bluuebunny/crossref_metadata_2025 huggingface dataset:
A heuristic elimination method for optimum selection of alternatives through simulation
Authors: Schmidt J.W. , Taylor R.E. , Bennett G.K.
Published: March 2008

This paper presents a technique for selecting an optimum alternative from among a limited set of possible alternatives. The method presented is an algorithmic successive-elimination procedure which uses simulation to measure the "cost" of each alter native. The algorithm requires the calculation of estimates of confidence intervals of the mean "cost" for each alternative after each replication of the simulation. By comparing the confidence limits and "costs" for each alternative after each replication, one or more alternatives may be elim inated from consideration. The procedure ends when only one alternative remains or when the criteria used indicate that further analysis would be uneconomical.
Interactive modeling as a forcing function for research in the physiology of human performance
Authors: Miller Nicholas C. , Walters Richard F.
Published: March 2008

Physiological models are frequently designed to study a single-organ system or to investigate the differ ences in response of alternative representations of the same system. In this study, an interactive model portrays the human circulatory, thermoregulatory, and energy-exchange systems as an intercoupled set and serves as a means of communication between mem bers of an interdisciplinary research team. The assumptions necessary to couple these systems are described, as are the research team's techniques for using the model. The goal is to develop the model to the point of accurately simulating the real-world behavior of the coupled systems in normal human beings and in those with certain diseases. The model serves to focus the team's attention on areas requiring additional experimentation, which in turn leads to modifications to improve the model.
Decision tables in discrete-system simulation
Authors: Davies N.R.
Published: March 2008

In this paper a review of the approaches to modelling adopted by programming languages currently available for discrete-system simulation leads to a close look at some of the advantages of languages which employ an "activity scan." These advantages include faster run-times for highly interrelated systems, simpler event routines, and increased security for the model. Decision tables provide a clear and concise format for specifying a complex set of conditions and the various consequent courses of action. They are therefore ideal for describing the conditions for interaction between component parts of a model as specified in the user-defined event routines. A preprocessor to make decision tables computer- readable would greatly enhance the process of modeZ ling and would allow a considerable extension of the range of conditioned statements to be used in the condition stubs of the table. A decision-table facility would form a useful extension to the many event-oriented simulation programming languages.
A note on sampling two correlated variables
Authors: Kleijnen Jack P. C.
Published: March 2008

Procedures are derived for sampling two variables, x and y, which have a predetermined correlation coefficient and possibly have prespecified marginal distributions. Instead of specifying a particular value for the correlation coefficient, the linear correlation or the dependence may be maximized.
Smooth
Authors: Sigal C. Elliott , Pritsker A. Alan B.
Published: March 2008

SMOOTH is a packaged network simulation language written in FORTRAN. It is based on the GASP TV and GERT IIIZ simulation languages and is capable of representing and analyzing models which include both continuous variables and discrete events. As a net work language, SMOOTH consists of a set of graphical symbols, users' input instructions, and a computer program. The basic symbols are nodes and branches: nodes perform specified functions on system varia bzes, while branches indicate precedence or function aZ relations between nodes. In using SMOOTH, the user models the system he wishes to study as a pair of interrelated networks and then describes the net works to the computer by means of the SMOOTH lan guage's input instructions. The SMOOTH computer pro gram analyzes the netzoork using simulation. No com puter programming or sophisticated mathematical tech nique is required on the part of the user.

This paper discusses the concepts and symbols of SMOOTH and includes as an example a SMOOTH model of a lake ecosystem. SMOOTH has been used to study biological systems, environmental pollution by trace metals and insecticides, and problems in systems dy namics. It is the first network simulation language capable of analyzing models of a combined continuous discrete nature.
Modified Merson's integration algorithm which saves two evaluations at each step
Authors: Chai Augustine S.
Published: March 2008

This paper discusses a modified version of Merson's integration algorithm which can save two evaluations of the system at each step. For a complex system the saving in computing time may come to 40%.

If you now use the ordinary Merson algorithm, you will find it easy to switch to the modified algorithm. The flow chart appended to this paper shows that switching to the modified algorithm involves adding on four blocks to Merson's method.
A mathematical model for the growth of giant kelp
Authors: Anderson Nick
Published: March 2008

A computer model in FORTRAN for the growth of the giant kelp, Macrocystis, which inhabits the coastal waters of southern California, has been developed. The present model considers only physical factors, water temperature and submarine light, as the factors that control the growth of single fronds in large kelp beds.

