Home About us Contact
|
Home About us Contact | ||
|
|
||
Large Networks (large + network)
Selected AbstractsVertical Networks, Integration, and ConnectivityJOURNAL OF ECONOMICS & MANAGEMENT STRATEGY, Issue 2 2009Pinar Do This paper studies competition in a network industry with a stylized two layered network structure, and examines: (i) price and connectivity incentives of the upstream networks, and (ii) incentives for vertical integration between an upstream network provider and a downstream firm. The main result of this paper is that vertical integration occurs only if the initial installed-base difference between the upstream networks is sufficiently small, and in that case, industry is configured with two vertically integrated networks, which yields highest incentives to invest in quality of interconnection. When the installed-base difference is sufficiently large, there is no integration in the industry, and neither of the firms have an incentive to invest in quality of interconnection. An industry configuration in which only the large network integrates and excludes (or raises cost of) its downstream rival does not appear as an equilibrium outcome: in the presence of a large asymmetry between the networks, when quality of interconnection is a strategic variable, the large network can exercise a substantial market power without vertical integration. Therefore, a vertically separated industry structure does not necessarily yield procompetitive outcomes. [source] Spatio-temporal shifts in gradients of habitat quality for an opportunistic avian predatorECOGRAPHY, Issue 2 2003Fabrizio Sergio We used the conceptual framework of the theory of natural selection to study breeding habitat preferences by an opportunistic avian predator, the black kite Milvus migrans. In Europe, black kite populations are mostly found near large networks of aquatic habitats, usually considered optimal for foraging and breeding. We hypothesized that proximity to wetlands could vary among individuals and affect their fitness, and thus be subject to natural selection. We tested the hypothesis first on a population on Lake Lugano (Italian pre-Alps) which has been monitored for nine years, and then on seven other populations, each studied for four,five years, located along a continuum of habitat from large water bodies to scarce aquatic habitat of any kind. In the Lake Lugano population, black kite abundance was negatively related to distance to the lake in all the nine years of study, consistent with long-term natural selection. There was evidence of ongoing directional selection on strategic nest location in three of the years, and evidence of stabilizing selection in two years. In eight of the nine years the trend was for a linear increase in fitness with increasing proximity to the lake. At the population level, results were consistent with adaptive habitat choice in relation to the previous year's spatial variation in fitness: higher associations between fitness and distance to the lake (i.e. higher selection gradients) resulted in higher density variations in the following year, in turn related to the availability of fish, the main local prey. The progressive decline of inland pairs and increase in the density of lakeshore pairs caused a directional long-term trend of declining mean distance to the lake. Breeding near aquatic habitats was associated with higher foraging success, and higher frequency and biomass of prey deliveries to offspring. There was weak evidence of selection in other populations. The inland-wetland gradient of habitat quality may have been affected by predation risk, as estimated by density of a major predator of adults and nestlings, the eagle owl Bubo bubo. Behavioral decisions at the level of the individual probably translated into population effects on density and distribution at various spatial scales. Populations in optimal habitats showed higher density and produced six times as many young per unit space as those in sub-optimal habitats. [source] Virtual base stations for wireless mobile ad hoc communications: an infrastructure for the infrastructure-lessINTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 8 2001Hossam Hassanein Abstract In this paper, we propose a new protocol for wireless mobile ad hoc networks, which establishes a dynamic wireless mobile infrastructure. The proposed protocol, namely, the virtual base stations (VBS) protocol, mimics and maintains the operation of the conventional fixed infrastructure in cellular networks. In the VBS protocol, a mobile node is elected from a set of nominees to act as a temporary base station within its zone. We provide proofs for the correctness of the VBS protocol, and show lower and upper bounds for its global convergence time. Likewise, we study the characteristics and performance of VBS by means of simulation. It is shown that VBS scales well to large networks of mobile stations, and that it outperforms other infrastructure-formation protocols in terms of stability. The VBS protocol would facilitate the development of a comprehensive and promising framework for quality of service (QoS) management in wireless mobile ad hoc networks once the proper integration of the MAC protocol with the routing and call admission control mechanisms is established. The VBS architecture lays the groundwork for assigning bandwidth, and/or implementing priorities, and hence for QoS-based routing by conveying the quality of a path prior to call setup. Copyright © 2001 John Wiley & Sons, Ltd. [source] A game-theoretic model for capacity-constrained fair bandwidth allocationINTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 6 2008Yonghe Yan Data stream providers face a hard decision to satisfy the requirements of their subscribers. Each user has a minimum and a maximum required bandwidth. The server should be able to decide which requests can be satisfied and how much bandwidth will be allocated to each. We present a theoretical framework in a distributed mechanism for fair bandwidth allocation on a network with various bottleneck links. In our model, a user is guaranteed a minimum bandwidth and charged a price for the bandwidth allocated. A utility function is defined over the allocated bandwidth for a specific maximum requested bandwidth. We then present a non-cooperative game with social welfare function to resolve users' conflicting bandwidth capacity requests at bottleneck links. We also show that our proposed game-theoretic solution guarantees fair bandwidth allocation as defined in our residual capacity fairness. In order to guarantee the minimum bandwidth requirement, we integrate an admission control mechanism in our solution. However, global optimal admission conditions are not easy to implement for large networks. Therefore, we propose a distributed admission