Search Results (165)

In this study, an accurate attenuation measurement system with high attenuation capability (≥100 dB) is presented, covering a broad radio frequency range from 1 GHz to 25 GHz. The system employs a dual-channel intermediate frequency (IF) substitution method, utilizing a programmable inductive voltage divider (IVD) that provides precise voltage ratios at a 1 kHz operating IF, serving as the primary attenuation standard. To ensure optimal inter-channel isolation, essential for accurate high-attenuation measurements, an optical fiber assembly, consisting of a laser diode, a wideband external electro-optic modulator, and a photodetector, is integrated between the channels. A comprehensive performance evaluation is presented, with particular emphasis on the programmable IVD calibration technique, which achieves an accuracy better than 0.001 dB across all attenuation levels, and on the role of the optical fiber assembly in enhancing isolation, demonstrating levels exceeding 120 dB across the entire frequency range. The system demonstrates measurement capabilities with expanded uncertainties (k = 2) of 0.004 dB, 0.008 dB, and 0.010 dB at attenuation levels of 20 dB, 60 dB, and 100 dB, respectively. Full article

The insulating rod of aramid fiber-reinforced epoxy resin composites (AFRP) is an important component of gas-insulated switchgear (GIS). Under complex working conditions, the high temperature caused by voltage, current, and external climate change becomes one of the important factors that aggravate the interface degradation between aramid fiber (AF) and epoxy resin (EP). In this paper, molecular dynamics (MD) simulation software is used to study the effect of temperature on the interfacial properties of AF/EP. At the same time, the mechanism of improving the interfacial properties of three nanoparticles with different properties (insulator Al₂O₃, semiconductor ZnO, and conductor carbon nanotube (CNT)) is explored. The results show that the increase in temperature will greatly reduce the interfacial van der Waals force, thereby reducing the interfacial binding energy between AF and EP, making the interfacial wettability worse. Furthermore, the addition of the three fillers can improve the interfacial adhesion of the composite material. Among them, Al₂O₃ and CNT maintain a large dipole moment at high temperature, making the van der Waals force more stable and the adhesion performance attenuation less. The Mulliken charge and energy gap of Al₂O₃ and ZnO decrease slightly with temperature but are still higher than AF, which is conducive to maintaining good interfacial insulation performance. Full article

Modern aerospace engineering places increasing emphasis on materials that combine low weight with high mechanical performance. Fiber metal laminates (FMLs), which merge metal layers with fiber-reinforced composites, meet this demand by delivering improved fatigue resistance, impact tolerance, and environmental durability, often surpassing the performance of their constituents in demanding applications. Despite these advantages, inspecting such thin, layered structures remains a significant challenge, particularly when they are difficult or impossible to access. As with any new invention, they always come with challenges. This study examines the effectiveness of the fundamental anti-symmetric Lamb wave mode (A0) in detecting weak interfacial defects within Carall laminates, a type of hybrid fiber metal laminate (FML). Delamination detectability is analyzed in terms of strong wave dispersion observed downstream of the delaminated sublayer, within a region characterized by acoustic distortion. A three-dimensional finite element (FE) model is developed to simulate mode trapping and full-wavefield local displacement. The approach is validated by reproducing experimental results reported in prior studies, including the author’s own work. Results demonstrate that the A0 mode is sensitive to delamination; however, its lateral resolution depends on local position, ply orientation, and dispersion characteristics. Accurately resolving the depth and extent of delamination remains challenging due to the redistribution of peak amplitude in the frequency domain, likely caused by interference effects in the acoustically sensitive delaminated zone. Additionally, angular scattering analysis reveals a complex wave behavior, with most of the energy concentrated along the centerline, despite transmission losses at the metal-composite interfaces in the Carall laminate. The wave interaction with the leading and trailing edges of the delaminations is strongly influenced by the complex wave interference phenomenon and acoustic mismatched regions, leading to an increase in dispersion at the sublayers. Analytical dispersion calculations clarify how wave behavior influences the detectability and resolution of delaminations, though this resolution is constrained, being most effective for weak interfaces located closer to the surface. This study offers critical insights into how the fundamental anti-symmetric Lamb wave mode (A0) interacts with delaminations in highly attenuative, multilayered environments. It also highlights the challenges in resolving the spatial extent of damage in the long-wavelength limit. The findings support the practical application of A0 Lamb waves for structural health assessment of hybrid composites, enabling defect detection at inaccessible depths. Full article

