Search Results (486)

Nuclear relaxation, $1/T_1$, is a very robust probe of electronic excitations in superconducting materials above and below the critical temperature of superconductivity, $T_{\mathrm{c}}$. Here, a relaxation phenomenology of hole-doped cuprate superconductors is presented based on the majority of the available literature data from the CuO₂ plane, without assumptions with respect to a hyperfine scenario, form factors, or particular theoretical models. Below a temperature similar to the pseudogap temperature, Heitler–Teller-type relaxation is uncovered universally; i.e., the nuclear spin relaxation above $T_{\mathrm{c}}$ is only determined by the absolute temperature, $1/T_1\propto T$. All materials condense out of this metal at $T_{\mathrm{c}}$, below which relaxation drops even faster, as expected from conventional superconductors, albeit without a Hebel–Slichter peak. It is a ’hidden metal’ in the sense that it has a vanishing uniform response and thus hardly affects the NMR shifts; it is also not seen in planar O relaxation. The hidden metal causes a temperature-independent but material-dependent planar Cu relaxation anisotropy that is strongly correlated with the size of $T_{\mathrm{c}}$. Moreover, the rate measured with the field in the CuO₂ plane is nearly the same for all cuprates: $1/{{}^{63}T}_{1\perp }T\approx 25/$Ks, where $1/{{}^{63}T}_{1\Vert }$ is mainly responsible for the change in anisotropy. Above the hidden metal, the relaxation behavior changes and can be described by an ordinary but renormalized metal, with a reduced Cu relaxation anisotropy. The relaxation phenomenology, which should hold clues to the so-called strange metal, is also discussed in the context of the two spin components previously uncovered in the shifts, as well as the pseudogap and relation to other probes. This new phenomenology should give a better foundation for the understanding of the cuprates. Full article

Gadolinium-doped polymer gel dosimeters enable experimental evaluation of dose enhancement in low-energy radiotherapy, although the high Gd concentrations required substantially alter their magnetic relaxation properties, making the optimal Magnetic Resonance Imaging (MRI) readout uncertain. This study characterized the dosimetric response of PAGAT and Gd-PAGAT (9 mg/mL Gd) irradiated with a 150 kVp X-ray beam from 1 to 10 Gy using quantitative 1.5 T MRI. Quantitative R₁ and R₂ maps were obtained from variable flip-angle spoiled gradient echo (SPGR) and multi-echo spin echo (MSE) sequences, respectively, and validated by UV-Vis spectrophotometry. R₁ showed no significant dose dependence in Gd-PAGAT because of severe T₁ shortening. In contrast, R₂ exhibited a robust response, with second-order polynomial fits (R² = 0.9984 for PAGAT and 0.9969 for Gd-PAGAT) and linear behavior between 1 and 7 Gy. The dose sensitivity of Gd-PAGAT was 2.84 ± 0.19 times higher than that of PAGAT (0.5328 vs. 0.1949 s⁻¹·Gy⁻¹). Spectrophotometry confirmed the PAGAT calibration but showed markedly lower sensitivity for Gd-PAGAT, particularly at low doses. These findings demonstrate that R₂ mapping overcomes the limitations imposed by extreme T₁ shortening, extending the applicability of Gd-PAGAT dosimeters for three-dimensional dose enhancement studies in low-energy radiotherapy. Full article

With the increasing penetration of renewable energy and the intensification of load fluctuations, power electrical equipment frequently operates under complex conditions such as heavy loads. Traditional spinning reserve allocation methods based on fixed outage rates are inadequate for accurately characterizing the dynamic operational risks of the system. To address this issue, this paper proposes an optimal spinning reserve allocation method for power systems considering operational reliability. First, by introducing the condition-dependent outage replacement rate (CDORR), a reliability model under multi-uncertainties is established, which considers load forecast errors, wind power randomness, and equipment operating conditions. Second, to overcome the “curse of dimensionality” caused by alternating iterative solving in complex scenarios, analytical expected energy not served (EENS) formulations based on the sensitivity method are derived to rapidly quantify the power flow variations between pre-contingency and post-contingency states. Finally, aimed at the non-convexity introduced by bilinear terms in the model, an improved segmented McCormick envelope relaxation algorithm is designed, which is combined with the Tangent Plane Cut Collection (TPCC) strategy to effectively eliminate redundant envelope regions. Case studies based on the IEEE 30-bus system demonstrate that, while ensuring evaluation accuracy, the proposed method accelerates computational speed by nearly 20 times compared to traditional nonlinear solvers. Moreover, it effectively mitigates potential operational risks under complex conditions, achieving an optimal balance between system reliability and economics. Full article

