Sabancı University

This study investigates the performance of high entropy alloys [Fe3Cr3Mn2NiV, HEA)] and high entropy oxides [(Fe3Cr3Mn2NiV)O4, HEO)] as electrode materials for supercapacitors. HEA is synthesized through mechanical alloying, followed by HEO forming via an oxidation process. XRD results demonstrate HEA comprises both amorphous and crystalline phases, whereas HEO has an entirely crystalline structure. SEM analyses showed HEA exhibits larger and irregular particles, whereas HEO displays a smaller and spherical morphology. EPR analyses revealed significant changes in defect structures and unpaired electron configurations during the transition from HEA to HEO. HEA is prone to diffusion‐controlled processes due to their regular structure and strong magnetic interactions; however, HEO exhibits capacitive behavior based on surface redox reactions and pseudo‐capacitive mechanisms due to their irregular structure and oxygen vacancies. CV analyses revealed that HEO contributes more capacitive via surface redox reactions, while GCPL results suggested that HEO demonstrated superior energy density (40.8 Wh kg⁻¹) and power density (14.3 kW kg⁻¹). Impedance analyses revealed that HEO exhibited reduced internal resistance and enhanced ion conductivity, whereas HEA demonstrated higher resistance and diffusion‐controlled processes. In conclusion, HEA and HEO exhibit distinct energy storage mechanisms, and these materials can be optimized for supercapacitor applications.

In this article, we use reductions of the Drinfeld modular curves $X_{0}(n)$ to obtain curves over finite fields ${\mathbb {F}}_{q}$ of a given genus with many ${\mathbb {F}}_{q}$-rational points. The main idea is to divide the Drinfeld modular curves by an Atkin–Lehner involution, which has many fixed points to obtain a quotient with a better $\frac{\#\lbrace \text {rational points}\rbrace }{\text {genus}}$ ratio. If we divide the Drinfeld modular curve $X_{0}(n)$ by an involution W, then the number of rational points of the quotient curve $W\backslash X_{0}(n)$ is not less than half of the original number. On the other hand, if this involution has many fixed points, then by the Hurwitz genus formula, the genus of the curve $W\backslash X_{0}(n)$ is much less than half of the $g(X_{0}(n))$.

Transition metal oxides hold great promise across a wide range of applications due to favorable properties such as high abundance, low toxicity, and excellent stability. Nanoengineering approaches are essential for...

Recently, the world saw a wave of elected leaders attack democracy. Why do people support leaders who remove checks and balances? I argue that aspiring autocrats gain more popular support when they present these institutions as obstacles to getting things done. In doing so, they exploit a critical tension between the possibility of gridlock and the abuse of power, which is inherent in democratic institutions. Using cross‐national data and leveraging an original survey experiment from Turkey, I show that effective checks and balances decrease democracy satisfaction and that aspiring autocrats gain more popular support when they present these institutions as obstacles. More interestingly, respondents perceive the aspiring autocrats' gridlock justification to dismantle checks and balances as a pro‐democratic attempt to remove the obstacles to a policy‐responsive regime. These results show that aspiring autocrats exploit the tension in democracies, making it harder for citizens to perceive the threat they face.

