| 1. |
- Thomas, HS, et al.
(author)
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- 2019
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swepub:Mat__t
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| 2. |
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| 3. |
- Muscarella, Robert, et al.
(author)
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The global abundance of tree palms
- 2020
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In: Global Ecology and Biogeography. - : Wiley. - 1466-822X .- 1466-8238. ; 29:9, s. 1495-1514
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Journal article (peer-reviewed)abstract
- AimPalms are an iconic, diverse and often abundant component of tropical ecosystems that provide many ecosystem services. Being monocots, tree palms are evolutionarily, morphologically and physiologically distinct from other trees, and these differences have important consequences for ecosystem services (e.g., carbon sequestration and storage) and in terms of responses to climate change. We quantified global patterns of tree palm relative abundance to help improve understanding of tropical forests and reduce uncertainty about these ecosystems under climate change.LocationTropical and subtropical moist forests.Time periodCurrent.Major taxa studiedPalms (Arecaceae).MethodsWe assembled a pantropical dataset of 2,548 forest plots (covering 1,191 ha) and quantified tree palm (i.e., ≥10 cm diameter at breast height) abundance relative to co‐occurring non‐palm trees. We compared the relative abundance of tree palms across biogeographical realms and tested for associations with palaeoclimate stability, current climate, edaphic conditions and metrics of forest structure.ResultsOn average, the relative abundance of tree palms was more than five times larger between Neotropical locations and other biogeographical realms. Tree palms were absent in most locations outside the Neotropics but present in >80% of Neotropical locations. The relative abundance of tree palms was more strongly associated with local conditions (e.g., higher mean annual precipitation, lower soil fertility, shallower water table and lower plot mean wood density) than metrics of long‐term climate stability. Life‐form diversity also influenced the patterns; palm assemblages outside the Neotropics comprise many non‐tree (e.g., climbing) palms. Finally, we show that tree palms can influence estimates of above‐ground biomass, but the magnitude and direction of the effect require additional work.ConclusionsTree palms are not only quintessentially tropical, but they are also overwhelmingly Neotropical. Future work to understand the contributions of tree palms to biomass estimates and carbon cycling will be particularly crucial in Neotropical forests.
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| 4. |
- Nuno, E., et al.
(author)
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Rendezvous of Nonholonomic Robots via Output-Feedback Control Under Time-Varying Delays
- 2022
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In: IEEE Transactions on Control Systems Technology. - : Institute of Electrical and Electronics Engineers (IEEE). - 1063-6536 .- 1558-0865. ; , s. 1-10
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Journal article (peer-reviewed)abstract
- We address the problem of making nonholonomic vehicles, with second-order dynamics and interconnected over a bidirectional network, converge to a formation centered at a nonprespecified point on the plane with a nonprespecified common orientation. We assume that only the Cartesian position of the center of mass of each vehicle and its orientation are available for measurement, but not the velocities. In addition, we assume that the interconnections are affected by time-varying delays. Our control method consists in designing a set of second-order systems that are interconnected with the robots' dynamics through virtual springs and transmit their own coordinates to achieve consensus. This and the virtual elastic couplings with the vehicles make the latter achieve consensus too. To the best of our knowledge, output-feedback consensus control of underactuated nonholonomic vehicles has been little studied, all the less in the presence of delays.
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| 5. |
- Restrepo, Esteban, et al.
(author)
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Consensus of Open Multi-agent Systems over Dynamic Undirected Graphs with Preserved Connectivity and Collision Avoidance
- 2022
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In: 2022 IEEE 61ST CONFERENCE ON DECISION AND CONTROL (CDC). - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 4609-4614
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Conference paper (peer-reviewed)abstract
- We address the consensus problem with collision avoidance for multi-agent systems under limited sensing ranges, in the case where new interconnections and agents may be added at any time. The graph topology is represented by a dynamic undirected graph, assumed to be connected only at an initial time, and the open multi-agent system is modeled via a multidimensional impulsive switched representation. We propose a barrier-Lyapunov-function-based consensus control law that guarantees inter-agent collision-avoidance and connectivity maintenance and, relying on the edge-agreement framework, we establish almost-everywhere asymptotic stability of the consensus manifold. The obtained results are also readily applicable to closed multi-agent systems with edge addition. A numerical simulation illustrates the effectiveness of the proposed approach.
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| 6. |
- Restrepo, Esteban, et al.
