1,720,959 research outputs found
Influence of Sporasarcina pasteurii cells on rheological properties of cement paste
No full textNowadays with the developments in the concrete materials technology, researches started to focus on highly flowable mixes with improved rheological properties. These highly flowable mixes generally require use of viscosity modifying agents (VMAs) to reduce bleeding and segregation. VMAs are water-soluble polymers that can be produced from acrylic polymers and polysaccharide-based biopolymers obtained from cellulose, starch or bacterial fermentation. Through the literature, nopal mucilage, brown algae and bacterial cell walls were proposed as alternatives to these bio-based admixtures. However, these alternatives also require extra processing which results again with a higher unit cost. This paper summarizes the rheological properties of a cement paste including bacterial cells. The main goal of this study was to investigate the influence of Sporasarcina pasteurii (S. pasteurii) cells on viscosity and yield stress of cement-based materials. The bacterial cells were directly incorporated to the mix water and influence of cells on viscosity and yield strength was evaluated by rheological tests. In addition, the influence of bacteria dosage, water to cement ratio (w/c), use of superplasticizers and fly ash on performance of biological VMA were investigated. Our results showed that the apparent viscosity and yield stress of the cement-paste mix were increased with the addition of the microorganisms. Moreover, the provided biological VMA was found to be compatible with the use of fly ash and superplasticizers depending on the w/c of cement paste.TÜBİTA
Rheoloji değiştirme ajanları : mikroorganizmalar ile geliştirilen anahtar teknoloji
No full textRecent development in concrete technology enabled the design of highly flowable mixes with improved workability. These advanced mixes require incorporation of fine materials or viscosity modifying agents (VMA) to reduce the possible segregation and bleeding due to the use of high range water reducers (such as superplasticizers). The VMAs used in concrete production are generally produced from acrylic polymers and polysaccharide-based biopolymers obtained from cellulose, starch or bacterial fermentation. Diutan gum, produced by fermentation of Sphinogomonas sp, and welan gum, which is a fermentation product of Alcaligenes sp, are the most commonly used polysaccharide VMAs. Similar polysaccharides can be obtained by fermentation of genetically modified bacteria or using plant cell walls. Most polysaccharide based VMAs are able to increase the viscosity of cement paste and exhibit shear thinning behavior such that increased shear rate results with a substantial decrease in apparent viscosity. This behavior is attributed to the long molecular structure of bio-based polysaccharides. Though highly effective bacterial fermentation products can resist the high PH environment of cement-paste, the ecological population of the species is not known. Thus, they are among the most expensive cement admixtures. Advances in construction technology and risen importance of sustainability initiatives reinforce the use of biological admixtures, however, their relatively high cost can be a major drawback in practical applications. Through the literature, nopal mucilage, brown algae, and bacterial cell walls were proposed as alternatives to these bacterial fermentation products. However, these alternatives also require extra processing which required bigger budget even compared to bacterial fermentation products. This project aims to incorporate bacteria cells to the cement-based mix as VMAs without any extra intervention. To achieve this goal, Sporosarcina pasteurii (S.pasteurii), Bacillus megaterium (B. megaterium), Bacillus subtilis (B. subtilis) and Paenibacillus polymyxa (P. polymyxa) were selected as suitable due to their abundant resource in nature. These Gram-positive bacterial cells include peptidoglycans and polysaccharides in their cell wall structure, which resembles the molecular structure of commercially used VMAs. In addition, these cells, particularly B. subtilis, can influence the viscosity of a suspension due to its motility. Throughout the study, these cells were grown in specified nutrient media and then harvested from the inoculum by centrifuging. Then, these cells were suspended in mixing water and their influence on the rheology of cement paste was evaluated. In addition, the influence of water to cement ratio, the dosage of cells added was evaluated along with the impacts of superplasticizers and fly ash on the performance of bacteria cells as VMAs. There are few established industrial and various small-scale companies that produce biological admixtures for