bluuebunny/crossref_metadata_2025 huggingface dataset:
BRAF and NRAS mutations in melanoma: potential relationships to clinical response to HSP90 inhibitors
Authors: Banerji Udai , Affolter Annette , Judson Ian , Marais Richard , Workman Paul
Published: March 2008

Oncogenic BRAF and NRAS mutations are frequent in malignant melanoma. BRAF that is activated by the common V600E and other mutations, as well as by upstream NRAS mutations, has been shown to require the molecular chaperone heat shock protein 90 (HSP90) for stabilization and is depleted by the HSP90 inhibitor 17-allylamino-17-demethoxygeldanamycin (17-AAG)]. Here, we explore the possible relationship between tumor BRAF and NRAS mutations and clinical response to 17-AAG in six patients with metastatic malignant melanoma who received pharmacologically active doses of 17-AAG as part of a phase I clinical trial. One patient with disease stabilization for 49 months had a G13DNRAS mutation and WTBRAF. A second patient who had stable disease for 15 months had a V600EBRAF mutation and WTNRAS. These preliminary results suggest that BRAF and NRAS mutation status should be determined in prospective phase II studies of HSP90 inhibitors in melanoma. [Mol Cancer Ther 2008;7(4):737–9]
"Each to His Own Inheritance" Geography as an Evaluative Tool in the Genesis Apocryphon
Authors: Machiela Daniel
Published: March 2008

The Genesis Apocryphon has often been compared with the Book of Jubilees; especially the parallel accounts of Noah's oversight of the earth's post-flood distribution between his sons and grandsons (1QapGenar 16–17//Jub. 8:8–9:15). A close examination of the Genesis Apocryphon demonstrates that, while this comparison is valid, the two works are more different than scholars have typically assumed. Not only is the treatment of Noah's special role and the earth's proper division more widespread and prominent in the Apocryphon than in Jubilees, but the most directly corresponding passage exhibits a different arrangement. This may suggest a common cartographic source, and attests to a more robust interest in such geographic matters on the part of the Apocryphon. While both authors clearly drew on similar traditions, it is suggested that the author of the Genesis Apocryphon was more occupied with the right of Israel to the Promised Land than the author of Jubilees.
A Tool for Simulated Social Experiments
Authors: Szilagyi Miklos N. , Szilagyi Zoltan C.
Published: March 2008

A new agent-based model is presented of the investiga tion of collective behavior with a large number of deci sion makers operating in a stochastic environment. (An agent is an entity that interacts with and contributes to its environment. A set of agents can be a simplified representation of a society.) The model has three distinc tive new features: the number of agents in the model is theoretically unlimited; the agents have various distinct user-defined "personalities;" and the agents are described as combinations of cellular and stochastic learning au tomata. The combination of different personalities with stochastic learning makes it possible to simulate human- like behavior in social situations when each group mem ber must choose between maximizing selfish interests or collective interests. Our model is a framework to per form various simulated social experiments and assess the propagation of information and human influence in large-scale conflicting environments, e.g., to simulate realistic multi-person social dilemmas. We have devel oped a computational tool to implement this model. This is a powerful tool for investigating group dynamics that is also an advance in nonlinear dynamic system simu lation. It may lead to the discovery of a number of fac tors influencing human collective behavior.
A Computational Framework for Boundary-Value Problem Based Simulations
Authors: Adomaitis Raymond A. , Lin Yi-hung , Chang Hsiao-Yung
Published: March 2008

A framework is presented for step-by-step imple mentation of weighted-residual methods (MWR) for simulations that require the solution of boundary-value problems. A set of MATLAB-based functions of the computationally common MWR solution steps has been developed and is used in the application of eigenfunction expansion, collo cation, and Galerkin-projection discretizations of time-dependent, distributed-parameter system models. Four industrially relevant examples taken from electronic materials and chemical processing applications are used to demonstrate the simula tion approach developed. This library of functions and several demonstration scripts can be obtained from the MWRtools project Website located at http://www.ench.umd.edu/software/MWRtools.
Using Simulation To Evaluate Resource Utilization Strategies
Authors: Dear Roger G. , Sherif Joseph S.
Published: March 2008

This paper presents a simulation model that demonstrates the capability of simulation to evaluate resource allocation and dispatching strategies for technicians performing on-site repairs. The model includes real-world com plexities such as variable travel times based on direction of travel and time of day, and variable arrival rates (non-stationary Pois son process). Technicians take lunch breaks as close to their normally scheduled times as possible. Strategies include "First-Come, First-Served" and "Closest (shortest) Ex pected Travel Time. " Options to allow and disallow roaming between regions are inves tigated.
Simulations Technologies in the Mission Operational Environment
Authors: Surdu John R. , Pooch Udo W.
Published: March 2008

