This dissertation consists of three empirical essays of which contributions consist, first, in developing spatial weight matrices based on more than just pure geographical proximity for the modeling of interregional externalities. Second, my essays propose different approaches to discover spatial heterogeneity in the data generating processes, including the interregional externalities, under investigation. This dissertation provides Economic Geographers and Regional Scientists interested in the modeling and measurement of spatial externalities a set of practical examples based on new datasets and state-of-the-art spatial econometric techniques to consider for their own work. I hope my dissertation will provide them with some guidance on how various aspects of spatial externalities can be incorporated in traditional spatial weight matrices and of how much the impact of externalities can be spatially heterogeneous. The results of the dissertation should help spatial and regional policy makers to understand better various aspects of interregional dependence in regional economic systems and to devise locally effective and place-tailored spatial and regional policies. The first essay investigates the negative spatial externalities of irrigation on corn production. The spatial externalities of irrigation water are well known but have never been examined in a spatial econometric framework so far. We investigate their role in a theoretical model of profit-maximizing farming and verify our predictions empirically in a crop production function measured across US Corn Belt counties. The interregional groundwater and surface water externalities are modeled based on actual aquifer and river stream network characteristics. The second essay examines the positive spatial externalities of academic and private R&D spending in the frame of a regional knowledge production function measured across US counties. It distinguishes the role of local knowledge spillovers that are determined by geographical proximity from distant spillovers that we choose to capture through a matrix of patent creation-citation flows. The advantage of the latter matrix is its capacity to capture the technological proximity between counties as well as the direction of knowledge spillovers. These two elements have been missed in the literature so far. The last essay highlights and measures the presence of spatial heterogeneity in the marginal effect of the innovation inputs, more especially of the interregional knowledge spillovers. The literature of knowledge production function has adopted geographically aggregated units and controlled for region-specific conditions to highlight the presence of spatial heterogeneity in regional knowledge creation. However, most empirical studies have relied on a global modeling approach that measures spatially homogenous marginal effects of knowledge inputs. This essay explains the source of the heterogeneity in innovation and then measures the spatial heterogeneity in the marginal effects of knowledge spillovers as well as of other knowledge input factors across US counties. For this purpose, the nonparametric local modeling approaches of Geographically Weighted Regression (GWR) and Mixed GWR are used.

Rates of microbial reactions are important in understanding groundwater chemistry and bioremediation. In aquifers, microbial rates depend on physicochemical and biological factors and also on how groundwater transport impacts microbial reactions at pore-scale. I numerically simulate microbial acetate consumption in a porous medium, focusing on how physical heterogeneity of the medium impacts the rates. My model is a 3-D cube, which represents a portion of a sandy aquifer. Acetate is supplied by groundwater flow through the cube, and microbes live on randomly distributed grain surfaces by oxidizing acetate. I simulated microbial acetate oxidation under a range of groundwater velocity, acetate concentrations, spatial heterogeneity, and other physicochemical conditions. The results demonstrate a significant gap in microbial kinetics between the pore-scale and continuum model. Specifically, microbial rates are larger in porous media of greater heterogeneity. For this reason, I propose that microbial parameters should not be applied directly to field-scale biogeochemical modeling.

