Accurate estimates for the molecular transport coefficients are critical to predicting the movement of gases in geological media. Here I present a novel methodology for using prompt gamma activation analysis to measure the effective diffusivity of noble gases in a porous medium. I also present a model to estimate the connectivity parameter of a soil from measurements of its saturated conductivity, macro porosity, and pore volume and pore surface fractal dimensions. Experiments with argon or xenon diffusing through a nitrogen saturated geological media were conducted. The noble gas concentration variations at its source were measured using prompt gamma activation analysis and later compared to a numerical diffusion model to estimate the effective diffusion coefficient. Numerical simulations using the estimated diffusivity and the experimental argon data produced results with a correlation parameter R² = 0.98. However, neglecting transport mechanisms other than diffusion largely under-predicted the xenon depletion rates observed during the first hours of experiment. To explain these results, a second model was developed which included the effect of pressure gradients and bulk convection that might arise from the faster molecular migration of the light species in a non-equimolar system and gravitational currents. Finally, the fractal model developed for this dissertation was used to estimate the connectivity parameters and walking fractal dimension of a group of geological samples that were previously characterized. This model successfully predicted positive connectivity factors and walking fractal dimensions between two and three for every sample analyzed. / text

Successful recognition memory decisions depend on mnemonic and decision making processes that are computed by multiple, distributed brain areas. However, little is known about what computations these areas perform or how these areas are connected. Here, I collected behavioral and functional magnetic resonance imaging data from humans during the performance of an old-new recognition memory task with retrospective confidence judgments. Across runs, choice bias was successfully manipulated by providing rewards for correct responses that were either symmetric (equal reward for hits and correct rejections) or asymmetric (one response worth more than the other). Successful recognition memory was associated with activation in anterior prefrontal, parahippocampal, posterior cingulate, and parietal cortex. Resting state functional connectivity demonstrated that these brain areas are organized into two distinct networks. The first network includes parahippocampal cortex and angular gyrus. The second network includes lateral prefrontal cortex and intraparietal sulcus. The hippocampal-cortical network was most active during old vs. new decisions, did not differentiate hits from false alarms, and was differentially active during low confidence old and new judgments. In contrast, while the frontoparietal network was robustly activated by hits, it was not activated during either false alarms or low confidence old judgments. Thus, these two distinct networks can be distinguished by their relative connectivity to the medial temporal lobe vs. lateral prefrontal cortex and their responses during uncertain old judgments and errors. The choice bias manipulation had opposing effects on the parietal components of these networks, which further suggests these networks make distinct contributions to mnemonic decision making. / Psychology

A novel progressive lossy-to-lossless coding method is proposed for mesh models of images whose underlying triangulations have arbitrary connectivity. For a triangulation T of a set P of points, our proposed method represents the connectivity of T as a sequence of edge flips that maps a uniquely-determined Delaunay triangulation (i.e., preferred-directions Delaunay triangulation) of P to T. The coding efficiency of our method is highest when the underlying triangulation connectivity is close to Delaunay, and slowly degrades as connectivity moves away from being Delaunay. Through experimental results, we show that our proposed coding method is able to significantly outperform a simple baseline coding scheme. Furthermore, our proposed method can outperform traditional connectivity coding methods for meshes that do not deviate too far from Delaunay connectivity. This result is of practical significance since, in many applications, mesh connectivity is often not so far from being Delaunay, due to the good approximation properties of Delaunay triangulations. / Graduate

