Dissertations / Theses on the topic 'Small World Network model'
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Taha, Samah M. Osman. "Small-world network models and their average path length." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/95834.
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Thesis (MSc)--Stellenbosch University, 2014.ENGLISH ABSTRACT: Socially-based networks are of particular interest amongst the variety of communication networks arising in reality. They are distinguished by having small average path length and high clustering coefficient, and so are examples of small-world networks. This thesis studies both real examples and theoretical models of small-world networks, with particular attention to average path length. Existing models of small-world networks, due to Watts and Strogatz (1998) and Newman and Watts (1999a), impose boundary conditions on a one dimensional lattice, and rewire links locally and probabilistically in the former or probabilistically adding extra links in the latter. These models are investigated and compared with real-world networks. We consider a model in which randomness is provided by the Erdos-Rényi random network models superposed on a deterministic one dimensional structured network. We reason about this model using tools and results from random graph theory. Given a disordered network C(n, p) formed by adding links randomly with probability p to a one dimensional network C(n). We improve the analytical result regarding the average path length by showing that the onset of smallworld behaviour occurs if pn is bounded away from zero. Furthermore, we show that when pn tends to zero, C(n, p) is no longer small-world. We display that the average path length in this case approaches infinity with the network order. We deduce that at least εn (where ε is a constant bigger than zero) random links should be added to a one dimensional lattice to ensure average path length of order log n.
AFRIKAANSE OPSOMMING: Sosiaal-baseerde netwerke is van besondere belang onder die verskeidenheid kommunikasie netwerke. Hulle word onderskei deur ’n klein gemiddelde skeidingsafstand en hoë samedrommingskoëffisiënt, en is voorbeelde van kleinwêreld netwerke. Hierdie verhandeling bestudeer beide werklike voorbeelde en teoretiese modelle van klein-wêreld netwerke, met besondere aandag op die gemiddelde padlengte. Bestaande modelle van klein-wêreld netwerke, te danke aan Watts en Strogatz (1998) en Newman en Watts (1999a), voeg randvoorwaardes by tot eendimensionele roosters, en herbedraad nedwerkskakels gebaseer op lokale kennis in die eerste geval en voeg willekeurig ekstra netwerkskakels in die tweede. Hierdie modelle word ondersoek en vergelyk met werklike-wêreld netwerke. Ons oorweeg ’n prosedure waarin willekeurigheid verskaf word deur die Erdös- Renyi toevalsnetwerk modelle wat op ’n een-dimensionele deterministiese gestruktureerde netwerk geimposeer word. Ons redeneer oor hierdie modelle deur gebruik te maak van gereedskap en resultate toevalsgrafieke teorie. Gegewe ’n wanordelike netwerk wat gevorm word deur skakels willekeurig met waarskynlikheid p tot ‘n een-dimensionele netwerk C(n) toe te voeg, verbeter ons die analitiese resultaat ten opsigte van die gemiddelde padlengte deur te wys dat die aanvang van klein-wêreld gedrag voorkom wanneer pn weg van nul begrens is. Verder toon ons dat, wanneer pn neig na nul, C(n, p) nie meer klein-wêreld is nie. Ons toon dat die gemiddelde padlengte in hierdie geval na oneindigheid streef saam met die netwerk groote. Ons lei af dat ten minste εn (waar εn n konstante groter as nul is) ewekansige skakels bygevoeg moet word by ’n een-dimensionele rooster om ‘n gemiddelde padlengte van orde log n te verseker.
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Vieira, Israel Teixeira. "Small world network models of the dynamics of HIV infection." Thesis, University of Southampton, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433933.
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Hedefalk, Finn. "Robustness of Spatial Databases: Using Network Analysis on GIS Data Models." Thesis, University of Gävle, Department of Technology and Built Environment, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-6625.
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Demands on the quality and reliability of Volunteered Geographic Information have increased because of its rising popularity. Due to the less controlled data entry, there is a risk that people provide false or inaccurate information to the database. One factor that affects the effect of such updates is the network structure of the database schema, which might reveal the database’s robustness against different kinds of false updates. Therefore, network analyses are needed. The aim is to analyse GIS data models, stored in UML class diagrams, for scale-free and small-world properties. Moreover, a robustness analysis is to be carried out on selected data models in order to find out their error and attack tolerance against, for example, false updates. Three graphs were specified from the UML class diagrams: (1) class graphs: classes as nodes and their interactive relationships as connections; (2) attribute graphs: classes and attributes as nodes, with connections between the classes and their attributes; and (3) schema graphs: attributes as nodes and their interactive relationships inside and outside the tables as links. The analysed class diagrams were stored in XMI, and therefore transformed with XSLT to the Pajek network format. Thereafter, small-world and scale-free analyses as well as a robustness analysis were performed on the graphs.
The results from the scale-free analyses showed no strict power-laws. Nevertheless, the classes’ relationships and attributes, and the betweenness in the schema graphs were long-tailed distributed. Furthermore, the schema graphs had small-world properties, and the analysed class and schema graphs were robust against errors but fragile against attacks. In a network structure perspective, these results indicate that false updates on random tables of a database should usually do little harm, but falsely updating the most central cells or tables may cause big damage. Consequently, it may be necessary to monitor and constrain sensitive cells and tables in order to protect them from attacks
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Luo, Hongwei, and Hongwei luo@rmit edu au. "Modelling and simulation of large-scale complex networks." RMIT University. Mathematical and Geospatial Sciences, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080506.142224.
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Real-world large-scale complex networks such as the Internet, social networks and biological networks have increasingly attracted the interest of researchers from many areas. Accurate modelling of the statistical regularities of these large-scale networks is critical to understand their global evolving structures and local dynamical patterns. Traditionally, the Erdos and Renyi random graph model has helped the investigation of various homogeneous networks. During the past decade, a special computational methodology has emerged to study complex networks, the outcome of which is identified by two models: the Watts and Strogatz small-world model and the Barabasi-Albert scale-free model. At the core of the complex network modelling process is the extraction of characteristics of real-world networks. I have developed computer simulation algorithms for study of the properties of current theoretical models as well as for the measurement of two real-world complex networks, which lead to the isolation of three complex network modelling essentials. The main contribution of the thesis is the introduction and study of a new General Two-Stage growth model (GTS Model), which aims to describe and analyze many common-featured real-world complex networks. The tools we use to create the model and later perform many measurements on it consist of computer simulations, numerical analysis and mathematical derivations. In particular, two major cases of this GTS model have been studied. One is named the U-P model, which employs a new functional form of the network growth rule: a linear combination of preferential attachment and uniform attachment. The degree distribution of the model is first studied by computer simulation, while the exact solution is also obtained analytically. Two other important properties of complex networks: the characteristic path length and the clustering coefficient are also extensively investigated, obtaining either analytically derived solutions or numerical results by computer simulations. Furthermore, I demonstrate that the hub-hub interaction behaves in effect as the link between a network's topology and resilience property. The other is called the Hybrid model, which incorporates two stages of growth and studies the transition behaviour between the Erdos and Renyi random graph model and the Barabasi-Albert scale-free model. The Hybrid model is measured by extensive numerical simulations focusing on its degree distribution, characteristic path length and clustering coefficient. Although either of the two cases serves as a new approach to modelling real-world large-scale complex networks, perhaps more importantly, the general two-stage model provides a new theoretical framework for complex network modelling, which can be extended in many ways besides the two studied in this thesis.
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Jiang, Jian. "Modeling of complex network, application to road and cultural networks." Phd thesis, Université du Maine, 2011. http://tel.archives-ouvertes.fr/tel-00691129.
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Many complex systems arising from nature and human society can be described as complex networks. In this dissertation, on the basis of complex network theory, we pay attention to the topological structure of complex network and the dynamics on it. We established models to investigate the influences of the structure on the dynamics of networks and to shed light on some peculiar properties of complex systems. This dissertation includes four parts. In the first part, the empirical properties (degree distribution, clustering coefficient, diameter, and characteristic path length) of urban road network of Le Mans city in France are studied. The degree distribution shows a double power-law which we studied in detail. In the second part, we propose two models to investigate the possible mechanisms leading to the deviation from simple power law. In the first model, probabilistic addition of nodes and links, and rewiring of links are considered; in the second one, only random and preferential link growth is included. The simulation results of the modelling are compared with the real data. In the third part,the probabilistic uncertainty behavior of double power law distribution is investigated. The network optimization and optimal design of scale free network to random failures are discussed from the viewpoint of entropy maximization. We defined equilibrium network ensemble as stationary ensembles of graphs by using some thermodynamics like notions such as "energy", "temperature", "free energy" for network. In the forth part, an union-division model is established to investigate the time evolution of certain networks like cultural or economical networks. In this model, the nodes represent, for example, the cultures. Several quantities such as richness, age, identity, ingredient etc. are used to parameterize the probabilistic evolution of the network. The model offers a long term view on the apparently periodic dynamics of an ensemble of cultural or economic entities in interaction.
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Rimer, Suvendi Chinnappen. "Energy efficient communication models in wireless sensor and actor networks." Thesis, University of Pretoria, 2012. http://hdl.handle.net/2263/23253.
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Sensor nodes in a wireless sensor network (WSN) have a small, non-rechargeable power supply. Each message transmission or reception depletes a sensor node’s energy. Many WSN applications are ad-hoc deployments where a sensor node is only aware of its immediate neighbours. The lack of a predefined route path and the need to restrict the amount of communication that occurs within the application area impose constraints on WSNs not prevalent in other types of networks. An area of active research has been how to notify the central sink (or monitoring hub) about an event in real-time by utilising the minimum number of messages to route a message from a source node to the destination sink node. In this thesis, strategies to limit communication within a WSN application area, while ensuring that events are reported on and responded to in real-time, is presented. A solution based on modelling a WSN as a small world network and then transmitting an initialisation message (IM) on network start-up to create multiple route paths from any sensor node to one or more sinks is proposed. The reason for modelling a WSN as a small world network is to reduce the number of nodes required to re-transmit a message from a source sensor node to a sink. The purpose of sending an IM at network start-up is to ensure that communication within the WSN is minimised. When routing a message to a static sink, the nodes closest to the static sink receive a disproportionate number of messages, resulting in their energy being consumed earlier. The use of mobile sinks has been proposed but to our knowledge no studies have been undertaken on the paths these mobile sinks should follow. An algorithm to determine the optimum path for mobile sinks to follow in a WSN application area is described. The purpose of an optimum path is to allow more equitable usage of all nodes to transfer an event message to a mobile sink. The idea of using multiple static sinks placed at specific points in the small world model is broadened to include using multiple mobile sinks called actors to move within a WSN application area and respond to an event in real-time. Current coordination solutions to determine which actor(s) must respond to the event result in excessive message communication and limit the real-time response to an event. An info gap decision theory (IGDT) model to coordinate which actor or set of actors should respond to the event is described. A comparison of the small world routing (SWR) model against routing using flooding and gossiping shows that the SWR model significantly reduces the number of messages transmitted within the network. An analysis of the number of IMs transmitted and received at individual node level shows that prudent selection of the hop count (number of additional nodes required to route a message to sink) to a sink node will result in a reduced number of messages transmitted and received per node within the network. The use of the IGDT model results in a robust decision on the actor(s) chosen to respond to an event even when uncertainty about the location and available energy of other actor(s) exists.Thesis (PhD(Eng))--University of Pretoria, 2012.
Electrical, Electronic and Computer Engineering
unrestricted
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Nguyen, Anh Dung. "Contributions to Modeling, Structural Analysis, and Routing Performance in Dynamic Networks." Phd thesis, Institut National Polytechnique de Toulouse - INPT, 2013. http://tel.archives-ouvertes.fr/tel-00908502.
