The geological record of life 3500 Ma ago: Coping with the rigors of a young earth during late accretion

Thin cherty sedimentary layers within the volcanic portions of the 3,500 to 3,300 Ma-old Onverwacht and Fig Tree Groups, Barberton Greenstone belt, South Africa, and Warrawoona Group, eastern Pilbara Block, Western Australia, contain an abundant record of early Archean life. Five principal types of organic and probably biogenic remains and or structures can be identifed: stromatolites, stromatolite detritus, carbonaceous laminite or flat stromalite, carbonaceous detrital particles, and microfossils. Early Archean stromatolites were reported from both the Barberton and eastern Pilbara greenstone belts. Systematic studies are lacking, but two main morphological types of stromatolites appear to be represented by these occurrences. Morphology of the stromalites is described. Preserved early Archean stromatolites and carbonaceous matter appear to reflect communities of photosynthetic cyanobacteria inhabiting shallow, probably marine environments developed over the surfaces of low-relief, rapidly subsiding, simatic volcanic platforms. The overall environmental and tectonic conditions were those that probably prevailed at Earth's surface since the simatic crust and oceans formed sometime before 3,800 Ma. Recent studies also suggest that these early Archean sequences contain layers of debris formed by large-body impacts on early Earth. If so, then these early bacterial communities had developed strategies for coping with the disruptive effects of possibly globe-encircling high-temperature impact vapor clouds, dust blankets, and impact-generated tsunamis. It is probable that these early Archean biogenic materials represent organic communities that evolved long before the beginning of the preserved geological record and were well adapted to the rigors of life on a young, volcanically active Earth during late bombardment. These conditions may have had parallels on Mars during its early evolution

Evidence for and implications of an Early Archean terrestrial impact record

Early Archean, 3.5 to 3.2 Ga, greenstone sequences in South Africa and Western Australia contain a well-preserved record of early terrestrial meteorite impacts. The main impact-produced deposits are layers, 10 cm to over 1 m thick, composed largely of sand-sized spherules, 0.1 to 4 mm in diameter. The beds studied to date show an assemblage of features indicating formation by the fall of debris from impact-generated ejecta clouds. Some presented data effectively rule out normal magmatic or sedimentary processes in the origin of these units and provide substantial support for an origin by large impacts on the early earth. The presence of at least four, remarkably thick, nearly pure spherule layers suggests that smaller-scale impact deposits may be even more abundant in these sequences. The existence of a well-preserved Archean terrestrial impact record suggests that a direct source of evidence is available regarding a number of important aspects of early earth history

I Need to See Me on TV: Parasocial Affirmations of Sexual and Gender Identity Development of LGBTQ+ Mass Media Consumers

This dissertation presents a new cycle model of media usage by LGBTQ+ community members in the United States that reveals a purpose previously unnamed and undefined. While parasocial contact, parasocial interaction, and parasocial relationships have been present in the academic literature for quite some time (as early as 1956 when Horton and Wohl first wrote of the phenomenon), use of media to parasocially affirm one’s LGBTQ+ status is unique to this study. This study used qualitative methods to examine a specific mass media audience, LGBTQ+ individuals, and asked them, in one-on-one interviews, how they utilize mass media to assist with their sexual and gender identity development. Participants in this study spoke of a moment of realization of the existence of LGBTQ+ identities and the stigma associated with those identities prior to their recognition or realization of their own sexual and gender identities. Additionally, they reported that no connection was made between this realization and their own sexual and gender identity at the time of this discovery. Participants then reported a variety of time frames passed before their own realizations (i.e., from as little as a few weeks up to 10 years). Next, participants spoke of their own realizations. At this point, most participants spoke of the stigma and fears associated with LGBTQ+ sexual and gender identities. Decisions were made by all to keep their realizations private. This self-imposed lack of interpersonal communication (created under real or imagined rejection scenarios) revealed a need to seek affirmation in more impersonal settings. Arguably, the most important finding is that: instead of parasocial interactions or parasocial relationships participants reported parasocial affirmations. Parasocial affirmations are defined by this dissertation as usage experiences of media characters/personalities that allow for visualization of self-acceptance. But viewing one media depiction or one interpersonal interaction is not enough to affirm one’s sexual and/or gender identity. These affirming associations in turn create a need for additional experiences and the process starts again. The affirmations include information about successful negotiation of sexual and/or gender identity and therefore, affirming their own sexual and gender identity. This process runs from as little as a few days to many years until the individual is secure enough to engage interpersonally with others about their sexual and gender identity. Theoretical implications of this dissertation include an extension of the parasocial interaction/relationship theory with the addition of parasocial affirmations. Practical implications of this dissertation describe how LGBTQ+ community members, allies, social workers, school counselors etc., could use these findings to enhance coping skills of LGBTQ+ community members. Additionally, mass media producers could use these findings to guide their creation of LGBTQ+ inclusive and supportive products

