Van der Waals spin valves

We propose spin valves where a 2D non-magnetic conductor is intercalated between two ferromagnetic insulating layers. In this setup, the relative orientation of the magnetizations of the insulating layers can have a strong impact on the in-plane conductivity of the 2D conductor. We first show this for a graphene bilayer, described with a tight-binding model, placed between two ferromagnetic insulators. In the anti-parallel configuration, a band gap opens at the Dirac point, whereas in the parallel configuration, the graphene bilayer remains conducting. We then compute the electronic structure of graphene bilayer placed between two monolayers of the ferromagnetic insulator CrI$_3$, using density functional theory. Consistent with the model, we find that a gap opens at the Dirac point only in the antiparallel configuration.Comment: 5 pages, 4 figure

An error-controlled methodology for approximate hierarchical symbolic analysis

Limitations of existing approaches for symbolic analysis of large analog circuits are discussed. To address their solution, a new methodology for hierarchical symbolic analysis is introduced. The combination of a hierarchical modeling technique and approximation strategies, comprising circuit reduction, graph-based symbolic solution of circuit equations and matrix-based error control, provides optimum results in terms of speech and quality of results.European Commission ESPRIT 21812Comisión Interministerial de Ciencia y Tecnología TIC97-058

Error control in simplification before generation algorithms for symbolic analysis of large analogue circuits

Circuit reduction is a fundamental first step in addressing the symbolic analysis of large analogue circuits. A new algorithm for simplification before generation is presented which is very efficient in terms of speed and the amount of circuit reduction, and solves the accuracy problems of previously reported approaches

Extended WKB method, resonances and supersymmetric radial barriers

Semiclassical approximations are implemented in the calculation of position and width of low energy resonances for radial barriers. The numerical integrations are delimited by t/T<<8, with t the period of a classical particle in the barrier trap and T the resonance lifetime. These energies are used in the construction of `haired' short range potentials as the supersymmetric partners of a given radial barrier. The new potentials could be useful in the study of the transient phenomena which give rise to the Moshinsky's diffraction in time.Comment: 12 pages, 4 figures, 3 table

Compressed k2-Triples for Full-In-Memory RDF Engines

Current "data deluge" has flooded the Web of Data with very large RDF datasets. They are hosted and queried through SPARQL endpoints which act as nodes of a semantic net built on the principles of the Linked Data project. Although this is a realistic philosophy for global data publishing, its query performance is diminished when the RDF engines (behind the endpoints) manage these huge datasets. Their indexes cannot be fully loaded in main memory, hence these systems need to perform slow disk accesses to solve SPARQL queries. This paper addresses this problem by a compact indexed RDF structure (called k2-triples) applying compact k2-tree structures to the well-known vertical-partitioning technique. It obtains an ultra-compressed representation of large RDF graphs and allows SPARQL queries to be full-in-memory performed without decompression. We show that k2-triples clearly outperforms state-of-the-art compressibility and traditional vertical-partitioning query resolution, remaining very competitive with multi-index solutions.Comment: In Proc. of AMCIS'201

El concepto de diversidad vegetal desde la etnia mapuche a la enseñanza formal en Chile

El estudio de la terminología botánica en la lengua mapuche revela la gran importancia que la diversidad vegetal ha tenido para sus tradiciones y usos. Un colectivo de estudiantes de enseñanza media de origen mapuche conserva entre sus conocimientos de biología vegetal un rico aporte de esta información etnobotánica; sin embargo estudiantes que inician estudios universitarios de ingeniería forestal y agronomía muestran un nivel de conocimiento muy inferior. La enseñanza formal chilena puede aprovechar este potencial cultural para incorporarlo en una educación científica intercultural que favorezca la protección y respeto de los ecosistemas del Chile Central gravemente amenazados por los intereses de las grandes multinacionales que explotan sus recursos naturales

