Search Results (226)

Background. Physicomechanical properties and clinical service of bulk-fill composites depend on their adequate polymerization and depth of cure. Some manufacturers claim that these composites can be adequately cured when used in bulks exceeding 4 mm. Objective. The aim of this study was to compare Vickers microhardness (VMH) and depth of cure (DOC) of six contemporary bulk-fill resin composites at depths of 4 mm and 6 mm. Material and methods. Six bulk-fill composites were evaluated in this study: 1. Tetric EvoCeram Bulk (Ivoclar Vivadent, Schaan, Liechtenstein), (TEC); 2. Filtek Bulk Fill Posterior (3M ESPE Dental Products Division, St. Paul, MN, USA), (FBF); 3. Filtek One Bulk Fill (3M ESPE Dental Products Division, St. Paul, MN, USA, (FOB); 4. SonicFill 2 (Kerr, Orange, CA, USA), (SF2); 5. Admira Fusion X-tra (Voco, GmbH, Cuxhaven, Germany), (AFX); 6. GrandioSO X-tra (Voco, GmbH, Cuxhaven, Germany), (GSX). The 18 specimens (3 of each composite) were prepared in split Teflon moulds of 4 mm diameter and 6 mm thickness. All composites were cured in standard mode for 20 s using LED LCU (D-Light Duo, RF-Pharmaceuticals Sarl, Geneva, Switzerland; 1200–1300 mW/cm). The VMH was measured using a digital Micro Hardness Tester Shimadzu (HMV-2T E, Shimadzu Corporation, Kyoto, Japan). A 50 g (0.5 N) load force was applied for 30 s. Each specimen was measured at five places selected by chance at each level (N = 15). The hardness ratio or DOC was calculated for all samples as the ratio of bottom and surface microhardness at levels of 4 and 6 mm. Data were analysed using one-way ANOVA and Tukey’s post hoc test. Results. Significant reduction in VMH was observed for all tested materials when comparing top surface and bottom (p < 0.01). The highest VMH was obtained for GSX and AFX, and the lowest for TEC. The results show that the degree of polymerization was adequate for all tested materials at a depth of 6 mm, since the hardness ratio exceeded 0.80 in all cases. The hardness ratio at 4 mm was high for all tested composites ranging from 0.91 for TEC to 0.98 for GSX. All composites showed adequate DOC at the bottom of the 6 mm bulk samples. However, the hardness ratio was the highest for Admira Fusion X-tra (0.96) and GrandioSO X-tra (0.97). Conclusions. All tested materials showed a significant decrease in microhardness from the top surface to the bottom. The DOC was adequate for all bulk-fill composites at a depth of 6 mm cured under standard mode for 20 s. All bulk-fill resin composites evaluated in this study can be used in bulk, up to 6 mm. Full article

Palladium (Pd) and titanium (Ti) exhibit opposite dielectric responses upon hydrogenation, with stronger effects observed in the near-infrared (NIR) region. Leveraging this contrast, we investigated Ti/Pd bilayer thin films as a platform for NIR hydrogen sensing—particularly at telecommunication-relevant wavelengths, where such devices have remained largely unexplored. Ti/Pd bilayers coated with Teflon AF (TAF) and fabricated via sequential electron-beam and thermal evaporation were characterized using optical transmission measurements under repeated hydrogenation cycles. The Ti (5 nm)/Pd (x = 2.5 nm)/TAF (30 nm) architecture showed a 2.7-fold enhancement in the hydrogen-induced optical contrast at 1550 nm compared to Pd/TAF reference films, attributed to the hydrogen ion exchange between the Ti and Pd layers. The optimized structure, with a Pd thickness of x = 1.9 nm, exhibited hysteresis-free sensing behavior, a rapid response time (${\mathrm{t}}_{90}$ < 0.35 s at 4% ${\mathrm{H}}_2$), and a detection limit below 10 ppm. It also demonstrated excellent selectivity with negligible cross-sensitivity to $\mathrm{C}{\mathrm{O}}_2$, $\mathrm{C}{\mathrm{H}}_4$, and CO, as well as high durability, showing less than 6% signal degradation over 135 hydrogenation cycles. These findings establish a scalable, room-temperature NIR hydrogen sensing platform with strong potential for deployment in automotive, environmental, and industrial applications. Full article