Genetic differentiation in phenotypic traits among populations from heterogeneous environments is often observed in common-garden studies on forest trees, but data on adaptive variation in Scots pine (Pinus sylvestris L.) in Scotland are limited. As a result, current seed transfer guidelines are based on earlier molecular marker studies and do not take into account environmental or adaptive genetic variation. An analysis of spatial variation in climate showed substantial differences in temperature and precipitation among the native Scots pine sites in Scotland. To investigate whether differentiation in response to environmental variation has occurred in Scotland, a glasshouse-based common-garden trial of ~3,360 seedlings from 21 populations and 84 open-pollinated families was established in 2007. At the beginning of the 2nd growing season, timing of bud flush showed evidence of genetic differentiation among populations, with those from cooler origins generally flushing earlier. Variation was also found among families within populations, suggesting that the trait is genetically controlled. Populations and families showed different levels of variability in this trait which could be partly due to variable levels of temporal climate fluctuation in different parts of Scotland. Chlorophyll fluorescence was used to examine drought response in three-year old seedlings from five populations on sites that experience contrasting levels of annual rainfall. It was found that the response was not related to rainfall, but possibly to more complex moisture variables that also take into account additional factors such as evaporation. Also, photosynthetic capacity in response to cold winter temperatures varied significantly among eight populations that were kept outdoors, and the largest reduction was seen in seedlings from the mildest, most maritime coastal site. The following spring, height growth and needle flush started earlier in seedlings from cooler locations. Earlier studies on genetic diversity of native pinewoods have shown high levels of selectively neutral variation in this predominantly outcrossing conifer, and a mating system analysis with a limited number of microsatellite markers supported this pattern. Together, these data suggest that despite significant historic population size decrease, environmental gradients have resulted in genetic differentiation among native pinewoods. In order to minimise the risk of planting poorly-adapted stock and to maximise the success of replanting programmes, it is important that the origins of planting stock are carefully considered in management guidelines for the species.

Motivated by the paucity of high quality stillbirth surveillance data and the spatial analyses of such data, the current research sets out to quantitatively describe the pattern of stillbirth events that may lead to mechanistic hypotheses. We broaden the appeal of Bayesian Poisson point process modeling to quantify excess risk while accounting for unobserved heterogeneity. We consider a practical data analysis strategy when fitting the point process model and study the utility of parameterizing the intensity function governing the point process to include a maternal contextual effect to account for variation due to multiple stillbirth events experienced by the same mother in independent pregnancies. Simulation studies suggest that our practical data analysis strategy is reasonable and that there is a variance-bias trade-off associated with the use of a maternal contextual effect. The methodology is applied to the spatial distribution of stillbirth events in Iowa during the years 2005 through 2011 obtained using an active, statewide public health surveillance approach. Several localized areas of excess risk were identified and mapped based on model components that captured the nuanced and salient features of the data. A conditional formulation of the point process model is then considered, which has two main advantages: the ability to easily incorporate covariate information attached to both stillbirth and live birth, as well as obviate the need to estimate the background intensity. We assess the utility of the conditional approach in the presence of unobserved heterogeneity, compare two Bayesian estimation techniques, and extend the conditional formulation to adequately capture spatio-temporal effects. The motivating study comes from the Iowa Registry for Congenital and Inherited Disorders who has a committed interest in the surveillance and epidemiology of stillbirth in Iowa and whether the occurrence might be geographically linked.

Although considerable research has been invested in disentangling the factors limiting species’ ranges at local and continental spatial scales, less attention has been granted to the relationship between species’ spatial distributions and landscape attributes at intermediate spatial scales. This research investigates the spatial relationship between avian species’ distributions (Ontario Breeding Bird Atlas [2001-2005] data) and landcover heterogeneity (Ontario Land Cover [1991-1998] data) in terms of their respective boundary locations (i.e., high rates of change in landcover composition and avian species turnover) in a vulnerable transitional zone in southern Ontario. Significant spatial overlap was found between landcover and avian boundaries. Given that land management decisions are most often made at the regional or landscape scales, this positive spatial relationship has important implications for conservation efforts. Future research should focus on assessing the spatial relationship between landcover heterogeneity and avian species’ distributions for different functional and taxonomic groups.

Although considerable research has been invested in disentangling the factors limiting species’ ranges at local and continental spatial scales, less attention has been granted to the relationship between species’ spatial distributions and landscape attributes at intermediate spatial scales. This research investigates the spatial relationship between avian species’ distributions (Ontario Breeding Bird Atlas [2001-2005] data) and landcover heterogeneity (Ontario Land Cover [1991-1998] data) in terms of their respective boundary locations (i.e., high rates of change in landcover composition and avian species turnover) in a vulnerable transitional zone in southern Ontario. Significant spatial overlap was found between landcover and avian boundaries. Given that land management decisions are most often made at the regional or landscape scales, this positive spatial relationship has important implications for conservation efforts. Future research should focus on assessing the spatial relationship between landcover heterogeneity and avian species’ distributions for different functional and taxonomic groups.

