James J. Nutaro

Oak Ridge National Laboratory | ORNL · Computational Sciences and Engineering Division

Although adoption of newer Point-of-Care (POC) diagnostics is increasing, there is a significant challenge using POC diagnostics data to improve epidemiological models. In this work, we propose a method to process zip-code level POC datasets and apply these processed data to calibrate an epidemiological model. We specifically develop a calibration...

Computational disease spread models can be broadly classified into differential equation-based models (EBMs) and agent-based models (ABMs). We examine these models in the context of illuminating their hidden assumptions and the impact these may have on the model outcomes. Drawing relevant conclusions about the usability of a model requires reliable...

With the transition towards a smart grid, the power system has become strongly intertwined with the information and communication technology (ICT) infrastructure. The interdependency of both domains requires a combined analysis of physical and ICT processes, but simulating these together is a major challenge due to the fundamentally different model...

In this article we illustrate the use of modeling and simulation early in the system life-cycle to improve security and reduce costs. The models that we develop for this illustration are inspired by problems in reliability analysis and supervisory control, for which similar models are used to quantify failure probabilities and rates. In the context...

We describe a cost-effective retrofit technology that uses collective control of multiple rooftop air conditioning units to reduce the peak power consumption of small and medium commercial buildings. The proposed control uses a model of the building and air conditioning units to select an operating schedule for the air conditioning units that maint...

We present a framework for verification and validation of simulation models of System of Systems that is based on an existing framework for modeling and simulation. The framework addresses problems arising especially in recently emerging Systems of Systems such as cyber-physical autonomous cooperative systems. The design of such systems presents ch...

Discrete Event Systems Specification (DEVS) is a widely used formalism for modeling and simulation of discrete and continuous systems. While DEVS provides a sound mathematical representation of discrete systems, its practical use can suffer when models become complex. Five main functions, which construct the core of atomic modules in DEVS, can real...

We propose an approach to addressing questions about the validity of a simulation model and we develop this approach in detail with respect to two objectives. The first objective is to decide when a successful test conducted on a model of a system justifies increased confidence in the system. The second objective is to decide when a model may be re...

Amdahl asserted that a program can run no faster than inversely related to the number of processors compared to what it can on a single processor. This speed up relation was originally stated as an assumption and has never been proved as such. For discrete event simulation, this implies that a distributed simulation is similarly limited in speed. I...

An agent-based simulation model hierarchy emulating disease states and behaviors critical to progression of diabetes type 2 was designed and implemented in the DEVS framework. This model was built to approximately reproduce some essential findings that were previously reported for a rather complex model of diabetes progression. Our models are trans...

This article describes a new back-end and run-time system for the OpenModelica compiler. This new back-end transforms a Modelica model into a module for the adevs discrete event simulation package, thereby extending adevs to encompass complex, hybrid dynamical systems. The new run-time system that has been built within the adevs simulation package...

System dynamics models are usually used to investigate aggregate level behavior, but these models can be decomposed into agents that have more detailed individual behaviors. Here we develop a simple model of the STEM workforce to illuminate the impacts that arise from the disaggregation and refinement of system dynamics models via agent-based model...

In the last three decades, there has been an exponential growth in the area of information technology providing the information processing needs of data-driven businesses in government, science, and private industry in the form of capturing, staging, integrating, conveying, analyzing, and transferring data that will help knowledge workers and decis...

Control systems are computer-based systems with networked units consisting of sensors, actuators, control processing units, and communication devices. The role of control system is to interact, monitor, and control physical processes. Reactive power control is a fundamental issue in ensuring the security of the power network. It is claimed that Syn...

Utility companies are integrating multiprotocol label switching (MPLS) technologies into existing backbone networks, including networks between substations and control centers. MPLS has mechanisms for efficient overlay technologies as well as mechanisms to enhance security: features essential to the functioning of the smart grid. However, with MPLS...

The success of data-driven business in government, science, and private industry is driving the need for seamless integration of intra and inter-enterprise data sources to extract knowledge nuggets in the form of correlations, trends, patterns and behaviors previously not discovered due to physical and logical separation of datasets. Today, as volu...

