bluuebunny/crossref_metadata_2025 huggingface dataset:
Creating Galaxies on a PC
Authors: Raczynski Stanislaw
Published: March 2008

It is shown that galactic simulation does not require a supercomputer. The capacity of new PCs is enough to simulate an N-body system with the number of bodies sufficient to see a galaxy formation from chaos to a disk with a spiral galactic structure. Naturally, simula tions with millions of bodies realized on paral lel supercomputers provide more realistic im ages. However, the number of bodies is not a crucial factor if rather qualitative results are expected. By simulating a pure gravitational system with only 500 particles on a PC, one can observe a fascinating history of a galaxy evolution. Some algorithms for N-body inte gration are discussed and an implementation af a simple "neighbor and far interactions" algorithm is presented. The complete history of a simulated galaxy is shown, including the initial collapse, expansion, formation of the early cloud with rotational movement and, finally, a spiral structure.
Simulating Colloidal Thickening: Virtual Papermaking
Authors: Scharcanski J. , Dodson C.T.J.
Published: March 2008

Paper is made by the continuous thickening of an aqueous suspension of cellulosic particles. In pub lished computer simulations, the interactions among cellulose fibers have mainly been considered the most relevant issue. However, colloidal particles are present in much larger numbers than cellulose fibers, and influence paper quality in different ways. In this study, we describe a new simulation proce dure for the interactions among fibers and fines, during the thickening process. Among the param eters involved in paper forming taken into consid eration are fiber and fine size distributions, fiber and fine concentration, fiber propensity to floccu late, and fiber flexibility, as well as parameters de scribing the process conditions, such as geometry of the filtering fabrics, drainage speed, turbulence intensity, and turbulence decay. Generated struc tures may be useful in interpreting physical pro cesses in the forming process, design of new mea suring instruments or estimation of product quality.
The Impact of Stochastic Tool Life on Shop Performance: A Simulation Study
Authors: Lyman Steven B. , Tan Keah-Choon , Wisner Joel D.
Published: March 2008

Much of the research in tool management has ignored the potential impact of tool life on shop performance. Tool management research has typically assumed that tool life is deterministic and can be predicted accurately. Since tool life is a function of its quality, cutting speed, depth and other environmental factors, no two identi cal tools exhibit the exact same tool life. An as sumption of stochastic tool life is more realistic on the actual shop floor. In this paper, we have developed a simulation model to examine the effects of stochastic tool life, dispatching rules and tool failure penalties on shop performance.
A Simulation Model for Availability Under Battlefield Situations
Authors: Sadananda Upadhya K. , Srinivasan N.K.
Published: March 2008

The availability of defence systems such as aircraft, battle tanks, ships and others, is a critical parameter for planning combat missions. Availability does not remain constant, due to battle damage, which depends on the intensity of the battle, and repair rates. As most high intensity conflicts do not continue for more than one to two weeks, transient solutions for availability are of greater interest than steady state solutions. In this paper we develop a simulation model to arrive at transient solutions to the availability of defence systems under battlefield situations. The model includes Monte Carlo methods applying dif ferent probability distributions for failure times due to battle damage and system unreliability, and for repair times. The simulations can be performed using exponential, Weibull or log-normal distribu tion, as appropriate. The simulation results indicate transient fluctuations in availability within one to two weeks of battle, which would seriously limit the possible combat missions in battles.
Simulation of Aircraft Pilot Flight Controls Using Nonlinear System Identification
Authors: Eklund J. Mikael , Korenberg Michael J.
Published: March 2008

This paper is concerned with modelling of the front end of an aircraft pilot flight control system's behav iour using a nonlinear system identification technique known as parallel cascade identification. Using this technique, we are able to model a critical part of a pi lot flight control system with sufficient accuracy to meet the objective test requirements of the U.S. Fed eral Aviation Administration for certifying full flight simulators. Traditional approaches to modelling such aircraft systems involve extensive analytical studies of the design of the system, lengthy and detailed empiri cal testing and recording of data from the physical system, and then considerable analysis to fit paramet ric models to the data. The approach presented in this paper virtually eliminates the need for analysis of the system in question, significantly reduces the number of signals that need be recorded from the real aircraft flight control system, and provides an extremely fast method of identifying the mathematical model based on these data. Overall, the time and costs associated with building an effective model are greatly reduced.
Impact of Emulation Code on the Performance Evaluation of Simulated Systems
Authors: Khalid Humayun
Published: March 2008

