Examining Melt Pond Dynamics and Light Availability in the Arctic Ocean via High Resolution Satellite Imagery

As the Arctic experiences consequences of climate change, a shift from thicker, multi-year ice to thinner, first-year ice has been observed. First-year ice is prone to extensive pools of meltwater (“melt ponds”) forming on its surface, which enhance light transmission to the ocean. Changes in the timing and distribution of melt pond formation and associated increases in under-ice light availability are the primary drivers for seasonal progression of water column primary production and warming. Observations of melt pond development and distribution require meter scale resolution and have traditionally been limited to airborne images. However, recent advances in high spatial resolution satellites now allow for observations of individual melt ponds from space. Images of pack ice in the Chukchi Sea during 2018 obtained from WorldView satellite systems showed minimal melt pond coverage in June, with a rapid increase in late June, leading to saturated and flooded ice floes by mid-July. Cumulative hours above freezing (air temperature) was a stronger predictor for pond development than daily average values of temperature and irradiance and was well represented by a logistic growth curve. Size distributions (normalized to total pond area) of melt pond area was dominated by small (≤10 m2) ponds at the onset of ponding, shifting towards medium sized ponds (mode of 100 to 1,000 m2) as surface melt progressed. Late in the summer when ice flows were saturated with ponds, the distribution was skewed towards a handful of very large ponds nearing 1,000,000 m2, connected by channels which created a myriad of complex shapes. A primary production model driven by under-ice light intensity estimated from our classified images revealed that initial small increases in melt pond fraction have a large impact on potential under-ice chlorophyll growth and carbon uptake, eventually trending towards a saturating upper limit as ponds continued to spread. Results shown here offer novel insights into melt pond growth and distribution, along with estimates of how ponding impacts primary production. These conclusions showcase physical, observable consequences of an Arctic Ocean dominated by thin, first-year ice, and can be employed to advise future efforts in Arctic modeling

Electric Grid Decarbonization Pathways: Landscape Impacts, Policy Interactions, and the Need for Cooperation

Climate change has motivated governments around the world to ratify aggressive greenhouse gas emissions reduction targets. Meeting these targets will require improved energy efficiency, behavior changes, and energy system decarbonization. Many climate change and energy policy targets imply the deployment of large amounts of low carbon, renewable energy resources like wind turbines and solar photovoltaic (PV) panels but do not specify how these resources will be sited on the landscape. The relationships between weather conditions, terrain, land cover, existing electric grid infrastructure, and electricity consumers will govern how these wind and solar PV infrastructure configurations develop and how quickly they will be implemented. This dissertation develops methods for modeling policy goal-compliant wind and solar PV infrastructure configurations and their land use requirements, extends these methods to explicitly account for the resulting land use/land cover change patterns, and concludes with a macro-scale discussion of energy system geographies and their co-evolution with the societies that rely upon them in a decarbonized electric grid future. Chapters 2 and 3 each feature a case study of Vermont and its ambitious energy and emissions-related goals. We find that Vermont can meet many of these goals with less than 1% of its land area occupied by wind and solar PV infrastructure using a wide variety of infrastructure ratios and siting strategies. Chapter 4 views energy systems through the proposed ‘energyshed’ lens. We define energysheds as the geographic area over which energy is produced, refined, transported, stored, distributed, and consumed. We argue that energy system decarbonization offers opportunities to democratize and decentralize energy systems physically and administratively and that the spatial relationships between energy system infrastructure, ownership, and energy consumers will dictate the trajectory of the electric grid decarbonization process

Response of Vegetation in Open and Partially Wooded Fens to Prescribed Burning at Seney National Wildlife Refuge

The health and function of northern peatlands, particularly for fens, are strongly affected by fire and hydrology. Fens are important to several avian species of conservation interest, notably the yellow rail (Coturnicops noveboracensis). Fire suppression and altered hydrology often result in woody encroachment, altering the plant community and structure. Woody encroachment and its effects on biodiversity have become an increasing concern in the conservation and management of plant communities. This study evaluated the effects of spring and summer prescribed burns on the plant community, cover, and structure in open and partially wooded fens at Seney National Wildlife Refuge, Michigan, using a before-after-control-impact design. Paired, 1-hectare blocks were established in two fen areas, C3 and Marsh Creek, and data were collected for 2 years before burning (2006–7) and 3 years after burning (2008–10). We used generalized linear mixed models and ordination to assess differences among four treatments: C3 control, C3 spring burn (May 2008), Marsh Creek control, and Marsh Creek summer burn (July 2008); results from a block burned under drier conditions in July 2007 also are reported. Variables include water depth; litter depth; graminoid height; species richness and diversity; percent cover of plant taxa, mosses, and open area; shrub height, number of patches, and cover; and visual obstruction readings. The 2008 prescribed burns were done under moderate fire conditions, whereas the 2007 summer burn on one block was done under high fire conditions because of prolonged drought. We identified 104 plant taxa over the 5 years and noted differences between C3 and Marsh Creek communities. We examined data for effects of treatment, year, and year × treatment interactions for percent open and the 28 most common taxa. Most differences among treatments were related to natural differences in the plant community and hydrology between the two areas rather than fire effects; year effects were likely related to annual differences in water conditions. We detected few effects of spring burning in C3, even in the same year of burning. In Marsh Creek, most treatment effects were in 2008, when data were collected within 3 weeks of burning. Some fire effects there, however, persisted one to two growing seasons (2009, 2010) and two to three growing seasons in the block burned in the more intense summer 2007 fire. Effects of burning on shrub measures were more apparent on summer-burned blocks, but most measures returned to preburn conditions by 2010. Our results demonstrate the heterogeneity of plant community and environmental conditions of fens within and among years and the interactions of water conditions with burning. The results also demonstrate that neither single spring nor summer burning under moderate fire conditions are effective in setting back woody cover. Maintaining more open conditions in fens may require different approaches to water management, more frequent fires, more aggressive fire management, or a combination of tools to control woody cover

