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| 2. |
- Ahonen-Jonnarth, Ulla, et al.
(författare)
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Simulation as a tool for the evaluation of forest management treatments
- 2010
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Ingår i: ESM'2010 - The 2010 European Simulation and Modelling Conference. - Ghent : EUROSIS-ETI. - 9789077381571 ; , s. 426-433
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Konferensbidrag (refereegranskat)abstract
- Cleaning of young forest stands is a multicriteria problem with conflicting goals. This kind of forest management treatment is performed by human beings but it is possible that this work may be performed by artificial agents in the future. The artificial agents need detailed information about how to clean a forest stand and/or what are the goals for cleaning. One problem in development of cleaning rules for artificial cleaning agents is that explicit knowledge about good cleaning results is not detailed. In this paper we present a tool for developing and testing rules and judging evaluation functions for cleaning. We illustrate this tool by presenting examples of some ways to clean forest stands in a computer environment and we present how the cleaning results can be evaluated. In order to obtain material for experiments it is also possible to simulate forest stands using this tool.
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| 4. |
- Edberg, Niklas J. T., et al.
(författare)
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Spatial distribution of low-energy plasma around comet 67P/CG from Rosetta measurements
- 2015
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 42:11, s. 4263-4269
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Tidskriftsartikel (refereegranskat)abstract
- We use measurements from the Rosetta plasma consortium Langmuir probe and mutual impedance probe to study the spatial distribution of low-energy plasma in the near-nucleus coma of comet 67P/Churyumov-Gerasimenko. The spatial distribution is highly structured with the highest density in the summer hemisphere and above the region connecting the two main lobes of the comet, i.e., the neck region. There is a clear correlation with the neutral density and the plasma to neutral density ratio is found to be approximate to 1-210(-6), at a cometocentric distance of 10km and at 3.1AU from the Sun. A clear 6.2h modulation of the plasma is seen as the neck is exposed twice per rotation. The electron density of the collisionless plasma within 260km from the nucleus falls off with radial distance as approximate to 1/r. The spatial structure indicates that local ionization of neutral gas is the dominant source of low-energy plasma around the comet.
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| 5. |
- Eriksson, Anders I., et al.
(författare)
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Cold and warm electrons at comet 67P/Churyumov-Gerasimenko
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 605
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Tidskriftsartikel (refereegranskat)abstract
- Context. Strong electron cooling on the neutral gas in cometary comae has been predicted for a long time, but actual measurements of low electron temperature are scarce. Aims. Our aim is to demonstrate the existence of cold electrons in the inner coma of comet 67P/Churyumov-Gerasimenko and show filamentation of this plasma. Methods. In situ measurements of plasma density, electron temperature and spacecraft potential were carried out by the Rosetta Langmuir probe instrument, LAP. We also performed analytical modelling of the expanding two-temperature electron gas. Results. LAP data acquired within a few hundred km from the nucleus are dominated by a warm component with electron temperature typically 5-10 eV at all heliocentric distances covered (1.25 to 3.83 AU). A cold component, with temperature no higher than about 0.1 eV, appears in the data as short (few to few tens of seconds) pulses of high probe current, indicating local enhancement of plasma density as well as a decrease in electron temperature. These pulses first appeared around 3 AU and were seen for longer periods close to perihelion. The general pattern of pulse appearance follows that of neutral gas and plasma density. We have not identified any periods with only cold electrons present. The electron flux to Rosetta was always dominated by higher energies, driving the spacecraft potential to order -10 V. Conclusions. The warm (5-10 eV) electron population observed throughout the mission is interpreted as electrons retaining the energy they obtained when released in the ionisation process. The sometimes observed cold populations with electron temperatures below 0.1 eV verify collisional cooling in the coma. The cold electrons were only observed together with the warm population. The general appearance of the cold population appears to be consistent with a Haser-like model, implicitly supporting also the coupling of ions to the neutral gas. The expanding cold plasma is unstable, forming filaments that we observe as pulses.
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| 6. |
- Goetz, Charlotte, et al.
