1,720,976 research outputs found
Oxygen Consumption of Laccase-Mediator-Systems (LMS)
No full textCrude oil as a non-renewable resource is presenting challenges for the future in many industrial sectors. Due to the dwindling of these resources, costs are increasing negatively affecting the wood based panels industry, which uses mainly petrochemical resins as components for binding agents. In addition harmful formaldehyde emissions arising from conventionally produced wood composites are demonstrable. In order to substitute these conventional binding agents for wood based panels, in particular medium density fiberboards (MDF), Laccase-Mediator-Systems (LMSs) were investigated in several researches. A popular and reliable method used to test the suitability of LMSs is the measurement of their oxygen consumption on wood fibers in aqueous suspension. This enzymatic catalyzed oxidation was the object of this study. The mediators 4-hydroxybenzoic acid (HBA), vanillic acid (VanA), vanillic alcohol (VAl), ethylvanillin (EVan), acetovanillone (AVan), ferulic acid (FA), caffeic acid (CA) and guajacol (Gu) were tested as possible components of the LMSs. The study showed that all of the LMSs have oxidized wood fibers more efficiently than laccase on its own. Among the different mediators, vanillic alcohol, guajacol and caffeic acid in LMSs have shown the fastest O2 consumption
Pre-pressing and Pre-heating via Hot-Air/Hot-Steam Process for the Production of Binderless Medium-Density Fiberboards
No full textThe hot-air/hot-steam process was used for the first time as a combined pre-pressing and pre-heating system for the production of medium-density fiberboards (MDF) at the pilot scale. Pre-heating systems are designed to pre-heat fiber mats before pressing by hot-presses. Using such techniques, pressing times are reduced significantly and the board properties are influenced positively; both are essential for effective MDF production. In recent years, industry has searched for alternatives to petrochemical binders. Primarily, MDF are bonded by urea-formaldehyde (UF) resins in Europe. To replace UF resins, a laccase-mediator-system (LMS) was used to activate the wood fibers’ self-cohesion. It was found that the internal bond strength (IB) and thickness swelling (TS) were noticeably improved by applying the hot-air/hot-steam process before final hot-pressing for both LMS and 10% UF binding systems. Simultaneously, the total pressing time could be reduced by 25% when combining the hot-air/hot-steam process with hot-pressing
Hot-Air/Hot-Steam Process for the Production of Laccase-Mediator-System Bound Wood Fiber Insulation Boards
No full textIn this study, a new technical process for hardening wood fiber insulation boards is introduced. During the dry-process, the fibers are usually glued with polymeric-diphenylmethane-diisocyanate (pMDI) and hardened to wood fiber insulation boards using a steam-air mixture. However, the maximum temperature reached in the steam-air process was 100 °C, and it was impossible to use an alternative binding agent for the gluing of the wood fiber insulation boards other than pMDI. When incubated with laccase-mediator-system (LMS) as a naturally based bonding system, temperatures of over 120 °C are required because of the chemical wood composition, especially the lignin. In this case, the hot-air/hot-steam process offers new technical opportunities for realizing temperatures above 100 °C. In this study, wood fiber insulation boards were glued with LMS, vs. reference boards with inactivated LMS, laccase alone, and 4% pMDI. Then, the boards were hardened using one of three processes: with steam-air mixture, with hot-air, and with hot-air/hot-steam. Through the hot-air/hot-steam process, temperatures of well over 120 °C were attainable. All the insulation boards hardened using the hot-air/hot-steam process showed better physical and technical properties than those hardened with steam-air mixture or hot-air alone. The reason for this is a sudden increase of temperature after the adding of steam because high temperatures insure that the LMS activated wood fiber surface lignins are completely plasticized. As a result the physical-technological properties such as internal bond strength, compression strength, and short term water absorption of insulation boards treated with LMS were comparable to those boards treated with 4% pMDI
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
Phenolics as Mediators to Accelerate the Enzymatically Initialized Oxidation of Laccase-Mediator-Systems for the Production of Medium Density Fiberboards
No full textCrude oil as a non-renewable resource is creating new challenges in many industrial sectors. Unsteady costs of crude oil at present and expected increases in the future are due to its limited availability as a finite resource, and these costs negatively impact the industry for wood-based panels, which use petrochemical resins in binding agents. Furthermore, wood panels that are conventionally bonded using urea formaldehyde diffuse formaldehyde into the surrounding air. To achieve independence from petrochemical products and harmful formaldehyde emissions, alternatives for their substitution are in demand. An alternative approach is the enzymatic activation of lignin located on the surface of thermomechanical pulp (TMP) fibers. The present study shows the results of internal bond strength (DIN EN 319 1993), modulus of rupture (DIN EN 310 1993), and thickness swelling (EN 317 2003) of medium-density fiberboards (MDF) bonded with laccase-mediator-system (LMS). Caffeic acid (CA), 4-hydoxy benzoic acid (HBA), and vanillic alcohol (VAl) were used as mediators. The physical and technological properties of MDF, such as internal bond strength, modulus of rupture, and thickness swelling, mostly fulfilled the European standards
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
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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