Consumers' behavior and the Bertrand paradox: an ACE approach

We analyze the classical Bertrand model when consumers exhibit some strategic behavior in deciding from which seller they will buy. We use two related but different tools. Both consider a probabilistic learning (or evolutionary) mechanism, and in the two of them consumers' behavior in uences the competition between the sellers. The results obtained show that, in general, developing some sort of loyalty is a good strategy for the buyers as it works in their best interest. First, we consider a learning procedure described by a deterministic dynamic system and, using strong simplifying assumptions, we can produce a description of the process behavior. Second, we use nite automata to represent the strategies played by the agents and an adaptive process based on genetic algorithms to simulate the stochastic process of learning. By doing so we can relax some of the strong assumptions used in the rst approach and still obtain the same basic results. It is suggested that the limitations of the rst approach (analytical) provide a good motivation for the second approach (Agent-Based). Indeed, although both approaches address the same problem, the use of Agent-Based computational techniques allows us to relax hypothesis and overcome the limitations of the analytical approach.

Simone Weil i Bertrand Russell : Dues reflexions sobre la pau a l'Europa dels anys trenta

Simone Weil i Bertrand Russell havien defensat posicions pacifistes, però davant del nazisme van justificar la guerra. S'han destacat alguns elements de reflexió en el canvi d'actitud: la importància dels mitjans de comunicació, la del llenguatge i del vessant psicològic del poder, la construcció mediàtica de l'enemic i la transcendència política de l'actuació individual i social davant l'Estat.

On bilateral agreements: just a matter of matching

This paper aims at assessing the importance of the initial technological endowments when firms decide to establish a technological agreement. We propose a Bertrand duopoly model where firms evaluate the advantages they can get from the agreement according to its length. Allowing them to exploit a learning process, we depict a strict connection between the starting point and the final result. Moreover, as far as learning is evaluated as an iterative process, the set of initial conditions that lead to successful ventures switches from a continuum of values to a Cantor set.

Contraction groups in complete Kac-Moody groups

Let G be an abstract Kac-Moody group over a finite field and G the closure of the image of G in the automorphism group of its positive building. We show that if the Dynkin diagram associated to G is irreducible and neither of spherical nor of affine type, then the contraction groups of elements in G which are not topologically periodic are not closed. (In those groups there always exist elements which are not topologically periodic.)

Análisis ráster de rutas de mínimo coste conGeomedia® PRO

Concretament, l'objectiu principal d'aquest projecte és el de construir un sistema de Informació Geogràfic que permeti l'anàlisi de les diferents rutes i camins existents entre Tarraco (Tarragona) i St Bertrand de Comminges (França) passant per Ilerda (Lleida) amb l'objectiu de trobar el camí de mínim cost travessant els Pirineus.

Additive utility with intransitive indifference and without independence: A homogeneous case

In the homogeneous case of one type of goods or objects, we prove theexistence of an additive utility function without assuming transitivityof indifference and independence. The representation reveals a positivefactor smaller than 1 that infuences rational choice beyond the utilityfunction and explains departures from these standard axioms of utilitytheory (factor equals to 1).

Dynamic price competition with fixed capacities

Many revenue management (RM) industries are characterized by (a) fixed capacities in theshort term (e.g., hotel rooms, seats on an airline flight), (b) homogeneous products (e.g., twoairline flights between the same cities at similar times), and (c) customer purchasing decisionslargely influenced by price. Competition in these industries is also very high even with just twoor three direct competitors in a market. However, RM competition is not well understood andpractically all known implementations of RM software and most published models of RM donot explicitly model competition. For this reason, there has been considerable recent interestand research activity to understand RM competition. In this paper we study price competitionfor an oligopoly in a dynamic setting, where each of the sellers has a fixed number of unitsavailable for sale over a fixed number of periods. Demand is stochastic, and depending on howit evolves, sellers may change their prices at any time. This reflects the fact that firms constantly,and almost costlessly, change their prices (alternately, allocations at a price in quantity-basedRM), reacting either to updates in their estimates of market demand, competitor prices, orinventory levels. We first prove existence of a unique subgame-perfect equilibrium for a duopoly.In equilibrium, in each state sellers engage in Bertrand competition, so that the seller withthe lowest reservation value ends up selling a unit at a price that is equal to the equilibriumreservation value of the competitor. This structure hence extends the marginal-value conceptof bid-price control, used in many RM implementations, to a competitive model. In addition,we show that the seller with the lowest capacity sells all its units first. Furthermore, we extendthe results transparently to n firms and perform a number of numerical comparative staticsexploiting the uniqueness of the subgame-perfect equilibrium.

Biased representation of homothetic preferences on homogeneous sets

In the homogeneous case of one-dimensional objects, we show that any preference relation that is positive and homothetic can be represented by a quantitative utility function and unique bias. This bias may favor or disfavor the preference for an object. In the first case, preferences are complete but not transitive and an object may be preferred even when its utility is lower. In the second case, preferences are asymmetric and transitive but not negatively transitive and it may not be sufficient for an object to have a greater utility for be preferred. In this manner, the bias reflects the extent to which preferences depart from the maximization of a utility function.

