This thesis examines the effects of coordinating highly sterically demanding and strongly electron donating saturated N-heterocyclic carbenes (NHCs) at late transition metal centres. Chapter III details the synthesis of a range of iridium complexes of the type (NHC)2IrHxCly [x = 1, 2; y = 0, 1], bearing the saturated NHCs 5-Mes, 6-Mes and 7-Mes. Unusually facile activation chemistry is observed in the reaction of [Ir(COE)2Cl]2 with 6-Mes and 7-Mes to form the doubly cyclometallated species (6-Mes')2IrH and (7-Mes')2IrH, which were fully characterised. The responses of these complexes to the addition of dihydrogen and HCl were studied, leading to the controlled synthesis of range of precursors to 14-electron iridium cations. In Chapter IV the formation of low valent iridium cations with weakly coordinating anions is targeted. Isolation of the cationic complexes [(NHC)(NHC')IrH][BArf4] and [(NHC)2IrH2][BArf4] (NHC = 6-Mes, 7-Mes) showcases the stabilising power offered by these expanded ring systems. This allowed the study the interaction of these low valent species with a range of amine-borane substrates which are known to be readily dehydrogenated. Thermodynamic data on the C-H bond activation processes occurring at these iridium centres were able to be obtained due to facile, reversible oxidative addition of C-H bonds across the 14-electron iridium. Chapter V focuses on the effects of increasing the steric bulk of these NHCs to limit the coordination of multiple ligands at the metal centre. Use of 2,6-diisopropyl-phenyl (Dipp) groups on the expanded ring NHCs, instead of mesityl groups, leads to an unprecedented mode of reactivity with [Ir(COE)2Cl]2. Activation and cleavage of C-N bonds in the carbene ring is observed, resulting in an open chain ligand chelating to the metal centre. Activation of the backbone in this manner has allowed the synthesis of saturated NHCs bearing a weakly coordinating anion on the ring. Here the first example of an anionic, saturated NHC is reported. In Chapter VI these highly sterically demanding NHCs are exploited to stabilise active species in low valent gold chemistry. The extreme steric bulk of the 6-Dipp ligand disfavours reduction of Au(I) to Au(0), however the resulting cation is observed to interact strongly with the weakly coordinating anion, [BArf4]-. Thus, attempts were made to optimise the anion and conditions to isolate a catalytically relevant intermediate. The strong donating power of these expanded ring NHCs is also exploited to activate gold hydride complexes of the type (NHC)AuH (NHC = 6-Dipp, 7-Dipp). Analogues of [H3]+ containing gold atoms ([{LAu}2H]+ and [LAuH2]+) supported by expanded ring NHCs were also targeted.

This thesis contains several contributions to the theoretical description and interpretation of biophysical single-molecule measurements: (i) For semiflexible polymers, we derive an efficient formulation of their local transverse dynamics in terms of a Generalized Langevin Equation. The elastic and frictional properties of the polymer are condensed into a memory kernel that is a function of the polymer\'s length and stiffness, the level of backbone tension, the position of the force probe along the polymer backbone and the boundary conditions at the polymer ends. At short times, the memory kernel attains a universal limiting form that depends neither on the polymer length nor on the boundary conditions; we obtain analytical results that accurately describe this regime. We discuss how to quickly and reliably evaluate the memory kernel for arbitrary times using a spectral decomposition method, and use an extensive body of numerical data to obtain analytical approximations to the memory kernel that cover the complementary long-time limit wherein polymer friction can be subsumed under a renormalized drag coefficient. (ii) Based on a systematic nonequilibrium treatment of an overdamped, one-dimensional stochastic escape process driven by external force, we develop a theory of Dynamic Force Spectroscopy (DFS) that generalizes previously available DFS theories to the high loading rates realized in novel experimental assays and in computer simulations. (iii) Extrapolating to future DFS experiments that may operate at far higher time resolution than presently achievable, we discuss the fast nonequilibrium relaxation of a semiflexible linker after bond rupture. Based on a rigorous theory of tension propagation in semiflexible polymers, we predict the relaxation of force within the force actuator, show that this relaxation is dominated by linker contraction, and demonstrate quantitative agreement of our predictions with experimental data obtained by a collaborating experimentalist group.

