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<p>Highly shear-thinning polymers that can easily flow upon the application of shear but form gels at rest have multiple potential applications in the eye. In the front of the eye, a formulation that can easily be administered via a conventional eye dropper but form a gel within the tear film once applied would be beneficial for prolonging drug release at the front of the eye, either alone or as a medium for entrapping nanoparticles or nano-objects loaded with drugs. In the back of the eye, vitreous substitutes that can be administered through a narrow gauge needle (and, ideally, removed via the same) may be beneficial for retinal surgeries.</p> <p>The overall objective of the proposed research is to chemically modify PVP through grafting strategies to improve its viscometric and mucoadhesive properties while maintaining the beneficial properties, which make it useful in ophthalmic applications.</p> <p>N-vinylpyrrolidone is copolymerized with N-vinylformamide to produce a functionalized grafting platform P(VP-co-VF), which is then grafted with low concentrations of short hydrophobic grafts to introduce non-Newtonian flow profile to the precursor.</p> <p>For applications at the back of the eye, the hydrophobic grafted PVP can be injected into the vitreous cavity of the eye in a liquid form to form subsequently a gel-like substance and function as a substitute for the vitreous humour. For application at the front of the eye, the shear thinning properties of hydrophobic-grafted PVP is combined with the mucoadhesive properties of phenylboronic acids (PBA) to improve the bioavailability of the drugs delivered to the front of the eye with eye drops.</p> <p>Rheological characterization of the solutions has shown the potential to form gel-like materials via hydrophobic associations without sacrificing the facile injectability of the material. Targeted gelation and mucoadhesion properties can be obtained by the synthesis of polymers with desired PBA and hydrophobic graft contents.</p> / Master of Applied Science (MASc)

Die hier dargelegte Dissertation ist motiviert durch die Vorschläge von Joyce, Doan und Walpuski zur Definitionen enumerativer Invarianten für G2-Mannigfaltigkeit, durch das Zählen gewisser kalibrierter Untermannigfaltigkeiten, sogenannter assoziativen Untermannigfaltigkeiten. In Kapitel 1, werde ich Definitionen und grundlegende Fakten über G2-Mannigfaltigkeit und deren assoziative Untermannigfaltigkeit wiederholen. Darüber hinaus erläutere ich die Konstruktion von G2-Mannigfaltigkeit als verdrehte verbundener Summe. Kapitel 2 schafft die nötige Grundlage für das darauf folgende dritte Kapitel. Hier definiere ich den Modul-Raum der asymptotisch zylindrischen assoziativen Untermannigfaltigkeiten zusammen mit seiner natürlichen Topologie und zeige, dass der Modul-Raum lokal homeomorph zur Urbild-Menge der Null einer glatten Abbildung zwischen zwei endlich-dimensionalen Räu- men ist. In besonderen Fällen ist dieser Modul-Raum eine Lagrangesche Untermannigfaltigkeit des Modul Raums der holomorphen Kurven einer asymptotisch zylindrischen Calabi-Yau Man- nigfaltigkeit. In Kapitel 3 beweise ich ein Klebe-Theorem für ein Paar von asymptotisch zylindrischen as- soziativen Untermannigfaltigkeiten in einem zusammenpassenden Paar von asymptotisch zylin- drischen G2-Mannigfaltigkeiten. Hiermit konstruiere ich neue geschlossene und starre (rigid) assoziative Untermannigfaltigkeiten in verdrehten verbundenen Summe G2-Mannigfaltigkeiten. In Kapitel 4 untersuche ich den Modul-Raum der konisch singulären assoziativen Un- termannigfaltigkeiten in G2-Mannigfaltigkeiten. Durch das Umformulieren des Indexes des Operators, der die Deformationstheorie kontrolliert, in bestimmte Stabilität-Indizes des zu- grundeliegenden assoziativen Kegels begründe ich, dass in einem generischen Pfad in dem Raum der ko-geschlossenen G2-Strukturen keine asymptotisch konischen