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| 2. |
- Hallén, Per, 1969, et al.
(författare)
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A Green Infrastructure Plan for Gothenburg, Sweden
- 2021
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Ingår i: Why cities need large parks. - Stockholm : Medströms bokförlag / Routledge. - 9789173291705 ; , s. 134-141
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 3. |
- Sauvage, Justine, et al.
(författare)
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The contribution of water radiolysis to marine sedimentary life
- 2021
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Ingår i: NATURE COMMUNICATIONS. - : Springer Science and Business Media LLC. - 2041-1723. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Water radiolysis continuously produces H-2 and oxidized chemicals in wet sediment and rock. Radiolytic H-2 has been identified as the primary electron donor (food) for microorganisms in continental aquifers kilometers below Earth's surface. Radiolytic products may also be significant for sustaining life in subseafloor sediment and subsurface environments of other planets. However, the extent to which most subsurface ecosystems rely on radiolytic products has been poorly constrained, due to incomplete understanding of radiolytic chemical yields in natural environments. Here we show that all common marine sediment types catalyse radiolytic H-2 production, amplifying yields by up to 27X relative to pure water. In electron equivalents, the global rate of radiolytic H-2 production in marine sediment appears to be 1-2% of the global organic flux to the seafloor. However, most organic matter is consumed at or near the seafloor, whereas radiolytic H-2 is produced at all sediment depths. Comparison of radiolytic H-2 consumption rates to organic oxidation rates suggests that water radiolysis is the principal source of biologically accessible energy for microbial communities in marine sediment older than a few million years. Where water permeates similarly catalytic material on other worlds, life may also be sustained by water radiolysis. The extent to which chemical products of water radiolysis could sustain subseafloor microbial life is unknown. Here the authors show that sediment catalyzes radiolytic production of H-2 and oxidants, providing the primary energy source for life in ancient marine sediment.
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| 4. |
- Doeser, Ludvig, et al.
(författare)
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Invariant Sets for Integrators and Quadrotor Obstacle Avoidance
- 2020
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Ingår i: Proceedings of the American Control Conference, ACC 2020. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 3814-3821
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Konferensbidrag (refereegranskat)abstract
- Ensuring safety through set invariance has proven a useful method in a variety of applications in robotics and control. However, finding analytical expressions for maximal invariant sets, so as to maximize the operational freedom of the system without compromising safety, is notoriously difficult for high-dimensional systems with input constraints. Here we present a generic method for characterizing invariant sets of nth-order integrator systems, based on analyzing roots of univariate polynomials. Additionally, we obtain analytical expressions for the orders n <= 4. Using differential flatness we subsequently leverage the results for the n = 4 case to the problem of obstacle avoidance for quadrotor UAVs. The resulting controller has a light computational footprint that showcases the power of finding analytical expressions for control-invariant sets.
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| 5. |
- Colledanchise, Michele, et al.
(författare)
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Synthesis of Correct-by-Construction Behavior Trees
- 2017
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Ingår i: 2017 IEEE/RSJ INTERNATIONAL CONFERENCE ON INTELLIGENT ROBOTS AND SYSTEMS (IROS). - : IEEE. - 9781538626825 ; , s. 6039-6046
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Konferensbidrag (refereegranskat)abstract
- In this paper we study the problem of synthesizing correct-by-construction Behavior Trees (BTs) controlling agents in adversarial environments. The proposed approach combines the modularity and reactivity of BTs with the formal guarantees of Linear Temporal Logic (LTL) methods. Given a set of admissible environment specifications, an agent model in form of a Finite Transition System and the desired task in form of an LTL formula, we synthesize a BT in polynomial time, that is guaranteed to correctly execute the desired task. To illustrate the approach, we present three examples of increasing complexity.
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| 6. |
- Fält, Mattias, et al.
(författare)
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Variable Elimination for Scalable Receding Horizon Temporal Logic Planning
- 2015
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Ingår i: 2015 American Control Conference (ACC). - 9781479986842 - 9781479917730 ; , s. 1917-1922
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Konferensbidrag (refereegranskat)abstract
- Correct-by-construction synthesis of high-level reactive control relies on the use of formal methods to generate controllers with provable guarantees on their behavior. While this approach has been successfully applied to a wide range of systems and environments, it scales poorly. A receding horizon framework mitigates this computational blowup, by decomposing the global control problem into several tractable subproblems. The existence of a global controller is ensured through symbolic checks of the specification, and local controllers are synthesized when needed. This reduces the size of the synthesized strategy, but still scales poorly for problems with dynamic environments because of the large number of environment strategies in each subproblem. Ad-hoc methods to locally restrict the environment come with the risk of losing correctness. We present a method for reducing the size of these subproblems by eliminating locally redundant variables, while maintaining correctness of the local (and thus global) controllers. We demonstrate the method using an autonomous car example, on problem sizes that were previously unsolvable due to the number of variables in the environment. We also demonstrate how the reduced specifications can be used to identify opportunities for reusing the synthesized local controllers.
