| 1. |
- Abat, E., et al.
(författare)
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Study of the response of the ATLAS central calorimeter to pions of energies from 3 to 9 GeV
- 2009
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002 .- 1872-9576. ; 607:2, s. 372-386
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Tidskriftsartikel (refereegranskat)abstract
- A fully instrumented slice of the ATLAS central detector was exposed to test beams from the SPS (Super Proton Synchrotron) at CERN in 2004. in this paper, the response of the central calorimeters to pions with energies in the range between 3 and 9 GeV is presented. The linearity and the resolution of the combined calorimetry (electromagnetic and hadronic calorimeters) was measured and compared to the prediction of a detector simulation program using the toolkit Geant 4. (C) 2009 Elsevier B.V. All rights reserved.
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| 2. |
- Aad, G., et al.
(författare)
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The ATLAS Experiment at the CERN Large Hadron Collider
- 2008
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 3:S08003
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Forskningsöversikt (refereegranskat)abstract
- The ATLAS detector as installed in its experimental cavern at point 1 at CERN is described in this paper. A brief overview of the expected performance of the detector when the Large Hadron Collider begins operation is also presented.
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| 3. |
- Johansson, Björn, et al.
(författare)
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On decentralized negotiation of optimal consensus
- 2008
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Ingår i: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 44:4, s. 1175-1179
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Tidskriftsartikel (refereegranskat)abstract
- A consensus problem consists of finding a distributed control strategy that brings the state or output of a group of agents to a common value, a consensus point. In this paper, we propose a negotiation algorithm that computes an optimal consensus point for agents modeled as linear control systems subject to convex input constraints and linear state constraints. By primal decomposition and incremental subgradient methods, it is shown that the algorithm can be implemented such that each agent exchanges only a small amount of information per iteration with its neighbors.
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| 4. |
- Tang, Ao, et al.
(författare)
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Window flow control : Macroscopic properties from microscopic factors
- 2008
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Ingår i: 27TH IEEE CONFERENCE ON COMPUTER COMMUNICATIONS (INFOCOM). - 9781424420254 ; , s. 538-546
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Konferensbidrag (refereegranskat)abstract
- This paper studies window flow control focusing on bridging the gap between microscopic factors such as burstiness in sub-RTT timescales, and observable macroscopic properties such as steady state bandwidth sharing and flow level stability. Using new models, we analytically capture notable effects of microscopic behavior on macroscopic quantities. For loss-based protocols, we calculate the loss synchronization rate for different flows and use it to quantitatively explain the unfair bandwidth sharing between paced and unpaced TCP flows. For delay-based protocols, we show that the ratios of round trip delays are critical to the stability of the system. These results deepen the fundamental understanding of congestion control systems. Packet level simulations are used to verify our theoretical claims.
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| 5. |
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| 6. |
- Årzén, Karl-Erik, et al.
(författare)
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Conclusions from the European Roadmap on Control of Computing Systems
- 2006
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Konferensbidrag (refereegranskat)abstract
- The use of control-based methods for resource management in real-time computing and communication systems has gained a substantial interest recently. Applications areas include performance control of web-servers, dynamic resource management in embedded systems, traffic control in communication networks, transaction management in database servers, error control in software systems, and autonomic computing. Within the European EU/IST FP6 Network of Exellence ARTIST2 on Embedded System Design a roadmap on Control of Real-Time Computing Systems has recently been completed. The focus of the roadmap is how flexibility, adaptivity, performance and robustness can be achieved in a real-time computing or communication system through the use of control theory. The item that is controlled is in most cases the allocation of computing and communication resources, e.g., the distribution or scheduling of CPU time among different competing tasks, jobs, requests, or transactions, or the communication resources in a network. Due to this, control of computing systems also goes under the name of feedback scheduling. The roadmap is divided into six research areas: control of server systems, control of CPU resources, control of communication networks, error control of software systems, feedback scheduling of control systems, and control middleware. For each area an overview is given and challenges for future research are stated. The aim of this position paper is to summarize the conclusions concerning these research challenges. In this paper, we will only cover the first four of the areas above. A preliminary version of the roadmap can be found on http://www.control.lth.se/user/karlerik/roadmap1.pdf
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| 7. |
- Årzén, Karl-Erik, et al.
