bluuebunny/crossref_metadata_2025 huggingface dataset:
Multivariable function generation by diode switching
Authors: Schubert Walter L.
Published: March 2008

This paper outlines the procedure for designing a nonincremental diode function generator. It empha sizes the practical aspects of designing circuits for generating line segments and chamfering their inter sections. Methods for optimizing diode logic include reduction to two stages and reduction by lattice theory. The first of these is outlined and its practical limitations are noted. Both methods are illustrated by a problem in radiation therapy which was actually executed on an analog computer.
Digital computation of inverse Laplace transforms
Authors: Olsen Charles F.
Published: March 2008

This note describes an algorithm for the digital computation of the inverse Laplace transform of a function containing multiple real or complex poles and discusses its advantages and disadvantages.

The algorithm utilizes a well-known, simple mathemat ical technique to evaluate a polynomial and its derivatives at a root of the polynomial. This method allows the nvmerator and denominator polynomials of the function to be treated separately by dividing each repeatedly by a first-order term. Synthetic

division of a first-order term into a polynomial when both contain complex coefficients is particularly suited to digital computation. Execution times for Pottle's algorithm and the algorithm proposed in this paper are compared. The paper concludes with a BASIC program which implements the latter algorithm.
An Application of Simulation in Retail Management
Authors: Hirschman Elizabeth C. , Bellenger Danny N. , Robertson Dan H.
Published: March 2008

Simulation appears to be a promising tool for applied market ing researchers. Marketing executives, however, have not yet learned to appreciate its value. This paper presents the re sults of a simulation study of the effects of subway construc tion on retail traffic flows and sales. It is to be hoped that this study and others like it will help to show the potential value of simulation to marketing management.
Transient response analysis of linear differential systems on minicomputers
Authors: Taylor Fred J.
Published: March 2008

A common problem in system simulation is producing the solution to a differential equation of the form x(t) = Ax(t) + Bu(t), where A and B are constants. In particular, simulation often requires solutions for a step, ramp, or constant-acceleration forcing function. Standard numerical integration methods may fail or be extremely slow when implemented on a mini computer because of its short wordlength. This paper presents a new deterministic integration method which will accurately and rapidly produce the solution. Some numerical experiments are shown to demonstrate the new method.
Design and analysis of simulations: practical statistical techniques
Authors: Kleijnen Jack P. C.
Published: March 2008

Using elementary statistical theory, we discuss sta tistical techniques that can be used to initialize a simulation run and to determine its length, distin guishing between terminating and nonterminating sys tems and between stationary and nonstationary time series. Confidence intervals and hypothesis tests are included (see Section 2). In the case of k sys tem variants (at least 2), multiple comparison proce dures are presented which can be used to obtain simultaneously valid confidence intervals and to select a subset containing the best population, assuming a fixed number of simulation runs. Other wise ranking procedures can be used to determine the number of runs required to select the best system (Section 3). If many parameters and variables exist, selecting a limited number of combinations requires an experimental design, which must be analyzed with a regression metamodel (Section 4). The metamodel of main effects and interactions applies to both quantitative and qualitative factors; its adequacy can be tested (Subsection 4.1). Experimental design is discussed in three steps: (1) screening designs for finding the important factors, namely, 2k-P designs, random, supersaturated, and group-screening designs (Subsection 4.2); (2) augmented 2K-P designs for further exploration (Subsection 4.3); (3) response surface methodology for optimization (Subsection 4.4). Three practical variance reduction techniques are summarized, namely, control variates, antithetics, and common random numbers (Section 5). Some of the statistical methods discussed are also applicable to deterministic models of continuous systems. This paper was written for readers with only an elementary background in statistics.
Determining parameters of dynamic systems from noisy measurements
Authors: Brueck Donald M. , Ward E. Dawson
Published: March 2008

This paper uses the method of least-squares k-spline approximation to generate time derivatives of sampled- data measurements required to determine values for parameters in models of linear and nonlinear dynamic systems. When identifying the parameter values in a nonlinear system in which signals are corrupted with measurement noise, the method developed in this paper provides more accurate values than does an approximate time-delay filter. In generating the required deriva tives in the presence of noise, the least-squares k- spline approximation yielded higher-order derivatives which were substantially more accurate than the same derivatives obtained from a low-pass filter. In a nonlinear case used as an illustrative example, the technique described in this paper resulted in as much as a 32% improvement in the accuracy of one of the identified model parameter values, and its largest error in any of the six parameters identified was 3.5 percent. The method was particularly effective in counteracting impulse noise caused by bad data points.
Simulation of Biological Systems: the Circulation of Blood
Authors: Coleman Thomas G.
Published: March 2008

