Search Results (7,487)

Accurate absolute radiometric calibration is critical for ensuring the data quality of spaceborne Synthetic Aperture Radar (SAR) systems and supporting quantitative remote sensing applications. Absolute radiometric calibration generally relies on ground reference targets with known radar cross-section (RCS) deployed at dedicated calibration sites. Such ground-based calibration methods are costly and time-consuming, and calibration frequency is constrained by the distribution of calibration sites and the satellite revisit cycles. Additionally, for specialized SAR missions, such as deep space exploration, deploying calibration equipment on the observed extraterrestrial surface is infeasible. This study proposes a space-based absolute calibration concept using a small calibration satellite carrying a well-characterized reference (e.g., a passive reflector or an active transponder) and flying in formation with the SAR satellite. The relative motion ensures a side-looking acquisition geometry, enabling the SAR to image the accompanying target and derive calibration factors. The overall calibration process is divided into two stages: determination of an in-orbit calibration factor using the calibration satellite, followed by its transformation to accommodate ground imaging conditions. This method effectively isolates the radar system gain to characterize the intrinsic hardware response. Furthermore, by operating entirely in space, it avoids atmospheric and ground-clutter distortions, ensuring a fully space-based, end-to-end calibration process dominated primarily by sensor systematic errors. Moreover, it allows for more frequent and flexible calibration, eliminating reliance on ground calibration sites and infrastructure. The feasibility and advantages of the proposed concept are demonstrated through comprehensive simulations, covering orbit analysis, echo simulation, and image processing. Full article

Heavy metal contamination in agricultural soils threatens ecosystem safety and sustainable land use, particularly in geologically sensitive areas. This study aimed to assess the pollution status, ecological risks and source contributions of eight heavy metals (Hg, Cd, Pb, As, Cr, Cu, Ni and Zn) in soils from a dry-hot agricultural region of central Yunnan, China. To improve source apportionment, this study applied and compared three models: APCS-MLR, PMF, and Random Forest. Analysis of 1790 soil samples showed mean concentrations (mg/kg) of 0.03 for Hg, 0.17 for Cd, 25.01 for Pb, 7.46 for As, 85.91 for Cr, 36.20 for Cu, 31.75 for Ni, and 69.24 for Zn. Pollution assessment indicated that Cu and Cd were the main pollutants, while ecological risk assessment identified Cd and Hg as the dominant ecological risk factors. Four major sources were identified: industrial hybrid sources, natural background, atmospheric deposition and agricultural activities, with industrial hybrid sources contributing the largest share. These results indicate that integrating APCS-MLR, PMF, and Random Forest provides a more reliable framework for source identification and supports targeted soil pollution control in regions affected by both natural and anthropogenic inputs. Full article

Review text in recommender systems provides rich insights into user preferences and experiences that cannot be fully captured by numerical ratings alone. While recent studies have increasingly leveraged review text to enhance recommendation accuracy, most have primarily focused on improving model performance, with limited attention to quantitatively examining how specific textual elements influence rating prediction. To address this gap, this study empirically investigates the impact of review text characteristics on prediction performance in review-based recommender systems. Specifically, we employ the Unstructured Context-Aware Model (UCAM), where contextual information is replaced with review text embedded using a pre-trained BERT model. Three key textual factors are examined: review length, aspect, and emotion type. Review length is divided into quartiles, and results show that removing shorter reviews significantly degrades performance, indicating their critical role. For analysis, reviews are categorized into food, service, price, atmosphere, and location, with service and food contributing most to performance improvements, while location shows relatively low influence. Emotion types are classified based on Plutchik’s framework, revealing that removing joy, trust, and anticipation reduces performance, whereas excluding sadness slightly improves it. Overall, this study highlights the differential importance of textual features and demonstrates their potential for enhancing recommender system design. Full article

