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Arakatmanlı sürtünme karıştırma punta kaynağının 304 paslanmaz çelik ve 6061 alüminyum alaşım üzerine uygulanması.
No full textThe Friction Stir Spot Welding (FSSW) is the modification of solid-state welding known as Friction Stir Welding (FSW). During the recent years, FSSW have become the most commonly used welding technique in the automotive, aerospace, and various manufacturing industries. The FSSW process is most suitable welding technique for joining such metals and alloys which cannot be welded using conventional fusion welding techniques. This welding technique can easily be employed to join dissimilar light weight alloys to reduce the weight of the components to manufacture energy efficient vehicles. Several researchers had applied this technique on various similar and dissimilar metal alloys to elaborate the dominance of this technique over other welding techniques and also to investigate the effects of processing parameters on the joint quality. Despite the superiority of this technique, keyhole that appears on the weld spot as a result of pin of the tool is a serious issue and several researchers focused on resolving this problem which results in the development of a novel technique called Interlayer Friction Stir Spot welding (IL-FSSW) which is developed in the Manufacturing Technologies Laboratory within MEMFIS at Ozyegin University. This study comprises of employment of IL-FSSW process in joining similar and dissimilar stainless steel and aluminium alloys. The weld joint fabricated by utilizing IL-FSSW technique has a magnificent surface appearance without any bulk deformation from the weld spot. The keyhole free weld joint has successfully been fabricated by utilizing this technique and this study elaborates the zero effect of the welding parameters on the surface appearance of the weld spot. The utilization of flat tip tool and intermediate layer helps to fabricate flat weld joint without keyhole in comparison of conventional FSSW techniques. The utilization of intermediate layer (IL) played an important role in improving the lap shear force (LSF) which is 1.5 times greater than the required limit of American Welding Society (AWS) standards and some of the welded samples showed 2 times higher LSF than the minimum required limit. To investigate the effect of operating parameters on the microstructures and mechanical behaviour of the weld joint Design of Experiments (DOE) based on Taguchi model L8 and L9 is developed for AISI304 stainless steel similar joint and Al6061/AISI304 dissimilar joint respectively, by using three parameters as variable by keeping other parameters constant and these three parameters as tool rotation speed, plunge depth and IL diameter. The analysis of variance (ANOVA) statistical model on the basis of lap shear force values elaborated that tool rotation speed has greatest influence on the joint strength. The mechanical behaviour of the weld joint was examined by utilizing tensile testing and Vicker's Hardness tests. Optical Microscopic analysis and micro-hardness tests performed on the nugget zone of AISI304 similar joint and Al6061/AISI304 dissimilar joint helped to discriminate the stir zone (SZ), thermomechanical affected zone (TMAZ), heat affected zone (HAZ) and base metal (BM) as micro-hardness values are different for each zone and OM differentiate these zones on the basis of average grain size (AGS). Scanning electron Microscopy (SEM) of the fracture surface for Al6061/AISI304 weld joint shows intergranular and transgranular fracture behaviour. The lap shear tensile tests showed that tool rotation speed and plunge depth have direct relation with lap shear force as with increasing tool rotation speed and plunge depth LSF is also increasing. The linear relation of plunge depth with LSF is up to certain limit because after that the thickness of spot weld starts to decrease which decrease the LSF as well. The OM analysis indicated the hook formation of intermediate layer with upper sheet and this hook formation plays important role in improving the strength of the weld joint.Sürtünme Karıştırma Nokta Kaynağı (SKNK), Sürtünme Karıştırma Kaynağı (SKK) olarak bilinen yöntemin katı hal kaynak modifikasyonudur. SKNK, son yıllarda otomotiv, havacılık gibi farklı endüstrilerde yaygın olarak kullanılan bir kaynak metodu haline gelmiştir. SKNK işlemi, geleneksel ergitme kaynağı teknikleri ile kaynak yapılamayan metal ve metal alaşımlarının birleştirilmesi için kullanılan en uygun metot olarak bilinmektedir. Bu kaynak tekniği, enerji verimliliği yüksek araçların üretiminde kullanılan bileşenlerin ağırlığını azaltmak amacıyla farklı ve hafif alaşımların birleştirmesi için kolaylıkla uygulanmaktadır. SKNK yönteminin diğer kaynak metotları ile karşılaştırılarak daha iyi sonuçlar elde edildiğini göstermek ve işlem parametrelerinin kaynak kalitesine etkisini araştırmak amacıyla hem aynı hem de farklı metal alaşımlar kullanılarak birçok çalışma yapılmıştır. Bu yöntemin diğer kaynak yöntemlerine göre