Search Results (52,989)

In the present study, post-heat treatment was applied to improve the mechanical and tribological performance of 3D-printed polymer components. Two polymers, i.e., polylactic acid (PLA) and polyether ether ketone (PEEK), were used as base materials. Re-entrant structures were incorporated into printed specimens to mitigate friction-induced vibrations (FIV). The results showed that the heat-treatment process effectively enhanced the mechanical properties of both materials by increasing their elastic modulus and yield strength. Specifically, the tensile and compressive strengths of heat-treated PLA increased from 44.14 MPa to 47.66 MPa and from 68 MPa to 82 MPa, respectively. A similar trend was observed for heat-treated PEEK, with tensile strength increasing from 75.53 MPa to 84.91 MPa and compressive strength from 106 MPa to 123 MPa. Furthermore, the increased stiffness enabled the re-entrant structures to more effectively reduce FIV during the sliding process of specimens. However, heat treatment produced contrasting effects on the wear performance of the two polymers. The specific wear rate of the heat-treated PLA sample with the re-entrant structure increased from 2.36 × 10⁻⁵ mm³/(N · m) to 4.5 × 10⁻⁴ mm³/(N · m), while it decreased for the PEEK sample from 3.18 × 10⁻⁶ mm³/(N · m) to 6.2 × 10⁻⁷ mm³/(N · m). Microscopic observations revealed that this difference was due to the variations in the brittleness of the treated materials, which influenced wear-debris formation and the development of the transfer film on the steel counterface. These findings demonstrate that post-heat treatment is an effective method for tailoring and optimizing the mechanical behavior of printed polymers while also emphasizing the necessity of systematically evaluating its influence on the tribological performance of printed engineering parts subjected to different sliding conditions. Full article

Background and Objectives: Cognitive disorders are a significant health problem in patients undergoing peritoneal dialysis and can profoundly impair both quality of life and treatment outcomes. Early identification of risk factors for the development of cognitive disorders in this population is therefore essential. This study aimed to (1) determine the prevalence of cognitive dysfunction in patients on peritoneal dialysis, (2) examine its association with sociodemographic characteristics, and (3) assess whether anaemia is associated with cognitive dysfunction in these patients. Materials and Methods: A cross-sectional study was conducted in November 2024 at the University Clinical Centre of Vojvodina, Clinic for Nephrology and Clinical Immunology, and included 36 patients on peritoneal dialysis. The Montreal Cognitive Assessment (MoCA) was used to evaluate cognitive function, while a structured questionnaire was used to collect sociodemographic data. Anaemia was determined based on haemoglobin levels. Results: Cognitive dysfunction was present in 69.4% of patients on peritoneal dialysis, while anaemia, as indicated by haemoglobin values, was present in 58.3% of the sample. Older age, rural residence, and lower haemoglobin levels were significantly associated with cognitive dysfunction in patients on peritoneal dialysis. Conclusions: Preserved cognitive function is a key prerequisite for the adequate implementation of peritoneal dialysis and for maintaining patients’ quality of life. The findings indicate the need for further research to identify effective strategies for preventing and treating anaemia, a factor associated with cognitive dysfunction in this patient population. Full article

This study presents a method for extracting lignin and hemicellulose from black liquor using organic acids (citric, malic, and acetic) in comparison to the traditional sulfuric acid method. We investigated and compared the influence of the acid type on the structural properties of the resulting precipitates in the context of their potential applications. The lignin fractions were characterized for their chemical structure (ATR-FTIR, NMR), thermal stability (TGA), morphology and surface elemental composition (SEM-EDS), bulk elemental composition (C, H, N, S), and molecular weight distribution (GPC). The hemicellulose fractions were analyzed for their molecular weight (GPC), surface elemental composition (EDS), and chemical structure (ATR-FTIR). These analyses revealed subtle differences in the properties of the individual materials depending on the extraction method. We showed that organic acids, particularly citric acid, can effectively precipitate lignin with yields comparable to the sulfuric acid method (47–60 g/dm³ vs. 50 g/dm³). Simultaneously, this method produces lignin with higher purity (regarding sulfur content) and an increased content of carboxyl groups. This latter aspect is of particular interest due to the enhanced potential of lignin’s adsorption functions towards metal ions. AAS analysis confirmed that lignin precipitated with citric acid showed better adsorption efficiency towards heavy metals compared to lignin precipitated with sulfuric acid, especially for Cu²⁺ ions (80% vs. 20%) and Cr³⁺ ions (46% vs. 2%). This enhanced adsorption efficiency of the isolated lignins, combined with the environmental benefits of using organic acids, opens a promising perspective for their application in water treatment and environmental remediation. Furthermore, the presented research on the valorization and reuse of paper industry by-products fully aligns with the fundamental principles of the Circular Economy. Full article

