Search Results (12,059)

The growing importance of sustainable technologies and environmental safety is promoting the implementation of green chemistry principles in the field of energetic materials. Traditionally, nitrocellulose-based propellants are plasticized with dibutyl phthalate (DBP), which is classified as a hazardous substance due to its toxicity and migration during storage. In this work, triethyl 2-acetylcitrate (ATEC) and tributyl 2-acetylcitrate (ATBC) were investigated as biodegradable and non-toxic alternatives to DBP. The objective of this study was to evaluate the thermal and chemical stability, physicochemical properties, and incorporation efficiency of these eco-friendly plasticizers in regard to propellants prepared from nitrocellulose of different origins and with nitrogen contents. The stability of the obtained propellants was assessed based on accelerated aging tests conducted in accordance with NATO STANAG 4582 and AOP-48 procedures. The results showed that both the ATEC- and ATBC-modified propellants meet the stability requirements corresponding to at least ten years of storage at 25 °C. The modified propellants showed slightly lower heats of combustion. Both plasticizers were effectively integrated into the nitrocellulose matrix without compromising density or stability. This study confirms that citric-acid-based plasticizers are promising green alternatives to conventional phthalates, offering improved environmental compatibility while maintaining the required performance and safety of nitrocellulose propellants. Full article

Apple purée is a processed food typically obtained from ground apples, where quality depends on colour, consistency, and shelf-life. Thermal treatments are commonly applied to adjust rheology and deactivate enzymes responsible for post-packaging deterioration. This study evaluated the effects of heating temperature (87–102 °C) and duration (6–17 min) on the physical and chemical properties of Golden Delicious apple purée. Three independent batches were processed to examine intra-varietal variability. Chemical analyses assessed enzyme activity and nutritional profile, while physical tests focused on rheology. Image analysis was employed to characterise colour and syneresis. Results showed that short-duration heating at higher temperatures (>100 °C, <12 min) achieved desirable rheological properties but intensified browning. No significant correlations were found between residual enzymatic activity, polyphenol content, antioxidant activity, and thermal treatment conditions. This suggests that changes in colour and texture are primarily related to the physical parameters of heating independently of the origin batch. In contrast, the batch had a significant impact on enzymatic and nutritional profiles, highlighting the need for strict monitoring of incoming fruit. Overall, the heating conditions influenced the visual and textural quality of the purée, while the variability in raw materials remained a significant factor affecting its biochemical characteristics. Full article

Efficient development of karst geothermal resources relies on the accurate identification of thermophysical and hydrogeological parameters. In this paper, the integrated wellbore–reservoir model of fluid and heat transport is applied to identify hydrothermal parameters of the karst geothermal system in Tianjin, China, based on multi-type field test data. A natural state model is conducted by fitting steady-state borehole temperature measurement results to identify formation thermal conductivity, while reservoir permeability is determined via the Gauss–Marquardt–Levenberg optimization algorithm based on dynamic temperature and pressure data from pumping tests. The parameter identification results indicate a reservoir permeability of 5.25 × 10⁻¹⁴ m² and a corrected bottom-hole temperature of 109 °C. Subsequently, productivity optimization for actual heating demands (1.33 × 10⁵ m²) yields an optimal heat extraction efficiency of 6.17 MW, with a flow rate of 80 m³/h, an injection well perforated length of 388 m, and an injection temperature of 30 °C. Additionally, addressing reservoir heterogeneity, the study finds that high-permeability zones between wells significantly shorten the safe operation duration of geothermal doublets, and reducing flow rate can mitigate thermal breakthrough risk to a certain extent. Full article

Soft actuators are widely explored as movers in various devices, human–machine interfaces, for medical purposes and other biomedical applications. Among them are soft actuators based on a foamed silicone matrix with the working liquid (WL) captured in its pores that undergo the liquid–gas phase transition. For the first time, to gain the actuation strain of such composites, we added, to the WL, a substance that sublimates during the composite actuation. C1–C3 alcohols were tested as WLs, while the sublimation substance (SS) used was benzoic acid dissolved in the WL. It was found that the rejuvenation procedure is able to fill the composite pores with WL + SS solution. The effect of benzoic acid addition was revealed using the two-stage heating mode. The sublimation substance effectively extends the composite strain for methanol and ethanol as WL for about 20%. For C3 propanols, the strain is left nearly unchanged. In the open-air conditions, the high diffusion of WL + SS in silicone allows only a single actuation that makes it a disposable actuator, i.e., a kind of safety switch is proposed. The results obtained in this work pave the way to future, powerful multipurpose “soft safeties” appliances. Full article

