Thèses sur le sujet « Networks dynamic »
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1
Horsch, Michael C. « Dynamic Bayesian networks ». Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/28909.
Texte intégralRésumé :
Given the complexity of the domains for which we would like to use computers as reasoning
engines, an automated reasoning process will often be required to perform under some state of uncertainty. Probability provides a normative theory with which uncertainty can be modelled. Without assumptions of independence from the domain, naive computations of probability are intractible. If probability theory is to be used effectively in AI applications,
the independence assumptions from the domain should be represented explicitly, and used to greatest possible advantage. One such representation is a class of mathematical structures called Bayesian networks.
This thesis presents a framework for dynamically constructing and evaluating Bayesian networks. In particular, this thesis investigates the issue of representing probabilistic knowledge which has been abstracted from particular individuals to which this knowledge
may apply, resulting in a simple representation language. This language makes the independence assumptions for a domain explicit.
A simple procedure is provided for building networks from knowledge expressed in this language. The mapping between the knowledge base and network created is precisely defined, so that the network always represents a consistent probability distribution.
Finally, this thesis investigates the issue of modifying the network after some evaluation has taken place, and several techniques for correcting the state of the resulting model are derived.Science, Faculty of
Computer Science, Department of
Graduate
2
Fard, Pedram J. « Dynamic reconfiguration of network topology in optical networks ». College Park, Md. : University of Maryland, 2007. http://hdl.handle.net/1903/7412.
Texte intégralRésumé :
Thesis (Ph. D.) -- University of Maryland, College Park, 2007.Thesis research directed by: Electrical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
3
Robinson, Anthony John. « Dynamic error propagation networks ». Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303145.
Texte intégral
4
Al-Dujaily, Ra'ed. « Embedded dynamic programming networks for networks-on-chip ». Thesis, University of Newcastle upon Tyne, 2013. http://hdl.handle.net/10443/1884.
Texte intégralRésumé :
Relentless technology downscaling and recent technological advancements in three dimensional integrated circuit (3D-IC) provide a promising prospect to realize heterogeneous system-on-chip (SoC) and homogeneous chip multiprocessor (CMP) based on the networks-onchip (NoCs) paradigm with augmented scalability, modularity and performance. In many cases in such systems, scheduling and managing communication resources are the major design and implementation challenges instead of the computing resources. Past research efforts were mainly focused on complex design-time or simple heuristic run-time approaches to deal with the on-chip network resource management with only local or partial information about the network. This could yield poor communication resource utilizations and amortize the benefits of the emerging technologies and design methods. Thus, the provision for efficient run-time resource management in large-scale on-chip systems becomes critical. This thesis proposes a design methodology for a novel run-time resource management infrastructure that can be realized efficiently using a distributed architecture, which closely couples with the distributed NoC infrastructure. The proposed infrastructure exploits the global information and status of the network to optimize and manage the on-chip communication resources at run-time. There are four major contributions in this thesis. First, it presents a novel deadlock detection method that utilizes run-time transitive closure (TC) computation to discover the existence of deadlock-equivalence sets, which imply loops of requests in NoCs. This detection scheme, TC-network, guarantees the discovery of all true-deadlocks without false alarms in contrast to state-of-the-art approximation and heuristic approaches. Second, it investigates the advantages of implementing future on-chip systems using three dimensional (3D) integration and presents the design, fabrication and testing results of a TC-network implemented in a fully stacked three-layer 3D architecture using a through-silicon via (TSV) complementary metal-oxide semiconductor (CMOS) technology. Testing results demonstrate the effectiveness of such a TC-network for deadlock detection with minimal computational delay in a large-scale network. Third, it introduces an adaptive strategy to effectively diffuse heat throughout the three dimensional network-on-chip (3D-NoC) geometry. This strategy employs a dynamic programming technique to select and optimize the direction of data manoeuvre in NoC. It leads to a tool, which is based on the accurate HotSpot thermal model and SystemC cycle accurate model, to simulate the thermal system and evaluate the proposed approach. Fourth, it presents a new dynamic programming-based run-time thermal management (DPRTM) system, including reactive and proactive schemes, to effectively diffuse heat throughout NoC-based CMPs by routing packets through the coolest paths, when the temperature does not exceed chip’s thermal limit. When the thermal limit is exceeded, throttling is employed to mitigate heat in the chip and DPRTM changes its course to avoid throttled paths and to minimize the impact of throttling on chip performance. This thesis enables a new avenue to explore a novel run-time resource management infrastructure for NoCs, in which new methodologies and concepts are proposed to enhance the on-chip networks for future large-scale 3D integration.
5
Hellmann, Tim. « Stable networks in static and dynamic models of network formation ». Hamburg Kovač, 2009. http://d-nb.info/1001547497/04.
Texte intégral
6
Ho, Koki. « Dynamic network modeling for spaceflight logistics with time-expanded networks ». Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/98557.
Texte intégralRésumé :
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 139-145).
This research develops a dynamic logistics network formulation for high-level lifecycle optimization of space mission sequences in order to find an optimal space transportation architecture considering its technology trades over time. The proposed methodology is inspired by terrestrial logistics analysis techniques based on linear programming network optimization. A new model with a generalized multi-commodity network flow formulation and a time-expanded network is developed for dynamic space logistics optimization. The developed methodology is applied to three case studies: 1) human exploration of Mars; 2) human exploration of a near-Earth object (NEO); 3) their combination (related to the concept of the Flexible Path). The results reveal multiple dynamic system-level trades over time and provide recommendations for an optimal strategy for human space exploration architecture. The considered trades include those between in-situ resource utilization (ISRU) and propulsion technologies as well as orbit and depot location selection over time. The numerical results show that using specific combinations of propulsion technologies, ISRU, and other space infrastructure elements effectively, we can reduce the initial mass in low- Earth orbit (IMLEO) by 45-50% compared with the baseline architecture. In addition, the analysis results also show that we can achieve 15-20% IMLEO reduction by designing Mars and NEO missions together as a campaign compared with designing them separately owing to their common space logistics infrastructure pre-deployment. This research serves as a precursor for eventual permanent settlement and colonization of other planets by humans, thus transforming us into a multi-planet species.
by Koki Ho.
Ph. D.
7
Bienkowski, Marcin. « Page migration in dynamic networks ». [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=976779188.
Texte intégral
8
May, Alex. « Tensor networks for dynamic spacetimes ». Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/62730.
Texte intégralRésumé :
Tensor networks give simple representations of complex quantum states. They have proven useful in the study of condensed matter systems and conformal fields, and recently have provided toy models of AdS/CFT. Underlying the tensor network - AdS/CFT connection is the association of a graph geometry with the tensor network. This geometry is most easily understood as containing only spatial directions. In the context of the AdS/CFT correspondence this limits tensor network toy models to describing static spacetimes. Here we look to extend tensor network models of AdS/CFT by capturing the geometry of a dynamic spacetime in a network description. We review the role of tensor networks in our understanding of AdS/CFT to motivate this extension, before proposing a network picture that captures key features of AdS/CFT.Science, Faculty of
Physics and Astronomy, Department of
Graduate
9
Lesiuk, Bryan Cameron. « Dynamic routing for measurement networks ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/MQ62556.pdf.
Texte intégral
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Afsariardchi, Niloufar. « Community detection in dynamic networks ». Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=114565.