sunduğu birçok avantaja rağmen, kaynak işlemi sonrasında kaynak pininin parça üzerinde anahtar deliği şeklinde bir iz oluşturması büyük ölçüde bir sorun olarak görülmekte ve birçok araştırmacı bu konunun çözümü üzerinde çalışmaktadır. Tüm çalışmalar sonucu yeni bir yöntem olan Orta Katmanlı Sürtünme Karıştırma Nokta Kaynağı (OK-SKNK) adı verilen metot ilk defa Özyeğin Üniversitesi İmalat Teknoloji Laboratuvarı'nda geliştirilmiştir. Bu çalışma, benzer ve farklı paslanmaz çelik ve alüminyum alaşımlarının OK-SKNK yöntemi kullanılarak birleştirilmesini içermektedir. OK-SKNK tekniği kullanılarak üretilen kaynak bağlantısı, kaynak noktasında herhangi bir deformasyon olmadığı için düzgün bir yüzeye sahiptir. Bu kaynak metodu kullanılarak anahtar deliği görüntüsü içermeyen bir kaynak bağlantısı başarıyla elde edilmiştir. Bu çalışmada kaynak parametrelerinin, kaynak noktasının yüzey görünümü üzerinde herhangi bir etki oluşturmaması detaylandırılmıştır. Düz uçlu aletin ve ara katmanın kullanılması, geleneksel SKNK teknikleri ile karşılaştırıldığında, anahtar deliği olmadan, düz kaynaklı bir bağlantının üretilmesine yardımcı olmaktadır. Ara katmanın (OT) kullanılması, AWS standartlarından 1,5 kat daha fazla olan bindirme kesme kuvvetinin (LSF) geliştirilmesinde önemli bir rol oynamış ve kaynaklı numunelerin bazıları, gerekli minimum değerden 2 kat daha fazla LSF göstermiştir. Bu tezde çalışma parametrelerinin kaynak bağlantısının mikro yapısı ve mekanik davranışı üzerindeki etkisini araştırmak için Taguchi modeline dayalı Deney Tasarımı (DOE) yöntemi kullanılmıştır ve diğer parametreler sabit tutulmak koşulu ile takım dönüş hızı, dalma derinliği ve OT çapı değişken olan üç parametre olarak belirlenmiştir. Varyans analizi (ANOVA) istatistiksel modeli ile yapılan çalışmada LSF değerleri temel alınarak, kaynak mukavemeti üzerinde en büyük etkiye sahip olan parametre takım dönüş hızı olarak tespit edilmiştir. Kaynak bağlantısının mekanik davranış analizi, çekme testi ve Vickers sertlik testleri kullanılarak yapılmıştır. AISI304 benzer ve Al6061/AISI304 benzer olmayan kaynakların, optik mikroskop (OM) analizleri ve mikro sertlik testleri sonucunda, kaynak merkezi (KM), termomekanik etkilenen bölge (TMEB), ısının tesiri altındaki bölge (ITAB) ve ana metal (AM) bölgelerinden elde edilen sertlik değerleri ve OM ile belirlenen tane boyutlarındaki farklılıklardan faydalanarak, bu bölgeler belirlenmiştir. Al6061/AISI304 kaynaklarının kırılma yüzeyleri Taramalı Elektron Mikroskobu (SEM) ile incelenmiş ve taneler içi ve taneler arası kırılma davranışları görülmüştür. Bindirme kesme çekme testleri, artan takım dönüş hızı ve dalma derinliği LSF'nin de arttığı gibi, takım dönüş hızı ve dalma derinliğinin de LSF ile doğrudan ilişkili olduğunu göstermiştir. Dalma derinliğinin LSF ile orantılı artışının belirli bir sınıra kadar olduğu gözlemlenmiştir. Bu durum sınırdan sonra nokta kaynağının kalınlığının azalmaya başladığı ve bunun da LSF'yi azalmasına neden olması ile açıklanmıştır. OM analizi, üst sac ile ara tabakada kanca şeklinde bir oluşumu göstermiştir ve bu kanca oluşumu, kaynak bağlantısının mukavemetini arttırmada önemli bir rol oynamaktadır
A comparative evaluation of propagation characteristics of vehicular VLC and MMW channels
No full textVehicle-to-vehicle (V2V) communication is an underlying key technology to realize future intelligent transportation systems. Both millimeter wave (MMW) communication and visible light communication (VLC) are strong candidates to address V2V connectivity. Most of the earlier literature focuses on an individual technology. In an effort to better highlight the differences and relative advantages of these two competing technologies, we provide a comprehensive one-to-one comparison between vehicular VLC and MMW channels in this paper. For this purpose, we utilize ray tracing simulations which enable the consideration of three-dimensional modeling of the propagation environment and allow the study of various system parameters and road conditions in both line-of-sight and non-line-of-sight conditions. Under the same settings, we present the received signal strengths for both systems and investigate the channel characteristics for communication between two vehicles in the same lane as well as in different lanes with a lateral shift. We also analyze the impact of low, medium, and high density of neighbor vehicles as well as partial and complete blockage
A longitudinal case study on Nexus transformation: Impact on productivity, quality, and motivation
No full textThere have been success stories reported regarding the adoption of agile software development methods in the industry. There also exist observations on their limitations. One of these limitations is scalability since agile methods like Scrum were originally designed for small software teams. Scalable agile frameworks were introduced to address this limitation. We conducted an industrial case study on the adoption of such a framework, called Nexus. Our study involves quantitative and qualitative evaluation based on observations within a product development organization over a period of 12 months. Scrum is used for the development of a product during the first 6 months of this period. Nexus is used in the remaining 6 months. Data are collected throughout the whole period for measuring productivity, quality, and team member motivation. Results suggest a significant increase in productivity and product quality after switching to Nexus. Team motivation was slightly improved as well
