Search Results (225)

Lightweight, lead-free polymer–mineral composites have attracted increasing interest as radiation-attenuating materials for applications where reduced mass and environmental compatibility are required. In this work, the $\gamma$-ray attenuation behavior of poly(ether ether ketone) (PEEK) reinforced with natural palygorskite and pumice was evaluated at filler concentrations of 10–40 wt%. Photon interaction parameters, including the linear attenuation coefficient ($\mu$), half-value layer (HVL), mean free path ($\lambda$), and effective atomic number ($Z_{\mathrm{eff}}$), were computed over the energy range 15 keV–15 MeV using the Phy-X/PSD platform and validated through full Geant4 Monte Carlo transmission simulations. At 15 keV, $\mu$ increased from $1.46{\mathrm{cm}}^{-1}$ for pure PEEK to $4.21{\mathrm{cm}}^{-1}$ and $8.499{\mathrm{cm}}^{-1}$ for the 40 wt% palygorskite- and pumice-filled composites, respectively, reducing the HVL from 0.69 cm to 0.24 cm and 0.11 cm. The corresponding $Z_{\mathrm{eff}}$ values increased from 6.5 (pure PEEK) to 9.4 (40 wt% palygorskite) and 15.3 (40 wt% pumice), reflecting the influence of higher-Z oxide constituents in pumice. At higher photon energies, the attenuation curves converged as Compton scattering became dominant, although pumice-filled PEEK retained marginally higher $\mu$ and shorter $\lambda$ up to the MeV region. These findings demonstrate that natural mineral fillers can enhance the photon attenuation behavior of PEEK while retaining the known thermal stability and mechanical performance of the polymer matrix as reported in the literature, indicating their potential use as lightweight, secondary radiation-attenuating components in medical, industrial, and aerospace applications. Full article

This study evaluates lead-free high-density polyethylene (HDPE) composites reinforced with high-Z oxides (Bi₂O₃, WO₃, Gd₂O₃, TeO₂, and a Bi₂O₃/WO₃ hybrid) as lightweight materials for gamma-ray and fast-neutron shielding. A hybrid computational framework combining Phy-X/PSD with Geant4 Monte Carlo simulations was used to obtain key shielding parameters, including the linear and mass attenuation coefficients (μ, μ/ρ), half-value layer (HVL), mean free path (MFP), effective atomic number (Z_eff), effective electron density (N_eff), exposure and energy-absorption buildup factors (EBF, EABF), and fast-neutron removal cross section (Σ_R). The incorporation of heavy oxides produced a pronounced improvement in gamma-ray attenuation, particularly at low energies, where the linear attenuation coefficient increased from below 1 cm⁻¹ for neat HDPE to values exceeding 130–150 cm⁻¹ for Bi- and W-rich composites. In the intermediate Compton-scattering region (≈0.3–1 MeV), all oxide-reinforced systems maintained a clear attenuation advantage, with μ values around 0.12–0.13 cm⁻¹ compared with ≈0.07 cm⁻¹ for pure HDPE. At higher photon energies, the dense composites continued to outperform the polymer matrix, yielding μ values of approximately 0.07–0.09 cm⁻¹ versus ≈0.02 cm⁻¹ for HDPE due to enhanced pair-production interactions. The Bi₂O₃/WO₃ hybrid composite exhibited attenuation behavior comparable, and in some regions slightly exceeding, that of the single-oxide systems, indicating that mixed fillers can effectively balance density and shielding efficiency. Oxide addition significantly reduced exposure and energy-absorption buildup factors below 1 MeV, with a moderate increase at higher energies associated with secondary radiation processes. Fast-neutron removal cross sections were also modestly enhanced, with Gd₂O₃-containing composites showing the highest values due to the combined effects of hydrogen moderation and neutron capture. The close agreement between Phy-X/PSD and Geant4 results confirms the reliability of the dual-method approach. Overall, HDPE composites containing about 60 wt.% oxide filler offer a practical compromise between shielding performance, manufacturability, and environmental safety, making them promising candidates for medical, nuclear, and aerospace radiation-protection applications. Full article

This paper proposes an optimized digital predistortion (DPD) framework. Firstly, a peak-detection-based loop-delay estimation is developed by leveraging the unique peak distribution of Orthogonal Frequency Division Multiplexing (OFDM) signals. It reduces the required number of samples to as small as two without compromising estimation accuracy. Then, a Biased Memory Polynomial (BMP) model is proposed for power amplifier modeling. It addresses low-power inaccuracies caused by circuit imperfections (e.g., DC offsets) by adding a bias term to conventional memory polynomials, improving linearization accuracy in low-power regime. Last, to improve the accuracy of coefficient derivation, Memory-Clustering Biased Memory Polynomial (MBMP) is proposed by grouping signals into clusters based on memory-attenuated input vectors and processing them with dedicated sub-models. It improves linearization accuracy in high-power regime. Experimental results demonstrate that the MBMP model reduces normalized mean square error (NMSE) by 16.12 dB, and reduces adjacent channel power ratio (ACPR) by about 12 dBm compared to conventional MP. Full article

