International Journal of Mechanical and Materials Engineering最新文献

This work presents a transfer learning approach for the forward design of composite unit cells of metasurfaces and frequency-selective surfaces (FSS). As a specific application, we target reconfigurable intelligent surfaces (RIS) for wireless communication. We demonstrate that forward models for dual-dipole unit cells can be trained using significantly fewer data by reusing pre-trained models of simpler, single-dipole structures. Our architecture reduces the required training data by up to a factor of 25 while maintaining a mean squared error (MSE) on the order of (10^{-2}). After establishing the forward model for the dual-dipole RIS, we use it in an inverse design framework to synthesize a composite 2-bit RIS unit cell operating at 26.5 GHz. The resulting RIS provides phase modulation in a 270(^circ) range by tuning the reverse bias voltage of integrated varactor diodes. Numerical simulations confirm the validity of the proposed approach, establishing transfer learning as a data-efficient and practical method for the design of composite unit cell structures.

The accumulation of space charges in high-voltage cable insulation layers significantly compromises electrical performance and accelerates material degradation. This study proposed a novel strategy to inhibit charge injection by incorporating highly conductive annealed MXene nanosheets into the semiconductive shielding material. Results demonstrate the introduction of MXene remarkably reduce positive temperature coefficient (PTC) of composites. With MXene content of 0.5 wt% (carbon black (CB) of 31.5 wt%), the PTC of composite decreases to 3.6 from 5.74 (pure CB sample), indicating enhanced thermal stability. Furthermore, MXene modified materials effectively suppress space charges accumulation, reducing the charge density in the insulation layer to 13.38 C/m³ (MXene content of 0.5 wt%) compared to 20.44 C/m³ for unmodified sample. These enhancements are attributed to MXene’s dual role in forming efficient conductive networks and introducing deep charge traps. This study sheds new light on the development of advanced semiconductive shielding materials for high-voltage cable applications.

Numerical methods are used to investigate the influence of ferrofluid integration on the operation of parabolic trough solar collectors. The total performance of the solar collector is predetermined by the capability of the tube to operate as an effective line-focus thermal collector. Ferrofluid is the working fluid. (Fe₃O₄ + H₂O). The ferrofluid is a mixture of Fe₃O₄ and water. The volumetric concentration of Fe₃O₄ (Ø) added to water ranges from Ø = 0.01, 0.02, 0.04, and 0.06. Performance evaluation is conducted by referencing experimental measurements and validated numerical correlations from existing literature. The results show close alignment with the experimental data. Compared to plain water, the Nu improved by 94.25%, and the friction factor reduced by 44.69%. With respect to the change in % volume fraction (Ø), the rate of heat transfer changes. The rate of heat transfer and the volume fraction (Ø) are directly related to each other. The influence of Ø is such that at lower Re, the heat transfer rises more as compared to higher Re. The effect of % Vol. of Fe₃O₄ results in a reduced friction factor but also a reduction in the heat transfer rate. Flow vortices that form in the fluid at lower Reynolds numbers can reduce wall friction and be useful for lowering pumping power.

Ag-doped TiO₂ nanoparticles were synthesized via a facile sol–gel method to investigate the synergistic effects of silver doping and pH on the photocatalytic degradation of methylene blue (MB). The catalysts, characterized comprehensively by XRD, SEM–EDS, FTIR, and UV–Vis DRS, revealed that Ag doping (1–2 mol%) successfully enhanced visible-light absorption and modified surface properties. However, characterization confirmed significant spatial heterogeneity in Ag distribution, which resulted in localized charge-separation "hot spots". Consequently, the TiO₂-Ag 1% catalyst exhibited optimal performance, achieving superior degradation kinetics (kₐₚₚ = 82.8 × 10⁻³ min⁻¹) specifically at pH 9. This enhanced activity is attributed to its balanced Ag dispersion, which, when combined with alkaline conditions, promoted enhanced •OH generation from surface-bound water and improved MB adsorption. Thus, this study demonstrates that photocatalytic efficiency depends critically not only on successful doping but also on the interplay between optimal Ag distribution (1% > 2%) and pH-dependent surface charge, offering key insights for designing TiO₂ catalysts for organic pollutant remediation.

Nickel–phosphorus–carbon nanotube (Ni–P–CNT) composite coatings demonstrate remarkable corrosion resistance and superior light absorption compared to conventional Ni–P coatings, making them highly suitable for solar absorber applications. This study explores the influence of CNT concentration (0–2.5 g·L⁻¹) in the plating bath on the corrosion performance of aluminum substrates before and after a blackening process involving nitric acid etching to enhance solar absorption. The coatings were characterized using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and electrochemical techniques such as open-circuit potential (OCP), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). Results revealed that CNT incorporation increased with concentration up to 2 g·L⁻¹ but decreased at 2.5 g·L⁻¹ due to agglomeration and particle precipitation. The optimal CNT loading of 1.5 g·L⁻¹ produced the most uniform morphology, minimal etching, and the highest corrosion resistance after blackening, attributed to well-dispersed CNTs and reduced surface porosity. In contrast, higher CNT concentrations led to increased coating defects and porosity, accelerating etching and corrosion. Overall, a CNT concentration of 1.5 g·L⁻¹ provided the best balance between corrosion protection and surface absorption efficiency, resulting in durable, high-performance coatings suitable for long-term solar energy applications.

