Showing papers on "Network theory published in 2001"

Network Information Theory

Abstract: A system with many senders and receivers contains many new elements in the communication problem: interference, cooperation and feedback. These are the issues that are the domain of network information theory. The general problem is easy to state. Given many senders and receivers and a channel transition matrix which describes the effects of the interference and the noise in the network, decide whether or not the sources can be transmitted over the channel. This problem involves distributed source coding (data compression) as well as distributed communication (finding the capacity region of the network). This general problem has not yet been solved, so we consider various special cases in this chapter. Examples of large communication networks include computer networks , satellite networks and the phone system. Even within a single computer, there are various components that talk to each other. A complete theory of network information would have wide implications for the design of communication and computer networks. Suppose that m stations wish to communicate with a common satellite over a common channel, as shown in Figure 14.1. This is known as a multiple access channel. How do the various senders cooperate with each other to send information to the receiver? What rates of communication are simultaneously achievable? What limitations does interference among the senders put on the total rate of communication? This is the best understood multiuser channel, and the above questions have satisfying answers. In contrast, we can reverse the network and consider one TV station sending information to m TV receivers, as in Figure 14.2. How does the sender encode information meant for different receivers in a common 374 Elements of Information Theory

Chain and network science: A research framework

Abstract: In this first article of the Journal on Chain and Network Science the base-line is set for a discussion on contents and scope of chain and network theory. Chain and network research is clustered into four main ‘streams’: Network theory, social capital theory, supply chain management and business economics and organizational theory. Furthermore a research agenda is formulated. The article ends with management implications of the different contributions to this first issue.

Balancing Ties: Boundary Spanning and Influence in the Organization's Extended Network of Communication.

Abstract: In this study of the business communication that connects an organization with others in its environment, we link boundary spanning with network theory and propose the concept of an extended networ...

Views on inter-enterprise relationships

Abstract: The paper gives an overview of major scientific approaches to inter-enterprise relationships. A distinction is made between approaches that focus on business process integration (Supply Chain Management, Costing approaches), approaches that focus on organizational collaboration (Transaction Cost Theory, Agency Theory), and approaches that focus on the business environment (Strategic Management, Network Theory, Resource Dependency Theory). Although these approaches are different with regard to their perspectives on collaboration, variables and methods, the paper shows that they are complementary tools in the analysis and design of inter-enterprise relationships.

Fast approximation of centrality

Abstract: Social studies researchers use graphs to model group activities in social networks. An important property in this context is the centrality of a vertex: the inverse of the average distance to each other vertex. We describe a randomized approximation algorithm for centrality in weighted graphs. For graphs exhibiting the small world phenomenon, our method estimates the centrality of all vertices with high probability within a (1 + ∈) factor in near-linear time.

End-to-end delay analysis for real-time networks

Abstract: This paper presents an application of real-time queueing network theory to a particular network which models a video-on-demand server. Packets from each stream have stochastic arrival patterns, computation times and end-to-end delay requirements. We derive closed form solutions for the deadline miss rate of the packets. This methodology can be used to design admission control policies that provide statistical quality of service guarantees. By considering the actual requirements rather than worst-case requirements, the realtime queueing network approach significantly increases the server, utilization. This paper, illustrates how realtime, queueing network theory can be used to accurately predict the behavior of real-time systems in heavy traffic conditions. It shows how one can calculate the fraction of tasks that will miss their end-to-end deadlines. It presents new results on product form equilibrium distributions for multidimensional reflected Brownian motion processes when nodes are scheduled using EDF. Lastly, it presents simulation results to illustrate the excellent accuracy of the real-time queueing network approach and how the methodology can be used to provide statistical QoS guarantees.

Small-world networks in geophysics

Abstract: Many geophysical processes can be modelled as interconnected networks. The small-world network model has recently attracted much attention in physics and applied sciences. In this paper, we modify and apply the small-world network theory to model geophysical processes such as diffusion and transport in disordered porous rocks. We develop an analytical approach as well as numerical simulations to characterize the properties of small-world networks in geophysics using system saturation time and fractal dimensions.

The Phenomenon of Diffusion

Abstract: Diffusion is at the core of WG 8.6.2 Employing Rogers’ diffusion theory while in principle addressing other sorts of phenomena is an historic research problem. The applicability of Rogers’ theory is discussed using the perspectives of mechanic and organic organizational settings, reaching the conclusion that Rogers’ diffusion theory has only limited validity. Diffusion is defined generically as the spread of IS/IT among almost any organizational unit and its constituencies. No theory of diffusion has been developed as yet. Hence, diffusion, at best, might is an umbrella for strategy, innovation, network theory, social structural theory, and a host of other approaches to understanding change in organizational settings. Researchers need to clearly define their research scope and theory base, if we as a group are to contribute to the cumulative research, the principal prerequisite for ensuring value for practice. No doubt, in the near future, more IS/IT products, frameworks, and methods will be seen. Organizations must embark on multiple change processes that require other business, managerial, and methods approaches than are in place today while at the same time maintaining the use of well established and understood practices. These are issues that WG8.6 should address.

A quick and practicable power flow tracing method on electric energy market. I. Theoretic fundament

Abstract: In a competitive market environment, to "fairly allocate the total cost of transmission", which is identical with the actual utilization of the network, is most important Based on network theory and graph theorem, this paper theoretically proves and extends the proportional sharing principle With it, the employment of transmission lines by different generators and loads can be confirmed theoretically, while energy consumers can be impartially, rationally charged, and quickly and truly ascertained according to the actual utilization of the network Also based on this principle, many problems in the electricity energy market field can be settled

A Quick& Practicable Power Flow Tracing Method On

Abstract: In a competitive market enwronment, "fairly allocate the total cost of transmission" which is identical with the actual utilization of the network is most important. Based on network theory and graph theorem, this paper theoretically proves and extends the proportional sharing principle, With it, the employ- ment of transmission lines by different generators and loads can be confirmed theoretically, while energy consumers can be )m- partlally, rationally charged, and fleetly and truly ascertained according to the actual utlllzatlon of the network. Also based on this principle, many problelms In electricity energy market field can be settled.

Network modelling of port terminals: development of a concept and a tool

Abstract: Network theory can be used to model and optimise logistic systems. The movement of goods is a major issue in our society and there is a large potential for increased efficiency in the transportation systems. Terminals and their equivalents are important in logistic systems. This is especially obvious when it comes to sea transport. The role of a port terminal is to collect goods on the landside before it can be loaded onto the ships and vice versa. A terminal is needed because of the large difference in the size between the vehicles feeding the ships and the ships themselves. If terminal operations can be improved the efficiency of the whole transportation system will be improved. The focus of this thesis is on the development and implementation of a tool for modelling port terminal operation. Results from the tool are the impact of infrastructural changes in the terminal and the impact of changing the routing of a cargo and resources through the terminal. Concepts and ideas behind the tool can also be used to model other terminals and transportation systems. The tool is based on networks. In a network the nodes play a very important role, because the flows are routed and rerouted there. All the flow changes in a system are made in the nodes. A modelling tool has to be based on strong theories and concepts. One such theory is combinatorial graph theory. This theory contains methods and algorithms for among other things handling flows on networks. Nodes with complex functionalities are, however, not handled very well by graph theory. There is a need for an extension of graph theory to include complex node functionalities to model logistic systems better. Part of this work is focused on the extension because it is needed for the development of the tool. The three problem areas addressed in the thesis are: The development and implementation of a tool for modelling port terminals based on an extended version of combinatorial graph theory. The extension of combinatorial graph theory to include complex node functionalities. The modelling of data and information associated with transportation.