Search Results (236)

In the polyurethane industry, catalytically generated carbodiimides can modify the properties of isocyanate and, thus, the resulting foams. In this work, a kinetic reaction study was carried out to investigate the formation of a simple, bifunctional carbodiimide from a widely used polyurethane raw material: 4,4′-methylenediphenyl diisocyanate (MDI). The experimental section outlines a catalytic process, using a 3-methyl-1-phenyl-2-phospholene-1-oxide (MPPO) catalyst in ortho-dichlorobenzene (ODCB) solvent, to model industrial circumstances. The reaction produces carbon dioxide, which was observed using gas volumetry at between 50 and 80 °C to obtain kinetic data. A detailed regression analysis with linear and novel nonlinear fits showed that the initial stage of the reaction is second-order, and the temperature dependence of the rate constant is $k(T)=(3.4\pm 3.8)\mathrm{‧}{10}^6\cdot e^{{\displaystyle \frac{-7192\pm 389}{T}}}$. However, the other isocyanate group of MDI reacts with new isocyanate groups and the reaction deviates from the second-order due to oligomer (polycarbodiimide) formation and other side reactions. A linearized Arrhenius equation was used to determine the activation energy of the reaction, which was E_a = 60.4 ± 3.0 kJ mol⁻¹ at the applied temperature range, differing by only 4.6 kJ mol⁻¹ from a monoisocyanate-based carbodiimide. In addition to experimental results, computationally derived thermochemical data (from simplified DFT and IRC calculations) were applied in transition state theory (TST) for a comprehensive prediction of rate constants and Arrhenius parameters. As a result, it was found that the activation energy of the carbodiimide bond formation reaction from theoretical and experimental results was independent of the number and position of isocyanate groups, which is consistent with the principle of equal reactivity of functional groups. Full article

Blast-furnace staves serve as critical protective components in ironmaking, requiring synergistic optimization of slag-coating behavior and self-protection capability to extend furnace lifespan and reduce energy consumption. Traditional integer-order heat transfer models, constrained by assumptions of homogeneous materials and instantaneous heat conduction, fail to accurately capture the cross-scale thermal memory effects and non-local diffusion characteristics in multiphase heterogeneous blast-furnace systems, leading to substantial inaccuracies in predicting dynamic slag-layer evolution. This review synthesizes recent advancements across three interlinked dimensions: first, analyzing design principles of zonal staves and how refractory material properties influence slag-layer formation, proposing a “high thermal conductivity–low thermal expansion” material matching strategy to mitigate thermal stress cracks through optimized synergy; second, developing a mechanistic model by introducing the Caputo fractional derivative to construct a non-Fourier heat-transfer framework (i.e., a heat-transfer model that accounts for thermal memory effects and non-local diffusion, beyond the instantaneous heat conduction assumption of Fourier’s law), which effectively describes fractal heat flow in micro-porous structures and interfacial thermal relaxation, addressing limitations of conventional models; and finally, integrating industrial case studies to validate the improved prediction accuracy of the fractional-order model and exploring collaborative optimization of cooling intensity and slag-layer thickness, with prospects for multiscale interfacial regulation technologies in long-life, low-carbon stave designs. Full article

This study investigates the dynamics of dust acoustic periodic waves in a three-component, unmagnetized dusty plasma system using generalized $(r^{\star },q^{\star })$ distributions. First, boundary conditions are applied to reduce the model to a second-order nonlinear ordinary differential equation. The Galilean transformation is subsequently applied to reformulate the second-order ordinary differential equation into an unperturbed dynamical system. Next, phase portraits of the system are examined under all possible conditions of the discriminant of the associated cubic polynomial, identifying regions of stability and instability. The Runge–Kutta method is employed to construct the phase portraits of the system. The Hamiltonian function of the unperturbed system is subsequently derived and used to analyze energy levels and verify the phase portraits. Under the influence of an external periodic perturbation, the quasi-periodic and chaotic dynamics of dust ion acoustic waves are explored. Chaos detection tools confirm the presence of quasi-periodic and chaotic patterns using Basin of attraction, Lyapunov exponents, Fractal Dimension, Bifurcation diagram, Poincaré map, Time analysis, Multi-stability analysis, Chaotic attractor, Return map, Power spectrum, and 3D and 2D phase portraits. In addition, the model’s response to different initial conditions was examined through sensitivity analysis. Full article