Many models have been developed to explore one aspect or another of the circulation of blood. The early models, when judged by today's standards, are rather elementary; in those days model building was constrained by limited computing power. More recently, the availability of power ful digital computers has encouraged the development of models of greater depth and breadth. This paper traces the progression from simple to complex, specific to general.
Simulation in the Service of Society
Authors: McLeod John , McLeod Suzette
Published: March 2008

This Newsletter was published independently from January 1971 through August 1976. Back issues are available from SITSOS, POB 994, La Jolla, CA 92038, for 75c per copy.
Simulating interregional interaction: a demographic-economic model for Great Britain
Authors: Madden M.
Published: March 2008

This paper describes the modelling of variables usually treated as exogenous parameters in regional simulation models, and identifies the areas where those variables are particularly important. A multi regional approach allows the direct modelling of interregional migration, unemployment differentials, and industrial growth changes; the paper describes the equations involved and discusses a multiregional model for Great Britain. Results from initial experimentation with the model are presented, and its ability to replicate real data is tested. The model permits the incorporation of policy decisions and programmes; simulation results show the application of a development area policy and a migration assist ance programme. Further development of the model by more detailed breakdown of the population and indus trial sectors is outlined.
Microprogramming and Simulation
Authors: Leventhal Lance A.
Published: March 2008

The simulation of such complex digital systems as com puters, industrial controllers, and communications net works has become an area of increasing importance. Micro programming not only is a method for simulating such sys tems but may also aid in their development and upgrading. The advent of low-cost high-speed memories and micro processors has greatly simplified the use of microprogram- ming and extended range ofapplications. This article will describe the purpose, history, and uses of this new simula tion method.
Frequency-response calculations with a programmable calculator
Authors: Mitchell E.E.
Published: March 2008

This paper describes an algorithm with which the user can compute frequency responses on a small pro grammable calculator. Inexpensive calculators like the Hewlett-Packard 25 allow such calculations for a system containing as many as four poles and zeros. The user must enter the proper sequence for a pole or zero, but the process is simple; the user does not have to depend on (and wait for) a large computer. The paper presents the solution of a typical problem.
Variance reduction for a replacement process
Authors: George Laurence L.
Published: March 2008

Prediction of replacement requirements for components (such as manufacturing equipment or engines) requires analysis of a replacement process. Unfortunately, unless component lives are exponentially distributed, that analysis requires transform methods, approxima tions, or simulation. Only simulation or approxima tion may be used for prediction of replacement re quirements when the replacement process is complicat ed, when it is subdivided into several periods of time, when replacements are not all new, or when several identical components that operate simulta neously are supplied from the same stock of spares.

This paper shows that in a simulation the use of complementary antithetic random variates in the generation of component lifetimes reduces the vari ance of the sample mean number of replacements in a multiple-component multiple-period replacement process in which the components may be either new or used. Reducing the variance results in more accurate predictions for fixed simulation runtimes or, alter natively, allows shorter runtimes (and hence lower costs) to achieve specified accuracy.
Analog simulation of bipolar-transistor circuits
Authors: Ranfft Roland , Rein Hans-Martin
Published: March 2008

This article describes a simple but efficient analog computer which has been specially developed for the transient analysis of nonsaturated bipolar transistor circuits. Its advantages, when compared to the usual digital computer simulation, are low costs, simple operation, and short simulation time, allowing a fast man-machine dialog. This simulation method has already been successfully used in the design of several high-speed integrated circuits.
The modeling of long-term ingestion of drugs in mammals
Authors: Lindstrom F.T.
Published: March 2008

This article describes a model of the effects of growth and changes in metabolism on drug residues in mammals. The model shows how changes in mass (i.e., growth) and metabolic activity affect the residual drug concentration in animals that are continuously exposed to a drug over long periods of time. These examples of the oral administration of the highly toxic pesticide dieldrin illustrate the gross features obtained by using a simplified model.
From Kops To Mops and Bops, Simulation's Future Is Tops
Authors: Nixon Floyd E.
Published: March 2008

I met Floyd Nixon shortly after going to the Naval Air Missile Test Center at Point Mugu, California in mid-'49. Floyd says he became involved in simulation in 1948 as a means of trying to find out why a certain missile (probably the Bullpup) didn't straighten up and fly right. He was with the Glenn L. Martin Company (now Martin Marietta Corporation) stationed at Point Mugu at the time, and his interest in simulation was influential in the establishment of the NAMTC Guidance Simulation Laboratory in my sec tion of the Guidance Division a couple of years later. Floyd also encouraged me in the formation of the first Simulation Council, and is a Charter Member of SCS by right of having participated in the founding meeting at the Colonial House in Oxnard., California on the evening of Friday, November 7, 1952. Floyd Nixon's career has been devoted almost exclusively to the development of guidance and control systems and - except for three years with the Aerospace Cor poration-that work has been with Martin Marietta.
Briefly Now, More Later
Authors: Rideout Vincent C.
Published: March 2008