Highly polarized ³He is widely used in precision magnetometry, neutron spin filtering, and fundamental symmetry tests, where magnetic field gradients can shorten relaxation and coherence times and introduce systematic uncertainties. We present the design, modeling, and experimental characterization of a compact four-square-coil Merritt system developed to provide a uniform holding field for precision measurements of polarized ³He. The magnetic field is calculated directly from analytical vector potentials and analyzed using a near-center expansion. By combining Maxwell’s equations with the spatial symmetries of square- and circular-coil systems, we show that the dominant second-order transverse gradients within the small central cell volume are determined by the axial curvature of $B_z$. The relevant gradient performance can therefore be characterized using a single axial scan, without routine complete three-dimensional mapping. The calculated performance of the Merritt configuration is quantitatively compared with that of the Helmholtz, Lee–Whiting, and Garrett systems. A prototype is constructed and measured using a three-axis fluxgate magnetometer mounted on a motorized translation stage.The measured axial field agrees well with the calculated profile, and the normalized magnetic field gradient in the central 10 cm region is below ${10}^{-4}$ cm⁻¹. This region fully covers the cylindrical ³He cell, whose diameter and length are both no greater than 5 cm. The Merritt configuration therefore provides a practical compromise between gradient suppression, compactness, optical access, and mechanical simplicity for polarized noble- gas sensors and precision measurements. Full article

We study the causality and stability of first-order relativistic spin hydrodynamics with particle-number conservation. By deriving the complete dispersion relations of linear perturbations around a global equilibrium state, we find that conserved-charge dynamics modifies the sound sector and introduces additional non-hydrodynamic modes absent in the charge-neutral theory, while the structure of spin relaxation modes remains unchanged. Moreover, the stability conditions acquire new contributions from charge diffusion and thermodynamic susceptibilities. More importantly, a particle-number-induced mode is shown to violate the causality condition in the short-wavelength limit. We further demonstrate that particle-number conservation does not remove the instability inherent in first-order spin hydrodynamics. These results reveal a nontrivial interplay between spin and conserved-charge dynamics and provide important constraints on relativistic spin hydrodynamic theories at finite density. Full article

Visual evoked potential (VEP) is widely used to assess optic nerve function, but its ability to differentiate optic neuropathies remains limited. This study investigated the diagnostic value of spin-exchange relaxation-free magnetoencephalography (SERF-MEG), alone and in combination with VEP, using machine learning. A total of 142 eyes, including 71 healthy controls (HC), 34 eyes with optic neuritis (ON), and 37 eyes with ischemic optic neuropathy (ION), were enrolled. Three feature sets were constructed from VEP, SERF-MEG, and their combination. Repeated stratified 5-fold nested cross-validation was used to evaluate nine supervised machine learning algorithms, and SHAP analysis was used to evaluate the interpretability of the models. The multilayer perceptron model obtained an AUC of 0.792 and an MCC of 0.470, whereas the combination VEP–MEG model performed the best in differentiating HC from optic neuropathies. The MEG model fared better than the VEP and combined models for distinguishing ON from ION, with logistic regression obtaining the greatest AUC of 0.847. Cortical network measurements and visually evoked response properties were found to contribute the most to model prediction, according to SHAP analysis. These results imply that SERF-MEG may enhance the diagnosis and differential diagnosis of optic neuropathies by offering supplementary neurophysiological data beyond traditional VEP. Full article