This paper proposes a methodotogy for applying sim ulation technology to the monitoring and control of operations, focusing on the use of intelligent agents. These agents monitor the course of the real operation and compare it with the near-real-time simulation of that operation. When these agents detect significant differences between the planned operation and the real operation, they explore the discrepancies to determine the impact on the desired outcome of the operation. These agents can launch additional simulations or other tools to make this determination. In cases in which the success of the plan is threatened, the agents advise the decision maker. The contributions of this research are (1) to help identify the requirements for a simulation designed for use during operations and (2) the development of a methodology for using sim ulation, along with rational agents, to compare the real, ongoing operation with the planned operation and make recommendations when appropriate. While several training simulations have been developed, there are currently no tools that provide this simula tion-based, agent-assisted operation monitoring/ analysis capability to decision makers.
Poisson Simulation—A Method for Generating Stochastic Variations in Continuous System Simulation
Authors: Gustafsson Leif
Published: March 2008

In continuous systems simulation a model is built as a system of differential equations. An implicit assump tion is that the number of items is so large that the changes can then be regarded as continuous. How ever, many systems can be modeled by differential equations when the numbers involved are moderately large. Such systems show stochastic variations that can be described in terms of events per time unit. If the events happen one at a time, and if the number of events during the interval is independent of both the number of past events and the times these events oc curred, we have a Poisson process. The system's variations can be modeled by replacing the flow to or from a state during the integration step with a Pois son probability. This not only adds variations to the model, but can also reveal system properties not cov ered by continuous system simulation. Furthermore, the "intensity parameter" controlling the flow may vary over time without further problems.
A Regression Approach For Developing Mathematical Models For Management and Operations Training Simulators
Authors: Chung Christopher A.
Published: March 2008

This paper presents a new linear regression- based approach for developing mathematical models suitable for use in management and operations training simulators. This novel approach modifies static cost-independent regression models into dynamic accountable simulator models that translate input resource decisions into output performance feedback. Entirely new techniques have been developed for accounting for time, determining resource allocation cost rates, translating resource allo cation into technical performance, and incor porating probabilistic effects. These techniques offer both empirical and probabilistic advan tages over existing methods.
A Simulation Approach for Establishing Limits on Quality Expenditures
Authors: Mackulak Gerald T. , Carter Joseph , Mendez Edward G.
Published: March 2008

This article proposes a methodology for quantitatively specifying the hidden cost of quality in a dry goods distribution ware house. Determining this cost is particularly important in manual paced environments since it is difficult to estimate the potential savings of quality improvements. We develop a simulation approach for predicting the manpower requirements as a function of a percentage error function. This method will quantitatively set a maximum expenditure limit for any proposed quality improvement effort. The methodology could also be adapted to any other flexible manual paced operation using autonomous operators.
Patient-Centered Simulation to Aid Decision-Making in Hospital Management
Authors: Moreno L. , Aguilar R.M. , Martín C.A. , Piñeiro J.D. , Estévez J.I. , Sigut J.F. , Sánchez J.L.
Published: March 2008

Computer simulation has eased the study of complex systems. A hospital is a complex sys tem that is formed by a large number of units with strong interrelationships. Even though resources are limited, patients must be effi ciently treated. This paper presents simulation as a tool to aid hospital management. In the first phase we present an introduction to the problem and its motivation. The next step is the description of how the system functions. The choice of the simulation model and the approach in dealing with it are described. Finally, the implementation of the simulation tool is pre sented. This tool is used for supporting the deci sion-making processes in hospital management.
A Simulation Framework for Subjective Listening Evaluation of Synthesized Automotive Sounds
Authors: Amman Scott A. , Das Manohar
Published: March 2008

This paper describes a simulation experiment to study the subjective listening evaluation of synthesized automotive sounds. Three types of digitized automotive sounds are used in the experiment: stationary, nonstationary, and impulsive. These are modeled and synthesized using a newly developed multipulse excitation technique, the characteristics of which can be controlled through careful selection of four key parameters. A blind subjective assessment scheme is devised and nine evaluators are asked to judge the qualities of the sounds syn thesized under varying parametric settings. An analysis of variance (ANOVA) performed on the experimental data reveals a number of useful relationships among the (perceived) qual ity, compression efficiency, and parametric set tings. The paper includes a detailed description of the simulation experiment and the results.
Flow Simulation in Stochastic Porous Media
Authors: Dodson C.T.J. , Sampson W.W.
Published: March 2008

