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Reoxidation and mobilization of previously reduced and immobilized uranium by dissolved-phase oxidants poses a significant challenge for remediating uranium-contaminated groundwater. Preferential oxidation of reduced sulfur-bearing species, as opposed to reduced uranium-bearing species, has been demonstrated to limit the mobility of uranium at the laboratory scale yet field-scale investigations are lacking. In this study, the mobility of uranium in the presence of nitrate oxidant was investigated in a shallow groundwater system after establishing conditions conducive to uranium reduction and the formation of reduced sulfur-bearing species. A series of three injections of groundwater (200 L) containing U(VI) (5 μM) and amended with ethanol (40 mM) and sulfate (20 mM) were conducted in ten test wells in order to stimulate microbial-mediated reduction of uranium and the formation of reduced sulfur-bearing species. Simultaneous push-pull tests were then conducted in triplicate well clusters to investigate the mobility of U(VI) under three conditions: 1) high nitrate (120 mM), 2) high nitrate (120 mM) with ethanol (30 mM), and 3) low nitrate (2 mM) with ethanol (30 mM). Dilution-adjusted breakthrough curves of ethanol, nitrate, nitrite, sulfate, and U(VI) suggested that nitrate reduction was predominantly coupled to the oxidation of reduced-sulfur bearing species, as opposed to the reoxidation of U(IV), under all three conditions for the duration of the 36-day tests. The amount of sulfate, but not U(VI), recovered during the push-pull tests was substantially more than injected, relative to bromide tracer, under all three conditions and further suggested that reduced sulfur-bearing species were preferentially oxidized under nitrate-reducing conditions. However, some reoxidation of U(IV) was observed under nitrate-reducing conditions and in the absence of detectable nitrate and/or nitrite. This suggested that reduced sulfur-bearing species may not be fully effective at limiting the mobility of uranium in the presence of dissolved and/or solid-phase oxidants. The results of this field study confirmed those of previous laboratory studies which suggested that reoxidation of uranium under nitrate-reducing conditions can be substantially limited by preferential oxidation of reduced sulfur-bearing species.

Owing to its amorphous structure, a chalcogenide glass exhibits a thermal conductivity k approaching the theoretical minimum of its composition, called the Einstein’s limit. In this work, this limit is beaten in an amorphous solid consisting of glassy particles joined by nanosized contacts. When amorphous particles are sintered below the glass transition temperature under a high pressure, these particles can be mechanically bonded with a minimized interfacial thermal conductance. This reduces the effective k below the Einstein’s limit while providing superior mechanical strength under a high pressure for thermal insulation applications under harsh environments. The lowest room temperature k for the solid counterpart can be as low as 0.10 W/m·K, which is significantly lower than k≈0.2 W/m·K for the bulk glass.

Author(s): Doughty, C; Oldenburg, CM | Abstract: Uncertainty in the long-term fate of CO2 injected for geologic carbon sequestration (GCS) is a significant barrier to the adoption of GCS as a greenhouse-gas emission-mitigation for industry and regulatory agencies alike. We present a modeling study that demonstrates that the uncertainty in forecasts of GCS site performance decreases over time as monitoring data are used to update operational models. We consider a case study of GCS in a depleted natural gas reservoir, with CO2 injection occurring over 20 years, with a 50-year post-injection site care period. We constructed a detailed model to generate the actual model output, which is considered synthetic observation data. A series of simpler operational models based on limited data and assumptions about how an operator would model such a site are then run and compared against actual model output at specific monitoring points after one year, two years, etc. The operational model is updated and improved using the synthetic observation data from the actual model at the same time intervals. Model parameter values and model features needed to be updated over time to improve matches to the actual model. These kinds of model adjustments would be a normal part of reservoir engineering and site management at GCS sites. Uncertainty in two key measures related to site performance decreases with time: extent of the CO2 plume up-dip migration, and radial extent of the pressure pulse. This conclusion should help allay the concerns of industry and regulators about uncertainty in long-term fate of CO2 at GCS sites.

While science matters for environmental management, creating science that is credible, salient to decision-makers, and deemed legitimate by stakeholders is challenging. Collaborative modeling is an increasingly-used approach to enable effective science-based decision-making. This work evaluates the modeling process conducted for two hydropower dam licensing negotiations, to explore how differences in the collaborative development of hydrological models affected differences in their use in subsequent decision-making. In one case, the model was developed iteratively through deliberation with stakeholders. Consequently, stakeholders understood the model and its limitations and trusted the model and modelers; the model itself was also better designed to evaluate resource managers’ questions. The collaboratively-developed model became the focal point for subsequent negotiations and enabled creative group problem-solving. Conversely, in the case with less engagement during model development, the model was not used subsequently by decision-makers. These differences are argued to result from trust built during the modeling process, applicability of the model to test real management scenarios, and the broader social context in which the models were used.

