| 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. |
- Huang, Yi, et al.
(author)
-
Prescribed performance formation control for second-order multi-agent systems with connectivity and collision constraints
- 2024
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In: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 160
-
Journal article (peer-reviewed)abstract
- This paper studies the distributed formation control problem of second-order multi-agent systems (MASs) with limited communication ranges and collision avoidance constraints. A novel connectivity preservation and collision-free distributed control algorithm is proposed by combining prescribed performance control (PPC) and exponential zeroing control barrier Lyapunov functions (EZCBFs). In particular, we impose the time-varying performance constraints on the relative position and velocity errors between the neighboring agents, and then a PPC-based formation control algorithm is developed such that the connectivity of the communication graph can be preserved at all times, and the prescribed transient and steady performance on the relative position and velocity error can be achieved. Subsequently, by introducing the EZCBFs method, an inequality constraint condition on the control input is derived to guarantee the collision-free formation motion. By regarding the PPC-based formation controller as a nominal input, an actual formation control input is given by solving the quadratic programming (QP) problem such that each agent achieves collision-free formation motion while guaranteeing the connectivity and prescribed performance as much as possible. Finally, numerical simulation is carried out to validate the effectiveness of the proposed algorithm.
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| 3. |
- Meng, Ziyang, et al.
(author)
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Attitude Coordinated Control of Multiple Underactuated Axisymmetric Spacecraft
- 2017
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In: IEEE Transactions on Control of Network Systems. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2325-5870. ; 4:4, s. 816-825
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Journal article (peer-reviewed)abstract
- Attitude coordinated control of multiple underactuated spacecraft is studied in this paper. We adopt the parametrization proposed by Tsiotras et al. (1995) to describe attitude kinematics, which has been shown to be very convenient for control of underactuated axisymmetric spacecraft with two control torques. We first propose a partial attitude coordinated controller with angular velocity commands. The controller is based on the exchange of each spacecraft's information with local neighbors and a self-damping term. Under a necessary and general connectivity assumption and by use of a novel Lyapunov function, we show that the symmetry axes of all spacecraft are eventually aligned. Full attitude control of multiple underactuated spacecraft is also considered and a discontinuous distributed control algorithm is proposed. It is shown that the proposed algorithm succeeds in achieving stabilization given that control parameters are chosen properly. Discussions on the cases without self damping are also provided for both partial and full attitude controls. Simulations are given to validate the theoretical results and different steadystate behaviors are observed.
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| 4. |
- Meng, Ziyang, et al.
(author)
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Behaviors of networks with antagonistic interactions and switching topologies
- 2016
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In: Automatica. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0005-1098 .- 1873-2836. ; 73, s. 110-116
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Journal article (peer-reviewed)abstract
- In this paper, we study the discrete-time consensus problem over networks with antagonistic and cooperative interactions. A cooperative interaction between two nodes takes place when one node receives the true state of the other while an antagonistic interaction happens when the former receives the opposite of the true state of the latter. We adopt a quite general model where the node communications can be either unidirectional or bidirectional, the network topology graph may vary over time, and the cooperative or antagonistic relations can be time-varying. It is proven that, the limits of all the node states exist, and the absolute values of the node states reach consensus if the switching interaction graph is uniformly jointly strongly connected for unidirectional topologies, or infinitely jointly connected for bidirectional topologies. These results are independent of the switching of the interaction relations. We construct a counterexample to indicate a rather surprising fact that quasi-strong connectivity of the interaction graph, i.e., the graph contains a directed spanning tree, is not sufficient to guarantee the consensus in absolute values even under fixed topologies. Based on these results, we also propose sufficient conditions for bipartite consensus to be achieved over the network with joint connectivity. Finally, simulation results using a discrete-time Kuramoto model are given to illustrate the convergence results showing that the proposed framework is applicable to a class of networks with general nonlinear dynamics.
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| 5. |
- Meng, Ziyang, et al.
(author)
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Control of Networked Dynamical System with Large Delays
- 2021
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In: Modelling, Analysis, and Control of Networked Dynamical Systems. - Cham : Springer Nature. ; , s. 99-108
-
Book chapter (peer-reviewed)abstract
- This chapter considers synchronization of networked linear systems over networks with nonuniform time-varying delays. Since delays are inevitable in real systems and may change the stability of the original system, it is necessary and beneficial to study synchronization in the presence of delays. We focus on the case where the internal dynamics are time-varying but non-expansive (stable dynamics with a quadratic Lyapunov function). The case of directed graph is considered and we show that global asymptotic P-norm synchronization can be achieved over a directed graph with joint connectivity and arbitrarily bounded delays. Simulation results are provided to validate the theoretical results.
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| 6. |
- Meng, Ziyang, et al.