Emulation affects accurate performance evalua tion of applications running on the present gen eration of computing machines. The emulation code is often passed onto the traces which, when used for the trace-driven performance evaluation of the next generation of architectures, results in highly incorrect evaluations. Although the sce nario captured by the traces is real, one major problem associated with such a fact is that if such traces are used for futvcre systems design, the underlying implicit assumption will be that the emulation problem will persist with the same degree of impact. This novel paper presents the performance evaluation problem and solutions associated with camputer systems executing relatively large amounts of emulation code.
Fuzzy Inductive Reasoning Model-Based Fault Detection Applied to a Commercial Aircraft
Authors: Mirats Tur Josep M. , Huber Garrido Rafael M.
Published: March 2008

This paper concentrates on progress made in fault detection using the Fuzzy Inductive Reasoning (FIR) methodology. The so-called envelope approach is presented and compared with previous research efforts published by the same group in SIMULATION in 1989 and 1994. The comparison is achieved simulating faults in a B-747 commercial aircraft, the same example that had been used in the previous pub lications. The previously used crisp detection has been replaced by a new approach, based on the computation of an acceptability interval for each predicted variable. The paper demonstrates the improved capabilities of the new approach to de tect faults earlier and in a more reliable manner.
Simulation Approach to Decision Assessment in Enterprises
Authors: Kljajic Miroljub , Bernik Igor , Skraba Andrej
Published: March 2008

The methodology of an integrated simulation system application for decision-making support in enterprises is described in this article. The use of visual interac tive modelling and animation can help users better understand simulation results, especially those who are not experts. Decision-makers are motivated by the aniniation while seeking better solutions for pro duction problems. The method was tested in a medium- sized company in order to improve operational plan ning and re-engineering. The real process was recorded on video, digitized, and implemented on a PC. Anima tion of the simulated process, synchronized with video of the real process, was projected in a room to achieve model validation and participant confidence. Opera tional production plans were simulated using current demands as the basis. Application of discrete event simulation in reengineering is also presented. The article shows how to develop a model, prepare sce narios and evaluate alternatives. Two criteria were evaluated for the alternative: the expected value and the value of multiple criteria evaluation, which was examined with the AHP method. Model validation and its use for alternative selection is also discussed.
Simulation in the Service of Society (S3)
Authors: McLeod John , McLeod Suzette
Published: March 2008

Professionalism The current interest in professionalism rang a bell with Suzette, who did some research on the subject that disclosed that Paul Roth gave a Keynote address on the sub ject at the March 1989 Eastern Simula tion Council meeting in Tampa, Florida and which in turn led to our publishing an article in S3 in the May 1989 issue of SIMULATION. Ex cerpts from that article follow.
The Simulation Education Homepage
Authors: Yurcik William
Published: March 2008

Both novice and experienced educators across dif ferent disciplines have expressed the need for a tool to help orient them to teach computer simula tion. This paper presents the Simulation Educa tion Homepage (http://www.acs.ilstu.edu/faculty/ dldoss/yurcik/nsfteachsim/indexnew.html) which was initiated as a result of an US National Sci ence Foundation sponsored Simulation Education Workshop held in August 1998 in Washington D.C. With input from leading simulation educa tors, web-based simulation education resources have been linked and cross-referenced in this one "virtual " location which serves as a meeting place for discussion about teaching simulation. After introducing the different categories of resources (software/courses/textbooks/people/etc.), data about categorization and use of the resources is presented. We found clear trends within categories and common characteristics between requests for information and recommendations for new links from all over the world. We also include discus sion of a future project to enhance the interactivity of this website using XML integrated with database processing.
A Design for a Simulation-based Multimedia Learning Environment
Authors: Roccetti Marco , Salomoni Paola , Bonfigli Maria Elena
Published: March 2008

The development of high performance computing and communications is enabling the creation of new excit ing automated learning environments. In particular, the creation of richer distance learning environments has been obtained by merging together the World Wide Web with the educational features of multimedia and simulation technologies. However, most of today's Web-based courseware tools is often limited to the presentation of non-customized instructional ma terials. Those tools are in essence equivalent to computer assisted learning systems-they are static and unable to personalize the interaction with the user. Contrariwise, new-generation distance learning software tools should be able to exploit (i) adaptive mechanisms, (ii) Web technologies, and (iii) net worked multimedia and simulation in order to drive each different student through his/her personalized learning path. This paper presents the design and the multimedia/hypermedia architecture of a simulation- based distance learning tool which has been designed and developed to provide instructional support tai lored to the personal profile and needs of each different user.
Proportion Estimation of Correlated Sequences
Authors: Chen E. Jack
Published: March 2008

