La perception consciente du monde extérieur repose sur la coordination spatiotemporelle de l’activité des neurones corticaux. Les aires corticales primaires chez les mammifères sont organisées en six couches. Il a été proposé que l’information sensorielle soit traitée de façon sérielle à travers les 6 couches du cortex. D’abord au niveau de la couche IV, cible des afférences thalamiques. Ensuite au niveau des couches II/III, innervées par les neurones excitateurs de la couche IV. Et enfin par les neurones des couches profondes, V et VI, qui sont innervés par les cellules pyramidales des couches II/III. Les neurones pyramidaux de la couche V constituant la principale sortie du néocortex.Il a récemment été montré que les neurones des couches profondes reçoivent également des informations sensorielles directement par des afférences thalamiques, ce qui pose la question du rôle de la connectivité interlaminaire dans le traitement sensoriel opéré par le cortex.J’ai ainsi tiré profit de la technique d’électroporation in utero qui permet d’exprimer spécifiquement des protéines photo-activables dans les cellules pyramidales des couches II/III du cortex somesthésique primaire de la souris. En procédant à des enregistrements unitaires des neurones corticaux à la fois chez des animaux anesthésiés et éveillés, j’ai montré que le recrutement des neurones pyramidaux des couches II/III amplifie les réponses sensorielles des neurones de la couche V. Par ailleurs, l’analyse de cette amplification en fonction de l’intensité des stimulations sensorielles indique que la connectivité interlaminaire joue un rôle majeur dans la modulation du gain des neurones de la couche de sortie du cortex. / The sensory perception of the external world relies on the coordinated activity in space and time of cortical neurons. Primary sensory areas of mammals are organized in six layers.It has been suggested that sensory information is processed serially through the six layers of the cortex. Sensory information is supposed to propagate first through the layer IV, principal target of thalamic axonal projections. Cortical layers II/III then receive sensory information relayed by layer IV excitatory neurons. Finally, deep cortical layers V and VI are connected by layer II/III pyramidal cells. Layer V pyramidal neurons are the principal output of the neocortex.Recently, it has been shown that deep layer neurons receive direct thalamic inputs relaying sensory information. The role of the translaminar connectivity during sensory processing remains an opened question.I took the advantage of in utero electroporation to express photo-sensitive proteins specifically in layer II/III pyramidal cells of the mouse primary somatosensory cortex.By proceeding to extracellular recordings of cortical neurons of either anesthetized or awake mice, I have shown that the recruitment of layer II/III pyramidal neurons amplifies layer V neurons sensory responses. Moreover, the analysis of this amplification phenomenon as a function the sensory stimulation intensity suggests that translaminar connectivity can operate a gain modulation of the layer V pyramidal neurons.

