Search Results (1,770)

Fiber-optic devices are widely used in communication, sensing, and other fiber-optic systems, and their quality directly affects system performance and reliability. However, internal defects in packaged devices remain difficult to characterize nondestructively, limiting their application in extreme environments. This work presents an active thermal-excitation method that uses the fiber embedded within the device as a distributed sensor. Controlled temperature changes are applied to excite the thermal response of the internal structure. Optical frequency-domain reflectometry (OFDR) then measures the distributed thermal strain along the fiber at millimeter-scale spatial resolution, enabling characterization of otherwise invisible internal defects. Using fused-fiber couplers as representative devices, we evaluated non-uniformity defects in the fused-taper and package-bonding regions. A finite-element model of an idealized coupler under thermal excitation was established to define the ideal thermal-response characteristics. The experimental results were broadly consistent with the simulated responses. Deviations from the predicted bonding-region symmetry and fused-taper uniformity indicated the possible presence of package-bonding and fused-taper defects, respectively. Dismantling representative couplers confirmed the locations and types of the defects. Applying the same criteria to the tested 2 × 2 and 1 × 3 couplers supported the applicability of the method across configurations within the present sample set. This method provides a transferable, high-spatial-resolution, and nondestructive means for quality assessment and reliability screening of packaged fiber-optic devices. Full article

Olive leaf extract (OLE) contains polyphenolic compounds with reported antioxidant and antimicrobial activities. In this study, OLE obtained by Naviglio extraction was incorporated into zirconia-based sol–gel hybrids at theoretical contents of 8, 25, 33, and 50 wt%. Colorimetric analysis showed that OLE acted as a natural coloring agent, producing composition-dependent changes from yellow to orange–brown tones. FT-IR spectra retained the characteristic bands of the zirconia-based matrix together with OLE-related contributions, while shifts in the O–H and Zr–O regions indicated changes in the local chemical environment after incorporation. Thermal analysis showed a progressive increase in the onset temperature of the main degradation stage, from 296.2 °C for bare ZrO₂ to 320.4 °C for ZrO₂/OLE50%, suggesting a stabilizing effect of OLE within the hybrid matrix. Release experiments in 95% (v/v) ethanol showed a clear dependence on OLE content. ZrO₂/OLE8% released almost completely within 5–6 h, whereas ZrO₂/OLE25% showed an initial burst followed by slower release, reaching 75–80% after 24 h. ZrO₂/OLE33% and ZrO₂/OLE50% showed slower release without a clear burst phase and released less than 30%. Agar-diffusion tests showed no enhancement of antibacterial activity against Escherichia coli or Enterococcus faecalis. These preliminary findings provide a basis for further investigation into the valorization of olive leaf extract as a natural component for the development of colored functional hybrid materials. Full article

Water stress reduces germination and seedling emergence by compromising the metabolic activity of seeds. Associated with this, extreme thermal events have intensified, and temperatures above 30 °C can significantly reduce maize yield. In this scenario, the selection of tolerant genotypes is essential. This study evaluated the germination potential of 22 maize genotypes, including open-pollinated genotypes and commercial varieties. Seeds were characterized by moisture content, thousand-seed weight, germination, and emergence in the field. Subsequently, they were subjected to thermal stress of 5, 15, 25, 35, and 40 °C, through the adapted standard germination test. For water stress, the seeds were subjected to different water retention capacities (15, 30, 60, and 100%). The results indicated relevant genetic variation among the genotypes. For thermal stress, there was no germination at extreme temperatures (5 and 40 °C), while at 15 °C, there were significant differences between genotypes. At 35 °C, there was a reduction in vigor and an increase in abnormalities. Open-pollinated genotypes showed superior physiological performance under stress conditions. For water stress, at 15% there was low performance; at 30%, initial improvement; at 60%, ideal conditions with greater vigor; and at 100%, maintenance of performance, with little significant gains. Maize genotypes showed tolerance to water stress between 15% and 100% of the water retention capacity, with normal germination and seedling formation. Materials 3, 4, 8, 12, 16, and 20 showed greater tolerance to water restriction, while 2, 10, 14, 18, and 22 had better performance in more humid environments. Materials 7, 9, and 10 stood out for their greater vigor and germination. Regarding thermal stress, germination occurred between 15 °C and 35 °C, even outside the ideal range. Material 3 (AS1598) showed higher thermal tolerance, with better physiological performance, higher germination, and higher vigor. Full article