The model has been used to examine two aspects of kelp growth in water of 20 meters depth. The opti mum time of the year for the start of new growth of fronds arising from the bottom in an established kelp bed was found to be early June. The optimum time of the year for regrowth of harvested canopy was found to be early July. In each case, the optimum time is interpreted as providing the shortest time for the frond to reach "maturity" (a length of 40 meters).

The penetration of sunlight into the hydrosphere is adversely affected by particulate matter in the water such as results from the introduction of sewage ef fluent. The simulation identifies the critical values for turbidity which will prevent new growth from occurring. At a depth of 20 meters, light absorbency of 18% per meter reduces the possible growing time by only 20%. But when absorbency is increased to only 24%, the growing time becomes zero. Simulation runs for other kelp-bed water depths revealed similar critical values of absorbency resulting in the restric tion of growth to shallower waters. This type of analysis to resource-management efforts is obvious.

The paper concludes with suggestions for modifying the integration techniques used and for incorporating additional quantifiable values to refine the model.
Simulation of a voltage-controlled filter
Authors: Lopez-Toledo A.A. , Minkow Bernard
Published: March 2008

A new technique for voltage-controlled filtering is presented in this work. The results to be expected from the technique are analyzed by simulation since the filter can be described analytically only through approximations. The filtering technique is based on a linear system with periodically operated synchronous switches. A hardware model of the filter was built and the digital simulation outputs are compared with those obtained with the hardware. Filtering performances in the simulation and in the hardware were in close agreement. Though only Butterworth filters were considered, the method is expected to have much broader appli cations.
An Experiment in Sensitivity Analysis On an Uncertain Model
Authors: Miller Donald R.
Published: March 2008

Experiments on a compartment model into which very large errors have been deliberately introduced show that sensitivity analysis continues to provide valid information about the relative importance of parameters long after other aspects of realism have been destroyed. Thus, sensitivity analysis may be the first area in which a mathematical model yields meaningful information as it progresses through its formulation and development stages, and data-base refinement may be started relatively early in the modelling process.
Models Based On Response Structure
Authors: Maguire Bassett
Published: March 2008

This paper outlines in very simple form how one may use the response-structure (RS) approach to analyze and model the dynamics of systems. It should be read before my longer article (Ecosystem Simulation through Use of Models of Subsystem Response Structure) which begins on page 149 of this issue. The broad picture presented in this paper will prove very helpful to the reader of the longer article, and it describes the essential feature of a relatively new and very useful technique for modeling and studying systems, including those that contain grow ing or decaying variables.
ANIBAL - a hybrid computer language for EAI 680-PDP 8/1, FPP 12
Authors: Højberg K. Søe
Published: March 2008

A hybrid programming language ANIBAL has been developed for use in an open-shop computing centre with an EAI-680 analog computer, a PDP8/I digital computer, and a FFP-12 floating point processor. An 8K core memory and 812k disk memory is included. The new language consists of standard FORTRAN IV and special hybrid computer commands. ANIBAL consists of a general-purpose analog interface subroutine ANI and the macro processor 8BAL (DECUS NO 8-497A.1). When a source program with FORTRAN and 8BAL statements is processed, the FORTRAN statements are transferred unchanged, while the 8BAL code is translated essentially to ANI sub-routine calls, which are defined in a macro library. The resulting code is translated by the standard FORTRAN compiler. The language is very flexible as the instructions can be changed and commands can be added to or excluded from the library .
Comparison of three methods for developing models of resource demand
Authors: Olver Leon A. , Burwell Brian H. , Brewer John W.
Published: March 2008

This paper compares a new rather general modeling procedure with "static" and "dynamic" econometric procedures. The resulting models can all be used to make projections of demand for natural resources.

If such models are combined with supply models, one can estimate the Long-term impact of resource policy. The particular resource discussed in this paper is natural gas in the Pacific Gas and Electric (PG&E) service area of California (large portions of the north and central sections of the state).

Of the three modeling procedures discussed, the most general is emphasized in this paper. This method, described in Section 3, is related to the modeling procedure proposed by Forrester10,11 combined with parameter identification.2,19,30 A precise state ment and critique of the method is provided by Mitchiner et al.19 The other two modeling proce dures, chosen for purposes of comparison, are stan dard econometric methods. The first of these is a modification of "static" (algebraic) linear regres sion modeling. The second is a "dynamic" linear regression procedure wherein a lagged value of demand is used as one of the input variables.1,3,5

The proposed general methodology was not inferior to the two "standard" procedures in any case investigated and was clearly superior in the analysis of firm in dustrial demand for natural gas. This result was expected because the standard procedures are special cases of the proposed methodology.
The scientific method and statistics in simulation
Authors: Arthur Mihram G.
Published: March 2008

