910 Mathematical and Computer Modelling Reports

The integrated Computer-Aided Modeling and Planning (CAMP) system offers a simple and coherent tool for the planner. A Data Definition Language provides the means for building data banks; a Model Definition Language provides the means for defining mathematical models featuring abstract linear programming, advanced array arithmetics, and assertions; a Picture Definition Language facilitates formation of tables and diagrams; a Text Definition Language combines word processing with illustrations of modeling results. The man-machine interface is based on interactive panels for controlling the planning process and on a command language for analyzing modeling results. A multilingual capability allows selection of the national language for interfacing with the system.

The architecture of CAMP is presented, and its design, implementation, and use in regional planning are discussed.

Key Words-Economics, languages, economical modeling, modeling languages, rural and urban planning, symbolic computation

Bull. m&h. Bid. Vol. 49. No. 6. pp. 651A69. 1987

MODELING WATER FLOW THROUGH ARTERIAL TISSUE

M. KLANCHAR and J. M. TARBELL

Department of Chemical Engineering and The Bioengineering Program, The Pennsylvania State University, 104 Fenske Laboratory,

University Park, PA 16802, U.S.A.

Abstract-A Simple model of water flow through deformable porous media has been developed with emphasis on application to arterial walls. The model incorporates a strain-dependent permeability function into Darcy’s Law which is coupled to the force balance for the bulk material. A simple analytical expression relating water flux (volume flux) to pressure differential is developed which shows how strain-dependent permeability can lead to a reduction in hydraulic conductivity with increasing differential pressure as observed in experiments with arteries. The variation of permeability with position in the wall, which may influence the convective diffusion of macromolecules, is determined for both cylindrical and planar segments and a marked influence of geometry is noted.

Math/ Biosci. Vol. 86, pp. 171-181, 1987

EFFORT FLUCTUATIONS IN A HARVEST MODEL WITH RANDOM PRICES

DENNIS RYAN

Department of Mathematics and Statistics, Wright State University, Dayton, OH 45435, U.S.A.

Abstract-The effect of a single increase in the unit price of biomass on the optimal harvest policy for an exploited population is studied numerically. The price of a unit is assumed constant until a random time, when the price increases by a given amount. The optimal policy corresponding to the expected return is computed from the Bellman equation of dynamic programming. The results are compared with a model in which prices remain constant as well as a “well-timed” model in which the price increases at the expected increase time of the random case. Both optimal expected return and optimal policy computed from the deterministic models may differ substantially from that calculated from the random model, particularly if marginal costs are large. The emphasis is on numerical computation.