5916 research outputs found
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Purchasing and remanufacturing decisions with different quality returned material and finished goods
No full textTo transition from a linear to a circular value chain, an effective refurbishment policy is crucial to preserve material value and functionality at the end of a product's life-cycle. This study examines a refurbisher that processes first- and second-quality returned materials to produce first- and second-quality products in a make-to-stock system. The refurbisher makes purchasing decisions for the returned materials and determines whether to refurbish or remain idle, and if refurbishing, how to convert them into finished goods of varying quality. There are five refurbishment decisions (converting first-quality to first- or second-quality, second-quality to first- or second-quality, or no production) and two purchasing decisions for the materials. With production and arrival times modelled as exponential random variables, the optimal control problem is formulated as a Markovian Decision Process, using a long-run average profit criterion to identify optimal decisions. A linear programming approach is employed for numerical optimisation. Results show that the most profitable option based solely on sales prices, purchasing, and conversion costs may not be optimal. Instead, the optimal policy is influenced by per-unit profit differences, returned material availability, demand rates, and production times across various refurbishment scenarios.European Union's Horizon 2020Publisher versio
Signal-dependent shot and relative intensity noise in channel estimation of laser diode-based indoor vlc systems
No full textLaser diode (LD) powered luminaires are already gaining traction in automotive applications and are expected to be increasingly deployed in homes and offices in the near future. This gives a unique opportunity to build visible light communication (VLC) systems with ultra-high-bandwidths offered by the LDs. However, LDs are subject to some inherent noise sources, notably signal-dependent shot noise (SDSN) and relative intensity noise (RIN). RIN basically describes the instability in the power level of a laser and quantifies the output power fluctuations. SDSN arises from variations in the photodetector's response to optical signals. Our research explores the interplay between SDSN and RIN, revealing their combined adverse effect on channel estimation accuracy in a VLC system. Towards this direction, we first derive the Cramer-Rao lower bound (CLRB) in the presence of the SDSN and the RIN, which gives a lower estimate for the variance of an unbiased estimator. Then, we present the derivation of least square (LS) and maximum likelihood (ML) channel estimators. Furthermore, we present the optimal receiver in ML sense and compare it with a simple threshold detector as a sub-optimal solution, quantifying the impact of channel estimation accuracy on both receivers. Our study results reveal the adverse impact of the joint presence of SDSN and RIN on the channel estimation error; consequently, it degrades the BER of the two proposed receivers. Moreover, RIN emerges as the dominant noise source, especially at higher levels of transmitted power.Natural Sciences and Engineering Research Council of Canada (NSERC) CGIA
Enhancing cervical spine health: A vibration-focused multibody dynamics model for neck support system design
No full textNeck injuries can range from mild discomfort to severe disability. Despite the abundance of biomechanical models of the cervical spine in the literature, their capabilities for modal and frequency response analysis are limited. A comprehensive head-cervical spine model was developed to address this gap, enabling frequency domain analysis. A multi-body dynamics (MBD) model with 20 degrees-of-freedom (DoFs) was created using ADAMS software's frequency response analysis capabilities. This model incorporates elements, including vertebrae, ligaments, and muscles. The validation was performed using OpenSim and existing experimental findings. The model was then employed to conduct a Design of Experiments (DoE) study, where key design factors of a conceptual neck support system were varied. Two vibration objective functions were selected to evaluate the parametric designs. The first function identifies the maximum value of the head's acceleration, while the second measures overall vibration within the frequency range of interest. In a case study, the model's capabilities were demonstrated, identifying key design parameters for the neck support system. The methodology has the potential to make significant contributions across multiple industries. Applications range from designing anti-vibration devices to reduce fatigue in the automotive and aerospace sectors to enhancing rehabilitation systems in healthcare, ultimately improving patient exercise effectiveness.TÜBİTA
Use of AI in assembly line design and worker and equipment management: Review and future directions
