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A SIMULATION-ORIENTED APPROACH TO THE DESIGN OF KANBAN INTEGRATED HEIJUNKA SYSTEM
(DAAAM International Vienna, 2025-06-01) Celebi, S.; Yilmaz, O. F.; Yalcin, S. Ene; Ozturk, N.; Mühendislik Fakültesi; Endüstri Mühendisliği Bölümü; AAG-8949-2021; AAG-9336-2021
Heijunka is a Japanese term that refers to a lean manufacturing approach used to reduce variability in production processes. Heijunka also known as production levelling was developed and implemented as a part of the Toyota Production System. The main purpose of Heijunka is to create a lean production process that is least affected by demand fluctuations. This method aims to decrease overproduction by aligning production plan with actual customer demand, avoiding bulk production in batches, and promoting a more balanced production flow. This paper presents a simulation-oriented approach to the design of a Kanban-controlled Heijunka system for the manufacture of automotive seal solutions. With the developed simulation model, the potential outputs of the planning pattern were estimated according to the demand fluctuations. Obtained results show that potential decreases in WIP stock levels and faster deliveries to the customers can be achieved. (Received in October 2024, accepted in March 2025. This paper was with the authors 2 weeks for 1 revision.)
SUTURE RETENTION STRENGTH OF BILAYER VASCULAR GRAFTS MADE OF PCL, PLA AND THEIR COPOLYMER
(2025-01-01) Ozdemir S.; Oztemur J.; Yolgosteren A.; Sezgin H.; Enis I.Y.; ; ;
The mechanical characteristics of small-diameter vascular grafts, including factors like modulus, elasticity, compliance, burst strength, and suture retention strength, need to be in line with those of native blood vessels. Even a slight mismatch in mechanical properties between the graft and the native vessel can lead to graft failure. Suture retention strength, a critical mechanical aspect, represents the force needed to remove a stitch from the graft or cause the graft wall to rupture. This property is vital for preventing leaks, maintaining proper blood flow, aiding tissue healing, ensuring long-term durability, and reducing complications in vascular grafts. In this study, bilayered vascular grafts are fabricated by electrospinning using polycaprolactone (PCL), poly (lactic acid) (PLA), and poly(l-lactide-co-caprolactone) (PLCL) polymers. The actual suturing conditions of vascular scaffolds are simulated and how the choice of polymer for the inner layer affects suture retention strength is assessed. At the post-mechanical stage, the morphologies of the scaffolds are investigated to gain a clearer understanding of how the material reacts to applied forces. The findings reveal that all the fabricated bilayer vascular scaffolds exhibit excellent suture performance, with strength values exceeding 10 N, and that polymer selection for the inner layer for the grafts significantly influences the results. Blending PCL and PLA in the inner layer is found to reduce suture retention strength, while using neat polymers results in better retention strength. This experiment offers a more precise assessment of suture retention strength for bilayer vascular grafts, facilitating further optimization of tissue-engineered grafts to meet specific mechanical requirements.
Evaluating biodegradation rates in neat PCL- and PCL/PLA-based biocompatible tubular scaffolds
(2025-01-01) Janset, O.; Suzan, O.; Havva, T. U.; Gulsah, C.; Hande, S.; Ipek, Y. E.; Ünlü, Havva Tezcan; ÇEÇENER, GÜLŞAH; Tıp Fakültesi; Tıbbi Biyoloji Ana Bilim Dalı; 59742907400; 59743240500
Vascular grafts are synthetic tubular structures that play an important role in replacing damaged vessels in the treatment of cardiovascular diseases. Existing grafts, especially in small-diameter vessels, face persistent issues such as thrombosis, immune rejection, and mechanical limitations. Vascular grafts designed with an innovative perspective to overcome these deficiencies are tubular scaffolds with a biodegradable structure and a layered design that mimics the native artery structure. This study focuses on the development of biodegradable and biocompatible tubular scaffolds with randomly distributed and radially oriented fibers in different layers to replicate the native structure of artery, utilizing neat polycaprolactone (PCL) and PCL/polylactic acid (PLA) blend with 4/1 polymer blend ratio. Electrospinning technique is employed to fabricate tubular fibrous structures. The biodegradation profiles of these scaffolds are assessed at 3, 6, and 9 months, with comparative analyses conducted to explore how polymer type and orientation level influence degradation rates and the structural integrity of the materials over time. The findings reveal that scaffolds with randomly distributed fibers exhibit higher biodegradation rates compared to those with oriented fibers, particularly in the PCL/PLA blends. Specifically, the study identifies PCL_R as having the highest degradation rate at 61% weight loss by the 9th month. Importantly, while PCL is known for its slow degradation, the high molecular weight of PLA leads to a slower degradation profile in the PCL/PLA samples. These insights underscore the critical role of scaffold morphology and composition in optimizing the performance and functionality of vascular grafts, highlighting the need for scaffolds that support cellular activities while effectively degrading to facilitate tissue regeneration without toxic effects.