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Cette thèse apporte des contributions à la modélisation, compréhension ainsi qu'à la communication efficace d'information dans les réseaux dynamiques peuplant la périphérie de l'Internet. Par réseaux dynamiques, nous signifions les réseaux pouvant être modélisés par des graphes dynamiques dans lesquels noeuds et liens évoluent temporellement. Dans la première partie de la thèse, nous proposons un nouveau modèle de mobilité - STEPS - qui permet de capturer un large spectre de comportement de mobilité humains. STEPS mets en oeuvre deux principes fondamentaux de la mobilité humaine : l'attachement préférentiel à une zone de prédilection et l'attraction vers une zone de prédilection. Nous proposons une modélisation markovienne de ce modèle de mobilité. Nous montrons que ce simple modèle paramétrique est capable de capturer les caractéristiques statistiques saillantes de la mobilité humaine comme la distribution des temps d'inter-contacts et de contacts. Dans la deuxième partie, en utilisant STEPS, nous analysons les propriétés comportementales et structurelles fondamentales des réseaux opportunistes. Nous redéfinissons dans le contexte des réseaux dynamiques la notion de structure petit monde et montrons comment une telle structure peut émerger. En particulier, nous montrons que les noeuds fortement dynamiques peuvent jouer le rôle de ponts entre les composants déconnectés, aident à réduire significativement la longueur du chemin caractéristique du réseau et contribuent à l'émergence du phénomène petit-monde dans les réseaux dynamiques. Nous proposons une façon de modéliser ce phénomène sous STEPS. À partir d'un réseau dynamique régulier dans lequel les noeuds limitent leur mobilité à leurs zones préférentielles respectives. Nous recablons ce réseau en injectant progressivement des noeuds nomades se déplaçant entre plusieurs zones. Nous montrons que le pourcentage de tels nœuds nomades est de 10%, le réseau possède une structure petit monde avec un fort taux de clusterisation et un faible longueur du chemin caractéristique. La troisième contribution de cette thèse porte sur l'étude de l'impact du désordre et de l'irrégularité des contacts sur la capacité de communication d'un réseau dynamique. Nous analysons le degré de désordre de réseaux opportunistes réels et montrons que si exploité correctement, celui-ci peut améliorer significativement les performances du routage. Nous introduisons ensuite un modèle permettant de capturer le niveau de désordre d'un réseau dynamique. Nous proposons deux algorithmes simples et efficaces qui exploitent la structure temporelle d'un réseau dynamique pour délivrer les messages avec un bon compromis entre l'usage des ressources et les performances. Les résultats de simulations et analytiques montrent que ce type d'algorithme est plus performant que les approches classiques. Nous mettons également en évidence aussi la structure de réseau pour laquelle ce type d'algorithme atteint ses performances optimum. Basé sur ce résultat théorique nous proposons un nouveau protocole de routage efficace pour les réseaux opportunistes centré sur le contenu. Dans ce protocole, les noeuds maintiennent, via leurs contacts opportunistes, une fonction d'utilité qui résume leur proximité spatio-temporelle par rapport aux autres noeuds. En conséquence, router dans un tel contexte se résume à suivre le gradient de plus grande pente conduisant vers le noeud destination. Cette propriété induit un algorithme de routage simple et efficace qui peut être utilisé aussi bien dans un contexte d'adressage IP que de réseau centré sur les contenus. Les résultats de simulation montrent que ce protocole superforme les protocoles de routage classiques déjà définis pour les réseaux opportunistes. La dernière contribution de cette thèse consiste à mettre en évidence une application potentielle des réseaux dynamiques dans le contexte du " mobile cloud computing ". En utilisant les techniques d'optimisation particulaires, nous montrons que la mobilité peut augmenter considérablement la capacité de calcul des réseaux dynamiques. De plus, nous montrons que la structure dynamique du réseau a un fort impact sur sa capacité de calcul.
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Younsi, Fatima-Zohra. "Mise en place d'un Système d'Information Décisionnel pour le suivi et la prévention des épidémies." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSE2005/document.
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Les maladies infectieuses représentent aujourd’hui un problème majeur de santé publique. Devant l’augmentation des résistances bactériennes, l’émergence de nouveaux pathogènes et la propagation rapide de l’épidémie, le suivi et la surveillance de la transmission de la maladie devient particulièrement importants. Face à une telle menace, la société doit se préparer à l'avance pour réagir rapidement et efficacement si une telle épidémie est déclarée. Cela nécessite une mise en place des dispositifs de suivi et de prévention. Dans ce contexte, nous nous intéressons, dans le présent travail, à l’élaboration d’un Système d’Information Décisionnel Spatio-temporel pour le suivi et la surveillance du phénomène de propagation de l’épidémie de la grippe saisonnière au sein de la population de la ville d’Oran (Algérie). L’objectif de ce système est double : il consiste, d’une part, à comprendre comment l’épidémie se propage par l’utilisation du réseau social Small World (SW) et du modèle à compartiments d’épidémie SEIR (Susceptible-Exposed-Infected-Removed), et d’autre part, à stocker dans un entrepôt les données multiples tout en les analysant par un outil d’analyse en ligne de donnée Spatiale dit SOLAP (Spatial On-Line Analytical Processing)Today, infectious diseases represent a major public health problem. With the increase of bacterial resistance, the emergence of new pathogens and the rapid spread of epidemic, monitoring and surveillance of disease transmission becomes important. In the face of such a threat, the society must prepare in advance to respond quickly and effectively if an outbreak is declared. This requires setting up monitoring mechanisms and prevention.In this context, we are particularly interested by development a Spatiotemporal decision support system for monitoring and preventing the phenomenon of seasonal influenza epidemic spread in the population of Oran (city at Algeria).The objective of this system is twofold: on one hand, to understand how epidemic is spreading through the social network by using SEIR (Susceptible-Exposed-Infected-Removed) compartmental model within Small World network, and on the other hand, to store multiple data in data warehouse and analyzing it by a specific online analysis tool Spatial OLAP (Spatial on-line Analytical Processing)
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Castro, Paulo Alexandre de. "Rede complexa e criticalidade auto-organizada: modelos e aplicações." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-14012008-165356/.
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Modelos e teorias científicas surgem da necessidade do homem entender melhor o funcionamento do mundo em que vive. Constantemente, novos modelos e técnicas são criados com esse objetivo. Uma dessas teorias recentemente desenvolvida é a da Criticalidade Auto-Organizada. No Capítulo 2 desta tese, apresentamos uma breve introdução a Criticalidade Auto-Organizada. Tendo a criticalidade auto-organizada como pano de fundo, no Capítulo 3, estudamos a dinâmica Bak-Sneppen (e diversas variantes) e a comparamos com alguns algoritmos de otimização. Apresentamos no Capítulo 4, uma revisão histórica e conceitual das redes complexas. Revisamos alguns importantes modelos tais como: Erdös-Rényi, Watts-Strogatz, de configuração e Barabási-Albert. No Capítulo 5, estudamos o modelo Barabási-Albert não-linear. Para este modelo, obtivemos uma expressão analítica para a distribuição de conectividades P(k), válida para amplo espectro do espaço de parâmetros. Propusemos também uma forma analítica para o coeficiente de agrupamento, que foi corroborada por nossas simulações numéricas. Verificamos que a rede Barabási-Albert não-linear pode ser assortativa ou desassortativa e que, somente no caso da rede Barabási-Albert linear, ela é não assortativa. No Capítulo 6, utilizando dados coletados do CD-ROM da revista Placar, construímos uma rede bastante peculiar -- a rede do futebol brasileiro. Primeiramente analisamos a rede bipartida formada por jogadores e clubes. Verificamos que a probabilidade de que um jogador tenha participado de M partidas decai exponencialmente com M, ao passo que a probabilidade de que um jogador tenha marcado G gols segue uma lei de potência. A partir da rede bipartida, construímos a rede unipartida de jogadores, que batizamos de rede de jogadores do futebol brasileiro. Nessa rede, determinamos várias grandezas: o comprimento médio do menor caminho e os coeficientes de agrupamento e de assortatividade. A rede de jogadores de futebol brasileiro nos permitiu analisar a evolução temporal dessas grandezas, uma oportunidade rara em se tratando de redes reais.Models and scientific theories arise from the necessity of the human being to better understand how the world works. Driven by this purpose new models and techniques have been created. For instance, one of these theories recently developed is the Self-Organized Criticality, which is shortly introduced in the Chapter 2 of this thesis. In the framework of the Self-Organized Criticality theory, we investigate the standard Bak-Sneppen dynamics as well some variants of it and compare them with optimization algorithms (Chapter 3). We present a historical and conceptual review of complex networks in the Chapter 4. Some important models like: Erdös-Rényi, Watts-Strogatz, configuration model and Barabási-Albert are revised. In the Chapter 5, we analyze the nonlinear Barabási-Albert model. For this model, we got an analytical expression for the connectivity distribution P(k), which is valid for a wide range of the space parameters. We also proposed an exact analytical expression for the clustering coefficient which corroborates very well with our numerical simulations. The nonlinear Barabási-Albert network can be assortative or disassortative and only in the particular case of the linear Barabási-Albert model, the network is no assortative. In the Chapter 6, we used collected data from a CD-ROM released by the magazine Placar and constructed a very peculiar network -- the Brazilian soccer network. First, we analyzed the bipartite network formed by players and clubs. We find out that the probability of a footballer has played M matches decays exponentially with M, whereas the probability of a footballer to score G gols follows a power-law. From the bipartite network, we built the unipartite Brazilian soccer players network. For this network, we determined several important quantities: the average shortest path length, the clustering coefficient and the assortative coefficient. We were also able to analise the time evolution of these quantities -- which represents a very rare opportunity in the study of real networks.
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Nguyen, Anh-Dung. "Contributions to modeling, structural analysis, and routing performance in dynamic networks." Phd thesis, Toulouse, INPT, 2013. http://oatao.univ-toulouse.fr/9725/1/nguyen.pdf.
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This thesis contributes to the modeling, understanding and efficient communication in dynamic networks populating the periphery of the Internet. By dynamic networks, we refer to networks that can be modeled by dynamic graphs in which nodes and links change temporally. In the first part of the thesis, we propose a new mobility model - STEPS - which captures a wide spectrum of human mobility behavior. STEPS implements two fundamental principles of human mobility: preferential attachment and attractor. We show that this simple parametric model is able to capture the salient statistical properties of human mobility such as the distribution of inter-contact/contact time. In the second part, using STEPS, we analyze the fundamental behavioral and structural properties of opportunistic networks. We redefine in the context of dynamic networks the concept of small world structure and show how such a structure can emerge. In particular, we show that highly dynamic nodes can play the role of bridges between disconnected components, helping to significantly reduce the length of network path and contribute to the emergence of small-world phenomenon in dynamic networks. We propose a way to model this phenomenon in STEPS. From a regular dynamic network in which nodes limit their mobility to their respective preferential areas. We rewire this network by gradually injecting highly nomadic nodes moving between different areas. We show that when the ratio of such nomadic nodes is around 10%, the network has small world structure with a high degree of clustering and a low characteristic path length. The third contribution of this thesis is the study of the impact of disorder and contact irregularity on the communication capacity of a dynamic network. We analyze the degree of disorder of real opportunistic networks and show that if used correctly, it can significantly improve routing performances. We then introduce a model to capture the degree of disorder in a dynamic network. We propose two simple and efficient algorithms that exploit the temporal structure of a dynamic network to deliver messages with a good tradeoff between resource usage and performance. The simulation and analytical results show that this type of algorithm is more efficient than conventional approaches. We also highlight also the network structure for which this type of algorithm achieves its optimum performance. Based on this theoretical result, we propose a new efficient routing protocol for content centric opportunistic networks. In this protocol, nodes maintain, through their opportunistic contacts, an utility function that summarizes their spatio-temporal proximity to other nodes. As a result, routing in this context consists in following the steepest slopes of the gradient field leading to the destination node. This property leads to a simple and effective algorithm routing that can be used both in the context of IP networks and content centric networks. The simulation results show that this protocol outperforms traditional routing protocols already defined for opportunistic networks. The last contribution of this thesis is to highlight the potential application of dynamic networks in the context of "mobile cloud computing." Using the particle optimization techniques, we show that mobility can significantly increase the processing capacity of dynamic networks. In addition, we show that the dynamic structure of the network has a strong impact on its processing capacity.
