| 1. |
- Cornelissen, Johannes H C, et al.
(författare)
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Global negative vegetation feedback to climate warming responses of leaf litter decomposition rates in cold biomes
- 2007
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 10:7, s. 619-627
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Tidskriftsartikel (refereegranskat)abstract
- Whether climate change will turn cold biomes from large long-term carbon sinks into sources is hotly debated because of the great potential for ecosystem-mediated feedbacks to global climate. Critical are the direction, magnitude and generality of climate responses of plant litter decomposition. Here, we present the first quantitative analysis of the major climate-change-related drivers of litter decomposition rates in cold northern biomes worldwide.Leaf litters collected from the predominant species in 33 global change manipulation experiments in circum-arctic-alpine ecosystems were incubated simultaneously in two contrasting arctic life zones. We demonstrate that longer-term, large-scale changes to leaf litter decomposition will be driven primarily by both direct warming effects and concomitant shifts in plant growth form composition, with a much smaller role for changes in litter quality within species. Specifically, the ongoing warming-induced expansion of shrubs with recalcitrant leaf litter across cold biomes would constitute a negative feedback to global warming. Depending on the strength of other (previously reported) positive feedbacks of shrub expansion on soil carbon turnover, this may partly counteract direct warming enhancement of litter decomposition.
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| 2. |
- Lohstroh, M., et al.
(författare)
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Invited : Actors revisited for time-critical systems
- 2019
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Ingår i: Proceedings - Design Automation Conference. - New York, NY, USA : Institute of Electrical and Electronics Engineers Inc.. - 9781450367257
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Konferensbidrag (refereegranskat)abstract
- Programming time-critical systems is notoriously difficult. In this paper we propose an actor-oriented programming model with a semantic notion of time and a deterministic coordination semantics based on discrete events to exercise precise control over both the computational and timing aspects of the system behavior.
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| 3. |
- Bagheri, M., et al.
(författare)
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Runtime compositional analysis of track-based traffic control systems
- 2017
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Ingår i: ACM SIGBED Review. - : Association for Computing Machinery (ACM). - 1551-3688. ; 14:3, s. 38-39
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we address the development of dependable self-adaptive systems focusing on the specific domain of track-based traffic control systems where timing issues are critical.
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| 4. |
- Cornelissen, C, et al.
(författare)
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Global change and arctic ecosystems : is lichen decline a function of increases in vascular plant biomass?
- 2001
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Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 89:6, s. 984-994
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Tidskriftsartikel (refereegranskat)abstract
- 1 Macrolichens are important for the functioning and biodiversity of cold northern ecosystems and their reindeer-based cultures and economics. 2 We hypothesized that, in climatically milder parts of the Arctic, where ecosystems have relatively dense plant canopies, climate warming and/or increased nutrient availability leads to decline in macrolichen abundance as a function of increased abundance of vascular plants. In more open high-arctic or arctic-alpine plant communities such a relationship should be absent. To test this, we synthesized cross-continental arctic vegetation data from ecosystem manipulation experiments simulating mostly warming and increased nutrient availability, and compared these with similar data from natural environmental gradients. 3 Regressions between abundance or biomass of macrolichens and vascular plants were consistently negative across the subarctic and mid-arctic experimental studies. Such a pattern did not emerge in the coldest high-arctic or arctic-alpine sites. The slopes of the negative regressions increased across 10 sites as the climate became milder (as indicated by a simple climatic index) or the vegetation denser (greater site above-ground biomass). 4 Seven natural vegetation gradients in the lower-altitude sub- and mid-arctic zone confirmed the patterns seen in the experimental studies, showing consistent negative relationships between abundance of macrolichens and vascular plants. 5 We conclude that the data supported the hypothesis. Macrolichens in climatically milder arctic ecosystems may decline if and where global changes cause vascular plants to increase in abundance. 6 However, a refining of our findings is needed, for instance by integrating other abiotic and biotic effects such as reindeer grazing feedback on the balance between vascular plants and lichens.
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| 5. |
- Angus-Dunne, Sarah J., et al.
(författare)
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Metallocene and organo-main group trifluoromethanesulfonates
- 2006
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Ingår i: Transition metal chemistry (Weinheim). - : Springer Science and Business Media LLC. - 0340-4285 .- 1572-901X. ; 31:2, s. 268-275
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Tidskriftsartikel (refereegranskat)abstract
- The substituted metallocene compounds Cp2M(OSO 2CF3)2 (Cp=η5-C 5H5; M = Ti, Zr, Hf, Nb, Mo), CpTi(OSO2CF 3)3 • 0.75(1,2-dimethoxyethane), and the organo-main group compounds (C6H5)3M′(OSO 2CF3) (M′=Si, Ge), (C6H5) 2Sn(OSO2CF3)2 and (C 6H5)3Sb(OSO2CF3) 2, were synthesized from the corresponding chloride or bromide compounds and silver trifluoromethanesulfonate (triflate) and characterized spectroscopically, including a detailed analysis of their IR spectra. Triflate coordination is typically monodentate, but CpTi(OSO2CF 3)3 • 0.75(1,2-dimethoxyethane) and the organo-germanium triflate show evidence of bidentate CF3SO 3 - ligands and are likely to have polymeric structures. Conductance measurements in nitromethane, acetone and acetonitrile have demonstrated the ease of triflate substitution, with a limited kinetic study of acetone solvation of the Ti and Hf compounds supporting an associative pathway. Three new catalysts for the polymerization of tetrahydrofuran, Cp 2HfCl2/Ag(OSO2CF3), CpTiCl 3/Ag(OSO2CF3) and (C6H 5)2SiCl2/Ag(OSO2CF3), are also reported.
