The Experts below are selected from a list of 227808 Experts worldwide ranked by ideXlab platform
Michael Kearns - One of the best experts on this subject based on the ideXlab platform.
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A Clustering Coefficient Network Formation Game
2012Co-Authors: Michael Brautbar, Michael KearnsAbstract:Abstract. Social and other Networks have been shown empirically to exhibit high edge clustering — that is, the density of local neighborhoods, as measured by the clustering coefficient, is often much larger than the overall edge density of the Network. In social Networks, a desire for tightknit circles of friendships — the colloquial “social clique ” — is often cited as the primary driver of such structure. We introduce and analyze a new Network Formation game in which rational players must balance edge purchases with a desire to maximize their own clustering coefficient. Our results include the following: – Construction of a number of specific families of equilibrium Networks, including ones showing that equilibria can have rather general binary tree-like structure, including highly asymmetric binary trees. This is in contrast to other Network Formation games that yield only symmetric equilibrium Networks. Our equilibria also include ones with large or small diameter, and ones with wide variance of degrees. – A general characterization of (non-degenerate) equilibrium Networks, showing that such Networks are always sparse and paid for by lowdegree vertices, whereas high-degree “free riders ” always have low utility. – A proof that for edge cost α ≥ 1/2 the Price of Anarchy grows linearly with the population size n while for edge cost α less than 1/2, the Price of Anarchy of the Formation game is bounded by a constant depending only on α, and independent of n. Moreover, an explicit upper bound is constructed when the edge cost is a ”simple” rational (small numerator) less than 1/2. – A proof that for edge cost α less than 1/2 the average vertex clustering coefficient grows at least as fast as a function depending only on α, while the overall edge density goes to zero at a rate inversely proportional to the number of vertices in the Network. – Results establishing the intractability of even weakly approximating best response computations. Several of our results hold even for weaker notions of equilibrium, such as those based on link stability. 2 Michael Brautbar and Michael Kearns
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a clustering coefficient Network Formation game
Algorithmic Game Theory, 2011Co-Authors: Michael Brautbar, Michael KearnsAbstract:Social and other Networks have been shown empirically to exhibit high edge clustering--that is, the density of local neighborhoods, as measured by the clustering coefficient, is often much larger than the overall edge density of the Network. In social Networks, a desire for tightknit circles of friendships -- the colloquial "social clique" -- is often cited as the primary driver of such structure. We introduce and analyze a new Network Formation game in which rational players must balance edge purchases with a desire to maximize their own clustering coefficient. Our results include the following: • Construction of a number of specific families of equilibrium Networks, including ones showing that equilibria can have rather general binary tree-like structure, including highly asymmetric binary trees. This is in contrast to other Network Formation games that yield only symmetric equilibrium Networks. Our equilibria also include ones with large or small diameter, and ones with wide variance of degrees. • A general characterization of (non-degenerate) equilibrium Networks, showing that such Networks are always sparse and paid for by lowdegree vertices, whereas high-degree "free riders" always have low utility. • A proof that for edge cost α ≥ 1/2 the Price of Anarchy grows linearly with the population size n while for edge cost a less than 1/2, the Price of Anarchy of the Formation game is bounded by a constant depending only on a, and independent of n. Moreover, an explicit upper bound is constructed when the edge cost is a "simple" rational (small numerator) less than 1/2. • A proof that for edge cost α less than 1/2 the average vertex clustering coefficient grows at least as fast as a function depending only on a, while the overall edge density goes to zero at a rate inversely proportional to the number of vertices in the Network. • Results establishing the intractability of even weakly approximating best response computations. Several of our results hold even for weaker notions of equilibrium, such as those based on link stability.
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a small world threshold for economic Network Formation
Neural Information Processing Systems, 2006Co-Authors: Eyal Evendar, Michael KearnsAbstract:We introduce a game-theoretic model for Network Formation inspired by earlier stochastic models that mix localized and long-distance connectivity. In this model, players may purchase edges at distance d at a cost of d∝, and wish to minimize the sum of their edge purchases and their average distance to other players. In this model, we show there is a striking "small world" threshold phenomenon: in two dimensions, if ∝ 2 then every Nash equilibrium results in a Network whose diameter grows as a root of the Network size, and thus is unbounded. We contrast our results with those of Kleinberg [8] in a stochastic model, and empirically investigate the "navigability" of equilibrium Networks. Our theoretical results all generalize to higher dimensions.
Luca Coluccidamato - One of the best experts on this subject based on the ideXlab platform.