I think I can best let Vince Rideout tell it for himself: "When I was a new assistant professor (about 1948) in the EE Department of the University of Wisconsin, struggling to introduce our first auto matic control course, my chairman, Harold A. Peterson, got me interested in the idea of using some of the new electronic analog computers in connection with this work. We purchased some Philbrick 'boxes,' and have been simulating ever since. During the summer of 1951 I worked for Boeing in Seattle and got some further familiarity with the use of analog computers there, and even more as a consultant for Allis Chalmers from 1956 on. In 1954 when I went to Bangalore.. India for a year at the Indian Institute of Science, I took along some plug-in op-amps., etc. and built India's first analog computer there. About 1964 I began to work on cardiovascular system simulation, and continue to do so. Also, about 1965 I was instrumental in getting a large hybrid instal lation at Wisconsin, and was director of our hybrid laboratory until 1972, when I left to become depart ment chairman. Since leaving the chairmanship a year ago, I have become interested in two new fields of research-array computer design and large-scale socioeconomic modeling."
General Comments Now, Specifics Later
Authors: Karplus Walter J.
Published: March 2008

Walter Karplus has been involved with simulation since 1950, when he was concerned with petroleum exploration and production problems. His MS thesis (University of California, Berkeley, 1951), his work at International Geophysics, Inc., and his PhD dis sertation (University of California, Los Angeles) all involved simulation. Walter has been a member of the faculty of UCLA since 1955 and has also been a con sultant since then to many companies and government organizations. He is a Fellow of IEEE and a recipi ent of the EAI Senior Scientific Simulation Award. No one has done more to advance the state of simula tion methodology, particularly with respect to the handling of distributed systems and associated par tial differential equations than Walter. And all the while he has given outstanding support to the Simula tion Councils (now SCS) by accepting appointments to official positions, by organizing and chairing ses sions and contributing outstanding papers to techni cal meetings, and by his continuing encouragement of all of us.
Fun!
Authors: Mason Maughan S.
Published: March 2008

Maughan Mason first got involved with simulation in 1953 at the White Sands Missile Range, where they had Beckman, Mid-Century, Reeves, Goodyear, and EAI analog equipment. In 1959 he joined ThiocoZ, where he established and managed an analog simulation facility. In 1966 he went digital (sort of) by joining IBM, first at Huntsville and since at Palo Alto. Maughan has been a stalwart of SCS (nee SCi) activities since his Thiocol days, having served as chairman of the Rocky Mountain Simulation Council (which he helped form) and later the Southeastern Simulation Council. He is a Past President (1962-64) and Life Member of our society and has made more valuable contributions to it and to simulation than can be credited here. Along the way, Maughan became interested in and made notable contributions to an allied art (literally), computer-aided art, which he has shown worldwide (and as the frontispiece of this editor's book Simulation, McGraw-HiZZ., 1968).
A “Thin” man Speaks
Authors: Kay Ira M.
Published: March 2008

As he indicates in his letter, Ira Kay got into simu lation at the U.S. Air Force Headquarters "before I could spell it." He retired from that job in 1965 and helped organize Southern Simulation Service, Inc. and has been general manager of that origanization ever since. Ira says that a highlight of his career was the discovery of SIMSCRIPT as a tool for simula ting, and that some milestones were retirement from the Air Force, starting SSSI, organizing the Annual Simulation Symposia, and departure from that activity after ten years as executive vice president. As the driving force behind SSSI and the short courses which that organization has conducted, and through his planning and leadership in connection with the Annual Simulation Symposia, Ira has not only done much to popularize simulation and teach others how to use it but he has also contributed substantially to the advancement of the state of our art.
A real-time simulation of a hierarchical computer network for process control
Authors: Engelberg George P. , Howard James A. , Mellichamp Duncan A.
Published: March 2008

Hierarchical computer networks are useful in process control because they decentralize processing and thereby result in easier system development and greater fault tolerance. This type of network can be characterized by the flow of jobs to and from a single node computer. In this work a three-level hierarchy with a single node computer has been simu lated using a dual minicomputer system. One of the machines is used to simulate the node computer, the other machine to represent the low-level computers and the overall master computer.

