Mustafa Istanbullu

Diyot içeren devrelerin analitik çözümü, literatürde kapsamlı biçimde ele alınmış; özellikle Lambert-W fonksiyonuna dayalı çözümler, sayısal çözücüler ve yinelemeli algoritmalar sıklıkla kullanılmıştır. Ancak bu yöntemler ya yüksek hesaplama yüküne sahiptir ya da doğruluktan ödün veren sadeleştirmeler içerir. Bu çalışmada, Schottky diyot denklemini yüksek doğruluk ve verimlilikle çözebilen, analitik ve yinelemeye ihtiyaç duymayan yeni bir yöntem sunulmaktadır. Önerilen yaklaşım, etkin ters doyma akımı I_seff ve üstel katsayı k olmak üzere iki temel parametrenin belirlenmesine dayanan iki aşamalı bir çözüm stratejisi benimsemektedir. Logaritmik temelli formülasyonuyla bu yöntem, doğrudan el ile hesaplamaya olanak tanımakta, böylece sayısal iteratif süreçleri devre dışı bırakmaktadır. Yöntem hem tekli hem çoklu diyot içeren devrelerde test edilmiş, SPICE simülasyonları ve mevcut analitik modellerle karşılaştırıldığında yüksek uyum ve doğruluk sergilemiştir. Elde edilen sonuçlar, diyot akımlarının el ile üç ondalık basamağa kadar hesaplanabildiğini göstermektedir. Ayrıca, diyot durumlarını önceden varsaymadan doğrudan çözüm sunabilmesi, özellikle çoklu diyotlu devrelerde önemli bir avantaj sağlamaktadır. Performans analizleri, yöntemin mevcut analitik yaklaşımlara kıyasla 2,3 kata kadar daha hızlı çalıştığını ortaya koymaktadır.

Biodegradable intravascular stents provide significant clinical advantages by avoiding long‐term complications caused by permanent metallic implants. Nevertheless, their poor radiopacity under X‐ray imaging has remained a major limitation, restricting precise intraoperative placement and reliable follow‐up monitoring. This study addresses the challenge by developing a composite filament composed of polylactic acid (PLA) and uniformly dispersed tantalum (Ta) microparticles at concentrations between 0.1 and 1.0 wt%. Filaments were fabricated through a two‐step extrusion process: twin‐screw compounding for uniform particle dispersion, followed by single‐screw extrusion for consistent dimensional tolerances, enabling fused deposition modeling‐based 3D‐printing. Intravascular stents were designed, printed, and implanted into a multilumen vascular phantom for radiographic evaluation. Radiopacity was assessed qualitatively using angiographic and radiographic imaging under clinically relevant conditions. Results revealed that Ta incorporation significantly improved X‐ray visibility, with optimal reinforcement of 0.75 wt% for angiography and 0.5 wt% for radiography. Above these levels, excess scattering and contrast saturation caused image blurring. The findings validate a scalable, marker‐free strategy that maintains biodegradability while providing real‐time stent visualization during angioplasty and throughout degradation. Additionally, the radiopaque feature facilitates integration with drug‐eluting designs and imaging‐based monitoring. Overall, the PLA–Ta system offers a clinically feasible solution to visibility limitations, enhancing procedural accuracy, complication detection, and patient outcomes.

