169,947 research outputs found
Investigation of the High Temperature Oxidation Behaviour of Cvd Aluminized Inconel 718 and Inconel 738lc Superalloys
No full textBu çalışma alüminize edilmiş Inconel 718 ve Inconel 738LC nikel bazlı süper alaşımların yüksek sıcaklık oksitlenme davranışlarını araştırmak ve karşılaştırmak amacıyla gerçekleştirilmiştir. Kaplamasız ve yüksek aktivite kimyasal buhar biriktirim (KBB) yöntemiyle alüminize edilmiş Inconel 718 ve Inconel 738LC numuneler 200 saat boyunca 925, 1000 ve 1050°C sıcaklıklarda havada oksitlenmeye maruz bırakılmıştır. Numunelerin oksidasyon mekanizmalarını araştırmak ve değerlendirebilmek amacıyla detaylı kesit incelemeleri, elementel analizler, ağırlık değişimi ölçümleri ve x-ışını kırınım çalışmaları yapılmıştır. Alüminizasyon sırasında numunelerin yüzeyinde oluşan NiAl fazının üstünde koruyucu Al2O3 tabakası oluşumu sayesinde hem 718 hem de 738LC alaşımında oksidasyon direncinin önemli ölçüde iyileştiği gözlemlenmiştir. Alüminizasyonun faydalı etkisinin tüm test sıcaklıklarında daha düşük oksidasyon hızı gösteren 738LC alaşımı numunelerde daha belirgin olduğu bulunmuştur. 738LC alaşımı altlığın daha yüksek alüminyum içeriğine sahip olmasının alüminyumun NiAl fazından difüzyon yoluyla uzaklaşmasını yavaşlattığı ve böylece bu alaşımın daha üstün oksidasyon direnci göstermesindeki ana neden olduğu öne sürülmüştür.This study was undertaken to investigate and compare the high temperature oxidation behavior of aluminized Inconel 718 and Inconel 738LC nickel based superalloys. Bare and high activity chemical vapor deposition (CVD) aluminized Inconel 718 and Inconel 738LC samples were oxidized in air at 925, 1000 and 1050°C for 200 hours. Detailed cross-sectional examinations, elemental analyses, weight change measurements, and x-ray diffraction studies were performed in order to investigate and evaluate the oxidation mechanisms of the samples. It was observed that the oxidation resistances of both 718 and 738LC alloys were significantly improved by the protective Al2O3 layer formed on the NiAl phase that was created on the surfaces of the samples during aluminizing. The beneficial effect of aluminizing was found to be more evident in the case of 738LC alloy samples which showed lower oxidation rates at all test temperatures. It is suggested that the higher aluminum content of the 738LC alloy substrate slows down the diffusion flux of Al away from the NiAl phase and hence this is the main reason for its superior oxidation resistance
A Comparison of the Ballistic Performances of Various Microstructures in Mil-A Armor Steel
No full textKonca, Erkan/0000-0001-8943-091XDue to their advantageous properties, there is a growing interest in developing armor steels containing fully or partially bainitic microstructures. In this study, bainitic and martensitic microstructures were obtained in rolled homogeneous armor (RHA) steel samples and their ballistic protection performances were investigated. RHA (MIL-A-12560) steel samples were subjected to isothermal heat treatments at three different temperatures, where one temperature (360 degrees C) was above the martensite formation start (Ms) temperature of 336 degrees C while the other two (320 degrees C and 270 degrees C) were below. For the assessment of the ballistic protection performance, the kinetic energy losses of the 12.7 mm bullets fired at the test samples were determined. The promising nature of the bainite microstructure was confirmed as the sample isothermally treated at 360 degrees C provided approximately 10% higher ballistic protection as compared to the regular RHA sample of tempered martensite microstructure. However, the ballistic performances of the isothermally treated samples decreased as the treatment temperature went below the Ms temperature. Following the ballistic tests, hardness measurements, impact tests at -40 degrees C, and macro- and microstructural examinations of the samples were performed. No correlation was found between the hardness and impact energies of the samples and their ballistic performances.ROKETSAN Missile Industries Inc. (Ankara, Turkey)This research was funded by ROKETSAN Missile Industries Inc. (Ankara, Turkey). The APC was paid for by the author
Effect of Aluminizing on the Oxidation of Inconel 718 and Inconel 738LC Superalloys at 925-1050 °C
No full textKonca, Erkan/0000-0001-8943-091XThis study was undertaken to investigate the effect of aluminizing on the oxidation of Inconel 718 and Inconel 738LC superalloys. Bare and high-activity chemical vapor deposition (CVD) aluminized Inconel 718 and Inconel 738LC samples were oxidized in air at 925, 1000, and 1050 degrees C for 200 h. Detailed cross-sectional examinations, elemental analyses, mass change measurements, and X-ray diffraction studies were performed. It was observed that the oxidation resistances of both alloys were significantly improved by the Al2O3 scale formed on the NiAl layer that was created on the surfaces of the samples during aluminizing. The beneficial effect of aluminizing was found to be more evident in the case of Inconel 738LC alloy samples which showed lower oxidation rates at all test temperatures. The results have been discussed on the basis of the differences in aluminum contents of the alloys and their effects on diffusion
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe 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
Mitomycin C in highly myopic eyes - Author reply
No full textOphthalmology. 2005 Feb;112(2):208-18; discussion 219.