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ruta graveolens water extract inhibits cell cell Network Formation in human umbilical endothelial cells via mek erk1 2 pathway
Experimental Cell Research, 2018Co-Authors: Maria Teresa Gentile, Rosita Russo, Olga Pastorino, Sara Cioffi, Federica Barbieri, Elisabeth Anne Illingworth, Michele Grieco, Angela Chambery, Luca ColuccidamatoAbstract:Abstract Angiogenesis is a process encompassing several steps such as endothelial cells proliferation, differentiation and migration to form a vascular Network, involving different signal transduction pathways. Among these, ERK1/2 signaling mediates VEGF-dependent signaling pathway. Here we report that the water extract of Ruta graveolens (RGWE), widely known as a medicinal plant, is able to impair in a dose-dependent manner, cell Network Formation without affecting cell viability. Biochemical analysis showed that the major component of RGWE is rutin, unable to reproduce RGWE effect. We found that RGWE inhibits ERK1/2 phosphorylation and that this event is crucial in cell Network Formation since the transfection of HUVEC with a constitutively active MEK (caMEK), the ERK1/2 activator, induces a robust cell Network Formation as compared to untransfected and/or mock transfected cells and, more importantly, caMEK transfected cells became unresponsive to RGWE. Moreover, RGWE inhibits VEGF and nestin gene expression, necessary for vessel Formation, and the caMEK transfection induces their higher expression. In conclusion, we report that RGWE is able to significantly impair vessels Network Formation without affecting cell viability, preventing ERK1/2 activation and, in turn, down-regulating VEGF and nestin expression. These findings point to RGWE as a potential therapeutic tool capable to interfere with pathologic angiogenesis.
Cheng Zhang - One of the best experts on this subject based on the ideXlab platform.
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selective location and conductive Network Formation of multiwalled carbon nanotubes in polycarbonate poly vinylidene fluoride blends
Composites Science and Technology, 2011Co-Authors: Chang Su, Lihuan Xu, Cheng ZhangAbstract:Multiwalled carbon nanotubes (MWCNTs)-filled polycarbonate (PC), poly(vinylidene fluoride) (PVDF) and PC/PVDF conductive composites were fabricated using melt mixing, respectively. The dynamic process of MWCNTs conductive Network Formation in the composites was in situ traced by recording the variation of electrical resistivity with time during annealing treatments. As a result, the percolation threshold for the MWCNTs-filled PC/PVDF system was much lower than those of MWCNTs-filled individual polymers and the MWCNTs were selectively located in the PC phase of PC/PVDF composite, which had been verified by scanning electron microscopy measurements. The activation energy of conductive Network Formation for PC/PVDF/MWCNTs composite was close to that of the PC/MWCNTs system, which further confirmed that MWCNTs were dispersed mainly in the PC phase. Furthermore, the assembly velocity of MWCNTs in the polymer melt increased with annealing temperature.
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conductive Network Formation and electrical properties of poly vinylidene fluoride multiwalled carbon nanotube composites percolation and dynamic percolation
Journal of Applied Polymer Science, 2009Co-Authors: Cheng Zhang, Jun Zhu, Mi Ouyang, Masao SumitaAbstract:Conductive Network Formation and its dynamic process for multiwalled carbon nanotubes (MWNTs) and carboxyl-tethered MWNT (MWNT-COOH) filled poly(vinylidene fluoride)(PVDF) systems were investigated. Based on real-time tracing the variation of electrical resistivity of systems with isothermal treatment time, the conductive Network Formation was evaluated. It was found that the conductive Network Formation was temperature and time dependent. The percolation time, characterized at a certain annealing time where the electrical resistivity started to decrease drastically, decreased with the increase of the filler concentration or the annealing temperature. However, the values of the percolation time and the activation energy of conductive Network Formation for the PVDF/MWNT-COOH system were higher than those of the PVDF/MWNT system, indicating that the interaction between MWNTs and PVDF molecules played an important role in the conductive Network Formation of the composites. Furthermore, a modified thermodynamic percolation model was proposed to predict the percolation time of PVDF/MWNT composites. It was found that the calculated results fit the experimental data very well. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
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temperature and time dependence of conductive Network Formation dynamic percolation and percolation time
Polymer, 2006Co-Authors: Cheng Zhang, Ping Wang, Masao SumitaAbstract:Abstract Temperature and time dependence of conductive Network Formation in vapor-grown carbon fiber (VGCF) filled high-density polyethylene (HDPE)/poly(methyl methacrylate) (PMMA), VGCF and ketjenblack (KB) filled HDPE/isotactic polypropylene (iPP) blends have been investigated. It is found that the filled conductive polymer composites are thermodynamically non-equilibrium systems, in which the conductive Network Formation is temperature and time dependent, a concept named as dynamic percolation is proposed. When the composites are annealed at a temperature above the melt point of polymer matrix, the dynamic process of conductive Network Formation can be monitored in a real time way. Such an in situ characterization method provides more interesting inFormation about the dispersion of conductive particles in the polymer matrix. Furthermore, a thermodynamic percolation model is modified to predict the percolation time for VGCF and KB filled HDPE/iPP multi-phase systems during the annealing treatment, and it expresses experimental results well.
Shie Mannor - One of the best experts on this subject based on the ideXlab platform.