The simulation allows the user to maintain control over all key network parameters and to adjust them dynamically if desired. The output data permits the detailed monitoring of the performance of the net work. Some typical operating results are presented which illustrate the use of the approach to evaluate alternate job-scheduling strategies or to optimize a single scheduling algorithm.
Sensible simulation for industrial systems
Authors: Johnson Marvin M.
Published: March 2008

This paper introduces a new series of short articles that will appear in Simulation in the coming months. Their common topic will be the use of simulation in solving industrial-process problems. This paper briefly surveys the use of operations-research (OR) methods by large industrial organizations and notes that only 60% of the OR projeets included in the sur vey were successful. The purpose of the new series is to identify those areas where simulation is an effective tool and those where it is not. Readers are asked to submit articles and letters on success ful and unsuccessful applications of simulation, on guidelines for using simulation in studying indus trial processes, and on better ways of using simula tion in operations research.
Some control and simulation aspects of the pelletizing of iron ore
Authors: Cross Mark , Wellstead Peter E.
Published: March 2008

An interactive digital simulation of the balling-drum circuits used in the pelletizing of iron ores has been developed in BASIC-PLUS on a DEC PDP 11/45 com puter running under the RSTS/E operating system. The simulation has been used to (1) demonstrate the con trol problems inherent in the conventional design of balling-drum circuits, (2) determine the factors which make effective control of the circuit so diffi cult, and (3) evaluate the conditions under which the most effective control may be achieved using conven tional control strategies.
Solving large scheduling problems by minimizing conflict
Authors: Ignizio James P.
Published: March 2008

The scheduling of tasks (such as jobs through a com puter, different pulses through a radar system, or machining efforts through a production line) is a problem that is encountered quite frequently in practice. Traditionally, analysts have endeavored to develop schedules that minimize make-span (the time that elapses between the start of the first task in a sequence until the finish of the last task in a sequence). However, there are often many other appropriate measures of scheduling effectiveness. In this paper we address the problem of maximizing the number of jobs completed in an environment where each job is in competition with other jobs for certain scarce resources. Further, we shall assume that the number of jobs and possible start times is so large as to eliminate the possibility of the use of any exact technqiue.
A View On the Simulation of Systems
Authors: Dekker L.
Published: March 2008

From its beginning about three decades ago, the simu lation of dynamic systems has made fast progress, but it can be expected that, like data processing, the maximum rate of advancement has already passed.

In the past, computer hardware has severely limited both data-processing power and the development of sys tems simulation. Recent advances in hardware have re moved hardware as a limiting factor in data processing; hereafter the limitations on the design of simulators will arise from the methodology rather than from the hard ware.

Future data-processing systems will combine parallel and serial computation in a hierarchical structure in time (serial) and space (parallel). This architecture will allow a strong one-to-one analogy between the computer model and the mathematical or conceptual model of the system under study. Such one-to-one analogies require develop ment of appropriate data-processing and simulation algo- ri thms.

The improved methodology for systems simulation will have beneficial consequences in the teaching of applied sciences by making it convenient to conduct meaningful experiments by simulation.

A few decades hence systems simulation will become a saturated art limited by human capabilities.
Programming languages for computer system simulation
Authors: Unger Brian W.
Published: March 2008

This paper describes the programming language facil ities required to simulate computer systems. The systems considered include large multiprocessor, virtual memory computing systems, and networks of these systems. The models considered range from those which only roughly describe system resources to those which fully describe all user and system software. The complex models at the latter level require powerful language facilities which promote program modularity. These basic language facilities include list processing and programmer-definable data structures and data types. The relevant features of the following languages are considered: the general- purpose languages FORTRAN, ALGOL 60, PL/I, ALGOL 68, SIMULA 67, and PASCAL; the general-purpose simulation languages SIMSCRIPT II, GPSS V, GASP, and SPURT 70; the computer simulation languages CSS, OSSL, ECSS, ASPOL, PSML, and CREAM; and the system implementation languages CONCURRENT PASCAL, CLU, ALPHARD, MODULA, and EUCLID. Of these languages only SIMULA 67 and the system implementation languages provide the basic facilities. These features are also useful in the implementation of any large, complex model, particu larly when programming effort must be minimized.
On validating simulation models of missile systems
Authors: Kheir Naim A. , Holmes Willard M.
Published: March 2008

Simulation of missile systems is mainly used to pre dict missile flight and terminal miss distance and to study flight safety. Computer simulations of mis sile systems produce results that otherwise could only be obtained by actual tests and missile flights. The increasing cost of firings limits their number and hence reduces the amount of available flight-test data. Theil's inequality coefficients (TIC) and their geometric representations are the basis for a procedure which provides insight into the validity of a simulation and reduces the dependence of validation on flight-test data.
A combined simulation of a rapid transit system
Authors: Eichler Jacob , Turnheim Amiel
Published: March 2008