Brown dwarfs are failed stars with very low mass (13 to 75 Jupiter mass), and an effective temperature lower than 2500 K. Their mass range is between Jupiter and red dwarfs. Thus, they play a key role in understanding the gap in the mass function between stars and planets. However, due to their faint nature, previous searches are inevitably limited to the solar neighbourhood (20 pc). To improve our knowledge of the low mass part of the initial stellar mass function and the star formation history of the MilkyWay, it is crucial to find more distant brown dwarfs. Using JamesWebb Space Telescope (JWST) COSMOS-Web data, this study seeks to enhance our comprehension of the physical characteristics of brown dwarfs situated at a distance of kpc scale. The exceptional sensitivity of the JWST enables the detection of brown dwarfs that are up to 100 times more distant than those discovered in the earlier all-sky infrared surveys. The large area coverage of the JWST COSMOS-Web survey allows us to find more distant brown dwarfs than earlier JWST studies with smaller area coverages. To capture prominent water absorption features around 2.7 μm, we apply two colour criteria, F115W – F277W + 1 < F277W – F444W and F277W – F444W > 0.9. We then select point sources by CLASS_STAR, FLUX_RADIUS, and SPREAD_MODEL criteria. Faint sources are visually checked to exclude possibly extended sources. We conduct SED fitting and MCMC simulations to determine their physical properties and associated uncertainties. Our search reveals 25 T-dwarf candidates and 2 Y-dwarf candidates, more than any previous JWST brown dwarf searches. They are located from 0.3 kpc to 4 kpc away from the Earth. The spatial number density of 900-1050 K dwarf is (2.0 ± 0.9) × 10 –6 pc –3 , 1050–1200 K dwarf is (1.2 ± 0.7) × 10 –6 pc –3 , and 1200–1350 K dwarf is (4.4 ± 1.3) × 10 –6 pc –3 . The cumulative number count of our brown dwarf candidates is consistent with the prediction from a standard double exponential model. Three of our brown dwarf candidates were detected by HST, with transverse velocities 12 ± 5 km s –1 , 12 ± 4 km s –1 , and 17 ± 6 km s –1 . Along with earlier studies, the JWST has opened a new window of brown dwarf research in the MilkyWay thick disk and halo.

There is a significant unmet clinical need to prevent amputations due to large bone loss injuries. We are addressing this problem by developing a novel, cost-effective osseointegrated prosthetic solution based on the use of modular pieces, bone bricks, made with biocompatible and biodegradable materials that fit together in a Lego-like way to form the prosthesis. This paper investigates the anatomical designed bone bricks with different architectures, pore size gradients, and material compositions. Polymer and polymer-composite 3D printed bone bricks are extensively morphological, mechanical, and biological characterized. Composite bone bricks were produced by mixing polycaprolactone (PCL) with different levels of hydroxyapatite (HA) and β-tri-calcium phosphate (TCP). Results allowed to establish a correlation between bone bricks architecture and material composition and bone bricks performance. Reinforced bone bricks showed improved mechanical and biological results. Best mechanical properties were obtained with PCL/TCP bone bricks with 38 double zig-zag filaments and 14 spiral-like pattern filaments, while the best biological results were obtained with PCL/HA bone bricks based on 25 double zig-zag filaments and 14 spiral-like pattern filaments.

Hematological malignancies originating from blood, bone marrow, and lymph nodes include leukemia, lymphoma, and myeloma, which necessitate the use of a distinct chemotherapeutic approach. Drug resistance frequently complicates their treatment, highlighting the need for predictive tools to guide therapeutic decisions. Conventional 2D/3D cell cultures do not fully encompass in vivo criteria, and translating disease models from mice to humans proves challenging. Organ-on-a-chip technology presents an avenue to surmount genetic disparities between species, offering precise design, concurrent manipulation of various cell types, and extrapolation of data to human physiology. The development of bone-on-a-chip (BoC) systems is crucial for accurately representing the in vivo bone microenvironment, predicting drug responses for hematological cancers, mitigating drug resistance, and facilitating personalized therapeutic interventions. BoC systems for modeling hematological cancers and drug research can encompass intricate designs and integrated platforms for analyzing drug response data to simulate disease scenarios. This review provides a comprehensive examination of BoC systems applicable to modeling hematological cancers and visualizing drug responses within the intricate context of bone. It thoroughly discusses the materials pertinent to BoC systems, suitable in vitro techniques, the predictive capabilities of BoC systems in clinical settings, and their potential for commercialization.

Microparticle production system utilizing a microfabricated nozzle array and piezoelectric technology enables precise and scalable polymeric microparticle production, offering significant improvements in drug delivery systems.

