In an era of pervasive water stress caused by population growth, urbanization, drought, and climate change, limiting the dissemination of microbial contaminants of emerging concern (MCECs) is of the utmost importance for the protection of public health. In this dissertation, two important subsets of MCECs, opportunistic pathogens (OP) and antibiotic resistant genes (ARG), are studied across several compartments of the urban water cycle, including surface water, stormwater, wastewater, recycled water, and potable water. Collectively, this dissertation advances knowledge about the occurrence of OPs and ARGs across these water systems and highlights trends that may be of value in developing management strategies for limiting their regrowth and transmission. Field studies of two surface water catchments impacted by stormwater runoff demonstrated the prevalence of ARGs in urban stormwater compared to pristine, unimpacted sites, or to days when no precipitation was recorded. The role of wastewater reuse in transmitting OPs and ARGs was also investigated. Traditional tertiary wastewater treatment plants producing water for non-potable use were found to be largely ineffective at removing ARGs, but plants using advanced oxidation processes or ozonation paired with biofiltration to produce direct potable reuse water were highly effective at removing ARGs. Non-potable reclaimed water consistently had greater quantities of sul1, a sulfonamide ARG, and Legionella and Mycobacterium, two OPs of significant public health concern, present than corresponding potable systems. Limited regrowth of OPs and ARGs did occur in simulated premise (i.e., building) plumbing systems operated with direct potable reuse waters, but regrowth was comparable to that observed in systems fed with potable water derived from surface or groundwater. Advancements were also made in understanding the role of several hypothesized driving forces shaping the antibiotic resistome in natural and engineered water systems: selection by antimicrobials and other compounds, horizontal gene transfer, and microbial community composition. Finally, whole-genome and metagenomic characterization were applied together towards profiling L. pneumophila in clinical and water samples collected from Flint, Michigan, where an economically-motivated switch to an alternative water source created conditions favorable for growth of this organism and likely triggered one of the largest Legionnaires' Disease outbreaks in U.S. history. / PHD / Population growth, urbanization, drought, and climate change have all driven many U.S. municipalities to utilize alternative water sources, such as recycled wastewater, to offset demand on traditional potable water sources. Many water providers have moved towards a modern paradigm of utilizing multiple available water sources, recognizing the interconnectedness of various components of the urban water cycle, leading to opportunities to improve sustainability, optimize infrastructure use, stimulate economic growth, increase coordination among water agencies, and identify new water resources from which to meet consumer needs. Though advancements in treatment technologies throughout the twentieth century have largely succeeded in eliminating waterborne disease outbreaks associated with contamination of municipal water supplies by fecal pathogens in developed countries, several microbial contaminants of emerging concern (MCECs) have garnered attention. Two major groups of MCECs are considered in this dissertation: antibiotic resistance, including antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARG), and opportunistic pathogens (OP), such as Legionella pneumophila, the causative agent of Legionnaires’ Disease. ARB are a rising cause of disease around the world and are a major challenge to modern medicine because they make antibiotics used for treatment ineffective. OPs, the leading cause of waterborne disease in the U.S. and other developed countries, have become prevalent in engineered water systems where low nutrient concentrations, warm water temperatures, and long stagnation times can facilitate their growth. Immunocompromised people, including smokers and the elderly, are especially vulnerable to infection with OPs. The role of the urban water cycle in facilitating the spread of these MCECs is not well understood. Here they were studied across several compartments of the urban water cycle, including surface water, stormwater, wastewater, recycled water (spanning a variety of intended uses, from non-potable to direct potable reuse), and potable water. Field studies were conducted of two watersheds impacted by stormwater runoff, one in the arid Colorado Front Range under conditions of a rare, 1-in-1,000 year rainfall event, and one in the humid climate of southwest Virginia, during three summer storms. Both studies demonstrated the prevalence of ARGs in urban stormwater compared to pristine, unimpacted sites, or to days when no precipitation was recorded. The role of wastewater reuse in transmitting OPs and ARGs was also investigated. Wastewater treatment plants producing water for non-potable use (i.e. applications such as irrigation, but not for human consumption) were found to be largely inefficient at removing ARGs, and this reclaimed water consistently had greater quantities of the sul1 ARG present than in corresponding potable systems. In these systems, genes associated with the OPs Legionella and Mycobacterium as well as total bacteria were more abundant in reclaimed water than in corresponding potable systems. In more advanced treatment plants utilizing advanced oxidation processes or ozonation paired with biofiltration to produce direct potable reuse water (i.e. water fit for human consumption), ARGs were very effectively removed by treatment, with abundances often found to be higher in corresponding