Contexte : […], le mode d'interaction entre les signaux corticaux et striataux reste flou. Dans la présente thèse, nous avons d’abord saisi l’opportunité d’enregistrements stéréoélectroencéphalographiques chez des patients atteints d’épilepsie pharamcorésistante pour analyser qualitativement et quantitativement l’activité ictale du striatum. Deuxièmement, nous avons créé un modèle primate de crises motrices focales sous-corticales induites par des injections striatales antagonistes GABAergiques. Première étude : Patients et méthode : onze patients ayant subi une évaluation SEEG ont été inclus prospectivement s'ils remplissaient deux critères d'inclusion: i) au moins un contact explorait le striatum, ii) au moins deux crises avaient été enregistrées. Les régions d'intérêt corticales et sous-corticales ont été définies et différentes périodes d'intérêt ont été analysées. Les signaux SEEG ont été inspectés visuellement et une analyse de corrélation non linéaire h2 a été réalisée pour étudier la connectivité fonctionnelle entre les régions corticales d’intérêt et le striatum. Résultats : Deux patterns principaux d'activation striatale ont été enregistrés : le plus fréquent était caractérisé par une activité alpha / bêta précoce débutant dans les cinq premières secondes suivant le début de la crise. Le second était caractérisé par une activité thêta / delta tardive plus lente. Une différence significative des indices de corrélation h2 a été observée au cours de la période préictale et début de crise par rapport au tracé de fond pour l'indice striatal global, l'indice mésio-temporal / striatal, l'index latérotemporal / striatal, l'index insulaire / striatal, l'index préfrontal / striatal. En outre, une différence significative des indices de corrélation h2 a été observée pendant la période de fin de crise par rapport à toutes les autres périodes d’intérêt. Deuxième étude : Matériel et méthode : Des injections antagonistes aiguës de GABAergic (bicuculline) ont été réalisées sur trois Macaca fascicularis dans la partie sensorimotrice du striatum. Les modifications comportementales ont été enregistrées et scorées selon une échelle de Racine modifiée. L'électromyographie, l'électroencéphalographie, les potentiels de champ locaux des noyaux gris centraux ont été enregistrés au cours de chaque expérience. Une analyse de retromoyenage a été effectuée pour chaque session enregistrée. Résultats: sur les 39 injections de bicuculline, 29 (74,3%) ont produit des changements comportementaux reproductibles caractérisés par des secousses myocloniques répétitives et pseudopériodiques avec des crises tonico-cloniques généralisées. Les injections de NaCl n'ont jamais entraîné de changement de comportement. Les secousses myocloniques étaient clairement détectables sur le signal EMG sous la forme d'une courte bouffée stéréotypée concomitante de pointes épileptiques anormales enregistrées sur l'EEG. Une analyse de rétromoyennage à partir des myoclonies EMG a montré que l'activité électrophysiologique commençait significativement plus tôt dans le striatum (p <0,0001), le GPe (p <0,0003) et le GPi (p <0,0086) que dans le cortex. Conclusion : Ces modifications du niveau de synchronisation entre les activités corticales et striatales pourraient s’inscrire dans un mécanisme endogène contrôlant la durée des oscillations anormales au sein de la boucle striato-thalamo-corticale et, de fait leur terminaison. Les interneurones GABAergic de type fast-spiking pourraient jouer un rôle crucial dans la synchronisation du réseau cortico-striato-thalamique et une modification GABAergique brutale du striatum peut provoquer une crise focale. Le rôle joué par les noyaux gris centraux dans le renforcement des mécanismes sous-jacents à la cessation de la propagation ictale devrait inspirer de nouveaux schémas de stimulation cérébrale profonde chez les patients atteints d'épilepsies focales pharmacorésistantes non chirurgicales. / Background: Although a number of experimental and clinical studies have pointed out participation or an even more prominent role of basal ganglia in focal seizures, the mode of interaction between cortical and striatal signals remains unclear. In the present thesis, we first we took the opportunity of stereoelectroencephalographic recordings in drug-resistant epilepsy patients, to qualitatively and quantitatively analyse the ictal striatum activity. Secondly, we created a primate model of subcortical focal motor seizures induced by GABAergic antagonist striatal injections First study: Patients and method: eleven patients who underwent SEEG evaluation were prospectively included if they fulfilled two inclusion criteria: i) at least one orthogonal intracerebral electrode contact explored the basal ganglia, in their either putaminal or caudate part, ii) at least two SEEG seizures were recorded. Cortical and subcortical regions of interest were defined and different periods of interest were analysed. SEEG was visually inspected and h2 non-linear correlation analysis performed to study functional connectivity between cortical region of interest and striatum. Results: Two main patterns of striatal activation were recorded: the most frequent was characterised by an early alpha/beta activity that started within the first five second after seizure onset. The second one was characterised by a late slower, theta/delta activity. A significant difference in h2 correlation indexes was observed during the preictal and seizure onset period compared to background for global striatal index, mesio-temporal/striatal index, latero-temporal/striatal index, insular/striatal index, prefrontal/striatal index. In addition, a significant difference in h2 correlation indexes was observed during the seizure termination period compared to all the other periods of interest. Second study: Material and method: Experiments were performed on three fascicularis monkeys. Acute GABAergic antagonist (bicuculine) injections were performed within the sensorimotor part of the striatum. Behavioural modifications were recorded and scored according to a modified Racine’s scale. Electromyography, electroencephalography, basal ganglia local field potentials were recorded during each experiment. A backaveraging analysis was performed for each recorded session. Results: over the 39 Bicuculline injections, 29 (74.3%) produced dramatic reproducible behavioural changes characterised by repetitive and pseudo-periodic myoclonic jerks with generalised tonic-clonic seizures. NaCl injections never produced any behavioural changes. Myoclonic jerks were clearly detectable on the EMG signal as short stereotypical EMG burst concomitant from abnormal epileptic spikes recorded on EEG. Back averaging analysis from EMG myoclonia showed that electrophysiological activity started significantly earlier in the striatum (p < 0.0001), the GPe (p < 0.0003) and the GPi (p < 0.0086) than in the cortex. Conclusion: These changes in synchronisation level between cortical and striatal activity might be part of an endogenous mechanism controlling the duration of abnormal oscillations within the striato-thalamo-cortical loop and thereby their termination. GABAergic fast-spiking interneurones might play a crucial role synchronising the cortico-striato-thalamic network and a drastic GABAergic modification of the striatum can induce focal seizures. The role of the basal ganglia role in strengthening mechanisms underlying cessation of ictal propagation should inspire new rationales for deep brain stimulation in patients with intractable focal epilepsy.

