Browsing by Author "Soto, A"

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    A multi-modal supply-demand equilibrium model for predicting intercity freight flows
    (PERGAMON-ELSEVIER SCIENCE LTD, 2003) Fernandez, JE; de Cea, J; Soto, A
    In this paper a new approach to intercity freight transportation system modeling is developed. Modeling formulation considers supply-demand equilibrium, where the demand side represents the behavior of shippers (cargo owners) and the supply side represents the behavior of carriers (transportation operators). Shippers decisions considered include choice of destination, mode, carrier for pure modes and transfer point for combined modes. Carriers take routing decisions over a multi-modal, multi-product and multi-operator network. A new mathematical formulation, not known before, is proposed to find consistent equilibrium solutions for modal O-D shipments, network flows and levels of service. Necessary conditions are deduced to show that the solutions obtained, from the mathematical formulations proposed, satisfy the behavioral principles assumed in each case. It is shown that special rationality conditions are required, with respect to fares charged and network routing decisions, to obtain consistent supply-demand equilibrium solutions. Sufficient conditions for the existence and uniqueness of solutions to diagonalized versions of the mathematical problem formulated are deduced. Finally, a general solution approach is proposed and an application example is developed to illustrate the characteristics of the model and solution algorithm. (C) 2003 Elsevier Science Ltd. All rights reserved.
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    A real time visual sensor for supervision of flotation cells
    (PERGAMON-ELSEVIER SCIENCE LTD, 1998) Cipriano, A; Guarini, M; Vidal, R; Soto, A; Sepulveda, C; Mery, D; Briseno, H
    This paper describes an expert system for the supervision of flotation plants based on ACEFLOT, a real time analyzer of the characteristics of the froth that is formed on.:the surface of flotation cells. The ACEFLOT analyzer is based on image processing and measures several physical variables of the froth, including colorimetric, geometric and dynamic information. On the other hand, the expert system detects abnormal operation states and suggests corrective actions, supporting operators on the supervision and control of the flotation plant. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.
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    Solving network equilibrium problems on multimodal urban transportation networks with multiple user classes
    (TAYLOR & FRANCIS LTD, 2005) de Cea, J; Fernandez, JE; Dekock, V; Soto, A
    A modelling approach for solving quite general network equilibrium problems ( with fixed trip productions and attractions) intrinsic to the urban transport planning process is presented. The framework can consider a variety of demand models and route choice behaviours within the same implementation, including multiple user classes and combined travel modes that interact on the same physical network. The demand choices are assumed to have a hierarchical structure. When trip distribution is variable, a doubly constrained entropy-maximizing model is considered at the first level of choice and a hierarchical logit model is used for the remaining demand choices ( time of departure, travel mode, transfer point for combined modes, etc.). If trip distribution is considered to be exogenous, the demand choices are modelled as a hierarchical logit. One of the main features of the model is that it considers the effects of congestion on the road network as well as congestion and capacity constraints effects in each public transport service network. The problem is formulated mathematically as a variational inequality, with asymmetric cost functions, and solved following the diagonalization procedure. Each iteration of the aforementioned procedure solves an optimization problem using the Evans algorithm. Sufficient conditions for the existence and uniqueness of the solution to the diagonalized problem are obtained. The main results of a simple example ( solved with an academic version of the proposed algorithm) are presented to show the consistency of the equilibrium flows and levels of services obtained using the model. Finally, a real scale implementation of the model is briefly described to show the feasibility of its application.