(författare)
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The plasma environment of comet 67P/Churyumov-Gerasimenko
- 2022
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Ingår i: Space Science Reviews. - : Springer. - 0038-6308 .- 1572-9672. ; 218:8
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Forskningsöversikt (refereegranskat)abstract
- The environment of a comet is a fascinating and unique laboratory to study plasma processes and the formation of structures such as shocks and discontinuities from electron scales to ion scales and above. The European Space Agency's Rosetta mission collected data for more than two years, from the rendezvous with comet 67P/Churyumov-Gerasimenko in August 2014 until the final touch-down of the spacecraft end of September 2016. This escort phase spanned a large arc of the comet's orbit around the Sun, including its perihelion and corresponding to heliocentric distances between 3.8 AU and 1.24 AU. The length of the active mission together with this span in heliocentric and cometocentric distances make the Rosetta data set unique and much richer than sets obtained with previous cometary probes. Here, we review the results from the Rosetta mission that pertain to the plasma environment. We detail all known sources and losses of the plasma and typical processes within it. The findings from in-situ plasma measurements are complemented by remote observations of emissions from the plasma. Overviews of the methods and instruments used in the study are given as well as a short review of the Rosetta mission. The long duration of the Rosetta mission provides the opportunity to better understand how the importance of these processes changes depending on parameters like the outgassing rate and the solar wind conditions. We discuss how the shape and existence of large scale structures depend on these parameters and how the plasma within different regions of the plasma environment can be characterised. We end with a non-exhaustive list of still open questions, as well as suggestions on how to answer them in the future.
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| 7. |
- Hjelmblom, Magnus, 1973-, et al.
(författare)
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jDALMAS: A Java/Prolog Framework for Deontic Action-Logic Multi-Agent Systems
- 2009
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Ingår i: Agent and Multi-Agent Systems. - Berlin/Heidelberg : Springer Berlin/Heidelberg. - 9783642016646 - 9783642016653 - 3642016642 ; , s. 110-119
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Bokkapitel (refereegranskat)abstract
- A norm-regulated Deontic Action-Logic Multi-Agent System (DALMAS) is regulated by a normative system consisting of norms, which are expressed in an algebraic notation based on the Kanger-Lindahl theory of normative positions. A general-level Prolog implementation of the abstract DALMAS architecture makes it possible to implement specific systems in Prolog. This work describes jDALMAS, a Java library that may be used to create DALMAS applications in Java. A jDALMAS application has a client/server architecture, where a Prolog implementation of a specific system acts as a logic server. Together, the general-level Prolog implementation and the jDALMAS packages offer a framework for implementation of specific systems. Two examples of such implementations are presented here.
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| 8. |
- Hjelmblom, Magnus, 1973-
(författare)
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Norm-Regulation of Agent Systems : Instrumentalizing an algebraic approach to agent system norms
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An architecture for norm-regulated multi-agent systems based on an algebraic approach to normative systems is instrumentalized and further developed. The core of the instrumentalization is a Prolog module, which together with a Java library can be used for creating client/server-based runtime systems. Norms are represented as conditional sentences, whose normative consequences are formulated by applying normative operators to descriptive conditions. From such general normative conditions follow normative sentences regarding specific states of affairs. These in turn result in permission or prohibition of individual actions in specific situations. Furthermore, an approach to turning runtime systems into instruments for problem-solving by using evolutionary mechanisms for evolving normative systems, is presented. The construction of norm-creating operators on conditions, which forms the basis for the representation of normative systems, is approached from two angles. (i) A logical analysis based on the Kanger-Lindahl theory of normative positions is conducted. This results in two extended sets of types of normative positions, and based on an algebraic version of one of these extended systems, a set of operators for creating agent-specific norms is constructed. (ii) An alternative analysis, which takes as its starting point a systematic exploration of types of state transitions, yields a set of norm-creating operators based on prohibition of transition types. It is furthermore argued that in the context of a class of transition systems, in which transitions are deterministic and associated with a single agent performing an act, operators based on (ii) specify a meaningful semantics of operators based on (i). Theoretical results together with shared code and example applications contribute to make possible theoretically sound, transparently described, and efficiently implemented norm-regulated autonomous agent systems.
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