Simulated estimates of proportions are needed in some simulation studies. We propose a quasi-in dependent method to determine the length of a simulation run so that the proportion estimates satisfy a pre-specified precision requirement. The method uses histogram approximation to generate confidence intervals with the desired precision. Because a histogram of the output sequence is constructed, several proportions can be estimated simultaneously without much extra effort. The assumptions required are that the stochastic pro cess output sequence is continuous and satisfies the ø-mixing conditions. An experimental perfor mance evaluation demonstrates the validity of the quasi-independent procedure with histogram ap proximation.
An Agent-based Data Filtering Mechanism for High Level Architecture
Authors: Tan Gary , Liang Xu
Published: March 2008

In the Runtime Infrastructure (RTI) of the High Level Architec ture (HLA), the purpose of the Data Distribution Management (DDM) services is to reduce the amount of irrelevant data communicated between federates (simulations) and cut network communication cost. The current DDM schemes proposed for the RTI, i.e., region-based and grid-based DDM, are both oriented to send as little irrelevant data to subscribers as possible, but they only manage to filter part of this information and some irrelevant data is still being sent. In this paper, we employ intelligent agents to perform data filtering in HLA to address these drawbacks. In our method, each time a federate subscribes to some data, intelligent mobile agents are launched to the publishers of those data. These agents will fetch the updated data, perform data filtering and then send the subscrib ers the exact information they require. At the same time, agents will be kept notified of the updated filtering range by keeping contact with the subscribers. Based on this idea, we implement an agent based RTI (ARTI) using the FDK RTI-kit. The RTI with region-based DDM and the RTI with grid-based DDM are also implemented to aid in the comparison. The ARTI is tested and compared with the other filtering mechanisms using the AWACS sensing aircraft simulation scenario and air traffic control simulation scenario. Experimental results show that the agent-based filtering approach performs best in data filtering and communicates only relevant data, minimizing network communication. It is also comparable in terms of time efficiency.
From a Graphical Interface to a Full Scope Training Simulator
Authors: Garcés M. , Corcuera P. , González C. , Pomposo R.
Published: March 2008

TSG++, a full scope training simulator with an interface entirely made up of soft panels, has been developed for a Spanish nuclear power plant. The simulation environment is OpenSim NT by RNI Technologies. The graphical interface, which in cludes fifty-seven PCs and monitors in its present configuration, has been developed using component software technology. The operators interact with the simulator by means of touch-screens. Specific appli cations give the instructor full control of all the computers and displays from his own console in a simple manner. An optimum choice of hardware for visualization and interaction, in terms of cost and performance, resulted in a facility much less expen sive than the classic hard panels replica simulators. Other benefits of the soft panels approach include automatic switch reposition and tagging, configura tion flexibility, low maintenance requirements and capability to support multiple users distributed across the company intranet. After exhaustive validation and testing, the training sessions are being con ducted successfully.
Performance Evaluation of ZOMA Preemptive Deadlock Recovery Mechanism for Wormhole Networks
Authors: Al-Awwami Z.H. , Obaidat M.S. , Al-Mulhem M.
Published: March 2008

This paper presents a novel deadlock recovery mechanism for fully adaptive routing in wormhole interconnection networks and its performance evaluation using simula tion madeling. ZOMA is an efficient mechanism that takes advantage of the concept of wormhole switching in terms of low hardware resource requirements. The perfor mance of the new mechanism can match that of other more expensive deadlock-recovery mechanisms, while requir ing lower hardware resources that are not on the critical path of the switching process. The proposed mechanism creates a new category of deadlock recovery techniques that we refer to as preemptive as opposed to the existing progressive and regressive categories. Performance evalu ation of the proposed mechanism against other routing algorithms and deadlock-recovery techniques is accom plished using the object-oriented simulation approach. The simulator, WormSim, was written in Java for various reasons. Most importantly are the modularity, hierarchy, extensibility, reusability, and flexibility aspects.
Allocating Soft Real-Time Tasks on Cluster
Authors: Weiping Zhu
Published: March 2008

We consider distributing soft real-time tasks on a clus ter of multiple homogeneous servers. The question con sidered here is how to assign incoming soft real-time tasks to these servers for better performance, measured by the fraction of tasks that miss their deadlines. In this paper, two architectures are taken into account-cen tralized and distributed. Within the distributed archi tecture, four dispatching policies-round robin, Ber noulli splitting, joining the shortest queue, and chop ping-are analyzed and evaluated under the same condition. In the analysis, an approximate method is proposed and evaluated for the joining the shortest queue policy. The results show that for the distributed architecture, the joining the shortest queue policy per forms the best. The chopping policy previously proposed has its limitation and when workload exceeds a moder ate level, it performs worse than round robin. In addi tion, we investigated the impact of using the earliest deadline first to schedule tasks assigned to the same server, and found it can further improve performance.
A Security Framework for the Agent-Based Environment for Linking Simulations (ABELS)
Authors: Mills-Tettey G. Ayorkor , Wilson Linda F.
Published: March 2008