A family of gamma distributions can be used to model the pore size distributions in a range of stochastic porous media. Our simu lator generates distributional and net flow data for different fluid flow regimes through such networks. The outputs from the simu lation show strong relationships between mean flow and the variance of pore radii for turbulent, laminar, molecular and capillary flow. We observe also affine relationships between the coefficient of variation of local flow rate and the variance of pore radii for each of the above flow modes.
Simulation of a Mobility Prediction Scheme Based on Neuro-Fuzzy Theory in Mobile Computing
Authors: Gil Joon-Min , Chan Yeol Park  , Hwang Chong-Sun , Han Youn-Hee , Jeong Young-Sik
Published: March 2008

Mobility prediction is an important issue for efficient management in mobile computing. Whenever users move to a new location, mobile systems should know about their location change so that the connection is not in terrupted. In this paper, we focus on the simulation of a user mobility prediction scheme based on neuro-fuzzy theory. Our scheme predicts future locations from the movement patterns of users accumulated over several days or months, i.e., the user's location history. In or der to model users' movements, we use a neuro-fuzzy inference system. Whenever a user moves to a new lo cation, the system autonomously learns various move ment patterns. The prediction of the future location to which users will move is obtained by the approximate reasoning of the neuro-fuzzy inference system. This ap proach can derive an appropriate future location from learned location information, even if the mobile systems do not know the actual location history. Simulation re sults show that our prediction scheme has high accuracy for various users' patterns. In addition, our scheme is applicable, with considerable prediction accuracy, to users whose history has not been learned by the neuro- fuzzy inference system.
Microprocessor Simulation and Program Assembling Using Spreadsheets
Authors: El-Hajj Ali , Kabalan Karim Y. , Mneimneh Maher , Karablieh Feras
Published: March 2008

In this paper, a method for simulating micro processor systems using modern spreadsheet programs is presented. The microprocessor architecture is depicted in one sheet and used to simulate the result of a step-by-step program execution. This simulation allows the user to write a program on a separate sheet from an instruction set available on two separate sheets. This program will then be assembled using the instruction information sheets and executed on the microprocessor architecture sheet. Additional sheets are also accessible for listing memory contents and input/output ports. This simula tion has been illustratively applied to the Z80 microprocessor.
Three-Dimensional Acoustic Simulation Based on Virtual Environments
Authors: Zhu Xiaoguang  , Hong Bingrong  , Wang Dongmu
Published: March 2008

In order to enhance fidelity and reduce confusion through compensation of vision, it is necessary to investigate three-dimensional acoustic simulation over headphones based on virtual environments. Localization cues that can provide positional infor mation such as head-related transfer function, in teraural time difference, and interaural intensity difference, play an important role in three-dimen sional acoustic simulation. Audio signal processing based on wavelet transform and Huffman encoding reduces data storage and transmission to meet lower bit rate requirements in interactive environments. Visual and aural fusion through a synchronic con trol mechanism make acoustic simulation environ ments closer to the natural world to achieve the goal of three-dimensional acoustic simulation based on virtual environments. Psychoacoustic tests of acous tic simulation based on virtual environments dem onstrate that this simulation method is efficient and reliable.
A Model of a Complex Family Economy
Authors: McDowell Cheryl
Published: March 2008

Model name "simFamily." This program is a model of a complex family economy. It first presents a defined family consisting of three family members (husband, wife, child) and a family pet (dog). The program prompts for different scenarios for this family's life time. After entering the different scenarios, the simu lation will output the family status for each year.
Simulation of UICCELL II
Authors: Chang Carl K. , Yong Liu  , Kenevan James , Murthy Thribhuvana , Mongkolwat Pattanasak
Published: March 2008

In this paper we discuss a new approach to Perfor mance Engineering called the Object-Oriented Per formance Engineering Approach (OOPEA). OOPEA is an innovative approach to performance modeling, simulation and design where an object-oriented per formance analysis model, a discrete-event simula tion model and an operational model are integrated into a modeling framework. We emphasize simula tion in this paper and present a case study on the UICCELL II (University of Illinois at Chicago CELLular II switching system), a software simula tor of a cellular phone system. The system can be divided into three main components: the Mobile Switching Center, Base Site, and Mobile Telephone Unit, which have client-server relationships and communicate with each other using IPC facilities, via message passing. The UICCELL II is implemented in a distributed environment on SUN SPARC 1 and 10 workstations using an Ethernet LAN. Sim ulation is used to examine the dynamic behavior of the system, and helps to capture the performance constraints, mainly the contention for resources.
A Parallel Simulation Methodology for Speedup and Obtaining Performance Estimates with Specific Accuracy: Experiences of its Application in Studies of Metropolitan Area Networks
Authors: Yau Victor , Pawlikowski Krzysztof
Published: March 2008

