We study cyber security issues in networked control of a linear dynamical system. Specifically, the dynamical system and the controller are assumed to be connected through a communication channel ...that face malicious attacks as well as random packet losses due to unreliability of transmissions. We provide a probabilistic characterization for the link failures which allows us to study combined effects of malicious and random packet losses. We first investigate almost sure stabilization under an event-triggered control law, where we utilize Lyapunov-like functions to characterize the triggering times at which the plant and the controller attempt to exchange state and control data over the network. We then provide a look at the networked control problem from the attacker's perspective and explore malicious attacks that cause instability. Finally, we demonstrate the efficacy of our results with numerical examples.
Stochastic linear quadratic control problems are considered from the viewpoint of risks. In particular, a worst-case conditional value-at-risk (CVaR) of quadratic objective function is minimized ...subject to additive disturbances whose first two moments of the distribution are known. The study focuses on three problems of finding the optimal feedback gain that minimizes the quadratic cost of: stationary distribution, one-step, and infinite time horizon. For the stationary distribution problem, it is proved that the optimal control gain that minimizes the worst-case CVaR of the quadratic cost is equivalent to that of the standard (stochastic) linear quadratic regulator. For the one-step problem, an approach to an optimal solution as well as analytical suboptimal solutions are presented. For the infinite time horizon problem, two suboptimal solutions that bound the optimal solution and an approach to an optimal solution for a special case are discussed. The presented theorems are illustrated with numerical examples.
In this paper, we provide an overview of recent research efforts on networked control systems under denial-of-service attacks. Our goal is to discuss the utility of different attack modeling and ...analysis techniques proposed in the literature for addressing feedback control, state estimation, and multi-agent consensus problems in the face of jamming attacks in wireless channels and malicious packet drops in multi-hop networks. We discuss several modeling approaches that are employed for capturing the uncertainty in denial-of-service attack strategies. We give an outlook on deterministic constraint-based modeling ideas, game-theoretic and optimization-based techniques and probabilistic modeling approaches. A special emphasis is placed on tail-probability based failure models, which have been recently used for describing jamming attacks that affect signal to interference-plus-noise ratios of wireless channels as well as transmission failures on multi-hop networks due to packet-dropping attacks and non-malicious issues. We explain the use of attack models in the security analysis of networked systems. In addition to the modeling and analysis problems, a discussion is provided also on the recent developments concerning the design of attack-resilient control and communication protocols.
In this article, we study communication-constrained networked control problems for linear time-invariant systems in the presence of Denial-of-Service (DoS) attacks, namely attacks that prevent ...transmissions over the communication network. Our article aims at exploring the tradeoffs between system resilience and network bandwidth capacity. Given a class of DoS attacks, we characterize the bit-rate conditions that are dependent on the unstable eigenvalues of the dynamic matrix of the plant and the parameters of DoS attacks, under which exponential stability of the closed-loop system can be guaranteed. Our characterization clearly shows the tradeoffs between the communication bandwidth and resilience against DoS. An example is given to illustrate the proposed approach.
Multi-agent consensus under jamming attacks is investigated. Specifically, inter-agent communications over a network are assumed to fail at certain times due to jamming of transmissions by a ...malicious attacker. A new stochastic communication protocol is proposed to achieve finite-time practical consensus between agents. In this protocol, communication attempt times of agents are randomized and unknown by the attacker until after the agents make their communication attempts. Through a probabilistic analysis, we show that the proposed communication protocol, when combined with a stochastic ternary control law, allows agents to achieve consensus regardless of the frequency of attacks. We demonstrate the efficacy of our results by considering two different strategies of the jamming attacker: a deterministic attack strategy and a more malicious communication-aware attack strategy.
A sampled-data Pyragas-type delayed feedback control framework is proposed for stabilizing both periodic solutions of linear periodic systems and unstable periodic orbits of nonlinear systems. The ...proposed framework uses the difference between two consecutive samples of the state as a feedback input. Furthermore, the controller is turned on and off periodically in an alternating fashion, allowing one to obtain a monodromy matrix for the closed-loop system. Asymptotic behavior of the closed-loop system state trajectories is investigated through an analysis of the obtained monodromy matrix. Then, an efficient feedback gain design method is developed by exploiting the properties of the monodromy matrix. Finally, the efficacy of the proposed framework is demonstrated with a numerical example.
Electroanalytical methods have undergone development and change from the first polarographic applications to the sensor strategies in today’s sense. However, the most important goals are always to ...detect a wide variety of analytes in complex environments with high selectivity, sensitivity, user-friendliness, and low cost. In these respects, electrochemistry has always been a prominent method. This review explains the evaluation of electrochemical applications from the past to the future. An overview of the electroanalytical techniques, such as cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS), and amperometry, is given with their most recent applications in the determination of various analytes. Today, it is aimed to develop next-generation strategies using electroanalytical techniques. Analyses with easily applicable, fast-response, portable sensor devices have been taken to a different level. Electrochemistry-based glucose sensors, biosensors, nanosensors, and wearable sensors developed for this purpose and their latest applications are discussed in detail. The point electroanalytical applications have reached today is the use and commercialization of highly advantageous sensor devices in biomedical, clinical, and environmental applications. This review aims to shed light on the developments from the past applications to the present, give an idea about current practices, and offer a comprehensive perspective to researchers who want to work in this field.
