No description available.

A key component of natural photosynthesis are the antenna chromophores (chlorophylls and carotenoids) that capture solar energy and direct it towards the reaction centers of photosystems I and II. Highlighted by highly-ordered crystal structures and synthetic tunability via crystal engineering, metal–organic frameworks (MOFs) have the potential to mimic the natural photosynthetic systems in terms of the efficiency and directionality of energy transfer. Owing to their larger surface areas, MOFs have large absorption cross sections, which amplifies the rate of photon collection. Furthermore, MOFs can be constructed using analogues of chlorophyll and carotenoids that can participate in long-range energy transfer. Herein, we aimed to design photoactive MOFs that can execute one of the critical steps involved in photosynthesis - photon collection and subsequent energy transfer. The influence of spatial arrangement of chromophores on the efficiency and directionality of excitation energy transfer (EET) was investigated in a series of mixed-ligand pyrene- and porphyrin-based MOFs. Due to the significant overlap between the emission spectrum of 1,3,6,8-tetrakis(p-benzoic acid)pyrene (TBAPy) and the absorption spectrum of meso-tetrakis(4-carboxyphenyl)porphyrin (TCPP), the co-assembly of these two ligands in a MOF should enable facile energy transfer. Bearing this in mind, three TBAPy-based MOFs with markedly different network topologies (ROD-7, NU-901, and NU-1000) were chosen and a small number of TCPP units were incorporated in their backbone. To gain insight into the photophysical properties of mixed-ligand MOFs, we conducted time-resolved and steady-state fluorescence measurements on them. Stern-Volmer analysis was performed on the fluorescence lifetime data of mixed-ligand MOFs to determine the quenching constants. The quenching constant values for ROD-7, NU-901, NU-1000, and TBAPy solution were found to be 15.03 ± 0.82 M-1, 10.25 ± 0.99 M-1, 8.16 ± 0.41 M-1, and 3.35 ± 0.30 respectively. In addition, the ratio of the fluorescence intensities of TCPP and TBAPy was used to calculate the EET efficiencies in each of the three MOFs. EET efficiencies were in the following order: ROD-7 > NU-901 > NU-1000 > TBAPy-solution. Based on the trends observed for quenching constants and EET efficiencies, two conclusions were drawn: (1) the ligand-to-ligand energy transfer mechanism in MOFs outperforms the diffusion-controlled mechanism in solution phase, (2) energy transfer in MOFs is influenced by their structural parameters and spectral overlap integrals. The enhanced EET efficiency in ROD-7 is attributed to shorter interchromophoric distance, larger orientation factor, and larger spectral overlap integral. Directionality of energy transfer in these MOFs was assessed by calculating excitonic couplings between neighboring TBAPy linkers using the atomic transition charges approach. Rate constants of EET (kEET) along different directions were determined from the excitonic couplings. Based on the kEET values, ROD-7 is expected to demonstrate highly anisotropic EET along the stacking direction. In order to explore the mechanistic aspects of EET in porphyrin-based MOFs, we studied the energy transfer characteristics of PCN-223, a zirconium-based MOF containing TCPP ligands. After performing structural characterization, the photophysical properties of PCN-223 and free TCPP were investigated using steady state and time-resolved spectroscopy. pH-dependent fluorescence quenching experiments were performed on both the MOF and ligand. Stern-Volmer analysis of quenching data revealed that the quenching rate constants for PCN-223 and TCPP were 8.06 ± 1011 M-1s-1 and 2.71 ± 1010 M-1s-1 respectively. The quenching rate constant for PCN-223 is, therefore, an order of magnitude larger than that for TCPP. Additionally, PCN-223 demonstrated a substantially higher extent of quenching (q = 93%) as compared to free TCPP solution (q = 51%), at similar concentrations of quencher. The higher extent of quenching in MOF is attributed to energy transfer from neutral TCPP linkers to N-protonated TCPP linkers. Using the Förster energy transfer model, the rate constant of EET in PCN-223 was calculated. The magnitude of rate constant was in good agreement with the kEET values reported for other porphyrin-based MOFs. Nanosecond transient absorption measurements on PCN-223 revealed the presence of a long-lived triplet state (extending beyond 200 μs) that exhibits the characteristic features of a TCPP-based triplet state. The lifetime of MOF is shorter than that of free ligand, which may be attributed to triplet-triplet energy transfer in the MOF. Lastly, femtosecond transient absorption spectroscopy was employed to study the ultrafast photophysical processes taking place in TCPP and PCN-223. Kinetic analysis of the femtosecond transient absorption data of TCPP and PCN-223 showed the presence of three distinct time components that correspond to: (a) solvent-induced vibrational reorganization of excitation energy, (b) vibrational cooling, and (c) fluorescence. Materials that allow control over the directionality of energy transfer are highly desirable. Core-shell nanocomposites have recently emerged as promising candidates for achieving long-distance, directional energy transfer. For our project, we aim to employ UiO-67-on-PCN‐222 composites as model systems to explore the possibility of achieving directional energy transfer in MOF-based core-shell structures. The core–shell composites were synthesized by following a previously published procedure. Appropriate amounts of Ruthenium(II) tris(5,5′-dicarboxy-2,2′-bipyridine), RuDCBPY, were doped in the shell layer to produce a series of Ru-UiO-67-on-PCN‐222 composites with varying RuDCBPY loadings (CS-1, CS-2, and CS-3). The RuDCBPY-doped core–shell composites were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) imaging, Nitrogen adsorption-desorption isotherms, and diffuse reflectance spectroscopy. Efforts are currently underway to quantify RuDCBPY loadings in CS-1, CS-2, and CS-3. After completing structural characterization, the photophysical properties of CS-1, CS-2, and CS-3 will be investigated with the help of time-resolved and steady-state fluorescence spectroscopy. / Doctor of Philosophy / The pigment−protein complexes in natural photosynthetic units (also known as light harvesting antennas) efficiently capture solar energy and transfer this energy to reaction centers that carry out water splitting reactions. The collective chromophoric behavior of antennas can be replicated by metal-organic frameworks (MOFs). MOFs are crystalline, self-assembled materials composed of metal clusters connected by organic molecules. In this dissertation, we study the factors that govern the energy transfer and light harvesting capabilities of MOFs. In chapter 2, we examined the role of 3D structure of MOFs in energy transfer. In chapter 3, we investigated the influence of pH and temperature on the photophysical properties of MOFs. In chapter 4, we explored the possibility of energy transfer in novel MOF-on-MOF composites. This work is intended to pave the way for the construction of highly efficient MOF-based materials that can serve as the light harvesting and energy-transfer components in solar energy conversion devices.

