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A chemical and biological characterization of marine mucilage that generates electricity in microbial fuel cells
No full textThe marine mucilage that emerged in the Marmara Sea in the spring of 2021 caused various environmental problems by affecting the sea surface and bottoms. In this study, a new approach for the electricity generation potential of marine mucilage and its remediation from the sea using microbial fuel cells was investigated for electricity generation, and chemical and biological characterization were demonstrated. The total carbohydrate amount, protein amount, optical density pH analyzes, and their removal before and after the operation were analyzed; In addition, the electrochemical and biochemical characterization of mucilage was indicated. Our results showed that electricity can be generated using marine mucilage in single-chamber microbial fuel cells. The highest current density was 0.0527 mA/cm2, the highest power density was 191.63 mW/m2, and the voltage was 394 mV. The total carbohydrate removal of the mucilage pretreated with sodium phosphate buffer was 20.57%. Proteobacteria was the dominant phylum represented by 55.75% of the reads. Rhodobacteraceae, Alteromonas, and Nonlabens genera were the most dominant groups with 8.63%, 8.28%, and 8.08%, respectively, in the mucilage sample. In conclusion, electricity can be produced in microbial fuel cells using marine mucilage, and this novel technology could help reduce marine pollution
Bent partition, vectorial dual-bent function and LP-packing constructions
No full textWe present secondary constructions of vectorial functions respectively partitions of elementary abelian groups, which simultaneously yield vectorial dual-bent functions with certain properties, bent partitions, and under some conditions, Latin square partial difference set packings (LP-packings). First, we analyse constructions via the direct sum of vectorial functions and then present a version of the generalized Maiorana-McFarland construction. Next, we generalize a construction of vectorial dual-bent functions by Wang, Fu, and Wei (2023). Finally, we use a lifting procedure of LP-packings from Jedwab and Li (2021) to construct vectorial dual-bent functions, bent partitions, and LP-packings in elementary abelian groups. With these constructions, a large variety of vectorial bent functions, bent partitions, LP-packings, and related amorphic association schemes can be obtained
In-situ acoustic emission based technique for damage detection and identification and failure mode prediction in scarf repaired composite structures
No full textOne of the great challenges facing adhesively bonded repair procedures in the industry is the absence of a reliable structural health monitoring technique to ensure that the repaired region is intact during service. To this end, this paper proposes a novel in-situ acoustic emission-based methodology to detect and identify damages as well as to predict failure modes at early stages. In this essence, two tapered-scarf repaired plates are produced with different patch materials. The first patch consists of neat carbon fiber prepregs whereas in the second thermally exfoliated graphene oxide integrated carbon fiber prepregs are utilized. Testing the constituents of the repair system individually while monitoring their acoustic activity makes it possible to separate each damage type precisely. Hence, when the specimens of the repaired panel are tested, very detailed information is revealed regarding the current structural status of the specimen and probable failure scenarios. The effectiveness and robustness of the proposed methodology in detecting and identifying damages of varying severity in addition to predicting the failure scenario are verified in the composite panels repaired with pristine and graphene integrated patches
Morphological impact on the supercapacitive performance of nanostructured ZnO electrodes
No full textThis study investigated the influence of the ZnO morphology on the energy storage capacity of symmetric supercapacitor devices, focusing on the defect centers present in the materials due to morpho-structural differences. Thus, ZnOs with five different morphologies were synthesized with varying methods in which the nanoparticles have the form of flowers, bullets, pyramids, hexagons, and rods. All materials were thoroughly characterized by scanning/transmission electron microscopy, X-ray diffraction, and spectroscopic techniques like photoluminescence, UV–Vis, Raman, and electron paramagnetic resonance spectroscopy. Subsequently, the ZnO-based materials were assembled in symmetric supercapacitor devices to test their energy storage capabilities. The ZnO with nanorod and hexagonal morphologies showed the best specific