Scale-free network provides an optimal pattern for knowledge transfer

We study numerically the knowledge innovation and diffusion process on four representative network models, such as regular networks, small-world networks, random networks and scale-free networks. The average knowledge stock level as a function of time is measured and the corresponding growth diffusion time, τ is defined and computed. On the four types of networks, the growth diffusion times all depend linearly on the network size N as τN, while the slope for scale-free network is minimal indicating the fastest growth and diffusion of knowledge. The calculated variance and spatial distribution of knowledge stock illustrate that optimal knowledge transfer performance is obtained on scale-free networks. We also investigate the transient pattern of knowledge diffusion on the four networks, and a qualitative explanation of this finding is proposed.     

Patent citation network in nanotechnology (1976–2004)

The patent citation networks are described using critical node, core network, and network topological analysis. The main objective is understanding of the knowledge transfer processes between technical fields, institutions and countries. This includes identifying key influential players and subfields, the knowledge transfer patterns among them, and the overall knowledge transfer efficiency. The proposed framework is applied to the field of nanoscale science and engineering (NSE), including the citation networks of patent documents, submitting institutions, technology fields, and countries. The NSE patents were identified by keywords “full-text” searching of patents at the United States Patent and Trademark Office (USPTO). The analysis shows that the United States is the most important citation center in NSE research. The institution citation network illustrates a more efficient knowledge transfer between institutions than a random network. The country citation network displays a knowledge transfer capability as efficient as a random network. The technology field citation network and the patent document citation network exhibit a␣less efficient knowledge diffusion capability than a random network. All four citation networks show a tendency to form local citation clusters.     

Synchronized stability in a reaction–diffusion neural network model

The reaction–diffusion neural network consisting of a pair of identical tri-neuron loops is considered. We present detailed discussions about the synchronized stability and Hopf bifurcation, deducing the non-trivial role that delay plays in different locations. The corresponding numerical simulations are used to illustrate the effectiveness of the obtained results. In addition, the numerical results about the effects of diffusion reveal that diffusion may speed up the tendency to synchronization and induce the synchronized equilibrium point to be stable. Furthermore, if the parameters are located in appropriate regions, multiple unstability and bistability or unstability and bistability may coexist.     

SAC-OCDM/TDM system for upgrading the TDM PON

A spectral amplitude coded-optical code division multiplexing time division multiplexing(SACOCDM/TDM) passive optical network(PON) for upgrading the traditional TDM PON is proposed.To the best of our knowledge,our work is the first to report on the use of both spectral and orthogonal code domains,which are transparent to optical network unit(ONU) for hybrid PON,in order to upgrade TDM PON seamlessly.The fewer encoder/decoders and cheaper optical source under the conditions of high bite rate and large ONU ac...     

Ising-like agent-based technology diffusion model: Adoption patterns vs. seeding strategies

The well-known Ising model used in statistical physics was adapted to a social dynamics context to simulate the adoption of a technological innovation. The model explicitly combines (a) an individual’s perception of the advantages of an innovation and (b) social influence from members of the decision-maker’s social network. The micro-level adoption dynamics are embedded into an agent-based model that allows exploration of macro-level patterns of technology diffusion throughout systems with different configurations (number and distributions of early adopters, social network topologies). In the present work we carry out many numerical simulations. We find that when the gap between the individual’s perception of the options is high, the adoption speed increases if the dispersion of early adopters grows. Another test was based on changing the network topology by means of stochastic connections to a common opinion reference (hub), which resulted in an increment in the adoption speed. Finally, we performed a simulation of competition between options for both regular and small world networks.     

Parameterization of meandering phenomenon in a stable atmospheric boundary layer

Accounting for the current knowledge of the stable atmospheric boundary layer (ABL) turbulence structure and characteristics, a new formulation for the meandering parameters to be used in a Lagrangian stochastic particle turbulent diffusion model has been derived. That is, expressions for the parameters controlling the meandering oscillation frequency in low wind speed stable conditions are proposed. The classical expression for the meandering autocorrelation function, the turbulent statistical diffusion theory and ABL similarity theory are employed to estimate these parameters. In addition, this new parameterization was introduced into a particular Lagrangian stochastic particle model, which is called Iterative Langevin solution for low wind, validated with the data of Idaho National Laboratory experiments, and compared with others diffusion models. The results of this new approach are shown to agree with the measurements of Idaho experiments and also with those of the other atmospheric diffusion models. The major advance shown in this study is the formulation of the meandering parameters expressed in terms of the characteristic scales (velocity and length scales) describing the physical structure of a turbulent stable boundary layer. These similarity formulas can be used to simulate meandering enhanced diffusion of passive scalars in a low wind speed stable ABL.     