Η συνδετικότητα εγκεφάλου αφορά σε πρότυπα δικτύων τόσο ανατομικών, όσο στατιστικά ή και αιτιακά συσχετισμένων συνδέσεων διακριτών μονάδων του νευρικού συστήματος του εγκεφάλου. Στην εργασία αυτή μελετάται τόσο η απόδοση όσο και η φυσιολογική ερμηνεία μετρικών υπολογισμού της στατιστικής καθώς και αιτιακής συνάφειας χρονοσειρών. Οι χρονοσειρές αφορούν σε καταγραφές περιοχών/ηλεκτροδίων του ηλεκτροεγκεφαλογραφήματος ύπνου φυσιολογικών ανθρώπων. Πιο συγκεκριμένα, οι μέθοδοι υπολογισμού της συνδετικότητας εφαρμόζονται μεταξύ περιοχών του εγκεφάλου και σε χρονικές στιγμές όπου λαμβάνουν χώρα μικρογεγονότα του ύπνου, όπως υπνικές άτρακτοι (sleep spindles) και K-συμπλέγματα (K-complexes), με απώτερο σκοπό την κατανόηση του ρόλου αυτών των γεγονότων στον ύπνο. / During Non-Rapid Eye Movement (NREM) sleep brain is considered to be relatively disconnected from the environment. Also connectedness between brain areas has been found decreased, although we do not know the role played in this by specific elements of sleep microstructure. We developed a method with millisecond time resolution appropriate for assessing brain connectivity during NREM sleep spindles, the φ-coherence. It is based on the observation by Nolte (2008) that when the phase between two signals is zero, the coherence value can be attributed to volume conduction rather than functional neuronal connection. So φ-coherence excludes this value. The new method counts among the effective connectivity measures as advantageous in (a) its superb time resolution (b) ability to study events clustered from different time periods or subjects (c) simultaneous study of any choice from all possible combinations of EEG electrodes and display their φ-coherence in time-frequency topological maps and (d) parameterization of all the plots included in the maps regarding frequency, time and φ-coherence threshold. Preliminary results from 360 fast spindles recorded in whole night sleep of two healthy volunteers the use of φ-coherence indicated a prevailing connectivity pattern of causal interactions mostly from centroparietal regions (C3, Cz, C4, Pz, P3, P4) to right frontotemporal regions (F8, T4). The study aims to help our understanding of the role played by spindles not only in sleep maintenance but also in memory consolidation and in several neuropsychiatric disorders.

Τα Ασύρματα Δίκτυα Αισθητήρων (Wireless Sensor Networks, WSN) αποτελούν σήμερα ένα πολλά υποσχόμενο πεδίο έρευνας στον τομέα των ασύρματων επικοινωνιών. Ωστόσο, λόγω κάποιων από τις ιδιαιτερότητές τους, οι κόμβοι ενός WSN υπόκεινται σε λειτουργικούς και σχεδιαστικούς περιορισμούς, που δημιουργούν νέες προκλήσεις και αντικείμενα έρευνας με σκοπό τη βελτιστοποίηση της απόδοσης του δικτύου. Ένα τέτοιο αντικείμενο έρευνας αποτελεί και η συνδεσιμότητα του συνολικού δικτύου, μια έννοια καθοριστική για τη δυνατότητα επικοινωνίας μεταξύ των κόμβων και ανταλλαγής πληροφοριών επί της παρατηρούμενης διεργασίας. Η χρησιμότητα των WSN σε συνδυασμό με την απαίτηση για συνδεσιμότητα αποτέλεσαν το σημείο εκκίνησης για την παρούσα διπλωματική εργασία. Ποιο συγκεκριμένα, επιχειρήθηκε η μεγιστοποίηση της περιοχής επικοινωνιακής κάλυψης σε ένα WSN αλλά και του αριθμού των επικοινωνούντων κόμβων. Η ιδιαιτερότητα της έρευνας εντοπίζεται στη χρήση του Δείκτη Ισχύος Ληφθέντος Σήματος (RSSI) για την εξαγωγή συμπερασμάτων για τη συνδεσιμότητα του δικτύου. Υλοποιήθηκε συνεπώς ένα WSN, αποτελούμενο από ένα ζευγάρι κόμβων αποστολέας-παραλήπτης, των οποίων η επικοινωνία βασίζεται στο πρότυπο της IEEE 802.15.4. Στόχος της πειραματικής διαδικασίας αποτέλεσε η μέτρηση (στην μεριά του παραλήπτη) του RSSI και ο υπολογισμός του ποσοστού των επιτυχώς ληφθέντων πακέτων για την επικοινωνία μεταξύ αποστολέα-παραλήπτη, μεταβάλλοντας την προγραμματιζόμενη ισχύ εκπομπής του αποστολέα αλλά και τη θέση του παραλήπτη σε μια δεδομένη περιοχή ενδιαφέροντος. Από το στάδιο αυτό της πειραματικής διαδικασίας προέκυψε η περιοχή επικοινωνιακής κάλυψης ενός κόμβου για τα διάφορα προγραμματιζόμενα επίπεδα ισχύος εκπομπής. Τα αποτελέσματα αυτά συνέβαλαν στην ανάπτυξη αλγορίθμου βελτιστοποίησης της συνδεσιμότητας του δικτύου, με βάση τον οποίο αναζητήθηκε η μέγιστη επικοινωνιακή κάλυψη του δικτύου και ο μέγιστος αριθμός ζευγών επικοινωνούντων κόμβων. / Wireless Sensor Networks consist a new research domain in the field of wireless communications. However, they are under many constraints, whisch open new research in this field. One such field consitutes connectivity in Wireless Sensor Networks, which was the stimulus of this Diploma Thesis. The initial goal was the extraction of the maximization of the connunication range of the network and of the number of the nodes tha communicate. The parsticularity of the reserch is the m,easurement of the Received Signal Strength. We deployed tow nodes in the area of interest and measured this indicator. Then the results wereused in an algorithm for the optimization of the communication range and the number of communicating nodes in the network.