Biased quantitative measurement of interval ordered homothetic preferences

We represent interval ordered homothetic preferences with a quantitative homothetic utility function and a multiplicative bias. When preferences are weakly ordered (i.e. when indifference is transitive), such a bias equals 1. When indifference is intransitive, the biasing factor is a positive function smaller than 1 and measures a threshold of indifference. We show that the bias is constant if and only if preferences are semiordered, and we identify conditions ensuring a linear utility function. We illustrate our approach with indifference sets on a two dimensional commodity space.

El origen de la construcción fenomenalista: Mach, Moore y Whitehead

It's usually believed that the idea of applying logical methods to constructivist phenomenalism was, --in general- a result of Russell's originality. In this paper is argued that some important ideas were in fact due to Mach, Moore and Whitehead. According to the author, Russell got from Mach the general idea of epistemology as an analysis of scientific concepts and, specially,the idea of sensations as the building blocks for his logical construction. Moore made Russell believe that only sensations are known in a direct way, and so, the existence of external objects as the cause of our perceptions is only inferred. Moreover, according to the author, Russell's views on sense data -his sensibilia- are also due to Moore. Finally, Russell got from Whitehead the idea of the phenomenical reconstruction as an alternative to the causal theory of perception, and also how the logical construction should be done. The author undertakes also a detailed analysis of some early works of Whitehead not very well known.

Bivalirudin for patients with acute coronary syndromes

Background: Current guidelines for patients with moderate- or high-risk acute coronary syndromes recommend an early invasive approach with concomitant antithrombotic therapy, including aspirin, clopidogrel, unfractionated or low-molecular-weight heparin, and glycoprotein IIb/IIIa inhibitors. We evaluated the role of thrombin-specific anticoagulation with bivalirudin in such patients. Methods: We assigned 13,819 patients with acute coronary syndromes to one of three antithrombotic regimens: unfractionated heparin or enoxaparin plus a glycoprotein IIb/IIIa inhibitor, bivalirudin plus a glycoprotein IIb/IIIa inhibitor, or bivalirudin alone. The primary end points were a composite ischemia end point (death, myocardial infarction, or unplanned revascularization for ischemia), major bleeding, and the net clinical outcome, defined as the combination of composite ischemia or major bleeding. Results: Bivalirudin plus a glycoprotein IIb/IIIa inhibitor, as compared with heparin plus a glycoprotein IIb/IIIa inhibitor, was associated with noninferior 30-day rates of the composite ischemia end point (7.7% and 7.3%, respectively), major bleeding (5.3% and 5.7%), and the net clinical outcome end point (11.8% and 11.7%). Bivalirudin alone, as compared with heparin plus a glycoprotein IIb/IIIa inhibitor, was associated with a noninferior rate of the composite ischemia end point (7.8% and 7.3%, respectively; P = 0.32; relative risk, 1.08; 95% confidence interval [CI], 0.93 to 1.24) and significantly reduced rates of major bleeding (3.0% vs. 5.7%; P<0.001; relative risk, 0.53; 95% CI, 0.43 to 0.65) and the net clinical outcome end point (10.1% vs. 11.7%; P = 0.02; relative risk, 0.86; 95% CI, 0.77 to 0.97). Conclusions: In patients with moderate- or high-risk acute coronary syndromes who were undergoing invasive treatment with glycoprotein IIb/IIIa inhibitors, bivalirudin was associated with rates of ischemia and bleeding that were similar to those with heparin. Bivalirudin alone was associated with similar rates of ischemia and significantly lower rates of bleeding. (ClinicalTrials.gov number, NCT00093158.)

Parentesco, redes familiares y sociabilidad en el mundo hispanoamericano en los siglos XVII y XIX

Hasta hace algunos años, el interés por la historia de la familia, aunque no era escaso, estaba orientado a enfoques de tipo macrohistórico, ya que el énfasis estaba puesto en las estructuras de la sociedad. La dominación de los planteamientos cuantitativistas impuestos por los Annales, así como la fuerte influencia del marxismo, coadyuvaron en la consideración de la familia, no como objeto de investigación en sí misma, sino como expresión o ilustración de un funcionamiento económico social global. Los numerosos y excelentes trabajos sobre la élite colonial americana ejemplifican esta clase de acercamiento, fundamentado a partir de una reflexión acerca de los grupos sociales definidos en base a criterios socio-económicos. De la misma marreta, si la familia servia de base a los estudios de demografía histórica,lo que se pretendía a través de ella era la deconstrucción de modelos de comportamiento demográfico para un espacio definido. Fuera de estos planteos con sesgos estructuralistas y funcionalistas, la historia de la familia fue el refugio de la historiografia más tradicional y a veces rancia, fundada muchas veces en la aplicación de la reconstrucción genealógica como único método de estudio de los sectotes sociales más poderosos a nivel económico o político.

Parentesco, redes familiares y sociabilidad en el mundo hispanoamericano en los siglos XVIII y XIX

Hasta hace algunos años, el interés por la historia de la familia, aunque no era escaso, estaba orientado a enfoques de tipo macrohistórico, ya que el énfasis estaba puesto en las estructuras de la sociedad. La dominación de los planteamientos cuantitativistas impuestos por los Annales, así como la fuerte influencia del marxismo, coadyuvaron en la consideración de la familia, fio como objeto de investigación en sí misma, sino como expresión o ilustración de un funcionamiento económico social global.