A factor model of seasonality in stock returns

Published as an article in: The Quarterly Review of Economics and Finance, 2004, vol. 44, issue 2, pages 224-236.

La fiscalidad de las cooperativas. Un modelo que fortalece los fondos propios

[ES] Las cooperativas son un modelo de empresa que tiene unas características particulares, entre las que destacan la distribución y el ejercicio del poder, la manera particular de distribución de resultados, la existencia de unos fondos obligatorios, la autoregulación del régimen de trabajo, el procedimiento de atribución de fondos económicos en el momento de la baja de un socio, y la participación de los asalariados en los resultados económicos positivos.

La pena de muerte en la Corona de Castilla en la Edad Media

[ES]A lo largo de este artículo se pasan revista a cinco cuentiones que muestran la evolución de la pena de muerte en la Corona de Castilla a lo largo de la Edad Media. En primer lugar, se presta atención al paso de la ejecución privada de la justicia a la pública y en qué casos se mantuvo la venganza, aunque con la autorización judicial. En segundo lugar, se pasa revista a las formas de aplicar la pena de muerte, privilegiando los siguientes tipos: el ahorcamiento por los pies, el asaeteamiento, el empozamiento y el encubamiento. En tercer lugar, se expone el ritual de ejecución de las penas capitales desde que el reo sale de la cárcel y es conducido al cadalso, hasta que el cuerpo es sepultado o queda expuesto a perpetuidad. En cuarto lugar, se reflexiona sobre la incidencia de la rebeldía o contumacia del acusado ante los requerimientos de la justicia en la imposición de la pena de muerte. En quinto y último lugar, se analizan las circunstancias que llevaron a la Corona de Castilla, a partir del último tercio del siglo XV, a relegar la pena de muerte entre el elenco punitivo y preferir castigos que tuvieran utilidad pública.

Justicia victimal. Contribuciones y retos

[ES]La pena de cárcel, como única respuesta al delito, no constituye ninguna solución para el hecho delincuencial. No es solución para la víctima porque queda en el más profundo de los desamparos. No es solución para el infractor porque la cárcel no sólo no rehabilita sino que puede generar más delincuencia, como lo acredita el alto índice de reincidencia. Finalmente, no es una solución para la Comunidad por los altos costes, no sólo penitenciarios. Sólo integrada con otras respuestas no carcelarias, la respuesta prisional permite un abordaje sensato de la delincuencia. Se aboga, por ello, por una justicia que reconozca la existencia de otras instancias reparadoras como: la mediación, el arbitraje, el diálogo víctima - agresor, etc.

