Modeling photopolymerization processes for enhanced part quality

When laser paths cross or when new layers are cured on top of existing layers, residual stresses are generated as the cure shrinkage of fresly gelled resin is constrained forming deflection or curl of the layers. The finite element method has been used to model the structural deformatins arising from the stereolithography build process. This includes the first layer polymerized during printing of an overhanged layer as subsequent rows of tetra-elements. The model does not include any resin beyond the external boundaries of the solid part. A standard linear static solution is carried out in order to get the properties of the fresh-resin

Find Your Personal Elements: An Engaging Approach to Introducing Chemistry to Secondary School Students

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUGThe Supporting Information is available at https://pubs.acs.org/doi/10.1021/acs.jchemed.1c00002 (https://pubs.acs.org/doi/suppl/10.1021/acs.jchemed.1c00002/suppl_file/ed1c00002_si_001.pdf)[Abstract] Creative educational methodologies capable of engaging students in interactive, enjoyable learning help to lessen students’ anxieties and motivate them. In this context and with the objective of making easier the learning of the chemical symbols and periodic table as well as introducing the concept of chemical formula, we have designed the activity called FYPE (FindYourPersonalElements). Conceived not as a game but as a fun and entertaining activity to introduce chemistry to secondary students, FYPE has been found to be very motivating. It is aimed at eighth-grade students (13–14 years old), corresponding to the second course of Compulsory Secondary Education in Spain, when the first contact of our students with chemistry as an independent subject occurs. FYPE is composed of three complementary and consecutive parts: (i) writing your “chemical name”, (ii) a flash presentation, and (iii) an art exhibition. It takes place over a month and a half, ending with an open activity in the main hall of the high school in which parents and relatives also participate, making this activity go beyond the classroom. In a pleasant way, the concept of chemical formula is easily understood by the students, who also discover for themselves many elements that they had never heard of. The students’ perception of the activity was assessed by means of a survey and found to be very positive, with a score of 8.20 (maximum 10). The result showed that 77% of the students considered FYPE to be “great fun”, and 82% of them admitted that FYPE “had helped them to get to learn about elements that they did not know existed”. Around 60% found that “chemistry is more interesting than I had thought”. The positive perception of this activity is even slightly higher for female students than for male students.https://pubs.acs.org/doi/suppl/10.1021/acs.jchemed.1c00002/suppl_file/ed1c00002_si_001.pd

Patriotismo y nacionalismo en la obra de Larra

RESUMEN: Este trabajo pretende ilustrar a través de la obra de Larra el papel nuclear que el discurso nacional español ha jugado en el pensamiento y la práctica de la tradición liberal y liberal-democrática en España. Lejos de aparecer como un elemento subsidiario o de escasa presencia, el patriotismo y la lealtad al Estado y a la nación de los españoles se constituyó como un hilo conductor del pensamiento político desde el liberalismo gaditano hasta la IIa República. Los diferentes escritos de Fígaro que aluden a la cuestión nacional permiten desvelar algunas de las claves de sus convicciones patrióticas, elemento éste que se configura como una de las primeras y más importantes líneas de continuidad dentro de la cosmovisión política de Mariano José de Larra. ABSTRACT: The aim of this work is to illustrate, through the works of Larra, the central role played by Spanish national discourse in the thought and practice of the liberal and liberal-democratic tradition in Spain. Far from being scarce or secondary elements, patriotism and loyalty to the State and the Spanish nation became a principal theme in political thought from the liberalism of the Constitution of Cádiz to the Second Republic. The different writings of Fígaro that allude to the national question allow us to unveil some of the keys to his patriotic convictions, which is a element that forms one of the first and most important lines of continuity within the political cosmovisión of Mariano José de Larra

Nationalism and patriotism in the work of Antonio Machado

La evidente significación política de la obra de Antonio Machado no ha recibido una gran atención. Entre la numerosa bibliografía machadiana, las consideraciones de carácter político en absoluto son comparables a las de carácter estrictamente literario, filosófico o hasta religioso. Y esta observación es aplicable al tema del patriotismo y el nacionalismo. La notable influencia política que alcanzó Antonio Machado a lo largo de la II República y, especialmente, la Guerra Civil, y su significado como símbolo antifranquista a la lo largo de la dictadura, no oculta el dato de que su formación política y la consistencia de su consiguiente cosmovisión política no se caracterizan por su solidez

El libro y la censura durante el franquismo : un estado de la cuestión y otras consideraciones