Performance measures obtained by stochastic simula tion are estimates, and one must consider the precision of the estimates before making any constructive con clusions about the investigated systems. This paper applies an automated distributed simulation method, called Spectral Analysis in Parallel Time Streams, to speed up production of performance estimates, and for run-length determination in the simulation of High- speed Metropolitan Area Networks (MANs). This method makes sequential simulators suitable for par allel execution on multiprocessors and/or networked computers. At runtime it estimates the information content of observations generated during simulation, generates a point estimate and confidence interval, and directs the run to continue until an estimate is obtained that achieves or exceeds our required level of precision. The application of this methodology for studying high-speed MANs, the speedup, intermachine communication and "warm-up" overhead, and the run lengths needed to produce estimates with a specific level of precision, are reported for each of the param eters investigated. Practical implications are discussed.
Personnel Airdrop Simulation
Authors: Fox Scott M. , Bailey T. Glenn , Carlton William B.
Published: March 2008

We develop an object-oriented simulation that models the airdrop mission of a U.S. transport aircraft, the C-1 7 Globemaster III. The simulation, written in MODSIM III, is based on three basic object types: an aircraft, a wake vortex, and a paratrooper. The aircraft object provides the required aerodynamic constants for simulating the wake vortices generated off each wingtip; the vortex object includes velocity field and decay models as well as a position algorithm; and the paratrooper object implements a 6-degree-of-freedom trajectory model. Using the simulation, we generate vortex encounter information for various formations and wind conditions, and quantify the associated risk of paratrooper/vortex encounters in a potential en counter rate. Time over the drop zone is a primary concern in any airdrop operation, and the results of this analysis form a tool that allows the ground com mander to assess the risk involved in decreasing that time.
Generating Driver Population for the Microscopic Simulation Model (CORSIM)
Authors: Chien Steven I.-Jy , Mouskos Kyriacos C. , Chowdhury Shoaib M.
Published: March 2008

CORSIM (CORridor SIMulator), an interval- based simulation model, was developed by the Federal Highway Administration (FHWA) to analyze traffic operations. In CORSIM, each ve hicle is a distinct object that moves every second, whose kinematic properties (speed, acceleration, and jerk) as well as its status (queued, moving, lane changing) are updated every second. Thus, driving behavior on roadways reflecting real- world traffic operations can be simulated. This paper suggests that the driving behavior repre sented by speed distributions over different driver types should be built in CORSIM to reflect more realistic patterns of driving behavior. The impact of the driver distribution to freeway capacity is demonstrated through simulation analysis.
Simulation Study of an Ideal Primary Care Delivery System
Authors: Pulat P. Simin , Kasap Suat , Splinter Garth L.
Published: March 2008

Health care delivery systems have gone through rapid changes in the last decade. As a result of these changes, researchers have conducted many studies on hospital resource planning, more specifically, on hospital bed planning. In this article, the strategic emphasis is on the primary care bed needs in the state of Oklahoma. Unlike most studies, this study focuses on designing an ideal primary care service delivery system, rather than evaluating the effec tiveness of the current system. The state is parti tioned into a minimum number of primary care ser vice centers satisfying accessibility constraints to assure quality service. A simulation model of the system is used to determine the minimum number of primary care beds needed in the state to provide service at targeted service levels at these centers. The results of the ideal scenario will give health care managers and planners a new perspective and help them in making strategic planning decisions in the future.
Modeling and Simulation in Systems Engineering
Authors: Sage Andrew P. , Olson Stephen R.
Published: March 2008

Simulation and modeling are major assets in the engineering of systems of all types. This two-part series addresses the much expanded role for M&S that is due to the prospect that evolutionary and adaptive engineering efforts are the wave of the future. The Department of Defense's Simulation BasedAcquisition initiative is a case in point, but some critical issues need to be addressed to bring it to fruition. In this first part, we set the background in systems engineering, information technology and the new role of complex adaptive system models that are changing our view of organizations as machines to organizations as organisms.
Modeling the Ultimate Seaweed Expansion
Authors: Hill D. , Coquillard P. , Aussem A. , de Vaugelas J. , Thibaut T. , Meinesz A.
Published: March 2008

Since 1984 the green tropical alga Caulerpa taxifolia (Chlorophyta), of aquarium origin, has spread rapidly along the north-western Mediterranean sea coast. This alga was recently discovered on the Mediterranean south coast (Tunisia) and the west coast of the United States. This paper presents modeling efforts to simu late Caulerpa taxifolia expansion. Three different mod els were built; the first model is based on stochastic discrete event simulation coupled with a geographical information system. The second model uses a neural network, trained with simulation data and is consid ered as a metamodel. The third is a multimodel de signed to simulate a biocontrol. Indeed, to control Caulerpa overhang, it may be possible to use special ized predator of C. taxifolia such as Elysia subornata (Mollusca, Ascoglossa). Simulation was mandatory before any introduction to estimate the potential re duction of the colonization by C. taxifolia. Encourag ing results concerning the use of E. subornata are pre sented.
Underestimation of Rare Event Probabilities in Importance Sampling Simulations
Authors: Smith Peter J.
Published: March 2008