Greenhouse agriculture in semi-arid regions faces persistent challenges from unpredictable thermal variability, frost events, and seasonal drought stress that are difficult to manage without anticipatory climate information. This paper presents the design, implementation, and validation of an end-to-end intelligent greenhouse monitoring and temperature forecasting system deployed in Donovan, San Luis Province, Argentina. The proposed platform integrates a three-layer IoT architecture with cloud-based statistical forecasting to support real-time decision making under semi-arid climatic conditions. The system integrates sensor nodes, a push-MQTT gateway co-located at the Universidad Nacional de San Luis to bypass regional API geo-restrictions, and a cloud application layer. Three forecasting strategies with a six-hour prediction horizon were evaluated: a univariate SARIMA baseline (Model 1), a SARIMAX model using four neighboring meteorological stations as individual exogenous regressors (Model 2), and a SARIMAX model employing a single correlation-weighted synthetic exogenous index (Model 3). The models were assessed using MAE, RMSE, and Diebold–Mariano statistical significance tests. The results show that directly incorporating multiple correlated exogenous variables does not improve forecast accuracy because of multicollinearity, whereas the proposed correlation-weighted synthetic index preserves the spatial predictive signal while reducing model complexity and achieving performance comparable to the baseline overall, with statistically significant improvement during the overnight block. Additional benchmarking against Random Forest, Support Vector Regression, Temporal Convolutional Networks, and Long Short-Term Memory models demonstrates that increasing model complexity does not necessarily translate into improved predictive performance for short-horizon greenhouse temperature forecasting. Together, the proposed IoT architecture and forecasting framework provide an operationally validated solution for intelligent greenhouse monitoring and predictive decision support in resource-constrained semi-arid environments. Full article

To improve the aging resistance of SBS-modified asphalt (SBSMA), this study prepared two metal oxide/montmorillonite nanocomposites, TiO₂/montmorillonite (TM) and CeO₂/montmorillonite (CM), and investigated their effects on the rheological properties and microstructure of SBSMA before and after long-term aging. The performance differences between the two nanocomposites under different aging modes were also compared. Conventional physical property tests, dynamic shear rheometer tests (temperature sweep and linear amplitude sweep), dynamic mechanical analysis (DMA), and fluorescence microscopy were employed to evaluate the physical properties, high- and low-temperature rheological properties, fatigue resistance, and the microscopic evolution of SBSMA. The results show that before aging, the incorporation of TM and CM significantly improved the high-temperature deformation resistance of SBSMA, enhanced the SBS polymer dispersion state, and promoted the formation of a continuous network structure of polymer phase. After long-term thermal-oxidative aging, both nanocomposites effectively retarded the aging of the asphalt matrix and the SBS network; CM exhibited superior thermal-oxidative aging resistance. After long-term ultraviolet (UV) aging, both nanocomposites also showed significant protective effects, and TM outperformed CM in UV aging resistance. In summary, TM and CM show differentiated advantages in UV protection and thermal-oxidative protection, respectively, providing a theoretical basis for the design of anti-aging materials for SBSMA based on service environments. Full article

Compared with traditional Al–Si die-cast alloys, which have good formability and low cost but poor brazeability and inadequate corrosion resistance, high-pressure die-cast (HPDC) Al–RE alloys exhibit superior comprehensive properties. To satisfy the demand for lightweight, high-performance materials in automotive thermal management, a controlled-atmosphere brazing (CAB) furnace was employed in this work to investigate the effect of the complete brazing cycle on the microstructure, mechanical properties, and corrosion resistance of the HPDC Al–RE alloy. In the as-cast state, the eutectic Al₁₁(La,Ce)₃ phase presents a lamellar structure. After the simulated brazing process, this phase transforms into dispersed near-spherical particles. Such microstructural evolution directly determines the mechanical and corrosion behaviors of the alloy. The yield strength and ultimate tensile strength decrease, while the elongation increases substantially owing to the alleviation of stress concentration. The corrosion resistance of the alloy depends on the service environment. After 960 h of neutral salt spray (NSS) testing, the alloy showed excellent corrosion resistance with only slight corrosion. Nevertheless, severe localized pitting corrosion (maximum pit depth: 0.932 mm) was observed after 480 h of sea water acidified accelerated test (SWAAT) exposure. This pitting phenomenon is directly associated with spheroidized Al₁₁(La,Ce)₃ particles. In acidic chloride-containing media, these intermetallic particles undergo preferential anodic dissolution relative to the α-Al matrix, resulting in micro-galvanic corrosion. In conclusion, after simulated brazing treatment, the ductility of the Al–RE alloy is remarkably improved at the cost of a moderate reduction in strength. The Al–RE alloy possesses good corrosion resistance in neutral saline environments. However, severe localized corrosion tends to occur in acidic environments due to the high electrochemical activity of spheroidized intermetallic phases. Full article

