple-well free energy in which the relative heights of the wells vary with temperature. We examine the temperature independent case, showing existence of a unique classical solution of a regularized system of partial differential equations using semigroup theory. This is followed by numerical study of a finite element algorithm for the temperature independent model. Finally, we present computational material concerning the temperature dependent model. / Ph. D.