Search Results (252)

Plastic pollution from polyethylene-based materials is a critical environmental concern due to their high persistence. Here, we report the first proof-of-concept application of a multitechnique analytical framework for quantifying linear low-density polyethylene (LLDPE) in Tenebrio molitor frass. Artificially enriched frass–LLDPE mixtures were analyzed using thermogravimetric analysis (TGA), TGA coupled with Fourier-Transform Infrared Spectroscopy (FTIR) and Mass Spectrometry (MS), TGA under inert atmosphere, and solid-state ¹³C nuclear magnetic resonance spectroscopy with Cross-Polarization and Magic Angle Spinning (CP-MAS NMR) ¹³C CP-MAS NMR combined with interval Partial Least Squares (iPLS) modeling. Thermal methods provided insight into decomposition pathways but showed reduced specificity at <1% w/w due to matrix interference. CP-MAS NMR offered matrix-independent quantification, with characteristic signals in the 10–45 ppm region and a calculated LOD and LOQ of 0.173% and 0.525% w/w, respectively. The LOQ lies within the reported ingestion range for T. molitor (0.8–3.2% w/w in frass), confirming biological relevance. This validated workflow establishes CP-MAS NMR as the most robust tool for quantifying polyethylene residues in complex matrices and provides a foundation for in vivo biodegradation studies and environmental monitoring. Full article

The study investigates the interaction of humic acids (HAs) with road petroleum bitumen to enhance its performance and resistance to technological aging. It addresses a critical gap in understanding the modification mechanisms. The research is motivated by the need for sustainable and effective bitumen modifiers to improve the durability of asphalt pavements. The primary objective was to characterize the interaction between HA and bitumen using advanced analytical techniques, including complex thermal analysis (DTA/DTG), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The results demonstrated that adding two wt.% HA to bitumen BND 70/100 increased its thermal stability, raising the onset temperature of thermo-oxidative processes from 214 to 237 °C and reducing the mass loss rate during heating from 2.5 to 1.9%·min⁻¹. FTIR analysis revealed chemical interactions between polar groups of humic acids (e.g., –COOH, –OH) and bitumen components, forming a denser structure. SEM images confirmed a more homogeneous microstructure with fewer microcracks in the modified bitumen. Practical improvements included a higher softening point (52.6 to 54 °C) and enhanced elastic recovery (17.5 to 28.7%). However, the study noted limitations such as reduced ductility (from 58 to 15 cm) and penetration (from 78 to 72 dmm), indicating increased stiffness. The findings highlight the potential of humic acids as eco-friendly modifiers to improve bitumen’s aging resistance and thermal performance, offering practical value for extending pavement lifespan. The effective use of HA will, in turn, allow the use of Ukrainian lignite, the balance reserves of which are estimated at 2.0–2.9 billion tons, in non-fuel technologies. Full article

This study aims to investigate the influences of strain rates on tensile and shear performances of carbon fiber-reinforced polypropylene (CF/PP) and glass fiber-reinforced polypropylene (GF/PP) thermoplastics. First, the differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests were conducted on the polypropylene to determine its melting and decomposition temperatures, identified as approximately 166 °C and 450 °C, respectively. Subsequently, CF/PP and GF/PP specimens were fabricated through the thermo-compression molding process, and subjected to the uniaxial tension and bias extension tests across six strain rates (1.7 × 10⁻⁶ s⁻¹, 0.5 s⁻¹, 5 s⁻¹, 50 s⁻¹, 250 s⁻¹, and 500 s⁻¹). The results indicated that the tensile modulus/strength and shear modulus/strength of both CF/PP and GF/PP specimens improved with the increase in strain rates, whereas the shear failure strain exhibited a decreasing trend due to the transition of polypropylene from ductile to brittle behaviors. At 500 s⁻¹, CF/PP exhibited 53.08%/53.6% and 52.5%/52.4% increases in tensile/shear modulus and tensile/shear strength compared to 1.7 × 10⁻⁶ s⁻¹, while GF/PP showed 54.6%/113.4% and 71.5%/92.3% improvements, respectively. Furthermore, fracture surfaces exhibited progressive roughening with increasing strain rates. The dynamic increase factor ($DIF$) quantitatively characterized the strain rate dependencies of elastic and strength properties, establishing an analytical model for developing rate-dependent constitutive models in future research. Full article

