WoS
Permanent URI for this collectionhttps://hdl.handle.net/20.500.14411/18
Browse
1524 results
Search Results
Article Robust Inference for an Interval-Monitored Step-Stress Experiment under Proportional Hazards(Taylor & Francis Ltd, 2026) Balakrishnan, Narayanaswamy; Jaenada, María; Pardo, LeandroAccelerated life tests (ALTs) are widely used in reliability analysis to infer on product lifetimes under normal operating conditions from data collected at higher stress levels. In step-stress ALTs, the stress is increased at predetermined times and kept constant between changes, accelerating failures and reducing test duration and cost. While many ALT studies assume a specific lifetime distribution, some applications require a more flexible formulation satisfying the proportional hazards (PH) assumption, under which stress acts multiplicatively on the hazard rate. In this paper, we study step-stress ALTs under a PH framework with linear and quadratic baseline hazard functions. We focus on settings where continuous monitoring is impractical and failures are observed only at scheduled inspections, yielding interval-censored count data. To achieve robustness and efficiency in this context, we introduce a family of minimum density power divergence estimators (MDPDEs) for model parameters, device reliability, and lifetime measures such as the mean lifetime and distributional quantiles. We derive the corresponding asymptotic distributions and construct approximate confidence intervals. Monte Carlo simulations assess the estimators' efficiency and robustness, and real-data examples illustrate the practical value of the proposed model and inferential methods.Article Robust Inference for Step-Stress Experiments under Interval-Censoring(Springer, 2026) Balakrishnan, Narayanaswamy; Jaenada, María; Pardo, LeandroMany moderns products have a long life before failure. Reliability analyses for such highly reliable devices therefore present a practical challenge as obtaining sufficient failure information to adequately assess lifetime behavior will require extended experimental duration. As an alternative, accelerated life testing (ALT) is commonly used to shorten the time to failure of units under test, with the results subsequently extrapolated to normal operating conditions. This paper provides a comprehensive review of robust inferential methods based on density power divergence for analyzing step-stress ALT data. Point estimates and approximate confidence intervals for model parameters, along with robust estimates of some important lifetime characteristics are developed for general lifetime distributions. Subsequently, explicit expressions are derived for four most prominent parametric lifetime distributions: exponential, Weibull, gamma, and lognormal. A semi-parametric approach based on the proportional hazards model and a competing risks scenario are also discussed as extensions of the proposed model. Throughout the manuscript, several open problems are highlighted, along with significant gaps in the literature, to motivate readers and also to promote further research in this important research area. Moreover, to illustrate the importance of step-stress ALTs and the practical utility of robust estimators, we also present some real data sets used in the literature and analyze one of them using robust methods. By analyzing real data, we demonstrate the stability of the Minimum Density Power Divergence Estimator (MDPDE) for different values of the tuning parameter in the presence of outliers. We also analyze the implications of distributional assumptions on parameter estimation. Confidence intervals, including transformed intervals, are examined, with transformed intervals resulting in confidence levels close to nominal level and also provide better interpretability. Our results highlight the importance of robust estimation techniques in the presence of data contamination and also in a careful selection of parametric models for modeling the lifetime data, as these choices significantly influence predictions of lifetime characteristics under normal operating conditions.Article Real-Time Experimental Investigation of Open- and Closed-Loop Speed Control for a Prototype EV Powertrain Incorporating a 2.2-kW BLDC Motor and Planetary Gearbox(IEEE-Inst Electrical Electronics Engineers Inc, 2026) Doruk, Resat; Hennache, Ali; Abouseda, Ayman Ibrahim; Amini, AliThis study presents an experimental investigation of open- and closed-loop speed control applied to a 2.2 kW brushless DC (BLDC) motor integrated with a planetary gearbox and evaluated under variable-speed and fixed-load conditions. The aim is to characterize the dynamic response, energy-conversion efficiency, and battery state-of-charge (SOC) behavior of the powertrain under real-time control strategies. A complete laboratory platform was developed using a commercial BLDC motor controller, a 60 V-17.4 Ah lithium-ion battery pack, an optical speed sensor, and an eddy-current dynamometer capable of applying load torques from 1.5 to 7.5 N & sdot;m. Open-loop operation regulated speed through direct voltage modulation, whereas closed-loop control was implemented using a proportional-integral-derivative (PID) algorithm executed in real time on a microcontroller. Real-time measurements of voltage, current, torque, and speed were used to compute electrical power, mechanical power, and system efficiency, while battery SOC variation was estimated using the Coulomb-counting method. The results indicate that open-loop control exhibits substantial speed-tracking errors, pronounced transient power surges during speed transitions, reduced efficiency, and an increased SOC depletion rate over the investigated speed