SIMULATION: Transactions of The Society for Modeling and Simulation International

Mushayabasa, Steady; Bhunu, Claver P

doi: 10.1177/0037549714528388pmid: N/A

Despite advances in hepatitis C therapy and better knowledge of viral/host factors related to disease progression, hepatitis C virus (HCV) remains the leading cause of chronic liver disease, causing progression to end-stage liver disease (ESLD) as well as the development of hepatocellular carcinoma. In this paper a mathematical model for assessing the impact of antiviral therapy, abstinence and relapse on the transmission dynamics of HCV is formulated and analyzed. A threshold quantity known as the reproductive number has been computed, and the stability of the steady states has been investigated. The dynamical analysis reveals that the model has globally asymptotically stable steady states. The impacts of antiviral therapy, abstinence and relapse on the transmission dynamics of HCV are discussed through the basic reproductive number and numerical simulations.

Huo, Feizhou; Song, Weiguo; Lv, Wei; Liew, K M

doi: 10.1177/0037549714526294pmid: N/A

The floor–stair interface is a critical component of the escape stairs in high-rise buildings, and the characteristics of the merging flow in the floor–stair interface is also significant for investigating the evacuation of high-rise buildings. In this paper, the original lattice gas model is extended by considering inner-side walking preferences, turning behavior and different desired speeds. Then the merging flow in the floor–stair interface is simulated with the extended model. The fundamental diagram of the simulation results has the same tendency as the empirical data and it is found that the merging at the floor–stair interface could retard the motion of pedestrians on the incoming stairs and reduce the motion speed in the case when the corridors are adjacent to the incoming stairs. The effect of two kinds of typical structures of the floor–stair interface on pedestrian merging behavior is investigated. The results show that the evacuation process will be improved when the corridor is connected to the landing opposite to the incoming stairs. The results given in this paper may be helpful in understanding the characteristics of pedestrian merging flow in floor–stair interfaces and in designing building structures.

Ahmed, Lubaid; Abhari, Abdolreza

doi: 10.1177/0037549714528268pmid: N/A

The main goal of this paper is building a novel transmission control protocol/internet protocol (TCP/IP) network simulator engine for simulation of distributed applications for which capturing both higher and lower layer network parameters are important. There are not many comprehensive simulators available in industry and academia to simulate distributed applications while reporting the parameters of all the layers of the TCP/IP network active in such simulations. The major problem in building a comprehensive simulation scenario for applications residing on the higher layers of a network by using currently available simulators is that a core simulator for lower layers of the network should be used together with add-ons or other programs simulating higher network layers to be able to simulate the whole TCP/IP network. This paper presents a novel idea for network simulation that has not been implemented before, which is using agents to simulate all layers of the network. In this simulator, each TCP/IP layer is simulated separately by using a separate agent and its behavior. It is an integrated environment based on agent systems capable of simulating all layers of a TCP/IP network, including application and lower layers. The final goal is other agent systems simulating a complex higher level web-based distributed application being easily used together with these agents, which are simulating the core TCP/IP network. For evaluation and testing purposes, a simple distributed application consisting of several remote procedure calls is simulated. For the validation of the conducted simulations, the achieved results are compared with the results of two non-agent-based simulators. For the verification of each individual agent function, a report is generated that shows the information flow between agents. The communication routes between agents are checked manually to make sure the route selection is based on the expected behavior of each agent. The scalability of the proposed multi-agent-based simulator is tested for the given distributed application.

Bergero, Federico; Kofman, Ernesto

doi: 10.1177/0037549714529833pmid: N/A

In this article we introduce an extension to the Discrete Event System (DEVS) formalism called Vectorial DEVS (VECDEVS) that allows to represent large scale systems in a graphic block diagram way. A pure VECDEVS model basically consist in an array of identical classic DEVS models that may differ in their parameters. The interconnection of VECDEVS models with some special classic DEVS models that can handle VECDEVS events allows us to easily represent large systems of arbitrary structure. A noticeable feature of this extension is that VECDEVS models can be easily split for parallel simulation. For that purpose, we developed an algorithm that automatically splits VECDEVS models into an arbitrary number of sub-models for parallel simulation. The implementation of VECDEVS and the partitioning algorithm in a DEVS simulation tool is also described and its usage is illustrated through some application examples.