Effects of Soret diffusion on the laminar flame speed and Markstein length of syngas/air mixtures

The effects of Soret diffusion on premixed syngas/air flames at normal and elevated temperatures and pressures are investigated numerically including detailed chemistry and transport. The emphasis is placed on assessing and interpreting the influence of Soret diffusion on the unstretched and stretched laminar flame speed and Markstein length of syngas/air mixtures. The laminar flame speed and Markstein length are obtained by simulating the unstretched planar flame and positively-stretched spherical flame, respectively. The results indicate that at atmospheric pressure the laminar flame speed of syngas/air is mainly reduced by Soret diffusion of H radical while the influence of H₂ Soret diffusion is negligible. This is due to the facts that the main reaction zone and the Soret diffusion for H radical (H₂) are strongly (weakly) coupled, and that Soret diffusion reduces the H concentration in the reaction zone. Because of the enhancement in the Soret diffusion flux of H radical, the influence of Soret diffusion on the laminar burning flux increases with the initial temperature and pressure. Unlike the results at atmospheric pressure, at elevated pressures the laminar flame speed is shown to be affected by the Soret diffusion of H₂ as well as H radical. For stretched spherical flame, it is shown that the Soret diffusion of both H and H₂ should be included so that the stretched flame speed can be accurately predicted. Similar to the laminar flame speed, the Markstein length is also reduced by Soret diffusion. However, the reduction is found to be mainly caused by Soret diffusion of H₂ rather than that of H radical. Moreover, the influence of Soret diffusion on the Markstein length is demonstrated to decrease with the initial temperature and pressure.     

Phase transition on speed limit traffic with slope

Through introducing a generalized optimal speed function to consider spatial position, slope grade and variable safe headway, the effect of slope in a single-lane highway on the traffic flow is investigated with the extended optimal speed model. The theoretical analysis and simulation results show that the flux of the whole road with the upgrade （or downgrade） increases linearly with density, saturates at a critical density, then maintains this saturated value in a certain density range and finally decreases with density. The value of saturated flux is equal to the maximum flux of the upgrade （or downgrade） without considering the slight influence of the driver＇s sensitivity. And the fundamental diagrams also depend on sensitivity, slope grade and slope length. The spatiotemporal pattern gives the segregation of different traffic phases caused by the rarefaction wave and the shock wave under a certain initial vehicle number. A comparison between the upgrade and the downgrade indicates that the value of saturated flux of the downgrade is larger than that of the upgrade under the same condition. This result is in accordance with the real traffic.     

Architectures and techniques for all-optical networks

Abstract

Some recent results on all-optical packet-switching and broadcasting networks are presented. The performance evaluation problem of packet-switching transparent optical networks with deflection routing is addressed. Transmission error arguments show how, for a given optical bit rate, the size of an all-optical nonregenerative multishop network is limited by the accumulation of noise and distortion in the optical fiber channel. Time-domain multiple access techniques are exploited in novel architectures based on recently proposed all-optical sampling gates to realize the matching of the ultrahigh optical speed allowed by the large bandwidth of the fiber with the lower speed of the electronic components needed at the user ends. These architectures allow great simplification of the node structure in the considered all-optical multihop and broadcast networks.     

Old Buildings Broadband Home Networks: Technologies and Services Overview

Abstract

Internet broadband access is becoming a reality in many countries. To fully exploit the benefits from high-speed connection, both suitable home network connectivity and advanced services support have to be made available to the user. In this article, issues relative to the upgrade of existing home networks, particularly in old buildings, together with networking and security requirements are addressed, and possible solutions are proposed.     

XPS study of low temperature diffusion in Au/Ni couples in the presence of arsenic

X-ray photoelectron spectroscopy, XPS, has been utilized to determine the low temperature grain boundary diffusion of nickel through gold thin films by means of surface accumulation. Surface accumulation is aided by a rapid oxidation of the nickel diffusant at the surface by arsenic vapor at very low (<10^-8 Torr) pressure causing a rapid accumulation of nickel arsenide product. The initial low temperature diffusion parameters of Au/Ni couples were measured in situ without interrupting the reaction-accumulation process. Accumulation and diffusion rates were obtained for temperatures ranging from 110 to 147° C. A discontinuity in an otherwise linear accumulation was observed after approximately 150 min. Evidence suggests that surface effects become rate limiting at this point.     

Sustainable Development and Spatial Inhomogeneities

Historical data, theory and computer simulations support a connection between growth and economic inequality. Our present world with large regional differences in economic activity is a result of fast economic growth during the last two centuries. Because of limits to growth we might expect a future world to develop differently with far less growth. The question that we here address is: “Would a world with a sustainable economy be less unequal?” We then develop integrated spatial economic models based on limited resources consumption and technical knowledge accumulation and study them by the way of computer simulations. When the only coupling between world regions is diffusion we do not observe any spatial unequality. By contrast, highly localized economic activities are maintained by global market mechanisms. Structures sizes are determined by transportation costs. Wide distributions of capital and production are also predicted in this regime.     

