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regularity for a class of averaging operators on the Heisenberg group
We prove boundedness for averaging operators
associated to a class of curves in the Heisenberg group via
estimates for related oscillatory integrals and Bourgain-Demeter
decoupling inequalities on the cone. We also construct a Sobolev space adapted
to translations on the Heisenberg group to which these averaging operators map
all functions boundedly.Comment: 28 Page
Regularity Estimates for a Class of Integral Operators with Fold Blowdown Singularities
We prove sharp regularity results for a class of generalized Radon
transforms for families of curves in a three-dimensional manifold associated to
a canonical relation with fold and blowdown singularities. The proof relies on
decoupling inequalities by Wolff and Bourgain-Demeter for plate decompositions
of thin neighborhoods of cones and estimates for related oscillatory
integrals.Comment: 31 pages. Reorganized the proof of Proposition 4. Revised version
incorporating referee's suggestions. To appear in The Journal of Geometric
Analysi
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Accounting For Biotic Variability In Streams With Low Levels of Impervious Cover: The Role of Reach- and Watershed-Scale Factors
As landscapes become increasingly urbanized, there is an associated increase in impervious cover. Impervious surfaces, such as roads, rooftops, and parking lots contribute to the physical, hydrological, chemical, and biological alteration of stream systems. Biotic assemblages consistently degrade with increased watershed impervious cover; however, at low levels of impervious cover, these assemblages exhibit wide variability in biotic integrity. This study investigated which reach- and watershed-scale factors explained biotic condition (i.e., richness, flow traits, thermal traits, and tolerance for macroinvertebrates and fishes) at similar levels of low imperviousness. The primary objective was to identify factors that confer resistance for biota, such that they retain high biotic integrity at low levels of impervious cover, and, conversely, to determine which factors make biota more vulnerable to urban disturbance, such that they have low biotic integrity despite low levels of impervious cover. Forty sites were selected across Massachusetts within two narrow bands of impervious cover: 1–4% (n = 20) and 7–10% (n = 20). Models with reach-scale variables (reflecting habitat heterogeneity, flow, temperature, or water quality) or watershed-scale variables (representing natural characteristics, land use, flow alterations, and other measures of urbanization or impervious) explained additional variance compared to models with impervious cover alone. Reach-scale factors tended to explain more variance than watershed-scale factors for all biotic responses except fluvial fishes, with overall more variance explained for fish than macroinvertebrate assemblages. At the reach scale, colder water temperatures, higher dissolved oxygen, and more large wood were related to higher proportions of fluvial, coldwater, and intolerant fishes. For macroinvertebrates, warmer water temperature, smaller sediment size, and higher nitrate were related to higher macroinvertebrate richness and tolerance. At the watershed scale, air temperature emerged as an important predictor for both taxonomic groups and across response metrics; air temperature was highly correlated with high-elevation watersheds. Other important watershed-scale predictors were open water and dams, flow alteration, and other urban measures such as housing density, impervious in a 120-m buffer, and road crossings. Restoration should focus on strategies to reduce impacts that would degrade in-stream conditions that allow for higher biotic integrity, such as habitat heterogeneity, more large wood, and colder water temperatures. Similarly, watersheds should be prioritized for protection with those characteristics potentially more resistant to urban disturbance, such as high-elevation regions that retained high biotic integrity despite higher dam density, more road crossings, and more flow alteration
Diffuse Reflection of Light
This thesis describes an attempt to determine the feasibility of measuring the ozone content in the air by absorption of light over a long path
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