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Supersonic flow behavior in jet engine nozzles from subsonic to supersonic regimes: Turbulence influence on shock structures and performance metrics
No full textThis study presents a numerical investigation of supersonic flows through a convergent conical rocket engine nozzle, focusing on the influence of turbulence models on shock structures and nozzle performance. Simulations were performed in ANSYS Fluent for nozzle pressure ratios (NPRs) from 1.4 to 7.0 under steady-state conditions. Four turbulence models [Realizable k–ε, Standard k–ω, Shear Stress Transport (SST) transition model, and Reynolds Stress Model (RSM)] were evaluated for their ability to predict Mach distributions, shock-cell structures, and pressure-based performance metrics. Results indicated that the SST k–ω model provided sharper, more accurate shock-cell structures and captured shock–boundary-layer interactions more effectively, especially at higher NPRs. At NPR = 5.0, the SST model predicteda maximum exit Mach number of 1.85, closely matching the experimental 1.88 ± 0.03, whereas the Realizable k–ε model underestimated it at 1.75. The k–ε model offered greater numerical stability and lower computational cost but tended to oversimplify flow features and underpredict shock intensity. RSM captured anisotropic turbulence effects but required more computational resources and exhibited higher sensitivity. Aerodynamic performance evaluation showed that the SST model predicted thrust and discharge coefficients (CV, CD) more accurately across all NPRs. At NPR = 4.0, it produced a CV of 0.92 and a CD within 3% of experimental values, compared to 0.87 and up to 7% deviation for the k–ε model. Therefore, the SST model was recommended for high-fidelity analyses requiring accurate prediction of shock behavior and nozzle performance, while the realizable k–ε model was suitable for preliminary analyses prioritizing faster, stable convergence with reduced detail
Assessment of bio-based, environmentally friendly epoxy coatings created via substituting bisphenol A epoxy with bio-based glycerol triglycidyl ether
No full textDespite the popularity of epoxy coatings based on Bisphenol A due to their superior mechanical properties, chemical resistance, favorable electrical characteristics, and low moisture absorption, they are deficient in terms of high brittleness, low impact resistance, and poor yellowing resistance. Bio-based epoxy resins have garnered increasing attention due to their economic and environmental advantages. The present study investigates the impact of substituting bisphenol A diglycidyl ether (DGEBA) with glycerol triglycidyl ether (GTGE) in varying proportions to develop bio-based, environmentally friendly epoxy coatings. The findings indicate that increasing the proportion of GTGE enhances the coatings' impact resistance, yellowing resistance, and scratch resistance. While substituting 25% of DGEBA with GTGE improved the bio-content and yellowing resistance, the overall coating characteristics remained largely unchanged. However, a complete substitution of DGEBA with GTGE significantly improved adhesiveness, impact resistance, and yellowing resistance, albeit at the cost of reducing hardness by approximately 50%. Furthermore, the contact angle of coatings with DGEBA (71.38°) was notably higher than those with a higher GTGE content (45.25°), indicating improved surface spreading with increased GTGE. These results demonstrate that increasing the GTGE content enhances surface smoothness and adhesiveness, offering potential advantages for environmentally friendly coating applications
High-solid acrylic resins based on bio-derived lauryl methacrylate for varnish and paint applications
No full textThe popularity of acrylic resin in the paint and coating industry has grown in recent years due to its superior chemical resistance, durability, and flexibility. However, there is a notable research gap in formulating high-solid acrylic resins from bio-based materials to reduce volatile organic compounds (VOCs) and improve sustainability. In this study, we developed two-component (2 K) acrylic resins based on bio-derived lauryl methacrylate (LMA) with 70% solid content and viscosity of up to 10 poises for durable coating applications for the first time. The acrylic copolymer resins were prepared by free radical polymerization using a low-toxicity solvent, n-butyl acetate. The resins were then mixed with aliphatic polyisocyanate to prepare the paint and varnish formulations. The results showed that higher OH levels increased the crosslink density and improved the hardness and hydrophobicity of the LMA-based resin. For example, the water contact angle and hardness increased from 65° and 105 Persoz to 85° and 210 Persoz, respectively, when the OH value increased from 1.5% to 4.5%. The incorporation of LMA greatly improved the adhesion properties, impact resistance, flexibility, and corrosion resistance of the resin. Notably, no visible detachment, cracking, or corrosion was observed in the LMA-based resin with 4.5% OH. In summary, optimizing OH levels and incorporating LMA monomer into high-solids acrylic resins can significantly enhance their performance, rendering them ideal for durable coatings with enhanced tear, abrasion, impact, and moisture resistance
Defending Social and Ecological Space: A Critical Analysis of the Documentary Film Dragon for Sale and Premium Tourism on Komodo Island, Indonesia
No full textThis research examines the controversy surrounding premium tourism development in Labuan Bajo. It specifically focuses on the eviction of the Ata Modo community from Komodo Island, as depicted in the documentary Dragon for Sale. The documentary is both a cinematic work and a journalistic report that documents real-life socio-political issues. Using Teun A. van Dijk's Critical Discourse Analysis (CDA), the study examines the tension between government-driven tourism policies and the rights of local communities. It delves into the government's plans for tourism development around Komodo dragons, highlighting the adverse impacts on local communities, including displacement and loss of cultural identity. The findings underscore the conflict and deprivation of community rights, emphasising the exclusion of local voices from decision-making and calling for more inclusive, equitable, and sustainable tourism policies