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Allen, Andrea J. "Average Shortest Path Length in a Novel Small-World Network." Oberlin College Honors Theses / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1516362622694547.
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Hamamousse, Nadjet. "Caractérisation des propriétés physiques des matériaux impliqués dans l'accélération des feux de forêt." Thesis, Aix-Marseille, 2021. http://www.theses.fr/2021AIXM0621.
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Les feux de forêt ravagent chaque année des millions d'hectares de végétation mettant en danger la vie de l’homme et la stabilité de la faune et la flore. Sur le terrain, les pompiers ont signalé l’existence d’un type particulier de feux qui apparait lors de la propagation. Ce sont les embrasements généralisés éclairs, ils ont un comportement assez inhabituel. D’abord, ils commencent par se propager de manière normale, puis, leur vitesse augmente soudainement. C’est ce qui s’est passé à Palasca en 2000 lorsque le feu s’est transformé en piège mortel mettant fin à la vie de deux jeunes pompiers et à la carrière de quatre autres qui ont été grièvement blessés. Une surface de 5 ha est partie en fumée en quelques minutes. Cette thèse est consacrée à la caractérisation des matériaux qui peuvent contribuer à l’accélération brutale des feux. D'abord, nous avons validé le modèle de Petit Monde sur un cas réel. L'étude de sensibilité a permis d'identifier les paramètres prépondérants du modèle qui influent la vitesse de propagation. Comme l'inflammabilité est affectée par la présence d'eau et les gaz inflammables, nous avons caractérisé expérimentalement ces deux paramètresEvery year, fires devastate millions of hectares of wildland and cause serious impacts on natural, economical, and human resources. Firefighters highlighted that some forest fires behave differently; they are called flashover. These fires are characterized by a sudden acceleration. Those fires are called flashover. Such phenomenon was observed in September 2000 in Palasca where two young firefighters passed away, four were seriously injured and about 5 hectares burned in few minutes. This thesis is devoted to the characterization of the physical properties of materials that can contribute to the sudden and unpredictable acceleration of fires. First, the Small World network model was validated on a historical fire. The sensitivity analysis of the model allows identifying the most important parameters that affect the fire spread. Since the flammability depends on the fuel moisture content and the flammable volatile organic compounds, these two parameters were characterized experimentally
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Kruckenberg, Norman E. "A piping network model program for small computer." Ohio : Ohio University, 1986. http://www.ohiolink.edu/etd/view.cgi?ohiou1183138191.
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Kruckenberg, Norman E. "A piping network model program for small computers." Ohio University / OhioLINK, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1183138191.
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Van, der Pol Johannes. "Social network of firms, innovation and industrial performance." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0207/document.
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L’objectif de cette thèse est de répondre à trois questions principales ; commentexpliquer et interpréter un réseau de collaboration, est-ce que des firmes avec une positionparticulière dans un réseau bénéficient d’une performance accrue et enfin, existe-t-il desstructures de réseaux qui favorisent l’innovation ?Pour répondre à ces questions, la thèse est organisée en trois parties. La première partieprésente, dans un premier chapitre, une revue analytique de la littérature suivie d’un chapitrequi présente la théorie derrière une des méthodes d’analyse réseau utilisée dans cette thèse :les Exponential Random Graph Models (ERGM).La seconde partie présente trois analyses empiriques. Le premier chapitre empirique analysel’impact du cycle de vie de la technologie sur la dynamique du réseau de collaboration autourdes composites structuraux en aéronautique. Les deux chapitres suivants se concentrent sursecteur aéronautique et le secteur des biotechnologies respectivement. L’objectif de ceschapitres est d’analyser la dynamique structurelle et d’identifier s’il existe un lien entreposition dans le réseau et la performance de la firme.La dernière partie cherche à identifier des structures de réseaux qui favorisent l’innovation.Un modèle à base d’agents (ABM) est proposé pour répondre à cette questionThis thesis aims to answer three main questions ; how can one explain andinterpret the structure of an innovation network, are there positions in a network which allowfor an increased performance for firms and finally, are there network structures which favourinnovation ? In order to answer these questions, the thesis is organised in three parts.The first part presents, in a first chapter, an analytical review of the literature followed by achapter presenting the theory behind one of the network analysis methods: ExponentialRandom Graph Models (ERGM).The second part of the thesis presents three empirical analyses. The first empirical chapteranalyses the impact of the life-cycle of the technology on the structural dynamics of thecollaboration network for Structural Composite Materials. The following two chapters focuson two sectors, the aerospace and biotech sector. The aim of these chapters is to analyse thestructural dynamics of collaboration networks as well as identifying a link between networkposition and firm performance.The third and final part of this thesis searches for network structures which might favourinnovation. An Agent-Based Model is used to answer this final question
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Dubreus, Terrance Maurice. "Monte Carlo simulations for small-world stochastic processes." Diss., Mississippi State : Mississippi State University, 2005. http://library.msstate.edu/content/templates/?a=72.
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Lima, Nicholas Veloso. "Difusão competitiva de produtos e inovações: um modelo de duopólio em redes complexas do tipo small world." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/100/100132/tde-30032016-081314/.
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Nos últimos 60 anos, os modelos de difusão de produtos e de inovações tiveram penetração tão ampla nos mais diversos campos de investigação científica que se tornaram ubíquos, sendo empregados em contextos diversos como no marketing, na Medicina, na Antropologia, na Geografia, por exemplo. Essa abrangência é devido ao papel vital que produtos, inovações e novas tecnologias têm na vida dos indivíduos e no impacto que exercem nas dinâmicas e no desenvolvimento de comunidades, países e de suas economias. Porém, após os grandes saltos dados nas décadas de 1960 e 1970, os estudos em difusão de bens de consumo duráveis deram lugar a pesquisas em sistemas de inovação nas duas décadas seguintes, só voltando a gerar maior interesse acadêmico a partir da década de 2000, com o surgimento dos sistemas de Gestão de Relacionamento com Clientes Customer Relationship Management (CRM) , que tornou disponível um enorme volume de dados; e, também, com o desenvolvimento de novas técnicas de análise, como a modelagem de sistemas complexos. Tendo em vista a carência de estudos integrando modelos de difusão competitiva com modelos de redes usando topologias de redes parcialmente conectadas (small world e livres de escala), este estudo tem como objetivo geral caracterizar a dinâmica da difusão competitiva proposta em redes small world do tipo Watts-Strogatz. Foram realizadas simulações tanto da formulação clássica do modelo de difusão de produtos e de inovações, proposto por Bass (1969), como de proposições mais modernas para difusão competitiva, como os propostos por Libai, Muller e Peres (2009a; 2009b; 2009c) e por Peres, Muller e Mahajan (2010), além de desenvolver um novo modelo incorporando ao de Libai, Muller e Peres (2009c) a topologia de redes de pequeno mundo e outras características de difusão competitiva não presentes na formulação original , permitindo fazer inferências sobre o comportamento da difusão em diversos cenários que não são explicitamente previstos nas formulações clássicas. Por sua lógica intuitiva e simples, o modelo proposto neste trabalho é de valor significativo para o ensino e para a pesquisa da difusão competitivaIn the last 60 years, product and innovation models were so widespread in so many fields of study that they became ubiquitous, being employed in such diverse backgrounds like marketing, medicine, anthropology and geography. Such widespread influence arises from the fact that products, innovations and Technologies have a big role in any individuals daily lives and a huge impact on the development and dynamics of communities, countries and its economies. After huge leaps on this field of research during the 1960s and 1970s, its study faded away from mainstream research in the following two decades. Only regaining widespread academic interest in the beginning of 21st century, with the advent of Customer Relationship Management systems, which made available huge amounts of data, other factors that contributed to this resurgence in diffusion literature were the advancements on new tools for research, notably the developments in complex systems theory and network theory. In the view of the still small, but rapidly increasing, number of studies integrating competitive diffusion and network models of partially connected networks (such as small world networks and scale-free networks), this study aims to characterize the dynamics of competitive diffusion in small world networks with the Watts-Strogatz topology. For its intended purpose, simulations were created, both for the classical formulation of the Bass Diffusion Model, as well as more modern approaches for competitive diffusion, such as the models proposed by Libai, Muller and Peres and Peres, Muller and Mahajan. A new model was developed in order expand the model proposed by Libai et al (2009c) in order incorporate the small world network topology and other characteristics associated to competition that were not explicitly represented. Allowing the inference of behaviors in various scenarios that are not explicitly covered in the classical formulations. For intuitive logic and simplicity, it is believed that this model is of significant value for teaching and for the study of competitive diffusion
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ZHONG, LI. "SHORTCUT BASED GRAPH COARSENING FOR PROTEIN INTERACTION NETWORK VISUALIZATION." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin997457452.
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Muda, Mohd Shaladdin. "A new world class manufacturing model for small and medium sized make-to-order companies." Thesis, Lancaster University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274204.
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Westlund, Johannes, and Jakob Svenningsson. "Examining network properties using breadth-first sampling : A case study of the network spanned by the kth.se domain." Thesis, KTH, Skolan för datavetenskap och kommunikation (CSC), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-208346.
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Many real life complex networks consists of a tremendous amount of nodes and edges which make them difficult to extract and analyze. This thesis aims to examine what network prop- erties that can be deduced when considering small samples of a complex network and how well they correspond to the characteristics of the complete network. This is of importance as sampling will most likely be the de facto method when analyzing complex networks in the future. The study examine the scale-free property, the small-world property and the com- munity structure of the network spanned by the KTH domain. The method consisted of gathering data about the network through sampling it in a breadth-first manner using a web crawler. The samples was then compared with respect to each property. The results was that good approximations of the scale-free property could be made from small samples of the KTH network. However, no good approximation could be made about the small-world property using the sampling technique. Good approximations about a node’s community affiliation could be observed. However, general conclusions of the com- plete network’s community structures could not be made. To summarize, the result indi- cate that small samples can be used to approximate some properties of the complete KTH network. However, to determine if the result is true for the general case more research is necessary.Komplexa nätverk i vår omvärld består av ett stort antal hörn och kanter vilket gör dem svå- ra att extrahera och analysera. Denna rapport undersöker vilka nätverksegenskaper som kan härledas vid undersökningen av små stickprov av ett nätverk och hur bra dessa representerar egenskaperna hos det fullständiga nätverket. Detta är av betydelse eftersom användandet av små stickprov kommer troligtvis att vara standarden vid undersökningar av nätverk i framtiden. Denna studie undersökte scale-free egenskapen, small-world egenskapen och community strukturen för nätverket som omfattas av KTH domaänen. Metoden innefattade att samla in data om nätverket genom stickprov baserat på en bredden-först sökning. Detta realiserades genom att använda en sökrobot. Sedan jämfördes de olika stickproven med avseende på de olika nätverksegenskaperna. Resultetat visade att nätverkets scale-free egenskap kunde approximaeras med små stickprov. Däremot var det inte möjligt att approximera nätverkets small-world egenskap genom användet av den givna stickprovsmetoden. Goda approximationer observerades för att avgöra ett hörns community tillhörighet men den allmäna community strukturen kunde inte approximeras. Sammanfattningsvis visade resultatet att stickprov kan användas för att approximera vissa egenskaper hos det fullständiga KTH nätverket men att mer forskning krävs för att avgöra om resultaten kan generaliseras.