No full textThe integration of Artificial Intelligence (AI) in manufacturing is a transformation towards increased operational efficiency, adaptability, and sustainability in response to the evolving industrial landscape of Industry 4.0. This study explores the multifaceted role of AI in optimizing manufacturing processes, focusing on its implementation in assembly line configurations, equipment selection, and worker management. We investigate the capabilities of AI to adapt assembly lines to fluctuating product designs and market demands, enhance equipment lifecycle management through predictive maintenance, and optimize workforce allocation based on skills and production needs. Our approach combines a systematic literature review with practical case studies to illustrate current applications and potential advancements AI brings to modern manufacturing. Based on our review of research and current industrial practices, we introduce a novel concept termed AI matchmaking. This tool automates the matching process between available equipment in the market and the specific requirements of factory owners. Our discussions with industry professionals underscore the considerable potential of this tool in facilitating the decision-making processes related to equipment procurement and task allocation. Our work also underscores the need for an integrated approach that considers economic, environmental, and societal sustainability dimensions. This paper highlights not only the technological advancements but also addresses the challenges of data integration, scalability of AI solutions, and workforce adaptation in the context of an increasingly automated industrial environment. Through detailed analysis and discussion, we provide a comprehensive overview of AI's transformative impact on workers and equipment management in assembly lines. We outline potential avenues for future research in which AI can substantially enhance assembly line management. These include developing predictive models to forecast product evolution, optimizing equipment replacement strategies to incorporate second-hand resources, and ethically integrating AI technologies into manufacturing processes, among others.European Commission through the Horizon Europe programm
Assessment of seismic liquefaction and structural instability in Adıyaman-Gölbaşı after the February 6, 2023, earthquakes in Türki̇ye
No full textTwo earthquakes, Mw = 7.8 Kahramanmaraş-Pazarcık, and Mw = 7.6 Elbistan, occurred on February 6, 2023, approximately 9 h apart. These earthquakes caused devastating effects in a total of 11 nearby cities on the east side of Türkiye (Adana, Adıyaman, Diyarbakır, Elazığ, Gaziantep, Hatay, Kahramanmaraş, Kilis, Malatya, Osmaniye, and Şanlıurfa) and the north side of Syria. These earthquakes provided an outstanding prospect to observe the effects of liquefaction in silty sand and liquefaction-like behavior in clays (cyclic softening) on the stability of structures. This paper specifically presents the post-earthquake reconnaissance at three sites and evaluations of four buildings within these sites in Adiyaman Province, Gölbaşı District. First, important role of post-earthquake piezocone penetration test (CPTu) in characterizing the subsurface conditions was presented. Then, the effect of soil liquefaction and cyclic softening on the performance of four buildings during the earthquakes was evaluated. These structures represent the typical new reinforced concrete buildings in Türkiye with 3 to 6-story, situated on shallow (raft) foundations, and demonstrated diverse structural performances from full resilience to moderate and extensive damage during the aforementioned earthquakes. Based on the interim findings from these sites, the potential factors that caused moderate to severe damage to buildings were inspected, and preliminary-immediate insights were presented on the relationship between structural design, soil properties, and the performance of buildings with shallow foundations.TÜBİTAKPublisher versio
Teamwork effectiveness in intensive care units: Development and validation of a brief and reliable assessment tool (TES-ICU)
No full textBackground Effective teamwork is essential for patient safety and quality of care in intensive care units (ICUs), where complexity, high cognitive demands, and multidisciplinary collaboration prevail. Despite its critical role, there is a lack of validated instruments specifically designed to assess teamwork effectiveness in ICUs. This study aimed to develop and validate a context-specific tool-the Teamwork Effectiveness Scale in Intensive Care Units (TES-ICU). Methods The study was conducted in two phases. In Study 1, a comprehensive item pool was generated through literature review and expert evaluation. Items were tested for clarity and distributional properties, and an exploratory factor analysis (EFA) was used to refine the pool. In Study 2, the psychometric properties of the resulting 30-item TES-ICU were