Graphene oxide (GO) has been widely reported to enhance the mechanical performance of cementitious composites. However, the fundamental hydration mechanisms underlying these improvements, such as GO’s role as a nucleation site, remain poorly explored and quantified. This study presents a comprehensive, non-destructive investigation into the time-dependent hydration behaviour of GO-induced cement pastes using time-domain ¹H Nuclear Magnetic Resonance (NMR) spectroscopy, supported by thermogravimetric analysis (TGA), humidity-controlled water-retention tests, and compressive strength tests. Cementitious composites containing 0.035%, 0.065%, and 0.08% GO by weight of cement (bwoc) were monitored from 4 h to 28 days to track the evolution of discrete water phases, including capillary, inter-hydrate, gel pore, and interlayer water. NMR results reveal that GO initially facilitates water redistribution by retaining free water within its layered structure, followed by a delayed but sustained release that promotes continued hydration and a progressive shift toward less mobile pore–water environments at later curing ages. TGA confirms enhanced formation of hydration products in GO-induced cementitious systems, with an optimal dosage of 0.035% bwoc achieving the most sustained hydration and highest compressive strength. Higher GO dosages accelerate early hydration but limit later-stage hydration due to diffusion barriers formed by hydration products. This study provides time-dependent scientific evidence of GO’s dual role as a hydration nucleation agent and water-release regulator, establishing a mechanistic basis for dosage optimization in nano-engineered cementitious composites. Full article

Silicon carbide (SiC) in its various structural modifications is widely used in power semiconductor electronics, operating under extreme conditions of high temperature, high voltage, and intense radiation. The discovery of spin defects (S > 0) with unique optical and coherent properties has further positioned SiC as a promising platform for quantum technologies. Here, we investigate a 6H-SiC single crystal co-doped with nitrogen and beryllium at concentrations of 10¹⁸ cm⁻³, using continuous-wave and pulsed electron paramagnetic resonance (EPR) and electron–nuclear double resonance (ENDOR). To enhance spectral resolution, experiments were conducted in the W-band (94 GHz; B = 3.4 T). Pulsed EPR identified nitrogen donors and beryllium acceptors in various lattice positions, allowing for the determination of their phase coherence and spin–lattice relaxation times. ENDOR measurements elucidated the electron–nuclear interactions with the local silicon and carbon environment, including distant coordination spheres. The observed hyperfine structures indicated highly delocalized spin density within the supercell. The TRIPLE resonance spectra verify coupled nuclear spin subspaces from different coordination spheres due to defect spin density. These results demonstrate the feasibility of incorporating dual impurities with distinct functional roles while preserving the crystal lattice’s structural features. Full article

This study investigated the effect of magnetic coupling of Fe³⁺ on Ho³⁺ luminescence in the double perovskite Cs₂NaScCl₆. Under 980 nm laser excitation, red emission from Ho³⁺ ions was observed in Cs₂NaScCl₆:Ho³⁺/Fe³⁺ samples. We propose that this arises from spin-selective up-conversion mediated by magnetic polarons (EMPs). However, green emission from the ⁵F₄/⁵S₂ levels was not observed in this system. The experimental results suggest that localized EMPs form via ferromagnetic short-range ordering between Fe³⁺ and Ho³⁺ or among Fe³⁺ ions. These EMPs can be directly excited to higher energy levels via a biexciton absorption transition, then relaxed to the ⁵F₅ level of Ho³⁺ through ferromagnetic coupling. Under X-ray excitation, the characteristic emission peaks of Ho³⁺ in Cs₂NaScCl₆:Ho³⁺/Fe³⁺ become smoother, lose fine structure, and significantly decrease in intensity with increasing Fe³⁺ concentration. Based on this, we prepared Fe³⁺-free Cs₂NaScCl₆:Ho³⁺ and explored its excellent scintillation performance, with a detection limit as low as 37.73 nGy_air s⁻¹, below the medical diagnostic dose, surpassing the performance of commercial scintillators such as LuAG:Ce and BGO. This work reports the phenomenon of using Fe³⁺ as a sensitizer to achieve up-conversion sensitization in chloride double perovskites and demonstrates the application potential of Fe-free systems in ultra-low-dose X-ray imaging. Full article