Artificial neural networks (ANNs) are widely used in engineering prediction, but excessive input dimensionality can reduce both accuracy and efficiency. This study proposes a two-stage feature-reduction framework, Feature Importance Ranking and Redundancy Elimination (FIRRE), to optimize ANN inputs by removing weakly informative and redundant variables. In Stage 1, four complementary ranking methods, namely Pearson correlation, recursive feature elimination, random forest importance, and F-test scoring, are combined into an ensemble importance score. In Stage 2, highly collinear features (ρ > 0.95) are pruned while retaining the more informative variable in each pair. FIRRE is evaluated on 32 civil engineering datasets spanning materials, structural, and environmental applications, and benchmarked against Principal Component Analysis, variance-threshold filtering, random feature selection, and K-means clustering. Across the benchmark suite, FIRRE consistently achieves competitive or improved predictive performance while reducing input dimensionality by 40% on average and decreasing computation time by 10–60%. A dynamic modulus case study further demonstrates its practical value, improving R² from 0.926 to 0.966 while reducing inputs from 25 to 7. Overall, FIRRE provides a practical, robust framework for simplifying ANN inputs and improving efficiency in civil engineering prediction tasks. Full article

This study investigates a hybrid processing route that integrates localized fusion-based additive manufacturing and hot forging for the production of complex-shaped components, with emphasis on metallurgical integrity and mechanical performance. The DIN 8555 E6-UM-60 alloy, traditionally classified as martensitic and applied under severe wear conditions, exhibited atypical metallurgical behavior during hybrid processing, notably the consistent formation of chromium carbides under specific thermomechanical conditions. Metallographic analyses, microhardness measurements, thermographic monitoring, hot tensile tests, and room-temperature tensile tests were performed to establish correlations between microstructure, thermal history, and mechanical response. Specimens produced by additive manufacturing and subsequently hot forged showed a significant reduction in porosity, improved microstructural homogeneity, and partial retention of hardening phases, enabling discussion of recrystallization mechanisms, phase stabilization, and precipitation phenomena in martensitic alloys processed by additive manufacturing. Hot tensile tests revealed limited hot workability of the alloy, while room-temperature tensile tests led to premature fracture, with failure consistently initiating at pre-existing microcracks formed during the forging stage. Although detrimental, these microcracks provide valuable insight into critical processing conditions and ductility limits of the material. Overall, the hybrid route demonstrates strong potential for industrial applications, highlighting the importance of precise thermomechanical cycle control to mitigate defects and enhance structural reliability. Full article

This work investigates the structural, acoustic, and thermo-oxidative degradation behavior of elastomeric composites made from neat EPDM and recycled devulcanized EPDM (EPDMd) blends, both with and without silica (SiO₂). SiO₂ plays a complex role in degradation, possibly acting as a catalyst and also affecting the properties of the materials. Samples were subjected to accelerated degradation at 80 °C for 30 days. The characterization included the mechanical, spectroscopical (FTIR-ATR), thermal (TGA), and morphological (SEM) studies of the samples. Given EPDM’s use in construction as a sound-absorber, its acoustic properties were also analyzed. The determination of the mechanical properties shows that the incorporation of SiO₂ improves the Young’s modulus (YM), maintains the tensile strength (TS) at similar values, and causes a decrease in elongation at break (EB). The content of EPDMd slightly decreases both the TS and the EB and increases the YM. The thermo-oxidative degradation of the studied composites does not affect the TS values, but it increases the YM for the samples with and without SiO₂ for EPDMd contents higher than 40 phr, and decreases the EB for samples with and without SiO₂ for all EPDMd contents. The FTIR-ATR, TGA, and SEM results show that the addition of SiO₂ catalyzes the thermo-oxidative degradation process, while the EPDMd inhibits structural degradation. Migration of the ZnSt₂ included in the formulations to the surface is common in these elastomers. In this case, EPDMd forms microaggregates, which retain the exudation of ZnSt₂ crystals, especially in the non-degraded samples. The degraded samples present irregular structures, with microcavities, cracks, and occlusions, which increase the acoustic absorption mainly at frequencies below 1500 Hz. Full article

