| 1. |
- Ali-Eldin, Ahmed, 1985-, et al.
(författare)
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Analysis and characterization of a Video-on-Demand service workload
- 2015
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Ingår i: Proceedings of the 6th ACM Multimedia Systems Conference, MMSys 2015. - New York, NY, USA : ACM Digital Library. - 9781450333511 ; , s. 189-200
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Konferensbidrag (refereegranskat)abstract
- Video-on-Demand (VoD) and video sharing services accountfor a large percentage of the total downstream Internet traf-fic. In order to provide a better understanding of the loadon these services, we analyze and model a workload tracefrom a VoD service provided by a major Swedish TV broad-caster. The trace contains over half a million requests gener-ated by more than 20000 unique users. Among other things,we study the request arrival rate, the inter-arrival time, thespikes in the workload, the video popularity distribution, thestreaming bit-rate distribution and the video duration distri-bution. Our results show that the user and the session ar-rival rates for the TV4 workload does not follow a Poissonprocess. The arrival rate distribution is modeled using a log-normal distribution while the inter-arrival time distributionis modeled using a stretched exponential distribution. Weobserve the “impatient user” behavior where users abandonstreaming sessions after minutes or even seconds of startingthem. Both very popular videos and non-popular videos areparticularly affected by impatient users. We investigate ifthis behavior is an invariant for VoD workloads.
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| 2. |
- Ali-Eldin, Ahmed, et al.
(författare)
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Efficient provisioning of bursty scientific workloads on the cloud using adaptive elasticity control
- 2012
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Ingår i: Proceedings of the 3rd workshop on Scientific Cloud Computing Date. - New York, NY, USA : Association for Computing Machinery (ACM). - 9781450313407 - 145031340X ; , s. 31-40
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Konferensbidrag (refereegranskat)abstract
- Elasticity is the ability of a cloud infrastructure to dynamically change theamount of resources allocated to a running service as load changes. We build anautonomous elasticity controller that changes the number of virtual machinesallocated to a service based on both monitored load changes and predictions offuture load. The cloud infrastructure is modeled as a G/G/N queue. This modelis used to construct a hybrid reactive-adaptive controller that quickly reactsto sudden load changes, prevents premature release of resources, takes intoaccount the heterogeneity of the workload, and avoids oscillations. Using simulations with Web and cluster workload traces, we show that our proposed controller lowers the number of delayed requests by a factor of 70 for the Web traces and 3 for the cluster traces when compared to a reactive controller. Ourcontroller also decreases the average number of queued requests by a factor of 3 for both traces, and reduces oscillations by a factor of 7 for the Web traces and 3 for the cluster traces. This comes at the expense of between 20% and 30% over-provisioning, as compared to a few percent for the reactive controller.
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| 3. |
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| 4. |
- Andersson, Alina, et al.
(författare)
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Analytic Parameterization of Stabilizing Controllers for the Surge Subsystem of the Moore-Greitzer Compressor Model
- 2013
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Ingår i: Proc. 2013 American Control Conference (ACC2013). - 0743-1619. - 9781479901777 ; , s. 5257-5262
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Konferensbidrag (refereegranskat)abstract
- This paper is based on a new procedure for dynamic output feedback design for systems with nonlinearities satisfying quadratic constraints. The new procedure is motivated by the challenges of output feedback control design for the 3-state Moore-Greitzer compressor model. First, we use conditions for stability of a transformed system and the associated matching conditions to find the data of the stabilizing controllers for the surge subsystem. Second, using the set of stabilizing controllers satisfying the given constraints for the closed-loop system with the dynamic output feedback controller we made optimization over the parameter set. We present the data of the stabilizing controllers and the new constraints for the corresponding parameters. The contributions in this paper are simplified conditions for the synthesis and optimization over the control parameter set.
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| 5. |
- Andersson, Alina, et al.
(författare)
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Robustness of the Moore-Greitzer Compressor Model's Surge Subsystem with New Dynamic Output Feedback Controllers
- 2014. - 3
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Ingår i: 19th IFAC World Congress. - : Elsevier. - 2405-8963. - 9783902823625 ; 47, s. 3690-3695
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Konferensbidrag (refereegranskat)abstract
- This work presents an extension of a design procedure for dynamic output feedback design for systems with nonlinearities satisfying quadratic constraints. In this work we used an axial gas compressor model described by the 3-state Moore-Greitzer compressor model (MG) that has some challenges for output feedback control design (Planovsky and Nikolaev 1990), (Rubanova 2013). The more general constraints for the investigation of the robustness with respect to parametric uncertainties and measurement noise are shown.