Two solvents, n-hexane and ethyl acetate, were employed to extract oil from Asphodelus tenuifolius Cav. seeds using the Soxhlet extraction technique. The process was optimized using Central Composite Design (CCD) and Response Surface Methodology (RSM). ANOVA and a second-order polynomial equation were applied to evaluate the effects of key operational factors, including extraction time (20–60 min) and solvent-to-solid ratio (0.2–0.6 g/mL), on oil yield. The physicochemical properties, fatty acid composition, and functional groups of the extracted oil were analyzed. While both solvents influenced oil yield and quality, the fatty acid composition remained consistent, with unsaturated fatty acids, particularly linoleic acid, identified as the main components. Under optimized conditions, the highest oil yields were 22% with n-hexane and 19.91% with ethyl acetate. FTIR spectroscopy confirmed the presence of ester groups, suggesting potential applications in biodiesel production. These findings offer valuable insights for producing oils rich in unsaturated fatty acids for food, cosmetic and renewable energy industries. These findings pave the way for further advancements in industrial applications by promoting the sustainable use of plant-derived oils. Full article

For transmission systems with regular order excitation, the order vibration will be conducted to each component of the system and affect the stability and service life of the system. A method with a regular non-circular active pulley is proposed in this paper, which is used to counteract the regular order excitation and the regular load excitation. A toothed belt drive system with second-order excitation is taken as an example. According to the existing analytical model of the tooth belt drive system, the modeling process and analytical solution algorithm of the system are derived. Based on the coordinate transformation, the algorithms for any position of an elliptical pulley and the common tangent of the circular pulley are given. And the algorithm for the arc length of the elliptical pulley at any arc degree is proposed. The influence of the phase and eccentricity in the elliptical pulley on the dynamic performance of the system is analyzed. Then the experimental verification is carried out. This shows that this system can generate excitation opposite to the main order rotational vibration of the driving pulley and opposite to the load of the driven pulley. Under the combined effect of other load pulleys in the system, there will be an amplification phenomenon in its vibration response. Considering the decrease in the belt span tension and the decline in the performance of energy-absorbing components after long operation, the presented method can better maintain the stability of system performance. This method can provide new ideas for the vibration reduction optimization process of systems with first-order wave excitation. Full article

Developing energy-efficient and environmentally benign synthesis protocols is crucial to agricultural waste-based adsorbent preparation. This study prepared novel walnut shell-derived adsorbents by enzymatic modification using a green process, and the as-prepared material was used for methylene blue (MB) removal from wastewater. The results showed that under the optimized conditions (100 mg L⁻¹ methylene blue (MB) solution, pH 7, 30 °C, 120 min adsorption time, and 0.14 g adsorbent dosage), WS-1 exhibited an MB removal efficiency of 93.67%, which was only slightly lower than that of WS-2 that was prepared by further carbonization of WS-1 using the low-temperature hydrothermal method (99.01%). Kinetic analysis confirmed WS-1 exhibited pseudo-second-order adsorption kinetics, which were generally similar to those of WS-2. However, the results obtained by the isotherm model followed by the Langmuir model of WS-1 indicated monolayer adsorption involving combined weak chemisorption and physisorption, which was different from the WS-2 (followed the Freundlich model that inferred multilayer chemisorption). In conclusion, this study successfully converted walnut shells, a type of agricultural waste, into functional adsorbents by a novel, simple, and greener enzymatic modification method, thereby achieving dual benefits of waste valorization and wastewater treatment. Full article