This study presents comprehensive experimental, analytical, and numerical analyses of heat transfer during countercurrent flow of Fluorinert FC-72 and distilled water within a multi-mini-channel (MMCH) module under steady-state conditions. The experimental investigation was conducted in a test section inclined at an angle of 165 degrees relative to the horizontal plane, utilizing an infrared camera to measure the external temperature of the heated mini-channel (MCH) wall. The test module comprised twelve MCHs: six hot (HMCH) and six cold mini-channels (CMCH), each with a rectangular cross-section. The dimensions of each MCH are 140 mm in length, 18.3 mm in width, and 1.5 mm in depth, with a hydraulic diameter of d_h = 2.77 mm. The heating system on the top wall of the external heated copper comprises a halogen heating lamp. Results include infrared thermographs, temperature distributions, and heat transfer coefficients (HTCs) along the channels. Local HTCs were calculated using a one-dimensional (1D) approach, a simple analytical method, at interfaces such as the heated plate—HMCHs, HMCHs—separating plate, separating plate—CMCHs, and CMCHs—closing plate. CFD simulations conducted with Simcenter STAR-CCM+ incorporated empirical data from experiments, using parameters like temperature, pressure, velocity profiles, and heat flux density to determine HTCs. The maximum difference between the 1D method and CFD results was 29% at the HMCHs/separating plate interface. In comparison, the minimum was 13.5% at the separating plate/CMCHs interface, with an average across all channels and heat flux densities. Full article

The addition of reinforcement particles can considerably improve the mechanical properties of 7xxx series aluminum alloy. In this work, the effects of TiB₂ reinforcement particles on the microstructure, mechanical properties, strengthening mechanisms, and aging precipitation of TiB₂/Al-Zn-Mg-Cu composites were systematically investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and tensile testing machine. The results indicate that when the TiB₂ content is 1 wt.%, the composite achieves a tensile strength of 831 MPa while maintaining an elongation of 6.7%, meeting the research objectives of this experiment. When the aging heat treatment temperature is set at 120 °C, the peak aging time is shortened to 20 h. The interfacial phase composed of solute elements preferentially nucleates near the TiB₂ particles during the cooling process. With the increase in TiB₂ content, clustering in localized regions slows down the diffusion rate of interfacial phases into the matrix, thereby increasing the required duration of the solution treatment. Excellent interfacial relationships exist between TiB₂ particles and both the aluminum matrix and the MgZn₂ phase. It is also found that with the increase in TiB₂ content, the aging-hardness response of TiB₂/Al-Zn-Mg-Cu composites is accelerated and the work hardening rate is reduced. In addition, a multi-component strengthening model for the yield strength of the composite was established based on various strengthening mechanisms, including second-phase strengthening, dislocation strengthening, age-precipitation strengthening, and fine-grain strengthening. The results indicate that age-precipitation strengthening and dislocation strengthening are the most significant contributors to strength in the composite. Full article

The aim was to optimize a series of aluminosilicate glasses for the synthesis of leucite glass-ceramics (GC) for dental applications. Appen predictive models were used to design a series of aluminosilicate glasses to control optical, thermal and mechanical properties. Glasses were produced using melt quenching methods, annealed and processed into powders and further heat-treated and milled to produce GC powders. Glasses/GCs were characterized using dilatometry, HTXRD, SEM and ²⁷Al MAS-NMR and GCs tested using biaxial flexural strength (BFS) for comparison to commercial leucite GC products. The results indicated good prediction to experimental measurement correlations (for coefficient of thermal expansion, refractive index and density) and provided evidence of leucite GCs’ optimization compared to commercial products. This included significant BFS and Weibull m increases, improved microstructural control and designed translucency, meeting the demands for strong, esthetic and durable single-tooth restorations. The simple predictive approach, combined with complementary characterization techniques, allowed structure–property relations of aluminosilicate glasses/glass-ceramics to be understood, and may find similar applications in other glass systems beyond dentistry. Full article