Three approaches to simulating a rail rapid-transit system are compared. The system is itself partly continuous in nature (equations of motion, for example) and partly discrete (dispatch of trains, for example). The three approaches are (1) a basi cally continuous model modified to accept discrete events, (2) a basically discrete model modified to accept representations of continuous portions, and (3) a combined model designed to accommodate both the discrete and continuous parts.
MEDECS, a simulator for mediterranean ecosystems
Authors: Miller Philip C. , Stoner Wayne A. , Richards Susan P.
Published: March 2008

MEDECS, the mediterranean ecosystem simulator, was developed to model the dynamics of mediterranean- type vegetation in southern California and central Chile. MEDECS is a difference/differential-equation model which simulates the seasonal patterns of resource use and plant response in one-day time steps. It uses submodels of plant growth, decompo sition, and inorganic nutrient release to describe the effects of physiological processes, nutrient availability, and environmental parameters. MEDECS is a compartmental model of the producer-decomposer system. In use, it simulates the seasonal progres sion of changes in each of the compartments. It is being used in on-going research to examine hypotheses about single-species and multiple-species (competi tive) communities of plants.
An experimental solution of the general stochastic programming problem
Authors: Gaither Norman
Published: March 2008

After reviewing existing approaches to the general stochastic programming problem, an improved experi mental method is proposed. This method uses a va riety of mathematical programming algorithms and any desired pattern of parameter variation. Statistical analysis of the results allows decision-makers to make probabilistic statements about the values of the decision variables and of the objective function. Illustrative examples are given.
Interactive simulation on minicomputers
Authors: Pearce J.G.
Published: March 2008

This paper describes the mechanisation of the ISIS interactive continuous-system simulation language, with particular emphasis on the compilation process. The language has extensive facilities, including line-by-line syntax checking and instant diagnostics. The special problems and constraints of minicomputer operation are discussed. Compilation takes place in two stages, the first occurring line by line as the program is entered into the host computer. The second step consists of a single pass that produces low-level interpretive code that can be executed immediately. The compiler itself is written in FORTRAN with a minimum of machine-dependent subrou tines for handling input/output., terminal graphics, keyboard interaction, and the like. As a result, ISIS is highly portable ; it has already been instal led on six different types of computers.
The method of lines and the advective equation
Authors: Carver Michael B. , Hinds H.W.
Published: March 2008

The linear advective equation is simple in form and yet it is one of the most difficult equations to solve accurately by numerical means. Because its be havior is similar to that of the conservation equa tions of compressible one- or two-phase flow, the advective equation is extremely useful for testing numerical schemes.

This paper summarizes techniques for solving the ad vective equation using, the method of lines on a digi tal or hybrid computer, and assesses how suitable they are for incorporation into large simulations. Some of the dangers of using artificial dissipation terms are described, and a weighted-residual tech nique is shown to be very effective.
Evaluation of startup policies in simulation experiments
Authors: Wilson James R. , Pritsker A. Alan B.
Published: March 2008

This paper describes a procedure for evaluating pro posed startup policies that define the initial condi tions and the truncation point in a simulation ex periment. The evaluation procedure involves the tabulation of bias, variance, and mean square error of the sample mean over a fixed range of truncation points and initial conditions. For each policy, the tabulated values are averaged with respect to an empirical truncation-point distribution based on independent model runs. These results are used to construct confidence intervals for the steady-state mean with the same average length for all policies; the corresponding average confidence interval cover age can then be used to compare policies.

To illustrate the procedure, several well-known policies are evaluated for two finite-state Markovian queueing systems—α single-server queue with a capac ity of 15 and a machine-repair system with 3 repair- men and 14 machines. The results for both systems indicate that the best initial condition is the most frequently observed value (the mode) of the steady- state distribution of the number-in-system process, and that the judicious selection of an initial condi tion is more effective than truncation in improving the performance of the sample mean as an estimator of the steady-state mean.
Simplification via aggregation for neural networks
Authors: Aggarwal Sudhir
Published: March 2008

Aggregation is a useful technique for simplifying multicomponent systems. We illustrate this by sim plifying a class of neural network models and com paring the behaviors of the simplified (lumped) model and the original (base) model. Naturally, in order for aggregation to be applicable, certain constraints on the neural network models are imposed. The lumped model obtained is a vastly simplified model and is deterministic, even though the base model is proba bilistic. Nevertheless, by experimenting with the lumped model and using the information obtained in the form of force field plots, we are able to cor rectly predict many aspects of base model behavior. A related probabilistic lumped model, similar to the deterministic lumped model, is also examined.
Simulation of a rotating track production line
Authors: Levi Adriana , De Luca Cardillo Dorotea
Published: March 2008