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This study reports a previously overlooked phenomenon in the green synthesis of graphene-based materials: a significant mass gain during the reduction of graphene oxide (GO) using olive leaf extract (OLE). While spectroscopic analyses (UV–Vis, FTIR) confirm effective reduction, the mass of the final product exceeded that of the starting graphite, with yields reaching up to 1.17 g of reduced graphene oxide (rGO) per 1.0 g of graphite. This apparent contradiction—reduction accompanied by mass increase—suggests that the process involves more than oxygen removal; we propose that polyphenolic compounds from the extract concurrently functionalize the carbon lattice. This work shifts the paradigm from viewing plant extracts solely as reducing agents to recognizing their potential as multifunctional modifiers in nanomaterial synthesis.

The disposal of spent activated carbon (SAC) remains a major environmental challenge worldwide, particularly in tropical regions where coconut husks serve as the primary precursor for activated carbon production. Conventional disposal methods, such as landfilling and incineration, raise ecological and health concerns due to the leaching of adsorbed contaminants and the release of greenhouse gases. This study investigates the potential of SAC as a sustainable additive in sculpturing composites. SAC was incorporated into epoxy, acrylic gel, Portland cement, and clay matrices at varying loadings (10–40 wt%). The composites were characterized for workability, durability, mechanical strength, bulk density, chemical stability, and aesthetic properties. Epoxy-SAC composites demonstrated superior strength (compressive 68 MPa; flexural 21 MPa), durability (< 2% weight loss in wet–dry cycles), and chemical stability, making them suitable for indoor and outdoor sculptures. Cementitious–SAC composites exhibited moderate strength (35 MPa) and durability (4% weight loss), making them ideal for outdoor applications. Acrylic-SAC composites provided excellent matte-black aesthetics for indoor art, while clay-SAC composites exhibited limited durability and low strength. The study confirms SAC’s feasibility as a value-added material for sculpting applications, contributing to circular economy principles and environmental sustainability.

Brazilianite, with the formula NaAl₃(PO₄)₂(OH)₄, exhibits an intriguing pale yellow to green coloration, a phenomenon not readily explained by the absence of conventional d-block chromophoric metal ions. This study investigates the synthesis of amorphous phosphate-based pigments compositionally analogous to Brazilianite, aiming to replicate and understand the origin of its distinctive coloration through controlled precursor stoichiometry and thermal processing. Sodium, aluminum, and phosphate precursors were precisely mixed and thermally treated. X-ray diffraction (XRD) confirmed the predominantly amorphous nature of the synthesized materials, irrespective of achieving long-range crystalline order analogous to mineral Brazilianite. Despite this, samples processed at intermediate temperatures (e.g., 300–400 °C) exhibited a consistent yellowish hue. This non-conventional coloration, attributed to intrinsic electronic or structural features within the amorphous phosphate network rather than traditional chromophores, represents a significant scientific innovation. This coloration was found to be intrinsically linked to the phosphate network itself. Stability assessments in acidic (0.1 wt% H₂SO₄) and basic (0.1 wt% NaOH) environments revealed significant vulnerability, attributed to the facile dissolution of sodium and aluminum phosphate species. Notably, the yellowish coloration persisted across various Na/Al/P compositional ratios, even with systematic variations in aluminum or sodium content. This strongly suggests that the observed color is not critically dependent on a precise Na: Al stoichiometry but is fundamentally governed by the local electronic structure within the phosphate network, potentially involving defect centers or specific P-O-Al/Na linkages. These findings offer valuable insights into designing novel, non-toxic, color-stable pigments where coloration arises from mechanisms beyond traditional transition metal ion incorporation, highlighting the potential role of controlled disorder in phosphate-based materials for sustainable applications.

Cassava‑based thermoplastic starch (TPS) is biodegradable yet constrained by brittleness, moisture sensitivity, and retrogradation. This study evaluates an amine‑rich deep eutectic solvent, choline chloride: monoethanolamine (ChCl: MEA, 1:2–1:5), as a dual plasticizer–compatibilizer for cassava TPS. Films (about 3 mm) were produced by twin‑screw extrusion and compression molding and benchmarked against glycerol‑plasticized TPS and a urea‑based DES (ChCl: urea, 1:2). ChCl: MEA markedly improved processability and properties: melt‑flow index increased from 1.02 to 2.36 g/10 min, glass‑transition temperature decreased from 72.4 to 36.8 °C, crystallinity index fell from 23.7% to 16.1%, thermal stability rose (286 °C to 320 °C), and water contact angle increased from 42° to 71.5°. The 1:3 composition achieved balanced mechanics (tensile strength 2.3 MPa; elongation 184%) and retained approximately 88% strength and approximately 81% elongation after 56 days at 23 °C/50% RH, outperforming glycerol (about 50% retention). All observed improvements were statistically significant (p < 0.05). Overall, the amine‑rich ChCl: MEA DES affords superior plasticization and aging resistance relative to glycerol and urea‑based DES, advancing cassava TPS toward robust, biodegradable packaging applications.

This study examines the influence of low-temperature plasma nitrocarburizing (LT-PNC) on the surface properties of 15 − 5 precipitation-hardening (PH) stainless steel. The material was treated at three temperatures, specifically 410 °C, 430 °C, and 460 °C, for duration of fifteen hours. The resulting surfaces were characterized by X-ray diffraction, microhardness measurements, salt fog testing, and potentiodynamic polarization. Plasma nitrocarburizing (PNC) produced a substantial increase in surface hardness, reaching approximately 70 HRC compared with the untreated value of about 42 HRC. At treatment temperatures of 430 °C and above, chromium nitride (CrN) formation was observed, which led to chromium depletion and a subsequent decline in corrosion resistance. In contrast, the sample processed at 410 °C achieved a balance between enhanced hardness and the preservation of corrosion resistance. Overall, the findings confirm that LT-PNCis an effective method for improving both durability and corrosion performance of 15 − 5 PH stainless steel, indicating its suitability for aerospace and other high-performance engineering applications.