Search Results (35,167)

Detecting changes in the permittivities of materials has important applications in electronic information, materials science, biomedicine, and many other fields. However, existing detection methods are limited by factors such as sample thickness and resonance intensity, making it difficult to achieve sensitive dielectric constant detection at desired frequency bands. This paper proposes a method for detecting the dielectric constant changes in samples based on destructive interference of spoof surface plasmon polaritons (SSPPs) in a dual-path transmission structure, which forms a characteristic absorption peak at the SSPPs’ cutoff frequency. Specifically, by utilizing the dependence of the SSPPs’ phase on the periodic unit, a constant π phase difference is formed at the cutoff frequency through the periodic unit number difference between the two paths, resulting in a cutoff frequency absorption peak. When the sample is coated on the SSPPs’ dual-path structure, the boundary conditions are altered, leading to a cutoff frequency shift, thereby enabling dielectric constant detection at the specified frequency. Simulation results show that, with proper structural design, the normalized characteristic frequency shift reaches 10.8%/${\epsilon }_S$ and further demonstrates dramatic robustness against initial phase difference, sample thickness and sample loss. In summary, this work provides a novel high-precision and high-robustness method for detecting dielectric constant changes in samples at specified frequencies. Full article

Identification of unknown individuals is challenging, and radiological imaging databases provide rich anatomical information for automated recognition. This study evaluated whether a single routine magnetic resonance imaging (MRI) slice contains sufficient person-specific features to identify individuals in large databases. It analyzed 11,078 head MRI examinations from 5770 individuals (age 52 ± 18 years, 2714 men) acquired between 2002 and 2025. For identification, 112 individuals were randomly selected across eight 10-year age groups, and one slice from four anatomical regions was extracted. The remaining 10,966 MRI examinations with 247,804 slices formed the reference database. Distinctive anatomical features were automatically extracted using computer vision (CV), and the identification rate was evaluated by rank. Using a single MRI slice, the identification rate at rank 1 reached 96% (107/112) for the best-performing region, the maxillary sinus, among 5770 potential identities. Across all regions, the rank 1 identification rate ranged from 91% to 96%; combining them increased rank 1 and 10 identification rates to 98% (110/112) and 99% (111/112). Identification rate remained stable over several years, with only two cases showing reduced rank 1 performance, likely due to age-related morphological changes. A single MRI slice contains stable, individualized features sufficient for reliable identification in large databases, supporting automated CV-based personal identification across years. Full article

Obstructive sleep apnea (OSA) is a widely known sleep disorder that leads to serious health problems and complications. The standard diagnosis method of OSA is polysomnography. However, the process is time-intensive, expensive, and not readily accessible. Machine learning (ML) has been increasingly applied in various medical imaging modalities; however, there is still a lack of research on applying ML to ultrasound imaging for OSA classification. Previous studies on ML applications in medical imaging adopt X-rays, Computed Tomography, and Magnetic Resonance Imaging, leaving ultrasound as an underexplored area. Using the You-Only-Look-Once version 8 algorithm and static tongue ultrasound images, we classified OSA severity: normal, mild, moderate, and severe. A total of 280 ultrasound images were augmented to 838 images using brightness scaling, which enhanced the training process of the model. The system was tested on 60 images, achieving an overall classification accuracy of 85%. The results demonstrate the possibility and potential of using machine learning and ultrasound imaging for classifying the severity of OSA, suggesting potential assistance to clinicians in diagnosing and intervening in this condition. Full article

Electronic coupling within InAs/InP quantum dots (QDs) influences carrier lifetime and thus QD laser performance. In this work, vertical electronic coupling between QDs is theoretically investigated based on a structure of five-layer QD stacks. This analysis illustrates that the resonant tunneling, a consequence of coherent coupling between QDs, should be considered for carrier redistribution. The carrier tunneling time of ground states is estimated by studying two structures of uniform and chirped five-layer QD stacks. The impact of resonant tunneling on optical properties of InAs/InP QD Fabery–Perot (FP) lasers, such as threshold current, light power-current temperature dependence, and relative intensity noise, is investigated through a comparison of uniform and chirped QD lasers. It is found that the carrier resonant tunneling leads to an increase in the threshold current, low characteristic temperature, and high relative intensity noise. By using the chirped QD stacks, the optical properties are improved thanks to less resonant tunneling. Full article