There has been little research comprehensively documenting wildlife species in Harenna Forest within the Bale Mountains National Park of Ethiopia. This area is one of the few remaining afro-alpine biodiversity hotspots and is home to numerous endemic plants and animals and offers socio-economic benefits to the neighboring communities. Human population pressure, weak land protection policies, and uncertain land tenure rights have led to increases in farmland for subsistence and coffee farming, livestock grazing, and reduction of afro-alpine, shrubland and grassland habitats. Given these challenges, I used 48 camera trap stations to produce an inventory of wildlife species and to determine factors influencing occupancy (i.e., habitat use), detection, and temporal activity and overlap. I recorded 26 terrestrial and arboreal mammalian species and I had sufficient data to model occupancy for 13 species and temporal activity for 14 species. Occupancy and detection were generally higher for herbivores and omnivores (occupancy: 0.28-0.97; detection: 0.1-0.54) than carnivores (occupancy: 0.31-0.80; detection: 0.04-0.18). I found more evidence of positive anthropogenic impacts on herbivore and omnivore occupancy than negative, while detection was influenced by habitat or landscape features, rather than by humans. Carnivore occupancy was largely unaffected by anthropogenic or habitat variables, but detection was strongly, and mostly positively, influenced by anthropogenic impacts. Temporal activity analyses revealed that, for herbivores and omnivores, only tree hyraxes (Dendrohyrax arboreus) and crested porcupines (Hystrix cristata) were nocturnal, Menelik bushbucks (Tragelaphus scriptus meneliki) were crepuscular, and the remaining species ranged from diurnal to cathemeral. Neither similar body size nor similar diet affected overlap between species pairs. However, overlap with human temporal activity was low for Menelik bushbucks (Δ=0.45) and common duikers (Sylvicapra grimmia) appeared to become less active at stations with high human use. For carnivores, leopards (Panthera pardus) and honey badgers (Mellivora capensis) were crepuscular, and the remaining species were nocturnal. I found evidence that carnivores overlapped less when they were more similar in body size to other carnivores (average Δ=0.67-0.71) compared to species more dissimilar in body size (average Δ=0.75), although there was variation across species. In general, carnivores overlapped much less with humans (average Δ=0.20) than did herbivores (average Δ=0.52) and omnivores (average Δ=0.43). Spotted hyenas (Crocuta crocuta), in particular, appeared to alter activity to reduce overlap with humans. This study provides baseline information on presence, distribution, and activity of large- and medium-sized terrestrial and arboreal mammals in an understudied biodiversity hotspot. My findings are concerning for biodiversity conservation as rare and endangered species (e.g., mountain nyalas (Tragelaphus buxtoni), Ethiopian wolves (Canis simensis)) were rarely or never photographed, and larger carnivores (e.g., lions (Panthera leo), leopards, jackals), generally had low capture rates. The species with higher capture rates, occupancy, and activity tended to be those that can tolerate or take advantage of human activity and disturbance. Species sensitive to human disturbance eventually may be lost unless measures can be put in place to reduce human impacts. This baseline knowledge is important for future studies examining trends in mammalian wildlife populations, such as site extinction and colonization, or changes in overlap with humans, in a landscape that is continuing to experience human-caused, landscape change. / Master of Science / Harenna forest, which is located in Bale Mountains National Park, Ethiopia is an important habitat to both wildlife and people. However, it faces a number of challenges as a result of population growth leading to increased coffee farming and livestock grazing resulting in reduced habitat for wildlife species. I used 48 cameras located across the forest to record presence of terrestrial mammals and document their distribution and daily activity across the landscape. I also used data such as vegetation indices, elevation, and distances to human-disturbed areas to determine what influenced wildlife species. Cameras recorded 26 species of mammals. I had enough data to determine distribution for 13 species and daily activity for 14 species. I found that presence across the landscape and activity of herbivores and omnivores was generally higher than that of carnivores. Additionally, I found that human activity or disturbance often had a positive influence on herbivore and omnivore distribution, but my ability to detect species in camera traps was primarily influenced by habitat or landscape features. Carnivore distribution on the landscape was not influenced much by humans or habitat, but their detectability was often positively influenced by presence of humans. In addition to daily activity, I also analyzed overlap in activity between species pairs and between species and humans, to determine whether wildlife changed their temporal activity to overlap less with similar sized competitors or in response to high human use. For herbivores and omnivores, I found that tree hyraxes and crested porcupines were active at night, Menelik's bushbucks were active at sunrise and sunset, and cape bushbucks, common duiker, olive baboon, bushpig, and giant forest hogs were active either during the day or throughout the day and night. I found little evidence that the herbivores or omnivores avoided each other temporally and only the Menelik bushbuck and duiker appeared to avoid humans. For carnivores, I found that leopards and honey badgers were active early morning and evening, and the common genet, African civet, white-tailed mongoose, and spotted hyenas were all active at night only. Carnivores generally overlapped less with humans than herbivores and omnivores. I found some evidence that carnivores more similar in body size had lower temporal overlap with each other and that spotted hyaenas appeared to avoid activity during times of day when humans were active. My study not only provides baseline information on terrestrial and arboreal mammals present in Harenna forest, Ethiopia, but is also necessary for understanding how wildlife species use the landscape and particularly how presence of humans influences wild animal behavior. My findings are concerning for biodiversity conservation because I had few to no photographs, respectively, of the endangered mountain nyala and Ethiopian wolf. In fact, most of the species with a wide distribution on the landscape, or with high activity, were common or smaller species that are tolerant of, or could take advantage of, human disturbance. Without concerted effort to curtail the current landscape change caused by humans, the area is likely to lose species less tolerant of humans, and biodiversity will ultimately decline.

