TY - CONF
AB - A stochastic graph game is played by two players on a game graph with probabilistic transitions. We consider stochastic graph games with omega-regular winning conditions specified as Rabin or Streett objectives. These games are NP-complete and coNP-complete, respectively. The value of the game for a player at a state s given an objective Phi is the maximal probability with which the player can guarantee the satisfaction of Phi from s. We present a strategy-improvement algorithm to compute values in stochastic Rabin games, where an improvement step involves solving Markov decision processes (MDPs) and nonstochastic Rabin games. The algorithm also computes values for stochastic Streett games but does not directly yield an optimal strategy for Streett objectives. We then show how to obtain an optimal strategy for Streett objectives by solving certain nonstochastic Streett games.
AU - Krishnendu Chatterjee
AU - Thomas Henzinger
ID - 3888
TI - Strategy improvement for stochastic Rabin and Streett games
VL - 4137
ER -
TY - CONF
AB - We study observation-based strategies for two-player turn-based games on graphs with omega-regular objectives. An observation-based strategy relies on imperfect information about the history of a play, namely, on the past sequence of observations. Such games occur in the synthesis of a controller that does not see the private state of the plant. Our main results are twofold. First, we give a fixed-point algorithm for computing the set of states from which a player can win with a deterministic observation-based strategy for any omega-regular objective. The fixed point is computed in the lattice of antichains of state sets. This algorithm has the advantages of being directed by the objective and of avoiding an explicit subset construction on the game graph. Second, we give an algorithm for computing the set of states from which a player can win with probability 1 with a randomized observation-based strategy for a Buchi objective. This set is of interest because in the absence of perfect information, randomized strategies are more powerful than deterministic ones. We show that our algorithms are optimal by proving matching lower bounds.
AU - Krishnendu Chatterjee
AU - Doyen, Laurent
AU - Thomas Henzinger
AU - Raskin, Jean-François
ID - 3889
TI - Algorithms for omega-regular games with imperfect information
VL - 4207
ER -
TY - CONF
AB - 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.
AU - Krishnendu Chatterjee
AU - de Alfaro, Luca
AU - Thomas Henzinger
ID - 3890
TI - The complexity of quantitative concurrent parity games
ER -
TY - CONF
AB - 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).
AU - Krishnendu Chatterjee
ID - 3891
TI - Concurrent games with tail objectives
VL - 4207
ER -
TY - JOUR
AB - 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.
AU - Ustinova, Jana
AU - Achmann, Roland
AU - Cremer, Sylvia
AU - Mayer, Frieder
ID - 3908
IS - 2
JF - Journal of Molecular Evolution
TI - Long repeats in a huge gemome: microsatellite loci in the grasshopper Chorthippus biguttulus
VL - 62
ER -
TY - JOUR
AB - 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.
AU - Cremer, Sylvia
AU - Ugelvig, Line V
AU - Lommen, Suzanne
AU - Petersen, Klaus
AU - Pedersen, Jes
ID - 3912
JF - Myrmecological News
TI - Attack of the invasive garden ant: aggression behaviour of Lasius neglectus (Hymenoptera: Formicidae) against native Lasius species in Spain
VL - 9
ER -
TY - JOUR
AB - 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.
AU - Heinze, Jürgen
AU - Cremer, Sylvia
AU - Eckl, Norbert
AU - Schrempf, Alexandra
ID - 3913
IS - 1
JF - Insectes Sociaux
TI - Stealthy invaders: the biology of Cardiocondyla tramp ants
VL - 53
ER -
TY - JOUR
AB - We compare the performances of established means of character selection for discriminant analysis in species distinction with a combination procedure for finding the optimal character combination (minimum classification error, minimum number of required characters), using morphometric data sets from the ant genera Cardiocondyla, Lasius and Tetramorium. The established methods are empirical character selection as well as forward selection, backward elimination and stepwise selection of discriminant analysis. The combination procedure is clearly superior to the established methods of character selection, and is widely applicable.