capacity (180 and 142 F/g), energy density (25 and 19 Wh/kg), and power density (211 and 252 kW/kg) values. The importance of the defect centers in the materials was highlighted, where the ratio between the Zn and O vacancies, evidenced by EPR spectroscopy, plays a crucial role in the ZnO materials’ energy storage capacity. The Raman results support the proposed model, which underlines the importance of oxygen vacancies. In contrast, BET measurements show that the specific surface area of the morphologically distinct ZnO materials does not change drastically, validating the importance of the defect centers in the materials. A so-called “bottle-neck” effect is proposed to describe the relation between the paramagnetic vacancies and the electric properties of the materials
Synergy between MgO and TiO2 doped with Mn2+ ions for supercapacitor applications
No full textSupercapacitors are unique energy storage devices that bridge the gap between Li-ion batteries and conventional capacitors with higher power/energy densities, longer life cycles, and more rapid charge/discharge rates. Research efforts are concentrated on optimizing the performance of supercapacitors (SCs), addressing a crucial component of these devices: the electrode materials, which should provide large active surface areas, display high electrical conductivities, and possess stable chemical properties. To achieve this, in this study, undoped and Mn-doped MgO−TiO2 nanocrystals and coffee-waste-derived carbon were used as electrode materials for symmetric and asymmetric supercapacitors yielding adequate performance. The structural study was performed by X-ray diffraction and Raman analysis, showing a phase mixture of tetragonal Anatase TiO2, cubic MgO, and orthorhombic MgTi2O5 nanocrystals. Electron paramagnetic resonance and photoluminescence spectroscopy analysis were used to provide insight into the defective structure of the composites. The electrochemical performance was tested by cyclic voltammetry, impedance, voltage holding, and galvanostatic cycling with potential limitations. The SCs exhibited promising results for specific capacitances up to 100 and 221 F/g for symmetric and asymmetric (containing coffee-waste-derived carbon as a counter electrode) supercapacitor devices, respectively. At the same time, enhanced energy and power density values of 30.7 Wh/kg and 122.8 kW/kg were reached
Top management teams hierarchical structures: an exploration of multi-level determinants
No full textAlthough the role structure of top management teams (TMT) is a relevant topic in strategic leadership research, the hierarchical structure of TMTs still needs to be explored. In this study, we conduct an exploratory analysis to understand better how TMTs are hierarchically structured and what drives different hierarchical configurations across TMTs. Our empirical analysis of 260 Standard & Poor firms between 2007 and 2018 offers unique insights. Primarily, we discover that even though TMT sizes remained constant between the years of observation, they became less hierarchical in structure, meaning that TMTs became relatively flatter. Moreover, we find that several factors related to CEO characteristics, strategic leadership, corporate governance, and firm and environmental conditions drove the changes in the hierarchical structure of TMTs. These combined empirical insights call for nuanced theoretical explanations of TMT hierarchical structures. We contribute to the TMT literature mainly by highlighting the development of different TMT hierarchical structures and providing new insights into their determinants
Thermodynamic analysis of the inverse electrocaloric effect in ferroelectric thin films
No full textInverse electrocaloric (i-EC) effect occurs in ferroelectrics when the applied electric field aligns anti-parallel to polarization. In this study, the dependence of the i-EC effect on temperature and misfit strain is formulated and applied to clamped BaTiO3 thin films using the Landau-Ginzburg-Devonshire formalism. It is found that an interplay exists between the pyroelectric coefficient and the maximum possible inverse electric field. We demonstrate that the temperature change is strongly dependent on the inverse field amplitude and is maximal at lower temperatures away from the ferroelectric-paraelectric transition for a given misfit strain. Such an outcome is opposite to the direct electrocaloric effect, where it is desirable to remain near the transition temperature for the maximum electrocaloric temperature change. The fact that the i-EC effect can be maximum at lower temperatures could allow for the potential tailoring of this effect in strained films at moderate temperatures for device applications
Fields into houses: local actors, society, and the making of a new urban landscape in Tarlabaşı and Tatavla in late Ottoman Istanbul
