Search Results (62)

Accurately predicting high-energy laser propagation toward fast-moving aerial targets is not straightforward, since the slant range, elevation angle, atmospheric path, accumulated turbulence, and thermal blooming all change along with target motion. Because of this coupled evolution, fixed-path or quasi-static models can hardly describe, in a complete way, the time-varying loss of beam transmission and the weakening of energy concentration. To address this problem, this paper builds on established wave-optics propagation methods to develop a dynamic multi-physics framework for high-speed moving-target engagements. The central idea is to rebuild the propagation environment at every time step according to the instantaneous target position so that the optical path can be linked with height-dependent extinction, refractive-index structure, and absorption profiles; meanwhile, relative motion is represented as an effective transverse sweeping velocity, which helps reduce the accumulation effect of thermal blooming. Based on a unified split-step Fourier method, the model combines Beer–Lambert path attenuation, Kolmogorov-spectrum multilayer phase screens, and thermal-blooming phase modulation, yielding time-resolved indicators such as transmittance, received power, peak irradiance, Strehl ratio, scintillation index, pointing error, and beam-quality factor. Simulation results show that, in a 500 m static horizontal path, the attenuation module reduces to the Beer–Lambert solution, with the maximum relative error kept below ${10}^{-14}$; the turbulence phase-screen implementation is validated against the absolute Kolmogorov prediction. Over the resolved inertial interval, the ensemble-averaged structure function yields a fitted exponent $p_{\mathrm{f}\mathrm{i}\mathrm{t}}=1.671$ (theoretical: $5/3=1.667$) and a relative normalization error of $2.5\mathrm{\%}$, confirming that the generated screens reproduce both the Kolmogorov scaling and the prescribed turbulence strength. For a 1.064 μm, 2 kW Gaussian beam propagating over a 50 s trajectory of about 8 km, when the target speed increases from 0 to 300 m/s, the thermal-blooming-related beam-quality factor decreases from roughly 1.8 to 1.2, which indicates that dynamic geometry, turbulence, attenuation, and thermal blooming need to be considered together when evaluating laser propagation performance. Full article

This study evaluated the effect of chitosan with a high degree of deacetylation (75–85%) and three different molecular weights—low (50–190 kDa), medium (190–310 kDa), and high (310–375 kDa)—on the coating of vesicular systems. Chitosan solutions were characterized in acidulated aqueous medium by determining changes in pH, electrical conductivity, zeta potential, surface tension, viscosity, transmittance, particle size, and polydispersity index (PDI) with respect to polymer concentration. Subsequently, nanoliposomes were developed using an ethanol injection method assisted by ultra-high-pressure homogenization (UHPH) prior to coating. The characterization of the vesicular systems involved particle size analysis, polydispersity index (PDI), and zeta potential, which were evaluated at zero time and at the fourth week prior to storage at 4 °C and 40 °C. The physicochemical characterization of chitosan solutions displayed an inflection point at 1 × 10⁻³ M, which was taken as the coating concentration. In general, non-coated liposomes ranged between 150 and 200 nm, with low polydispersity (<0.3) and negative zeta potentials around ~−43 mV. Chitosan coating significantly increased particle size and PDI, while decreasing zeta potential values, but within the same negative value range, suggesting a slight interfacial coating effect. Finally, the systems subjected to UHPH and coated with high- and medium-molecular-weight chitosan showed interesting stabilization against storage conditions in the thermal stress tests. Full article

Infrared cameras used in radio telescopes often suffer image degradation in complex optical and thermal environments. Solar radiation, convergent reflected light, and thermal emission from support structures can substantially impair imaging performance. To address this problem, this paper proposes a split reflective ellipsoidal baffle for suppressing infrared imaging degradation. Unlike conventional baffles, which mainly rely on structural occlusion and surface absorption, the proposed design functions as an upstream stray light regulation unit. It also establishes a computational framework integrating ellipsoidal vane geometry, realistic edge microtopography modelling, ray-tracing simulation, and detector plane irradiance response analysis. First, the reflective properties of the ellipsoidal surface are used to construct an off-axis stray light propagation constraint model. Under this model, incident stray radiation is redirected away from the effective imaging path or guided into light-trapping regions between adjacent vanes. Second, a laser confocal microscope is used to capture the true three-dimensional edge morphology of vanes with different materials and machining angles. This strategy addresses the limitations of the conventional 0.02 mm rounded edge approximation, which cannot accurately represent real scattering behaviour. The measured morphologies are then converted into high-fidelity computational models compatible with ray-tracing analysis. Furthermore, stray light suppression performance is evaluated using point source transmittance, detector plane irradiance distribution, and grey scale response in experimental images. Simulation and darkroom experiments show that the proposed baffle suppresses residual stray light more effectively than conventional absorptive baffles. The results demonstrate a computable, manufacturable, and experimentally verifiable strategy for front-end stray light control and baffle optimisation. This strategy can also support image quality enhancement in infrared imaging systems operating under complex optical and thermal environments. Full article

