Search Results (412)

The key to metallic fuel development is the fabrication of uranium metal and alloys into fuel forms. U-Nb alloys are one of the best candidates for a metallic fuel alloy with high-temperature strength sufficient to support the core, acceptable nuclear properties, good fabricability, and compatibility with usable coolant media. Melt processing has been a key component of the metallic fuel cycle, and process models require thermophysical parameters at elevated temperatures, particularly above the melting temperatures, regarding which experimental data are scarce, for accurate simulations and process development. By means of ab initio density-functional theory (DFT) quantum molecular dynamics (QMD), we have calculated the main thermophysical parameters—the density, thermal expansion coefficient, specific heat, thermal conductivity, melting temperature, latent heat of fusion, and viscosity—used in the modeling of the U-6 wt.% Nb alloy casting. The melting temperature of the U-6 wt.% Nb alloy at ambient pressure is obtained by means of QMD simulations using the Z-method. The ambient volume change and latent heat of melting of U-6 wt.% Nb are also derived from QMD simulations in conjunction with analytical fitting for the energy and pressure. The thermal conductivity for the solid U-Nb alloy is calculated from the semi-classical Boltzmann transport equation combined with an estimate of the electron relaxation time obtained from DFT simulations. Full article

Persistent uncertainty in translating low-field nuclear magnetic resonance (NMR) T₂ relaxation spectra into geometrically meaningful pore–throat metrics has long hindered the quantitative characterization of tight reservoirs. To address this issue, this study develops an enhanced conversion framework that incorporates scale-dependent pore geometry, enabling more realistic estimation of pore–throat radius distributions. Core samples were collected from the first member of the Shanxi Formation and the eighth member of the Shihezi Formation in the Ordos Basin. A comprehensive experimental dataset was established, including porosity and permeability measurements, X-ray diffraction (XRD) mineral analysis, NMR experiments, high-pressure mercury intrusion (HPMI), and constant-rate mercury injection (CRMI). The results demonstrate that total clay content exhibits weak correlations with pore size and porosity. In contrast, the occurrence and morphology of specific clay minerals exert significant control on pore connectivity and flow behavior. In particular, fibrous illite increases pore–throat complexity, while early chlorite coatings help preserve primary intergranular pores. A single geometric model cannot fully represent the complex pore–throat system in tight sandstones. For pores, a spherical geometry is most appropriate and indeed necessary. Smaller throats connecting these pores often exhibit geometries more consistent with cylindrical shapes. Within the coarse pore size range, large pores dominate the reservoir space and generally exhibit geometries that better conform to a spherical shape. And larger pores dominate the volumetric contribution in the coarse pore-size range. These observations suggest that a scale-dependent composite model could further improve the accuracy of NMR-based pore-size estimations. Therefore, the spherical-pore model provides a physically meaningful framework for characterizing pore structures in tight reservoirs. At the same time, incorporating scale-dependent considerations offers a promising avenue for future methodological development. Full article

The electronic properties of high-temperature superconducting cuprates are encoded in NMR data. Without microscopic theory, reliable NMR phenomenologies are in demand. Here we make use of the extensive literature data to develop a different understanding of the cuprates from the shifts of the ${\mathrm{CuO}}_2$ plane. The Cu shift analysis is based only on the symmetry of the two Cu hyperfine couplings, without assumptions about their size. We use an anisotropic $A_{\alpha }$ and isotropic B, as from atomic Cu orbitals, and find two spin components (A- and B-spins) that explain all the shift data. The components differ in size and temperature dependence according to simple rules. Upon doping the cuprates, metallic B-spin appears above a pseudogap temperature, which is shared with the A-spin. Further doping decreases the pseudogap temperature and increases the B-spin, but less so the A-spin. The apparent linear rate of increase in the density of states of the B-spin with doping is nearly threefold above $x=0.20$, where the pseudogap disappears. The pseudogap temperature is a measure of the coupling between A and B, which suppresses the shifts but not nuclear relaxation. Spin-singlet pairing involves A and B according to three simple condensation rates, which will be discussed. The optimal $T_{\mathrm{c}}$ demands a special match between A and B. However, the shifts do not simply predict the highest $T_{\mathrm{c}}$ of all cuprates, in contrast to nuclear relaxation anisotropy and charge sharing between planar Cu and O. Relations to other probes are discussed. Full article