In this study, the impact resistance of WUF-B steel frame beam–column joints under fire was investigated using ABAQUS finite element software through a sequential thermal–mechanical coupling approach. By integrating a room-temperature impact model with a single-sided fire field applied to the lower flange of the steel beam, the multi-parameter influence mechanisms—including temperature (150–750 °C), fire area distribution, and impact momentum—were systematically analyzed. Results indicate that elevated temperatures significantly degrade structural impact resistance. At 750 °C, the peak impact force decreases by 73.3% compared to room temperature, while the mid-span bending moment increases by 63.3%. When the fire zone is near the impact point, localized thermal softening further reduces the peak impact force. Under constant impact energy, lower momentum (i.e., higher velocity) accelerates the rebound of the falling mass, revealing the role of momentum transfer efficiency in governing the transient response of high-temperature structures. Additionally, an analytical prediction model based on Timoshenko beam theory and thermo-mechanical stiffness degradation is developed. By introducing a segmented temperature reduction function, the model significantly enhances the accuracy of mid-span displacement predictions for steel structures under fire. Full article

Protaetia brevitarsis seulensis (Kolbe, 1886) larvae have traditionally been used in East Asian medicine and have recently attracted attention as functional food ingredients because of their pharmacological potential. However, chemical investigations remain limited, and no marker compounds have been established for quality control. This study aimed to isolate and identify a primary constituent from the 70% ethanol extract of P. brevitarsis (PBE) and to develop an analytical method for its quantification. Among the solvent-partitioned fractions, the n-butanol fraction (PBE-B) exhibited a major peak in HPLC analysis. The compound was purified through a combination of vacuum liquid chromatography (VLC), medium-pressure liquid chromatography (MPLC), and recycling preparative HPLC. Its structure was identified as L-tryptophan based on HR-ESI-MS and NMR spectroscopy. Quantitative analysis was conducted using HPLC-DAD under optimized analytical conditions, employing a Thermo Scientific™ Acclaim™ Polar Advantage II column and an acidified mobile phase (0.1% formic acid in water and methanol) to improve resolution. The method demonstrated excellent linearity (r² > 0.9999), and the L-tryptophan content in PBE was determined to be 1.93 ± 0.05 μg/mg. The analyte was well separated with minimal interference, supporting the reproducibility of the method. These results indicate that L-tryptophan is a promising candidate Q-marker for the quality control of P. brevitarsis extracts. Full article

Thermal stimulation represents an effective method for enhancing reservoir permeability, thereby improving geothermal energy recovery in Enhanced Geothermal Systems (EGS). The phase-field method (PFM) has been widely adopted for its proven capability in modeling the fracture behavior of brittle solids. Consequently, a coupled thermo-mechanical phase-field model (TM-PFM) was developed in COMSOL 6.2 Multiphysics to probe thermal fracturing mechanisms in reservoir rocks. The TM-PFM was validated against the analytical solutions for the temperature and stress fields under steady-state heat conduction in a thin-walled cylinder, three-point bending tests, and thermal shock tests. Subsequently, two distinct thermal fracturing modes in reservoir rock under high-temperature conditions were investigated: (i) fracture initiation driven by sharp temperature gradients during instantaneous thermal shocks, and (ii) crack propagation resulting from heterogeneous thermal expansion of constituent minerals. The proposed TM-PFM has been validated through systematic comparison between the simulation results and the corresponding experimental data, thereby demonstrating its capability to accurately simulate thermal fracturing. These findings provide mechanistic insights for optimizing geothermal energy extraction in EGS. Full article