This study assessed the cross-modal agreement between spin-exchange relaxation-free magnetoencephalography (SERF-MEG) and conventional visual evoked potentials (VEPs) in patients with optic nerve injury using comparable pattern-reversal visual stimulation paradigms. Forty-five patients with optic neuritis (ON), ischemic optic neuropathy (ION), and traumatic optic neuropathy (TON) were enrolled, and a paired-eye design was applied to assess interocular electrophysiological changes between the affected and fellow eyes. Both modalities indicated consistent impairment of visual pathway function, reflected by reduced response amplitudes and prolonged latencies. For latency measures, MEG-derived M100 showed moderate directional concordance and a significant correlation with VEP P100, whereas amplitude measures demonstrated similar directional changes but limited quantitative correlations across modalities. Compared with the MaxP2P method, the channel-averaged method displayed higher stability and cross-modal concordance. These findings show that SERF-MEG can capture clinically relevant visual pathway impairment and may complement conventional VEP by providing additional information on cortical response patterns. Overall, SERF-MEG shows potential as an objective functional biomarker for neuro-ophthalmic assessment of optic nerve injury. Full article

Patients with muco-obstructive lung disease (MOLD) exhibit chronic bronchitis and inflammation, along with a progressive decline in lung function. Lung monitoring is typically performed using spirometry, especially by measuring the forced expired volume in the first second (FEV₁). However, the limitations of spirometry motivated the exploration of alternative approaches. The spin–spin relaxation time (T_2m) and the spin–lattice relaxation time (T_1m) of sputum water hydrogens were measured using low-field nuclear magnetic resonance (LF-NMR) in 38 MOLD patients and 16 controls. The levels of TNFα/IL-6, the sputum microbiome composition/amount/indices and FEV₁ were determined in parallel. We also investigated the correlation between T_2m/T_1m and the disease index (I_D); I_D, calculated relying on patient FEV₁/TNFα/IL-6/bacteria concentration C_b values, is a measure of the patient’s distance from the average healthy control. We observed the following significant correlations: T_2m/T_1m with I_D, T_2m with C_b, a potential correlation of T_2m with the bacteria genera Streptococcus and Staphylococcus, T_2m with the Shannon index, which reflects the broadness of the bacterial community in the sputum, and T_2m with TNFα. FEV₁ did not show any correlation. Our noninvasive/radiation-free/portable method of T_2m/T_1m measurement shows potential value in monitoring lung conditions in MOLD patients and may contribute to improved clinical decision-making. Full article

Magnetic resonance cholangiopancreatography (MRCP) is widely used for biliopancreatic imaging; however, hyperintense gastrointestinal fluids in heavily T2-weighted sequences may interfere with visualization of the biliary and pancreatic ducts. Natural manganese-containing beverages have been investigated in MRCP-related imaging contexts, and yerba mate (Ilex paraguariensis A. St.-Hil.) has been studied to this end. However, its concentration- and sequence-dependent signal behavior under MRCP-like phantom conditions remains insufficiently characterized. This preclinical phantom study evaluated the concentration- and sequence-dependent MRI signal intensity behavior of an aqueous extract of Ilex paraguariensis. The extract was characterized by means of elemental analysis, total manganese and iron quantification, total phenolic content, antioxidant capacity, and LC-ESI-MS analysis. MRI phantom experiments were run at different extract concentrations using T1-weighted, T2-weighted, and single-shot turbo spin echo (SSHTSE) sequences. The dried extract contained 1.22 ± 0.04 mg/g total manganese and 0.40 ± 0.01 mg/g total iron. Calculated total Mn concentrations in phantom dilutions ranged from 0.06 to 0.97 mg/dL. The extract showed concentration- and sequence-dependent signal behavior, with T1-weighted signal enhancement and progressive signal suppression in T2-weighted and SSHTSE sequences. No T1/T2 mapping or r1/r2 relaxivity measurements were performed. LC-ESI-MS identified MS1-based putatively assigned phenolic features without MS/MS confirmation of extract peaks. Ilex paraguariensis aqueous extract showed preliminary concentration- and sequence-dependent MRI signal intensity changes under phantom conditions, including signal suppression in MRCP-like heavily T2-weighted sequences. These findings do not establish clinical applicability, safety, tolerability, comparative efficacy, or improved duct visualization. Further studies are needed, incorporating relaxometric measurements, comparator agents, formulation assessment, in vivo evaluation, and clinical validation. Full article