Axitinib, which is a potent and highly selective inhibitor, differs from previously used drugs by its higher activity potential of inhibition of vascular endothelial growth factor receptor tyrosine ...kinase. The sensitive, time-saving, and environmentally friendly voltammetric methods were developed, for the first time, for the quantification of axitinib using glassy carbon and boron-doped diamond electrodes. The effect of the pH, supporting electrolyte, and scan rate on the peak current and potentials of axitinib were studied for both electrodes. Using cyclic voltammetry, two irreversible anodic peaks, Ep1 and Ep2, were observed at 1.10 and 1.22 V for glassy carbon, 1.15, and 1.30 V for boron-doped diamond electrodes, respectively, in 0.1 M sulfuric acid. By cyclic voltammetry, the electrochemical oxidation process of axitinib showed diffusion-controlled using the boron-doped diamond electrode; while it exhibited adsorption-controlled using the glassy carbon electrode. The mechanism of the oxidation process was evaluated with model compounds. The calibration curves were linearly obtained in the concentration ranges of 8 × 10−8–2 × 10−6 M and 6 × 10−7–8 × 10−5 M for adsorptive stripping differential pulse voltammetry using the glassy carbon electrode and differential pulse voltammetry using the boron-doped diamond electrode, respectively. The proposed sensors were utilized for the quantification of axitinib in pharmaceutical dosage forms and biological samples with excellent recovery and precision results. The limit of quantifications was calculated as 2.84 × 10−9 and 3.67 × 10−8 M in serum samples in pH 2.0 Britton Robinson buffer on glassy carbon and boron-doped diamond electrodes, respectively. The proposed methods were also evaluated in the presence of some potentials interference compounds and ions.
Cancer is one of the leading causes of death worldwide. It is very important to regulate drug doses for cancer patients in the treatment of cancer with drugs. Determination of drugs used as ...anticancer at low concentrations and determination of them with high sensitivity is of great importance for the follow-up of these drugs. Electrochemical techniques offer a wide variety of detection techniques that provide user-friendly, low-cost, and real-time monitoring compared to other conventional methods and provide low sensitivity and detection limits. By modifying the electrode surfaces with various materials, their sensitivity and detection limits can be increased. This review focuses on new electrocatalytic approaches and current developments for the electrochemical determination of anticancer drugs. In addition, anticancer drugs are classified in detail. Electrochemical sensors used in studies in recent years and verification parameters such as detection limit, linear dynamic range, sensitivity are given in tables.
A novel methodology has been applied to generate a porous molecularly imprinted material for highly selective and sensitive recognition of Janus kinase inhibitor ruxolitinib (RUX). The porous ...material-based nucleobase-derivative functional monomer was developed by a photopolymerization method. The thymine methacrylate (ThyM) as a functional monomer was synthesized and copolymerized with 2-hydroxyethyl methacrylate (HEMA) in the presence of ethylene glycol dimethacrylate (EGDMA) onto the glassy carbon electrode glassy carbon electrode/molecularly imprinted polymer@poly(2-hydroxyethyl methacrylate-co-thymine methacrylate), (GCE/MIP@PHEMA-ThyM) for the first time. The presence of ThyM results in the functional groups in imprinting binding sites, while the presence of poly(vinyl alcohol) (PVA) allows to generate porous materials for sensitive sensing. The characterization of GCE/MIP@PHEMA-ThyM was investigated by Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and impedance spectroscopy technique. Then, the porous MIP modified glassy carbon electrode was optimized with effecting parameters including removal agent, removal time, and incubation time to get a better response for RUX. Under well-controlled optimum conditions, the GCE/MIP@PHEMA-ThyM linearly responded to the RUX concentration up to 0.01 pM at the limit of detection (LOD) of 0.00191 pM. The non-imprinted polymer (NIP) was also prepared to serve as a control in the same way but without the template. The proposed method improves the accessibility of binding sites by generating the porous material resulting in highly selective and sensitive recognition of drugs in the pharmaceutical dosage form and synthetic human serum samples.
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•Polymerizable thymine derivates was the first synthesized and used in electrochemical sensor.•Molecularly imprinted electrochemical sensor (MIECs) was the first fabricated to detect Ruxolitinib (RUX).•The presence of PVA as a sacrificial polymer allowed to create a porous structure.•A quite high selectivity with low detection limit.•An excellent linear response in the range of 0.01–0.1 pM RUX with LOD of 0.00191 pM.
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