Search Results (873)

Spontaneous imbibition modified by surfactants is a key technology for enhancing shale oil recovery. Currently, relevant studies mainly concentrate on marine shale worldwide, while the pore–fluid coupling characteristics of widely distributed medium-TOC terrestrial shale remain poorly understood. Against this background, this paper takes typical Paleogene terrestrial shale as the research object and integrates N₂/CO₂ adsorption and NMR T₂ spectroscopy to jointly characterize multiscale pore structures and dynamic fluid evolution during imbibition. The results show that the shale is dominated by mesopores in terms of pore volume, while micropores provide most of the specific surface area. The zwitterionic surfactant HPSB can greatly reduce oil–water interfacial tension and alter rock wettability, thereby breaking the high capillary resistance of micropores. During imbibition, water invades macropores first, followed by mesopores and micropores, and the entire process exhibits remarkable nonlinear dynamics controlled by multiscale pores. The 0.15% HPSB solution shows the best effect on activating micropores. This study innovatively quantifies the influence of surfactant concentration on fluid migration across different pore scales and reveals the internal mechanism of staged imbibition and micropore lag activation in terrestrial shale. It not only complements the global research system of shale imbibition theory but also offers practical guidance for the optimization of fracturing fluid systems in mesopore-dominated shale oil reservoirs. Full article

Reconfigurable photonic metasurfaces enable tunable thermal-emission engineering in the long-wave infrared (LWIR), particularly within the 8–13 μm atmospheric window. This work includes the investigation on a concentric-ring VO₂/SiO₂/Au metasurface for LWIR spectral-emissivity modulation. Full-wave simulations showed that, in the metallic phase (σ = 2 × 10⁵ S/m where σ is conductivity), the structure exhibited an absorption over 90% across the 9.3–15 μm sub-band, with two near-unity resonances near 10.2 and 13.3 μm. Control structures, gap-dependent spectra, E-field maps, and current-density Cartesian multipole decomposition supported a hybridized-ring mechanism in which both dominant resonances were predominantly electric-dipole-like ring branches whose spectral positions and field localizations were modified by inter-ring coupling. Across the conductivity sweep, the normal-incidence band-averaged 8–13 μm emissivity changed from 0.0184 to 0.8844, corresponding to a switching ratio of 48.06. The four-fold symmetry of unit cell also yielded polarization-insensitive and angularly robust LWIR absorption, while the simplified endpoint thermal-balance estimate indicated a metallic-state net cooling power of 49.3 W m⁻² at T = T_amb = 300 K, where T_amb was the ambient temperature, and an estimated equilibrium temperature drop of 4.4 K below the ambient for the metallic-state endpoint, whereas the insulating-state one suppressed this response. These results identify concentric VO₂ ring metasurfaces as promising candidates for switchable LWIR thermal-emission control. Full article