Walter, Michael; Storch, Markus; Wartzack, Sandro

doi: 10.1177/0037549714529834pmid: N/A

Simulations not only facilitate new and unprecedented insights in highly sophisticated science areas, but also support product design in engineering in terms of improved functionality, cost and time issues. However, as a matter of fact, simulations examine limited excerpts of real systems with accompanying simplifications, abstractions and idealizations. Hence, there is a distinct need to be aware of upcoming risks in simulation outcomes caused by uncertainties. These influence every step of forward-thinking simulation design which is not only restrained by modeling practice but begins with reality perception itself.The intention of the paper is to embed an awareness of uncertainty in the context of simulation by linking major classes of uncertainty with uncertainties within simulations in engineering design. Besides the decisive inclusion of reality as the starting point, mathematic approaches are also used to understand how those uncertainty classes evolve through exponential knowledge creation of systems. The transfer to statistical tolerance analysis shall finally put emphasis on the practical classification of uncertainty, starting from data preparation via concept design and mathematical implementation to result depiction. In the end, the reader’s conception of possible uncertainties in special simulation cases shall be sharpened which, vice versa, shall lead to even better and well-thought-out simulation outcomes.

Ma, Tieju; Zhu, Ya; Liu, Peipei; Chi, Chunjie

doi: 10.1177/0037549714530780pmid: N/A

Existing agent-based models of co-diffusion of alternative fuel vehicles and their corresponding filling stations are very stylized. In addition, there is a lack of methodologies for linking such models with a real social and economic background. Aiming at solving this problem, this paper puts forward a method that uses widely available social, economic, and spatial data to generate driver agents’ commute trips, which play an important role in such models. We tested the method with the data of Shanghai and Beijing, two of the largest cities in China, and found the commute times resulting from the method were in accordance with survey results, which validates the potential usefulness of the method.

Zhang, Xin; Chang, Gang-Len

doi: 10.1177/0037549714530795pmid: N/A

In design of plans for major metropolitan areas, it should be recognized that a potentially large percentage of the population is walking instead of driving. The massive number of pedestrians may cause tremendous burden to vehicles in the roadway network, and thus should be adequately accommodated. However, limited research has been done to qualitatively evaluate the effectiveness of different control plans at such mixed-flow intersections. Hence, the development of a simulation tool, capable of replicating the realistic road conditions for both the pedestrian and vehicle flows, is an imperative task. Such a simulation tool should be able to account for conflicts between pedestrians, between vehicles, and between pedestrians and vehicles. In this study, we attempt to address this vital subject with the mixed-cellular automata (MCA) method. Our proposed simulation model has integrated the strengths of the CA method with some probabilistic functions, offering a realistic mechanism to reflect the competing and conflict interactions between vehicle and pedestrian flows. To ensure the proposed model’s applicability, this study has used field data to demonstrate the parameter calibration process and examples of some applications. Our extensive experimental results clearly indicate that the simulation model could realistically capture the behaviors and characteristics of mixed flows, offering an effective tool for potential real-world applications.

Behr, Joshua G; Diaz, Rafael

doi: 10.1177/0037549714531055pmid: N/A

This article discusses the dynamics inherent in modeling and simulation (M&S) standards development processes within the context of the competitive struggle for resources and market dominance. A conceptual framework is presented that provides the theoretical logic for the tension between inclusive, consensus-driven standards development processes and exclusive, preferential processes. Standards development is conceptualized as a porous process subject to both cooperative interests and competitive pressures. We elucidate how the tension between these two process ideals shapes the adoption and conformity of M&S standards and, in turn, how these processes facilitate broader system values. Normative questions are explicated about the proper tradeoffs among the desire to realize collective efficiencies gained through standards, the drive to create, own, and financially exploit new, emerging technologies through the concept of intellectual property, and the objective of economic development through fostering innovation. Both the organizational and individual incentives to engage in standards processes are discussed, together with how the politics of participation may shape standards development. This research contributes a compelling theoretical perspective not fully developed in the growing and changing discipline of M&S. The significance of exploring these questions is found in that there is a national interest in M&S standards development activities that contribute to our technological innovation and economic competitiveness.

Kirke, Alexis; Miranda, Eduardo

doi: 10.1177/0037549714531060pmid: N/A

Pulsed Melodic Affective Processing (PMAP) is a method for the processing of artificial emotions in affective computing. PMAP is a data stream designed to be listened to, as well as computed with. The affective state is represented by numbers that are analogues of musical features, rather than by a binary stream. Previous affective computation has been done with emotion category indices, or real numbers representing various emotional dimensions. PMAP data can be generated directly by sound (e.g. heart rates or key-press speeds) and turned directly into music with minimal transformation. This is because PMAP data is music and computations done with PMAP data are computations done with music. This is important because PMAP is constructed so that the emotion that its data represents at the computational level will be similar to the emotion that a person “listening” to the PMAP melody hears. Thus, PMAP can be used to calculate “feelings” and the result data will “sound like” the feelings calculated. PMAP can be compared to neural spike streams, but ones in which pulse heights and rates encode affective information. This paper illustrates PMAP in a range of simulations. In a multi-agent simulation, initial results support that an affective multi-robot security system could use PMAP to provide a basic control mechanism for “search-and-destroy”. Results of fitting a musical neural network with gradient descent to help solve a text emotional detection problem are also presented. The paper concludes by discussing how PMAP may be applicable in the stock markets, using a simplified order book simulation.