evaluated using a nationwide sample of ICU professionals in T & uuml;rkiye (N = 716). Validity was assessed by examining associations with job satisfaction, organizational commitment, burnout, and turnover intention. Reliability was evaluated using Cronbach's alpha. Results EFA revealed a three-factor structure explaining 56.76% of the variance: (1) Teamwork Effectiveness (16 items), (2) Effective Communication and Error Management (11 items), and (3) Effective Leadership (3 items). All subscales demonstrated high internal consistency (alpha > 0.85). The TES-ICU showed strong construct validity; it was positively associated with job satisfaction and commitment and negatively associated with burnout and turnover intention. Conclusions The TES-ICU is a reliable and valid tool to assess teamwork effectiveness in ICU settings. It can guide interventions aimed at improving team dynamics, enhancing staff well-being, and ultimately contributing to better patient outcomes. The 16-item core scale may be used as a shorter form for research or quality improvement efforts.Publisher versio
Turkey's rising tide of dissent: charting the wave of non-legal strikes in the mid-2010s
No full textIn Turkey, legal strikes have been on the decline since the mid-1990s. This is a trend that has accelerated since the mid-2010s under the ruling Adalet ve Kalk & imath;nma Partisi as the government increasingly resorted to banning legal strikes against a backdrop of increasing autocratisation. Nevertheless, the country has witnessed non-legal strikes that are neither formally recognised nor documented. The data collated here through a protest event analysis methodology sheds light on these non-legal strikes, revealing a substantial, arguably historic strike wave in 2015. This study delves into the trajectory, dynamics and outcomes of this strike wave. The fact that workers managed to organise such a significant strike wave demonstrates the continuing relevance of working-class agency in today's world. Particularly noteworthy is that it is primarily the workers themselves, without union support, who organised this strike wave. This working-class agency proved to be effective to a certain extent, demonstrating that its efforts were not in vain. Together with other social movements, the strike wave formed Turkey's rising tide of dissent in the mid-2010s, prompting the regime to resort to further autocratisation to suppress it
The role of drones in disaster response: A literature review of operations research applications
No full textThe increasing use of drones has led to growing interest in their potential applications in disaster response. In this study, we examine the role of drones in disaster management under three categories of operation types, which are information collection, delivery, and communication network recovery. Focusing on an operations research (OR) perspective, we analyze and summarize the important characteristics of different problem structures and highlight the solution approaches. We also identify gaps and limitations in the current literature and propose future directions for further investigation. Overall, the study provides a comprehensive summary and valuable insights for researchers and practitioners interested in exploring the use of drones for humanitarian purposes and developing OR-based approaches to support decision-making.TÜBİTAKPublisher versio
Perceived overqualification, prosocial service behavior, job crafting and person-group fit of the flight attendants: Testing a moderated-mediation model
No full textThis research aimed to comprehend how prosocial service behaviors of flight attendants can be improved in the airline industry, which is a crucial element of competitive advantage in human-centered sectors. We established a model comprising perceived overqualification, prosocial service behavior, job crafting, and person-group fit to achieve this purpose, under the framework of person-job fit theory. 315 flight attendants from two airline companies took part in this research, located in Istanbul, Turkey. IBM AMOS 21.0 software was applied for testing by establishing a structural equation model. The findings indicate that perceived overqualification of employees had a significant direct effect on their prosocial service behavior, as well as an indirect effect through job crafting. Moreover, person-group fit was established as the boundary condition that increases the influence of perceived overqualification on job crafting, displaying a moderated mediation effect. Our model is a novel attempt at the literature, being the first study to investigate the conditional influence of person-group fit in the airline industry under the context of person-job fit theory. This research explains how perceived overqualification can be a source of competitive advantage for companies aiming to excel through customer service by highlighting the importance of person-group fit in this association, which are valuable contributions to theory and practice