The researcher faced with a computationally intensive simulation will either seek powerful processing capa bilities or turn to variance reduction techniques. In many situations, a combination of both approaches is required to achieve the desired accuracy. In the study of rare events, importance sampling (IS) is the only variance reduction technique which has been shown to offer the potential for substantial run time im provement. Indeed the dramatic improvements in run time demonstrated in the literature is strong motiva tion for the researcher to adopt IS as a day-to-day simulation tool. For this reason, it is important to have a clear understanding of the problems inherent in IS as well as the possibilities for improvement it offers. Hence in this paper, we discuss the potential problem with IS in underestimating the probability of rare events. We describe and illustrate the problem and suggest diagnostic plots to check for its occur rence. These diagnostics are quick and simple to use in any simulation and give the experimenter an easily interpreted output to identify the possible presence of underestimation in the simulation.
An Adaptive Control Mechanism for Management of Networked Information Consistency
Authors: Lin Ming-tang , Lee Chungnan , Lu Tain-chi , Shen Hung-Che
Published: March 2008

This paper discusses techniques for managing in formation consistency and controlling the dy namic shared state for a large-scale virtual envi ronment. Depending on the system load, this ap proach can automatically switch the dynamic shared state from one level to another to prevent performance degradation. Simulations were used to evaluate the proposed adaptive control mecha nism, the three-level consistency approach, and the shared repository technique. Performance results show that both the proposed mechanism and the three-level consistency approach can maintain low system load over a wide range of participants, but the adaptive control mechanism can adapt to the state of server load and provide a better service quality.
A Case Study on the Impact of Web-based Technology in a Simulation Analysis Course
Authors: Court Mary
Published: March 2008

A case study is presented on the use of web-based technol ogy to transition from a lecture-based delivery system to an online/multimedia technology delivery system at the University of Oklahoma's School of Industrial Engineer ing. Coupling web and multimedia technology with a pyramid approach to a simulation course sequence, the goal is to provide both undergraduate and graduate stu dents with strong simulation skills in both modeling and analysis. Web-based technology is used to provide course access to non-traditional students, to re-enforce prerequi site knowledge, and to support learning statistical con cepts. The approach has been successful at (i) generating two types of graduates, the simulation modeler and the simulation analyst/consultant, (ii) increasing the reten tion of non-traditional students (industrial engineering students with full-time jobs and other engineering majors without strong statistical backgrounds), and (iii) gradu ating two non-traditional students in the School's master's degree program as based on their research in simulation analysis. However, online technologies are not without their disadvantages. While the burden has been eased on student learning and their out-of-class activities, the faculty is now tasked with an increased load of sup porting online courses and utilizing web-based technolo gies both within and outside the classroom.
Enhancing Instructions Using Interactive Multimedia Simulations
Authors: Budhu Muniram
Published: March 2008

In this paper, simulations to enhance learning and retention in a course in Civil Engineering (Soil Mechanics) are presented. One type of simulation deals with the delivery of course con tent to better elucidate on selected basic concepts using interactive animations. Another type of simulation deals with the development of a vir tual laboratory in which the student can conduct laboratory tests and interpret the results as if they were in a real laboratory. Both of these types of simulations can be delivered on the Web or on portable storage media such as CD. The simula tions are integrated into an interactive multimedia courseware that contains interactive problem solving, electronic quizzes, a glossary, notation, a notepad, and computer program utilities in ad dition to the virtual laboratory and interactive animations of the selected topics. The simulations were developed using various royalty-free, com mercial software such as Authorware. Prelimi nary evaluations indicate that simulations can significantly enhance the presentation of some topics and improve learning and retention.
Free-surface Flow Simulations Using Parallel Finite Element Method
Authors: Aliabadi Shahrouz , Shujaee Khalil
Published: March 2008

In this paper, we present recent results in numeri cal simulation of free-surface flows using the paral lel finite element method. In our approach, the gov erning equations are the Navier-Stokes equations written for two incompressible fluids. We solve these equations over a non-moving mesh. An inter face function with two distinct values serves as a marker identifying the location of the free-surface. This function is transported throughout the com putational domain with a time-dependent advec tion equation. The stabilized finite element method is used to discretize the governing equations. The finite element formulations are implemented in parallel using Message Passing Interface libraries. High performance computing tools and optimized techniques are utilized to solve applications on un structured meshes with more than one billion tetra hedral elements. Numerical examples include the simulation of sloshing in tanker trucks and ships hydrodynamics.
Model-following Control of Nonlinear Servo Systems Using Neural Networks
Authors: Ouyang X. , Morgan C. , Nwagboso C.
Published: March 2008