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<p>This thesis investigates paper structure and how its spatial heterogeneity affects the electrostatic and contact forces responsible for the toner transfer in Xerographic printing. Modeling predictions and experiments are reported which link length scales of variation in toner density distribution in Xerographic printing with certain structural length scales in paper.</p> <p>A modified 3D fibre network model is introduced, which is used to simulate handsheet paper microstructure. Specific measures addressed by the model include formation, surface roughness and porosity. Simulated (i.e. virtual) handsheet paper structure is compared with that from specially prepared laboratory handsheet, obtaining a good correspondence between theory and experiments.</p> <p> An efficient Multigrid Poisson solver is used to simulate the electrostatic fields involved in the Xerographic toner transfer process. The distribution of dielectric property is input into the solver either analytically or from simulated 3D paper webs prepared by the fibre network model of paper. A spectral analysis is used to elucidate the relative importance of spatial variations of paper surface, filler and porosity in establishing spatial variations of the electrostatic field. It is found that only long wavelength variations in either surface height, bulk filler or porosity affect variations in electrostatic toner transfer forces to any relevant degree. Furthermore, it is shown that the long wavelength perturbations of the electrostatic field can be modeled using a new 1D effective capacitor model. Direct use of simulated handsheet paper webs - which are described by several heterogeneous measures - shows that to lowest order it is the paper surface structure not formation is responsible in shaping the electrostatic toner field variations.</p> <p> A new platform for modeling toner transfer in Xerographic printing is also introduced. It combines the 3D stochastic fibre network model of paper, the 3D electrostatic field solver, paper compression in the printing nip, and contact adhesion forces acting on toner particles during Xerographic printing. The modeling platform is used to demonstrate that paper-press interactions are critical in shaping the surface of paper, which, in turn, has the greatest influence in controlling both the electrostatic and contact adhesion forces responsible for shaping the distribution of toner transferred to paper during Xerography.</p> / Thesis / Doctor of Philosophy (PhD)

Malpighian (renal) tubules of the fruit fly Drosophila melanogaster consist of three functional domains: a non-secretory distal segment, a secretory main segment and a reabsorptive lower segment. In this study a computer-controlled micropositioning system and a self-referencing K^+ microelectrode were used to measure K^+ concentration gradients of extracellular unstirred layers associated with specific epithelial domains. K^+ fluxes were calculated from the measured gradients. This is the first time: that an accurate assessment of the concentration gradients of the unstirred layer of Drosophila melanogaster could be assessed due to the enhanced sensitivity of this self-referencing technique over conventional ion-selective microelectrodes. The technique permits high resolution spatial and temporal mapping of the flux patterns in response to stimulation or inhibition of ion transport. Variations in K^+ transport over time and at different sites suggest that transport is non-uniform within any one functional domain. / Thesis / Master of Science (MSc)

A study was conducted at the Savannah River Site near Aiken, SC to: 1) characterize the spatial patterns of soil and forest floor variables (moisture, pH, soil phosphate, forest floor and soil carbon and nitrogen, and soil available nitrogen), 2) assess the spatial patterns of the plant community, and 3) investigate spatial relationships among the variables and between the variables and woody vegetation. Spatial soil and litter samples were collected on five 0.25 hectare plots, and relationships were explored using Pearson's correlation tests, canonical correlation analysis, variogram modeling and kriging. The average range of spatial autocorrelation for the forest floor variables was >45 m, while that for soil variables was 12 m. Woody stem basal area exhibited spatial autocorrelation at ranges of less than 12 m, and was only weakly correlated with forest floor and soil resource patterns. Few strong spatial correlations among the forest floor and soil variables were observed. The means and variances of the variables were low, and differences in resource levels probably had little impact on the spatial pattern of vegetation. Results indicate a weak, differential effect of species group on litter quality, a weak relationship between large pine trees and soil nitrogen patterns, and a general homogeneity of the stands. / Master of Science