Development and characterization of form-stable porous TiO2/tetradecanoic acid based composite PCM with long-term stability as solar thermal energy storage material

The present study focused on the preparation of form-stable composites of 1-tetradecanoic acid (TDA)/titanium dioxide (TiO₂) powder via a facile impregnation method. The use of powdered TiO₂ as porous material and thermal conductivity enhancer for TDA is a novel attempt. The morphological, chemical, and crystalline properties of form-stable composite PCMs (Fs-CPCMs), containing different amounts of TiO₂, were characterized using field emission scanning electron microscope, Fourier transform infrared spectroscopy, and X-ray diffraction techniques. The finding supports that the produced composites were chemically and structurally stable. The latent heat storage (LHS) properties of composites were obtained from differential scanning calorimeter instrument, and the findings revealed that the Fs-CPCM with 50 mass% TDA has a melting temperature of 52.04°C and a considerably good LHS capacity of 97.75 J/g. The thermal conductivity of TDA was increased remarkably by the addition of TiO₂ micro particles. The results obtained from thermogravimetric analysis and thermal cycling test exhibited that the Fs-CPCM, containing 50 mass% TiO₂, possesses great thermal degradation durability, cycling chemical stability, and thermal reliability. This composite PCM can be very well used for passive thermal management of electronic devices, automotive components, photovoltaic thermal hybrid designs, solar air/water heating systems, etc.     

SEISMIC EVENTS IN THE UPPER MIOCENE – PLIOCENE SEDIMENTARY SUCCESSION IN THE GULF OF İZMİR (WESTERN ANATOLIA): IMPLICATIONS FOR HYDROCARBON PROSPECTIVITY

An analysis of multi-channel seismic reflection data integrating reflection tomography, pre-stack depth migration, AVO analysis, seismic modelling and seismic attribute analysis was used to investigate the Miocene – Quaternary stratigraphy of the Gulf of İzmir, western Anatolia. In this area, the east-west oriented Gediz graben intersects with the NE-SW oriented Bakırçay Graben. A velocity-depth model together with pre-stack depth migration allowed two seismic stratigraphic units (SSU1 and SSU2) to be distinguished. These units can be correlated with the stratigraphic succession at the offshore Foça-1 well and correspond to the Upper Miocene to Recent Bozköy, Ularca and Bayramiç Formations with a combined thickness of 1.75 km. The units rest on acoustic basement (SSU3) which has a basin-and-ridge morphology, and which corresponds to the Lower-Middle Miocene Yuntdağ Volcanics. A number of lateral velocity variations were identified. In particular, a ~90 m wide and ~500 m long lenticular-shaped low-velocity zone with an interval velocity of 1.68 km/s was identified in the Quaternary Bayramiç Formation. The structure is bounded by negative reflections whose amplitude increases with offset at the top and by strong positive reflections whose amplitude increases with offset at the base, interpreted as possible bright and flat spots respectively. These amplitude events point to the presence of gas-saturated sediments within the study area. The lenticular structure is bounded by strike-slip faults on either side, and by a Miocene – Pliocene unconformity surface below and by shales of the Bayramiç Formations above. It is therefore interpreted as a possible structural – stratigraphic trap. The strike-slip faults may allow the migration of hydrocarbons from source rocks located at greater depths. The presence of a low-velocity zone above the lenticular structure reaching up to seafloor may indicate the upward leakage of hydrocarbons from the trap. These observations will contribute to future hydrocarbon exploration activities in the study area.     

Performance evaluation of whisker-reinforced ceramic tools under nano-sized solid lubricants assisted MQL turning of Co-based Haynes 25 superalloy

Ceramics are widely used in machining of high temperature alloys i.e., Co-based Haynes 25 alloy due to its superior characteristics. The present paper is focused on the performance of whisker-reinforced ceramic cutting tool (WRCCT) under nano-sized solid lubricants dispersed in MQL (nanofluid-MQL) during turning of Co-based Haynes 25 alloy. The turning experiments were performed under several cutting environments (dry, base fluid MQL (BF-MQL), hBN based nanofluid MQL (hBN-NMQL), MoS₂ based nanofluid MQL (MoS₂-NMQL), graphite based nanofluid MQL Gr-NMQL) by varying cutting speed (200 and 300 m/min) and feed rate (0.1 and 0.15 mm/rev) values. Initially, the viscosity and thermal conductivity of nanofluids were evaluated and then the prepared nanofluids were used for machining experiments. The results reveal that the rate of increase in thermal conductivity coefficient relative to base cutting fluid was 11.90% in hBN-nanofluid, 16.29% in MoS₂-nanofluid and 14.12% in Gr-nanofluid. In terms of machining performance, on the one hand, the minimum surface roughness was obtained from Gr-NMQL assisted machining, on the other hand, the hBN-NMQL has been successful in limiting of notch wear and nose wear values. Compared to dry turning, the temperature was reduced up to 27.18% with hBN doped nanofluids, while it was 34.95% with MoS₂ doped nanofluids and 29.32% with graphene doped nanofluids.     