range of 1000-2600 rpm. In contrast, the closed-loop PID controller maintains steady-state speed errors within approximately 1 % across all load levels, suppresses current fluctuations, mitigates transient losses, and enhances overall system efficiency by approximately 14-19 percentage points. Closed-loop operation further reduces SOC depletion by 0.49-0.75 percentage points, depending on the applied load torque. These findings demonstrate the effectiveness of feedback control in improving stability, energy utilization, and electric powertrain performance in BLDC-based propulsion systems, with direct relevance to electric-vehicle and hybrid powertrain systems.Article Robust Arrow-Hurwicz Method for High-Rayleigh Number Boussinesq Flow(Springer-Verlag Italia SRL, 2026) Takhirov, Aziz; Eroglu, Fatma G.; Aggul, Mustafa; Ergen, Sinan; Kaya, SongülWe develop and analyze a robust Arrow-Hurwicz (AH) iterative method for the numerical solution of steady Boussinesq flows with nonhomogeneous partitioned Dirichlet boundary conditions. Although a direct AH formulation may be applied to the momentum equation alone, we demonstrate that incorporating an AH-type update for the temperature equation is crucial for stability and convergence in buoyancy-driven systems, particularly at high Rayleigh numbers. The resulting Improved Arrow-Hurwicz (IAH) scheme avoids solving saddle-point systems at each iteration and yields a fully decoupled algorithm with low computational cost per step. We establish existence, uniqueness, uniform boundedness, and convergence under standard small-data assumptions, and provide corresponding error estimates for the finite element discretization. Extensive two- and three-dimensional numerical experiments verify the theoretical findings, demonstrate significant acceleration over the alternative AH scheme and the Penalty-Picard iteration, and confirm robust convergence in high-Rayleigh number regimes. The proposed method offers a scalable and efficient solver for steady natural convection and provides a promising alternative to continuation-based approaches traditionally used for high-Rayleigh flows.Article Rethinking the Second Life of Post-Disaster and Post-Conflict Temporary Housing(Ubiquity Press Ltd, 2026) Ay, Bekir Özer; Dino, İpek Gürsel; Akdede, NilProviding temporary housing (TH) units after natural hazards and social conflicts is often an urgent necessity. Beyond their initial configuration, the second life of these units is crucial, given their temporary nature. Despite growing interest in second-life strategies, many TH units and associated infrastructure remain unused or inefficiently managed after their initial deployment. Second-life strategies are presented for post-disaster and post-conflict (PDPC) TH units and settlements in Türkiye, using two case studies-the 2011 Van earthquakes and Syrians under temporary protection-and expert insights from the Disaster and Emergency Management Presidency of Türkiye (Afet ve Acil Durum Yönetimi Başkanlığı-AFAD). Athree-step methodology was employed, including a literature review, semi-structured expert interviews and hybrid deductive-inductive thematic analysis. Findings reveal that second-life outcomes are largely shaped by policy gaps, operational conditions, tenure constraints, institutional decisions and user practices rather than by design-based circular approaches. The proposed framework provides practical guidance for policymakers and practitioners in Türkiye and other crisis-prone contexts to improve resource efficiency and integrate second-life planning into preparedness and recovery processes.Article Performance of Publicly Supported Technology Transfer Offices in Turkiye: A DEA-MPI-GM(1, N) Approach(Springer, 2026) Belgin, Onder; Apaydin Avsar, BasakTechnology transfer plays a critical role in the commercialization of knowledge generated by research organizations, with Technology Transfer Offices (TTOs) serving as key institutional intermediaries in this process. This study evaluates the efficiency, productivity change and influencing factors of efficiency of publicly supported TTOs by The Scientific and Technological Research Council of Turkiye (TuBİTAK) in Turkiye using a relational multi-period Data Envelopment Analysis (DEA), the Malmquist Productivity Index (MPI) and the GM(1,N) model of Grey Theory. The study covers the period between 2020 and 2022. The inputs are the number of staff and the number of research requests from industry; the outputs are the number of spin-offs, the number of start-ups, the number of applied and granted patents. The results reveal that TTOs in Turkiye have an increasing efficiency and productivity growth from 2020 to 2022. Furthermore, the size of TTOs, the number of contracted university-industry collaboration projects, the age of TTOs and the number of matching activities between researchers and firms organized by TTOs have a positive effect on the efficiency of TTOs. To the best of our knowledge, this study is the first to analyze the performance and influencing factors of efficiency of the publicly supported TTOs using DEA, MPI and GM(1,N) model.Article Investigating Emotional Conveyance in AI-Generated Interior Design: A User Perception Experiment(Gazi Univ, FAC Engineering Architecture, 2026) Hatunoğlu, Doğan Can; Ünal, Bülent; Güneş, ElifPurpose: This study aims to investigate the effectiveness of AI-generated interior environments in conveying specific emotional impressions, focusing on user recognition of core emotions through visual perception. Theory and Methods: Grounded in environmental psychology and emotion theory, the study used MidJourney (v5) to generate 28 hotel lobby images based on six basic emotions