In this study, the hydrogen embrittlement (HE) susceptibility and hydrogen-induced cracking behavior of X70 pipeline steel were investigated in CH₄–H₂ mixed-gas environments containing 5–20% H₂ at a total pressure of 7 MPa. Slow strain rate tensile tests, thermal desorption spectroscopy, fractography, and electron backscatter diffraction (EBSD) were employed to correlate hydrogen uptake, mechanical degradation, fracture morphology, and crack evolution. The results showed that increasing the hydrogen fraction progressively deteriorated the mechanical performance of X70 pipeline steel, as evidenced by reductions in tensile strength and elongation. This degradation was accompanied by a fracture-mode transition from micro-void coalescence to quasi-cleavage fracture. More importantly, EBSD analysis revealed a hydrogen-content-dependent change in the role of the heterogeneous microstructure. At relatively low hydrogen fractions, fine-grained regions and microstructural heterogeneity acted as effective barriers to hydrogen-induced crack propagation. However, at higher hydrogen fractions, this intrinsic crack-arresting capability was substantially weakened. Newly formed cracks were observed to initiate ahead of pre-existing cracks and propagate preferentially along grain boundaries, with limited local plastic deformation. These findings demonstrate that the increased HE susceptibility of X70 pipeline steel under high-H₂ mixed-gas conditions is associated with the progressive loss of the crack-arresting resistance provided by its heterogeneous microstructure. Full article

Urban streets are important heat-exposure environments, yet the relationships of two-dimensional (2D) planar plant morphology and three-dimensional (3D) vegetation structure with land surface temperature (LST) remain insufficiently integrated at a continuous street scale. We analyzed 42,603 street-scale study units in the central urban area of Wuhan, defined at 50 m sampling intervals with a 150 m radius. The 2D variables comprised green-space area (A), mean patch perimeter (P_mean), and perimeter–area ratio (P_A), while the 3D variables comprised green view index (GVI), mean 3D green volume (NV_mean), mean canopy height (CH_mean), and canopy-height variability (CH_sd). Anselin Local Moran’s I identified High–High (HH) and Low–Low (LL) zones; linear regression (LR), random forest (RF), and SHAP characterized linear, nonlinear, and model-based contributions; and buffered spatial cross-validation and spatial resampling evaluated robustness. Under the original random 80–20% train–test split, LR/RF R² values were 0.2153/0.4002 for the overall study area, 0.1940/0.3539 for the HH zone, and 0.0488/0.4853 for the LL zone. Under five-fold buffered spatial cross-validation, the corresponding pooled out-of-fold R² values were 0.1940/0.2237, 0.1427/0.0965, and −0.0942/−0.0231, showing that the RF advantage weakened after spatial separation and did not persist in the HH and LL zones. In the original fitted RF models, A, P_mean, and NV_mean had the largest mean absolute SHAP contributions overall; A, P_A, and P_mean ranked highest in the HH zone; and GVI, CH_sd, and CH_mean ranked highest in the LL zone. Repeated buffered spatial validation showed no stable overall 2D predominance because the median 2D share of 52.1% had a 46.5–58.8% percentile range, but it supported stable 2D relative predominance in the HH zone (61.0% [55.5–66.7%]) and stable grouped 3D relative predominance in the LL zone (61.9% [52.3–70.3%]), despite unstable LL variable-level rankings. SHAP relationships were nonlinear and zone-dependent: A and P_mean showed clearer directional transitions overall and in the HH zone, whereas the LL zone and most 3D variables exhibited multiple directional changes. Spatial-block bootstrap analysis examined 40 full-sample zero-crossing candidates, of which 39 met the predefined stability criteria; these ranges represent model-derived directional transitions rather than ecological thresholds or causal planning standards. The findings demonstrate thermal-context-dependent, model-based associations between 2D and 3D plant morphology and street-scale LST, while emphasizing that model performance and some importance rankings are spatially sensitive and require local validation. Full article

