Dissertations / Theses on the topic 'Network resilience'
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Ban, Buri. "Network Resilience under Dynamic Changes." Thesis, University of Louisiana at Lafayette, 2019. http://pqdtopen.proquest.com/#viewpdf?dispub=10981286.
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The main purpose of this research is to discuss scenarios when some common dynamic changes happen to Wireless Sensor Networks/Autonomous Networked Robots, what the negative effect will be, along with our proposed strategies to keep networks resilient to such influence because communication between sensors/robots is fundamental to cooperation, hence the central role of the network. The first part of this dissertation considers scenarios where dynamic changes happen to static wireless sensor network, causing sensors in some sub-areas to not function anymore. Our work explores two resilient routing strategies to maintain communication links between any two sensors under such situations. Further, the second part of this dissertation brings mobility into wireless sensor networks. Specifically, we consider a more complex scenario where a group of Autonomous Networked Robots are given orders to march from a current field of interest to new one. And our work explores a resilient redeployment strategy that tries to keeps original communication links as many as possible. The dynamic changes and network models in this research are very common in reality; therefore, this research has much practical significance.
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Oliveira, Rodrigo Ruas. "Toward cost-efficient Dos-resilient virtual networks with ORE : opportunistic resilience embedding." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2013. http://hdl.handle.net/10183/71908.
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O atual sucesso da Internet vem inibindo a disseminação de novas arquiteturas e protocolos de rede. Especificamente, qualquer modificação no núcleo da rede requer comum acordo entre diversas partes. Face a isso, a Virtualização de Redes vem sendo proposta como um atributo diversificador para a Internet. Tal paradigma promove o desenvolvimento de novas arquiteturas e protocolos por meio da criação de múltiplas redes virtuais sobrepostas em um mesmo substrato físico. Adicionalmente, aplicações executando sobre uma mesma rede física podem ser isoladas mutuamente, propiciando a independência funcional entre as mesmas. Uma de suas mais promissoras vantagens é a capacidade de limitar o escopo de ataques, através da organização de uma infraestrutura em múltiplas redes virtuais, isolando o tráfego das mesmas e impedindo interferências. Contudo, roteadores e enlaces virtuais permanecem vulneráveis a ataques e falhas na rede física subjacente. Particularmente, caso determinado enlace do substrato seja comprometido, todos os enlaces virtuais sobrepostos (ou seja, alocados neste) serão afetados. Para lidar com esse problema, a literatura propõe dois tipos de estratégias: as que reservam recursos adicionais do substrato como sobressalentes, protegendo contra disrupções; e as que utilizam migração em tempo real para realocar recursos virtuais comprometidos. Ambas estratégias acarretam compromissos: o uso de recursos sobressalentes tende a tornar-se custoso ao provedor de infraestrutura, enquanto a migração de recursos demanda um período de convergência e pode deixar as redes virtuais inoperantes durante o mesmo. Esta dissertação apresenta ORE (Opportunistic Resilience Embedding – Mapeamento com Resiliência Oportunística), uma nova abordagem de mapeamento de redes para proteger enlaces virtuais contra disrupções no substrato físico. ORE é composto por duas estratégias: uma proativa, na qual enlaces virtuais são alocados em múltiplos caminhos para mitigar o impacto de uma disrupção; e uma reativa, a qual tenta recuperar, parcial ou integralmente, a capacidade perdida nos enlaces virtuais afetados. Ambas são modeladas como problemas de otimização. Ademais, como o mapeamento de redes virtuais é NP-Difícil, ORE faz uso de uma meta-heurística baseada em Simulated Annealing para resolver o problema de forma eficiente. Resultados numéricos mostram que ORE pode prover resiliência a disrupções por um custo mais baixo.Recently, the Internet’s success has prevented the dissemination of novel networking architectures and protocols. Specifically, any modification to the core of the network requires agreement among many different parties. To address this situation, Network Virtualization has been proposed as a diversifying attribute for the Internet. This paradigm promotes the development of new architectures and protocols by enabling the creation of multiple virtual networks on top of a same physical substrate. In addition, applications running over the same physical network can be isolated from each other, thus allowing them to coexist independently. One of the main advantages of this paradigm is the use of isolation to limit the scope of attacks. This can be achieved by creating different, isolated virtual networks for each task, so traffic from one virtual network does not interfere with the others. However, routers and links are still vulnerable to attacks and failures on the underlying network. Particularly, should a physical link be compromised, all embedded virtual links will be affected. Previous work tackled this problem with two main strategies: using backup resources to protect against disruptions; or live migration to relocate a compromised virtual resource. Both strategies have drawbacks: backup resources tend to be expensive for the infrastructure provider, while live migration may leave virtual networks inoperable during the recovery period. This dissertation presents ORE (Opportunistic Resilience Embedding), a novel embedding approach for protecting virtual links against substrate network disruptions. ORE’s design is two-folded: while a proactive strategy embeds virtual links into multiple substrate paths in order to mitigate the initial impact of a disruption, a reactive one attempts to recover any capacity affected by an underlying disruption. Both strategies are modeled as optimization problems. Additionally, since the embedding problem is NP-Hard, ORE uses a Simulated Annealing-based meta-heuristic to solve it efficiently. Numerical results show that ORE can provide resilience to disruptions at a lower cost.
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Holovatch, T. "Complex transportation networks : resilience, modelling and optimisation." Thesis, Coventry University, 2011. http://curve.coventry.ac.uk/open/items/eafefd84-ff08-43cf-a544-597ee5e63237/1.
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Klaus, Christian. "Network design for reliability and resilience to attack." Thesis, Monterey, California: Naval Postgraduate School, 2014. http://hdl.handle.net/10945/41406.
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Approved for public release; distribution is unlimited.We define and solve two network-design problems. In the first, (1) a defender uses limited resources to select a portfolio of paths or design a sub-network; (2) an attacker then uses limited attack resources to destroy network arcs, and then (3) the defender operates the damaged network optimally by ending a shortest path. The solution identifies a network design that minimizes post-attack path length. We show how the tri-level problem is equivalent to a single-level mixed integer program (MIP) with an exponential number of rows and columns, and solve that MIP using simultaneous row and column generation. Methods extend to network operations denied through general now constructs. The second problem considers a stochastic logistics network where arcs are present randomly and independently. Shipping from a source to a destination may be delayed until a path connecting the two is available. In the presence of storage capacity, cargo can be shipped partway. The problem's solution identifies the storage locations that minimize the cargo's waiting time for shipment. We develop and demonstrate practical methods to solve this #P-complete problem on a model instance derived from a Department of Defense humanitarian shipping network.
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Li, Yuhong. "Disruption Information, Network Topology and Supply Chain Resilience." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/78352.
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This dissertation consists of three essays studying three closely related aspects of supply chain resilience.
The first essay is "Value of Supply Disruption Information and Information Accuracy", in which we examine the factors that influence the value of supply disruption information, investigate how information accuracy influences this value, and provide managerial suggestions to practitioners. The study is motivated by the fact that fully accurate disruption information may be difficult and costly to obtain and inaccurate disruption information can decrease the financial benefit of prior knowledge and even lead to negative performance. We perform the analysis by adopting a newsvendor model. The results show that information accuracy, specifically information bias and information variance, plays an important role in determining the value of disruption information. However, this influence varies at different levels of disruption severity and resilience capacity.
The second essay is "Quantifying Supply Chain Resilience: A Dynamic Approach", in which we provide a new type of quantitative framework for assessing network resilience. This framework includes three basic elements: robustness, recoverability and resilience, which can be assessed with respect to different performance measures. Then we present a comprehensive analysis on how network structure and other parameters influence these different elements. The results of this analysis clearly show that both researchers and practitioners should be aware of the possible tradeoffs among different aspects of supply chain resilience. The ability of the framework to support better decision making is then illustrated through a systemic analysis based on a real supply chain network.
The third essay is "Network Characteristics and Supply Chain Disruption Resilience", in which we investigate the relationships between network characteristics and supply chain resilience. In this work, we first prove that investigating network characteristics can lead to a better understanding of supply chain resilience behaviors. Later we select key characteristics that play a critical role in determining network resilience. We then construct the regression and decision tree models of different supply chain resilience measures, which can be used to estimate supply chain network resilience given the key influential characteristics. Finally, we conduct a case study to examine the estimation accuracy.Ph. D.
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Dunn, Sarah, and Sean M. Wilkinson. "Increasing the resilience of air traffic networks using a network graph theory approach." Elsevier, 2015. https://publish.fid-move.qucosa.de/id/qucosa%3A72825.
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Air traffic networks are essential to today’s global society. They are the fastest means of transporting physical goods and people and are a major contributor to the globalisation of the world’s economy. This increasing reliance requires these networks to have high resilience; however, previous events show that they can be susceptible to natural hazards. We assess two strategies to improve the resilience of air traffic networks and show an adaptive reconfiguration strategy is superior to a permanent re-routing solution. We find that, if traffic networks have fixed air routes, the geographical location of airports leaves them vulnerable to spatial hazard.
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Memarian, Neda. "Resilience of Water Distribution Networks." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
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Resilience is widely interpreted as the capacity of a system to resist (preparation phase), absorb and withstand (responding phase), and rapidly recover from (restoration phase) exceptional conditions. During this study, a mixed variety of calculations were assessed in order to find the best solution for determination of resilience and reliability of a simple network. Then, Todini’s formula and failure index was applied to estimate reliability of system in different scenarios as constant demands in period of 24 hours, constant demands in period of 72 hours when tank will be empty (failure of tank), variable demands in period of 24 hours. At first hydraulic simulation of those scenarios was done by EPANET and validated by MATLAB-TOOLKIT. Then, Resilience index (RI), Failure Index (FI) and reliability (R) of system were measured. Finally, an optimization procedure was done to make a water distribution network with highest resilience and lowest failure probability. All these procedures have been applied on a real network as WDS of Modena. It concluded that this method can be used for every water system without considering the type of failure. As a result, first scenario has a constant decreased and increased trend of RI and FI respectively because of diminishing of water level in tank. During second scenario, there is significant change after the tank will be empty (or it is broke). Third scenario is more like a real network with variable demand during a day. It was concluded that there is a minimum resilience parameter during day when a peak time of water demand expected. It can be justified that the reservoir and pump system had to sustain more pressure to satisfy the demands of junctions. Maximum resilience is related to night during a day with less demands and providing water by tank to other junctions. This modelling could be useful to optimize the dimensions and features of instruments to increase availability and reliability of system.
