Scale-Free Phenomena in Communication Networks: A Cross-Atlantic Comparison

?Small-world networks? have a high degree of local clustering or cliqueness, like a regular lattice and a relatively short average minimum path, like a completely random network. The huge appeal of ?small-world networks? lies in the impact they are said to have on dynamical systems. In a transportation network, ?small-world? topology could improve the flow of people or goods through the network, which has important implications for the design of such networks. Preliminary research has shown that ?small-world network? phenomenon can arise in traffic networks possessing ?small-world? network topology (i.e., in a network that has a structure somewhere in between a regular lattice and random graph) and that, at least under certain circumstances, traffic appears to flow more efficiently through a network with such topology (Schintler and Kulkarni, 2000). This paper will explore this further through simulation under varying assumptions regarding the size of the network (i.e., in terms of number of nodes and edges), the level of traffic in the network, the uniformity of nodes and edges and the information levels of travelers in the network. The simulations will be done using the random rewiring process introduced by Watts and Strogatz (1998), where each time the network is rewired, the distribution of traffic and congestion through the network, and the ?small-world? network parameters, shortest average minimum path and clustering coefficient, will be examined. Traffic flow will be estimated using a gravity model framework and a route choice optimization program. The simulations will also be used to reveal whether or not there are certain nodes or links that suffer at the expense of the entire network becoming more efficient. In addition, the possibility of a self-organised criticality (SOC) structure will be examined. The concept, introduced by Bak et al.,(1987), gained a great deal of attention in past decades for its capability to explore the significant and structural transformation of a dynamic system. SOC sets out how prominent exogenous forces together with strong localized interactions at the micro level lead a system to a critical state at the macro-level. A further step in our analysis is the investigation of whether a power-law distribution, characteristic of the SOC state, evolves in the traffic network. While ?small-world? network topology may be shown to improve the efficiency of traffic flow through a network, it should be recognized that ?small-world? networks are sparse by nature. The shut down or major disruption of any link in such a network, particularly one with heavy congestion, could provoke significant disorder. This paper will also explore the effect that disruptions of this nature have on networks designed with a high degree of local clustering and a short average minimum path. The fact that a ?small-world? network is sparse also raises other issues for the transportation planner. If ?small-world? topology is in fact a desirable property for transportation networks, how do we transform existing networks to produce these results? Unlike other networks, such as those for telecommunications or socialization, a transportation network cannot be rewired to achieve a more efficient network structure. This issue will also be addressed in the paper. REFERENCES Bak, P., C. Tang, and K. Wiesenfeld (1987), ?Self-Organised Criticality?, Physical Review Letters, Vol. 59 (4), pp. 381-384. Watts, D.J. and S.H. Strogatz (1998). ?Collective Dynamics of ?Small-World? Networks? Nature, Vol 393, 4, pp. 440-442. Schintler, L.A. and R. Kulkarni (2000). ?The Emergence of Small-World Phenonmenon in Urban Transportation Networks? in Reggiani, A. (ed.), Spatial Economic Science: New Frontiers in Theory and Methodology, Springer-Verlag, Berlin-NewYork, pp. 419-434.

Disentangling agglomeration and network externalities : a conceptual typology

Agglomeration and network externalities are fuzzy concepts. When different meanings are (un)intentionally juxtaposed in analyses of the agglomeration/network externalities-menagerie, researchers may reach inaccurate conclusions about how they interlock. Both externality types can be analytically combined, but only when one adopts a coherent approach to their conceptualization and operationalization, to which end we provide a combinatorial typology. We illustrate the typology by applying a state-of-the-art bipartite network projection detailing the presence of globalized producer services firms in cities in 2012. This leads to two one-mode graphs that can be validly interpreted as topological renderings of agglomeration and network externalities

City networks in cyberspace and time : using Google hyperlinks to measure global economic and environmental crises

Geographers and social scientists have long been interested in ranking and classifying the cities of the world. The cutting edge of this research is characterized by a recognition of the crucial importance of information and, specifically, ICTs to cities’ positions in the current Knowledge Economy. This chapter builds on recent “cyberspace” analyses of the global urban system by arguing for, and demonstrating empirically, the value of Web search engine data as a means of understanding cities as situated within, and constituted by, flows of digital information. To this end, we show how the Google search engine can be used to specify a dynamic, informational classification of North American cities based on both the production and the consumption of Web information about two prominent current issues global in scope: the global financial crisis, and global climate change