This paper describes the use of simulation in plan ning a production line. Simulation allows the mani pulation of critical factors that determine the effi ciency of the line. The model requires some special techniques such as inverting the roles of the elements and advancing the track in irregular steps to decrease simulation time while retaining proper synchroniza tion. For part of the analysis the model simplifies the behavior of the machines by disregarding accidents, which facilitates finding the optimal values of the controllable parameters. More accurate measures of line efficiency would require the inclusion of the neglected factors. Model validation required the calibration of fixed mechanical parameters so that simulation results could be checked against the theo retical productivity of the line as it was simulated. Proper starting and ending conditions are defined.
Dynamic modeling and simulation of a relief valve
Authors: Ray Asok
Published: March 2008

A nonlinear dynamic model of a relief valve is for mulated in state-space form from fundamental princi ples of rigid-body motion and fluid dynamics. Model parameters are calculated from steady-state character istics and the physical dimensions of the valve. The transient response of the nonlinear model (as well as system eigenvalues and the frequency response of a linearized model) is obtained by digital simulation. Results indicate that the opening time of the valve is linearly related to the dimensionless parameter given by the ratio of orifice length to its radius.

The analysis provides design information and perform ance evaluation for fluid systems incorporating relief valves. It is particularly suitable for relief valves for liquids and it can be adapted for other applications.
Analogue computer simulation of a rotor system containing a transverse crack
Authors: Okah-Avae B.E.
Published: March 2008

This paper describes the analogue computer simulation of a complete rotor and bearing system. The physical equations of motion of the rotor with its shaft are derived in rotating coordinates and those of the bearings in stationary coordinates. The system is modelled to have four degrees of freedom, taking into consideration the flexibility, damping, and cross- coupling of the hydrodynamic bearings. The model can be reduced to two degrees of freedom by assuming that the rotor is rigidly supported. The simulation of a transverse fatigue crack in the rotor shaft is pre sented and its effect on the dynamic response of the system is briefly examined.
Integration across discontinuities in ordinary differential equations using power series
Authors: Halin H.J.
Published: March 2008

Numerical integration of ordinary differential equa tions containing nonanalytical functions is error- prone and time-consuming. Because of this problem, the simulation of the hydraulic servo drive of a machine tool produced unsatisfactory results. How ever, applying power-series expansions provided fast and accurate solutions. Due to its pieceuise semi- analytic character, this method is particularly suited to handling discontinuities. Although it re quires the calculation of higher derivatives by means of recursion formulas, the power-series method can be completely automated. A simulation package for this purpose is currently under development. Two examples compare its performance with that of Runge-Kutta- Merson integration.
Analog/hybrid simulation of rail vehicle lateral dynamics
Authors: Heller Rainer , Malstrom Carl W. , Law E. Harry
Published: March 2008

Analog/hybrid computer simulation is a promising tool for research into the lateral dynamics of rail vehi cles. The complexity and nonlinearity of these dynamics makes hybrid computing cost-effective. This paper describes the progressive development of analog/ hybrid simulations beginning with the basic model of the trao-degree-of-freedom wheezset and evolving into a complex, multi-degree-of-freedom, nonlinear model of a freight car. Simulation results include the limit-cycle behavior of a nonlinear wheelset model and the response of an idealized model of a freight- car. Extension of this work to more realistic freight-car models is discussed.
Computed temperature-time excursions at succeeding locations in an industrial reactor
Authors: Franks Roger G. E. , Miller Donald N.
Published: March 2008

Traveling thermal transients have been observed in deep-bed catalytic reactors. With certain combina tions of parameters and stimuli, these transients can increase in amplitude with increasing axial distance into the bed. The resulting peak temperatures can exceed structural equipment limitations and cause catalyst deactivation or physical deterioration. Reaction systems in which abrupt changes in operating parameters can occur are particularly susceptible. An understanding of the causes of such transients is important not only for design but also in operations where optimization of output and product quality is essential.

This paper describes a numerical procedure that effi ciently simulates thermal transients on a digital computer. Results are shown for a generalized reactior, scheme that includes the effects of reaction rate, activation energy, absorption, heat of reaction, heat capacities of gas and solids, and catalyst bed depth. Also covered is initiation through various stimuli such as feed rate, composition and temperature dis continuities, pressure variations, and abrupt activity changes.

The transients travel because the solid fixed-bed heat capacity causes temperature to lag concentration re sponses with step changes in operating conditions. An interesting result is that temperatures in the bed move in the direction opposite to the initiating stimulus. A decrease in feed temperature, for example, produces a positive peak wave temperature. A computer simulation of the phenomenon can aid in developing effective control strategies and operating procedures.
Simulating modular microcomputers
Authors: Langley Frank J. , Sheehan Joan , LaGro Gerald
Published: March 2008

Detailed logic design followed by breakboarding of microprocessor-based systems makes development costly. This paper reports on the use of a high-order language for designing simulation models of microcomputer functional elements ("macromodules") at the register level and for verifying the timing and interface requirements for a family of microcomputer configura tions. The definitions of these microcomputer macro modules (i.e., microprocessors, memories, and input/ output interface modules) was derived in previous system analyses and simulation work reported in References 1 through 5, which were sponsored by the Office of Naval Research.