Background/Objectives: Achillea millefolium is a well-known plant used in traditional medicine for the treatment of inflammation, gastrointestinal disorders, respiratory diseases, hypertension, and diabetes, among others. These effects are attributed to the metabolite content of flavonoids and terpenes such as achillin (1) and leucodin (2). Thus, the current investigation aims to standardize the extracts from A. millefollium based on the presence of 1 and 2 and relate them to their relaxant effect in ex vivo assays. Methods: A validated High-Performance Liquid Chromatography (HPLC) method was used to determine the concentration of the main compounds, employing standard molecules previously isolated from the same species and characterized by nuclear magnetic resonance (NMR) and X-ray diffraction. Also, the relaxant effects of both compounds and their combinations were assayed on aortic and tracheal rat rings in an organ bath. Results: Compounds (1) and (2) are the main compounds in hexane, dichloromethane, and hydroalcoholic extracts, present in different proportions. The relaxant effects in ex vivo models of the aorta and trachea showed that the sesquiterpene lactones achillin (1) [Trachea, maximum effect (Emax): 67.67 ± 5.01%, medium effective concentration (EC50): 304.44 ± 2.61 µM; Aorta: Emax: 63.94 ± 6.28%, EC50: 225.73 ± 4.49 µM)] and leucodin (2) (Trachea: Emax: 76.71 ± 4.73%, EC50: 266.40 ± 2.05 µM; Aorta, Emax: 72.96 ± 1.73%, EC50: 163.29 ± 2.99 µM) are responsible for the relaxant effects shown by the extracts. The observed effect is proportional to the concentration of these molecules, with hexane extracts being more active. Additionally, we demonstrate the safety of molecules 1 and 2 through toxicological studies recommended by the OECD. Conclusions: The isolated compounds achillin and leucodin are the primary constituents in the flowers of A. millefolium, with higher concentrations found in hexane extracts, particularly of achillin, which shows a correlation of 2.33 with respect to leucodin. This correlation is closely related to their relaxant effect, as these compounds are the main contributors to the relaxant response in the trachea and aorta, being more effective when used together. Full article

High-pressure hydrogen exposure may induce transport and diffusion–relaxation–controlled changes in elastomeric sealing materials that differ from conventional fluid aging. Hydrogen uptake through solution–diffusion processes can lead to swelling, redistribution of molecular mobility, viscoelastic evolution, and, under certain conditions, cavitation or microvoid formation during decompression, which may affect long-term sealing performance. This review compiles experimental results for commonly used elastomers, including Nitrile Butadiene Rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), Fluoroelastomer (FKM), Ethylene Propylene Diene Monomer (EPDM), and silicone, and summarizes reported ranges of hydrogen diffusivity, solubility, and permeability under high-pressure conditions. These transport characteristics are compared with mechanical and microstructural observations obtained from Dynamic Mechanical Analysis (DMA), Nuclear Magnetic Resonance (NMR), decompression testing, and micro-computed tomography (µXCT) imaging. Available evidence suggests that hydrogen-induced changes are predominantly governed by physical processes, including swelling, plasticization-like mobility changes, and constraint redistribution, while extensive chemical degradation of the polymer backbone is generally limited under clean hydrogen conditions. Materials with similar conventional mechanical properties may, therefore, exhibit different hydrogen uptake, viscoelastic response, and resistance to decompression damage. Conventional single-point mechanical tests, such as tensile measurements, may not fully capture the time-dependent viscoelastic evolution relevant to sealing performance. This work proposes a multiscale characterization framework integrating transport, viscoelastic, molecular, and microstructural analysis for more reliable evaluation of elastomers in hydrogen service, supporting improved qualification strategies for high-pressure hydrogen systems. Full article

