Search Results (642)

We investigate the effects of post-annealing in oxygen (O₂) and nitrogen (N₂) on tin-doped vanadium oxide (V_xSn_yO_z) films for microbolometer applications. The films were deposited using magnetron sputtering in an Ar:O₂ environment. We demonstrate that low Sn doping combined with N₂ post-annealing provides an effective approach to optimize the temperature coefficient of resistance (TCR), resistivity, and 1/f-noise. Compared to undoped VO_x, V_xSn_yO_z films exhibit an enhanced TCR, moderate resistivity, and reduced 1/f-noise. The 135 nm thick V_0.46Sn_0.03O_0.51 film after post-annealing in N₂ shows a TCR of −4.08%/K and a resistivity of 7.3 × 10⁻² Ω⋅cm at 300 K, an absorptance of 63–68% in the 900–2500 nm wavelength range, and low noise voltage power spectral density (1.77 × 10⁻¹⁶ V²/Hz at 100 Hz under 0.3μA bias current). These results indicate that Sn-doped VO_x films are promising sensing materials for microbolometer applications. Full article

Spaceborne hyperspectral imaging spectrometers enable refined retrieval and quantification of methane point-source emissions. However, the conventional matched filter (MF) systematically underestimates methane enhancements under high-concentration conditions and remains sensitive to spectral inconsistencies across varying observation scenarios. To address these limitations, we improve MF-based retrieval from two aspects: the observation model and the unit absorption spectrum (UAS) representation. First, a Levenberg–Marquardt matched filter (LMMF) is developed by extending the MF framework to a nonlinear retrieval formulation while retaining its data-driven and background-statistics-based characteristics. Specifically, the exponential absorption term is preserved, and methane enhancement is iteratively solved in the nonlinear domain, enabling a more physically consistent retrieval without requiring precise external prior knowledge. Building upon this framework, a spectrally corrected LMMF (SC-LMMF) is further proposed by introducing a lookup-table-based dynamic UAS correction to account for variations in observation geometry, surface elevation, and atmospheric state. Comprehensive validation using idealized and noise-perturbed simulations, end-to-end simulations, and controlled-release experiments demonstrates that the LMMF mitigates high-concentration underestimation relative to the MF. The SC-LMMF further reduces cross-scene systematic biases, shifting retrievals toward a near 1:1 relationship. In controlled-release experiments, the SC-LMMF increased the coefficient of determination (R²) by approximately 50% while reducing the root mean square error (RMSE) and mean absolute error (MAE) by approximately 70% relative to the MF. Overall, the proposed framework enhances the robustness and quantitative consistency of methane point-source retrievals across multisource hyperspectral satellite observations. Full article

Noise pollution poses significant challenges to human health and quality of life; thus, high-performance damping materials are attracting increasing attention. Rubber has been extensively applied in these materials due to its viscoelasticity. However, the damping performance of these materials is often constrained by the intrinsically limited energy-dissipation capability of the polymer backbone, which lacks sound-absorbing functionalities. Herein, a cross-linked sliding graft copolymer (SGC) was incorporated into isobutylene-isoprene rubber (IIR) and chlorinated butyl rubber (ClIR) to fabricate high-strength damping elastomers. Unlike conventional covalently cross-linked polymers, the cross-linked SGC features mobile junctions, which can slide along the polyrotaxane backbone to redistribute and equalize chain tension, giving rise to the “pulley effect”. Benefiting from the intrinsically high energy-dissipation capability of SGC and the cooperative contribution of interfacial hydrogen bonding, the obtained SGC/IIR and SGC/ClIR blends exhibit both enhanced damping performance and mechanical properties. The synergistic improvement in damping capacity and mechanical robustness renders the SGC/rubber blends as promising candidates for advanced sound-absorption applications. Full article

Cavity ring-down spectroscopy has significant potential for detecting trace volatile organic compounds, owing to its long absorption path and high sensitivity. However, in practical measurements, noise severely decreases the accuracy of decay curves and the reliability of concentration retrieval. To address this, we developed a deep learning-based denoising model called decay-upsampling FC-Net. Experimental results showed that the model improved the signal-to-noise ratio from 13.86 dB to 26.79 dB and processed a single decay curve in only 0.000207 s on average. Moreover, under high-noise conditions, it determined the ring-down time more accurately than conventional methods. This study provides an effective signal processing solution to enhance the practical reliability of Cavity ring-down spectroscopy gas detection systems. Full article

