| 1. |
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- 2019
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Abbasi, Rasha, et al.
(författare)
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IceCube search for neutrinos from GRB 221009A
- 2023
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Ingår i: Proceedings of 38th International Cosmic Ray Conference (ICRC 2023). - : Sissa Medialab Srl.
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Konferensbidrag (refereegranskat)abstract
- GRB 221009A is the brightest Gamma Ray Burst (GRB) ever observed. The observed extremelyhigh flux of high and very-high-energy photons provide a unique opportunity to probe the predictedneutrino counterpart to the electromagnetic emission. We have used a variety of methods to searchfor neutrinos in coincidence with the GRB over several time windows during the precursor, promptand afterglow phases of the GRB. MeV scale neutrinos are studied using photo-multiplier ratescalers which are normally used to search for galactic core-collapse supernovae neutrinos. GeVneutrinos are searched starting with DeepCore triggers. These events don’t have directionallocalization, but instead can indicate an excess in the rate of events. 10 GeV - 1 TeV and >TeVneutrinos are searched using traditional neutrino point source methods which take into accountthe direction and time of events with DeepCore and the entire IceCube detector respectively. The>TeV results include both a fast-response analysis conducted by IceCube in real-time with timewindows of T0 − 1 to T0 + 2 hours and T0 ± 1 day around the time of GRB 221009A, as well asan offline analysis with 3 new time windows up to a time window of T0 − 1 to T0 + 14 days, thelongest time period we consider. The combination of observations by IceCube covers 9 ordersof magnitude in neutrino energy, from MeV to PeV, placing upper limits across the range forpredicted neutrino emission.
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| 3. |
- Abelev, Betty, et al.
(författare)
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Long-range angular correlations on the near and away side in p-Pb collisions at root S-NN=5.02 TeV
- 2013
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Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 719:1-3, s. 29-41
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Tidskriftsartikel (refereegranskat)abstract
- Angular correlations between charged trigger and associated particles are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV for transverse momentum ranges within 0.5 < P-T,P-assoc < P-T,P-trig < 4 GeV/c. The correlations are measured over two units of pseudorapidity and full azimuthal angle in different intervals of event multiplicity, and expressed as associated yield per trigger particle. Two long-range ridge-like structures, one on the near side and one on the away side, are observed when the per-trigger yield obtained in low-multiplicity events is subtracted from the one in high-multiplicity events. The excess on the near-side is qualitatively similar to that recently reported by the CMS Collaboration, while the excess on the away-side is reported for the first time. The two-ridge structure projected onto azimuthal angle is quantified with the second and third Fourier coefficients as well as by near-side and away-side yields and widths. The yields on the near side and on the away side are equal within the uncertainties for all studied event multiplicity and p(T) bins, and the widths show no significant evolution with event multiplicity or p(T). These findings suggest that the near-side ridge is accompanied by an essentially identical away-side ridge. (c) 2013 CERN. Published by Elsevier B.V. All rights reserved.
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| 4. |
- Abelev, Betty, et al.
(författare)
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Measurement of prompt J/psi and beauty hadron production cross sections at mid-rapidity in pp collisions at root s=7 TeV
- 2012
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :11
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Tidskriftsartikel (refereegranskat)abstract
- The ALICE experiment at the LHC has studied J/psi production at mid-rapidity in pp collisions at root s = 7 TeV through its electron pair decay on a data sample corresponding to an integrated luminosity L-int = 5.6 nb(-1). The fraction of J/psi from the decay of long-lived beauty hadrons was determined for J/psi candidates with transverse momentum p(t) > 1,3 GeV/c and rapidity vertical bar y vertical bar < 0.9. The cross section for prompt J/psi mesons, i.e. directly produced J/psi and prompt decays of heavier charmonium states such as the psi(2S) and chi(c) resonances, is sigma(prompt J/psi) (p(t) > 1.3 GeV/c, vertical bar y vertical bar < 0.9) = 8.3 +/- 0.8(stat.) +/- 1.1 (syst.)(-1.4)(+1.5) (syst. pol.) mu b. The cross section for the production of b-hadrons decaying to J/psi with p(t) > 1.3 GeV/c and vertical bar y vertical bar < 0.9 is a sigma(J/psi <- hB) (p(t) > 1.3 GeV/c, vertical bar y vertical bar < 0.9) = 1.46 +/- 0.38 (stat.)(-0.32)(+0.26) (syst.) mu b. The results are compared to QCD model predictions. The shape of the p(t) and y distributions of b-quarks predicted by perturbative QCD model calculations are used to extrapolate the measured cross section to derive the b (b) over bar pair total cross section and d sigma/dy at mid-rapidity.
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| 5. |
- Abelev, Betty, et al.
(författare)
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Underlying Event measurements in pp collisions at root s=0.9 and 7 TeV with the ALICE experiment at the LHC
- 2012
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; :7
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Tidskriftsartikel (refereegranskat)abstract
- We present measurements of Underlying Event observables in pp collisions at root s = 0 : 9 and 7 TeV. The analysis is performed as a function of the highest charged-particle transverse momentum p(T),L-T in the event. Different regions are defined with respect to the azimuthal direction of the leading (highest transverse momentum) track: Toward, Transverse and Away. The Toward and Away regions collect the fragmentation products of the hardest partonic interaction. The Transverse region is expected to be most sensitive to the Underlying Event activity. The study is performed with charged particles above three different p(T) thresholds: 0.15, 0.5 and 1.0 GeV/c. In the Transverse region we observe an increase in the multiplicity of a factor 2-3 between the lower and higher collision energies, depending on the track p(T) threshold considered. Data are compared to PYTHIA 6.4, PYTHIA 8.1 and PHOJET. On average, all models considered underestimate the multiplicity and summed p(T) in the Transverse region by about 10-30%.
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| 6. |
- Kato, Norihiro, et al.
(författare)
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Trans-ancestry genome-wide association study identifies 12 genetic loci influencing blood pressure and implicates a role for DNA methylation
- 2015
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Ingår i: Nature Genetics. - : Nature Publishing Group. - 1061-4036 .- 1546-1718. ; 47:11, s. 1282-1293
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Tidskriftsartikel (refereegranskat)abstract
- We carried out a trans-ancestry genome-wide association and replication study of blood pressure phenotypes among up to 320,251 individuals of East Asian, European and South Asian ancestry. We find genetic variants at 12 new loci to be associated with blood pressure (P = 3.9 × 10−11 to 5.0 × 10−21). The sentinel blood pressure SNPs are enriched for association with DNA methylation at multiple nearby CpG sites, suggesting that, at some of the loci identified, DNA methylation may lie on the regulatory pathway linking sequence variation to blood pressure. The sentinel SNPs at the 12 new loci point to genes involved in vascular smooth muscle (IGFBP3, KCNK3, PDE3A and PRDM6) and renal (ARHGAP24, OSR1, SLC22A7 and TBX2) function. The new and known genetic variants predict increased left ventricular mass, circulating levels of NT-proBNP, and cardiovascular and all-cause mortality (P = 0.04 to 8.6 × 10−6). Our results provide new evidence for the role of DNA methylation in blood pressure regulation.
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| 7. |
- Abbassi, Fariba, et al.
(författare)
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Novel Benchmark Values for Redo Liver Transplantation Does the Outcome Justify the Effort?