Objective: The aim of this study was to evaluate the consistency and reproducibility of attenuation coefficient (AC) measurements using different commercial ultrasound (US) across via a phantom experiment to investigate the relationship between the AC and MRI-derived proton density fat fraction (MRI-PDFF) values and the conversion equation. Methods: Twelve phantoms containing varying fat proportions (0–100%) were constructed. Phantom ACs were estimated via three US attenuation systems, including attenuation imaging (ATI), ultrasound attenuation analysis (USAT), and the US-guided attenuation parameter (UGAP), along with MRI-PDFF. Agreement among the AC values from the three ultrasonic attenuation systems was evaluated. Linear correlation analysis was used to explore the ACs, fat concentrations of the phantom, and MRI-PDFF measurements, from which a linear conversion formula between the ultrasonic attenuation parameters and the MRI-PDFF was derived. Results: MRI-PDFF and phantom fat concentration measurements appeared with a strong linear correlation (R² = 0.996, p < 0.001). For the three US attenuation parameters, both inter-operator and intra-operator intraclass correlation coefficients (ICCs) ranged from 0.990 to 0.995 and 0.989 to 0.995, respectively. Bland–Altman analysis revealed no significant differences between the above three (all p > 0.05). Significant linear relationships were demonstrated between ultrasound attenuation parameters and phantom fat concentration (r = 0.938–0.986; all p < 0.001), as well as between ultrasound attenuation parameters and MRI-PDFF values (r = 0.922–0.982; all p < 0.001). A conversion formula (fat proportions ≤ 50%) was derived: US (dB/cm/MHz) = 0.501 + 0.012 MRI-PDFF (%). Conclusions: AC across different commercial ultrasound devices demonstrated significant diagnostic value in fat concentrations that appeared good consistency in measuring phantom fat concentration both between and within groups. The linear relationship between AC and MRI-PDFF enables the application of a conversion formula. Full article

This study investigates the modulation effects of varying infill densities and phase angles on the radiation attenuation properties of three 3D-printed polymers: acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), and thermoplastic polyurethane (TPU). Using the EpiXS software for radiation attenuation calculations, the study assessed the linear attenuation coefficients (LACs) of the materials under different infill densities (30%, 50%, 70%, 90%, and 100%) and phase angles (0°, 30°, 45°, 60°, and 90°) for radiation in the 1–100 keV energy range, which corresponds to the X-ray spectrum. TPU demonstrated the highest attenuation values, with a baseline coefficient of 20.199 cm⁻¹ at 30% infill density, followed by PLA at 18.835 cm⁻¹, and ABS at 13.073 cm⁻¹. Statistical analysis via the Kruskal–Wallis test confirmed that infill density significantly impacts attenuation, while phase angle exhibited no significant effect, with p-values exceeding 0.05 across all materials. TPU showed the highest sensitivity to infill density, with a slope of 1.1194, compared to 0.7257 for ABS and 0.9251 for PLA, making TPU the most suitable candidate for radiation protection applications, particularly in applications where flexibility and high attenuation are required. The findings support the potential of 3D printing to produce customized, cost-effective radiation protection gear for medical and industrial applications. Future work can further optimize material designs by exploring more complex infill geometries and testing under broader radiation spectra. Full article

Background/Objectives: Sarcopenia, an underdiagnosed musculoskeletal disorder, is a serious cause of disability, poor quality of life, and healthcare costs in an increasingly elderly population. This study aimed to examine an ultrasound (US)-based, inexpensive, simple, and reproducible alternative to magnetic resonance imaging (MRI) for assessing muscle quality. A study compared Dixon MR fat fraction with US attenuation imaging (ATI) and echo intensity (EI) in the rectus femoris (RF) and biceps brachii (BB). Methods: The US images were acquired from 34 participants who had previously received a whole-body MRI. The ATI measurements were carried out using a linear array on a Canon Aplio i800 scanner. The measurements of EI were assessed by manually tracing the cross-sectional border of the right RF and BB muscles. Corresponding T1-weighted Dixon VIBE-based fat and water images were required for the MRI fat fraction percentage (MR %FF) measurements. Results: Using Pearsons correlation coefficient, a good correlation was found between MR %FF and EI measurements. The results between operators’ measurements showed a strong correlation and were highly repeatable. Attenuation imaging revealed no correlation with MR %FF or EI. Conclusions: Echo intensity offers a low-cost, non-invasive, and widely accessible US-based imaging modality for screening patients at risk for sarcopenia. No correlation was found between the ATI and MR %FF or between the ATI and EI. Further adapted protocols and software adjustments are needed so that ATI has the potential to prove itself as an additional US-based method for assessing fat infiltration in muscles. Full article