Texte intégralRésumé :
A reasonable representation of some complex systems such as social and biological systems is a network topology that allows its components and interactions among them to change over time. Understanding the time-dependence of these networks can lead to invaluable insight about characteristics and structure of time-varying networks. In this thesis, several classes of static and dynamic clustering algorithms and ideas are reviewed. A challenge arising in dynamic clustering schemes is that the detected communities are not independent over time and the identified clusters at one point of time should not dramatically deviate from the results of previous timesteps. It is especially important to reduce large short term variations and ensure that communities smoothly change over time. Here we present a novel method which is built upon a probabilistic generative Bayesian model to address the problem of identifying consistent and stable overlapping communities in dynamic networks. Synthetic and real networks are used to evaluate the performance with respect to different parameter settings, the model order selection, and the run-time of the proposed algorithm. Performance analysis indicates thatthe algorithm proposed in this thesis outperforms several other state-of-the-art algorithms and provides valuable insights into the evolution and underlying structure.Une représentation raisonnable de certains systèmes complexes tels que les systèmes sociaux et biologiques est une topologie de réseau qui permet à ses composants et les interactions entre eux de changer au fil du temps. Comprendre la dépendance temporelle de ces réseaux, conduire à de précieux renseignements sur les caractéristiques et la structure de variables dans le temps des réseaux. Dans cette thèse, plusieurs classes d'algorithmes de clustering statiques et dynamiques et des idées sont passées en revue. Un défi se pose dans des plans de regroupement dynamiques est que les communautés détectées ne sont pas indépendants dans le temps et les grappes fondées à un moment donné du temps ne doit pas s'écarter de façon spectaculaire à partir des résultats de pas de temps précédents. Spécialement, il est de l'importance de diminuer de fortes variations à court terme et d'assurer que les communautés progressivement changer au fil du temps. Ici, nous présentons une nouvelle méthode qui repose sur un modèle bayésien génératif probabiliste pour résoudre le problème de l'identification des communautés stables et cohérentes qui se chevauchent dans les réseaux dynamiques. Réseaux synthétiques et réelles sont utilisées pour évaluer la performance par rapport à différents paramètres, la sélection pour modèle, et le moment de l'exécution de l'algorithme proposé. Analyse de la performance indique quel'algorithme proposé dans cette thèse surpasse plusieurs autres algorithmes et révèle l'aperçu inestimable d'un réseau e-mail réelle.
11
Laws, Christopher Neil. « Dynamic routing in queueing networks ». Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385435.
Texte intégral
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Cairns, David Edward. « Synchronization in dynamic neural networks ». Thesis, University of Stirling, 1993. http://hdl.handle.net/1893/21611.
Texte intégralRésumé :
This thesis is concerned with the function and implementation of synchronization in networks of oscillators. Evidence for the existence of synchronization in cortex is reviewed and a suitable architecture for exhibiting synchronization is defined. A number of factors which affect the performance of synchronization in networks of laterally coupled oscillators are investigated. It is shown that altering the strength of the lateral connections between nodes and altering the connective scope of a network can be used to improve synchronization performance. It is also shown that complete connective scope is not required for global synchrony to occur. The effects of noise on synchronization performance are also investigated and it is shown that where an oscillator network is able to synchronize effectively, it will also be robust to a moderate level of noise in the lateral connections. Where a particular oscillator model shows poor synchronization performance, it is shown that noise in the lateral connections is capable of improving synchronization performance. A number of applications of synchronizing oscillator networks are investigated. The use of synchronized oscillations to encode global binding information is investigated and the relationship between the form of grouping obtained and connective scope is discussed. The potential for using learning in synchronizing oscillator networks is illustrated and an investigation is made into the possibility of maintaining multiple phases in a network of synchronizing oscillators. It is concluded from these investigations that it is difficult to maintain multiple phases in the network architecture used throughout this thesis and a modified architecture capable of producing the required behaviour is demonstrated.
13
Clegg, Richard G. « The statistics of dynamic networks ». Thesis, University of York, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412635.
Texte intégral
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Pensuwon, Wanida. « Stochastic dynamic hierarchical neural networks ». Thesis, University of Hertfordshire, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366030.
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15
Ou, Jihong. « Dynamic scheduling of queueing networks ». Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13479.
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Rajagopalan, Shreevatsa. « Distributed averaging in dynamic networks ». Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62315.
Texte intégralRésumé :
Thesis (S.M.)--Massachusetts Institute of Technology, Sloan School of Management, Operations Research Center, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (p. 39-40).
The question of computing average of numbers present at nodes in a network in a distributed manner using gossip or message-passing algorithms has been of great recent interest across disciplines -- algorithms, control and robotics, estimation, social networks, etc. It has served as a non-trivial, representative model for an important class of questions arising in these disciplines and thus guiding intellectual progress over the past few decades. In most of these applications, there is inherent dynamics present, such as changes in the network topology in terms of communication links, changes in the values of numbers present at nodes, and nodes joining or leaving. The effect of dynamics in terms of communication links on the design and analysis of algorithms for averaging is reasonably well understood, e.g. [14][2][8][4]. However, little is known about the effect of other forms of dynamics. In this thesis, we study the effect of such types of dynamics in the context of maintaining average in the network. Specifically, we design dynamics-aware message-passing or gossip algorithm that maintains good estimate of average in presence of continuous change in numbers at nodes. Clearly, in presence of such dynamics the best one can hope for is a tradeoff between the accuracy of each node's estimate of the average at each time instant and the rate of dynamics. For our algorithm, we characterize this tradeoff and establish it to be near optimal. The dependence of the accuracy of the algorithm on the rate of dynamics as well as on the underlying graph structure is quantified.
by Shreevatsa Rajagopalan.
S.M.
17
Turcotte, Melissa. « Anomaly detection in dynamic networks ». Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/24673.
Texte intégralRésumé :
Anomaly detection in dynamic communication networks has many important security applications. These networks can be extremely large and so detecting any changes in their structure can be computationally challenging; hence, computationally fast, parallelisable methods for monitoring the network are paramount. For this reason the methods presented here use independent node and edge based models to detect locally anomalous substructures within communication networks. As a first stage, the aim is to detect changes in the data streams arising from node or edge communications. Throughout the thesis simple, conjugate Bayesian models for counting processes are used to model these data streams. A second stage of analysis can then be performed on a much reduced subset of the network comprising nodes and edges which have been identified as potentially anomalous in the first stage. The first method assumes communications in a network arise from an inhomogeneous Poisson process with piecewise constant intensity. Anomaly detection is then treated as a changepoint problem on the intensities. The changepoint model is extended to incorporate seasonal behaviour inherent in communication networks. This seasonal behaviour is also viewed as a changepoint problem acting on a piecewise constant Poisson process. In a static time frame, inference is made on this extended model via a Gibbs sampling strategy. In a sequential time frame, where the data arrive as a stream, a novel, fast Sequential Monte Carlo (SMC) algorithm is introduced to sample from the sequence of posterior distributions of the changepoints over time. A second method is considered for monitoring communications in a large scale computer network. The usage patterns in these types of networks are very bursty in nature and don't fit a Poisson process model. For tractable inference, discrete time models are considered, where the data are aggregated into discrete time periods and probability models are fitted to the communication counts. In a sequential analysis, anomalous behaviour is then identified from outlying behaviour with respect to the fitted predictive probability models. Seasonality is again incorporated into the model and is treated as a changepoint model on the transition probabilities of a discrete time Markov process. Second stage analytics are then developed which combine anomalous edges to identify anomalous substructures in the network.
18
Dong, Dawei Hopfield John J. Hopfield John J. « Dynamic properties of neural networks / ». Diss., Pasadena, Calif. : California Institute of Technology, 1991. http://resolver.caltech.edu/CaltechETD:etd-06202007-092922.