Distributed photovoltaic storage charging piles in remote rural areas can solve the problem of charging difficulties for new energy vehicles in the countryside, but these storage charging piles contain a large number of power electronic devices, and there is a risk of resonance in the system under weak grid conditions. Firstly, the topology of a photovoltaic storage charging pile is introduced, including a bidirectional DC/DC converter, unidirectional DC/DC converter, and single-phase grid-connected inverter. Then, the maximum power tracking control strategy based on improved conductance micro-increment is derived for a photovoltaic power generation system, and a constant voltage and constant current charge–discharge control strategy is derived for energy storage equipment. Additionally, a segmented reflective charging control strategy is introduced for charging piles, and the quasi-PR controller is introduced for single-phase grid-connected inverters. In addition, an improved second-order general integrator phase-locked loop (SOGI-PLL) based on feed-forward of the grid current is derived. Finally, a simulation model is built to verify the performance of the solar–storage charging pile and lay the technical groundwork for future integrated control strategies. Full article

Carbonaceous sorbents were prepared from Chlorella vulgaris via hydrothermal carbonization (200 °C and 250 °C) and slow pyrolysis (300–500 °C) to assess their effectiveness in removing the herbicide metribuzin from water. The biomass was cultivated under controlled laboratory conditions, allowing for consistent feedstock quality and traceability throughout processing. Using a single microalgal feedstock for both thermal methods enabled a direct comparison of hydrochar and pyrochar properties and performance, eliminating variability associated with different feedstocks and allowing for a clearer assessment of the influence of thermal conversion pathways. While previous studies have examined algae-derived biochars for heavy metal adsorption, comprehensive comparisons targeting organic micropollutants, such as metribuzin, remain scarce. Moreover, few works have combined kinetic and isotherm modeling to evaluate the underlying adsorption mechanisms of both hydrochars and pyrochars produced from the same algal biomass. Therefore, the materials investigated in the present work were characterized using a combination of standard physicochemical and structural techniques (FTIR, SEM, BET, pH, ash content, and TOC). The kinetics of sorption were also studied. The results show better agreement with the pseudo-second-order model, consistent with chemisorption, except for the hydrochar produced at 250 °C, where physisorption provided a more accurate fit. Freundlich isotherms better described the equilibrium data, indicating heterogeneous adsorption. The hydrochar obtained at 200 °C reached the highest adsorption capacity, attributed to its intact cell structure and abundance of surface functional groups. The pyrochar produced at 500 °C exhibited the highest surface area (44.3 m²/g) but a lower affinity for metribuzin due to the loss of polar functionalities during pyrolysis. This study presents a novel use of Chlorella vulgaris-derived carbon materials for metribuzin removal without chemical activation, which offers practical benefits, including simplified production, lower costs, and reduced chemical waste. The findings contribute to expanding the applicability of algae-based sorbents in water treatments, particularly where low-cost, energy-efficient materials are needed. This approach also supports the integration of carbon sequestration and wastewater remediation within a circular resource framework. Full article

Chirped radio-frequency signals are essential waveforms in radar systems. To enhance resolution and improve the signal-to-noise ratio through higher energy transmission, chirps with high time–bandwidth products are highly desirable. Photonic technologies, with their ability to handle broad electrical bandwidths, have been widely employed in the generation, filtering, processing, and detection of broadband electrical waveforms. In this work, we propose a photonics-based large-TBWP RF chirp generator utilizing dual optical frequency combs with a small difference in the repetition rate. By employing dispersion modules for frequency-to-time mapping, we convert the spectral interferometric patterns into a temporal RF sinusoidal carrier signal whose frequency is swept through the optical shot-to-shot delay. We derive analytical expressions to quantify the system’s performance under various design parameters, including the comb repetition rate and its offset, the second-order dispersion, the transform-limited optical pulse width, and the photodetector’s bandwidth limitations. We benchmark the expected system performance in terms of RF bandwidth, chirp duration, chirp rate, frequency step size, and TBWP. Using realistic dual-comb source parameters, we demonstrate the feasibility of generating RF chirps with a duration of 284.44 $\mathsf{\mu }$s and a bandwidth of 234.05 GHz, corresponding to a TBWP of $3.3\times {10}^7$. Full article

