Pushdown Compression

The pressing need for eficient compression schemes for XML documents has recently been focused on stack computation [6, 9], and in particular calls for a formulation of information-lossless stack or pushdown compressors that allows a formal analysis of their performance and a more ambitious use of the stack in XML compression, where so far it is mainly connected to parsing mechanisms. In this paper we introduce the model of pushdown compressor, based on pushdown transducers that compute a single injective function while keeping the widest generality regarding stack computation. The celebrated Lempel-Ziv algorithm LZ78 [10] was introduced as a general purpose compression algorithm that outperforms finite-state compressors on all sequences. We compare the performance of the Lempel-Ziv algorithm with that of the pushdown compressors, or compression algorithms that can be implemented with a pushdown transducer. This comparison is made without any a priori assumption on the data's source and considering the asymptotic compression ratio for infinite sequences. We prove that Lempel-Ziv is incomparable with pushdown compressors

Democràcia i política educativa espanyola, 1975-1985

L'article presenta, fonamentalment, una revisió d'importants actuacions de política educativa amb una incidència destacada en la construcció i consolidació del procés de democratització que viu la societat espanyola al llarg de l'etapa històrica anomenada Transició. Són temes importants que ajuden a precisar la contribució del sistema educatiu a una tasca tan decisiva. Per una part, es mostra la tasca de definir i establir el marc jurídic de drets i llibertats, del pluralisme...; per l'altra, els instruments dirigits a garantir l'exigible igualtat d'oportunitats educatives per a tots i totes. També s'ofereix una perspectiva referida a l'aplicació del principi de participació social a l'ensenyament, així com una observació de les noves propostes d'una educació per a la ciutadania.Este artículo revisa diferentes aspectos del sistema educativo en los que se produce o repercute un proceso de democratización durante esa importante etapa de la historia española. Por lo tanto trata de estudiar las formas en las que el sistema educativo pudo contribuir a la construcción de nuestra sociedad democrática. Por una parte, se precisan las bases para el establecimiento de los derechos y libertades en materia educativa, y la consecución de un consenso o acuerdo sobre el marco jurídico básico de la educación; también se analiza la aplicación de los principios de igualdad de oportunidades y de participación social en la enseñanza; y finalmente el esfuerzo desplegado para desarrollar una nueva educación para la ciudadanía.This article presents a review of the major aspects of the educational policy that significantly influenced the construction and consolidation of the democratisation process of Spanish society throughout the historical period known as the «transition to democracy». These important issues help pinpoint the education system’s contribution to that decisive test. On the one hand, it shows the efforts expended to establish the legal framework of rights, freedoms and pluralism and the instruments aimed to guarantee equal educational opportunities for all. On the other, it offers a view of the application of the principle of social participation to education, as well as an observation of new proposals for education in citizenship

Are There Arbitrage Opportunities in Credit Derivatives Markets? A New Test and an Application to the Case of CDS and ASPs

This paper analyzes possible arbitrage opportunities in credit derivatives markets using selffinancing strategies combining Credit Default Swaps and Asset Swaps Packages. We present a new statistical arbitrage test based on the subsampling methodology which has lower Type I error than existing alternatives. Using four different databases covering the period from 2005 to 2009, long-run (cointegration) and statistical arbitrage analysis are performed. Before the subprime crisis, we find long-run arbitrage opportunities in 26% of the cases and statistical arbitrage opportunities in 24% of the cases. During the crisis, arbitrage opportunities decrease to 8% and 19%, respectively. Arbitrage opportunities are more frequent in the case of relatively low rated bonds and bonds with a high coupon rate.statistical arbitrage, credit derivatives, credit spreads, cointegration, subsampling