For this dissertation I studied groundwater and surface water interactions in the Kenai Lowlands, Alaska. In particular, I examine two important aspects of groundwater and surface water interactions: 1) Groundwater's influence on surface-water temperature; and 2) Groundwater's role in forming hydrologic flow paths that can connect uplands to streamside wetlands and streams. Chapter 2 investigates the controls on stream temperature in salmon-bearing headwater streams in two common hydrogeologic settings: 1) drainage-ways, which are low-gradient streams that flow through broad valleys; and 2) discharge-slopes, which are high gradient streams that flow through narrow valleys. The results from chapter 2 showed significant differences in stream temperatures between the two hydrogeologic settings. Observed stream temperatures were higher in drainage-way sites than in discharge-slope sites, and showed strong correlations as a continuous function with the calculated topographic metric flow-weighted slope. Additionally, modeling results indicated that the potential for groundwater discharge to moderate stream temperature is not equal between the two hydrogeologic settings, with groundwater having a greater moderating effect on stream temperature at the low gradient drainage-way sites. Chapter 3 examines the influence of groundwater on juvenile coho salmon winter habitat along the Anchor River. Two backwater habitats were selected from the larger set of 25 coho overwintering sites from a previous study for an in-depth hydrologic analysis. The results from chapter 3 showed that the type of groundwater discharge (i.e., focused versus diffuse groundwater discharge) can play an important role in determining habitat suitability in these backwater sites. During winter, focused discharge from a local groundwater seep maintained higher surface-water temperatures and higher concentrations of dissolved oxygen compared to the site with more diffuse groundwater discharge. Chapter 4 investigates the linkages along hydrologic flow paths among alder (Alnus spp.) stands, streamside wetlands, and headwater streams. Chapter 4 tested four related hypotheses: 1) groundwater nitrate concentrations are greater along flow paths with alder compared to flow paths without alder; 2) on hillslopes with alder, groundwater nitrate concentrations are highest when alder stands are located near the streamside wetlands at the base of the hillslope; 3) primary production of streamside wetland vegetation is N limited and wetlands are less N limited when alder stands are located nearby along flow paths; and 4) stream reaches at the base of flow paths with alder have higher nitrate concentrations than reaches at the base of flow paths without alder. The results from chapter 4 showed that groundwater nitrate concentrations were highest along flow paths with alder, however no difference was observed between flow paths with alder located near versus alder located further from streamside wetlands. Vegetation had a greater response to N fertilization in streamside wetlands that were connected to flow paths without alder and less when alder stands were near. Finally, higher nitrate concentrations were measured in streams at the base of flow paths with alder. The combined results of this dissertation showed that, in the Kenai Lowlands, groundwater and surface water interactions have a direct influence on the local ecology and that a fundamental understanding of the hydrology can aid in the successful management and protection of this unique and important ecosystem.

Advancements in web technology such as the integration of operating platforms, the application of mobile applets and connectivity with databases into an encompassing web environment has promoted the development of complex web-based systems for enterprise computing. In this integration the inherent security flaws and associated problems of these technological advancements are also brought together under this web environment. These flaws, when exploited, could lead to system compromises of various kinds including stealing of security sensitive information, system take-over fabrication of fake electronic documents and illegal alteration to web sites contents. Therefore, the successful, prompt and appropriate responses of these complex web-based systems to security threats and breaches, such as in the cases of document tampering and misrepresentation from illegal users, are imperative in promoting the user's willingness and confidence when interacting with these systems. Accordingly, this has become one of the major concerns in development, management and operation of web-based systems. This thesis also studies the authentication of dynamic web contents through the application of a one-time digital signature. To this effect, relevant concepts and possible approaches have been discussed. Authentication and verification of dynamic contents, efficiently in the web environment, is suggested as a separate research area and as a direction for future work. / Master of Science (Honours) Computing