We study a directed network design problem called the $k$-$(S,T)$-connectivity problem; we design and analyze approximation algorithms and give hardness results. For each positive integer $k$, the minimum cost $k$-vertex connected spanning subgraph problem is a special case of the $k$-$(S,T)$-connectivity problem. We defer precise statements of the problem and of our results to the introduction. For $k=1$, we call the problem the $(S,T)$-connectivity problem. We study three variants of the problem: the standard $(S,T)$-connectivity problem, the relaxed $(S,T)$-connectivity problem, and the unrestricted $(S,T)$-connectivity problem. We give hardness results for these three variants. We design a $2$-approximation algorithm for the standard $(S,T)$-connectivity problem. We design tight approximation algorithms for the relaxed $(S,T)$-connectivity problem and one of its special cases. For any $k$, we give an $O(\log k\log n)$-approximation algorithm, where $n$ denotes the number of vertices. The approximation guarantee almost matches the best approximation guarantee known for the minimum cost $k$-vertex connected spanning subgraph problem which is $O(\log k\log\frac{n}{n-k})$ due to Nutov in 2009.

Detrital subsidy from highly productive kelp beds and forests to adjacent habitats represents a major form of connectivity between coastal ecosystems that regulates regional patterns of community organization and production. In this thesis, I investigated environmental and biological factors that influence the rate of detrital production in Nova Scotian kelp beds, with emphasis on the role of invasive species in altering these dynamics. The rate of blade erosion of the dominant kelp species (Saccharina latissima and Laminaria digitata) increased significantly with the level of encrustation by the invasive bryozoan Membranipora membranacea and the extent of grazing damage by the native snail Lacuna vincta, and by increased water temperature and site exposure. The rate of detrital production (as dry mass) ranged from 0.5 to 1.71 kg m-2 y-1 across 5 sites, and increased linearly with kelp bed biomass. Spatial variation in the total level of grazing damage on kelp blades by L. vincta was explained in part by a negative relationship with site exposure, and the distribution of grazing along blades was regulated by kelp growth rate and the associated production of grazing-deterrent polyphenolics. Grazing damage by L. vincta that exceeded 0.5 to 1.0% of blade area caused increased rates of erosion during heavy wave action associated with a passing hurricane. The maximum stress before breakage, toughness, and extensibility of blade tissues decreased with the degree of encrustation by M. membranacea or grazing damage by L. vincta, which cause degradation and removal of the outer cell layers of kelp tissues, resulting in stress concentration and breakage at lower force applications than required to break undamaged tissues. The invasive green alga Codium fragile and S. latissima differed with respect to nutritional quality and changes in biochemical composition that occurred over the course of degradation on a sandy bottom adjacent to a kelp bed. Macrofaunal communities colonizing detrital deposits responded to these differences. These findings demonstrate that invasive species can alter the quantity and quality of detritus produced from subtidal kelp beds, and that their community-level effects can extend well beyond the invaded habitats via the export of detritus.