The Agent-Based Environment for Linking Simulations (ABELS) framework is designed to allow independent and physically distributed simulations and other data resources to form a “data cloud” for the exchange of information. In particular, it uses a distributed brokering system to facilitate dynamic linkings between independently designed, autonomous participants, without requiring the use of stringent standards to which participants must conform. This article discusses the various security threats that can arise in the ABELS architecture and presents the current design and implementation of a security framework for the system.
The Simulation of a Highly Dependable Distributed Computing Environment
Authors: Chen Yinong , He Zhongshi
Published: March 2008

The aim of the research is to investigate techniques that support the development of highly dependable applications in a distributed system environment. Techniques developed include redundant task allocation, load balancing, fault-tolerant computing, and communication. The application the authors have implemented in the system is a firewall application. The firewall runs in redundant mode. Each incoming or outgoing packet is checked by two or more copies of the firewall application. Only when the majority of the firewall copies decide to accept the packet can the packet go through the firewall. Disagreed decision from the different firewall copies signify a possible hardware fault or a software error in the underlying system. This article reports a recent implementation of a simulation system in which computing nodes, redundant copies of tasks, and packet queues are implemented as independent threads, as well as experiment results obtained based on queuing models.
A Location-Based Service Application for a Mobile Computing Environment
Authors: Silva Aloizio P. , Mateus Geraldo R.
Published: March 2008

The convergence of multiple technologies has given rise to new types of information utilities called mobile location-based services. Specifically, the authors examine a context in which people need to move physically from one location to another via taxis. In this scenario, the user is in control of the location information associated with the mobile device. However, problems arise when a fleet management application uses that dynamic information to provide the best taxi assignment. This particular vehicle-routing problem aims to allocate a taxi fleet to a number of mobile units to minimize the running distance and time. This article presents a new approach to the taxi assignment problem in a mobile environment based on optimization and simulation. Its specific interest is to predict the impact of the interaction between the assignment algorithm and fleet management in the mobile environment on the desired quality of service for mobile users.
A Formal Model Conversion Approach to Developing a DEVS-Based Factory Simulator
Authors: Choi Byoung-Kyu , Park Bum-Chul , Park Jeong-Hyeon
Published: March 2008

This article presents a model conversion approach to developing a 3D discrete event system specification (DEVS)-based factory simulator, in which the target automated manufacturing systems (AMS) are modeled by employing a job-resource relation network (JR-net), and this input JR-net model is systematically converted to a DEVS model. For this purpose, the JR-net modeling framework has been extended further to handle 3D geometric information while providing a formal specification of the JR-net. Also, a hierarchical DEVS model architecture and a systematic conversion method for converting a JR-net model into a DEVS model are proposed. Based on the proposed approach, a 3D factory simulator has been developed in C++ with OpenGL and a DEVS engine. The proposed factory simulator may be used as a virtual prototyping tool for designing new AMS. Its validity is demonstrated by constructing a virtual factory of a special type of AMS called a flexible manufacturing system.
Optimization of Multiparameter Systems By Hybrid Computer Techniques
Authors: Bekey George A.
Published: March 2008

The following is essentially the first part of Chapter XV of a set of notes prepared for a course in Hybrid Computation by Walter J. Karplus (Department of Engineering, Univ. of California) and George A. Bekey. It is one of the series on Education in Simulation promised in the editorial "Education: A Vital Responsibility" in the January issue of SIMULATION.
Digital Program Control for Iterative Differential Analyzers
Authors: Eckes H.R. , Korn G.A.
Published: March 2008

This report identifies the timing pulses and sequential digital logic needed for practical control of iterative- differential-analyzer programs and proposes a syste matic notation. Against this background, the design of a very flexible and convenient digital control unit developed for the University of Arizona's new ASTRAC II, an all-solid-state machine employing both "fast" ±10-volt amplifiers capable of iteration rates up to 1 Kc and "slow" ±100-volt amplifiers. A variety of "packaged" iteration routines is pro duced with a minimum of digital-logic patching. Digital-clock circuits can, in particular, control sta tistical evaluation of thousands of Monte-Carlo-type random-process simulations with automatic param eter changes, and will also control displays or analog- digital linkages.
Analog Computer Techniques for the Prediction of Transient Nuclear Radiation Effects On Transistor Circuits
Authors: Kosenkranius Lembit
Published: March 2008