Walking is the main mode of transportation for many of the world's people, particularly those in cities of the majority world. In the metropolitan region of Jakarta, walking in the public realm constitutes the main transportation mode for almost 40 percent of trips--a massive contribution to urban mobility. On the other hand, there is no comprehensive planning for pedestrians in an analogous manner to other modes of transportation. Pedestrian facilities are often dilapidated, damaged, dangerous, or missing completely. Additionally, there is no process for assessing the inventory of pedestrian facilities, planning pedestrian facilities at a region-wide level, or even identifying the location of vernacular pedestrian routes in low-income and informal areas. Provincial pedestrian planning focuses on piecemeal, symbolic spaces such as monumental plazas that serve the nation-building project, but overlooks the functional network of routes that address the daily needs of the city's residents. This dissertation examines the issue of walkability planning in Jakarta by investigating what matters to pedestrians and how pedestrian space is produced. The research employs mixed methods, including pedestrian network groundtruthing, structured streetscape observations, multimodal traffic counts, pedestrian activity mapping, pedestrian surveys and interviews with policy-makers. Data is analyzed through a combination of in-depth qualitative analysis as well as quantitative and statistical analysis. Based on this research, six key elements of walkability planning are proposed for Jakarta: multidisciplinarity, ethnography, accessibility, legibility, integrated activity, and shared streets. A literature review of walkability metrics reveals that walking is a highly multidisciplinary activity, with very different metrics emerging from different fields. In order to effectively encourage pedestrian activity, new multidisciplinary metrics should integrate the perspectives of all of these related disciplines and pedestrian planning should occur through inter-agency coordination. In Jakarta, interviews with policy-makers suggested that pedestrian planning is hindered by the fact that there is no lead agency for pedestrian planning, and there is a lack of cooperation between the different agencies that plan and produce urban public space. Pedestrian planning is also hindered by a discursive framework that is both modally and geographically biased--favoring motorized, long-distance modes of transportation and employing method derived from a Western research and planning norms. In order to overcome this discursive bias, ethnography should become a standard part of urban research, planning and design. The need for ethnography and qualitative analysis was made visible by the mismatch between standard transportation terminology, and prevailing practices observed in pedestrian mapping exercises and raised by pedestrians in on-the-street interviews. For example, standard survey categories do not account for informal or integrated activity patterns like mobile street vending. From surveys conducted with mobile street vendors, it was difficult to separate their pedestrian activities into categories of travel from home to work, business-related travel, and visiting friends and relatives. In fact, it was difficult to even separate their travel from their activities since many vendors carried out business as they made their way through the neighborhood. With a large portion of the population engaged in the informal sector, the discrepancy between assumed and actual behavior severely compromises the quality of transportation-related research that is conducted in Jakarta and many other majority world cities. Ethnographic and qualitative research methods may therefore assist in producing more context-sensitive planning data and outcomes. These context-sensitive methods could include new analytical methods that focus on integrated activity, rather than trip-based or activity-based analysis. In relation to pedestrian activity, context-sensitive planning encompasses new approaches to accessibility that combine the notion of transportation accessibility with disabled access and universal access standards. The need for such an approach was revealed during interviews with policy-makers, who described accessibility in terms of market goods rather than human rights. Within the market for urban public space, ordinary pedestrians were unable to compete with other modes of transportation; within the market for urban impressions, ordinary pedestrian spaces were outcompeted by prominent, symbolic spaces; and within the market for cultural capital, ordinary pedestrians were excluded from planning processes because even the discourse of pedestrian planning was inaccessible to regular residents. In response to this problem of exclusion, integrated accessibility may facilitate inclusion in both planning processes and urban spaces within the city. In particular, integrated accessibility would aim to provide comprehensive routes of travel for all pedestrians, rather than isolated pockets of so-called accessible (yet unreachable) facilities. More context sensitive planning would also be facilitated through greater legibility of fine-grained and vernacular pedestrian networks that were missing from standard planning maps. These fine-grained networks represent highly connected facilities that serve much of Jakarta's pedestrian transportation task. While the current synoptic illegibility of these areas may conveniently allow some communities to avoid state intrusion, it also means that low-income populations are chronically underserved with respect to basic urban planning and services. Increased legibility therefore allows for improvement and maintenance of urban systems like safe, functional pedestrian networks, and it may also play a role in increasing tenure security for Jakarta's significant floating population. In many of these vernacular spaces, new street design approaches would also benefit pedestrians, who tend to use the streets as shared spaces, rather than spaces that are rigidly segregated by mode. Pedestrian activity mapping revealed that only an overwhelming majority of pedestrians used streets as hybrid spaces, with activity types falling into the categories of surface-sensitive, risk-averse, distance-minimizing and stationary pedestrians. More realistic shared street designs would therefore accommodate--rather than ignore--the types of activities that occur along Jakartan streets. Design standards for "great streets" in Jakarta would also emphasize the safe sharing of streets through self-enforcing approaches to speed limits, and the integration of various urban elements like drainage, mobility and public-private interaction. While walkability planning in Jakarta displays many "wicked problem" features, there is much that can be done to improve, if not resolve, conditions for pedestrians within the region. Recommended strategies for walkability planning in Jakarta include a regional walkability plan and environmental policy developed using participatory planning, reformed governance and institutional arrangements, and a constituency building approach. The strategies also include expansion of road designations and an integrated accessibility strategy that draws upon new data sources from a WikiPlaces network map, an integrated activity study and pedestrian network cost-benefit analysis. In addition to Jakarta-specific proposals, a number of proposals are made to advance discourse on walkability more generally. These approaches include decentered analysis of integrated activity, informal economic activity analysis, vernacular placemaking and Asian shared street design. Pedestrians and pedestrian plans traverse diverse physical, administrative and disciplinary spaces in cities of the world. Integrated and multidisciplinary approaches are therefore required to understand and accommodate these key users of public space. In Jakarta, walkability planning has potential to improve urban transportation efficiency while contributing to traffic safety, economic vitality, environmental quality and democratic governance. Successful walkability planning in Jakarta may also provide a model for planning in other cities where Western models of planning are unrealistic, inequitable and inappropriate. Jakartan lessons on walkability planning are particularly relevant, and improvements in walkability are particularly powerful, for cities characterized by relatively low median incomes, high land use densities, a substantial informal sector, rapid urbanization and rapid motorization. By improving walkability planning in Jakarta and other cities of the majority world, policy-makers and planners can move toward more sustainable, socially equitable and efficient cities.

