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The majority of stars form in clusters which are themselves birthed in Giant Molecular Clouds (GMCs). The radiation produced by clusters during their formative phase heats and ionizes the surrounding gas and drives outflows via radiation pressure. The combination of these processes, referred to as radiative feedback, is a proposed mechanism for limiting the star formation efficiency (SFE) in molecular clouds. In this thesis, we use 3D numerical simulations of turbulent GMCs, completed using the code FLASH and a sophisticated radiative transfer scheme, to explore the effects of radiative feedback on cluster formation and the larger scale interstellar medium (ISM). We present suites of simulations that vary the initial GMC mass from 10^4 to 10^6 M$_{\odot}$ and consider both gravitationally bound and unbound clouds. We find that clusters form within the highly filamentary clouds where they can undergo subsequent merging. Radiative feedback only plays a minor role in lowering the SFE of 10^6 M$_{\odot}$ GMCs. However, it completely disrupts intermediate mass clouds (~10^5 M$_{\odot}$), reducing the SFE by a factor of two. We then examine the escape fraction of UV photons from GMCs --- a quantity relevant to the structure of the ISM and cosmic reionization. We show that the escape fraction is dynamic and can vary by factors of two over short timescales because of the rapid growth and collapse of HII regions. The escape fractions from massive GMCs are typically low (~5%) while intermediate mass models are characterized by escape fractions nearing 100%. We combine our GMC models to represent the escape fraction from a population of clouds in dwarf starburst and spiral-type galaxies. We successfully reproduce the star formation rates in these galaxies and find typical escape fractions of 8% in all cases. These results place important constraints on galactic-scale models studying the ISM and cosmic reionization. / Thesis / Doctor of Philosophy (PhD)

Addition reactions of ten neutral nucleophiles and seven anionic nucleophiles with the pentaosmium pentadecacarbonyl carbido cluster Os5C(CO)15 have been kinetically studied and several important reactivity trends have been established. The calculated activation parameters support an associative mechanism involving the attack of nucleophiles on the parent cluster in the rate-limiting step. Decarbonylation reactions of neutral arachno clusters Os5C(CO)15L have also been kinetically studied and different reactivity trends have been observed. Reactions of Os5C(CO)15 with both neutral and anionic nucleophiles produce corresponding arachno clusters in good yield. Neutral arachno clusters decarbonylate when heated to yield corresponding nido clusters. All studied anionic arachno clusters are resistant to decarbonylation, but most of them readily react with organic acids to form corresponding hydrido clusters. Reactions of anionic arachno clusters with methyl triflate yielded several new clusters. Exploration of metal-ligand bond lengths in the respective pairs of arachno and nido clusters yielded a valuable conclusion with regard to steric effects prevalent in these molecules. The mechanisms for polyhedral structural rearrangements between arachno and nido derivatives of the pentaosmium carbido cluster have been proposed. Thermolysis of cluster Ru3[Ph2PCH(Me)PPh2](CO)10 in the presence of diphenylacetylene yields alkyne-substituted clusters Ru3(PhCCPh)[Ph2PCH(Me)PPh2](CO)8 and Ru3(PhCCPh)[Ph2PCH(Me)PPh2](CO)7 as the major products. The backbone-modified diphosphine in both clusters has facilitated the growth of single crystals suitable for X-ray crystallography. The kinetics for the conversion between two clusters have been investigated and the calculated activation parameters were found to be inconsistent with a rate-limiting step involving a dissociative loss of CO.

This is an exploratory study that applies the dominant theories of the community power structure literature to the trend of regional cluster-based economic development policy in order to develop a conceptual framework of the political/institutional context of this "new" approach. In order to develop a framework that can be utilized by practitioners, field studies were conducted in Austin, Texas; Portland, Oregon; Greenville/Spartanburg, South Carolina; Lynchburg, Virginia; and Roanoke, Virginia. The findings are that the major community power structure theories (i.e., market model, economic forces, civic culture, regime theory, the growth machine, and civic entrepreneurs) all provide important insights for the adoption of cluster-based policies. Other important factors that need to be considered are the importance of public administrators, performance metrics, state context, institutional arrangements, elected officials, tax structure, and historical path dependency. The implication for public administration is that the role of public administrators is contingent on the nature of the network governance structure. / Ph. D.