Analog-computer representation of transistor circuits was developed for predicting transient responses of these circuits during nuclear radiation bursts. Tran sistors were simulated from the measured or man ufacturer-specified characteristic curves. Radiation effects in the transistors were added in the form of transient increase in emitter-to-base potential, and by the reduction of current gain (beta) of the tran sistor with a radiation-controlled negative feedback.* Linear networks between transistors were simulated from the transfer functions of these networks. A com parison is made between the responses of real and simulated single stage common emitter amplifiers and the real and simulated radiation bursts, respec tively.
Hybrid Simulation of Adapte Path Control
Authors: Halbert P.W. , Landauer J.P. , Witsenhausen Hans S.
Published: March 2008

Adaptive path control of a two-dimensional maneu ver under lunar attraction is simulated at high speed by a hybrid system comprising general-purpose analog and digital computers and programmable parallel logic and conversion components. The opti mization criterion selected leads to both on-off and continuous control variables. The digital computer performs a high-precision simulation of the rocket motion and transmits velocity and position informa tion to the analog computer at small time intervals. The analog, after each information transfer, solves a boundary value problem by high-speed iteration to obtain the optimum thrust control functions, trans ferring back to the digital computer only that portion of the control functions which is needed until the next information transfer. For any perturbation in the data—such as changes in the goal, the optimiza tion criterion, or operating characteristics of the rocket—a new optimum control will be calculated immediately and the system will adjust. The effective ness of the simulation hinges upon the use of a flex ible linkage system to provide data conversion, tim ing, and parallel logical control. Programming aspects of the hybrid system are emphasized.
Pactolus
Authors: Brennan Robert D.
Published: March 2008

In the last 10 years over a dozen block-oriented sim ulation languages have been developed for general- purpose digital computers. Several of these succeeded rather well in the semantics aspect of the problem. Almost without exception, however, they failed to provide the human operator with the operational flexibility which is the forte of the analog computer. In the opinion of the author, digital simulation has a most promising future. Unfortunately, at present it seems "stuck dead-center," and will probably remain so until we achieve a much greater measure of man- machine intimacy. PACTOLUS is an attempt to make a small, general-purpose digital computer not only act but, more importantly, feel like an analog com puter. Alas, it can't be called an unqualified success; it is hopefully a step in the right direction.

PACTOLUS is a digital analog simulator program developed for the IBM 1620. Plotter, typewriter, and sense switches are combined to provide a flexible modus operandi. The configuration, initial condi tions, and parameters of the simulation are simply and conveniently specified and may be varied at will. The operator may monitor the results as they are being plotted and interrupt the run if the results suggest a change in the specifications. Variables of secondary interest are recorded at specified time intervals by the typewriter. The program includes all standard analog computer elements plus many spe cial circuit elements: e.g., bang-bang, absolute value, clipper, pulse generator, and zero-order hold.
Iterative-Differential-Analyzer Study of Prediction Networks
Authors: Melsa James L. , Wozny Michael J.
Published: March 2008

Iterative-differential-analyzer methods are presented which allow experimental studies of prediction net works to be performed without the use of delay lines. Two classes of problems are examined in this paper:

1. Prediction of stochastic signals with no noise present.

2. Prediction and filtering of deterministic signals masked by noise. Measurement techniques are de veloped for each case, and experimental verification is included.
The Use of Parameter Influence Coefficients in Computer Analysis of Dynamic Systems
Authors: Meissinger Hans F.
Published: March 2008

A new computer technique is described which yields the partial derivatives of problem variables with re spect to pertinent system parameters simultaneously with the solution of the original system differential equations. These derivatives, known as parameter influence coefficients, are valuable to the analyst in enhancing his understanding of system characteris tics. If the problem solution x(t, λ) and the parameter influence coefficient ∂x/∂λ (t, λ) is known for a par ticular operating point where λ= λ0, then it is pos sible to make a first-order prediction of system behavior at a neighboring point having the new parameter value λ1 = λ0 + Δλ. Similar predictions can be made if not one but several parameters are to be varied. Thus, the knowledge of parameter in fluences often helps to reduce the total number of computer runs required in a parametric system study. Typical applications of the technique are: linear ex trapolation in the neighborhood of a known solution, determination of design tolerances of a system, and prediction of critical parameter values and stability boundaries. The most useful application pertains to systems disturbed by random noise where normally a very large number of computer runs would be re quired to analyze the system on a statistical basis in a variety of operating conditions. Several illustrative examples are presented in the paper.
A Mathematical Model of Short-Term Memory
Authors: Adey W. Ross , Findler N.V.
Published: March 2008

It is attempted in this paper to give a mathematical description of the short-term memory. Instead of using the microscopic properties of individual neu rons, such as the number of interconnections, neuron density, threshold value, etc., the cerebral cortex is regarded as a "neuron gas" that is a vast conglomer ate of neurons with statistically distributed charac teristics.