potable waters derived from surface or groundwater. Limited regrowth of ARGs as well as OPs did occur in simulated home plumbing systems operated with these waters, but regrowth was comparable to that observed in systems fed with potable water derived from surface or groundwater. Finally, a study of L. pneumophila in the Flint, Michigan drinking water system during use of an alternative water source that has been identified as a likely cause of two Legionnaires’ Disease outbreaks revealed presence of multiple strains of the OP in the system. Genomic comparisons revealed that strains isolated from hospital and residential water samples were highly similar to clinical strains associated with the outbreaks. Advancements were also made in understanding the role of several hypothesized driving forces in shaping the antibiotic resistome in natural and engineered water systems: selection by antimicrobials and other compounds, horizontal gene transfer, and microbial community composition. Together, these chapters describe an advancement in knowledge regarding the occurrence of OPs and ARGs in a variety of water systems, and highlight trends that may be of value in developing management strategies for limiting regrowth or transmission of these bacteria in various compartments of the urban water cycle.

A sociological approach is used to analyze incidences of extreme opportunism in financial markets. Through an analysis of arguably the most widely publicized "rogue" trader events in recent history, a determination is made of the validity of explaining these events as aberrations, attributable to the actions of "rogues". The primary focus is the role of structural factors underlying these incidences of extreme opportunism in financial markets. A diverse range of documentary and other sources is used to avoid any form of bias as far as possible. It was found that structural factors act as countervailing forces to inhibit such behavior or as motivators and facilitators acting as catalysts for extreme opportunism. The balance between these factors largely determines the level of opportunistic behavior in a particular environment. Extreme opportunism is therefore not an aberration or "rogue" occurrence but a manageable phenomenon intrinsic to the social structural context within which it occurs. By conceptualizing these factors as countervailing forces one is forced to view structural factors, like compensation structures and formal and informal restraints, relative to one another and no longer in isolation. This realization translates into the conclusion that restraints and oversight systems for example, should be designed relative to the relevant motivators and facilitators in its area of application. In an environment where traders of highly geared financial products are motivated with multimillion USD incentive packages, a low budget oversight system and inexperienced regulatory staff, is clearly not the appropriate tools to control and manage extreme opportunism. / Criminology / D.Phil. (Sociology)

A sociological approach is used to analyze incidences of extreme opportunism in financial markets. Through an analysis of arguably the most widely publicized "rogue" trader events in recent history, a determination is made of the validity of explaining these events as aberrations, attributable to the actions of "rogues". The primary focus is the role of structural factors underlying these incidences of extreme opportunism in financial markets. A diverse range of documentary and other sources is used to avoid any form of bias as far as possible. It was found that structural factors act as countervailing forces to inhibit such behavior or as motivators and facilitators acting as catalysts for extreme opportunism. The balance between these factors largely determines the level of opportunistic behavior in a particular environment. Extreme opportunism is therefore not an aberration or "rogue" occurrence but a manageable phenomenon intrinsic to the social structural context within which it occurs. By conceptualizing these factors as countervailing forces one is forced to view structural factors, like compensation structures and formal and informal restraints, relative to one another and no longer in isolation. This realization translates into the conclusion that restraints and oversight systems for example, should be designed relative to the relevant motivators and facilitators in its area of application. In an environment where traders of highly geared financial products are motivated with multimillion USD incentive packages, a low budget oversight system and inexperienced regulatory staff, is clearly not the appropriate tools to control and manage extreme opportunism. / Criminology and Security Science / D.Phil. (Sociology)

In this thesis we study several resource management problems in two classes of wireless networks. The thesis is in two parts, the first being concerned with game theoretic approaches for cellular networks, and the second with control theoretic approaches for mobile opportunistic networks. In Part I of the thesis, we first investigate optimal association and power control for the uplink of multichannel multicell cellular networks, in which each channel is used by exactly one base station (BS) (i.e., cell). Users have minimum signal to interference ratio(SINR) requirements and associate with BSs where least transmission powers are required. We formulate the problem as a non-cooperative game among users. We propose a distributed association and power update algorithm, and show its convergence to a Nash equilibrium of the game. We consider network models with discrete mobiles(yielding an atomic congestion game),as well as a continuum of mobiles(yielding a population game). We find that the equilibria need not be Pareto efficient, nor need they be system optimal. To address the lack of system