@inproceedings{3890,
abstract = {We consider two-player infinite games played on graphs. The games are concurrent, in that at each state the players choose their moves simultaneously and independently, and stochastic, in that the moves determine a probability distribution for the successor state. The value of a game is the maximal probability with which a player can guarantee the satisfaction of her objective. We show that the values of concurrent games with w-regular objectives expressed as parity conditions can be decided in NP boolean AND coNP. This result substantially improves the best known previous bound of 3EXPTIME. It also shows that the full class of concurrent parity games is no harder than the special case of turn-based stochastic reachability games, for which NP boolean AND coNP is the best known bound. While the previous, more restricted NP boolean AND coNP results for graph games relied on the existence of particularly simple (pure memoryless) optimal strategies, in concurrent games with parity objectives optimal strategies may not exist, and epsilon-optimal strategies (which achieve the value of the game within a parameter epsilon > 0) require in general both randomization and infinite memory. Hence our proof must rely on a more detailed analysis of strategies and, in addition to the main result, yields two results that are interesting on their own. First, we show that there exist epsilon-optimal strategies that in the limit coincide with memoryless strategies; this parallels the celebrated result of Mertens-Neyman for concurrent games with limit-average objectives. Second, we complete the characterization of the memory requirements for epsilon-optimal strategies for concurrent games with parity conditions, by showing that memoryless strategies suffice for epsilon-optimality for coBachi conditions.},
author = {Krishnendu Chatterjee and de Alfaro, Luca and Thomas Henzinger},
pages = {678 -- 687},
publisher = {SIAM},
title = {{The complexity of quantitative concurrent parity games}},
doi = {10.1145/1109557.1109631},
year = {2006},
}
@inproceedings{3891,
abstract = {We study infinite stochastic games played by two-players over a finite state space, with objectives specified by sets of infinite traces. The games are concurrent (players make moves simultaneously and independently), stochastic (the next state is determined by a probability distribution that depends on the current state and chosen moves of the players) and infinite (proceeds for infinite number of rounds). The analysis of concurrent stochastic games can be classified into: quantitative analysis, analyzing the optimum value of the game; and qualitative analysis, analyzing the set of states with optimum value 1. We consider concurrent games with tail objectives, i.e., objectives that are independent of the finite-prefix of traces, and show that the class of tail objectives are strictly richer than the omega-regular objectives. We develop new proof techniques to extend several properties of concurrent games with omega-regular objectives to concurrent games with tail objectives. We prove the positive limit-one property for tail objectives, that states for all concurrent games if the optimum value for a player is positive for a tail objective Phi at some state, then there is a state where the optimum value is 1 for Phi, for the player. We also show that the optimum values of zero-sum (strictly conflicting objectives) games with tail objectives can be related to equilibrium values of nonzero-sum (not strictly conflicting objectives) games with simpler reachability objectives. A consequence of our analysis presents a polynomial time reduction of the quantitative analysis of tail objectives to the qualitative analysis for the sub-class of one-player stochastic games (Markov decision processes).},
author = {Krishnendu Chatterjee},
pages = {256 -- 270},
publisher = {Springer},
title = {{Concurrent games with tail objectives}},
doi = {10.1007/11874683_17},
volume = {4207},
year = {2006},
}
@article{3908,
abstract = {It is commonly believed that both the average length and the frequency of microsatellites correlate with genome size. We have estimated the frequency and the average length for 69 perfect dinucleotide microsatellites in an insect with an exceptionally large genome: Chorthippus biguttulus (Orthoptera, Acrididae). Dinucleotide microsatellites are not more frequent in C. biguttulus, but repeat arrays are 1.4 to 2 times longer than in other insect species. The average repeat number in C. biguttulus lies in the range of higher vertebrates. Natural populations are highly variable. At least 30 alleles per locus were found and the expected heterozygosity is above 0.95 at all three loci studied. In contrast, the observed heterozygosity is much lower (≤0.51), which could be caused by long null alleles.},
author = {Ustinova, Jana and Achmann, Roland and Cremer, Sylvia and Mayer, Frieder},
journal = {Journal of Molecular Evolution},
number = {2},
pages = {158 -- 167},
publisher = {Springer},
title = {{Long repeats in a huge gemome: microsatellite loci in the grasshopper Chorthippus biguttulus}},
doi = {10.1007/s00239-005-0022-6},
volume = {62},
year = {2006},
}
@article{3912,
abstract = {Invasive species often dramatically change native species communities by directly and indirectly out-competing native species. We studied the direct interference abilities of the invasive garden ant, Lasius neglectus VAN LOON, BOOMSMA & ANDRÁSFALVY, 1990, by performing one-to-one aggression tests of L. neglectus workers towards three native Lasius ant species that occur at the edge of a L. neglectus supercolony in Seva, Spain. Our results show that L. neglectus is highly aggressive against all three native Lasius species tested (L. grandis FOREL, 1909, L. emarginatus (OLIVIER, 1792), and L. cinereus SEIFERT, 1992), expressed as a higher attack rate of L. neglectus and behavioural dominance throughout the aggressive encounters. Attacks of L. neglectus were performed fastest and most frequent against L. grandis, and also the highest antennation frequencies were observed in encounters between these two species. This could be due to the largest difference in body size, or due to a greater overlap in ecological niche between L. neglectus and L. grandis compared to the other two native species. There was only weak support for L. neglectus workers from the periphery of the supercolony to be more aggressive relative to workers from the centre, even though the former encounter native ant species on a daily basis at the edge of the supercolony.},
author = {Cremer, Sylvia and Ugelvig, Line V and Lommen, Suzanne and Petersen, Klaus and Pedersen, Jes},
journal = {Myrmecological News},
pages = {13 -- 19},
publisher = {Österreichische Gesellschaft für Entomofaunistik},
title = {{Attack of the invasive garden ant: aggression behaviour of Lasius neglectus (Hymenoptera: Formicidae) against native Lasius species in Spain}},
volume = {9},
year = {2006},
}
@article{3913,
abstract = {Many invasive ant species, such as the Argentine ant or the red imported fire ant, have huge colonies with thousands of mass-foraging workers, which quickly monopolise resources and therefore represent a considerable threat to the native ant fauna. Cardiocondyla obscurior and several other species of this myrmicine genus have similarly been transferred throughout the tropics by human activities. However, because their colonies are tiny and workers forage solitarily, Cardiocondyla are often not recognized as successful invaders. Here, we document that the life history of Cardiocondyla closely resembles that of the more conspicuous tramp species, with polygyny, intranidal mating, budding, worker sterility, low genetic variability, and possibly also unicoloniality. Given that introduced Cardiocondyla may locally reach a very high population density, the effects of these stealthy invaders on the native arthropod fauna should receive more attention.},
author = {Heinze, Jürgen and Cremer, Sylvia and Eckl, Norbert and Schrempf, Alexandra},
journal = {Insectes Sociaux},
number = {1},
pages = {1 -- 7},
publisher = {Springer},
title = {{Stealthy invaders: the biology of Cardiocondyla tramp ants}},
doi = {10.1007/s00040-005-0847-4},
volume = {53},
year = {2006},
}