| 1. |
- Janson, Axel, et al.
(författare)
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Analysis of a Networked SIS Multi-Virus Model with a Shared Resource
- 2020
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Ingår i: IFAC PAPERSONLINE. - : Elsevier BV. - 2405-8963. ; , s. 797-802
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Konferensbidrag (refereegranskat)abstract
- In this paper, we introduce a continuous-time competing virus model with a shared resource. We say that the system is in the healthy state if all the agents are healthy, and the shared resource is not contaminated. If the epidemic remains persistent, and the shared resource is contaminated, we say that the system is in the endemic state. First of all we show, under appropriate assumptions, that the model we introduce is well-posed. Secondly, we establish sufficient conditions for exponential (resp. asymptotic) eradication of a virus. Thirdly, for the single-virus case with a shared resource, we establish conditions that lead to existence of an endemic equilibrium. Finally, we provide a necessary and sufficient condition for uniqueness of the healthy state.
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| 2. |
- Milosevic, Jezdimir, et al.
(författare)
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Actuator Security Indices Based on Perfect Undetectability : Computation, Robustness, and Sensor Placement
- 2020
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Ingår i: IEEE Transactions on Automatic Control. - : IEEE. - 0018-9286 .- 1558-2523. ; 65:9, s. 3816-3831
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Tidskriftsartikel (refereegranskat)abstract
- We propose an actuator security index that can be used to localize and protect vulnerable actuators in a networked control system. Particularly, the security index of an actuator equals to the minimum number of sensors and actuators that need to be compromised, such that a perfectly undetectable attack against that actuator can be conducted. We derive a method for computing the index in small-scale systems and show that the index can potentially be increased by placing additional sensors. The difficulties that appear once the system is of a large-scale are then outlined: The index is NP-hard to compute, sensitive with respect to system variations, and based on the assumption that the attacker knows the entire system model. To overcome these difficulties, a robust security index is introduced. The robust index can characterize actuators vulnerable in any system realization, can be calculated in polynomial time, and can be related to limited model knowledge attackers. Additionally, we analyze two sensor placement problems with the objective to increase the robust indices. We show that the problems have submodular structures, so their suboptimal solutions with performance guarantees can be computed in polynomial time. Finally, we illustrate the theoretical developments through examples.
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| 3. |
- Milosevic, Jezdemir, et al.
(författare)
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Estimating the impact of cyber-attack strategies for stochastic networked control systems
- 2020
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Ingår i: IEEE Transactions on Control of Network Systems. - : Institute of Electrical and Electronics Engineers Inc.. - 2325-5870. ; 7:2, s. 747-757
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Tidskriftsartikel (refereegranskat)abstract
- Risk assessment is an inevitable step in implementation of a cyber-defense strategy. An important part of this assessment is to reason about the impact of possible attacks. In this paper, we study the problem of estimating the impact of cyber-attacks in stochastic linear networked control systems. For the stealthiness constraint, we adopt the Kullback-Leibler divergence between attacked and nonattacked residual sequences. Two impact metrics are considered: the probability that some of the critical states leave a safety region and the expected value of the infinity norm of the critical states. For the first metric, we prove that the optimal value of the impact estimation problem can be calculated by solving a set of convex problems. For the second, we derive efficiency to calculate lower and upper bounds. Finally, we show compatibility of our framework with a number of attack strategies proposed in the literature and demonstrate how it can be used for risk assessment in an example.
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| 4. |
- Miloševiç, Jezdimir, et al.
(författare)
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Security Measure Allocation for Industrial Control Systems : Exploiting Systematic Search Techniques and Submodularity
- 2020
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Ingår i: International Journal of Robust and Nonlinear Control. - : Wiley. - 1049-8923 .- 1099-1239. ; 30:11, s. 4278-4302
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Tidskriftsartikel (refereegranskat)abstract
- To protect industrial control systems from cyberattacks, multiple layers of security measures need to be allocated to prevent critical security vulnerabilities. However, both finding the critical vulnerabilities and then allocating security measures in a cost‐efficient way become challenging when the number of vulnerabilities and measures is large. This paper proposes a framework that can be used once this is the case. In our framework, the attacker exploits security vulnerabilities to gain control over some of the sensors and actuators. The critical vulnerabilities are those that are not complex to exploit and can lead to a large impact on the physical world through the compromised sensors and actuators. To find these vulnerabilities efficiently, we propose an algorithm that uses the nondecreasing properties of the impact and complexity functions and properties of the security measure allocation problem to speed up the search. Once the critical vulnerabilities are located, the security measure allocation problem reduces to an integer linear program. Since integer linear programs are NP‐hard in general, we reformulate this problem as a problem of minimizing a linear set function subject to a submodular constraint. A polynomial time greedy algorithm can then be applied to obtain a solution with guaranteed approximation bound. The applicability of our framework is demonstrated on a control system used for regulation of temperature within a building.