Attention allows us to select important aspects of incoming sensory information while filtering out irrelevant information. It has crucial significance in understanding neurophysiological, emotional and behavioral outcomes. The research reported here focused on one central question: how do attentional manipulations influence various stages of cognition and emotion to result in goal-directed behavior? In six experiments, I used behavioral and functional Magnetic Resonance Imaging (fMRI) measures to investigate the impact of attention on visual recognition, mood and self-regulation. The results showed that attention influences functional connectivity between body-selective visual processing areas in occipito-temporal cortex. Changes in the scope of attention were also found to influence mood and self-regulation. Broadening attentional focus improves mood and self-regulation. Narrowing attentional focus impairs mood and self-regulation. Self-regulation was also aided through the pre-engagement of attentional inhibition. This diverse set of methodologies and experimental paradigms provides converging evidence that attention influences goal-relevant functional connections to facilitate visual processing, promotes fluency of information to result in better mood and prioritizes goal-relevant representations to result in successful self-regulation. / NSERC

While much evidence suggests that ecosystem functioning is closely related to biodiversity, present rates of biodiversity loss are high. With the emergence of the metacommunity concept ecologists have become increasingly aware that both local processes (e.g. competition, predation), and regional processes (e.g. dispersal and regional heterogeneity) affect ecological communities at multiple spatial scales. I experimentally investigated the effects of habitat connectivity and regional heterogeneity on biodiversity, community composition, and ecosystem functioning of artificial pond metacommunities of freshwater invertebrates at the local (α), among-community (β), and regional (γ) spatial levels. There was a significant effect of habitat connectivity on mean local richness, but mean local Simpson diversity, mean local functional diversity (FD), and all the three indices of ecosystem functioning investigated (regional abundance, invertebrate biomass, and chlorophyll a concentration) were unaffected by connectivity levels. Regional heterogeneity had no effect on local diversity, but enhanced both among-community richness and among-community Simpson diversity. Conversely, connectivity reduced among-community Simpson diversity. All indices of regional diversity were unaffected by either connectivity or heterogeneity. Despite expectations that there would be strong interactions between the effects of connectivity and heterogeneity on species richness, there were no interactions for any index of biodiversity at any spatial scale. Invertebrate community composition was unaffected by either connectivity or heterogeneity, though there was a significant effect of heterogeneity on its variance. Neither connectivity nor heterogeneity had significant effects on any index of ecosystem functioning, nor among-community coefficients of variation of ecosystem functioning. Connectivity appears to act mainly as a force homogenizing habitat patches in a region, as opposed to having strong effects in and of itself on communities. Conversely, heterogeneity acts largely as a diversifying force, maintaining differences between communities within a region, but, similar to connectivity, it does not have clear effects on communities at the local scale. Despite the different processes expected to act in homogeneous and heterogeneous regions, it does not appear that connectivity and heterogeneity interact strongly. / Thesis (Master, Biology) -- Queen's University, 2008-10-16 09:06:33.103

Background: Street connectivity, an important aspect of the built environment, refers to the directness of links and the density of connections in road networks. Street connectivity of youth’s neighborhoods may impact upon both physical activity patterns and the occurrence of physical activity injuries in street locations. Objectives: The objectives of the two studies comprising this thesis were to examine, among Canadian youth in grades 6 to 10: (1) the relationship between street connectivity and physical activity, and (2) the relationship between street connectivity and physical activity injuries occurring in the street. Methods: 9,717 youth in grades 6-10 from 188 schools across Canada participated in the 2006 Health Behaviour in School-aged Children (HBSC) survey. A street connectivity composite measure was gathered objectively using a geographic information system database, and was based on intersection density, average block length, and connected node ratio in a 5km radius around each school. Physical activity was measured via students’ self-reported hours of moderate-to-vigorous physical activity per week outside of school hours. Injury was measured via students’ self-reports to questions regarding whether they had suffered an injury while playing in the street in the past 12 months. Multi-level regression analyses were used to examine the relations between street connectivity and both physical activity and injury. Results: Compared to students living in the highest street connectivity quartile, those in the second (Relative Risk (RR) 1.22; 95% confidence interval (CI) 1.10-1.35), third (RR 1.25; 95% CI 1.13-1.37), and fourth (lowest; RR 1.21; 95% CI 1.09-1.34) quartiles reported considerably higher levels of physical activity outside of school hours. Conversely, students living in neighbourhoods with low street connectivity reported higher occurrence of physical activity injuries occurring in the street relative to students living in highly connected neighbourhoods (Odds Ratio (OR) 1.47; 95% CI 0.94 -2.31). Conclusions: Neighbourhoods with low street connectivity may be conducive to youth physical activity, yet they may also result in an increased risk of injury. Further, the relationship between street connectivity and physical activity reported in Canadian youth is not consistent with the relationship reported for adult populations. This variation requires consideration in applied health policy. / Thesis (Master, Community Health & Epidemiology) -- Queen's University, 2010-09-14 15:26:49.565