optimality, we propose pricing mechanisms. We show that these prices weakly enforce system optimality in general, and strongly enforce it in special settings. We also show that these mechanisms can be implemented in distributed fashions. Next, we consider the hierarchical problems of user association and BS placement, where BSs may belong to the same(or, cooperating) or to competing service providers. Users transmit with constant power, and associate with base stations that yield better SINRs. We formulate the association problem as a game among users; it determines the cell corresponding to each BS. Some intriguing observations we report are:(i)displacing a BS a little in one direction may result in a displacement of the boundary of the corresponding cell to the opposite direction;(ii)A cell corresponding to a BS may be the union of disconnected sub-cells. We then study the problem of the placement of BSs so as to maximize service providers’ revenues. The service providers need to take into account the mobiles’ behavior that will be induced by the placement decisions. We consider the cases of single frequency band and disjoint frequency bands of operation. We also consider the networks in which BSs employ successive interference cancellation(SIC) decoding. We observe that the BS locations are closer to each other in the competitive case than in the cooperative case, in all scenarios considered. Finally, we study cooperation among cellular service providers. We consider networks in which communications involving different BSs do not interfere. If service providers jointly deploy and pool their resources, such as spectrum and BSs, and agree to serve each others’ customers, their aggregate payoff substantially increases. The potential of such cooperation can, however ,be realized only if the service providers intelligently determine who they would cooperate with, how they would deploy and share their resources, and how they would share the aggregate payoff. We first assume that the service providers can arbitrarily share the aggregate payoff. A rational basis for payoff sharing is imperative for the stability of the coalitions. We study cooperation using the theory of transferable payoff coalitional games. We show that the optimum cooperation strategy, which involves the acquisition of channels, and deployment and allocation of BSs to customers, is the solution of a concave or an integer optimization problem. We then show that the grand coalition is stable, i.e., if all the service providers cooperate, there is an operating point offering each service provider a share that eliminates the possibility of a subset of service providers splitting from the grand coalition; this operating point also maximizes the service providers’ aggregate payoff. These stabilizing payoff shares are computed by solving the dual of the above optimization problem. Moreover, the optimal cooperation strategy and the stabilizing payoff shares can be obtained in polynomial time using distributed computations and limited exchange of confidential information among the service providers. We then extend the analysis to the scenario where service providers may not be able to share their payoffs. We now model cooperation as a nontransferable payoff coalitional game. We again show that there exists a cooperation strategy that leaves no incentive for any subset of service providers to split from the grand coalition. To compute this cooperation strategy and the corresponding payoffs, we relate this game and its core to an exchange market and its equilibrium. Finally, we extend the formulations and the results to the case when customers are also decision makers in coalition formation. In Part II of this thesis, we consider the problem of optimal message forwarding in mobile opportunistic wireless networks. A message originates at a node(source), and has to be delivered to another node (destination). In the network, there are several other nodes that can assist in relaying the message at the expense of additional transmission energies. We study the trade-off between delivery delay and energy consumption. First, we consider mobile opportunistic networks employing two-hop relaying. Because of the intermittent connectivity, the source may not have perfect knowledge of the delivery status at every instant. We formulate the problem as a stochastic control problem with partial information, and study structural properties of the optimal policy. We also propose a simple suboptimal policy. We then compare the performance of the suboptimal policy against that of the optimal control with perfect information. These are bounds on the performance of the proposed policy with partial information. We also discuss a few other related open loop policies. Finally, we investigate the case where a message has to be delivered to several destinations, but we are concerned with delay until a certain fraction of them receive the message. The network employs epidemic relaying. We first assume that, at every instant, all the nodes know the number of relays carrying the packet and the number of destinations that have received the packet. We formulate the problem as a controlled continuous time Markov chain, and derive the optimal forwarding policy. As observed earlier, the intermittent connectivity in the network implies that the nodes may not have the required perfect knowledge of the system state. To address this issue, we then obtain an ODE(i.e., a deterministic fluid) approximation for the optimally controlled Markov chain. This fluid approximation also yields an asymptotically optimal deterministic policy. We evaluate the performance of this policy over finite networks, and demonstrate that this policy performs close to the optimal closed loop policy. We also briefly discuss the case where message forwarding is accomplished via two-hop relaying.