This paper introduces the dynamic hygrothermal performances of existing walls in humid climates using the EN ISO 15026 procedure. Water content, mould formation and freezing risk were investigated considering rock wool (RW) and expanded polystyrene (EPS) allocated at different points of two typologies of existing walls requiring renovation. Results show that RW is recommended for insulation on the external side, whereas EPS is more suitable for the internal side. A freezing risk occurs in massive walls insulated internally with RW in severe winter climates. Mould formation appears in the initial phases on the renovated side, driven by the built-in humidity of the new layers. Wall thermal transmittance shows large fluctuations, especially in lightweight structures renovated with EPS, reaching an increase of over 22% at the beginning of the heating period, driven by EPS water content peaks of 1.9 kg/m² in cold climates when installed on the external side, achieved in a stabilized regime and independently from the wall’s technical solution. Outcomes confirm transient hygrothermal analysis as the recommended approach to evaluate the component behaviour over a long-term projection, facilitating sizing in the design phase and ensuring compliance with regulations for retrofitted elements. Full article

This study evaluates the optical and thermal performance of near-infrared (NIR)-blocking spectacle lenses at luminous transmittance grades of 0, 2, and 3. Ten lens types were tested, including clear, tinted, and NIR-blocking spectacle lenses (NIBSL). The NIR blocking rate was measured across 780–1100 nm and 1100–1400 nm wavelength bands. Color reproduction was assessed using sharpness (MTF 50), point spread function (PSF), and color accuracy (ΔE₀₀) under 1000 lux outdoor illumination. Thermal insulation was analyzed by monitoring porcine skin temperature at 36 °C and 60 °C under each lens type. As a result, the NIBSL showed better near-infrared blocking performance than other types of lenses in both wavelength ranges, and the coated NIBSL blocked near-infrared more effectively than the polymerized lenses. Compared with other types of lenses, NIBSL showed no difference in object identification, color recognition, and reproducibility, so there is no problem in using them together. Strong correlations were observed between lens surface temperature and underlying pig skin temperature, and inverse correlations between NIR blocking rate and pig skin temperature gradient. These findings confirm that NIBSL offer enhanced protection against NIR-induced thermal effects without compromising optical performance, supporting their use in daily environments for ocular and skin safety. Full article

Titanium thin films with thicknesses of up to 105 nm were deposited on borosilicate glass implementing low-power continuous (25 W) and pulsed (85 W, with an ultra-low duty cycle) DC magnetron sputtering. The characteristics of the resulting films were studied via atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), VIS spectroscopy, and four-point-probe measurements. Both deposition modes yield films with low surface roughness, and AFM analysis showed no topographical features indicative of columnar-and-void structures. The films exhibited high optical reflectivity and stable transmittance and reflectance across the visible spectrum. The electric resistivity could be measured even at single nanometer thickness, emphasizing the metallic character of the films and approaching the bulk titanium value at higher film thicknesses. The low power regime of magnetron sputter deposition not only offers the possibility of studying the development of physical characteristics during the growth of ultra-thin films but also provides the advantage of extremely low heat development and no evident mechanical stress on the substrate during the coating process. These results outline a path for low-power DC sputtering as a reliable approach for studying the evolution of functional properties in ultra-thin films and for the gentle fabrication of coatings where thermal stress must be avoided, making the method compatible with temperature-sensitive applications. Full article