Heterogeneous catalysis plays a significant role in the chemical industry and the global economy. Most heterogeneous catalysts in the chemical industry and laboratory consist of supported metal nanoparticles, clusters and isolated (single) atoms. Understanding structure sensitivity and identifying the active site or sites are crucially essential for designing efficient catalysts. To determine the active sites of a catalyst for a particular chemical reaction, in-situ/operando spectroscopy, such as diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and X-ray absorption fine structure (XAFS) spectroscopy, is usually implemented as characterization tools. However, understanding the limitation of the characterization tools is crucial to eliminate misleading conclusions. Therefore, the main object of this work is not only to characterize the catalyst before and after the reaction but to investigate the reliability of the characterization tools as well as the stability of the metal clusters and single atoms during CO oxidation. There are four main findings that will be present in this work. First, a high-flux X-ray beam can induce structural change that leads to a reduction of the metal and agglomeration of metal clusters. This finding is very important since X-ray beam damage is uncommon for heterogeneous catalysis as for homogeneous catalysts and biological samples. In the study, the effect of high-flux X-ray on the Rh clusters and nanoparticles was highlighted along with providing mitigation strategies in order to reduce the damage caused by the high-flux X-ray beam. The second important finding is about the characterization of Rh clusters and nanoparticles during CO reduction treatment using DRIFTS. In this study, the integration of low-temperature CO oxidation kinetics as a characterization tool with DRIFTS, XAFS and scanning/transmission electron microscopy (STEM) was found to be necessary to improve the characterization of Rh single atoms. Implementing CO oxidation measurements at low temperatures can provide a rough estimation of the percentage of Rh single atoms. The third finding is related to the stability of Rh clusters upon exposure to CO, oxygen and CO oxidation at different temperatures. The study shows an unexpected dynamic structural change that the Rh cluster undergoes during exposure to oxygen even at room temperature in which the Rh clusters disperse to form Rh single atoms. This dispersion phenomenon was found to be size, gas environment and temperature dependent. For example, small clusters tend to disperse while large nanoparticles resist dispersion. additionally, increasing the temperature to ∼ 160 with CO and oxygen lead to an increase in the percentage of Rh single atoms. More importantly, the dispersed catalyst (Rh single atoms) exhibits higher CO oxidation activity than Rh nanoparticles by 350x. This finding can also be used for Rh single atoms synthesis for different oxide supports such as MgAl2O4, TiO2, and CeO2. Finally, the fourth finding is about investigating the CO oxidation kinetics and mechanism. The kinetics of Rh single atoms differ from Rh nanoparticles. Implementing in-situ spectroscopy helps to identify the resting state of the Rh complex during CO oxidation which is Rh(CO)2. By combining CO oxidation kinetics and in-situ spectroscopy, the plausible mechanism was suggested to be Eley-Rideal/Mars Van Krevelen mechanism. / Doctor of Philosophy / Heterogeneous catalysts are solid materials that scientists and chemical engineers use to convert undesirable raw reactants (liquid or gas) to other products (liquid or gas). One example of a heterogeneous catalyst is a catalytic converter used in most cars around the world. One goal of the catalytic converter is to convert CO (toxic gas) to CO2 (less toxic). The catalyst in a catalytic converter contains precious metals as nanoparticles such as Platinum (Pt), Palladium (Pd) and Rhodium (Rh) deposits on oxide supports (inert materials) such as Al2O3. These Pt, Pd and Rh nanoparticles help to accelerate the chemical reaction (e.g.CO oxidation) in which converting the toxic gas CO to CO2 at a relatively low temperature compared to if the reaction proceeds without those metal nanoparticles. In order to improve the performance of the catalyst, scientists and engineers implement characterization techniques to identify the active site based on the shape and size of the nanoparticles. One method to improve the catalyst performance is to decrease the particle size below 2 nm or even to reach isolated atoms. Unfortunately, synthesizing isolated (single) atoms supported on oxide support is very challenging. One main discovery presented in this work is that Rh single atoms can be synthesized using a simple but effective method. More importantly, Rh single atoms show higher performance than Rh nanoparticles by 350 times which helps to convert CO the toxic gas to CO2 at room temperature. This finding is important in which that the synthesis presented here can be used for different chemical reactions such as methane oxidation and methanol carbonylation.