In this study, first-principles molecular dynamics (FPMD) simulations were employed to systematically investigate the effects of temperature and composition on the microstructure and transport properties of CaCl₂–CaI₂ mixed molten salts at the atomic scale. Structural analysis shows that the system exhibits good relaxation behavior and thermodynamic stability, with coordination strength following Ca-Cl > Ca-I. The transport properties reveal a coupled dependence on temperature and composition: increasing CaI₂ content enhances the diffusion of I⁻ ions, whereas at 1173 K, a decrease in diffusion coefficients is observed for all ionic species. Arrhenius analysis indicates that increasing CaI₂ content lowers the activation energy for ion migration. The shear viscosity follows the order η(Ca²⁺) > η(Cl⁻) ≥ η(I⁻), and decreases with increasing temperature and CaI₂ concentration, indicating improved fluidity. Notably, the results reveal a competitive coordination mechanism between Cl⁻ and I⁻ around Ca²⁺, as well as a non-monotonic transport behavior at high temperatures, reflecting the complex coupling between composition and ionic dynamics in mixed halide melts. This study provides a theoretical basis for the optimization of molten salt electrolysis processes and nuclear energy materials, and offers insight for future multiscale simulations and experimental validation. Full article

The application of low-field time-domain nuclear magnetic resonance (TD-NMR) to measure water content and assess moisture-related relaxation behavior in sludge samples has been investigated. The results of TD-NMR measurements on 26 dewatered sludge samples revealed a strong correlation between sludge water content and key features of the T₂ distribution curves, including the maximum relaxation time and peak area, demonstrating the potential of the TD-NMR method for estimating sludge moisture content. No consistent relationship was observed between the peaks in T₂ relaxation distribution curves obtained by Inverse Laplace Transform (ILT) and the expected water fraction ratios, apparently because the sludge structure is highly variable from sample to sample. Despite the complex and heterogeneous nature of sludge samples, the direct correspondence between key features of the T₂ relaxation curves and moisture content demonstrates the high potential of TD-NMR as a tool for rapid and reliable moisture monitoring, even in an online device configuration. Full article

Background and aims. Liver mechanical properties’ (stiffness/viscoelasticity) evaluation is relevant for diagnosing/monitoring liver fibrosis. Due to limitations of the commonly used elastography, we propose the use of rheology and Low Field-Nuclear Magnetic Resonance (LF-NMR). Methods. In 30 liver samples from patients undergoing bariatric surgery and 18 control samples, we evaluated the shear modulus G/critical stress τc (elastic properties) and mean complex modulus $G_{\mathrm{a}}^{*}$ (elastic/viscous properties) by rheology. LF-NMR was used to measure the spin–spin relaxation time (T_2m), reflecting iron content. The expression of iron-related proteins and of pro-fibrotic proteins were evaluated by qRT-PCR. Tissue histology was also determined. Results. $G_{\mathrm{a}}^{*}$/G/τ_c were higher in pathological samples, which also showed increased expression of pro-fibrotic proteins. Fibrosis determination displayed a correspondence of 4/30 samples for elastography/histology and 17/30 for rheology/histology. T_2m was significantly lower in pathological livers, indicating iron accumulation as confirmed by increased expression of iron-related proteins. T_2m was more effective than histology in detecting iron. An inverse correlation was observed between T_2m and $G_{\mathrm{a}}^{*}$/G showing that iron accumulation is associated with increased liver elasticity/viscoelasticity, i.e., fibrosis. Additionally, an inverse correlation of $G_{\mathrm{a}}^{*}$/G with transferrin, was observed. Conclusion. As our patients mostly have mild liver fibrosis, the combined use of rheology/LF-NMR can effectively detect early changes in liver mechanical properties, aiding in staging and diagnosis of fibrosis. Full article

This study resolves the apparent breakdown of the Korringa relation in disordered liquid metals by investigating Ga-based alloys (EGaIn and Galinstan). By integrating temperature-dependent Knight shifts (K) with longitudinal (T₁) and transverse (T₂) relaxation measurements, we demonstrate that deviations from classical behavior arise from neglecting transverse spin dephasing induced by structural and electronic disorder. While solid-state alloys follow the conventional Korringa law, the liquid phase exhibits significant discrepancies between T₁ and T₂ due to enhanced electron scattering and fluctuating hyperfine fields. By explicitly incorporating T₂ into a modified framework, the proportionality between the Knight shift and nuclear relaxation is quantitatively restored. This establishes transverse relaxation as a critical parameter for describing nuclear spin dynamics in complex liquid metals, reinforcing NMR as a powerful local probe for optimizing next-generation liquid metal technologies. Full article