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| 5. |
- Pare, Philip E., et al.
(författare)
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Analysis, Online Estimation, and Validation of a Competing Virus Model
- 2020
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Ingår i: 2020 American Control Conference (ACC). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 2556-2561
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Konferensbidrag (refereegranskat)abstract
- In this paper we introduce a discrete time competing virus model and the assumptions necessary for the model to be well posed. We analyze the system exploring its different equilibria. We provide necessary and sufficient conditions for the estimation of the model parameters from time series data and introduce an online estimation algorithm. We employ a dataset of two competing subsidy programs from the US Department of Agriculture to validate the model by employing the identification techniques. To the best of our knowledge, this work is the first to study competing virus models in discretetime, online identification of spread parameters from time series data, and validation of said models using real data. These new contributions are important for applications since real data is naturally sampled.
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| 6. |
- Pare, P. E., et al.
(författare)
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Data-Driven Distributed Mitigation Strategies and Analysis of Mutating Epidemic Processes
- 2020
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Ingår i: Proceedings of the IEEE Conference on Decision and Control. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 6138-6143
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Konferensbidrag (refereegranskat)abstract
- In this paper we study a discrete-time SIS (susceptible-infected-susceptible) model, where the infection and healing parameters and the underlying network may change over time. We provide conditions for the model to be well-defined and study its stability. For systems with homogeneous infection rates over symmetric graphs, we provide a sufficient condition for global exponential stability (GES) of the healthy state, that is, where the virus is eradicated. For systems with heterogeneous virus spread over directed graphs, provided that the variation is not too fast, a sufficient condition for GES of the healthy state is established. Appealing to the first stability result, we present two data-driven mitigation strategies that set the healing parameters in a centralized and a distributed manner, respectively, in order to drive the system to the healthy state.
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| 7. |
- Stefansson, Elis, et al.
(författare)
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Modeling the decision-making in human driver overtaking
- 2020
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Ingår i: IFAC PAPERSONLINE. - : Elsevier BV. - 2405-8963. ; , s. 15338-15345
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Konferensbidrag (refereegranskat)abstract
- We propose models for the decision-making process of human drivers in an overtaking scenario. First, we mathematically formalize the overtaking problem as a decision problem with perceptual uncertainty. Then, we propose and numerically analyze risk-agnostic and risk-aware decision models, which are able to judge whether an overtaking is desirable or not. We show how a driver's decision-making time and confidence level can be primarily characterized through two model parameters, which collectively represent human risk-taking behavior. We detail an experimental testbed for evaluating the decision-making process in the overtaking scenario. Finally, we present some preliminary experimental results from two human drivers.
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| 8. |
- Vrabac, Damir, et al.
(författare)
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Overcoming Challenges for Estimating Virus Spread Dynamics from Data
- 2020
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Ingår i: Proceedings of the 2020 54th Annual Conference on Information Sciences and Systems, CISS 2020. - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- In this paper we investigate estimating the parameters of a discrete time networked virus spread model from time series data. We explore the effect of multiple challenges on the estimation process including system noise, missing data, time-varying network structure, and quantization of the measurements. We also demonstrate how well a heterogeneous model can be captured by homogeneous model parameters. We further illustrate these challenges by employing recent data collected from the ongoing 2019 novel coronavirus (2019-nCoV) outbreak, motivating future work.
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| 9. |
- Wei, J., et al.
(författare)
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Finite-time consensus protocols for multi-dimensional multi-agent systems
- 2020
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Ingår i: Control Theory and Technology. - : South China University of Technology. - 2095-6983 .- 2198-0942. ; 18:4, s. 419-430
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Tidskriftsartikel (refereegranskat)abstract
- A finite-time consensus protocol is proposed for multi-dimensional multi-agent systems, using direction-preserving signum controls. Filippov solutions and nonsmooth analysis techniques are adopted to handle discontinuities. Sufficient and necessary conditions are provided to guarantee infinite-time convergence and boundedness of the solutions. It turns out that the number of agents which have continuous control law plays an essential role in finite-time convergence. In addition, it is shown that the unit balls introduced by ℓp norms, where p∈ [1 , ∞] , are invariant for the closed loop.
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