assoziative Unter- mannigfaltigkeiten existieren, die mindestens eine Singularität besitzen, die auf einem Kegel mit Stabiltätsindex größer als eins modeliert werden. Dieses Resultat lässt sich auf alle speziellen Lagrangesche-Kegel außer den Harvey-Lawson-T2-Kegel und die Vereinigung zweier speziellen Lagrangesche-Flächen anwenden. Zusätzlich lässt sich das Ergebnis auch auf alle konischen assoziativen Untermannigfaltigkeiten anwenden, deren zugrundeliegende Verschlingung (link) holomorphe Kurven mit Null-Torsion in S6 sind. Des Weiteren dienen Teile des vierten Kapitels als Grundlage für das darauf folgende Kapitel 5. Aufgrund einiger Übergangsphänomene entlang eines generischen Pfades von G2-Strukturen, führt das naive Zählen von assoziativen Untermannigfaltigkeiten zu keiner Invariante. Tat- sächlich wurde vermutet, dass a) eine assoziative Untermannigfaltigkeit aus einer assoziativen Untermannigfaltigkeit mit Selbstsschnitt (self-intersection) geboren werden kann, und, dass b) drei assoziative Untermannigfaltigkeiten aus einer konisch singulären assoziativen Un- termannigfaltigkeit, deren Singularität durch den Harvey-Lawson-T2-Kegel modelliert wird, entspringen. In Kapitel 5, beweise ich ein Desingularitätstheorem für konisch singulären assoziative Untermannigfaltigkeit entlang eines Pfades von ko-geschlossenen G2-Strukturen. Somit verifiziere ich Vermutung b) bewiesen und teilweise auch Vermutung a). / The dissertation presented here is motivated from the proposals made by Joyce, Doan and Walpuski to define enumerative invariants of G2-manifolds by counting certain calibrated submanifolds, called associative submanifolds. In Chapter 1, I review the definitions and basic facts of G2-manifolds and associative submanifolds. Moreover, I explain the construction of G2-manifolds as twisted connected sums. Chapter 2 serves as a necessary groundwork for Chapter 3. Here, I define the moduli space of asymptotically cylindrical associative submanifolds with its natural topology and prove that the moduli space is locally homeomorphic to the zero set of a smooth map between two finite-dimensional spaces. In the best scenario, this moduli space is a Lagrangian submanifold of the moduli space of holomorphic curves in the asymptotic Calabi-Yau 3-fold. In Chapter 3, I prove a gluing theorem for a pair of asymptotically cylindrical associative submanifolds in a matching pair of asymptotically cylindrical G2-manifolds. Using this I construct new closed and rigid associative submanifolds of twisted connected sum G2-manifolds. In Chapter 4, I study the moduli space of conically singular associative submanifolds in G2-manifolds. By reformulating the index of the operator that controls the deformation theory in terms of certain stability-index of the associative cones, I establish that in a generic path of co-closed G2-structures there are no conically singular associative submanifolds that have at least one singularity modeled on a cone of stability-index greater than one. This result applies to all special Lagrangian cones, except the Harvey-Lawson T2-cone and a union of two special Lagrangian planes. Additionally, it applies to all associative cones whose links are null-torsion holomorphic curves in S6. Furthermore, parts of Chapter 4 also serve as a necessary groundwork for Chapter 5. The naive counting of associative submanifolds does not lead to an invariant due to several transitions that may occur along a generic path of G2-structures. In fact it was conjectured that a) an associative submanifold born out of an associative submanifold with self intersection, and b) three associative submanifolds arise from a conically singular associative submanifold whose singularity is modeled on Harvey-Lawson T2-cone. In Chapter 5, I prove a desingularization theorem for conically singular associative submanifolds along a path of co-closed G2-structures. Consequently, I verify conjecture b) and partially confirm conjecture a).