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Higashi, Susan. "MiRNA and co : methodologically exploring the world of small RNAs." Thesis, Lyon 1, 2014. http://www.theses.fr/2014LYO10252/document.
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La principale contribution de cette thèse est le développement d'une méthode fiable, robuste, et rapide pour la prédiction des pré-miARNs. Deux objectifs avaient été assignés : efficacité et flexibilité. L'efficacité a été rendue possible au moyen d'un algorithme quadratique. La flexibilité repose sur deux aspects, la nature des données expérimentales et la position taxonomique de l'organisme (en particulier plantes ou animaux). Mirinho accepte en entrée des séquences de génomes complets mais aussi les très nombreuses séquences résultant d'un séquençage massif de type NGS de “RNAseq”. “L'universalité” taxonomique est obtenu par la possibilité de modifier les contraintes sur les tailles de la tige (double hélice) et de la boule terminale. Dans le cas de la prédiction des miARN de plantes la plus grande longueur de leur pré-miARN conduit à des méthodes d'extraction de la structure secondaire en tige-boule moins précises. Mirinho prend en compte ce problème lui permettant de fournir des structures secondaires de pré-miARN plus semblables à celles de miRBase que les autres méthodes disponibles. Mirinho a été utilisé dans le cadre de deux questions biologiques précises l'une concernant des RNAseq l'autre de l'ADN génomique. La première question a conduit au traitement et l'analyse des données RNAseq de Acyrthosiphon pisum, le puceron du pois. L'objectif était d'identifier les miARN qui sont différentiellement exprimés au cours des quatre stades de développement de cette espèce et sont donc des candidats à la régulation des gènes au cours du développement. Pour cette analyse, nous avons développé un pipeline, appelé MirinhoPipe. La deuxieme question a permis d'aborder les problèmes liés à la prévision et l'analyse des ARN non-codants (ARNnc) dans la bactérie Mycoplasma hyopneumoniae. Alvinho a été développé pour la prédiction de cibles des miRNA autour d'une segmentation d'une séquence numérique et de la détection de la conservation des séquences entre ncRNA utilisant un graphe k-partite. Nous avons finalement abordé un problème lié à la recherche de motifs conservés dans un ensemble de séquences et pouvant ainsi correspondre à des éléments fonctionnelsThe main contribution of this thesis is the development of a reliable, robust, and much faster method for the prediction of pre-miRNAs. With this method, we aimed mainly at two goals: efficiency and flexibility. Efficiency was made possible by means of a quadratic algorithm. Flexibility relies on two aspects, the input type and the organism clade. Mirinho can receive as input both a genome sequence and small RNA sequencing (sRNA-seq) data of both animal and plant species. To change from one clade to another, it suffices to change the lengths of the stem-arms and of the terminal loop. Concerning the prediction of plant miRNAs, because their pre-miRNAs are longer, the methods for extracting the hairpin secondary structure are not as accurate as for shorter sequences. With Mirinho, we also addressed this problem, which enabled to provide pre-miRNA secondary structures more similar to the ones in miRBase than the other available methods. Mirinho served as the basis to two other issues we addressed. The first issue led to the treatment and analysis of sRNA-seq data of Acyrthosiphon pisum, the pea aphid. The goal was to identify the miRNAs that are expressed during the four developmental stages of this species, allowing further biological conclusions concerning the regulatory system of such an organism. For this analysis, we developed a whole pipeline, called MirinhoPipe, at the end of which Mirinho was aggregated. We then moved on to the second issue, that involved problems related to the prediction and analysis of non-coding RNAs (ncRNAs) in the bacterium Mycoplasma hyopneumoniae. A method, called Alvinho, was thus developed for the prediction of targets in this bacterium, together with a pipeline for the segmentation of a numerical sequence and detection of conservation among ncRNA sequences using a kpartite graph. We finally addressed a problem related to motifs, that is to patterns, that may be composed of one or more parts, that appear conserved in a set of sequences and may correspond to functional elements
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Ruffels, Aaron. "Model-Free Damage Detection for a Small-Scale Steel Bridge." Thesis, KTH, Bro- och stålbyggnad, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-232363.
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Around the world bridges are ageing. In Europe approximately two thirds of all railway bridges are over 50 years old. As these structures age, it becomes increasingly important that they are properly maintained. If damage remains undetected this can lead to premature replacement which can have major financial and environmental costs. It is also imperative that bridges are kept safe for the people using them. Thus, it is necessary for damage to be detected as early as possible. This research investigates an unsupervised, model-free damage detection method which could be implemented for continuous structural health monitoring. The method was based on past research by Gonzalez and Karoumi (2015), Neves et al. (2017) and Chalouhi et al. (2017). An artificial neural network (ANN) was trained on accelerations from the healthy structural state. Damage sensitive features were defined as the root mean squared errors between the measured data and the ANN predictions. A baseline healthy state could then be established by presenting the trained ANN with more healthy data. Thereafter, new data could be compared with this reference state. Outliers from the reference data were taken as an indication of damage. Two outlier detection methods were used: Mahalanobis distance and the Kolmogorov-Smirnov test. A model steel bridge with a span of 5 m, width of 1 m and height of approximately 1.7 m was used to study the damage detection method. The use of an experimental model allowed damaged to be freely introduced to the structure. The structure was excited with a 12.7 kg rolling mass at a speed of approximately 2.1 m/s (corresponding to a 20.4 ton axle load moving at 47.8 km/h in full scale). Seven accelerometers were placed on the structure and their locations were determined using an optimal sensor placement algorithm. The objectives of the research were to: identify a number of single damage cases, distinguish between gradual damage cases and identify the location of damage. The proposed method showed promising results and most damage cases were detected by the algorithm. Sensor density and the method of excitation were found to impact the detection of damage. By training the ANN to predict correlations between accelerometers the sensor closest to the damage could be detected, thus successfully localising the damage. Finally, a gradual damage case was investigated. There was a general increase in the damage index for greater damage however, this did not progress smoothly and one case of ‘greater’ damage showed a decrease in the damage index.
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Mrawira, Mrawira Donath Massawe. "Streamlining the World Bank's Highway Design and Maintenance Standards model (HDM-III) for network-level application." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq21372.pdf.
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Damaj, Samer. "SWH, application "Small-world" à la génération des réseaux d'interconnexion pour les architectures massivement parallèles." Brest, 2011. http://www.theses.fr/2011BRES2076.
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Les possibilités d'intégration sont de plus en plus importantes et le nombre de transistors disponibles sur un composant n'est plus aussi critique que dans le passé. Cependant les structures de traitement du type monoprocesseur ne bénéficient plus de cette augmentation de ressources et on voit apparaître des composants du type MP Soc (multiprocessors on Chip) qui intègre plusieurs coeurs de processeur sur une même puce. Le problème consiste donc à faire passer à l'échelle des architectures systèmes du type MIMD (Multiple Instruction stream Multiple Data stream). Si on considère des coeurs de processeur complexe alors le problème reste actuellement assez maîtrisable car leur nombre reste limité (2 voit 4 processeurs). Par contre l'utilisation de noeuds de traitement de plus petite taille autorise l'intégration de dizaines voire de centaines de processeurs sur un même circuit. Les besoins en puissance de calcul ne se satisfont plus des limites rencontrées sur des processeurs complexes. La généralisation des composants du type MPSoC qui intègrent un nombre toujours plus important de processeurs sur une puce. Cependant, interconnecter un grand nombre de processeurs sur une puce est un délicat. Essentiellement, les structures adaptées aux contraintes de la puce sont trop peu générales, et les schémas de l’interconnexion plus globale engendrent des coûts de fabrication trop élevés. Ce problème se décompose en deux sous problèmes intimement liés qui sont la recherche d'une topologie permettant d'atteindre un niveau de connectivité acceptable et le coût matériel de sa réalisation. C'est dans ce dernier cas qui s'inscrit le contexte scientifique de ce mémoire. Les concepteurs se basent sur des différentes architectures pour réaliser des puces. Les architectures à mémoire partagée où il y a une saturation d’accès mémoire avec un grand nombre de PEs (Processeurs Élémentaires) comme par exemple TILERA Corporation. Les architectures à mémoire distribué où il se manifeste le problème des programmes fortement communicants. Ce type d'architecture est structuré autour d'un Noc (Network-on-Chip). De nombreuses études ont déjà été réalisées sur la problématique des architectures et de leurs réalisations avec pour motivations de trouver une manière élégante de supporter des Pes qui est de plus en plus nombreux et rapide en limitant le nombre de fils et pour obtenir des réseaux réguliers où le coût et le temps de développement du layout sont très court. Pour cette raison, nous sommes à la recherche d'une nouvelle plate-forme homogène avec des multicoeurs réguliers et massivement parallèles. C'est dans ce dernier cas qui s'inscrit le contexte industriel de ce mémoire de thèse. Pour des raisons techniques, il faut rendre les circuits homogènes, réguliers et denses parce que le coût et le temps de développement du layout d'un circuit non régulier sont très longs. Pour cette raison, il faut s'appuyer sur des architectures massivement parallèles. Les processeurs doivent communiquer entre eux, ils sont donc connectés via un réseau qui implémente une topologie. Pour une topologie donnée, on dispose de métriques grossières telles que le nombre de noeuds (le nombre de sommets dans un graphe donné), le degré (le nombre de liens entrants et sortants pour chaque sommet dans ce graphe donné) et le diamètre (la distance maximale entre deux noeuds ou sommets quelconques dans le graphe). Dans ce cas, comme on veut un circuit régulier, où les CPUs sont organisés en grille 2D pour les techniques actuels et éventuellement 3D pour les futurs techniques alors il faut obtenir le coût silicium pour mapper la topologie choisie sur cette grille. Le passage de la topologie (mapping) à la réalisation sera qualifié de placement-routage" physique (le terme "placement" veut dire de placer les sommets de ce graphe donné sur une grille 2D et le terme "routage" veut dire de faire communiquer ces sommets entre eux)Graphs with a minimum diameter have applications in the design of building-block switching systems, communication networks, and distributed computer systems. Several methods of constructing directed graphs with a small diameter are proposed. First, the dissertation presents as background several (delta, D) graphs including the Hypercube and de Bruijn. It shows the major disadvantages when implementing these topologies in practice for large scale. To achieve our goal, we propose a regular graph called Small World Heuristic (SWH) suitable for large parallel computers. This graph has a maximum degree ! and a small diameter D, while maintaining an acceptable level of connectivity. We show that this heuristic can connect on short distance thousands of nodes as little as 4 links per node. ̕Finally, we present a new integrated placement and routing algorithm to implement this heuristic on 2D VLSI
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Pacini, Clare. "Inferring condition specific regulatory networks with small sample sizes : a case study in Bacillus subtilis and infection of Mus musculus by the parasite Toxoplasma gondii." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/269711.