Multi-criteria decision-making model for risk management in modular construction projects
No full textThe modular sector needs a precise guide to determine the most efficient risk management approaches. The main research objective of this study is to develop a multi-criteria decision-making model to find the most efficient risk management approach according to the relevant risk criteria. The risk criteria and risk management approaches for modular construction projects were also identified and classified within this scope. A systematic literature review, semi-structured interviews, and open-ended questionnaires were performed for identification and classification purposes. For ranking and quantifying the identified risks and risk approaches, as well as developing the decision-making model, the Delphi method and the Analytical Hierarchy Process (AHP) were conducted. A two-round Delphi method, with eleven experts, was conducted to achieve efficient performance scores of the identified risk management approaches. The percentage standard deviation decreased, Relative Importance Index (RII), Cronbach’s alpha, and Kendall’s coefficient of concordance (Kendall’s W) were calculated to ensure the outputs’ reliability, validity, and agreement level. The AHP method opted to quantify the Delphi method outputs, solve the multi-criteria decision-making process, and develop the multi-criteria decision-making model for risk management of modular construction projects. Triangulation results show that the critical risk categories are supply chain, health and safety, stakeholders, and governmental support. Lean principles such as the Last Planner System, Value Stream Mapping, Just in Time, and Kaizen are top-rated risk management approaches. This research’s novelty is identifying and analyzing crucial risk categories, providing the relevant risk management approaches ranked according to efficiency performance, and presenting a decision-making model as a guideline for risk management of modular construction projects
Lump solutions of the fractional Kadomtsev–Petviashvili equation
No full textOf concern is the fractional Kadomtsev–Petviashvili (fKP) equation and its lump solution. As in the classical Kadomtsev–Petviashvili equation, the fKP equation comes in two versions: fKP-I (strong surface tension case) and fKP-II (weak surface tension case). We prove the existence of nontrivial lump solutions for the fKP-I equation in the energy subcritical case α>45 by means of variational methods. It is already known that there exist neither nontrivial lump solutions belonging to the energy space for the fKP-II equation [9] nor for the fKP-I when α≤45 [26]. Furthermore, we show that for any α>45 lump solutions for the fKP-I equation are smooth and decay quadratically at infinity. Numerical experiments are performed for the existence of lump solutions and their decay. Moreover, numerically, we observe cross-sectional symmetry of lump solutions for the fKP-I equation.Wallenberg foundationPublisher versio
Teaching earthquake-resistant structural systems in architecture department: a hands-on learning experience
No full textThis paper addresses challenges in teaching earthquake-resistant structural systems to architecture students and seeks to enhance efficiency. Developing a compatible teaching approach is crucial for better collaboration with engineers. The impact of a lack of knowledge about earthquake-resistant systems is more evident in quake-prone regions. The study highlights the importance of hands-on experience in teaching structural theory, fostering better learning and comprehension. The study showcases an undergraduate-level course that diverged from traditional exams. Instead, students undertook a project where groups designed scaled models representing different structural responses, which underwent testing on a handmade shake table. Analysis highlighted demonstrations of various responses like soft stories, dynamic behaviour, pounding and weak columns. The hands-on approach enriched students’ practical insights into structural behaviour, aiding informed design choices. This approach enhances overall learning, deepens comprehension, and readies students to apply seismic design principles conscientiously. Learning by doing proves pivotal in mastering earthquake-resistant structural systems
A framework for explainable multi-purpose virtual assistants: a nutrition-focused case study