- 2022
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Ingår i: Annals of Surgery. - : Lippincott Williams & Wilkins. - 0003-4932 .- 1528-1140. ; 276:5, s. 860-867
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Tidskriftsartikel (refereegranskat)abstract
- Objective: To define benchmark cutoffs for redo liver transplantation (redo-LT). Background: In the era of organ shortage, redo-LT is frequently discussed in terms of expected poor outcome and wasteful resources. However, there is a lack of benchmark data to reliably evaluate outcomes after redo-LT. Methods: We collected data on redo-LT between January 2010 and December 2018 from 22 high-volume transplant centers. Benchmark cases were defined as recipients with model of end stage liver disease (MELD) score <= 25, absence of portal vein thrombosis, no mechanical ventilation at the time of surgery, receiving a graft from a donor after brain death. Also, high-urgent priority and early redo-LT including those for primary nonfunction (PNF) or hepatic artery thrombosis were excluded. Benchmark cutoffs were derived from the 75th percentile of the medians of all benchmark centers. Results: Of 1110 redo-LT, 373 (34%) cases qualified as benchmark cases. Among these cases, the rate of postoperative complications until discharge was 76%, and increased up to 87% at 1-year, respectively. One-year overall survival rate was excellent with 90%. Benchmark cutoffs included Comprehensive Complication Index CCI (R) at 1-year of <= 72, and in-hospital and 1-year mortality rates of <= 13% and <= 15%, respectively. In contrast, patients who received a redo-LT for PNF showed worse outcomes with some values dramatically outside the redoLT benchmarks. Conclusion: This study shows that redo-LT achieves good outcome when looking at benchmark scenarios. However, this figure changes in high-risk redo-LT, as for example in PNF. This analysis objectifies for the first-time results and efforts for redo-LT and can serve as a basis for discussion about the use of scarce resources.
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| 8. |
- Braun, Robert, 1984-, et al.
(författare)
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TLM-Based Asynchronous Co-simulation with the Functional Mockup Interface
- 2019
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Ingår i: Proceedings of the IUTAM Symposium on Solver-Coupling and Co-Simulation, Darmstadt, Germany, September 18-20, 2017. - Switzerland : Springer International Publishing. - 9783030148829 - 9783030148836 ; , s. 27-41
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Konferensbidrag (refereegranskat)abstract
- Numerical stability is a key aspect in co-simulation of physical systems. Decoupling a system into independent sub-models will introduce time delays on interface variables. By utilizing physical time delays for decoupling, affecting the numerical stability can be avoided. This requires interpolation, to allow solvers to request input variables for the time slot where they are needed. The FMI for co-simulation standard does not support fine-grained interpolation using interpolation tables. Here, various modifications to the FMI standard are suggested for improved handling of interpolation. Mechanical and thermodynamic models are used to demonstrate the need for interpolation, as well as to provide an industrial context. It is shown that the suggested improvements are able to stabilize the otherwise unstable connections.
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| 9. |
- Braun, Robert, 1984-, et al.
(författare)
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Transmission line modeling co-simulation with distributed delay-size control using steady-state identification
- 2023
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Ingår i: Engineering with Computers. - : Springer. - 0177-0667 .- 1435-5663.
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Tidskriftsartikel (refereegranskat)abstract
- Combining performance and numerical stability is a key issue in co-simulation. The Transmission Line Modeling method uses physically motivated communication delays to ensure numerical stability for stiff connections. However, using a fixed communication delay may limit performance for some models. This paper proposes Steady-State Identifcation for enabling variable communication delays. Three algorithms for online Steady-State Identification are evaluated in three different co-simulation models. All algorithms are able to identify steady-state and can thereby determine when communication delays can be allowed to increase without compromising accuracy and stability. The results show a reduction in number of the solver derivative evaluations by roughly 40-60% depending on the model. The proposed method additionally supports connections with asymmetric communication delays, which allows each sub-model to independently control the delay of its input variables. Models supporting delay-size control can thereby be connected to those that do not so that the step length of each individual sub-model is maximized. Controlling the delay-size in sub-models also makes the method independent of the master co-simulation algorithm.
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| 10. |
- Brownstein, Catherine A., et al.
(författare)
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An international effort towards developing standards for best practices in analysis, interpretation and reporting of clinical genome sequencing results in the CLARITY Challenge
- 2014
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Ingår i: Genome Biology. - : Springer Science and Business Media LLC. - 1465-6906 .- 1474-760X. ; 15:3, s. R53-
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Tidskriftsartikel (refereegranskat)abstract
- Background: There is tremendous potential for genome sequencing to improve clinical diagnosis and care once it becomes routinely accessible, but this will require formalizing research methods into clinical best practices in the areas of sequence data generation, analysis, interpretation and reporting. The CLARITY Challenge was designed to spur convergence in methods for diagnosing genetic disease starting from clinical case history and genome sequencing data. DNA samples were obtained from three families with heritable genetic disorders and genomic sequence data were donated by sequencing platform vendors. The challenge was to analyze and interpret these data with the goals of identifying disease-causing variants and reporting the findings in a clinically useful format. Participating contestant groups were solicited broadly, and an independent panel of judges evaluated their performance. Results: A total of 30 international groups were engaged. The entries reveal a general convergence of practices on most elements of the analysis and interpretation process. However, even given this commonality of approach, only two groups identified the consensus candidate variants in all disease cases, demonstrating a need for consistent fine-tuning of the generally accepted methods. There was greater diversity of the final clinical report content and in the patient consenting process, demonstrating that these areas require additional exploration and standardization. Conclusions: The CLARITY Challenge provides a comprehensive assessment of current practices for using genome sequencing to diagnose and report genetic diseases. There is remarkable convergence in bioinformatic techniques, but medical interpretation and reporting are areas that require further development by many groups.
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| 11. |
- Feng, Shaohong, et al.
(författare)
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Dense sampling of bird diversity increases power of comparative genomics
- 2020
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 587:7833
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Tidskriftsartikel (refereegranskat)abstract
- Whole-genome sequencing projects are increasingly populating the tree of life and characterizing biodiversity(1-4). Sparse taxon sampling has previously been proposed to confound phylogenetic inference(5), and captures only a fraction of the genomic diversity. Here we report a substantial step towards the dense representation of avian phylogenetic and molecular diversity, by analysing 363 genomes from 92.4% of bird families-including 267 newly sequenced genomes produced for phase II of the Bird 10,000 Genomes (B10K) Project. We use this comparative genome dataset in combination with a pipeline that leverages a reference-free whole-genome alignment to identify orthologous regions in greater numbers than has previously been possible and to recognize genomic novelties in particular bird lineages. The densely sampled alignment provides a single-base-pair map of selection, has more than doubled the fraction of bases that are confidently predicted to be under conservation and reveals extensive patterns of weak selection in predominantly non-coding DNA. Our results demonstrate that increasing the diversity of genomes used in comparative studies can reveal more shared and lineage-specific variation, and improve the investigation of genomic characteristics. We anticipate that this genomic resource will offer new perspectives on evolutionary processes in cross-species comparative analyses and assist in efforts to conserve species. A dataset of the genomes of 363 species from the Bird 10,000 Genomes Project shows increased power to detect shared and lineage-specific variation, demonstrating the importance of phylogenetically diverse taxon sampling in whole-genome sequencing.
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| 12. |
- Fritzson, Peter, 1952-, et al.
(författare)
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The OpenModelica Integrated Environment for Modeling, Simulation, and Model-Based Development
- 2020
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Ingår i: Modeling, Identification and Control. - Kristiansand, Norway : Norsk Forening for Automatisering. - 0332-7353 .- 1890-1328. ; 41:4, s. 241-295
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Tidskriftsartikel (refereegranskat)abstract
- OpenModelica is a unique large-scale integrated open-source Modelica- and FMI-based modeling, simulation, optimization, model-based analysis and development environment. Moreover, the OpenModelica environment provides a number of facilities such as debugging; optimization; visualization and 3D animation; web-based model editing and simulation; scripting from Modelica, Python, Julia, and Matlab; efficient simulation and co-simulation of FMI-based models; compilation for embedded systems; Modelica-UML integration; requirement verification; and generation of parallel code for multi-core architectures. The environment is based on the equation-based object-oriented Modelica language and currently uses the MetaModelica extended version of Modelica for its model compiler implementation. This overview paper gives an up-to-date description of the capabilities of the system, short overviews of used open source symbolic and numeric algorithms with pointers to published literature, tool integration aspects, some lessons learned, and the main vision behind its development.