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| 7. |
- Raman, Vasumathi, et al.
(författare)
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Online Horizon Selection in Receding Horizon Temporal Logic Planning
- 2015
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Ingår i: , 2015 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS). - 9781479999941 ; , s. 3493-3499
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Konferensbidrag (refereegranskat)abstract
- Temporal logics have proven effective for correct-by-construction synthesis of controllers for a wide range of robotic applications. Receding horizon frameworks mitigate the computational intractability of reactive synthesis for temporal logic, but have thus far been limited by pursuing a single sequence of short horizon problems to the goal. We propose a receding horizon algorithm for reactive synthesis that automatically determines a path to the currently pursued goal at runtime, responding as needed to nondeterministic environment behavior. This is achieved by allowing each short horizon to have multiple local goals, and determining which local goal to pursue based on the current global goal, the currently perceived environment and a pre-computed invariant dependent on the global goal. We demonstrate the utility of this additional flexibility in grant-response tasks, using a search-and-rescue example. Moreover, we show that these goal-dependent invariants mitigate the conservativeness of the receding horizon approach.
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| 8. |
- Jonsson, Vanessa, et al.
(författare)
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A Scalable Formulation for Engineering Combination Therapies for Evolutionary Dynamics of Disease
- 2014
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- It has been shown that optimal controller synthesis for positive systems can be formulated as a linear program. Leveraging these results, we propose a scalable iterative algorithm for the systematic design of sparse, small gain feedback strategies that stabilize the evolutionary dynamics of a generic disease model. We achieve the desired feedback structure by augmenting the optimization problems with l1 and l2 regularization terms, and illustrate our method on an example inspired by an experimental study aimed at finding appropriate HIV neutralizing antibody therapy combinations in the presence of escape mutants.
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| 9. |
- Mickelin, Oscar, et al.
(författare)
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Synthesis of Correct-by-construction Control Protocols for Hybrid Systems Using Partial State Information
- 2014
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Ingår i: 2014 American Control Conference (ACC). - : Institute of Electrical and Electronics Engineers (IEEE). - 9781479932740 ; , s. 2305-2311
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Konferensbidrag (refereegranskat)abstract
- This paper considers the problem of synthesizing output-feedback control laws for a class of discrete-time hybrid systems in order for the trajectories of the system to satisfy certain high-level specifications expressed in linear temporal logic. By leveraging ideas from robust interpretation of temporal logic formulas and bounded-error estimation, we identify a subclass of systems for which it is possible to reduce the problem to a state-feedback form. In particular, we use locally superstable hybrid observers to resolve the partial information at the continuous level. This allows us to use recent results in temporal logic planning to synthesize the desired controllers based on two-player perfect-information games. The overall control architecture consists of a hybrid observer, a highlevel switching protocol and a low-level continuous controller. We demonstrate the proposed framework in a case study on designing control protocols for an aircraft air management system.
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| 10. |
- Rogersten, Robert, et al.
(författare)
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Control Software Synthesis and Validation for a Vehicular Electric Power Distribution Testbed
- 2014
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Ingår i: Journal of Aerospace Information Systems. - 1940-3151. ; 11:10, s. 665-678
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Tidskriftsartikel (refereegranskat)abstract
- Modern aircraft increasingly rely on electric power, resulting in high safety criticality and complexity in their electric power generation and distribution systems. Motivated by the resulting rapid increase in the costs and duration of the design cycles for such systems, the use of formal specification and automated correct-by-construction control protocols synthesis for primary distribution in vehicular electric power networks is investigated. A design workflow is discussed that aims to transition from the traditional "design and verify" approach to a "specify and synthesize" approach. An overview is given of a subset of the recent advances in the synthesis of reactive control protocols. These techniques are applied in the context of reconfiguration of the networks in reaction to the changes in their operating environment. These automatically synthesized control protocols are also validated on high-fidelity simulation models and on an academic-scale hardware testbed.
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