cement-based materials. However, nationwide these biological admixtures (for instance chitosan) are only produced for the food industry. The product obtained by the end of this study is a novel and sustainable practice in Turkey, where the construction industry leads the economy.Günümüzde gelişen beton teknolojisi, yeni kuşak çimento esaslı malzemelerin gelişiminin önünü açmıştır. Akışkanlığı ve işlenebilirliği yüksek harç ve betonların kullanımı gittikçe artmaktadır. Bu tür malzemelerde dağıtma gücü çok yüksek akışkanlaştırıcı katkıların neden olduğu ayrışmayı (segregasyon) ve terlemeyi önleyebilmek için daha ince tanecikli malzemeler veya viskozite düzenleyici katkıların (VDK) kullanımı artmaktadır. VDK, akışkanlığı yüksek olan beton ya da harçların kararlılığını (stabilizesini) arttırmakta ve taze çimento hamuru performansını yükseltmektedir. Günümüzde beton üretiminde kullanılan VDK’lar suda çözünen polivinil alkol veya polimerlerden oluşmaktadır. VDK’lar akrilik polimerlerden, selülozdan, nişastadan veya bakteri fermantasyonu gibi polisakkarit bazlı biyopolimerlerden elde edilmektedir. Bakterilerden elde edilen polisakkaritlerden CP Kelco adlı şirketin Sphingomonas bakterisinin fermantasyonu ile elde ettiği diutan sakızı, Merck & CO adlı şirketin Alcaligenes bakterisini kullanarak ürettiği welan sakızı çimento esaslı malzemelerde VDK olarak sıkça kullanılmaktadır. Benzer şekilde piyasada bakterilerin genleri ile oynanarak ya da bitkilerin hücre duvarları kullanılarak farklı polisakkaritler elde edilebildiği bilinmektedir. Çimento esaslı malzemelerde VDK olarak kullanılan biyolojik polisakkaritler çimento hamurunun viskozitesini arttırdığı belirlenirken, yapılan testlerde kayma hızı arttırılırken malzemenin inceldiği (shear-thinning) gözlemlenmiştir. Bu özelliklerin biyolojik polisakkaritlerin uzun moleküler yapısı ile ilişkili olduğu bilinmektedir. Bu fermantasyonun ürünü olan polisakkaritler yüksek PH değerlerine dayanma özellikleriyle ön plana çıkarken, bunları üretecek mikroorganizmaların ekolojik olarak popülasyonu bilinmemektedir. Bu nedenle birim fiyat yükselmektedir. İlerleyen teknoloji ve sürdürülebilirlik bilinci biyolojik katkı malzemelerinin inşaat sektöründe kullanımının artmasını teşvik ederken, maliyetlerinin yüksek olması bir dezavantaj yaratmaktadır. Uluslararası literatürde bu fermantasyon ürünlerine alternatif olarak göllerden toplanan yosunlar ve bakterilerin, sadece hücre duvarlarının ayrıştırılarak kullanılması incelenmiştir. Ancak bu iki ürünün elde edilmesinde özel işçilik gerektirecek farklı işlemlerin uygulanması, maliyetlerin yine yükselmesine sebep olmuştur. Bu projenin amacı doğadan kolayca elde edilen mikroorganizmaları, hücre duvarını ayrıştırılması gibi özel işlemler gerektirmeden, çimento esaslı malzemelerde VDK olarak kullanarak reolojisi iyileştirilmiş bir çimento harcı (ürün) elde etmektir. Bu amaç doğrultusunda Sporosarcina pasteurii, Bacillus magetrium, Bacillus subtilis ve Paenibacillus polymyxa bakteri suşları seçilmiştir. Bu çalışma süresince, bakteriler besi yerlerinde büyütüldükten sonra santrifüj edilerek ortamdan ayrıştırılmıştır. Ardından bu hücreler çimento karışım suyuna eklenmiş ve çimento hamurunun reolojisine olan etkileri test edilmiştir. Ayrıca farklı su oranlarında ve bakteri dozajlarının test edileceği karışımlara, süperakışkanlaştırıcıların ve uçucu külün bakterilere olan etkisi incelenmiştir
Crack remediation in mortar via biomineralization: effects of chemical admixtures on biogenic calcium carbonate
No full textLimited research on biomineralization in cement-based systems suggested that self-healing of surface cracks could be obtained by triggering biogenic calcium carbonate (CaCO3) precipitation within the cracks. While this is encouraging, there is not enough information regarding the influence of admixtures on crack remediation and durability of the biogenic CaCO3 against weathering conditions. In this study, the microorganisms were introduced to mortar with their growth medium, which included corn steep liquor (CSL) and urea. With this approach, the cracks on mortar surface were sealed with the CaCO3 and the water absorption capacity of the so-called self-healed mortar decreased compared to its counterpart cracked mortar samples. The biogenic CaCO3 precipitate was found to be durable against freeze-thaw; however the precipitate was unstable under rain water and light. While the addition of air entraining agents (AEA) did not influence the self-healing ability of cells, use of superplasticizers improved the self-healing ability in terms of crack sealing, water absorption, and durability of the precipitate.TÜBİTA
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
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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