Texte intégral
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Dickison, Mark E. « Dynamic and interacting complex networks ». Thesis, Boston University, 2012. https://hdl.handle.net/2144/31536.
Texte intégralRésumé :
Thesis (Ph.D.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.
This thesis employs methods of statistical mechanics and numerical simulations to study some aspects of dynamic and interacting complex networks. The mapping of various social and physical phenomena to complex networks has been a rich field in the past few decades. Subjects as broad as petroleum engineering, scientific collaborations, and the structure of the internet have all been analyzed in a network physics context, with useful and universal results. In the first chapter we introduce basic concepts in networks, including the two types of network configurations that are studied and the statistical physics and epidemiological models that form the framework of the network research, as well as covering various previously-derived results in network theory that are used in the work in the following chapters. In the second chapter we introduce a model for dynamic networks, where the links or the strengths of the links change over time. We solve the model by mapping dynamic networks to the problem of directed percolation, where the direction corresponds to the time evolution of the network. We show that the dynamic network undergoes a percolation phase transition at a critical concentration Pc, that decreases with the rate r at which the network links are changed. The behavior near criticality is universal and independent of r. We find that for dynamic random networks fundamental laws are changed: i) The size of the giant component at criticality scales with the network size N for all values of r, rather than as N^(2/3) in static network, ii) In the presence of a broad distribution of disorder, the optimal path length between two nodes in a dynamic network scales as N^(1/2), compared to N^(1/3) in a static network. The third chapter consists of a study of the effect of quarantine on the propagation of epidemics on an adaptive network of social contacts. For this purpose, we analyze the susceptible-infected-recovered model in the presence of quarantine, where susceptible individuals protect themselves by disconnecting their links to infected neighbors with probability w and reconnecting them to other susceptible individuals chosen at random. Starting from a single infected individual, we show by an analytical approach and simulations that there is a phase transition at a critical rewiring (quarantine) threshold We separating a phase (w < wc) where the disease reaches a large fraction of the population from a phase (w > wc) where the disease does not spread out. We find that in our model the topology of the network strongly affects the size of the propagation and that wc increases with the mean degree and heterogeneity of the network. We also find that wc is reduced if we perform a preferential rewiring, in which the rewiring probability is proportional to the degree of infected nodes. In the fourth chapter, we study epidemic processes on interconnected network systems, and find two distinct regimes. In strongly-coupled network systems, epidemics occur simultaneously across the entire system at a critical value f3e· In contrast, in weakly-coupled network systems, a mixed phase exists below f3e, where an epidemic occurs in one network but does not spread to the coupled network. We derive an expression for the network and disease parameters that allow this mixed phase and verify it numerically. Public health implications of communities comprising these two classes of network systems are also mentioned.
2031-01-01
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Stapelberg, Dieter. « Link failure recovery among dynamic routes in telecommunication networks ». Thesis, Stellenbosch : University of Stellenbosch, 2009. http://hdl.handle.net/10019.1/2591.
Texte intégralRésumé :
Thesis (MSc (Mathematical Sciences. Computer Science))--University of Stellenbosch, 2009.ENGLISH ABSTRACT: Since 2002 data tra c has overtaken voice tra c in volume [1]. Telecom / Network operators still generate most of their income carrying voice tra c. There is however a huge revenue potential in delivering reliable guaranteed data services. Network survivability and recovery from network failures are integral to network reliability. Due to the nature of the Internet, recovery from link failures needs to be distributed and dynamic in order to be scalable. Link failure recovery schemes are evaluated in terms of the survivability of the network, the optimal use of network resources, scalability, and the recovery time of such schemes. The need for recovery time to be improved is highlighted by real-time data tra c such as VoIP and video services carried over the Internet. The goal of this thesis is to examine existing link failure recovery schemes and evaluate the need for their extension, and to evaluate the performance of the proposed link failure recovery schemes. i
AFRIKAANSE OPSOMMING: Sedert 2002 het data verkeer die stem verkeer in volume verbygesteek [1]. Telekommunikasie / netwerk operateurs genereer egter steeds die meeste van hul inkomste met stem verkeer. Netwerk oorlewing en die herstel van netwerk mislukkings is integraal tot netwerk stabiliteit. Die samestelling van die Internet noodsaak dat die herstel van skakel mislukkings verspreid en dinamies van natuur moet wees. Die herstel-skema van skakel mislukkings word evalueer in terme van die oorleefbaarheid van die netwerk, die mees e ektiewe benutting van network bronne, aanpasbaarheid, en die herstel tydperk van die skema. Die vinnig moontlikste herstel tydperk word genoodsaak deur oombliklike data verkeer soos VoIP en beeld dienste wat oor die Internet gedra word. The doel van hierdie tesis is om bestaande skakel mislukking herstel skemas te evalueer, en dan verder ondersoek in te stel na hul uitbreiding. Daarna word die voorgestelde skakel mislukking skema se e ektiwiteit gemeet.
21
Avidan, Lenoy. « Dynamic Shifting of Virtual Network Topologies for Network Attack Prevention ». DigitalCommons@CalPoly, 2019. https://digitalcommons.calpoly.edu/theses/1986.
Texte intégralRésumé :
Computer networks were not designed with security in mind, making research into the subject of network security vital. Virtual Networks are similar to computer networks, except the components of a Virtual Network are in software rather than hardware. With the constant threat of attacks on networks, security is always a big concern, and Virtual Networks are no different. Virtual Networks have many potential attack vectors similar to physical networks, making research into Virtual Network security of great importance. Virtual Networks, since they are composed of virtualized network components, have the ability to dynamically change topologies. In this paper, we explore Virtual Networks and their ability to quickly shift their network topology. We investigate the potential use of this flexibility to protect network resources and defend against malicious activities.
To show the ability of reactively shifting a Virtual Network’s topology to se- cure a network, we create a set of four experiments, each with a different dynamic topology shift, or “dynamic defense”. These four groups of experiments are called the Server Protection, Isolated Subnet, Distributed Port Group, and Standard Port Group experiments. The Server Protection experiments involve detecting an attack against a server and shifting the server behind a protected subnet. The other three sets of experiments, called Attacker Prevention experiments, involve detecting a malicious node in the internal network and initiating a dynamic de- fense to move the attacker behind a protected subnet. Each Attacker Prevention experiment utilizes a different dynamic defense to prevent the malicious node from attacking the rest of the Virtual Network. For each experiment, we run 6 different network attacks to validate the effectiveness of the dynamic defenses. The network attacks utilized for each experiment are ICMP Flooding, TCP Syn Flooding, Smurf attack, ARP Spoofing, DNS Spoofing, and NMAP Scanning. Our validation shows that our dynamic defenses, outside of the standard port group, are very effective in stopping each attack, consistently lowering the at- tacks’ success rate significantly. The Standard Port Group was the one dynamic defense that is ineffective, though there are also a couple of experiments that could benefit from being run with more attackers and with different situations to fully understand the effectiveness of the defenses. We believe that, as Virtual Networks become more common and utilized outside of data centers, the ability to dynamically shift topology can be used for network security purposes.
22
Holzhauer, Sascha [Verfasser]. « Dynamic Social Networks in Agent-based Modelling : Increasingly Detailed Approaches of Network Initialisation and Network Dynamics / Sascha Holzhauer ». Kassel : Kassel University Press, 2017. http://d-nb.info/1137030445/34.
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Kachani, Soulaymane, et Georgia Perakis. « Modeling Travel Times in Dynamic Transportation Networks ; A Fluid Dynamics Approach ». Massachusetts Institute of Technology, Operations Research Center, 2001. http://hdl.handle.net/1721.1/5224.