Mitomycin C modulation of corneal wound healing after photorefractive keratectomy in highly myopic eyes.
Gambato C, Ghirlando A, Moretto E, Busato F, Midena E.
SourceRefractive Surgery Service and Antimetabolite Therapy Research Unit, Department of Ophthalmology, University of Padova, Padova, Italy.
Abstract
PURPOSE: To evaluate the role of topical mitomycin C in corneal wound healing (CWH) after photorefractive keratectomy (PRK) in highly myopic eyes.
DESIGN: Prospective, double-masked, randomized clinical trial.
PARTICIPANTS: Seventy-two eyes of 36 patients affected by high (>7 diopters) myopia.
METHODS: In each patient, one eye was randomly assigned to PRK with intraoperative topical 0.02% mitomycin C application, and the fellow eye was treated with a placebo. Postoperatively, mitomycin C-treated eyes received artificial tears (3 times daily, tapered in 3 months), whereas the fellow eye was treated with fluorometholone sodium 2% and artificial tears (3 times daily, tapered in 3 months).
MAIN OUTCOME MEASURES: Uncorrected visual acuity (UCVA) and best-corrected visual acuity (BCVA), contrast sensitivity, manifest refraction, and biomicroscopy. Contrast sensitivity was determined using the Pelli-Robson chart. Corneal confocal microscopy documented CWH.
RESULTS: Mean follow-up was 18 months (range, 12-36). No side effects or toxic effects were documented. At 12-month follow-up examination, UCVAs (logarithm of the minimum angle of resolution) were 0.4+/-0.48 and 0.5+/-0.53 (P = .03) in mitomycin C-treated eyes and corticosteroid-treated eyes, respectively. At 1 year, corneal haze developed in 20% of corticosteroid-treated eyes, versus 0% of mitomycin C-treated eyes. At 12, 24, and 36 months, corneal confocal microscopy showed activated keratocytes and extracellular matrix significantly more evident in untreated eyes (Ps = 0.004, 0.024, and 0.046, respectively).
CONCLUSION: Topical intraoperative application of 0.02% mitomycin C can reduce haze formation in highly myopic eyes undergoing PRK.
Comment in
Ophthalmology. 2006 Feb;113(2):357; author reply 357-8
Dispelling the Myths Behind First-author Citation Counts
No full textWe 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
Effects of Solutionizing and Aging Conditions on the Hardness, Microstructure and Wear Resistance of Cast Fe-Mn-Al-C-Si Lightweight Steel
No full textBu çalışma, çözündürme ve yaşlandırma ısıl işlemlerinin östenit matrisli deneysel döküm Fe-Mn-Al-C-Si hafif çeliğinin mekanik özellikleri ve içyapısı üzerine etkilerini incelemeyi amaçlamıştır. Hedeflenen kompozisyonda ve 6,60 g/cm³ yoğunluğunda dökümler yapılmıştır. Çözündürme işlemleri 950°C-1150°C arasında 2, 4 ve 16 saat uygulanmış, ardından 400°C ile 700°C arasında 4, 16 ve 64 saat yaşlandırma işlemleri gerçekleştirilmiştir. Isıl işlemlerin etkilerini değerlendirmek amacıyla makro/nano sertlik ölçümleri, optik mikroskopi, enerji saçılım spektroskopisi ve elektron geri saçılma kırınımı ile donatılmış elektron mikroskobu, x-ışını kırınım analizleri ve aşınma testleri yapılmıştır. Elde edilen verilere göre, yaşlandırma öncesinde 1000°C'de 4 saat süreyle uygulanan çözündürme ısıl işleminin iç yapısal kararlılık ve mekanik özellikler açısından en uygun sonucu verdiği görülmüştür. 400°C–700°C sıcaklık aralığında 16 saat süreyle uygulanan yaşlandırmanın özellikle sertlik artışı açısından en uygun koşul olduğu söylenebilir. Yaşlandırma işlemleri içyapı içerisinde sertlik artışına katkıda bulunan κ-karbürlerin oluşumuyla sonuçlanmıştır. Ancak, yaşlandırmanın çok uzun süreyle yapılması mekanik özellikleri olumsuz etkilemesi nedeniyle istenmeyen tane sınırı çökeltilerinin oluşumuna yol açmıştır.This study aimed to investigate the effects of solutionizing and aging treatments on the mechanical properties and microstructure of an experimentally cast Fe-Mn-Al-C-Si lightweight steel of austenite matrix. Castings of target composition were made with a density of 6.60 g/cm³. Solutionizing treatments were applied at 950°C-1150°C for 2, 4, and 16 hours, followed by aging at temperatures ranging from 400°C to 700°C for 4, 16, and 64 hours. Macro/nano hardness measurements, optical microscopy, electron microscopy with energy-dispersive spectroscopy, electron backscatter diffraction, x-ray diffraction analyses, and wear tests were performed to evaluate the effects of heat treatments. Based on the obtained data, it was found that solution treatment at 1000°C for 4 hours prior to aging provided the optimum results in terms of microstructural stability and mechanical properties. Aging for 16 hours within the 400°C–700°C temperature range was suggested as the most promising condition, particularly for hardness improvement. Notably, aging treatments resulted in the formation of κ-carbides within the microstructure, contributing to hardness enhancement. However, aging for even longer times induced undesirable grain boundary precipitations, which adversely affected the mechanical properties