Fresnel high-concentration photovoltaic/thermal (HCPV/T) systems operating in sandy environments are susceptible to natural lens soiling, which attenuates the effective concentrated solar input and alters electrical and thermal performance. Natural-soiling comparison tests were conducted over 0–28 d, and an SD-CNN-BiLSTM-Attention model was developed to forecast cell-center temperature and electrical power 5, 10, and 20 min ahead. At a surface soiling density of 10.760 g·m⁻², current and electrical power decreased by 38.37% and 39.28%, respectively, relative to the concurrently operated clean-reference unit; cell-center temperature and water-tank temperature rise decreased by 7.74% and 15.13%. Thermal power also showed an overall downward trend, although the magnitude was affected by relatively large measurement uncertainty. Under grouped cross-validation, temperature RMSEs were 0.473, 0.515, and 0.555 °C at 5, 10, and 20 min, corresponding to reductions of 8.34%, 21.68%, and 44.07% relative to Persistence. Electrical-power RMSEs were 0.661, 0.618, and 0.640 W, with an 18.24% reduction relative to Persistence at 20 min. Ablation analysis showed a limited contribution from surface soiling density at 5 and 10 min but a clearer contribution at 20 min. These results support electrical and thermal performance assessment and short-term operational forecasting of Fresnel HCPV/T systems in sandy environments. Full article

Electrocatalytic water splitting offers a viable route to sustainable hydrogen generation, yet the development of non-noble metal catalysts that combine high efficiency with long-term stability remains a significant hurdle. Zeolitic imidazolate framework-67 (ZIF-67) has emerged as a potential electrocatalyst, but its activity is often limited by insufficient active sites and poor conductivity. In this study, Mn, Fe, and Ni doped derivatives of ZIF-67 (ZIF-67/M, M = Mn, Fe, Ni) were synthesized via a post-synthetic modification method to improve the electrocatalytic performance. The effects of metal doping on structure, morphology, and water splitting activity were systematically investigated. XRD and FTIR confirmed the successful incorporation of heteroatoms without destroying the crystalline framework, while TGA revealed altered thermal stability. BET measurements showed a transformation from microporous to mesoporous structures upon doping, and SEM exhibited crystal distortion, aggregation, and increased surface roughness. Electrochemical tests demonstrated that doping significantly enhanced both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performances. At 10 mA cm⁻², ZIF-67/Fe exhibited the lowest overpotentials for OER (271 mV) and HER (338 mV), outperforming ZIF-67/Mn, ZIF-67/Ni, and pristine ZIF-67. Overall water splitting tests on ZIF-67/Fe showed negligible overpotential change after 24 h, confirming good ambient stability. In summary, metal doping effectively enhances the electrocatalytic water splitting performance of ZIF-67 by modulating its coordination environments and active site distribution, with ZIF-67/Fe exhibiting the best overall performance as a promising bifunctional electrocatalyst. Full article

Bulk compressibility of reservoir rocks can be characterized dynamically or statically, and both vary with burial depth due to increasing temperature and pressure. To quantify these effects, cyclic hydrostatic compression tests are conducted on two reservoir sandstones under confining pressure up to 50 MPa at three temperatures (30 °C, 70 °C, and 110 °C). Experimental results show that static bulk compressibility is consistently larger than dynamic values across all tested conditions. As confining pressure increases, static compressibility decreases more sharply than dynamic compressibility, leading to a gradual reduction in their discrepancy. In contrast, temperature exerts a weaker yet more complex influence. Elevated temperature increases dynamic bulk compressibility, but has opposite effects on static compressibility upon loading versus unloading: it reduces static compressibility upon hydrostatic loading but enhances it upon unloading. This complex temperature dependence is attributed to thermally induced stress, which resists hydrostatic compression during loading but assists decompression during unloading. The influence of thermal stress is more pronounced at low confining pressures. These findings highlight that temperature not only alters the magnitude of static compressibility but also introduces path-dependent asymmetry between loading and unloading, which has important implications for reservoir geomechanics, subsidence prediction, and production-induced compaction in high-temperature environments. Full article

Amid the low-carbon transition, university teaching buildings feature high occupancy and energy use, making the synergistic enhancement of their daylighting and thermal environments crucial for “dual carbon” goals. However, traditional “north–south homogenization” designs in cold regions fail to address the spatial heterogeneity of solar radiation and climate resources, intensifying the trade-off between natural daylighting and Heating Energy Use Intensity (E_h) while restricting space performance optimization. Focusing on a typical cold-region teaching building, this study proposes a “parametric modeling–multi-objective optimization–machine learning” integrated framework. Targeting spatial daylight autonomy (sDA), useful daylight illuminance (UDI), and E_h, we compared the homogeneous baseline model with the Pareto-optimal solution set, demarcated key design parameter boundaries, and developed an ensemble-based rapid prediction model. Based on the parametric simulation analysis of this representative case building in a cold region, results indicate that: (1) Compared to the baseline, the overall optimal scheme reduced E_h by 17.43% while increasing UDI and sDA by 12.0% and 10.5%, respectively. (2) The Pareto set strictly converges toward a due-south orientation and a “deep-south, shallow-north” layout (depth ratio: 0.66–0.77); thermal configurations exhibit “enhanced northern insulation and southern heat gain,” confirming heterogeneous design matches cold climates better. (3) The four constructed machine learning models (MLP, LightGBM, XGBoost, and Random Forest) uniformly achieved test recall rates exceeding 99%, enabling highly precise, rapid classification of top-performing design scenarios during early-stage design. This study overcomes climate-matching blindness in traditional design, providing a multi-objective synergistic optimization path balancing low energy and high-quality daylighting with substantial engineering and theoretical value. Full article