In this study, a battery case was developed using a 3D (three dimensional)-printed composite of hexagonal boron nitride (hBN) and polylactic acid (PLA) to enhance the thermal performance of lithium-ion battery (LiB) modules. A 10 wt.% amount of hBN was incorporated into the PLA matrix to improve the composite’s thermal conductivity while maintaining electrical insulation. A 3S2P (3 series and 2 parallel) battery configuration was initially evaluated based on the results of a baseline study for comparison and subsequently subjected to a newly developed test procedure to assess the thermal behavior of the designed case under identical environmental conditions. Initially, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were utilized for material characterization, and their results verified the successful integration of hBN by confirming its presence in the hBN-PLA composite. In thermal tests, experimental results revealed that the fabricated hBN-PLA composite battery case significantly enhanced heat conduction and reduced surface temperature gradients compared to the previous baseline study with no case. Specifically, the maximum cell temperature (T_max) decreased from 48.54 °C to 45.84 °C, and the temperature difference (ΔT) between the hottest and coldest cells was reduced from 4.65 °C to 3.75 °C, corresponding to an improvement of approximately 20%. A 3S2P LiB module was also tested under identical environmental conditions using a multi-cycle charge–discharge procedure designed to replicate real electric vehicle (EV) operation. Each cycle consisted of sequential low and high discharge zones with gradually increased current values from 2 A to 14 A followed by controlled charging and rest intervals. During the experimental procedure, the average ΔT between the cells was recorded as 2.38 °C, with a maximum value of 3.50 °C. These results collectively demonstrate that the 3D-printed hBN-PLA composite provides an effective and lightweight passive cooling solution for improving the thermal stability and safety of LiB modules in EV applications.

Electrical impedance-based imaging techniques offer a noninvasive and radiation-free alternative for assessing internal tissue structures. In this study, a novel bioimpedance measurement (BIM) system featuring a planar concentric ring electrode configuration was proposed to improve the spatial resolution and practicality of traditional electrical impedance tomography (EIT) approaches. Inspired by the 360° scanning principle of computed tomography (CT), the system enables multiangle current injection and voltage measurement through a structured stimulation protocol. A total of 32 electrodes, arranged in four concentric rings, were used to capture impedance variations across different angular perspectives, enhancing the detection of localized anomalies. The system was validated through both simulation and experimental studies. Simulations conducted using the EIDORS environment demonstrated successful localization of inhomogeneities within a modeled medium, whereas experimental tests using a saline-filled tank and embedded objects confirmed the system’s practical effectiveness. Data acquired from the system were reconstructed into impedance images via the Gauss-Newton algorithm with total variation regularization, followed by image processing steps for improved visualization and boundary identification. The proposed system combines a cost-effective hardware design with a robust measurement and image reconstruction framework, offering a portable and accurate solution for biomedical diagnostics and laboratory research. The results highlight its potential for clinical and nonclinical applications requiring noninvasive monitoring.

Cardiovascular diseases cause the highest global mortality rates and are often treated with surgical interventions such as stent or vascular plug placement. However, in‐stent restenosis develops over time depending on the material composition and interactions with body fluids. Current strategies to address restenosis include balloon angioplasty or placing a secondary stent at the same site. A key concern with overlapping stents is the increasing risk of galvanic corrosion, as most cardiovascular stents have metallic composition. This study examines galvanic corrosion rates in different vascular stent and plug combinations using electrochemical corrosion characterization techniques. Three metallic vascular specimens with varying compositions are evaluated. The specimens are immersed in simulated body fluid at 37°C under individual and overlapping conditions. Electrochemical impedance spectroscopy and current density measurements, conducted via potentiostat, provide insights into the corrosion behavior of each specimen configuration. Additionally, inductively coupled plasma mass spectrometry quantifies metal ion release through SBF samples. Results show that combining dissimilar materials in overlapping placements significantly increases galvanic corrosion and metal ion release. The corrosion current density (i_corr) significantly increased from 11.75 μA/cm² in the individual bare‐metallic stent to 522.3 μA/cm² in the stent‐on‐plug configuration. A similar increase was observed in the stent‐on‐stent configuration, with an i_corr of 132.6 μA/cm². These results corresponded with notable decreases in electrochemical impedance and polarization resistance, measured as low as 0.039 kΩ (Z_T) and 0.057 kΩ cm² (R_P) for the stent‐on‐plug system. Consequently, the calculated corrosion rate escalated to 2254 μm/year, with a mass loss reaching 42.22 mg/cm²·year. ICP‐MS analysis supported these findings, showing the highest levels of metal ion release in the stent‐on‐plug configuration, with 23.86 ppm of Ni and 0.41 ppm of Cr. These findings highlight the importance of stent‐material selection in reducing corrosion‐related complications. Implementing material‐specific strategies in secondary stent placement can lower the risks of inflammatory host response, stent failure, and their long‐term effects.