Solar energy harvesting and self-cleaning of surfaces by an impacting water droplet

The self-cleaning of surfaces via impacting water droplets is examined pertinent to solar energy applications. The mechanism of spreading and retraction of the impacting droplet onto the dust and cleaned hydrophobic surfaces is considered in the analysis. The spreading factor of the impacting droplet is formulated incorporating the energy balance on the hydrophobic surface. High-speed photography is used to monitor the impacting droplet behavior. The functionalized silica particles coating is introduced towards generating hydrophobic wetting state on the glass surfaces. Environmental dust particles are characterized prior to self-cleaning impacting tests. It is found that spreading rate predicted for the impacting droplet agrees well with that obtained from the experiments. The droplet Weber number incorporated in the experiments does not result in droplet breaking on the surface upon impacting. The dusts are dissimilar in shapes and consist of several elements. Impacting droplet gives rise to cloaking of the dust on the surface during spreading and retraction. Almost all the dusts are removed from the surface through the impacting droplets; however, few dust residues are left on the impacting surface, which cover only 0.03% of the total surface area. Hence, we have demonstrated that self-cleaning of a surface can be achieved by an impacting droplet for renewable energy applications.     

Thermal energy storage properties of polyethylene glycol grafted styrenic copolymer as novel solid-solid phase change materials

Polymeric solid-solid phase change materials (S-SPCMs) are functional materials with phase transition-heat storing/releasing ability. With this respect, a series of polyethylene glycol (PEG) grafted styrenic copolymer were produced as novel S-SPCMs. PEGs with three different molecular weights were used for synthesis of isocyanate-terminated polymers (ITPs). To achieve cross-linking S-SPCMs, the ITPs were grafted with styrene-co-ally alcohol) (PSAA) at three different PSAA:PEG mole ratios. The produced polymers were characterized using Fourier transform infrared (FT-IR), proton nuclear magnetic resonance (¹H NMR), and X-ray diffraction (XRD) technique. The crystalline-amorphous phase transitions of the polymers were examined using polarized optical microscopy (POM). The FT-IR, NMR, and XRD results confirmed the expected chemical structures and crystallization performances of the polymers. Thermal energy storage (TES) properties of the S-SPCMs were determined by differential scanning calorimetry (DSC). The DSC results revealed that the polymers with grafting ratio of PSAA:PEG(1:1) had phase transition enthalpies between about 74 and 142 J/g and phase transition temperatures between about 26°C and 57°C. Thermogravimetric analysis (TGA) measurements demonstrated that the S-SPCMs were resistant to thermal decomposition until about 300°C. Thermal conductivities of the produced S-SPCMs were measured in a range of about 0.18 to 0.19 W/mK. Furthermore, TES properties of the S-SPCMs were slightly changed as their chemical structures were remained after 5000 thermal cycles. By overall evaluation of the findings, it can be foreseen that particularly PSAA-g-PEG(1:1) polymers can be considered as promising S-SPCMs for some TES practices such as air conditioning of buildings, thermoregulation of food packages, automobile components, electronic devices, and solar photovoltaic panels.     

Die kinematische Geometrie der allgemeinräumlichen Relativbewegung von drei Gliedern

Zusammenfassung In einer vorangehenden Arbeit wurde der von Aronhold-Kennedy angegebene wichtige Dreipolsatz der ebenen Kinematik (Getriebelehre) eingehend untersucht. Dieser Satz lautet: Bei der relativen Bewegung dreier Ebenen liegen die relativen Momentanpole auf einer Geraden, d.h. diese sind kollinear. Bei eben beweglichen starren K?rpern treten anstelle der Momentanpole die parallelen Momentanpolachsen auf. Insbesondere werden s?mtliche Entartungsf?lle dieses Satzes als Folge der speziellen Lagen der Momentandrehachsen angegeben. In der vorliegenden Arbeit werden diese Untersuchungen auf die r?umlichen relativen Bewegungen dreier K?rper ausgedehnt. Hier steht der folgende bekannte Satz im Vordergund: Bei den allgemein r?umlichen Relativbewegungen von drei K?rpern haben die drei Schraubachsen stets eine gemeinsame Normale. In der Arbeit sind die folgenden Kombinationen dieser Achsen in Betracht gezogen worden: Schraubenpaar-Schraubenpaar, Schraubenpaar-Drehpaar, Schraubenpaar-Schiebepaar, Drehpaar-Drehpaar, Drehpaar-Schiebepaar und Schiebepaar-Schibepaar. Au?erdem werden deren Beziehungen zum sogenannten Zylindroid (einer Regelfl?che dritter Ordnung) eingehend untersucht. Die Entatungsf?lle dieses Zylindroids werden für spezielle Lagen und Parameter dieser Achsen angegeben. Schlie?lich werden die Ergebnisse in Form von Tabellen zusmmengefa?t.     