Developing sustainable and molecularly selective adsorbents for heavy-metal removal remains a critical challenge in water purification. Herein, we report a green molecular-engineering approach for fabricating aza-crown ether functionalized sodium alginate aerogels (ACSA) capable of highly selective Cu²⁺ capture. The aerogels were synthesized via saccharide-ring oxidation, Cu²⁺-templated self-assembly, and reductive amination, enabling the covalent integration of aza-crown ether motifs within a hierarchically porous biopolymer matrix. Structural analyses (FTIR, ¹³C NMR, XPS, SEM, TGA) confirmed the in situ formation of macrocyclic N/O coordination sites. Owing to their interconnected porosity and chemically stable framework, ACSA exhibited rapid sorption kinetics following a pseudo-second-order model (R² = 0.999) and a Langmuir maximum adsorption capacity of 150.82 mg·g⁻¹. The material displayed remarkable Cu²⁺ selectivity over Zn²⁺, Cd²⁺, and Ni²⁺, arising from the precise alignment between Cu²⁺ ionic radius (0.73 Å) and crown-cavity dimensions, synergistic N/O chelation, and Jahn-Teller stabilization. Over four regeneration cycles, ACSA retained more than 80% of its original adsorption capacity, confirming excellent durability and reusability. This saccharide-ring modification strategy eliminates crown-ether leaching and weak anchoring, offering a scalable and environmentally benign route to bio-based adsorbents that combine molecular recognition with structural stability for efficient Cu²⁺ remediation and beyond. Full article

Due to the heightened flood risk resulting from climate change, innovative and advanced green building materials are required to enhance the durability and biological resistance of concrete structures exposed to persistent moisture. This study investigates the use of nanosilver-enriched plasticizers as a novel modification of concrete for applications in flood-prone environments. The findings demonstrate that the incorporation of nanosilver enhances the mechanical strength of concrete by reducing surface tension and porosity, thereby enhancing durability and extending service life. Moreover, nanosilver-modified concrete exhibits significant antimicrobial activity, effectively limiting microbial-induced corrosion. Preliminary microbiological analyses showed a reduction of sulfur-oxidizing bacteria (SOB) and sulfate-reducing bacteria (SRB) by 85–92%, as well as a decrease of over 80% in potentially pathogenic microbial genera. This study also highlights the importance of skilled labor and adequate training to ensure the responsible implementation of nanosilver-based technologies in sustainable construction. Overall, nanosilver-enriched plasticizers represent an innovative green building material that supports flood-resilient, durable, and sustainable concrete construction. Full article

The COREX smelting-reduction route is a representative non-blast furnace technology, but its scale-up is hindered by insufficient gas and liquid permeability in the melter gasifier. To improve the gas and liquid permeability of the melter gasifier, coke is charged together with an iron-bearing material to partly replace lump coal to increase the burden voidage. The charged coke undergoes successive physical and chemical attacks that progressively weaken its strength, finally reducing the coke particle size and impairing overall burden permeability. Drilling “in situ” coke samples from the tuyere zone is an effective method to study coke behaviors inside a working melter gasifier. This work obtained tuyere coke samples by direct coke sample drilling during a melter gasifier blow-out and then systematically investigated the coke deterioration behaviors in the melter gasifier. The results show that the mean particle size decreased from an initial 50.3 mm to 31.6 mm at the tuyere, evidencing the severe fragmentation of coke. Basic oxides and alkali metals in the coke ash increased, indicating alkali recycling and enrichment occurred in the melter gasifier. Microcrystalline structure analysis of coke revealed a high degree of graphitization. Furthermore, coke degradation was further accelerated by both alkalis trapped in the coke pores and slag infiltration into the pores. This study clarifies the properties of the coke in the tuyere of the COREX melter gasifier and provides a theoretical basis for its operational optimization. Full article