The question of the need for "camps" of simulationists (the "deterministic-continuous" and the "stochastic-discrete" camps) is addressed by delineating both the differences and the likenesses of their approach.
DARE P—a portable CSSL-type simulation language
Authors: Lucas John J. , Wait John V.
Published: March 2008

This paper describes a batch-mode FORTRAN-based continuous-system simulation Language that retains the features of the DARE family of languages1,2,3 but is structured to facilitate implementation on a wide variety of computer systems. Except for a small set of necessarily system-dependent routines (for character packing and unpacking, job abortion, etc.) the system is coded entirely in FORTRAN IV. It is highly modular, and uses system-independent FORTRAN-based methods for writing and manipulating solution files on mass storage. The system has thus far been run on a CDC-6400 (requiring about 21,000 decimal words of core memory), and a DEC-10 (requiring about 17,000 words). This paper announces the availability of DARE P, which we plan to make available to interested users who would like to implement it on their particular system, without the usual high surcharge that often accompanies other similar software packages.

Our DARE IIIB, 3 which was specifically coded for the CDC-6000 series computers (including a COMPASS assembly-language translator overlay), was not portable. It has, nevertheless, been distributed and successfully used at many installations around the world. DARE P (Differential Analyzer REplacement- Portable) has been developed in response to requests for a version that would run on other computers. It is easy for the user to modify, e.g., he can easily add new integration rules, run-time strategies, or special library subprograms. DARE P can accommo date problems with 100 parameters and 200 state or output variables.

In DARE P problem equations are entered in a form close to ordinary mathematical notation; the associ ated procedural language is FORTRAN. User-chosen variable names in the problem description are accommo dated by a special translator overlay which translates DARE problem statements into FORTRAN IV subprograms and builds a communication file. Run-time data is entered via free-form data cards. A variety of out put options are provided, including line-printer listings and plots, and CalComp plotter displays.

Complete simulation studies may be directed by a FORTRAN-coded logic block. Single- or multiple-run problems may be specified with storage files used for saving output data for subsequent cross-plotting, reentry into future runs, etc. DARE P includes an internal collection of library functions, and the user may add his own special functions written in FORTRAN and his own one- or two-variable table-lookup function- generators. DARE P provides a choice of several internal fixed- and variable-step integration routines.
A hybrid cell-sharing technique for solving ion-bombardment problems
Authors: Pearce J.G.
Published: March 2008

This paper describes a hybrid cell-sharing technique which allows a limited amount of analog equipment to be used to solve the large number of equations associated with ion-bombardment problems. The tech nique was implemented on a HS7/PDP8L hybrid computer for the case of an argon ion interacting with two atoms of a gold crystal and the results agreed well with those obtained by digital simulation.
Applications of optimal control to the modeling and management of ecosystems
Authors: Vincent Thomas L. , Lee Cho Seng , Pulliam H. Ronald , Everett Lorne G.
Published: March 2008

A complete ecosystem analysis may be possible from the point of view of optimal control theory. Such an analysis has three parts:

(1) Determination of model structure

(2) Determination of coefficients for a given model

(3) Determination of optimal management programs for the model obtained by (1) and (2).

The methods of optimal control theory are suitable for examining these three parts separately. The essential ingredients for each part is an optimization concept.

Only the second and third parts are examined in detail here. For concreteness, a specific model structure for a prey-predator system is used. It is then shown that certain coefficients of this model are determined directly, given that the predator feeds in such a way as to maximize his caloric intake. By adding man's external controls to the model, the system can then be managed in a fashion to minimize some cost criterion.

To illustrate this latter point, the methods of optimal control theory are used to determine a manage ment program for controlling water quality in a natural lake at minimum cost. Man's control is re presented by the application of an algacide on the phytoplankton-zooplankton (prey-predator) system in the lake. The introduction of temperature dependence as a driving force in a simple dynamical model appears to be adequate for the determination of the optimal control program.
Pesticide residue dynamics in a forest ecosystem: a compartment model
Authors: Webb Warren L. , Schroeder Henry J. , Norris Logan A.
Published: March 2008

This paper presents a computer model of the movement of pesticide residues in a forest ecosystem. As such, the paper deals primarily with the potential direct effects on target and nontarget organisms, but does not address the very long-term consequences of restructuring the vegetation in an ecosystem. Simulations using the model trace the movement of two herbicides (2,4,5-T and picloram) through two different environments, one typical of an Oregon forest and the other typical of southern California chaparral. The model is written in DYNAMO.
The construction and implementation of metamodels
Authors: Blanning Robert W.
Published: March 2008

