DSpace Arşivi :: Ana Sayfa

İstanbul Gelişim Üniversitesi Kurumsal Açık Erişim Arşivi

DSpace@Gelişim, İstanbul Gelişim Üniversitesi tarafından doğrudan ve dolaylı olarak yayınlanan; kitap, makale, tez, bildiri, rapor, araştırma verisi gibi tüm akademik kaynakları uluslararası standartlarda dijital ortamda depolar, Üniversitenin akademik performansını izlemeye aracılık eder, kaynakları uzun süreli saklar ve yayınların etkisini artırmak için telif haklarına uygun olarak Açık Erişime sunar.

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Free Vibration Analysis of Functionally Graded Nanobeams Via Complementary Functions Method in The Laplace Domain
(SPRINGER, ONE NEW YORK PLAZA, SUITE 4600 , NEW YORK, NY 10004, UNITED STATES, 2026) Alhasan, Ahmed Mohammad Wasfi; Noori, Ahmad Reshad
This study presents a unified framework for the free vibration analysis of functionally graded (FG) nanobeams within Eringen’s nonlocal elasticity, consistently formulated under Euler–Bernoulli (EBT) and Timoshenko (TBT) beam theories. The canonical first-order governing equations are derived in a unified closed-form manner and solved using the Complementary Functions Method (CFM) in the Laplace domain. A comprehensive parametric study addresses four boundary conditions with variations in slenderness ratios, gradation indices, and nonlocal parameters. The primary contribution of this work lies in providing a unified closed-form canonical state-space formulation for nonlocal FG nanobeams under both EBT and TBT, and in demonstrating that the Laplace–CFM implementation offers a stable and efficient eigen-solver with consistent boundary enforcement across multiple support conditions. The resulting benchmark frequencies can serve as a reliable reference for verifying of future refined or multi-physics nanobeam models. The results confirm monotonic frequency softening with increasing nonlocal parameter and with grading toward the softer constituent. The EBT–TBT discrepancy is most pronounced for low-slenderness ratios, highlighting the role of shear deformation and rotary inertia in short/thick nanobeams, while the two theories converge as slenderness increases.
Carbon-Neutral Tri- and Multi-Generation Plants With CO2 Capture Unit İntegrated Modified Gas Turbine, Recuperative Steam Rankine, Absorption Chiller, and MED: Life Cycle Assessment and Multi-Scenario Chameleon Swarm Optimization With Xgboost Modeling
(PERGAMON-ELSEVIER SCIENCE LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, ENGLAND, 2026) Abokhalil, Ahmed G.; Basem, Ali; Balla, Hyder H. Abed; Alkhatib, Omar J.; Abood, Ahmed Sabeeh Abed; Ayadi, Mohamed; Dutta, Ashit Kumar; Bayhan, Zahra; Fouad, Yasser; Mahariq, Ibrahim
The decarbonization of fossil fuel-powered systems remains a critical challenge due to the energy penalties and economic burdens associated with conventional CO₂ capture technologies. This issue is particularly pronounced in tri- and multi-generation systems, where integrating carbon capture without compromising efficiency and profitability requires advanced system-level solutions. Addressing this challenge is essential to enable reliable low-carbon energy supply while meeting increasing demands for electricity, heating, cooling, and freshwater. This study proposes and systematically examines advanced carbon-neutral tri- and multi-generation energy systems featuring deep thermal integration and alternative heat supply strategies for CO₂ capture. Two integration scenarios are investigated: a methane-fueled tri-generation system incorporating a MEA-based CO₂ capture unit (System I), and an extended multi-generation configuration supported by geothermal energy to drive CO₂ capture and desalination (System II). Comprehensive thermo-enviro-economic assessments, gate-togate life cycle assessment, and data-driven multi-objective optimization using XGBoost surrogate modeling and advanced metaheuristic algorithms are employed. System I achieves 54.00% exergy efficiency and 98.78% CO₂ removal, reducing emissions to 21.47 kg/h, while System II further enhances performance, attaining 54.51% exergy efficiency, reducing specific GWP to 0.0179 kg/kWh, and increasing NPV to 14.07 M$. Optimized operation yields exergy efficiency up to 55.28% with minimal economic and environmental impact. The proposed systems provide a scalable and economically viable pathway for deploying carbon-neutral multi-generation plants in industrial and urban energy hubs, supporting long-term decarbonization and sustainable energy transition strategies.
