For a sign-changing function a(x) E C^αloc(Rn) with bounded Ω+ = {x E R^n |a(x) > O}, we study non-negative entire solutions u(x) ≥ 0 of the semilinear elliptic equation -Δu = a(x)u^q + b(x)u^p in R^n with n ≥ 3.0 < q < 1, p > q, and λ > 0. We consider two types of coefficient b(x) E C^αloc(R^n), either b(x) ≤ 0 in (R^n) or b(x) ≡ 1. In each case, we give sufficient conditions on a(x) for which all solutions must have compact support. In case Ω+ has several connected components, we also give conditions under which there exist "dead core'' solutions which vanish identically in one or more of these components. In the "logistic" case b(x) ≤ 0, we prove that there can be only one solution with given dead core components. In the case b(x) ≡ 1, the question of existence is more delicate, and we introduce a parametrized family of equations by replacing a(x) by ay = ya^+(x) - a^- (x). We show that there exists a maximal interval y E (0, f] for which there exists a stable (locally minimizing) solution. Under some hypotheses on a^- near infinity, we prove that there are two solutions for each y E (0, f). Some care must be taken to ensure the compactness of Palais-Smale sequences, and we present an example which illustrates how the Palais-Smale condition could fail for certain a(x). The analysis is based on a combination of comparison arguments, a priori estimates, and variational methods. / Thesis / Doctor of Philosophy (PhD)

No description available.

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

Long-term Stationary Phase Behavior of Streptococcus pyogenes Biofilms Department of Microbiology and Immunology Streptococcus pyogenes is the etiological agent of many human diseases ranging from mild superficial skin infections and pharyngitis to life-threatening necrotizing fasciitis. There can be several complications as a result of S. pyogenes infection including post-streptococcal glomerulonephritis and rheumatic fever, which leads to rheumatic heart disease. Despite the significant virulence associated with the pathogen, the bacteria can also persist asymptomatically in human host carriers. S. pyogenes is characterized by significant strain-to-strain variation with many single nucleotide polymorphisms and differences in genetic content of up to 33% of the genome. Active infection is associated with the rapid growth of the pathogen, whereas survival or carriage is associated with slow growth. Our laboratory has demonstrated that during survival in long-term stationary phase cultures and in eukaryotic cells, S. pyogenes diversifies into a mixed population. Isolates from this population show diversification in their proteome, in metabolism, and in virulence factor transcription patterns. These are stable, heritable changes with unique mutations in global gene regulators in some isolates, suggesting that an accumulation of genetic mutations leads to diversification. There are two proposed modes of survival in the human host; by taking residence intracellularly in host cells and as biofilms. Previous studies showed that isolates surviving within eukaryotic cells acquire heritable changes in metabolism and virulence factor expression. Biofilms are highly organized structures formed by many bacteria, which provide resiliency to harsh environmental conditions. It has been demonstrated that S. pyogenes form biofilms in vivo and in vitro, and up to 90% of clinical isolates can form biofilms. Considering the resiliency of biofilms, and the organized roles played by individual cells in biofilms, we hypothesized that biofilms may provide S. pyogenes with a niche for persistence and diversification. Despite the capacity for survival of planktonic cells, we have found that viable cells could not be isolated from static biofilms after 10 days. No metabolic variants were found among biofilm isolates prior to loss of biofilm viability. Biofilm structure was examined using confocal microscopy to image cells after LiveDead® staining. These experiments revealed that the biofilms lost viability rapidly, and also appeared to disperse. Dispersion of 2-day old biofilms could be induced with culture supernatants collected from 7-day old planktonic cells. Overall, the results of these studies suggest that secreted factors from late stationary phase cultures induce biofilm dispersion and biofilms do not serve as a niche for long-term survival and diversification of S. pyogenes. Therefore, S. pyogenes biofilms may be more critical for initial colonization of the oropharynx. These studies may provide a valuable insight to the role of biofilms in S. pyogenes infections. / Microbiology and Immunology