This paper suggests a computationally economical alternative to the common method of using simulation for sensitivity studies, i.e., by making repeated simulation runs with incrementally changed inputs and then observing the magnitudes of the resulting changes in the outputs of interest. Although no theory now exists for constructing the requisite "metamodels" for direct sensitivity analysis, it is possible to construct them, as is illustrated by three examples in the field of operations research.
A hybrid compiler with automatic patching system
Authors: Hecht Volker , Reuss Walter , Rzehak Helmut
Published: March 2008

This paper describes a hybrid compiler system which enables a user to program the analog and digital portions in a homogeneous language. The features of a well-suited language are deduced. The boundary of the analog and digital regions is optional. It is shown that this degree of freedom is necessary to permit transfer of programs from one machine to another. The compiler requires use of an autopatch system which is described. An algorithm is presented for mapping the analog part of the problem into the switching network of the autopatch system.
Hybrid simulation of a gas-transport system using the directional- difference method
Authors: Buis J. Paul
Published: March 2008

This report describes a hybrid simulation developed at the Hybrid Computation Department of the Delft University of Technology Computation Center in response to an order of the Dutch blast-furnaces and steel-mills industry, Hoogovens IJmuiden B.V., at IJmuiden, the Netherlands. The system to be simu lated is the gas-transport system used to carry blast furnace exhaust gases into a neighboring thermal power plant where the gas is used for the generation of electricity. The simulation is based on the use of the directional-difference method, which is used to solve the hyperbolic partial differential equa tions describing tube flow. Some attention is also devoted to the analysis of boundary values, and the approach toward a solution for this particular flow problem is outlined. The hybrid model is based on the cell-multiplexed method.

The simulation showed that the system as originally designed could be marginal in certain respects. Some design changes were therefore incorporated in the simulation and it was rerun until a satisfactory operational performance of the gas-transport system was reached.

The Hybrid Computation Department facility used for the implementation of the simulation consists of an Applied Dynamics AD-4 analog/hybrid computer and an IBM-1800 digital computer.
A stochastic method for the solution of the diffusion equation
Authors: Swillens Stéphane
Published: March 2008

Numerical methods for solving the diffusion equation are based on discretizing space and time so as to transform the partial differential equations into a set of ordinary differential equations or into an algebraic system. (Hybrid computers may make time or one space dimension continuous.) The purpose of this paper is to present another method, namely the stochastic method, which is derived from the physical knowledge of the diffusion process and not from the mathematical equation. The paper concludes with a comparison of the stochastic method, which may be programmed on small digital computers, with two well- known numerical methods and showing their respective advantages and disadvantages in computing time, accuracy, and ease of programming and suggests areas in which the different methods are appropriate.
Second-order response surface designs in computer simulation
Authors: Montgomery Douglas C. , Evans Daniel M.
Published: March 2008

Computer simulation models are frequently used to determine the combination of levels for a set of independent variables at which a response variable is optimized. This process leads to problems of experi mental design, i.e., the choice of levels of the independent variables at which the simulation model is to be run and at which the model's responses are to be observed. This paper considers second-order response-surface designs and optimization procedures for use in this situation. Several classes of designs are constructed and applied to surfaces typically generated by computer simulation models. Results are obtained which should assist in the selection of de signs in general or for use on specific surfaces. An application of second-order response-surface de signs to a digital simulator of a street network is presented; the object is to find optimal settings for the traffic signals during the morning peak of traffic flow.
Modeling !N the Social Sciences: an Approach To Good Theory and Good Policy
Authors: Strauch Patricia G.
Published: March 2008

The use of simulation modeling in the social sciences re quires both an adaptation of the technique to meet the special quantification requirements of these disciplines and an introduction to social scientists of the potential that this technique holds for their field. It is the purpose of this paper to provide an overview of simulation modeling useful to the social scientist interested in this technique and its applicability to his research. Additionally, this paper in cludes some insights into simulation modeling by a social scientist who has used it in research.
NEEDS: Nuclear Energy Electrical Demand Simulation
Authors: Willke Theodore L.
Published: March 2008

A computer model is presented called NEEDS — an acro nym for Nuclear Energy Electrical Demand Simulation- which can simuZate the nuclear sector of the United States electric power economy. The code can forecast the impact of various nuclear-reactor growth patterns over the next fifty years in terms of economics, resource utilization, and the requirements for a supporting fuel-cycle industry. NEEDS was developed for the Office of Energy Research and Development Policy of the National Science Foundation as a tool to help evaluate alternative fission reactor develop ment strategies involving advanced reactor concepts, including advanced high-temperature gas-cooled reac tor (HTGR) systems, the gas-cooled fast reactor (GCFR), the molten-salt breeder reactor (MSBR), the Zight-raater breeder reactor (LWBR), and the heavy- water reactor (HWR) . The objectives of the study were to calculate the impacts, benefits, and require ments of various nuclear growth patterns and to determine the sensitivity of these measures to input parameters which are dominating, uncertain, or sub ject to wide variations.

