Pushing wireless data traffic onto small cells is important for alleviating congestion in the over-loaded macrocellular network. However, the ultimate potential of such load balancing and its effect on overall system performance is not well understood. With the ongoing deployment of multiple classes of access points (APs) with each class differing in transmit power, employed frequency band, and backhaul capacity, the network is evolving into a complex and “organic” heterogeneous network or HetNet. Resorting to system-level simulations for design insights is increasingly prohibitive with such growing network complexity. The goal of this dissertation is to develop realistic yet tractable frameworks to model and analyze load balancing dynamics while incorporating the heterogeneous nature of these networks. First, this dissertation introduces and analyzes a class of user-AP association strategies, called stationary association, and the resulting association cells for HetNets modeled as stationary point processes. A “Feller-paradox”-like relationship is established between the area of the association cell containing the origin and that of a typical association cell. This chapter also provides a foundation for subsequent chapters, as association strategies directly dictate the load distribution across the network. Second, this dissertation proposes a baseline model to characterize downlink rate and signal-to-interference-plus-noise-ratio (SINR) in an M-band K-tier HetNet with a general weighted path loss based association. Each class of APs is modeled as an independent Poisson point process (PPP) and may differ in deployment density, transmit power, bandwidth (resource), and path loss exponent. It is shown that the optimum fraction of traffic offloaded to maximize SINR coverage is not in general the same as the one that maximizes rate coverage. One of the main outcomes is demonstrating the aggressive of- floading required for out-of-band small cells (like WiFi) as compared to those for in-band (like picocells). To achieve aggressive load balancing, the offloaded users often have much lower downlink SINR than they would on the macrocell, particularly in co-channel small cells. This SINR degradation can be partially alleviated through interference avoidance, for example time or frequency resource partitioning, whereby the macrocell turns off in some fraction of such resources. As the third contribution, this dissertation proposes a tractable framework to analyze joint load balancing and resource partitioning in co-channel HetNets. Fourth, this dissertation investigates the impact of uplink load balancing. Power control and spatial interference correlation complicate the mathixematical analysis for the uplink as compared to the downlink. A novel generative model is proposed to characterize the uplink rate distribution as a function of the association and power control parameters, and used to show the optimal amount of channel inversion increases with the path loss variance in the network. In contrast to the downlink, minimum path loss association is shown to be optimal for uplink rate coverage. Fifth, this dissertation develops a model for characterizing rate distribution in self-backhauled millimeter wave (mmWave) cellular networks and thus generalizes the earlier multi-band offloading framework to the co-existence of current ultra high frequency (UHF) HetNets and mmWave networks. MmWave cellular systems will require high gain directional antennas and dense AP deployments. The analysis shows that in sharp contrast to the interferencelimited nature of UHF cellular networks, mmWave networks are usually noiselimited. As a desirable side effect, high gain antennas yield interference isolation, providing an opportunity to incorporate self-backhauling. For load balancing, the large bandwidth at mmWave makes offloading users, with reliable mmWave links, optimal for rate. / text

The ability to grip on petal surfaces is of crucial importance for the interactions between bees and flowers. In this thesis, I explore the biomechanics of attachment and morphological diversity of bee attachment devices, linking this to the behavioural ecology of bee interactions with flowers. Attachment devices come in two main kinds: claws or spines, and adhesive pads. Claw functioning is poorly described, particularly in terms of how their performance depends on body size, claw geometry, and surface roughness. Claw attachment performance was investigated using several insect species, each covering a large range of body masses. Weight-specific attachment forces decreased with body size, with claw sharpness seemingly playing a role. In bees there is considerable interspecific variation in tarsal claw morphology. This variation, and arolia presence/absence, was categorised for the large bee family Apidae. Cleft/bifid claws were shown to be present in the majority of the Apidae, often with differences between sexes and clades. Using Bombus terrestris, there was no evidence that cleft claws are important for pollen collection; however, I found that the inner tooth of cleft claws can act as a backup if the main tooth breaks. Although this may be one function of cleft claws, there are clearly other unresolved functions well worth further exploration. Investigations were undertaken to explore how petal surface roughness affects bee foraging behaviour. Lab-based foraging trials on B. terrestris visiting artificial flowers varying in slope, surface texture and sugar reward revealed a trade-off between the biomechanical difficulty of visiting and handling the ‘flowers’ and the quality of the reward offered. Flowers that were difficult to grip were often avoided even if they offered a higher reward. To further investigate reward preferences of bees, the effect of sucrose concentration on honey stomach offloading times was also explored. Although the majority of petals do have a rough surface, some have slippery petals. In the field, bumblebees avoided landing on slippery hollyhock petals in favour of the easy-to-grip staminal column. In contrast, honey bees, which are smaller and have larger adhesive pads, landed on both the staminal column and the petals. Slippery petals may be an adaptation to increase contact with plant reproductive structures. Grip is also important to allow the honey bee parasite Varroa destructor to climb on to their host. Attachment forces experiments found that V. destructor could support > 300 times their body mass on honey bees, giving them strong attachment even when bees attempt to remove them through grooming. A grooming-based device for treating V. destructor was tested in an apiary trial. The device was ineffective, providing valuable information for beekeepers considering using this product. In summary, this thesis improves our understanding of the biomechanics of attachment as well as identifying several important aspects of grip in bee-plant interactions.