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Modelling interactions between genes and their regulators is fundamental to understanding how, for example a disease progresses, or the impact of inserting a synthetic circuit into a cell. We use an existing method to infer regulatory networks under multiple conditions: the Joint Graphical Lasso (JGL), a shrinkage based Gaussian graphical model. We apply this method to two data sets: one, a publicly available set of microarray experiments perturbing the gram-positive bacteria Bacillus subtilis under multiple experimental conditions; the second, a set of RNA-seq samples of Mouse (Mus musculus) embryonic fibroblasts (MEFs) infected with different strains of the parasite Toxoplasma gondii. In both cases we infer a subset of the regulatory networks using relatively small sample sizes. For the Bacillus subtilis analysis we focused on the use of these regulatory networks in synthetic biology and found examples of transcriptional units active only under a subset of conditions, this information can be useful when designing circuits to have condition dependent behaviour. We developed methods for large network decomposition that made use of the condition information and showed a greater specificity of identifying single transcriptional units from the larger network using our method. Through annotating these results with known information we were able to identify novel connections and found supporting evidence for a selection of these from publicly available experimental results. Biological data collection is typically expensive and due to the relatively small sample sizes of our MEF data set we developed a novel empirical Bayes method for reducing the false discovery rate when estimating block diagonal covariance matrices. Using these methods we were able to infer regulatory networks for the host infected with either the ME49 or RH strain of the parasite. This enabled the identification of known and novel regulatory mechanisms. The Toxoplasma gondii parasite has shown to subvert host function using similar mechanisms as cancers and through our analysis we were able to identify genes, networks and ontologies associated with cancer, including connections that have not previously been associated with T. gondii infection. Finally a Shiny application was developed as an online resource giving access to the Bacillus subtilis inferred networks with interactive methods for exploring the networks including expansion of sub networks and large network decomposition.
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Abdesselam, Kahina. "Network Distribution and Respondent-Driven Sampling (RDS) Inference About People Who Inject Drugs in Ottawa, Ontario." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/38744.
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Respondent-driven sampling (RDS) is very useful in collecting data from individuals in hidden populations, where a sampling frame does not exist. It starts with researchers choosing initial respondents from a group which may be involved in taboo or illegal activities, after which they recruit other peers who belong to the same group. Analysis results in unbiased estimates of population proportions though with strong assumptions about the underlying social network and RDS recruitment process. These assumptions bear little resemblance to reality, and thus compromise the estimation of any means, population proportions or variances inferred from studies. The topology of the contact network, denoted by the number of links each person has, provides insight into the processes of infectious disease spread. The overall objective of the thesis is to identify the topology of an injection drug use network, and critically review the methods developed to produce estimates. The topology of people who inject drugs (PWID) collected by RDS in Ottawa, 2006 was compared with a Poisson distribution, an exponential distribution, a power-law distribution, and a lognormal distribution. The contact distribution was then evaluated against a small-world network characterized by high clustering and low average distances between individuals. Last a systematic review of the methods used to produce RDS mean and variance estimates was conducted. The Poisson distribution, a type of random distribution, was not an appropriate fit for PWID network. However, the PWID network can be classified as a small world network organised with many connections and short distances between people. Prevention of transmission in such networks should be focussed on the most active people (clustered individuals and hubs) as intervention with any others is less effective. The systematic review contained 32 articles which included the development and evaluation of 12 RDS mean and 6 variance estimators. Overall, the majority of estimators perform roughly the
same, with the exception of RDSIEGO which outperformed the 6 other RDS mean estimators. The Tree bootstrap variance estimate does not rely on modelling RDS as a first order Markov (FOM) process, which seems to be the main limitation of the other existing estimators. The lack of FOM as an assumption and the flexible application of this variance estimator to any RDS point estimate make the Tree bootstrapping estimator a more efficient choice.
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Sun, Xiaowei. "Comparative Analysis of Urban Morphology: Evaluating Space Syntax and Traditional Morphological Methods." Thesis, Högskolan i Gävle, Avdelningen för Industriell utveckling, IT och Samhällsbyggnad, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-15492.
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This thesis examines the urban morphology of fifty cities using spatial syntax analysis. The analysis compares the urban street networks of European, USA, Islamic and East Asian cities. Street connectivity was the main metric and natural roads were the basis for the analysis. The aim of the study was to analyze determine how sensitive space syntax methods are for uncovering the hierarchical patterns of urban street networks and examining their scale-free and small-world properties. Street data was collected from OpenStreetMap. ArcGIS 10 with the Axwoman extension was used to study the hierarchical levels of street networks. Matlab provided the platform to examine the scale-free property of street data. Pajek software was used to measure the small-world behavior. Based on the hierarchical representation, the fifty sample cities were classified into different groups and their scale-free and small-world properties were studied. From a traditionally morphological perspective, it was found that some cities in Europe have a close-knit cellular and organic urban morphology. Cities in the USA exhibit gridiron patterns on the whole. Some Islamic cities have special urban structure with houses grouped around the cul-de-sac lanes. Several of the East Asian cities studied also have grid forms. According to the space syntax analysis, urban street networks that have a connectivity value greater than the average value were less than 40%. The results showed that for most cities, the street connectivity distribution follows a power-law distribution and exhibits scale-free properties. Urban street networks of all sample cities were found to have a small-world property. Space syntax cannot detect all of the morphological patterns recognized in traditional morphological studies. The method can, however, efficiently quantify the spatial configuration of a large sample. Space syntax’s topological and scaling metrics thus provide a way to compare urban street networks. These metrics can thus help classify cities according to their street patterns but also contribute to an understanding of human behavior within and thus the design of urban spaces. For example, an urban street network with a small-world property could have high efficiency for traffic flows at local and global levels and should be considered in further study.
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Hildebrand, Thomas. "Two-sided markets in the online world." Doctoral thesis, Humboldt-Universität zu Berlin, Wirtschaftswissenschaftliche Fakultät, 2011. http://dx.doi.org/10.18452/16339.
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Diese Dissertation besteht aus drei Aufsätzen, in denen verschiedene Aspekte von zweiseitigen Märkten untersucht werden. Dabei handelt es sich um Märkte mit zwei verschiedenen Nutzergruppen, von denen jede Netzwerkeffekte auf die jeweils andere Seite ausübt. Im ersten Aufsatz werden die Wechselwirkungen zwischen den traditionellen (offline) Nachfragekanälen und den neuen (online) Nachfragekanälen in der deutschen Zeitschriftenindustrie analysiert. Dabei liegt der Fokus insbesondere auf den Effekten zwischen Offlinewerbung und Onlinewerbung. Das Ergebnis der Schätzung eines dafür entwickelten ökonomischen Modells ist, dass Offline- und Onlinewerbung moderate Substitute füreinander sind. Dies erklärt die Verlagerung von Offline- zu Onlinewerbung, die man in den vergangen Jahren beobachten konnte. Im zweiten Aufsatz wird ein semistruktureller Ansatz zur Messung von Netzwerk-Effekten auf potentiell zweiseitigen Monopol-Plattformen entwickelt. Der Test ist hinreichend, wenn lediglich Daten zum Gesamtumsatz der Plattform zur Verfügung stehen. Sind getrennte Umsatzdaten für die beiden Seiten verfügbar, dann ist der Test sowohl notwendig als auch hinreichend. Der dritte Aufsatz untersucht Mechanismen und Anreize, die die Koordination von Angebot und Nachfrage auf Kreditmärkten ermöglichen, in denen es keine Finanzintermediäre mit eigener finanzieller Beteiligung an den vergebenen Darlehen gibt. Dazu wird der Online-Direktkreditmarkt analysiert, in welchem an die Stelle von klassischen Finanzintermediären ein System von Gruppen tritt. Anhand eines Differenz-in-Differenzen-Ansatzes wird gezeigt, dass Entgelte für die Leiter dieser Gruppen zu adversen Anreizen führen können. Nach Abschaffung der Entgelte differenzieren die Leiter der Gruppen deutlich stärker bei der Auswahl derjenigen Kreditgesuche, die sie als investitionswürdig empfehlen. Gleiches ist zu beobachten, wenn die Leiter der Gruppen selbst zu einem großen Teil an den entsprechenden Darlehen beteiligt sind.This dissertation investigates various aspects of two-sided markets - markets with at least two distinct user groups each of which exerts inter-group network effects on the other side - in the online world. In the first paper, I examine the interactions between the traditional (offline) demand channels and the new (online) demand channels in the German magazines industry, focusing in particular on the link between offline and online advertising. I find that offline and online advertising are substitutes although not perfect ones. This explains the shift from offline to online advertising observed in recent years. In the second paper, I develop a semi-structural approach to identify network effects on two-sided monopoly platforms without data on prices and quantities. A sufficient test for the existence of network effects is derived when only data on total revenue is available. If separate revenue data is available on the two sides, then the test is both necessary and sufficient. The third paper investigates the certification mechanisms and incentives that enable lending markets to match demand and supply despite the absence of financial intermediaries with skin in the game. The institutional setting for this analysis is the online social lending market, in which potential lenders and borrowers interact directly without a financial intermediary but can create self-organized groups instead. A difference-in-difference approach is used to examine how the same groups behave before and after the exogenously imposed elimination of rewards for the leaders of these groups. Allowing group leader rewards is found to be detrimental for the market outcome. Group leaders become more careful in screening after the elimination of these rewards, and if their loan participation is high, i.e. when they have skin in the game and are thus severely hurt by a borrower default.
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Kontos, Kevin. "Gaussian graphical model selection for gene regulatory network reverse engineering and function prediction." Doctoral thesis, Universite Libre de Bruxelles, 2009. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210301.
Full textAbstract:
One of the most important and challenging ``knowledge extraction' tasks in bioinformatics is the reverse engineering of gene regulatory networks (GRNs) from DNA microarray gene expression data. Indeed, as a result of the development of high-throughput data-collection techniques, biology is experiencing a data flood phenomenon that pushes biologists toward a new view of biology--systems biology--that aims at system-level understanding of biological systems.Unfortunately, even for small model organisms such as the yeast Saccharomyces cerevisiae, the number p of genes is much larger than the number n of expression data samples. The dimensionality issue induced by this ``small n, large p' data setting renders standard statistical learning methods inadequate. Restricting the complexity of the models enables to deal with this serious impediment. Indeed, by introducing (a priori undesirable) bias in the model selection procedure, one reduces the variance of the selected model thereby increasing its accuracy.
Gaussian graphical models (GGMs) have proven to be a very powerful formalism to infer GRNs from expression data. Standard GGM selection techniques can unfortunately not be used in the ``small n, large p' data setting. One way to overcome this issue is to resort to regularization. In particular, shrinkage estimators of the covariance matrix--required to infer GGMs--have proven to be very effective. Our first contribution consists in a new shrinkage estimator that improves upon existing ones through the use of a Monte Carlo (parametric bootstrap) procedure.
Another approach to GGM selection in the ``small n, large p' data setting consists in reverse engineering limited-order partial correlation graphs (q-partial correlation graphs) to approximate GGMs. Our second contribution consists in an inference algorithm, the q-nested procedure, that builds a sequence of nested q-partial correlation graphs to take advantage of the smaller order graphs' topology to infer higher order graphs. This allows us to significantly speed up the inference of such graphs and to avoid problems related to multiple testing. Consequently, we are able to consider higher order graphs, thereby increasing the accuracy of the inferred graphs.