scheme. As a result, the paper presents fair and practical distributed algorithms for bandwidth allocation and admission control in enterprise networks. Our simulation and evaluation study shows that the distributed approach is sufficiently close to the global optimal solution. Copyright © 2008 John Wiley & Sons, Ltd. [source] Efficient visualization of large routing topologiesINTERNATIONAL JOURNAL OF NETWORK MANAGEMENT, Issue 2 2004Siew Cheong Au As the Internet grows in size and complexity, network managers face a significant challenge in trying to understand the behaviour of routing protocols in large networks. In this paper, we present a tool called VLNT (visualizing large network topologies), which helps network managers to analyse complex routing topologies. A key contribution of our system is a novel hybrid layout algorithm, which significantly reduces the computation time required to layout large network topologies in comparison to conventional layout approaches. In addition our algorithm includes a novel termination criterion that avoids unnecessary iterations when optimizing the network layout. We demonstrate how the visualization features of VLNT can be used to analyse and improve BGP routing topologies, and provide examples using real-life routing data.,Copyright © 2004 John Wiley & Sons, Ltd. [source] A new approach for detecting scientific specialties from raw cocitation networksJOURNAL OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE AND TECHNOLOGY, Issue 2 2009Matthew L. Wallace We use a technique recently developed by V. Blondel, J.-L. Guillaume, R. Lambiotte, and E. Lefebvre (2008) to detect scientific specialties from author cocitation networks. This algorithm has distinct advantages over most previous methods used to obtain cocitation "clusters" since it avoids the use of similarity measures, relies entirely on the topology of the weighted network, and can be applied to relatively large networks. Most importantly, it requires no subjective interpretation of the cocitation data or of the communities found. Using two examples, we show that the resulting specialties are the smallest coherent "groups" of researchers (within a hierarchy of cluster sizes) and can thus be identified unambiguously. Furthermore, we confirm that these communities are indeed representative of what we know about the structure of a given scientific discipline and that as specialties, they can be accurately characterized by a few keywords (from the publication titles). We argue that this robust and efficient algorithm is particularly well-suited to cocitation networks and that the results generated can be of great use to researchers studying various facets of the structure and evolution of science. [source] A mean-variance model for the minimum cost flow problem with stochastic arc costsNETWORKS: AN INTERNATIONAL JOURNAL, Issue 3 2010Stephen D. Boyles Abstract This article considers a minimum cost flow problem where arc costs are uncertain, and the decision maker wishes to minimize both the expected flow cost and the variance of this cost. Two optimality conditions are given, one based on cycle marginal costs, and another based on concepts of network equilibrium. Solution methods are developed based on these conditions. The value of information is also studied, and efficient approximation techniques are developed for the specific case of learning the exact cost of one or more arcs a priori. Finally, numerical results compare the solution methods developed in this work: the minimum mean cycle canceling algorithm performs better on all of the networks tested, although the equilibrium-based algorithm is more competitive for large networks. Solution sensitivity to input parameters is also examined, as is the performance of the approximation techniques for the value of information. Approximation techniques based on arc cost distributions were found to outperform those based on properties of optimal flows. © 2009 Wiley Periodicals, Inc. NETWORKS, 2010 [source] The absolute center of a network,NETWORKS: AN INTERNATIONAL JOURNAL, Issue 2 2004Dov Dvir Abstract This paper presents a new algorithm for finding an absolute center (minimax criterion) of an undirected network with n nodes and m arcs based on the concept of minimum-diameter trees. Local centers and their associated radii are identified by a monotonically increasing sequence of lower bounds on the radii. Computational efficiency is addressed in terms of worst-case complexity and practical performance. The complexity of the algorithm is 0(n2 ,g n + mn). In practice, because of its very rapid convergence, the algorithm renders the problem amenable even to manual solution for quite large networks, provided that the minimal-distance matrix is given. Otherwise, evaluation of this matrix is the effective computational bottleneck. An interesting feature of the algorithm and its theoretical foundations is that it synthesizes and generalizes some well-known results in this area, particularly Halpern's lower bound on the local radius of a network and properties of centers of tree networks. © 2004 Wiley Periodicals, Inc. [source] Thermal-contraction-crack networks as evidence for late-Pleistocene permafrost in Inner Mongolia, ChinaPERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2004J. Vandenberghe Abstract Numerous wedges on the Ordos Plateau show typical characteristics of periglacial sand wedges that enable them to be distinguished from desiccation cracks in clayey illuviation soil horizons. The sand wedges are organized in two generations of polygonal networks. The older generation is a large-scale network with a diameter of 8 to 9,m and wedge depths up to more than 2,m. The younger generation has a mean diameter of 3 to 4,m and is formed within the large networks. It consists of shallow (0.6 to 1,m deep) but relatively wide wedges. In contrast to the typical sand wedges that form within continuous permafrost, the shallow wedges formed probably as ,ground wedges' by seasonal freezing. Ice wedges and cryoturbations developed only rarely, and exclusively in the most humid areas. Thermal-contraction cracking occurred mainly between 26 and 20,ka BP, indicating mean annual temperatures at least 13°C lower than present. Before and after that period mean annual temperatures were at least 7 to 8.5° lower than today. The presence of these periglacial phenomena show that the southern limit of continuous permafrost in Inner Mongolia occurred south of 38°N during the Last Glacial Maximum. Copyright © 2004 John Wiley & Sons, Ltd. [source] "Less is more" and the art of modeling complex phenomena: Simplification may but need not be the key to handle large networksCOMPLEXITY, Issue 2 2005Peter Schuster Editor in Chief of Complexity No abstract is available for this article. [source] | |||||||||||||