Ultrasonic motors have attracted considerable attention in precision actuation applications because of their advantages over conventional electromagnetic motors, such as compact structure, high positioning accuracy, immunity to electromagnetic interference, noise-free operation, and suitability for low-temperature environments. However, conventional traveling-wave linear ultrasonic motors usually rely on boundary constraints to establish stable traveling waves, which may limit their structural flexibility and self-propelled capability. To address this issue, this paper proposes a free-boundary traveling-wave linear ultrasonic motor capable of realizing self-propelled motion. The motor features a projection structure at each end of the stator. Two piezoelectric ceramics are placed at one end for excitation, while a damping material is arranged at the other end for energy absorption. This design enables the motor to generate traveling waves without requiring fixed boundary conditions. The motor operates in the B(3,1) out-of-plane vibration mode to enhance the energy absorption capacity of the non-excited end and reduce its standing wave ratio (SWR). A finite element model of the motor is established to investigate its vibration characteristics. In addition, a novel method for estimating the standing wave ratio is proposed by using piezoelectric ceramics attached to the motor surface, replacing the traditional calculation approach. A prototype is fabricated to verify the feasibility of the proposed design. Experimental results show that the prototype achieves a minimum SWR of 1.81, a no-load speed of 42.1 mm/s, and a maximum output force of 0.465 N. These results confirm the feasibility of the proposed scheme and provide a new approach for the design of free-boundary traveling-wave linear ultrasonic motors. Full article

Ultra-high-field (UHF) magnetic resonance imaging, defined as imaging at field strengths of 7 Tesla (7T) and above, represents a frontier technology in neuroimaging with emerging applications in prenatal brain research. This narrative review examines the current evidence on the potential benefits of UHF-MRI for investigating embryonic and fetal brain development. Through analysis of 97 studies identified across multiple databases, we find that UHF-MRI offers substantial advantages in spatial resolution, tissue contrast, and anatomical detail compared to conventional clinical field strengths (1.5T and 3T). The primary applications to date have been in ex vivo imaging of post-mortem fetal specimens and preclinical animal models, where UHF-MRI has enabled unprecedented visualization of laminar cortical organization, early sulcation patterns, microstructural development, and subtle anatomical features critical for understanding normal and abnormal neurodevelopment. Key benefits include enhanced delineation of transient developmental zones, improved characterization of cortical folding, superior detection of subtle malformations, and the ability to create high-resolution three-dimensional atlases of fetal brain development. However, significant technical and safety challenges currently limit in utero human applications, including concerns about specific absorption rate, acoustic noise, and fetal motion artifacts. This review identifies critical knowledge gaps and future directions for translating UHF-MRI technology to clinical prenatal diagnostics. Full article

Noise pollution has become an increasingly discussed environmental problem in recent years. Developing a traffic infrastructure and recent sustainability goals require new solutions to mitigate noise pollution. This paper investigates the efficiency of the noise barrier made entirely of recycled materials. This solution would help achieve the United Nations sustainable development goals (SDGs). The proposed barrier target SDGs are: Good Health and Well-being (SDG 3); Industry, Innovation, and Infrastructure (SDG 9); Sustainable Cities and Communities (SDG 11); Climate Action (SDG 13). The changed barrier parameters were the parameters of the perforated panel and the air gap behind the porous material. To solve the optimisation problem, the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method was used. The results showed that the proposed barrier configuration was the following: perforation shape—round, perforation diameter—5 mm, increment angle perforation—30°, thickness of the perforated panel—10 mm, porous absorbing material (composite rubber granule and hemp shive panel (RGHS))—50 mm thick, 20% of hemp shive content, air gap between absorbing material and the rigid backing—100 mm. The total thickness of the noise barrier was 180 mm. The acoustic parameters of the noise barrier structure were: α_avg. = 0.24, peaking at 0.51 (1250 Hz) and R_W = 39.7 ± 1.0 dB. These results indicate that the proposed barrier made of recycled materials could be a sustainable alternative for noise pollution mitigation and improving people’s quality of life. Full article

Spin-exchange relaxation-free (SERF) atomic magnetometers have emerged as highly promising candidates for ultra-weak magnetic field detection, particularly in biomagnetic imaging, owing to their exceptional sensitivity, amenability to miniaturization, and near-room-temperature operation. While current miniaturized magnetometers typically employ laser chips with fixed optical power, the quantitative impact of laser power on critical performance metrics remains to be fully elucidated. This study systematically investigates the influence of laser power on sensitivity, bandwidth, and dynamic range by incorporating considerations of power broadening, saturation absorption, and noise constraints. A miniaturized probe, integrated with an actively controlled vertical-cavity surface-emitting laser (VCSEL), was developed for experimental validation. Theoretical and experimental results consistently demonstrate that as optical power increases, sensitivity exhibits a non-monotonic dependence, whereas both bandwidth and dynamic range manifest a monotonic upward trend, aligning well with theoretical simulations. The optimized sensor achieved a peak sensitivity of 16 fT/√Hz at 300 μW, while the bandwidth and dynamic range reached 230 Hz and ±5.4 nT at 500 μW, respectively. This work establishes a robust theoretical and experimental framework for the comprehensive performance optimization of laser-integrated miniaturized atomic magnetometers. Full article

