Istanbul Technical University
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Advancing Human Geography with GeoAI: Transforming Land Use and Land Cover Analysis
No full texthttps://doi.org/10.1007/978-3-031-87421-5_2
Effect of mandrel position on bending quality in the rotary draw bending process
No full textThe mandrel plays a critical role in supporting tubes within the bending region during tube bending operations. This research explores the impact of varying mandrel positions on bending quality. Therefore, both experimental and finite element analyses were conducted for five different mandrel positions. The study focuses on bending of AA6061-W (water condition) tubes with an outer diameter of 50.8 mm and a wall thickness of 0.889 mm, bent to a radius of 101.6 mm. Conducted experiments revealed ovality values ranging from a minimum of 0.83% to a maximum of 1.81%, depending on the mandrel position. Furthermore, minimum wall thickness measured on the outer side of the tube was 0.686 mm. Additionally, wrinkle and bump formations of varying densities were observed on the tube material, corresponding to different mandrel positions. Results indicate that the mandrel position has a direct effect on the severity of thinning, ovality, bump, and wrinkle formation. The ovality increased as the mandrel was pulled backwards. Finally, the same defect types were detected at similar regions for both finite element and experimental studies which they are in accord.https://doi.org/10.1177/14644207251318362https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=85218143055&origin=inwardhttps://hdl.handle.net/11511/11396
Aftershock Effect on Seismic Behavior of 3D Steel Moment-Resisting Frames
No full textAftershocks are inevitable phenomena following a mainshock, especially after a major earthquake. However, the cumulative damage caused by aftershocks and its impact on structural performance evaluation has only recently received significant attention. This study explores the effects of mainshock–aftershock (MS–AS) sequences, including multiple consecutive aftershocks, acting on 3D steel moment-resisting frame structures. Following nonlinear time history analysis, several fundamental variables such as residual interstory drift, maximum displacement, plastic hinge formation, and base shear are evaluated to examine cumulative damage. In this context, the findings depicted in terms of aftershocks play a significant role in exacerbating plastic deformations and damage accumulation in steel moment frames. Subsequently, to mitigate cumulative damage on steel moment frames, retrofitting strategies were implemented. Retrofitting strategies effectively reduce cumulative damage and improve seismic resilience under multiple earthquake events. This research highlights the limitations of single-event seismic assessments and the need to incorporate sequential earthquake effects in design and retrofit practices. Furthermore, it provides new insights into mitigating further damage by retrofitting existing structures under multiple earthquakes.https://doi.org/10.3390/buildings1515261
Mathematical Modeling on the Strategies of Imperfect Vaccination, Quarantine, and Natural Immunity in a Future Epidemic
No full textABSTRACTIn this paper, we present a mathematical analysis of the extent to which contact measures such as masks and distancing need to be balanced with vaccine efficacy, vaccination rate, natural immunity, and quarantine to mitigate the outbreak in the event of a future pandemic and formulate a method to answer the question of what to implement, when, and how. At the end, we have simulated various strategies from the time that there is no vaccine for different time periods, one after the other, as a course of action in the fight against the pandemic. The model is written as a system of nonlinear ordinary differential equations of nonvaccinated, vaccinated, exposed, quarantined, infected, and recovered individuals. Basic reproduction number and vaccine and quarantine reproduction numbers are determined. It is proven that the disease‐free equilibrium point is locally asymptotically stable if and globally asymptotically stable if there exists such so that . The sensitivity analysis has also been investigated. The derived conditions between constrains state the balance of the effects of vaccine rate, efficiency, contact rate, mask, lockdown policy, and the quarantine rate by the various nature of the virus. The theoretical results are confirmed by simulation of the numerical results. For a future pandemic, the conditions in which natural immunity could play a role in controlling the outbreak is also discussed by simulations.https://doi.org/10.1002/mma.10980https://zbmath.org/808205
Power MOSFET Degradation and Statistical Investigation of the Degradation Effect on DC–DC Converters and Converter Parameters
No full texthttps://doi.org/10.1007/978-3-031-85455-2_