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| 13. |
- Hällqvist, Robert, 1983-, et al.
(författare)
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A Novel FMI and TLM-based Desktop Simulator for Detailed Studies of Thermal Pilot Comfort
- 2018
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Ingår i: ICAS congress proceeding. - : International Council of the Aeronautical Sciences. - 9783932182884
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Modelling and Simulation is key in aircraft system development. This paper presents a novel, multi-purpose, desktop simulator that can be used for detailed studies of the overall performance of coupled sub-systems, preliminary control design, and multidisciplinary optimization. Here, interoperability between industrially relevant tools for model development and simulation is established via the Functional Mockup Interface (FMI) and System Structure and Parametrization (SSP) standards. Robust and distributed simulation is enabled via the Transmission Line element Method (TLM). The advantages of the presented simulator are demonstrated via an industrially relevant use-case where simulations of pilot thermal comfort are coupled to Environmental Control System (ECS) steadystate and transient performance.
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| 14. |
- Hällqvist, Robert, 1983-, et al.
(författare)
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Early Insights on FMI-based Co-Simulation of Aircraft Vehicle Systems
- 2017
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Ingår i: Proceedings of 15:th Scandinavian International Conference on Fluid Power, June 7-9, 2017, Linköping, Sweden. - Linköping : Linköping University Electronic Press. - 9789176853696 ; , s. 262-270
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Modelling and Simulation is extensively used for aircraft vehicle system development at Saab Aeronautics in Linköping, Sweden. There is an increased desire to simulate interacting sub-systems together in order to reveal, and get an understanding of, the present cross-coupling effects early on in the development cycle of aircraft vehicle systems. The co-simulation methods implemented at Saab require a significant amount of manual effort, resulting in scarcely updated simulation models, and challenges associated with simulation model scalability, etc. The Functional Mock-up Interface (FMI) standard is identified as a possible enabler for efficient and standardized export and co-simulation of simulation models developed in a wide variety of tools. However, the ability to export industrially relevant models in a standardized way is merely the first step in simulating the targeted coupled sub-systems. Selecting a platform for efficient simulation of the system under investigation is the next step. Here, a strategy for adapting coupled Modelica models of aircraft vehicle systems to TLM-based simulation is presented. An industry-grade application example is developed, implementing this strategy, to be used for preliminary investigation and evaluation of a cosimulation framework supporting the Transmission Line element Method (TLM). This application example comprises a prototype of a small-scale aircraft vehicle systems simulator. Examples of aircraft vehicle systems are environmental control systems, fuel systems, and hydraulic systems. The tightly coupled models included in the application example are developed in Dymola, OpenModelica, and Matlab/Simulink. The application example is implemented in the commercial modelling tool Dymola to provide a reference for a TLM-based master simulation tool, supporting both FMI and TLM. The TLM-based master simulation tool TLMSimulator is investigated in terms of model import according to the FMI standard with respect to a specified set of industrial needs and requirements.
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| 15. |
- Hällqvist, Robert, 1983-, et al.
(författare)
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Methods for automating model validation : Steady-state identification applied on gripen fighter environmental control system measurements
- 2016
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Ingår i: Proceedings of the 30th congress of the International Council of the Aeronautical Sciences. - : International Council of the Aeronautical Sciences. - 9783932182853
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Konferensbidrag (refereegranskat)abstract
- Model Validation and Verification (V&V) has historically often been considered a final step in the model development process. However, to justify model-based design decisions throughout the entire system development process, a methodology for continuous model V&V is essential. That is, model V&V activities should be fast and easy to reiterate as new information becomes available.Using a high fidelity simulation model of the Environmental Control System (ECS) in the Saab Gripen fighter aircraft as a guiding example, this paper further extends to an existing semiautomatic framework for model steady-state validation developed during ECS model validation efforts. Generic methods for identification of steady-state operation are a prerequisite for steady-state validation of industry grade physics based models against insitu measurements. Four different established methods for steady-state identification are investigated and compared: steady-state conditions on the standard deviation estimated from in-situ measurements, conditions on the variation coefficient, t-test on the slope of a simple regression line, and comparison of differently estimated variances. The methods’ applicability, on ECS measurements in particular, is evaluated utilizing steady-state identification needs defined during Gripen ECS model validation activities.
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| 16. |
- Hällqvist, Robert, 1983-
(författare)
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On Standardized Model Integration : Automated Validation in Aircraft System Simulation
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Designing modern aircraft is not an easy task. Today, it is not enough to optimize aircraft sub-systems at a sub-system level. Instead, a holistic approach is taken whereby the constituent sub-systems need to be designed for the best joint performance. The State-of-the-Art (SotA) in simulating and exchanging simulation models is moving forward at a fast pace. As such, the feasible use of simulation models has increased and additional benefits can be exploited, such as analysing coupled sub-systems in simulators. Furthermore, if aircraft sub-system simulation models are to be utilized to their fullest extent, opensource tooling and the use of open standards, interoperability between domain specific modeling tools, alongside robust and automated processes for model Verification and Validation (V&V) are required.The financial and safety related risks associated with aircraft development and operation require well founded design and operational decisions. If those decisions are to be founded upon information provided by models and simulators, then the credibility of that information needs to be assessed and communicated. Today, the large number of sensors available in modern aircraft enable model validation and credibility assessment on a different scale than what has been possible up to this point. This thesis aims to identify and address challenges to allow for automated, independent, and objective methods of integrating sub-system models into simulators while assessing and conveying the constituent models aggregated credibility.The results of the work include a proposed method for presenting the individual models’ aggregated credibility in a simulator. As the communicated credibility of simulators here relies on the credibility of each included model, the assembly procedure itself cannot introduce unknown discrepancies with respect to the System of Interest (SoI). Available methods for the accurate simulation of coupled models are therefore exploited and tailored to the applications of aircraft development under consideration. Finally, a framework for automated model validation is outlined, supporting on-line simulator credibility assessment according to the presented proposed method.
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| 17. |
- Hällqvist, Robert, 1983-
(författare)
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On the Realization of Credible Simulations in Aircraft Development : Efficient and Independent Validation Enabled by Automation
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Designing modern aircraft is not an easy task. Today, it is not enough to optimize aircraft subsystems at a subsystem level. Instead, a holistic approach is necessary whereby the constituent subsystems need to be designed for the best joint performance. The State-of-the-Art (SotA) in simulating and ex-changing simulation models is moving forward at a fast pace. As such, the feasible use of simulation models has increased and additional benefits can be exploited, such as analyzing coupled subsystems in simulators. Furthermore, if aircraft subsystem simulation models are to be utilized to their fullest extent, open-source tooling and the use of open standards, interoperability between domain specific modeling tools, alongside efficient and automated processes for model Verification and Validation (V&V) and credibility assessment are required.The financial and safety related risks associated with aircraft development and operation require well founded design and operational decisions. If those decisions are to be founded upon information provided by models and simulators, then the credibility of that information needs to be assessed and communicated. Today, the large number of sensors available in modern aircraft enable model validation and credibility assessment on a different scale than what has been possible up to this point. This thesis aims to identify and address challenges to allow for automated, independent, and objective methods of integrating subsystem models into simulators while assessing and conveying the constituent models aggregated credibility.The results of the work include a proposed method for presenting the individual models’ aggregated credibility in a simulator. As the communicated credibility of simulators here relies on the credibility of each included model, the assembly procedure itself cannot introduce unknown discrepancies with respect to the System of Interest (SoI). Available methods for the management, distribution, and accurate simulation of coupled models are therefore exploited and tailored to the applications of aircraft development under consideration. Finally, a framework for automated model validation is outlined and established that supports both on-line and on-line simulator credibility assessment.
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| 18. |
- Hällqvist, Robert, 1983-, et al.