Diffusion of Na in sodium borate glasses

Diffusion of ²²Na in ion-conducting xNa₂O·(1−x)B₂O₃ glasses (x=0.2 and 0.3) was investigated under standard conditions and under high pressure employing the radiotracer sectioning method. A slight decrease of the diffusion coefficients with increasing time of diffusion annealing is observed and attributed to a structural relaxation of the glass network. The temperature dependence of diffusion was measured below and also in a small temperature range above the glass transition temperature (T_G). Below T_G the diffusion coefficients obey Arrhenius relations. Diffusion in the glass with x=0.3 is fast and associated with an activation enthalpy of 71 kJ mol⁻¹. The diffusion coefficients of the glass with x=0.2 are significantly smaller with an activation enthalpy of 112 kJ mol⁻¹. The activation volume ΔV of Na-diffusion in 0.3Na₂O·0.7B₂O₃ was determined from high pressure diffusion studies at 623 K. A value of 0.52 molar volume of the glass matrix was obtained. According to our knowledge this is the first measurement of an activation volume of diffusion in ion-conducting glasses. The present results will be discussed and compared with dc conductivity data for borate glasses and diffusion results for other oxide glasses reported in the literature.     

A novel block encryption scheme based on chaos and an S-box for wireless sensor networks

The wireless sensor network (WSN) has been widely used in various fields, but it still remains in the preliminary discovery and research phase with a lack of various related mature technologies. Traditional encryption schemes are not suitable for wireless sensor networks due to intrinsic features of the nodes such as low energy, limited computation capability, and lack of storage resources. In this paper, we present a novel block encryption scheme based on the integer discretization of a chaotic map, the Feistel network structure, and an S-box. The novel scheme is fast, secure, has low resource consumption and is suitable for wireless sensor network node encryption schemes. The experimental tests are carried out with detailed analysis, showing that the novel block algorithm has a large key space, very good diffusion and disruptive performances, a strict avalanche effect, excellent statistical balance, and fast encryption speed. These features enable the encryption scheme to pass the SP800-22 test. Meanwhile, the analysis and the testing of speed, time, and storage space on the simulator platform show that this new encryption scheme is well able to hide data information in wireless sensor networks.     

Dynamic domain networks

A model for a dynamic network consisting of changing local interactions is presented in this work. While the network maintains solely local connections, certain properties known only to Small World Networks may be extracted due to the dynamic nature of the model. At each time step the individuals are grouped into clusters creating neighborhoods or domains of fully connected agents. The boundaries of these domains change in time, corresponding to a situation where the links between individuals are dynamic only throughout the history of the network. A question that we pose is whether our model, which maintains a local structure such that diffusion calculations are possible, might lead to analytic or conceptual advances for the much more complicated case of diffusion on a static disordered network that exhibits the same macroscopic properties as our dynamic ordered network. To answer this, we compare certain properties which characterize the dynamic domain network to those of a Small World Network, and then analyze the diffusion coefficients for three possible domain mutations. We close with a comparison and confirmation of previous epidemiological work carried out on networks.     

Analyzing the Coevolution of Mobile Application Diffusion and Social Network: A Multi-Agent Model

The successful diffusion of mobile applications in user groups can establish a good image for enterprises, gain a good reputation, fight for market share, and create commercial profits. Thus, it is of great significance for the successful diffusion of mobile applications to study mobile application diffusion and social network coevolution. Firstly, combined with a social network’s dynamic change characteristics in real life, a mobile application users’ social network evolution mechanism was designed. Then, a multi-agent model of the coevolution of a social network and mobile application innovation diffusion was constructed. Finally, the impact of mobile applications’ value perception revenue, use cost, marketing promotion investment, and the number of seed users on the coevolution of social network and mobile application diffusion were analyzed. The results show that factors such as the network structure, the perceived value income, the cost of use, the marketing promotion investment, and the number of seed users have an important impact on mobile application diffusion.     

Semantic networks based on titles of scientific papers

In this paper we study the topological structure of semantic networks based on titles of papers published in scientific journals. It discusses its properties and presents some reflections on how the use of social and complex network models can contribute to the diffusion of knowledge. The proposed method presented here is applied to scientific journals where the titles of papers are in English or in Portuguese. We show that the topology of studied semantic networks are small-world and scale-free.     

Cascading dynamics in congested complex networks

Cascading failures often occur in congested complex networks. Cascading failures can be expressed as a three phase process: generation, diffusion and dissipation of congestion. Different from betweenness centrality, we propose a congestion function to represent the extent of congestion on a given node. By introducing the concept of “delay time”, we construct an intergradation between permanent removal and nonremoval. We also build a new evaluation function of network efficiency, based on congestion, which measures the damage caused by cascading failures. Finally, based on Statnet and Webgraph topologies we investigate the effects of network structure and size, delay time, processing ability and traffic generation speed on congestion propagation. Also we uncover cascading process composed of three phases and some factors affecting cascade propagation.     

Architectures and techniques for all-optical networks

Some recent results on all-optical packet-switching and broadcasting networks are presented. The performance evaluation problem of packet-switching transparent optical networks with deflection routing is addressed. Transmission error arguments show how, for a given optical bit rate, the size of an all-optical nonregenerative multishop network is limited by the accumulation of noise and distortion in the optical fiber channel. Time-domain multiple access techniques are exploited in novel architectures based on recently proposed all-optical sampling gates to realize the matching of the ultrahigh optical speed allowed by the large bandwidth of the fiber with the lower speed of the electronic components needed at the user ends. These architectures allow great simplification of the node structure in the considered all-optical multihop and broadcast networks.