1,720,958 research outputs found
Pultrusion moldings for continuous natural fiber reinforced thermoplastic composites
Full text link京都工芸繊維大学博士（学術）The use of natural fibers from which derived annually renewable resource as reinforcement in composite is provides the positive benefit with respect to environment, ecological advantage and the attractive mechanical properties. Jute fibers are the natural fibers superior on light weight, good mechanical properties with low specific mass, low cost and environmental friendly. Silk fiber is a high tensile strength fiber, good elasticity and excellent toughness. Both natural fibers are commercially available in a continuous fiber type and suitable to fabricate continuous fiber reinforced composite. Pultrusion is a special technique use to shape polymeric composite materials into parts with constant cross section. It is suitable for produce the continuous composite with uniform cross sections, high mechanical properties due to the continuous fiber, mass production and low cost. The reinforcement fibers in the form of continuous fiber are impregnated with matrix and pulled through the heat die to form composites. Therefore putrusion process was selected to manufacture the composite in this research. Usually the pultrusion composite is fabricated by unidirectional fiber and one problem of the unidirectional fiber reinforced composites is the anisotropic of mechanical properties. Braiding technique was introduced to overcome the anisotropic properties since braided fabric can change the braiding angle and selecting number of fiber, therefore the braiding technique can control the degree of anisotropic properties according to the requirements. The design concept of braided composite by pultrusion molding was described to achieve successful implementation of continuous fiber reinforced composite, which consist of materials design, structure design and processing design. Material designs involve the volume fraction and configuration of yarn for intermediate materials with reinforcing fiber and resin. Meanwhile braiding angle, gap between braiding yarns and filling ratio, are the important parameter of the structure design. The processing designs were consisted of molding condition such as molding temperature, pulling speed and pulling force. The objective of this thesis is to investigate the operating parameter to fabricate continuous natural fiber reinforced thermoplastic composite through pultrusion technique in terms of materials, structure and processing design. The manufacturing of tubular braided composite using jute spun yarn and silk fiber reinforced PLA by pultrusion molding was investigated and, braiding technique was used to prepare the tubular preform. The braided fabric consists of fiber bundles called braiding yarns which continuously and spiral oriented along longitudinal direction. The fiber bundle can be inserted between braiding yarns called middle end yarn and angle between braiding yarns called braiding angle. The important structure design parameters of braided composite are braiding angle, gap between the braiding yarn and filling ratio which means the ratio of the volume of fiber and resin to the volume of molding. The tubular preform with only natural fiber was not strong enough for pultrusion, glass fiber was used as the middle end fiber. Thermoplastic resins contain high melt viscosities, which make melt resin impregnation into the reinforcement difficult. For this reason, various intermediate materials have been developed to overcome these problems. The configuration of yarn such as micro braided yarn, paralleled yarn and commingled yarn was investigated to fabricate the tubular braided preforms. The processing parameters were studied and it was clarified that impregnation quality and mechanical properties of composite were increased by increasing the filling ratio. The molding temperature affected the impregnation quality; high molding temperature showed better impregnation property and resulted to increase in the bending modulus. While the bending strength was decreased due to the heat deterioration of silk and jute fiber caused by the molding temperature. The commingled yarn is desirable to achieve better flow of melt resin in molding die and relate to the pultusion speed. Jute spun yarn was mixed with PLA resin fiber and need longer distance for resin flow to fill the fiber bundle and need longer time for impregnation, therefore low speed is appropriated for fabricate jute/PLA tubular braided composite. Meanwhile, silk fibers were commingled with PLA resin fiber and the distance of resin flow is reduced to achieve full impregnate, hence macro-flow occurred around the fiber bundle, however at lower speed macro-flow still continuous and flow out from consolidation state. Therefore higher speed is appropriated for fabricate silk/PLA tubular braided composite. While the speed is increased, the macro-flow was not sufficient to flush the trapped air bubble from consolidation state before the end of taper of molding die, therefore some void occurred in the composite. The designed processing in this thesis could be the step towards the economically viable production of continuous composite by using braiding technique
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
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
Fabrication and Mechanical Properties of Jute Spun Yarn/PLA Unidirection Composite by Compression Molding
No full textAbstractThe unidirection composites of jute spun yarn/Polylactic acid were fabricated using compression molding. The reinforcement fibers were paralleled with matrix resin fiber and were used as intermediate materials to prepare the unidrection preforms. The parallel yarn was winded onto the metallic frame. The wound paralleled yarns were dried in convection oven before molding. The metallic frame containing the paralleled yarns was placed in heated mold for consolidation to produce the unidirection composite specimens with various molding temperature. The heated mold was cooled by the cooling system of the compression machine. Consolidation process involved three stages. At first, under certain temperature, the solid fibrous matrix materials became softened and then the matrix in the liquid form soaked and infiltrated the reinforcing fibers and finally during cooling stage, the matrix turned into solid form to hold the fibers in a definite position. The molding temperature was affected to the mechanical properties of the unidirection composite. The jute spun yarn/PLA composite were characterized in the term of mechanical properties and the fabrication quality was examined by cross-section observation. The impregnation quality and dispersion of fiber bundle were increased with increasing the molding temperature and achievement ratio of elastic modulus increase. While increasing the molding temperature, the achievement ratio of tensile strength was decreased because of deterioration of jute fiber. The optimum compression molding temperature was 185 - 195C for fabricated the jute spun yarn/PLA unidirection composite
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Mechanical Properties of Jute Spun Yarn/PLA Tubular Braided Composite by Pultrusion Molding
No full textAbstractPultrusion is a continuous process with application in the manufacture of fiber-reinforced composite. The thermoplastic pultrusion molding is a manufacturing process in which generated by the resin fiber and reinforcement fibers are pulled through the heat die. The pressure was generated, also the resin fiber start melt and impregnate into the reinforcement fiber. In this investigation study the mechanical properties of jute spun yarn/PLA tubular braided composite by pultrusion molding. The systems for jute spun yarn/PLA braided composite were described in the term of materials design, structure design and processing design. The intermediate materials were prepared by comingle technique. The braiding technique manufactured preform which had jute fiber diagonally oriented at certain angles with the glass fiber inserted into the braiding yarns along the longitudinal direction of braiding structure. The braided preforms were pulled through the heated die where consolidation flow took place due to reduced matrix viscosity. The pultrusion experiments were fabricated the tubular braided composite with varying the structure of braided preform and pultrusion molding condition. The configuration of intermediate material and the molding temperature are influenced to the mechanical properties of jute spun yarn/PLA tubular braided composite. The quality of pultruded composite was evaluated by cross-section observation and mechanical properties evaluated by 4-point bending test
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