The majority of funding for research and development (R&D) in cyber-security is focused on the end of the software lifecycle where systems have been deployed or are nearing deployment. Recruiting of cyber-security personnel is similarly focused on end-of-life expertise. By emphasizing cyber-security at these late stages, security problems are found...

Investments in the cyber-security of critical infrastructure must balance preventing intrusion, detecting a cyber-attack, and mitigating the attacker's physical effects on computer controlled equipment. For this purpose, we outline a method for making optimal investment decisions that balance these three aspects of a cyber-defense. The proposed met...

When large software projects fail, it is often because of inappropriate, misunderstood, or poorly conceived requirements. When a project is successful, the cost of building the system can be exceeded by the cost of correcting problems discovered after delivery. This is particularly true of cybersecurity problems, which are typically discovered afte...

This paper is motivated by the need to design model validation strategies for epidemiological disease-spread models. We consider both agent-based and equation-based models of pandemic disease spread and study the nuances and complexities one has to consider from the perspective of model validation. For this purpose, we instantiate an equation-based...

Observations of slow frequency signals in power systems have been explained by continuum wave equations that approximate the system's electromechanical dynamics. These continuum models predict that the signal speed is a function of the rotational inertia of the generators and impedances of the transmission lines. Here, we show that frequency signal...

Accurate radio channel modeling is essential for deploying advanced wireless sensors in harsh industrial and urban environments. Site-specific propagation modeling tools are required to understand the channel parameters with in these environments. Multipath delay spread determines the frequency-selective fading characteristics of the channel. This...

Frontier is a framework for a highly adaptable, stably reconfigurable, web–accessible intelligent decision engine developed to a) optimize the design of complex (particularly multi– asset or fractionated) systems, as well as b) simulate and operate systems distributed spatially and temporally in response to evolving needs and environments in suppor...

Loads acting autonomously on a local frequency signal can improve the response of a power system to sudden changes in supply, demand, or both. In this paper we address the use of load for regulating frequency by using feedback control. We extend prior research that focused on continuous proportional control, whereby one assumes that the load respon...

Today's complex technological systems cater to a wide variety of stakeholders and their construction involves a multitude of development disciplines. This paper reports on the design of a Modeling Support Environment (MSE) intended to support a large development project concerning the design of fractionated spacecraft architectures. We discuss uniq...

This paper introduces a new method for calculating frequency at an electrical load in simulations of electro-mechanical transients. The method is designed for simulation studies that require accurate models of sensors such as phasor measurement units and F-Net devices, which measure frequency at locations away from generating plants. These sensors...

The efficient and accurate management of time in simulations of hybrid models is an outstanding engineering problem. General a priori knowledge about the dynamic behavior of the hybrid system (i.e. essentially continuous, essentially discrete, or 'truly hybrid') facilitates this task. Indeed, for essentially discrete and essentially continuous syst...

The system performance metric “availability” is a central concept with respect to the concerns of a plant’s operators and owners, yet it can be abstract enough to resist explanation at system levels. Hence, there is a need for a system-level metric more closely aligned with a plant’s (or, more generally, a system’s) raison d’être. Historically, ava...

Fault tree analysis is a method for evaluating reliability and availability in terms of equipment system “states”, but this method does not lend itself easily to the evaluation of eq uipment interactions through time. This makes fault trees difficult to use for the analysis of systems whose reliability and availability depend on complex interaction...

Infrastructure-as-a-Service has revolutionized the manner in which users commission computing infrastructure. Coupled with Big Data platforms (Hadoop, Cassandra), IaaS has democratized the ability to store and process massive datasets. For users that need to customize or create new Big Data stacks, however, readily available solutions do not yet ex...

Future electric grid technology is envisioned on the notion of a smart grid in which responsive end-user devices play an integral part of the transmission and distribution control systems. Detailed simulation is often the primary choice in analyzing small network designs, and the only choice in analyzing large-scale electric network designs. Here,...