Background: Amnestic mild cognitive impairment (aMCI) is considered a transitional state between normal aging and dementia, often without visible abnormalities on standard brain magnetic resonance (MR) images. The aim of the study was to analyze both microstructural and functional brain abnormalities using advanced MR techniques. Methods: The study included 27 patients with aMCI and an age-matched control group (CG) of 25 healthy subjects. All MR studies were performed on a 3T MR scanner (Philips, Ingenia) with a 32-channel head and neck coil using volumetric 3D T1 sequences, followed by a resting-state functional MRI (rs-fMRI) sequence. Volumetric analysis was performed using the Destrieux atlas to assess potential structural differences between groups. Seed-to-voxel functional connectivity analyses were conducted using the bilateral hippocampi and both anterior and posterior divisions of the parahippocampal gyri as seed regions. Results: Compared to healthy controls, reduced cortical thickness was observed in aMCI subjects in the temporal regions, frontal and orbitofrontal areas, limbic areas, parietal and sensorimotor cortices, as well as occipito-temporal regions. Additionally, significantly increased functional connectivity was observed between bilateral medial temporal lobe (MTL) regions and the right thalamus. Conclusions: Cortical thinning in various brain regions along with the increased functional connectivity between the MTL regions and the right thalamus may reflect potential compensatory mechanisms in response to initial subtle degenerative changes, emphasizing the importance of using both functional and structural imaging to detect early changes in aMCI patients. Full article

Fabry–Perot resonator (FPR) sensors are widely implemented in optical and microwave waveguides because their interference fringe spectra enable highly sensitive, stable, and calibration-free measurements. In contrast, despite the extensive use of beams and plates as waveguides in vibration- and ultrasound-based structural health monitoring (SHM), an explicit FPR framework for these mechanical waveguides has not been established. This paper demonstrates that flexural beams can be rigorously treated as FPRs despite their inherently dispersive nature. Through analytical derivation, wave-propagation analysis, and fringe-based group-velocity extraction, we show that flexural-beam resonances arise from multi-reflection interference analogous to Fabry–Perot interference. A closed-form relationship between the frequency-dependent group velocity and the FPR free spectral range (FSR) is established, enabling inverse determination of mechanical or environmental perturbance from the FPR fringe spectrum. By extending FPR-based fringe analysis to dispersive mechanical waveguides, this work introduces a theoretical framework for implementing dispersive mechanical waveguide-based FPR sensors. Full article

Mitral transcatheter edge-to-edge repair (M-TEER) has emerged as a cornerstone in the management of severe mitral regurgitation, serving as a robust, low-risk alternative to conventional mitral valve surgery. Although thromboembolic risk remains a critical clinical challenge, that varies significantly across the clinical continuum, from pre-procedural substrates to post-procedural management. This review highlights the role of atrial cardiomyopathy in creating a prothrombotic milieu even prior to intervention, while during the procedure, device time emerges as a potentially dominant independent predictor of embolic burden, marking the periprocedural window as the period of peak hazard. Furthermore, this article addresses the notable disparity between the near-universal presence of subclinical ischemic lesions on magnetic resonance imaging and the infrequent incidence of overt neurological deficits. As the post-procedural phase is considered, we discuss the shift from standardized antithrombotic protocols to individualized strategies and the potential role of concomitant left atrial appendage occlusion. Ultimately, integrating these stage-specific clinical and procedural determinants with emerging technologies—like digital twins and artificial intelligence—represents a promising frontier for mitigating embolic risks, optimizing procedural planning and patient safety in the evolving landscape of mitral valve interventions. Full article