In this study, an improved bit-array representation method for structural topology optimization using the Genetic Algorithm (GA) is proposed. The issue of representation degeneracy is fully addressed and the importance of structural connectivity in a design is further emphasized. To evaluate the constrained objective function, Deb's constraint handling approach is further developed to ensure that feasible individuals are always better than infeasible ones in the population to improve the efficiency of the GA. A hierarchical violation penalty method is proposed to drive the GA search towards the topologies with higher structural performance, less unusable material and fewer separate objects in the design domain in a hierarchical manner. Numerical results of structural topology optimization problems of minimum weight and minimum compliance designs show the success of this novel bit-array representation method and suggest that the GA performance can be significantly improved by handling the design connectivity properly. / Singapore-MIT Alliance (SMA)

Caribbean spiny lobster (Panulirus argus) is a popular and heavily exploited seafood throughout its range. This species supports the primary fishery in many Caribbean countries, especially in the Bahamas, which reports the highest catches and where spiny lobster serves as the number one food export. P. argus possesses one of the longest pelagic larval durations of any marine species, ranging from 6-12 months. This allows for the possibility of long-range dispersal, which would make it difficult to determine if local adult populations originate from areas close-by or within the same countries/jurisdictions, thus presenting implications for conservation and management of the species. This project seeks to explore the policy implications of lobster larval dispersal in the Bahamas by examining the larval connectivity of locally spawned P. argus in order to determine the mean dispersal kernel and to identify hotspots of settlement within the area. A coupled biophysical model was used to simulate larval transport from scaled egg production of 47 release locations within the Bahamas. The model was initialized bi-weekly from April through May, the highest months of larvae production in the Bahamas, with each model run occurring for a maximum of 180 days. The dispersal kernel for the Bahamas was calculated to be an average of 100-300 km, indicating that the larvae released within its boundaries typically settled there as well. Due to the long pelagic larval duration, larval particles were able to travel extensive distances, averaging trajectories covering distances of 4000 km and greater from the source locations. Yet, those same larval particles still settled in locations within the Bahamas, suggesting local retention, which varies from the common perception that lobster in the Bahamas originate elsewhere. This knowledge can be used to assess and perhaps reevaluate conservation and management strategies related to the Bahamian P. argus fishery, including the implementation of MPAs and/or MPA networks, input and output management controls, and other management tools.

The supply of coral reef fish larvae from the open ocean to reefs is vital for the persistence of local fish populations. Whether larvae are dispersed over hundreds of km or only few km depends on biophysical interactions between larvae and their environment. Relationships between environmental variables, larval swimming behavior, and larval transport were examined for reef fish larvae in the Florida Straits. In a series of research cruises, the upper 100 m of the water column was sampled with plankton nets fishing at four different depths. Variability in the vertical distributions of most larvae was not consistently related to measured environmental variables. Relative densities of larvae were predictably related to sampling depth in five taxa. In seven taxa, more developed larvae were distributed significantly deeper than less developed larvae, revealing ontogenic vertical migrations. In three taxa, vertical distributions varied significantly between day and night, revealing diel migrations. Since the Florida Current was strongest near the surface, observed vertical distributions and migrations resulted in reduced larval transport relative to surface currents. To identify cues involved in regulating vertical distributions, behavioral experiments were conducted with larvae from four reef fish families. All four groups showed significant responses to pressure cues, swimming up in response to high pressure and down in response to low pressure. In two families there was a significant correlation between capture depth and experimental pressure preference, suggesting that larvae use similar behavior to regulate depth in situ. To study horizontal swimming behavior, late-stage larvae of one species were caught in light-traps and observed by SCUBA divers ~1 km offshore of the Florida Keys barrier reef. All larvae swam remarkably straight, but their swimming directions were distributed randomly. A simulation model was used to generate swimming trajectories of longer duration than could be observed directly. Observed and simulated trajectories indicated that horizontal swimming by larvae with or without an external reference frame was important at spatial scales of several km. Overall, some larvae exercised a strong influence on transport, either by vertical or horizontal swimming. Behaviors varied between species and families, highlighting the need for more species-specific data.