This paper concerns the assessment of the lunar regolith ability to consolidate in the presence of liquid water and develop and sustain cohesion after drying. This type of cohesion originates from interparticle adhesion and can be potentially improved through grading modification. The research was conducted using the lunar regolith simulant (EAC-1A) reproducing the PSD of real lunar soil delivered from the Moon. LRS was subjected to water and elevated temperature (equal to the highest temperature on the Moon) to produce specimens of consolidated material, CCR (Capillary-Consolidated Regolith) and to test flexural strength. In order to adapt to potentially small stresses, tests were performed according to the modified EN 196-1 procedure intended for Portland cement testing: specimens scaled to 20 mm × 20 mm × 80 mm (new molds with Polytetrafluoroethylene/Teflon^® coatings reducing adhesion were created), supports spacing in the three-point flexural test reduced to 50 mm and apparatus adjusted to precisely apply small loads. CCR developed flexural strength exceeding 0.025 MPa. Then, analogous tests were performed using LRS subjected to grinding in a disc mill prior to consolidation. It was shown that simple mechanical grinding enabled the improvement of interparticle adhesion with capillary forces, resulting in improved flexural strength of the consolidated material (0.123 MPa). Full article

The dependence of polyethylene deformation on applied mechanical stress under varying load conditions and radiation doses was investigated experimentally. Obtained results reveal significant alterations in the mechanical properties of polyethylene following irradiation with krypton ions at doses of 1.5 × 10⁶, 1.6 × 10⁷, 5.0 × 10⁸, and 1.0 × 10⁹ ions/s. The stress–strain curves obtained for both the unirradiated and irradiated samples are numerically modeled using frameworks developed by the authors. The findings indicate that irradiation with krypton ions at an energy level of 147 MeV exerts a pronounced impact on the deformation and strength characteristics of polyethylene. Notably, increasing the radiation dose to 10⁹ particles/s results in a 2.5-fold increase in the rate of mechanical stress. Furthermore, the degree of deformation distortions in molecular chains induced by high-energy Kr¹⁵⁺ ion irradiation has been quantified as a function of irradiation fluence. Increasing the irradiation fluence from 10⁶ ion/cm² to 10⁷ ion/cm² causes only minor variations in deformation distortions, which are attributed to the localized isolation of latent tracks and associated changes in electron density. A comparative analysis of the mechanical behavior of irradiated polymer materials further revealed differences between ion and electron irradiation effects. It was observed that Teflon films lose their plasticity after irradiation, whereas polyethylene films exhibit enhanced elongation and tearing performance at higher strain values relative to their non-irradiated counterparts. This behavior was consistently observed for films irradiated with both ions and electrons. However, an important distinction was identified: high-energy electron irradiation degrades the strength of polyethylene, whereas krypton ion irradiation at 147 MeV does not result in strength reduction. Full article

Biodegradable films are a viable alternative to conventional plastics, thereby contributing to environmental pollution reduction. This study investigates the impact of substrate type on the properties of starch-based films produced using a plasticizer-assisted casting method. Four different substrates, namely, glass, copper, copper-free laminate, and Teflon^®, were evaluated, addressing a research gap in which previous studies primarily focused on film composition. The films were analyzed for color, tensile strength, surface free energy, and surface morphology using optical and electron microscopy. The results demonstrated a substrate-dependent impact on surface properties, particularly optical transparency, surface roughness, and adhesion. The films cast on glass and laminate exhibited higher transparency and lower roughness, while copper substrate induced micro-striations and strong adhesion. Teflon^® substrates replicated surface imperfections, which may be advantageous for optical applications, but caused film delamination. Tensile strength did not show statistically significant differences across substrates, although reduced elongation was observed for the films cast on Teflon^®. Water vapor permeability was also not significantly affected, indicating a dominant role of bulk material properties. It averaged 25 kg per day per square meter, which means high vapor permeability. Surface free energy analysis revealed marked variations between top and bottom layers, with values ranging from 35 to 70 mJ·m⁻² depending on the substrate. These findings confirm that the type of casting substrate plays a critical role in determining the surface and optical properties of starch-based films, even at the laboratory scale. This study provides new insights into substrate–film interactions and establishes a foundation for optimizing biodegradable film fabrication for industrial and application-specific needs. Full article

