1,721,003 research outputs found
Preparation and characterization of natural fiber- filled polybutylenesuccinate composites
No full textLisansüstü Eğitim Enstitüsü, Metalurji ve Malzeme Mühendisliği Ana Bilim DalıBu çalışma ile, biyolojik olarak parçalanabilen çevre dostu, yüksek elastisiteye, belirli ölçüde ısısal ve kimyasal dirence sahip, eriyik işlenebilirliği mevcut ve düşük maliyetli polimer türü olan Polibütilen Süksinatın (PBS) özelliklerinin, farklı doğal takviye materyalleri olan Jüt elyaf (JF) ve Keten elyaf (KF) kullanılarak geliştirilmesi ve ayrıca yüzey modifikasyonunun kompozitlerin mekanik, ısısal, termogravimetrik, aşınma, su emme ve morfolojik özellikleri üzerine etkilerinin araştırılması amaçlanmıştır. Jüt ve keten elyaflara alkalileme ve silanlama ile yüzey modifikasyon işlemleri uygulanmıştır. Kompozit malzemelerin mekanik, ısısal, termomekanik, aşınma, su emme ve morfolojik özellikleri incelenmiştir. Modifikasyon uygulanmış ve uygulanmamış jüt ve keten elyafların yüzey özellikleri FTIR ve SEM ile karakterize edilmiştir. Polimer matris ve dolgu maddeleri çift vidalı ekstrüderde karıştırıldıktan sonra enjeksiyonlu kalıplama ile şekillendirilmiştir. Elde edilen kompozit numuneleri çekme, sertlik, termogravimetrik analiz (TGA), dinamik mekanik analiz (DMA), aşınma ve su emme testleri ve alan etkili taramalı elektron mikroskopisi (FESEM) ile analiz edilmiştir. Yapılan analizler sonucunda, JF ve KF ilavelerinin kompozit malzemelerin mekanik ve ısısal özelliklerini olumlu biçimde etkilediği görülmüştür. Jüt ve keten elyaflara yüzey modifikayonunun dolgu maddesi ile polimer matris arasındaki yüzey uyumsuzluk problemini çözdüğü ve PBS/modifiye JF, PBS/modifiye KF kompozitlerinin mekanik ve ısısal özelliklerini geliştirdiği elde edilmiştir.In this study, the properties of Polybutylene Succinate (PBS), which is a biodegradable, environmentally friendly, high elasticity, thermal and chemical resistance to a certain extent, melt processable and low-cost polymer, were enhanced by different natural reinforcement materials such as Jute fiber (JF) and Flax fiber (KF) and additionally the effects of surface modification on the mechanical, thermal, thermogravimetric, wear, water absorption and morphological properties of composites were investigated. Surface modification processes were applied to jute and flax fibers by alkalization and silanization. Mechanical, thermal, thermomechanical, wear, water absorption, and morphological properties of composite materials were investigated. The surface properties of modified and unmodified jute and flax fibers were characterized by FTIR and SEM. After the melt-mixing of the polymer matrix and fillers in a twin screw extruder, they were shaped by injection molding. Tensile, hardness, thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), abrasion, and water absorption tests, and field-effect scanning electron microscopy (FESEM) analyzes were performed on composite samples. As a result of the analysis, it was seen that the additions of JF and KF positively affected the mechanical and thermal properties of composite materials. It was obtained that the surface modification of jute and flax fiber solved the problem of surface incompatibility between the filler and the polymer matrix and improved the mechanical and thermal properties of PBS/modified JF, PBS/modified KF composites. Surface modification of Jute fiber and Flax fiber creates a more favorable interfacial interaction between the filler material and the polymer matrix, and higher structural, mechanical, and thermal properties were obtained for PBS/modified JF, PBS/modified KF composites
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
Influence of Conductive Additive Inclusions in Pla-Based Composites
No full textBu çalışmada, PLA matrisine %1, %10, %20 ve %30 yükleme oranları ile Oltu taşı tozu (OS) ve mika bazlı Fe3O4 iletken pigment (CP) eklenerek optimum konsantrasyonlar araştırıldı. Elde edilen kompozitlere çekme, sertlik ve darbe testleri, dinamik mekanik analiz testi, doğrusal dört nokta iletkenlik ölçümü, erime akış indeksi ölçümleri ve taramalı elektron mikroskobu kullanılarak sırasıyla mekanik, termomekanik, elektriksel iletkenlik, erime akışı ve morfolojik ölçümler yapılarak elde edilen kompozitlerin özellikleri tanımlanmaya çalışıldı. Kompozitlerin çekme testleri incelendiğinde , gerek PLA'nın çekme mukavemetinde ve modulüs değerlerinde gerek ise uzama miktarlarında OS ve CP artışı ile azaldıkları