1,721,316 research outputs found
Sepiolite-PAN intercalation used as Si3N4 forming precursor
No full textKURT, Ali/0000-0002-0204-9655WOS: 000166860400026Silicon nitride (Si3N4) formation was investigated using sepiolite and polyacrylonitrile as silicon and carbon source, respectively. It was found that purified sepiolite could readily adsorb a sufficient amount of acrylonitrile (AN) reagent without pre-treatment. Polymerisation of sepiolite-AN mixtures and subsequent cyclization of the polymerised complex yielded a precursor, which was found ideal as a starting material in carbothermal reduction-nitridation (CRN) for the formation of silicon nitride powders. The quantity of silicon nitride, grain size and morphology were found to be dependent on the reaction conditions and starting reagent. Fine grain size, high surface area (up to approx. 12.4 m(2)/g) powders of mainly beta -Si3N4 were obtained via pyrolysis of sepiolite-PAN complex after 4 h heating at 1400 degreesC in 1000 ml/min nitrogen flow with a heating rate of 300 degreesC/h. Mg retained in the molecular structure of the mineral must have promoted the formation of beta -grains in CRN process. (C) 2001 Kluwer Academic Publishers
The investigation of Gumusdamla (Aydintepe-Bayburt) skarn mineralization as geological, mineralogical and genesis
No full textYÖK Tez No: 542814İnceleme alanı, Bayburt ilinin kuzeyinde yer alan Aydıntepe İlçesi Gümüşdamla Köyü yakın çevresini kapsamaktadır. Bu çalışmada bölgenin 1/25000 ölçekli jeolojik haritası ve cevherleşme alanında 1/2000 ölçekli detay maden jeoloji haritası yapılmıştır. Çalışma alanında Kabaköy Formasyonu'nun tortul birimleri ve Kaçkar Granitoyidine ait kayaçlar yüzeyleme vermektedir. Detaylı inceleme yapılan cevherleşme alanı ve yakın çevresi Eosen yaşlı Kaçkar Granitoyidi ile Kabaköy Formasyonu kontağında bulunmaktadır. İnceleme alanında cevherleşmenin parajenezini belirlemek amacıyla sistematik örnekleme yapılmış, parlak kesitler hazırlanarak cevher mikroskobu altında incelenmiştir. Cevherleşmenin parajenezini ağırlıklı olarak manyetit ve hematit az oranda ise pirit ve kalkopirit oluşturmaktadır. Arazide yapılan gözlemler sonucunda hematitleşme, limonitleşme, epidotlaşma ve killeşme türü alterasyonlar tespit edilmiştir. petrokimyasal verilere göre volkanik kayaçlar andezit, andezit/bazalt ve trakiandezit türünde olup, negatif Nb, Ta, Ti ve Zr anomalileri ile karakteristiktir. Bu durum volkanitlerin yitimle ilişkili kıtasal yay mağmatizmasından itibaren türediğini işaret etmektedir. Bununla birlikte, tektonik ayırtman diyagramları volkanik kayaçların kalk-alkali bazalt özelliğinde olduğu göstermektedir. Granitik kayaçların ise monzogranit ve granit bileşiminde, subalkalen karakterli, yüksek potasyumlu kalk alkali içerikli metalümin ve peralümin karakterli ve I tipinde volkanik yay graniti olduğu saptanmıştır. Th, K, Rb gibi elementlerdeki zenginleşme kabuk etkisini, Nb ve Ti elementlerindeki negatif anomali ise granitik kayaçların ana magmalarının gelişiminde yitim etkisinin olduğunu göstermektedir. Cevherli örneklerden yapılan mineral kimyası analiz sonuçlarına göre piroksenlerin diyopsit, plajiyoklasların andezin ve anortit, granatların grossular ve andradit bileşiminde olduğu belirlenmiştir. Piroksen ve granatların mineral kimyası değerlerine göre çalışma alnında bulunan skarn cevherleşmesinin Fe-Skarn tipinde olduğu sonucuna varılmıştır.The study area is located in the vicinity of Gümüşdamla Village of Aydıntepe District in the north of Bayburt province. In this study, 1/25000 scale geological map of the region and 1/2000 scale detailed mining geology map of mineralization area was made. The sedimentary units of Kabaköy Formation and rocks belonging to Kaçkar Granitoid outcrops in the study area. Detailed investigation of the mineralized area and its immediate surroundings are in the contact of Eocene aged Kaçkar Granitoid with Kabaköy Formation. In order to determine the paragenesis of mineralization in the study area, polished sections were prepared from the systematically collected samples and these are examined under ore microscope. The paragenesis of the mineralization is composed of intensively magnetite and hematite and to a lesser amount pyrite and chalcopyrite are also found. As a result of field observations, hematitization, limonitization, epidotization and argilitization were determined as the alteration types. The observed volcanic rocks are andesite, andesite / basalt and trachyandesite, according to chemical naming diagram of volcanic rocks of Nb/Y versus Zr/TiO2*0.0001. The