190 research outputs found
Algebras for Agent Norm-Regulation
An abstract architecture for idealized multi-agent systems whose behaviour is
regulated by normative systems is developed and discussed. Agent choices are
determined partially by the preference ordering of possible states and
partially by normative considerations: The agent chooses that act which leads
to the best outcome of all permissible actions. If an action is non-permissible
depends on if the result of performing that action leads to a state satisfying
a condition which is forbidden, according to the norms regulating the
multi-agent system. This idea is formalized by defining set-theoretic
predicates characterizing multi-agent systems. The definition of the predicate
uses decision theory, the Kanger-Lindahl theory of normative positions, and an
algebraic representation of normative systems.Comment: 25 page
An essay on msic-systems
A theory of many-sorted implicative conceptual systems (abbreviated msic-systems) is outlined. Examples of msic-systems include legal systems, normative systems, systems of rules and instructions, and systems expressing policies and various kinds of scientific theories. In computer science, msic-systems can be used in, for instance, legal information systems, decision support systems, and multi-agent systems. In this essay, msic-systems are approached from a logical and algebraic perspective aiming at clarifying their structure and developing effective methods for representing them. Of special interest are the most narrow links or joinings between different strata in a system, that is between subsystems of different sorts of concepts, and the intermediate concepts intervening between such strata. Special emphasis is put on normative systems, and the role that intermediate concepts play in such systems, with an eye on knowledge representation issues. In this essay, normative concepts are constructed out of descriptive concepts using operators based on the Kanger-Lindahl theory of normative positions. An abstract architecture for a norm-regulated multi-agent system is suggested, containing a scheme for how normative positions will restrict the set of actions that the agents are permitted to choose from
Solar wind interaction with comet 67P: impacts of corotating interaction regions
International audienceWe present observations from the Rosetta Plasma Consortium of the effects of stormy solar wind on comet 67P/Churyumov-Gerasimenko. Four corotating interaction regions (CIRs), where the first event has possibly merged with a coronal mass ejection, are traced from Earth via Mars (using Mars Express and Mars Atmosphere and Volatile EvolutioN mission) to comet 67P from October to December 2014. When the comet is 3.1â2.7 AU from the Sun and the neutral outgassing rate âŒ1025â1026 sâ1, the CIRs significantly influence the cometary plasma environment at altitudes down to 10â30 km. The ionospheric low-energy (âŒ5 eV) plasma density increases significantly in all events, by a factor of >2 in events 1 and 2 but less in events 3 and 4. The spacecraft potential drops below â20 V upon impact when the flux of electrons increases. The increased density is likely caused by compression of the plasma environment, increased particle impact ionization, and possibly charge exchange processes and acceleration of mass-loaded plasma back to the comet ionosphere. During all events, the fluxes of suprathermal (âŒ10â100 eV) electrons increase significantly, suggesting that the heating mechanism of these electrons is coupled to the solar wind energy input. At impact the magnetic field strength in the coma increases by a factor of 2â5 as more interplanetary magnetic field piles up around the comet. During two CIR impact events, we observe possible plasma boundaries forming, or moving past Rosetta, as the strong solar wind compresses the cometary plasma environment. We also discuss the possibility of seeing some signatures of the ionospheric response to tail disconnection events
Spatial distribution of low-energy plasma around 2 comet 67P/CG from Rosetta measurements
International audienceWe use measurements from the Rosetta plasma consortium (RPC) Langmuir probe (LAP) and mutual impedance probe (MIP) 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 âŒ1-2·10 â6 , at a cometocentric distance of 10 km and at 3.1 AU from the sun. A clear 6.2 h modulation of the plasma is seen as the neck is exposed twice per rotation. The electron density of the collisonless plasma within 260 km from the nucleus falls of with radial distance as âŒ1/r. The spatial structure indicates that local ionization of neutral gas is the dominant source of low-energy plasma around the comet
Investigating short-time-scale variations in cometary ions around comet 67P
The highly varying plasma environment around comet 67P/ChuryumovâGerasimenko inspired an upgrade of the ion mass spectrometer (Rosetta Plasma Consortium Ion Composition Analyzer) with new operation modes, to enable high time resolution measurements of cometary ions. Two modes were implemented, one having a 4 s time resolution in the energy range 0.3â82 eV/q and the other featuring a 1 s time resolution in the energy range 13â50 eV/q. Comparing measurements made with the two modes, it was concluded that 4 s time resolution is enough to capture most of the fast changes of the cometary ion environment. The 1462âh of observations done with the 4 s mode were divided into hour-long sequences. It is possible to sort 84âperâcent of these sequences into one of five categories, depending on their appearance in an energyâtime spectrogram. The ion environment is generally highly dynamic, and variations in ion fluxes and energies are seen on time-scales of 10 s to several minutes
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