Invariant-free deduction systems for temporal logic

In this thesis we propose a new approach to deduction methods for temporal logic. Our proposal is based on an inductive definition of eventualities that is different from the usual one. On the basis of this non-customary inductive definition for eventualities, we first provide dual systems of tableaux and sequents for Propositional Linear-time Temporal Logic (PLTL). Then, we adapt the deductive approach introduced by means of these dual tableau and sequent systems to the resolution framework and we present a clausal temporal resolution method for PLTL. Finally, we make use of this new clausal temporal resolution method for establishing logical foundations for declarative temporal logic programming languages. The key element in the deduction systems for temporal logic is to deal with eventualities and hidden invariants that may prevent the fulfillment of eventualities. Different ways of addressing this issue can be found in the works on deduction systems for temporal logic. Traditional tableau systems for temporal logic generate an auxiliary graph in a first pass.Then, in a second pass, unsatisfiable nodes are pruned. In particular, the second pass must check whether the eventualities are fulfilled. The one-pass tableau calculus introduced by S. Schwendimann requires an additional handling of information in order to detect cyclic branches that contain unfulfilled eventualities. Regarding traditional sequent calculi for temporal logic, the issue of eventualities and hidden invariants is tackled by making use of a kind of inference rules (mainly, invariant-based rules or infinitary rules) that complicates their automation. A remarkable consequence of using either a two-pass approach based on auxiliary graphs or aone-pass approach that requires an additional handling of information in the tableau framework, and either invariant-based rules or infinitary rules in the sequent framework, is that temporal logic fails to carry out the classical correspondence between tableaux and sequents. In this thesis, we first provide a one-pass tableau method TTM that instead of a graph obtains a cyclic tree to decide whether a set of PLTL-formulas is satisfiable. In TTM tableaux are classical-like. For unsatisfiable sets of formulas, TTM produces tableaux whose leaves contain a formula and its negation. In the case of satisfiable sets of formulas, TTM builds tableaux where each fully expanded open branch characterizes a collection of models for the set of formulas in the root. The tableau method TTM is complete and yields a decision procedure for PLTL. This tableau method is directly associated to a one-sided sequent calculus called TTC. Since TTM is free from all the structural rules that hinder the mechanization of deduction, e.g. weakening and contraction, then the resulting sequent calculus TTC is also free from this kind of structural rules. In particular, TTC is free of any kind of cut, including invariant-based cut. From the deduction system TTC, we obtain a two-sided sequent calculus GTC that preserves all these good freeness properties and is finitary, sound and complete for PLTL. Therefore, we show that the classical correspondence between tableaux and sequent calculi can be extended to temporal logic. The most fruitful approach in the literature on resolution methods for temporal logic, which was started with the seminal paper of M. Fisher, deals with PLTL and requires to generate invariants for performing resolution on eventualities. In this thesis, we present a new approach to resolution for PLTL. The main novelty of our approach is that we do not generate invariants for performing resolution on eventualities. Our method is based on the dual methods of tableaux and sequents for PLTL mentioned above. Our resolution method involves translation into a clausal normal form that is a direct extension of classical CNF. We first show that any PLTL-formula can be transformed into this clausal normal form. Then, we present our temporal resolution method, called TRS-resolution, that extends classical propositional resolution. Finally, we prove that TRS-resolution is sound and complete. In fact, it finishes for any input formula deciding its satisfiability, hence it gives rise to a new decision procedure for PLTL. In the field of temporal logic programming, the declarative proposals that provide a completeness result do not allow eventualities, whereas the proposals that follow the imperative future approach either restrict the use of eventualities or deal with them by calculating an upper bound based on the small model property for PLTL. In the latter, when the length of a derivation reaches the upper bound, the derivation is given up and backtracking is used to try another possible derivation. In this thesis we present a declarative propositional temporal logic programming language, called TeDiLog, that is a combination of the temporal and disjunctive paradigms in Logic Programming. We establish the logical foundations of our proposal by formally defining operational and logical semantics for TeDiLog and by proving their equivalence. Since TeDiLog is, syntactically, a sublanguage of PLTL, the logical semantics of TeDiLog is supported by PLTL logical consequence. The operational semantics of TeDiLog is based on TRS-resolution. TeDiLog allows both eventualities and always-formulas to occur in clause heads and also in clause bodies. To the best of our knowledge, TeDiLog is the first declarative temporal logic programming language that achieves this high degree of expressiveness. Since the tableau method presented in this thesis is able to detect that the fulfillment of an eventuality is prevented by a hidden invariant without checking for it by means of an extra process, since our finitary sequent calculi do not include invariant-based rules and since our resolution method dispenses with invariant generation, we say that our deduction methods are invariant-free.

Actividad agraria y urbanización: Desarrollo de un protocolo de valoración

[ES] Con demasiada frecuencia, especialmente en los espacios periurbanos, el suelo agrario es ocupado por actividades urbanas. Las explotaciones se reducen progresivamente y el paisaje rural deja paso a una mezcolanza de usos, con una evidente pérdida de calidad. Este proceso rara vez es sometido a estudios de impacto ambiental y la intervención se reduce a una retribución económica al agricultor por el suelo que es ocupado. En este artículo proponemos una metodología que valore el impacto real que la actuación urbanística tiene tanto sobre la explotación como sobre el suelo agrario que se pierde obligando a compensar económica y territorialmente al agricultor.