Texte intégralRésumé :
In this paper, we take a fluid dynamics approach to determine the travel time in traversing a network's link. We propose a general model for travel time functions that utilizes fluid dynamics laws for compressible flow to capture a variety of flow patterns such as the formation and dissipation of queues, drivers' response to upstream congestion or decongestion and drivers' reaction time. We examine two variants of the model, in the case of separable velocity functions, which gives rise to two families of travel time functions for the problem; a polynomial and an exponential family. We analyze these travel time functions and examine several special cases. Our investigation also extends to the case of non-separable velocity functions starting with an analysis of the interaction between two links, and then extending it to the general case of acyclic networks.
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Alfred, Asterjadhi. « Network Coding for Cognitive Radio Networks ». Doctoral thesis, Università degli studi di Padova, 2011. http://hdl.handle.net/11577/3422021.
Texte intégralRésumé :
Cognitive Radio Networks are a promising technology likely to be deployed in the very near future as a viable solution to the spectrum shortage problems faced by traditional wireless systems. Technological breakthroughs in the field of Software Defined Radios enabled the development of flexible cognitive radio transceivers capable of dynamically changing their transmission parameters in order to efficiently exploit the available wireless resources. This increased capability of cognitive radios to self adapt based on interactions with the surrounding environment makes them the perfect candidates for opportunistic spectrum access in those bands that are assigned to primary users. While these primary users are allowed to access their licensed spectrum resources anytime and anywhere, within the contractual limits imposed by spectrum management authorities, cognitive radios have to scan and identify any unused spectrum in the licensed bands. Most importantly, in order not to interfere with primary users, they have to rapidly vacate the licensed spectrum as soon as the primary user begins to use its legitimate spectrum resources.
The coexistence of cognitive radios with such primary users is very challenging. When considering the natural evolution of cognitive radio networks to more complex systems, the challenges and problems to be faced increase substantially. More specifically, the inherent capability of cognitive radios to base their decisions on their view of the wireless spectrum makes their operation susceptible to a variety of malicious attacks. Hence, in such a challenging environment, mechanisms such as cooperation, learning, and negotiation help cognitive radios make the necessary decisions to ensure reliable communications in a non-interfering manner.
We hereby investigate a novel architectural solution for Cognitive Radio Networks that uses network coding for fast control information exchange among cognitive radios, enabling them to maintain coherent and reliable information regarding the status of the wireless environment. This control information is used by cognitive radios to perform cooperative detection of primary users and efficient reuse of the available spectrum resources while guaranteeing robust communication and a prompt reaction to wireless environmental changes.Le Reti Radio Cognitive sono una tecnologia promettente che potrà essere utilizzata in un futuro molto prossimo, come soluzione possibile al problema di spettro limitato riscontrato nelle reti wireless tradizionali. Le recenti innovazioni tecnologiche su Software Defined Radio hanno permesso lo sviluppo di ricetrasmettitori radio sufficientemente flessibili, in grado di modificare dinamicamente i loro parametri di trasmissione, al fine di sfruttare in modo efficiente le risorse radio disponibili. Questa maggiore capacita di auto-adattarsi in risposta alle interazioni con l'ambiente circostante rende le radio cognitive i candidati ideali per l'accesso opportunistico nelle bande dello spettro radio utilizzate dagli utenti primari. Poiché gli utenti primari hanno diritto ad accedere alle proprie risorse dello spettro in qualsiasi momento e luogo, entro i limiti contrattuali imposti dalle autorità di gestione dello spettro radio, le radio cognitive devono effettuare la scansione e identificare le porzioni dello spettro non utilizzate dagli utenti primari. Inoltre, al fine di non interferire con tali utenti, esse devono liberare rapidamente lo spettro radio, ogniqualvolta l'utente primario inizi ad utilizzare la propria banda di frequenze. La coesistenza tra radio cognitive e utenti primari e' un obiettivo molto ambizioso. Inoltre, quando si considera la normale evoluzione delle reti radio cognitive a sistemi più complessi, le sfide e i problemi da affrontare aumentano notevolmente. In particolare, la capacita intrinseca delle radio cognitive di basare le proprie decisioni sulla propria visione locale dello spettro radio rende il loro funzionamento sensibile a molte tipologie di attacco. Quindi, in tale ambiente, meccanismi come la cooperazione, l'apprendimento e la negoziazione sono di aiuto alle radio cognitive nel prendere le decisioni necessarie a garantire le proprie comunicazioni senza interferire con quelle degli utenti primari. In questa tesi si presenta un'architettura innovativa per le Reti Radio Cognitive che utilizza la tecnica di network coding per lo scambio di informazioni di controllo tra i nodi, riguardo lo stato dell'ambiente radio, in modo rapido, coerente e affidabile. Questa informazione viene successivamente utilizzata dalle radio cognitive per eseguire il rilevamento cooperativo degli utenti primari e il riutilizzo efficiente dello spettro a disposizione, garantendo una comunicazione robusta e una reazione tempestiva ai cambiamenti dello stato delle risorse radio.
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Ewell, Cris Vincent. « Detection of Deviations From Authorized Network Activity Using Dynamic Bayesian Networks ». NSUWorks, 2011. http://nsuworks.nova.edu/gscis_etd/146.
Texte intégralRésumé :
This research addressed one of the hard problems still plaguing the information security profession; detection of network activity deviations from authorized accounts when the deviations are similar to normal network activity. Specifically, when user and administrator type accounts are used for malicious activity, harm can come to the organization. Accurately modeling normal user network activity is hard to accomplish and detecting misuse is a complex problem.
Much work has been done in the past with intrusion detection systems, but being able to detect masquerade events with high accuracy and low false alarm rates continues to be an issue. Bayesian networks have been successfully used in the past to reason under certainty by combining prior knowledge with observed data. The use of dynamic Bayesian Networks, such as multi-entity Bayesian network, extends the capability and can address complex problems.
The goal of the research was to extend previous research with multi-entity Bayesian networks along with discretization methods to improve the effectiveness of the detection rate while maintaining an acceptable level of false positives. Preprocessing continuous variables has proven effective in prior research but has not been applied to multi-entity Bayesian networks in the past. Five different discretization methods were used in this research. Analysis using receiver operating characteristic curves, confusion matrix, and other comparison methods were completed as part of this research.
The results of the research demonstrated that a multi-entity Bayesian network model based on multiple data sources and the relationship between the user attributes could be used to detect unauthorized access to data. The supervised top down discretization methods had better performance related to the overall classification accuracy. Specifically, the class-attribute interdependence maximization discretization method outperformed the other four discretization methods. When compared to previous masquerade detection methods, the class-attribute interdependence maximization discretization method had a comparable true positive rate with a lower false positive rate.
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Junuthula, Ruthwik Reddy. « Modeling, Evaluation and Analysis of Dynamic Networks for Social Network Analysis ». University of Toledo / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1544819215833249.
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Bradford, Robert D. « Solving dynamic battlespace movement problems using dynamic distributed computer networks / ». Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2000. http://handle.dtic.mil/100.2/ADA380802.
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Bradford, Robert D. III. « Solving dynamic battlespace movement problems using dynamic distributed computer networks ». Thesis, Monterey, California. Naval Postgraduate School, 2000. http://hdl.handle.net/10945/7794.
