Scientists and land managers often focus on the Southeastern Plains and Coastal Plain of the southeastern United States when considering the ecology, restoration, and management of longleaf pine (Pinus palustris P. Mill.) communities and ecosystems. However, the range of this foundation tree species and its associated communities and ecosystems also extend into the Piedmont and Montane Uplands: the Piedmont of Alabama, Georgia, North and South Carolina and Virginia; the Ridge and Valley of Alabama and Georgia; and the Southwestern Appalachians of Alabama. The composition, structure, and dynamics of Piedmont and Montane Uplands longleaf pine communities have been understudied compared to their Southeastern Plains and Coastal Plain counterparts, and knowledge is based on historical accounts and a handful of studies at site-specific scales. The biogeography and ecology of Piedmont and Montane Uplands longleaf pine communities differ significantly from those in the Southeastern Plains and Coastal Plain. My research combines geospatial and ecological approaches to provide insights on current composition, structure, and dynamics of longleaf pine communities in the Southeastern Plains, Piedmont, and Ridge and Valley at multiple scales and highlights differences and similarities with communities in the Coastal Plain. The Piedmont and Montane Uplands longleaf pine communities showed high variation in canopy tree diversity compared to those in the Coastal Plain. Longleaf pine was sometimes the only canopy tree, while in other communities longleaf pine was one constituent in a mixed oak-pine canopy. My study showed that longleaf pine communities were not just restricted to south-facing slopes as previously thought, but were found on northwestern-facing slopes as well. Analysis of tree rings across my study sites showed that as longleaf pine approaches its northern range margin in the Piedmont and Montane Uplands, its radial growth is restricted by minimum temperature especially at longleaf pine's elevational, latitudinal, and longitudinal extremes; at all sties radial growth was influenced by drought and precipitation. At the local scale, I found that an Alabama Piedmont longleaf pine community showed a diameter-class distribution typical of an old-growth site but contrary to current knowledge, diameter was not a good indicator of age. / Ph. D.

The processes by which plant spatial patterns are formed, and the effects of those patterns on plant community dynamics, remain important areas of research in plant ecology. Plant spatial pattern formation has been linked to many ecological processes that act to structure plant communities at different spatiotemporal scales. Past studies of pattern formation are common, but recent methodological advances in data collection and analysis have permitted researchers to conduct more advanced observational studies of pattern formation in space and time. While studies of the effects of plant spatial patterns were formally rare, they have increased in the last decade as new types of experiments and analysis have been developed to better understand the myriad effects of plant patterns on community dynamics. My dissertation research examined both the causes and consequences of plant spatial patterns in the context of natural and experimental Great Basin semi-arid plant communities. In both cases, I implemented novel methodologies for data collection, experimental design, and data analysis in an attempt to address current gaps in knowledge related to the processes by which plant spatial patterns are formed, as well as the effect of plant spatial patterns on community dynamics. The results inform both basic and applied plant ecology, and set the stage for further research on the causes and consequences of plant spatial patterns in semi-arid plant communities.

<p>Instability in the propagation of nonlinear electro-chemical waves in the heart is responsible for life-threatening disease. This thesis describes an investigation of the effects of boundaries on cardiac wave propagation that arises from a site where an electrical stimulus is applied or from boundaries beyond which current does not flow. It is generally believed that the spatial scale for boundary effects is approximately equal to the passive length constant, lambda, of the tissue, the distance over which a a voltage pulse decays when it is below the threshold for wave generation. From the results of <em>in vitro</em> experiments with bullfrog cardiac tissue and through numerical simulations, I find that boundaries affect wave propagation over a much larger spatial scale and that the spatial variation in some cardiac restitution properties is correlated statistically with the onset of alternans, a possible precursor to fibrillation in the human heart.</p><p>An optical imaging system using novel illumination based on LEDs is used to determine the spatial dependence of action potential duration (APD) and the slope of the dynamic restitution curve S_DRC, which describes the relationship between steady-state APD and diastolic interval. For tissue with nearly identical cells, I find that APD is longest near the stimulus and shortest near the physical boundary with significant changes (~100 ms) over a distance of ~10lambda. S_DRC decreases with distance from the stimulus at a constant rate (~0.1-1.5 /mm) over the surface of the tissue. Simulations using a two-variable cardiac model confirm that spatial patterns of APD and S_DRC can be induced by boundaries.</p><p>Additional measurements with the simultaneous impalement of two microelectrodes are used to determine the spatial differences of other restitution properties. These studies indicate that APD and S_DRC, as well as the slopes of the constant-BCL and S1S2 restitution curves, vary in space and that the spatial differences and onset of alternans at rapid pacing are correlated. If similar correlations are evident in humans, such measurements may identify patients who are susceptible to arrhythmias and allow for early treatment.</p> / Dissertation