Cigarette smoke significantly impacts teeth and dental composites, making smoking simulators vital for studying discoloration, staining, surface roughness, and topography. Conventional simulators face challenges such as incomplete process simulation, inadequate smoke exposure unit design, and improper specimen positioning. This study presents a novel, accurate, and automatic tobacco smoking simulator addressing these issues. The simulator includes a life-sized artificial mouth unit, 3D-printed jaw models for natural dental sample positioning, a vacuum system to simulate positive/negative pressure, and a reprogrammable microcontroller for customizable smoking profiles. Tested with 140 cigarettes over 14 days, the system effectively demonstrated color changes in dental materials. Adjustable parameters such as puff volume, inhalation/exhalation time, smoke density, and smoking speed allow replication of low, moderate, and high-intensity smoking profiles. Portable, low-cost, and versatile, the simulator provides a robust solution for research and education, enabling investigations into the effects of smoke on teeth and dental materials under realistic conditions.

Researchers use smoking simulators to evaluate discoloration, staining, surface roughness, and surface topography issues. Although accurate simulation of the smoking process is crucial to obtain correct measurement results, conventional smoking simulators suffer from significant problems such as partial simulation of the smoking process, inaccurate design in dimensions of the smoke exposure unit, and incorrect positioning of dental specimens. The objective of this study is to design and realization of an accurate and automatic tobacco smoking simulator. The simulator presented here contains an artificial mouth unit, a 3D printed upper/lower jaw model, a vacuum system to generate positive and negative pressure, and a microcontroller-based reprogrammable controlling part to adjust the simulator for different smoking profiles. In this study, the volume of the artificial mouth unit is identical to that of an adult person to ensure appropriate smoke exposure. Dental composites are placed on the 3D printed upper/lower jaw models to provide natural teeth positioning. Furthermore, the innovative vacuum and controlling systems simulate the whole smoking process of an average smoker, which has not been studied yet in the literature. The developed novel system offers a portable, simple, low-cost, and application-specific reprogrammable smoking simulator. Additionally, the proposed simulator can also be employed in education to show the effects of smoke on teeth or any dental materials.

Analytical solution to diode-containing circuits has been investigated for a long time, and many researchers have offered approximations using the Lambert-W function and numerical/iterative methods. However, a simple method without complex calculations and iterations has not been proposed in the literature. This paper proposes a two-step method to model a diode with the Schottky equation and solve the diode circuit with the transcendental equations. The proposed method depends on extracting two fitting coefficients using the LMS algorithm and utilizing them in a logarithm-based hand solution. The proposed solution method is applied to several multi-diode circuits and compared with the SPICE simulations. Diode currents in case studies are calculated by hand with no error by considering three digits after the comma. The proposed method is also compared with the state of art studies and tested with commercially available 40XX series diodes and 1N4532 high-speed diode. The method not only solves the transcendental diode equation but also characterizes the commercially available actual diodes. Case study results and comparisons with the studies in the literature prove the efficiency of the proposed hand solution method for the transcendental diode equation. Besides, the method brings a new approach to the straightforward solution of multi-diode circuits.

In this study, the electrical circuit equivalents of the previously designed novel CNT/MOSFET based active electrode and commonly used wet electrode are simulated by applying different biopotentials. Responses of the electrode models are compared within the certain skin surface circumstances. Fourier transforms and total harmonic distortion calculations of obtained biopotentials are examined to assess the electrodes. The simulation results demonstrate that the CNT / MOSFET based electrode predominates the wet electrode and can measure biopotentials with high quality.