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Network Formation bilateral contracting and myopic dynamics
IEEE Transactions on Automatic Control, 2009Co-Authors: Esteban Arcaute, Ramesh Johari, Shie MannorAbstract:We consider a Network Formation game where nodes wish to send traffic to each other. Nodes contract bilaterally with each other to form bidirectional communication links; once the Network is formed, traffic is routed along shortest paths (if possible). Cost is incurred to a node from four sources: 1) routing traffic; 2) maintaining links to other nodes; 3) disconnection from destinations the node wishes to reach; and 4) payments made to other nodes. We assume that a Network is stable if no single node wishes to unilaterally deviate, and no pair of nodes can profitably deviate together (a variation on the notion of pairwise stability). We study such a game under a form of myopic best response dynamics. In choosing their action, nodes optimize their single period payoff only. We characterize a simple set of assumptions under which these dynamics converge to a stable Network; we also characterize an important special case, where the dynamics converge to a star centered at a node with minimum cost for routing traffic. In this sense, our dynamics naturally select an efficient equilibrium.
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Network Formation bilateral contracting and myopic dynamics
Workshop on Internet and Network Economics, 2007Co-Authors: Esteban Arcaute, Ramesh Johari, Shie MannorAbstract:We consider a Network Formation game where a finite number of nodes wish to send traffic to each other. Nodes contract bilaterally with each other to form bidirectional communication links; once the Network is formed, traffic is routed along shortest paths (if possible). Cost is incurred to a node from four sources: (1) routing traffic; (2) maintaining links to other nodes; (3) disconnection from destinations the node wishes to reach; and (4) payments made to other nodes. We assume that a Network is stable if no single node wishes to unilaterally deviate, and no pair of nodes can profitably deviate together (a variation on the notion of pairwise stability). We study such a game under a form of myopic best response dynamics. In choosing their best strategy, nodes optimize their single period payoff only. We characterize a simple set of assumptions under which these dynamics will converge to a pairwise stable Network topology; we also characterize an important special case, where the dynamics converge to a star centered at a node with minimum cost for routing traffic. In this sense, our dynamics naturally select an efficient equilibrium. Further, we show that these assumptions are satisfied by a contractual model motivated by bilateral Rubinstein bargaining with infinitely patient players.
Claudia Fischbach - One of the best experts on this subject based on the ideXlab platform.
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collagen fiber orientation regulates 3d vascular Network Formation and alignment
ACS Biomaterials Science & Engineering, 2018Co-Authors: Michael G Mccoy, Jane M Wei, Siyoung Choi, Julian Palacios Goerger, Warren R Zipfel, Claudia FischbachAbstract:Alignment of collagen type I fibers is a hallmark of both physiological and pathological tissue remodeling. However, the effects of collagen fiber orientation on endothelial cell behavior and vascular Network Formation are poorly understood because of a lack of model systems that allow studying these potential functional connections. By casting collagen type I into prestrained (0, 10, 25, 50% strain), poly(dimethylsiloxane) (PDMS)-based microwells and releasing the mold strain following polymerization, we have created collagen gels with varying fiber alignment as confirmed by structural analysis. Endothelial cells embedded within the different gels responded to increased collagen fiber orientation by assembling into 3D vascular Networks that consisted of thicker, more aligned branches and featured elevated collagen IV deposition and lumen Formation relative to control conditions. These substrate-dependent changes in microvascular Network Formation were associated with altered cell division and migration p...
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collagen i hydrogel microstructure and composition conjointly regulate vascular Network Formation
Acta Biomaterialia, 2016Co-Authors: Michael G Mccoy, Siyoung Choi, Bo Ri Seo, Claudia FischbachAbstract:Abstract Neovascularization is a hallmark of physiological and pathological tissue remodeling that is regulated in part by the extracellular matrix (ECM). Collagen I hydrogels or Matrigel are frequently used to study vascular Network Formation; however, in isolation these materials do not typically mimic the integrated effects of ECM structure and composition that may influence endothelial cells in vivo . Here, we have utilized microfabricated 3D culture models to control collagen I microstructure in the presence and absence of Matrigel and tested the effect of these variations on vascular Network Formation by human cerebral microvascular endothelial cells (hCMECs). Varied collagen microarchitecture was achieved by adjusting the gelation temperature and subsequently confirmed by structural analysis. Casting at colder temperature increased collagen fiber thickness and length, and inclusion of Matrigel further pronounced these differences. Interestingly, the presence of Matrigel affected vascular Network Formation by modulating hCMEC growth, whereas altered collagen fiber structure impacted the morphology and maturity of the developed vascular Network. These differences were related to substrate-dependent changes in interleukin-8 (IL-8) secretion and were functionally relevant as vascular Networks preformed in more fibrillar, Matrigel-containing hydrogels promoted angiogenic sprouting. Our studies indicate that collagen hydrogel microstructure and composition conjointly regulate vascular Network Formation with implications for translational and basic science approaches. Statement of Significance Neovascularization is a hallmark of both tissue homeostasis and disease and is in part regulated by cell remodeling that occurs in the extracellular matrix (ECM). The use of bio-mimetic hydrogel cell culture systems has been used to study the effects of the ECM on cell behavior. Here, we employ a hydrogel system that enables control over both the structure and composition of the ECM and subsequently investigated the effects that these have on blood vessel dynamics. Finally, we linked these differences to changes in protein secretion and the implications that this may play in scientific translation.