(författare)
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Optimal Selection of Model Validation Experiments : Guided by Coverage
- 2021
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Ingår i: Journal of Verification, Validation and Uncertainty Quantification. - New York : The American Society of Mechanical Engineers. - 2377-2158 .- 2377-2166. ; 6:3
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Tidskriftsartikel (refereegranskat)abstract
- Modeling and Simulation (M&S) is seen as a means to mitigate the difficulties associated with increased system complexity, integration, and cross-couplings effects encountered during development of aircraft subsystems. As a consequence, knowledge of model validity is necessary for taking robust and justified design decisions. This paper presents a method for using coverage metrics to formulate an optimal model validation strategy. Three fundamentally different and industrially relevant use-cases are presented. The first use-case entails the successive identification of validation settings, and the second considers the simultaneous identification of n validation settings. The latter of these two use-cases is finally expanded to incorporate a secondary model-based objective to the optimization problem in a third use-case. The approach presented is designed to be scalable and generic to models of industrially relevant complexity. As a result, selecting experiments for validation is done objectively with little required manual effort.
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| 19. |
- Hällqvist, Robert, et al.
(författare)
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Realizing Interoperability between MBSE Domains in Aircraft System Development
- 2022
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Ingår i: Electronics. - : MDPI. - 2079-9292. ; 11:18
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Tidskriftsartikel (refereegranskat)abstract
- Establishing interoperability is an essential aspect of the often-pursued shift towards Model-Based Systems Engineering (MBSE) in, for example, aircraft development. If models are to be the primary information carriers during development, the applied methods to enable interaction between engineering domains need to be modular, reusable, and scalable. Given the long life cycles and often large and heterogeneous development organizations in the aircraft industry, a piece to the overall solution could be to rely on open standards and tools. In this paper, the standards Functional Mock-up Interface (FMI) and System Structure and Parameterization (SSP) are exploited to exchange data between the disciplines of systems simulation and geometry modeling. A method to export data from the 3D Computer Aided Design (CAD) Software (SW) CATIA in the SSP format is developed and presented. Analogously, FMI support of the Modeling & Simulation (M&S) tools OMSimulator, OpenModelica, and Dymola is utilized along with the SSP support of OMSimulator. The developed technology is put into context by means of integration with the M&S methodology for aircraft vehicle system development deployed at Saab Aeronautics. Finally, the established interoperability is demonstrated on two different industrially relevant application examples addressing varying aspects of complexity. A primary goal of the research is to prototype and demonstrate functionality, enabled by the SSP and FMI standards, that could improve on MBSE methodology implemented in industry and academia.
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| 20. |
- Hällqvist, Robert, 1983-, et al.
(författare)
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Toward Objective Assessment of Simulation Predictive Capability
- 2023
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Ingår i: Journal of Aerospace Information Systems. - : American Institute of Aeronautics and Astronautics. - 1940-3151. ; 20:3, s. 152-167
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Tidskriftsartikel (refereegranskat)abstract
- Two different metrics quantifying model and simulator predictive capability are formulated and evaluated; both metrics exploit results from conducted validation experiments where simulation results are compared to the corresponding measured quantities. The first metric is inspired by the modified nearest neighbor coverage metric and the second by the Kullback-Liebler divergence. The two different metrics are implemented in Python and in a here-developed general metamodel designed to be applicable for most physics-based simulation models. These two implementations together facilitate both offline and online metric evaluation. Additionally, a connection between the two, here separated, concepts of predictive capability and credibility is established and realized in the metamodel. The two implementations are, finally, evaluated in an aeronautical domain context.
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| 21. |
- Oliveros, Carl H., et al.
(författare)
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Earth history and the passerine superradiation
- 2019
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 116:16, s. 7916-7925
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Tidskriftsartikel (refereegranskat)abstract
- Avian diversification has been influenced by global climate change, plate tectonic movements, and mass extinction events. However, the impact of these factors on the diversification of the hyper-diverse perching birds (passerines) is unclear because family level relationships are unresolved and the timing of splitting events among lineages is uncertain. We analyzed DNA data from 4,060 nuclear loci and 137 passerine families using concatenation and coalescent approaches to infer a comprehensive phylogenetic hypothesis that clarifies relationships among all passerine families. Then, we calibrated this phylogeny using 13 fossils to examine the effects of different events in Earth history on the timing and rate of passerine diversification. Our analyses reconcile passerine diversification with the fossil and geological records; suggest that passerines originated on the Australian landmass ∼47 Ma; and show that subsequent dispersal and diversification of passerines was affected by a number of climatological and geological events, such as Oligocene glaciation and inundation of the New Zealand landmass. Although passerine diversification rates fluctuated throughout the Cenozoic, we find no link between the rate of passerine diversification and Cenozoic global temperature, and our analyses show that the increases in passerine diversification rate we observe are disconnected from the colonization of new continents. Taken together, these results suggest more complex mechanisms than temperature change or ecological opportunity have controlled macroscale patterns of passerine speciation.
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| 22. |
- Thompson, Luke R., et al.
(författare)
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A communal catalogue reveals Earth's multiscale microbial diversity
- 2017
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 551:7681, s. 457-463
-
Tidskriftsartikel (refereegranskat)abstract
- © 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. Our growing awareness of the microbial world's importance and diversity contrasts starkly with our limited understanding of its fundamental structure. Despite recent advances in DNA sequencing, a lack of standardized protocols and common analytical frameworks impedes comparisons among studies, hindering the development of global inferences about microbial life on Earth. Here we present a meta-analysis of microbial community samples collected by hundreds of researchers for the Earth Microbiome Project. Coordinated protocols and new analytical methods, particularly the use of exact sequences instead of clustered operational taxonomic units, enable bacterial and archaeal ribosomal RNA gene sequences to be followed across multiple studies and allow us to explore patterns of diversity at an unprecedented scale. The result is both a reference database giving global context to DNA sequence data and a framework for incorporating data from future studies, fostering increasingly complete characterization of Earth's microbial diversity.
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| 23. |
- Acciari, V. A., et al.
(författare)
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Radio Imaging of the Very-High-Energy gamma-Ray Emission Region in the Central Engine of a Radio Galaxy
- 2009
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 325:5939, s. 444-448
-
Tidskriftsartikel (refereegranskat)abstract
- The accretion of matter onto a massive black hole is believed to feed the relativistic plasma jets found in many active galactic nuclei (AGN). Although some AGN accelerate particles to energies exceeding 10(12) electron volts and are bright sources of very-high-energy (VHE) gamma-ray emission, it is not yet known where the VHE emission originates. Here we report on radio and VHE observations of the radio galaxy Messier 87, revealing a period of extremely strong VHE gamma-ray flares accompanied by a strong increase of the radio flux from its nucleus. These results imply that charged particles are accelerated to very high energies in the immediate vicinity of the black hole.
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| 24. |
- Ahlenius, Henrik, et al.
(författare)
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Adaptor Protein LNK Is a Negative Regulator of Brain Neural Stem Cell Proliferation after Stroke.
- 2012
-
Ingår i: The Journal of Neuroscience : the official journal of the Society for Neuroscience. - 1529-2401. ; 32:15, s. 5151-5164
-
Tidskriftsartikel (refereegranskat)abstract
- Ischemic stroke causes transient increase of neural stem and progenitor cell (NSPC) proliferation in the subventricular zone (SVZ), and migration of newly formed neuroblasts toward the damaged area where they mature to striatal neurons. The molecular mechanisms regulating this plastic response, probably involved in structural reorganization and functional recovery, are poorly understood. The adaptor protein LNK suppresses hematopoietic stem cell self-renewal, but its presence and role in the brain are poorly understood. Here we demonstrate that LNK is expressed in NSPCs in the adult mouse and human SVZ. Lnk(-/-) mice exhibited increased NSPC proliferation after stroke, but not in intact brain or following status epilepticus. Deletion of Lnk caused increased NSPC proliferation while overexpression decreased mitotic activity of these cells in vitro. We found that Lnk expression after stroke increased in SVZ through the transcription factors STAT1/3. LNK attenuated insulin-like growth factor 1 signaling by inhibition of AKT phosphorylation, resulting in reduced NSPC proliferation. Our findings identify LNK as a stroke-specific, endogenous negative regulator of NSPC proliferation, and suggest that LNK signaling is a novel mechanism influencing plastic responses in postischemic brain.