This study investigates the synthesis, structural characterization, and dielectrophoretic alignment of potassium strontium niobate—KSN (KSr2Nb5O15) particles to develop textured 0–3 piezocomposites with enhanced dielectric and piezoelectric properties for tactile sensor applications. KSN particles were synthesized using a molten salt process. Anisometric needle-like morphology of the particles were confirmed by electron microscopy and their single crystalline nature by electron diffraction techniques. Dielectrophoretic alignment under an alternating current (AC) electric field facilitated particle orientation along the [001] c-axis of the tetragonal structure, as confirmed by x-ray diffraction and quantified using the Lotgering factor (f(00l)). An f(00l) = 0.83 was achieved for piezocomposite containing 5 vol% KSN particles and cured under an AC field of 2 kV mm⁻¹ at 200 Hz. Electrical characterization revealed a strong correlation between particle alignment and properties. Compared to random piezocomposites prepared without AC field, increase in dielectric constant of up to two-folds, in polarization of up to ten folds, and in piezoelectric charge coefficient of up to 3 folds were observed in textured piezocomposites. A tactile sensor prototype developed using these textured piezocomposites exhibited voltage output proportional to particle orientation, demonstrating the importance of particle alignment in enhancing the functional properties of piezocomposites.

In this paper, we give a new combinatorial interpretation for the Rogers–Ramanujan–Gordon partitions for k=3. Our interpretation is given by base partition and moves ideas. We conclude the paper with some research questions related to the generalization of this approach.

Thermoresponsive polymers, which undergo phase transitions within physiologically tolerated temperatures, are key to developing drug delivery systems (DDS) with precise spatial and temporal control, potentially addressing challenges associated with the treatment of complex diseases. Inorganic nanoparticles with unique optical, electronic, and magnetic properties serve as efficient transducers, converting external stimuli into localized heat to trigger thermoresponsive nanocarriers. This review explores the design and application of thermoresponsive nanocarriers transduced by inorganic nanoparticles as DDS. Following a brief description of temperature‐triggered phase transition of polymers and heat generation mechanisms by inorganic nanoparticles, strategies to integrate these components into hybrid systems are described. Examples demonstrating the utility of these hybrid systems as advanced DDS are discussed, highlighting their potential for precise drug release alongside theranostic capabilities by combining therapy with imaging. Despite the challenges in design, synthesis, and biological applications, thermoresponsive polymer‐inorganic hybrids hold immense promise for transforming drug delivery and biomedical innovations.

In May and June of 2021, a series of YouTube videos posted by Sedat Peker, a Turkish crime boss, disclosed inside information implicating senior government officials and other public figures in major corruption scandals and crimes. Peker quickly gained popularity and became for the opposition a symbol of the impending fall of the Erdoğan regime. Based on a systematic analysis of these videos and the public debate they engendered, this article argues that the efficacy of Peker’s political campaign depended as much on the stylistic elements and cultural references of his performances as on the grave nature of his allegations about public officials. By showing how the antihero narrative—a genre ubiquitous in contemporary popular culture—is put to use in political performances, the study fills an important gap in narrative genre analysis in cultural sociology.

Hydrogen peroxide (High Test Peroxide, HTP) emerges as a promising candidate for green space propulsion applications due to its lower toxicity compared to liquid conventional propellants such as hydrazine and nitrogen tetroxide. This study aims to optimize the performance and reliability of HTP monopropellant thrusters, focusing on catalyst bed stability, efficiency, and durability during extended steady-state operations. Key parameters, including catalyst bed packing, pellet size, bed load, and HTP concentration, were investigated in this study for their impact on the steady-state performance, using the pressure loss across the catalyst bed as an indicator of catalyst deterioration. Results indicate that an optimal pressure drop of 1–1.5 bar across the catalyst bed provides optimal stability and durability. To evaluate transient characteristics, effects of bed load, HTP concentration, and pre-heating temperature on thruster response times were investigated. Following the optimization process, a lifetime test with an HTP throughput of 6 kg was conducted to monitor performance variations over time. Additionally, the blowdown characteristics of the thruster were analyzed to assess performance under end-of-life conditions. The experiments in this study demonstrate that HTP monopropellant thrusters are viable candidates for reliable space missions, particularly for long-duration operations such as station-keeping maneuvers.

