| 1. |
- Altaf, Faisal, et al.
(author)
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Wireless event-triggered controller for a 3D tower crane lab process
- 2011
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In: 2011 19th Mediterranean Conference on Control and Automation, MED 2011. - 9781457701252 - 9781457701245 ; , s. 994-1001
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Conference paper (peer-reviewed)abstract
- This paper studies the design and real-time implementation of an event-triggered controller for a nonlinear 3D tower crane where the communication between the controller and the actuators is performed over a low-power wireless network. A flexible Event-Generation Circuit (EGC) is proposed in order to implement event-driven controllers for Networked Control Systems. Furthermore, a detailed experimental analysis on the performance of the event-triggered controller and the influence of packet losses on the transmitted actuation messages are presented. The results show that the event-triggered controllers in networked control systems are able to maintain the same level of performance as compared to periodic controllers, while increasing the sensors/actuators lifetime by reducing network bandwidth utilization.
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| 2. |
- Araújo, José, et al.
(author)
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Self-triggered control for industrial wireless sensor and actuator networks
- 2011
-
Conference paper (peer-reviewed)abstract
- Energy and communication bandwidth are scarceresources in wireless sensor and actuator networks. Recentresearch efforts considered the control of physical processes oversuch resource limited networks. Most of the existing literatureaddressing this topic is dedicated to periodically sampled controlloops and scheduled communication, because it simplifies theanalysis and the implementation. We propose instead an aperiodicnetwork transmission scheme that reduces the number oftransmission instances for the sensor and control nodes, therebyreducing energy consumption and increasing network lifetime,without sacrificing control performance. As an added benefit,we show the possibility of dynamically allocating the networkbandwidth based on the physical system state and the availableresources. In order to allow timely, reliable, and energy efficientcommunication, we propose a new co-design framework forthe wireless medium access control, compatible with the IEEE802.15.4 standard. Furthermore, we validate our approach in areal wireless networked control implementation.
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| 3. |
- Araújo, José, et al.
(author)
-
Self-triggered control over wireless sensor and actuator networks
- 2011
-
Conference paper (peer-reviewed)abstract
- Energy and communication bandwidth are scarce resources in wireless sensor and actuator networks. Recent research efforts considered the control of physical processes over such resource limited networks. Most of the existing literature addressing this topic is dedicated to periodically sampled control loops and scheduled communication, because it simplifies the analysis and the implementation. We propose instead an aperiodic network transmission scheme that reduces the number of transmission instances for the sensor and control nodes, thereby reducing energy consumption and increasing network lifetime, without sacrificing control performance. As an added benefit, we show the possibility of dynamically allocating the network bandwidth based on the physical system state and the available resources. In order to allow timely, reliable, and energy efficient communication, we propose a new co-design framework for the wireless medium access control, compatible with the IEEE 802.15.4 standard. Furthermore, we validate our approach in a real wireless networked control implementation.
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| 4. |
- Chen, Xin, et al.
(author)
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Mobilization and fractionation of Ti-Nb-Ta during exhumation of deeply subducted continental crust
- 2022
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In: Geochimica et Cosmochimica Acta. - : Elsevier. - 0016-7037 .- 1872-9533. ; 319, s. 271-295
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Journal article (peer-reviewed)abstract
- The behavior of Ti-Nb-Ta is crucial to reveal the genesis of island arc magmatism. However, mobilization and fractionation of Ti-Nb-Ta in subduction zone settings remain poorly understood. The discovery of felsic veins rich in coarse-grained rutile within retrograde eclogite of the North Qaidam UHP metamorphic belt provides a unique and novel opportunity to study age variation during rutile formation and alteration, as well as Ti-Nb-Ta mobility and fractionation during fluid/ melt-rock interaction. Rutile high-resolution elemental mapping, and U-Pb bulk grain (ID-TIMS), and in-situ U-Pb geochronology have been utilized to focus on the properties of rutile in both, felsic vein and retrograde eclogite host to gain insight into possible similarities and differences. Three groups of rutile were distinguished according to its host rock, trace elements signature, and genetical connection to ilmenite: eclogite-hosted rutile (Rt-1), felsic vein-hosted rutile not associated with ilmenite (Rt-2a), and associated with ilmenite (Rt-2b). Field evidence and rutile trace elements characteristics document the source of vein-hosted rutile to be mainly derived from the eclogite during fluid/melt-rock interaction. Principal Component Analysis reveals that Nb, Ta, Sn, and W are more enriched in Rt-2a compared to Rt-1; Rt-2b has higher Nb, U, and Hf than Rt-2a. High-resolution mapping across large rutile grains shows the enrichment of high field strength elements (HFSEs) in rutile near to ilmenite, which indicates a HFSEs back diffusion from the rutile-ilmenite boundary during the replacement of rutile by ilmenite. The Nb/Ta ratios of Rt-2a