(författare)
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Conclusions of the ARTIST2 Roadmap on Control of Computing Systems
- 2006
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Ingår i: ACM SIGBED Review. - 1551-3688. ; 3:3
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Tidskriftsartikel (refereegranskat)abstract
- he use of control-based methods for resource manage- ment in real-time computing and communication systems has gained a substantial interest recently. Applications ar- eas include performance control of web-servers, dynamic resource management in embedded systems, traffic con- trol in communication networks, transaction management in database servers, error control in software systems, and au- tonomic computing. Within the European EU/IST FP6 Net- work of Exellence ARTIST2 on Embedded System Design a roadmap on Control of Real-Time Computing Systems has recently been completed. The focus of the roadmap is how flexibility, adaptivity, performance and robustness can be achieved in a real-time computing or communication system through the use of control theory. The item that is controlled is in most cases the allocation of computing and communication resources, e.g., the distribution or schedul- ing of CPU time among different competing tasks, jobs, re- quests, or transactions, or the communication resources in a network. Due to this, control of computing systems also goes under the name of feedback scheduling. The roadmap is divided into six research areas: con- trol of server systems, control of CPU resources, control of communication networks, error control of software systems, feedback scheduling of control systems, and control mid- dleware. For each area an overview is given and challenges for future research are stated. The aim of this position paper is to summarize the conclusions concerning these research challenges.
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| 8. |
- Flärdh, Oscar, et al.
(författare)
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A Control Framework for Online Error Control Adaptation in Networked Applications
- 2006
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Ingår i: Proceedings of IEEE Second International Symposium on Control, Communications, and Signal Processing.
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Konferensbidrag (refereegranskat)abstract
- For many real-time applications running over packet-switched networks, it is important to maintain delivered data quality using a limited amount of network resources. It is therefore natural to employ cost functions that allow online trade-off between the experienced application quality and the resource usage. However, minimizing such cost functions requires perfect knowledge of the network state at the transmission side, while, in general, such information is only partially available. In this paper, we introduce a new adaptive error correction algorithm that optimizes the amount of redundancy based on the available information from the application and the network. An extremum-seeking control algorithm is employed to deal with the high level of uncertainty in the network models. The validity of our approach is illustrated in simulations with varying network loads and loss correlation.
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| 9. |
- Flärdh, Oscar, 1980-
(författare)
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Modelling, analysis and experimentation of a simple feedback scheme for error correction control
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Data networks are an important part in an increasing number of applications with real-time and reliability requirements. To meet these demands a variety of approaches have been proposed. Forward error correction, which adds redundancy to the communicated data, is one of them. However, the redundancy occupies communication bandwidth, so it is desirable to control the amount of redundancy in order to achieve high reliability without adding excessive communication delay. The main contribution of the thesis is to formulate the problem of adjusting the redundancy in a control framework, which enables the dynamic properties of error correction control to be analyzed using control theory. The trade-off between application quality and resource usage is captured by introducing an optimal control problem. Its dependence on the knowledge of the network state at the transmission side is discussed. An error correction controller that optimizes the amount of redundancy without relying on network state information is presented. This is achieved by utilizing an extremum seeking control algorithm to optimize the cost function. Models with varying complexity of the resulting feedback system are presented and analyzed. Conditions for convergence are given. Multiple-input describing function analysis is used to examine periodic solutions. The results are illustrated through computer simulations and experiments on a wireless sensor network.
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| 10. |
- Jacobsson, Krister, et al.
(författare)
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ACK-clocking dynamics: Modelling the interaction between windows and the network
- 2008
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Ingår i: 27TH IEEE CONFERENCE ON COMPUTER COMMUNICATIONS (INFOCOM). - 9781424420254 ; , s. 181-185
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Konferensbidrag (refereegranskat)abstract
- A novel continuous time fluid flow model of the dynamics of the interaction between ACK-clocking and the link buffer is presented.. A fundamental integral equation relating the instantaneous flow rate and the window dynamics is derived. Properties of the model, such as well-posedness and stability, are investigated. Packet level experiments verily that this new model is more accurate than existing models, correctly predicting qualitatively different behaviors, for example when round trill delays are heterogeneous.
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