The daily variation in background light intensity (irradiance) can entrain the endogenous clock in the suprachiasmatic nucleus (SCN) to the external environment. The only source of this photic information in mammals is the eye, which is primarily a visual organ. It is therefore highly specialised to detect high frequency spatiotemporal modulations. This together with the adaptation which occurs within the retina could be present difficulties when encoding global irradiance. This raises the question of whether spatial patterns, which are present in our everyday viewing, might affect the ability of the SCN to receive 'true irradiance' signals and entrain to the external environment. My first approach was to determine whether individual SCN cells might receive a 'true irradiance' signal. To this end I mapped and characterised the receptive field properties of SCN neurons using in vivo electrophysiology. Indeed a handful of neurons (full field cells) responded to light anywhere in the visual scene and thus may act as 'irradiance detectors'. However, the vast majority of cells only sampled local radiance from a limited area of the visual scene. Having mapped the receptive field properties it became clear that cells which sampled from a limited area of the visual scene would be sensitive to spatial contrast (patterns). To examine the effect of spatiotemporal contrast on the SCN I examined two SCN outputs: locomotor activity and neuronal firing rates. Although spatiotemporal modulation in light intensity could induce large amplitude oscillations in neuronal activity; the time averaged firing rate and locomotor activity, which are believed to be determined by irradiance, were largely unaffected by spatial patterns. This led to the conclusion that the SCN can multiplex photic information into information regarding irradiance, and spatial information by encoding them under different timescales. Melanopsin has been heralded as the key photopigment for encoding irradiance and entraining the SCN. However such experiments have been only performed using diffuse light stimuli. Here I investigated the role of melanopsin under natural viewing conditions which incorporated spatial patterns. Under such stimuli the SCN response can be almost entirely accounted for by the melanopic irradiance of the stimuli.

This study investigates the variation in the spatial patterns of Diptera and Collembola throughout the forest canopy due to seasonal changes in temperature and humidity in the monsoon climate of West Africa. There is a very distinct turnover in climate from the end of the dry season (the hottest and driest time of the year) to the beginning of the rains and this coincides with significant increases and decreases in the overall abundance of many forest dwelling Diptera and Collembola species. The study investigates spatial patterns on two gradients; vertically from the ground to the high canopy and laterally from the edge of the forest to the core, with the added complexity of the affects of anthropogenic burning of adjacent savannah. The results show that seasonality and the starting of the rains significantly affect both the overall abundance and the spatial patterns, providing species with a strategic change in habitat niche. During seasonal conditions that are less conducive to species' overall abundance, spatial patterns are suppressed by environmental conditions. However when environmental conditions are optimum for increased species abundance, spatial patterns are only suppressed by the availability of resources within the habitat (feeding or reproductive resources for example). Successive late burning events may have changed the structure of the forest edge introducing a significantly more open forest structure changing environmental conditions and thus creating a habitat more suitable for species which prefer lower humidity and higher temperatures.