The primary objective of this paper is to derive a non-relativistic system of equations for a spin-2 particle in the presence of an external Coulomb field, solve these equations, and determine the corresponding energy spectra. We begin with the known radial system of 39 equations formulated for a free spin-2 particle and modify it to incorporate the effects of the Coulomb field. By eliminating the 28 components associated with vector and rank-3 tensor fields, we reduce the system to a set of 11 second-order equations related to scalar and symmetric tensor components. In accordance with parity constraints, this system naturally groups into two subsystems consisting of three and eight equations, respectively. To perform the non-relativistic approximation, we employ the method of projective operators constructed from the matrix ${\Gamma }^0$ of the original matrix equation. This approach allows us to derive two non-relativistic subsystems corresponding to the parity restrictions, comprising two and three coupled differential equations. Through a linear similarity transformation, we further decouple these into five independent equations with a Schrödinger-type non-relativistic structure, leading to explicit energy spectra. Special attention is given to the case of the minimal quantum number of total angular momentum, $j=0$, which requires separate consideration. Full article

Water pollution is a global concern, especially due to iron and manganese, which, at high concentrations, affect water quality by altering taste, odor, and color. This work explores the sustainable synthesis of hydrochar from orange peel and bagasse using hydrothermal carbonization (HTC) and a 2³ factorial design to optimize Fe²⁺ and Mn²⁺ removal for water treatment polishing. HTC was performed by varying (1) temperature (100–200 °C), (2) residence time (8–14 h), and (3) activation agent (H₃PO₄ or NaOH), with a central point at 150 °C for 11 h without activation. Characterization was performed using FTIR, TGA, SEM, nitrogen adsorption (BET) for surface area determination, elemental analysis, Brønsted acidity measurements, and zeta potential analysis. The hydrochar synthesized at 100 °C for 14 h with NaOH (HC6) showed the best Fe²⁺ and Mn²⁺ removal performance. The equilibrium time was 400 min, with pseudo-first-order kinetics best fitting the Fe²⁺ adsorption data, while pseudo-second-order kinetics provided the best fit for Mn²⁺ adsorption. The adsorption process was best described by the Freundlich and Langmuir isotherms, with maximum adsorption capacities (q_max) of 21.44 and 33.67 mg g⁻¹ for Fe²⁺ and Mn²⁺, respectively. It can be concluded that HTC-derived hydrochars offer a sustainable and efficient solution for Fe²⁺ and Mn²⁺ removal. This strategy presents a potentially valuable approach for sustainable water treatment, offering advantages for industrial application by operating at lower temperatures and eliminating the need for biomass drying, thereby reducing energy consumption and environmental impact. Full article

To address the resource utilization challenges of residual plastic film in Xinjiang and the issues of low reliability, poor cutting length qualification rates, and high energy consumption in existing film-mixed residue choppers, a rotary knife-type mixed film residue chopper was designed based on the “single support cutting + sliding cutting” principle. The device primarily consists of an adaptive feeding mechanism, a chopping mechanism, and a transmission system. The main structural and motion parameters of the mechanisms were determined through the analysis of feeding and chopping conditions. The primary factors affecting the cotton stalk chopping length qualification rate (CLCR-CS), residual film chopping length qualification rate (CFCR-RF), and specific energy consumption (SEC) were identified as the feeding roller speed, chopper speed, and the gap between the moving and fixed blades. Vibration characteristic analysis of the chopper was conducted using ANSYS software. The first six natural frequencies of the chopper were found to range from 112.54 to 186.65 Hz, with maximum deformation ranging from 0.885 to 1.237 mm. The excitation frequency was significantly lower than the first natural frequency, ensuring that the chopper met reliability and operational performance standards. A prototype was fabricated, and a second-order rotational orthogonal experiment was performed with CLCR-CS, CFCR-RF, and SEC as the test indicators and feeding roller speed, chopper speed, and the gap between the moving and fixed blades as the experimental factors. Variance and response surface analyses were conducted using Design-Expert software to clarify the effects and interactions of experimental factors on the test indicators. The second-order polynomial response surface model was optimized, and the optimal factor values were derived based on practical operational conditions. Verification experiments confirmed that the optimal operating parameters were a feeding roller speed of 32.40 r/min, a chopper speed of 222.0 r/min, and a blade gap of 1.0 mm. Under these conditions, CLCR-CS was 89.96%, CFCR-RF was 91.62%, and SEC was 5.36 kJ/kg, meeting the design specifications of the mixed film residue chopper. Full article