This paper presents a theoretical model of a thin, penny-shaped piezoelectric actuator bonded to an isotropic thermo-elastic substrate under coupled electrical-thermal-diffusive loading. The problem is assumed to be axisymmetric, and the peeling stress of the film is neglected in accordance with membrane theory, yielding a simplified equilibrium equation for the piezoelectric film. By employing potential theory and the Hankel transform technique, the surface strain of the substrate is analytically derived. Under the assumption of perfect bonding, a governing integral equation is established in terms of interfacial shear stress. The solution to this integral equation is obtained numerically using orthotropic Chebyshev polynomials. The derived results include the interfacial shear stress, stress intensity factors, as well as the radial and hoop stresses within the system. Finite element analysis is conducted to validate the theoretical predictions. Furthermore, parametric studies elucidate the influence of material mismatch and actuator geometry on the mechanical response. The findings demonstrate that, the performance of the piezoelectric actuator can be optimized through judicious control of the applied electrical-thermal-diffusive loads and careful selection of material and geometric parameters. This work provides valuable insights for the design and optimization of piezoelectric actuator structures in practical engineering applications. Full article

This study introduces an analytical framework that integrates the state-space method with generalized thermoelasticity theory to obtain exact solutions for the static and dynamic behaviors of laminated plates featuring imperfect interfaces and resting on a Winkler foundation. The model comprehensively accounts for the foundation-structure interaction, interfacial imperfection, and the coupling between the thermal and mechanical fields. A parametric analysis explores the impact of the dimensionless foundation coefficient, interface flexibility coefficient, and thermal conductivity on the static and dynamic behaviors of the laminated plates. The results indicate that a lower foundation stiffness results in higher sensitivity of structural deformation with respect to the foundation parameter. Furthermore, an increase in interfacial flexibility significantly reduces the global stiffness and induces discontinuities in the distribution of stress and temperature. Additionally, thermal conductivity governs the continuity of interfacial heat flux, while thermo-mechanical coupling amplifies the variations in specific field variables. The findings offer valuable insights into the design and reliability evaluation of composite structures operating in thermally coupled environments. Full article

Monitoring the peak junction hotspot temperature in IGBT modules is critical for ensuring the reliability of high-power industrial multilevel inverters, particularly when operating under extreme thermal conditions, such as in traction applications. This study presents a comprehensive chip-level analytical loss and thermal model for estimation of the peak junction hotspot temperature in a three-level T-type neutral-point-clamped (TNPC) IGBT module. The developed model includes a detailed analytical assessment of conduction and switching losses, along with transient thermal network modeling, based on the actual electrical and thermal characteristics of the IGBT module. Additionally, a hybrid thermal–electrical stress experimental setup, designed to replicate real operating conditions, was implemented for a balanced three-phase inverter circuit utilizing a Semikron three-level IGBT module, with testing currents reaching 100 A and a critical case temperature of 125 °C. The analytically estimated module losses and peak junction hotspot temperatures were validated through direct experimental measurements. Furthermore, thermal simulations were conducted with Semikron’s SemiSel benchmark tool to cross-validate the accuracy of the thermo-electrical model. The outcomes show a relative estimation error of less than 1% when compared to experimental data and approximately 1.15% for the analytical model. These findings confirm the model’s accuracy and enhance the reliability evaluation of TNPC-IGBT modules in extreme thermal environments. Full article