Stimuli from the environment cause the receptor neurons to emit virtual electromagnetic waves into the brain. A self-optimizing process of the brain tis sue is here described by which the useful, informa tion-carrying energy reaching the long-term memory tends to maximum.

It is emphasized that in the following a brain model is described and the physical processes in volved may have no direct equivalent in reality.
The DES-1A New Digital Computer for Solving Differential Equations
Authors: Levine Leon
Published: March 2008

The DES-1 is a new digital computer system, espe cially designed for the solution of ordinary differ ential equations. The major components are (1) the SDS 9300, a high-speed digital computer, ( 2) a mathe matical operator language, and (3) a console.

The mathematical operator language is analogous to the computing elements of the analog computer. Thus both the DES-1 and analog computer can be programmed the same way (although the DES-1 has several more operations). Consequently an analog computer operator can learn to program the DES-1 easily and can use much of the programming expe rience acquired on the analog computer. Further more, the use of floating-point arithmetic eliminates all need for amplitude scaling.

The console provides rapid communication between the operator and the DES-1 and allows problem mode control and changes even as the com putations are being made. Some of the modes are RESET, OPERATE, and HOLD, while typical changes include parameters, initial conditions, and even equa tion structure.

The DES-1, therefore, combines the advantages of the digital computer

1. Accuracy 2. Reliability 3. Ease of program and data storage 4. Ability to perform algebraic operations

with those of the analog computer

1. Convenience of programming through use of the mathematical operator language 2. Rapid communication between operator and computer

to produce a computer which has advantages over both conventional analog and digital computers in solving differential equations.
Using Pontryagin's Maximum Principle to Solve One-Dimensional Optimization Problems, with and without Constraints, on an Iterative Analog Computer
Authors: Steinmetz Hans L.
Published: March 2008

An analog computer technique is presented which enables application of Pontryagin's maximum prin ciple to the problem of optimizing control systems. The key problem in using Pontryagin's maximum principle is the extremization of the Hamiltonian function at every instant of time. Since the analog computer is an excellent differential equation solver, it is of advantage to convert this task into a dynamic problem. The technique used to do this is based upon the steepest ascent method. The method is applied to a one-dimensional control problem; higher-di mensional control problems can be treated using the same approach.

The argument that an analog computer can solve differential equations with only one independent variable, corresponding to machine time, is true only in a technical sense. In practice it is feasible for cer tain types of problems to integrate one set of differ ential equations sufficiently fast enough so that, while integrating another set of differential equations at a much slower rate, the solution error associated with this approach remains within acceptable limits.

When using the analog computer in this way, one time domain always corresponds to the solution time required for solving the differential equations de scribing the system; a second time domain corre sponds to the solution time required for solving an auxiliary set of differential equations which has no direct relationship with the system.

Technological improvements and innovations made in the analog computer field during the recent past have contributed to the successful application of this approach.
Hybrid techniques in statistical analysis II
Authors: Mitchell B.A.
Published: March 2008

This note follows the report last month outlining the technique of using digital memory for accumulating statistical functions for cumulative, probability, and correlation distributions.
Study on time-shared analog computation technique
Authors: Miura Takeo , Iwata Junzo
Published: March 2008

Methods of time-sharing computing elements or cir cuits to achieve economy in analog computing are studied.

The conventional method of time-sharing is to scan inputs and outputs with synchronized switches and to hold the computer solutions after each scan ning. This method is practical only when the scanning interval is short enough compared to the period of solution to reduce error to an acceptable level.

The method presented here allows elimination of hold circuits and keeps good accuracy even with long scanning intervals. In particular, this method is shown to be without phase lag, and this is confirmed by experiments.

For the conventional method, the equivalent dead time (the predominant source of error) is calculated, and several compensation techniques are presented.

Comparisons of all these methods are also made.
Analog simulation of Hanford dual-purpose reactor plant
Authors: Coughren K.D. , Swanson C.D. , Thieme G.G.
Published: March 2008

An analog simulation of the dual-purpose Hanford N-reactor was undertaken.1 Studies were performed to determine the dynamic characteristics of the plant and to determine the effects of possible plant, oper ator, and control-system malfunctions. Various op erational procedures and proposed design changes were also studied.