negative Nb, Ta, Ti and Zr anomalies detected in the REE diagrams indicate that the volcanics in the studied areas carry features of subduction related continental arc magmas, and according to the tectonic discrimination graphs, they are the calc-alkaline basalt in characters. When the results were transferred to the granitic rocks classification diagram, it was determined that the samples are monzogranite and granite in composition with subalkalenic, high-potassium calc-alkaline-containing metaluminous and peraluminous character and they found to be I type of volcanic arc granite. The enrichment in elements such as Th, K, Rb expresses the crustal effect , and the negative anomaly in Nb and Ti indicates relation of subduction in the development of the main magma of the granitic rocks. According to the results of mineral chemical analysis, it was determined that pyroxene is diopside, plagioclase is andezine and anorthite, garnet is grossular and andradite in composition. Considering the mineral chemical values of pyroxene and garnets, it is concluded that skarn mineralization found in the study area is Fe-Skarn type
Heat transfer analysis using ANNs with experimental data for air flowing in corrugated channels
No full textThe objective of this work is to use artificial neural networks (ANNs) for heat transfer analysis in corrugated channels. A data set evaluated experimentally is prepared for processing with the use of neural networks. Back propagation algorithm, the most common learning method for ANNs, was used in training and testing the network. To solve this algorithm a computer program using C++ has been developed. The accuracy between experimental and ANNs approach results was achieved with a mean absolute relative error less than 4%. (C) 2003 Elsevier Ltd. All rights reserved
Synthesis of Si3N4 using sepiolite and various sources of carbon
No full text0000-0002-0204-9655WOS: 000172368200023Sepiolite of Turkish origin was used as Si precursor in the syntheses of silicon nitride (Si3N4) powders by carbothermal reduction-nitridation (CRN) by mixing with several reducing agents i.e. charcoal, carbon black and petroleum coke as discrete particles and acrylonitrile as an intercalation medium. Purified sepiolite samples with a pre-determined C/SiO2 ratio of 4 yielded Si3N4 powders after firing at temperatures 1300-1475 degreesC under continuous nitrogen flow. The various sepiolite-reducing agent combinations were evaluated. The alpha/beta ratio and secondary phase content of the powders after CRN were found to depend on temperature, time, heating rate and on the physicochemical properties of the precursor used such as, surface area and mixing of the reactants. (C) 2001 Kluwer Academic Publishers
Prediction of centrifugal slurry pump head reduction: An artificial neural networks approach.
No full textThe feasibility of using artificial neural networks (ANN) in the prediction of head reduction of centrifugal pumps handling slurries is examined. An ANN model is proposed and compared with the empirical correlation given by the present authors earlier The comparison showed that the ANN could successfully be used for the prediction of head reductions of centrifugal slurry pumps. The mean deviation between predicted and experimental values is 5.86% which is reasonable for slurry handling processes
Investigation of the mechanical properties of metal and ceramic powders pressed by a computer controlled uniaxial die
No full textUlusal Toz Metalürjisi KonferansıThis study is about the investigation of the mechanical properties of metal and ceramic powders pressed by a uniaxial die. The bronze powders have spherical particles, copper powders are of oval, iron powders are of porous and alumina and silicon nitride powders are of irregular shaped particles. The measurements of microhardness in metal powders have been done up to 1000 MPa with 200 MPa intervals and they have been found to be 118, 134 and 195 kg/mm2, respectively, for copper, iron, and bronze powders. Since the particle size of ceramic powders considered were extremely small (dm?5 m?), it was not possible to measure their microhardness. Similarities in densification behaviour of seramic powders have been observed. Copper and bronze powders have displayed similar densification behaviours while an increased densification gradient is observed in iron powders. Severe deformations are observed in metal powders under scanning electron microscope examinations
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
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