SIMULATION

This column focuses on a single topic within the field of computer simulation. All the material comes directly from the electronic news group (bulletin board) called Simulation Digest. The Digest can be obtained over INTERNET by accessing the news group 'comp.simulation' or by sending e-mail to: 'simulation-request@bikini.cis.ufledu'

The Model Development Language (or MDL) is a simulation language and system which uses an assignment statement notation tailored for 2-dimensional layered neural networks. The key features are: (1) Operations occur on 2-dimensional arrays which correspond to the layout of many brain structures. (2) A spatial convolution operation models spatial summation occurring in dendritic trees. (3) Arbitrary time invariant expressions and differential equations may be specified by simple assignment statements. (4) Numerical methods are automatically taken care of in the MDL environment rather than in the user's specification of the model. These features allow high level modeling using leaky integrator model neurons and modeling of detailed biophysical properties, such as the Hodgkin-Huxley equations and voltage clamp experiments. Conciseness of the language allows specification of a moderately complex retina model in only one or two pages of code. The parallel structure of the language allows highly optimized implementation on parallel or vector processing computers. Use of the language is illustrated through two ex amples.

The Airway Science Simulation Labora tory (ASSL) was established in 1987 at. Embry Riddle Aeronautical University. The objective of this laboratory is to further develop and promote aviation education. One project that has emerged from this laboratory is the described below Air Traffic Control Simulation System (ATCSS). The ATCSS is designed to facilitate an environ ment in which students participate and interact as both pilots and air traffic controllers. This interaction simulates the real-time teamwork between pilots and air traffic controllers.

The purpose of this paper is to describe the simulation design concept, its components, and its potential for a variety of aviation uses. This description will include: the methods of interfacing, software and hardware requirements, feasibility of operating in multitasking environment, parallel processing, and ATC requirements with respect to oriented-towards-human- factors aviation training.

When the mathematical model of the read write(R/W) simulation of write once and read many (WORM) optical disk and drive was formulated and numerical analysis and software implementation of the simulation were carried out for the noise-free R/W process, it was found that the numerical process of the simulation introduced artificial noise in the read back signal. The artificial noises were due to finite precision of integration, finite density of written spot, and finite number of pits simulated. The noises can be reduced, but at the expense of computational time.

Heterogeneous simulation models are used in the initial, multistage design of discrete parts manufacturing systems. Current research is directed toward the development of an object-oriented, model-base environ ment which will facilitate heterogeneous modeling. To this end, the GIBSS (General ized Interaction Based Simulation Specifica tion) frameworks have been developed. The GIBSS conceptual frameworks permits the modular specification of heterogeneous models through the logical assemblage of entity, interaction, and transition objects. The GIBSS logic framework defines the synchronous execution of objects which use various mixtures of continuous and discrete event simulation techniques and/or manage multiple attribute sets. This paper describes the GIBSS frameworks and provides a case study of their application.