(author)
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On Asymptotic Stability of Leader–Follower Multiagent Systems Under Transient Constraints
- 2022
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In: IEEE Control Systems Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 2475-1456. ; 6, s. 3164-3169
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Journal article (peer-reviewed)abstract
- We address the agreement-based coordination of first-order multiagent systems interconnected over arbitrary connected undirected graphs and under transient and steady-state constraints. The system is in a leader-follower configuration where only a part of the agents, the leaders, are directly controlled via an external control input, in addition to the agreement protocol. We propose a control law for the leaders, based on the gradient of a potential function, that achieves consensus and guarantees that the trajectories of the inter-agent distances of the entire system remain bounded by a performance function. Relying on the edge-agreement framework and Lyapunov’s first method, we establish strong stability results in the sense of asymptotic stability of the consensus manifold and, in the leaderless case, nonuniform-in-time input-to-state stability with respect to additive disturbances. A numerical simulation illustrates the effectiveness of the proposed approach.
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| 7. |
- Restrepo, Esteban, et al.
(author)
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Robust Consensus of High-Order Systems Under Output Constraints : Application to Rendezvous of Underactuated UAVs
- 2023
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In: IEEE Transactions on Automatic Control. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9286 .- 1558-2523. ; 68:1, s. 329-342
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Journal article (peer-reviewed)abstract
- We solve output- and state-consensus problems for multiagent high-order systems in feedback form. We consider systems interconnected over arbitrary (connected) undirected-topology networks as well as directed spanning-trees and directed cycles. We assume that the systems may be subject to multiple restrictions in the form of output or state constraints, such as limited-range measurements and physical limitations. In addition, we suppose that the systems may be subject to external disturbances. Under these conditions, we present a control framework and a formal analysis that establishes robust stability in the input-to-state sense. The former relies on a modified backstepping method and the latter on multistability theory. Finally, we apply our approach to a case-study of interest in the aerospace industry: Safety-aware rendezvous control of underactuated UAVs subject to connectivity and collision-avoidance constraints.
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| 8. |
- Restrepo, Esteban, et al.
(author)
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Robust Rendezvous Control of UAVs with Collision Avoidance and Connectivity Maintenance
- 2022
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In: 2022 American control Conference (ACC). - : IEEE. ; , s. 4733-4738
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Conference paper (peer-reviewed)abstract
- We address the rendezvous control problem of a group of thrust-propelled Unmanned Aerial Vehicles (UAVs) interconnected over an undirected graph and subject to interagent constraints. The proposed distributed control law achieves the desired formation using only local information and guarantees inter-agent collision-avoidance as well as connectivity maintenance. Relying on the edge-agreement framework and on singular-perturbation theory of multi-stable systems we establish almost-everywhere practical input-to-state stability of the desired formation with respect to disturbances. In the absence of perturbations, asymptotic convergence to the consensus manifold is ensured. A numerical simulation illustrates the effectiveness of the proposed approach.
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| 9. |
- Restrepo, Esteban, et al.
(author)
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Simultaneous Synchronization and Topology Identification of Complex Dynamical Networks
- 2023
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In: 2023 62nd IEEE Conference on Decision and Control, CDC 2023, Proceedings. - : Institute of Electrical and Electronics Engineers (IEEE). - 9798350301243 ; , s. 393-398
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Conference paper (peer-reviewed)abstract
- We propose a new method for simultaneous synchronization and topology identification of a complex dynamical network that relies on the edge-agreement framework and on adaptive-control approaches by design of an auxiliary network. Our method guarantees the identification of the unknown topology and it guarantees that once the topology is identified the complex network achieves synchronization. Under our identification algorithm we are able to provide stability results for the estimation errors in the form of uniform semiglobal practical asymptotic stability. Finally, we demonstrate the effectiveness of our approach with an illustrating example.
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| 10. |
- Restrepo, Esteban, et al.
(author)
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Simultaneous Topology Identification and Synchronization of Directed Dynamical Networks
- 2023
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In: IEEE Transactions on Control of Network Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 2325-5870. ; , s. 1-11
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Journal article (peer-reviewed)abstract
- We propose an approach for simultaneous topology identification and synchronization of a complex dynamical network with directed interconnections that relies on the edge-agreement framework and on adaptive-control approaches by design of an auxiliary synchronizing network. Our method guarantees the identification of the unknown directed topology without the need for verifying the Linear Independence Conditions normally required by previous works in the literature. Furthermore, it also guarantees that the complex network reaches synchronization as determined by the internal dynamics of the system. Under our identification algorithm we provide strong stability results for the estimation errors in the form of uniform semiglobal practical asymptotic stability of the estimation errors. Finally, we demonstrate the effectiveness of our approach with a numerical example.
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