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Lean, Kirstin. "Creating family resilience?" Thesis, University of Exeter, 2012. http://hdl.handle.net/10036/3395.
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The balance between family support and child protection services is continuously challenged by high-profile cases. These highlight shortcomings both of the UK system and of research on the effectiveness of child maltreatment interventions (Munro, 2011). One such intervention is the Resolutions Approach to ‘denied’ child abuse (Turnell and Essex, 2006) – a systemic approach which creates a support network including extended family, friends, community members and professionals. There is, however, only limited research analysing the supporters’ experience of this intervention. In the present study five semi-structured group interviews were conducted in order to investigate how the family support network members made sense of their participation in Resolutions. Through a thematic analysis three related themes: returning hope; building safety and trusting a professional were identified. Additionally, special attention was paid to processes linked to the creation of family resilience (Walsh, 2003). Based on two contrasting case studies the potential creation of family resilience through Resolutions was discussed and clinical recommendations for creating family resilience within support networks were outlined.
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Ganguly, Amlan. "Transient error resilience in network-on-chip communication fabrics." Online access for everyone, 2007. http://www.dissertations.wsu.edu/Thesis/Spring2007/A_Ganguly_043007.pdf.
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Yu, Yue. "Resilience Strategies for Network Challenge Detection, Identification and Remediation." Thesis, The University of Sydney, 2013. http://hdl.handle.net/2123/10277.
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The enormous growth of the Internet and its use in everyday life make it an attractive target for malicious users. As the network becomes more complex and sophisticated it becomes more vulnerable to attack. There is a pressing need for the future internet to be resilient, manageable and secure. Our research is on distributed challenge detection and is part of the EU Resumenet Project (Resilience and Survivability for Future Networking: Framework, Mechanisms and Experimental Evaluation). It aims to make networks more resilient to a wide range of challenges including malicious attacks, misconfiguration, faults, and operational overloads. Resilience means the ability of the network to provide an acceptable level of service in the face of significant challenges; it is a superset of commonly used definitions for survivability, dependability, and fault tolerance. Our proposed resilience strategy could detect a challenge situation by identifying an occurrence and impact in real time, then initiating appropriate remedial action. Action is autonomously taken to continue operations as much as possible and to mitigate the damage, and allowing an acceptable level of service to be maintained. The contribution of our work is the ability to mitigate a challenge as early as possible and rapidly detect its root cause. Also our proposed multi-stage policy based challenge detection system identifies both the existing and unforeseen challenges. This has been studied and demonstrated with an unknown worm attack. Our multi stage approach reduces the computation complexity compared to the traditional single stage, where one particular managed object is responsible for all the functions. The approach we propose in this thesis has the flexibility, scalability, adaptability, reproducibility and extensibility needed to assist in the identification and remediation of many future network challenges.
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Burnard, Kevin J. "Establishing the resilient response of organisations to disruptions : an exploration of organisational resilience." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12489.
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The focus of this thesis is to investigate resilience at an organisational level. The research aims to identify and establish the features of resilience within the response of an organisation to disruptive and crisis events. Natural disasters, pandemic disease, terrorist attacks, economic recession, equipment failure and human error can all pose both a potentially unpredictable and severe threat to the continuity of an organisation's operations. As a result, disruptive events highlight the need to develop robust and resilient organisational and infrastructural systems capable of adapting and overcoming complex disruptive events.
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Khalili, Sanaz. "A Temporal Social Resilience Framework of Communities to Disasters in Australia and Social Network Enabled Social Resilience." Thesis, The University of Sydney, 2017. http://hdl.handle.net/2123/16840.
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The frequency and impact of disasters is on an upward trajectory and, given considerations of climate change and population growth, is projected to continue to increase. There is therefore an imminent need to advance research on factors of disaster resilience and recovery in order to reduce the impacts of these future extreme events on society. This research focuses on identifying social resilience indicators and providing a novel framework for quantifying social resilience with the aim of enhancing the ability of communities to withstand disaster. Although there has been considerable research interest in various aspects of community resilience to disasters, there have been no studies to the author’s knowledge that have gathered all social resilience indicators and constructed a unified holistic framework to cover the three phases of the disaster management cycle (i.e., pre-disaster, response and recovery). Similarly, there have not been any studies that have used social network analysis to explore the impact of the role of social network positionality and structure on social resilience. Therefore, the objectives of this study were to (i) identify the most essential social resilience indicators within communities from previous similar studies in all phases of disaster, (ii) assess these indicators against different case studies, through interviews with subject matter experts within the New South Wales State Emergency Service, then (iii) provide a unified and novel model for social resilience through the addition of (iv) data collected through an online survey within the SES volunteers from which the author (v) propose a framework for the effect of social networks on social resilience. To this effect, the author conducted two phases of research, the first relying on literature review and in-depth interviews and the second relying an online survey for data collection. The results of these were then used to propose the addition of social network analysis. The study seeks not only to advance the state of knowledge on social resilience to disaster, but also to produce actionable knowledge that can improve community preparation for and response to disaster.
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Suraev, Maxim. "Denial-of-service attack resilience of the GSM access network." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for telematikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-13313.
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GSM network capable of connecting to any operator providing SIP trunk has beenconstructed to serve as a target for controlled experiment on DoS attacks againstGSM. The usage of this network as a tool to perform DoS attack against mobilephones was also investigated and documented.Open source implementation of testing tool to check DoS resilience of any GSMbase station against RACH flood attack was developed as part of this thesis.Additionally, the analysis of the GSM flaws which opened the possibility for DoSattacks, and the analysis of potential countermeasures is presented.
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Zhang, Xian. "Network-provider-independent overlays for resilience and quality of service." Thesis, Queen Mary, University of London, 2011. http://qmro.qmul.ac.uk/xmlui/handle/123456789/2443.
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Overlay networks are viewed as one of the solutions addressing the inefficiency and slow evolution of the Internet and have been the subject of significant research. Most existing overlays providing resilience and/or Quality of Service (QoS) need cooperation among different network providers, but an inter-trust issue arises and cannot be easily solved. In this thesis, we mainly focus on network-provider-independent overlays and investigate their performance in providing two different types of service. Specifically, this thesis addresses the following problems: Provider-independent overlay architecture: A provider-independent overlay framework named Resilient Overlay for Mission-Critical Applications (ROMCA) is proposed. We elaborate its structure including component composition and functions and also provide several operational examples. Overlay topology construction for providing resilience service: We investigate the topology design problem of provider-independent overlays aiming to provide resilience service. To be more specific, based on the ROMCA framework, we formulate this problem mathematically and prove its NP-hardness. Three heuristics are proposed and extensive simulations are carried out to verify their effectiveness. Application mapping with resilience and QoS guarantees: Assuming application mapping is the targeted service for ROMCA, we formulate this problem as an Integer Linear Program (ILP). Moreover, a simple but effective heuristic is proposed to address this issue in a time-efficient manner. Simulations with both synthetic and real networks prove the superiority of both solutions over existing ones. Substrate topology information availability and the impact of its accuracy on overlay performance: Based on our survey that summarizes the methodologies available for inferring the selective substrate topology formed among a group of nodes through active probing, we find that such information is usually inaccurate and additional mechanisms are needed to secure a better inferred topology. Therefore, we examine the impact of inferred substrate topology accuracy on overlay performance given only inferred substrate topology information.
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Martin, Rüdiger. "Resilience, Provisioning, and Control for the Network of the Future." Würzburg Univ. Würzburg, Inst. für Informatik, Lehrstuhl für Verteilte Systeme, 2008. http://www.opus-bayern.de/uni-wuerzburg/volltexte/2008/2849/.
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Garg, Arun. "Quantifying resilient safety culture using complex network theory." Thesis, Griffith University, 2022. http://hdl.handle.net/10072/411532.
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Safety is defined as the absence of accidents where accident is an event which lead to unacceptable loss. Previously, most systems employed conventional risk management systems to deal with risks which was based on knowledge of previous experiences, failure reporting and risk assessments by computing historic data. But today, these are traced to organizational factors, functional performance variability and unexpected outcomes or it can be pointed towards systems thinking. Resilience engineering is recognized as other alternative to traditional approaches in safety management. The idea behind resilience engineering is that an organization must continually manage risks and create an anticipating, monitoring, responding and learning culture. This is resilient safety culture. Resilient safety culture is a new concept which has been proposed in order to cover the weaknesses of traditional approaches of safety culture. It is a safety culture with resilience, learning, continuous improvements and cost effectiveness. This resilience takes into consideration the dynamic aspect of the safety culture which makes it resilient to any risks which a safety system faces. The main drawback is the dynamic aspect of the culture is not taken into consideration which is the interaction between people, technology and administration. These interactions are quite complex in nature and difficult to understand and quantify. That is why this study investigates the understanding of these interactions using complex network theory. Once these interactions are understood to some extent, the prediction and prevention of incidents can be done to some extent.
There are four different kinds of indicators in the system. Two are system performance indicators, leading and lagging and the other two are the risk indicators that as well leading and lagging. The system performance indicators are indicators which show how the system is performing either in current state which is leading and the system performance indicator which is lagging is gauged by efficiency of the system after a time such as injury rate. Risk indicators leading is found by understanding the various risks which are prevalent in the system and lagging risk indicators are the indicators which led to an accident in previous time frame. Since the system is dynamic, it needs to be understood that these indicators have a time value attached to it. If there is an accident which happened due to some lagging risk indicator, that is in previous time frame, that may have already changed by the time the accidents happened so safety-1 concept which looked at just lagging indicators to dictate the future evaluations of the organization need to be modified and thus resilient safety culture methodology is getting evolved using resilience engineering.
