1,720,999 research outputs found
Size effect on bending strenght in sawntimber of Argentinean Populus deltoides
Full text linkEn el artículo se analiza el efecto de las dimensiones de la sección transversal sobre la resistencia a flexión en piezas de madera aserrada de Populus deltoides ‘Australiano 129/60’ y ‘Stoneville 67’, cultivados en el delta del río Paraná, Argentina. El programa experimental se llevó a cabo según las normas europeas sobre un total de 820 cuerpos de prueba separados en 5 muestras exhibiendo las dimensiones estructurales usuales. Los resultados mostraron que el aumento de la altura de la sección fue acompañado de una tendencia decreciente de la tensión de rotura en flexión, pero no permiten afirmar que esa relación está vinculada a la calidad de la madera. Se confirmó que puede despreciarse una correlación entre la resistencia y el ancho de la sección. El análisis puso en evidencia que la relación entre la altura de la sección y la resistencia del material investigado está adecuadamente expresada por el criterio europeo, el cual fue adoptado por la normativa de Argentina.The present paper reports the results of an investigation regarding the study of size effects on bending strength in sawn timber of Argentinean Populus deltoides ‘Australian 129/60’ and ‘Stoneville 67’. An empirical research project with 5 samples containing a total of 820 specimens in usual structural sizes was carried out according to European standards. Results showed that strength decreases when depth increases but no clear influence of either the timber quality or the specimen thickness on size effects was found. The analysis evidenced that the European criterion -adopted by Argentinean standards- is suitable for considering the influence of depth on bending strength in the investigated species.Fil: Guillaumet, Alfredo Aníbal. Universidad Tecnológica Nacional. Facultad Regional Venado Tuerto; Argentina.Fil: Piter, Juan Carlos Jesús. Universidad Tecnológica Nacional. Facultad Regional Concepción del Uruguay. Departamento Ingeniería Civil. Grupo de Estudio de Maderas; Argentina.Fil: Manavella, Roberto Daniel. Universidad Tecnológica Nacional. Facultad Regional Venado Tuerto; Argentina.Fil: Acuña Rello, Luis. Universidad de Valladolid. E.T.S. de Ingenierías Agrarias. Departamento Ingeniería Agrónoma y Forestal; España.Peer Reviewe
Determinación de la edad de transición de madera juvenil a madura y caracterización tecnológica de ambos leños en Pinus contorta Douglas ex. Loudon var. murrayana proveniente de la provincia de Neuquén
Full text linkEl porcentaje de madera juvenil en coníferas de rápido crecimiento, como ocurre con las especies del género Pinus en Argentina, es un factor determinante de las propiedades básicas y elasto-resistente de la madera, ya que su proporción aumenta a medida que disminuye la edad de rotación. Dicha madera se caracteriza por presentar menor longitud y espesor de pared de traqueidas y mayor ángulo microfibrilar, lo cual se traduce en propiedades tecnológicas más bajas. Para delimitar la edad transición de madera juvenil a madura se realiza el análisis radial de alguna de las características antes mencionadas. La importancia de establecer dicha edad radica en la estimación de los volúmenes de madera de ambos leños, para definir su calidad y potencialidad de uso. A su vez, esta proporción puede variar entre especies y entre individuos de la misma especie, según calidades de sitio de las plantaciones, prácticas silviculturales aplicadas, entre otras. Dado lo expuesto, el objetivo de esta investigación fue determinar la edad de transición mediante la longitud y el espesor de pared de traqueidas, analizar cuantitativamente ambas variables y comparar las propiedades físico mecánicas y elasto-resistentes de los leños juvenil y maduro en Pinus contorta Douglas ex. Loudon var. murrayana proveniente de dos plantaciones de la provincia de Neuquén, Argentina. Se realizaron mediciones de las variables anatómicas en cada anillo de crecimiento para obtener la edad de transición, se determinaron las propiedades tecnológicas básicas en probetas libres de defectos y la caracterización elasto-resistente mediante ensayos no destructivos y destructivos en piezas estructurales. De acuerdo con los resultados obtenidos, utilizando la longitud de traqueidas la edad de transición del pino contorta resultó estar entre los 14.5 y 17.5 años y utilizando el espesor de pared entre los 13 y 18 años, para los sitios Melliquina y Abra Ancha respectivamente. Mediante los parámetros determinados en piezas macizas libres de defectos y estructurales se logró una caracterización general y específica de cada sitio y leño, generando una amplia base de datos de esta especie para la región, ausente hasta el momento, que servirá como base para dar a conocer el uso potencial de la madera del pino contorta en la zona patagónica, considerándose como posible alternativa en el mercado local y regional frente a la importación de otras maderas del resto del país, disminuyendo el flete de transporte y beneficiando a los actores locales involucrados en el abastecimiento, procesamiento y comercialización en la región, ayudando así a desarrollar la economía zonal y logrando beneficios para el sector foresto-industrial “in situ”.Asesor: Gabriel Darío KeilDoctor de la Facultad de Ciencias Agrarias y ForestalesUniversidad Nacional de La PlataFacultad de Ciencias Agrarias y Forestale