The NEEDS model is currently being used to answer such questions as: What benefits would the United States realize by developing the MSBR, the GCFR, or the LWBR as alternatives to the LWR/HTGR/LMFBR power economy? What are the potential impacts on enrich ment requirements and uranium demand of changing per cent tails assay? How does a power economy based upon a thorium-U233 fuel cycle compare with a pluto nium economy? The model has been used to relate the research-and-development requirements for developing an advanced reactor concept to the availability of the reactor system and its impact on the nuclear economy.

In summary, the NEEDS model was developed to study questions of national nuclear policy using a simple modeling approach and minimal input data requirements. The model can forecast the impact of nuclear power development under selected national policy options and potential growth scenarios.
Advanced Continuous Simulation Language (ACSL)
Authors: Mitchell Edward E. L. , Gauthier Joseph S.
Published: March 2008

This paper describes ACSL, a continuous system simu lation language designed to help the engineer or scientist with a mathematical model analyze the behavior of his system. The computer calculates dynamic responses and interactively provides pictures (plots) and tabular display of selected variables. The user has a choice of two Runge-Kutta integration algorithms and two variable stepsize algorithms which includes Gear's implicit method for stiff sys tems. Any other programmable algorithm can be readily incorporated. The main features of the lan guage are illustrated by a detailed example.
Comparing means and variances of two simulations
Authors: Kleijnen Jack P. C.
Published: March 2008

Two systems are simulated using the same random- number stream. To compare their means one can use standard statistical techniques, e.g., the t-test for paired comparisons. To compare their variances, however, the standard F-test fails. Three approaches are suggested. Approach 1 uses the traditional F- statistic and is conservative. Approach 2 splits the observations into two groups. For each group the F- statistic is exact. It is shown how to combine the two F-statistics in a very simple way. This approach is also conservative. Approach 3 was developed in 1946 by Wilks. It is slightly more complicated but exact.
Effect of national transportation/energy policy on regional transportation phenomena
Authors: Flory John E. , Pearce Meredith A. , Hunter Peter J. , Mosman Nancy J.
Published: March 2008

Most regional transportation modeling studies have focused on microlevel phenomena operating within the region. In contrast, the model presented in this paper utilizes a hierarchical causality approach to examine the impact of higher-level (i.e., national) policies on macrolevel regional transportation characteristics. Specifically, the individual and joint effects of national trends in gasoline price, transit funding, and fuel economy of automobiles are examined with respect to their influence on two Sacramento regional variables: transit usage and transportation fuel consumption. The authors con clude that given the uncertain future of causal forces that are beyond the region's control (e.g., gasoline price), a macrolevel analysis may be a more judicious use of limited transportation planning resources.
Making Management Simulations Useful
Authors: Maisel Herbert
Published: March 2008

Simulation is a powerful but too little used tool for man agement decision-making. Management will make greater use of it if managers or their surrogates participate in the development of the simulation model from the beginning and state as clearly as possible how they would use the model and what questions they want it to help answer. Dur ing the development of the model, managers should receive progress reports and guide the development, answering questions on how policymaking and supervisory decisions are made and providing other inputs to the simulation team as appropriate. All communication with management must be in a language natural to managers and should occur at times convenient to management. When the model has been developed, managers must find it easily accessible and must receive credible "answers" from simulations in forms that they can understand and use. If managers or their surro gates have participated in all major decisions during devel opment of the model, simulation results are likely to be credible and to be used in management decision-making.
Ecosystem models and environmental policy
Authors: Cooper Charles F.
Published: March 2008

The use of models for guiding environmental policy should be distinguished from their use in imple menting management policies already decided upon. Ecosystem models are of potentially great value for guiding and informing incremental decisions regard ing environmental policy. They are unlikely to be used as a basis for comprehensive restructuring of programs. Their greatest use may lie in identifying points of leverage, where incremental policy changes will have the greatest long-term beneficial impact. For this reason, provision for formal sensitivity analysis is essential in models used to guide envi ronmental policy. Ecological models are more likely to influence policy decisions if they incorporate features which should be a part of any good model but which are often skimped: adequate documentation, reasonableness of prediction, explanation of limits and probable range of error, flexibility to deal with unanticipated problems, and effective presenta tion and display.
Hybrid techniques for generation of arbitrary functions
Authors: Rubin Arthur I.
Published: March 2008

A discussion of the implementation of a true hybrid func tion generator module is presented. Included is a detailed description of how two of these modules, when used in conjunction with a hybrid computer, are used simultane ously to generate a continuous function of two variables, and how four modules are used to generate a continuous function of three variables. From a variety of possible con figurations, an optimum choice for a general-purpose HFG module is made, taking into account digital coefficient storage requirements and analog multiplier requirements.