Actuellement les smartphones possèdent un grand éventail de fonctionnalités. Ces objets tout en un, sont constamment connectés. Il est l'appareil favori plébiscité par les utilisateurs parmi tous les dispositifs de communication existants. Les applications actuelles développées pour les smartphones doivent donc faire face à une forte augmentation de la demande en termes de fonctionnalités tandis que - dans un même temps - les smartphones doivent répondre à des critères de compacité et de conception qui les limitent en énergie et à un environnement d'exécution pauvre en ressources. Utiliser un système riche en ressource est une solution classique introduite en informatique dans les nuages mobiles (Mobile Cloud Computing), celle-ci permet de contourner les limites des appareils mobiles en exécutant à distance, toutes ou certaines parties des applications dans ces environnements de nuage. Certaines architectures émergent, mais peu d'algorithmes existent pour traiter les propriétés dynamiques de ces environnements. Dans cette thèse, nous focalisons notre intérêt sur la conception d'ACOMMA (Ant-inspired Collaborative Offloading Middleware for Mobile Applications), un interlogiciel d'exécution déportée collaborative inspirée par le comportement des fourmis, pour les applications mobiles. C'est une architecture orientée service permettant de décharger dynamiquement des partitions d'applications, de manière simultanée, sur plusieurs clouds éloignés ou sur un cloud local créé spontanément, incluant les appareils du voisinage. Les principales contributions de cette thèse sont doubles. Si beaucoup d'intergiciels traitent un ou plusieurs défis relatifs à l'éxecution déportée, peu proposent une architecture ouverte basée sur des services qui serait facile à utiliser sur n'importe quel support mobile sans aucun exigence particulière. Parmi les principaux défis il y a les questions de quoi et quand décharger dans cet environnement très dynamique. A cette fin, nous développons des algorithmes de prises de décisions bio-inspirées : un processus de prise de décision bi-objectif dynamique avec apprentissage et un processus de prise de décision en collaboration avec les autres dispositifs mobiles du voisinage. Nous définissons un mécanisme de dépôt d'exécution avec une méthode de partitionnement grain fin de son graphe d'appel. Nous utilisons les algorithmes des colonies de fourmis pour optimiser bi-objectivement la consommation du CPU et le temps total d'exécution, en incluant la latence du réseau. Nous montrons que les algorithmes des fourmis sont plus facilement re-adaptables face aux modifications du contexte, peuvent être très efficaces en ajoutant des algorithmes de cache par comparaison de chaîne (string matching caching) et autorisent facilement la dissémination du profil de l'application afin de créer une exécution déportée collaborative dans le voisinage. / Not bounded by time and place, and having now a wide range of capabilities, smartphones are all-in-one always connected devices - the favorite devices selected by users as the most effective, convenient and neces- sary communication tools. Current applications developed for smartphones have to face a growing demand in functionalities - from users, in data collecting and storage - from IoT device in vicinity, in computing resources - for data analysis and user profiling; while - at the same time - they have to fit into a compact and constrained design, limited energy savings, and a relatively resource-poor execution environment. Using resource- rich systems is the classic solution introduced in Mobile Cloud Computing to overcome these mobile device limitations by remotely executing all or part of applications to cloud environments. The technique is known as application offloading. Offloading to a cloud - implemented as geographically-distant data center - however introduces a great network latency that is not acceptable to smartphone users. Hence, massive offloading to a centralized architecture creates a bottleneck that prevents scalability required by the expanding market of IoT devices. Fog Computing has been introduced to bring back the storage and computation capabilities in the user vicinity or close to a needed location. Some architectures are emerging, but few algorithms exist to deal with the