The most useful property of neural networks for system identification and control is their ability to approximate arbitrary nonlinear mappings. In this paper, a new neural network model-following control method is proposed for nonlinear servo systems. First, three-layer artificial neural net works are trained to describe the forward and in verse dynamic characteristics of one type of speci fied nonlinear servo systems by using the backpropagation algorithm. Then the neural net work inverse model is used as a feedforward con troller for model-following control of the nonlin ear servo systems. Computer simulation results obtained from MATLAB verify the applicability of neural network identification and control for nonlinear servo systems.
A Simulation Environment for Multi-Sensor Planning
Authors: Hodge Lovell , Kamel Mohamed
Published: March 2008

The aim of this work is to design a flexible multi- agent environment for simulating the deployment of multiple sensors for a given sensing task. The envi ronment is based on a multi-agent architecture such that each sensor is controlled by an autonomous in telligent agent. This allows the user great flexibility in manipulating the number of sensors and also the capabilities of each sensor. The simulation system permits the user to visualize the outcome of the de ployment for various sensor configurations prior to implementation in the real world. Currently, the system focuses on the use of cameras for visual in spection tasks in which a single camera would be inadequate due to occluding objects in the scene or the sheer size of the target.
Simulation in the Service of Society
Authors: McLeod John , McLeod Suzette
Published: March 2008

Last month we presented our condensed ver sion of articles which had appeared in OP TIONS, journal of the International Insti tute for Applied Systems Analysis (IIASA, located in Laxenburg, Austria) which dealt with the Adaptive Dynamics Network project. Herewith further material from IIASA on the ADN study as applied to the evolution and adaptation of pathogens and their victims.—JM
Generalized Discrete Event Simulation of Bond Graph
Authors: Naamane A. , Giambiasi N. , Damiba A.
Published: March 2008

We propose a new approach dealing with the com bination of bond-graph with GDEVS formalism for modeling and simulation of complex systems using discrete event techniques. We show how to build discrete event simulation models for bond graph elements, with either piecewise linear in put-output trajectories or any kind of polynomial trajectories. One of the main advantages of our method is the reduction in the number of simula tion steps, and therefore the possibility of study ing dynamic hybrid systems using only the dis crete event paradigm.
The Integration of 3-D Visualization into the Simulation-based Planning Process of Logistics Systems
Authors: Wenzel Sigrid , Jessen Ulrich
Published: March 2008

The integration of information and communication tech nology into existing business processes effects all areas of a company, including factory planning. The structure of the process of change is based on model-supported pro cesses as well as tools and techniques that are already in use. These include established discrete event simulation tools that have been used in the area of production and logistics planning for several years, and innovative visual ization techniques such as 3-D animation, Virtual Reality (VR) and Augmented Reality (AR). Visualization has become very necessary in the planning, realization and operation of a factory because the data for the different target groups within a company, from the operating staff up to management, has to be processed into realizable in formation. The authors, motivated by this initial situation, have placed the conceptual universality of the use of meth ods in the foreground, using distributed architecture and the targeted use of 3-D modeling in logistics planning as an add-on to discrete event simulation. This article intro duces a generally applicable concept for the user-defined mapping of discrete event simulation models onto anima tion models, describes the aspects of realization, and con siders integration into an animation pipeline.
Visualization of Mobile Network Simulations
Authors: Dahlberg T.A. , Subramanian K.R.
Published: March 2008

The use of adaptive techniques in mobile networks permits scalable resource allocation policies to meet varying demand as well as Quality of Service (QoS) performance objectives. As these algorithms operate at multiple layers of the communications architecture, evaluation of such techniques must take into account a variety of scenarios, which are in turn parameterized by a large number of variables. The need to monitor algorithm behavior in real time results in a data explosion. In this work, we propose new real-time metrics to characterize and identify the critical states of a mobile network in the wake of channel failures, congestion, signal degradation, etc. We use these metrics to define a survivability index, a measure of mobile network performance in the wake of failures. We demonstrate the effectiveness of information visu alization techniques in understanding the complex spatial and temporal relationships between perfor mance and cost metrics that influence adaptive algo rithms. Our visualization system is highly scalable and interactive, permitting multiple algorithms to be simultaneously evaluated. We demonstrate applica tions to network monitoring and to the design and evaluation of adaptive admission control algorithms.
Parallel and Sequential Job Scheduling in Heterogeneous Clusters: A Simulation Study Using Software in the Loop
Authors: Collins David E. , George Alan D.
Published: March 2008