INTERACTIONS BETWEEN NON-NEWTONIAN BLOOD FLOW AND DEFORMABLE WALLS OF A PATIENT-SPECIFIC ANEURYSM
No full textThe movements of the walls of a patient-specific cerebral aneurysm were studied by using fluid–structure interaction approach, where the non-Newtonian blood flow was modeled through the Casson viscosity model and its interactions with the deformable dome were modeled using the finite element method. The coupling was achieved using the preCICE multi-physics toolkit, applying an Arbitrary Lagrangian–Eulerian formulation with Interface Quasi-Newton with Inverse Jacobian from a Least-Squares acceleration for optimum convergence. Given the complex geometry of aneurysms, the Nearest Projection mapping technique was used to handle non-conformal fluid-solid interfaces with enhanced numerical accuracy. Results showed that the uniformity of the flow field seems to be critically important, and its degradation leads to the high values of the von Mises stresses, which in turn lead to high wall displacements. The spatial distribution of the von Mises stress also puts evidence that the maximum values of the von Mises stress exactly coincide with the highest oscillatory shear index and relative residence time, accompanied by the lowest time-averaged wall shear stress values. Furthermore, it is shown that these locations generally overlap with the flow impingement zone. Indeed, during the pulsation cycle, the locations of the maximum displacements ramble around the surface of the dome but are often concentrated over the region of the impingement. This study provides novel results regarding the dynamic wall response of cerebral aneurysms under physiological conditions, highlighting the effects of hemodynamic variations on structural degradation.https://doi.org/10.1142/s021951942550012
Morpholinoethoxy-Substituted Cationic Metal-Free and Metallo Phthalocyanines: In Vitro Photodynamic Therapy Activities, PDT-Induced ROS Level Measurements, and Cellular Death Mechanism
No full texthttps://doi.org/10.1021/acsbiomedchemau.5c00137https://pubmed.ncbi.nlm.nih.gov/40860036/https://pmc.ncbi.nlm.nih.gov/articles/PMC12371505
Deep Data for Deep Soil: Multiscale Prediction of Saturated Hydraulic Conductivity Using Hybrid AI
No full texthttps://doi.org/10.2139/ssrn.560556
A MIMO Antenna Utilizing Modified Apollonian Fractal for Sub-6 5G Wireless Applications
No full textIn this paper, a quad-element multiple-input multiple-output (MIMO) antenna is designed using a modified Apollonian fractal shape for 5G Wireless communication. The proposed antenna comprises four radiating Apollonian fractal elements placed at optimal positions, along with a bottom layer incorporating a segmented ground plane. Each radiating element is composed of a microstrip feed with a quarter-wave transformer to improve impedance matching. The proposed Apollonian fractal-shaped MIMO antenna operates over the frequency range of 3.3–3.8 GHz, achieving an impedance bandwidth where S11 is less than -10 dB and mutual coupling below -20 dB. The envelope correlation coefficient (ECC) remains below 0.05, ensuring excellent diversity performance. Furthermore, the performance parameters of the Apollonian fractal- shaped MIMO antenna are evaluated based on S-parameters, such as the envelope correlation coefficient and channel capacity. Experimental measurements show that the ECC is lower than 0.05, while the channel capacity loss is below 0.6, reflecting reasonable agreement with the simulation results.https://doi.org/10.19072/ijet.154305
Kohezif ara yüzey elemanlar aracılığıyla dairesel yığma kemerlerin sistematik olarak modellenmesi ve kırılma mekanizmalarının belirlenmesi
No full textBu çalışmada, yığma kemerler geliştirilen basitleştirilmiş mikro modelleme tekniği ile modellenmekte ve yığma kemerlerin doğrusal olmayan davranışları 3 boyutlu sonlu elemanlar kullanılarak analiz edilmektedir. Yığma kemerlerin doğrusal olmayan davranışı, kohezif bölge malzemesi (KBM) kullanılarak temas ve hedef elemanlarla elde edilmektedir. Sunulan modelde, yığma kemerleri oluşturan yığma birim sayısı, yığma birimlerin yerleştirildiği açı değeri, kemer üzerinde yükün etki ettiği bölgeler göz önüne alınarak sistematik şekilde ara yüzey elemanlar oluşturulmaktadır. Ayrıca yığma kemerlerin analizlerinde önemli bir aşama olan yığma kemer geometrisinin oluşturulması konusunda pratik bir yaklaşım sunulmaktadır. Böylece farklı geometrik parametrelere sahip yığma kemerler modele kolaylıkla dâhil edilebilmektedir. Oluşturulan model ile hem düzlem içi hem de düzlem dışı davranış incelenebilmektedir. Oluşturulan model ile yığma kemerlerin kırılma mekanizmaları pratik şekilde analiz edilmekte ve model kullanılarak mafsal bölgeleri başarıyla belirlenmektedir. Bu çalışmayla yığma kemerlerin doğrusal olmayan davranışlarının analizine katkı sağlayan bir model sunularak bu yapıların analizleri için pratik olarak kullanılabilir bir çözüm aracı ortaya konulmaktadır.https://doi.org/10.28948/ngumuh.159086