Texte intégralRésumé :
Approved for public release, distribution is unlimitedThis thesis develops an architecture for dynamic distributed military operations research. This architecture assumes that a network of heterogeneous computing devices connects forces throughout the battlespace. Both the raw data about the battlespace and the operations research models used to analyze this data are accessible to devices on this network. The thesis designs a system using this architecture that invokes operations research network optimization algorithms to solve problems involving movement of people and equipment over dynamic road networks. A specific application is, implemented to help a medic find the nearest aid station using a shortest path algorithm. This application marshals the most current data on unit locations and road conditions (distributed across the computing network) and locates on the network an appropriate algorithm that is then used to construct a solution. The answer is returned to the user as a web page in a form appropriate for his computing device. The application is implemented with existing technologies including the Java computer language, Konig, a Java-based tool for representing networks and graphs, and Hypertext Markup Language, a format for shared information on the Internet. This system uses operations research tools to transform data into decisions in real-time or near real-time.
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Periorellis, Panayiotis. « Dynamic enterprise modelling : a methodology for animating dynamic social networks ». Thesis, University of Newcastle Upon Tyne, 2000. http://hdl.handle.net/10443/2134.
Texte intégralRésumé :
Since the introduction of the Internet and the realisation of its potential companies have either transformed their operation or are in the process of doing so. It has been observed, that developments in I.T., telecommunications and the Internet have boosted the number of enterprises engaging into e-commerce, e-business and virtual enterprising. These trends are accompanied by re-shaping, transformation and changes in an enterprise's boundaries. The thesis gives an account of the research into the area of dynamic enterprise modelling and provides a modelling methodology that allows different roles and business models to be tested and evaluated without the risk associated with committing to a change.
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Eriksson, Kristoffer. « Dynamic Resource Allocation in Wireless Networks ». Thesis, Linköping University, Communication Systems, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-56776.
Texte intégralRésumé :
In this thesis we investigate different algorithms for dynamic resource allocation in wireless networks. We introduce a general framework for modeling systems whichis applicable to many scenarios. We also analyze a specific scenario with adaptivebeamforming and show how it fits into the proposed framework. We then studytwo different resource allocation problems: Quality-of-Service (QoS) constraineduser scheduling and sum-rate maximization. For user scheduling, we select some“good” set of users that is allowed to use a specific resource. We investigatedifferent algorithms with varying complexities. For the sum-rate maximizationwe find the global optimum through an algorithm that takes advantage of thestructure of the problem by reformulating it as a D.C. program, i.e., a minimizationover a difference of convex functions. We validate this approach by showing that itis more efficient than an exhaustive search at exploring the space of solutions. Thealgorithm provides a good benchmark for more suboptimal algorithms to comparewith. The framework in which we construct the algorithm, apart from being verygeneral, is also very flexible and can be used to implement other low complexitybut suboptimal algorithms.
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Lin, Wuqin. « Dynamic Control in Stochastic Processing Networks ». Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7105.
Texte intégralRésumé :
A stochastic processing network is a system that takes materials of various kinds as inputs, and uses processing resources to produce other materials as outputs. Such a network provides a powerful abstraction of a wide range of real world, complex systems, including semiconductor
wafer fabrication facilities, networks of data switches, and large-scale call centers. Key performance measures of a stochastic processing network include throughput, cycle time, and
holding cost. The network performance can dramatically be affected by the choice of operational policies.
We propose a family of operational policies called maximum pressure policies. The maximum pressure policies are attractive in that their implementation uses minimal state information of the network. The deployment of a resource (server)
is decided based on the queue lengths in its serviceable buffers and the queue lengths in their immediate downstream buffers.
In particular, the decision does not use arrival rate information that is often difficult or impossible to estimate reliably. We prove that a maximum pressure policy can maximize throughput
for a general class of stochastic processing networks. We also establish an asymptotic optimality of maximum pressure policies for stochastic processing networks with a unique
bottleneck. The optimality is in terms of minimizing workload process. A key step in the proof of the asymptotic optimality is to show that the network processes under maximum pressure policies exhibit a state space collapse.
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Baldine, Ilia. « Dynamic Reconfiguration in Broadcast WDM Networks ». NCSU, 1998. http://www.lib.ncsu.edu/theses/available/etd-19980723-230505.
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In this research we study the problems associated with dynamic reconfiguration of broadcast WDM networks.Adaptability to the changing traffic conditions is viewed as one of the key features of multiwavelength optical networks, and this is the first comprehensive in-depth study of this problem area.Our contribution consists of identifying the three main questions related to network reconfiguration: a) how to balance the load across multiple wavelengths; b) deciding when it is best to reconfigure the network and c) performing the actual reconfiguration in an efficient manner, that minimizes cell losses.We provide novel solutions to each of these problems.Our solutions consist of an algorithm we call GLPT, which balances the cell load across wavelengths, an optimal reconfiguration policy, derived from representing the problem as a Markovian Decision Process, and a class of retuning strategies that allow us to reconfigure the system.In addition, we perform a simulated comparison of static and dynamically reconfigurable networks in order to verify the validity of our approach.The simulation also provides us with valuable insights into the behavior of an adaptable optical network.
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Li, Caiwei. « Dynamic scheduling of multiclass queueing networks ». Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/24339.
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Garside, Simon. « Dynamic prediction of road traffic networks ». Thesis, Lancaster University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387431.
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Alnwaimi, Ghassen R. « Dynamic spectrum sharing in heterogeneous networks ». Thesis, University of Surrey, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.606694.
Texte intégralRésumé :
The increasing demands for wireless spectrum and limited radio resources emphasise the need. for more efficient spectrum sharing mechanisms. Dynamic spectrum sharing (DSS) has been cited as a promising mechanism for managing the radio spectrum. The objectives are to achieve flexible spectrum usage, improve spectrum efficiency, and combat spectrum scarcity problem, which constitute the main motivations setting out the scope of. this thesis_ This thesis, first, presents a comprehensive survey of the general principles of current and state of art spectrum sharing practices, and approaches to future ones. A concise cell-coupling-based approach has been introduced as a model for the investigation of the influence when several competing mobile networks simultaneously coexist and share a common pool of radio resources. A simple centralised medium-term DSS (CDSS) model has been employed in order to enhance spectrum utilisation and achieve an interference-free communication environment. The global view of the CDSS leads to a quick path in reaching a stable system and achieving a near optimum spectrum configuration. To align with the current trends, the thesis also investigates enabling technology for DSS in heterogeneous networks (HetNets) deployment, where factors such as ad hoc and distributed. nature of network topology, heterogeneous network infrastructures, and several power profiles make the spectrum and interference management problem more intractable. The HetNet is modelled as a layer of closed access, randomly-located femtocells (FCs) overlaid upon a LTE radio access mobile network. In the context of dynamic learning games, this work proposes multi-objectives, fully distributed strategy based on heterogeneous reinforcement learning (RL) model (CODIPAS-HRL) for the femtocells opportunistic access. We present two different learning strategies; the modified Bush and Mosteller (MBM) and the modified Roth-Erev (MRE). The self-organisation capability enables FCs to autonomously identify available spectrum for opportunistic use, using HRL schemes, and tune their parameters accordingly in order to operate under restrictions of avoiding interference and satisfy QoS requirements. Finally, the proposed work takes the advantages of calculating the learning cost, the convergence behaviour for different learning rates and provides comparisons between different learning strategies. The simulation results show the convergence of the learning model to a solution concept based on satisfaction equilibrium, under the uncertainty of the HetNet environment and heterogeneous learning. Such a distributed intelligent scheme can provide a practical solution to the main challenges of spectral opportunity identification and interference management in future networks.