This is a study of how literal and phenomenal transparency inform the development and understanding of a design ordered by two overlapping reference systems. A mixed-use building serves as the project to resolve the complexities of overlap that result from rotation, and to explore ideas of transparency. / Master of Architecture

Violence is a pervasive public health issue that disproportionately affects certain populations, particularly young black males in urban settings. Though this population experiences higher rates of violent victimization and perpetration, race should not be analyzed as an isolated variable. The social disorganization theory posits that social, cultural, and structural environmental factors shape a person’s behavior; this theory would suggest that higher rates of violence in young black men can be attributed to environmental factors rather than intrinsic traits like race. Young black males in urban settings experience high rates of poverty and institutional oppression, which primes these communities for excessive psychological trauma. The lasting effects of trauma, through Adverse Childhood Experiences and post-traumatic stress disorder, increase a person’s risk of violent victimization and perpetration, creating a cycle of violence in the community. Likewise, the high rates of firearm ownership create more opportunity for violent confrontation, especially in impoverished areas where joining a gang is perceived as one of the only options for economic and social survival as per the “Code of the Street.” In order to alleviate the burden of violence on this population, the root causes of violence, such as socioeconomic inequity and under-resourcing of disadvantaged communities, must be addressed by providing appropriate social services to those whom are most affected. / Urban Bioethics