Background: Radiology underpins diagnosis and treatment across pediatrics, yet most artificial intelligence (AI) tools are developed for adults and validated on adult datasets only. Of more than 200 AI systems cleared by the United States (U.S.) Food and Drug Administration (FDA), only about 3% include pediatric validation. Because children differ from adults in anatomy, physiology, pathology, epidemiology, and imaging protocols, adult-trained models often perform sub-optimally in pediatric settings. Methods: A narrative review of peer-reviewed literature from 2000 to 2025 was conducted using PubMed, MEDLINE, Google Scholar, and Scopus. Studies involving AI applications in pediatric X-ray, ultrasound, computed tomography (CT), magnetic resonance imaging (MRI), echocardiography, and point-of-care ultrasound with quantitative performance metrics were included. Findings were synthesized by imaging modality, clinical task, and differences between high-income countries (HICs) and low- and middle-income countries (LMICs). Results: AI demonstrated strong performance across multiple pediatric imaging tasks. In X-ray interpretation, AI detected fractures with area under the curve (AUC) values up to 0.96 (sensitivity, 90.8%; specificity, 88.7%). Pneumonia classification achieved 76.5% accuracy, and foreign body aspiration detection showed 95.3% specificity in HICs. In ultrasound, AI improved junior sonographers’ detection of intussusception (AUC 0.857 to 0.966) and reduced scan time by more than 50%. AI-assisted bone age estimation achieved a mean error of 0.39 years. In echocardiography, AI-derived ejection fraction showed excellent agreement with experts’ interclass correlation coefficient (ICC 0.983), and AI support improved atrioventricular septal defect detection (84.4% to 86.5%). In MRI, the use of AI enhanced lesion detection and supported quantitative analysis. Deep-learning models trained on routine T1- and T2-weighted sequences predicted liver stiffness across multi-site datasets, while advanced neuroimaging pipelines improved the identification of subtle epileptogenic lesions that are often missed on conventional pediatric MRI. However, adult-trained models showed limited generalizability to children. Still, excluding children under the age of two years improved the reading accuracy of pediatric chest X-rays (CXRs) by adult-trained models from 88% to 97%. AI faces challenges beyond the development of age-specific models. Substantial heterogeneity, limited pediatric-specific datasets, and unresolved medicolegal responsibility further restrict adoption worldwide. Challenges are amplified in LMICs, where unstable electricity, limited radiology resources, weak digital infrastructure, and scarce pediatric providers limit implementation. Additionally, many large language models underperform and lack inclusive algorithms suitable for pediatric radiology in many LMICs. Conclusions: AI can enhance diagnostic accuracy, efficiency, and access to pediatric imaging, particularly in resource-limited settings, through task-shifting and decision support. However, it cannot replace pediatric radiologists as of today. Safe adoption requires pediatric-specific model development, standardized validation metrics, diverse datasets that include LMIC populations, stronger digital infrastructure, robust radiologist training in AI capabilities, and the establishment of clear guidelines and medicolegal policies. Full article

In this study, we present a thermal-aware design of a compact hybrid plasmonic grating (HPG) TE-pass polarizer on X-cut lithium niobate on insulator (LNOI) for fiber-optic gyroscopes (FOGs). In a three-dimensional simulation, the optimization of the trapezoidal sidewall angle (θ = 78°) and the thickness of the Ag grating (13 nm) yield a polarization extinction ratio of 36.2 dB at 1550 nm (with a peak of 41.4 dB at 1548 nm) within a sub-10 μm grating length. This represents a ~3–8 dB improvement over prior LNOI HPG polarizers at the same footprint. A multiphysics thermo-optic analysis over the wide industrial FOG envelope (from −45 to +85 °C) demonstrates that the operating-wavelength polarization extinction ratio remains within the range of 24.7–36.2 dB across the entire 130 K span (worst case 24.7 dB at −25 °C), constrained solely by a modest 10 pm/K Bragg detuning stemming from the pronounced (~5) thermo-optic anisotropy of LN. The insertion loss exhibits a negligible drift of merely 0.73 dB. A fabrication tolerance study identified the Ag thickness as the predominant budgetary constraint (±1 nm tolerance, PER dropping ~10 dB at the resonance edge), while the ridge width and oxide buffer demonstrated comparatively greater flexibility. The device, therefore, fulfills the criteria for FOG-grade polarization suppression across most of the operational temperature range. The −25 °C point is established at the 25 dB threshold, thereby providing concrete design guidelines for ensuring environmentally stable on-chip polarization control on LNOI. Full article

Excitation using nonlinear gradient magnetic fields is investigated as a means of sub-volume magnetic resonance imaging (MRI). Conventional gradient fields provide encoding along a single direction, whereas nonlinear gradient fields encode information simultaneously along at least two directions. This leads to excitation regions (FOX) that have curvilinear boundaries, which may be more tolerant to aliasing artifacts when the encoded field of view (FOV) is smaller than the FOX. This reduces the complexity of the required radiofrequency (RF) excitation pulses and enables accelerated reduced-FOV imaging with standard slice-selection RF-pulses. We demonstrate the approach using a Z2-harmonic field for cylindrical regions of interest (ROIs) with various radius/height ratios. The minimum-FOV that should be encoded is formulated in terms of ROI and RF pulse parameters to allow a theoretical evaluation of feasibility during study design. The investigated method is compared to one-dimensional and two-dimensional selective RF pulses in terms of echo time, scan time and specific absorption rate (SAR) using simulations and phantom experiments. The investigated method yields lower scan time while keeping the SAR unaltered compared to a conventional slice-selective RF pulse, and is more efficient in terms of SAR, echo time and scan time compared to two-dimensional selective excitation. Full article