Mass spectrometry (MS) and coupled gas chromatography-mass spectrometry (GC-MS) are globally recognized as the primary techniques for the analysis of gases or vapors due to their selectivity, sensitivity, accuracy, and reproducibility. When thermal stress is applied, vapors or gases are released as a result of the reactions and changes that occur. The analysis of these gases during the thermally induced reaction is scientifically referred to as evolved gas analysis (EGA), which is essential for confirming the occurrence of the induced reactions. Pyrolyzers, thermobalances, or simple heaters can increase the temperature of the analyzed samples according to a programmed and software-managed ramp, allowing for control over both the heating rate and isothermal stages. The atmosphere can also be varied to simulate pyrolysis or thermo-oxidative processes. This way, each induced reaction generates a unique evolved gas, which can be linked to a theoretically hypothesized mechanism. Mass spectrometry (MS) and coupled gas chromatography–mass spectrometry (GC-MS) are fundamental analytical methods used for on-line thermally induced evolved gas analysis (OLTI-EGA). Full article

To investigate the slope instability caused by differential frost heaving mechanisms from the slope crest to the toe during frost heave processes, this study takes a typical silty clay slope in Xinjiang, China, as the research object. Through indoor triaxial consolidated undrained shear tests, eight sets of natural and frost-heaved specimens were prepared under confining pressure conditions ranging from 100 to 400 kPa. The geotechnical parameters of the soil in both natural and frost-heaved states were obtained, and a spatiotemporal thermo-hydro-mechanical coupled numerical model was established to reveal the dynamic evolution law of anchor rod axial forces and the frost heave response mechanism between the frame and slope soil. The analytical results indicate that (1) the frost heave process is influenced by slope boundaries, resulting in distinct spatial variations in the temperature field response across the slope surface—namely pronounced responses at the crest and toe but a weaker response in the mid-slope. (2) Under the coupled drive of the water potential gradient and gravitational potential gradient, the ice content in the toe area increases significantly, and the horizontal frost heave force exhibits exponential growth, reaching its peak value of 92 kPa at the toe in February. (3) During soil freezing, the reverse stress field generated by soil arching shows consistent temporal variation trends with the temperature field. Along the height of the soil arch, the intensity of the reverse frost heave force field displays a nonlinear distribution characteristic of initial strengthening followed by attenuation. (4) By analyzing the changes in anchor rod axial forces during frost heaving, it was found that axial forces during the frost heave period are approximately 1.3 times those under natural conditions, confirming the frost heave period as the most critical condition for frame anchor design. Furthermore, through comparative analysis with 12 months of on-site anchor rod axial force monitoring data, the reliability and accuracy of the numerical simulation model were validated. These research outcomes provide a theoretical basis for the design of frame anchor support systems in seasonally frozen regions. Full article

Underground production and injection operations result in mechanical compaction and mineral chemical reactions that alter porosity and permeability. These changes impact the flow and, eventually, the long-term sustainability of reservoirs utilized for CO₂ sequestration and geothermal energy. Even though mechanical and chemical deformations in rocks take place at the pore scale, it is important to investigate their impact at the continuum scale. Rock deformation can be examined using intergranular pressure solution (IPS) models, primarily for uniaxial compaction. Because the reaction rate parameters are estimated using empirical methods and the assumption of constant mineral saturation indices, these models frequently overestimate the rates of compaction and strain by several orders of magnitude. This study presents a new THMC algorithm by combining thermo-mechanical computation with a fractal approach and hydrochemical computations using PHREEQC to evaluate the pressure solution. Thermal stress and strain under axisymmetric conditions are calculated analytically by combining a derived hollow circle mechanical structure with a thermal resistance model. Based on the pore scale, porosity and its impact on the overall excessive stress and strain rate in a domain are estimated by applying the fractal scaling law. Relevant datasets from CO₂ core flooding experiments are used to validate the proposed approach. The comparison is consistent with experimental findings, and the novel analytical method allows for faster inspection compared to numerical simulations. Full article

