| 1. |
- Beal, Jacob, et al.
(author)
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Robust estimation of bacterial cell count from optical density
- 2020
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In: Communications Biology. - : Springer Science and Business Media LLC. - 2399-3642. ; 3:1
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Journal article (peer-reviewed)abstract
- Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data.
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| 2. |
- Han, Duo, et al.
(author)
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An Opportunistic Sensor Scheduling Solution to Remote State Estimation Over Multiple Channels
- 2016
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In: IEEE Transactions on Signal Processing. - : IEEE Press. - 1053-587X .- 1941-0476. ; 64:18, s. 4905-4917
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Journal article (peer-reviewed)abstract
- We consider a sensor scheduling problem where the sensors have multiple choices of communication channel to send their local measurements to a remote state estimator for state estimation. Specifically, the sensors can transmit high-precision data packets over an expensive channel or low-precision data packets, which are quantized in several bits, over some cheap channels. The expensive channel, though being able to deliver more accurate data which leads to good estimation quality at the remote estimator, can only be used scarcely due to its high cost (e.g., high energy consumption). On the other hand, the cheap channel, though having a small cost, delivers less accurate data which inevitably deteriorates the remote estimation quality. In this work we propose a new framework in which the sensors switch between the two channels to achieve a better tradeoff among the communication cost, the estimation performance and the computational complexity, where the two-channel case can be easily extended to a multiple-channel case. We propose an opportunistic sensor schedule which reduces the communication cost by randomly switching among the expensive and cheap channels, and in the meantime maintains low computational complexity while introducing data quantization into the estimation problem. We present a minimum mean square error (MMSE) estimator in a closed-form under the proposed opportunistic sensor schedule. We also formulate an optimization problem to search the best opportunistic schedule with a linear quantizer. Furthermore, we show that the MMSE estimator in the limiting case becomes the standard Kalman filter.
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| 3. |
- Han, Duo, et al.
(author)
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Stochastic Sensor Scheduling for Multiple Dynamical Processes over a Shared Channel
- 2016
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In: 2016 IEEE 55th Conference on Decision and Control, CDC 2016. - : IEEE. - 9781509018376 ; , s. 6315-6320
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Conference paper (peer-reviewed)abstract
- We consider the problem of multiple sensor scheduling for remote state estimation over a shared link. A number of sensors monitor different dynamical processes simultaneously but only one sensor can access the shared channel at each time instant to transmit the data packet to the estimator. We propose a stochastic event-based sensor scheduling framework in which each sensor makes transmission decisions based on both the channel accessibility and the self event-triggering condition. The corresponding optimal estimator is explicitly given. By ultilizing the realtime information, the proposed schedule is shown to be a generalization of the time based ones and outperform the time-based ones in terms of the estimation quality. By formulating an Markov decision process (MDP) problem with average cost criterion, we can find the optimal parameters for the event-based schedule. For practical use, we also design a simple suboptimal schedule to mitigate the computational complexity of solving an MDP problem. We also propose a method to quantify the optimality gap for any suboptimal schedules.
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| 4. |
- Han, YeDuo, et al.
(author)
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On Stochastic Sensor Network Scheduling for Multiple Processes
- 2017
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In: IEEE Transactions on Automatic Control. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9286 .- 1558-2523. ; 62:12, s. 6633-6640
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Journal article (peer-reviewed)abstract
- We consider the problem of multiple sensor scheduling for remote state estimation of multiple process over a shared link. In this problem, a set of sensors monitor mutually independent dynamical systems in parallel but only one sensor can access the shared channel at each time to transmit the data packet to the estimator. We propose a stochastic event-based sensor scheduling in which each sensor makes transmission decisions based on both channel accessibility and distributed event-triggering conditions. The corresponding minimum mean squared error estimator is explicitly given. Considering information patterns accessed by sensor schedulers, time-based ones can be treated as a special case of the proposed one. By ultilizing real-time information, the proposed schedule outperforms the time-based ones in terms of the estimation quality. Resorting to solving a Markov decision process (MDP) problem with an average cost criterion, we can find optimal parameters for the proposed schedule. As for practical use, a greedy algorithm is devised for parameter design, which has rather low computational complexity. We also provide a method to quantify the performance gap between the schedule optimized via MDP and any other schedules.
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| 5. |
- Li, Zishuo, et al.
(author)
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Secure State Estimation against Sparse Attacks on a Time-varying Set of Sensors
- 2023
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In: IFAC-PapersOnLine. - : Elsevier BV. ; , s. 270-275
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Conference paper (peer-reviewed)abstract
- This paper studies the problem of secure state estimation of a linear time-invariant (LTI) system with bounded noise in the presence of sparse attacks on an unknown, time-varying set of sensors. At each time, the attacker has the freedom to choose an arbitrary set of no more than p sensors and manipulate their measurements without restraint. To this end, we propose a secure state estimation scheme and guarantee a bounded estimation error irrespective of the attack signals subject to 2p-sparse observability and a mild, technical assumption that the system matrix has no degenerate eigenvalues. The proposed scheme comprises a design of decentralized observers for each sensor based on the local observable subspace decomposition. At each time step, the local estimates of sensors are fused by a median operator to obtain a secure estimation, which is then followed by a local detection-and-resetting process of the decentralized observers. The estimation error is shown to be upper-bounded by a constant which is determined only by the system parameters and noise magnitudes. Moreover, we design the detector threshold to ensure that the benign sensors never trigger the detector. The efficacy of the proposed algorithm is demonstrated by its application on a benchmark example of IEEE 14-bus system. We show that our proposed scheme can effectively tolerate sparse attacks on an unknown set of sensors, ensuring a bounded estimation error and effectively detecting and resetting the attacked sensors.