The task of designing and optimizing job scheduling algorithms for heterogeneous computing environments requires the ability to predict scheduling performance. The complexity of heterogeneous scheduling issues re quires that the experiments devised to test a scheduling paradigm to be both flexible and extensive. Experimen tally determined models for the prediction of job execu tion times on both sequential and parallel computing resources are combined with the implementation of a novel scheduling algorithm and a software-in-the-loop (SWIL) simulation. The result is a potent design and analysis approach for job scheduling algorithms and implementations intended for heterogeneous environ ments. This paper develops the concepts, mechanisms, and results of a SWIL design and analysis approach. The merits of this approach are shown in four case stud ies, which determine overhead, scheduling performance, and the impact of preemption and priority policies. These case studies illustrate the contributions of this research in the form of a new parallel job scheduling algorithm for heterogeneous computing and in the novel application of SWIL simulation to the analysis of job scheduling systems.
Comparison of Load Balancing Strategies on Cluster-based Web Servers
Authors: Yong Meng Teo  , Ayani Rassul
Published: March 2008

This paper focuses on an experimental analysis of the perfor mance and scalability of cluster-based web servers. We carry out the comparative studies using two experimental platforms, namely, a hardware testbed consisting of sixteen PCs, and a trace-driven discrete-event simulator. Dispatcher and web server service times used in the simulator are determined by carrying out a set of experiments on the testbed. The simulator is validated against stochastic queuing models and the testbed. Experiments on the testbed are limited by the hardware configu ration, but our complementary approach allows us to carry out scalability studies on the validated simulator. The three dis patcher-based scheduling algorithms analyzed are: round robin scheduling, least connected based scheduling, and least loaded based scheduling. The least loaded algorithm is used as the baseline (upper performance bound) in our analysis and the performance metrics include average waiting time, average re sponse time, and average web server utilization. A synthetic trace generated by the workload generator called SURGE, and a public-domain France Football World Cup 1998 trace are used. We observe that the round robin algorithm performs much worse in comparison with the other two algorithms for low to medium workload. However, as the request arrival rate increases, the performance of the three algorithms converge with the least con nected algorithm approaching the baseline algorithm at a much faster rate than the round robin. The least connected algorithm performs well for medium to high workload. At very low load, the average waiting time is two to six times higher than the baseline algorithm but the absolute value between these two waiting times is very small.
Alternative Solutions for Distributed Simulation Cloning
Authors: Chen Dan , Turner Stephen John , Gan Boon Ping , Cai Wentong , Wei Junhu , Julka Nirupam
Published: March 2008

Simulation cloning is designed to satisfy the requirement of examining alternative scenarios concurrently. This article discusses the issues involved in cloning distributed simulations based on the High Level Architecture (HLA) and proposes tentative solutions. Alternative solutions are compared from both the qualitative and quantitative point of view. In terms of federation organization, candidate solutions can be classified into the single-federation and the multiple-federation categories. To guarantee the correctness and optimize the performance of the whole cloning-enabled distributed simulation, the single-federation solution requires an additional mechanism to isolate the interactions among alternative executions. Data distribution management (DDM) is one of the candidate approaches. To measure the trade-off between complexity and efficiency, the authors introduce a series of experiments to benchmark various solutions at the runtime infrastructure (RTI) level. The benchmark results indicate that the single-federation solution provides encouraging performance when using DDM.
HIPERSIM: A Sense Range Distinctive Simulation Environment for HiperLAN Systems
Authors: Papadimitriou G. I. , Lagkas T. D. , Pomportsis A. S.
Published: March 2008

This paper presents the simulator “HIPERSIM” which was developed and used to examine the behavior of HIPERLAN (Type 1). HIPERSIM simulates the HIPERLAN network under various conditions, assuming that the communication range and the sense range (signal detection range) of a node are different. In a wireless LAN, like HIPERLAN, the medium access protocol, the hidden nodes, the packet forwarding and the power saving mechanism are important issues that significantly affect the overall performance. The intention is to provide a HIPERLAN specialized tool (HIPERSIM) which can simulate most of the features of this WLAN protocol, in order to examine the performance of HIPER-LAN. The main focus is to simulate the channel access mechanism accurately, so as to examine the effectiveness of the EY-NPMA protocol, and underline its advantages and the elements that need improvement. Also, in HIPERSIM, there is emphasis on the “hidden nodes” issue. More specifically, we distinguish between the communication range and the signal detection range of a node, since this is a characteristic of the wireless nature and it affects the network operation. The simulation results show that EY-NPMA is effective and suitable for WLANs. Probably there could be some improvement in order to avert the collisions close to the receiver.
Real-Time Analog-Digital Computation
Authors: Connelly Mark E.
Published: March 2008

The relative advantages of analog and digital tech niques in simulating complex, nonlinear systems in real-time are discussed. A hybrid configuration is suggested consisting of a basic digital computer and peripheral, high-speed analog elements used on a time-shared basis under the control of the digital program. Programs for function generation and for the solution of the aircraft roll equation are presented to illustrate the operation of the hybrid computer and the significant increase in the effective computing speed of the digital computer that results from the incorporation of peripheral analog elements. Further gains can be made by tailoring the order code and logic of the digital computer to the specific prob lem class of interest.