High-entropy alloys (HEAs) are typically produced using high-temperature metallurgical routes; however, alternative synthesis approaches based on wet-chemical processing remain relatively unexplored. In this study, a compositionally complex two-phase AgCuCoNiFe high-entropy alloy was synthesized using a precipitation–reduction strategy involving co-precipitation of mixed metal carbonates followed by thermal reduction in a reducing atmosphere. The objective of the work was to evaluate the feasibility of this hydrometallurgical route for preparing compositionally complex alloys and to investigate the structural evolution of the material as a function of reduction time. Quantitative MP-AES analysis confirmed efficient co-precipitation of all five elements, enabling the preparation of a precursor with near-equimolar metal composition. Structural characterization using SEM, EDS, and XRD revealed the presence of surface compositional heterogeneity in the as-reduced state, characterized by Ag-enriched domains. After controlled surface abrasion, the internal material exhibited significantly more uniform elemental distribution, although the obtained composition was not equimolar. X-ray diffraction patterns showed a transition from multiple sharp reflections at the surface to broadened peaks in the bulk, consistent with enhanced alloying within the bulk compared to the surface, while still revealing a two-phase character. Microhardness measurements indicated moderate hardness with mean values in the range of 187–221 HV with no significant dependence on reduction time, while wettability analysis revealed moderately hydrophilic behavior with contact angles in the range of approximately 75–83°. The results suggest that precipitation–reduction can be a viable alternative route for the synthesis of multicomponent HEAs, enabling the formation of chemically mixed alloy structures without the use of conventional melting-based processing. However, the obtained alloy exhibits incomplete chemical homogeneity, indicating that further optimization of the synthesis conditions is required to achieve a fully uniform composition. Full article

Accurate retrieval of visibility grades is critical for transportation safety. Due to the highly complex meteorological backgrounds, traditional global deep learning models frequently struggle with limited physical traceability and feature heterogeneity. To address these challenges by enhance physical traceability and reduces heterogeneity, this study proposes a scenario-adaptive visibility retrieval framework based on multi-source synergy, namely TabPFN-ExtraTrees (TabPFN-ET), targeting major transportation routes in Anhui Province, China. Fusing Fengyun-4 (FY-4A/4B) satellite multispectral observations with ground meteorological data, this framework utilizes the divide-and-conquer routing mechanism of ExtraTrees to decouple the complex, heterogeneous feature space into highly homogeneous sub-scenarios. Subsequently, the TabPFN model conducts high-precision inference within each specific subspace. Evaluations on a class-balanced benchmark demonstrate that TabPFN-ET achieves an Overall Accuracy of 0.681, outperforming baseline models such as SAINT across various metrics. Furthermore, this paper conducts a physically consistent analysis of the framework. Feature importance and node profiling corroborate its physical consistency: the FY-4 upper-level water vapor channel (Channel 09) and near-surface humidity act as the macroscopic atmospheric stability and microscopic thermodynamic constraints, respectively, driving the model’s scene decoupling and inference. Cross-regional tests in Jiangsu provide preliminary indications of context-specific transferability. Full article

The paper presents experimental data on the observation of artificial airglow of the ionosphere induced by HF radio wave pumping by the SURA heating facility during the presence of a blocking sporadic E layer of the ionosphere. Optical observations were carried out on 5 August 2024 using a three-channel photometer and CCD cameras with narrow-band filters. Emission of atomic oxygen at the wavelength $\lambda$ = 557.7 nm (green line), as well as airglow close to the red line of atomic oxygen at $\lambda$ = 630 nm and the band of molecular nitrogen ions $1NG{N}_2^{+}(0-0)$ at $\lambda$ = 391.4 nm (blue band), were recorded. The induced emission intensity in the green line reached ∼270 R, larger than ever measured. Additional lower-intensity glow spots in the green line southwest and northeast of the main spot (∼12° from zenith), detected by the CCD camera, could be due to the side lobes of the SURA antenna pattern. The atypical behavior of the time course of the intensity in the red line with sharp fronts of increase and decrease may indicate the detection of emission lines of hydroxyl groups in the OH(9-3) and OH(5-0) bands, spectrally close to 630 nm. More detailed analysis of the results obtained and new similar experiments will lead to a deeper understanding of the processes occurring in the upper atmosphere/lower ionosphere during conditions of high solar activity. Full article

