No description available.

No description available.

No description available.

<p>Endocrine disrupting substances have been frequently reported to exist in potent concentrations in wastewater treatment plant effluent and other surface waters. Common techniques of wastewater treatment have varied effectiveness to remove estrogens from wastewater. A thermo-responsive smart membrane technology is investigated for its use in adsorptive removal of 17β-estradiol from a background electrolyte solution. A simplified fabrication method is adapted for hydrogel-substrate composite thermo-responsive membranes. Deposition of hydrogel occurs through aqueous polymerization in a coating process dissimilar to common grafting techniques. Acrylamide and acrylic acid monomers are polymerized in two different structures, a random copolymer as well as an interpenetrating network, to form a positive volume-phase transition hydrogel coating. Subsequent membranes experience high permeability at low temperatures with a gating mechanism reducing permeability upon heating. The effects of crosslinker content, monomer ratio, mass loading and butylmethacrylate content are investigate. Only mass loading was found to have significant influence on the behaviour of the membranes in all cases. The variations of the other factors were too little to have great influence. The membranes with the most stable permeability response function were then used in 17β-estradiol adsorption tests, investigating the binding capacity at both colder water temperatures (10oC) and warmer water temperatures (40oC). In the collapse and swelling of the volume-phase transitions, the membranes changed their solution properties which were hypothesized to also alter surface functionality. After introducing the estradiol sample, the membranes were subjected to temperature change with the expectation that any bound material would elute once the surface functionality of the membranes became adequately altered. Only some membranes produced an elution fraction while others appeared to undergo irreversible binding with a possible delayed elution. Removal of dosed 17β-estradiol is reported as adsorbed mass per area of membrane.</p> / Master of Applied Science (MASc)

<p>This thesis is centered around three infinite dimensional diffusion processes:</p> <p>(i). the infinitely-many-neutral-alleles diffusion model [Ethier and Kurtz, 1981],</p> <p>(ii). the two-parameter infinite dimensional diffusion model [Petrov, 2009] and [Feng and Sun, 2010],</p> <p>(iii). the infinitely-many-alleles diffusion with symmetric dominance [Ethier and Kurtz, 1998].</p> <p>The partition structures, the ergodic inequalities and the asymptotic theory of these three models are discussed. In particular, the asymptotic theory turns out to be the major contribution of this thesis.</p> <p>In Chapter 2, a slightly altered version of Kingman's one-to-one correspondence theorem on partition structures is provided, which in turn becomes a handy tool for obtaining the asymptotic result on the partition structures associated with models (i) and (ii).</p> <p>In Chapter 3, the three diffusion models are briefly introduced. New representations of the transition densities of models (i) and (ii) are obtained simply by rearranging the previous representations obtained in [Ethier, 1992] and [Feng et al., 2011] respectively. These two new representations have their own advantages, by making use of which the corresponding ergodic inequalities easily follow. Furthermore, thanks to the functional inequalities in [Feng et al., 2011], the ergodic inequality for model (iii) becomes available as well.</p> <p>In Chapter 4, the asymptotic properties of models (i) and (ii) are thoroughly studied. Various asymptotic results are obtained, such as the weak limits of models (i) and (ii) at different time scales when the mutation rate approaches infinity, and the large deviation principle for models (i) and (ii) at a fixed time, and that of the transient partition structures of models (i) and (ii). Of all these results, the weak limit and the large deviation principle of the transient partition structures are of particular interest.</p> <p>In Chapter 5, the asymptotic results on the stationary distribution and the transient distribution of model (iii) are both obtained. The weak limit of the infinitely-many- alleles diffusion with symmetric overdominance at fixed time t serves as an alternative answer to Gillespie's conjecture [Gillespie, 1999]. The weak limit of the stationary distribution of the infinitely-many-alleles diffusion with symmetric overdominance provides a complete solution to the remaining problem in [Feng, 2009].</p> / Doctor of Philosophy (PhD)