This paper reports the spinning and wear comfort properties of polyethylene terephthalate (PET)/copolymer-PET (Co-PET) hollow yarns and their fabrics, as well as the effect of the wt.% of inorganic particles embedded in the core of the bicomponent yarns. The results are discussed in terms of the types and amounts of inorganic particles (titanium dioxide (TiO₂) and calcium carbonate (CaCO₃)) embedded in the sheath of the bi-component yarns (Kolon semi-dull (KSD), Kolon full-dull (KFD), and Kolon calcium carbonate (KCC) PET/Co-PET yarns). The three sheath/3-core bicomponent yarns developed in this study exhibited good spinnability and weavability with relatively strong tenacity and breaking strain. Their optimal spinning conditions were determined. The KCC PET/Co-PET fabric showed the greatest hollowness ratio, followed by the KFD PET/Co-PET and KSD PET/Co-PET fabrics. This might be attributed to the higher wt.% (2.5 wt.%) of CaCO₃ particles embedded in the sheath of the KCC PET/Co-PET yarns and to the larger particle size (0.8 μm) of CaCO₃. Regarding the wear comfort, the moisture management system (MMT) test indicated that the KFD PET/Co-PET fabric is suitable for market applications because of its good moisture absorption and rapid drying. The KFD PET/Co-PET fabric is useful for winter clothing applications because of its relatively high heat retention rate and lack of durability issues with washing. An examination of the wearing performance for fitness with a tactile hand feel showed that KFD and KCC/Co-PET fabrics imparted a softer tactile hand feel than the KSD PET/Co-PET fabric. On the other hand, the KCC PET/Co-PET fabric was assumed to have some issues with wearing durability. Full article

Outdoor environments typically require intensive cooling during the day, while nighttime cooling demands are comparatively modest. Conventional radiative-cooling systems deliver strong cooling at night but often underperform during daytime solar exposure. Here, we develop a PCM-integrated radiative cold-storage system (RCSS) that couples a polymer metasurface radiative-cooling (PMRC) film with a paraffin cold-storage tank via a helical-tube heat exchanger, and validate it through outdoor tests supplemented by CFD-based analysis. Under representative outdoor conditions, the RCSS cools circulating water at an average nighttime rate of 3.1 K h⁻¹ and maintains stable performance for initial water temperatures of 25–55 °C. Using PMRC’s cooling power as the benchmark for effective radiative-cooling power, we quantify the system-level heat-transfer pathways and provide design sensitivities with respect to film area, exchanger geometry, and tank dimensions. The results establish a practical route to all-day thermal management by storing “cold” at night and releasing it on demand, thereby facilitating scalable deployment of radiative-cooling technologies. Full article

Despite severe particulate matter (PM) pollution in Central Asia, limited air composition and health impact data are hindering sustainable air quality management and resilient urban planning. This study provides the first comprehensive assessment of PM_2.5 and PM_2.5–10 in the urban environment of Astana, Kazakhstan, a rapidly expanding city with intense winter heating demands. We characterized PM and atmospheric precipitation and assessed health risks using bioaccessible fractions of PM-bound potentially toxic elements (PTEs). Among 388 samples, PM_2.5 and PM_2.5–10 concentrations peaked at 534 and 1564 μg·m⁻³, respectively. Scanning electron microscopy (SEM) identified soot and coal fly ash, indicating fossil fuel combustion as a major source. Precipitation characterization also showed elevated SO₄²⁻ (17.8 μg⋅L⁻¹), V (108 μg⋅L⁻¹), Ni (84.0 μg⋅L⁻¹), and Mn (63.2 μg⋅L⁻¹). Bioaccessibility tests showed high solubility for Fe (16,229 mg·kg⁻¹) followed by V: key indicators of combustion emissions. Non-carcinogenic risk for Ni and V exceeded acceptable limits for adults and children (e.g., HQ: 6.07 for V for adults). Carcinogenic risk exceeded the threshold 10⁻⁶ for Cd (adults), Co, Cr, and Ni. These findings may help advance urban air quality management via integrating bioaccessibility-based health risk assessment and source apportionment, supporting evidence-driven policies for environmentally responsible development in rapidly urbanizing cold-climate regions. Full article

High-strength S690 steel is becoming increasingly popular in Hong Kong because of its numerous advantages in terms of mechanical properties and cost-effectiveness. Compared to normal-strength steel, the welding parameters such as preheat temperature, inter-pass temperature, and heat input energy of high-strength S690 steel should be controlled more strictly; additional post-weld heat treatment should be carried out for hydrogen diffusion in some situations. These strict requirements pose challenges to welding operations at construction sites. In Hong Kong, all field connections of high-strength S690 steel components are made using bolted connections, and there are currently no precedents for welded connections on site. To verify the reliability of on-site welding and optimize the welding process to facilitate operation, on-site welding tests of high-strength S690 steel with various welding procedures were conducted. These welding tests were first performed on the steel plates, followed by tests on the H-section steel components, to examine the mechanical reliability of the welding connections under tension and compression. The effects of heat input energy, welding joints, post-weld heat treatment, and wind blocking measures on welding quality and welding efficiency were studied. Full article