Atmospheric nitrogen (N) deposition is altering global forest ecosystems, with nitrate rising to rival ammonium as a dominant N form, yet how leaf ontogeny orchestrates carbon–nitrogen (C-N) metabolic coordination under contrasting N forms remains poorly understood. We conducted a field experiment investigating the physiological and metabolic responses of young and old leaves of Chinese fir (Cunninghamia lanceolata) to ammonium and nitrate addition. Young leaves, functioning as active sinks, exhibited enhanced photosynthetic performance and growth-oriented N assimilation under N addition, with disproportionately stronger responses to nitrate. In contrast, old leaves, acting as source tissues, showed limited photosynthetic plasticity but accumulated higher non-structural carbohydrates and elevated N assimilation enzyme activities, particularly under nitrate addition. Phytohormone profiles supported this ontogenetic divergence, with young leaves showing higher auxin levels while old leaves exhibited increased abscisic acid and salicylic acid contents. Metabolomic analysis further revealed age-dependent reprogramming of amino acid metabolism, identifying key metabolites coordinating C-N balance. These findings demonstrate a leaf ontogeny-mediated spatial division of metabolic labor in Chinese fir, wherein old leaves function as metabolic buffers stabilizing whole-plant C-N homeostasis under fluctuating N supply, providing new insights into plantation responses to contrasting N deposition regimes. Full article

Anthropogenic polymers have become an increasingly important class of emerging contaminants in terrestrial ecosystems. While extensive research has focused on microplastics in aquatic environments, their interactions with soil systems and particularly with soil organic matter (SOM) remain insufficiently understood. Soil represents a major environmental sink for polymer residues originating from agricultural practices, urban activities, and atmospheric deposition. Accordingly, associations between polymers and SOM, including humic substances, may significantly influence the retention, mobility, and transformation of carbon in soil systems. This review synthesizes current knowledge on the influence of synthetic polymers on soil organic matter dynamics. A bibliometric and qualitative literature analysis based on publications indexed in Web of Science and Scopus from 1979 to 2025 was conducted to identify major research trends and knowledge gaps. The results indicate that polymer particles can alter soil structure, microbial activity, and sorption processes, thereby affecting the stability and cycling of soil organic carbon. Interactions between polymer surfaces and humic substances may modify aggregation processes and influence the persistence and mobility of both polymers and organic carbon compounds. Despite the rapid growth of research on microplastics, studies addressing polymer–SOM interactions remain limited and methodologically heterogeneous. Greater integration between polymer research, soil science, and land use studies is necessary to better understand the implications of polymer contamination for soil quality and carbon cycling. The findings highlight the need for standardized analytical approaches and interdisciplinary research frameworks to assess the long-term effects of polymers in soil ecosystems. Full article

This work investigates the δ→σ phase transformation in 24Cr-14Ni stainless steel, specifically focusing on how heat treatment temperature, time, and nitrogen atmospheric ratios (NARs) dictate microstructural stability. Understanding the formation mechanism of the σ phase is critical for alloy design, as it remains the most detrimental intermetallic phase in austenitic steels. The results show that δ-ferrite decomposes into σ and secondary γ₂ phases through a cellular eutectoid reaction driven by elemental diffusion. Higher Cr and Si levels stabilize δ-ferrite and promote σ phase precipitation, accelerating the δ→σ transformation. Furthermore, the σ phase exhibits the highest Cr_eq/Ni_eq ratio among all constituent phases. The σ phase fraction is highest with 0 vol.% NAR during 1–8 h of aging and decreases progressively with increasing NARs (20–40 vol.%), reaching a minimum at 80 vol.% under all conditions. JMAK model analysis (n ≈ 0.531, k ≈ 0.905) indicates that σ phase precipitation at 800 °C with 40 vol.% NAR is governed by diffusion-controlled growth with early nucleation site saturation in δ-ferrite. Consequently, rapid σ phase formation occurs, reaching ~21.3% within 1 h. This behavior is attributed to the instability of δ-ferrite and the faster diffusion of Cr and Si compared to austenite. Full article

