An empirical way to correct some drawbacks of mulliken population analysis

Indexación: ScieloThe problem of negative electronic populations and of occupation numbers greater than 2 has plagued Mulliken Population Analysis since the very beginning. Through the analysis of three model molecular systems, several basis sets and the relevant literature, we conclude that there is not enough evidence to assign the origin of these errors to the self-consistent scheme, to Mulliken's partition, to the basis set structure or to a combination of these. As Mulliken Population Analysis is still widely used, we have developed an empirical method to eliminate negative electronic populations and occupation numbers greater than 2. This method can be used for any partition of the electron density (not only Mulliken's), for any basis set and for any LCAO-MO methodology (semiempirical or ab initio). Finally, the method does not produce any change in the original atomic net charges.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072009000400036&lng=es&nrm=is

Non-Minimal Flavored S3⊗Z2{\bf S}_{3}\otimes {\bf Z}_{2} Left-Right Symmetric Model

We propose a non-minimal left-right symmetric model (LRSM) with Parity Symmetry where the fermion mixings arise as result of imposing an ${\bf S}_{3}\otimes {\bf Z}_{2}$ flavor symmetry, and an extra ${\bf Z}^{e}_{2}$ symmetry is considered to suppress some Yukawa couplings in the lepton sector. As a consequence, the effective neutrino mass matrix possesses approximately the $\mu-\tau$ symmetry. The breaking of the $\mu-\tau$ symmetry induces sizable non zero $\theta_{13}$, and the deviation of $\theta_{23}$ from $45^{\circ}$ is strongly controlled by an $\epsilon$ free parameter and the complex neutrino masses. Then, an analytic study on the extreme Majorana phases is done since these turn out to be relevant to enhance or suppress the reactor and atmospheric angle. So that we have constrained the parameter space for the $\epsilon$ parameter and the lightest neutrino mass that accommodate the mixing angles. The highlighted results are: a) the normal hierarchy is ruled out since the reactor angle comes out being tiny, for any values of the Majorana phases; b) for the inverted hierarchy there is one combination in the extreme phases where the values of the reactor and atmospheric angles are compatible up to $2, 3~\sigma$ of C. L., but the parameter space is tight; c) the model favors the degenerate ordering for one combination in the extreme Majorana phases. In this case, the reactor and atmospheric angle are compatible with the experimental data for a large set of values of the free parameters. Therefore, this model may be testable by the future result that the Nova and KamLAND-Zen collaborations will provide.Comment: Version three. I added references and corrected typos. 19 pages. All figures replaced, section II changed. Analytic study improved. Conclusions unchange

The Politics of Abstract Art. Forma 1 and the Italian Communist Party

Este artículo examina el papel del grupo de artistas abstractos Forma 1 en relación con la política cultural del Partido Comunista Italiano durante la posguerra, como ejemplo de los intentos de superar la dicotomía establecida en Italia entre arte abstracto y realismo socialista y producir una alternativa a la confrontación entre ambos discursos estéticos. Mientras los artistas realistas socialistas subrayaban la necesidad de expresar contenidos políticos explícitos con un estilo que asegurase su máxima legibilidad para una audiencia de masas, los artistas de Forma 1 argumentaban que la abstracción significaba una crítica de la representación pictórica que podía contribuir a la crítica de la ideología burguesa, armonizando de este modo el marxismo con los desarrollos artísticos más avanzados. El PCI, por su parte, basaba su política artística en amplias alianzas de artistas e intelectuales antifascistas, que cada vez eran más difíciles de mantener en el clima de creciente confrontación política y cultural que siguió a la II Guerra Mundial

An Extension of the Core solution Concept.

A solution concept for cooperative games, the extended core, is introduced. This concept is always nonempty yet coincides with the core whenever it is nonempty. Moreover, a non-cooperative framework can generate the extended core. Every transferable utility game is associated with a two-player zero-sum non-cooperative game. The min-max values of the associated zerosum games characterize when cooperative games have nonempty cores. If the core is empty, the min-max value determines how an exogenous regulator can impose costs on proper coalition formation so that there are no incentives to deviate from extended core imputations, which are necessarily feasible in the original game. In order to choose among the imputations belonging to the extended core, a proportional version of the nucleolus is proposed as a selection device.

Bargaining and Incentive Compatibility: A Pareto Frontier Approach.

Two agents negotiate, according to the Nash bargaining solution, over the allocation of a single (divisible) commodity (or multiple commodities with fixed ordinal preferences). It has been shown that in this situation agents find dominant to report their least risk averse utility functions. This result depends crucially on the fact that in this kind of "distortion game", agents have been restricted to report risk-averse utility functions. This paper studies the distortion game originated when agents are also allowed to claim non risk-averse utility functions. Contrasting with previous literature, we find multiple Nash equilibria, multiple payo outcomes and the existence of a first-mover advantage.

Portfolio delegation under short-selling constraints

In this paper we study delegated portfolio management when the manager's ability to short-sell is restricted. Contrary to previous results, we show that under moral hazard, linear performance-adjusted contracts do provide portfolio managers with incentives to gather information. The risk-averse manager's optimal effort is an increasing function of her share in the portfolio's return. This result affects the risk-averse investor's optimal contract decision. The first best, purely risk-sharing contract is proved to be suboptimal. Using numerical methods we show that the manager's share in the portfolio return is higher than the „rst best share. Additionally, this deviation is shown to be: (i) increasing in the manager's risk aversion and (ii) larger for tighter short-selling restrictions. When the constraint is relaxed the optimal contract converges towards the first best risk sharing contract.Third best effort, linear performance-adjusted contracts, short-selling constraints

Transmission Mechanisms and Inflation Targeting: The Case of Colombia Disinflation

Colombia has been on a steady disinflation path since the early 1990s. The paper presents a model of the transmission mechanisms of monetary policy in Colombia, in order to examine this disinflation. The model is used to describe the evolution of inflation in response to shocks to the terms of trade, the risk premium, across different monetary policy rules; and in particular, under different assumptions about the formation of inflation expectations. We then ilustrate the behaviour of the economy under a permanent shift to the inflation target and quantify the sacrifice ratio under different kinds of formation of inflation expectations. This helps us to judge to what extent the shift towards a more forward-looking wage and price setting affects the disinflation process and its cost. Finaly, we estimate the welfare gains from disinflation and provide a inflation forecast for Colombia.