görüldü. Kompozitlerin maksimum çekme performansı OS ve CP miktarlarının %20 olduğu örneklerde elde edildi. Saf PLA'nın Shore D değerinin, OS ve CP eklemeleri ile arttığı gözlemlendi. Aynı yükleme seviyelerinde, karbon bazlı OS, demir oksit ve alümina silikat içeren CP'ye kıyasla nispeten daha yüksek sertlik değerlerine ulaştı. Özetle, hem OS hem de CP için %20'lik bir yükleme oranı sergileyen kompozit numuneler, diğer kompozitlerle karşılaştırıldığında kısmen daha iyi mekanik ve termomekanik özellikler gösterdikleri saptandı. Elektrostatik paketlemede %1 katkılı kompozit filmler kullanılabilir. Üretilen kompozitler, uygun mekanik ve elektriksel iletkenlik özelliklerinin gerekli olduğu uygulamalar için 3D baskılı bileşenler oluşturmak için dizayn edilebilir.The OS powder and Fe 3O4 mica-based conductive pigment developed for this thesis were added to the PLA matrix in four different concentrations for loading ratios of 1%, 10%, 20%, and 30% to determine the optimal concentration. Using the tensile, hardness, and impact tests, dynamic mechanical analyses test, linear four-probe method, melt flow index measurements, and scanning electron microscopy methodology, respectively, the mechanical, thermo-mechanical, electrical conductivity, melt-flow, and morphological properties of composites were reported. Tensile test results, tensile strength, and modulus characteristics of PLA decrease with additive integration, according to test results. However, PLA's elongation value decreased as OS and CP loadings increased. The composites' maximum tensile performance was attained as 20% of both CP and OS amounts were added. The unfilled PLA's Shore D value was increased by including OS and CP. At the same loading levels, carbon-based OS produced comparatively higher hardness values than CP, which comprised iron oxide and alumina silicate. In summary, composite samples exhibiting a 20% loading ratio of both OS and CP showed significantly improved mechanical and thermo-mechanical performances compared to other composites. Composite films with 1% additives can be used in electrostatic packing. Additionally, fabricated composites can be used to produce 3D-printed components for applications where appropriate mechanical resistance and electrical conductivity specifications are required
Thermoplastic polyurethane/wood flour ecocomposites
No full textFen Bilimleri Enstitüsü, Metalurji ve Malzeme Mühendisliği Ana Bilim DalıBu çalışmada, talaş tozunun (WF) biyobazlı termoplastik poliüretan (TPU) matrisine yapışmasını iyileştirmek amacıyla alkali ve silan uygulamaları yapılmıştır. TPU/WF ekokompozitler, eriyik karıştırma yöntemi ile ağırlıkça % 30'luk sabit bir oranda hazırlanmıştır. Mekanik, termomekanik, eriyik akış, su emme ve morfolojik özellikler incelenmiştir. Sonuçlara göre, yüzey silanlama işleminden sonra WF ve TPU matrisi arasında yapışma arttığından, silanlama işlemi gören WF ile dolgulanmış kompozit işlem görmemiş WF'a göre daha iyi mekanik performans sergilemiştir. Silanlanmış WF içeren kompozit en düşük su emme değerini vermiştir. Sonuçlar, WF'a silan uygulamasının, TPU bazlı kompozitlerin mekanik ve fiziksel özellikleri üzerinde önemli iyileşmeye yol açtığını ve bununla birlikte dış ortam uygulamaları için suya direncinin arttığını doğrulamıştır.In this study, alkaline and silane treatments were applied to wood flour (WF) to enrich its adhesion to bio-based thermoplastic polyurethane (TPU) matrix. TPU/WF eco-composites were prepared at a constant ratio of 30 wt% by melt blending process. Their mechanical, thermo-mechanical, melt-flow, water uptake and morphological properties were investigated. Silane treated WF filled composite exhibited better mechanical performance with respect to untreated WF due to enhancement of adhesion between WF and TPU matrix after surface treatments. Silanized WF containing composites gave the lowest water absorption value. Results confirmed that silane treatment of WF led to significant improvement on the mechanical and physical properties of TPU based composites in addition to gain water-resistance for their outdoor applications. Results confirmed that silane treatment of WF led to significant improvement on the mechanical and physical properties of TPU based composites in addition to gain water-resistance for their outdoor applications
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
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
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