In the present paper, In₂O₃ NPs were synthesized by a wet-chemical method, in the absence and presence of the surfactant, and deposited as thin films on silicon substrates. After deposition, the films were subjected to rapid thermal annealing (RTA) at 550 °C, 750 °C, and 900 °C, for 300 s, under an inert atmosphere. The correlation between the morphological, structural, and optical characteristics, the wetting capacity of In₂O₃ films synthesized under different synthesis conditions, and the influence of the RTA treatment are presented. The vibrations of In-O bonds for In₂O₃ samples were confirmed using FTIR spectroscopy. Structural analysis shows that In₂O₃ NPs have a cubic crystalline structure, but with the increase in temperature at 900 °C, diffraction peaks characteristic of the tetragonal phase of indium appear, correlated with a decrease in lattice parameters, as a result of the crystallinity. The morphology of the In₂O₃ samples was studied by SEM, revealing predominantly spherical and uniformly distributed particles with nanometric sizes. The absorption spectra of the In₂O₃ NPs showed peaks in the ultraviolet region, and the high energy bandgap value of the In₂O₃ films varied between 3.28 and 4.33 eV, depending on the samples and RTA treatment. The contact angle measurements of In₂O₃ films determined the wetting capacity of the surface, reflecting changes in surface morphology and structure induced by the RTA process. The results suggest that In₂O₃ thin films with spherical nanoparticles, good wettability, and percolation can be used for the development of sensors with increased selectivity and sensitivity. Full article

The eddy covariance technique has become one of the most popular methods for measuring CO₂ exchange between ecosystems and the atmosphere. Flux averaging intervals typically range from 15 to 60 min, with 30 min being the most commonly adopted setting. However, due to variations in site conditions and turbulent regimes, the choice of averaging interval can substantially influence flux calculations. In this study, we applied the eddy covariance method to examine how different averaging intervals affect CO₂ flux measurements in a subtropical Moso bamboo forest during winter in Jinggangshan, Jiangxi Province, China. The results showed that the bamboo forest maintained a relatively high CO₂ uptake rate even in winter. When relative humidity exceeded 80%, the averaging interval had a pronounced effect on CO₂ flux estimates, and in some cases even altered the direction of the flux. Based on a comparative analysis, an average interval of 60 min is recommended. These findings offer practical guidance for eddy covariance observations in subtropical Moso bamboo forests and provide useful insights for flux measurements in humid environments more broadly. Full article

This work presents an experimental aerodynamic study of a Mars rover model, aimed at characterizing its flow behavior under Martian environmental conditions. Due to the extremely low Reynolds numbers associated with Mars’ thin atmosphere, the experiments were conducted using a scaled model of the rover manufactured via additive techniques. The study first focuses on understanding how the geometry of the rover influences the overall flow field, identifying key aerodynamic features such as separation zones, vortical structures, and flow reattachment regions driven by the complexity of the vehicle. A comprehensive investigation of the flow around the model was performed using both a hydrodynamic towing tank with dye injection for qualitative visualization, and particle image velocimetry (PIV) for quantitative flow field analysis in wind tunnel tests. After the general flow characterization, a more detailed local analysis was conducted using laser Doppler anemometry (LDA). This phase of the study targeted precise velocity measurements at specific locations corresponding to the MEDA (Mars Environmental Dynamics Analyzer) wind sensors onboard the rover. Quantitative results indicate that the central body induces a local flow acceleration of 20% to 40% relative to the free stream while severe turbulence was recorded in specific angular sectors, with velocity fluctuations reaching up to 120% for Sensor 1 and 90% for Sensor 2. Full article