Underground cold storage gives rise to special challenges that require innovative solutions to ensure maximum energy efficiency. Conventional energy systems tend to be based on high energy use, so sustainable solutions are crucial. This study explores the novel idea of biomimetics and how it might be used in the planning and building of underground cold storage facilities as well as other infrastructure projects. Biomimetic strategies, inspired by termite mounds, gentoo penguin feathers, and beehive structures, are applied to minimize reliance on energy-intensive cooling systems. These natural models offer efficient thermal regulation, airflow optimization, and passive cooling mechanisms such as geothermal energy harvesting. The integration of naturally driven convection and ventilation ensures stable internal temperatures under varying conditions. Biomimicry was employed in Revit Architecture, coupled with structural optimization, to eliminate urban space’s limitations and further increase energy efficiency. The analytical work for this paper utilized a set of formulas that represent heat flow, thermal resistance, R-value, thermal transmittance, U-value, solar absorption, and G-value. The results pointed to very good insulation, with exterior walls having an R-value of 10.2 m²K/W and U-value of 0.98 W/m²K. Among the chosen 3-layer ETFE cushion with a U-value of 1.96 W/m²K, with a G-value of 0.50, showed good heat regulation and daylight management. Furthermore, bagasse-cement composites with a very low thermal conductivity of 0.10–0.30 W/m·K provided good insulation. This research proposes a scalable and sustainable approach in the design of underground cold storage by merging modelling based on Revit with thermal simulations. Biomimicry has been demonstrated to have the potential for changing subterranean infrastructure, conserving energy consumption, and creating eco-friendly construction practices. Full article

A series of Si-H- or Si-Vi-terminated, branched and linear oligomers containing Me₂SiO segments were prepared by equilibrium polymerization or non-equilibrium polymerization initiated by living anions, respectively. These oligomers were used to improve the defects of concentrated crosslinking points and the high hardness of crosslinked products when using phenyltris(dimethylsiloxy)silane or 1,1,5,5-tetramethyl-3,3-diphenyl trisiloxane as crosslinking agents in the preparation of silicone gel. NMR, FT-IR, and GPC characterized the structure and molecular weight information of the prepared oligomers. The effects of equilibrium polymerization and the anionic non-equilibrium ring-opening polymerization methods on the structure of oligomers were investigated in detail, together with the structure, the molar ratio of SiH to SiVi, and the phenyl content on the thermal properties and the transmittance retention yield of the silicone gel. The introduction of phenyl groups increases the glass transition temperature of silicone gel from −121.29 °C to −117.71 °C when the phenyl content increased from 0.88 wt% to 3.17 wt%. Meanwhile, the thermal decomposition temperature of silicone gel at 10% weight loss in the N₂ atmosphere increased from 440.5 °C to 480.0 °C. When the SiH/SiVi molar ratio is close to 1.0, the transmittance retention yield of the prepared silicone gel using Si-Vi-terminated phenyl T-shaped polysiloxane as the matrix and α, ω-dimethylsiloxyl-terminated PDMS as the crosslinking agent could reach 88.9% after 25 min of UV irradiation. Full article

Although much information can be gained about thermally induced microstructural changes in metals through the measurement of their thermophysical properties using a differential scanning calorimeter (DSC), due to competing influences on the signal, not all microstructural changes can be fully characterised this way. For example, accurate characterisation of recrystallisation, tempering, and changes in retained delta ferrite in alloyed steels becomes complex due to additional signal changes due to the Curie point, oxidation, and the rate (and therefore the magnitude) of transformation. However, these types of microstructural changes have been shown to invoke strong magnetic and electromagnetic (EM) responses; therefore, simultaneous EM measurements can provide additional complementary data which can help to emphasise or deconvolute these complex signals and develop a more complete understanding of certain metallurgical phenomena. This paper discusses how a DSC machine has been modified to incorporate an EM sensor consisting of two copper coils printed onto either side of a ceramic substrate, with one coil acting as a transmitter and the other as a receiver. The coil is interfaced with a custom-built data acquisition system, which provides current to the transmit coil, records signals from the receive coil, and is controlled by a graphical user interface which allows the user to select multiple excitation frequencies. The equipment has a useable frequency range of approximately 1–100 kHz and outputs phase and magnitude readings at a rate of approximately 50 samples per second. Simultaneous DSC-EM measurements were performed on a nickel sample up to a temperature of 600 °C, with the reversable ferromagnetic to paramagnetic transition in the nickel sample invoking a clear EM response. The results show that the combined DSC-EM apparatus has the potential to provide a powerful tool for the analysis of thermally induced microstructural changes in metals, feeding into research on steel production, development of magnetic and conductive materials, and many more areas. Full article

A high-temperature-resistance single-crystal magnesium oxide (MgO) extrinsic Fabry–Perot (FP) interferometer (EFPI) fiber-optic vibration sensor is proposed and experimentally demonstrated at 1000 °C. Due to the excellent thermal properties (melting point > 2800 °C) and optical properties (transmittance ≥ 90%), MgO is chosen as the ideal material to be placed in the high-temperature testing area. The combination of wet chemical etching and direct bonding is used to construct an all-MgO sensor head, which is favorable to reduce the temperature gradient inside the sensor structure and avoid sensor failure. A temperature decoupling method is proposed to eliminate the cross-sensitivity between temperature and vibration, improving the accuracy of vibration detection. The experimental results show that the sensor is stable at 20–1000 °C and 2–20 g, with a sensitivity of 0.0073 rad (20 °C). The maximum nonlinearity error of the vibration sensor measurement after temperature decoupling is 1.17%. The sensor with a high temperature resistance and outstanding dynamic performance has the potential for applications in testing aero-engines and gas turbine engines. Full article