The relationship between brain drain and human capital: evidence from Turkey
(Emerald Publishing, 2025-06-06) Akyildiz, Ibrahim Ethem; Baskol, Murat Ozan; Eryigit, Kadir Yasin; AKYILDIZ, İBRAHİM ETHEM; BAŞKOL, MURAT OZAN; ERYİĞİT, KADİR YASİN; 0000-0001-6850-115X; JCO-1260-2023; ENE-7933-2022; AAH-1618-2021; 59928338700; 55331482100; 35766379800
Purpose: This study investigates the relationship between brain drain and human capital in Turkey from 1984 to 2022. It aims to identify the macroeconomic and institutional factors influencing skilled labour migration and assess their impact on human capital. The study offers policy recommendations to mitigate brain drain based on the findings.Design/methodology/approach: The study employs the Bai and Perron method to analyse the relationship between brain drain and human capital in Turkey, focusing on economic and institutional factors using annual data from 1984 to 2022. The model estimates structural breaks to capture the time-varying effects of these factors. Findings: The model estimation reveals significant structural breaks in 1994 and 2006. Notably, the increase in human capital from 2006 to 2022 was associated with a rise in brain drain. The findings indicate that macroeconomic factors are the most critical determinants of brain drain, with institutional factors also exerting a significant impact across all sub-periods.Originality/value: This study represents a pioneering effort in Turkey, offering the first comprehensive analysis of the relationship between brain drain and human capital. Integrating econometric methodology with macroeconomic and institutional factors provides a novel and holistic framework for understanding this critical issue. The study provides strategic recommendations for policymakers to preserve Turkey's human capital and prevent brain drain.
Sustainable textiles colored with tea waste in the printing process
(Chamber of Textile Engineers, 2025-01-01) Ordu, Doğa Sude; Başyiğit, Zeynep Ömeroğulları; ÖMEROĞULLARI BAŞYİĞİT, ZEYNEP; İnegöl Meslek Yüksekokulu; Tekstil, Giyim, Ayakkabı ve Deri Bölümü; 0000-0002-1526-8662; 57202916974
The primary aim of the study is to explore the use of tea waste, a natural and sustainable material, as an alternative to synthetic dyes that pose risks to human health and the environment in the printing process of 100% cotton fabrics. For this purpose, tea waste was processed using an extraction method to obtain a natural dye extract, which was then added to the printing paste to carry out the printing process. To enhance the wash durability of fabrics dyed with the natural dye derived from tea waste, a softener formulation was modified by incorporating different ratios of quaternary ammonium compounds. The study investigated the applicability of tea waste extract in dyeing 100% cotton woven fabrics and examined the wash fastness of these fabrics. Fastness tests were conducted on the dyed fabrics in accordance with relevant standards, and the results showed that the fastness values were at the highest levels based on the gray scale evaluation. SEM was employed to perform characterization analyses on tea waste and fabric samples. Additionally, SEM-EDX was used to analyze the elemental composition of the materials. According to thes test results, it was found that cotton fabric dyed using tea waste as a natural dye pigment had the highest K/S value when compared to untreated fabric. Fastness properties did not change significantly after application or washing processes. According to SEM analysis, it was determined that the chemical particles of the printing paste were located between the fibers of the treated samples. By repurposing tea waste for use in textile finishing, the study contributes to the production of sustainable textile products.