The hypothesis is presented that a hybrid computer is technically feasible today that would be competitive with analog techniques on the basis of both cost and the ability to simulate natural aircraft frequencies in real-time. Moreover, such a computer would offer substantial advantages with respect to accuracy, dynamic range, flexibility, size, power consumption, and reliability.
Analog Computer Solution of the Orbital Flight Equations
Authors: Fogarty L.E. , Howe R.M.
Published: March 2008

A modified flight-path axis system is introduced to simplify computer mechanization of the orbital flight equations. Complete six degree-of-freedom equa tions are presented, including aerodynamic, power- plant, and control forces. Electronic differential analyzer mechanization of these equations in both real and fast time is described, including a novel technique for division which preserves favorable multiplier scaling. Specific machine results are presented which demonstrate accurate solution of close-satellite tra jectories, including re-entry from satellite altitudes to sea level. With no change in circuit or scaling the same computer mechanization yields zero-drag orbits which close within several hundred feet of altitude.
A Dynamic Simulation Laboratory as a Teaching Aid
Authors: Brickman Arthur D. , Park William H.
Published: March 2008

Dynamic simulation of mechanical systems can add an important new dimen sion to the study of engineering design. A student laboratory that gives equal emphasis to analog simulation and actual experimentation as aids in problem- solving has recently been incorporated into an existing course at Penn State.*
Optimization of Analog Computer Linear System Dynamic Characteristics
Authors: Sengle Charles H. , Billinghurst Edward M.
Published: March 2008

The characteristics of the linear computing elements of the general-purpose electronic differential an alyzer are discussed. Equivalent circuits are given for these elements. Criteria for optimization of the linear computing system in order to obtain maximum computational accuracy are given. Examples of the effects of optimization in improving system stability, transient response, and in increasing bandwidth of high- and medium-accuracy computation are shown.
Itching to Get Into Print?
Authors: Rogers Stanley
Published: March 2008

WE SOLICIT ARTICLES and papers presenting surveys, tutorial reviews, or interesting applications of simulation. When submit ting material for publication, you can save us time and greatly help our staff by observing the following guidelines
A Heuristic Approach to the Maximum Principle
Authors: Witsenhausen Hans S.
Published: March 2008

This is a companion article to Hybrid Simulation of Adaptive Path Control (page R-24 in this issue) in that it explains a prin ciple which is used to advantage in the adaptive control study.
A Comparison of Higher-Order Difference Methods in the Solution of Beam-Vibration Problems
Authors: Greenwood Donald T.
Published: March 2008

Several higher-order difference methods are investi gated and compared for the problem of finding the natural frequencies of the lateral vibration of a beam. All of the methods considered are applicable to either digital or analog computers, although particu lar reference is made to the analog computer.

The methods considered in most detail use the same basic central difference approximation, the variations occurring in the method of representing boundary conditions. Three higher-order approaches to the problem of boundary conditions are pre sented. They are 1) the use of one-sided differences of fourth order, 2) the use of symmetry assumptions, and 3) the passive-circuit approach. Each method is shown to have its advantages, the final choice de pending upon the particular requirements of the problem.

Results are presented in the form of curves of per centage mode-frequency error vs number of cells for the various approximation methods.
A Simulator Study of a Two-Parameter Adaptive System
Authors: McGrath R.J. , Rideout V.C.
Published: March 2008

The use of sinusoidal parameter perturbation applied to a feedback control system to obtain an adaptive scheme which optimizes the system for changes in inputs and/or system parameters is discussed. It is shown that if a parameter perturbation signal is cross- correlated with the system error squared, the corre lator output can be used to adjust the parameter to minimize the mean-square error. Other error meas ures may also be used. Two or more parameters may be simultaneously adjusted, if they are perturbed at different frequencies and each is provided with an independent adaptive loop. A computer simulation of a third-order system having two adjustable param eters was examined for a variety of inputs including random signals. It is shown that the scheme mini mizes the mean-square error in all cases.
The Heat and Mass Flow Analyzer
Authors: Paschkis V.
Published: March 2008

After having introduced in a simplified way the RC circuit-heat conduction analogy in one- and two- dimensional problems, the influence of variable properties is added to the electrical setup.

The processes involving freezing and melting of pure metals and alloys are studied as an important application of these simulators.

Problems with repetitive processes are particularly suited to be solved by computers. Networks can be built for simulating heat exchange.

These simulators can be made more flexible by introducing active elements like voltage-dependent voltage- and current-sources. One application of these devices is the simulation of a thermal regen erator.

A DC-electrolytic tank has been developed for the study of three-dimensional problems.