To address the current absence of targeted gradation design for porous asphalt pavements both domestically and internationally, this study employs the Coarse Aggregate Void Filling (CAVF) method to design the gradation of porous asphalt mixtures. Marshall stability tests, rutting tests, and scattering tests were conducted to investigate the relationship between coarse aggregate proportions and the structural stability of the mixture skeleton. An orthogonal experimental design was further utilized to examine the influence of three levels of fine aggregate gradation on the acoustic absorption characteristics of the mixture, and to analyze the effects of aggregate gradation on the primary pore diameter, connected pore diameter, and connected pore length. The results indicate that the coarse aggregate gradation predominantly governs the skeleton strength and overall pavement performance of the mixture, whereas the fine aggregate gradation exhibits significant effects on the interconnected void ratio, pore structure, and sound absorption performance. The optimal roughness range of coarse aggregates in porous asphalt mixtures is determined to be 0.46–0.52. The proportion of 0.6–1.18 mm aggregates has a pronounced influence on the primary pore diameter, connected pore diameter, and connected pore length. By integrating the design considerations for both coarse and fine aggregate gradations, a recommended gradation range for porous asphalt mixtures is proposed that achieves a balance between pavement performance and sound absorption/noise-reduction effectiveness. Full article

Wavelength modulation spectroscopy (WMS) is a representative implementation of tunable diode laser absorption spectroscopy (TDLAS), enabling reliable gas component analysis with concentration-related information derived from harmonic component extraction, while offering enhanced noise immunity for trace gas sensing in open environments. However, due to the strong coupling between laser wavelength and intensity, wavelength modulation inevitably introduces residual amplitude modulation (RAM), which significantly degrades measurement accuracy. To address this issue, this study introduces a RAM suppression algorithm based on multiple harmonic component decoupling (MHCD), using the second-harmonic lateral peak inclination angle (LPIA) as a characteristic indicator. Unit harmonic operators for the first, second, and third harmonics are designed, and an original harmonic reconstruction model is established via linear superposition of harmonic components. The optimal harmonic component ratio is determined at the composite operator with the maximum cross-correlation coefficient, and RAM noise is eliminated through a multi-harmonic decoupling matrix. Repetitive measurements on 22 mm pharmaceutical vials with 4% oxygen concentration demonstrate that MHCD reduces the second-harmonic LPIA from 18.07° to 8.56°. Concentration discrimination experiments conducted on seven groups of 22 mm vials with 2% concentration steps (0–12%) show that MHCD increases the true positive rate by 6–11% and decreases the false positive rate by 4–9%, confirming its effectiveness for pharmaceutical online inspection applications. Full article

Underwater acoustic coatings are widely used to suppress low-frequency noise radiation and sonar reflection in underwater vehicles. In this study, an underwater acoustic coating model consisting of viscoelastic rubber layers and micro-perforated panel (MPP) structures is investigated, with particular emphasis on the low-frequency sound absorption mechanism and predictive modeling. Based on an improved transfer function method, a novel Micro-Perforated Panel Acoustic Coating Layer (MPPACL) model is developed to describe the coupled acoustic behavior of multilayer coatings under underwater conditions. The low-frequency sound absorption performance is primarily governed by the viscoelastic characteristics of the rubber layer, including material damping and complex modulus, while the incorporation of the MPP further enhances absorption through resonance effects. To efficiently explore the relationship between structural parameters and acoustic response, an ensemble learning-based deep neural network (ELDNN) is constructed using analytically generated data, enabling both forward prediction of sound absorption performance and inverse prediction of structural design parameters. The results show that the frequency prediction accuracy of the IDNN model is 3.7 times that of the DNN model. Furthermore, the proposed MPPACL model has achieved a significantly enhanced sound absorption effect within the frequency range of 50 to 2000 hertz. This effect has also been further verified through underwater experiments. The proposed framework provides an efficient and reliable approach for the design and optimization of underwater acoustic coatings. Full article