Another important challenge in bioinformatics is the prediction of gene function. An example of such a prediction task is the identification of genes that are targets of the nitrogen catabolite repression (NCR) selection mechanism in the yeast Saccharomyces cerevisiae. The study of model organisms such as Saccharomyces cerevisiae is indispensable for the understanding of more complex organisms. Our third contribution consists in extending the standard two-class classification approach by enriching the set of variables and comparing several feature selection techniques and classification algorithms.
Finally, our fourth contribution formulates the prediction of NCR target genes as a network inference task. We use GGM selection to infer multivariate dependencies between genes, and, starting from a set of genes known to be sensitive to NCR, we classify the remaining genes. We hence avoid problems related to the choice of a negative training set and take advantage of the robustness of GGM selection techniques in the ``small n, large p' data setting.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Rosetti, Daniele. "Analisi di blockchain come reti complesse: Bitcoin ed Ethereum." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18476/.
Full textAbstract:
Le blockchain sono una tecnologia innovativa che ha destato interesse fin da subito, pur trovando utilizzo in alcuni campi, ancora non sono state capite appieno. Lo scopo del seguente documento è quello di effettuarne un'analisi per comprenderle meglio. Nei primi capitoli si esamineranno alcune delle loro caratteristiche e verranno fornite delle basi sui grafi. Successivamente verrà mostrato il progetto realizzato, composto da due parti. La prima si occupa della generazione di un grafo basato sulle transazioni delle blockchain e la seconda è incaricata della sua analisi. Infine verranno esaminati i risultati prodotti.
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Zhuang, Yuwen. "Metric Based Automatic Event Segmentation and Network Properties Of Experience Graphs." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1337372416.
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Soto, Betancourt Daniela, and Oehsen Tonja von. "The Effectiveness of TikTok in Building small Businesses: A quantitative study of a Media Sharing Network based on the Task-Technology fit model." Thesis, Jönköping University, Tekniska Högskolan, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-54300.
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The main purpose of this paper’s research aims to evaluate the effectiveness of a Media Sharing Network (MSN) in building small businesses. The effectiveness is measured by means of raising the website traffic numbers. Due to its’ novelty, there is a lack of research on TikTok, creating a research gap requiring further investigation for this MSN. Therefore this social media is used as a tool for data collection for this paper’s investigation. In addition, the effectiveness of the various features is evaluated to identify the one most fit for the set task of raising brand awareness through MSNs.
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Miller, Jeanette Kay. "An Adapted Model for Small Business Innovation Networks: The Case of an Emergent Wine Region in Southern California." Digital Archive @ GSU, 2012. http://digitalarchive.gsu.edu/bus_admin_diss/6.
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Small businesses and small business networks have become increasingly important over the past two decades. However, limited empirical research has been carried out on the interactions of these small businesses, specifically within supportive networks. This research focuses on the interaction of firms and organizations within a successful small business innovation network, and how innovative business practices are developed. Innovation network theory was used as a lens to view the dynamics within an innovation network comprised entirely of small businesses and organizations. For this research, a qualitative case study was undertaken, with an emergent wine region in Southern California targeted as an ideal case in which to study a small business innovation network. This research showed that in this instance of a small business innovation network, a hub firm, as defined by innovation network theory does not exist to orchestrate and manage the interactions within the network. Thereby, an adapted model for small business innovation networks is proposed and the results from this qualitative case study are mapped using this adapted theory. The results show a constellation of firms and organizations at the core of the network composition, undertaking deliberate and emergent strategies that affect the outcome and success of all members of the small business innovation network. The research identified a significant sense of place embedded in the regional culture and the importance of effective regional planning in positively impacting the success of the small business innovation network.
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Volpone, Sabrina DeeAnn. "IT IS A SMALL WORLD AND IT IS ONLY GETTING SMALLER: EXPLORING THE RELATIONSHIP BETWEEN SOCIAL NETWORK CHARACTERISTICS AND OUTCOMES WHILE ACCOUNTING FOR THE INFLUENCE OF MEDIATORS AND MODERATORS." Diss., Temple University Libraries, 2013. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/220318.
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Business Administration/Human Resource ManagementPh.D.
In this manuscript I examine outcomes associated with social networks in organizations. Specifically, I consider how two characteristics of social networks (i.e., centrality, tie strength) can affect the performance and satisfaction of employees at work. Then, I explore the role that perceptions of fit (i.e., person-group fit, person-organization) may play in mediating the relationship between social network characteristics and (a) employee performance and (b) job satisfaction. Moreover, I investigate boundary conditions of the aforementioned mediated relationships (i.e., social network characteristics - fit perceptions - employee performance; social network characteristics - fit perceptions - job satisfaction). First, I consider how individual differences (i.e., racioethnicity, sex) generate employee dissimilarity that likely moderates the relationship between structural network characteristics and perceived fit in the mediated relationships proposed. Second, I examine an organizational variable (i.e., perceived diversity climate) as a first and second stage moderator of the aforementioned mediated relationships. Overall, it is necessary to investigate the relationships proposed in the model, because studying social networks helps us to understand why employees interact with certain individuals (or not with others) and how organizational outcomes are affected by employees' choices regarding their social networks.
Temple University--Theses
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Jovanovic, Mihajlo A. "Modeling Large-scale Peer-to-Peer Networks and a Case Study of Gnutella." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin989967592.
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Öberg, Emil. "Small-worlds och rich-clubs bland bloggar : En nätverksanalys av den svenska bloggosfären under FRA-debatten 2008." Thesis, Uppsala universitet, Medier och kommunikation, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-144588.
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Purpose/Aim: To find power structures within the blog network. Material/Method: Using keywords to find all available blog posts about the National Defence Radio Establishment from the blog search engine Twingly, and thereafter using the same blog search engine to find inlinks from other blogs, to those posts. The data is set into the context of the small-world networks models of Duncan J. Watts and rich-club models of Sergi Valverde och Ricard V. Sole. Main results: 5183 unique blogs have written about the subject in 22779 blog posts to which 28128 inlinks from other blogposts are made. Just over one fifth of the blogs are linkted to each other in one big network, where the remaining blogs stand without any ingoing or outgoing links. The first bloggers are the one who continue to write for longer period of time and also the ones who attracts most inlinks. The blogosphere around this subject is highly connected, shows features as one would find in a small-world network, displays a power-law distribution for inlinks and is highly clustered around a few rich- club nodes.
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Moran, Michael. "On Comparative Algorithmic Pathfinding in Complex Networks for Resource-Constrained Software Agents." ScholarWorks, 2017. https://scholarworks.waldenu.edu/dissertations/3951.
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Software engineering projects that utilize inappropriate pathfinding algorithms carry a
significant risk of poor runtime performance for customers. Using social network theory,
this experimental study examined the impact of algorithms, frameworks, and map
complexity on elapsed time and computer memory consumption. The 1,800 2D map
samples utilized were computer random generated and data were collected and processed
using Python language scripts. Memory consumption and elapsed time results for each of
the 12 experimental treatment groups were compared using factorial MANOVA to
determine the impact of the 3 independent variables on elapsed time and computer
memory consumption. The MANOVA indicated a significant factor interaction between
algorithms, frameworks, and map complexity upon elapsed time and memory
consumption, F(4, 3576) = 94.09, p < .001, h2 = .095. The main effects of algorithms,
F(4, 3576) = 885.68, p < .001, h2 = .498; and frameworks, F(2, 1787) = 720,360.01, p
.001, h2 = .999; and map complexity, F(2, 1787) = 112,736.40, p < .001, h2 = .992, were
also all significant. This study may contribute to positive social change by providing
software engineers writing software for complex networks, such as analyzing terrorist
social networks, with empirical pathfinding algorithm results. This is crucial to enabling
selection of appropriately fast, memory-efficient algorithms that help analysts identify
and apprehend criminal and terrorist suspects in complex networks before the next attack.
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Kromer, Justus Alfred. "Noise in adaptive excitable systems and small neural networks." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2017. http://dx.doi.org/10.18452/17683.
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Neuronen sind erregbare Systeme. Ihre Antwort auf Anregungen oberhalb eines bestimmten Schwellwertes sind Pulse. Häufig wird die Pulserzeugung von verschiedenen Rückkopplungsmechanismen beeinflusst, die auf langsamen Zeitskalen agieren. Das kann zu Phänomenen wie Feuerraten-Adaptation, umgekehrter Feuerraten-Adaptation oder zum Feuern von Pulsen in Salven führen. Weiterhin sind Neuronen verschiedenen Rauschquellen ausgesetzt und wechselwirken mit anderen Neuronen, in neuronalen Netzen. Doch wie beeinflusst das Zusammenspiel von Rückkopplungsmechanismen, Rauschen und der Wechselwirkung mit anderen Neuronen die Pulserzeugung? Diese Arbeit untersucht, wie die Pulserzeugung in rauschgetriebenen erregbaren Systemen von langsamen Rückkopplungsmechanismen und der Wechselwirkung mit anderen erregbaren Systemen beeinflusst wird. Dabei wird die Pulserzeugung in drei Szenarien betrachtet: (i) in einem einzelnen erregbaren System, das um einen langsamen Rückkopplungsmechanismus erweitert wurde, (ii) in gekoppelten erregbaren Systemen und (iii) in stark gekoppelten salvenfeuernden Neuronen. In jedem dieser Szenarien wird die Pulsstatistik mit Hilfe von analytischen Methoden und Computersimulationen untersucht. Das wichtigste Resultat im ersten Szenario ist, dass das Zusammenspiel von einer stark anregenden Rückkopplung und Rauschen zu rauschkontrollierter Bistabilität führt. Das erlaubt es dem System zwischen verschiedenen Modi der Pulserzeugung zu wechseln. In (ii) wird die Pulserzeugung stark von der Wahl der Kopplungsstärken und der Anzahl der Verbindungen beeinflusst. Analytische Näherungen werden abgeleitet, die einen Zusammenhang zwischen der Anzahl der Verbindungen und der Pulsrate, sowie der Pulszugvariabilität herstellen. In (iii) wird festgestellt, dass eine hemmende Rückkopplung zu sehr unregelmäßigem Verhalten der isolierten Neuronen führt, wohingegen eine starke Kopplung mit dem Netzwerk ein regelmäßigeres Feuern von Salven hervorruft.Neurons are excitable systems. Their responses to excitations above a certain threshold are spikes. Usually, spike generation is shaped by several feedback mechanisms that can act on slow time scales. These can lead to phenomena such as spike-frequency adaptation, reverse spike-frequency adaptation, or bursting. In addition to these, neurons are subject to several sources of noise and interact with other neurons, in the connected complexity of a neural network. Yet how does the interplay of feedback mechanisms, noise as well as interaction with other neurons affect spike generation? This thesis examines how spike generation in noise-driven excitable systems is influenced by slow feedback processes and coupling to other excitable systems. To this end, spike generation in three setups is considered: (i) in a single excitable system, which is complemented by a slow feedback mechanism, (ii) in a set of coupled excitable systems, and (iii) in a set of strongly-coupled bursting neurons. In each of these setups, the statistics of spiking is investigated by a combination of analytical methods and computer simulations. The main result of the first setup is that the interplay of strong positive (excitatory) feedback and noise leads to noise-controlled bistability. It enables excitable systems to switch between different modes of spike generation. In (ii), spike generation is strongly affected by the choice of the coupling strengths and the number of connections. Analytical approximations are derived that relate the number of connections to the firing rate and the spike train variability. In (iii), it is found that negative (inhibitory) feedback causes very irregular behavior of the isolated bursters, while strong coupling to the network regularizes the bursting.
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Severin, Mats, Stefan Knutsson, and John Söderberg. "Business in the Cloud : Internationalization of a small enterprise in the age of cloud services." Thesis, Uppsala universitet, Företagsekonomiska institutionen, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-176088.