In this paper, a high-gain wideband filtering antenna with metasurface structures is presented for Sub-6 GHz 5G applications. The proposed antenna consists of a 3 × 3 metasurface array, a driven patch, a short-circuited stepped impedance resonator (SIR) feedline, and two parasitic patches. The metasurface is used to manipulate the modal behavior of the radiator and to introduce an additional resonant mode for bandwidth enhancement. Meanwhile, two radiation nulls are generated by different mechanisms to realize filtering performance. The low-frequency radiation null at 2.81 GHz is introduced by the short-circuited SIR feedline, whereas the high-frequency radiation null at 5.76 GHz is produced by radiation cancelation among the driven patch, parasitic patches, and metasurface. The measured results show a 10 dB impedance bandwidth of 35.5% from 3.62 to 5.18 GHz and an average realized gain of 8.61 dBi. In addition, the proposed antenna achieves lower- and upper-band selectivity of 42.57 dB/GHz and 33.43 dB/GHz, respectively. The proposed antenna also achieves a compact radiation aperture of 0.60 × 0.60 λ₀² and effective out-of-band radiation suppression, making it a promising candidate for integrated 5G RF front-ends. Full article

This study explored the influence of high silver (Ag) loading (5–10 mol%) on the photocatalytic performance of zirconium (Zr) co-doped TiO₂ (AZT) with a low Zr content. Although various Ag/Zr ratios have been reported, the effect of high Ag loading combined with low Zr content remains largely unrevealed, particularly in low-temperature synthesis where the role of Zr as a phase inhibitor is less critical. To address this gap, the AZT photocatalyst was fabricated via a solvothermal method combined with organic-free peroxy route. Characterization indicated Zr⁴⁺ incorporated into the TiO₂ lattice, inducing structural distortions and promoting Ti³⁺ defect states. Simultaneously, silver existed as ternary Ag species, which functioned as visible light responsive co-catalysts that enhanced light absorption via Surface Plasmon Resonance (SPR) and facilitated efficient charge separation. Photocatalytic performance was evaluated through Methylene Blue (MB) decolorization under household LED lamp. The optimized 7% Ag loaded catalyst achieved 99.4% removal efficiency within 6 h, with a reaction rate ten times higher than the Zr-doped sample. This superior activity was attributed to a p-n heterojunction and the SPR effect, narrowing the optical band gap to 2.60 eV. Radical scavenger experiments confirmed that the process was primarily driven by photogenerated holes. Full article

Total, momentum-transfer, and differential cross sections, together with spin-polarization (Sherman) functions, are reported for elastic scattering of low-energy electrons from neutral strontium atoms over the energy range 0.001–15 eV. The calculations are performed within a fully relativistic Dirac framework for the continuum states. The target structure is described using multi-configuration Dirac–Hartree–Fock wavefunctions obtained with the GRASP2018 package, while continuum orbitals are generated using the recently developed GRASPC extension. Long-range target polarization effects are incorporated using a dipole model potential, and exchange interactions are treated explicitly for the large and small components of the continuum wavefunctions. Particular attention is given to the ultralow-energy regime, where reliable cross section data for Sr remain limited. The calculated total cross section exhibits a broad maximum near 1 eV, while the momentum-transfer cross section shows a shallow minimum near 0.05–0.06 eV. The differential cross sections are in good agreement with earlier static-exchange-plus-polarization calculations over much of the 1–5 eV range, whereas at lower energies, visible differences appear, especially at forward angles where the results are most sensitive to the polarization interaction. In the ultralow-energy region, the present differential cross sections remain smooth and show no indication of additional low-lying shape resonances within the adopted model. The calculated Sherman functions follow the general trends of earlier theoretical studies at higher energies and decrease rapidly in the sub-eV range. Overall, the present results provide a consistent relativistic dataset for elastic e–Sr scattering at low energies, with emphasis on the near-threshold region. Full article

The use of sound absorption materials has traditionally been restricted to medium-to-high frequencies due to their limitations at low frequencies, where the large wavelength of sound waves imposes rather bulky solutions. However, recent materials and designs allow for the absorption of sound waves with more practical sizes and weights, reviving interest in this frequency range. Some of these low-frequency absorbers, also named acoustic metamaterials or sub-wavelength sound absorbers, based on microperforated panels, are reviewed in this article. These include multilayer and multicavity microperforated panels, hybrid passive–active absorbers, multiple Helmholtz resonators, and microperforated panels with labyrinthine cavities or sonic black holes. Full article

