MATHEMATICAL MODELS FOR DEVELOPING REGIONAL SOLID WASTE MANAGEMENT POLICIES

Various mathematical programming models are applied to evaluate operational (static one-period) and dynamic investment. (multiperiod) policies of regional solid waste management (SWM). Special attention is paid to the use of mixed integer programming (MIP) models for dynamic investment policies.

The common objective of minimizing the present value of overall investment and/or management costs is extended to deal explicitly with land-use policies by evaluating the sequencing of landfilling operations. The question of abandonment or upgrading of facilities is introduced into the mathematical framework because of its importance in the light of more restrictive standards. The decision as to which process should be installed at what location and at what time, as well as the decision which landfill should be operated and when, is identified in the MIP model.

Considering the limitations of the data base and the model formalism, the question of the usefulness of relying on one optimal solution from a model is discussed. The insensitivity of the ordinary present value criterion is displayed by analyzing substantially different policies which have only slightly different values of the criterion function. Attempts at introducing the notion of regret for the policy selection are presented in the context of Paretian environmental analysis.     

Experimental study of MESFET travelling-wave structures

Wave impedances and propagation constants of waves travelling along the electrodes of a long FET structure were experimentally investigated. For this purpose, a GaAs MESFET with large gate width was fabricated. Connecting pads on both ends of the gate and drain electrodes make it possible to measure the four-port S-parameters of the structure. Using these results, it is shown that a great improvement in the gain is possible, if the normally open ends of the FET are connected to the optimum terminations.     

Measurement of the distributed properties of GaAs-MESFETs

Using the 4-port admittance matrix of a GaAs-MESFET, it is shown how the distributed properties such as wave impedances and propagation constants can be derived. The procedure can equally be used for any active device with 2 homogeneous electrodes. For this purpose the 4-port admittance matrix Y for an arbitrary active device is derived. Afterwards it is demonstrated how the wave properties can be extracted from the matrix Y. An example of the measurement of a GaAs-MESFET is added.