This article presents a novel microstrip patch sensor featuring four rectangular rings represented by single complementary split-ring resonance (SC-SRR) to calculate the complex permittivity of saline solutions within the range of 0 ppt to 100 ppt. This sensor operates via the turbulence technique, utilizing its resonant properties as indicators to find the parameters of the liquid under test (LUT), which arise due to the variations in the salt concentration altering the complex permittivity. This alteration influences the resonant frequency (f_r), reflection coefficient (S₁₁), and quality factor (Q). The sensor was designed by using a high-frequency structure simulator (HFSS) and by using an FR-4 substrate and a Teflon box with a height of 1.4 mm and 13.7 mm, respectively. The values of S₁₁ at resonance frequency were −34.48 dB, and 2.1328 GHz, respectively. A computer numerical control (CNC) machine was used to fabricate the sensor and Teflon box, and the Teflon box was situated above the four rings to create a strong interaction between the induced electric field and the LUT, thereby achieving high sensitivity in a non-contacting and non-destructive manner. The measurement and simulation results were consistent and aligned with those of Klien and Meissner (in comparison to the theoretical values derived from the single and double Debye models). We derived numerical equations for the conductivity (S/m), dielectric constant permittivity, and concentrations (ppt) using curve fitting origin software, and the results are in good agreement. Due to its performance, we expect that the proposed sensor could be used in agricultural applications to identify freshwater and in medical applications to detect the concentration of salt in saliva or blood and to identify diseases, in addition to many other applications involving mixed liquids. Full article

This paper presents the development and analysis of a bridge bearing database consistent with the 2020 Italian Guidelines (LG2020), currently enforced by the Italian law for risk classification and management of existing bridges. The database was developed by putting together the contribution of 24 research teams from 18 Italian universities in the framework of a research project foreseen by the agreement between the High Council of Public Works (CSLP, part of the Italian Ministry of Transportation) and the research consortium ReLUIS (Network of Italian Earthquake and Structural Engineering University Laboratories). This research project aimed to apply LG2020 to a set of about 600 bridges distributed across the Italian country, in order to find possible issues and propose modifications and integrations. The database includes almost 12,000 bearing defect forms related to a portfolio of 255 existing bridges located across the entire country. This paper reports a preliminary analysis of the dataset to provide an overview of the bearings installed in a significant bridge portfolio, referring to major highways and state roads. After a brief state of the art about the main bearing types installed on the bridges, along with inspection procedures, the paper describes the database structure, showing preliminary analyses related to bearing types and defects. The results show the prevalence of elastomeric pads, representing more than 55% of the inspected bearings. The remaining bearings are pot, low-friction with steel–Teflon surfaces and older-type steel devices. Lastly, the study provides information about typical defects for each type of bearing, while also underscoring some issues related to the current version of the LG2020 bearing inspection form. Full article

The aim of this in vitro study is to evaluate the effect of resin type and placement technique on the hardness of resin-based composites (RBCs). A total of 300 samples consisting of five RBCs (Filtek Z250 microhybrid, Filtek P60 packable, Tetric Ceram hybrid, Admira ORMOCER, and Tetric Flow flowable RBCs) were prepared. Each RBC was placed into Teflon molds with a 4 mm diameter and 2 or 8 mm depths with standard, bulk and incremental techniques and was polymerized by second-generation LED (Hilux Ledmax 1055, 229.153 mW/cm²) and UV (ELC-410, 26.106 mW/cm²) light-curing units (LCUs) in standard mode (n = 10). The Vickers hardness number (VHN) was measured from the top and bottom surfaces of the RBCs. Data were statistically analyzed with a one-way ANOVA. Multiple comparisons were made using the Tukey, Scheffe, and t-tests (p < 0.05). The VHN of the RBCs polymerized with LED and UV LCUs varied between 110.33 and 25.16 and between 104.86 and 34.20, respectively. The Tetric Flow RBC did not polymerize with the LCUs on either surface. The RBCs placed using the bulk technique could not polymerize with the UV LCU on the top surface, except for the Filtek P60 RBC, but showed a higher VHN on the bottom surface. These significant findings highlight that the hardness is specific to the RBC material and placement technique. Full article

