Closeness Centralities of Lollipop Graphs

Closeness is one of the most studied characteristics of networks. Residual closeness is a very sensitive measure of graphs robustness. Additional closeness is a measure of growth potentials of networks. In this article we calculate the closeness, vertex residual closeness, link residual closeness, and additional closeness of lollipop graphs

Robust Distributed Routing in Dynamical Networks - Part I: Locally Responsive Policies and Weak Resilience

Original manuscript March 25, 2011Robustness of distributed routing policies is studied for dynamical networks, with respect to adversarial disturbances that reduce the link flow capacities. A dynamical network is modeled as a system of ordinary differential equations derived from mass conservation laws on a directed acyclic graph with a single origin-destination pair and a constant total outflow at the origin. Routing policies regulate the way the total outflow at each nondestination node gets split among its outgoing links as a function of the current particle density, while the outflow of a link is modeled to depend on the current particle density on that link through a flow function. The dynamical network is called partially transferring if the total inflow at the destination node is asymptotically bounded away from zero, and its weak resilience is measured as the minimum sum of the link-wise magnitude of disturbances that make it not partially transferring. The weak resilience of a dynamical network with arbitrary routing policy is shown to be upper bounded by the network's min-cut capacity and, hence, is independent of the initial flow conditions. Moreover, a class of distributed routing policies that rely exclusively on local information on the particle densities, and are locally responsive to that, is shown to yield such maximal weak resilience. These results imply that locality constraints on the information available to the routing policies do not cause loss of weak resilience. Fundamental properties of dynamical networks driven by locally responsive distributed routing policies are analyzed in detail, including global convergence to a unique limit flow. The derivation of these properties exploits the cooperative nature of these dynamical systems, together with an additional stability property implied by the assumption of monotonicity of the flow as a function of the density on each link.National Science Foundation (U.S.). Office of Emerging Frontiers in Research and Innovation (ARES Grant 0735956)United States. Air Force Office of Scientific Research (Grant FA9950-09-1-0538

Robust Distributed Routing in Dynamical Flow Networks - Part I: Locally Responsive Policies and Weak Resilience

Robustness of distributed routing policies is studied for dynamical flow networks, with respect to adversarial disturbances that reduce the link flow capacities. A dynamical flow network is modeled as a system of ordinary differential equations derived from mass conservation laws on a directed acyclic graph with a single origin-destination pair and a constant inflow at the origin. Routing policies regulate the way the inflow at a non-destination node gets split among its outgoing links as a function of the current particle density, while the outflow of a link is modeled to depend on the current particle density on that link through a flow function. The dynamical flow network is called partially transferring if the total inflow at the destination node is asymptotically bounded away from zero, and its weak resilience is measured as the minimum sum of the link-wise magnitude of all disturbances that make it not partially transferring. The weak resilience of a dynamical flow network with arbitrary routing policy is shown to be upper-bounded by the network's min-cut capacity, independently of the initial flow conditions. Moreover, a class of distributed routing policies that rely exclusively on local information on the particle densities, and are locally responsive to that, is shown to yield such maximal weak resilience. These results imply that locality constraints on the information available to the routing policies do not cause loss of weak resilience. Some fundamental properties of dynamical flow networks driven by locally responsive distributed policies are analyzed in detail, including global convergence to a unique limit flow.Comment: 32 pages, 5 figures, journal submissio

Tracking socioeconomic vulnerability using network analysis: insights from an avian influenza outbreak in an ostrich production network