The purpose of this study was to determine the community power structure and its influence on the outcome of bond elections in four selected school districts in the State of Texas. The investigation of the following subproblems was necessary: 1. To determine the involvement of power structure in the decision-making process of the school district. 2. To determine the community people who have exercised the greatest influence in school matters. 3. To determine the educator's need to become cognizant of the nature of power structure. 4. To determine to what extent leaders in school bond elections are also leaders in non-school issues.

The thermochemistry of several species, and the kinetics of various H atom radical reactions relevant to atmospheric and combustion chemistry were investigated using ab initio theoretical techniques and the flash photolysis / resonance fluorescence technique. Using ab initio quantum mechanical calculations up to the G3 level of theory, the C-H bond strengths of several alkanes were calculated. The bond strengths were calculated using two working reactions. From the results, it is apparent that the bond strengths decrease as methyl groups are added to the central carbon. The results are in good agreement with recent experimental halogenation kinetic studies. Hydrogen bond strengths with sulfur and oxygen were studied via CCSD(T) theory, together with extrapolation to the complete basis set limit. The results for the bond dissociation energies (ground state at 0 K, units: kJ mol-1) are: S-H = 349.9, S-D = 354.7, HS-H = 376.2, DS-D = 383.4, and HO-H = 492.6. These data compare well with experimental literature. The rate constants for the isotopic reactions of H + H2S, D + H2S, H + D2S, and D + D2S are studied at the QCISD(T)/6-311+G(3df,2p) level of theory. The contributions of the exchange reaction versus abstraction are examined through transition state theory. The energy of NS was computed via CCSD(T) theory, together with extrapolation to the complete basis set limit. The results were employed with three working reactions to find ΔfH0(NS) = 277.3 ± 2 kJ mol-1 and ΔfH298(NS) = 278.0 ± 2 kJ mol-1. This thermochemistry is consistent with, but much more precise than, earlier literature values. A kinetic study of the reaction of H + CH2CCl2 was conducted over the temperature range of 298 - 680 K. The reaction was found to be pressure dependent and results of the rate constants and their interpretation via unimolecular rate theory are presented.

This thesis is a personal journey. My work on VCU’s production of SWEENEY TODD began in the Spring of 2012 when I came on board the production as dramaturg. Part of what is contained within is both an explanation of my dramaturgical research method as well as samples of the research I have compiled. However, my role was drastically changed in the Fall of 2012 when I was cast as the primary antagonist in the production. The thesis chronicles the rehearsal process as my role as dramaturg increasingly gave way to my role as actor. It attempts to answer the question, “Is it possible to be both dramaturg and actor on a single production?” Finally, the thesis is a reflection of the overall process of working on a challenging theatrical production in an academic setting.

The purpose of the current study was to develop a bonding method that can achieve clinically acceptable bond strength values while leaving a minimum amount of adhesive on the tooth surface during the debonding process. One hundred teeth were randomly assigned into groups. Five different enamel surface preparation protocols were tested (N = 20, each): Conventional acid etch, standard SEP, SEP applied with a light brush stroke (altered SEP 1), SEP applied directly to the composite of pre-coated bracket (altered SEP 2), and Primer Only groups. Brackets were debonded using an Instron universal testing machine (Instron, Canton, MA) in shear mode and the mean shear bond strength values were calculated. In addition, enamel surfaces were examined under light microscope to determine the location of failure using ARI. The Primer Only group had significantly lower mean shear strength (0.14 MPa, P0.05). With respect to ARI values, there was a significant difference among these four groups. 85% of samples in the altered SEP 2 group had 10% or less composite resin left on their surfaces. This group had also a mean shear bond strength value of 11.43 MPa, significantly above the minimal strength needed for orthodontic attachment bonding, and the lowest ARI values overall. Therefore, application of SEP directly to the composite resin of the pre-coated brackets may be an ideal bonding method by providing adequate bond strength and leaving a minimum amount of composite resin on the tooth surface during debonding. It should be kept in mind that future in-vivo studies would be needed to confirm the findings obtained from the current in-vitro study.