The Zircaloy-4 alloy is a key structural material for nuclear reactor cores. However, its behavior under warm deformation conditions and during phase transformations requires in-depth investigation to improve technologies for producing ultrafine-grained (UFG) structures using severe plastic deformation methods. This work presents a comprehensive study of the rheological properties, phase stability, and microstructural evolution of the alloy in the temperature range from 20 to 950 °C at strain rates of 0.5 and 15 s⁻¹. The experimental part included plastometric testing, dilatometric analysis, and microstructural characterization. It was established that the optimal window for plastic deformation corresponds to warm deformation at 650 °C. Dilatometric analysis confirmed that heating to 650 °C ensures the preservation of a stable initial α-phase structure, since the formation of secondary phases and the α→β transformation are initiated at higher temperatures, namely 694 °C (onset) and 847 °C (completion). At 650 °C, the deformation resistance decreases by approximately 70% compared to cold processing, while the strain-rate sensitivity of the flow stress is minimized. EBSD analysis showed that deformation under these conditions leads to intensive grain fragmentation via mechanisms of dynamic recovery and the initial stages of continuous dynamic recrystallization. The decisive role of the kinetic factor was demonstrated: reducing the strain rate to 0.5 s⁻¹ promotes the formation of a finer and more homogeneous grain structure. In contrast, high strain-rate deformation (15 s⁻¹) results in coarser grains and increased non-relaxed intragranular residual stresses. The obtained results provide a physical basis for optimizing thermomechanical processing regimes and can be used to produce UFG structures in zirconium alloys without the risk of phase degradation. Full article

Long-term safety assessment of deep geological repositories for spent nuclear fuel requires explicit evaluation of thermo-mechanical (TM) processes induced by decay heat and their influence on fractured host rock. A safety-relevant, though low-probability, scenario concerns shear reactivation of fractures intersecting deposition holes, which could compromise canister integrity if displacement exceeds design limits. This study presents a three-dimensional discrete element modelling approach to analyze the thermal evolution of the Forsmark repository (Sweden) and the associated long-term response of a discrete fracture network (DFN) during the post-closure phase. The model explicitly represents repository panel, deterministic deformation zones, and a stochastically generated fracture network embedded in a bonded particle assembly representing the rock for Particle Flow Code (PFC) numerical simulations. Time-dependent heat release from spent nuclear fuel canisters is implemented using a physically based decay power function. A deposition panel-scale heat-loading formulation accounts for deposition-hole and tunnel spacing. Two emplacement scenarios are analyzed: (a) a simultaneous all-panel heating scenario, used as a conservative bounding case, and (b) a sequential panel heating scenario representing staged emplacement and closure. The simulations show that temperature and thermally induced stress evolution are sensitive to the emplacement and closure sequence. Sequential heating produces a more gradual thermal build-up and lower peak temperatures than simultaneous heating, indicating that thermal and stress perturbations in the host rock can be influenced not only through repository design, but also by operational strategy. Thermally induced fracture shear displacement displays a systematic temporal response. Fractures located within the deposition panel footprint develop shear displacement rapidly during the early post-closure period, reaching peak values at approximately 200 years, followed by gradual relaxation as temperatures decline. The average peak shear displacement on fractures is on the order of 2–3 mm, while fractures outside the panel footprint show smaller early-time displacements and a more prolonged long-term response. All simulated shear displacements remain more than one order of magnitude below the commonly cited canister damage threshold for Forsmark of approximately 50 mm, even for the conservative simultaneous heating case. These results indicate that thermally induced fracture shear is unlikely to cause direct mechanical damage to canisters. At the same time, the persistence of residual shear displacement after heating implies permanent fracture dilation, which may influence long-term hydraulic properties and indirectly affect processes such as groundwater flow and canister corrosion. The modelling framework and results presented here were conducted for review purposes independently from the Swedish safety case, and provide a mechanistic basis for evaluating thermally induced fracture deformation in crystalline rock repositories and contribute to bounding the role of thermo-mechanical processes in the safety assessment of spent nuclear fuel disposal at Forsmark. Full article