dynamic properties of these environments. In this thesis, we focus our interest on designing ACOMMA, an Ant-inspired Collaborative Offloading Middleware for Mobile Applications that allowing to dynamically offload application partitions - at the same time - to several remote clouds or to spontaneously-created local clouds including devices in the vicinity. The main contributions of this thesis are twofold. If many middlewares dealt with one or more of offloading challenges, few proposed an open architecture based on services which is easy to use for any mobile device without any special requirement. Among the main challenges are the issues of what and when to offload in a dynamically changing environment where mobile device profile, context, and server properties play a considerable role in effectiveness. To this end, we develop bio-inspired decision-making algorithms: a dynamic bi-objective decision-making process with learning, and a decision-making process in collaboration with other mobile devices in the vicinity. We define an offloading mechanism with a fine-grained method-level application partitioning on its call graph. We use ant colony algorithms to optimize bi-objectively the CPU consumption and the total execution time - including the network latency.

Freqüentemente os profissionais da construção naval tomam decisões para selecionar os elementos que devem ser especificados na composição de determinado projeto. Além da experiência e do conhecimento necessários para optar por um caminho adequado, a escolha deve atender eficientemente ao problema proposto e às preferências do projetista. A seleção de componentes do projeto de estruturas flutuantes para exploração de campos de petróleo no mar envolve aspectos objetivos e subjetivos. O trabalho apresenta e aplica alguns métodos de auxílio à tomada de decisão possibilitando ao projetista aprimorar sua sensibilidade. O objetivo da pesquisa é apresentar de forma sumária as duas bases para a decisão sobre o projeto, que são os métodos de apoio e os requisitos que as instalações FPSO devem atender, fornecendo como resultado um procedimento que permitirá aos usuários a melhor escolha dos componentes e aumentar a sensibilidade dos projetistas na seleção entre as possíveis opções (fazer totalmente novo ou aproveitar o existente). O trabalho apresenta uma revisão dos princípios da análise da decisão, informações sobre métodos de apoio à decisão, os dados de entrada do problema proposto, o método de projetos navais, os requisitos básicos para construção de estruturas flutuantes de exploração de petróleo no mar e os requisitos básicos para uma instalação FPSO. Para a solução do problema se aplicaram os métodos de árvore de decisão, para a parte correspondente às decisões sob risco e o método de análise hierárquica AHP para as decisões tomadas sob certeza. / Frequently, naval construction engineers take decisions to select the elements which must specified for the composition of a determined project. Besides the necessary experience and the knowledge to choose a proper way, the option must fulfil efficiently the problem requirements and the preferences of the designer. The choice of components in the design off-shore structures for production in sea oilfields, involves objective and subjective aspects. This work introduces and uses a few methods of decision aids, helping the designer to improve his sensibility. The objective of this research is to present in a simple way two foundations to decide about the project, which are the aid decision methods and the requirements which the FPSO (Floating Production Storage and Offloading System) must fulfil, supplying a procedure that enables the designer to take the best choice of components and to increase his sensibility referring to the selection among the possible options, wich are to make a completely new FPSO or to use an existing one. This work offers a revision of the principles of the decision analysis theory, the data input of the problem, the classic naval design method, the basic requirements to build floating structures to off-shore oil extraction, and the basic requirements for a FPSO installation. To solve the problem the decision tree method, for decision under risk, and the AHP (Analytic Hierarchy Process), for decision under certainty, were applied.