This study proposes a novel coplanar spiral-varying-channel space-coiled acoustic metamaterial (CSV-SCAM) for efficient low-frequency noise control in the range of approximately 200–400 Hz. By integrating continuously graded spiral channels with secondary spiral branches, the proposed structure enables multi-stage acoustic impedance matching and enhanced thermo-viscous dissipation, effectively overcoming the bulkiness and limited low-frequency efficiency of conventional porous absorbers. Finite element simulations and impedance tube experiments demonstrate that the CSV-SCAM achieves near-unity deep-subwavelength sound absorption, with a peak sound absorption coefficient exceeding 0.99 around 750–850 Hz using a thickness of only 10 mm. Furthermore, hybrid configurations composed of units with different branch numbers significantly broaden the effective absorption bandwidth by more than 20% while maintaining high absorption levels. Compared with traditional Helmholtz resonators, the proposed metamaterial exhibits superior compactness, structural robustness, and design flexibility, providing a promising solution for practical low-frequency noise mitigation in space-constrained engineering applications. Full article

Rapid point of care assessment of pulmonary surfactant composition by measuring the lecithin/sphingomyelin (L/S) ratio could improve management of patients with neonatal respiratory distress syndrome (nRDS). Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) offers a practical route to making such measurements, but the influence of the sample solvent prior to drying on measurement repeatability is poorly understood. We compare films dried from dichloromethane (DCM) and water (AQ) solvents (DCM-dry route vs. AQ-dry route) by ATR-FTIR and show that spectra from the AQ-dry route increased the signal-to-noise ratio (SNR) of a representative (2920 cm⁻¹) absorption peak for the mixture from 20.13 to 128.20 and for human endotracheal aspirate (ETA) from 6.33 to 8.13. A mixed nested analysis of variance (ANOVA) showed that drying route accounted for 89.52% of mixture peak height variance and reduced percent relative standard deviation (%RSD) from 23.5% to 16.2%, corroborated by multivariate analysis for ETA. We further demonstrate that partial least squares regression (PLSR) models trained on AQ-dry mixture spectra predicted L/S (R² = 0.91; root mean square error (RMSE) = 0.31) with 95% prediction interval grey-zone interpretation around L/S = 2.2, complemented by a receiver operating characteristic area under the curve (ROC-AUC) of 0.978. Full article

Injection-related errors remain a common clinical issue and can cause patient discomfort, hematoma formation, and procedural inefficiencies. The visualization of subcutaneous veins using near-infrared (NIR) imaging has gained attention as an effective approach to reducing such errors, as blood exhibits a higher absorption of NIR light than surrounding tissue. In this study, a low-cost, non-invasive vein visualization system is presented to support safer and more accurate venous access. The proposed system integrates an NIR illumination source and a modified webcam within a compact equipment enclosure, allowing subjects to be conveniently examined by placing their arm inside the device. Vein images are automatically acquired using a laptop-based platform, followed by digital image processing techniques for vein enhancement and visualization. Laboratory-scale experiments were conducted on healthy volunteers to evaluate system performance under multiple conditions, including different vein locations (upper and lower arm regions), varying distances between the NIR light source and the arm (15 cm and 20 cm), and ambient illumination interference (light sources on and off). The experimental results demonstrate the successful implementation and reliable operation of the proposed system. Effective vein visualization was achieved across all test conditions, as confirmed by qualitative visual assessment and quantitative image quality metrics, including the Peak Signal-to-Noise Ratio (PSNR) and Mean Squared Error (MSE). Overall, the proposed system offers a practical, accessible, and cost-effective solution for vein visualization, showing strong potential for clinical and experimental applications aimed at reducing injection errors and improving venous access reliability. Full article

Airframe noise generated at wing trailing edges and high-lift devices, such as flaps, remains a major challenge during landing, with significant contributions in the low-frequency band of 500–1500 Hz. While solid surfaces reflect this acoustic energy, metallic porous materials can effectively absorb it through viscous and thermal dissipation within their internal pore structure. To address this, the present study examines the acoustic absorption characteristics of open-cell AlSi porous cylinders featuring controlled pore diameters between 0.3 mm and 2.25 mm. Measurements were conducted in an acoustic impedance tube according to the ISO 10534-2:2023 standard, using six cylindrical samples (28 mm diameter, 70 mm length). Two sets of measurements were performed for each sample (front and rear faces), and the average values were used. The findings indicate that the normal-incidence sound absorption coefficient α rises as pore size increases, reaching 0.93–0.97 at low frequencies of 500–700 Hz for the samples with the largest pores (1.8–2.25 mm). These results indicate that open-cell AlSi alloys offer strong low-frequencies sound absorption, positioning them as promising options for aeroacoustic noise mitigation, including applications such as porous trailing edge and hybrid flap designs. Full article