Using fault tree analysis, the interactions of various components in a safety system can be understood. Resilient safety culture is treated as a system and it has three sub systems. The sub system further has factors which are important relationships to understand the whole system. These relations between the factors and subsystem are used to measure the resilience of the whole system. This is an innovative quantifying way in which we can improve the resilience in safety culture of an organization.
In this study, the qualitative variables defined using the literature are correlated using qualitative as well as quantitative approaches. In the qualitative approach, Leximancer tool is used which model the variables using the literature data. Next, the resilient safety culture model is generated and then fault tree analysis is used to decipher the complex interactions which can help understand which relationships can lead to incident. This study would generate a tool which would help organizations look at the weak links and nodes in their organization to better equip and enhance resources to make the organization more resilient against any safety risks. Multiple case studies are done to validate this model and to show how the whole process is done to understand a way to reduce and mitigate risks. Resilience index is generated which helps in finding which constructs are lagging or weak in giving that index number and the index can be used to compare to companies or organizations irrespective of the number of respondents or the type of indicators which are used. It also helps in reducing the linguistic bias.
The findings of this study show that in resilient safety culture model, which components should be focussed first and how the components of resilient safety culture model are related with each other. This helps in optimization of the components or subcomponents to get the maximum resilience in an organization. It is also found that weak areas in an organization can be successfully deciphered using the fault tree analysis approach along with visualization of failure paths.
This resilience safety culture model generated along with the methodology adopted in this study can help the industry to making right decisions in enhancing the resilience of the organizations with minimum intervention. It can help the industry find the weak areas where the intervention is needed. It can also give leading indicators which can cause future incidents.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
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Pandit, Arka. "Resilience of urban water systems: an 'infrastructure ecology' approach to sustainable and resilient (SuRe) planning and design." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53443.
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Increasing urbanization is a dominant global trend of the past few decades. For cities to become more sustainable, however, the infrastructure on which they rely must also become more efficient and resilient. Urban infrastructure systems are analogous to ecological systems because they are interconnected, complex and adaptive, are comprised of interconnected components, and exhibit characteristic scaling properties. Analyzing them together as a whole, as one would do for an ecological system, provides a better understanding about their dynamics and interactions, and enables system-level optimization. The adoption of this “infrastructure ecology” approach will result in urban development that costs less to build and maintain, is more sustainable (e.g. uses less materials and energy) and resilient, and enables a greater and more equitable creation of wealth and comfort. Resilience, or the capacity of a system to absorb shocks and perform under perturbations, can serve as an appropriate indicator of functional sustainability for dynamic adaptive systems like Urban Water Systems. This research developed an index of resilience (R-Index) to quantify the “full-spectrum” resilience of urban water systems. It developed five separate indices, namely (i) Index of Water Scarcity (IWS), (ii) Relative Dependency Index (RDI), (iii) Water Quality Index (WQI), (iv) Index of Network Resilience (INR), and (v) Relative Criticality Index (RCI), to address the criticalities inherent to urban water systems and then combines them to develop the R-Index through a multi-criteria decision analysis method. The research further developed a theoretical construct to quantify the temporal aspect of resilience, i.e. how quickly the system can return back to its original performance level. While there is a growing impetus of incorporating sustainability in decision making, frequently it comes at the cost of resilience. This is attributable to the fact that the decision-makers often lack a life-cycle perspective and a proven, consistent and robust approach to understand the tradeoff between increased resilience and its impact on sustainability. This research developed an approach to identify the sustainable and resilient (SuRe) zone of urban infrastructure planning and design where both sustainability and resilience can be pursued together.
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Li, He. "A Resilience-Oriented and NFV-Supported Scheme for Failure Detection in Software-Defined Networking." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/38306.
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As a recently emerging network paradigm, Software-Defined Networking (SDN) has attracted considerable attention from both industry and academia. The most significant advantage of SDN is that the paradigm disassociates the control logic (i.e., control plane) from the forwarding process (i.e., data plane), which are usually integrated into traditional network devices. Thanks to the property of centralized control, SDN enables the flexibility of dispatching flow policies to simplify network management. However, this property also makes the SDN environment vulnerable, which will cause network paralysis when the sole SDN controller runs malfunction. Although several works have been done on deploying multiple controllers to address the failure of a centralized controller, their drawbacks are leading to inefficiency and balance loss of controller utilization, provoking resource idling as well as being incapable to suffice flow outburst.
Additionally, the network operators often put a great deal of effort into discovering failure nodes to recover their networks, which can be mitigated by applying failure detection before the network deterioration occurs. Network traffic prediction can serve as a practical approach to evaluate the state of the OpenFlow-based switch and consequently detect SDN node failures in advance. As far as prediction solution is concerned, most researchers investigate either statistical modeling approaches, such as Seasonal Autoregressive Integrated Moving Average (SARIMA), or Artificial Neural Network (ANN) methods, like Long Short-Term Memory (LSTM) Neural Network. Nonetheless, few of them study the model merging these two mechanisms regarding multi-step prediction.
This thesis proposes a novel system associated with Network Function Virtualization (NFV) technique to enhance the resilience of SDN network. A hybrid prediction model based on the combination of SARIMA and LSTM is introduced as part of the detection module of this system, where the potential node breakdown can be readily determined so that it can implement smart prevention and fast recovery without human interaction. The results show the proposed scheme improves the performance concerning time complexity compared with that of previous work, reaching up to 95% accuracy while shortening the detection and recovery time by the new combined prediction model.
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Murić, Goran. "Resilience of the Critical Communication Networks Against Spreading Failures." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-228883.
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A backbone network is the central part of the communication network, which provides connectivity within the various systems across large distances. Disruptions in a backbone network would cause severe consequences which could manifest in the service outage on a large scale. Depending on the size and the importance of the network, its failure could leave a substantial impact on the area it is associated with. The failures of the network services could lead to a significant disturbance of human activities. Therefore, making backbone communication networks more resilient directly affects the resilience of the area. Contemporary urban and regional development overwhelmingly converges with the communication infrastructure expansion and their obvious mutual interconnections become more reciprocal.
Spreading failures are of particular interest. They usually originate in a single network segment and then spread to the rest of network often causing a global collapse. Two types of spreading failures are given focus, namely: epidemics and cascading failures. How to make backbone networks more resilient against spreading failures? How to tune the topology or additionally protect nodes or links in order to mitigate an effect of the potential failure? Those are the main questions addressed in this thesis.
First, the epidemic phenomena are discussed. The subjects of epidemic modeling and identification of the most influential spreaders are addressed using a proposed Linear Time-Invariant (LTI) system approach. Throughout the years, LTI system theory has been used mostly to describe electrical circuits and networks. LTI is suitable to characterize the behavior of the system consisting of numerous interconnected components. The results presented in this thesis show that the same mathematical toolbox could be used for the complex network analysis.
Then, cascading failures are discussed. Like any system which can be modeled using an interdependence graph with limited capacity of either nodes or edges, backbone networks are prone to cascades. Numerical simulations are used to model such failures. The resilience of European National Research and Education Networks (NREN) is assessed, weak points and critical areas of the network are identified and the suggestions for its modification are proposed.
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Pant, Sunil Babu. "Transportation Network Resiliency: A Study of Self-Annealing." DigitalCommons@USU, 2012. https://digitalcommons.usu.edu/etd/1434.
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Transportation networks, as important lifelines linking communities and goods, are indispensable for the smooth functioning of society. These networks are, however, fragile and vulnerable to natural and manmade disasters, which can disrupt their vital functionality. The role of the transportation sector becomes more crucial during disasters due to its role in pre-disaster evacuation as well as post-disaster recovery. The ability of transportation systems to retain performance during and after disasters undergoing little to no loss and their ability to return to the normal state of operation quickly after disasters defines their resilience. Authorities need to understand the degree of resilience within the transportation system under their jurisdiction and plan for improvements. In this research, attempts have been made to deal with resilience in quantitative ways to provide defensible data to decision makers to support investment strategies.
Total loss in the network performance can be quantified by dealing with the variation of network performance over time after disasters and the network resilience can be measured by the ability to minimize this loss. It has been shown that robust networks retain better performance after disruptions and recovery works, which follow optimized recovery paths, in spite of constraints of resources and time, help to minimize the total losses and enhance the network resilience. The objective of this research is to create a conceptual framework to quantify resilience and discuss quantitatively the properties determining resilience of transportation networks. The concepts presented are applied to a test network to illustrate the mathematical procedures. Such methods can help decision makers analyze relative improvements in resiliency as a consequence of proposed project alternatives and help to perform benefit-cost analysis for such projects.
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Carpenter, Ann Marie. "Resilience in the social and physical realms: lessons from the Gulf Coast." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/49034.
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Community resilience to disasters is an affected area’s ability to rebound after a catastrophic event. The mounting frequency and scale of natural disasters, increasing urbanization, a growing reliance on interdependent technologies and infrastructure systems, and inflated expectations of interventions are responsible for greater disaster vulnerability and demonstrate the need to develop more resilient communities. Given the increasing shocks of natural disasters, a more complete understanding of resilience is important for creating safer, more sustainable communities.
One factor that is known to impact resilience is social networks. Urban planning research has shown that walkable, mixed-use neighborhoods can encourage the development of social networks and place attachment through an increase in interactions and a higher density of neighborhood amenities, including characteristics of the built environment that influence social networks, such as varied land uses and pedestrian-oriented design. The built environment connects residents to a place and can serve as a benchmark for recovery. Therefore, it is possible that the traditional planning domain of urban design can be harnessed to foster greater resilience by facilitating stronger social networks.
In order to determine the legitimacy of this supposition, this research examines how social networks and the built environment create greater resilience to disasters. Given that social networks increase community resilience to all types of disasters, social networks are shown to be influenced by certain types of space, and the built environment is a common intervention for planners, this research explores the potential for creating cities that are more resilient by creating spaces that foster social networks.
The Mississippi Gulf Coast was chosen as a case study area in order to explore the above relationships. In 2005, Hurricane Katrina struck the region, resulting in massive wind and storm surge damage to the Mississippi Coast. Communities in the area have recovered at varying rates and levels. Therefore, this region provided an opportunity to contrast higher and lower resilience communities and to test the above research questions.