are lower than those of Rt-1, which result from different partition coefficients of Nb and Ta during fluid/melt-rock interaction. The diffusion-influenced rutile exhibits suprachondritic Nb/Ta ratios and demonstrates that diffusion of Nb in rutile is higher than that of Ta under identical P-T conditions. Rutiles Rt-1 and Rt2a yield consistent Pb-206/U-238 ages of 426-423 Ma, which is similar to the 433 +/- 3 Ma determined by ID-TIMS results of bulk rutile grains. This indicates that Ti-Nb-Ta must have been mobilized during the exhumation of deeply subducted continental crust. However, the diffusion-influenced rutile shows a large variation of ages compared to the rutile not associated with ilmenite, demonstrating that the back-diffusion may affect the U-Pb system in rutile. Therefore, when rutile is partially altered into ilmenite or titanite, its dating should be used with caution. Thus, this study demonstrates volume diffusion is a very important geological process to result in extreme HFSEs fractionation and age variation of rutile on the mineral scale. The rutile aggerates that occur in the felsic veins in 3-5 m distance to the adjacent retrograde eclogite suggest that Ti-Nb-Tarich melts/fluids were transported over a distance of at least several meters and that rutile does not represent a residual phase of the Na-Si-Al-, F-and CH4-bearing fluid/melt environment that formed during anatexis of the subducted continental crust. The formation of rutile-rich aggregates during the generation, transport, and crystallization of subducted continental crust derived melts/fluids in the deep roots of orogenic belts may be a critical trigger for the depletion of HFSEs in arc magmatic rocks during the formation of the continental crust.(c) 2021 Elsevier Ltd. All rights reserved.
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| 5. |
- Hernandez, Aitor, et al.
(author)
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Inverted Pendulum Control over an IEEE 802.15.4 Wireless Sensor and Actuator Network
- 2011
-
Conference paper (peer-reviewed)abstract
- Recent research efforts are considering the problem of performing control of dynamical systems over wireless sensor and actuator networks. However, existing results lack an experimental evaluation in real platforms. In this demonstration an inverted pendulum system is controlled over an IEEE 802.15.4 wireless sensor and actuator network. This platform can evaluate several sensor networks and control algorithms and is currently used as an educational tool at KTH Royal Institute of Technology, Sweden.
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| 6. |
- Junesand, Carl, et al.
(author)
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Defect reduction in heteroepitaxial InP on Si by epitaxial lateral overgrowth
- 2014
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In: Materials Express. - : American Scientific Publishers. - 2158-5849 .- 2158-5857. ; 4:1, s. 41-53
-
Journal article (peer-reviewed)abstract
- Epitaxial lateral overgrowth of InP has been grown by hydride vapor phase epitaxy on Si substrates with a thin seed layer of InP masked with SiO2. Openings in the form of multiple parallel lines as well as mesh patterns from which growth occurred were etched in the SiO2 mask and the effect of different growth conditions in terms of V/III ratio and growth temperature on defects such as threading dislocations and stacking faults in the grown layers was investigated. The samples were characterized by cathodoluminescence and by transmission electron microscopy. The results show that the cause for threading dislocations present in the overgrown layers is the formation of new dislocations, attributed to coalescence of merging growth fronts, possibly accompanied by the propagation of pre-existing dislocations through the mask openings. Stacking faults were also pre-existing in the seed layer and propagated to some extent, but the most important reason for stacking faults in the overgrown layers was concluded to be formation of new faults early during growth. The formation mechanism could not be unambiguously determined, but of several mechanisms considered, incorrect deposition due to distorted bonds along overgrowth island edges was found to be in best agreement with observations.
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| 7. |
- Weimer, James, et al.
(author)
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Periodic Constraint-Based Control Using Dynamic Wireless Sensor Scheduling
- 2011
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In: 2011 50th IEEE Conference on Decision and Control andEuropean Control Conference (CDC-ECC). ; , s. 4789-4796
-
Conference paper (peer-reviewed)abstract
- Constraint-based control over wireless sensor networks(WSNs) require control strategies that achieve a desiredclosed-loop system performance while using minimal networkresources. In addition to constraints associated with distributedcontrol, WSNs have limitations on bandwidth, energy consumption,and transmission range. This paper introduces andexperimentally evaluates a new receding-horizon approach forperforming constraint-based control using a WSN. By leveragingthe system controllability, the receding-horizon controller isformulated as a mixed-integer programming problem which, ateach time step, simultaneously generates a control sequence andsensor selection schedule such that the desired performance isachieved while minimizing the energy required to perform dataacquisition and control. For systems containing many sensors,a multi-step state estimator is employed to implement thereceding-horizon controller using a conservative abstractionrelaxationapproach that simplifies the original mixed-integerprogramming problem into a convex quadratic programmingproblem. A wireless process control test bed consisting of8 coupled water tanks and 16 wireless sensors are used toexperimentally evaluate the receding-horizon controller.
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