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Neophytou, Constantinos. « Dynamic Tree Switching for IP Networks ». Thesis, Queen Mary, University of London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.498910.
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Wright, Robert John. « Water distribution networks with dynamic topology ». Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/58191.
Texte intégralRésumé :
The subdivision of water distribution networks (WDN) into zones, known as district metered areas (DMAs), is a popular approach to leakage management used by water companies. The DMAs are formed by permanently closing isolation valves at the boundaries of each zone (known as boundary valves). By forming discrete zones in the WDN, leakage estimates can be made at night when demand is low, which is used to prioritise pipe repair and replacement programmes. However, the permanent closure of boundary valves has also caused several disadvantages, including reduced network resilience to failure, sub-optimal pressure management, and water quality problems. This thesis introduces a novel approach to the operational management of WDNs, where DMAs are dynamically aggregated for improved network resilience, pressure management and water quality, and segregated for leakage monitoring at night. This is facilitated by replacing closed boundary valves with self-powered, remote control valves (dynamic boundary valves). The operation of a dynamic topology can therefore successfully eliminate the disadvantages of conventional DMAs, whilst retaining or improving their success in leakage monitoring. The investigation is carried out both analytically and experimentally on a real, operational UK network supplying approximately 8,000 properties in order to establish the benefits and challenges of the proposed approach. An extensive review of the current and emerging forms of pressure and DMA management from around the world is carried out. A case study using a real large scale network (3,148km of pipeline) demonstrates the current state of DMAs and their conformity to DMA design guidelines, and identifies how a dynamic DMA topology can improve network performance. A novel resilience index (the Reserve Capacity) is then used in the design of the dynamic DMA topology in the experimental programme. The analytical and experimental investigation has demonstrated a 27% reduction in leakage using a dynamic DMA topology over the most common approach to pressure management, and strong improvements in network resilience to failure where 1,400 customers maintained a supply during a real, major burst incident that would otherwise have been disconnected. In order to actuate near optimal control in the experimental programme, a novel optimisation algorithm based on sequential convex programming (SCP) is proposed for the control of valves. The SCP method takes advantage of computationally efficient solvers that facilitate prompt and reliable convergence. The algorithm also includes the development of a novel, convex valve model that can be integrated into efficient null space algorithms. In order to actuate the control, a novel approach for valve control in DMAs with dynamic topology is proposed, where time varying flow modulation curves are used based on the dynamic connectivity of DMAs.
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Klu, Joyce Kafui. « Opinion formation in dynamic social networks ». Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:6418f526-5cda-41a2-9eb5-842ab40ca5f2.
Texte intégralRésumé :
Opinion dynamics in a society of interacting agents may lead to consensus or to the coexistence of different opinions. The interplay between social network change and opinion formation is complex, because the agents, their social interactions and the changing social structure over time, are themselves complex. DeGroot proposed a prescriptive model for achieving consensus, where agents revise their opinions at each time step by taking a weighted average of the opinions of neighbours. This thesis contains three main contributions. First, we introduce a generalisation of the DeGroot model and examine the long-time behaviour of the model, with and without insistent agents. Second, we consider opinion formation on networks which are themselves dynamic, where the dynamics may be completely random or based on homophily and triadic closure. The weights that agents place on the opinions of neighbours are also dynamic, based on a rule where weights decrease with increased difference in opinions. Third, we examine the effect of a sudden, temporary or permanent shift in the opinions of some agents. Two dynamics are considered for the network change over time; random switching (RS) network dynamics, and homophily and triadic closure (HT) network dynamics. We prove that the RS network dynamics enhances consensus formation and network connectivity, compared to the HT network dynamics where we show by simulation that different opinions can persist. We investigate the in uence of the presence of a minority of insistent agents and prove that for a connected static network, insistent agents with the same opinion in uence the final opinions to converge to their own opinion, thus leading to consensus. In contrast, lack of consensus persists when insistent agents have different opinions. This conclusion also holds for the RS network dynamics model. However, for the HT network dynamics model, coexistence of different opinions can persist even when insistent agents have the same opinion. This finding regarding the HT dynamics is of particular interest as it relates to observations in the real-world. We also investigate the in uence of a sudden shift in the opinions of some agents on the outcome of final opinions. The case of either a temporary shift in opinions or a permanent shift in opinions is examined. Additionally, the in uence of the time of the introduction of a shift, the number and the network positions of initial recipients of the shift in opinions is investigated. The overall effect of an opinion shift is measured by its in uence on the stabilisation time of the final opinions.
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Pavone, Marco Ph D. Massachusetts Institute of Technology. « Dynamic vehicle routing for robotic networks ». Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/59665.
Texte intégralRésumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 149-156).
Recent years have witnessed great advancements in the sciences and technology of autonomy, robotics and networking. This dissertation develops concepts and algorithms for dynamic vehicle routing (DVR), that is, for the automatic planning of optimal multi-vehicle routes to provide service to demands (or more generally to perform tasks) that are generated over time by an exogenous process. We consider a rich variety of scenarios relevant for robotic applications. We begin by reviewing some of the approaches available to tackle DVR problems. Next, we study different multi-vehicle scenarios based on different models for demands (in particular, demands with time constraints, demands with different priority levels, and demands that must be transported from a pick-up to a delivery location). The performance criterion used in these scenarios is either the expected waiting time of the demands or the fraction of demands serviced successfully. In each specific DVR scenario we adopt a rigorous technical approach, which we call algorithmic queueing theory and which relies upon methods from queueing theory, combinatorial optimization, and stochastic geometry. Algorithmic queueing theory consists of three basics steps: 1) queueing model of the DVR problem and analysis of its structure; 2) establishment of fundamental limitations on performance, independent of algorithms; and 3) design of algorithms that are either optimal or constant-factor away from optimal. In the second part of the dissertation, we address problems concerning the implementation of routing policies in large-scale robotic networks, such as adaptivity and decentralized computation. We first present distributed algorithms for environment partitioning, and then we apply them to devise routing policies for DVR problems that (i) are spatially distributed, scalable to large networks, and adaptive to network changes, and (ii) have remarkably good performance guarantees. The technical approach developed in this dissertation is applicable to a wide variety of DVR problems: several possible extensions are discussed throughout the thesis.
by Marco Pavone.
Ph.D.
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Wion, Adrien. « Control plane in dynamic software networks ». Electronic Thesis or Diss., Institut polytechnique de Paris, 2021. http://www.theses.fr/2021IPPAT007.