The research was conducted in two stages. In the first stage, a quantitative model was developed in order to address whether there are statistically significant effects on resilience due to the built environment. In the second stage, a qualitative case study analysis of communities was undertaken using interviews with local residents. The results demonstrate that certain aspects of the built environment are associated with greater resilience, including intersection density, net residential density, the density of historic sites, and community amenities where social networks gather. Furthermore, urban design features with the greatest capacity to increase resilience were also useful features for the types of local social networks that were found to be most important for resilience.
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Chen, Ruiliang. "Enhancing Attack Resilience in Cognitive Radio Networks." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/26330.
Full textAbstract:
The tremendous success of various wireless applications operating in unlicensed bands has resulted in the overcrowding of those bands. Cognitive radio (CR) is a new technology that enables an unlicensed user to coexist with incumbent users in licensed spectrum bands without inducing interference to incumbent communications. This technology can significantly alleviate the spectrum shortage problem and improve the efficiency of spectrum utilization. Networks consisting of CR nodes (i.e., CR networks)---often called dynamic spectrum access networks or NeXt Generation (XG) communication networks---are envisioned to provide high bandwidth to mobile users via heterogeneous wireless architectures and dynamic spectrum access techniques.
In recent years, the operational aspects of CR networks have attracted great research interest. However, research on the security aspects of CR networks has been very limited. In this thesis, we discuss security issues that pose a serious threat to CR networks. Specifically, we focus on three potential attacks that can be launched at the physical or MAC layer of a CR network: primary user emulation (PUE) attack, spectrum sensing data falsification (SSDF) attack, and control channel jamming (CCJ) attack. These attacks can wreak havoc to the normal operation of CR networks. After identifying and analyzing the attacks, we discuss countermeasures. For PUE attacks, we propose a transmitter verification scheme for attack detection. The scheme utilizes the location information of transmitters together with their signal characteristics to verify licensed users and detect PUE attackers. For both SSDF attacks and CCJ attacks, we seek countermeasures for attack mitigation. In particular, we propose Weighted Sequential Probability Ratio Test (WSPRT) as a data fusion technique that is robust against SSDF attacks, and introduce a multiple-rendezvous cognitive MAC (MRCMAC) protocol that is robust against CCJ attacks. Using security analysis and extensive numerical results, we show that the proposed schemes can effectively counter the aforementioned attacks in CR networks.Ph. D.
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Baggio, Jacopo Alessandro. "Analyzing social-ecological systems : linking resilience, network theory, and agent based modelling." Thesis, University of East Anglia, 2011. https://ueaeprints.uea.ac.uk/34240/.
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Barker, Scarlett J. V. (Scarlett Jazmine). "Cognitive resilience is mediated by the MEF2 network in mice and humans." Thesis, Massachusetts Institute of Technology, 2021. https://hdl.handle.net/1721.1/130809.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Brain and Cognitive Sciences, February, 2021Cataloged from the official PDF version of thesis. "February 2021."
Includes bibliographical references (pages 119-126).
Recent increases in human longevity have been accompanied by a rise in the incidence of dementia. While a large proportion of aged individuals display pathological hallmarks of neurodegenerative disease, a small number of these individuals are able to maintain healthy cognitive function even in the presence of extensive brain pathology. The molecular mechanisms that govern this neuro-protected state remain unknown, but individuals that exhibit cognitive resilience (CgR) represent a unique source of insight into potential therapies that could preserve brain function in the face of neurodegenerative disease. Here, we employ a two-pronged approach to dissect the mechanism underlying CgR. First, using multiple integrated repositories of clinical and brain transcriptomic data we identified individuals who maintained normal cognition despite harboring a large burden of Alzheimer's disease (AD) pathology.
We observe significant up-regulation of MEF2 family members in these resilient patients when compared to patients whose cognition declined in the presence of pathology. Second, we utilize the only existing animal model of CgR -- environmental enrichment --
to investigate the molecular mechanisms involved in the induction of resilience. Accessibility of Mef2 binding sites, and expression of Mef2 targets are significantly increased upon enrichment. Additionally, knockdown of Mef2 family members just prior to the initiation of enrichment block its cognitive benefits, demonstrating the necessity of Mef2 activity for achieving the enhanced cognitive potential afforded by enrichment. Neurons lacking Mef2 are hyperexcitable, which is also one of the earliest pathological alterations observed in AD. These results suggest a potential mechanistic link between the Mef2 transcriptional network induced by enrichment and the prevention of disease-associated hyperexcitability. To determine the causal impact of Mef2 on cognition in the context of neurodegeneration, we use a viral approach to manipulate the PS19 mouse model of tauopathy.
Remarkably, in the absence of enrichment, Mef2 overexpression alone is sufficient to improve cognition and reduce hyperexcitability in PS19 mice. Overall, our findings reveal a novel role for MEF2 transcription factors in promoting cognition throughout life, and maintaining cognitive resilience in the context of neurodegenerative disease.
by Scarlett J.V. Barker.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Brain and Cognitive Sciences
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Stemberger, Sara <1990>. "The governance of UNESCO's transboundary biosphere reserves, social network analysis for resilience." Master's Degree Thesis, Università Ca' Foscari Venezia, 2016. http://hdl.handle.net/10579/8897.
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Resilience emphasizes the capacities of a social-ecological system to deal with change, to recover, to adapt and to transform the system. Grounded by the work of Biggs et al., 2015, the resilience of a systems can be assessed and enhanced by the performance of seven principles. Environmental governance is one of resilience’s stepping stones, a provider of insights in conservation, sustainable livelihoods and local values. Social-ecological systems often encompass the frontiers between nations and UNESCO’s transboundary biosphere reserves may be examples of testing sites for sustainability, of environmental integrity and frameworks committed to transboundary cooperation. In this study, it has been chosen to focus on the governance of transboundary biosphere reserves with the scrutiny of their social networks and the performance of a social network analysis (SNA). This thesis assumes that with a SNA technique it is possible to recognize in the governance structures the importance of some resilience principles, such as connectivity, enhanced learning and polycentric governance systems. This theory is, hence, supported by qualitative data from semi-structured interviews with biosphere managers and quantitative data from a social network analysis of the involved institutions in two transboundary biosphere reserves.
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Basaglia, Irene. "Complex networks theory for water distribution networks modelling and resilience assessment. An explorative analysis." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/22858/.
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Il tema della sostenibilità e del conseguente utilizzo di nuove tecniche per la gestione delle risorse idriche è da sempre molto complesso. La digitalizzazione e l'impiego di nuove tecnologie in campo idrico ha ridotto sia i costi che le tempistiche di molteplici processi. Un valido esempio è costituito dalla modellazione surrogata: Il tema centrale della tesi ha come scopo la
costruzione di un modello surrogato di rete di distribuzione idrica utilizzando i principi di Complex Network Theory. In particolare, per condurre questo tipo di studio è stato scelto di analizzare da un punto di vista interdisciplinare i concetti di robustezza e di resilienza ai malfunzionamenti. Le reti di distribuzione idrica possono essere facilmente assimilabili alle reti complesse presenti nella teoria dei grafi. Gli elementi strutturali delle reti idriche sono convertiti nell'equivalente grafo complesso costituito da archi e nodi. Al fine di indagare una possibile correlazione tra le reti di entrambe le discipline, sono state eseguite una serie di simulazioni idriche e valutazioni strutturali calibrando i modelli in base alle euristiche proposte in letteratura. Gli esperimenti eseguiti valutano l'effetto "small world" e altre misure per l'analisi di reti presenti nella teoria dei grafi in relazione all'intensità e alla durata dei malfunzionamenti.
Dai risultati è stata riscontrata una correlazione inversa tra la proprietà di "small world" e l'indice di durata dei malfunzionamenti. In aggiunta, i risultati ottenuti evidenziano una tendenza generale alla correlazione, sia diretta che indiretta. Un ulteriore evidenza emersa dall'analisi è la doppia correlazione presente tra altezza dei nodi, durata dei malfunzionamenti e indice di centralità per vicinanza.
Questo lavoro può dunque aiutare nell'individuazione di parametri più puntuali e adeguati suggerendo nuove vie e tecniche per una ancora più corretta creazione di modelli surrogati tramite tecniche di Complex Network.
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Edgar, Perez. "Developing a Resilient Network Ambidexterity Scale." Antioch University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=antioch152615319318394.
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Pourvali, Mahsa. "Resilience of Cloud Networking Services for Large Scale Outages." Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6664.
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Cloud infrastructure services are enabling organizations and enterprises to outsource a wide range of computing, storage, and networking needs to external service providers. These offerings make extensive use of underlying network virtualization, i.e., virtual network (VN) embedding, techniques to provision and interconnect customized storage/computing resource pools across large network substrates. However, as cloud-based services continue to gain traction, there is a growing need to address a range of resiliency concerns, particularly with regards to large-scale outages. These conditions can be triggered by events such as natural disasters, malicious man-made attacks, and even cascading power failures.
Overall, a wide range of studies have looked at network virtualization survivability, with most efforts focusing on pre-fault protection strategies to set aside backup datacenter and network bandwidth resources. These contributions include single node/link failure schemes as well as recent studies on correlated multi-failure \disaster" recovery schemes. However, pre-fault provisioning is very resource-intensive and imposes high costs for clients. Moreover this approach cannot guarantee recovery under generalized multi-failure conditions. Although post-fault restoration (remapping) schemes have also been studied, the effectiveness of these methods is constrained by the scale of infrastructure damage. As a result there is a pressing need to investigate longer-term post-fault infrastructure repair strategies to minimize VN service disruption. However this is a largely unexplored area and requires specialized consideration as damaged infrastructures will likely be repaired in a time-staged, incremental manner, i.e., progressive recovery.
Furthermore, more specialized multicast VN (MVN) services are also being used to support a range of content distribution and real-time streaming needs over cloud-based infrastructures. In general, these one-to-many services impose more challenging requirements in terms of geographic coverage, delay, delay variation, and reliability. Now some recent studies have looked at MVN embedding and survivability design. In particular, the latter contributions cover both pre-fault protection and post-fault restoration methods, and also include some multi-failure recovery techniques. Nevertheless, there are no known efforts that incorporate risk vulnerabilities into the MVN embedding process. Indeed, there is a strong need to develop such methods in order to reduce the impact of large-scale outages, and this remains an open topic area.