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| 25. |
- Axin, Mikael, 1984-, et al.
(författare)
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Next Generation Simulation Software using Transmission Line Elements
- 2010
-
Ingår i: Fluid Power and Motion Control. - : Centre for Power Transmission and Motion Control. - 9781861971814 ; , s. 265-276
-
Konferensbidrag (refereegranskat)abstract
- A suitable method for simulating large complex dynamic systems is represented by distributed modelling using transmission line elements. The method is applicable to all physical systems, such as mechanical, electrical and pneumatics, but is particularly well suited to simulate systems where wave propagation is an important issue, for instance hydraulic systems. By using this method, components can be numerically isolated from each other, which provide highly robust numerical properties. It also enables the use of multi-core architecture since a system model can be composed by distributed simulations of subsystems on different processor cores.Technologies based on transmission lines has successfully been implemented in the HOPSAN simulation package, develop at Linköping University. Currently, the next generation of HOPSAN is developed using an object-oriented approach. The work is focused on compatibility, execution speed and real-time simulation in order to facilitate hardware-in-the-loop applications. This paper presents the work progress and some possible features in the new version of the HOPSAN simulation package.
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| 26. |
- Blazhev, A, et al.
(författare)
-
High-energy Excited States in 98Cd
- 2010
-
Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596. ; 205
-
Tidskriftsartikel (refereegranskat)abstract
- In 98Cd a new high-energy isomeric γ-ray transition was identified, which confirms previous spin-parity assignments and enables for the first time the measurement of the E2 and E4 strength for the two decay branches of the isomer. Preliminary results on the 98Cd high-excitation level scheme are presented. A comparison to shell-model calculations as well as implications for the nuclear structure around 100Sn are discussed.
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| 27. |
- Boutachkov, P., et al.
(författare)
-
High-spin isomers in 96Ag : excitations across the Z=38 and Z=50, N=50 closed shells
- 2011
-
Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 84:4
-
Tidskriftsartikel (refereegranskat)abstract
- Excited states in (96)Ag were populated in fragmentation of an 850-MeV/u (124)Xe beam on a 4-g/cm(2) Be target. Three new high-spin isomers were identified and the structure of the populated states was investigated. The level scheme of (96)Ag was established, and a spin parity of (13(-)), (15(+)), and (19(+)) was assigned to the new isomeric states. Shell-model calculations were performed in various model spaces, including pi nu(p(1/2), g(9/2), f(5/2), p(3/2)) and the large-scale shell-model space pi nu(gds), to account for the observed parity changing M2 and E3 transitions from the (13(-)) isomer and the E2 and E4 transitions from the (19(+)) core-excited isomer, respectively. The calculated level schemes and reduced transition strengths are found to be in very good agreement with the experiment.
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| 28. |
- Boutachkov, P., et al.
(författare)
-
Isomer and Beta-decay Spectroscopy of Tz=1 Isotopes Below the N=Z=50 Shell Gap
- 2011
-
Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 312:9
-
Tidskriftsartikel (refereegranskat)abstract
- The RISING setup at the GSI-FRS facility was used to investigate the isomer and beta decays in N~Z~50 Cd, Ag and Pd isotopes. A preliminary analysis of the data has revealed new results on the Tz=1, 94Pd, 96Ag and 98Cd isotopes. In 94Pd a new high-spin isomer was observed, whilst in 96Ag 3 new isomeric states were identified, including core-excited states. In 98Cd a new high-energy isomeric γ-ray transition is observed, thus enabling us to confirm the previous spin assignment for the core-excited 12+ isomer.
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| 29. |
- Braun, Benjamin, et al.
(författare)
-
Detecting the integer decomposition property and Ehrhart unimodality in reflexive simplices
- 2018
-
Ingår i: Advances in Applied Mathematics. - : Academic Press. - 0196-8858 .- 1090-2074. ; 100, s. 122-142
-
Tidskriftsartikel (refereegranskat)abstract
- A long-standing open conjecture in combinatorics asserts that a Gorenstein lattice polytope with the integer decomposition property (IDP) has a unimodal (Ehrhart) h*-polynomial. This conjecture can be viewed as a strengthening of a previously disproved conjecture which stated that any Gorenstein lattice polytope has a unimodal h*-polynomial. The first counterexamples to unimodality for Gorenstein lattice polytopes were given in even dimensions greater than five by Mustata and Payne, and this was extended to all dimensions greater than five by Payne. While there exist numerous examples in support of the conjecture that IDP reflexives are h*-unimodal, its validity has not yet been considered for families of reflexive lattice simplices that closely generalize Payne's counterexamples. The main purpose of this work is to prove that the former conjecture does indeed hold for a natural generalization of Payne's examples. The second purpose of this work is to extend this investigation to a broader class of lattice simplices, for which we present new results and open problems.
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| 30. |
- Braun, Gabriel A., et al.
(författare)
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On the Mechanism of Self-Assembly by a Hydrogel-Forming Peptide
- 2020
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 21:12, s. 4781-4794
-
Tidskriftsartikel (refereegranskat)abstract
- Self-assembling peptide-based hydrogels are a class of tunable soft materials that have been shown to be highly useful for a number of biomedical applications. The dynamic formation of the supramolecular fibrils that compose these materials has heretofore remained poorly characterized. A better understanding of this process would provide important insights into the behavior of these systems and could aid in the rational design of new peptide hydrogels. Here, we report the determination of the microscopic steps that underpin the self-assembly of a hydrogel-forming peptide, SgI37-49. Using theoretical models of linear polymerization to analyze the kinetic self-assembly data, we show that SgI37-49 fibril formation is driven by fibril-catalyzed secondary nucleation and that all the microscopic processes involved in SgI37-49 self-assembly display an enzyme-like saturation behavior. Moreover, this analysis allows us to quantify the rates of the underlying processes at different peptide concentrations and to calculate the time evolution of these reaction rates over the time course of self-assembly. We demonstrate here a new mechanistic approach for the study of self-assembling hydrogel-forming peptides, which is complementary to commonly used materials science characterization techniques.
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| 31. |
- Braun, Robert, 1984-, et al.
(författare)
-
An Explicit Method for Decoupled Distributed Solvers in an Equation-Based Modelling Language
- 2014
-
Ingår i: Proceedings of the 6th International Workshop on Equation-Based Object-Oriented Modeling Languages and Tools. - New York : Association for Computing Machinery (ACM). - 9781450329538 ; , s. 57-64
-
Konferensbidrag (refereegranskat)abstract
- The Modelica language offers an intuitive way to create object-oriented models. This makes it natural also to use an object-oriented solver, where each sub-model solves its own equations. Doing so is possible only if sub-models can be made independent from the rest of the model. One way to achieve this is to use distributed solvers by separating sub-models with transmission line elements. This offers robust and predictable simulations, simplified model debugging and natural parallelism. It also makes it possible to use different time steps and solver algorithms in different parts of the model to achieve an optimal trade-off between performance and accuracy. The suggested method has been implemented in the Hopsan simulation environment. Different modelling techniques for taking advantage of the distributed solver approach are explained. Finally, three example models are used to demonstrate the method.
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| 32. |
- Braun, Robert, 1984-, et al.