Geometric discontinuities are unavoidable in additively manufactured polymer components and can significantly alter their mechanical response; however, their effects are rarely quantified in a systematic and geometry-comparative manner. In this study, the tensile behavior of FDM-printed PLA+ specimens with three different geometries—dog-bone, circular-hole, and U-notched (manufactured and tested in accordance with ASTM D638 (Type IV))—was experimentally and numerically investigated. Tensile tests were conducted using a universal testing machine equipped with an extensometer, while finite element simulations were performed using an experimentally calibrated Ramberg–Osgood-based elastic–plastic material model. The dog-bone specimens exhibited an ultimate tensile strength (UTS) of 41–43 MPa and a Young’s modulus of 3.06 GPa, representing the intrinsic material response under nearly homogeneous stress conditions. Circular-hole specimens maintained comparable strength (38–42 MPa) but showed reduced ductility (1.4–1.6%) and a slightly increased apparent modulus of 3.17 GPa due to localized deformation. In contrast, U-notched specimens displayed the highest apparent modulus (≈5.30 GPa) and nominal UTS (46–49 MPa), accompanied by a pronounced reduction in ductility (0.9–1.0%), indicating severe stress concentration and predominantly brittle fracture behavior. Finite element analysis showed excellent agreement with experimental results, with peak von Mises stresses reaching approximately 42 MPa for all geometries, corresponding closely to the experimentally measured tensile strength. These results demonstrate that geometric discontinuities strongly govern stress localization, apparent stiffness, and fracture initiation in FDM-printed PLA+ components. The validated Ramberg–Osgood-based modeling framework provides a reliable tool for predicting geometry-dependent mechanical behavior under quasi-static loading and supports geometry-aware design of additively manufactured polymer structures. Full article

Traditional villages, protected as cultural heritage in our country, are rich in historical information, cultural landscapes, and traditional domestic architecture. This article explores the spatial distribution of traditional villages and proposes a new paradigm for the sustainable development of traditional dwellings. It addresses the challenges these villages face, such as natural, social, and inherent issues, arising from rapid socioeconomic development and urbanization. This study analyzes the spatial distribution and architectural features of traditional villages and dwellings in Northern Shaanxi based on 179 national and provincial villages. Using ArcGIS 10.1, the geographic concentration index, kernel density analysis, and the analytic hierarchy process, this study applied both macro and micro level perspectives. The research shows that: (1) The traditional villages in northern Shaanxi exhibit a spatial distribution pattern of “overall aggregation, local dispersion, and uneven distribution.” This pattern is influenced by interactions between natural and human factors. (2) Traditional dwellings in these villages are primarily cave dwellings and courtyard buildings, each reflecting unique architectural features in terms of floor plan layout, facade form, structure, materials, and decoration. (3) Traditional village dwellings in northern Shaanxi face practical challenges related to protection, development, and governance. The top three challenges, based on weighted indicators, are issues related to inheritance, an imperfect protection mechanism, and inherent shortcomings of the buildings. Based on these findings, this study proposes three practical suggestions for the sustainable development of traditional village dwellings in Northern Shaanxi. These suggestions aim to enhance the comprehensive and multi-dimensional sustainable development of traditional village dwellings. Full article

In this paper, a nano-layered transmission GaAs photocathode structure is proposed. The near-infrared absorption of the photocathode is enhanced by inserting a “sandwich” structure of nano-SiO₂ layer + Si₃N₄ nanopillar array + nano-SiO₂ layer between the cathode optical window and the photocathode. Compared with the flat film structure GaAs photocathode used in the current third-generations image intensifiers, the optical absorption of the optimized “sandwich” structure GaAs photocathode in the near-infrared band has been significantly improved: when the wavelength λ is 868 nm and 896 nm, the optical absorption is increased by 41.69%, 55.08%, respectively. The effects of structural parameters including film thickness and grating filling medium on the light absorption of photocathode are investigated. The results show that the near-infrared light absorption enhancement is the most obvious when Si₃N₄ is selected as the grating filling medium for the current design, and the deposition of SiO₂ film with 10 nm thickness could effectively prevent the damage of Si₃N₄ during bonding with the photocathode. The theoretical analyses offer important guidance in material selection and structural optimization in the grating cathode optical window used in the third-generation image intensifier for improving performance. Full article