This thesis examines the spatial patterns, convergence dynamics, and causes of regional wage disparities in post-apartheid South Africa. The analysis is conducted using a unique dataset for 354 regions constructed from the 1996, 2001 and 2011 population censuses. The thesis comprises of six chapters including the introduction and conclusion. The general introduction is followed by Chapter two that presents a theoretical and empirical review of the causes of regional wage disparities. Emphasis is placed on theoretical insights derived from the new economic geography theory. The subsequent 3 chapters comprise the empirical analysis. Chapter three applies exploratory spatial data analysis techniques to the 1996, 2001 and 2011 population censuses data and examines the spatial patterns that characterise the distribution of wages across regions in South Africa. An objective is to assess the consistency of these patterns with predictions from alternative theories. The results point to significant disparities in the distribution of wages across regions in South Africa that are greater than regional wage disparities in other countries. These disparities are characterised by positive and negative spatial autocorrelation between regions suggesting the coexistence of new economic geography forces (positive autocorrelation) and alternative economic theory (negative autocorrelation) features. These findings provide important context and input into the subsequent empirical chapters of the thesis. Chapter four examines the convergence dynamics of wages across regions in post-apartheid South Africa. The aim of the chapter is to assess the extent to which wages have converged or diverged across regions in South Africa over the period 1996 – 2011. The convergence dynamics are analysed using a range of complementary measures, namely, the kernel density estimator and indicators of α - convergence and β - convergence. These measures consistently reveal evidence of regional wage divergence between 1996 and 2001, but strong and robust evidence of regional wage convergence from 2001 to 2011. During the period 2001 – 2011, the unconditional β- convergence is estimated at 3.7% per year, suggesting that it could take about 19 years to reduce the gap in wages between rich and poor regions by half. However, conditional β- convergence, after controlling for initial human capital, local unemployment, market potential, industrial stucture and homeland status, is much higher, at 13% per year. This implies that it could have taken about 5 years to reduce the wage gap between rich and poor regions by half, if differences in regional specific factors had been eliminated between 2001 and 2011. The results suggest that regional specific factors, some of which can be influenced by policy, constrain regional wage convergence in South Africa. The fifth Chapter empirically tests whether the prediction of the Helpman-Hanson wage equation derived from the new economic geography theory is consistent with observed regional wage disparities in South Africa. The chapter extends the Helpman-Hanson model to include other potential explanatory factors concerning regional wages. The results suggest that regional wage disparities in South Africa are well explained by new economic geography forces such as access to markets, but only after controlling for regional specific factors such as human capital, mineral resource endowments, local climatic conditions, local unemployment, and homeland status. The findings of this study imply that new economic geography theory alone is not sufficient to explain regional wage disparities in South Africa. Its proper application hinges on the incorporation of other regional specific factors. This finding is consistent with an emerging economy that is characterised by moderate industrial and transport sectors, on the one hand, and a strong primary sector driven by natural resource exploitation, on the other hand. Overall, the thesis shows that, while regional wage disparities are converging over time in South Africa, they remain high compared to other countries. Convergence is very slow and is influenced by regional specific factors such as human capital, access to markets, mineral resource endowments, local climatic conditions, local unemployment and homeland status. Accordingly, complementary policies promoting human capital accumulation, access to markets, and development of former homeland areas, and improving labour market outcomes will substantially enhance wage convergence. Nevertheless, even with these policies, regional wage disparities will remain a feature of the South African economy as these are in part driven by economic forces associated with new economic geography. The thesis thus highlights how differences in access to markets and regional factor endowments exacerbate and constrain regional wage disparities in South Africa.

No description available.

Brain-computer interfaces are an emerging technology that could provide channels for communication and control to severely disabled people suffering from locked-in syndrome. It has been found that motor imagery can be detected and classified from EEG signals. The motivation of the present work was to compare several algorithms for motor imagery classification in EEG signals as well as to test several novel algorithms. The algorithms tested included the popular method of common spatial patterns (CSP) spatial filtering followed by linear discriminant analysis (LDA) classification of log-variance features (CSP+LDA). A second set of algorithms used classification based on concepts from Riemannian geometry. The basic idea of these methods is that sample spatial covariance matrices (SCMs) of EEG epochs belong to the Riemannian manifold of symmetric positive-definite (SPD) matrices and that the tangent space at any SPD matrix on the manifold is a finite-dimensional Euclidean space. Riemannian classification methods tested included minimum distance to Riemannian mean (MDRM), tangent space LDA (TSLDA), and Fisher geodesic filtering followed by MDRM classification (FGDA). The novel algorithms aimed to combine the CSP method with the Riemannian geometry methods. CSP spatial filtering was performed prior to sample SCM calculation and subsequent classification using Riemannian methods. The novel algorithms were found to improve classification accuracy as well as reduce the computational costs of Riemannian classification methods for binary, synchronous classification on BCI competition IV dataset 2a. / Master of Science