Texte intégralRésumé :
Au cours de ces dernières années, les réseaux se sont transformés passant d'une infrastructure à base de matériel dédié implémentant des fonctions statiques à des solutions logicielles plus flexibles. D'un côté, le SDN (Software Defined Networks) permet de contrôler les opérations de transmission, alors que de l'autre le NFV (Network Function Virtualization) crée des fonctions élastiques qui peuvent s'adapter à la demande. Jusqu'à présent, ces solutions ont été utilisées pour simplifier la gestion et l'exploitation des réseaux mais elles laissent également envisager un réseau qui peut automatiquement réagir à des événements réseaux. Dans cette thèse, nous explorons dans quelle mesure ces nouveaux réseaux logiciels peuvent être utilisés pour s'adapter à la dynamique inhérentes aux réseaux. Notre première contribution s'intéresse au chaînage de service, c'est à dire la capacité de diriger des flux de données à travers un ensemble de points intermédiaires, qui hébergent des fonctions, avant d'atteindre leur destination. Nous montrons qu'un plan de contrôle distribué, qui s'appuie sur les protocoles de routage existants et qui est constitué par des noeuds autonomes, peut dynamiquement diriger le trafic à travers des chaines de services. Notre solution adapte sa décision au trafic sur le réseau et équilibre automatiquement la charge induite sur les fonctions présentes sur le réseau. De plus, notre proposition, au contraire des solutions existantes, peut être déployée progressivement dans les réseaux actuels. Dans notre seconde contribution, nous comparons deux types de décision de chaînage : une approche centralisée avec une vue de bout en bout de la chaîne et une approche distribuée qui dirige uniquement les flux d'une fonction à l'autre. Nous montrons que ces deux décisions sont proches dans des topologies réalistes. Ainsi, un chaînage saut par saut pourrait être utilisé sans affecter les performances du réseau.Finalement, nous explorons comment les réseaux logiciels peuvent réagir à la dynamique des réseaux dans les centres de données. Jusqu'à présent, des équilibreurs de charges utilisaient des politiques statiques afin de répartir le trafic sur les serveurs, ce qui amenait du déséquilibre et gâchait des ressources. Nous proposons d'asservir le système et d'adapter dynamiquement la politique à la variation de charge des serveurs. Notre approche MPC (Model Predictive Control) est efficace afin de réduire le déséquilibre de charge à une basse fréquence de contrôle améliorant ainsi le nombre de requêtes qu'un ensemble de serveur peut traiterDuring the last years, network infrastructure has moved from dedicated-hardware solutions implementing fixed functions to more flexible software based ones. On one hand, SDN (Software Defined Network) can flexibly control forwarding operations, while on the other, NFV (Network Function Virtualization) creates elastic functions that can scale with the user demands. So far, these solutions have been used to simplify network management and operations, but they let envision a network that can automatically react to network events. In this thesis, we explore to what extent these new software networks can be used to react and adapt finely to the network dynamics.Our first contribution focuses on service chaining: the ability to steer flows through a set of waypoints hosting functions before they reach their destinations. We show that a distributed control plane that relies on existing routing protocols and is constituted by autonomous nodes can dynamically steer traffic through chains of services. Our solution finely adapts its decision to the network traffic and automatically balances the induced load on the functions present in the network. Moreover, our proposal, contrary to existing solutions, can be incrementally deployed in today's network.In our second contribution, we compare two types of chaining decisions: a centralized one with an end-to-end view of the chain and a distributed approach that solely routes flow from a function to another. We show that the two decisions are close in realistic topologies. Thus, hop-by-hop chaining could be used without affecting chaining performance. Finally, we explore how software networks can react to network dynamics in datacenters. So far, load balancers use static policies to spread incoming traffic on servers, which leads to imbalance and overprovisioning. We propose to close the loop and dynamically adapt the policy to the server load variation. Our MPC (Model Predictive Control) approach proved to be efficient to reduce load imbalance at a slow pace, thus improving the number of requests a cluster can process
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Moose, Robert Lewis. « Analysis of networks with dynamic topologies ». Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/49862.
Texte intégralRésumé :
Dynamic hierarchical networks represent an architectural strategy for employing adaptive behavior in applications sensitive to highly variable external demands or uncertain internal conditions. The characteristics of such architectures are described, and the significance of adaptive capability is discussed. The necessity for assessing cost/benefit tradeoffs leads to the use of queueing network models. The general model, a network of M/M/1 queues in a random environment, is introduced and then is simplified so that the links may be treated as isolated M/M/1 queues in a random environment. This treatment yields a formula for approximate mean network delay by combining matrix-geometric results (mean queue length and mean delay) for the individual links. Conditions under which the analytic model is considered valid are identified through comparison with a discrete event simulation model. Last, performance of the dynamic hierarchy is compared with that of the static hierarchy. This comparison establishes conditions for which the dynamic architecture enables performance equal or nearly equal to performance of the static architecture.Ph. D.
incomplete_metadata
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McCallen, Scott J. « Mining Dynamic Structures in Complex Networks ». Kent State University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=kent1204154279.
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Robinson, Jace D. « A Model for Seasonal Dynamic Networks ». Wright State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=wright1525195522616039.
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Ashibani, Majdi Ali Atoomi. « Dynamic bandwidth allocation in ATM networks ». Doctoral thesis, University of Cape Town, 2002. http://hdl.handle.net/11427/12572.
Texte intégralRésumé :
Includes bibliographical references.This thesis investigates bandwidth allocation methodologies to transport new emerging bursty traffic types in ATM networks. However, existing ATM traffic management solutions are not readily able to handle the inevitable problem of congestion as result of the bursty traffic from the new emerging services. This research basically addresses bandwidth allocation issues for bursty traffic by proposing and exploring the concept of dynamic bandwidth allocation and comparing it to the traditional static bandwidth allocation schemes.
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Von, Dassow George Robert Hartmann. « How dynamic networks animate living embryos / ». Thesis, Connect to this title online ; UW restricted, 2000. http://hdl.handle.net/1773/5237.
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Dib, Omar. « Dynamic rerouting in multimodal transportation networks ». Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCA015/document.
Texte intégralRésumé :
La mobilité humaine s'organise de nos jours dans un contexte multimodal avec des systèmes de transport particulièrement complexes. Le nombre d'usagers va croissant et de nouveaux modes de transport émergent jour après jour en même temps que de nouveaux comportements de mobilité. En conséquence, les utilisateurs se trouvent généralement confrontés à la nécessité de choisir entre plusieurs possibilités pour se rendre d'un point d'origine à leur lieu de destination. Dans le but de les aider à naviguer facilement à travers ces réseaux complexes, un système efficace d'information voyageurs doit être construit. Grâce à ce système, les opérateurs de transport cherchent non seulement à fournir des itinéraires optimaux, mais aussi des solutions efficaces et fiables en cas de perturbations. En réalité, les passagers ne cherchent pas seulement à minimiser le temps de trajet. Ils ont aussi tendance à considérer d'autres critères tels que le confort et l'effort qu'il s'agit alors d'optimiser. Un système de routage efficace devrait donc tenir compte des préférences de chaque passager. En outre, les modes de transport sont souvent enclins à des retards. La prise en considération de l'incertitude est donc un aspect très important pour un calculateur d'itinéraires. Les itinéraires multimodaux proposés doivent non seulement être réalisables dans un cas statique, mais également suffisamment robustes face à des aléas. En outre, tout en intégrant des contraintes essentielles telles que la capacité limitée des véhicules, une attention particulière devrait aussi être accordée à la complexité temporelle des algorithmes de routage développés. L'objectif principal de cette thèse est d'élaborer une formulation qui permet de représenter adéquatement un réseau de transport multimodal. En nous basant sur cette formulation, nous proposons plusieurs algorithmes de routage. Nous nous concentrons en particulier sur la résolution de problèmes de plus courts chemins dans un contexte mono/multicritère dans un réseau de transport dynamique et stochastique. Des métaheuristiques telles que les Algorithmes Génétiques (GA), la méthode de Recherche à Voisinage Variable (VNS) et les Algorithmes Mémétiques (MA) ont été utilisés pour fournir des résultats en temps réel. La performance de calcul a été évaluée en résolvant des requêtes de routage à l'échelle du réseau de transport de la Région française Île-de-France. Les résultats indiquent que les nombreuses instances traitées ont été résolues dans un laps de temps raisonnable et que nos algorithmes de routage sont suffisamment performants pour être intégrés dans un calculateur d'itinéraire multimodal opérationnelThe human mobility is nowadays organized in a multimodal context with more and more complex transport networks. The number of passengers is increasing and new transport modes enter the system day after day simultaneously with new mobility behaviors. As a result, users usually find themselves more confused when choosing between several possibilities to go from one place to their destination. For the sake of helping them to efficiently navigate through this intricate transportation scheme, an efficient Travelers Information System (TIS) has to be built. Thanks to such a system, the transport operators seek not only to provide passengers with optimal itineraries, but also with efficient and reliable solutions in case of disruptions. In fact, commuters do not only seek short time travels, but they usually consider several other criteria such as comfort and effort. An efficient routing system should therefore take into account the various needs and preferences of each passenger. Besides, transport modes are often prone to delays. Thus, handling uncertainty is also a very important aspect of practical journey planning systems. Moreover, the proposed multimodal routes should not only be feasible in a static case, but also robust against the dynamic and stochastic variations of the transport system. Furthermore, crucial constraints should be taken into account such as the capacity limitation of vehicles and the time complexity of the developed routing algorithms. The main objective of this thesis is to propose a formulation that adequately allows representing a multimodal network. Based on our formulation, we elaborate several efficient routing algorithms. In particular, we focus on solving the Earliest Arrival Problem in a single/multiple criteria context, both in dynamic and stochastic environments. To deal with the real time complexity issue, metaheuristics such as Genetic Algorithms (GA), Variable Neighborhood Search (VNS) and Memetic Algorithms (MA) have been used. The computational performance of this work has been assessed by developing a real world route planning system, and solving real life itinerary planning problems defined on the transport network of the French Region Île-de-France that includes the city of Paris and its suburbs. The emerging computational results indicate that the numerous basic and complex instances were solved within a reasonable amount of time and the integration of the proposed routing framework as a module of an operational TIS is relevant
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Alt, Eric Allen. « Structural modeling of dynamic polymer networks ». Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122711.