(author)
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Coordinated output regulation of heterogeneous linear systems under switching topologies
- 2015
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In: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 53, s. 362-368
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Journal article (peer-reviewed)abstract
- In this paper, we construct a framework to describe and study the coordinated output regulation problem for multiple heterogeneous linear systems. Each agent is modeled as a general linear multiple-input multiple-output system with an autonomous exosystem which represents the individual offset from the group reference for the agent. The multi-agent system as a whole has a group exogenous state which represents the tracking reference for the whole group. Under the constraints that the group exogenous output is only locally available to each agent and that the agents have only access to their neighbors' information, we propose observer-based feedback controllers to solve the coordinated output regulation problem using output feedback information. A high-gain approach is used and the information interactions are allowed to be switching over a finite set of networks containing both graphs that have a directed spanning tree and graphs that do not. Simulations are shown to validate the theoretical results.
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| 7. |
- Meng, Ziyang, et al.
(author)
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Coordinated output regulation of multiple heterogeneous linear systems
- 2013
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In: 2013 IEEE 52nd Annual Conference on Decision and Control (CDC). - : IEEE conference proceedings. - 9781467357142 ; , s. 2175-2180
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Conference paper (peer-reviewed)abstract
- The coordinated output regulation problem for multiple heterogeneous linear systems is studied in this paper. Each agent is modeled as a linear multiple-input multiple-output (MIMO) system with an exogenous input which represents the individual tracking objective for the agent. The multi-agent system as a whole has a group exogenous input which represents the tracking objective for the whole group. Under the constraints that the group exogenous input is only locally available to each agent and that the agents have only access to their neighbors' information, we propose an observer-based feedback controller to solve the coordinated output regulation problem. A high-gain approach is introduced and the information interactions are allowed to be switching over a finite set of fixed networks containing both graphs having a spanning tree and graphs that do not. A lower bound of the high gain parameters is explicitly given. It describes a fundamental relationship between the information interactions, the dwell time, the non-identical dynamics of different agents, and the high gain parameters.
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| 8. |
- Meng, Ziyang, et al.
(author)
-
Introduction
- 2021
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In: Modelling, Analysis, and Control of Networked Dynamical Systems. - Cham : Springer Nature. ; , s. 1-8
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Book chapter (peer-reviewed)abstract
- Coordination of networked dynamical systems has drawn significant attention due to its broad applications in biology, social science, computer science, and engineering in recent years. Although different problems are modeled from different disciplines, the basic assignment of these networked dynamical systems is to accomplish a common desirable objective in a cooperative manner. One approach is through a completely centralized strategy, where a single decision maker gathers the entire system’s information, performs the computation, and sends back the solution to an individual agent. This centralized framework is subject to performance limitations, such as a single point of failure, high communication requirement and cost, substantial computational burden, limited flexibility and scalability, and lack of privacy. To overcome these limitations, an alternative distributed approach has received substantial attention in the area of systems and control. The idea is that by carefully designing distributed controllers, a group of autonomous agents can achieve a collective task by cooperatively and locally exchanging information. Interactions are local in the sense that an agent can only interact with a subset of agents. Under such a distributed framework, this book aims to provide some recent results on modeling, analysis, control, and applications of networked dynamical systems.
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| 9. |
- Meng, Ziyang, et al.
(author)
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Leader-Follower Coordinated Tracking of Multiple Heterogeneous Lagrange Systems Using Continuous Control
- 2014
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In: IEEE Transactions on robotics. - 1552-3098 .- 1941-0468. ; 30:3, s. 739-745
-
Journal article (peer-reviewed)abstract
- In this paper, we study the coordinated tracking problem of multiple heterogeneous Lagrange systems with a dynamic leader. Only nominal parameters of Lagrange dynamics are assumed to be available. Under the local interaction constraints, i.e., the followers only have access to their neighbors' information and the leader being a neighbor of only a subset of the followers, continuous coordinated tracking algorithms with adaptive coupling gains are proposed. Except for the benefit of the chattering-free control achieved, the proposed algorithm also has the attribute that it does not require the neighbors' generalized coordinate derivatives. Global asymptotic coordinated tracking is guaranteed, and the tracking errors between the followers and the leader are shown to converge to zero. Examples are given to validate the effectiveness of the proposed algorithms.
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| 10. |
- Meng, Ziyang, et al.
(author)
-
Multi-agent systems with compasses : Cooperative and cooperative-antagonistic networks
- 2014
-
Conference paper (peer-reviewed)abstract
- In this paper, we first study agreement protocols for coupled continuous-time nonlinear dynamics over cooperative multi-agent networks. To guarantee convergence for such systems, it is common in the literature to assume that the vector field of each agent is pointing inside the convex hull formed by the states of the agent and its neighbors given the relative states between each agent and its neighbors are available. This convexity condition is relaxed in this paper, as we show that it is enough that the vector field belongs to a strict tangent cone based on a local supporting hyperrectangle. The new condition has the natural physical interpretation of adding a compass for each agent in addition to the available local relative states, as each agent needs only to know in which orthant each of its neighbor is. It is proven that the multi-agent system achieves exponential state agreement if and only if the time-varying interaction graph is uniformly jointly quasi-strongly connected. Cooperative-antagonistic multi-agent networks are also considered. For these systems, the (cooperative-antagonistic) relation has a negative sign for arcs corresponding to antagonistic interactions. State agreement may not be achieved for cooperative-antagonistic multi-agent systems. Instead it is shown that asymptotic modulus agreement is achieved if the time-varying interaction graph is uniformly jointly strongly connected.
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