Several yeast species had previously been isolated from water systems in the North West Province, South Africa. Some of the identified species had, in other studies, been associated with superficial mucosal infections to life threatening diseases. Antifungal drugs are used to treat such yeast infections. However, due to prophylactic usage and continuous exposure some yeast species have developed resistance to some antifungal agents. The aim of this study was to determine the diversity and antifungal susceptibility of yeasts in selected rivers, Mooi River and Harts River in the North West Province, South Africa. Waters samples were collected from the rivers in summer and winter seasons. Physico-chemical parameters such as pH, temperature, total dissolved solids, chemical oxygen demand, nitrates and phosphates were measured to determine the water quality. Yeast colonies were enumerated at room temperature and 37°C using yeast-malt-extract agar (containing 100 ppm chloramphenicol). Pure isolates from 37°C were identified by biochemical tests and 26S rRNA gene sequencing. Yeast sequences of isolated yeasts were sent to Genbank. Phylogenetic tree was conducted to determine phylogenetic relationship between the yeast isolates. Disk diffusion antifungal susceptibility tests were conducted on the yeast species. Physico-chemical parameters of the water were within target water quality range for livestock farming but in most sampling sites out of range for irrigation use. pH, Nitrates, phosphates and chemical oxygen demand levels ranged from 7.40 to 8.64, 0 to 5.4 mg/L, 0 to 7.14 mg/L and 31 to 43 mg/L, respectively. Elevated levels of total dissolved solids were measured in all the sampling sites. Total yeast counts ranged between 320-4200 cfu/L and 27-2573 cfu/L for room temperature and 37˚C. All the yeast colonies isolated were non-pigmented. Diazonium Blue B tests determined the yeasts isolates as ascomycetes. Haemolysin and extracellular enzyme production tests were negative on all the isolates. Yeasts isolates were identified and belonged to the genera Arxiozyma, Candida, Clavispora, Cyberlindnera, Lecythophora, Pichia, Saccharomyces, and Wickerhamomyces. Saccharomyces cerevisiae and Candida glabrata were mostly isolated species. Furthermore, the results indicated that levels of yeast could be correlated to physico-chemical quality of water. A large number of isolates were resistant to azoles, especially fluconazole as well as other antifungal classes. Most of the Candida species were resistant to almost all the antifungals. Several of the isolated yeast species are opportunistic pathogens. They could cause infections in sensitive individuals during occasional direct contact especially immune compromised people. Resistance of these yeast species to antifungal agents is a major health concern. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

Several yeast species had previously been isolated from water systems in the North West Province, South Africa. Some of the identified species had, in other studies, been associated with superficial mucosal infections to life threatening diseases. Antifungal drugs are used to treat such yeast infections. However, due to prophylactic usage and continuous exposure some yeast species have developed resistance to some antifungal agents. The aim of this study was to determine the diversity and antifungal susceptibility of yeasts in selected rivers, Mooi River and Harts River in the North West Province, South Africa. Waters samples were collected from the rivers in summer and winter seasons. Physico-chemical parameters such as pH, temperature, total dissolved solids, chemical oxygen demand, nitrates and phosphates were measured to determine the water quality. Yeast colonies were enumerated at room temperature and 37°C using yeast-malt-extract agar (containing 100 ppm chloramphenicol). Pure isolates from 37°C were identified by biochemical tests and 26S rRNA gene sequencing. Yeast sequences of isolated yeasts were sent to Genbank. Phylogenetic tree was conducted to determine phylogenetic relationship between the yeast isolates. Disk diffusion antifungal susceptibility tests were conducted on the yeast species. Physico-chemical parameters of the water were within target water quality range for livestock