In recent years, polymer-based hybrid nanocomposites have emerged as promising alternatives to traditional heavy metal shields due to their low density, flexibility, and environmental safety. In this study, the synthesis of PS-PEG copolymers and the gamma radiation-shielding properties of PS-PEG/As₂O₃, PS-PEG/BN, and PS-PEG/As₂O₃/BN nanocomposites with different compositions are investigated. The goal is to find the optimal nanocomposite composition for gamma radiation shielding and dosimetry. Therefore, the mass attenuation coefficient (MAC), linear attenuation coefficient (LAC), half-value layer (HVL), tenth-value layer (TVL), effective atomic number, mean free path (MFP), radiation shielding efficiency (RPE), electron density, and specific gamma-ray constant were presented. Gamma rays emitted by the Eu source were detected by a high-purity germanium (HPGe) detector device. GammaVision was used to analyze the given data. Photon energy was in the vicinity of 121.8–1408.0 keV. The MAC values in XCOM simulation tools were used to compute. Gamma-shielding efficiency was increased by an increased number of NPs at a smaller photon energy. At 121.8 keV, the HVL of a composite with 70 wt% As₂O₃ NPs is 2.00 cm, which is comparable to the HVL of lead (0.56 cm) at the same energy level. Due to the increasing need for lightweight, flexible, and lead-free shielding materials, PS-b-PEG copolymer-based nanocomposites reinforced with arsenic oxide and BN NPs will be materials of significant interest for next-generation radiation protection applications. Full article

Environmentally friendly materials with superior structural, physical, optical, and shielding capabilities are of great technological importance and are continually being investigated. In this work, novel multicomponent borate glasses with the composition xTiO₂-10BaO-5Al₂O₃-5WO₃-20Bi₂O₃-(60-x) B₂O₃, where 0 ≤ x ≤ 15 mol%, were produced via the melt-quenching technique. The increase in TiO₂ content results in a decrease in molar volume and a corresponding increase in density, indicating the formation of a compact, rigid, and mechanically hard glass network. Elastic constant measurements further confirmed this behavior. FTIR analysis confirms the transformation of BO₃ to BO₄ units, signifying improved network polymerization and structural stability. The prepared glasses exhibit an optical absorption edge in the visible region, demonstrating their strong ultraviolet light blocking capability. Incorporation of TiO₂ leads to an increase in refractive index, optical basicity, and polarizability, and a decrease in the optical band gap and metallization number; all of these suggest enhanced electron density and polarizability of the glass matrix. Radiation shielding properties were evaluated using Phy-X/PSD software. The outcomes illustrate that the Mass Attenuation Coefficient (MAC), Effective Atomic Number (Z_eff), Linear Attenuation Coefficient (LAC) increase, while Mean Free Path (MFP) and Half Value Layer (HVL) decrease with increasing TiO₂ at the expense of B₂O₃, confirming superior gamma-ray attenuation capability. Additionally, both TiO₂-doped and undoped samples show higher fast neutron removal cross sections (FNRCS) compared to several commercial glasses and concrete materials. Overall, the incorporation of TiO₂ significantly enhances the optical performance and radiation-shielding efficiency of the environmentally friendly glass system, making these potential candidates for advanced photonic devices and radiation-shielding applications. Full article

The vertical attenuation coefficient of photosynthetically active radiation ($K_d\left(PAR\right)$) is essential for characterizing the underwater light field and for operational marine monitoring. Although there have been efforts to use the standard satellite light attenuation product at 490 nm ($K_d\left(490\right)$) to estimate ($K_d\left(PAR\right)$) over a decade, earlier approaches were constrained by limited data. This study used a globally representative robust database of in-situ and satellite observations spanning diverse marine optical conditions and applied rigorous quality control. Three empirical models (linear, power, and a higher-order polynomial) were developed using four $K_d\left(490\right)$ satellite variants validated against an independent dataset and benchmarked against six published algorithms (36 total approximations). Performance was assessed using a Model Performance Index (MPI), where values closer to 1 indicate a better model. The best model was a power regression driven by the standard satellite $K_d\left(490\right)$, which yielded an MPI of 0.8704, indicating a robust performance under a wide variability of marine optical conditions. These results highlight the value of multisensor products, which with a rigorous quality control protocol, could be used to estimate the $K_d\left(PAR\right)$ from the standard satellite $K_d\left(490\right)$. The objective of the proposed algorithm is to generate long-term $K_d\left(PAR\right)$ time series. This algorithm will be operational for implementation in marine ecosystem monitoring systems and can contribute to strengthening decision-making. Full article