Ice accretion is a significant drawback in an aircraft’s and wind turbine’s aerodynamic performance in cold climate weather. Plasma actuators are an attractive technology for ice removal; however, dielectric barriers are typically restricted to borosilicate glass and various polymers, such as Teflon^® and Kapton^®. Nevertheless, new materials capable of withstanding prolonged exposure to charged particles are needed. In this work, Y₂O₃-ZrO₂, MgO-CaZrO₃, and MgO-Al₂O₃ ceramic samples were manufactured and their thermal properties as DBD plasma actuators were measured. As foreseen, the results showed that the higher the power consumed, the higher the temperature surface of the plasma actuators. The Y₂O₃-ZrO₂ dielectric showed the highest power consumption and ceiling temperatures (20.7 W and 155 °C at 10 kVpp, respectively), followed by MgO-CaZrO₃ (9.6 W and 62 °C at 10 kVpp, respectively) and by MgO-Al₂O₃ (5.6 W and 47 °C at 10 kVpp, respectively). It was concluded that MgO-Al₂O₃ presented stable magnitudes across the entire dielectric area, whilst Y₂O₃-ZrO₂ showed a more concentrated temperature field. Therefore, considering that about 65 to 95% of the total power supplied to the DBD plasma actuator is dissipated as heat, it becomes natural to propose ceramic-based DBD plasma actuators as de-/anti-icing means for aero-dynamic structures. Full article

Yttria-Stabilized Zirconia (YSZ) is an important material in thermal barrier coatings (TBCs), which are widely applied in aviation engines and ground gas turbines. Therefore, the quality inspection of the YSZ layer is of great significance for the safety of engines and gas turbines. In this work, the YSZ powder is mixed with Polytetrafluoroethylene (also known as teflon) in different mass ratios and pressed into tablets with different thicknesses. A terahertz time-domain spectroscopy system is used to obtain their time-domain spectra, and their frequency spectra are then obtained by fast Fourier transform. Based on theory formulas, we obtained the frequency-dependent curves of the absorption coefficient, refractive index, and absorbance of the YSZ tablets. The results show that the YSZ tablets have characteristic absorption peaks in the terahertz band, and these peaks are affected by the mass ratio of YSZ to teflon and the thickness of the tablets. Finally, we conducted a terahertz Raman spectroscopy test of the YSZ tablets for the first time. The results show that in the range from 0 to 1600 cm⁻¹, there are about ten strong Raman peaks. More importantly, these peaks are approximately independent of the mass ratio and the thickness of tablets. This study is of great significance for the nondestructive testing of TBC quality using terahertz spectroscopy technology. Full article

This in vitro study investigates the impact of the chemical modification of resin composite surfaces on repair bond strength of micro-hybrid resin composite material. First, 7 mm circular × 3 mm thick resin composite disks were prepared using teflon molds. Then, 50 specimens out of 100 were allocated for stimulated aging using a thermo-cycling (10,000 cycles) device. Both the 24 h and 1-year-aged composite discs were embedded in epoxy resin using a 2.5 cm wide × 1.5 cm thick circular mold. The surfaces were treated with Clearfil S3 bond alone or with the additional application of silane or porcelain primer. The other two groups were bonded with CRB bond with or without a porcelain primer. Using a teflon mold, a 2 mm circular and 3 mm high repair composite cylinder was built on the treated surfaces. The specimens were then stressed to de-bond by applying shear force to measure repair bond strength, and they were observed under the microscope to determine the failure pattern. The data were analyzed using SPSS26.0. Univariate analysis showed a significant effect (p = 0.013) of the bonding protocol on the repair bond strength; however, the effect of aging was insignificant (p = 0.170). The S3 bond with additional silane and the CRB bond showed the significantly higher repair bond strength of the 1-year-aged micro-hybrid composite. However, in case of 24 h aged specimens, the repair bond strength was statistically insignificant among the tested groups (p = 0.340). Chemical surface modification with silane has the potential to improve the repair bond strength of micro-hybrid resin composite materials. Full article