farming but in most sampling sites out of range for irrigation use. pH, Nitrates, phosphates and chemical oxygen demand levels ranged from 7.40 to 8.64, 0 to 5.4 mg/L, 0 to 7.14 mg/L and 31 to 43 mg/L, respectively. Elevated levels of total dissolved solids were measured in all the sampling sites. Total yeast counts ranged between 320-4200 cfu/L and 27-2573 cfu/L for room temperature and 37˚C. All the yeast colonies isolated were non-pigmented. Diazonium Blue B tests determined the yeasts isolates as ascomycetes. Haemolysin and extracellular enzyme production tests were negative on all the isolates. Yeasts isolates were identified and belonged to the genera Arxiozyma, Candida, Clavispora, Cyberlindnera, Lecythophora, Pichia, Saccharomyces, and Wickerhamomyces. Saccharomyces cerevisiae and Candida glabrata were mostly isolated species. Furthermore, the results indicated that levels of yeast could be correlated to physico-chemical quality of water. A large number of isolates were resistant to azoles, especially fluconazole as well as other antifungal classes. Most of the Candida species were resistant to almost all the antifungals. Several of the isolated yeast species are opportunistic pathogens. They could cause infections in sensitive individuals during occasional direct contact especially immune compromised people. Resistance of these yeast species to antifungal agents is a major health concern. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2015

When in physical proximity, data can be directly exchanged between the mobile devices people carry - for example over Bluetooth. If people cooperate to store, carry and forward messages on one another's behalf, then an opportunistic network may be formed, independent of any fixed infrastructure. To enable performant routing within opportunistic networks, use of social network information has been proposed for social network routing protocols. But the decentralised and cooperative nature of the networks can however expose users of such protocols to privacy and security threats, which may in turn discourage participation in the network. In this thesis, we examine how to mitigate privacy and security threats in opportunistic networks while maintaining network performance. We first demonstrate that privacy-aware routing protocols are required in order to maintain network performance while respecting users' privacy preferences. We then demonstrate novel social network routing protocols that mitigate specific threats to privacy and security while maintaining network performance.

In urban search and rescue (USAR) operations, there is a considerable amount of danger faced by rescuers. The use of mobile robots can alleviate this issue. Coordinating the search effort is made more difficult by the communication issues typically faced in these environments, such that communication is often restricted. With small numbers of robots, it is necessary to break communication links in order to explore the entire environment. The robots can be viewed as a broken ad hoc network, relying on opportunistic contact in order to share data. In order to minimise overheads when exchanging data, a novel algorithm for data exchange has been created which maintains the propagation speed of flooding while reducing overheads. Since the rescue workers outside of the structure need to know the location of any victims, the task of finding their locations is two parted: 1) to locate the victims (Search Time), and 2) to get this data outside the structure (Delay Time). Communication with the outside is assumed to be performed by a static robot designated as the Command Station. Since it is unlikely that there will be sufficient robots to provide full communications coverage of the area, robots that discover victims are faced with the difficult decision of whether they should continue searching or return with the victim data. We investigate a variety of search techniques and see how the application of biological foraging models can help to streamline the search process, while we have also implemented an opportunistic network to ensure that data are shared whenever robots come within line of sight of each other or the Command Station. We examine this trade-off between performing a search and communicating the results.