(författare)
-
An Open-Source Framework for Efficient Co-simulation of Fluid Power Systems
- 2017
-
Ingår i: Proceedings of 15th Scandinavian International Conference on Fluid Power, SICFP’17. - Linköping : Linköping University Electronic Press. - 9789176853696 ; , s. 393-400
-
Konferensbidrag (refereegranskat)abstract
- Simulation of fluid power systems typically requires models from multiple disciplines.Achieving accurate load dynamics for a system with complex geometry, for example, mayrequire both a 1D model of the hydraulic circuit and a 3D multi-body model. However, mostsimulation tools are limited to a single discipline. A solution to these kinds of problems isco-simulation, where different tools are coupled and simulated together. Co-simulation canprovide increased accuracy, improved modularity and facilitated collaboration between dif-ferent organizations. Unfortunately, tool coupling typically requires tedious and error-pronemanual work. It may also introduce numerical problems. For these reasons, co-simulation isoften avoided as long as possible. These problems have been addressed by the developmentof an open-source framework for asynchronous co-simulation. Simulation tools can be inter-connected through a stand-alone master simulation tool. An extensive range of tools is alsosupported via the Functional Mockup Interface standard. A graphical user interface has beenimplemented in the OpenModelica Connection Editor. System models can be created andedited from both a schematic view and a 3D view. Numerical robustness is enforced by theuse of transmission line modelling. A minimalistic programming interface consisting of onlytwo functions is used. An example model consisting of a hydraulic crane with two arms, twoactuators and a hanging load is used to verify the framework. The composite model consistsof nine multi-body models, one hydraulic system model and a controller. It is shown thatmodels from various simulation tools can be replaced with a minimal amount of user input.
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| 33. |
- Braun, Robert
(författare)
-
Distributed System Simulation Methods : For Model-Based Product Development
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Distributed system simulation can increase performance, re-usability and modularity in model-based product development. This thesis investigates four aspects of distributed simulation: multi-threaded simulations, simulation tool coupling, distributed equation solvers and parallel optimization algorithms.Multi-threaded simulation makes it possible to split up the workload over several processing units. This reduces simulation time, which can save both time and money during the product development cycle. The transmission line element method (TLM) is used to decouple models to independent sub-models.Different simulation tools are suitable for different problems. Tool coupling makes it possible to use the best suited tool for simulating each part of the whole product. Models from different tools can then be coupled into one aggregated simulation model. An emerging standard for tool coupling is the Functional Mock-up Interface (FMI). It is investigated how this can be used in conjunction with TLM.Equation-based object-oriented languages (EOOs) are becoming increasing popular. A logical approach is to let the equation solvers maintain the same structure that was used in the modelling process. Methods for achieving this using TLM and FMI are implemented and evaluated.In addition to parallel simulations, it is also possible to use parallel optimization algorithms. This introduces parallelism on several levels. For this reason, an algorithm for profile-based multi-level scheduling is proposed.
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| 34. |
- Braun, Robert, et al.
(författare)
-
Full Vehicle Simulation of Forwarder with Semi Active Suspension using Co-simulation
- 2016
-
Konferensbidrag (refereegranskat)abstract
- A major concern in the forest industry is impact on the soil caused by forest machines during harvesting. A six-wheel pendulum arm forwarder is being developed. The new forwarder aims at reducing soil damage by an even pressure distribution and smooth torque control and thereby also improving the working environment. The suspension contains pendulum arms on each wheel controlled by a hydraulic load sensing system in combination with accumulator.A natural approach is to model each part of a system in the bestsuited software. In this case, the hydraulic system is modelled in the Hopsan simulation tool, while the vehicle mechanics is modelled in Adams. To understand the whole system it is necessary to simulate all subsystems together. An open standard for this is the Functional Mock-up Interface. This makes it possible to investigate the interaction between the hydraulic system and the multi-body mechanic model.This paper describes how different simulation tools can be combined to support the development process. The technique is applied to the forwarder’s pendulum suspension. Controllers for height and soil force are optimized to minimize soil damage and maximize comfort for the operator.
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| 35. |
- Braun, Robert, 1984-, et al.
(författare)
-
High Performance System Simulation Using Multiple Processor Cores
- 2011
-
Ingår i: The Twelfth Scandinavian International Conference on Fluid Power, SICFP'11. - 9789521525179 - 9789521525209 - 9789521532733
-
Konferensbidrag (refereegranskat)abstract
- Future research and development will depend on high-speed simulations, especially for large and complex systems. Rapid prototyping, optimization and real-time simulations require simulation tools that can take full advantage of computer hardware. Recent developments in the computer market indicate a change in focus from increasing the speed of processor cores towards increasing the number of cores in each processor. HOPSAN is a simulation tool for fluid power and mechatronics, developed at Linköping University. It is based upon the transmission line modeling (TLM) technique. This method is very suitable for taking advantage of multi-core processors. This paper presents the implementation of multi-core support in the next generation of HOPSAN. The concept is to divide the model into equally sized groups of independent components, to make it possible to simulate them in separate threads. Reducing overhead costs and finding an effective sorting algorithm constitute critical steps for maximizing the benefits. Experimental results show a significant reduction in simulation time. Improvement of algorithms in combination with a continuous increase in the number of processor cores can potentially lead to further increases in simulation performance.
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| 36. |
- Braun, Robert, 1984-, et al.
(författare)
-
Hopsan: An Open-Source Tool for Rapid Modelling and Simulation of Fluid and Mechatronic Systems
- 2020
-
Ingår i: Proceedings of the BATH/ASME 2020 Symposium on Fluid Power and Motion Control (FPMC2020). - : American Society of Mechanical Engineers (ASME). - 9780791883754
-
Konferensbidrag (refereegranskat)abstract
- Hopsan is an open-source simulation package developed as a collaboration project between industry and academia. The simulation methodology is based on transmission line modelling, which provides several benefits such as linear model scalability, numerical robustness and parallel simulation. All sub-models are pre-compiled, so that no compilation is required prior to starting a simulation. Default component libraries are available for hydraulic, mechanic, pneumatic, electric and signal domains. Custom components can be written in C++ or generated from Modelica and Mathematica. Support for simulation-based optimization is provided using population-based, evolutionary or direct-search algorithms. Recent research has largely focused on co-simulation with other simulation tools. This is achieved either by using the Functional Mock-up Interface standard, or by tool-to-tool communications. This paper provides a description of the program and its features, the current status of the project, and an overview of recent and ongoing use cases from industry and academia.
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| 37. |
- Braun, Robert, et al.
(författare)
-
Improved Scheduling Techniques for Parallel Distributed-Solver System Simulation
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Shortening simulation time is an important step towards efficient simulation-based product development. A long-used method is to exploit physically motivated time delays to split up the model into distributed solvers. In this way, the use of a centralized sequential solver can be circumvented. For maximum simulation performance, however, an efficient scheduling technique is also required. Four task scheduling methods for distributed-solver simulations has been implemented and evaluated. Experiments indicate that the best choice largely depend on model size, load distribution and granularity. Lock-based barrier synchronization provides the highest speed-up for small models. A fork-join implementation, with implicit synchronization and work-stealing scheduling, works better for models with a large total workload. It is common that workload and load distribution of a simulation model varies during execution depending on the current state of the simulation. Three of the implemented schedulers support dynamic load balancing during execution. Results show that task-stealing is the most efficient method for the specific test model. A possible continuation of this work is an automatic selection of the best scheduling technique based on knowledge about model properties and available computer resources.
