Chapter 2 deals with a linear city model à la Hotelling where the two firms share linear transport costs with their customers. Mill pricing and uniform delivery pricing are special limiting cases. We characterize the conditions for the existence of a pure strategy equilibrium in the two-stage location-price game. These enable us to identify the causes for non-existence in the two limiting cases. We solve for the equilibrium of a location game between the duopolists with an exogenously given price. When the two firms are constrained to locate at the same central spot, we show the nonexistence of pure strategy equilibria, conjecture the existence of mixed strategy equilibria, and show that any such possible equilibria will always yield positive expected profits. Chapter 3 provides simulations as well as theoretical analysis of potential spatial separation of heterogeneous agents operating on a two-dimensional grid space that represents a city. Heterogeneity refers to a characteristic which is also a determinant of individual valuation of land. We study spatial separation with respect to the distinguishing characteristic and investigate the details of emerging spatial patterns. Simulations suggest that the process of interaction with little trade friction goes through stages which resemble its end-state with high trade friction. Several theoretical examples exhibit a distinguishing characteristic upon which the simulations are based. They reflect some of the causes for spatial separation. Examples for the absence of spatial separation are also given. In Chapter 4 simulations, in addition to some theory, are used to investigate certain aspects of a city formation process. The model assumes two types of economic agents, workers and employers, operating on a two-dimensional grid. The agents have simple preferences, positive for the opposite type and negative for the own type in the own location. In addition, they have positive or negative preference for agglomeration in the own location. The model helps build intuition about a potentially important factor for agglomeration formation, namely, the disparity between entrepreneurial and technical skills in localities. We also determine the minimum level of positive preference for agglomeration that leads to agglomeration formation. / Ph. D.

The effectiveness of self-recording and self-reinforcement procedures implemented in the classroom setting with six pre-adolescent children classified as Educable Mentally Retarded was determined relative to changes in on-task behavior. A multiple baseline design was used and each subject was exposed to both a self-recording procedure and a self-reinforcement procedure. After an initial baseline period, three subjects were exposed to self-recording first, and three subjects went through self-reinforcement first. Contingent reinforcement was not provided for accuracy in either self-recording or self-reinforcement patterns. Observations were conducted to investigate generalization effects of each procedure, and two weeks of follow-up observations were conducted to determine durability effects. The findings indicated that for five of the subjects the self-recording procedure and the self-reinforcement procedure were effective in fostering significant positive increases in on-task behavior. Regarding accuracy, without contingent reinforcement, three of the subjects demonstrated at least 70% agreement with observer recordings during self-recording phases, and four subjects demonstrated at least 70% agreement with observer recordings in their self-reinforcement pattern. Generalization effects were found with two of the subjects, and maintenance effects were evident with one subject. A combined treatment approach, presenting both procedures simultaneously, was implemented with three of the subjects after the study was completed. These results indicated that the combined approach was not more effective than the singular presentation approach taken in the main study. Suggestions were made for future refinements in self-control procedures to increase applicability with special population.

An experiment was conducted to contrast the effectiveness of Behavior Therapy administered in self, individual, or group therapy versus a no-treatment control condition. The therapy conditions were administered to two subgroups, high and low self reinforcers, as defined by Rosensky and Bellack (1976). The general hypothesis was that high self reinforcers would engage in countercontrol and therefore do poorly in group and individual therapy, but would lose weight in self therapy. Individual behavior therapy showed the best long term results, but self and group therapies also showed significant weight loss. It was also found that low self reinforcers as a group lost more weight than did high self reinforcers.

L'acquisition autonome de representations et de fonctionnalites en robotique pose de nombreux problemes theoriques. Aujourd'hui, les systemes robotiques autonomes sont concus autour d'un ensemble de fonctionnalites. Leurs representations du monde sont issues de l'analyse d'un probleme et d'une modelisation prealablement donnees par les concepteurs. Cette approche limite les capacites d'apprentissage. Nous proposons dans cette these un systeme ouvert de representations et de fonctionnalites. Ce systeme apprend en experimentant son environnement et est guide par l'augmentation d'une fonction de valeur. L'objectif du systeme consiste a agir sur son environnement pour reactiver les representations dont il avait appris une connotation positive. Une analyse de la capacite a generaliser la production d'actions appropriees pour ces reactivations conduit a definir un ensemble de proprietes necessaires pour un tel systeme. Le systeme de representation est constitue d'un reseau d'unites de traitement semblables et utilise un codage par position. Le sens de l'etat d'une unite depend de sa position dans le reseau. Ce systeme de representation possede des similitudes avec le principe de numeration par position. Une representation correspond a l'activation d'un ensemble d'unites. Ce systeme a ete implemente dans une suite logicielle appelee NeuSter qui permet de simuler des reseaux de plusieurs millions d'unites et milliard de connexions sur des grappes heterogenes de machines POSIX. Les premiers resultats permettent de valider les contraintes deduites de l'analyse. Un tel systeme permet d'apprendre dans un meme reseau, de facon hierarchique et non supervisee, des detecteurs de bords et de traits, de coins, de terminaisons de traits, de visages, de directions de mouvement, de rotations, d'expansions, et de phonemes. NeuSter apprend en ligne en utilisant uniquement les donnees de ses capteurs. Il a ete teste sur des robots mobiles pour l'apprentissage et le suivi d'objets.