The effect of broadband infrastructure on entrepreneurial activities: The case of Germany

This paper investigates whether the local infrastructure favours entrepreneurial activities. Besides the physical and knowledge infrastructure we take into account a county's broadband availability by building an index which accounts for county-related specificities. We find that broadband availability fosters entrepreneurial activities particularly in high-tech sectors for which efficient ways of knowledge transfer is crucial. --broadband provision,physical and knowledge infrastructure,local entrepreneurial activities

The geography of .pt top level domain. The internet diffusion in Portugal and its implications for the decrease of spatial disparities.

The radical role of information and communication technology (ICT) is one of the most visible topic in the media today and seems to grow from day to day, as well as telecommunications are gradually becoming the central infrastructure tying together our society. The advent of these technologies during the past decades, and their widespread use, is radically transforming the dynamics of communication and our understanding of spatial relationships (by the reduce of distances and the increase of accessibility to information and new services). If there are many studies, attempting to show how city management and regional development policies can creatively address the complex linkages between ICT and urban and regional prosperity (influencing the objective of increasing urban living conditions, combating inwardness, promoting employment and economic competitiveness and supporting social integration policies), there are also many authors arguing that electronic communications reinforce existing patterns of physical communication rather than create new patterns. These suppositions are usually theoretical discussions, that needs to be rigorously tested with empirical analysis and comparative perspectives. The main objective of this paper is precisely to present a detailed study about Portugal, with the purpose of questioning the decrease of spatial disparities due to the potential influence of ICT’s. This research is mostly based on new spatial statistics, collected, mapped and analysed in order to understand the diffusion process of the most sophisticated, diverse and capable telecommunication infrastructures, and consequently verify the plasticity of space throughout Portugal, and the ways it has been stretched or compressed. We will be focusing the globally-interconnected set of computer networks, known as ‘The Internet’, which is widely used by millions of individuals, firms and institutions every day, as a way to get into an invisible domain, popularly known as cyberspace, in order to seek information, marketing new services and products, and as means of communication within and between organizations. We believe that this invisible territories of the cyberspace do have a geography and, in an attempt to reveal its topography, we should analyse the spatial patterns of the ownership of Internet space. Despite the rapid growth of Internet in recent years, and the gradually recognition of its implications, there is a lack of knowledge about its geographic diffusion and its attendant implication for regional urban development. Specially in what concerns to its effective role to generate substantial adjustments on traditional portuguese regional dichotomies, or instead, if it is an unexpected contribute to reinforce territorial disintegration tendencies. For the empirical research will try to find links between cyberspace and the portuguese physical geography. In our opinion a good way to achieve this goal is discovering which and where are located the portuguese entities that recognize the importance to distribute globally information, about their activities and services, through the use of the Internet. For that we will explore the compulsory registration of all .pt domain names on one single institution –Foundation for National Scientific Computing- (FNSC), which performs all the registration services for the geographical .pt domain.

The Diffusion of the Internet and the Geography of the Digital Divide in the United States

This paper analyses the rapid diffusion of the Internet across the United States over the past decade for both households and firms. We put the Internet's diffusion into the context of economic diffusion theory where we consider costs and benefits on the demand and supply side. We also discuss several pictures of the Internet's physical presence using some of the current main techniques for Internet measurement. We highlight different economic perspectives and explanations for the digital divide, that is, unequal availability and use of the Internet.

A New Method for Assessing the Resiliency of Large, Complex Networks

Designing resilient and reliable networks is a principle concern of planners and private firms. Traffic congestion whether recurring or as the result of some aperiodic event is extremely costly. This paper describes an alternative process and a model for analyzing the resiliency of networks that address some of the shortcomings of more traditional approaches – e.g., the four-step modeling process used in transportation planning. It should be noted that the authors do not view this as a replacement to current approaches but rather as a complementary tool designed to augment analysis capabilities. The process that is described in this paper for analyzing the resiliency of a network involves at least three steps: 1. assessment or identification of important nodes and links according to different criteria 2. verification of critical nodes and links based on failure simulations and 3. consequence. Raster analysis, graph-theory principles and GIS are used to develop a model for carrying out each of these steps. The methods are demonstrated using two, large interdependent networks for a metropolitan area in the United States.