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Susceptibility of Populus x euramericana ‘I-214’ of Spanish origin to xylophagous attacks: durability tests for its possible inclusion in European standard
Full text linkAim of study: to assess the natural durability of Populus x euramericana ‘I-214’ against xylophagous fungi and termites, and to carry out a macro-microscopic analysis of the alterations caused by each xylophagous agent in order to get the necessary information for its possible inclusion in existing European standards.Area of study: A 20-years-old commercial plantation Populus x euramericana‘I-214’ located in Quintanilla de Sollamas (42° 36′ 00″N - 05° 49′ 00″ W), Spanish community of Castile-LeonMaterial and methods: material sampling and selection was carried out following EN 350:2017 for commercial sawn timber. Poplar resistance to xylophagous basidiomycete, soft rot fungi and subterranean termites was determined according to CEN/TS 15083-1:2005, CEN/TS 15083-2:2005 and EN 117:2012, respectively. The durability and use classes were estimated according to EN 350:2016 and EN 335:2013, respectively. The anatomical studies were carried out with Optical and Scanning Electron Microscope. Material characterization was carried out by reference to Anagnost (1998) and Schwarze (2007).Main results: ‘I-214’ poplar wood proved to be “Not-durable” to the action of basidiomycetes, soft rot fungi and termites, use classes 1-2, and showed macro-microscopic evidence of these types of decay.Research highlights: the information obtained in this study would allow the inclusion of clone I-214 in the standard EN 350 and its explicit classification within it.Keywords: wood-decay fungi; termites; EN 350.Abbreviations used: TM: test material; RM: reference material; RH: relative humidity; ML: mass loss; mi: initial dry mass; mf: final dry mass; DC: durability class; OM: Optical Microscope; SEM: Scanning Electron Microscope; TS: transverse section samples; LS: longitudinal section samples; CI: robust confidence intervals; F: fibre; V: vessel; h: hole; t: erosion trough; R: radial parenchyma cell; ep: erosion pitting; Fc: fungal colonization; fr: fracture; c: cavity; b: bore hole; m: mycelium
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
White-rot fungi control on Populus spp. Wood by pressure treatments with silver nanoparticles, chitosan oligomers and propolis
Full text linkThere is growing interest in the development of non-toxic, natural wood preservation agents to replace conventional chemicals. In this paper, the antifungal activities of silver nanoparticles, chitosan oligomers, and propolis ethanolic extract were evaluated against white-rot fungus Trametes versicolor (L.) Lloyd, with a view to protecting Populus spp. wood. In order to create a more realistic in-service type environment, the biocidal products were assessed according to EN:113 European standard, instead of using routine in vitro antimicrobial susceptibility testing methods. Wood blocks were impregnated with the aforementioned antifungal agents by the vacuum-pressure method in an autoclave, and their biodeterioration was monitored over 16 weeks. The results showed that treatments based on silver nanoparticles, at concentrations ranging from 5 to 20 ppm, presented high antifungal activity, protecting the wood from fungal attack over time, with weight losses in the range of 8.49% to 8.94% after 16 weeks, versus 24.79% weight loss in the control (untreated) samples. This was confirmed by SEM and optical microscopy images, which showed a noticeably higher cell wall degradation in control samples than in samples treated with silver nanoparticles. On the other hand, the efficacy of the treatments based on chitosan oligomers and propolis gradually decreased over time, which would be a limiting factor for their application as wood preservatives. The nanometal-based approach is thus posed as the preferred choice for the industrial treatment of poplar wood aimed at wood-based engineering products (plywood, laminated veneer lumber, cross-laminated timber, etc.)
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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