Background/Objectives: To assess the association between early pregnancy carbohydrate quality, as measured by the Carbohydrate Quality Index (CQI), and the risk of delivering a large-for-gestational-age (LGA) infant in a Mediterranean pregnant cohort of northern Greece. Methods: We analyzed singleton pregnancies from the BORN 2020 prospective cohort in Greece. Dietary intake was assessed via a validated food frequency questionnaire, and CQI was computed from glycemic index, fiber density, whole-to-refined grain ratio, and solid-to-liquid carbohydrate ratio. Multivariable logistic regression was used to estimate the association between CQI (in tertiles) and LGA risk, defined as birthweight >90th percentile. Results: Among the 797 participants, 152 (19.1%) delivered LGA infants, and 117 (14.7%) were diagnosed with GDM. Of those with GDM, 23 (19.7%) delivered LGA infants. In the total population, higher maternal weight (p < 0.001), height (p = 0.006), and pre-pregnancy BMI (p = 0.004) were significantly associated with LGA. A greater proportion of women with LGA had a BMI > 25 (p = 0.007). In the GDM subgroup, maternal height remained significantly higher in those who delivered LGA infants (p = 0.017). In multivariable models, moderate CQI was consistently associated with increased odds of LGA across all models (Model 1: aOR = 1.60 (95% CI: 1.03–2.50), p = 0.037, Model 2: aOR = 1.57 (95% CI: 1.01–2.46), p = 0.046, Model 3: aOR = 1.58 (95% CI: 1.01–2.47), p = 0.044, Model 4 aOR: 1.70; 95% CI: 1.08–2.72; p = 0.023), whereas high CQI was not. In the GDM subgroup, a significant association between high CQI and increased LGA risk was observed in less adjusted models (Model 1 aOR: 6.74; 95% CI: 1.32–56.66; p = 0.039, Model 2 aOR: 6.64; 95% CI: 1.27–57.48; p = 0.044), but this was attenuated and became non-significant in the fully adjusted model (aOR: 3.05; 95% CI: 0.47–30.22; p = 0.28). When examining CQI components individually, no consistent associations were observed. Notably, a higher intake of low-quality carbohydrates (≥50% of energy intake) was significantly associated with increased LGA risk in the total population (aOR: 4.25; 95% CI: 1.53–11.67; p = 0.005). Conclusions: Higher early pregnancy intake of low-quality carbohydrates was associated with an elevated risk of LGA in the general population. However, CQI itself showed a non-linear and inconsistent relationship with LGA, with moderate, but not high, CQI linked to increased risk, particularly in GDM pregnancies, where associations were lost after adjustment. Both carbohydrate quality and quantity evaluations are essential, particularly in high-risk groups, to inform dietary guidance in pregnancy. Full article

We consider light, high-absorbance, low-reflectance, electrically large layered sheet structures composed of thin carbon nanotube films. Such structures can be utilized in electromagnetic absorption and shielding applications in the X-band. They are of increasing interest in sensor-enabling technologies, stealth systems, and EMI shielding of electronic components. Especially in aerospace, this is crucial, as sensors are integral to aerospace engineering, enhancing the safety, efficiency, and performance of aircraft and spacecraft. To that end, sheets with carbon nanotube films embedded in a glass fiber polymer matrix are fabricated. The films have a thickness of around 70 μm. As shown, they cause a significant attenuation of the electromagnetic field. For shielding applications, a single-film sheet structure with total thickness of 1.65 mm presents an attenuation of around 25 dB in the transmission coefficient, while the attenuation can reach 37 dB for a two-film sheet structure with thickness of 1.8 mm. Shielding effectiveness performance is found to be greater than 35 dB for the two-film sheet structure. For applications requiring both high shielding and absorption, a two-layered structure with a thickness of 4.65 mm has been designed. The absorption, represented by the Loss Factor, is calculated to achieve values greater than 90%. The simulation results show good agreement with the measured data. The findings demonstrate a promising structure for materials suitable for sensor housings and smart electromagnetic environments where the suppression of electromagnetic interference is critical. In conclusion, the addition of carbon nanotube films, even at micrometer thicknesses, within a glass fiber polymer matrix significantly enhances both electromagnetic shielding and absorption performance. Full article