Direct chiral separations of the non-steroidal drugs of 2-methylarylpropionic acids (profens) on the chiral stationary phases (CSPs) of amylose tris(3,5-dimethylphenyl-carbamate), Chiralpak AD, and cellulose tris(3,5-dimethylphenylcarbamate), Chiralcel OD, were investigated. Chiralpak AD and Chiralcel OD are CSPs coated on silica gel and have the same type of constituents. However, they have different higher order structures arising from their different arrangements of the glucose units, i.e., the former has an a-(1,4)-D-glucose linkage and the latter has a b-(1,4)-D-glucose linkage. The orders of optimum enantioselectivity of racemic acids were reversed on the two CSPs which demonstrated that the enantioseparating abilities of these CSPs are complementary. This phenomenon also confirmed that the chiral recognition abilities of both CSPs were dependent on their higher order structures. Mechanisms for retention and chiral recognition for the separation of racemic 2-methylarylpropionic acids on Chiralpak AD and Chiralcel OD were explored. In depth studies of the dependence of retention and enantioselectivity on temperature and mobile phase compositions were made. The thermodynamic parameters, the differences in free energy, enthalpy, and entropy of association between enantiomers and the CSP were evaluated. The results indicated that the retention of racemic acids on both CSPs is mainly dependent on the hydrogen bonding interaction between the acid proton of the carboxyl moiety of the analyte and the carbonyl oxygen of the carbamate moiety of the CSP. The chiral recognition mechanism for Chiralpak AD involves: (1) the formation of transient diastereomeric analyte-CSP complexes through hydrogen bonding interactions between the carboxyl and the carbamate moieties of the acid and CSP, respectively; (2) stabilization of these complexes by insertion of the aromatic portion of the analytes into the chiral cavities of the CSP, as well as pi-pi, dipole-dipole, and additional hydrogen bonding interactions between analyte and CSP; and (3) chiral discrimination between enantiomer analytes arising from the additional hydrogen bond between analyte and CSP. For Chiralcel OD, the chiral recognition mechanisms involve: (1) the formation of transient diastereomeric analyte-CSP complexes through hydrogen bonding interactions between the carboxyl and the carbamate moieties of the acid and CSP, respectively; (2) stabilization of these complexes by insertion of the aromatic portion of the analytes into the chiral cavities of the CSP, as well as pi-pi and dipole-dipole interactions between analyte and CSP; and (3) chiral discrimination due to: (a) the difference in the steric fit of enantiomers into the chiral cavity of the CSP (entropy controlled); and (b) dipole-dipole or p-p interactions between enantiomer analytes and CSP (enthalpy controlled). Chromatographic and quantitative thermodynamic data showed that there are at least two different chiral recognition mechanisms for Chiralcel OD. One mechanism was characterized by negative values for the enthalpy and entropy differences of the association between enantiomers and CSP that classifies the enantioseparation to be enthalpy controlled. This behavior was exhibited by racemic 2-methylarylpropionic acids with fused rings that were favorably separated at low temperatures. The other mechanism was associated with positive values for the enthalpy and entropy differences of the association between enantiomers and CSP, and the enantioseparation is said to be entropy controlled. The analytes with "free" phenyl moieties favored high temperatures for their enantioseparations. Both studies on the effects of temperature and mobile phase composition also indicated that the higher order structures of CSPs influence their chiral recognition abilities. / Ph. D.

The last glacial cycle (c. 115-12 kyr BP) was the most recent in a series of recurring glaciations of the subpolar continents. Massive ice sheets evolved in Eurasia and North America, which, at their maximum, were of continental scale and together lowered the global sea-level by approximately 100 m. The paleo-modelling community has focused on the last glacial maximum (LGM, ~ 20 kyr BP), leaving the longer period when the ice sheets evolved to their LGM configurations largely unexplored. In this thesis we study the mutual interaction between the time-mean atmospheric circulation and the evolution of the Northern Hemisphere ice sheets over the build-up phase of the last glacial cycle. Experiments are conducted with coupled atmosphere-ice-sheet models and a circulation model forced by geologically consistent reconstructions of the ice-sheet topography at key stages of the glacial cycle. The main findings from these studies are that the ice evolution in North America may have been controlled by circulation anomalies induced by the background topography in conjunction with the ice sheets themselves. A geologically consistent pre-LGM ice sheet could only be obtained when including the North American Cordillera. However, the ice sheets' influence on the local climate conditions is also found to be paramount for this configuration. We further suggest that the incipient ice sheets may have had a limited influence on the large-scale winter circulation as a result of their location relative the westerly mean flow. The LGM Laurentide Ice Sheet (LIS) was, however, different because of its continent-wide extent, and it may therefore have had a large influence on the planetary-scale circulation, especially in the Atlantic sector. We find that the planetary waves forced by the LIS were considerably larger than at earlier times, and, as a result of a more frequent planetary wave reflection over the Atlantic Ocean basin, an altered stationary wave field and a zonalised winter jet. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: Manuscript.</p>