AU - Moder, Karl
AU - Schlick Steiner, Birgit
AU - Steiner, Florian
AU - Cremer, Sylvia
AU - Christian, Erhard
AU - Seifert, Bernhard
ID - 3914
IS - 1
JF - Journal of Zoological Systematics and Evolutionary Research
TI - Optimal species distinction by discriminant analysis: comparing established methods of character selection with a combination procedure using ant morphometrics as a case study
VL - 45
ER -
TY - JOUR
AB - OBJECTIVES: The EGFR is expressed in malignant ovarian tumor tissue, and tissue content of EGFR has been directly associated with poor prognosis in patients with ovarian cancer. The uPA system plays a role in pericellular proteolysis, cell migration, invasion, and is over-expressed in ovarian cancer. This study explored the effects of EGF on uPAR expression in the ovarian cancer cell line OVCAR-3. METHODS: We used OVCAR-3 cells and the following methods: cell migration assay, time-lapse video microscopy, real-time PCR, assays for cellular binding of 125I-uPA and cellular degradation of 125I-uPA:PAI-1 complex, biosynthetic labeling using 35S-methionin, Western blot, Northern blot, and ELISAs for uPA, PAI-1, and uPAR. RESULTS: EGF up-regulates both protein and mRNA not only for uPAR, but also for the ligand uPA and its inhibitor PAI-1. Cell surface uPAR, in control as well as EGF-stimulated cells, is present only in the intact, not the cleaved, form. Ligand binding experiments showed an increase of endogenously occupied uPAR, whereas non-occupied receptor sites were not increased. In addition, EGF treatment resulted in decreased degradation of radiolabeled uPA:PAI-1 complex. This suggests decreased internalization of uPAR, since the complex is internalized together with uPAR. Like EGF, colchicine, which inhibits endocytosis, increased cell surface expression of uPAR. In addition, we found an immediate increase of uPAR after exposing the cells to EGF and this was accompanied by a transient increase of cell migration. The increase of cell surface uPAR in response to EGF is accompanied by increased release of the soluble form of uPAR (suPAR) to the medium as well as by increased cell migration. Both uPAR and suPAR increased in cells treated with the endocytosis inhibitor colchicine even though cell migration was inhibited, suggesting that the mechanism of uPAR shedding is not related to cell migration. CONCLUSION: Increased cell surface uPAR in response to EGF stimulation results from mobilization of uPAR from detergent-resistant domains, increased expression of uPAR mRNA, and decreased internalization and degradation of uPAR. Both the anti-uPAR antibody R3, which inhibits binding of uPA, and the EGFR phosphorylation inhibitor Iressa inhibited cell migration in response to uPA as well as to EGF, suggesting that EGFR and uPAR are engaged in the same multiprotein assembly on the cell surface.
AU - Henic, Emir
AU - Michael Sixt
AU - Hansson, Stefan
AU - Høyer-Hansen, Gunilla
AU - Casslén, Bertil
ID - 3932
IS - 1
JF - Gynecologic Oncology
TI - EGF-stimulated migration in ovarian cancer cells is associated with decreased internalization, increased surface expression, and increased shedding of the urokinase plasminogen activator receptor
VL - 101
ER -
TY - JOUR
AB - T cells develop in the thymus in a highly specialized cellular and extracellular microenvironment. The basement membrane molecule, laminin-5 (LN-5), is predominantly found in the medulla of the human thymic lobules. Using high-resolution light microscopy, we show here that LN-5 is localized in a bi-membranous conduit-like structure, together with other typical basement membrane components including collagen type IV, nidogen and perlecan. Other interstitial matrix components, such as fibrillin-1 or -2, tenascin-C or fibrillar collagen types, were also associated with these structures. Three-dimensional (3D) confocal microscopy suggested a tubular structure, whereas immunoelectron and transmission electron microscopy showed that the core of these tubes contained fibrillar collagens enwrapped by the LN-5-containing membrane. These medullary conduits are surrounded by thymic epithelial cells, which in vitro were found to bind LN-5, but also fibrillin and tenascin-C. Dendritic cells were also detected in close vicinity to the conduits. Both of these stromal cell types express major histocompatibility complex (MHC) class II molecules capable of antigen presentation. The conduits are connected to blood vessels but, with an average diameter of 2 mum, they are too small to transport cells. However, evidence is provided that smaller molecules such as a 10 kDa dextran, but not large molecules (>500 kDa), can be transported in the conduits. These results clearly demonstrate that a conduit system, which is also known from secondary lymphatic organs such as lymph nodes and spleen, is present in the medulla of the human thymus, and that it might serve to transport small blood-borne molecules or chemokines to defined locations within the medulla.
AU - Drumea-Mirancea, Mihaela
AU - Wessels, Johannes T
AU - Müller, Claudia A
AU - Essl, Mike
AU - Eble, Johannes A
AU - Tolosa, Eva
AU - Koch, Manuel
AU - Reinhardt, Dieter P
AU - Michael Sixt
AU - Sorokin, Lydia
AU - Stierhof, York-Dieter
AU - Schwarz, Heinz
AU - Klein, Gerd
ID - 3934
IS - Pt 7
JF - Journal of Cell Science
TI - Characterization of a conduit system containing laminin-5 in the human thymus: a potential transport system for small molecules
VL - 119
ER -