Many plants, especially grasses, have Nitrogen (N) as their growth-limiting nutrient. Large amounts of N fertilizer (>100 kg N ha-1) are used in managed systems to maximize crop productivity. However, the plant captures less than 50% of the (~12 million tons per year, U.S.) applied N-fertilizer. The remaining mobile N lost through leaching and denitrification accumulates in waterways and the atmosphere, respectively. Losses of fertilizers create environmental and economic concerns globally and create conditions that support the invasion of exotic plants in the natural landscapes. There is thus a need to come up with biological solutions to better manage nitrogen for plant growth and ecosystem sustainability. Microbial communities in the rhizosphere are known to potentially have beneficial effects on plant growth. Diazotrophs, for example, are bacteria that can convert the atmospheric nitrogen to ammonia, a process called 'nitrogen fixation.' Utilizing the natural process of associative nitrogen fixation to support most of the plant's N needs would substantially reduce fertilizer use and thus reduce production and environmental costs. The goal of this dissertation was to determine the structure and function of root-zone microbial communities for increasing productivity of native plants. Towards this end, we study the root-zone bacterial and fungal communities of native and exotic invasive plants. This study identifies that shifts in rhizosphere microbial communities are associated with invasion and highlights the importance of rhizosphere associated structure and function of microbes. A study of root-zone associated microbes in switchgrass (Panicum virgatum L.) - a U.S. native, warm-season, perennial, bioenergy crop indicates that high biomass yield and taller growth are associated with increased plant N-demand and supportive of bacteria with greater rates of N2-fixation in the rhizosphere. Another crucial outcome of the thesis is a better description of the core and cultivar-specific taxa that comprise the switchgrass root-zone associated microbiome. The work in this dissertation has brought us closer to designing N supply strategies by utilizing the natural microbial communities to balance the N-cycle in agroecosystems and support a sustainable environment. / Ph. D.

La tesi indaga il ruolo specifico agito dalle organizzazioni di terzo settore in reti associative multilivello, dal punto di vista della capacità di generare e valorizzare le relazioni con gli altri membri e con l'ambiente esterno. Per reti multilivello si intendono quegli organismi, a diversi gradi di formalizzazione, che riuniscono al loro interno entità locali, di secondo livello, ed eventualmente di livelli coordinativi superiori, con lo scopo di fornire supporto all'attività dei gruppi affiliati o di coordinarne le risorse materiali e immateriali per il benessere sociale della comunità. Le indagini condotte hanno incluso nel campo di osservazione sia le reti che comprendono esclusivamente organizzazioni di terzo settore le organizzazioni multilivello di terzo settore sia i network di partnership miste con enti pubblici. La dimensione della produttività sociale delle reti è stata letta attraverso la lente del concetto di capitale sociale, inteso come la dotazione, da parte di una rete, di relazioni caratterizzate da codici normativi e prassi di fiducia, reciprocità e collaborazione. I risultati delle tre indagini presentate, di carattere sia quantitativo che qualitativo, mostrano che: a) esiste uno specifico capitale sociale prodotto da organizzazioni multilivello di terzo settore che è in grado di connetterle sia all'interno del network (funzione bonding) che all'esterno (funzione bridging); b) che tale capitale sociale di terzo settore possiede delle sue proprie qualità che lo distinguono dalla relazionalità agita in reti di servizio pubbliche; c) che la relazionalità delle organizzazioni di terzo settore è in grado, in certe condizioni, di svilupparsi verso l'esterno in reti di partnership miste con soggetti del settore pubblico, determinando nuove dinamiche relazionali ed esiti societari peculiari. / The dissertation deals with the specific role played by third sector organizations in multilevel associative networks in terms of capacity to generate and foster relationships with other members and with the outer context. Multilevel associative networks are defined as those entities that gather local agencies, second level and higher coordination level entities with the aim of providing support for the affiliated groups and/or coordinating material and immaterial resources for the benefit of the community. The research field included networks comprising third sector organizations only so-called third sector multilevel organizations as well as plural partnership networks with other public agencies. The social productivity dimension was studied through the lenses of the social capital concept, defined as that specific set of resources possessed by those networks endowed with relationships of trust, reciprocity and collaboration. The results of the three research projects presented, carried out with quantitative and qualitative techniques, show that: a) there is a specific social capital produced by third sector multilevel organizations which connects actors both within the network (bonding function) and with the outer world (bridging function); b) the third sector's social capital presents some distinctive characteristics compared with the relational properties of public service networks; c) third sector organizations are able, under certain circumstances, to develop social capital networks also with public agencies, setting new dynamics and peculiar social outcomes.