Topological regularization and self-duality in four-dimensional anti-de Sitter gravity

It is shown that the addition of a topological invariant (Gauss-Bonnet term) to the anti-de Sitter (AdS) gravity action in four dimensions recovers the standard regularization given by holographic renormalization procedure. This crucial step makes possible the inclusion of an odd parity invariant (Pontryagin term) whose coupling is fixed by demanding an asymptotic (anti) self-dual condition on the Weyl tensor. This argument allows to find the dual point of the theory where the holographic stress tensor is related to the boundary Cotton tensor as $T_{j}^{i}=\pm (\ell ^{2}/8\pi G)C_{j}^{i}$, which has been observed in recent literature in solitonic solutions and hydrodynamic models. A general procedure to generate the counterterm series for AdS gravity in any even dimension from the corresponding Euler term is also briefly discussed.Comment: 13 pages, no figures; enlarged discussion on self-duality condition for AAdS spacetimes, references added, final version for PR

EVALUATION OF THE ANTIOXIDANT ACTIVITY OF THE FLAVONOIDS ISOLATED FROM HELIOTROPIUM SINUATUM RESIN USING ORACFL, DPPH AND ESR METHODOLOGIES

Indexación: Web of Science; Scielo.The antioxidant capacity has been determined for a number of flavonoid compounds from Heliotropium sinuatum, a plant that grows in arid areas in the north of Chile. The methodologies used were: ORAC(FL) (oxygen radical absorbance capacity - fluorescein), DPPH (2,2-diphenyl-2-picrylhydrazyl) bleaching and electron spin resonance (ESR). These compounds were studied in homogeneous and heterogeneous media. The results showed that the 7-o-methyleriodictiol and 3-o-methylisorhamnetin are those with the highest antioxidant capacity.http://ref.scielo.org/m82cz

Xenoestrogens released from lacquer coatings in food cans

We present data showing that some foods preserved in lacquer-coated cans and the liquid in them may acquire estrogenic activity. Hormonal activity was measured using the E-screen bioassay. The biological activity of vegetables packed in cans was a result of plastic monomers used in manufacturing the containers. The plastic monomer bisphenol-A, identified by mass spectrometry, was found as a contaminant not only in the liquid of the preserved vegetables but also in water autoclaved in the cans. The amount of bisphenol-A in the extracts accounted for all the hormonal activity measured. Although the presence of other xenoestrogens cannot be ruled out, it is apparent that all estrogenic activity in these cans was due to bisphenol-A leached from the lacquer coating. The use of plastic in food-packaging materials may require closer scrutiny to determine whether epoxy resins and polycarbonates contribute to human exposure to xenoestrogens.This work was supported by grant 94/1551 from the Fondo de Investigaciones Sanitarias (FIS), Spanish Ministry of Health

ANATRI 1.0: representation of dichotomous and polytomous item characteristic functions

El programa ANATRI permite estudiar varios modelos de Teoría de la Respuesta al Item para items dicotómicos y politómicos. Los modelos para items dicotómicos incluidos son los denominados como de 1, 2, 3 y 4 parámetros, en sus versiones normal y logística. Los modelos para items politómicos son el modelo de respuesta graduada, el modelo de crédito parcial y el modelo de respuesta nominal. El usuario selecciona el modelo y especifica los parámetros de uno o varios items. Mediante el programa se obtienen las curvas características de los items y, en su caso, las funciones de regresión asociadas a las diversas segmentaciones. Permite analizar en profundidad las propiedades particulares de los items, con lo que se facilita la didáctica de los diferentes modelosThe ANATRI program helps the user in studying dichotomous and polytomous Item Response Theory models. Normal and logistic versions for the 1-, 2-, 3- and 4-parameter models are included. Three polytomous models (Partial Credit, Nominal Response and Graded Response) are also available. The user chooses the model and specifies its parameters for one or more items. Items characteristic (or operating characteristic) curves are depicted. A deep analysis of just one item is also possible. This option allows a better understanding of peculiarities of each mode

Fostering the cooperative learning of mathematics in engineering schools through the "Teacher-Apprentice" group dynamics

In this presentation, we report on the experience gained and the results obtained from an educational innovation project that has sought to introduce cooperative learning into the mathematics subjects of the first year of the Engineering degrees at the University of Malaga. In particular, we focus on the teamwork-based learning method that we have called the "Teacher-Apprentice" dynamics: Groups of 3-5 members are formed in which one of the members takes on the role of the Teacher, while the rest are the Apprentices. We introduce a system of incentives such that the group that progresses adequately in the subject has the right to group bonuses, which count towards the final grade awarded to each of the group members and which are different for the Teacher and for the Apprentices to allow for some level of competitiveness within the group. The selection of the Teacher is reviewed after each scheduled assessment test, where the student in the group who has obtained the highest score from among the group members will become the (possibly new) Teacher. The results collected to date reveal that group dynamics increase the motivation with which students face math learning, while helping them to correct conceptual errors through discussion with their peers.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. “I Plan Propio Integral de Docencia” de la Universidad de Málaga (PIE17-025

Determination of bisphenol A and related aromatic compounds released from bis-GMA-based composites and sealants by high performance liquid chromatography

'Reproduced with permission from Environmental Health Perspectives'Most of the composites and sealants used in dentistry are based on bisphenol A diglycidylether methacrylate (Bis-GMA). Reports revealed that in situ polymerization is not complete and that free monomers can be detected by different analytic methods. Concerns about the estrogenicity of bisphenol A (BPA) and other aromatic components leached from commercial products have been expressed. We studied biphenolic components eluted from seven composites and one sealant before and after in vitro polymerization using HPLC and gas chromatography/mass spectrometry and we investigated how pH modifications affect the leaching of these components. We found BPA (maximal amount 1.8 microg/mg dental material), its dimethacrylate derivative (Bis-DMA, 1.15 microg/mg), bisphenol A diglycidylether (6. 1 microg/mg), Bis-GMA (2.0 microg/mg), and ethoxylate and propoxylate of bisphenol A in media in which samples of different commercial products were maintained under controlled pH and temperature conditions. Our results confirm the leaching of estrogenic monomers into the environment by Bis-GMA-based composites and sealants in concentrations at which biologic effects have been demonstrated in in vivo experimental models. The main issue with implications for patient care and dentist responsibility is to further determine the clinical relevance of this estrogenic exposure.This research was supported by grants from the Spanish Ministry of Health (FIS, 95/1959) and Education (CICYT, AMB97-1194-CE) and the Andalusian Regional Government, Department of Health (Consejeria de Salud, JA, 231/97)