Background: Photon-counting computed tomography (PCCT) represents a major technological advance in clinical CT imaging, offering superior spatial resolution, enhanced material discrimination, and potential radiation dose reduction compared to conventional energy-integrating detector systems. As the first clinically approved PCCT scanner becomes available, establishing a comprehensive characterization of its image quality is essential to understand its performance and clinical impact. Methods: Image quality was evaluated using a commercial quality assurance phantom with acquisition protocols typically used for three anatomical regions—head, abdomen/thorax, and inner ear—representing diverse clinical scenarios. Each region was scanned using both ultra-high-resolution (UHR, 120 × 0.2 mm slices) and conventional (144 × 0.4 mm slices) protocols. Conventional metrics, including signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), slice thickness accuracy, and uniformity, were assessed following international standards. Task-based analysis was also performed through target transfer function (TTF), noise power spectrum (NPS), and detectability index (d′) to evaluate diagnostic relevance. Results: UHR protocols provided markedly improved spatial resolution, particularly in the inner ear imaging, as confirmed by TTF analysis, though with increased noise and reduced low-contrast detectability in certain conditions. CT numbers showed linear correspondence with known attenuation coefficients across all protocols. Conclusions: This study establishes a detailed technical characterization of the first clinical PCCT scanner, demonstrating significant improvements in terms of spatial resolution and accuracy of the quantitative image analysis, while highlighting the need for noise–contrast optimization in high-resolution imaging. Full article

Lightweight and lead-free radiation shields are increasingly developed to overcome the toxicity and handling challenges associated with conventional heavy-metal-based materials. In this study, the $\gamma$-ray attenuation behavior of polymer–zeolite composites was examined by reinforcing high-density polyethylene (HDPE) and polylactic acid (PLA) with natural clinoptilolite zeolite at concentrations of 10–40 wt%. Photon-interaction parameters, including the linear attenuation coefficient ($\mu$), half-value layer (HVL), mean free path ($\lambda$), and effective atomic number ($Z_{\mathrm{eff}}$), were evaluated over 15 keV–15 MeV using the Phy-X/PSD platform. Zeolite incorporation consistently enhanced photon attenuation, particularly at low energies dominated by the photoelectric effect. At 15 keV, the HVL decreased from 0.60 cm to 0.08 cm for HDPE and from 0.043 cm to 0.033 cm for PLA as the zeolite loading increased to 40 wt%. Correspondingly, $Z_{\mathrm{eff}}$ increased from 2.7 to 4.3 for HDPE and from 6.5 to 11.6 for PLA, while $\mu$ reached approximately 41 cm⁻¹ and 56 cm⁻¹ at 15 keV for the respective 40 wt% composites. Beyond about 1 MeV, differences between compositions became minimal as Compton scattering dominated. PLA–zeolite composites exhibited higher $\mu$ and lower HVL than HDPE–zeolite, whereas HDPE maintained an advantage in mixed-field environments owing to its hydrogen-rich matrix. The results confirm that zeolite-reinforced polymers are safe, low-cost, and lightweight materials suitable for radiation shielding in medical, nuclear, and aerospace applications. Full article

Numerous studies aimed to validate new shielding materials with the transition of medical radiation-shielding tools toward eco-friendly materials. In this study, we assessed the feasibility of ceramic composites, recently adopted in aerospace for internal shielding, as candidates for medical applications. Specifically, three types of ceramic composite mixtures were examined: bismuth oxide-based (Bi₂O₃), cerium oxide-based (CeO₂), and tantalum oxide-based (Ta₂O₅) ceramic composites. Two approaches—theoretical simulations and direct experiments—validated the performance under clinical conditions. Monte Carlo simulation results reveal that CeO₂, with its high linear attenuation coefficient, exhibits the strongest theoretical shielding. In terms of density measurements, Ta₂O₅ composite sheets yielded the highest density (3.318 g/cm³), followed by CeO₂ composites (3.228 g/cm³) and Bi₂O₃ composites (3.091 g/cm³). Although relatively slight differences in density were observed among the fabricated sheets, Ta₂O₅ composites tended to have slightly higher densities. However, Ta₂O₅ composites outperformed the other composites in direct clinical experiments. This discrepancy between the theoretical and experimental results highlights the influence of other factors, such as the energy characteristics of the materials and variations in the fabrication process. Overall, this study supports the development of eco-friendly radiation shields through theoretical and clinical validation. Full article