High efficiency thermal to electric energy conversion using selective emitters and spectrally tuned solar cells

Thermophotovoltaic (TPV) systems are attractive possibilities for direct thermal-to-electric energy conversion, but have typically required the use of black body radiators operating at high temperatures. Recent advances in both the understanding and performance of solid rare-earth oxide selective emitters make possible the use of TPV at temperatures as low as 1500 K. Depending on the nature of parasitic losses, overall thermal-to-electric conversion efficiencies greater than 20 percent are feasible

Sedimentology of the ~3.3 Ga upper Mendon Formation, Barberton Greenstone Belt, South Africa

The Mendon Formation is the uppermost unit of the 3.5-3.26 Ga Onverwacht Group in the Barberton Greenstone Belt, South Africa. It consists of a cyclic stack of komatiitic volcanic units separated by thin cherty sedimentary layers. In most areas, the uppermost Mendon Formation is a sedimentary interval characterized by black chert, banded black-and-white chert, and banded ferruginous chert, although the detailed patterns of lithofacies in different sections are more complex. Previously reported zircon U/Pb ages suggest that Mendon deposition could represent more than 70 Myr of time between ∼3,334 Ma and ∼3,260 Ma. This study presents sedimentological and petrographic observations of the upper Mendon Formation from across the central part of the Barberton Greenstone Belt in order to investigate sediment sources, depositional processes, and environments of sedimentation. The dominant mode of sedimentation was quiet settling of carbonaceous grains and, in the deepest sections below storm wave base, fine ferruginous material, resulting in finely laminated black and grey chert. In situ carbonaceous laminations are rare, suggesting that benthic microbial mat growth had little direct influence on deposition. The hemipelagic background deposition was punctuated by occasional inputs of fine pyroclastic debris, formation and deposition of silica granules, and reworking by infrequent storm events. Storm deposits are represented by coarse-grained, poorly-sorted intraclast breccias, some of which include distinctive intraclasts sampling lithofacies that are not observed in situ. Despite considerable lateral variability, correlative temporal trends are resolvable in many Mendon sections: there is an upward-deepening of the overall depositional setting recorded in the oldest upper Mendon sections, consistent with the previous interpretation that Mendon time was characterized by rifting ( Lowe, 1994a; Lowe, 1999a). Younger Mendon cycles include thick, relatively ferruginous basal sections, interpreted to reflect the deepest water deposition. These sections are capped by black chert and silicified ashes with more evidence of disturbance and reworking by storms, reflecting gradual shoaling. This sedimentological analysis is broadly consistent with previous geochemical and tectonic analyses and provides a better picture of depositional patterns during uppermost Onverwacht time, before the distinct change in tectonic regime marked by impact spherule layer S2 and the onset of Fig Tree Group orogenesis and related siliciclastic deposition

Thin-Film Selective Emitter

Direct conversion of thermal energy into electrical energy using a photovoltaic cell is called thermophotovoltaic energy conversion. One way to make this an efficient process is to have the thermal energy source be an efficient selective emitter of radiation. The emission must be near the band-gap energy of the photovoltaic cell. One possible method to achieve an efficient selective emitter is the use of a thin film of rare-earth oxides. The determination of the efficiency of such an emitter requires analysis of the spectral emittance of the thin film including scattering and reflectance at the vacuum-film and film-substrate interfaces. Emitter efficiencies (power emitted in emission band/total emitted power) in the range 0.35-0.7 are predicted. There is an optimum optical depth to obtain maximum efficiency. High emitter efficiencies are attained only for low (less than 0.05) substrate emittance values, both with and without scattering. The low substrate emittance required for high efficiency limits the choice of substrate materials to highly reflective metals or high-transmission materials such as sapphire

Application of Kinetic Relationships to Phenol Removal in the Activated Sludge Process

Bioenvironmental Engineerin

Texture-specific Si isotope variations in Barberton Greenstone Belt cherts record low temperature fractionations in early Archean seawater