Of the several simulation or emulation methods avail able for studying the design of computer architecture, the technique adopted here provides the level of simulation required to verify timing, interface logic, and data flow within and between macromodules in the family for subsequent simulations of system performance.

Furthermore, module-level simulation using discrete logic forms the necessary link between system design and the ultimate description of hardware for a low cost, step-by-step design process. Writing and executing the module simulation programs provides a disciplined approach to hardware design, since the components have to be modeled in detail to follow the flow of data and timing in a microcomputer. The modeling was done in a register-transfer language called Computer Design Language, which is very con venient for this kind of simulation model. Examples of programs in CDL are included.
Improving ecological simulation through sensitivity analysis
Authors: Thornton Kent W. , Lessem Allan S. , Ford Dennis E. , Stirgus Connie A.
Published: March 2008

Ecosystem models require extensive data for initial ization and calibration. Since data collection is expensive and time-consuming, it should be guided by knowledge of the model's sensitivity to initial con ditions, coefficients, and update intervals. These factors were studied using an ecological model of a reservoir. For this model, it was found that

(a) biological and chemical variables need to be considered in addition to temperature during calibra tion, (b) changes in the effective diffusion coeffi cients produce the greatest changes in the model's responses, (c) nutrient update intervals of less than one week yield results similar to those for one week but dissimilar to those for two weeks or one month, and (d) nutrient concentrations strongly affect the model's sensitivity to small changes in a number of coefficients.
Model of short-term regulation of calcium-ion concentration
Authors: Járos George G. , Coleman Thomas G. , Guyton Arthur C.
Published: March 2008

This paper describes a digital simulation model of the short-term regulation of the concentration of calcium ions in the extracellular fluids of the body. The model includes four major classes of systems: terminal, intermediary, distribution, and coordinat ing. The terminal systems are the intestines (pri marily uptake) and the kidney (primarily excretion). The intermediary systems consist of two bone compart ments, viz., solid bone containing stable calcium salts and "fluid" bone in which recently formed unstable calcium salts are in equilibrium with the fluid that surrounds them. The distribution system is the extra-cellular fluid consisting of blood plasma and fluid between the cells in the tissues. The coordinating system functions via three hormones, viz., one secreted by the parathyroid glands (para thormone, PTH), one from the thyroid gland (calcitonin), and one derived from vitamin D through activation processes by the skin, liver, and kidney (1.25 dihydroxycholecalciferol). These four systems and their interrelationships are described in FORTRAN IV in conjunction with special simulation software. To illustrate the fundamental principles which govern calcium concentration, simple well-known experiments are simulated. These include calcium infusion, parathormone infusion under conditions of normal and abnormal high calcium concentration, and partial and total removal of the parathyroid glands. These simulations agree quite well with experimental findings. The model is designed to be expanded as new information becomes available.
Hybrid computer optimization of a class of impact absorbers
Authors: Sankar Seshadri , Hargreaves David R.
Published: March 2008

This paper describes the use of a hybrid computer in the optimal design of impact absorbers. The objec tive is to minimize the maximum acceleration of the mass (load) being protected by the absorber during a transient, subject to the constraint of available "rattle space" within which the mass may move with out hitting the stops. The mathematical model of the absorber was implemented on the analog section of the computer, while the digital section performed parameter optimization and controlled the analog computer. The results are presented in the form of normalized curves showing the optimum stiffness and damping coefficients for various conditions and the resulting maximum acceleration levels in each case. The results show that hybrid computer optimization is fast and very effective for the optimal design of nonlinear impact absorbers.
Cross-impact gaming applied to global planning
Authors: Helmer Olaf
Published: March 2008

Several efforts to deal with the problem of shrink ing global resources have succeeded in alerting the public to the threatening disastrous consequences of a continuing laissez-faire attitude in the face of currently observable population and industrial ization trends. But little has been done to provide positive, realistic plans for countering these threats.
The Energy-Environment Simulator: a new tool for education
Authors: Amend John R. , Eliezer Isaac
Published: March 2008

A significant problem facing the world today is the development of an energy-literate public. Interactive simulation using special-purpose analog and digital computers has proven to be an effective method of public education. This article provides a brief in troduction to the educational use of interactive simulation and discusses the functional and elec tronic design of an Energy-Environment Simulator.
Analysis of time-varying video information
Authors: Berkey F.T. , McRae John R.
Published: March 2008

Deriving quantitative information from time-varying signals recorded on video tape can be cumbersome. This paper discusses an interface between a hybrid computer and a video integrator that quantifies in formation from a portion of the video signal which is variable in size and location within the television raster.
Simulation of the nonlinear behavior of an electrohydraulic exciter
Authors: Lebrun Michel , Scavarda Serge
Published: March 2008

This paper presents a computer simulation of the non linear behavior of an electrohydraulic exciter. The experimental results and the simulated results are compared.