Texte intégralRésumé :
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2019Cataloged from PDF version of thesis.
Includes bibliographical references (pages 125-131).
Polymer network based gels are an important class of materials with a wide range of applications. Dynamic polymer networks, which crosslink via the formation of reversible bonds, in particular have great potential as stimuli responsive, mechanically tunable, and self-healing materials. Many important emergent properties of these materials, such as mechanical strength, are mediated by their underlying network structure, which can be characterized by the network topology and spatial distribution of nodes. Therefore, unlocking the full potential of these materials through rational design requires an understanding of how network structure arises as a function of network-forming precursor design. Because the bonds that crosslink dynamic polymer networks are reversible, stresses initially present or otherwise induced in these systems can be relieved through network rearrangement. As such, given sufficient time to relax, the network structure is determined by equilibrium thermodynamics.
This work presents a thermodynamic formalism which characterizes the free energy of a network in terms of node positional, network topological, and polymer conformational entropies. Through this lens, and aided by numerical calculations and simulations of model networks, we show how the free energy landscape with respect to density relates to factors which can be readily controlled through precursor design, such as polymer length and node size. Additionally, Monte Carlo simulations of explicit networks reveal that thermodynamic relaxation can give rise to spatial heterogeneity in the arrangement of network nodes. In the last chapter we use the tools developed in the earlier chapters to explore how these same design parameters influence the topological statistics of equilibrium networks. In addition to showing how internode connectivity increases with polymer length and system density, we find that inhomogeneity due to spatial relaxation can also lead to greater network connectivity.
Finally, we explore the weakening of network topologies due to substitution of polymer-linked node forming components with topologically non-functional counterparts, finding that larger nodes fare better than their smaller counterparts in maintaining network connectivity when these substitutions are made.
by Eric Allen Alt.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Chemistry
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Aliye, Kuerban <1988>. « Dynamic modelling trophic networks with BioPEPA ». Master's Degree Thesis, Università Ca' Foscari Venezia, 2016. http://hdl.handle.net/10579/8140.
Texte intégralRésumé :
We consider a process algebra for modelling and the analysis of biochemical network, called Bio-PEPA. It is based on PEPA, a process algebra originally defined for the performance analysis of computer systems, and extended in order to handle some features of biochemical networks, such as stoichiometry and different kinds of kinetic laws. In Bio-PEPA we can make different kinds of analysis, static and dynamic. In this thesis we focus on the dynamic analysis of trophic networks. A trophic network represents an ecological community of organisms and their feeding relations. We will first consider a toy case of trophic network described in a Bio-PEPA model, and then we apply the same ideas to a real case of trophic network, namely the Venice Lagoon.
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Favier, Arnaud. « Eventual Leader Elections in Dynamic Networks ». Electronic Thesis or Diss., Sorbonne université, 2022. http://www.theses.fr/2022SORUS059.
Texte intégralRésumé :
L'élection de leader est importante pour les services tolérants aux pannes dans les systèmes distribués asynchrones. En coordonnant les actions d'un ensemble de processus, elle permet de résoudre des problèmes d'accord comme le consensus, un problème fondamental en informatique distribuée. Des algorithmes de consensus, tel que Paxos, s'appuient sur un service d'élection de leader ultime, également appelé Omega. Omega renvoie l'identité d'un processus du système et garantit qu'après un certain temps, l'identité du même processus correct est toujours renvoyée. Plusieurs algorithmes d'élection de leader ont été proposés dans la littérature pour implémenter Omega. Parmi ceux considérant les systèmes dynamiques, la plupart ne choisissent pas le leader selon un critère topologique. Or, la position du leader dans le réseau impacte directement les performances des algorithmes utilisant le service d'élection, car le leader doit souvent interagir avec les autres processus pour, par exemple, collecter les informations d'une majorité de processus dans le cas du consensus. Cette thèse étudie le problème d'élection de leader ultime dans les réseaux dynamiques. Deux algorithmes d'élection sont proposés pour les réseaux mobiles ad hoc. Ceux-ci maintiennent et exploitent la connaissance de la topologie du réseau pour élire à terme un unique leader par composante connexe ayant la meilleure centralité de proximité. Des évaluations sur simulateurs avec différents modèles de mobilité montrent que ces algorithmes présentent de meilleures performances que d'autres algorithmes de la littérature, notamment moins de messages, des chemins plus courts vers le leader, et une meilleure stabilitéLeader election is important for many fault-tolerant services in asynchronous distributed systems. By coordinating actions of a set of processes, it allows solving agreement problems like the consensus, a fundamental problem of distributed computing. Several consensus algorithms, such as Paxos, rely on an eventual leader election service, also known as the Omega failure detector. Omega returns the identity of a process in the system, ensuring that eventually the identity of the same correct process is always returned. Many leadership algorithms were proposed in the literature to implement Omega. Among those that consider dynamic systems, most of them do not choose the leader according to a topological criterion. However, the position of the leader in the network directly impacts the performance of algorithms using the leader election service, since the leader must often interact with other processes, for example, to collect information from a majority of processes in consensus algorithms. This thesis studies the eventual leader election problem in dynamic evolving networks and performance related issues. Two eventual leader election algorithms are proposed for Mobile Ad Hoc Networks. They maintain and exploit the knowledge of the network topology to eventually elect one leader per connected component with the best closeness centrality. Evaluations were conducted on simulators with different mobility models and performance results show that these algorithms present better performance than other algorithms of the literature, including fewer messages, shortest paths to the leader, and better stability
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Wong, Wan-Ching. « SALM : an efficient application-level multicast protocol for dynamic groups / ». View Abstract or Full-Text, 2003. http://library.ust.hk/cgi/db/thesis.pl?COMP%202003%20WONGW.
Texte intégralRésumé :
Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003.Includes bibliographical references (leaves 75-79). Also available in electronic version. Access restricted to campus users.