Open source software has a leading role in research on simulation technology for electrical power systems. Research simulators demonstrate new features for which there is nascent but growing demand not yet provided for by commercial simulators. Of particular interest is the inclusion of models of software-intensive and communication-intensive contr...

Collaborative modelling enables dispersed users to develop component-based system models in group settings. A realization of such an approach requires coordinating and maintaining the causality of the users’ activities. We propose the Collaborative DEVS Modelling (CDM) approach and its realization based on the Computer Supported Collaborative Work...

From a modeling and simulation perspective, studying dynamic systems consists of focusing on changes in states. According to the precision of state changes, generic algorithms can be developed to track the activity of sub-systems. This paper aims at describing and applying this more natural and intuitive way to describe and implement dynamic system...

Functional ModelingA Robotic TankDesign of the Tank SimulatorExperimentsSummary

Grid Friendly Appliances (GFAs) are water heaters, refrigerators, and other domestic electrical appliances that sense and respond to frequency problems in the electric power grid. The controller in a GFA monitors the power signal at its plug and turns the device off when the frequency drops below 59.95 Hz. When the frequency recovers its nominal va...

The U.S federal government's strategic vision encouraging renewable energy production has motivated several new energy generation projects. Among them are large-scale renewable energy farm building efforts, where one considers the renewable resource potential along with land, equipment, and installation costs. The goal in the planning phase of thes...

This paper presents a framework for creating a common spatial canvass that can bring together considerations of resource availability, infrastructure reliability, and development costs while strategizing renewable energy investment. We describe the underlying models and methodologies that annotate an investment plan for potential sites over a time-...

Cognitive radio systems are currently a popular topic and are a good prospect for research when combined with control technology. In this paper, we consider the control and estimation via a two switch model which can represent a cognitive radio system. We provide an optimal estimator for this model and demonstrate that the optimal LQG controller is...

We discuss the evolving role of communication and control for automatic load management in electric distribution systems. We start by reprising a description of the Athens project - one of the earliest deployed examples of automatic load management at consumers enabled by communication signals. We observe that the use of communication for such syst...

With the modernization of Department of Defense (DoD) systems and the growing complexity of communication equipment, traditional test methods and processes have to evolve in order to maintain their effectiveness. DoD acquisition policy requires the use of modeling and simulation (M&S) in all phases of system development life-cycles in order to ensu...

Critical infrastructure sites and facilities are becoming increasingly dependent on interconnected physical and cyber-based real-time distributed control systems (RTDCSs). A mounting cybersecurity threat results from the nature of these ubiquitous and sometimes unrestrained communications interconnections. Much work is under way in numerous organiz...

This paper considers state estimation of linear stochastic discrete-time systems through an unreliable network. Packet losses from the sensor to the estimator are assumed to follow a Bernoulli distribution, while information loss is not assumed to be available at the receiver at any time. The optimal estimator provides a satisfactory estimate under...

Emergency evacuations are carried out in anticipation of a disaster such as hurricane landfall or flooding, and in response to a disaster that strikes without a warning. Existing emergency evacuation modeling and simulation tools are primarily designed for evacuation planning and are of limited value in operational support for real time evacuation...

We generalize a model, proposed by Alvarado, of the electric power market by including the effects of control and communication. To simulate realistic markets, our model issues control signals only at given times and those signals are delayed during transmission. These two effects transform Alvarado's continuous system into a hybrid system, with co...

Combat resiliency is the ability of a commander to prosecute, control, and consolidate his/her's sphere of influence in adverse and changing conditions. To support this, an infrastructure must exist that allows the commander to view the world in varying degrees of granularity with sufficient levels of detail to permit confidence estimates to be lev...

The Computational Sciences and Engineering Division of the Oak Ridge National Laboratory is partnering with the University of Tennessee Graduate School of Medicine to design a computational model describing various factors related to the development of intimal hyperplasia (IH) in response to arterial injury. This research focuses on modeling the ch...

This paper considers the estimation of a linear stochastic discrete-time system through an unreliable network. Packet losses from the sensor to the estimator are assumed to follow a Bernoulli distribution, while information loss at any time is not assumed to be available at the receiver. A new estimator is derived from the Kalman filter by using th...

