Network Modeling Framework Research Articles

Topology of the world trade web.

Economy, and consequently trade, is a fundamental part of human social organization which, until now, has not been studied within the network modeling framework. Here we present the first, to the best of our knowledge, empirical characterization of the world trade web, that is, the network built upon the trade relationships between different countries in the world. This network displays the typical properties of complex networks, namely, scale-free degree distribution, the small-world property, a high clustering coefficient, and, in addition, degree-degree correlation between different vertices. All these properties make the world trade web a complex network, which is far from being well described through a classical random network description.

Duality of rate coding and temporal coding in multilayered feedforward networks.

A functional role for precise spike timing has been proposed as an alternative hypothesis to rate coding. We show in this article that both the synchronous firing code and the population rate code can be used dually in a common framework of a single neural network model. Furthermore, these two coding mechanisms are bridged continuously by several modulatable model parameters, including shared connectivity, feedback strength, membrane leak rate, and neuron heterogeneity. The rates of change of these parameters are closely related to the response time and the timescale of learning.

Modeling the global Internet

A new scalable modeling framework and scalable parallel simulations make it possible to analyze the detailed behaviour of large, multidomain multiprotocol Internet models. The article focuses on simulation research. It describes the software designs that let us construct and run appropriately large models. After several years of research, we have developed a scalable network modeling framework, a scalable simulation framework (SSF), and scalable parallel discrete event simulators capable of modeling the Internet at unprecedented scales.

Spectral Compressibility at the Metal-Insulator Transition of the Quantum Hall Effect

The spectral properties of a disordered electronic system at the metal-insulator transition point are investigated numerically. A recently derived relation between the anomalous diffusion exponent $\ensuremath{\eta}$ and the spectral compressibility $\ensuremath{\chi}$ at the mobility edge, $\ensuremath{\chi}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{\eta}/2d$, is confirmed for the integer quantum Hall delocalization transition. Our calculations are performed within the framework of a unitary network model and represent a new method to investigate spectral properties of disordered systems.

Network organization of cell metabolism: monosaccharide interconversion.

The structural properties of carbohydrate metabolism are being studied. The present contribution focuses mainly on those processes involving the transfer of carbon fragments among sugars. It is shown how enzymatic activities fix the way the system self-organizes stoichiometrically at the steady state. It is proven that there exists a specific correspondence between the set of all possible enzymic activities, the activity set, and the set of stoichiometrically compatible flux distributions through the pathway. On the one hand, there are enzymic activities that do not allow a stoichiometrically feasible coupling at the steady state of the reactions involved in the conversion. On the other hand, there are enzymic activities that are related to one or more flux distributions at the steady state (i.e. with one or several rate vectors respectively). For this latter group, it can be demonstrated that the structure of the system depends on other non-structural factors, such as boundary constraints and the kinetic parameters. As a consequence, it is suggested that this kind of metabolic process must be viewed as a complex reaction network instead of a sequential number of steps. Some implications of these derivations are illustrated for the particular conversion of CO2 --> C3. General remarks are also discussed within the framework of network models of cell metabolism.

Heat exchanger network modelling framework for optimal design and retrofitting

A new framework for addressing the practical industrial heat exchanger network (HEN) synthesis problem is presented. The new framework is based on a new object oriented representation of the HEN synthesis that allow handling of models of different complexity. To handle the increased complexity of the resulting optimisation problem a Simulated Annealing algorithm is adapted similar to that of Dolan et al (1989, 1990). The proposed framework is implemented as the software tool HEN Explorer that successfully is tested on problems of varying complexity.

Communication and consciousness: A neural network conjecture

AbstractThe communicative aspects of the contents of consciousness are analyzed in the framework of a neural network model of animal communication. We discuss some issues raised by Gray, such as the control of the contents of consciousness, the adaptive value of consciousness, conscious and unconscious behaviors, and the nature of a model's consciousness.

Boron Induced Changes in the Structural Properties of Amorphous Silicon Boron Alloys

AbstractThin films of an amorphous Si-B alloy with B contents 1–50% were deposited by low pressure chemical vapor deposition (LPCVD) from diborane (B2H6) and silane (SilH4) gases. XRD patterns of the as deposited films showed them to be completely amorphous. The films were annealed in N2 at 600–800°C for 30 minutes and characterized by Raman spectroscopy. Wet oxidation of the film was carried out 700°C for 30 minutes, and the films examined by XRD. The structural changes induced by B in the a-Si network discussed in the conceptual framework of the continuous random network (CRN) model. We conclude that the boron incorporation enhances the structural disorder and induces topological changes in the amorphous network.