Artificial neural network-based prediction technique for wear loss quantities in Mo coatings

Mo coated materials are used in automotive, aerospace, pulp and paper industries in order to protect machine parts against wear and corrosion. In this study, the wear amounts of Mo coatings deposited on ductile iron substrates using an atmospheric plasma-spray system were investigated for different loads and environment conditions. The Mo coatings were subjected to sliding wear against AISI 303 counter bodies under dry and acid environments. In a theoretical study, cross-sectional microhardness from the surface of the coatings, loads, environment and friction test durations were chosen as variable parameters in order to determine the amount of wear loss. The numerical results obtained via a neural network model were compared with the experimental results. Agreement between the experimental and numerical results is reasonably good.     

Domain-Size-Dependent Residual Stress Governs the Phase-Transition and Photoluminescence Behavior of Methylammonium Lead Iodide

Methylammonium lead iodide (MAPbI₃) perovskite has garnered significant interest as a versatile material for optoelectronic applications. The temperature-dependent photoluminescence (TDPL) and phase-transition behaviors revealed in previous studies have become standard indicators of defects, stability, charge carrier dynamics, and device performance. However, published reports abound with examples of irregular photoluminescence and phase-transition phenomena that are difficult to reconcile, posing major challenges in the correlation of those properties with the actual material state or with the subsequent device performance. In this paper, a unifying explanation for the seemingly inconsistent TDPL and phase-transition (orthorhombic-to-tetragonal) characteristics observed for MAPbI₃ is presented. By investigating MAPbI₃ perovskites with varying crystalline states, ranging from polycrystal to highly oriented crystal as well as single-crystals, key features in the TDPL and phase-transition behaviors are identified that are related to the extent of crystal domain-size-dependent residual stress and stem from the considerable volume difference (ΔV ≈ 4.5%) between the primitive unit cells of the orthorhombic (at 80 K) and tetragonal phases (at 300 K) of MAPbI₃. This fundamental connection is essential for understanding the photophysics and material processing of soft perovskites.     

Incremental <Emphasis Type="Italic">k</Emphasis>-core decomposition: algorithms and evaluation

A k-core of a graph is a maximal connected subgraph in which every vertex is connected to at least k vertices in the subgraph. k-core decomposition is often used in large-scale network analysis, such as community detection, protein function prediction, visualization, and solving NP-hard problems on real networks efficiently, like maximal clique finding. In many real-world applications, networks change over time. As a result, it is essential to develop efficient incremental algorithms for dynamic graph data. In this paper, we propose a suite of incremental k-core decomposition algorithms for dynamic graph data. These algorithms locate a small subgraph that is guaranteed to contain the list of vertices whose maximum k-core values have changed and efficiently process this subgraph to update the k-core decomposition. We present incremental algorithms for both insertion and deletion operations, and propose auxiliary vertex state maintenance techniques that can further accelerate these operations. Our results show a significant reduction in runtime compared to non-incremental alternatives. We illustrate the efficiency of our algorithms on different types of real and synthetic graphs, at varying scales. For a graph of 16 million vertices, we observe relative throughputs reaching a million times, relative to the non-incremental algorithms.     

Fabrication,characterization, and performance of YbDSB ternary compounds for IT‐SOFC applications

(Yb₂O₃)_x(Dy₂O₃)_y(Bi₂O₃)_1?x?y (0.04≤x+y≤0.20) powders (xYbyDSB) were synthesized by modified sol‐gel Pecchini method. The powders were characterized for structural, surface morphological, thermal, and electrical properties and power density measurements by means of X‐ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis/thermal gravimetry (DTA/TG), and impedance spectroscopy, respectively. Lattice parameters and crystalline size of δ‐phase of Yb₂O₃‐ and Dy₂O₃‐doped Bi₂O₃ samples were calculated from the X‐ray diffraction data. Surface and grain properties of the related phases were determined by SEM analysis. In the investigated system, the maximum electrical conductivity was observed as σ=0.954 S cm^?1 for 6% mol Yb₂O₃ and 6% mol Dy₂O₃ at 800°C among all δ‐YbDSB systems. Cathode supported electrochemical cell was fabricated and 6Yb6DSB was used as the electrolyte. Maximum power density of single cell with an active area of 1.5 cm² is 72.50 mW/cm² at 700°C.