Starches plasticized with glycerol/citric acid/stearic acid and tributyl 2-acetylcitrate (ATBC), respectively, were processed with poly (butylene adipate-Co-terephthalate (PBAT) via extrusion and a film-blown process. All the composite films were determined for morphology, mechanical, thermal stability, crystalline, and optical properties. Results show that the most improved morphology was in the 30% glycerol plasticized PBAT/thermoplastic starch (TPS) composite films, characterized by the smallest and narrowest distribution of TPS particle sizes and a more uniform dispersion of TPS particles. However, the water absorption of PBAT/TPS composite films plasticized with glycerol surpassed that observed with ATBC as a plasticizer. Mechanical properties indicated insufficient plasticization of the starch crystal structure when using 10% ATBC, 20% ATBC, and 20% glycerol as plasticizers, leading to poor compatibility between PBAT and TPS. This resulted in stress concentration points under external forces, adversely affecting the mechanical properties of the composites. All PBAT/TPS composite films exhibited a negative impact on the initial thermal decomposition temperature compared to PBAT. Additionally, the haze value of PBAT/TPS composite films exceeded 96%, while pure PBAT had a haze value of 47.42%. Films plasticized with 10% ATBC, 20% ATBC, and 20% glycerol displayed lower transmittance values in the visible light region. The increased transmittance of films plasticized with 30% glycerol further demonstrated their superior plasticizing effect compared to other PBAT/TPS composite films. This study provides a simple and feasible method for preparing low-cost PBAT composites, and their extensions are expected to further replace general-purpose plastics in daily applications. Full article

Nowadays, the measurement of heat stress indices is of principal importance due to the escalating impact of global warming. As temperatures continue to rise, the well-being and health of individuals are increasingly at risk, which can lead to a detrimental effect on human performance and behavior. Hence, monitoring and assessing heat stress indices have become necessary for ensuring the safety and comfort of individuals. Thermal comfort indices, such as wet-bulb globe temperature (WBGT), Tropical Summer Index (TSI), and Predicted Heat Strain (PHS), as well as parameters like mean radiant temperature (MRT), are typically used for assessing and controlling heat stress conditions in working and urban environments. Therefore, measurement and monitoring of these parameters should be obtained for any environment in which people are constantly exposed. Modern cities collect and publish this relevant information following the Smart City concept. To monitor large cities, cost-effective solutions must be developed. This work presents the results of a Heat Stress Monitoring (HSM) system prototype network tested in the Benicalap-Ciutat Fallera district in Valencia, Spain. The scope of this work is to design, commission, and test a low-cost prototype that is able to measure heat stress indices. The Heat Stress Monitoring system comprises a central unit or receiver and several transmitters communicating via radiofrequency. The transmitter accurately measures wind speed, air temperature, relative humidity, atmospheric pressure, solar irradiation, and black globe temperature. The receiver has a 4G modem that sends the data to an SQL database in the cloud. The devices were tested over one year, showing that radio data transmission is reliable up to 700 m from the receiver. The system’s power supply, composed of a Photovoltaic panel and Lithium-ion batteries, provided off-grid capabilities to the transmitter, with a tested backup autonomy of up to 36 days per charge. Then, indicators such as WBGT, TSI, and MRT were successfully estimated using the data collected by the devices. The material cost of a 12-point network is around EUR 2430 with a competitive price of EUR 190 per device. Full article