The Random Phase Approximation and beyond Random Phase Approximation methods based on Adiabatic Connection Fluctuation Dissipation Theorem (ACFD) are tested for structural phase transitions of different groups of materials, including metal to metal, metal to semiconductor, semiconductor to semiconductor transitions. Also the performance assessment of semilocal density functionals with or without empirical long range dispersion corrections has been explored for the same cases. We have investigated the structural phase transitions of three broad group of materials, semi- conductor to metal transitions involving two symmetric structures, semiconductor to metal and wide bandgap semiconductor to semiconductor transitions involving at least one lower symmetric structure and lastly special cases comprising metal to metal transitions and transitions between energetically very close structural phases. The first group contains Si (diamond → β-tin), Ge (diamond → β-tin) and SiC (zinc blende → rocksalt), second group contains GaAs (zinc blende → cmcm) and SiO 2 (quartz → stishovite) and third group contains Pb (fcc → hcp), C(graphite → diamond) and BN (cubic → hexagonal) respectively. We have found that the difference in behavior of exchange and correlation in semilocal functionals and ACFD methods is striking. For the former, the exchange potential and energy often comprise the majority of the binding described by density functional approximations, and the addition of the correlation energy and potential often induce only a (relatively) small shift from the exchange- only results. For the ACFD, however, non self-consistent EXX typically underbinds by a considerable degree resulting in wildly inaccurate results. Thus the addition of correlation leads to very large shifts in the exchange-only results, in direct contrast to semilocal correlation. This difference in behavior is directly linked to the non-local nature of the EXX, and even though the exchange-only starting point is often nowhere close to experiment, the non-local correlation from the ACFD corrects this deficiency and yields the missing binding needed to produce accurate results. Thus we find the ACFD approach to be vital in the validation of semilocal results and recommend its use in materials where experimental results cannot be straightforwardly compared to other approximate electronic structure calculations. Utilizing the second-order approximation to Random Phase Approximation renormalized (RPAr) many-body perturbation theory for the interacting density-density response function, we have used a so-called higher-order terms (HOT) approximation for the correlation energy. In combination with the first-order RPAr correction, the HOT method faithfully captures the infinite- order correlation for a given exchange-correlation kernel, yielding errors of the total correlation energy on the order of 1% or less for most systems. For exchange-like kernels, our new method has the further benefit that the coupling-strength integration can be completely eliminated resulting in a modest reduction in computational cost compared to the traditional approach. When the correlation energy is accurately reproduced by the HOT approximation, structural properties and energy differences are also accurately reproduced, as confirmed by finding interlayer binding energies of several periodic solids and compared that to some molecular systems along with some phase transition parameters of SiC. Energy differences involving fragmentation have proved to be challenging for the HOT method, however, due to errors that do not cancel between a composite system and its constituent pieces which has been verified in our work as well. / Physics

<p> Poly(N-isopropylacrylamide) (PNIPAM) has attracted much attention as a thermo-responsive polymer. However, the molecular weight (MW) dependence of its phase transition temperature is still controversial. This situation is largely due to the difficulty in synthesizing narrow-disperse PNIPAM. We have addressed the challenge and developed an atom transfer radical polymerization (ATRP) method to prepare narrow-disperse PNIPAM with moderate to high conversions, using branched alcohols as solvents. Aqueous solutions of these narrow-disperse PNIPAMs showed a dramatic decrease of the phase transition temperature with increasing molecular weight, as measured by turbidimetry and differential scanning calorimetry. Four other series of narrow-disperse PNIPAM with well-controlled molecular weights and with end groups of varying hydrophobicity were also synthesized by ATRP using the corresponding initiators, which enabled us to resolve the MW and end group effects. All the four series of samples showed an inverse molecular weight (MW) dependence of their phase transition temperature. The magnitude of the MW dependence decreased when using more hydrophobic end groups. The end groups were observed to have effects on the cloud point temperature, on the shape of the cloud point curves, and on the enthalpy of the phase transition.</p> / Thesis / Master of Science (MSc)

<p> The purpose of this research is to develop a general method for capturing and separating specific targets. Nucleic acid aptamers are short sequences of single-stranded DNA or RNA which have the ability to bind to the small organic or inorganic molecules such as protein and metal ions with high binding affinity. In this study, a bioconjugate re-usable system was developed. It can reversibly load or unload DNA aptamers.</p> <p> To allow separation, a thermally responsive polymer (N-isopropylacrylamide, PNIPAM) is used. This polymer can undergo a reversible phase transition upon adding NaCl and/or increasing temperature. A short sequence of single stranded DNA (ssDNA) was coupled to PNIPAM. The ssDNA will experience a reversible phase transition because of the PNIPAM.</p> <p> The DNA sequence for an aptamer can be extended to contain a sequence that is complementary to that of the ssDNA coupled to PNIPAM. Adding this extended aptamer to the conjugate will result in spontaneous hybridization of the two strands of DNA. These strands can be separated using an agent (e.g. urea) that destroys hydrogen bonding. The conjugate can be recovered using a reversible inverse phase transition.</p> <p> The same PNIPAM-ssDNA conjugate can be used reversibly for coupling different aptamers. The aptamers did not lose their binding ability when coupled with PNIPAM-ssDNA conjugates. In the process of precipitation separation targets, the PNIPAM-ssDNA conjugate showed little loss with applied phase transition. Moreover, the coupling efficiency of the ssDNA to PNIPAM conjugates was determined. The binding ability of the ATP aptamers to ATP was also investigated.</p> / Thesis / Master of Applied Science (MASc)