A study of the characteristics of sand movement by wind

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The synthesis and benzannulation reactions of (trialkylsilyl)vinylketenes

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, February 2008.Vita.Includes bibliographical references.(Trialkylsilyl)vinylketenes ("TAS-vinylketenes") are versatile four-carbon building blocks in a variety of methods for the synthesis of carbocyclic and heterocyclic compounds. This thesis discusses the development of a new benzannulation strategy for the synthesis of phenols based on the reaction of TAS-vinylketenes with lithium ynolates. Studies have shown that the reaction proceeds by formation and electrocyclic ring closure of 3-oxidodienylketene intermediates, followed by an intramolecular 1,3-silyl migration to provide highly substituted 3-siloxy phenols. Further transformations of these products providing efficient access to ortho-benzoquinones and benzofuran, benzoxepine, and benzoxocine ring systems are described. Additionally, unsuccessful attempts to prepare TAS-vinylketenes by the rearrangement of siloxy alkynes and by cross-metathesis are discussed.by Wesley F. Austin.Ph.D

Ultra-High-Resolution Patterning And Pattern Transfer Via Nanocrystal Colloidal Lithography

The ability to design, pattern, and process materials at the nanoscale has enabled vast research opportunities ranging from fundamental science to technological applications and device integration. The continued development of nanoscience and nanotechnology relies on pushing the limits of nanoscale fabrication capabilities. After decades of development, this frontier has moved to the sub-10 nm length scale to explore novel physical properties and functionalities for next-generation technology. However, conventional “top-down” strategies that have carried nanofabrication to this point have severe limitations for practically improving the resolution capabilities of deep nanoscale fabrication. In this dissertation, we demonstrate ultra-high-resolution patterning and pattern transfer using nanocrystal (NC) colloidal lithography. This innovative nanofabrication platform integrates bottom-up methods, that combine NC synthesis and self-assembly approaches, with well-established top-down techniques such as dry etching and thin film deposition. We employ monodisperse NC building blocks with self-assembly methods to establish high-density, well-ordered patterns, where the inorganic core of each NC serves as a discrete hard mask used for high-fidelity pattern transfer into a desired substrate material. We demonstrate the use of isotropic NCs to establish various sub-10 nm pattern morphologies and examine the stability of the NC pattern upon dry etching, comparing NC monolayers and bilayers. We extend the NC colloidal lithography scheme using anisotropic NCs to demonstrate high-density, anisotropic pattern transfer into various substrate materials down to the sub-5 nm regime. The presented fabrication strategy offers further opportunities to leverage various combinations of NC morphologies and materials afforded by the extensive NC library for more complex pattern design. Additionally, this approach can be extended to process various substrate material classes at the deep nanoscale. The NC colloidal lithography platform enables broader access to single-digit nanoscale fabrication for the scientific community worldwide, which could impact various research sectors ranging from integrated circuits to memory devices, optoelectronics, metasurfaces, quantum devices and more

Accreditation and certification in the non-profit sector: organizational and economic implications

The non-profit sector of the US economy is a special class of entities with an expansive array of organizations and activities dedicated to the common good and well-being of others. Even though this sector has constructed creative and forward thinking initiatives, obstacles remain which interfere with the accomplishment of significant achievements. In order to stay competitive, non-profit organizations are constantly assessing their current capacity to deliver unique needed services. Today, many umbrella associations of non-profits have implemented accreditation and certification programs intended to improve organizational contribution to member organizations. Throughout the sector, non-profit organizations are now seeking to become more ethical, accountable and credible in the eyes of stakeholders. Guided by institutional and agency theories, the research reported herein is designed to offer preliminary insights regarding the organizational and economic implications of pursuing accreditation. Technological enhancements in this context are also examined