Monolayer molybdenum disulfide (MoS₂) holds great promise for strain-tunable optoelectronic devices. The strain-dependent dielectric function is a core parameter to characterize the tunability of optoelectronic properties. However, due to the extremely short light–matter interaction path length for atomically thin materials, measurements are challenging. In this work, we measured the dielectric function of strained monolayer MoS₂ using the surface plasmon resonance (SPR) method with the simulated annealing particle swarm optimization (SAPSO) algorithm. When the applied strain ranged from −0.23% (compressive strain) to +0.20% (tensile strain), the dielectric function at seven characteristic wavelengths around the exciton absorption peaks was extracted. Our results demonstrate that both the real part (ε_2r) and the imaginary part (ε_2i) of the dielectric function evolved almost linearly with the applied strain from −0.23% to +0.20%. Based on these results, we further obtained the strain-induced variations in the refractive index (n) and the extinction coefficient (k). At exciton absorption peak B (600 nm), the strain-induced change rate for n reached a maximum of about −0.0141%⁻¹. At the rising edge of the B exciton absorption (580 nm), the strain-induced change rate for k reached a maximum of about −0.3261%⁻¹. This work presents a quantitative extraction of strain-dependent dielectric function of monolayer MoS₂ over excitonic band-edge wavelengths using phase SPR–SAPSO fitting. The proposed method can be extended to the measurement of other atomically thin materials. Full article

With the rapid development of wireless communications, electromagnetic interference (EMI) in complex environments has become a critical factor affecting communication quality. Addressing the EMI issues caused by multi-band coexistence in indoor scenarios, traditional metallic resonant structures, while effective in filtering, often compromise optical transparency due to light blockage. To resolve this trade-off, this paper proposes a dual-ring resonant frequency-selective surface (FSS) based on Indium Tin Oxide (ITO) films. This design aims to achieve efficient transmission in specific C-band frequencies and suppress out-of-band interference, realizing excellent optical transmittance while ensuring electromagnetic shielding effectiveness. The designed metasurface targets a passband of 5.35–5.40 GHz for sub-6 GHz indoor communications. Experimental results confirm superior transmission in this range and significant out-of-band suppression. Furthermore, featuring high optical transparency, the structure can be directly integrated onto glass surfaces. It is not only suitable for optically transparent devices but also provides a compact passive solution for anti-EMI applications in smart buildings and sub-6 GHz indoor communications. Full article

This paper presents a systematic analytical approach for designing Class EF inverters that achieve zero-voltage switching (ZVS) over a wide load range with a fixed duty cycle and constant AC output. The method is based on modeling the load’s complex impedance at the switching frequency and deriving explicit design equations, enabling direct and systematic topology synthesis without relying on numerical simulations. An experimental demonstration at 15 MHz and 25 VDC, over loads from 30 $\mathsf{\Omega }$ to 2700 $\mathsf{\Omega }$, confirms the validity and robustness of the approach. The method provides a practical foundation for future designs targeting further reduction of switching losses and electromagnetic interference. Full article