Current research on dosimeters based on radiation-induced attenuation (RIA) primarily focused on enhancing radiation sensitivity or reducing dependencies from interference factors. However, their intrinsic sensing performance has received limited attention. This work proposed application and analysis methods for RIA-based dosimeters, validated by a low-cost apparatus using commercial fibers. Initially, a generic protocol of high-dose detection after low-dose calibration was suggested to overcome the various dependencies of RIA, enabling repetitive monitoring of near-stable radiation by simple replacement of commercial fibers. Experiments comparing three dose-loss models demonstrated that the saturation-exponential model exhibited superior accuracy, achieving absolute errors below 4 Gy within a measurable range of up to ~300 Gy. Subsequently, the system’s RIA-based sensitivity was ~125.6 dB·Gy⁻¹·km⁻¹. The resolution and sensitivity expressed by optical power were newly defined, effectively quantifying the decline in precision and response ratio during detection. Moreover, an additional structure was introduced to extend the measurable range. Simulations and experiments under 1-MeV electron irradiation verified that adjustable ranges could be achieved through configuration of attenuation layers. In summary, these advancements provided critical guidance for component selection and operational evaluation, facilitating the commercialization and practical deployment of RIA-based dosimeters. Full article

Silk weighting is a process used to compensate for the weight loss caused by degumming, achieved by adding agents such as metallic salts to enhance the hand feel and appearance of the fibers. With the development of tin weighting procedures (ca. 1870s), the production of weighted silk tremendously increased, as the fast decay of such fabrics was attributed to the process itself. The weighted silk was largely used for evening wear and high-fashion garments, many of which nowadays are stored in textile collections, and often characterized by poor conservation conditions. Within the present work, a multi-analytical and interdisciplinary non-destructive protocol was established for studying the finishing techniques, characterizing the materials as well as the state of preservation of historic tin-weighted silk. The protocol involves a visual and haptic approach typical of conservation professionals, as well as analytical investigations such as X-Ray Fluorescence analyses, 3D digital microscopy, Scanning Electron Microscopy with Energy Dispersive Spectroscopy, and Fourier-transform Infrared Spectroscopy (FTIR) in Attenuated Total Reflection. Elemental analyses are effective for studying the technology of production, while FTIR emerged as a powerful tool for assessing the condition, through the carbonyl and crystallinity indices. Full article

This work presents a high-speed hybrid communication system integrating Underwater Optical Wireless Communication (UOWC), Multimode Fiber (MMF), and Free-Space Optics (FSO) channels, leveraging Orbital Angular Momentum (OAM) beams for enhanced data transmission. A Photodetector, Remodulate, and Forward Relay (PRFR) is employed to enable wavelength conversion from 532 nm for UOWC to 1550 nm for MMF and FSO links. Four distinct OAM beams, each supporting a 5 Gbps data rate, are utilized to evaluate the system’s performance under two scenarios. The first scenario investigates the effects of absorption and scattering in five water types on underwater transmission range, while maintaining fixed MMF length and FSO link. The second scenario examines varying FSO propagation distances under different fog conditions, with a consistent underwater link length. Results demonstrate that water and atmospheric attenuation significantly impact transmission range and received optical power. The proposed hybrid system ensures reliable data transmission with a maximum overall transmission distance of 1125 m (comprising a 25 m UOWC link in Pure Sea (PS) water, a 100 m MMF span, and a 1000 m FSO range in clear weather) in the first scenario. In the second scenario, under Light Fog (LF) conditions, the system achieves a longer reach of up to 2020 m (20 m UOWC link + 100 m MMF span + 1900 m FSO range), maintaining a BER ≤ 10⁻⁴ and a Q-factor around 4. This hybrid design is well suited for applications such as oceanographic research, offshore monitoring, and the Internet of Underwater Things (IoUT), enabling efficient data transfer between underwater nodes and surface stations. Full article