Statement of problem. Clinicians have used disinfection materials to remove surface contaminants during cavity preparation. It has been postulated that disinfection materials may negatively affect shear bond strength of restorative materials. If so, large numbers of restorations may be predestined for early failure with the use of a disinfection protocol.Purpose. To determine whether there is a difference in the bond strength between dentin and composite resin with a 3-step disinfection technique compared to a conventional bonding technique without the additional disinfection protocol.Material and Methods. Sixty human molar teeth were sectioned parallel to the occlusal surface to expose mid-coronal dentin and mounted parallel to a bond shearing device on a universal testing machine (Instron) and randomly divided into 2 groups. In Group I (n=30), specimens were treated with chlorhexidine, tubulicid red, and sodium hypochlorite before dentin bonding, following the manufacturer's instructions for All Bond 2. In Group II (n=30), specimens were treated only with the bonding protocol of All Bond 2. To ensure a uniform bond surface area, core paste was syringed into a cylindrical mold (diameter 2.38mm, height 2.00mm) that was in contact with the dentin bonding surface of each specimen, and allowed to set under constant force. All specimens were subjected to fracture by shear loading in a universal testing machine (Instron) at a uniform crosshead speed of 0.02 inch per minute and expressed as MPa. Statistical analysis, using nonpaired student's t-test, was performed. Results. A statistically-significant higher shear bond strength was found for the 3-step disinfection group (mean shear bond strength, 25.3; STD, 4.6) compared to the conventional bonding group (mean shear bond strength, 20.5, STD, 3.4) (PConclusions. The 3-step disinfection technique group showed a significantly stronger dentin shear bond strength compared to the conventional bonding technique without disinfection.

In vitro bond strength studies are of great importance and interest since they allow the prediction of clinical success of orthodontic adhesives. There are many studies that have investigated bond strength values of bonding systems. However, due to the variation in the materials and methods employed, it is very difficult and often impossible to make comparisons among data. The use of a substrate as an alternate to enamel for mechanical tests would minimize these variables and reduce the challenges faced with in vitro bond strength tests. The purpose of this study was to investigate the suitability of Macor as a substrate for bond strength testing of orthodontic adhesives. Macor samples were custom prepared in a shape similar to that of a human maxillary premolar. The groups tested were: Group 1: acid-etched with 9.6% hydrofluoric acid (HFA) for 60 seconds; Group 2: acid-etched with 9.6% HFA for 90 seconds; Group 3: acid-etched with 9.6% HFA for 120 seconds; Group 4: surface roughened with silicon carbide (Sic); and control group: human premolars etched with 37% phosphoric acid. Following surface preparation, samples were primed and brackets were bonded using Transbond XT (3MlUnitek). Mounted samples were stored in water for 24 hours at 37OC until mechanical testing. Brackets were debonded in the shear mode using an Instron Universal Testing Machine and the force at debond was recorded. The nature of adhesive bond failure among the groups was also compared using an adhesive remnant index (ARI). One-way ANOVA and Weibull analysis statistical tests were used to evaluate and compare the groups. Sample surfaces were analyzed under the light microscope to determine the mode of bond failure for ARI. The Kruskall-Wallis test was used to determine differences in the ARI scores. There were statistically significant differences in shear bond strengths among the enamel and Macor groups (p 0.05). The shear bond strength values of the Macor groups were significantly lower than those of the enamel control group, (p < 0.05). ARI scores were significantly different between the groups (p 10.0001); Macor samples treated with hydrofluoric acid had more adhesive remaining on their surfaces than those in the control and Sic groups. Based on the results of this study, Macor may not be a suitable substrate for bond strength testing in orthodontics.

A large percentage of Americans own pets which may impact their health. This study examines pet ownership’s effect on well being in older adults looking at race/ethnicity. A sample of 6,565 older adults (>60) was selected from the Third National Health and Nutrition Survey. Pet owners comprised 28.3% of the sample. The theories of symbolic interaction and social integration were used to examine pet ownership’s effect on physical components of well-being. The descriptive results showed statistically significant differences in age, education, income, and marital status between pet owners and non-pet owners. Pet owners were younger, more educate, higher income and married. Similar results were found for Caucasians, African Americans and Mexican Americans. Logistic regression for the entire sample revealed pet owners were more likely to have a positive self perception of health, normal blood pressure, improved function, less chronic conditions, improved function and more falls. Multiple regression revealed pet owners had more hospital stays, but fewer physician visits and nursing home stays than non-pet owners. When examined by race/ethnicity differences were found between pet owners and non-pet owners that differed from the general sample results. This research revealed that pets overall positively impact their owners’ health but it appears to differ based on race/ethnicity. Further research is needed on pet ownership’s effect on older adults specifically in regards to race.