The American alligator (Alligator mississippiensis) has been frequently studied in large reservoirs and coastal marshes. Large ontogenetic shifts in their diet and morphology have been linked with changes in habitat use, with adult males using deep, open water and juveniles and nesting females relying on vegetated marsh. In certain regions of the inland portion of the alligator’s range, these different aquatic habitats are represented by seasonal wetlands and riverine systems that are separated by a terrestrial matrix. Ontogenetic habitat shifts, therefore, would require overland movements between systems, which has important implications for conservation of the species. I tested several commonly used methods of surveying alligator populations to determine the most effective method of studying alligators in seasonal wetlands. I then used systematic trapping, nest surveys and radio telemetry to determine habitat use and overland movement rates by different sex and size classes. I found that seasonal wetlands provided nesting and nursery sites for these inland alligator populations, but that both juveniles undergoing an ontogenetic shift and nesting females move between the wetlands and riverine systems. Overland movements by alligators between the wetland and riverine habitats establish a level of functional connectivity between these aquatic ecosystems. I constructed a habitat suitability index of both the wetlands and the surrounding landscape to determine which patch and landscape characteristics were important to wetland use by alligators. I found that both descriptive wetland characteristics and the spatial relationships between wetlands were important predictors of alligator use. Overland movement was related to upland landuse as well as distance between aquatic habitats. Conserving a variety of wetland sizes and types within an intact upland matrix is critical to maintaining connectivity across the landscape. Furthermore, understanding how species may act as mobile links between ecosystems, particularly those with ontogenetic niche shifts, illustrates the importance of approaching conservation from a landscape perspective.

Semi-natural grasslands, which are a declining and fragmented habitat in Europe, contain a high biodiversity, and are therefore of interest to conservation. This thesis examines how plant diversity is influenced by the landscape context, and how plant and fungal diversity can be targeted by practical conservation using indicator species and congruence between species groups. Reproduction and recruitment of the dioecious herb Antennaria dioica was also investigated, providing a case study on how fragmentation and habitat degradation may affect grassland plants. Grassland size and heterogeneity were of greater importance for plant diversity in semi-natural grassland, than present or historical connectivity to other grasslands, or landscape characteristics. Larger grasslands were more heterogeneous than smaller grasslands, being the likely reason for the species-area relationship. A detailed study on A. dioica discovered that sexual reproduction and recruitment may be hampered due to skewed sex-ratios. Sex-ratios were more skewed in small populations, suggesting that dioecious plants are likely to be particularly sensitive to reduced grassland size and fragmentation. A study on indicators of plant species richness, used in a recent survey of remaining semi-natural grasslands in Sweden, revealed several problems. A high percentage of all indicator species were missed by the survey, removing an otherwise significant correlation between indicator species and plant species richness. Also, a null model showed that the chosen indicator species did not perform significantly better than species chosen at random from the available species pool, questioning the selection of the indicators in the survey. Diversity patterns of the threatened fungal genus Hygrocybe were not congruent with plant species richness or composition. Plants are thus a poor surrogate group for Hygrocybe fungi, and probably also for other grassland fungi. Implications from this thesis are that conservation of semi-natural grasslands should target several species groups, and that an appropriate scale for plant conservation may be local rather than regional.

Background: The world of today is immensely interconnected. Over the past decades, national economies have been de-bordered and the promoting of the flows of goods, people, capital and services across the borders is evident, as opposed to when flows only moved within national economies. Former vertical structures of old nations have been replaced by a horizontal flow structure in a complex and intertwined global economy. Attracting flows is essential for the growth and survival of cities. Hubs functions as important connection points for these flows and are therefore highly important. Research procedure: The purpose of this thesis is to describe how city regions function from a hub perspective by mapping the most important hubs in the Oresund Region, and investigating the connectivity and collaboration between these hubs. This study has a qualitative and inductive approach with a case study design and the empirical findings is based on twelve interviews with representatives of different fields. Results: The most important hubs were divided into three categories: transport, economic and infrastructure hubs, illustrated in the hub categorization model. The results indicate that there is a interconnectivity issue with interdependencies between the different hubs in the Oresund Region. This is illustrated through the hub relationship model. Collaboration seems to take place mostly within sectors and through the municipalities..