Human exposure models often make the simplifying assumption that school children attend school in the same census tract where they live. This paper analyzes that assumption and provides information on the temporal and spatial distributions associated with school commuting. The data were obtained using Oak Ridge National Laboratory's LandScan USA po...

Discrete event models have become an important tool in theoretical biology. There is, at the same time, a growing awareness of the methodological issues that arise in connection with discrete event systems. Synchronization between discrete event and continuous model components and the handling of simultaneous events are technical issues that many s...

This article describes a Time Warp simulation algorithm for discrete event models that are described in terms of the Discrete Event System Specification (DEVS). The article shows how the total state transition and total output function of a DEVS atomic model can be transformed into an event processing procedure for a logical process. A specific Tim...

DEVS is a formalism intended to model both discrete and continuous systems. The use of discrete events, rather than time steps, as the basis for simulation has been shown to reduce the computation time in many applications. Parallel DEVS is an extension to standard DEVS, which provides means to handle simultaneous scheduling. In this paper, we pres...

This paper describes a method for creating synthetic air tracks without the aide of a sophisticated simulator. The proposed method creates a position and velocity function for an aircraft given its starting location and speed, altitude, and heading on each leg of its height. An optimization procedure is used to fit the position and velocity functio...

Purpose This paper aims to address a central concern in modeling and simulating electric grids and the information infrastructure that monitors and controls them. The paper discusses the need for and methods to construct simulation models that include important interactions between the physical and computational elements of a large power system. D...

Modeling and simulation is essential for understanding complex ecological systems. However, knowledge of the structure and behavior of these systems is limited, and models must be revised frequently as our understanding of a system improves. Moreover, the dynamic, spatial distribution of activity in very large systems necessitates mapping natural m...

We describe a scalable method for predicting radio channel path-loss in cluttered environments. The method is designed for constructing path-loss look-up tables that can be integrated with a mobile wireless network simulation. The proposed simulation technique is a much simplified version of the transmission line matrix method; the simplifications...

This paper establishes a link between the stability of a first order, explicit discrete event integration scheme and the stability criteria for the explicit Euler method. The paper begins by constructing a time-varying linear system with bounded inputs that is equivalent to the first order discrete event integration scheme. The stability of the dis...

As the network centric warfare and distributed operations paradigms unfold, there is a growing need for robust wireless network deployment tools. These tools must take into consideration the terrain of the operating theater, and facilitate modeling of end to end network performance based on accurate RF propagation predictions. It is well known that...

The modern power grid is strongly integrated with its communication network. While a power system primarily consists of elements that are modeled by continuous equations, a communication system has discrete event dynamics. We model the integrated operation of these two systems with a hybrid modeling and simulation technique. Systematically combinin...

This paper proposes a second order accurate, Adams- Bashforth type, asynchronous integration scheme for numerically solving systems of ordinary differential equations. The method has three aspects; a local integration rule with third order truncation error, a third order accurate model of local influencers, and local time advance limits. The role o...

Computer simulation of a system described by differential equations requires that some element of the system be approximated by discrete quantities. There are two system aspects that can be made discrete; time and state. When time is discrete, the differential equation is approximated by a difference equation (i.e., a discrete time system), and the...

This paper characterizes a class of hybrid systems that can be readily integrated with discrete event models and seamlessly simulated using available discrete event simulation software. We characterize this class of hybrid systems in terms of the discrete event system specification, hybrid input/output automata, and as an event oriented simulation...

Migration of vascular smooth muscle cells is a fundamental process in the development of intimal hyperplasia, a precursor to development of cardiovascular disease and a potential response to injury of an arterial wall. Boyden chamber experiments are used to quantify the motion of cell populations in response to a chemoattractant gradient (i.e., cel...

The combination of DoDAF operational views, which capture the requirements of an architecture, and System views, which provide its technical attributes, forms the basis for semi-automated construction of simulation models. In this paper, we describe an enhanced Model-View-Controller paradigm that works in tandem with the DEVS M&S framework. We also...