CuMn_1−xMg_xO₂ (x = 0–0.06) polycrystalline samples were prepared using the hydrothermal method at T = 100 °C for 24 h in Teflon-line stainless steel autoclaves. The samples were crystallized, forming crednerite structures (C2/m space group), and the Mg²⁺ substitution onto the Mn³⁺ site induced small changes in the unit cell parameters and volume. Based on complex impedance measurements made between 20 Hz and 2 MHz, at different concentrations of Mg ions (x), the electrical conductivity (σ), the electric modulus (M), and the complex dielectric permittivity (ε) were determined. The conductivity spectrum, σ(f, x), follows the Jonscher universal law and enables the determination of the static conductivity (σ_DC) of the samples. The results showed that, when increasing the concentration x from 0 to 6%, σ_DC varied from 15.36 × 10⁻⁵ S/m to 16.42 × 10⁻⁵ S/m, with a minimum of 4.85 × 10⁻⁵ S/m found at a concentration of x = 4%. Using variable range hopping (VRH) and correlated barrier hopping (CBH) theoretical models, the electrical mechanism in the samples was explained. The band gap energy (W_m), charge carrier mobility (μ), number density (N_C) of effective charge carriers, and hopping frequency (ω_h) were evaluated at different concentrations (x) of substitution with Mg. In addition, using measurements of the temperature dependence of σ_DC(T) between 300 and 400 K, the thermal activation energy (E_A) of the samples was evaluated. Additionally, the dielectric behavior of the samples was explained by the interfacial relaxation process. This knowledge of the electrical properties of the CuMn_1−xMgxO₂ (x = 0–0.06) polycrystalline crednerite is of interest for their use in photocatalytic, electronic, or other applications. Full article

Terahertz (THz) is an emerging technology particularly well suited for the non-destructive investigation of inner structures in polymers. To realize its full potential, THz imaging systems adapted to industrial constraints as well as more application studies in areas of interest are needed. In this work, we present a fast and flexible THz imaging system comprising hardware and software and demonstrate its capabilities for the investigation of defects in glass fiber-reinforced polymers (GFRPs), particularly for the detection of drilling-induced delaminations. Measurement data obtained by raster scanning of GFRP samples are gathered in 3D volumetric images. THz images of the drilled holes are then compared to reference images of the same holes obtained from X-ray computed tomography measurements. We show that THz imaging is capable of identifying not only artificial defects in the form of aluminum and Teflon inlays, but also real defects such as delaminations generated by drilling operations, and is suitable for non-destructive testing in industrial conditions. Full article

The degree of conversion (DC) is crucial in determining the mechanical and clinical performance of resin-based composites (RBCs). This in vitro study aimed to evaluate the effect of the resin type and placement technique on the DC of RBCs (micro-hybrid, packable, hybrid, ormocer-based and flowable) polymerized with a second-generation LED light-curing unit (LCU). A total of 75 RBC samples were divided into three groups. Each RBC was placed into 4 mm diameter and 2 and 8 mm heigh Teflon molds with conventional standard, bulk, and incremental techniques (n = 5) and polymerized by LED LCU (229.153 mW/cm²) using the standard mode. After 24 h, DC was determined by FTIR spectrophotometry. The data were analyzed with two-way ANOVA and Tukey’s HSD test (p < 0.05). The DC of the RBCs varied between 62.8 and 29.2%. While the same DC was obtained for 2 mm samples at the top and the bottom surfaces, the DC of the 8 mm samples gradually diminished from the top surface to the bottom surface. Significant differences were observed in the DC of the RBCs. An optimal DC was obtained for packable, micro-hybrid and ormocer-based RBCs polymerized by LED LCU with the recommended curing times. Considering that the polymerization process is versatile, further in vitro studies are needed. Full article

Fourier transform infrared spectroscopy (FT-IR) is a vibrational technique largely adopted for the study of bacterial biofilms. FT-IR is a non-destructive method allowing multiple analyses of the same biofilm. Pseudomonas aeruginosa represents a class of bacteria largely investigated since it is an opportunistic pathogen, and it is now considered a primary infectious agent, especially for its ability to form multi-resistant biofilms. In the present investigation, we aimed to characterize P. aeruginosa biofilms grown on different substrates to better define the experimental conditions more useful for investigating the interaction of these biofilms with external agents. In particular, we investigated biofilms grown on Teflon membranes, CaF₂ windows, and MirrIR slides (specific reflection FT-IR spectroscopy microscope slides). Different geometries were used for collecting spectra using the microscope stage of a Perkin Elmer Spectrum One spectrometer and a Universal Attenuated Total Reflection (UATR) device. Multiple acquisitions of spectra were conducted, and statistical criteria were applied for monitoring and comparing them. The positive and negative aspects of the different examined substrates for biofilm formation and acquisition modes are presented and discussed. Full article