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| 38. |
- Braun, Robert
(författare)
-
Multi-Threaded Distributed System Simulations : Using Bi-Lateral Delay Lines
- 2013
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As the speed increase of single-core processors keeps declining, it is important to adapt simulation software to take advantage of multi-core technology. There is a great need for simulating large-scale systems with good performance. This makes it possible to investigate how different parts of a system work together, without the need for expensive physical prototypes. For this to be useful, however, the simulations cannot take too long, because this would delay the design process. Some uses of simulation also put very high demands on simulation performance, such as real-time simulations, design optimization or Monte Carlo-based sensitivity analysis. Being able to quickly simulate large-scale models can save much time and money.The power required to cool a processor is proportional to the processor speed squared. It is therefore no longer profitable to keep increasing the speed. This is commonly referred to as the "power wall". Manufacturers of processors have instead begun to focus on building multi-core processors consisting of several cores working in parallel. Adapting program code to multi-core architectures constitutes a major challenge for software developers.Traditional simulation software uses centralized equation-system solvers, which by nature are hard to make parallel. By instead using distributed solvers, equations from different parts of the model can be solved simultaneously. For this to be effective, it is important to minimize overheadcosts and to make sure that the workload is evenly distributed over the processor cores.Dividing an equation system into several parts and solving them separately means that time delays will be introduced between the parts. If these occur in the right locations, this can be physically correct, since it also takes some time for information to propagate in physical systems. The transmission line element method (TLM) constitutes an effective method for separating system models by introducing impedances between components, causing physically motivated time delays.Contributions in this thesis include parts of the development of the new generation of the Hopsan simulation tool, with support for TLM and distributed solvers. An automatic algorithm for partitioning models has been developed. A multi-threaded simulation algorithm using barrier synchronization has also been implemented.Measurements of simulation time confirm that the simulation time is decreased almost proportionally to the number of processor cores for large models. The decrease, however, is reduced if the cores are divided on different processors. This was expected, due to the communication delay for processors communicating over shared memory. Experiments on real-time systems with four cores show that a four times as large model can be simulated without losing real-time performance.The division into distributed solvers constitutes a sort of natural cosimulation. A future project could be to use this as a platform for linking different simulation tools together and simulating them with high performance. This would make it possible to model each part of the system in the most suitable tool, and then connect all parts into one large model.
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| 39. |
- Braun, Robert, et al.
(författare)
-
Multi-Threaded Distributed System Simulations Using the Transmission Line Element Method
- 2016
-
Ingår i: Simulation (San Diego, Calif.). - : Sage Publications. - 0037-5497 .- 1741-3133. ; 92:10, s. 921-930
-
Tidskriftsartikel (refereegranskat)abstract
- By introducing physically motivated time delays, simulation models can be partitioned into decoupled independent sub-models. This enables parallel simulations on multi-core processors. An automatic algorithm is used for partitioning and running distributed system simulations. Methods for sorting and distributing components for good load balancing have been developed. Mathematical correctness during simulation is maintained by a busy-waiting thread synchronization algorithm. Independence between sub-models is achieved by using the transmission line element method. In contrast to the more commonly used centralized solvers, this method uses distributed solvers with physically motivated time delays, making simulations inherently parallel. Results show that simulation speed increases almost proportionally to the number of processor cores in the case of large models. However, overhead time costs mean that models need to be over a certain size to benefit from parallelization.
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| 40. |
- Braun, Robert, 1984-, et al.
(författare)
-
Multi-Threaded Real-Time Simulations of Fluid Power Systems Using Transmission Line Elements
- 2012
-
Konferensbidrag (refereegranskat)abstract
- The demand for large-scale real-time simulations of fluid power systems is in-creasing, due to growing demands for added functionality. Real-time simulationscan be used in for example hardware-in-the-loop experiments and embeddedcontrol systems. In order to achieve real-time performance, it is often necessaryto use small or simplified models, reducing the usefulness and accuracy of theresults. This article proposes the use of transmission line modelling (TLM) forexploiting multi-core hardware in real-time and embedded systems. The charac-teristics of the TLM method are analysed to identify difficulties and possibilities.A method for how to parallelise TLM models is then presented. Subsequently, aprogramming interface for implementing the parallel models in the target systemsis introduced. Practical experiments show that the approach works and that themethod is applicable. So far, however, it has required great effort on the part ofthe engineer, both when it comes to programming, compiling and importing themodel into the target environments, although some attempts to automate the pro-cedure have been successful, reducing the level of complexity.
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| 41. |
- Braun, Robert, 1984-, et al.
(författare)
-
Numerically robust co-simulation using transmission line modeling and the Functional Mock-up Interface
- 2022
-
Ingår i: Simulation (San Diego, Calif.). - : Sage Publications Ltd. - 0037-5497 .- 1741-3133. ; 98:11, s. 1057-1070
-
Tidskriftsartikel (refereegranskat)abstract
- Modeling and simulation are important tools for efficient product development. There is a growing need for collaboration, interdisciplinary simulation, and re-usability of simulation models. This usually requires simulation tools to be coupled together for co-simulation. However, the usefulness of co-simulation is often limited by poor performance and numerical instability. Achieving stability is especially hard for stiff mechanical couplings. A suitable method is to use transmission line modeling (TLM), which separates submodels using physically motivated time delays. The most established standard for tool coupling today is the Functional Mock-up Interface (FMI). Two example models in one dimension and three dimensions are used to demonstrate how the next version of FMI for co-simulation can be used in conjunction with TLM. The stability properties of TLM are also proven by numerical analysis. Results show that numerical stability can be ensured without compromising on performance. With the current FMI standard, this requires tailor-made models and custom solutions for the interpolation of input variables. Without using custom solutions, variables must be exchanged using sampled communication and extrapolation. In this case, stability properties can be improved by reducing communication step size. However, it is shown that stability cannot be achieved even when using unacceptably small communication steps. This motivates the need for the next version of FMI to include an intermediate update mode, where variables can be interchanged in between communication points. It is suggested that the FMI standard should be extended with optional callback functions for providing intermediate output variables and requesting intermediate input variables.
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| 42. |
- Braun, Robert, et al.
(författare)
-
Parallel Implementations of the Complex-RF Algorithm
- 2017
-
Ingår i: Engineering optimization (Print). - : Taylor & Francis. - 0305-215X .- 1029-0273. ; 49:9, s. 1558-1572
-
Tidskriftsartikel (refereegranskat)abstract
- Even though direct-search optimization methods are more difficult to parallelize than population-based methods, there are many unexploited opportunities. Five methods for parallelizing the Complex-RF methods have been implemented and evaluated. Three methods are based on the unchanged original algorithm, while two require modifications. The methods have been tested on two test function and one real simulation model. An analysis of the algorithm has been performed. This provides a basis for parametrization of the parallel methods. Without changing the original algorithm, speed-up of 2.5-3 is achieved. With allowing modifications, a speed-up of up to 5 is obtained without significantly reducing the probability of finding the global minimum. Speed-up does not scale linear to the number of threads. When more threads are added, parallelization efficiency decreases. However, a comparison with a particle swarm method shows that Complex-RF performs better regardless of the number of threads, due to its fast convergence rate.
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| 43. |
- Braun, Robert, et al.
(författare)
-
Tool-Independent Distributed Simulations Using Transmission Line Elements And The Functional Mock-up Interface
- 2013
-
Konferensbidrag (refereegranskat)abstract
- This paper describes how models from different simulation tools can be connected and simulated on different processors by using the Functional Mockup Interface (FMI) and the transmission line element method (TLM). Interconnectivity between programs makes it possible to model each part of a complex system with the best suited tool, which will shorten the modelling time and increase the accuracy of the results. Because the system will be naturally partitioned, it is possible to identify weak links and replace them with transmission line elements, thereby introducing a controlled time delay. This makes the different parts of the system naturally independent, making it possible to simulate large aggregated system models with good performance on multi-core processors. The proposed method is demonstrated on an example model. A suggestion of an XML extension to the FMI standard for describing TLM ports is also presented.
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| 44. |
- Braun, Robert, 1984-, et al.
(författare)
-
Towards A Parallel Distributed Equation-Based Simulation Environment
- 2012
-
Ingår i: 53rd SIMS Conference on Simulation and Modelling.
-
Konferensbidrag (refereegranskat)abstract
- Distributed solvers provide several benefits, such as linear scalability and good numerical robustness. By separating components with transmission line elements, simulations can be run in parallel on multi-core processors. At the same time, equation-based modelling offers an intuitive way of writing models. This paper presents an algorithm for generating distributed models from Modelica code using bilinear transform. This also enables hard limitations on variables and their derivatives. The generated Jacobian is linearised and solved using LU-decomposition. The algorithm is implemented in the Hopsan simulation tool. Equations are transformed and differentiated by using the SymPy package for symbolic mathematics. An example model is created andverified against a reference model. Simulation results are similar, but the equation-based model is four to five times slower. Further optimisation of the algorithm is thus required. The future aim is to develop a distributed simulation environment with integrated support for equation-based modelling.