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| 6. |
- Bagheri, Maryam, et al.
(författare)
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Coordinated actor model of self-adaptive track-based traffic control systems
- 2018
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Ingår i: Journal of Systems and Software. - : Elsevier. - 0164-1212 .- 1873-1228. ; 143, s. 116-139
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Tidskriftsartikel (refereegranskat)abstract
- Self-adaptation is a well-known technique to handle growing complexities of software systems, where a system autonomously adapts itself in response to changes in a dynamic and unpredictable environment. With the increasing need for developing self-adaptive systems, providing a model and an implementation platform to facilitate integration of adaptation mechanisms into the systems and assuring their safety and quality is crucial. In this paper, we target Track-based Traffic Control Systems (TTCSs) in which the traffic flows through pre-specified sub-tracks and is coordinated by a traffic controller. We introduce a coordinated actor model to design self-adaptive TTCSs and provide a general mapping between various TTCSs and the coordinated actor model. The coordinated actor model is extended to build large-scale self-adaptive TTCSs in a decentralized setting. We also discuss the benefits of using Ptolemy II as a framework for model-based development of large-scale self-adaptive systems that supports designing multiple hierarchical MAPE-K feedback loops interacting with each other. We propose a template based on the coordinated actor model to design a self-adaptive TTCS in Ptolemy II that can be instantiated for various TTCSs. We enhance the proposed template with a predictive adaptation feature. We illustrate applicability of the coordinated actor model and consequently the proposed template by designing two real-life case studies in the domains of air traffic control systems and railway traffic control systems in Ptolemy II.
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| 7. |
- Bagheri, Maryam, et al.
(författare)
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Coordinated actors for reliable self-adaptive systems
- 2017
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Ingår i: FACS 2016. - Cham : Springer. - 9783319576657 - 9783319576664 ; , s. 241-259
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Konferensbidrag (refereegranskat)abstract
- Self-adaptive systems are systems that automatically adapt in response to environmental and internal changes, such as possible failures and variations in resource availability. Such systems are often realized by a MAPE-K feedback loop, where Monitor, Analyze, Plan and Execute components have access to a runtime model of the system and environment which is kept in the Knowledge component. In order to provide guarantees on the correctness of a self-adaptive system at runtime, the MAPE-K feedback loop needs to be extended with assurance techniques. To address this issue, we propose a coordinated actor-based approach to build a reusable and scalable model@runtime for self-adaptive systems in the domain of track-based traffic control systems. We demonstrate the approach by implementing an automated Air Traffic Control system (ATC) using Ptolemy tool.We compare different adaptation policies on the ATC model based on performance metrics and analyze combination of policies in different configurations of the model. We enriched our framework with runtime performance analysis such that for any unexpected change, subsequent behavior of the model is predicted and results are used for adaptation at the change-point. Moreover, the developed framework enables checking safety properties at runtime. © Springer International Publishing AG 2017.
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| 8. |
- Bagheri, Maryam, et al.
(författare)
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Lightweight Formal Method for Robust Routing in Track-based Traffic Control Systems
- 2020
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Ingår i: 2020 18TH ACM-IEEE INTERNATIONAL CONFERENCE ON FORMAL METHODS AND MODELS FOR SYSTEM DESIGN (MEMOCODE). - : IEEE. ; , s. 115-124
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Konferensbidrag (refereegranskat)abstract
- In this paper, we propose a robust solution for the path planning and scheduling of the moving objects in a Track-based Traffic Control System (TTCS). The moving objects in a TTCS pass over pre-specified sub-tracks. Each sub-track accommodates at most one moving object in-transit. Due to the uncertainties in the context of a TTCS, we assign an arrival time window to each moving object for each sub-track in its route, instead of an exact value. The moving object can safely enter into the sub-track in the mentioned time window. To develop a safe plan, we adapt the tagged-signal model and provide a rigorous mathematical formalism for the actor model of a TTCS. To illustrate the applicability of the provided semantics, we provide a formal model of TTCSs in the Alloy language and use its analyzer to verify the developed model against system safety properties.
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| 9. |
- Castleton, Christopher, 1969-, et al.
(författare)
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Benchmarking Density Functional Theory Functionals for Polarons in Oxides : Properties of CeO2
- 2019
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society. - 1932-7447 .- 1932-7455. ; 123:9, s. 5164-5175
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Tidskriftsartikel (refereegranskat)abstract
- We examine methods for studying polarons in metal oxides with density functional theory (DFT), using the example of cerium dioxide and the functionals, local density approximation + U (LDA+U), generalized gradient approximation + U (GGA+U) in the Perdew-Burke-Ernzerhof parametrization (PBE+U), as well as the hybrid functionals B3LYP, Heyd?Scuseria?Ernzerhof (HSE)03, HSE06, and PBE0. We contrast the four polaron energies commonly reported in different parts of the literature: formation energy, localization/relaxation energy, density-of-states level, and polaron-hopping activation barrier. Qualitatively, all these functionals predict "small" (Holstein) polarons on the scale of a single lattice site, although LDA+U and GGA+U are more effective than the hybrids at localizing the Ce 4f electrons. The improvements over pure LDA/GGA appear because of changes in the filled Ce 4f states when using LDA/GGA+U but due to changes in the empty Ce 4f states when using the hybrids. DFT is shown to have sufficient correlation to predict both adiabatic and (approximate) diabatic hopping barriers. Overall, LDA+U = 6 eV provides the best description in comparison to the experiment, followed by GGA+U = 5 eV. The hybrids are worse, tending to overestimate the gap and significantly underestimate the polaron-hopping barriers.
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| 10. |
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