In light of the above, this dissertation develops some novel solutions to further improve the resiliency of the network virtualization services in the presence of large outages. Foremost, new multi-stage (progressive) infrastructure repair strategies are proposed to improve the post-fault recovery of VN services. These contributions include advanced simulated annealing metaheuristics as well as more scalable polynomial-time heuristic algorithms. Furthermore, enhanced \risk-aware" mapping solutions are also developed to achieve more reliable multicast (MVN) embedding, providing a further basis to develop more specialized repair strategies in the future. The performance of these various solutions is also evaluated extensively using custom-developed simulation models.
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Dunn, Sarah. "An investigation to improve community resilience using network graph analysis of infrastructure systems." Thesis, University of Newcastle upon Tyne, 2014. http://hdl.handle.net/10443/2421.
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Disasters can have devastating effects on our communities and can cause great suffering to the people who reside within them. Critical infrastructure underpins the stable functioning of these communities and the severity of disasters is often linked to failure of these systems. Traditionally, the resilience of infrastructure systems is assessed by subjecting physically based models to a range of hazard scenarios. The problem with this approach is that it can only inform us of inadequacies in the system for the chosen scenarios, potentially leaving us vulnerable to unforeseen events. This thesis investigates whether network graph theory can be used to give us increased confidence that the system will respond well in untested scenarios by developing a framework that can identify generic system characteristics and hence describe the underlying resilience of the network. The novelty in the work presented in this thesis is that it overcomes a shortcoming in existing network graph theory by including the effects of the spatial distribution of geographically dispersed systems. To consider spatial influence, a new network generation algorithm was developed which incorporated rules that connects system components based on both their spatial distribution and topology. This algorithm was used to generate proxy networks for the European, US and China air traffic networks and demonstrated that the inclusion of this spatial component was crucial to form the highly connected hub airports observed in these networks. The networks were then tested for hazard tolerance and in the case of the European air traffic network validated using data from the 2010 Eyjafjallajökull eruption. Hazard tolerance was assessed by subjecting the networks to a series of random, but spatially coherent, hazards and showed that the European air traffic network was the most vulnerable, having up to 25% more connections disrupted compared to a benchmark random network. This contradicts traditional network theory which states that these networks are resilient to random hazards. To overcome this shortcoming, two strategies were employed to improve the resilience of the network. One strategy ‘adaptively’ modified the topology (crises management) while the other ‘permanently’ modified it (hazard mitigation). When these modified networks were subjected to spatial hazards the ‘adaptive’ approach Page i produced the most resilient network, having up to 23% fewer cancelled air routes compared to the original network, for only a 5% change in airport capacity. Finally, as many infrastructure networks are flow based systems, an investigation into whether graph theory could identify vulnerabilities in these systems was conducted. The results demonstrated that by using a combination of both physically based and graph theory metrics produced the best predictive skill in identifying vulnerable nodes in the system. This research has many important implications for the owners and operators of infrastructure systems. It has demonstrated the European air traffic network to be vulnerable to spatial hazard and shown that, because many infrastructure networks possess similar properties, may therefore be equally vulnerable. It also provides a method to identify generic system vulnerabilities and strategies to reduce these. It is argued that as this research has considered generic networks it can not only increase infrastructure resilience to known threats but also to previously unidentified ones and therefore is a useful method to help protect these systems to large scale disasters and reduce the suffering for the people in the communities who rely upon them.
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Pai, Raikar Siddhesh Prakash Sunita. "Network Fault Resilient MPI for Multi-Rail Infiniband Clusters." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1325270841.
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Helmberg, Christoph, Sebastian Richter, and Dominic Schupke. "A Chance Constraint Model for Multi-Failure Resilience in Communication Networks." Universitätsbibliothek Chemnitz, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-175454.
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For ensuring network survivability in case of single component failures many routing protocols provide a primary and a back up routing path for each origin destination pair. We address the problem of selecting these paths such that in the event of multiple failures, occuring with given probabilities, the total loss in routable demand due to both paths being intersected is small with high probability. We present a chance constraint model and solution approaches based on an explicit integer programming formulation, a robust formulation and a cutting plane approach that yield reasonably good solutions assuming that the failures are caused by at most two elementary events, which may each affect several network components.
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Wang, Wenjun. "Modeling influence diffusion in networks for community detection, resilience analysis and viral marketing." Diss., University of Iowa, 2016. https://ir.uiowa.edu/etd/2165.
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The past decades have seen a fast-growing and dynamic trend of network science and its applications. From the Internet to Facebook, from telecommunications to power grids, from protein interactions to paper citations, networks are everywhere and the network paradigm is pervasive. Network analysis and mining has become an important tool for scientific research and industrial applications to diverse domains. For example, finding communities within social networks enables us to identify groups of densely connected customers who may share similar interests and behaviors and thus generate more effective recommender systems; investigating the supply-network topological structure and growth model improves the resilience of supply networks against disruptions; and modeling influence diffusion in social networks provides insights into viral marketing strategies. However, none of these tasks is trivial. In fact, community detection, resilience analysis, and influence-diffusion modeling are all important challenges in complex networks. My PhD research contributes to these endeavors by exploring the implicit knowledge of connectivity and proximity encoded in the network graph topology.
Our research originated from an attempt to find communities in networks. After carefully examining real-life communities and the features and limitations of a set of widely-used centrality measures, we develop a simple but powerful reachability-based influence-diffusion model. Based upon this model, we propose a new influence centrality and a novel shared-influence-neighbor (SIN) similarity. The former differentiates the comprehensive influence significance more precisely, and the latter gives rise to a refined vertex-pair closeness metric. Then we develop an influence-guided spherical K-means (IGSK) algorithm for community detection. Further, we propose two novel influence-guided label propagation (IGLP) algorithms for finding hierarchical communities in complex networks. Experiments on both real-life networks and synthetic benchmarks demonstrate superior performance of our algorithms in both undirected/directed and unweighted/weighted networks.
Another research topic we investigated is resilience analysis of supply networks.
Supply networks play an important role in product distribution, and survivability is a critical concern in supply-network design and analysis. We exploit the resilience embedded in supply-network topology by exploring the multiple-path reachability of each demand node to other nodes, and propose a novel resilience metric. We also develop new supply-network growth mechanisms that reflect the heterogeneous roles of different types of units in supply networks. We incorporate them into two fundamental network topologies (random-graph topology and scale-free topology), and evaluate the resilience under random disruptions and targeted attacks using the new resilience metric. The experimental results verify the validity of our resilience metric and the effectiveness of our growth model. This research provides a generic framework and important insights into the construction of robust supply networks.
Finally, we investigate activation-based influence-diffusion modeling for viral marketing. One of the fundamental problems in viral marketing is to find a small set of initial adopters who can trigger the largest further adoptions through word-of-mouth-based influence propagation in the network. We propose a novel multiple-path asynchronous threshold (MAT) model, in which we quantitatively measure influence and keep track of its diffusion and aggregation during the diffusion process. Our MAT model captures both direct and indirect influence, influence attenuation along diffusion paths, temporal influence decay, and individual diffusion dynamics. Our work is an important step toward a more realistic diffusion model. Further, we develop two effective and efficient heuristics (IV-Greedy and IV-Community) to tackle the influence-maximization problem. Our experiments on four real-life networks demonstrate their excellent performance in terms of both influence spread and efficiency. Our work provides preliminary but significant insights and implications for diffusion research and marketing practice.
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BERLUSCONI, GIULIA. "LAW ENFORCEMENT AND CRIMINAL NETWORK RESILIENCE: THE IMPACT OF LAW ENFORCEMENT ACTION ON THE STRUCTURE OF MAFIA-RELATED DRUG TRAFFICKING NETWORKS." Doctoral thesis, Università Cattolica del Sacro Cuore, 2014. http://hdl.handle.net/10280/2457.
Full textAbstract:
Per comprendere la capacità delle organizzazioni criminali di resistere alle indagini da parte delle forze di polizia, alcuni studiosi hanno introdotto il concetto di resilienza nel campo della ricerca sul crimine organizzato. Il termine si riferisce alla capacità di un gruppo criminale di affrontare le pressioni esterne e riorganizzarsi.
Adottando un approccio di rete e facendo riferimento a precedenti ricerche sulla resilienza dei gruppi criminali, il presente studio analizza l’evoluzione nel corso del tempo di due gruppi legati alla ‘Ndrangheta. L’obiettivo consiste nel comprendere come questi gruppi si sono adattati alla pressione da parte delle forze dell’ordine e nell’identificare i meccanismi che hanno favorito la loro evoluzione e i cambiamenti che hanno riguardato la loro struttura organizzativa.
I risultati mostrano che i due gruppi criminali hanno potuto fare affidamento su diverse fonti di resilienza. La presenza di legami di natura non economica, che non sono conseguenza della loro partecipazione nei mercati illegali, ha consentito ai gruppi mafiosi di sostituire i soggetti arrestati in modo rapido ma parziale. Una minor importanza attribuita alla struttura gerarchica da parte dei gruppi mafiosi coinvolti in traffici internazionali ha invece permesso a questi gruppi di dotarsi di una organizzazione interna più flessibile.To understand mafia persistence over time and address the problem of the impact of law enforcement interventions on criminal groups, some scholars have introduced the concept of resilience into organized crime research; this refers to the ability of criminal groups to deal with ongoing changes and reorganize themselves accordingly. Adopting a network approach to organized crime and drawing on previous studies on criminal network resilience, this study analyses the evolution of two ‘Ndrangheta criminal groups over around two years, seeking to understand how they adapted to the external pressure of law enforcement agencies, and to identify the mechanisms that drove their evolution and the structural changes that they experienced. The results show that the two mafia groups had several sources of resilience. The possibility to rely on non-economic ties, which are not the consequence of their participation in illegal markets, enabled the mafia groups to rapidly, though partially, replace the actors arrested. A less prominent role of the formal hierarchy of the ‘Ndrangheta in criminal networks mainly involved in drug trafficking instead gave rise to a more flexible internal configuration.