Environmental loading is a major driver of nonlinear GNSS vertical displacements, yet its spatiotemporal heterogeneity remains insufficiently understood in regions with complex topography. In this study, we investigate the environmental loading effects on GNSS vertical motions across Southwest China using observations from a network of 66 stations. Singular Spectrum Analysis (SSA) and Empirical Orthogonal Function (EOF) analysis were applied to extract annual signals, while component-wise RMS reduction quantified hydrological and atmospheric loading contributions. Spatial statistical analysis, cross-wavelet transform, and k-means clustering examined correlation patterns and phase hysteresis between GNSS observations and modeled loads. Results show that hydrological loading dominates seasonal vertical oscillations, but crustal responses exhibit pronounced spatial heterogeneity controlled by regional topography and hydro-climatic gradients. EOF analysis reveals a dipole pattern induced by the Hengduan Mountains’moisture-blocking effect. Atmospheric loading anomalously dominates the eastern Sichuan Basin, whereas Yunnan displays strong amplitudes with high heterogeneity due to karst hydrogeology. Phase analysis identifies three distinct regimes: a rapid elastic response on the Tibetan Plateau, (with the lag of ~20 ± 5 days, correlation coefficient R ≈ 0.65), intermediate delays in Yunnan (~60 ± 5 days, R ≈ 0.58), and pronounced hysteresis in the Sichuan Basin (~105 ± 5 days, R ≈ 0.38) linked to slow groundwater diffusion and poroelastic processes. These findings highlight the critical role of local hydrogeological dynamics in modulating GNSS vertical deformation and provide new insights for improving environmental loading corrections in complex mountainous regions. Full article

MoSi₂-based intermetallics are interesting materials for high-temperature applications, due to their moderate density, high melting point and significant oxidation resistance. In this paper, MoSi₂-based materials in the form of multi-layered structures were fabricated by tape casting and pressureless sintering. Composites containing up to 20 wt.% of NbSi₂ were produced, with the aim of obtaining biphasic structures with low pest oxidation at low temperature. The prepared samples were characterised with regard to phase composition, microstructure, mechanical properties and oxidation resistance. It was shown that the addition of a limited amount of NbSi₂ prevents the pest oxidation phenomenon characteristic of pure MoSi₂. Silica inclusions responsible for lowering the material toughness, were observed to disappear in the sintered silicides, thanks to the presence, during the binder burn-out, of a reducing atmosphere and to the carbonaceous residua. The phase and composition analysis also revealed the formation of small amounts of secondary phases like silicon carbide. Full article

The present work investigated the thermodynamic behaviors of oxygen in a liquid Fe–Ti alloy over a wide Ti concentration range of 11.6–71.2 wt% at 1873 K by integrating equilibrium experiments with thermodynamic modeling. To prevent excessive oxidation during the equilibrium experiments, the liquid alloys were equilibrated in a purified Ar atmosphere with an oxygen partial pressure below ~10⁻²⁰ atm. Two quenching methods—furnace quenching with He gas injection and water quenching via quartz tube suction—were employed to evaluate the effect of cooling rate on total oxygen measurements. While He gas quenching led to higher measured oxygen contents owing to the formation of secondary Ti oxides, the quartz tube suction quenching method consistently yielded significantly lower oxygen values. The dissolved oxygen content increased with increasing Ti content. Electron probe microanalysis identified TiO as a stable equilibrium oxide phase above 11.6 wt% Ti, which was characterized as a face-centered cubic (FCC) rock-salt structure via electron backscatter diffraction analysis. Based on these results, a thermodynamic assessment of oxygen behavior in a liquid Fe–Ti alloy in equilibrium with TiO was performed for the first time using a modified quasichemical model. Consequently, the present model successfully reproduced the Ti–O relationship in the liquid Fe–Ti alloy across both the high-Ti concentration region saturated with TiO and the low-Ti concentration region saturated with Ti₂O₃ and Ti₃O₅. Full article