Network structure and mechanical properties of sulfur-cured rubbers

The effect of sulfur/accelerator amount (at fixed ratio) and accelerator type (n-cyclohexylbenzothiazole-2-sulfenimide, diphenylguanidine) on network parameters (network chain density, cross-linking density, tube diameter, trapping factor) of styrene-butadiene copolymer networks is investigated via uniaxial stress-strain measurements up to large extensions. The mechanical properties are discussed in the framework of a non-Gaussian network model. It includes topological constraints for the network chains and the network junctions (cross-link and trapped entanglements). The model assumes a trapped entanglement contribution to the stress that does not vanish in the infinite strain limit

Indirect semantic priming in schizophrenic patients

Schizophrenic patients and normal controls performed a lexical decision task involving the recognition of words which were preceded (primed) by either associated, indirectly associated, or non-associated words. In contrast to normal control subjects who showed no indirect semantic priming effect at an inter-stimulus interval (ISI) of 0 ms, a trend towards such an indirect semantic priming effect was found in schizophrenic patients. With a longer ISI of 500 ms, an indirect semantic priming effect was obtained in both groups. In the framework of network models of semantic memory, the results are interpreted as further evidence for an increase in activation or decrease in inhibition in the spreading of associational activation in schizophrenic patients.

Structure of randomly crosslinked poly(dimethylsiloxane) networks produced by electron irradiation

The structure of randomly cross-linked poly(dimethylsiloxane) networks is studied as a function of cross-link density. The network are produced by irradiating a polydisperse polymer melt with 10-MeV electrons. Average molecular weights in between elastically effective link are obtained from macroscopic equilibrium swelling measurements that are interpreted in the framework of classical phantom network models. The values agree with results from a statistical approach based on the Flory-Stockmayer theory assumptions for the cross-lining process. Small-angle neutron scattering measurements were perforined on polymer network swollen to equilibrium in deuterated solvent and on polymer solutions

Red nucleus: role in motor control

Experimental reports in the past year have provided a better understanding of the motor functions of excitatory and inhibitory neurotransmitters in the red nucleus, and of the sensorimotor properties of single rubral neurons. These data fit well within the framework of a neural network model of the rubrocerebellar system.

Dynamic network models and driver information systems

Dynamic network models are needed to analyze traffic congestion patterns for new real-time motorist information systems. In previous research, a dynamic network modeling framework incorporating behavioral models of drivers' route and departure time choices and their day-to-day adjustment processes was developed. Network performance in this framework is represented by time dependent arrival and departure rates, link occupancies, and queuing delays. The purpose of this paper is to extend this framework to include explicit models of drivers' information acquisition and integration. The need for these models is motivated by considering the possible beneficial and counter-productive effects that may be caused by enhanced motorist information. Information on network conditions influences the set of routes considered by a driver and also affects the perceived values of the level of service attributes. The paper presents the structure of a dynamic model in which newly acquired information may affect pretrip and en-route travel decisions. To assess the potential magnitudes of the effects that were identified further theoretical and empirical research is needed.

Raman studies of structural order in amorphous silicon-boron alloys

A new amorphous Si 1- x B x alloy with composition of boron x ranging from 0.01 to 0.5 was produced in a low pressure chemical vapor deposition (LPCVD) system. We performed Raman scattering experiments on the a- Si 1- x B x alloys and specifically monitored the Si-Si TO-like mode at around 480cm −1 and the TA-like mode at around 150cm −1. A pronounced broadening of the TO-like band as well as a decrease of the intensity ratio I TO / I TA are observed with an increase of boron concentration in the a- Si 1- x B x alloys. Based on the Raman spectra, the mechanisms of structural changes induced by boron incorporation in the a-Si network are discussed in the conceptual framework of the continuum random network (CRN) model. We conclude that boron incorporation enhances the structural disorder.

Raman Studies of Boron Induced Structural Changes in Amorphous Silicon-Boron Alloys

ABSTRACTA new amorphous Si1-x.Bx. alloy with composition of boron x ranging from 0.01 to 0.5 was produced in a low pressure chemical vapor deposition (LPCVD) system. We performed Raman scattering experiments on the a-Si1−xBx alloys and specifically monitored the Si-Si TO-like mode at around 480cm−1 and the TA-like mode at around 130cm−1. A pronounced broadening of the TO-like band as well as a decrease of the intensity ratio ITo/ITA are observed with an increase of boron concentration in the a-Si1−x Bx alloys. Based on the Raman spectra, the structural changes induced by boron incorporation in the a-Si network are discussed in the conceptual framework of the continuum random network (CRN) model. We conclude that boron incorporation enhances the structural disorder and induces topological changes in the amorphous network.

Combining queueing network and Generalized Stochastic Petri Net models for the analysis of some software blocking phenomena

Much work has been done on the modeling of hardware resources; far fewer studies have been conducted on the impact of software systems on the underlying hardware. The authors address one such case in which blocking is present because of critical sections of code; this cannot be treated within the framework of product-form queuing network models. They show how a combination of generalized stochastic petri nets and queuing networks can easily model the situation under consideration. In addition, they show how a simple extension of this model can be applied to studying realistic systems with several domains.

Problems

Successful implementation of major projects requires careful management of uncertainty and risk. Yet such uncertainty is rarely effectively calculated when analysing project costs and benefits. This paper presents a Bayesian Network (BN) modelling framework to calculate the costs, benefits, and return on investment of a project over a specified time period, allowing for changing circumstances and trade-offs. The framework uses hybrid and dynamic BNs containing both discrete and continuous variables over multiple time stages. The BN framework calculates costs and benefits based on multiple causal factors including the effects of individual risk factors, budget deficits, and time value discounting, taking account of the parameter uncertainty of all continuous variables. The framework can serve as the basis for various project management assessments and is illustrated using a case study of an agricultural development project.