Contra la afirmación, que ya amenazaba con volverse lugar común, de que «la censura del libro en el periodo franquista ha sido ya muy estudiada», este artículo sostiene la hipótesis contraria. Para ello, se fia realizado un estudio del estado de la cuestión que se ha procurado exhaustivo, en tanto la censura afecta tanto al emisor como al receptor y por ende al propio texto. En el mismo se apuntan también algunas causas de ese desconocimiento, y entre ellas la confusión terminológica existente entre «censura» y «represión cultural», realizando, en este último caso, algunas teorizaciones que intentan definir con precisión ambos términos. Finalmente, se aporta una bibliografía que podría servir de punto de partida para otras investigaciones.Contrary to the statement threatening to become a granted assumption —that the books censorship during Franco's regime has already been well studied— this article holds the opposite hypothesis. Since the censorship affects in the same way both the transmitter (the author) and the receiver (the reader), therefore also the text itself, a thorough research about the heart of the matter has been carried out. Some of the reasons for the lack of knowledge about this question are also ponted out in this article being one of them the terminological confusión between «censorship» and «cultural repression». Regarding this last issue and in order to define accuarately both terms, some thories ha ve been developed. Finally, a bibliography maybe useful as a starting point for further research is included

Modelling of the mechanical behaviour of the photopolymerization processes of resins intended for additive manufacturing (AMT) using laserstereolithography: The influence on part quality

This study presents a simplified model of the polymerization process of photo-cured epoxy resin, with the aim of finding theoretical values for the mechanical properties of the material in its transition stage from liquid to solid state, approximating these properties to a single figure at the instant of its gelation in the time denominated as tg. By evaluating a phenomenon observed during the fabrication of samples using a stereolithography additive manufacturing printer, it is hoped to fit a model that will replicate the mechanical forces undergone by the manufactured part. The introduction of new hypotheses to simplify the case under study will be tested by simulating these cases using the finite element method, taking the values obtained from previous publications that used experimental and analytical analysis so that the congruence of the results will be constant throughout the model. Finding these theoretical values will help develop future criteria for the feasibility of manufacturing the parts using laser stereolithography and therefore have a direct influence on the quality of the end part

Zn(II), Cd(II) and Pb(II) complexation with pyridinecarboxylate containing ligands

[Abstract] Herein, we report the coordination properties towards Zn(II), Cd(II) and Pb(II) of two hexadentate ligands containing pyridinecarboxylate groups with ethane-1,2-diamine (bcpe) or cyclohexane-1,2-diamine (bcpc) backbones. The X-ray crystal structures of [Zn(bcpe)], [Cd(bcpe)] and [Cd(bcpc)] show hexadentate binding of the ligand to the metal ions, with the coordination polyhedron being best described as a severely distorted octahedron. The X-ray crystal structure of the Pb(II) analogue shows the presence of tetrameric structural units [Pb4(bcpe)4] in which the four Pb(II) ions are bridged by carboxylate oxygen atoms. While in the Zn(II) and Cd(II) complexes the bcpe ligand adopts a twist–wrap (tw) conformation in which the ligand wraps around the metal ion by twisting the pyridyl units relative to each other, for the Pb(II) complex a twist–fold (tf) conformation, where a slight twisting of the pyridyl units is accompanied by an overall folding of the two pyridine units relative to each other is observed. Theoretical calculations performed at the DFT (B3LYP) level on the [Pb(bcpe)] and [Pb(bcpc)] systems indicate that the tf conformation is more stable than the tw form both in the solid state and in aqueous solution. The analysis of the natural bond orbitals (NBOs) indicate that the Pb(II) lone-pair is polarized by a substantial 6p contribution, which results in a hemi-directed coordination geometry around the metal ion. Potentiometric studies have been carried out to determine the protonation constants of the ligands and the stability constants of the complexes with Zn(II), Cd(II), Pb(II) and Ca(II). The replacement of the ethylene backbone of bcpe by a cyclohexylene ring causes a very important increase in the stability constant of the Pb(II) complex (ca. 2.3 logK units), while this effect is less important for Cd(II) (ca. 1.4 logK units). However, the introduction of the cyclohexylene ring does not substantially affect the stability of the Zn(II) and Ca(II) complexes. The ligand bcpc shows Pb/Ca and Cd/Ca selectivities [108.9 and 109.8, respectively] superior to those of extracting agents, such as EDTA, already used in Pb(II) and Cd(II) removal from contaminated water and soils.Galicia. Consellería de Innovación, Industria e Comercio; PGIDIT06TAM10301P