The model used takes into account the nonlinearities of the two-stage servovalve and the jack. Major nonlinearities included in the simulation are torque- motor hysteresis, flow forces acting on the servovalve spool, the pressure-flow relationships in the orifices (particularly near the null region), compressibility of the hydraulic fluid, clearance of the mechanical feedback link, fluid leakages, sticking forces, and variations of dead volumes.
Simulation in the Service of Society
Authors: McLeod John , McLeod Suzette
Published: March 2008

This Newsletter was published independently from January 1971 through August 1976. Back issues are available from SITSOS, 8484 La Jolla Shores Drive, La Jolla, CA 92037, for 75ç per copy.
A model of the temperature-dependent operation of a MOSFET
Authors: Akers Lex A.
Published: March 2008

Nonuniform temperature distributions can greatly affect the operation of semiconductor devices. At present, computer programs using numerical methods can be used to simulate the steady-state or transient response of one- or two-dimensional models of semi conductor devices operating at constant temperature. Recently developed programs allow the steady-state analysis of semiconductor devices under nonisothermal conditions. The transient response, the mode of operation for most high-power semiconductor devices, has not been analyzed for a MOSFET.

This paper presents a one-dimensional mathematical model for predicting the nonisothermal behavior of a MOSFET under pulse excitation. Both the transient electrical and temperature responses are shown. Redistribution of voltages and carriers resulting from the differences in the electrical and tempera ture time constants is discussed.
A decision-optimization module for SLAM
Authors: Pegden C. Dennis , Gately Michael P.
Published: March 2008

This paper describes a decision-optimization module for use with SLAM simulation models. When appended to the SLAM software package, the optimization module provides capability for the automatic optimization of decisions with respect to an arbitrary user-defined objective function. The purpose of this paper is to describe the optimization technique and the proce dures required to invoke the module from within a SLAM simulation model. An example illustrating the use of the module to determine the optimum timing of traffic lights is presented.
A nonlinear model of the U.S. economy
Authors: Niedercorn John H. , Kalaba Robert , Kandoole Benson F.
Published: March 2008

According to orthodox Keynesian economic theory, sig nificant unemployment and inflation should not occur simultaneously (i.e., "stagflation" should not exist) in a highly developed modern economy. However, both have occurred simultaneously in the United States since 1973.

This paper describes an economic model being developed to investigate the causes of stagflation; this model includes nonlinearities and discontinuities not in corporated in other macroeconomic models. In its present form the model does not include all the var iables necessary to achieve its purpose, and its parameters and initial conditions have been set at arbitrary "reasonable" values. Much work remains to be done before it can simulate stagflation in the economy of the United States. The responses of the present model to initial conditions leading to stag nation, moderate growth, and high-pressure growth situations are reported and analyzed in this paper.

The results obtained by experiments conducted on the model reflect the behavior of an idealized competi tive capitalistic economy with implicitly flexible prices and explicitly flexible interest rates. The model eventually produces full employment and steady growth regardless of the initial conditions used. This behavior implies that the simultaneous occur rence of unemployment and inflation should not exist very long in such an economy.
A communication mechanism for multiprocessor simulation systems
Authors: O'Grady E. Pearse
Published: March 2008

This paper describes the organization of a multi processor system designed to analyze large systems such as power systems, global weather, and complex real-time systems. The configuration discussed handles up to 256 processors which can be inter connected using a new, high-speed communication method that takes advantage of the iterative com puting requirements of simulation problems. The communication scheme uses parallelism and address- mapping memories to achieve a very high interprocessor data-transfer rate. The solution of a large, sparse set of linear equations illustrates how the communi cation mechanism operates.
Simulation of road traffic conflicts at T-junctions
Authors: Darzentas J. , Cooper Dale F. , Storr P.A. , McDowell M.R.C.
Published: March 2008

This paper describes an event-stepping (discrete- event) simulation model of a nonurban T-junction. The model is intended for investigating the risk of traffic accidents at such junctions, using a version of the traffic-conflict technique. The model uses empirical data and predicts the number and severity of conflicts as a function of various traffic and behavioural parameters. Some applications of the model are outlined. The traffic-handling capacity of the junction and delays at it are not considered.