A detailed error analysis compares the errors produced in generating an arbitrary function using the HFG module with the errors produced by the classical hybrid (or purely digital) method of generating an arbitrary function by table look-up and interpolation for discrete values of the argu ment. The conclusion is reached that the hybrid method can be an order of magnitude more accurate than the classical discrete method for generating arbitrary functions and has further advantages in that the hybrid method does not require a 100% duty cycle in the digital processor for accurate function generation.
Automatic optimum-seeking program for digital simulation
Authors: Smith Dennis E.
Published: March 2008

A modular computer program has been developed to assist in the task of seeking optimum solutions to problems being simulated on a digital computer. This ANS FORTRAN IV program may be interfaced with any FORTRAN simulation to monitor use of the statistical techniques of Response Surface MethodoZogy (RSM). The automated RSM program, which may be used for con strained or unconstrained optimum-seeking in conjunc tion with deterministic or Monte CarZo simulations, is now available to potential users. This paper out- Zines the theoretical basis of the program, describes its main computational aspects, and discusses its application.
Approximate dynamic simulation of constrained mechanical systems
Authors: Rooney George T. , Rai Jaswant
Published: March 2008

This paper describes a method of finding the dynami cally dictated position, velocity, and acceleration of a point along a constrained path. The dynamic equations of motion are formulated on the assumption that reaction forces are available. In the circuit these reaction forces are replaced by magnified errors in velocity constraints. This paper shows that this technique produces a very good approxima tion to the true dynamic equations. The method is suitable for analogue or digital computation and can be applied in other fields.
Semiconductor technologies and semiconductor memories
Authors: Leventhal Lance A.
Published: March 2008

In this article, we discuss the semiconductor techno logies from which microprocessors are constructed and the semiconductor memories with which microprocessors are commonly used. We will discuss the characteristics of the technologies and memories from the user's point of view and will not discuss either the inner workings or the manufacturing techniques involved. We will describe the standard logic families, the technologies used in microprocessors, and the interfacing of micro processors and devices from the standard logic families. We will then consider the types of semi conductor memories and how they are used with micro processors. We will also briefly discuss future trends in both semiconductor technologies and semicon ductor memories.
Direct digital control of a chemical reactor
Authors: Bianchi R.J. , Pinder K.L. , Meisen A.
Published: March 2008

This paper presents a senior-level experiment to familiarize the student with the use of Direct Digital Control (DDC) of a continuous process. The z- transform technique is applied to the control of a simple stirred-tank reactor.
A remote terminal for accessing large hybrid computers
Authors: Ricci Fred J. , Nixon Floyd E.
Published: March 2008

Hybrid computers can be controlled from remote termi nals which provide both alphanumeric and continuous waveform plots of the problem solution. For many scientific problems, hybrid computers have demonstrat ed computational speeds several orders of magnitude faster than digital computers. As the need for hybrid computation grows, more and more users will want ac cess to hybrid computers in order to take advantage of their speed and economy. This paper discusses the progress to date in the development of an experimental hybrid-computer network (EHCN) and describes a simula tion that has been performed using this network. The paper emphasizes the advantages of utilizing large- scale hybrid facilities accessed from remote termin als.

Specifically, a network has been established between several locations. Details on the design and develop ment of the terminals associated with this network are presented and future applications of the network in government, industry, and universities are outlined. Transmission standards are being established so that additional locations which are either hybrid computa tional centers or remote terminals can be readily con nected.