Plastidic Phosphoglucose Isomerase Is an Important Determinant of Starch Accumulation in Mesophyll Cells, Growth, Photosynthetic Capacity, and Biosynthesis of Plastidic Cytokinins in Arabidopsis

Phosphoglucose isomerase (PGI) catalyzes the reversible isomerization of glucose-6-phosphate and fructose-6-phosphate. It is involved in glycolysis and in the regeneration of glucose-6-P molecules in the oxidative pentose phosphate pathway (OPPP). In chloroplasts of illuminated mesophyll cells PGI also connects the Calvin-Benson cycle with the starch biosynthetic pathway. In this work we isolated pgi1-3, a mutant totally lacking pPGI activity as a consequence of aberrant intron splicing of the pPGI encoding gene, PGI1. Starch content in pgi1-3 source leaves was ca. 10-15% of that of wild type (WT) leaves, which was similar to that of leaves of pgi1-2, a T-DNA insertion pPGI null mutant. Starch deficiency of pgi1 leaves could be reverted by the introduction of a sex1 null mutation impeding beta-amylolytic starch breakdown. Although previous studies showed that starch granules of pgi1-2 leaves are restricted to both bundle sheath cells adjacent to the mesophyll and stomata guard cells, microscopy analyses carried out in this work revealed the presence of starch granules in the chloroplasts of pgi1-2 and pgi1-3 mesophyll cells. RT-PCR analyses showed high expression levels of plastidic and extra-plastidic beta-amylase encoding genes in pgi1 leaves, which was accompanied by increased beta-amylase activity. Both pgi1-2 and pgi1-3 mutants displayed slow growth and reduced photosynthetic capacity phenotypes even under continuous light conditions. Metabolic analyses revealed that the adenylate energy charge and the NAD(P) H/NAD(P) ratios in pgi1 leaves were lower than those of WT leaves. These analyses also revealed that the content of plastidic 2-C-methyl-D-erythritol 4-phosphate (MEP)-pathway derived cytokinins (CKs) in pgi1 leaves were exceedingly lower than in WT leaves. Noteworthy, exogenous application of CKs largely reverted the low starch content phenotype of pgi1 leaves. The overall data show that pPGI is an important determinant of photosynthesis, energy status, growth and starch accumulation in mesophyll cells likely as a consequence of its involvement in the production of OPPP/glycolysis intermediates necessary for the synthesis of plastidic MEP-pathway derived hormones such as CKs.

Analytical method development for the uptake study of different organic pollutants by crops cultivated in compost-amended soils

256 p.

Early response to nanoparticles in the Arabidopsis transcriptome compromises plant defence and root-hair development through salicylic acid signalling

Background: The impact of nano-scaled materials on photosynthetic organisms needs to be evaluated. Plants represent the largest interface between the environment and biosphere, so understanding how nanoparticles affect them is especially relevant for environmental assessments. Nanotoxicology studies in plants allude to quantum size effects and other properties specific of the nano-stage to explain increased toxicity respect to bulk compounds. However, gene expression profiles after exposure to nanoparticles and other sources of environmental stress have not been compared and the impact on plant defence has not been analysed. Results: Arabidopsis plants were exposed to TiO2-nanoparticles, Ag-nanoparticles, and multi-walled carbon nanotubes as well as different sources of biotic (microbial pathogens) or abiotic (saline, drought, or wounding) stresses. Changes in gene expression profiles and plant phenotypic responses were evaluated. Transcriptome analysis shows similarity of expression patterns for all plants exposed to nanoparticles and a low impact on gene expression compared to other stress inducers. Nanoparticle exposure repressed transcriptional responses to microbial pathogens, resulting in increased bacterial colonization during an experimental infection. Inhibition of root hair development and transcriptional patterns characteristic of phosphate starvation response were also observed. The exogenous addition of salicylic acid prevented some nano-specific transcriptional and phenotypic effects, including the reduction in root hair formation and the colonization of distal leaves by bacteria. Conclusions: This study integrates the effect of nanoparticles on gene expression with plant responses to major sources of environmental stress and paves the way to remediate the impact of these potentially damaging compounds through hormonal priming.

Dendrorremediación: El uso de Betula alba para monitorizar y reducir el contenido de metales en suelos mineros.