Dynamic Power Management (DPM) refers to the strategies employed at system level to reduce energy expenditure (i.e. to prolong battery life) in embedded systems. The trade-off involved in DPM techniques is between the reductions of energy consumption and latency incurred by the jobs to be executed by the system. Such trade-offs need to be decided at runtime making DPM an on-line problem. In this context, the contributions of this thesis are two-fold. Firstly, we formulate the DPM problem as a hybrid automaton control problem. We model a timed hybrid automaton to mathematically analyze various opportunities in optimizing energy in a given system model. Secondly, stochastic control is added to the automata model, whose control strategy is learnt dynamically using stochastic learning automata (SLA). Several linear and non-linear feedback algorithms are incorporated in the final Stochastic Learning Hybrid Automata (SLHA) model. Simulation-based experiments show the expediency of the feedback systems in stationary environments. Further experiments are conducted using real trace data to compare stochastic learning strategies to the outcomes of several former predictive algorithms. These reveal that SLHA attains better trade-offs than the other studied methods under certain trace data. Advanced characterization of trace sequences, which allows a better performance of SLHA, is a subject of further study. / Master of Science

It is evident that human activity has an important impact on climate. Constantly increasing energy demand is one of the biggest causes of climate change. The fifth assessment report of the Inter-governmental panel on climate change states that decarbonisation of electricity generation is a key component of climate change mitigation. Increased awareness of this fact and escalating concerns around energy security has brought public attention to the energy industry, especially sustainable power generation systems. Future energy systems may need to include hydrogen as an energy carrier in order to achieve necessary levels of CO2 emission reductions, and overcome the challenges renewable energy systems present. Fuel cells could be a corner stone of future hydrogen inclusive energy solutions. New solutions like fuel cells have to compete with existing technologies and overcome the shortcomings of emerging technology. Though these shortcomings are well-recognised, fuel cells also have many advantages which makes continued research and development in the field highly worthwhile and viable. Key to their adoption is the identification of a niche market to utilise their advantages while overcoming their shortcomings with continuous research and development. This thesis aims to evaluate some of the stationary fuel cell applications and determine whether one could become the niche market as an entry point for fuel cells. This is achieved by economic evaluations of real and hypothetical applications. Results of the studies here imply that to decrease the total life cycle impacts of fuel cells to more acceptable levels, resource use in the manufacturing phase and recycling in decommissioning should be shown more attention. Results also present a picture showing that none of the applications investigated are economically feasible, given the current state of technology and energy prices. However, fuel cell-based combined cooling, heating and power systems for data centres show the potential to become the niche market that fuel cells need to grow. A further conclusion is that a broad market, longer stack lifetime, the possibility of selling electricity back to the grid and governmental subsidies are essential components of an environment in which fuel cells can permeate through the niche market to the mainstream markets. / <p>QC 20151210</p>

A new class of scintillation detector has emerged that combines columnar scintillators and CCD/CMOS sensors for high-resolution imaging. Originally developed for single-photon gamma-ray imaging, these detectors provide better than an order-of-magnitude improvement in spatial resolution compared to conventional photomultiplier tube (PMT)-based gamma cameras; sub-100 micron detector resolutions have been achieved. This work reviews the several detector configurations developed in recent years, with a specific emphasis on a type of CCD/CMOS detector developed at the Center for Gamma-Ray Imaging, which we call BazookaSPECT, that amplifies scintillation light using an image intensifier to achieve both high spatial resolution and high event-rate capability.Ongoing research into scintillator deposition techniques has led to a new form of scintillation material where crystallites are organized into columns. Similar to optical fibers, this columnar structure helps to channels scintillation light towards an exit face while restricting lateral light spread. However, because they are not perfect optical fibers, light spreads laterally and is absorbed by an amount relating to the interaction depth. Taking advantage of this phenomenon, we discuss the use of maximum-likelihood methods to estimate the 3D position and energy of gamma-ray interactions in columnar CsI(Tl)/EMCCD-based detectors.Finally, we present new imaging applications that have arisen from BazookaSPECT. These include the the development of a gamma-ray microscope using micro-coded apertures, feasibility studies for photon-counting digital mammography and eventually X-ray CT, and FastSPECT III -- a third generation small animal stationary SPECT imager. FastSPECT III system design, fabrication methods, data acquisition system, system calibration procedure, and initial tomographic reconstructions are presented.

No description available.