Comparatives structural and mechanical assessment of hot forged and hot press sintered 1%-Mo 16MnCr5 case hardening steel
No full textThe 16MnCr5 alloy, a low-carbon case-hardening steel, widely utilized in automotive and machinery industries owing to its high surface hardness, core toughness along with wear resistance. Traditional manufacturing methods often result in extensive material wastage and limited geometric flexibility, whereas powder metallurgy (PM) offers near-net-shape processing, However, accomplishing full densification through conventional sintering remains to pose difficulties resulting from residual porosity, which may degrade mechanical performance. This study systematically investigates three PM processing routes for 16MnCr5 alloy containing 1 wt% Mo: (1) conventional sintering, (2) conventional sintering followed by hot forging and annealing and (3) hot press sintering, the resulting materials are designated as 16MnCr5-S, 16MnCr5-SFA and 16MnCr5-HPS, respectively. The samples were characterized for microstructure, density, and hardness using optical/SEM microscopy, XRD, EDS, and Archimedes density measurements. Results show that conventional sintering solely led to coarse ferritic grains, porosity, and the lowest density and hardness values. Hot press sintering achieved a homogeneous, fine-grained microstructure with reduced porosity due to simultaneous heat and pressure, but moderate hardness compared to 16MnCr5-SFA. The latter, displayed the highest density and hardness which can be ascribed to plastic deformation, strain-induced recrystallization refining grains, higher carbon diffusion, and stress relief during annealing in the same line, EDS revealed localized Cr and Mn segregation attributed to carbide precipitation. Overall, post-sintering thermomechanical treatment demonstrated most effective for enhancing density, hardness, and microstructural refinement in PM 16MnCr5, whereas hot press sintering offers a viable alternative for producing structurally uniform and chemically homogeneous components
Microbial threats in raw food products: prevalence of bacterial pathogens Ameaças microbianas em produtos alimentícios crus: prevalência de patógenos bacterianos
No full textFood safety has emerged as a major global public health concern due to microbiological risks associated with raw food products. This study aimed to determine the prevalence of bacterial pathogens in raw beef, raw chicken, fish, leafy greens (lettuce, parsley, spinach), and raw milk samples collected in Kocaeli, Türkiye, between May and October 2024. A total of 220 samples were analyzed using standardized microbiological methods for Escherichia coli, Staphylococcus aureus, Salmonella spp., Listeria monocytogenes, and Shigella spp. The colony counts were determined and expressed as CFU/g or CFU/mL according to ISO protocols. E. coli was detected in 59.54% of the samples analyzed, S. aureus in 31.81%, Salmonella spp. in 10%, and L. monocytogenes in 0.9%. The detected microbial counts, particularly for E. coli and S. aureus, exceeded the limits established by the Turkish Food Codex and EU regulations for raw food products, indicating potential health risks. The elevated microbial counts may be explained by hygiene deficiencies during production, handling, and storage, including inadequate sanitation, contaminated equipment, and environmental exposure. E. coli was the most frequently detected bacterium, particularly in raw milk (80%) and leafy greens (75%). Salmonella spp. was mainly found in raw chicken (17.5%) and fish meat (11.9%), while S. aureus was most prevalent in raw milk (53.33%) and fish meat (47.61%) samples. L. monocytogenes was detected at low levels only in raw beef (2.04%) and raw chicken (2.5%), while Shigella spp. was not detected in any of the samples. The results suggest that hygiene deficiencies may be among the potential factors contributing to contamination, along with other possible contamination sources throughout the production and handling chain
ULK1-driven autophagy modulation alters tumor-promoting pathways in triple-negative breast cancer
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Evaluation of neutrophil-to-lymphocyte and platelet-to-lymphocyte ratios for stroke predictability in postoperative patients with carotid artery stenosis
No full textBackground/Objectives: Previous studies have reported that inflammatory biomarkers have prognostic value in various fields, including vascular surgery. Biomarkers such as neutrophil-lymphocyte ratio (NLR) and platelet-lymphocyte ratio (PLR) help identify patients at higher risk for cerebrovascular events, as well as in the treatment and follow-up of patients. There are studies investigating the usefulness of these biomarkers for carotid artery disease. However, data on whether they help predict neurological complications after carotid artery surgery are limited. This study examined the correlation between preoperative carotid arterial stenosis severity, symptomatic presentation, and PLR and NLR levels as potential biomarkers for predicting postoperative neurological complications. Methods: We retrospectively analyzed the preoperative and postoperative demographics, physical examination, and laboratory results of patients who underwent carotid endarterectomy for carotid artery stenosis in our clinic between January 2019 and January 2023. Results: While our findings did not demonstrate a statistically significant correlation between NLR and PLR levels and postoperative neurological complications, elevated platelet counts were associated with such complications, underscoring the importance of antiplatelet therapy in managing carotid artery disease. Conclusions: The study linked high platelet counts to postoperative complications and highlights the importance of antiplatelet therapy in managing carotid artery disease. The differences in findings highlight the complexity of stroke prediction and the need for a multifactorial approach