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During the past decade, advances in information technology have facilitated the rapid international expansion of small and medium-sized enterprises (SMEs). Cloud computing has enabled a new wave of firms to offer services on the web regardless of geographic distances. The aim of this study is to explore how cloud computing affect the external variables network and culture in the internationalization process of an SME. In order to explore the impact on these external variables, a qualitative case study is carried out on a business-to-business SME offering cloud services within small and open economies. The findings explain why closeness was important and why the cloud service firm was limited to a gradual internationalization process although the technology has the potential to break this pattern or accelerate it. The results from this study are valuable for scholars since the internationalization process of cloud service firms is an under-researched area. It is also useful for cloud service SMEs when making strategic decisions in the internationalization process.
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Meier, Glen, and Manuel Staehli. "Taking off from Switzerland : A qualitative study of how Swiss Start-Ups internationalize into foreign markets." Thesis, Linnéuniversitetet, Institutionen för marknadsföring (MF), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-56256.
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The purpose of this thesis is to evaluate how Start-Ups from Switzerland pattern their expansion to foreign markets and how prevalent traditional internationalization models are among Start-Ups. In order to conduct the research, the term Start-Up has been defined in comparison to other forms of enterprises. The first part of the literature review has been conducted regarding key concepts within the field of international business such as psychic distance or the choice of the right entry mode. The second part of the literature review has been conducted regarding relevant traditional internationalization theories as well as the international entrepreneurship theory, as counterpart to traditional internationalization theories. The theories have resulted in a conceptual framework that reveals the relations between the different theories. The thesis is built on a qualitative approach on the basis of a multiple case study by means of three interviews with Swiss Start-Ups. Further the thesis has followed a deductive approach to first build a profound knowledge about the internationalization process of Start-Ups. The authors of this thesis consider a good pre understanding of the research area as relevant to observe a pattern from the empirical observations. In the analysis chapter the differences and similarities between the theory and the empirical findings were discussed. The structure of both chapters, empirical findings and analysis, are structured in accordance with the conceptual framework. On the basis of the analysis, the conclusion chapter presents the responses of three research questions. Further the final chapter consists of theoretical and practical implications and recommendations as well as limitations and ends with proposals for a further research.
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Jan, Naeem A. "Anomalous Nature Of Metamaterial Inclusion and Compact Metamaterial-Inspired Antennas Model For Wireless Communication Systems. A Study of Anomalous Comportment of Small Metamaterial Inclusions and their Effects when Placed in the Vicinity of Antennas, and Investigation of Different Aspects of Metamaterial-Inspired Small Antenna Models." Thesis, University of Bradford, 2017. http://hdl.handle.net/10454/16003.
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Metamaterials are humanly engineered artificial electromagnetic materials which produce electromagnetic properties that are unusual, yet can be observed readily in nature. These unconventional properties are not a result of the material composition but rather of the structure formed. The objective of this thesis is to investigate and design smaller and wideband metamaterial-inspired antennas for personal communication applications, especially for WiMAX, lower band and higher band WLAN applications. These antennas have been simulated using HFSS Structure Simulator and CST Microwave Studio software. The first design to be analysed is a low-profile metamaterial-inspired CPW-Fed monopole antenna for WLAN applications. The antenna is based on a simple strip loaded with a rectangular patch incorporating a zigzag E-shape metamaterial-inspired unit cell to enable miniaturization effect. Secondly, a physically compact, CSRR loaded monopole antenna with DGS has been proposed for WiMAX/WLAN operations. The introduction of CSRR induces frequency at lower WLAN 2.45 GHz band while the DGS has provided bandwidth enhancement in WiMAX and upper WLAN frequency bands, keeping the radiation pattern stable. The next class of antenna is a compact cloud-shaped monopole antenna consisting of a staircase-shaped DGS has been proposed for UWB operation ranges from 3.1 GHz to 10.6 GHz. The novel shaped antenna along with carefully designed DGS has resulted in a positive gain throughout the operational bandwidth. Finally, a quad-band, CPW-Fed metamaterial-inspired antenna with CRLH-TL and EBG is designed for multi-band: Satellite, LTE, WiMAX and WLAN.
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Jaiteh, Marli, and Tobias Jakobsson. "It is when we all play safe that we create a world of utmost insecurity : A qualitative study of Swedish B2B SMEs risk perception when internationalizing to East Africa." Thesis, Linnéuniversitetet, Institutionen för marknadsföring (MF), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-35775.
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The purpose of this thesis is to describe and analyze how five Swedish business-to-business (B2B) small- and medium sized enterprises (SME) perceive risk when internationalizing to East African countries. By distinguishing these risks the aim has been to increase the understanding and awareness of the affect that these risks can have on a firm’s internationalization process. To be able to gain a deeper insight of the reality the study has been conducted with a qualitative method and an inductive research approach. The primary data has been collected by conducting interviews with the firms that has been a part of this multiple case study. In order to increase the understanding and thereby fulfill the purpose of this study, the main research question is formulated as follows: how do Swedish B2B SMEs perceive the various risks that they face when internationalizing to East African countries? The theoretical framework has its foundation within the risk theory which is connected to the Uppsala internationalization model, the network theory, motives and triggers for internationalization and the choice of entry mode. The empirical data describes how the case companies entered the East African market, which risks they have encountered and how knowledge has affected their risk perception. In the analysis the empirical data and the theoretical framework is discussed in order to see whether the theories corresponds with the reality of these firms. Furthermore the analysis describes how the firms’ knowledge and relations affect their perception of risk, which risks the firms have encountered within the general environment, industry environment and the firm specific environment as well as how their previous knowledge has affected their perception of risk. The conclusion indicates that Swedish B2B SMEs internationalizing to East African countries encounter several risks, however the perception of these risks differentiates based on the firms previous knowledge of the market. The significance lie within being aware of the risks and thereby being able to see these risks as strategically manageable.
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Göransson, Daniel, and Simon Svenman. "Managing Across Theories : - A profound study of International Entrepreneurship in the field of internationalization theories." Thesis, Linnéuniversitetet, Ekonomihögskolan, ELNU, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-12183.
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The world market has during recent decades become an increasingly globalized arena, in which lowered trade barriers, enhanced technology, worldwide communication and containerization have made internationalization an easily obtainable option for companies. The once dominating multinational enterprises are present day challenged by small- and medium sized enterprises as global actors, and competitiveness is an ever-increasing factor, making the pursuit and exploitation of opportunities essential. The International Entrepreneurship Theory has during the last two decades emerged as a theory explaining the phenomena of small- and medium sized enterprises internationalizing their operations at an early age; a theory comprehending entrepreneurial behavior, the ability to explore and take advantage of opportunities overlooked by others in order to create value in the organization. The purpose of this thesis is to create an understanding of the emergence, definition and theoretical framework of the International Entrepreneurship Theory. By implementing a deductive research approach and a quantitative research method, empirical data is collected in order to confront the theoretical framework in the analysis. The analysis will further be the basis for conclusions and recommendations that will conclude our thesis.
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Kulkarni, Nitish Shrinivas, and Namratha Kumar Vemulkar. "Analysis for the utilization of social media in a Swedish-based SME’s business network : A case study on the service-based startup." Thesis, Uppsala universitet, Institutionen för samhällsbyggnad och industriell teknik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-446652.
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Social media (SM) is an innovative strategy used to develop new forms of communication channels and platforms. This has led to a positive transformation in the marketing strategy for both small-and-medium enterprises (SMEs) and large enterprises. There has been a lot of research conducted on the utilization of SM by Business-to-Consumer (B2C) marketing. However, the use of SM in Business-to-Business (B2B) marketing has not been explored as much in comparison to B2C marketing. The aim of this study is to understand the role of SM channels in B2B service-based SMEs, while also analyzing the challenges and opportunities incorporated by the integration of the SM platforms and the impact it has on B2B relationships. Our research builds on the Industrial Marketing and Purchasing (IMP) related “Activities-Resources-Actors (ARA) Model” and the interconnection between the three layers to understand and analyze the utilization of SM. This study takes a qualitative case study approach to answer the research question formulated in this study by conducting semi-structured interviews. The interviewees included five respondents: two from the focal company and three from their existing business networks. From the findings, three themes were formulated to understand and analyze the data collected: Adoption decision of SM channels in the case SME and the network firm, Collaboration process with the business customers, and Content co-creation. Based on the findings we conclude that SM is an emerging tool for SMEs to incorporate it in their marketing strategy. It can help the firm to improve the bonds between the actors within the organization as well as with their customers and networks. However, the successful utilization of SM in SMEs depends on the commitment of SMEs to incorporate SM tools effectively in their operations. This can be achieved by the “Hybrid approach” by integrating SM communication with the conventional modes of communication for B2B marketing.
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Attah, Alhassan. "A model for forest and product certification in Ghana : the perception and attitudes of forest enterprises in Ghana." Thesis, Bucks New University, 2011. http://bucks.collections.crest.ac.uk/10085/.
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Forest and product certification was initially promoted as a means of enhancing sustainable management of forests in the tropics. However after almost two decades, there is still very little evidence of certified timber products originating from tropical countries. A number of approaches have been suggested to enhance the growth of forest certification in the tropics. These approaches such as that of the Forest Stewardship Council, Global Forest Trade Network of the World Wide Fund for Nature (WWF), Sustainable Forest Initiative and various private sector initiatives have all failed to facilitate forest certification. Therefore to enhance the development of forest certification in Ghana, the research work amongst others, draws on experiences in certification from other sectors such as cocoa, fisheries, tourism and oil palm to develop a model for promoting forest certification in Ghana. The research work uses elements identified in the literature review in developing a questionnaire for the survey of timber firms in Ghana. The research work identified stakeholder consultations, legal framework, resource rights, and the regulation of the domestic market as key elements for promoting forest certification in Ghana. The research recommends a phased approach to promoting forest certification with the first phase being verification of legality that adopts the European Union Forest Law Enforcement, Governance and Trade (FLEGT) and the Voluntary Partnership Agreement (VPA) initiative. The study identifies this approach not only as a means of reducing cost to the private sector in pursuing forest certification but a means of drawing on support measures to enhance the regulation of the domestic market; a key component for promoting forest certification. The report argues that it is only through a well regulated domestic market can tropical timber producing countries achieve sustainable forest management and hence forest certification. The domestic market is therefore seen as a strong means of promoting certification since it will be internalised in the producing countries. None of the research on certification has so far identified the domestic market as a key factor to promoting forest certification and the research work argues that the slow pace of certification has been the lack of demand for certified products on the domestic market. Developing the domestic market is therefore seen as a key policy instrument for promoting the uptake of forest certification in Ghana and the tropics in general.
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Billaud, Yann. "Modélisation hybride stochastique-déterministe des incendies de forêts." Thesis, Aix-Marseille 1, 2011. http://www.theses.fr/2011AIX10100/document.