[EN] The intense industrial activity that took place over the past century resulted in large contaminated áreas. This is an important risk to human health and environmental safety. Recent biotechnological techniques for bioremediation include phytoremediation, which uses plants to remove or stabilize contaminants in soils. In our study we choose birch (Betula alba) as the preferred species to remedy mining soils, due to it produces a large biomass and can accumulate high levels of toxic elements in its tissues. The aim of this study was (i) to determine the possibility of using this species in reforestation and/or remediation of mining soils (ii) to elucidate the potential of tocopherol levels as indicators of heavy metal pollution. Trees growing in mining soils with high concentrations of Zn, Cd and Pb were sampled and the metal content in various organs and in tree rings was analyzed. α-tocoferol levels were also analyzed as an indicator of stress. The results showed a different distribution of metals in plant tissues. Zn and Cd had a higher accumulation in leaves, whereas Pb was stored in the timber. In addition, the metal content in tree rings was higher in older rings, leading to a conclusion that older tissues present a detoxification strategy. Furthermore, we saw how the presence of α- tocoferol on branches can be an indicator of metal stress in plants and it can be also used as a monitoring factor.

Intercepción de la lluvia del dosel arbóreo y la hojarasca

[es]La intercepción de la lluvia, tanto por el dosel como por la hojarasca, es un proceso importante que influye en las condiciones de humedad del suelo, ya que una parte vuelve mediante evaporación a la atmosfera. Por lo tanto el objetivo de este estudio es profundizar más en el conocimiento de la capacidad de almacenaje e intercepción de los robles (Quercus robur) y en especial analizar si el tamaño de los árboles influye la intercepción. El estudio se llevo a cabo en dos robledales diferenciados por su tamaño durante tres estaciones del año: otoño, invierno y primavera (2014-2015) en las que se obtuvieron medidas de intercepción del dosel de la precipitación. También se obtuvieron muestras de hoja verde y hojarasca con objeto de calcular su capacidad máxima de retención de agua. Los resultados mostraron que el tamaño de los árboles es una característica que influye en el Índice de área foliar (LAI), y por tanto en la intercepción, pero que su efecto parece ser menos importante que el efecto causado por la variabilidad del volumen de lluvia. Del mismo modo, la intercepción relativa (en relación al volumen de lluvia) dependió de la interacción entre la estacionalidad y el tamaño de los árboles. Finalmente, la cantidad máxima de almacenamiento de agua fue mayor en la hojarasca que en la hoja verde, siendo mayor en el robledal de mayor tamaño al presentar significativamente mayor cantidad de hojarasca acumulada.

Photosynthetic responses of trees in high-elevation forests: comparing evergreen species along an elevation gradient in the Central Andes

Plant growth at extremely high elevations is constrained by high daily thermal amplitude, strong solar radiation and water scarcity. These conditions are particularly harsh in the tropics, where the highest elevation treelines occur. In this environment, the maintenance of a positive carbon balance involves protecting the photosynthetic apparatus and taking advantage of any climatically favourable periods. To characterize photoprotective mechanisms at such high elevations, and particularly to address the question of whether these mechanisms are the same as those previously described in woody plants along extratropical treelines, we have studied photosynthetic responses in Polylepis tarapacana Philippi in the central Andes (18 degrees S) along an elevational gradient from 4300 to 4900 m. For comparative purposes, this gradient has been complemented with a lower elevation site (3700 m) where another Polylepis species (P. rugulosa Bitter) occurs. During the daily cycle, two periods of photosynthetic activity were observed: one during the morning when, despite low temperatures, assimilation was high; and the second starting at noon when the stomata closed because of a rise in the vapour pressure deficit and thermal dissipation is prevalent over photosynthesis. From dawn to noon there was a decrease in the content of antenna pigments (chlorophyll b and neoxanthin), together with an increase in the content of xanthophyll cycle carotenoids. These results could be caused by a reduction in the antenna size along with an increase in photoprotection. Additionally, photoprotection was enhanced by a partial overnight retention of de-epoxized xanthophylls. The unique combination of all of these mechanisms made possible the efficient use of the favourable conditions during the morning while still providing enough protection for the rest of the day. This strategy differs completely from that of extratropical mountain trees, which uncouple light-harvesting and energy-use during long periods of unfavourable, winter conditions.