BACKGROUND: The focus of management in many complex systems is shifting towards facilitation, adaptation, building resilience, and reducing vulnerability. Resilience management requires the development and application of general heuristics and methods for tracking changes in both resilience and vulnerability. We explored the emergence of vulnerability in the South African domestic ostrich industry, an animal production system which typically involves 3-4 movements of each bird during its lifetime. This system has experienced several disease outbreaks, and the aim of this study was to investigate whether these movements have contributed to the vulnerability of this system to large disease outbreaks. METHODOLOGY/PRINCIPAL FINDINGS: The ostrich production system requires numerous movements of birds between different farm types associated with growth (i.e. Hatchery to juvenile rearing farm to adult rearing farm). We used 5 years of movement records between 2005 and 2011 prior to an outbreak of Highly Pathogenic Avian Influenza (H5N2). These data were analyzed using a network analysis in which the farms were represented as nodes and the movements of birds as links. We tested the hypothesis that increasing economic efficiency in the domestic ostrich industry in South Africa made the system more vulnerable to outbreak of Highly Pathogenic Avian Influenza (H5N2). Our results indicated that as time progressed, the network became increasingly vulnerable to pathogen outbreaks. The farms that became infected during the outbreak displayed network qualities, such as significantly higher connectivity and centrality, which predisposed them to be more vulnerable to disease outbreak. Conclusions/Significance Taken in the context of previous research, our results provide strong support for the application of network analysis to track vulnerability, while also providing useful practical implications for system monitoring and management

Dynamic Shifting of Virtual Network Topologies for Network Attack Prevention

Computer networks were not designed with security in mind, making research into the subject of network security vital. Virtual Networks are similar to computer networks, except the components of a Virtual Network are in software rather than hardware. With the constant threat of attacks on networks, security is always a big concern, and Virtual Networks are no different. Virtual Networks have many potential attack vectors similar to physical networks, making research into Virtual Network security of great importance. Virtual Networks, since they are composed of virtualized network components, have the ability to dynamically change topologies. In this paper, we explore Virtual Networks and their ability to quickly shift their network topology. We investigate the potential use of this flexibility to protect network resources and defend against malicious activities. To show the ability of reactively shifting a Virtual Network’s topology to se- cure a network, we create a set of four experiments, each with a different dynamic topology shift, or “dynamic defense”. These four groups of experiments are called the Server Protection, Isolated Subnet, Distributed Port Group, and Standard Port Group experiments. The Server Protection experiments involve detecting an attack against a server and shifting the server behind a protected subnet. The other three sets of experiments, called Attacker Prevention experiments, involve detecting a malicious node in the internal network and initiating a dynamic de- fense to move the attacker behind a protected subnet. Each Attacker Prevention experiment utilizes a different dynamic defense to prevent the malicious node from attacking the rest of the Virtual Network. For each experiment, we run 6 different network attacks to validate the effectiveness of the dynamic defenses. The network attacks utilized for each experiment are ICMP Flooding, TCP Syn Flooding, Smurf attack, ARP Spoofing, DNS Spoofing, and NMAP Scanning. Our validation shows that our dynamic defenses, outside of the standard port group, are very effective in stopping each attack, consistently lowering the at- tacks’ success rate significantly. The Standard Port Group was the one dynamic defense that is ineffective, though there are also a couple of experiments that could benefit from being run with more attackers and with different situations to fully understand the effectiveness of the defenses. We believe that, as Virtual Networks become more common and utilized outside of data centers, the ability to dynamically shift topology can be used for network security purposes

Assessing transportation networks vulnerability for the decision making in humanitarian logistics

Transportation networks are vulnerable to natural disasters, which can degrade their functionality and generate negative impacts over people, especially during the emergency phase, where timely access of humanitarian operations is critical. An interruption of humanitarian relief supply chains at the short-term emergency stage increases the human suffering (deprivation costs) resulting from the lack of access to essential goods or services. These costs are generally not considered in the mathematical formulations used for assessing vulnerability in transportation networks, which can lead to inappropriate strategies for humanitarian assistance. Consequently, in this doctoral thesis a vulnerability assessment model for the development of high impact humanitarian logistics operations is presented. The model is based on an economic analysis that involves both the logistical costs of humanitarian distribution operations and the deprivation cots derived from the delays in the provision of basic supplies

A System-of-Systems Framework for Exploratory Analysis of Climate Change Impacts on Civil Infrastructure Resilience