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Les grands incendies de forêts sont responsables de la quasi-totalité de la surface brulée et contribuent, par les émissions de particules et de gaz à effet de serre qu’ils génèrent, au réchauffement climatique. Des observations satellitaires ont mis en évidence un comportement fractal que l’on attribue aux hétérogénéités locales (topographie, végétation, conditions météorologiques) rencontrées par ces feux lors de leur propagation. Le présent travail a été consacré au développement et à la validation d’un modèle hybride de propagation d’incendie, capable de reproduire ce comportement. Ce modèle est une extension du modèle original de réseau de « petit monde » où les phénomènes qui se produisent à l’échelle macroscopique, comme le rayonnement du front de flammes et l’inflammation pilotée de la strate végétale sont traités de façon déterministe. Pour décrire le rayonnement, nous avons utilisé un modèle de flamme solide couplé à une méthode de Monte Carlo. La validation a porté sur des configurations simples, mais aussi plus complexes, comme le rayonnement d’un front hétérogène de flammes ou celui d’une flamme d’éthanol. Un modèle d’inflammation a ensuite été élaboré et appliqué à des litières d’aiguilles de pin. Les paramètres du modèle ont été optimisés par un algorithme génétique, conduisant au meilleur accord avec les résultats expérimentaux, en termes de temps d‘inflammation et de perte de masses. Il a été montré que l’oxydation du résidu charbonneux joue un rôle prépondérant sur l’inflammation à bas flux. Le modèle de propagation de petit monde a été validé sur un brûlage dirigé et sur un feu historique, montrant un bon accord en termes de surface brûlée, de vitesse de propagation, de contours de feu, et de propriétés fractales. On a montré qu’il pouvait être utilisé pour le dimensionnement d’ouvrages de défense, comme les coupures de combustible, ou pour expliquer le comportement atypique du feu dans certaines situations (talweg, ruptures de pente, etc.). Son application a également permis d’optimiser le nombre et l’emplacement d’un réseau de capteurs déployés dans la végétation dans le but de localiser précisément et détecter précocement le départ d’un feuMost of the area burned by forest fires is attributable to the few fires that escape initial attack to become large. As a consequence large-scale fires produce a large amount of green-house gases and particles which contribute to the global warming. Heterogeneous conditions of weather, fuel, and topography are generally encountered during the propagation of large fires. This shapes irregular contours and fractal post-fire patterns, as revealed by satellite maps. Among existing wildfire spread models, stochastic models seem to be good candidates for studying the erratic behavior of large fires, due to the above-mentioned heterogeneous conditions. The model we developed is a variant of the so-called small-world network model. Flame radiation and fuel piloted ignition are taken into account in a deterministic way at the macroscopic scale. The radiative interaction domain of a burning cell is determined from Monte Carlo simulation using the solid flame model. Some cases are studied, ranging from relatively simple to more complex geometries like an irregular flame fronts or an ethanol pool fire. Then, a numerical model is developed to investigate the piloted ignition of litters composed of maritime pine needles. A genetic algorithm is used to locate a set of model parameters that provide optimal agreement between the model predictions and the experimental data in terms of ignition time and mass loss. The model results had shown the importance of char surface oxidation for heat fluxes close to the critical flux for ignition. Finally, the small-world network model was used to simulate fire patterns in heterogeneous landscapes. Model validation was achieved to an acceptable degree in terms of contours, burned area and fractal properties, through comparison of results with data from a small controlled bushfire experiment and a historical Mediterranean fire. Therefore, it has been proven to be a powerful tool in the sizing of fortifications as fuel break areas at the wildland urban interface or in the understanding of atypical behavior in particular configurations (talweg, slope breaking, etc.). It has also been used for the optimization of an in-situ sensor network whose purpose is to detect precociously and to locate precisely small fires, preventing them from spreading and burning out of control. Our objective was to determine the minimum number and placement of sensors deployed in the forest
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Duarte, Gerdivane Ferreira. "F?sica estat?stica aplicada a sistemas sociais atrav?s do estudo de redes complexas." Universidade Federal do Rio Grande do Norte, 2014. http://repositorio.ufrn.br:8080/jspui/handle/123456789/18609.
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Previous issue date: 2014-02-21Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
In this work a study of social networks based on analysis of family names is presented. A basic approach to the mathematical formalism of graphs is developed and then main theoretical models for complex networks are presented aiming to support the analysis of surnames networks models. These, in turn, are worked so as to be drawn leading quantities, such as aggregation coefficient, minimum average path length and connectivity distribution. Based on these quantities, it can be stated that surnames networks are an example of complex network, showing important features such as preferential attachment and small-world character
Neste trabalho ? apresentado um estudo das redes sociais baseado na an?lise dos nomes de fam?lias. Faz-se uma abordagem b?sica do formalismo matem?tico dos grafos e em seguida apresenta-se os principais modelos te?ricos para as Redes Complexas com o objetivo de fundamentar a an?lise das redes dos sobrenomes. Estas, por sua vez, s?o trabalhadas de modo a serem extra?das as principais grandezas, tais como coe ciente de agrega??o, menor caminho m?dio e distribui??o de conectividades. Com base nestas grandezas, pode-se a rmar que as redes de sobrenomes s?o um exemplo de rede complexa, exibindo caracter?sticas importantes como liga??o preferencial e o car?ter de mundo pequeno.
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Bonfá, Sérgio. "Fatores críticos para a implementação de um modelo de gestão em micro e pequenas empresas." Universidade Federal de São Carlos, 2011. https://repositorio.ufscar.br/handle/ufscar/3662.
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Previous issue date: 2011-02-19The purpose of this study is to analyze factors that contribute and hinders the implementation of a world-class business model for micro and small enterprises. Micro and small enterprises represent a significant portion of Brazil economy and its competitiveness, and ultimately, your success is the interest of all. The success of any business is related to its business model. For this study the Modelo de Excelência da Gestão ®, developed by the Fundação Nacional da Qualidade, has been adopted as a reference. This business model has been used in Prêmio MPE Brasil. This model combines the management best practices implemented in organizations around the world, derived from the total quality management. A case study research was conducted with finalists from the state step Sao Paulo Prêmio MPE Brasil. Based on the case study evidence the entrepreneurs competences and attitudes are critical for the business model implementation success, in particular: management knowledge, commitment to the business model, focus, persistence and constancy of purpose.
O objetivo deste trabalho é analisar fatores críticos para a implementação de um modelo de gestão de classe mundial em micro e pequenas empresas. Estas empresas representam uma parcela significativa da economia do país e a sua competividade, e em última análise, o seu sucesso, interessa a todos. Neste estudo foi adotado como referência de modelo de gestão o Modelo de Excelência da Gestão® disseminado pela Fundação Nacional da Qualidade, e que é usado no Prêmio MPE Brasil. Este modelo reúne as melhores práticas de gestão utilizadas por empresas do mundo todo, derivadas do movimento de qualidade total. As conclusões se basearam em um estudo de caso realizado com empresas finalistas da etapa estadual São Paulo do Prêmio MPE Brasil. De acordo com os empresários participantes, ficou evidenciada e importância das competências e atitudes do líder para o sucesso deste processo e, em especial, o conhecimento em gestão pela liderança, o comprometimento da liderança com o modelo de gestão, foco, persistência e constância de propósito. Outros fatores considerados importantes, de acordo com os resultados obtidos na pesquisa de campo, foram a participação da força de trabalho e o processo usado para conduzir a implementação de um modelo de gestão.
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Magne, Pierre. "Contribution à l'étude de la stabilité et à la stabilisation des réseaux DC à récupération d'énergie." Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0119/document.
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Ce mémoire est consacré à l'étude du phénomène d'instabilité pouvant apparaître sur les bus continus des réseaux DC. En effet, l'interaction entre les différents sous-systèmes électriques (source, charge, filtre) composant le réseau DC peut conduire, sous certaines conditions, à l'instabilité du système. A partir de la modélisation des charges sous forme de "Charge à Puissance Constante" (notée CPL), des méthodes d'études permettant l'analyse de la stabilité "petit-signal" et "grand-signal" des systèmes électriques sont présentées. Celles-ci permettent de mettre en évidence le fait qu'un réseau DC ne peut pas fournir n'importe quelle puissance à ses charges sans devenir instable. Ces puissances limites dépendent à la fois de la structure du réseau et des valeurs de ses éléments passifs et de sa tension de bus. Afin de pouvoir augmenter l'amortissement/les marges de stabilité du système, des méthodes de stabilisation sont présentées dans ce mémoire. Elles proposent d'adapter les commandes des charges de manière à assurer sa stabilité. Ceci se fait grâce à l'addition d'un signal stabilisant sur la référence de chaque charge. Ce signal n'est visible que durant les régimes transitoires de la charge afin de ne pas modifier le point de fonctionnement demandé. Néanmoins, plus on voudra stabiliser une charge et plus son signal stabilisant sera important. Un bon compromis doit donc être trouvé afin d'assurer la stabilité du système sans altérer les performances dynamiques des charges. Deux approches différentes sont proposées afin de générer ces commandes stabilisantes. La première se base sur la mise en place d'un stabilisateur centralisé. Deux méthodes centralisées sont alors proposées : la première s'appuie sur la théorie des multimodèles de Takagi-Sugeno alors que la seconde s'appuie sur la théorie de Lyapunov. Cette dernière permettra d'orienter les efforts de stabilisation sur les charges souhaitées pour par exemple, les diriger principalement vers les organes de récupération d'énergie. La seconde approche se base sur la mise en place d'un système de stabilisation multi-agent. Celui-ci présente une structure décentralisée où chaque agent correspond à un bloc de stabilisation. Ceux-ci vont compenser localement les impacts déstabilisants de leur charge respective et leurs actions combinées permettront d'assurer la stabilité du système. De plus, on propose d'utiliser un algorithme d'optimisation sous contraintes qui permettra de donner un dimensionnement du système minimisant les efforts de stabilisation tout en considérant des cas de défaut tels que la perte de l'un des agents ou la reconfiguration du réseauThis thesis is devoted to the analysis of the instability phenomenon that may appear on the DC bus of DC microgrids. Indeed, interaction between the different electrical subsystems of the grid (source, load, filters) can lead, under certain conditions, to the system instability. From the "Constant Power Load" (CPL) hypothesis for the loads, this thesis presents studying methods for "small-signal" and "large-signal" stability analysis of electrical systems. This highlights that a DC microgrid cannot power the loads more than a maximum limit without becoming unstable. This power limitation depends on the structure of the grid, the value of its passive components, and its bus voltage. In order to improve the microgrid stability, stabilization methods are presented in this thesis. They propose to adapt the loads control to ensure the system stability. This is achieved by the addition of a stabilizing signal to the reference of each load. This signal is only visible during the load power transient mode to not change the requested operating point. However, a good trade-off must be found to ensure system stability without affecting the dynamic performance of its loads. Two approaches are investigated to generate the stabilizing commands. The first one is based on the establishment of a centralized stabilization block. Two centralized methods have been developed: the first one is based on the Takagi-Sugeno theory while the second is based on the Lyapunov theory. This latest permits to guide the stabilizing effort on the desired loads. For example, stabilizing effort can be oriented on the energy storage device. The second approach is based on the establishment of a multi-agent stabilizing system. It consists of a decentralized structure in which each agent corresponds to a stabilization block. These will locally compensate the destabilizing impact of their respective load on the microgrid, and their combined actions ensure the system stability. To design the system, the use of a constrained optimization algorithm is proposed. This permits to minimize stabilization efforts while considering faulty events such as the failure of one of the agents or a reconfiguration of the microgrid
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Hsiao, Ping-Nan, and 蕭炳南. "A Small World with Scale Free Model for Network Communication." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/67517557425671723948.
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碩士淡江大學
資訊工程學系
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The small world network model has been popular to describe human social relations and network formed by biological entities such as neurons. The network model achieves small diameter with relatively few links as measured by the ratio of clustering coefficient and the number of links. It is quite natural to consider email communication as similar to social network pattern. Quite surprisingly we find from our empirical study that email network follows a different type of network model that falls into the category of scale-free network. We propose a new network model to describe such communication topology from linked edge, degree and messages size aspect.