Massive, long-lived deep-sea red tree corals (Primnoa pacifica) form a solid, layered axis comprised of calcite and gorgonin skeleton. They are abundant on the outer continental shelf and upper slope of the Northeast Pacific, providing habitat for fish and invertebrates. Yet, their large size and arborescent morphology makes them susceptible to disturbance from fishing activities. A better understanding of their growth patterns will facilitate in-situ estimates of population age structure and biomass. Here, we evaluated relationships between ages, growth rates, gross morphological characteristics, and banding patterns in 11 colonies collected from depths of ~141–335 m off the Alaskan coast. These corals ranged in age from 12 to 80 years old. They grew faster radially (0.33–0.74 mm year-1) and axially (2.41–6.39 cm year-1) than in previously measured older colonies, suggesting that growth in P. pacifica declines slowly with age, and that basal diameter and axial height eventually plateau. However, since coral morphology correlated with age in younger colonies (< century), we developed an in-situ age estimation technique for corals from the Northeast Pacific Ocean providing a non-invasive method for evaluating coral age without removing colonies from the population. Furthermore, we determined that annual bands provided the most accurate means for determining coral age in live-collected corals, relative to radiometric dating. Taken together, this work provides insight into P. pacifica growth patterns to inform coastal managers about the demographics of this ecologically important species. With this new ability to estimate the age of red tree corals in-situ, we can readily determine the age-class structure and consequently, the maturity status of thickets, using non-invasive video survey techniques when coupled with mensuration systems such as lasers or stereo-cameras. Enhanced surveys could identify which populations are most vulnerable to disturbance from human activities, and which should be highlighted for protection.

The goal of the work in this dissertation is to understand and overcome the limiting optoelectronic processes in emerging second generation photovoltaic devices. There is an urgent need to mitigate global climate change by reducing greenhouse gas emissions. Renewable energy from photovoltaics has great potential to reduce emissions if the energy to manufacture the solar cell is much lower than the energy the solar cell generates. Two emerging thin film solar cell materials, organic semiconductors and hybrid organic-inorganic perovskites, meet this requirement because the active layers are processed at low temperatures, e.g. 150 °C. Other advantages of these two classes of materials include solution processability, composted of abundant materials, strongly light absorbing, highly tunable bandgaps, and low cost.Organic solar cells have evolved significantly from 1% efficient devices in 1989 to 11% efficient devices today. Although organic semiconductors are highly tunable and inexpensive, the main challenges to overcome are the large exciton binding energies and poor understanding of exciton dynamics. In my thesis, I optimized solar cells based on three new solution processable azadipyrromethene-based small molecules. I used the highest performing molecule to study the effect of increasing the permittivity of the material by incorporating a high permittivity small molecule into the active layer. The studies on two model systems, small donor molecules and a polymer-fullerene bulk heterojunction, show that Frenkel and charge transfer exciton binding energies can be manipulated by controlling permittivity, which impacts the solar cell efficiency.Hybrid organic-inorganic perovskite materials have similar advantages to organic semiconductors, but they are not excitonic, which is an added advantage for these materials. Although photovoltaics based on hybrid halide perovskite materials have exceeded 20% efficiency in only a few years of optimization, the loss mechanisms are not understood but critical to systematically improve the efficiency towards the theoretical limit. Thus, I correlated morphology to local power conversion efficiency determining properties by mapping local short circuit current, open circuit voltage, and dark drift current in state-of-the-art methylammonium lead iodide solar cells with sub-30 nm spatial resolution using photoconductive atomic force microscopy. I found, within individual grains, spatially-correlated heterogeneity in short circuit current and open circuit voltage. This heterogeneity is attributed to a facet-dependent density of trap states. These results imply that controlling crystal grain and facet orientation will enable a systematic optimization of hybrid halide perovskite photovoltaics.