Starch-based bioplastics offer a promising alternative to conventional plastics. However, they exhibit certain limitations, notably in terms of mechanical strength and barrier properties. These challenges could potentially be addressed through the incorporation of nanocellulose as a reinforcing agent. In this study, we fabricated bioplastic films using a casting and blending approach, employing highly linear pure amylose (AM) in combination with cellulose nanofibers (CNF) or cellulose nanocrystals (CNC) at various ratios. This allowed for a direct comparison of CNF and CNC functionality within the AM matrix. We systematically assessed mechanical properties and water barrier characteristics, encompassing parameters such as water permeability, moisture content, swelling, solubility, crystallinity, thermal stability, transmittance, and opacity. Additionally, we investigated water vapor and oxygen permeability. Furthermore, we delved into distinctions between CNC and CNF biocomposites. Incorporation of either type of nanocellulose yielded enhancements in film properties, with CNF exerting a more pronounced positive influence compared to CNC. Particularly noteworthy were the mechanical properties, wherein CNF composite films demonstrated markedly higher tensile strength and Young’s modulus compared to their CNC counterparts. For instance, the inclusion of 1% CNF led to a substantial increase in AM tensile strength from 66.1 MPa to 144.8 MPa. Conversely, water vapor permeability exhibited a converse behavior, as the addition of 1% CNF resulted in a significant reduction of water barrier properties from 8.7 to 1.32 g mm m⁻² 24 h⁻¹kPa⁻¹. Intriguingly, CNC films displayed greater elongation at the point of rupture in comparison to CNF films. This can be attributed to the larger surface area of the CNC and the favorable interfacial interaction between AM and CNC. Notably, the introduction of nanocellulose led to reduced film opacity and improved thermal stability. In summary, nanocellulose interacted synergistically with the AM matrix, establishing a robust hydrogen-bonded network that greatly enhanced the performance of the biocomposite films. Full article

The thermal behavior and aggregation process of the poly(N-isopropyl acrylamide), poly[oligo(ethylene glycol) methyl ether methacrylate], and poly[(2-hydroxyethyl methacrylate)-co-oligo(ethylene glycol) methyl ether methacrylate] thermoresponsive polymers were studied in a commonly used Dulbecco’s Modified Eagle Medium (DMEM) cell culture medium and solutions of its individual components in the same concentration as found in DMEM. All studied copolymers exhibited an unexpected transmittance profile in the DMEM. During heating above the cloud point temperature (T_CP), the polymers additionally aggregated, which led to the formation of their precipitates. The behavior of the polymers was further studied to evaluate how individual salts affected the transition temperature, size (D_h), and stability of the polymer particles. Organic additives, such as amino acids and glucose, had a significantly lesser impact on the thermoresponsive aggregation of the polymers than inorganic ones. Changes to the T_CP were small and the formation of precipitates was not observed. The presence of small amounts of amino acids caused a decrease in the polymer aggregate sizes. Obtained results are of utmost importance in thermoresponsive drug nanocarrier studies. Full article

The Fresnel lens is an optical system consisting of a series of concentric diamond grooves. One surface of the lens is smooth, while the other is engraved with concentric circles of increasing size. Optical interference, diffraction, and sensitivity to the angle of incidence are used to design the microstructure on the lens surface. The imaging of the optical surface depends on its curvature. By reducing the thickness of the lens, light can still be focused at the same focal point as with a thicker lens. Previously, lenses, including Fresnel lenses, were made of glass due to material limitations. However, the traditional grinding and polishing methods for making Fresnel lenses were not only time-consuming, but also labour-intensive. As a result, costs were high. Later, a thermal pressing process using metal moulds was invented. However, the high surface tension of glass caused some detailed parts to be deformed during the pressing process, resulting in unsatisfactory Fresnel lens performance. In addition, the complex manufacturing process and unstable processing accuracy hindered mass production. This resulted in high prices and limited applications for Fresnel lenses. These factors prevented the widespread use of early Fresnel lenses. In contrast, polymer materials offer advantages, such as low density, light weight, high strength-to-weight ratios, and corrosion resistance. They are also cost effective and available in a wide range of grades. Polymer materials have gradually replaced optical glass and other materials in the manufacture of micro-optical lenses and other miniaturised devices. Therefore, this study focuses on investigating the manufacturing parameters of Fresnel lenses in the injection moulding process. We compare the quality of products obtained by two-stage injection moulding, injection compression moulding, and IMD (in-mould decoration) techniques. The results show that the optimal method is IMD, which reduces the nodal displacement on the Fresnel lens surface and improves the transmission performance. To achieve this, we first establish a Kriging model to correlate the process parameters with optimisation objectives, mapping the design parameters and optimisation objectives. Based on the Kriging model, we integrate the NSGA-II algorithm with the predictive model to obtain the Pareto optimal solutions. By analysing the Pareto frontier, we identify the best process parameters. Finally, it is determined that the average nodal displacement on the Fresnel surface is 0.393 mm, at a holding pressure of 320.35 MPa and a melt temperature of 251.40 °C. Combined with IMD technology, product testing shows a transmittance of 95.43% and an optimisation rate of 59.64%. Full article