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BERLUSCONI, GIULIA. "LAW ENFORCEMENT AND CRIMINAL NETWORK RESILIENCE: THE IMPACT OF LAW ENFORCEMENT ACTION ON THE STRUCTURE OF MAFIA-RELATED DRUG TRAFFICKING NETWORKS." Doctoral thesis, Università Cattolica del Sacro Cuore, 2014. http://hdl.handle.net/10280/2457.
Full textAbstract:
Per comprendere la capacità delle organizzazioni criminali di resistere alle indagini da parte delle forze di polizia, alcuni studiosi hanno introdotto il concetto di resilienza nel campo della ricerca sul crimine organizzato. Il termine si riferisce alla capacità di un gruppo criminale di affrontare le pressioni esterne e riorganizzarsi.
Adottando un approccio di rete e facendo riferimento a precedenti ricerche sulla resilienza dei gruppi criminali, il presente studio analizza l’evoluzione nel corso del tempo di due gruppi legati alla ‘Ndrangheta. L’obiettivo consiste nel comprendere come questi gruppi si sono adattati alla pressione da parte delle forze dell’ordine e nell’identificare i meccanismi che hanno favorito la loro evoluzione e i cambiamenti che hanno riguardato la loro struttura organizzativa.
I risultati mostrano che i due gruppi criminali hanno potuto fare affidamento su diverse fonti di resilienza. La presenza di legami di natura non economica, che non sono conseguenza della loro partecipazione nei mercati illegali, ha consentito ai gruppi mafiosi di sostituire i soggetti arrestati in modo rapido ma parziale. Una minor importanza attribuita alla struttura gerarchica da parte dei gruppi mafiosi coinvolti in traffici internazionali ha invece permesso a questi gruppi di dotarsi di una organizzazione interna più flessibile.To understand mafia persistence over time and address the problem of the impact of law enforcement interventions on criminal groups, some scholars have introduced the concept of resilience into organized crime research; this refers to the ability of criminal groups to deal with ongoing changes and reorganize themselves accordingly. Adopting a network approach to organized crime and drawing on previous studies on criminal network resilience, this study analyses the evolution of two ‘Ndrangheta criminal groups over around two years, seeking to understand how they adapted to the external pressure of law enforcement agencies, and to identify the mechanisms that drove their evolution and the structural changes that they experienced. The results show that the two mafia groups had several sources of resilience. The possibility to rely on non-economic ties, which are not the consequence of their participation in illegal markets, enabled the mafia groups to rapidly, though partially, replace the actors arrested. A less prominent role of the formal hierarchy of the ‘Ndrangheta in criminal networks mainly involved in drug trafficking instead gave rise to a more flexible internal configuration.
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Tewari, Anurag. "Upstream supply chain vulnerability, robustness and resilience : a systematic review of literature." Thesis, Cranfield University, 2013. http://dspace.lib.cranfield.ac.uk/handle/1826/12490.
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Purpose: In the last decade, supply chains of many global firms have been exposed to severe and costly supply chain disruptions. Triggered by either a manmade or a natural disaster, these disruptions are often a result of the increased network complexity and interdependency. One of the many contributing factors to this increased network complexity is the conscious effort by organizations to over optimise their efficiency and performance.
The field of supply chain resilience, robustness and vulnerability studies, a new and growing area of knowledge, is contributing towards discovering the causes leading to supply chain disasters and measures to tackle them. Criticized to be highly fragmented and fraught with conceptual ambiguity, the filed has been evolving by incorporating vulnerability and resilience research from other interdisciplinary domains.
This present research aims at mapping the intellectual territory of the resilience, robustness and vulnerability domain by conducting a literature review. The review also aims to establish a conceptual clarity in the definition of terms and constructs relevant to the field and to discover conceptual and methodological gaps in the existing body of literature.
Design/methodology/approach: This literature review is conducted using a systematic review approach which benefits from a clearly defined audit and decision trail. After filtering through 2077 titles, the review is taken up for 43 articles.
Findings: The review demonstrates that the drivers of vulnerability and strategies to tackle it can be grouped into three themes, Structural, Operational and Strategic. The review also demonstrates that the field is still plagued with conceptual ambiguity. By the analysis of the findings, a number of research directions were identified.
Research limitations/implications: Major limitations to this study were the associated personal bias in quality assessment of included and excluded articles. Also, due to blurred definitions of terms and constructs in the literature, the thematic classification of findings could be challenged. Lastly, it cannot be stated with conviction that the chosen 43 articles are sufficient.
Practical implications: This research highlights the future conceptual and methodological prospects in the field of resilience, robustness and vulnerability. The direction of structural research proposed in the thesis has a very high potential to secure future supply chains.
Originality/value: This review is first to address the issue of SCV, SCRel and SCRob. The review provides an extensive overview of the present extant of the vulnerability, robustness research and it proposes a thematic framework to further extend the knowledge in this filed.
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Yngve, Adam. "Resilience against social anxiety : The role of social networks in social anxiety disorder." Thesis, Linköpings universitet, Institutionen för beteendevetenskap och lärande, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-131140.
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Resilience refers to the capacity to quickly return to normal levels of functioning in the face of adversity. This capacity has previously been linked to social support. The purpose of this study was to investigate the role of social networks in the association between resilience and social anxiety in a clinical group with social anxiety disorder (n = 41) and a control group of university students (n = 40). The results showed that controls were significantly more resilient than the clinical group. Controls had significantly larger, more diverse and active social networks than the clinical group. Resilience was negatively associated with social anxiety in both groups. In the clinical group, there was a significant partial mediation effect of resilience on social anxiety through the size of the social network, a x b = –0.33, 95% CI [–0.718, –0.111]. Potential clinical applications of these results were discussed.
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Martin, Rüdiger [Verfasser]. "Resilience, provisioning, and control for the network of the future / vorgelegt von Rüdiger Martin." Würzburg : Inst. für Informatik, Lehrstuhl für Verteilte Systeme, 2008. http://d-nb.info/999914782/34.
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Randall, Christian Eric. "THE EFFECTS OF COLLABORATION ON THE RESILIENCE OF THE ENTERPRISE: A NETWORK-ANALYTIC APPROACH." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1357229379.
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Zhang, Jian Electrical Engineering Australian Defence Force Academy UNSW. "Error resilience for video coding services over packet-based networks." Awarded by:University of New South Wales - Australian Defence Force Academy. School of Electrical Engineering, 1999. http://handle.unsw.edu.au/1959.4/38652.
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Error resilience is an important issue when coded video data is transmitted over wired and wireless networks. Errors can be introduced by network congestion, mis-routing and channel noise. These transmission errors can result in bit errors being introduced into the transmitted data or packets of data being completely lost. Consequently, the quality of the decoded video is degraded significantly. This thesis describes new techniques for minimising this degradation. To verify video error resilience tools, it is first necessary to consider the methods used to carry out experimental measurements. For most audio-visual services, streams of both audio and video data need to be simultaneously transmitted on a single channel. The inclusion of the impact of multiplexing schemes, such as MPEG 2 Systems, in error resilience studies is also an important consideration. It is shown that error resilience measurements including the effect of the Systems Layer differ significantly from those based only on the Video Layer. Two major issues of error resilience are investigated within this thesis. They are resynchronisation after error detection and error concealment. Results for resynchronisation using small slices, adaptive slice sizes and macroblock resynchronisation schemes are provided. These measurements show that the macroblock resynchronisation scheme achieves the best performance although it is not included in MPEG2 standard. The performance of the adaptive slice size scheme, however, is similar to that of the macroblock resynchronisation scheme. This approach is compatible with the MPEG 2 standard. The most important contribution of this thesis is a new concealment technique, namely, Decoder Motion Vector Estimation (DMVE). The decoded video quality can be improved significantly with this technique. Basically, this technique utilises the temporal redundancy between the current and the previous frames, and the correlation between lost macroblocks and their surrounding pixels. Therefore, motion estimation can be applied again to search in the previous picture for a match to those lost macroblocks. The process is similar to that the encoder performs, but it is in the decoder. The integration of techniques such as DMVE with small slices, or adaptive slice sizes or macroblock resynchronisation is also evaluated. This provides an overview of the performance produced by individual techniques compared to the combined techniques. Results show that high performance can be achieved by integrating DMVE with an effective resynchronisation scheme, even at a high cell loss rates. The results of this thesis demonstrate clearly that the MPEG 2 standard is capable of providing a high level of error resilience, even in the presence of high loss. The key to this performance is appropriate tuning of encoders and effective concealment in decoders.
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Beech, Daniel. "Managing volcanic hazards : an actor-network of technology and communication." Thesis, Aberystwyth University, 2017. http://hdl.handle.net/2160/a519ac39-c8ff-4c8d-be18-1cd8c1a61331.
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The scientific and socio-political dimensions of volcanic hazards have been realigned since the eruption of Eyjafjallajökull in 2010, and have highlighted the need for volcanic activity to be studied from interdisciplinary perspectives. By focussing on communication, adaptability and resilience, this research explains the links between hazard management and social constructivism. The research question asks how Iceland’s networked approach to managing volcanoes can be understood by analysing the development of communication channels between human stakeholders and non-human technical devices and systems. Fieldwork was conducted in both Iceland and the UK, and a mixed methods approach was used to engage with the network. Research methods consisted of semi-structured interviews, participant observations and archival research. Findings explain the evolution of knowledge exchange, the value of technical innovation, and the need for interactions between local, national and international stakeholders. The study concludes that actors are increasingly empowered by the use of participatory technologies within hazard management, and the development of collaborative engagements between stakeholder communities from scientific and socio-political backgrounds. This research is relevant as it illustrates how the adaptive capacity of hazard networks can be expanded, potentially influencing the approaches that are taken to manage volcanic hazards in less economically developed contexts. In addition, this study can encourage continued interaction between scientists, at-risk communities and the aviation industry in multi-hazard environments such as Iceland.
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Ernstson, Henrik. "In Rhizomia : Actors, Networks and Resilience in Urban Landscapes." Doctoral thesis, Stockholms universitet, Systemekologiska institutionen, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-8137.