Effect of Heat Treatment on the Hardness, Microstructure and Wear Resistance of Cast Fe-Mn-Al-Ni-C Lightweight Steel
No full textDüşük yoğunluklu çeliklere olan ilgi giderek artmaktadır. Bu tez çalışmasında döküm Fe-Mn-Al-Ni-C hafif çeliğinde çözündürme ve yaşlandırma ısıl işlemlerinin içyapı ve mekanik özellikler üzerindeki etkileri araştırılmıştır. Çözündürme işlemleri 850- 1150°C sıcaklık aralığında, 2, 4 ve 16 saatlik sürelerle uygulanmıştır. Takiben, 550°C ve 700°C'de 1, 4, 8 ve 16 saatlik yaşlandırma işlemleri gerçekleştirilmiştir. Isıl işlemlerin etkileri; optik ve elektron mikroskopisi, makro ve nano sertlik ölçümleri, aşınma testleri, EBSD ve XRD analizleri ile değerlendirilmiştir. Döküldüğü haliyle 477 HB olan sertlik, 1150°C'de 2 saat çözeltiye alma sonrası 258 HB'ye düşmüş, yaşlandırma ile %46-%88 oranında artış gözlenmiştir. Faz analizi sonucunda, as-cast numunelerde östenit, B2 ve κ-karbür fazları tespit edilirken, ısıl işlem sonrasında östenit fazı ve B2 fazının farklı morfolojilerdeki çökeltilerinin oluştuğu görülmüştür. Elde edilen sonuçlar doğrultusunda, 1150°C'de 2 saat çözündürme ve ardından 700°C'de 8 saat yaşlandırma işleminin, içyapı homojenliği ve aşınma direnci açısından en uygun ısıl işlem parametreleri olduğu belirlenmiştir.There is a growing interest in steels with low density. This thesis study investigated the effects of solutionizing and aging heat treatments on the microstructure and mechanical properties of cast Fe-Mn-Al-Ni-C lightweight steel with a density of 6.83 g/cm3. Solutionizing treatments were applied in the temperature range of 850-1150°C for 2, 4, and 16 hours. Subsequently, aging treatments were carried out at 550°C and 700°C for 1, 4,8, and 16 hours. The effects of the heat treatments were evaluated by optical and electron microscopy, macro and nano hardness measurements, wear tests, EBSD, and XRD analysis. The as-cast hardness of 477 HB decreased to 258 HB after 2 hours of solution treatment at 1150°C, and an increase of 46%-88% was observed with subsequent aging. XRD analyses revealed the presence of austenite, B2, and κ- carbide phases in the as-cast samples while heat treatment caused significant differences both in the relative amounts and morphologies of these phases. Based on the results, solution treatment at 1150°C for 2 hours followed by aging at 700°C for 8 hours was determined to be the most suitable heat treatment procedure in terms of microstructural homogeneity and wear resistance
A Multi-Language Comparison of Influences on Author Verification using Character N-Grams
No full textWe create a new multi-language corpus for author verification based on Wikipedia talkpages, and evaluate the influence that differences in topic and time have on character n-gram author profiles. Topic alignment between two texts is found to increase author verification precision, and an authors writing style is found to change over time, but not more significantly after 3 years than after 1 year.Information ArchitectureWISElectrical Engineering, Mathematics and Computer Scienc
A 0.12mm<sup>2</sup> Wien-Bridge Temperature Sensor with 0.1°C (3σ) Inaccuracy from -40°C to 180°C
No full text Resistor-based temperature sensors can achieve much higher resolution and energy efficiency than conventional BJT-based sensors [1], but they typically occupy more area (> 0.25 mm 2 ) and have lower operating temperatures (le 125 {circ} {C}) [2]-[4]. This work describes a 0.12mm 2 resistor-based sensor that uses a Wien-bridge (WB) filter to achieve 0.1 {circ} {C} (3 sigma) inaccuracy from - 40 {circ} {C} to 180 {circ} {C}. Compared to a state-of-the-art WB sensor [4], it occupies 6 × less area and achieves comparable relative accuracy over a 76% wider operating range. Session 10.3 Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic InstrumentationMicroelectronic
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