Controlling the surface morphology and degree of crystallinity of poly(L-lactic acid) (PLLA) substrates have recently attracted considerable attention because of their applications in cell adhesion, tissue engineering, and drug delivery. Several techniques have been used to fabricate PLLA substrates, some of which may be invalid because PLLA can degrade during fabrication processes. This dissertation provides the Langmuir-Blodgett (LB) technique as a mechanism for fabricating PLLA substrates at temperatures where PLLA degradation is uncommon. In order to fully understand surface morphologies of PLLA LB-films, studies of Langmuir monolayers at the air/water (A/W) interface using surface pressure-area (Pi-A) isotherm and Brewster angle microscopy (BAM) are vital. PLLA exhibits a first-order liquid expanded to condensed (LE/LC) phase transition with molar mass dependent critical phenomena, the first such observation for a homopolymer Langmuir monolayer. Atomic force microscopy (AFM) images of PLLA LB-films prepared in the LC phase exhibit well-ordered lamellar structures. Molar mass scaling of lamellar dimensions, x-ray reflectivity, and reflection absorption infrared spectroscopy (RAIRS) measurements on PLLA LB-films are consistent with PLLA existing as single molecule 10/3-helices at the A/W interface. Morphologies observed after collapse of the LC monolayer are dependent upon the collapse mechanism and subsequent thermal treatment. For temperatures below the LE/LC critical temperature (Tc), two mechanisms are identified for the formation of three dimensional structures: a buckling and stacking of lamellar monolayers on top of existing lamellae during constant compression rate experiments, and a modified nucleation and growth mechanism during isobaric area relaxation experiments. PLLA LB-films prepared in different Langmuir film phases at temperatures below Tc all contain lamellae with different surface roughnesses and similar helical content. Conventional thermal annealing studies on PLLA LB-films reveal that well-ordered lamellar features are destroyed after annealing the LB-films at bulk crystallization temperature through a melting-recrystallization process, which is confirmed by RAIRS and AFM. Our results may prove useful for studying critical behavior and experimentally testing scaling predictions for two dimensions, the development and testing of theories for crystallization in confined geometries, and separating the roles that roughness and crystallinity play in cell adhesion and spreading on biocompatible polymer surfaces. / Ph. D.

Titanium-7%wt-Aluminum (Ti-7Al) has been of interest to the aerospace industry owing to its good structural and thermal properties. However, extensive research is still needed to study the structural behavior and determine the material properties of Ti-7Al. The homogenized macro-scale material properties are directly related to the crystallographic structure at the micro-scale. Furthermore, microstructural uncertainties arising from experiments and computational methods propagate on the material properties used for designing aircraft components. Therefore, multi-scale modeling is employed to characterize the microstructural features of Ti-7Al and computationally predict the macro-scale material properties such as Young's modulus and yield strength using machine learning techniques. Investigation of microstructural features across large domains through experiments requires rigorous and tedious sample preparation procedures that often lead to material waste. Therefore, computational microstructure reconstruction methods that predict the large-scale evolution of microstructural topology given the small-scale experimental information are developed to minimize experimental cost and time. However, it is important to verify the synthetic microstructures with respect to the experimental data by characterizing microstructural features such as grain size and grain shape. While the relationship between homogenized material properties and grain sizes of microstructures is well-studied through the Hall-Petch effect, the influences of grain shapes, especially in complex additively manufactured microstructure topologies, are yet to be explored. Therefore, this work addresses the gap in the mathematical quantification of microstructural topology by developing measures for the computational characterization of microstructures. Moreover, the synthesized microstructures are modeled through crystal plasticity simulations to determine the material properties. However, such crystal plasticity simulations require significant computing times. In addition, the inherent uncertainty of experimental data is propagated on the material properties through the synthetic microstructure representations. Therefore, the aforementioned problems are addressed in this work by explicitly quantifying the microstructural topology and predicting the material properties and their variations through the development of surrogate models. Next, this work extends the proposed multi-scale models of microstructure-property relationships to magnetic materials to investigate the ferromagnetic-paramagnetic phase transition. Here, the same Ising model-based multi-scale approach used for microstructure reconstruction is implemented for investigating the ferromagnetic-paramagnetic phase transition of magnetic materials. The previous research on the magnetic phase transition problem neglects the effects of the long-range interactions between magnetic spins and external magnetic fields. Therefore, this study aims to build a multi-scale modeling environment that can quantify the large-scale interactions between magnetic spins and external fields. / Doctor of Philosophy / Titanium-Aluminum (Ti-Al) alloys are lightweight and temperature-resistant materials with a wide range of applications in aerospace systems. However, there is still a lack of thorough understanding of the microstructural behavior and mechanical performance of Titanium-7wt%-Aluminum (Ti-7Al), a candidate material for jet engine components. This work investigates the multi-scale mechanical behavior of Ti-7Al by computationally characterizing the micro-scale material features, such as crystallographic texture and grain topology. The small-scale experimental data of Ti-7Al is used to predict the large-scale spatial evolution of the microstructures, while the texture and grain topology is modeled using shape moment invariants. Moreover, the effects of the uncertainties, which may arise from measurement errors and algorithmic randomness, on the microstructural features are quantified through statistical parameters developed based on the shape moment invariants. A data-driven surrogate model is built to predict the homogenized mechanical properties and the associated uncertainty as a function of the microstructural texture and topology. Furthermore, the presented multi-scale modeling technique is applied to explore the ferromagnetic-paramagnetic phase transition of magnetic materials, which causes permanent failure of magneto-mechanical components used in aerospace systems. Accordingly, a computational solution is developed based on an Ising model that considers the long-range spin interactions in the presence of external magnetic fields.