332 research outputs found
Cooperation in Networks and Scheduling.
No full textThis thesis deals with various models of cooperation in networks and scheduling. The main focus is how the benefits of this cooperation should be divided among the participating individuals. A major part of this analysis is concerned with stability of the cooperation. In addition, allocation rules are investigated, as well as properties of the underlying situations and games.
Sequencing Games with Controllable Processing Time
No full textIn this paper we study a class of cooperative sequencing games that arise from sequencing situations in which the processing times are not fixed.We show that these games are balanced by obtaining two core elements that depend only on the optimal schedule for the grand coalition.Furthermore we show that, although these games are not convex in general, many marginal vectors are core elements. We also consider convexity for special instances of the sequencing situation.cooperative games
Simple Combinatorial Optimisation Cost Games
No full textIn this paper we introduce the class of simple combinatorial optimisation cost games, which are games associated to {0, 1}-matrices.A coalitional value of a combinatorial optimisation game is determined by solving an integer program associated with this matrix and the characteristic vector of the coalition.For this class of games, we will characterise core stability and totally balancedness.We continue by characterising exactness and largeness.Finally, we conclude the paper by applying our main results to minimum colouring games and minimum vertex cover games.Combinatorial optimisation game;core stability;totally balancedness;largeness;exactness
On the Balancedness of Relaxed Sequencing Games
No full textThis paper shows that some classes of relaxed sequencing games, which arise from the class of sequencing games as introduced in Curiel, Pederzoli, Tijs (1989), are balanced.sequencing situations;sequencing games;balancedness;game theory
Core Stability in Chain-Component Additive Games
No full textChain-component additive games are graph-restricted superadditive games, where an exogenously given line-graph determines the cooperative possibilities of the players.These games can model various multi-agent decision situations, such as strictly hierarchical organisations or sequencing / scheduling related problems, where an order of the agents is fixed by some external factor, and with respect to this order only consecutive coalitions can generate added value. In this paper we characterise core stability of chain-component additive games in terms of polynomial many linear inequalities and equalities that arise from the combinatorial structure of the game.Furthermore we show that core stability is equivalent to essential extendibility.We also obtain that largeness of the core as well as extendibility and exactness of the game are equivalent properties which are all sufficient for core stability.Moreover, we also characterise these properties in terms of linear inequalities.Core stability;graph-restricted games;large core;exact game
X-ray eruptions every 22 days from the nucleus of a nearby galaxy
No full textGalactic nuclei showing recurrent phases of activity and quiescence have
recently been discovered, with recurrence times as short as a few hours to a
day -- known as quasi-periodic X-ray eruption (QPE) sources -- to as long as
hundreds to a thousand days for repeating nuclear transients (RNTs). Here we
present a multi-wavelength overview of Swift J023017.0+283603 (hereafter Swift
J0230+28), a source that exhibits repeating and quasi-periodic X-ray flares
from the nucleus of a previously unremarkable galaxy at 165 Mpc, with a
recurrence time of approximately 22 days, an intermediary timescale between
known RNTs and QPE sources. The source also shows transient radio emission,
likely associated with the X-ray emission. Such recurrent soft X-ray eruptions,
with no accompanying UV/optical emission, are strikingly similar to QPE
sources. However, in addition to having a recurrence time that is
times longer than the longest-known QPE source, Swift J0230+28's eruptions
exhibit somewhat distinct shapes and temperature evolution than the known QPE
sources. Scenarios involving extreme mass ratio inspirals are favored over disk
instability models. The source reveals an unexplored timescale for repeating
extragalactic transients and highlights the need for a wide-field, time-domain
X-ray mission to explore the parameter space of recurring X-ray transients.Comment: Final version, appeared on Nature Astronomy on 12 January 202
Shifts of attention in the early blind: an ERP study of attentional control processes in the absence of visual spatial information