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| 6. |
- Andersson, Alina, et al.
(författare)
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Sufficient Conditions for Dynamic Stabilization of 3-State Moore-Greitzer Compressor Model
- 2015
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Ingår i: 2015 IEEE 54th Annual Conference on Decision and Control (CDC). - 9781479978861 - 9781479978847 ; , s. 4394-4399
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Konferensbidrag (refereegranskat)abstract
- We consider the classical 3-state Moore-Greitzer model, which is commonly used for approximating dynamics of deviations of flow and pressure variables in an axial compressor from their nominal steady-state values. The linearization of the nonlinear system is not controllable and, therefore, even local asymptotic stability cannot be achieved using methods of linear control theory. We propose a family of parametrized partialstate feedback control laws and derive sufficient conditions to guarantee global asymptotic stability of the closed-loop system. The stability analysis uses the integral quadratic constraints technique for the case of non-strict frequency condition and novel arguments for characterization of omega-limit sets.
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| 7. |
- Andersson, Martin, et al.
(författare)
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An upgrade of the internal dosimetry computer program IDAC
- 2012
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Ingår i: Medical Physics in the Baltic States. - : Kaunas University of Technology. - 1822-5721. ; , s. 120-123
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Konferensbidrag (refereegranskat)abstract
- A full update of the internal dosimetry computer program IDAC has been conducted. The new update is based on new and more accurate computational phantoms to calculate effective dose and absorbed dose to organs and tissues. The new ICRP Adult Reference Computational Phantoms has been adopted as well as the latest of the ICRP standardized biokinetic models. The updated computer program includes a user-friendly graphical user interface.
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| 8. |
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| 9. |
- Benedek, Hunor, et al.
(författare)
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Strategies for quality assurance of intensity modulated radiation therapy
- 2015
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Ingår i: 8TH INTERNATIONAL CONFERENCE ON 3D RADIATION DOSIMETRY (IC3DDOSE). - : Institute of Physics (IOP). ; 573, s. 012015-012015
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Konferensbidrag (refereegranskat)abstract
- In late 2011 The Swedish Society of Radiation Physics formed a working group to concentrate on the Quality Assurance of modern radiation therapy techniques. The given task was to identify and summarise the different QA strategies in Sweden and also the international recommendations. This was used to formulate recommendations for practical guidelines within Sweden. In this paper a brief summery of the group's work is presented. All the Swedish radiation therapy centres do a pre treatment verification measurement as QA for every new IMRT and VMAT plan. Physicists do it and they believe it to be time consuming. A general standpoint from all the centres was that new guidelines and legislation is needed to allow QA that does not require a measurement. Based on various international publications and recommendations the working group has presented two strategies, one where all new plans are checked through measurement and one where no measurement is needed. The measurement-based strategy is basically the same as the one used today with an extended machine QA part. The other presented strategy is process oriented where all the different parts of the treatment chain are checked separately. The final report can be found in Swedish on http://www.radiofysik.org.
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| 10. |
- Bengmark, Samuel, 1965, et al.
(författare)
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PREP- Pragmatic Research on Educational Practice
- 2023
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Ingår i: SEFI 2023 - 51st Annual Conference of the European Society for Engineering Education : Engineering Education for Sustainability, Proceedings - Engineering Education for Sustainability, Proceedings. - : SEFI. - 9782873520267 ; , s. 163-172
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Konferensbidrag (refereegranskat)abstract
- We investigate a concept called PREP - Pragmatic Research on Educational Practice, with the goal of engaging engineering educators in studying, documenting and sharing their initiatives to improve teaching practices. This concept is compared to other methodologies where the researcher and educational practitioner sometimes coincide. The study is based on a pilot, with six participants following the PREP program for three months, which we study autoethnographically. We also carried out a focus group discussion (n=12) to investigate to what extent university teachers regard the ideas from the PREP program as helpful for studying educational activities and sharing what they do and find.
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