The increasing demand for sustainable and multifunctional materials in radiation shielding and optical applications has driven research toward utilizing natural and waste-derived reinforcements in polymer matrices. However, achieving effective attenuation performance across different radiation types using eco-friendly fillers remains a significant challenge. In this study, polyvinyl chloride (PVC)/Polystyrene (PSt) blend composites (1:1 weight ratio) were reinforced with powdered snail shell (SSP) as a biogenic additive, aiming to enhance their shielding and optical performance. Composites containing 5%, 10%, 20%, and 30% SSP (w/v) were fabricated and characterized. Key parameters including linear attenuation coefficient (LAC), mass attenuation coefficient (MAC), mean free path (MFP), half-value layer (HVL), and effective atomic number (Zeff) were measured using a variable-energy X-ray source (13.37–59.54 keV) and ULEGe detector. Fast neutron shielding performance and theoretical values for build-up factor (EBF) and macroscopic neutron cross-sections were also calculated. The results showed a marked improvement in X-ray attenuation with increasing SSP content (SSP30 > SSP20 > SSP10 > SSP5), while neutron shielding declined due to the high oxygen content of SSP. Among the tested samples, the SSP30 composite exhibited the highest X-ray attenuation efficiency, whereas the SSP5 composition showed the greatest enhancement in optical reflectance and neutron absorption, indicating optimal performance in these respective tests. Additionally, 5% SSP incorporation improved optical reflectance by 12%, indicating enhanced photon backscattering at the material surface. This behavior contributes to improved gamma shielding efficiency by reducing photon penetration and enhancing surface-level attenuation. These findings highlight the potential of snail shell-based fillers as low-cost, sustainable reinforcements in multifunctional polymer composites. Full article

This study investigates the design and experimental evaluation of Fe–B–Si-based bilayer composites engineered for dual shielding against gamma rays and thermal neutrons. The materials integrate a boron-enriched amorphous Fe matrix with surface coatings of high-Z fillers—lead (Pb) and tungsten (W)—dispersed in an epoxy resin. W or Pb powders (20–40 µm) were dispersed in epoxy resin at a high filler loading (60–70 wt% metal, approximately several tens to one by weight). This ensured a dense and uniform coating structure. The metallic fillers were high-purity (≥99.9%) powders. Gamma-ray attenuation was examined using ¹³⁷Cs and ⁶⁰Co sources at photon energies of 661.7, 1173, and 1332 keV, while thermal neutron shielding was assessed with a moderated Am-Be neutron source. The effects of boron concentration (13–21 at%) in the matrix and coating thickness (80–400 μm) were systematically evaluated. Increasing boron content markedly enhanced thermal neutron attenuation, reaching up to 29%, whereas Pb- and W-filled coatings achieved more than 85% gamma-ray attenuation at 661.7 keV. All measurements were repeated three times; standard deviations were below 2% across conditions, confirming reproducibility and indirectly indicating uniform coating dispersion. At 661.7 keV, the half-value and tenth-value layers (HVL/TVL) were derived from the measured linear attenuation coefficients to benchmark performance. Notably, W coatings delivered shielding efficiency comparable to Pb while offering advantages in environmental safety, mechanical robustness, and regulatory compliance. These results highlight the potential of Fe–B–Si bilayer composites as lightweight, scalable, and lead-free shielding materials for aerospace electronics, portable radiation protection devices, and modular panels for satellites and nuclear facilities. Full article

Reliable inflow forecasting represents a challenging and representative problem in long-horizon time series forecasting. Although long-term time series forecasting (LTSF) algorithms have shown strong performance in other domains, their applicability to hydrological inflow prediction has not yet been systematically assessed. Therefore, this study examined two LTSF linear models for inflow forecasting: NLinear and DLinear. LTSF models were trained with a 24 h input window and evaluated for 24 h lead times at eight major dams in South Korea. Long Short-Term Memory (LSTM) network and eXtreme Gradient Boosting (XGBoost) were employed as a conventional AI model. LSTM consistently achieved the highest coefficient of determination (R²) and the lowest normalized root mean square error, DLinear minimized normalized mean square error, and NLinear delivered superior hydrological consistency as measured by Kling–Gupta efficiency. XGBoost showed comparatively larger variability across sites. Spatial heterogeneity was evident; sites were grouped into high-performing, transition, and vulnerable groups. Peak-flow analysis revealed amplitude attenuation and phase lag at longer horizons. Full article