Theoretical and Computational Analysis of A Novel Fractional-Order Mathematical Model For HIV Transmission Dynamics
(ELSEVIER, RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2026) Zakirullah; Shah, Kamal; Khashan, M. Motawi; Abdalla, Bahaaeldin; Abdeljawad, Thabet
We develop a five-class fractional mathematical model to investigate HIV transmission using the Caputo–Fabrizio (CF) derivative. The population is divided into susceptible, acute, chronic, treated and AIDS classes to capture the key stages of HIV progression and the effects of antiretroviral therapy. Existence and uniqueness of solutions are established using the fixed point theorem, a bounded invariant region is identified, and the basic reproduction threshold 𝑅0 is derived using the next-generation matrix. Analytical results demonstrate the local and global stability of both the infection-free equilibrium and the endemic equilibrium. Lower fractional orders are shown to slow convergence to equilibrium, reflecting the memory effects inherent in fractional dynamics. The CF operator therefore provides a flexible and realistic framework for understanding HIV transmission and assessing the influence of treatment, disease progression, and memory effects on long-term epidemic outcomes. The Ulam–Hyers (UH) stability of the considered HIV model under CF derivative is proved. In addition, numerical solutions are obtained by using the Adams–Bashforth method corresponding to the CF derivative. Simulations show that early initiation of antiretroviral therapy, reduced treatment dropout, and improved viral suppression substantially decrease HIV prevalence.
Herd Investing and Market Inefficiency in Forex Markets Over the COVID-19 Outbreak: The Multifractality Analysis
(Springer Nature, 2026) Özdemir, Onur; Yalçıntaş, Selin
This study investigates how the coronavirus pandemic influenced the 5-day-week multifractal characteristics of top five foreign exchange rates - USD/EUR, USD/ GBP, CNY/USD, JPY/USD, and CHF/USD - using weekday index data covering the period from 2 January 2018 to 20 July 2022. The major objective is to determine whether herd investing behavior and the degree of market inefficiency changed between the pre-first-lockdown period (2 January 2018–22 March 2020) and the post-first-lockdown period (23 March 2020–20 July 2022). The generalized Hurst exponents are estimated using the multifractal detrended fluctuation analysis (MFDFA). The empirical findings indicate that multifractality is present in each of the examined exchange rates during the COVID-19 outbreak. Moreover, the degree of market inefficiency varies across the selected spot rates. The results further suggest that the post-first-lockdown period was more prone to herd investing for USD/EUR, USD/GBP, and CHF/USD. In addition, based on the MLM (inefficiency) index, empirical evidence reveals that USD/EUR and CHF/USD became more vulnerable in the post-first-lockdown period. Considering the impacts of this far-reaching global shock, the highest MLM (inefficiency) index value is associated with CNY/USD before the first lockdown and with USD/EUR after the first lockdown.
A Brief Review of the Structure and Extraction Methods of Lignin
(Elsevier B.V., 2026) Yıldırım, Mert
One of the three basic components of lignocellulosic biomass (LB), lignin is the second most plenty of natural polymer on the planet after cellulose. It has the power to become the aromatic raw material of the future for industry. However, this potential has not been fully realized due to its structure has not yet been fully elucidated and its largely underexploited industrial availability. Lignin extraction methods are divided into two main processes are sulfur-containing and non-sulfur-containing. Sulfur processes contain sulfite and kraft (alkaline) pulping methods; the main types of lignin obtained by these methods are kraft lignin and lignosulfonates. Nonsulfur processes contain solvent-based pulping (organosolv) and soda pulping methods; the main types of lignin obtained by these methods are organosolv lignin and soda lignin. In addition to these methods, there are also other chemical-based delignification processes, such as acid hydrolysis from bio-ethanol production and vapor spraying methods with the application of high-temperature and high-pressure steam. In this context, understanding the structure and extraction of lignin is important to fully exploit its potential. This review provides an overview of the structure, chemical properties, and extraction methods of lignin.