Especially in real-world circumstances with uneven road surfaces and impulsive shocks, nonlinear dynamic effects in vehicle systems can greatly skew biometric data utilized to track passenger and driver physiological states. By creating a thorough multibody human–seat–chassis model, this work tackles the effect of vehicle-induced vibrations on the accuracy and dependability of biometric measures. The model includes external excitation from road-induced inputs, nonlinear damping between structural linkages, and vertical and angular degrees of freedom in the head–neck system. Motion equations are derived using a second-order Lagrangian method; simulations are run using representative values of a typical car and human body segments. Results show that higher vehicle speed generates more vibrational energy input, which especially in the head and torso enhances vertical and angular accelerations. Modal studies, on the other hand, show that while resonant frequencies stay constant, speed causes a considerable rise in amplitude and frequency dispersion. At speeds ≥ 50 km/h, RMS and VDV values exceed ISO 2631 comfort standards in the body and head. The results highlight the need to include vibration-optimized suspension systems and ergonomic design approaches to safeguard sensitive body areas and preserve biometric data integrity. This study helps to increase comfort and safety in both traditional and autonomous car uses. Full article

For the first time, neodymium nickel manganites NdNa₂NiMnO₅ and NdK₂NiMnO₅ were synthesized via the solid-state interaction method, and they crystallize in a cubic system. Using experimental dynamic calorimetry in the temperature range of 298.15–673 K, the temperature dependences of the heat capacity of NdNa₂NiMnO₅ and NdK₂NiMnO₅ were studied. At 423 K, both compounds exhibited anomalous heat capacity jumps on the C⁰_p~f(T) dependency, likely corresponding to second-order phase transitions. Considering the phase transition temperatures, equations for the temperature dependence of heat capacity were derived, accurately describing the experimental data. Based on the experimental C⁰_p(T) data and calculated S⁰ (298.15) values, temperature dependences of C⁰_p(T) and the thermodynamic functions S⁰(T), H°(T)–H⁰(298.15), and Φ^xx(T) were determined for the studied compounds within the 298.15–673 K range. The analysis of electrophysical data confirmed the semiconducting and metallic nature of the conductivity, as well as identified the band gap and activation energy of conductivity. These results are valuable for the application of these materials in electronics and for controlling conductivity. Full article

The short-term performance of ground heat exchangers (GHEs) is crucial for the optimal design of ground-source heat pumps (GSHPs), enhancing their contribution to sustainable energy solutions. Local short-time thermal response functions, or short-time g-functions (STGFs) derived from thermal response tests (TRTs), are of great interest for predicting the heat exchange due to their fast and simple applicability. The aim of this work is to perform a sensitivity analysis to assess the impact of thermal parameter variability and TRT operating conditions on the accuracy of the average fluid temperature (T_f) predictions obtained through a local STGF. First, the uncertainties associated with the borehole thermal resistance (R_b), transmitted from the soil volumetric heat capacity (C_S) or some models dependent on GHE characteristics, such as the Zeng model, were found to have a low impact in T_f resulting in long-term deviations of ±0.2 K. Second, several TRTs were carried out on the same borehole, changing input parameters such as the volumetric flow rate and heat injection rate, in order to obtain their corresponding STGF. Validation results showed that each T_f profile consistently aligned well with experimental data when applying intermittent heat rate pulses (being the most unfavorable scenario), implying deviations of ±0.2 K, despite the variabilities in soil conductivity (λ_S), soil volumetric heat capacity (C_S), and borehole thermal resistance (R_b). Full article