Sedimentary cherts are unusually abundant in early Archean (pre-3.0 Ga) sequences, suggesting a silica cycle that was profoundly different than the modern system. Previously applied for the purpose of paleothermometry, Si isotopes in ancient cherts can offer broader insight into mass fluxes and mechanisms associated with silica concentration, precipitation, diagenesis, and metamorphism. Early Archean cherts contain a rich suite of sedimentological and petrographic textures that document a history of silica deposition, cementation, silicification, and recrystallization. To add a new layer of insight into the chemistry of early cherts, we have used wavelength-dispersive spectroscopy and then secondary ion mass spectrometry (SIMS) to produce elemental and Si and O isotope ratio data from banded black-and-white cherts from the Onverwacht Group of the Barberton Greenstone Belt, South Africa. This geochemical data is then interpreted in the framework of depositional and diagenetic timing of silica precipitation provided by geological observations. SIMS allows the comparison of Si and O isotope ratios of distinct silica phases, including black carbonaceous chert beds and bands (many including well-defined sedimentary grains), white relatively pure chert bands including primary silica granules, early cavity-filling cements, and later quartz-filled veins. Including all chert types and textures analyzed, the δ^(30)Si dataset spans a range from −4.78‰ to +3.74‰, with overall mean 0.20‰, median 0.51‰, and standard deviation 1.30‰ (n = 1087). Most samples have broadly similar δ^(30)Si distributions, but systematic texture-specific δ^(30)Si differences are observed between white chert bands (mean +0.60‰, n = 750), which contain textures that represent primary and earliest diagenetic silica phases, and later cavity-filling cements (mean −1.41‰, n = 198). We observed variations at a ∼100 μm scale indicating a lack of Si isotope homogenization at this scale during diagenesis and metamorphism, although fractionations during diagenetic phase transformations may have affected certain textures. We interpret these systematic variations to reflect fractionation during silica precipitation as well as isotopically distinct fluids from which later phases originated. SIMS δ^(18)O values fall in a range from 16.39‰ to 23.39‰ (n = 381), similar to previously published data from bulk gas source mass spectrometry of Onverwacht cherts. We observed only limited examples of texture-related variation in δ^(18)O and did not observe correlation of δ^(18)O with δ^(30)Si trends. This is consistent with hypotheses that Si isotope ratios are more resistant to alteration under conditions of rock-buffered diagenesis (Marin-Carbonne et al., 2011). Our results indicate that low temperature processes fractionated silicon isotopes in early Archean marine basins, a behavior that probably precludes the application of chert δ^(30)Si as a robust paleothermometer. The values we observe for facies that sedimentological and petrographic observations indicate formed as primary and earliest diagenetic silica precipitates from seawater are more ^(30)Si-rich than that expected for bulk silicate Earth. This is consistent with the hypothesis that the silicon isotope budget is balanced by the coeval deposition of ^(30)Si-enriched cherts and ^(30)Si-depleted iron formation lithologies. Precipitation of authigenic clay minerals in both terrestrial and marine settings may have also comprised a large ^(30)Si-depleted sink, with the corollary of an important non-carbonate alkalinity sink consuming cations released by silicate weathering

The Effect of Temperature on the Radiative Performance of Ho-Yag Thin Film Selective Emitters

We present the emitter efficiency results for the thin film 25 percent Ho YAG (Yttrium Aluminum Garnet, Y3Al5O12) selective emitter from 1000 to 1700 K with a platinum substrate. Spectral emittance and emissive power measurements were made (1.2 less than lambda less than 3.2 microns) and used to calculate the radiative efficiency. The radiative efficiency and power density of rare earth doped selective emitters are strongly dependent on temperature and experimental results indicate an optimum temperature (1650 K for Ho YAG) for thermophotovoltaic (TPV) applications

High efficiency direct thermal to electric energy conversion from radioisotope decay using selective emitters and spectrally tuned solar cells

Thermophotovoltaic (TPV) systems are attractive possibilities for direct thermal-to-electric energy conversion, but have typically required the use of black body radiators operating at high temperatures. Recent advances in both the understanding and performance of solid rare-earth oxide selective emitters make possible the use of TPV at temperatures as low as 1200K. Both selective emitter and filter system TPV systems are feasible. However, requirements on the filter system are severe in order to attain high efficiency. A thin-film of a rare-earth oxide is one method for producing an efficient, rugged selective emitter. An efficiency of 0.14 and power density of 9.2 W/KG at 1200K is calculated for a hypothetical thin-film neodymia (Nd2O3) selective emitter TPV system that uses radioisotope decay as the thermal energy source