La communauté de la Visualisation d'Information (Infovis) accorde une importance primordiale à la conception de techniques de visualisation nouvelles, efficaces, ou spécialisées. Alors qu'une technique de visualisation est composée à la fois de techniques de représentation et de techniques d'interaction, la conception de nouvelles techniques d'interaction pour l'Infovis passe souvent au second plan. Dans cette thèse, centrée sur l'interaction en Infovis, j'explore la conception de nouvelles techniques d'interaction afin de rendre des techniques de visualisation existantes plus efficaces, plus adaptées aux tâches utilisateur, et plus engageantes. Afin que ces techniques d'interaction soient efficaces, il est nécessaire d'abandonner les outils interactifs (widgets) standards et proposer des interfaces utilisateur allant au-delà des interfaces à fenêtres, icônes, menus et pointeur connues sous le nom d'interfaces WIMP (Window/Icon/Menu/Pointer).Dans cette thèse, je soutiens que la conception de nouvelles techniques d'interaction pour la visualisation devraient être basée sur le paradigme de la manipulation directe et sur le modèle de l'interaction instrumentale, et s'inspirer de paradigmes d'interaction établis en Interaction Homme-Machine (IHM) mais trop peu connus et reconnus en Infovis. En me basant sur plusieurs projets que j'ai menés au court de ma thèse, je démontre que la conception opportuniste d'interactions nouvelles peut rendre des techniques de visualisation plus efficaces. Ces différents projets soulèvent des problèmes de conception des techniques d'interaction, tels que le compromis entre la congruence cognitive d'une technique d'interaction et sa généricité, le problème de la conception d'interactions engageant l'utilisateur, et les mérites de l'interaction fluide et ininterrompue. Enfin, je propose un ensemble de règles dérivées des différents projets de cette thèse et je soumets des perspectives de travaux futurs, afin de contribuer au grand défi d'établir une théorie de l'interaction pour l'Infovis. / There is a tremendous effort from the information visualization (Infovis) community to design novel, more efficient or more specialized desktop visualization techniques. While visual representations and interactions are combined to create these visualizations, less effort is invested in the design of new interaction techniques for Infovis. In this thesis, I focus on interaction for Infovis and explore how to improve existing visualization techniques through efficient yet simple interactions. To become more efficient, the interaction techniques should reach beyond the standard widgets and Window/Icon/Menu/Pointer (WIMP) user interfaces. In this thesis, I argue that the design of novel interactions for visualization should be based on the direct manipulation paradigm, instrumental interaction, and take inspiration from advanced interactions investigated in HCI research but not well exploited yet in Infovis. I take examples from multiple projects I have designed to illustrate how opportunistic interactions can empower visualizations and I explore design implications raised by novel interaction techniques, such as the tradeoff between cognitive congruence and versatility, the problem of engaging interaction, and the benefits of seamless, fluid interaction. Finally, I provide guidelines and perspectives, addressing the grand challenge of building or consolidating the theory of interaction for Infovis.