Brain tumor detection from magnetic resonance imaging (MRI) is fundamental to computer-aided diagnosis, yet automated models must remain robust to heterogeneous imaging conditions. Despite strong recent progress, many deep learning and transformer-based approaches primarily optimize performance accuracy without explicitly improving feature selectivity and spatial localization, and they typically produce deterministic output without uncertainty estimates, which limits reliability. To overcome these limitations, we introduce UA-EffNet-DA, an uncertainty-aware EfficientNet framework that addresses these limitations through three complementary components. First, EfficientNet-B4 serves as an efficient backbone for discriminative feature extraction. Second, lightweight dual attention modules, comprising channel and spatial attention in parallel, are applied to the model to emphasize what and where discriminative features to focus within MRI slices. Third, Monte Carlo dropout is employed during inference to quantify predictive uncertainty and enable confidence-aware decision. Experiments on two public benchmarks demonstrate strong performance, yielding accuracies of 98.73% on the Figshare dataset and 99.23% on the Kaggle dataset. In addition, explainable AI analysis using Gradient-weighted Class Activation Mapping (Grad-CAM) further indicates that the proposed model concentrates on diagnostically relevant tumor regions rather than background structures, supporting transparent decision-making. Ablation studies confirm the complementary contribution of dual attention refinement and uncertainty-aware inference. Overall, the proposed UA-EffNet-DA framework offers an efficient and interpretable approach for brain tumor detection that supports more reliable clinical decision support through uncertainty-aware predictions. Full article

A micro-cavity based on phase-change material is a very important strategy for the realization of tunable absorption and conversion of terahertz waves. In this work, a tunable terahertz metamaterial absorber based on the phase-change material germanium–antimony–tellurium (GST) is demonstrated. The device features a metal–insulator–metal triple-layer structure, where the dynamic switching of absorption characteristics is achieved via thermally controlled GST phase transition. In the amorphous state, the absorber exhibits a single absorption peak at 7.7 THz. Upon crystallization, the absorption switches to dual peaks at 5.1 THz and 8.3 THz, achieving near-perfect absorption in both states. Full-wave electromagnetic simulations and theoretical analysis based on a multiple-reflection interference model indicate that this performance tuning originates from the GST-phase-transition-induced change in the equivalent optical cavity length. This corresponds to a switch between two resonant modes: coupled inner–outer ring resonance and independent outer ring resonance. These results provide a foundation for developing dynamically tunable terahertz devices with promising applications in terahertz communications, imaging, and sensing. Full article

To improve the low sensitivity of electromagnetic acoustic testing (EMAT) to micro-debonding defects in metal–rubber bonded structures, this study proposes a detection framework combining a magnetic-field-enhanced focusing EMAT with entropy-weighted multi-feature fusion imaging. First, a Halbach-type focusing magnet was designed and evaluated through finite element simulations, showing a substantial enhancement of the effective bias magnetic field in the working region. Then, three complementary echo features, namely amplitude (AMP), time-domain integral (TDI), and power spectral density (PSD), were extracted from the acquired resonance signals and integrated using an adaptive entropy-weighted fusion strategy. Comparative and ablation analyses were further conducted to distinguish the respective contributions of probe enhancement and feature fusion, and to compare entropy-weighted fusion with single-feature imaging and equal-weight fusion. The results indicate that the focused probe mainly improves the defect-response strength at the hardware level, whereas feature fusion mainly improves image contrast, background suppression, and segmentation consistency at the image level. Among the compared methods and under the present experimental conditions, entropy-weighted fusion provides the best overall imaging performance. Under the present experimental conditions, the proposed framework enables reliable detection of 5 mm debonding defects in aluminum-alloy–rubber bonded specimens and 10 mm debonding defects in titanium-alloy–rubber bonded specimens. These results suggest that the combined use of magnetic-field focusing and adaptive multi-feature fusion is a promising approach for the detection and quantitative characterization of micro-debonding defects in metal–rubber bonded structures. Full article