Integrated digital human modeling has seen increased interest over the last decade. We describe two efforts to develop computational frameworks for digital human modeling and describe the progress toward understanding the requirements for implementation. Both projects addressed data repository, computational envi- ronment, and visualization of resu...

This article describes a discrete event interpretation of the finite difference time domain (FDTD) and digital wave guide network (DWN) wave simulation schemes. The discrete event method is formalized using the discrete event system specification (DEVS). The scheme is shown to have errors that are proportional to the resolution of the spatial grid....

The systematic study of discrete event numerical integration schemes can be greatly aided by an understanding of their general form. This paper describes the structure of DEVS models that can be used to construct multi-point discrete event integration methods. The structure is shown to be sufficient for describing two known methods. The utility of...

This paper compares ray tracing, finite difference time domain, and the event driven transmission line matrix models as tools for making site specific path-loss predictions in cluttered environments. A brief overview of each type of model is presented. The accuracy and computational cost of a ray tracing, FDTD, and event based TLM model are compare...

Discrete Event System Specification (DEVS) simulation libraries commonly make use of indirection and, essen-tially, typeless events as part of their interface specifi-cation. This forces library users to employ downcasting and/or strong data coupling in the design of their sim-ulation applications. These techniques are anathema to good object orien...

Results will be presented for kinetics of matrix metalloproteinases (MMP), enzymes that play a significant role in vascular remodeling. Three different computational approaches for well-mixed kinetics processes will be analyzed and compared. The kinetics of one MMP, namely MMP2, were elucidated using a model and rate constants from published litera...

Complex spatially-extended systems consist of numerous sub-systems leading to large simulation execution times. One approach to reducing these execution times is designing a simulation engine to allocate its attention to subsystems in proportion to their activity levels. In this paper, we consider a large scale simulation of a physics-based fire sp...

This article presents a framework for distributed simulation that is based on system-theoretic and logical-process concepts. The framework describes a three-part worldview for developing simulation models. These are modeling formalisms, abstract simulators, and computational environments. A unified view of time and causality allows for the applicat...

Defense-related simulation efforts are increasingly focused on component-based simulation development. This focus is reflected in efforts to design new simulation software in terms of interacting components that can be understood and reused in isolation or collectively and to modify legacy simulators to incorporate new component-based simulation te...

The DEVS (Discrete Event Systems Specification) formalism has been applied to continuous and discrete phenomena. The use of discrete events, rather than time steps, as a basis for simulation has been shown to reduce computation time by orders of magnitude in many applications. However, the application of DEVS to partial differential equation (pde)...

This paper presents a framework for distributed simulation that is based on system-theoretic and logical-process concepts. The framework describes a three-part world-view for developing simulation models. These are modeling formalisms, abstract simulators, and computational environments. A unified view of time and causality allows for the applicati...

This paper discusses a concept of DEVS middleware that would provide a set of services for constructing discrete event models and executing them in simulation or in real-time. Although generic middleware such as CORBA and MPI supports simulation and simulation-oriented middleware such as High Level Architecture Runtime Infrastructure exists, there...

Optimistic and conservative simulation algorithms have been effective for speeding up the execution of many simulation programs. Event stepped techniques have also been shown to be effective for certain types of problems. This paper presents a conjecture that sparse systems are effectively simulated by conservative and optimistic techniques, where...

This article provides perspectives on how a test organization can organize and plan for enterprise-wide adoption of advances in emerging technologies and techniques, whether developed in-house or acquired from external sources. This article enumerates capabilities that greatly enhance a test organization's ability to support the impending testing d...

With the modernization of Department of Defense (DoD) systems and the growing complexity of communication equipment, traditional test methods and processes have to evolve in order to maintain their effectiveness. DoD acquisition policy requires using modeling and simulation in all phases of system development life-cycles to ensure technical certifi...

Numerous socio-environmental studies, including those in public health, utilize population data as one of the essential elements of modeling and analysis. Typically population data are reported by administrative or accounting units. For example, in the US the Census Bureau reports population counts by census blocks, block groups, and tracts. At any...