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| 45. |
- Brock, T. S., et al.
(författare)
-
Observation of a new high-spin isomer in Pd-94
- 2010
-
Ingår i: Physical Review C. Nuclear Physics. - 0556-2813 .- 1089-490X. ; 82:6, s. 061309-
-
Tidskriftsartikel (refereegranskat)abstract
- A second gamma-decaying high-spin isomeric state, with a half-life of 197(22) ns, has been identified in the N = Z + 2 nuclide Pd-94 as part of a stopped-beam Rare Isotope Spectroscopic INvestigation at GSI (RISING) experiment. Weisskopf estimates were used to establish a tentative spin/parity of 19(-), corresponding to the maximum possible spin of a negative parity state in the restricted (p(1/2), g(9/2)) model space of empirical shell model calculations. The reproduction of the E3 decay properties of the isomer required an extension of the model space to include the f (5/2) and p(3/2) orbitals using the CD-Bonn potential. This is the first time that such an extension has been required for a high-spin isomer in the vicinity of Sn-100 and reveals the importance of such orbits for understanding the decay properties of high-spin isomers in this region. However, despite the need for the extended model space for the E3 decay, the dominant configuration for the 19(-) state remains (p p(1/2)(-1)g(9/2)(-3))(11)circle times(nu g(9/2)(-2))(8). The half-life of the known, 14(+), isomer was remeasured and yielded a value of 499(13) ns.
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| 46. |
- Carozzi, Tobia, 1966, et al.
(författare)
-
Differentially Rotated SKALA4.1 Antennas in Vogel Configurations
- 2023
-
Ingår i: 2023 35th General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2023.
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Konferensbidrag (refereegranskat)abstract
- We have studied the effects of non-aligned SKALA4.1 antennas in dense arrays with a Vogel layout. We find that the Vogel array is too dense at 2 m minimum inter-element distance for differential alignments to mitigate mutual-coupling, but polarimetric performance can be improved regardless.
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| 47. |
- Chernobryvko, Mykola, et al.
(författare)
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High-Q Ku-band Microstrip Spiral Resonator in Fan-out Wafer-Level Packaging (FoWLP) Technology for VCO Applications
- 2023
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Ingår i: Advancing Microelectronics. - 2222-8748. ; 2023:Special issue EMPC, s. 57-60
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a planar spiral resonator operating at 13 GHz is investigated. The resonator was fabricated using fan-out wafer level packaging (FoWLP) technology. The field analysis highlights the importance of via fence. Two thick film resistors suppress an undesired resonance in proximity of targeted one. The measurements demonstrate a very good correlation in comparison with full-wave simulations. The measured Q-factor defined based on analysis of feedback oscillatory system is about 48. The proposed configuration is suitable for voltage-controlled oscillators (VCOs) with a resonator realized in package.
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| 48. |
- Chodnicki, Marek, et al.
(författare)
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Project-Based Collaborative Research and Training Roadmap for Manufacturing Based on Industry 4.0
- 2024
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Ingår i: Flexible Automation and Intelligent Manufacturing. - : Springer Nature. ; , s. 708-715
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Konferensbidrag (refereegranskat)abstract
- The importance of the economy being up to date with the latest developments, such as Industry 4.0, is more evident than ever before. Successful implementation of Industry 4.0 principles requires close cooperation of industry and state authorities with universities. A paradigm of such cooperation is described in this paper stemming from university partners with partly overlapping and partly complementary areas of expertise in manufacturing. Specific areas that are targeted include Additive Manufacturing, cloud computing and control, Virtual Reality, Digital Twins, and Artificial Intelligence. The manufacturing system domains that are served pertaining to process planning and optimization, process and system monitoring, and innovative / precision manufacturing. The described collaborative research and training framework involves a combination of pertinent targeted individual exploratory innovation projects as well as a synthetic multifaceted common research project. Based on these, the research and innovation project knowledge will be transferred to the industry by building a Cluster of Excellence, i.e., a network consisting of academic and industrial stakeholders.
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| 49. |
- Deleu, Magali, et al.
(författare)
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Effects of surfactin on membrane models displaying lipid phase separation
- 2013
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Ingår i: Biochimica et Biophysica Acta - Biomembranes. - : Elsevier BV. - 0005-2736. ; 1828:2, s. 801-815
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Tidskriftsartikel (refereegranskat)abstract
- Surfactin, a bacterial amphiphilic lipopeptide is attracting more and more attention in view of its bioactive properties which are in relation with its ability to interact with lipids of biological membranes. In this work, we investigated the effect of surfactin on membrane structure using model of membranes, vesicles as well as supported bilayers, presenting coexistence of fluid-disordered (DOPC) and gel (DPPC) phases. A range of complementary methods was used including AFM, ellipsometry, dynamic light scattering, fluorescence measurements of Laurdan, DPH, calcein release, and octadecylrhodamine B dequenching. Our findings demonstrated that surfactin concentration is critical for its effect on the membrane. The results suggest that the presence of rigid domains can play an essential role in the first step of surfactin insertion and that surfactin interacts both with the membrane polar heads and the acyl chain region. A mechanism for the surfactin lipid membrane interaction, consisting of three sequential structural and morphological changes, is proposed. At concentrations below the CMC, surfactin inserted at the boundary between gel and fluid lipid domains, inhibited phase separation and stiffened the bilayer without global morphological change of liposomes. At concentrations close to CMC, surfactin solubilized the fluid phospholipid phase and increased order in the remainder of the lipid bilayer. At higher surfactin concentrations, both the fluid and the rigid bilayer structures were dissolved into mixed micelles and other structures presenting a wide size distribution. (C) 2012 Elsevier B.V. All rights reserved.
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| 50. |
- Eberbeck, D., et al.
(författare)
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Magneto-structural characterization of different kinds of magnetic nanoparticles
- 2023
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Ingår i: Journal of Magnetism and Magnetic Materials. - 0304-8853. ; 583
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Tidskriftsartikel (refereegranskat)abstract
- Using well-established measurement techniques like transmission electron microscopy (TEM), dynamic light scattering (DLS), small and wide angle X-ray scattering (SAXS, WAXS), susceptometry, and magnetorelaxometry, the distribution of the physical and magnetic size (magnetic moments) and magnetic anisotropy of a variety of structurally different magnetic nanoparticle samples (MNPs) is analyzed and compared. A term which accounts for the presence of weak magnetic areas (WMAs) within the MNPs was introduced to the widespread analysis model for M(H) data, enabling a consistent interpretation of the data in most of the systems. A comparison of the size distributions as obtained for the physical and the magnetic diameter suggests a multidomain structure for three single core systems under investigation, in all probability evoked by the presence of a wustite phase, as identified by WAXS. Analyzing the relationship d < dm < dc between the average single core diameter d, the effective magnetic (domain) size dm and the cluster diameter dc quantitatively, two qualitatively different magnetic structures in multicore MNP (MCMNP) systems were identified: (i) The magnetic moments of single cores within the MCMNP of fluidMAG tend to build flux closure structures, driven by dipole–dipole interaction. (ii) The magnetic behavior of Resovist® was attributed to the presence of domain sizes of about 12 nm within MCMNP, exceeding the single core diameters of 5 nm. Thereby, WAXS revealed a bimodal crystallite size distribution suggesting a crystallite merging process within the MCMNP. The value of the effective magnetic moment of these MCMNP could be explained within the presented “random moment cluster model” (RMCM). We conclude that the combination of physical and magnetic structure parameters obtained from complementary measurement methods allows a reliable assessment of the magnetic structure of single and multicore MNPs.
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