and a neutral control. Participants matched each image with a perceived emotion in an online survey. Results: The results indicated high recognition rates for happiness, surprise, and fear, while emotions such as disgust and anger were often misidentified. Spatial cues like light, openness, material, and color were frequently cited as influencing emotional responses. Conclusion: AI-based generative tools can successfully convey certain emotional atmospheres in interior design. However, their ability to communicate more complex or negatively valenced emotions remains limited, suggesting future improvements in AI-human emotional alignment are needed.Article Hybrid Sequential Processing of Mixed Sn-Pb Narrow-Bandgap Perovskite Solar Cells(Royal Soc Chemistry, 2026) Yerci, Selcuk; Dehnavi, Mohammad; Sessolo, Michele; Saygili, Yasemin; Bolink, Henk; Ventosinos, FedericoHybrid vapor-solution sequential deposition of perovskites is a well-established method that enables large-area processing of perovskite films and solar cells. In this study, for the first time, we applied the hybrid sequential deposition method to the fabrication of narrow-bandgap mixed Sn-Pb perovskite films. We obtained compact, large-grained perovskite films with power conversion efficiency values exceeding 10% under 1 sun illumination with hole-transport-material-free devices. The applied method eliminates the oxidative degradation risks of solvents during perovskite formation and provides an easy way to develop additive and passivation strategies to improve photovoltaic properties.Article Hotel Concierge Services: A Comprehensive Legal and TourismBased Analysis(Istanbul Univ, FAC Law, 2025) Erdal, Fehmi Bugra; Hizir, SerdarHotel concierge services play a crucial role in luxury hotels by assisting hotel customers with reservations, ticket purchases, lodging, shopping, and travel planning. Despite their importance, the lack of explicit regulations regarding these services, particularly concerning contractual relationships and liabilities, leads to practical uncertainty. The main purpose of this study is to define and clarify hotel concierges and their services in the hospitality industry from the perspectives of certain fields of law, namely commercial law and law of obligation. In principle, two contractual sources of concierge services exist for hotels. One of these sources is the independent hotel concierge agreement, which explicitly defines the scope of services. Alternatively, provisions related to such services can be included in hotel/accommodation contracts. In practice, a typical service provider is typically hotelier. However, the service is provided by concierges employed at hotels, who generally hold the status of commercial agents with special authority. The hotel concierge agreement can be classified as an atypical, innominate, or imperfectly bilateral contract. As a principle, provisions regarding the contract of mandate are applicable to such agreements. Liabilities arising from concierge services depend on whether the service is provided by hoteliers or by independent professionals. In principle, the hotelier and concierge cannot be held liable for services provided by third parties in connection with the concierge services. A concierge agreement may be terminated by mutual consent, unilateral termination, or the impossibility of performance. If concierge services are part of the hotel/accommodation contract, failure to provide such services may affect the validity of the contract. This study is novel in its aim of drawing attention to the need for more investigation and regulation of hotel concierge services and those providing them, and may serve as a guideline for future attempts in this field.Article Examination of Effective Parenting within the Framework of Domains-of-Socialization Approach: A Qualitative Study in a Turkish Sample(Istanbul Univ, FAC Letters, Dept Psychology, 2025) Yenen, Zeynep Betul; Alsancak-Akbulut, Cansu; Yon, Feyzanur; Saritas-Atalar, Dilek; Metin-Orta, IremAccording to the domain-specific socialization approach, socialization occurs across five different domains -protection, reciprocity, control, guided learning, and group participation - each emerging in response to evolutionary needs and characterized by distinct goals, mechanisms, and outcomes. This study aims to examine how Turkish mothers of children aged 3 to 6 interact with their children across these five socialization domains. To achieve this, mothers participated in the Domain-Specific Parenting Interview (DSPI), a semi-structured interview designed to assess parenting practices in response to their children's needs across different socialization domains. During the interviews, mothers were asked to provide real-life examples and elaborate on their experiences, parenting approaches, emotions, motivations, their children's reactions, and the perceived impact of these interactions. The collected data were analyzed using deductive content analysis, identifying how parenting practices were structured in each domain, their goals, and the potential consequences of these practices. Findings indicate that parent-child interactions differ across socialization domains, and parents use various strategies to transmit social values, emotional regulation strategies, and cultural norms to their children. Furthermore, while parenting practices largely aligned with the core principles of the domain-specific socialization approach, some unexpected tendenciese merged. In conclusion, this study provides comprehensive insights into the real-life applications of the domain-specific socialization approach and highlights how parent-child interactions are shaped by contextual variables.