The simulation of the reactor plant was made up of a series of subsystems which were coupled to gether. Each subsystem had been studied in detail previous to being assembled into the total reactor plant simulation.
Further developments in the handling of implicit functions
Authors: Blechman G.E. , Petersen H.E. , Sansom F.J.
Published: March 2008

One area in which considerable work must yet be done in the field of digital simulation is the efficient handling of implicit functions or algebraic loops. The "digital type" can't simply stick in a capacitor to quiet the durned thing down; instead he must resort to iteration and some scheme for determin ing when the result is sufficiently accurate. The following two notes are presented to show two methods presently used and to encourage further correspondence on this topic of technical interest. (For background information on MIDAS see SIMULATION for September and October 1964, and Octo ber 1965.)
A consideration on the solution of partial differential equations by analog computer
Authors: Miura Takeo , Iwata Junzo
Published: March 2008

When solving partial differential equations with an analog computer, they are usually transformed first to difference equations. This transformation causes truncation errors because of the finite number of sections. In this paper, a method is proposed whereby two solutions involving trun cation errors are extrapolated to find the true solution. The proposed extrapolation formula is based on the fact that the error in the solution is approximately proportional to the square of the section length. It is a quite simple method and has a wide area of application. Application to the diffusion equation resulted in good accuracy. The method is shown to be effective in estimating the error and the optimum number of sections in a traditional dif ference equation solution.
Pulsed prediction filters applied to digital and hybrid simulation
Authors: Matlock David L.
Published: March 2008

The increasing use of digital computers in the simulation of dynamic systems presents a number of new problems. In particular, the inclusion of a digital computer in a predominantly analog environment introduces time base problems. The digital computer appears to the analog circuitry to be a particular pulsed filter. Time delays due to sampling, computation, and output appear dynamically as ideal transportation delays.

The effects of time delays1 can be compensated for at the digital-to-analog or analog-to-digital interfaces by either analog2 or digital lead filters. Considerations with respect to problem constraints and the available equip ment dictate where and by what means the compensation is to be mechanized. Problem constraints involve the num ber of variables to be interfaced, the characteristics of the variables to be predicted (i.e., not highly nonlinear or dis continuous) and the effects of prediction errors on the variables. Digital simulation of a system of equations usu ally results in a higher order system of difference equations. The attendant problem of stability and attenuation or am plification of prediction errors may make compensation at the D/A interface more desirable. Equipment availability in terms of amplifiers, computation time and the number and type, sequential or parallel, of converter channels in fluence the choice of analog or digital filters.

The purpose of this paper is to apply both classical numerical analysis methods and phase and gain error cri teria to the problem of digital time prediction. A modified maximally flat phase criterion is applied to prediction co efficients to illustrate a filter used in a common simulation problem. Finally, phase and amplitude curves are included to show the advantages of the derived filters for simulation purposes as compared to classical polynomial extrapola tion.
Digital simulation of paper machine dynamics
Authors: Sullivan P.R. , Schoeffler J.D.
Published: March 2008

This paper presents a technique for simulation of the stock preparation and Fourdrinier dynamics which is flexible, convenient, and detailed enough to allow the user to study physical process modifications and transient response dur ing upsets and "furnish" (fibers with different character istics, fillers, dyes, etc.) changes and to evaluate simplified mathematical models and control schemes.

The technique uses digital simulation in a block diagram form, each block of which corresponds to one type of physical unit in the process (e.g., cleaner or tanks). Simu lation of a particular process then involves specification of the particular parameters of each physical unit together with the way in which they are interconnected. Individual components of the furnish may be traced through the whole process.

A complete wet-end configuration, including the white water recovery system, is simulated using the technique described in the paper, and typical results obtained during grade changes and disturbances are presented.
A hybrid computer technique for power spectrum analysis
Authors: Thomas Lee C.
Published: March 2008

A technique is presented by which the power density spectrum of an analog computer waveform may be meas ured to a specified amplitude precision and frequency resolution. The procedure involves sampling the wave form, storing the samples in a digital computer, and dig itally computing the autocorrelation function and the cosine transform of the autocorrelation function to yield the power spectrum. The theory required for selection of the parameters of sampling and computation is presented as are the required methods of data smoothing and proces sing. A description is given of an application of the tech nique to the design of a solid-state frequency multiplier.

The computational system is designer-controlled and is capable of giving rapid indications of the effect of changes in the process being simulated on the analog computer.
Optimization using a remote control console for a digital computer
Authors: Kirby D.B.
Published: March 2008

A general-purpose optimization program, using the meth ods of steepest descent and multidimensional Newton- Raphson, has been developed for the IBM 7094. The program can be used independently or as part of a man- machine optimization system in which the engineer can quickly appraise the effect of changes in problem param eters. Man-machine interaction at a remote location is provided through an experimental console which con sists of a Packard-Bell PB-250 computer and associated input-output equipment.

The program and equipment configuration used for interaction will be described and an example of network optimization using this system will be presented.