Rising global temperatures are driving an urgent need for buildings that consume less energy while maintaining comfort. Cooling demand is surging worldwide, yet conventional air-conditioning remains energy-intensive and carbon-heavy. Against this backdrop, radiative cooling materials have gained attention as a passive solution capable of reflecting incoming solar radiation while emitting thermal energy to the sky. This study aims to establish a climate-informed framework that quantitatively predicts the energy-saving potential of façade-integrated radiative-cooling materials across diverse East Asian climates. By synergizing hour-by-hour building-energy simulation with three novel atmospheric suitability indices, we provide a transferable methodology for selecting and optimizing passive cooling strategies at urban and regional scales. Three façade configurations were tested, i.e., a conventional absorptive surface, a common radiative cooling surface, and an idealized high-reflectance and high-emissivity surface. The results show that the ideal case can reduce wall surface temperatures by up to 20 °C, suppress diurnal heat flux swings by 60–80%, and cut annual cooling demand by 5–80 kWh per square meter, depending on climate conditions. To generalize these findings, three new indices—the Weather Structure Index, Diurnal Temperature Index, and Composite Climate Applicability—were proposed. Regression models with R² values above 0.9 confirm the Composite Climate Applicability index as a robust predictor of energy-saving potential. The outcomes demonstrate that radiative cooling is not only highly effective in hot, humid regions but also unexpectedly beneficial in clear, cold climates, offering a practical, climate-informed framework for advancing low-carbon building design. Full article

In this cross-sectional, ecological study of Los Angeles County ZIP codes, we evaluated the association between tree canopy coverage and asthma prevalence. Urban tree canopy has been promoted as a way to improve air quality and mitigate urban heat, but its relationship with asthma is not well established. Previous studies have shown mixed results, and little is known about whether associations differ between children and adults or across communities with varying demographic compositions. This study evaluated the association between tree canopy coverage and asthma prevalence across Los Angeles County ZIP codes. Data from 75 ZIP codes with complete information on canopy cover and asthma prevalence were analyzed using correlation, t-tests, and regression models adjusting for population density and minority population composition. Greater canopy coverage was associated with lower pediatric asthma prevalence (β = −0.625, p < 0.001); pediatric rates were 12.7% in low-canopy ZIP codes compared with 10.5% in high-canopy ZIP codes (t = 6.07, p < 0.001). This inverse relationship was stronger in ZIP codes with higher minority populations (interaction β = –0.0145, p = 0.006). In contrast, canopy coverage showed a weak but statistically significant positive association with adult asthma prevalence (β = 0.33, p < 0.001). These findings suggest that urban tree canopy may play a role in reducing pediatric asthma disparities, underscoring the potential of equitable urban forestry strategies as part of public health planning. Full article

The paper focuses on fault diagnosis in nonlinear analog circuits, a topic that has been explored in the literature for over 50 years but remains unresolved due to its complex nature. It reviews various aspects of nonlinear circuit diagnosis, including methods for assessing testability, selecting diagnostic tests, and conducting diagnostic processes through simulation before and after test methods. The paper also discusses the use of artificial intelligence tools in this context. Given the specific characteristics of nonlinear circuits used as DC-DC converters and the wealth of the existing literature—including review papers on the subject—this issue is addressed only briefly. The main aim of the paper is to identify research challenges in fault diagnosis for a general class of nonlinear circuits. To illustrate and discuss these challenges, the paper provides examples, including ambiguity in diagnostic equation solutions, multiple equilibrium points, and the effects of self-heating. These examples can serve as simple benchmarks for new proposals to advance comprehensive diagnosis methods for nonlinear circuits. Full article

This study looks into the parameters that affect the heat transfer coefficient (h₂) on the wet surfaces of vertical tube indirect evaporative coolers (VTIEC). An experimental platform was used to investigate the impact of secondary-to-primary airflow ratios (AFR) and spray water density on the HTC. The findings show that raising the primary air temperature drop, expanding the outside dry-bulb and wet-bulb temperature differences, and decreasing the air-to-water ratio improve heat transmission. The HTC of the wet sides ranged from 34.79 to 924.5 W/(m²·°C) throughout testing. To achieve optimal performance, aim for a spray water density of 2.07 to 3.46 m³/(m²·h), an AFR of 0.5 to 0.6, and a primary air temperature drop of at least 6 °C. These factors help keep the h₂ above 350 W/(m²·°C). Full article