Aportaciones al conocimiento florístico de la Sierra de Aracena (Huelva, España)

A check�list of the Sierra de Aracena (Huelva, Spain) is presented. A total of 900 vascular plants have been identificated.Se ha realizado un catálogo floristico de la Sierra de Aracena (Huelva, España), en el que se citan 900 táxones de plantas vasculares

Lossy network correlated data gathering with high-resolution coding

Sensor networks measuring correlated data are considered, where the task is to gather data from the network nodes to a sink. A specific scenario is addressed, where data at nodes are lossy coded with high-resolution, and the information measured by the nodes has to be reconstructed at the sink within both certain total and individual distortion bounds. The first problem considered is to find the optimal transmission structure and the rate-distortion allocations at the various spatially located nodes, such as to minimize the total power consumption cost of the network, by assuming fixed nodes positions. The optimal transmission structure is the shortest path tree and the problems of rate and distortion allocation separate in the high-resolution case, namely, first the distortion allocation is found as a function of the transmission structure, and second, for a given distortion allocation, the rate allocation is computed. The second problem addressed is the case when the node positions can be chosen, by finding the optimal node placement for two different targets of interest, namely total power minimization and network lifetime maximization. Finally, a node placement solution that provides a tradeoff between the two metrics is proposed

Network correlated data gathering with explicit communication: NP-completeness and algorithms

We consider the problem of correlated data gathering by a network with a sink node and a tree-based communication structure, where the goal is to minimize the total transmission cost of transporting the information collected by the nodes, to the sink node. For source coding of correlated data, we consider a joint entropy-based coding model with explicit communication where coding is simple and the transmission structure optimization is difficult. We first formulate the optimization problem definition in the general case and then we study further a network setting where the entropy conditioning at nodes does not depend on the amount of side information, but only on its availability. We prove that even in this simple case, the optimization problem is NP-hard. We propose some efficient, scalable, and distributed heuristic approximation algorithms for solving this problem and show by numerical simulations that the total transmission cost can be significantly improved over direct transmission or the shortest path tree. We also present an approximation algorithm that provides a tree transmission structure with total cost within a constant factor from the optimal

OPTIMAL FISCAL POLICY IN A BUSINESS CYCLE MODEL: ALTERNATIVE IDENTIFICATIONS OF THE OPTIMAL EXPOST CAPITAL INCOME TAX RATES

This paper deals with the indeterminacy of optimal fiscal policy treated by Zhu (1992) and Chari, Christiano and Kehoe (1994). These authors identify the optimal fiscal policy restricting the debt return to be uncontingent to the state of nature. In this paper we use other kind of restrictions in order to identify the optimal fiscal policy. Using the solution method proposed by Sims (1998), we can select an equilibrium by enforcing a stable path for the bonds allocation, to identify all the fiscal policy variables contingent to the state of nature. We also use a decomposition of the expectational terms that allow us to obtain the ex-ante capital income tax rate in order to be compared with the ex-post (contingent) tax rate. We can demonstrate that the risk aversion changes the relationship between the expectational errors of the private agents and the sources of fluctuations. The numerical simulation provides some different results: the optimal tax rate on capital incom e is constant, instead of the very volatile tax rate obtained by Chari, Christiano and Kehoe (1994). This property remains unaltered when we use alternative restrictions (exogenous debt path and exogenous expectational errors) to identify the contingent optimal fiscal policy.

Optimal Oil Taxation in a Small Open Economy

The international oil market has been very volatile over the past three decades. In industrialized economies, especially in Europe, taxes represent a large fraction of oil prices and governments do not seem to react to oil price shocks by using oil taxes strategically. The aim of this paper is to analyze optimal oil taxation in a dynamic stochastic general equilibrium model of a small open economy that imports oil. We obtain that in general it is not optimal to distort the oil price paid by firms with taxes. Extending the model in several ways this result could be reversed depending on environmental considerations and available fiscal instruments.Optimal oil taxation, general equilibrium, small open economies