No full textExisting agent-based chatbot frameworks need seamless mechanisms to include explainable dialogic engines within the contextual flow. To this end, this paper presents a set of novel modules within the EREBOTS agent-based framework for chatbot development, including dialog-based plug-and-play custom algorithms, agnostic back/front ends, and embedded interactive explainable engines that can manage human feedback at run time. The framework has been employed to implement an explainable agent-based interactive food recommender system. The latter has been tested with 44 participants, who followed a nutrition recommendation interaction series, generating explained recommendations and suggestions, which were, in general, well received. Additionally, the participants provided important insights to be included in future work.Chist-Era ; Swiss National Science Foundation (SNSF) ; TÜBİTA
Right-wing populism in Turkey and the 2023 elections
No full textThis article examines right-wing populism in the May 2023 elections of Turkey, mainly focussing on the Justice and Development Party (Adalet ve Kalkinma Partisi-AKP). Using the ideational approach of populism, I first briefly examine the AKP's predecessors, the Democratic Party (Demokrat Parti-DP) and the National Outlook (Milli Gorus) movement, which exploited the divide between secular elites and devout Muslims, based on a cultural conflict between two contrasting visions of a good society rooted in secularism and Islam. The AKP carries three characteristics of populism: people-centrism, anti-elitism, and a Manichean outlook, widely applied in the party's discourse during recent elections. This study illustrates the fact that populism in Turkey damages the democratic game, where opponents are seen as legitimate rivals, as evidenced in the country's democracy scores. Also, right-wing populism during the 2023 elections depicted the opposition as illegitimate enemies, both non-native and non-national, illustrating the moralistic imagination of politics
Machine learning prediction of Gleason grade group upgrade between in-bore biopsy and radical prostatectomy pathology
No full textThis study aimed to enhance the accuracy of Gleason grade group (GG) upgrade prediction in prostate cancer (PCa) patients who underwent MRI-guided in-bore biopsy (MRGB) and radical prostatectomy (RP) through a combined analysis of prebiopsy and MRGB clinical data. A retrospective analysis of 95 patients with prostate cancer diagnosed by MRGB was conducted where all patients had undergone RP. Among the patients, 64.2% had consistent GG results between in-bore biopsies and RP, whereas 28.4% had upgraded and 7.4% had downgraded results. GG1 biopsy results, lower biopsy core count, and fewer positive cores were correlated with upgrades in the entire patient group. In patients with GG>1, larger tumor sizes and fewer biopsy cores were associated with upgrades. By integrating MRGB data with prebiopsy clinical data, machine learning (ML) models achieved 85.6% accuracy in predicting upgrades, surpassing the 64.2% baseline from MRGB alone. ML analysis also highlighted the value of the minimum apparent diffusion coefficient (ADC(min) GG>1 patients. Incorporation of MRGB results with tumor size, (ADC(min)) for GG >1 value, number of biopsy cores, positive core count, and Gleason grade can be useful to predict GG upgrade at final pathology and guide patient selection for active surveillance.Publisher versio
Association of visual-based signals with electroencephalography patterns in enhancing the drowsiness detection in drivers with obstructive sleep apnea
No full textIndividuals with obstructive sleep apnea (OSA) face increased accident risks due to excessive daytime sleepiness. PERCLOS, a recognized drowsiness detection method, encounters challenges from image quality, eyewear interference, and lighting variations, impacting its performance, and requiring validation through physiological signals. We propose visual-based scoring using adaptive thresholding for eye aspect ratio with OpenCV for face detection and Dlib for eye detection from video recordings. This technique identified 453 drowsiness (PERCLOS ≥ 0.3 || CLOSDUR ≥ 2 s) and 474 wakefulness episodes (PERCLOS < 0.3 and CLOSDUR < 2 s) among fifty OSA drivers in a 50 min driving simulation while wearing six-channel EEG electrodes. Applying discrete wavelet transform, we derived ten EEG features, correlated them with visual-based episodes using various criteria, and assessed the sensitivity of brain regions and individual EEG channels. Among these features, theta–alpha-ratio exhibited robust mapping (94.7%) with visual-based scoring, followed by delta–alpha-ratio (87.2%) and delta–theta-ratio (86.7%). Frontal area (86.4%) and channel F4 (75.4%) aligned most episodes with theta–alpha-ratio, while frontal, and occipital regions, particularly channels F4 and O2, displayed superior alignment across multiple features. Adding frontal or occipital channels could correlate all episodes with EEG patterns, reducing hardware needs. Our work could potentially enhance real-time drowsiness detection reliability and assess fitness to drive in OSA drivers.TÜBİTAKPublisher versio