Nanoporous material liquid systems (NMLSs) demonstrate promising potential for blast protection due to their high energy absorption density. This investigation numerically evaluated the use of NMLSs in mitigating blast effects on fiber–composite circular structures. The coupled Eulerian–Lagrangian method was employed to establish the numerical models of fiber alone, water–fiber, and NMLS–fiber, subjected to the internal close-field blast loading. The simulations focused on a widely studied NMLS, nanoporous silica particles immersed in distilled water. Four NMLSs, featuring varying particle-to-water ratios yet identical densities to that of water, were designed to modulate the energy absorption capacity while maintaining identical mass. These NMLSs were modeled by Equation of State (EOS) compaction. The dynamic responses of the fiber circles in the simulations were compared to evaluate the blast mitigation of different liquids. When the explosive mass was relatively small or medium, both the water and NMLSs exhibited blast mitigation. The NMLSs outperformed water because the energy absorption capacity caused a greater attenuation of blast pressure in the NMLSs. In the small-mass explosive cases, all four NMLSs could rapidly reduce the blast pressure to the infiltration pressure but their wave impedances decreased as the particle-to-water ratio increased, resulting in that a NMLS with greater energy absorption capacity, however, had inferior blast mitigation performance. When the explosive mass was relatively large, all the fiber circles experienced significant fiber failure and only the NMLS with the greatest energy absorption capacity exhibited blast mitigation. Full article

This study focuses on investigating the stability of modern and contemporary paints based on manganese violet pigment PV16 (NH₄MnP₂O₇) when exposed to atmospheric pollutants, specifically sulfur dioxide (SO₂) in the presence of high relative humidity. In particular, this study aims to investigate the role of PV16 in increasing the degradation processes of various modern binders. Therefore, the objectives of this research can be divided into (i) evaluating the chemical modifications involving PV16, (ii) investigating the degradation processes that occur in different organic matrices (i.e., drying oil, alkyd resin, and acrylic and styrene–acrylic emulsions), and (iii) comparing the chemical stability of model and commercial paints. The paints were analyzed by 3D Optical Microscopy, Attenuated total Reflection–Fourier-Transform Infrared spectroscopy (ATR-FTIR) and μ-Raman Spectroscopy, Scanning Electron Microscope coupled with Energy Dispersive X-Ray spectroscopy (SEM-EDX), X-Ray Powder Diffraction (XRPD), Fiber Optic Reflectance Spectroscopy (FORS), Pyrolysis–Gas Chromatography–Mass Spectrometry (Py-GC/MS), and Thermally assisted Hydrolysis and Methylation (THM) of Py-GC/MS (THM-Py-GC/MS). The results show that when exposed to high relative humidity and SO₂, PV16 presents a colorimetric change from violet to grey; several compounds crystallize on the surface; and, depending on the binder, various degradation reactions occur. This study highlights the susceptibility of manganese violet pigment PV16 under certain environmental conditions, which may be considered to define adequate conservation strategies for works of art containing this specific pigment. Additionally, the results obtained within this investigation point out the need to expand the chemical knowledge of this material for engineering, sensing, and industrial applications. Full article

The widespread use of electronic devices in daily life, industry and military has led to a large amount of electromagnetic pollution, which has become an increasingly serious security issue. To eliminate or mitigate such risks and hazards, various advanced microwave absorption technologies and materials have been reported. As a new type of microwave absorber, biomass-derived carbon-based materials have received extensive attention. They have the characteristics of low cost, easy preparation, high porosity and environmental friendliness while retaining the advantageous adjustable dielectric properties, high conductivity and good stability of traditional carbon materials. The development of biomass microwave-absorbing materials not only provides a new idea for solving electromagnetic radiation but also helps to create an environmentally friendly and harmonious environment. Herein, various biomass-derived carbon-based microwave-absorbing materials (MAMs) including plant shells, plant fibers and other potential biomass materials are generalized and discussed including their preparation technology, microstructure design and so on. The two critical factors affecting microwave absorption properties, impedance matching and attenuation characteristics, are analyzed in detail. Finally, the confronting challenges and future development prospects of biomass-based microwave-absorbing materials are pointed out. Full article