Passivity Breakdown of Titanium in LiBr solutions

The passive behavior of titanium and its susceptibility to undergo localized attack in different LiBr solutions at 25 degrees C have been investigated using different electrochemical techniques: potentiodynamic polarization curves, potentiostatic passivation tests, EIS measurements and Mott-Schottky analysis. In low and moderately concentrated LiBr solutions, the breakdown potential E-b decreased with increasing bromide concentrations, while in highly concentrated LiBr solutions, E-b increased with increasing LiBr concentration. In the most concentrated LiBr solution (11.42M) Ti did not undergo passivity breakdown even at 9 V-Ag/AgCl. This observation can be explained by a a decrease in the activity of water in highly concentrated LiBr solutions. (C) 2013 The Electrochemical Society.We wish express our gratitude to the Ministerio de Ciencia e Innovacion (Project CTQ2009-07518), and to Dr. M. Asuncion Jaime. for her translation assistance.Fernández Domene, RM.; Blasco-Tamarit, E.; García-García, D.; García Antón, J. (2014). Passivity Breakdown of Titanium in LiBr solutions. Journal of The Electrochemical Society. 161(1):25-35. https://doi.org/10.1149/2.035401jesS25351611Been J. Grauman J. S. , in: Uhlig's Corrosion Handbook, 2nd ed., Winston Revie R. (ed.), 863-885, Wiley Interscience, New York (2000).Blasco-Tamarit, E., Igual-Muñoz, A., García Antón, J., & García-García, D. (2007). Corrosion behaviour and galvanic coupling of titanium and welded titanium in LiBr solutions. Corrosion Science, 49(3), 1000-1026. doi:10.1016/j.corsci.2006.07.007Huang, Y. Z., & Blackwood, D. J. (2005). Characterisation of titanium oxide film grown in 0.9% NaCl at different sweep rates. Electrochimica Acta, 51(6), 1099-1107. doi:10.1016/j.electacta.2005.05.051Pan, J., Thierry, D., & Leygraf, C. (1996). 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Materials Chemistry and Physics, 126(3), 859-865. doi:10.1016/j.matchemphys.2010.12.028Kong, D.-S., Lu, W.-H., Feng, Y.-Y., Yu, Z.-Y., Wu, J.-X., Fan, W.-J., & Liu, H.-Y. (2009). Studying on the Point-Defect-Conductive Property of the Semiconducting Anodic Oxide Films on Titanium. Journal of The Electrochemical Society, 156(1), C39. doi:10.1149/1.3021008Roh, B., & Macdonald, D. D. (2007). Effect of oxygen vacancies in anodic titanium oxide films on the kinetics of the oxygen electrode reaction. Russian Journal of Electrochemistry, 43(2), 125-135. doi:10.1134/s1023193507020012Sazou, D., Saltidou, K., & Pagitsas, M. (2012). Understanding the effect of bromides on the stability of titanium oxide films based on a point defect model. Electrochimica Acta, 76, 48-61. doi:10.1016/j.electacta.2012.04.158Roberge P. R. , Handbook of Corrosion Engineering, p. 756, McGraw-Hill, New York (2000).Basame, S. B., & White, H. S. (1995). Scanning electrochemical microscopy of native titanium oxide films. 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Impedance spectroscopy at semiconductor electrodes: Review and recent developments. Electrochimica Acta, 41(7-8), 967-973. doi:10.1016/0013-4686(95)00427-0Da Cunha Belo, M., Hakiki, N. ., & Ferreira, M. G. . (1999). Semiconducting properties of passive films formed on nickel–base alloys type Alloy 600: influence of the alloying elements. Electrochimica Acta, 44(14), 2473-2481. doi:10.1016/s0013-4686(98)00372-7Hakiki, N. B., Boudin, S., Rondot, B., & Da Cunha Belo, M. (1995). The electronic structure of passive films formed on stainless steels. Corrosion Science, 37(11), 1809-1822. doi:10.1016/0010-938x(95)00084-wHamadou, L., Kadri, A., & Benbrahim, N. (2005). Characterisation of passive films formed on low carbon steel in borate buffer solution (pH 9.2) by electrochemical impedance spectroscopy. Applied Surface Science, 252(5), 1510-1519. doi:10.1016/j.apsusc.2005.02.135Wijesinghe, T. L. S. L., & Blackwood, D. J. (2008). 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Effect of Water Activity on Corrosion. CORROSION, 48(4), 277-280. doi:10.5006/1.3315933Frankel, G. S. (1998). Pitting Corrosion of Metals. Journal of The Electrochemical Society, 145(6), 2186. doi:10.1149/1.1838615Blasco-Tamarit, E., Igual-Muñoz, A., & García-Antón, J. (2007). Galvanic corrosion of high alloyed austenitic stainless steel welds in LiBr systems. Corrosion Science, 49(12), 4452-4471. doi:10.1016/j.corsci.2007.05.020Crozier, P. S., & Rowley, R. L. (2002). Activity coefficient prediction by osmotic molecular dynamics. Fluid Phase Equilibria, 193(1-2), 53-73. doi:10.1016/s0378-3812(01)00734-8Burstein, G. T. (1989). The Dissolution and Repassivation of New Titanium Surfaces in Alkaline Methanolic Solution. Journal of The Electrochemical Society, 136(5), 1313. doi:10.1149/1.2096913Banaś, J., Stypuła, B., Banaś, K., Światowska-Mrowiecka, J., Starowicz, M., & Lelek-Borkowska, U. (2008). Corrosion and passivity of metals in methanol solutions of electrolytes. 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Assessment of fissionable material behaviour in fission chambers

A comprehensive study is performed in order to assess the pertinence of fission chambers coated with different fissile materials for high neutron flux detection. Three neutron scenarios are proposed to study the fast component of a high neutron flux: (i) high neutron flux with a significant thermal contribution such as BR2, (ii) DEMO magnetic fusion reactor, and (iii) IFMIF high flux test module. In this study, the inventory code ACAB is used to analyze the following questions: (i) impact of different deposits in fission chambers; (ii) effect of the irradiation time/burn-up on the concentration; (iii) impact of activation cross-section uncertainties on the composition of the deposit for all the range of burn-up/irradiation neutron fluences of interest. The complete set of nuclear data (decay, fission yield, activation cross-sections, and uncertainties) provided in the EAF2007 data library are used for this evaluation