Amid the ongoing acceleration of climate change over recent decades, extreme precipitation events have become more frequent and intense on a global scale, triggering severe natural hazards and considerable socioeconomic damage. Nevertheless, how extreme precipitation has evolved at the national level over long time spans, and what role atmosphere–ocean teleconnections play in driving regional differences, remains insufficiently explored. This study addresses that knowledge gap by conducting a comprehensive assessment of eight ETCCDI-based extreme precipitation indices (PRCPTOT, CWD, R20, R95p, R99p, RX1day, RX5day, and SDII) across six climatic sub-regions of China (Northeast, North, East, Central South, Northwest, and Southwest) over 1960–2020, drawing on daily records from 695 quality-controlled meteorological stations. Key atmospheric and oceanic circulation drivers were further diagnosed and their joint influence was quantified via multiple wavelet coherence (MWC). The analysis shows that five of the eight indices (CWD, R95p, R99p, RX1day, and RX5day) underwent statistically significant fluctuating changes (p < 0.05) throughout the 61-year record. Seven indices, all except CWD, demonstrated upward tendencies, with mutation points clustering after 2010, most notably between 2011 and 2016. Wavelet power spectra indicates elevated energy concentrations at multiple time scales, although only CWD exhibited a statistically significant periodicity of approximately 8–10 a (p < 0.05 against red noise). In terms of spatial patterns, index magnitudes generally increased along a northwest-to-southeast gradient. Stations registering significant upward shifts were concentrated in East and Central South China, whereas significant downward shifts appeared mainly in North China and the northern portion of East China. An altitude-dependent pattern was also detected: CWD rose with elevation, while the remaining indices declined sharply below 1288 m, fluctuated in the 1288–2090 m band, and dropped again above 2090 m. Wavelet coherence analysis uncovered significant resonance between extreme precipitation and four circulation indices—SCSMMI, WPSHI, PNA, and NAO. MWC further identified three driver combinations—ENSO-PNA, SCSMMI-WPSHI, and ENSO-NAO-EASMI—as the most influential, acting both individually and synergistically. These results furnish an empirical basis for forecasting, preventing, and managing precipitation-related disasters across China under future climate scenarios. Full article

Bowl-shaped gold nanoparticles (BAuNPs) are of significant interest due to their tunable localized surface plasmon resonance (LSPR) properties. This report presents a new synthesis method that uses hemispherical hydrogen nanobubbles on planar, non-conducting surfaces as templates for gold shell deposition. Initial synthesis under stagnant conditions yielded non-uniform sub-micron particles, attributed to localized hydrogen concentration gradients. The cyclonic flow was introduced aiming to reduce these gradients, although simultaneously inducing significant particle aggregation, obscuring the open structure. To overcome these challenges, an electrochemical microfluidic system was implemented to create a laminar flow environment. This configuration optimizes ion distribution and introduces shear forces that promote particle detachment, successfully limiting particle dimensions to below 200 nm, and preventing the accumulation. Systematic optimization identified optimal parameters: an ideal channel length of 7.5 mm, an applied potential of −0.6 V, and a flow rate of 0.028 µL s⁻¹. These parameters that strike a balance between nanobubble growth and gold deposition kinetics can produce highly uniform BAuNPs with a well-defined open structure and thin solid gold shells, with an outer diameter of 105.3 ± 12.1 nm and a core diameter of 80.1 ± 11.9 nm. These structural parameters successfully shift the plasmonic resonance to 760 nm, which responds perfectly with the first biological window for potential in vivo biomedical applications. Full article

This paper develops an analytical treatment of vibro-acoustic wave propagation in a cylindrical waveguide containing two clamped elastic membranes and a central flexible-shell segment. The acoustic field obeys the time-harmonic Helmholtz equation, the shell motion is described by Donnell–Mushtari thin-shell theory under axisymmetric loading, and the membrane response is governed by classical membrane theory and incorporated through a tailored Galerkin scheme. The resulting coupled fluid–structure boundary-value problem is solved by the Mode-Matching Method: the acoustic potentials are expanded in orthogonal radial eigenfunctions within each subregion, and continuity of pressure, normal velocity, and structural displacement are enforced at every interface. The mirror symmetry of the configuration is exploited by an exact decomposition into symmetric and anti-symmetric sub-problems, each of which reduces to a truncated linear algebraic system of dimension $4N+4$ for the unknown modal amplitudes. Acoustic power-balance identities provide a quantitative consistency check on the numerical implementation and diagnose convergence with respect to the truncation order; structural damping is accommodated through complex-modulus substitutions for the shell and the membrane tension without altering the algebraic structure of the system. The numerical results demonstrate that the dual-membrane configuration delivers transmission-loss values exceeding $25\mathrm{dB}$ across the low-frequency band relevant to HVAC and automotive applications, with a representative plateau near $13\mathrm{dB}$ at the reference geometry, through resonance-driven modal coupling between the acoustic field and the compliant interfaces. Parametric studies identify the excitation frequency, the inner-membrane radius, the shell radius, and the chamber length as effective design parameters for tuning the attenuation. The formulation furnishes a unified and computationally efficient analytical tool for predicting and optimising noise attenuation in flexibly coupled cylindrical duct systems. Full article