We prove a central limit theorem for smooth linear statistics associated with zero divisors of standard Gaussian holomorphic sections in a sequence of holomorphic line bundles with Hermitian metrics of class ${\mathscr {C}}^{3}$ over a compact Kähler manifold. In the course of our analysis, we derive first-order asymptotics and upper decay estimates for near and off-diagonal Bergman kernels, respectively. These results are essential for determining the statistical properties of the zeros of random holomorphic sections.

We present a new application of multi-orbit cyclic subspace codes to construct large optical orthogonal codes, with the aid of the multiplicative structure of finite fields extensions. This approach is different from earlier approaches using combinatorial and additive (character sum) structures of finite fields. Consequently, we immediately obtain new classes of optical orthogonal codes with different parameters.

This article examines intergenerational educational mobility among various ethnic and religious groups in Turkey. We focus on directional mobility and show that ethnic Kurds have significantly lower upward mobility than ethnic Turks, and Alevis observe marginally higher upward mobility relative to their Sunni counterparts. The region an individual is born into also makes a difference. Those who are born in the eastern part of the country exhibit lower mobility than those who are born in the west. There is a significant difference in mobility between men and women irrespective of their ethnic origin or religious affiliation as well.

Frequency estimation plays a critical role in many applications involving personal and private categorical data. Such data are often collected sequentially over time, making it valuable to estimate their distribution online while preserving privacy. We propose AdOBEst-LDP, a new algorithm for adaptive, online Bayesian estimation of categorical distributions under local differential privacy (LDP). The key idea behind AdOBEst-LDP is to enhance the utility of future privatized categorical data by leveraging inference from previously collected privatized data. To achieve this, AdOBEst-LDP uses a new adaptive LDP mechanism to collect privatized data. This LDP mechanism constrains its output to a subset of categories that ‘predicts’ the next user's data. By adapting the subset selection process to the past privatized data via Bayesian estimation, the algorithm improves the utility of future privatized data. To quantify utility, we explore various well-known information metrics, including (but not limited to) the Fisher information matrix, total variation distance, and information entropy. For Bayesian estimation, we utilize posterior sampling through stochastic gradient Langevin dynamics, a computationally efficient approximate Markov chain Monte Carlo (MCMC) method. We provide a theoretical analysis showing that (i) the posterior distribution of the category probabilities targeted with Bayesian estimation converges to the true probabilities even for approximate posterior sampling, and (ii) AdOBEst-LDP eventually selects the optimal subset for its LDP mechanism with high probability if posterior sampling is performed exactly. We also present numerical results to validate the estimation accuracy of AdOBEst-LDP. Our comparisons show its superior performance against non-adaptive and semi-adaptive competitors across different privacy levels and distributional parameters.

Minimally invasive methods were sought for faster recovery from benign prostatic hyperplasia (BPH) and lower urinary tract (LUTS) symptoms. For this, the search for effective, low-side-effect methods for tissue ablation, particularly for managing BPH and certain bladder pathologies, has been continued to advance. In this regard, the energy released during the formation of hydrodynamic cavitation bubbles offers an alternative treatment method. In this study, we present the feasibility of the use of hydrodynamic cavitation with a flexible cystoscopy device prototype designed for the treatment of LUTS-related diseases. The developed flexible cystoscopy device prototype allows easy access to the urinary bladder through urethra with minimal pain, demonstrating its suitability as a minimally invasive approach. Precisely targeted cavitation exposure prevents prostatic capsule and bladder perforation. Moreover, an automatic actuating mechanism supports steering for real-time visual feedback. The developed device prototype was first tested on an ex vivo human bladder and then on an in vivo porcine bladder. Histopathological analyses were performed after both species were tested. For both analyses, significant tissue ablation at the targets was observed upon exposure to cavitating flows. Finally, the temperature profile on the device was obtained using a thermal camera. Accordingly, it was observed that the temperature increase during the procedure was not significant. The developed device prototype can thus realize mechanical ablation-based therapy, avoids unintended heat deposition which might appear in laser ablation and leads to fewer side effects such as uncontrolled tissue damage and low target area effectiveness that might occur in minimally invasive tissue ablation methods.