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With accelerating urbanization it is crucial to understand how urban ecosystems play a part in generating ecosystem services for urban dwellers, such as clean water, spaces for recreation, stress relief and improved air quality. An equally important question relate to who gets to enjoy these benefits, i.e. the distribution of ecosystem services, and how issues of power and equity influence the management of ecosystems. Through case studies from the urban landscape of Stockholm, this doctoral thesis engages with these perspectives through combining ecological theory with social theory, including social network analysis, actor-network theory and social movement theory. Strategies for how to improve urban ecosystem management are presented along with frameworks for how to analyze issues of power and equity in relation to natural resource management. Paper I shows that ecosystem management can be studied through analyzing the structure of social networks, i.e. the patterns of relations between agencies, stake-holders and user groups. Paper II and Paper III analyze, based on a network survey of 62 civil society organizations and in-depth interviews, a transformational process of how an urban local movement managed to protect a large urban green area from exploitation (The Stockholm National Urban Park). Paper IV discusses, based on several case studies from Stockholm, a conducive network structure for linking managers and user groups (e.g. allotment gardens, cemetery managers, and urban planners) across spatial ecological scales so as to improve urban green area management. Paper V presents a framework to analyze the social-ecological dynamics behind the generation and distribution of ecosystem services in urban landscapes. The thesis points towards the notion of "a social production of ecosystem services" and argues for deeper engagement with urban political ecology and critical geography to inform governance and collective action in relation to urban ecosystems.
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Biswas, Shuchismita. "Power Grid Partitioning and Monitoring Methods for Improving Resilience." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/104684.
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This dissertation aims to develop decision-making tools that aid power grid operators in mitigating extreme events. Two distinct areas are focused on: a) improving grid performance after a severe disturbance, and b) enhancing grid monitoring to facilitate timely preventive actions. The first part of the dissertation presents a proactive islanding strategy to split the bulk power transmission system into smaller self-adequate islands in order to arrest the propagation of cascading failures after an event. Heuristic methods are proposed to determine in what sequence should the island boundary lines be disconnected such that there are no operation constraint violations. The idea of optimal partitioning is further extended to the distribution network. A planning problem for determining which parts of the existing distribution grid can be converted to microgrids is formulated. This partitioning formulation addresses safety limits, uncertainties in load and generation, availability of grid-forming units, and topology constraints such as maintaining network radiality. Microgrids help maintain energy supply to critical loads during grid outages, thereby improving resilience. The second part of the dissertation focuses on wide-area monitoring using Phasor Measurement Unit (PMU) data. Strategies for data imputation and prediction exploiting the spatio-temporal correlation in PMU measurements are outlined. A deep-learning-based methodology for identifying the location of temporary power systems faults is also illustrated. As severe weather events become more frequent, and the threats from coordinated cyber intrusions increase, formulating strategies to reduce the impact of such events on the power grid becomes important; and the approaches outlined in this work can find application in this context.Doctor of Philosophy
The modern power grid faces multiple threats, including extreme-weather events, solar storms, and potential cyber-physical attacks. Towards the larger goal of enhancing power systems resilience, this dissertation develops strategies to mitigate the impact of such extreme events. The proposed schemes broadly aim to- a) improve grid performance in the immediate aftermath of a disruptive event, and b) enhance grid monitoring to identify precursors of impending failures. To improve grid performance after a disruption, we propose a proactive islanding strategy for the bulk power grid, aimed at arresting the propagation of cascading failures. For the distribution network, a mixed-integer linear program is formulated for identifying optimal sub-networks with load and distributed generators that may be retrofitted to operate as self-adequate microgrids, if supply from the bulk power systems is lost. To address the question of enhanced monitoring, we develop model-agnostic, computationally efficient recovery algorithms for archived and streamed data from Phasor Measurement Units (PMU) with data drops and additive noise. PMUs are highly precise sensors that provide high-resolution insight into grid dynamics. We also illustrate an application where PMU data is used to identify the location of temporary line faults.
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Cincotta, Salvatore. "Resilience-based optimal fire fighting in process plants." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.
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In the recent years, fire domino effects have been involved in some extremely severe accidents in the chemical and process industries. In the need of a better understanding of the prevention of fire escalation scenarios, the present study focuses on emergency firefighting which compared to passive and active fire protection measures has received less attention. In the present study, a resilience-based firefighting methodology has been introduced to increase the absorptive capacity of process plants in withstanding the expanding disruptions of fire escalation scenarios. The proposed resilience metric allows to measure the resilience and performance deficiencies and facilitates the identification of optimal intervention actions that lead to the lowest loss of resilience.
The modeling of fire escalation scenarios has been conducted using a Bayesian network approach while the modeling and investigating the effect of different firefighting strategies has been performed by extending the Bayesian network to an influence diagram. The area above the resilience curve, which is equal to the loss of resiliency, has been considered as a metric and discriminating factor to identify the optimal firefighting strategy. The results of this innovative investigation allow to better understand the effectiveness and reliability of the emergency protection interventions in a chemical plant and to study how the domino effect risk assessment can be enriched by new concepts optimizing the distribution of human and material resources in fire fighting operations.
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Tukamuhabwa, Rwakira Benjamin. "Supply chain resilience : a case study analysis of a supply network in a developing country context." Thesis, Lancaster University, 2015. http://eprints.lancs.ac.uk/78228/.
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In recent years, building Supply Chain Resilience (SCRES) has gained considerable interest as the best way firms can face up to disruptions and gain a competitive advantage. The need for more empirical work on SCRES is well expressed in the literature, but there are few prior empirical studies on SCRES to date; and their focus has been on the developed world, especially Western Europe and North America. Yet, developing countries constitute a significant part of the world population and global supply chains; and there is evidence to believe that developing countries have also faced disastrous effects of supply chain failures. And the current global interconnectedness suggests that such effects can propagate into the developed world. Further, while several potential strategies for improving SCRES have been proposed in the literature, the relationships between them remain ambiguous, with some researchers arguing they are independent and others considering them to be interrelated – meaning they could contradict or reinforce each other, potentially affecting SCRES. This thesis presents findings from the case study of a supply network of 20 manufacturing firms in the developing country of Uganda, to answer the following related questions: what do manufacturing firms in Uganda perceive to be the threats to their supply chains? What strategies do they adopt to build resilience? What are the outcomes of implementing these strategies? The thesis also investigates how the threats and strategies are interrelated, and what it means for SCRES. The findings reveal that the context of a developing country characterised, for example, by weak legal controls and social acceptance of certain customs and practices can produce threats to SCRES like corruption and dishonest employees that are less pronounced in the developed world. It is also found that the threats to SCRES are mainly chronic and endogenous events rather than the exogenous discrete, large-scale catastrophic events typically emphasised in the literature. This study initially applies Complex Adaptive Systems (CAS) theory to interpret the data, which shows how environmental conditions, supply chain threats, and resilience strategies are inherently inter-related. This proves to be a useful theory frame – it emerges that the systemic nature of the threats to SCRES and of the strategies for dealing with these threats clearly produces non-linear and non-stationary outcomes. But it was also found that these systemic relationships among threats, strategies and their outcomes are explained by the context in which the supply chain is situated. Hence an embeddedness perspective was adopted to show that the political, cultural and territorial embeddedness of supply networks in a developing country can produce threats or render resilience strategies either ineffective or even counterproductive. This study therefore finds that both CAS and embeddedness perspectives are needed jointly to explain SCRES – it is embeddedness in a developing country that contributes to the phenomenon of “supply chain risk migration”, whereby an attempt to mitigate one threat produces another threat and/or shifts the threat to another point in the supply network. This portrays resilience as a continual process of supply network members responding to chronic and catastrophic events that may be endogenous and/or exogenous, and to the outcomes of their own previous responses – not to a specific set of structures or practices. These findings have implications for managers wishing to build SCRES. For example, managers are informed that supply chain events of continuous possibilities deserve attention. Managers are also reminded of the potential migration of threats – they should thus understand how threats, strategies and potential outcomes are interconnected. Further, managers should understand the contexts in which their supply chains are embedded.
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Hu, Yajie. "Exploring Equity and Resilience of Transportation Network through Modeling Travel Behavior: A Study of OKI Region." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1554212469614412.
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Catanese, Salvatore Amato. "New perspectives in criminal network analysis: multilayer networks, time evolution, and visualization." Doctoral thesis, Università di Catania, 2017. http://hdl.handle.net/10761/3793.
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The work presented in this Dissertation reflects a long-term human, professional and cultural path started some years ago when I first developed LogAnalysis, a tool for the analysis and visualization of criminal and social networks. Since then, I devoted myself to the development of frameworks, algorithms and techniques for supporting intelligence and law enforcement agencies in the task of unveiling the CN structure hidden in communication data, identifying the target offenders for their removal or selecting effective strategies to disrupt a criminal organization. In a natural way, I successively focused on the evaluation of the resilience of criminal networks and on the multiplex formalism, which takes into account the various relationships existing within a criminal organization.
In this context I introduce criminal network analysis tools: LogAnalysis, LogViewer, Semantic viewer and Failure simulator. I have been involved in the design, modeling, and writing of all of the works presented. In particular, I have also developed and tested all the visual tools included therein.
Finally, I introduce Multiplex PBFS (Mx-PBFS) a novel multi-threaded parallel Breadth-First Search algorithm for categorical and inter-layer couplings multiplex networks, and the framework CriMuxnet (still under development) for multilayer criminal networks analysis based on high-quality 3D visualizations of network data. CriMuxnet was designed to work in conjunction with a 3D computer graphics (CG) packages: Autodesk Maya or Blender. CriMuxnet exploits 3D engine features to significantly improve both exploratory search and visualization strategy.
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DE, SANCTIS ILARIA. "Lean implementation and its relationship with operational responsiveness, failure factors and resilience." Doctoral thesis, Università Politecnica delle Marche, 2017. http://hdl.handle.net/11566/245368.
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Lean Management (LM) is a multi-faceted socio-technical approach that requires organizations to strive along several dimensions simultaneously.
Initially, a conceptual model has been proposed for investigating the network of influences among lean practices, operational responsiveness and company growth performances in Italian companies. A structural equation modelling and a second order confirmatory factor analysis have been used to test the hypothesized relationships in the structural models.