Les structures en béton armé sont amenées à répondre à différentes exigences pouvant dépasser la simple résistance mécanique. Pendant le processus de fissuration, les contraintes dans le béton armé sont progressivement redistribuées entre l’acier et le béton via l’interface entre ces deux matériaux. Cette redistribution de contraintes a un impact direct sur l’état de fissuration final et doit donc être prise en compte dans la modélisation. Il existe différents modèles numériques capables de représenter les effets de la liaison acier-béton. Cependant, leur usage est, pour l’instant, incompatible avec les applications concernant les structures de grandes dimensions (difficultés de maillage, coût de calcul…). Dans ce cadre d’application, l’hypothèse de liaison parfaite entre l’acier et le béton (déplacement identique) est donc toujours utilisée. On se propose ici de développer un nouveau modèle éléments finis de liaison acier-béton qui soit à la fois représentatif des phénomènes physiques se produisant à l’interface entre les deux matériaux et compatible avec les contraintes de modélisation des structures de grandes dimensions. Ce travail de thèse se découpe en trois grandes parties : - le développement d’un modèle élément fini de liaison acier-béton adapté aux contraintes de modélisation des structures de grandes dimensions. Ce modèle numérique permet ainsi de tenir compte des interactions mécaniques entre le béton et les armatures d’acier représentées à l’aide d’éléments barres. - la caractérisation du comportement de la liaison acier-béton. Un modèle de loi d’adhérence (évolution de la contrainte d’adhérence en fonction du glissement) basé sur des observations expérimentales (campagne expérimentale de pull-out menée au cours de la thèse et données bibliographiques) est proposé. Il permet en particulier de différencier le cas d’une rupture par arrachement, d’une rupture par éclatement en tenant compte des caractéristiques matériaux et géométriques de la structure. - l’application du modèle proposé à un élément structurel (poutre). Un essai de poutre en flexion quatre points visant à caractériser l’évolution de la fissuration (évolution de l’ouverture de fissure mesurée à l’aide de la technique de corrélation d’images notamment) a ainsi été proposé. Ces résultats ont ensuite été comparés à ceux de simulations numériques tenant compte de la liaison acier-béton d’une part ou de l’hypothèse de liaison parfaite d’autre part. Les deux modélisations donnent une bonne approximation du comportement extérieur de la structure (comportement global et ouvertures de fissure des surfaces extérieures de la poutre). Le modèle de liaison acier-béton apporte cependant une meilleure caractérisation de la phase de fissuration active (apparition des fissures) et modifie plus particulièrement le comportement local de la structure à proximité directe des armatures (limitant le développement de l’endommagement du béton le long des renforts). / Reinforced concrete structures may have to fulfill functions that go beyond their simple mechanical resistance. During the cracking process, stresses are progressively transferred from steel to concrete through the steel-concrete interface. This stress transfer has a direct impact on the crack properties. Taking into account these effects seems thus essential to predict correctly the cracking of reinforced concrete structures. Different models exist to represent the steel-concrete bond behavior. However, these models are rarely compatible with large scale simulations (meshing difficulties, heavy computational cost…). To overcome these difficulties, a perfect relation between steel and concrete (same displacements) is generally considered for structural applications. In this contribution, a new finite element approach is proposed to represent the steel-concrete bond effects in a context adapted for large scale simulations. This thesis is divided in three parts: - the development of a finite element steel-concrete bond model adapted for large scale structural applications . This model takes into account mechanical interactions between concrete and steel reinforcement represented by truss elements. - the characterization of the steel-concrete bond behavior. A model for the bond stress-slip law based on experimental observations (experimental campaign on pull-out test carried out during the thesis and data of literature) is proposed. This model differentiates the case of a pull-out failure and of splitting failure and takes into account the material properties and the geometric characteristics of the structure. - an application of the proposed model on a structural element (beam). A four point bending beam is experimentally tested. This test aims to characterize the crack evolution (in particular the crack opening using the image correlation technique). Experimental results are then compared with numerical simulations taking into account the bond–slip effect between steel and concrete or considering the perfect relation hypothesis. The two simulations give a good approximation of the external behavior of the structure (global behavior and crack opening on the external face of the beam). Nevertheless, the bond model improves the cracking description during the active cracking phase (beginning of crack apparition) and influences the local behavior of the structure especially near the steel bars (avoiding the propagation of the damage of concrete along the steel reinforcement).