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| 6. |
- Li, Zishuo, et al.
(author)
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Secure State Estimation with Asynchronous Measurements against Malicious Measurement-Data and Time-Stamp Manipulation
- 2023
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In: 2023 62nd IEEE Conference on Decision and Control, CDC 2023. - : Institute of Electrical and Electronics Engineers (IEEE). - 9798350301243 - 9798350301250 ; , s. 7073-7080
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Conference paper (peer-reviewed)abstract
- This paper proposes a secure state estimation scheme with asynchronous non-periodic measurements for con-tinuous LTI systems under false data attacks on measurement transmission channels. Each sensor transmits the measurement information in a triple comprised of its sensor index, the time-stamp, and the measurement value to the fusion center via unprotected communication channels. A malicious attacker can corrupt a subset of sensors by (i) manipulating the time-stamp and the measurement value, (ii) blocking transmitted measurement triples, or (iii) injecting fake measurement triples. To deal with such attacks, we propose a secure state estimator by designing decentralized local estimators and fusing all the local states by the median operator. The local estimators receive the sampled measurements and update their local state in an asynchronous manner, while the fusion center triggers the fusion and generates a secure estimation in the presence of a local update. We prove that local estimators of benign sensors are unbiased with stable error covariance. Moreover, the fused secure estimation error has bounded expectation and covariance against at most p corrupted sensors as long as the system is 2p-sparse observable. The efficacy of the proposed scheme is demonstrated through a benchmark example of the IEEE 14-bus system.
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| 7. |
- Liu, Hanxiao, et al.
(author)
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Active Detection Against Replay Attack : A Survey on Watermark Design for Cyber-Physical Systems
- 2021
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In: Lecture Notes in Control and Information Sciences. - Cham : Springer Science and Business Media Deutschland GmbH. ; , s. 145-171
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Conference paper (peer-reviewed)abstract
- Watermarking is a technique that embeds digital information, “watermark”, in a carrier signal to identify ownership of the signal or verify the authenticity or integrity of the carrier signal. It has been widely employed in the fields of image and signal processing. In this chapter, we survey some recent physical watermark design approaches for Cyber-Physical Systems (CPS). We focus on how to design physical watermarking to actively detect cyber-attacks, especially replay attacks, thereby securing the CPS. First, the system and the attack model are introduced. A basic physical watermarking scheme, which leverages a random noise as a watermark to detect the attack, is discussed. The optimal watermark signal is designed to achieve a trade-off between control performance and intrusion detection. Based on this scheme, several extensions are also presented, such as watermarks generated by a hidden Markov model and online data-based watermark generation. These schemes all use an additive watermarking signal. A multiplicative watermark scheme is also presented. The chapter is concluded with a discussion on some open problems on watermark design.
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| 8. |
- Liu, Hanxiao, et al.
(author)
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An On-line Design of Physical Watermarks
- 2018
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In: 2018 IEEE CONFERENCE ON DECISION AND CONTROL (CDC). - : IEEE. - 9781538613955 ; , s. 440-445
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Conference paper (peer-reviewed)abstract
- This paper considers the problem of designing physical watermark signals to protect a control system against replay attacks. We first introduce the replay attack model, where an adversary replays the previous sensory data in order to fool the controller to believe the system is still operating normally. The physical watermarking scheme, which leverages a random control input as a watermark to detect the replay attack is introduced. The optimal watermark signal design problem is then proposed as an optimization problem, which achieves the optimal trade-off between the control performance and attack detection performance. For the system with unknown parameters, we provide a procedure to asymptotically derive the optimal watermarking signal. Numerical examples are provided to illustrate the effectiveness of the proposed strategy.
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| 9. |
- Liu, Hanxiao, et al.
(author)
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An Online Approach to Physical Watermark Design
- 2020
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In: IEEE Transactions on Automatic Control. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9286 .- 1558-2523. ; 65:9, s. 3895-3902
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Journal article (peer-reviewed)abstract
- This article considers the problem of designing physical watermark signals in order to optimally detect possible replay attack in a linear time-invariant system, under the assumption that the system parameters are unknown and need to be identified online. We first provide a replay attack model, where an adversary replays the previous sensor data in order to fool the system. A physical watermarking scheme, which leverages a random input as a watermark to detect the replay attack, is then introduced. The optimal watermark signal design problem is cast as an optimization problem, which aims to achieve the optimal trade-off between control performance and intrusion detection. An online watermarking design and system identification algorithm is provided to deal with systems with unknown parameters. We prove that the proposed algorithm converges to the optimal one and characterize the almost sure convergence rate. An industrial process example is provided to illustrate the effectiveness of the proposed strategy.
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| 10. |
- Quevedo, Daniel, et al.
(author)
-
Technical Committee on Networks and Communication Systems [Technical Activities]
- 2016
-
In: IEEE Control Systems. - 1066-033X. ; 36:4, s. 13-15
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Journal article (peer-reviewed)abstract
- The IEEE Control Systems Society (CSS) Technical Committee on Networks and Communication Systems (TC-NCS) focuses on areas that involve the interplay between networks, communication, and systems control. TCNCS currently has 47 members and is organized into eight working groups. These are Control of Network Systems, Networked Sensing and Sensor Networks, Optimization and Game-Theoretic Methods in Networks, Resource Allocation and Network Economics, Information Networks and Control, Cybersecurity and Privacy, Infrastructure Networks, and Internet of Things. In addition to organizing invited sessions and workshops at the CDC, the American Control Conference, and other conferences, over the last couple of years the TC has organized several special issues in journals.
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