Background and Objectives: The anatomically demanding structure of curved root canals increases the technical difficulty of retreatment procedures. This study aimed to evaluate the retreatment efficacy of various rotary and reciprocating instruments in curved root canals obturated with cold and warm techniques regarding root canal filling material removal, apical transportation, and retreatment time. Materials and Methods: Sixty-four curved mesial root canals of mandibular molars with Vertucci type IV morphology were prepared using the ProTaper Gold system and obturated with AH Plus sealer using either the single-cone (SC) (n = 32) or continuous wave vertical compaction (CWC) (n = 32) technique. Each group was divided into four subgroups (n = 8) and retreated using MicroMega Remover (MM Remover), ProTaper Universal Retreatment (PTUR), Reciproc (Rec), and Hedstrom file systems. Micro-computed tomography was used to assess residual filling material volume and apical transportation. The time required for retreatment was recorded. The level of statistical significance was set at p < 0.05. Results: Across both obturation techniques, the MM Remover and PTUR groups demonstrated shorter retreatment times compared with the CWC–Hedstrom group (p < 0.05). No statistically significant differences were observed among the file systems in terms of filling material removal and apical transportation (p > 0.05). Conclusions: All tested instruments effectively preserved root canal anatomy within clinically acceptable apical transportation limits. The MM Remover and PTUR systems achieved significantly shorter retreatment times, indicating clinical advantages in efficiency. None of the evaluated systems achieved complete removal of the filling materials in either obturation technique. This study provides one of the first comparative evaluations of the MM Remover system, supporting its applicability in complex canal configurations. Full article

The continuous degradation of mangrove ecosystems, considered among the most vulnerable worldwide, reveals multiple threats driven by human activities and climate change. In the Peruvian context, particularly in the Tumbes Mangrove ecosystem, these pressures are intensified by the absence of integrated spatial and educational infrastructures capable of supporting conservation efforts while engaging local communities. In response, this research proposes a Sustainable Interpretation Center for Conservation and Environmental Education in Ecologically Sensitive Areas of the Tumbes Mangrove, Peru. The methodology includes climate data analysis, identification of local flora and fauna, and site topography characterization, supported by digital tools such as Google Earth, AutoCAD 2025, Revit 2025, and 3D Sun Path. The results are reflected in an architectural proposal that incorporates sustainable materials compatible with sensitive ecosystems, including eco-friendly structural solutions based on algarrobo timber, together with resilient strategies addressing climatic variability, such as lightweight structures, elevated platforms, and passive environmental solutions that minimize impact on the mangrove. Furthermore, the proposal integrates a photovoltaic energy system consisting of 12 solar panels with a unit capacity of 450 W, providing a total installed capacity of 5.4 kWp, complemented by a 48 V LiFePO₄ battery storage system designed to ensure energy autonomy during periods of low solar availability. In conclusion, the proposal adheres to principles of sustainability and energy efficiency and aligns with the Sustainable Development Goals (SDGs) 7, 8, 12, 14, and 15, reinforcing the use of clean energy, responsible tourism, sustainable resource management, and the conservation of marine and terrestrial ecosystems. Full article

Special-shaped, concrete-filled steel tubes (SCFSTs) enhance the space efficiency of residential structures and improve aesthetics by avoiding exposed columns. However, the flat steel-plate connection sections are susceptible to local buckling. To mitigate this, corrugated steel plates are incorporated to enhance the local buckling resistance of the structure. This study examines the axial-compression performance and damage characteristics of SCFSTs connected by double-corrugated steel plates (DCP-SCFST) through full-scale static-loading tests. A finite element analysis explores the impact of column height, corrugated plate thickness, material strength, and connection length on the load-carrying capacity of DCP-SCFSTs. The study also presents the sectional strength and design method for these structures. The results indicate that the DCP-SCFSTs exhibit high bearing capacity and ductility under axial compression. The corrugated plates effectively restrain the concrete, markedly improving the buckling behavior of the connection section. Moreover, the corrugation wave size does not significantly affect the bearing capacity, whereas increasing the corrugated plate’s thickness enhances both the bearing capacity and ductility. This is attributed to the indirect confinement effect of corrugated plates. Additionally, the paper proposes design methods for sectional strength and overall stability, offering accurate formulas that offer valuable reference for the design of concrete-filled, corrugated plate members. Full article