Harmalol is a β-carboline alkaloid exhibiting promising antioxidant properties; however, a comprehensive understanding of its radical scavenging mechanisms in aqueous media across a wide pH range remains limited. In this study, the antioxidant activity of harmalol toward hydroperoxyl radicals was investigated theoretically at the M06-2X/6-311+G(d,p)/PCM(water) level by combining thermodynamic and kinetic analyses over the pH range 2–13. The calculations revealed that the antioxidant behavior of harmalol strongly depends on its protonation state, tautomeric form, and the surrounding pH. Under physiological conditions, the monocationic form predominates, with a smaller contribution from the neutral/zwitterionic I and II species, and radical scavenging proceeds predominantly via proton-coupled electron transfer (PCET)-type hydrogen-transfer reactions involving the monocationic, neutral and zwitterionic I forms as well as radical adduct formation (RAF) mechanism involving zwitterion I. Analysis of SOMO distributions, spin densities, and atomic charges confirmed that the hydrogen transfer reactions for monocationic, neutral and zwitterionic I forms do not follow a classical hydrogen atom transfer (HAT) mechanism. The zwitterion I and neutral forms of harmalol exhibited significantly higher apparent rate constants for the PCET reaction than the monocationic species. Under alkaline conditions, the monoanionic forms exhibit the most favorable thermodynamic parameters toward radical scavenging via formal hydrogen transfer mechanism. Relaxed potential energy surface scans suggest that hydrogen transfer from both monoanionic forms may proceed through a barrierless pathway, while radical adduct formation can also contribute to the antioxidant activity under strongly basic conditions. In addition, monoanion II efficiently participates in single-electron transfer (SET) reactions characterized by very high apparent rate constants. Overall, the results demonstrate that the antioxidant efficiency of harmalol increases with increasing pH and provide detailed insight into the pH-dependent radical scavenging mechanisms of β-carboline derivatives in aqueous environments. Full article

We report on the finite temperature staggered spin susceptibility $\chi \left(Q\right)$ as a function of the mode–mode coupling constant $y_1$ in the self-consistent renormalization theory of two-dimensional antiferromagnetic spin fluctuations with zero-point quantum fluctuations just at the quantum critical point ($y_0$ = 0). We find that the value $y_1$ = 0.1 is a criterion to classify the effect of the zero-point spin fluctuations on the temperature dependence of $\chi \left(Q\right)$ into a Curie law for weak $y_1<$ 0.1 and a Curie–Weiss type or a power law type for strong $y_1>$ 0.1. The absence of a Curie–Weiss temperature can serve as an identifying criterion for QCP ($y_0$ = 0) in systems with weak mode–mode coupling ($y_1<$ 0.1). Experimental application on the $y_1$ classification is shown to several itinerant layered antiferromagnetic systems through an analysis of nuclear spin–lattice relaxation rates. Full article

The structure, relative stability, spin-state preference, and preliminary oxygen-release behavior of small nickel–oxygen clusters, (NiO₂)_n (n = 1–4), were investigated using density functional theory at the M06-2X/def2-TZVP level of theory. Several initial topologies and spin multiplicities were explored to distinguish between dissociated Ni···O₂ solutions, bonded dioxo-like arrangements, and side-on metal–dioxygen motifs. For the monomer, the lowest-energy solution of the fully explored set corresponds to a non-bonded Ni···O₂ arrangement; however, when the analysis is restricted to chemically bonded NiO₂ minima, the linear high-spin O–Ni–O structure is the most stable configuration. The side-on η²-O₂ motif was found as a higher-energy bonded minimum, retaining an elongated O–O bond and therefore representing an activated dioxygen-like species. ELF and LOL analyses were used as complementary localization descriptors to distinguish between the electronically separated oxo-like domains of the linear structure and the more coupled localization pattern of the side-on dioxygen adduct. Aggregation from n = 2 to n = 4 suggests a transition from compact bridged motifs to more open Ni–O frameworks. However, the size-dependent trend is discussed only within the explicitly explored conformational space. Preliminary analysis of O₂ release from the tetramer indicates that oxygen evolution is not a simple dissociation event but involves substantial structural reorganization. Overall, the results support the view that small (NiO₂)_n clusters may behave as metastable oxygen-rich intermediates, while also highlighting the strong sensitivity of their energetic ordering to spin state, topology, and structural relaxation. Full article