No full textTo investigate the role of visual spatial information in the control of spatial attention, event-related brain potentials (ERPs) were recorded during a tactile attention task for a group of totally blind participants who were either congenitally blind or had lost vision during infancy, and for an age-matched, sighted control group who performed the task in the dark. Participants had to shift attention to the left or right hand (as indicated by an auditory cue presented at the start of each trial) in order to detect infrequent tactile targets delivered to this hand. Effects of tactile attention on the processing of tactile events, as reflected by attentional modulations of somatosensory ERPs to tactile stimuli, were very similar for early blind and sighted participants, suggesting that the capacity to selectively process tactile information from one hand versus the other does not differ systematically between the blind and the sighted. ERPs measured during the cue–target interval revealed an anterior directing attention negativity (ADAN) that was present for the early blind group as well as for the sighted control group. In contrast, the subsequent posterior late direction attention negativity (LDAP) was absent in both groups. These results suggest that these two components reflect functionally distinct attentional control mechanisms which differ in their dependence on the availability of visually coded representations of external space
Polarimetry of the transient relativistic jet of GRB 110328/Swift J164449.3+573451
No full textWe present deep infrared (Ks-band) imaging polarimetry and radio (1.4- and 4.8-GHz) polarimetry of the enigmatic transient Swift J164449.3+573451. This source appears to be a short-lived jet phenomenon in a galaxy at redshift z= 0.354, activated by a sudden mass accretion on to the central massive black hole, possibly caused by the tidal disruption of a star. We aim to find evidence for this scenario through linear polarimetry, as linear polarization is a sensitive probe of jet physics, source geometry and the various mechanisms giving rise to the observed radiation. We find a formal Ks-band polarization measurement of Plin= 7.4 ± 3.5 per cent (including systematic errors). Our radio observations show continuing brightening of the source, which allows sensitive searches for linear polarization as a function of time. We find no evidence of linear polarization at radio wavelengths of 1.4 and 4.8 GHz at any epoch, with the most sensitive 3σ limits as deep as 2.1 per cent. These upper limits are in agreement with expectations from scenarios in which the radio emission is produced by the interaction of a relativistic jet with a dense circumsource medium. We further demonstrate how polarization properties can be used to derive properties of the jet in Swift J164449.3+573451, exploiting the similarities between this source and the afterglows of gamma-ray bursts
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Thermodynamic and rheological properties of solid-liquid systems in coal processing
No full textNone of the models available in the literature are known to work very well for aromatic compounds such as the ones that occur in coal derived materials. Two models - one by Van Velzen et al. (Ind Eng. Chem. Fundam. Vol 11, 1972, pp. 20-25) using a group contribution method and the other by Hwang et al (Ind. Eng. Chem. Process Des. Dev., Vol. 21, 1982, pp. 127-134) using a corresponding states method - were tested for some typical compounds that occur in coal liquids. These methods give errors ranging from 10 to 50% for viscosities of such compounds. These errors are too high and considering further errors in extension of these models to coal liquids, these models were considered unacceptable in our work. We have therefore set out to develop a new model for viscosities of aromatic compounds. We plan to base the model on the procedure similar to that of Van Velzen, however developed for just aromatic compounds. Our model, once developed will therefore be a group contribution method centered around the benzene ring structure
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Thermodynamic and rheological properties of solid-liquid systems in coal processing. Quarterly technical report, September 1, 1992--November 30, 1992
No full textNone of the models available in the literature are known to work very well for aromatic compounds such as the ones that occur in coal derived materials. Two models - one by Van Velzen et al. (Ind Eng. Chem. Fundam. Vol 11, 1972, pp. 20-25) using a group contribution method and the other by Hwang et al (Ind. Eng. Chem. Process Des. Dev., Vol. 21, 1982, pp. 127-134) using a corresponding states method - were tested for some typical compounds that occur in coal liquids. These methods give errors ranging from 10 to 50% for viscosities of such compounds. These errors are too high and considering further errors in extension of these models to coal liquids, these models were considered unacceptable in our work. We have therefore set out to develop a new model for viscosities of aromatic compounds. We plan to base the model on the procedure similar to that of Van Velzen, however developed for just aromatic compounds. Our model, once developed will therefore be a group contribution method centered around the benzene ring structure
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