This research investigated several aspects of passive acoustic monitoring (PAM) which were previously unexplored or understudied. A comparison of autonomous recording units (ARUs) for use with BirdNET for the purpose of bird monitoring was conducted. Four ARUs were compared, including AudioMoth, SM4, SMMicro, and SwiftOne. We found that, of the performance metrics for which ARU choice made a statistically significant difference (P>0.01), which included sensitivity, specificity, F1 harmonic mean, and Matthews Correlation Coefficient, (but not precision: P = 0.94), AudioMoth had the best performance for all statistically significant performance metrics except for specificity, for which SMMicro had the highest. The same audio was then processed using 18 combinations of Overlap and Sensitivity, including default settings. We found that Overlap and Sensitivity values were highly significant (P>0.001) for all performance metrics: precision, sensitivity, specificity, F1 harmonic mean, and Matthews Correlation Coefficient. No individual Overlap-Sensitivity setting combination performed outperformed others in most of the performance metrics; however, in general, as Overlap or Sensitivity increased, the number of true and false positive species reports increased while the number of false negatives decreased. Four confidence-based threshold types were then used to filter BirdNET output to compare threshold performances, comparing two arbitrary thresholds and two species-specific thresholds which were calculated using manual validation data. Of the thresholds tested, one of the arbitrary threshold types and one of the species-specific threshold types achieved a precision ≥ 0.95. We hope this research will help guide PAM decisions regarding ARU choice, BirdNET settings, and threshold type choice.

Estudamos neste trabalho o comportamento da impureza oxigênio em rede cristalina de silício, usando primeiramente o método INDO (lntermediate Neglect of Differential Overlap) com parametrização espectroscópica e incluímos os efeitos de muitos elétrons via Método CI-(Interacão de Configuração). Fazemos uma análise sobre as possíveis origens do posicionamento não-central (off-center) dessa impureza, - se decorrente de uma distorsão Pseudo Jahn-Teller: - se originária de um CR Reconstrução Química. Quando o átomo de Oxigênio é deslocado ao longo da direção [100] ocupa um sitio de mínimo absoluto. O oxigênio introduz no gap de banda um orbital anti-ligante de simetria a1 totalmente ocupado, situação semelhante à dos anti-sitios em materiais semi-condutores III-V. Estudamos também o comportamento dessa impureza quando a mesma é deslocada ao longo da direção [111], verificando que é criada uma posição de Instabilidade mas, os auto-valores têm comportamento não esperado para orbitais anti-ligantes. / In this work we studied the Oxygen impurity in Silicon. The calculations were performed using a semi-empirical method (INDO/S) with Configuration Interaction to account for many-electron effects. We analyse the origin of the off-center position for substitutional oxygen. Pseudo Jahn-Teller distortion or Chemical Rebonding effects. The oxygen introduces an a1 anti-bonding state in the forbidden band-gap similar to anti-site defects in III-V materials. To answer the question about distortion, we also studied oxygen dislocation in the (111) direction and we obtained a metastable state but his eigen-value has a non-expected behavior for anti-bonding orbitals.

Estudamos neste trabalho o comportamento da impureza oxigênio em rede cristalina de silício, usando primeiramente o método INDO (lntermediate Neglect of Differential Overlap) com parametrização espectroscópica e incluímos os efeitos de muitos elétrons via Método CI-(Interacão de Configuração). Fazemos uma análise sobre as possíveis origens do posicionamento não-central (off-center) dessa impureza, - se decorrente de uma distorsão Pseudo Jahn-Teller: - se originária de um CR Reconstrução Química. Quando o átomo de Oxigênio é deslocado ao longo da direção [100] ocupa um sitio de mínimo absoluto. O oxigênio introduz no gap de banda um orbital anti-ligante de simetria a1 totalmente ocupado, situação semelhante à dos anti-sitios em materiais semi-condutores III-V. Estudamos também o comportamento dessa impureza quando a mesma é deslocada ao longo da direção [111], verificando que é criada uma posição de Instabilidade mas, os auto-valores têm comportamento não esperado para orbitais anti-ligantes. / In this work we studied the Oxygen impurity in Silicon. The calculations were performed using a semi-empirical method (INDO/S) with Configuration Interaction to account for many-electron effects. We analyse the origin of the off-center position for substitutional oxygen. Pseudo Jahn-Teller distortion or Chemical Rebonding effects. The oxygen introduces an a1 anti-bonding state in the forbidden band-gap similar to anti-site defects in III-V materials. To answer the question about distortion, we also studied oxygen dislocation in the (111) direction and we obtained a metastable state but his eigen-value has a non-expected behavior for anti-bonding orbitals.

No description available.

No description available.