Secondly, including manufacturing firms belonging to 23 different countries, the factors influencing the success of LM and human, cultural, economic, strategic and supply chain integration barriers during the start-up and the sustainment phase of lean projects have been analysed.
Thus, taking an organizational network view, this thesis provides a definition for Resilience and a model able to calculate the resilience of a lean organization taking into account both the organizational topology as well as the attitude and the learning curves of operators.
Nodes have been modelled using the Hidden Markov Model and characterized by a learning curve. The resilience is calculated as the area included between the KPI trend during the time of the disruption event and the straight line parallel to the time axes. A case study has been analysed to explain the proposed model.
Results of this thesis highlights that the operational responsiveness is only partially connected to a Lean strategy of a company and there is no direct relationship between lean bundles and firm’s performances. In addition the results revealed that some cultural aspects such as Performance Oriented and Gender Egalitarianism help to maintain a lean culture. Finally, results from this study will have a practical implication assisting human resource managers and production managers in predicting and evaluating global and local effects of the personnel relocation and possible reduction in performance of the workstations.
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Halgin, Daniel. "Effects of Social Identity, Network Connectivity, and Prior Performance on Career Progression and Resilience: A Study of NCAA Basketball Coaches." Thesis, Boston College, 2009. http://hdl.handle.net/2345/643.
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Thesis advisor: Stephen P. BorgattiThis study was an investigation of the effects of social identity on career progression and career resilience. Particular attention was given to the predictive impact of social identity of membership in an identifiable professional sub-grouping. Using NCAA basketball coaches as an empirical setting, quantitative and qualitative analyses were conducted to predict the status of next employer for job seekers who voluntarily changed jobs (n = 282), and the employability resilience of job seekers who were fired (n = 151). Job seekers with the social identity of membership in an identifiable professional sub-grouping (in this empirical setting, defined as membership in a coaching family or coaching tree) were hired for positions with employers of higher status, and exhibited greater employability resilience than was the case for job seekers without such a social identity. Because membership in an identifiable professional sub-grouping signals concise information about the social identity of an individual above and beyond prior performance, network connectivity and status affiliations, it is theorized that individuals with such a social identity are more easily understood, more predictable, and are therefore more valuable in the labor market. Additional career benefits are accrued by individuals who claim their ascribed identity, and by individuals who have social identities characterized as relational actors. Recommendations for future research on social identity of membership in an identifiable professional sub-grouping are offered
Thesis (PhD) — Boston College, 2009
Submitted to: Boston College. Carroll School of Management
Discipline: Organization Studies
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Khaghani, Farnaz. "Resilience-based Operational Analytics of Transportation Infrastructure: A Data-driven Approach for Smart Cities." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/99206.
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Studying recurrent mobility perturbations, such as traffic congestions, is a major concern of engineers, planners, and authorities as they not only bring about delay and inconvenience but also have consequent negative impacts like greenhouse gas emission, increase in fuel consumption, or safety issues. In this dissertation, we proposed using the resilience concept, which has been commonly used for assessing the impact of extreme events and disturbances on the transportation system, for high-probability low impact (HPLI) events to (a) provide a performance assessment framework for transportation systems' response to traffic congestions, (b) investigate the role of transit modes in the resilience of urban roadways to congestion, and (c) study the impact of network topology on the resilience of roadways functionality performance. We proposed a multi-dimensional approach to characterize the resilience of urban transportation roadways for recurrent congestions. The resilience concept could provide an effective benchmark for comparative performance and identifying the behavior of the system in the discharging process in congestion. To this end, we used a Data Envelopment Analysis (DEA) approach to integrate multiple resilience-oriented attributes to estimate the efficiency (resilience) of the frontier in roadways. Our results from an empirical study on California highways through the PeMS data have shown the potential of the multi-dimensional approach in increasing information gain and differentiating between the severity of congestion across a transportation network. Leveraging this resilience-based characterization of recurrent disruptions, in the second study, we investigated the role of multi-modal resourcefulness of urban transportation systems, in terms of diversity and equity, on the resilience of roadways to daily-based congestions. We looked at the physical infrastructure availability and distribution (i.e. diversity) and accessibility and coverage to capture socio-economic factors (i.e. equity) to more comprehensively understand the role of resourcefulness in resilience. We conducted this investigation by using a GPS dataset of taxi trips in the Washington DC metropolitan area in 2017. Our results demonstrated the strong correlation of trips' resilience with transportation equity and to a lesser extent with transportation diversity. Furthermore, we learned the impact of equity and diversity can mostly be seen at the recovery stage of resilience. In the third study, we looked at another aspect of transportation supply in urban areas, spatial configuration, and topology. The goal of this study was to investigate the role of network topology and configuration on resilience to congestion. We used OSMnx, a toolkit for street network analysis based on the data from OpenStreetMap, to model and analyze the urban roadways network configurations. We further employed a multidimensional visualization strategy using radar charts to compare the topology of street networks on a single graphic. Leveraging the geometric descriptors of radar charts, we used the compactness and Jaccard Index to quantitatively compare the topology profiles. We use the same taxi trips dataset used in the second study to characterize resilience and identify the correlation with network topology. The results indicated a strong correlation between resilience and betweenness centrality, diameter, and Page Rank among other features of a transportation network. We further looked at the capacity of roadways as a common cause for the strong correlation between network features and resilience. We found that the strong correlation of link-related features such as diameter could be due to their role in capacity and have a common cause with resilience.Doctor of Philosophy
Transportation infrastructure systems are among the most fundamental facilities and systems in urban areas due to the role they play in mobility, economy, and environmental sustainability. Due to this importance, it is crucial to ensure their resilience to regular disruptions such as traffic congestions as a priority for engineers and policymakers. The resilience of transportation systems has often been studied when disasters or extreme events occur. However, minor disturbances such as everyday operational traffic situations can also play an important part in reducing the efficiency of transportation systems and should be considered in the overall resilience of the systems. Current literature does not consider traffic performance from the lens of resilience despite its importance in evaluating the overall performance of roads. This research addresses this gap by proposing to leverage the concept of resilience for evaluation of roadways performance and identifying the role of urban characteristics in the enhancement of resilience. We first characterized resilience considering the performance of the roadways over time, ranging from the occurrence of disruptions to the time point when the system performance returns to a stable state. Through a case study on some of the major highways in the Los Angeles metropolitan area and by leveraging the data from the Performance Measurement System (PeMS), we have investigated how accounting for a proposed multi-dimensional approach for quantification of resilience could add value to the process of road network performance assessment and the corresponding decision-making. In the second and third parts of this dissertation, we looked at the urban infrastructure elements and how they affect resilience to regular disruptive congestion events. Specifically, in the second study, we focused on alternative transit modes such as bus, metro, or bike presence in the urban areas. We utilized diversity and equity concepts for assessing the opportunities they provide for people as alternative mobility modes. The proposed metrics not only capture the physical attributes of the multi-modal transportation systems (i.e. availability and distribution of transit modes in urban areas) but also consider the socio-economic factors (i.e. the number of people that could potentially use the transit mode). In the third study, we investigated how urban road networks' form and topology (i.e., the structure of roadway networks) could affect its resilience to recurrent congestions. We presented our findings as a case study in the Washington DC area. Results indicated a strong correlation between resilience and resourcefulness as well as topology features. The findings allow decision-makers to make more informed design and operational decisions and better incorporate the urban characteristics during the priority setting process.
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Atkinson, Stuart. "A futures approach to water distribution and sewer network (re)design." Thesis, University of Exeter, 2013. http://hdl.handle.net/10871/10730.
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When designing urban water systems (i.e. water distribution and sewer systems) it is imperative that uncertainty is taken into consideration. However, this is a challenging problem due to the inherent uncertainty associated with both system loading requirements and the potential for physical components failure. It is therefore desirable to improve the reliability of each system in order to account for these uncertainties. Although it is possible to directly evaluate the reliability of a water distribution systems (WDS) (using reliability measures), the calculation processes involved are computationally intensive and therefore unsuitable for some state-of-the-art, iterative design approaches (such as optimisation). Consequently, interest has recently grown in the use of reliability indicators, which are simpler and faster to evaluate than conventional direct reliability methods. In this thesis, a novel measure (the RUF) is developed to quantify reliability in urban water systems with a view to enhance their robustness under a range of future scenarios (Policy Reform, Market Forces, Fortress World and New-Sustainability Paradigm). The considered four future scenarios were synthesized in the EPSRC supported multidisciplinary 4 year project: Urban Futures. Each investigated urban future scenario is characterised by a distinct household water demand and local demand distribution (emerging due to different urban forms evolving in future scenarios). In order to assess the impact of urban futures, RUF has been incorporated into Urban Water System (UWS) dynamic simulations for both WDSs and Foul Sewer Systems (FSSs) using open source codes of EPANET and SWMM. Additionally, in order to overcome extensive computational effort, resulting from the use of traditional reliability measures, a new holistic reliability indicator, the hydraulic power entropy (IHPE) has been developed and compared to existing reliability indicators. Additionally, the relationship between the new reliability indicator and the above mentioned RUF reliability measure is investigated. Results suggest that the magnitude of the IHPE in network solutions provides a holistic indication of the hydraulic performance and reliability for a WDS. However, the performance of optimal solutions under some Urban Futures indicates that additional design interventions are required in order to achieve desired future operation. This thesis also proposes a new holistic foul sewer system (FSS) reliability indicator (the IFSR). The IFSR represents sewer performance as a function of excess pipe capacity (in terms of available increase and also decrease in inflow). The indicator has been tested for two case studies (i.e. different sewer network layouts). Results suggest that the magnitude of IFSR has positive correlations with a number of identified key performance indicators (i.e. relating to capacity, velocity, blockages). Finally, an Integrated Design Approach (IDA) has been developed in order to assess the implications of applying design interventions on both a WDS and downstream FSS. The approach holistically considers present and future operation of each interconnected system. The approach was subsequently demonstrated using two proposed design interventions. Results suggest that, for the considered design interventions, there is trade-off between the simultaneous improvement of both WDS and FSS operation and reliability.