Cotton micronaire (MIC) is an essential fiber quality index that characterizes both fiber maturity and fineness components. This study compared how MIC affects the fiber high volume instrument (HVI) and advanced fiber information system (AFIS) qualities between Deltapine^® and PhytoGen upland varieties. There were noticeable differences among HVI and AFIS qualities from Deltapine^® fiber samples and PhytoGen samples, with significant differences om HVI strength and elongation. MIC development benefited fiber HVI strength enhancement and also HVI short fiber index (SFI), AFIS neps, AFIS short fiber contents, and AFIS immature fiber content (IFC) reduction, all of which were desired. Adversely, MIC evolution could cause undesired HVI Rd lowering, HVI +b boosting, and AFIS UQL(w), and a decrease in L5%(n) in fiber. Further, MIC values were not related with lint turnout, but they were positively and greatly correlated with algorithmic M_IR values of the attenuated total reflection in Fourier transform infrared (ATR FT-IR) spectra. The results demonstrated the applicability of the ATR FT-IR technique combined with the M_IR approach for rapid laboratory MIC assessment at early MIC testing in remote/breeding locations. Full article

SiO₂ aerogels have garnered significant attention for thermal insulation applications due to their exceptional hydrophobicity and thermal resistance. However, the organic functional groups enabling hydrophobicity introduce flammability concerns, limiting their safe implementation in high-temperature environments. This study presents a novel TiO₂ doping strategy (SA/TiO₂) that simultaneously enhances thermal safety while preserving the material’s intrinsic advantages. The optimized SA/TiO₂ composite demonstrates remarkable fire resistance, achieving a 44% reduction in gross calorific value (GCV) and a 25.4% decrease in total heat release (THR) compared to conventional aerogels. Thermogravimetric analysis reveals substantial thermal stability improvements, with TiO₂ incorporation elevating the initial and peak decomposition temperatures by 207 °C and 167 °C, respectively. When integrated into fiber-reinforced SiO₂ aerogel composites, the 10% TiO₂-doped formulation achieves an ultra-low GCV of 2.75 MJ/kg while maintaining superior insulation performance (~18 mW/m·K). Notably, the composite demonstrates exceptional high-temperature stability, retaining minimal thermal conductivity of 25.5 mW/m·K at 600 °C. The titanium dioxide phase effectively attenuates thermal radiation transmission while preserving the matrix’s nanoporous architecture, thereby synergistically enhancing both fire safety and thermal insulation capabilities in demanding operational environments. Full article

Beta attenuation monitors (BAMs) are widely used for the regulatory monitoring of fine particulate matter (PM_2.5) and fence line monitoring of industrial sites. The elemental analysis of BAM filter tapes potentially could enable additional source PM_2.5 attribution. However, the chemical characterization of the glass fiber filters is hindered by high background metal values. A sample preparation method was developed using the ultrasonic extraction of particulate matter from BAM filter spots in nitric acid and the analysis of metals by inductively coupled plasma–mass spectrometry (ICP-MS) and scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM-EDS). To demonstrate the utility of this method, BAM filter spots were analyzed from wildfire smoke periods in the San Francisco Bay Area in California in Fall 2023 and indicated elevated levels of chromium compared to a non-wildfire period in Spring 2023. The SEM-EDS of the BAM tape was used to probe individual particulate morphology, but it only detected Fe and Ba at levels above the blank media. The ultrasonic extraction method of BAM filter spots could be used in future wildfire smoke events to extend the characterization of beta attenuation monitor filters in PM_2.5 monitoring. Full article

Metabolic dysfunction and hepatic abnormalities, such as those associated with high-fat, high-fructose (HFHFr) diets, are major contributors to obesity-related health issues. The growing interest in sustainable dietary interventions has highlighted the potential of plant-based byproducts. Dragon fruit (Hylocereus undatus) peel waste, rich in bioactive compounds such as dietary fibers, phenolics, and betacyanins, represents a promising functional ingredient for managing these disorders. This study investigated the effects of dragon fruit peel powder (DFP) on metabolic dysfunction and hepatic abnormalities induced by a HFHFr diet in rats. Over 12 weeks, the rats were fed a standard AIN-93M diet (control or C), C with 5% (w/w) DFP (C + DFP), a HFHFr diet, or a HFHFr diet with 5% (w/w) DFP (HFHFr + DFP). DFP supplementation significantly reduced HFHFr-induced body weight gain, visceral adiposity, insulin resistance, and dyslipidemia while also lowering systolic blood pressure and systemic oxidative stress markers. In the liver, DFP supplementation attenuated fat accumulation and lipid peroxidation, reduced glycogen storage abnormalities, and modulated the expression of lipid metabolism and inflammatory genes. These findings suggest that DFP may serve as a functional dietary supplement for preventing and managing metabolic disorders and liver abnormalities associated with excessive fat and fructose consumption. Full article