Les réseaux opportunistes sont des réseaux mobiles qui se forment spontanément et de manière dynamique grâce à un ensemble d'utilisateurs itinérants dont le nombre et le déplacement ne sont pas prévisibles. En conséquence, la topologie et la densité de tels réseaux évoluent sans cesse. La diffusion de bout-en-bout d'informations, dans ce contexte, est incertaine du fait de la forte instabilité des liens réseaux point à point entre les utilisateurs. Les travaux qui en ont envisagé l'usage visent pour la plupart des applications impliquant l'envoi de message de petite taille. Cependant, la transmission de données volumineuses telles que les vidéos représente une alternative très pertinente aux réseaux d'infrastructure, en cas d'absence de réseau, de coût important ou pour éviter la censure d'un contenu. La diffusion des informations de grande taille en général et de vidéos en particulier dans des réseaux oppnets constitue un challenge important. En effet, permettre, dans un contexte réseau très incertain et instable, au destinataire d’une vidéo de prendre connaissance au plus vite du contenu de celle-ci, avec la meilleure qualité de lecture possible et en encombrant le moins possible le réseau reste un problème encore très largement ouvert. Dans cette thèse, nous proposons un nouveau mécanisme de diffusion de vidéos dans un réseau opportuniste de faible densité, visant à améliorer le temps d'acheminement de la vidéo tout en réduisant le délai de lecture à destination. La solution proposée se base sur le choix d'encoder la vidéo en utilisant l'encodage SVC, grâce auquel la vidéo se décline en un ensemble de couches interdépendantes (layers), chacune améliorant la précédente soit en terme de résolution, soit en terme de densité, soit en terme de perception visuelle. Notre solution se décline en trois contributions. La première consiste à proposer une adaptation du mécanisme de diffusion Spray-and-Wait, avec comme unités de diffusion, les couches produites par SVC. Les couches sont ainsi diffusées avec un niveau de redondance propre à chacune, adapté à leur degré d'importance dans la diffusion de la vidéo. Notre seconde contribution consiste à améliorer le mécanisme précédent en prenant en compte une granularité plus fine et adaptative en fonction de l'évolution de la topologie du réseau. Cette amélioration a la particularité de ne pas engendrer de coût de partitionnement, les couches vidéos dans l'encodage SVC étant naturellement déclinées en petites unités (NALU) à base desquelles l'unité de transfert sera calculée. Enfin, la troisième contribution de cette thèse consiste à proposer un mécanisme hybride de complétion des couches vidéos arrivées incomplètes à destination. Cette méthode se caractérise par le fait d'être initiée par le destinataire. Elle combine un protocole de demande des parties manquantes aux usagers proches dans le réseau et des techniques de complétion de vidéo à base d’opérations sur les frames constituant la vidéo. / Opportunistic networks are human-centric mobile ad-hoc networks, in which neither the topology nor the participating nodes are known in advance. Routing is dynamically planned following the store-carry-and-forward paradigm, which takes advantage of people mobility. This widens the range of communication and supports indirect end-to-end data delivery. But due to individuals’ mobility, OppNets are characterized by frequent communication disruptions and uncertain data delivery. Hence, these networks are mostly used for exchanging small messages like disaster alarms or traffic notifications. Other scenarios that require the exchange of larger data are still challenging due to the characteristics of this kind of networks. However, there are still multimedia sharing scenarios where a user might need switching to an ad-hoc alternative. Examples are the cases of 1) absence of infrastructural networks in far rural areas, 2) high costs due limited data volumes or 3) undesirable censorship by third parties while exchanging sensitive content. Consequently, we target in this thesis a video dissemination scheme in OppNets. For the video delivery problem in the sparse opportunistic networks, we propose a solution that encloses three contributions. The first one is given by granulating the videos at the source node into smaller parts, and associating them with unequal redundancy degrees. This is technically based on using the Scalable Video Coding (SVC), which encodes a video into several layers of unequal importance for viewing the content at different quality levels. Layers are routed using the Spray-and-Wait routing protocol, with different redundancy factors for the different layers depending on their importance degree. In this context as well, a video viewing QoE metric is proposed, which takes the values of the perceived video quality, delivery delay and network overhead into consideration, and on a scalable basis. Second, we take advantage of the small units of the Network Abstraction Layer (NAL), which compose SVC layers. NAL units are packetized together under specific size constraints to optimize granularity. Packets sizes are tuned in an adaptive way, with regard to the dynamic network conditions. Each node is enabled to record a history of environmental information regarding the contacts and forwarding opportunities, and use this history to predict future opportunities and optimize the sizes accordingly. Lastly, the receiver node is pushed into action by reacting to missing data parts in a composite backward loss concealment mechanism. So, the receiver asks first for the missing data from other nodes in the network in the form of request-response. Then, since the transmission is concerned with video content, video frame loss error concealment techniques are also exploited at the receiver side. Consequently, we propose to combine the two techniques in the loss concealment mechanism, which is enabled then to react to missing data parts.