The results of the experiments on the transport process of fluid flow through a pipeline under temperature gradient conditions between the internal and external environments, and on continuous gas generation at the contact boundary of the transported media, are presented in this paper. The test results showed that under non-isothermal flow conditions, a slippage effect will impact flow velocity and pressure, as well as the temperature distributions in variable cross-section pipes. Laboratory experiments were conducted in order to study the effects of the gas nucleus at the pipe walls on the hydrodynamic characteristics of the fluid flow. It is shown that the throughput capacity of the pipe is affected by the temperature difference between the oil and the pipe walls. The test results also demonstrated that at certain temperature gradients on the border layer, the pipe’s capacity reaches its maximum value. Quantitatively, the hydroconductivity of Q/ΔP increased from about 1.45 × 10⁻⁵ m³/(s·MPa) under relatively isothermal conditions to a maximum value of approximately 2.04 × 10⁻⁵ m³/(s·MPa) with a temperature difference in the oil–pipe-wall zone of about 3–5 K, which corresponds to an increase of about 41%. With a further increase in the temperature difference, the hydroconductivity decreased to about 1.64 × 10⁻⁵ m³/(s·MPa) at 10 K and then stabilized in the range of (1.60–1.64) × 10⁻⁵ m³/(s·MPa). This non-monotonic behavior is explained by the temperature-induced release of gas and the formation of a gas-saturated wall zone, which initially reduces the effective resistance of the wall and creates an apparent sliding effect. At high temperature differences, gas accumulation, thermal insulation of the wall area and two-phase flow disturbances limit this effect, which leads to the decrease and subsequent stabilization of the pipe capacity. Full article

The benefits of additive manufacturing (AM, i.e., 3D printing) have made it one of the most widely used and favored production techniques across a variety of industries. In the current study, the influence of geometry and thermal aging on the mechanical strength of AMed parts has been investigated. In this context, specimens based on fused deposition modeling were printed using polylactic acid material. The specimens with three distinct geometries were created and analyzed since the geometry of AMed parts affects their mechanical performance. In this study, tensile tests were conducted under static loading circumstances, specifically on dumbbell-shaped, smooth, and V-notched test coupons. Furthermore, we conducted accelerated thermal aging between $-5 °$C and 35 °C, which is below the glass temperature of the material under investigation, to assess the impact of the thermal environment. In addition, a series of finite element models were developed to study the stress distribution and deformation in the examined components. According to the results, for unaged specimens, smooth samples demonstrated the highest fracture load at 1980.5 N, while dumbbell-shaped samples recorded the lowest at 1173.9 N. Moreover, the V-notched specimens sustained higher fracture loads compared to dumbbell-shaped samples across both aged and unaged conditions. This study’s findings demonstrate that in designing 3D-printed parts, consideration must be given to their geometric appearance and environmental operating circumstances. Full article

This paper presents the results of a low-cost environmental testing campaign performed on commercial off-the-shelf components intended for aerospace applications, specifically a housekeeping system designed for suborbital launchers. These tests encompass a broader range of thermal and mechanical testing procedures than is typically reported in the literature, providing a more comprehensive assessment of the system’s robustness. The housekeeping system is subjected to sine-equivalent dynamic loads representative of launch environments expected by vehicles such as Ariane 6, VEGA, and Falcon 9 using a shaker. In addition, thermal vacuum testing is conducted to evaluate system performance under temperature and pressure conditions representative of high-altitude flight. Following each test, the system’s functionality is assessed by comparing its performance against baseline laboratory conditions using telemetry data acquired by the system; most importantly, a critical failure on telemetry data acquisition is verified, which determines the survivability of the system. The successful completion of these environmental tests demonstrates the survivability of the housekeeping system, validating its reliability and suitability for operation in suborbital launcher missions. Full article