The Private Memory of Aggregate Shocks

We study constrained efficient aggregate risk sharing and its consequence for thebehavior of macro-aggregates in a dynamic Mirrlees’s (1971) setting. Privately observedidiosyncratic productivity shocks are assumed to be independent of i.i.d. publiclyobserved aggregate shocks. Yet, private allocations display memory with respectto past aggregate shocks, when idosyncratic shocks are also i.i.d.. Under a mild restrictionon the nature of optimal allocations the result extends to more persistentidiosyncratic shocks, for all but the limit at which idiosyncratic risk disappears, andthe model collapses to a pure heterogeneity repeated Mirrlees economy identical toWerning [2007]. When preferences are iso-elastic we show that an allocation is memorylessonly if it displays a strong form of separability with respect to aggregate shocks.Separability characterizes the pure heterogeneity limit as well as the general case withlog preferences. With less than full persistence and risk aversion different from unityboth memory and non-separability characterize optimal allocations. Exploiting thefact that non-separability is associated with state-varying labor wedges, we apply abusiness cycle accounting procedure (e.g. Chari et al. [2007]) to the aggregate datagenerated by the model. We show that, whenever risk aversion is great than one ourmodel produces efficient counter-cyclical labor wedges.

Timing of Wage Setting when Firms Invest in R&D

Also published as Working Paper Ikerlanak 2003-08unions, R&D, productivity of labor, wage setting

Partial cross-ownership and strategic environmental policy

This paper analyzes the effect that passive investment in rival firms has on the setting of cooperative and non-cooperative environmental taxes. We consider two firms located in different countries, one of which owns a stake in its rival. We show that partial cross-ownership affects the taxes set by the countries in the cooperative and non-cooperative cases. Depending on the stake that one firm has in its rival we show that cooperative taxes may he higher or lower than non-cooperative taxes. Moreover, for intermediate values of the stake, the non-cooperative tax is higher in one country and lower in the other than the cooperative tax.environmental taxes, international trade, local pollution, partial ownership

Determining efficient temperature sets for the simulated tempering method

In statistical physics, the efficiency of tempering approaches strongly depends on ingredients such as the number of replicas $R$, reliable determination of weight factors and the set of used temperatures, ${\mathcal T}_R = \{T_1, T_2, \ldots, T_R\}$. For the simulated tempering (SP) in particular -- useful due to its generality and conceptual simplicity -- the latter aspect (closely related to the actual $R$) may be a key issue in problems displaying metastability and trapping in certain regions of the phase space. To determine ${\mathcal T}_R$'s leading to accurate thermodynamics estimates and still trying to minimize the simulation computational time, here it is considered a fixed exchange frequency scheme for the ST. From the temperature of interest $T_1$, successive $T$'s are chosen so that the exchange frequency between any adjacent pair $T_r$ and $T_{r+1}$ has a same value $f$. By varying the $f$'s and analyzing the ${\mathcal T}_R$'s through relatively inexpensive tests (e.g., time decay toward the steady regime), an optimal situation in which the simulations visit much faster and more uniformly the relevant portions of the phase space is determined. As illustrations, the proposal is applied to three lattice models, BEG, Bell-Lavis, and Potts, in the hard case of extreme first-order phase transitions, always giving very good results, even for $R=3$. Also, comparisons with other protocols (constant entropy and arithmetic progression) to choose the set ${\mathcal T}_R$ are undertaken. The fixed exchange frequency method is found to be consistently superior, specially for small $R$'s. Finally, distinct instances where the prescription could be helpful (in second-order transitions and for the parallel tempering approach) are briefly discussed.Comment: 10 pages, 14 figure

As téchnai da cidade e a competência do filósofo

El propósito de esta comunicación es examinar la competencia del filósofo en el texto que hoy conocemos como Primer Alcibíades o Alcibíades Mayor. El trabajo propone la lectura del diálogo como un texto de filosofía política. La hipótesis sostenida es que el diálogo fue escrito con la intención de explicar la filosofía como una forma de intervenir políticamente basada en la exégesis filosófica de la sentencia apolínea "Conócete a ti mismo". Se argumenta que la perspectiva del texto se fundamenta en el principio de que la frase lleva consigo una exhortación a ejercer la política de manera recta. El diálogo, pues, no sólo contiene un análisis filosófico sobre la competencia adecuada para el ejercicio del poder, sino que también analiza cómo esta competencia se relaciona con la política, lo que pone a la filosofía en conflicto con las téchnai practicadas en la ciudadThe purpose of this paper is to examine the competence of the philosopher in the text known as First Alcibiades or Alcibiades Major. This work proposes a reading of the dialogue as a text of Political Philosophy. My hypothesis is that the dialogue was written under the intention of explaining philosophy as a form of political intervention based on philosophical exegesis of the Apollonian sentence "Know thyself". It is argued that the point of view of the dialogue is originated in the principle that the sentence from Delphes contains an exhortation to the practice of politics in a just and virtuous way. The dialogue, therefore, not only proposes a philosophical analysis of the needed competence for the exercise of power, but presents a examination of this competence related to politics, what drives philosophy to a conflict with the téchnai practiced in the cit

A heuristic for the stability number of a graph based on convex quadratic programming and tabu search

Recently, a characterization of the Lov´asz theta number based on convex quadratic programming was established. As a consequence of this formulation, we introduce a new upper bound on the stability number of a graph that slightly improves the theta number. Like this number, the new bound can be characterized as the minimum of a function whose values are the optimum values of convex quadratic programs. This paper is oriented mainly to the following question: how can the new bound be used to approximate the maximum stable set for large graphs? With this in mind we present a two-phase heuristic for the stability problem that begins by computing suboptimal solutions using the new bound definition. In the second phase a multi-start tabu search heuristic is implemented. The results of applying this heuristic to some DIMACS benchmark graphs are reported