Pluripotent embryonic stem cells (ESCs) can differentiate into all somatic cell types, making them a useful platform for studying a variety of cellular phenomenon. Furthermore, ESCs can be induced to form aggregates called embryoid bodies (EBs) which recapitulate the dynamics of development and morphogenesis. However, many different factors such as gradients of soluble morphogens, direct cell-to-cell signaling, and cell-matrix interactions have all been implicated in directing ESC differentiation. Though the effects of individual factors have often been investigated independently, the inherent difficulty in assaying combinatorial effects has made it difficult to ascertain the concerted effects of different environmental parameters, particularly due to the spatial and temporal dynamics associated with such cues. Dynamic computational models of ESC differentiation can provide powerful insight into how different cues function in combination both spatially and temporally. By combining particle based diffusion models, cellular agent based approaches, and physical models of morphogenesis, a multi-scale, rules-based modeling framework can provide insight into how each component contributes to differentiation. I propose to investigate the complex regulatory cues which govern complex morphogenic behavior in 3D ESC systems via a computational rules based modeling approach. The objective of this study is to examine how spatial patterns of differentiation by ESCs arise as a function of the microenvironment. The central hypothesis is that spatial control of soluble morphogens and cell-cell signaling will allow enhanced control over the patterns and efficiency of stem cell differentiation in embryoid bodies.

The thesis deals with the ecology of lichens in two contrasting types of forest, epiphytic lichens in old Picea abies forest of the fi re-refugia type and epigeic as well as epixylic lichens in a successional sequence of fire- susceptible Pinus sylvestris forests. Results in five separate papers form the basis for a discussion of general patterns of dispersal, succession and life strategies in lichens. The study sites were located in Medelpad and Väs­terbotten, in the central and northern part of Sweden, respectively. Special attention has been paid to the rare, pendulous, spruce-1ichen Usnea longissima and the coexisting lichen species. U. longissima is largely restricted to north-facing hill slopes covered with old, mesic spruce forest that is characterized by a very long continuity not disturbed by fire. A mar­ked decline in the number of sites with U. longissima was found. The decline was mainly due to the effect of different forestry practices as the species is very sensitive to environmental disturbances. The epiphytic lichen vegetation of six tree species occurring in the spruce forest is described. Clear successional trends with increasing tree size were • obtained for Alectoria sarmentosa, Bryoria fuscescens coll., B. nadvornikiana, Usnea filipendula' and U. subflorida'na, to a lesser extent for Bryoria capii-“" laris while U. longissima had no relationship to tree size or age. TTstudy of the litterfall of macrofragments of epiphytic lichens showed that thallus fragments were dispersed throughout the year with late autumn, winter and early spring as the most critical periods. It is suggested that dispersal through thallus fragmentation is more important in fruticose than in foliose species and that U. longissima has a shorter range of propagule transport than the other species of Alectoria, Bryoria and Usnea studied. The latter proposition was supported through a study of the horizontal patterns of lichen occurrence in the spruce forest. It is shown that the diversity in ground vegetation, after an initial in­crease, declines with succession in the pine forests. A mechanism of succes­sion in ground vegetation is presented which suggest that variations in habi­tat heterogeneity, i.e. the diversity of substrates caused by the initial dis­turbance and the stand development, largely determines diversity changes dur­ing succession. Trends of increasing thallus size, increasing size of asexual reproductive propagules and increased competitive ability with succession formed the basis for recognizing three types of strategies in Cladonia» It is concluded that lichens have features that are compatible with the r-K continuum and that they are variously adapted to both the stability of the substrates and that of the forest as a whole. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1983, härtill 5 uppsatser</p> / digitalisering@umu