This study examines the behavior of Rayleigh waves propagating through a homogeneous, isotropic material, analyzed using a three-phase-lag thermoelastic diffusion framework enhanced by modified couple stress theory. The mathematical model integrates coupled thermoelastic and diffusive effects, incorporating phase-lags associated with (1) temperature gradients, (2) heat flux, and (3) thermal displacement gradients. By solving the derived governing equations analytically subject to stress-free, thermally insulated, and impermeable boundary conditions, we obtain the characteristic secular equation for Rayleigh wave propagation. Numerical simulations conducted on a copper medium evaluate how the secular equation’s determinant, wave velocity, and attenuation coefficient vary with angular frequency. The analysis focuses particularly on the influence of phase-lag parameters, including thermal and diffusion gradients and relaxation times. Results demonstrated that increasing the displacement gradient phase-lag elevated the secular determinant but reduced wave velocity and attenuation, while temperature gradient phase-lags exhibited the opposite trend. The study highlights the sensitivity of Rayleigh wave propagation to thermo-diffusive coupling and microstructural effects, offering insights applicable to seismic wave analysis, geophysical exploration, and material processing. Comparisons with prior theories underscore the model’s advancement in capturing size-dependent and memory-dependent phenomena. Full article

The focus in microplastic research has shifted from marine ecosystems towards freshwater ecosystems. Still, most studies are based on small sample numbers, both spatially and temporally. Little is known about the spatiotemporal variability of microplastics (MPs) in large river systems such as the Rhine River, Germany. Within our study, we performed four cross-sectional sampling campaigns at two sites in the Rhine River, at Koblenz and Emmerich, involving depth-distributed sampling over a particle size range from 10 µm to 25 mm. For plastic particle analysis, we used both optical and thermoanalytical approaches to determine mass-based polymer concentrations. Our results show that MP variability within the water column is complex, but mostly follows the particles density: the ratio between superficial MPs concentration and mean concentration of the verticals was >1 for lighter polymers with a density below 1.04 g/cm³ and <1 for polymers with a density above 1.04 g/cm³ among all size classes with only a few exceptions, even though the Rouse theory would indicate a more homogeneous distribution for small particle sizes. Large sampling volumes are essential, particularly for larger MP particles, as the coefficient of variation rises with particle size. At our study sites, no significant lateral variation was apparent, while during a flood event, MP concentrations were significantly higher than during low and mean water stages. This study is the first to (i) gain insights into cross-sectional MPs distribution in the Rhine River and (ii) account for particle mass concentrations, and thus lays the foundation for potential future MPs flux monitoring. Full article

A new complex, tetrakis(1,10-phenanthroline)-bis(succinate)-(µ₂-oxo)-bis(iron(III)) nonahydrate, [Fe₂(Phen)₄(Succinate)₂(μ-O)](H₂O)₉, was synthesized using the slow evaporation method. This study provides a comprehensive characterization of this coordination compound, focusing on its structural, spectroscopic, and thermal properties, which are relevant for applications in catalysis, material science, and chemical engineering processes. Single-crystal X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared (FT-IR), ultraviolet-visible (UV-Vis) spectroscopy, and thermoanalytical analyses were employed to investigate the material properties. Intermolecular interactions were further explored through Hirshfeld surface analysis. XRD results revealed a monoclinic crystal system with the C2/c space group, lattice parameters: a = 12.7772(10) Å, b = 23.0786(15) Å, c = 18.9982(13) Å, β = 93.047(2)°, V = 5594.27(7) ų, and four formulas per unit cell (Z = 4). The crystal packing is stabilized by C–H⋯O, C–O⋯H, C–H⋯π, and π⋯π intermolecular interactions, as confirmed by vibrational spectroscopy. The heteroleptic coordination environment, combining weak- and strong-field ligands, results in a low-spin state with an estimated crystal field stabilization energy of −4.73 eV. Electronic properties indicate direct allowed transitions (γ = 2) with a maximum optical band gap of 2.66 eV, suggesting potential applications in optoelectronics and photochemical processes. Thermal analysis demonstrated good stability within the 25–136 °C range, with three main stages of thermal decomposition, highlighting its potential for use in high-temperature processes. These findings contribute to the understanding of Fe(III)-based complexes and their prospects in advanced material design, catalytic systems, and process optimization. Full article