John McLeod

Toward uniform documentation -PHYSBE and 1130 CSMP

But the price paid in duplication of effort can only be justified as an inescapable &dquo;development cost&dquo; incurred in the formative stages of our evolving technology. In my opinion, the time has come when that price can and should be significantly reduced. &dquo;To each his own&dquo; should continue to describe the modeler/model relationship, provided we consider only the ultimate model used for a specific simulation. But today there is no theoretical reason for the modeler to &dquo;start from scratch&dquo; unless his simuland is unlike anything that has been modeled before-an unlikely contingency. However, there are practical reasons for starting from scratch-all related to inadequate communications. The potential simulator does not usually know of related work already accomplished. If he does know of related work, he will often find inadequate documentation of the model that has been developed. Or he may find the model described in such a way that it is easier to start from scratch than to try to understand the description. The result of all these practical difficulties is not only duplication of effort but of even greater consequence to all of us in this field a stifling of

Simulation: From Art To Science for Society

Simulation can be a more effective tool for the study of problems of our times if the practitioners will adopt pro cedures which will make simulation more a science than an art. A big step in that direction would be the develop ment and use of a standard format that would assure ade quate and uniform documentation. Such a format is pro posed, and criticism is solicited.

Computer Simulation of the Hydrodynamics of the Cardiovascular System

The purpose of this paper is to present a technique which, although it is disarmingly simple, is nevertheless a powerful tool for the analysis and synthesis of complex physical systems as well as the investigation of physiological systems which for various reasons might defy classical mathematical treatment. To illustrate the method, I have chosen to show how it may be applied to study certain aspects of the cardiovascular system. The method to be described is based on the fact that an electrical analogy can be found for most physical and physiological systems. In the case of the cardiovascular system, the primary factors which influence the blood flow are, the strength and rate of contraction of the ventricles, the characteristics of the four heart valves, and the elasticity and resistance to flow of the blood vessels and capillary beds. These in turn control the volume and distribution of the blood in the system. If we defer for the moment the dynamics of the heart, it is easy to imagine a closed, lumped-constant electrical circuit made up of capacitors and resistors in which the capacitors are analogous to elastic vessels, and in which the resistors connecting them resist the flow of the electric current just as the blood vessels resist the flow of blood. If all capacitors and resistors are adjustable, we can set them to correspond, according to some convenient scale, to the compliance of the various blood vessels and to the resistance to the flow of blood through them. If these compliances and resistances are not known, reasonable estimates will suffice for a first approximation. Then, when the &dquo;heart&dquo; is made to &dquo;pump,&dquo; the *Originally prepared for presentation at the 5th International Conference on Medical Electronics, Liege, Belgium, July 22-26, 1963. The author is grateful to Dean L. Franklin, Scripps Clinic and Research Foundation, La Jolla, California, for presenting the paper in his absence. current flow through the electrical circuit will correspond to blood flow, the voltages appearing at various points in the circuit will be analogous to the pressures at corresponding points in the physiological system, and the charges on the capacitors will correspond to the quantity of blood in the parts of the system which they represent. Simulating the dynamics of the heart might at first thought seem somewhat difficult, but that, too, yields to the proposed technique once we realize that the contraction of the heart muscle actually only changes the compliance of the ventricles. Therefore, we need only reduce the value of the capacitors which repre-

The simulation of difficult systems

Ever since publication in the July ’69 issue of SIMULATION of the proposal that work be started to develop a World Simulation, my correspondence has increased markedly. Letters range from the &dquo;Great idea, I wish you luck!&dquo; variety through concrete offers of help to &dquo;Can’t do&dquo; types. It is to those with serious reservations concerning the advisability of undertaking such an audacious task that I

Computer modeling and simulation: The changing challenge

The use of computers to model things, both real and imaginary, and the use of those models as surrogates for investigative and experimental purposes, constitute the art and science of simulation. Since its inception in the late nineteen forties simulation has undergone some interesting evolutionary changes. Paced by the development of rapidly improving computing and allied equip ment, the technology and methodology of simulation have faced — and to varying degrees learned to cope with - changing chal lenges as the ever-widening fields of application have multiplied. Hard limits are not in sight. However, vestiges of some original problems remain while others have been solved as simulation progresses from an art toward becoming a science.

Project MAC (methodology, acceptance, credibility)

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 75c per copy.

Application of Computer Simulation To Research in the Life Sciences

The paper summarizes guidelines for applying computer simulation to life sciences research. It provides brief answers to the following questions: To what extent can problems be rigorously solved by simu lation—especially complicated problems—and how is this to be done? What can a given simulation study be expected to accomplish, and when can it be considered complete? Of what value are the properties of a model in understanding the living system under study? What should be the proper interaction between simulationists and subject-matter experts in a collaboration? What constitutes ethical conduct for a simulationist? To what extent should the same person do both experiments and simu lation? How should simulationists be trained?

Simulation Today—and Yesterday

Looking over our shoulder a bit (but not nearly as far as the prehistoric mud pies!), we find the works of some early modelers described by E. R. Lewis.’ One was a rhomboidal rope configuration contrived by Alfonso Borelli in the seventeenth century to study muscle contractility. Another was a laminated pewterplate/leather/pewter-plate model of a Torpedo (Figure 1), an electric ray-one of many varieties of fish and eels capable of producing electric shocks-which was constructed by Henry Cavendish in the eighteenth century.

Good Intentions-and that well-known road

To date I have received an even dozen letters of encouragement (a relatively good return-it seems SIMULATION readers are not writers), and no discouraging ones (probably because those who do not agree just consider me some kind of a kook, not to be taken seriously). A number of letters on this subject will be published in full in our &dquo;Dear John&dquo; column. Here, however, I would like to quote from some, and comment. One respondent delineates an important aspect of the problem:

Simulation in the Service of Society (S3)

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.