No full textIn the late nineteenth and early twentieth centuries, as Istanbul’s modernization led to its expansion northward from Galata, uninhabited or sparsely inhabited areas evolved into a dense urban sprawl. This urbanization process has been studied primarily through the lenses of architectural history and urban studies while broader historical examinations have often concentrated on state planning and administrative reorganization. This article, however, explores the role of local agency in driving these changes, highlighting the active participation of diverse social actors in shaping the new urban landscape. It argues that wide sections of society did not merely react to change, but they created, perceived and acted upon new urban opportunities. Specifically, the article weaves together the role of property owners and entrepreneurs, professional and occupational sectors, lower-income groups and local communities in constructing, renting and utilizing urban spaces. Focusing on the Tatavla and Tarlabaşı neighborhoods, which were key areas in the immediate growth zone of the city, the article draws on state and community records, contemporary histories, memoirs and maps
Highly linear wideband low-noise amplifiers for sub-6 GHz using cascode and diode-connected postdistortion circuits
No full textThis article presents two types of postdistortion (PD) circuits - diode-connected PD (DCPD) and cascode PD (CPD) - positioned subsequent to low noise amplifiers (LNAs) operating in the 2.2-5-GHz frequency range. Each LNA with PD design, performance, and comparison is based on a core two-stage cascode topology, using identical transistor dimensions and bias voltages. The purpose of this study was to compare the linearity performance and linearity bandwidth of DCPD and CPD and achieve optimum performance in gain, noise figure (NF), bandwidth, and linearity simultaneously. The auxiliary circuits were designed to cancel third-order nonlinearities, thereby improving the third-order input intercept point (IIP3). Both LNAs achieved a gain of 30.5 dB, an NF of 0.85 dB, and an output power of 14dBm at 1-dB compression at a center frequency of 3.5 GHz with a power consumption of 240 mW. The auxiliary circuits used in the LNA design showed varying IIP3 based on the type of PD circuit employed. The CPD circuit demonstrated a linearity improvement at the center frequency, achieving an IIP3 of 1.5dBm. On the other hand, the DCPD circuit delivers an IIP3 of 10 dBm, one of the highest values reported in current state-of-the-art designs. In addition, a low-power mode of operation is measured with a power consumption of 68 mW for both LNAs. In this mode, the CPD circuit achieves an IIP3 of 5 dBm at 4.5GHz, while the DCPD circuit demonstrates an IIP3 of 3 dBm across the 4-4.5-GHz range
Fundamentals of cooling/lubrication effect in grinding of Inconel 718 employing an inverse thermo-mechanical model
No full textCutting fluids are essential in grinding to control the intense heat generated at the wheel–workpiece interface. This study investigates the cooling/lubrication effect using an inverse thermo-mechanical model to support the understanding and optimization of sustainable cooling strategies. A hybrid analytical–experimental method is developed for determining the heat partition ratio and the convective heat transfer coefficient (h), which are critical to understanding thermal behavior in grinding. The inverse modeling approach considers the thermal behaviour of coolants and workpiece materials under elevated temperatures, where their thermo-physical properties differ significantly from those at room temperature. It further incorporates the effects of grinding parameters, wheel-workpiece contact length, and coolant supply conditions. Additionally, chemical reactions in the grinding zone, which can either absorb or release heat, are accounted for, further influencing heat transfer dynamics. The model is applied to evaluate several eco-friendly cooling/lubrication techniques, including cryogenic liquid nitrogen, carbon dioxide, minimum quantity lubrication (MQL), and their hybrid combinations, and compared to conventional flood and dry grinding. Key performance indicators such as grinding forces, temperature, surface finish, and elemental composition are analyzed. A generalized formula for the heat partition ratio is proposed based on the inverse method, enabling consistent evaluation of thermal effects across different cooling conditions. This integrated modeling approach enhances the understanding of coolant behavior in realistic grinding environments and supports the transition toward sustainable, high-efficiency manufacturing by guiding the selection and optimization of environmentally friendly cooling/lubrication methods