Access to a hybrid computer offers computer terminal users four distinct advantages which users will find highly beneficial: the economy of hybrid, analog graphics, high solution speed, and voice communica tion with computer specialists.
A decision model for the estate management problem
Authors: Boehlje M.D. , Eisgruber L.M.
Published: March 2008

Estate management planning requires the development of a comprehensive plan (a) to insure successful economic management of the estate property during and after the lifetime of the owner, and (b) to produce the desired legal consequences in the disposition of the property after death. For adequate analysis, both changes in the ownership and in the size of the estate over time and the uncertainty of the death of the testators must be considered. This paper develops a dynamic decision model that can be used to evaluate how well alternative legal and financial tools satis fy specified estate-management goals. The conceptual model is stated in mathematical form and is trans formed into a stochastic, multistage computer simula tion model. The paper includes an example illustra ting the use of simulation in a practical case.
Dispersion of active pollutants in a shallow sea
Authors: Adam Yves
Published: March 2008

Shallow coastal seas are the "priviledged" places for the dumping of wastes of all kinds: sewage, mud re leases, and chemical refuses are typical examples. In most cases, the shallow coastal seas are therefore very polluted. This paper describes a digital simu lation of the diffusion and transportation of pollu tants released in the shallow sea bordering Belgium. The model of course has much wider application. The principal new development in this paper is the method of integration of equations which describe such systems.

The equations of the model have dominant advection terms, mixed derivatives, and nonlinear interaction terms, and are solved by a special predictor- corrector scheme consisting of three distinct steps. The mixed derivative is separated into second deri vatives along the grid axes and an auxiliary axis. The first two steps (implicit and locally one-dimen sional) form the predictor. The third one is the corrector, and it yields a consistent discrete approximation of the time derivative. The accuracy is 0(τ2 + τh + h2). A stability condition is derived and some problems in implementing the method are discussed. The paper concludes by presenting the results of a simulation of pollutant dumping in the North Sea near Ostend.
Microcomputer architecture : memory and input/output sections
Authors: Leventhal Lance A.
Published: March 2008

This article begins our discussion of microcomputer architecture. We briefly consider the basic features of computer architecture and describe the functions of the various sections of a computer. We then dis cuss the memory and input/output sections in more detail and show how these sections are implemented in microcomputers and how standard logic elements and special-purpose LSI interfaces are used.
Interactive simulation language for hybrid computers
Authors: Benham R.D. , Taylor Glenn R.
Published: March 2008

The Interactive Simulation Language (ISL) is a power ful and easy-to-use software system for hybrid com puters using any of several different minicomputers. Its principal features are:
AQUARIUS: a simulation of communit water planning
Authors: Howard Richard A. , Wessler Eliot J.
Published: March 2008

Simulation is used to give students of resources management an opportunity to form and evaluate a water resources plan. The focus of the planning problem is a mythical New England city called Aquar ius. In the first stage of the simulation, students work as a planning group and design a fifty-year comprehensive water plan. The students assume dif ferent roles and report to a director as they would in a real planning agency.

In the second stage of the simulation, students use a computer model to simulate the operation of the water resources plan. They can observe the impacts of their plan over a period of years and revise the plan as needed.
Simulation with hard - wired analog subprograms
Authors: Wahlström Björn , Juslin Kaj
Published: March 2008

This paper discusses the use of dedicated hard-wired analog subprograms as part of a hybrid simulation model. Such subprograms are a practical and economi caZ means for extending the computing capacity of a hybrid computer when a simulation model is to be used many times. The hard-wired analog subprograms are especially suitable for small hybrid-computer laboratories because the investment required to extend the computing capacity of the hybrid computer can be kept reasonable.
A parameter optimization module for CSSL-based simulation software
Authors: Birta Louis G.
Published: March 2008

This paper describes a subprogram module which sim plifies the implementation of parameter optimization studies in continuous dynamic systems. The module is an enhancement to CSSL-based simulation software and relies on its host software for the specification and solution of the dynamic equations of the system under study. The module includes several different optimization algorithms -a feature which can be of great value in difficult problems. It has output documentation routines and is organized so as to be transparent to the user.
Toward guidelines for designing experiments in queuing simulation
Authors: Turnquist Mark A. , Sussman Joseph M.
Published: March 2008

The simulation of complex queuing systems is an im portant application for discrete-event digital simula tion. In many cases, the object of the analysis is estimation of steady-state measures (e.g., mean and variance of waiting time) for the system. The initial conditions in the system at the start of a simulation run may introduce a "bias" into the experimental re sults; several methods have been suggested to eliminate this bias. One common approach is a warm-up period at the beginning of the simulation run, during which no data are collected. The length of this warm-up period is determined by a tradeoff between the reduction in bias caused by the initial conditions and the increase in variance of the statistical estimates resulting from discarding the initial data, given that the analyst is operating with a fixed experimental budget.