Climate change has various chronic and acute impacts on civil infrastructure systems (CIS). A long-term assessment of resilience in CIS requires understanding the transformation of CIS caused by climate change stressors and adaptation decision-making behaviors of institutional agencies. In addition, resilience assessment for CIS includes significant uncertainty regarding future climate change scenarios and subsequent impacts. Thus, resilience analysis in CIS under climate change impacts need to capture complex adaptive behaviors and uncertainty in order to enable robust planning and decision making. This study presented a system-of-systems (SoS) framework for abstraction and integrated modeling of climate change stressors, physical infrastructure performance, and institutional actors’ decision making. The application of the proposed SoS framework was shown in an illustrative case study related to the impacts of sea level rise and subsequent saltwater intrusion on a water system. Through the use of the proposed SoS framework, various attributes, processes, and interactions related to physical infrastructure and actor’s decision making were abstracted and used in the creation of a computational simulation model. Then, the computational model was used to simulate various scenarios composed of sea level rise and adaptation approaches. Through an exploratory analysis approach, the simulated scenario landscape was used to identify robust adaptation pathways that lead to a greater system resilience under future uncertain sea level rise. The results of the illustrative case study highlight the various novel capabilities of the SoS framework: (i) abstraction of various attributes and processes that affect the long-term resilience of infrastructure under climate change; (ii) integrated modeling of CIS transformation based on simulating the adaptive decision-making processes, physical infrastructure performance, and climate change impacts; and (iii) exploratory analysis and identification of robust pathways for adaptation to climate change impacts

Avaliação da vulnerabilidade da rede de transporte rodoviário de carga no Brasil

Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Civil e Ambiental, Programa de Pós-Graduação em Transportes, 2014.Este trabalho se propõe a contribuir com o desenvolvimento de um método que possibilite a identificar a vulnerabilidade da rede de transporte rodoviária de carga no Brasil. Para isso,definiu-se como objetivo avaliar a vulnerabilidade da rede de transporte rodoviário de carga, de modo a identificar e classificar os elementos da infraestrutura criticas, avaliando o impacto no custo logístico e o impacto territorial. Para alcançar esse objetivo foi levantado um ferramental teorico-conceitual relativo a rede transporte, transporte de carga no Brasil,infraestrutura critica e vulnerabilidade. Com essas referencias e desenvolvido o método para analisar a vulnerabilidade da rede de transporte rodoviário de carga onde se defini a infraestrutura critica pela medida de centralidade de intermediação e se avalia a vulnerabilidade dos elementos da rede de transporte em estudo. Por fim, a abordagem desenvolvida e aplicada ao estudo de caso feito no principal corredor de exportação de soja no Brasil. Este estudo foi feito pela avaliação do impacto no custo logístico e o impacto territorial. O estudo de caso proposto de mostra a aplicabilidade do método proposto, e se mostra uma como uma ferramenta aos gestores de políticas publicas para identificar e hierarquizar os principais arcos dentro de uma rede de transporte rodoviário de carga para alocar os recursos públicos e privados. ________________________________________________________________________________________ ABSTRACTThis paper purposes itself to contribute with the development of a method that makes itpossible to identify the cargo road transport network vulnerability in Brazil. In order toachieve that, it has been defined as an objective to assess the cargo road transport network,as to identify and classify the critical infrastructure elements, assessing the impact upon thelogistic cost and territorial impact. To achieve that goal, it has been raised a theoricconceptualtool concerning the transport network, cargo transport in Brazil, criticalinfrastructure and vulnerability. With these references, the method has been developed toassess the cargo road transport network vulnerability, in which the infrastructure is definedby the measure of intermediation centrality and the vulnerability of the transport networkelements is assessed. Finally, the developed approach is applied to the case study of themain soy exportation corridor in Brazil. This study was made by the assessment of theimpact over the logistic cost and the territorial impact. The case study purposed shows theapplicability of the purposed method, and it shows itself as a useful tool for the publicpolitic managers to identify and rank the main arcs inside a cargo road transport network inorder to allocate public and private resources

IRGC Resource guide on Resilience

An edited collection of authored pieces comparing, contrasting, and integrating risk and resilience with an emphasis on ways to measure resilienc