An optimization scheme which is designed for a digital computer offers a more sophisticated strategy and better accuracy than a scheme designed for an analog computer. The current interaction system is of limited form; never theless, work done with it has aided in defining the ob jectives for a more flexible man-digital machine interac tion system.
On boundary generation and detection in random walk problems
Authors: Little W.D. , Soudack A.C.
Published: March 2008

In the Monte Carlo solution of boundary value problems modeled by partial differential equations ,1,2,3 the bound aries of the regions in question and the boundary condi tions must be generated and detected. This note is a discussion of such techniques developed at the University of British Columbia, Hybrid Computer Laboratory. Only electronic comparators and diode function generators are required in implementing these techniques.
Solution of optimal control problems on a high-speed hybrid computer
Authors: Maybach Richard L.
Published: March 2008

This paper presents a method for finding the solutions to minimum-time optimal control problems. The procedure is to implement Pontryagin's Maximum Principle on an iterative hybrid computer. The state and adjoint equations as well as the control law are simulated using conven tional analog components. The troublesome two-point boundary-value problem, which is always associated with Maximum Principle, is solved by iteration, using a digital parameter optimizer. Thus, a manual trial-and-error search for the proper initial values of the adjoint variables is un necessary.

We show that, for a large class of systems, it is not necessary to generate the Hamiltonian, because the neces sary condition that it normally must satisfy is redundant. This allows many problems to be greatly simplified. We also present an optimizing routine that solves the boun dary-value problem. This permits the proposed method to be used on any hybrid computer that incorporates a general-purpose digital computer.

The solutions to two problems show that the proposed method is feasible. Average convergence times range from less than one second to about 70 seconds. These vary with the initial conditions on the state variables. The examples were solved using ASTRAC II, a small (40 amplifier), high speed (up to 1000 solutions per second), iterative hybrid computer with only modest component accuracy (0.25 per cent).

Although the discussion and examples are limited to a minimum-time performance index, the method is easily extended to cover other criteria.
An "electronic lung" in the stud Y of pulmonary function
Authors: Lewis Benjamin M.
Published: March 2008

A mathematical model of the lung, consisting of two regions and a common dead space, is described. An analog computer is used to solve the equations of this model. Two examples are given. In the first, curves of the mixing of an inert gas and the absorption of carbon monoxide obtained in emphysema patients are analyzed. Such curves were the result, in terms of our model, of a small, well-ventilated region with a low diffusing capacity and a large poorly ventilated region having most of the diffusing capacity of the lung. The computer model is modified and used to predict the effects on inert gas washout of ventilating the lung in various sequences. The slowest washout is obtained when the poorly ventilated region filled first and emptied last, the most rapid when this region filled last and emptied last. Sequential ventilation alone can produce relatively minor delays in inert gas washout. Error in estimating reg ional ventilation from inert gas washout is small when the poorly ventilated region fills first and empties last, but appreciable when this region fills last and empties last.
Root-locus plotting machine for classroom demonstration
Authors: Kingma Y.J.
Published: March 2008

A root-locus plotting machine built from inexpensive com ponents is described. The device is primarily for demon strational use but may be used for design as well. The plotting board, mounted vertically on a dolly (which houses the auxiliary equipment) measures three by four feet. This makes the device useful even in large classrooms. A worked-out example is included.
Computer simulation of economic systems ... an example model
Authors: Sasser W. Earl , Naylor Thomas H.
Published: March 2008

This research was supported by a grant from the National Science Foundation, GS-1104, for the project entitled Design of computer simulation experiments for economic systems.
APE II...A modern analog/hybrid computer for laboratory instruction
Authors: Korn Granino A.
Published: March 2008

The APE (Arizona PEdagogical) II computer system com prises a 12-amplifier solid-state analog computer (iterative differential analyzer) capable of both real-time and repeti tive operation, and a digital-logic module with patchable digital logic. A flexible digital clock generates computer- reset and sampling pulses. Random and pseudo-random noise generators and digital readout counters permit a wide variety of statistical studies as well as simulation ex periments with sampled-data control systems, automatic optimization, boundary-value problems, and simple com bined analog-digital computation at minimum cost. Special experiments can be stored on removable patchboards. Perhaps the most interesting technical feature of the new computer is its novel packaging technique: amplifier and integrated-circuit logic cards plug directly into the rear of the inexpensive patchbay receivers, which serve, thus, as card cages and save much inter-unit wiring.
Hybrid-oriented Simulation programs
Authors: Dames R.T.
Published: March 2008

Both existing and newly proposed digital analog simulator programs have a rather minimal hybrid orientation. This lack of emphasis is attributed to the numerous types of analog interfaces and the various "modi operandi" of different installations. Nevertheless, it is ironic that the hybrid user, who seems to have received the least software attention, is yet frequently the one who could use it most.

The intent of this paper is to point out at least two direc tions in which the hybrid user might extend a simulator program. The extensions, either as proposed or in modified form, would tend to simplify several hybrid programming tasks.