Background: Rare appendicular pathologies (RAP) are uncommon clinical entities with important diagnostic and therapeutic implications. These conditions frequently mimic acute appendicitis, yet they may require different operative strategies and, in selected cases, oncological management. Methods: We performed a retrospective cohort study including all patients who underwent surgery with the intention of performing an appendectomy at the First Surgical Clinic, Emergency County University Hospital of Cluj-Napoca, between 2018 and 2021. During this interval, 330 appendectomies were performed. Patients with a histopathological diagnosis of RAP were included. Clinical, imaging, surgical, histopathological, postoperative, and follow-up data were analyzed, with particular attention to the preoperative diagnostic work-up and imaging-based suspicion of rare appendicular pathology. Results: Ten patients (3.03%) were diagnosed with RAP, including low-grade appendiceal mucinous neoplasm (LAMN; n = 5), mucinous cystadenoma (n = 2), appendiceal adenocarcinoma (n = 1), appendicular diverticulum (n = 1), and stump appendicitis (n = 1). Computed tomography was the main diagnostic modality, particularly in patients with atypical presentation or suspicion of complicated or neoplastic appendiceal disease, while magnetic resonance imaging and colonoscopy provided additional information in selected cases. Preoperative suspicion of a rare or neoplastic appendiceal pathology was achieved in 70% of patients. Laparoscopic appendectomy was performed in 6 patients, open appendectomy in 1 patient, open ileocecal resection in 1 patient, open right hemicolectomy in 1 patient, and laparoscopic right hemicolectomy in 1 patient. Histopathological examination confirmed the diagnosis in all cases. Immediate postoperative outcomes were favorable, without perioperative mortality or major complications; during follow-up, the patient with adenocarcinoma required oncological treatment and resection of a local recurrence 1 year after surgery. Conclusions: RAP represent a small but clinically significant subset of appendiceal disease. Structured preoperative imaging, intraoperative recognition of atypical findings, and an individualized surgical strategy are essential for optimal outcomes and appropriate oncological management. Full article

Thermoacoustic power generation holds significant promise for applications such as solar thermal utilization, industrial waste heat recovery, and distributed energy systems, owing to its high efficiency and reliability. Conventional standing-wave and traveling-wave thermoacoustic generators, however, are often limited by bulky resonators and substantial acoustic power dissipation. Replacing the resonator with a linear alternator (LA) offers an effective means to improve system compactness and output performance. Nonetheless, under standing-wave acoustic conditions, the LA’s large piston swept volume increases the device size, thereby constraining overall compactness. To address this limitation, a novel moving-magnet LA with electromagnetic components integrated into the moving piston is proposed. Compared to conventional configurations, this design significantly reduces the size and weight of the alternator. Furthermore, the influence of different magnetic circuit configurations on output performance is systematically investigated, enabling optimization of the alternator design. Results demonstrate that the proposed alternator achieves a more compact structure while delivering output performance comparable to that of conventional external magnetic-circuit designs, thereby validating the feasibility of the proposed approach. Full article

Atypical Parkinsonisms are a diverse group of diseases associated with multiple pathologies, including synucleinopathies and tauopathies. Atypical Parkinsonisms include progressive supranuclear palsy, corticobasal degeneration, multiple system atrophy, and dementia with Lewy bodies. The examination of these diseases is complicated due to their overlapping clinical manifestations. Hence, tools enabling reliable supplementary assessment of atypical Parkinsonisms are needed. The most common methods involve neuroimaging; however, these evaluations generally involve basic magnetic resonance imaging and indicate possible morphological changes. Less attention is given to disease background assessment. Biochemical assessment enables a more detailed examination of the factors impacting neurodegenerative processes. The features that may impact the pathophysiology of these diseases include metabolic abnormalities, excessive inflammation, and environmental factors. In this context, proteomic evaluation, as analyzed in this article, could partly address the insufficiently described aspects of the unclear pathological mechanisms related to atypical Parkinsonisms. Full article

The present study focuses on liquid-precursor-mediated chemical vapor deposition (under ambient pressure and moderate temperature range) of WSe₂ on sapphire using ammonium meta-tungstate and sodium cholate. The investigation provides additional results and information for the WSe₂ cluster formations on sapphire as an extension of our previous study, especially based on structural, chemical and morphological characterization of the observed largest and predominant polygonal WSe₂ domains whose lateral size can reach several hundreds of micrometers. In addition, highly symmetrical shapes were also observed. The Raman spectroscopy and atomic force microscopy identified the formation of both mono- and multilayered WSe₂. Moreover, the Raman spectrum analysis shows a complex peak structure with unusual splitting effects in the second-order modes marking strong activity of excitonic-resonance processes. Full article