This paper explores the effect of initial conditions and the warm-up period on the design of simulation experiments for the simple case of a single-server queuing system with Poisson input and exponential service times. The experimental design problem is to determine the number of independent replications of a simulation run, the length of the warm-up period, and the length of the data-collection period, which together minimize the mean-square error of the estimated mean waiting time, subject to a budget constraint on the total number of customers whose progress through the system can be simulated. Optimal experiment design was found to be strongly affected by how busy the system is.
Simulating the consumption of gasoline
Authors: Wong Edwin , Venegas E.C. , Antiporta D.B.
Published: March 2008

This study used econometric models to estimate the parameters of gasoline demand. The first model re lates gasoline consumption directly to income and price variables. The second model takes account of the market split between small and large cars, as well as the fuel-efficiency rating for each car type. Gasoline consumption is indirectly estimated through the relationship of vehicle miles traveled and price of gasoline and income. Both models allow for be havioral changes over time so that long-term response is greater than short-term response.

Both models were fitted to Minnesota data and used to simulate future consumption under alternative price, income, and fuel efficiency scenarios. The effects of income level dominate the effects of price level in both models. Consequently, changes in real income level are important for forecasting future energy demands for automobiles in the state.
Catastrophe theory applied to ecological systems
Authors: Jones Dixon D.
Published: March 2008

Catastrophe theory is a new field in mathematical topology that allows the formulation of comprehensive qualitative models of systems which have previously eluded rigorous mathematical formulation. Because the models have a topological foundation, many seem ingly dissimilar phenomena can be related to a common underlying topological structure. The properties of that structure can then be studied in a convenient form and the conclusions related back to the original problem. This paper provides an introduction to catastrophe theory and defines the principal condi tions required for its application. The basic prop erties of bimodality, discontinuity (catastrophe), hysteresis, and divergence are defined and illustra ted using the simplest structures of the theory.

In this paper the spruce budworm/forest ecosystem of eastern Canada illustrates how catastrophe theory may be applied in ecology. With only a minimum of general descriptive information about the budworm system, a qualitative catastrophe theory model is hypothesized. This model is rich in its ability to provide predictions and insight about the global behavior of the system. To further check and verify the assumptions of this qualitative model, an exist ing detailed simulation model is analyzed from the perspective of catastrophe theory and is found to exhibit a basic underlying structure that is very similar to the catastrophe theory model. A detailed examination of the simulation model shows that catas trophe theory provides a consistent framework for analyzing and interpreting the behavior of this eco system.
Simulating nonstationary Poisson processes: a comparison of alternatives including the correct approach
Authors: Kaminsky Frank C. , Rumpf David L.
Published: March 2008

This paper describes three inexact methods that are commonly used to generate arrivals for a nonstation ary Poisson process and compares them to an exact method. Different patterns are assumed for the arrival rate as a function of time. The exact method is shown to produce accurate results, whereas all three inexact methods produce results that are sig nificantly different in a statistical sense. All four methods require similar amounts of computer time.
Simulation as an Aid to Corporate Decision-Making
Authors: Cox James F. , Ledbetter William N. , Smith Jeannette M.
Published: March 2008

This article both discusses and measures the use of sim ulation modeling in decision support systems in major cor porations in the U.S.A. The effective use of quantitative techniques requires that managers develop decision sup port systems which include both adequate data bases and the capability of structuring decision models compatible with their corporations' information systems. Since simu lation is one of the most widely used quantitative tech niques, its use in such decision support systems is exam ined. Specifically, this paper attempts (1) to measure the development and use of simulation at all decision- making levels (operational, tactical, and strategic), (2) to examine the use of simulation within each functional area of business, and (3) to identify specific areas within each of the business functions where simulation is being used.
Multiple response surface methods in computer simulation
Authors: Montgomery Douglas C. , Bettencourt Vernon M.
Published: March 2008

This paper reviews the application of multiple re sponse surfaces to multiple-variable optimization problems and describes how these techniques may be used in analyzing computer simulation experiments. An example with four response surfaces illustrates the method. In it a simulation of a tank duel is analyzed to determine the values of two independent (input) variables that will optimize four dependent (output) variables simultaneously. The problem examined is that of training battle-tank crews, and the optimization procedure used is based on the Geoffrion-Dyer interactive vector maximal algorithm.
Recollections of a Pioneer
Authors: Skramstad Harold K.
Published: March 2008

I remember when I first laid eyes on Skram; it was at NACA Moffett Field (now NASA Ames Research Center), where he was pointed out as one of the most knowledge able of people in analog simulation. That was in the early fifties-so admittedly he didn't have much com petition. But Harold had been trying to make those early analogs work for some ten years already. Skram was with the Naval Ordinance Laboratory, Corona, California, and with the National Bureau of Standards both there and in Washington. Then he went academic and as a result earned his current titles. The value of the contributions Harold Skramstad has made to our art and science since his early start are in direct contrast to the brevity of his contribution to this issue, which follows.