The spin relaxation rate of Xe isotopes is a key characteristic of nuclear magnetic resonance gyroscopes (NMRGs). A pump-induced biphasic relaxation (PBR) model is proposed to describe the pump dependence of the transverse relaxation rate of ¹²⁹Xe nuclear spin. The distribution of electron polarization is theoretically analyzed based on the Bloch–Torrey equations and the volume-averaged polarization is evaluated through NMR frequency shift measurements. Experimental results confirm the theoretical quadratic dependence between Γ and $P_{Rb}$ with a high fitting accuracy (R² = 0.9969). The predicted linear (R² > 0.9966) and hyperbolic (R² > 0.9942) regimes of Γ versus pump power are also observed. Validation across different pump power conditions shows agreement between the model and measurements, with an average relative deviation of 0.2169%. The multi-stage process of nuclear spin relaxation is quantified, thereby providing a robust validation for the PBR model. Full article

Motion and path planning are fundamental to intelligent robotic systems, enabling navigation. The objective is to generate collision-free trajectories in obstacle-rich configuration spaces (C-spaces) while meeting performance constraints. In environments with narrow passages planning becomes especially difficult, as feasible regions have low measure and are rarely reached by random sampling. Classical sampling-based planners are probabilistically complete but inefficient in such regions. Learning-based planners like MPNet offer fast inference but often produce infeasible paths in cluttered areas, requiring expensive postprocessing. To address this trade-off, we propose a hybrid framework that combines improved sampling, structural abstraction, and neural prediction. A modified bridge-test sampler applies directional perturbations and corridor checks to generate reliable narrow passage samples. These are clustered into a sparse set of representative bridge points, which serve as nodes in a global graph. At query time, a greedy heuristic search explores this graph, using a neural local segment generator to connect nodes. We validate the approach on 2D maze maps, 3D voxel environments, and a 12-DOF manipulator performing a plugging task inside a simulated nuclear steam generator. Across all tasks, our method significantly outperforms classical and learning-based baselines in terms of success rate and planning time in narrow-passage-dominated scenarios. The inclusion of the repair module, under relaxed assumptions, also allows the framework to retain a generalized form of probabilistic completeness. Full article

Surface collisions at Pyrex walls limit the spin coherence in nuclear magnetic resonance gyroscopes (NMRG) vapor cells, while the cavity–stem junction introduces geometry dependent exchange that perturbs the transverse spin relaxation time $T_2$ of ¹²⁹Xe atoms. We combine $T_2$ measurements with Monte Carlo simulations of confined diffusion and surface collisions to decompose the relaxation of Xe atoms and derive a cavity–stem geometry correction for wall relaxation. A structural coupling factor (SCF) is introduced to compress stem length and aperture diameter into a dimensionless metric for diffusion-limited mixing, enabling prediction of the transverse relaxation rate versus geometry. Across eight simulated configurations, the model yields $R^2=0.982$ and agrees with experiments within 7–$9\%$, comparable to the measurement uncertainty ($\pm 0.015{\mathrm{s}}^{-1}$). Using the validated framework, geometry optimization reduces the relaxation rate from $0.225$ to $0.131{\mathrm{s}}^{-1}$ (a $41.8\%$ improvement). This Pyrex surface-collisional analysis provides an in-situ, $T_2$-based route to compare effective surface depolarization across fabrication and surface-treatment protocols while accounting for cavity–stem coupling. Full article

This study reports the first preparation and characterization of an acrylic acid–glucose–polyvinyl alcohol (ACAGLPVA) polymer gel dosimeter incorporating glucose as an organic additive for radiation oncology applications. Five formulations with glucose concentrations of 0, 10, 20, 25, and 30 wt% were irradiated using a 6-MV photon beam at doses of 0–60 Gy, and the transverse relaxation rate (R₂) was measured by nuclear magnetic resonance (NMR) relaxometry. The optimal formulation (25 wt% glucose) demonstrated an excellent linear dose response between 0 and 30 Gy (R² = 0.9979) with a sensitivity of 0.177 s⁻¹ Gy⁻¹, followed by a non-linear response at 30–60 Gy. The dosimeter exhibited dose rate independence (200–600 cGy/min), energy independence (6–15 MV), temperature independence (5–35 °C), and post-irradiation stability for at least 7 days. These characteristics demonstrate the potential of ACAGLPVA gel dosimeters for accurate three-dimensional dose verification in modern radiotherapy applications. Full article