Search Results (4,419)

In order to solve the problems of mass transfer polarization spatiotemporal distribution variations, uncontrollable regulation error, and accelerated capacity decay caused by ion crossover in high-power vanadium liquid flow batteries (VFBs), a three-dimensional battery model with a flow-type flow field based on the three-dimensional transient COMSOL Multiphysics^® 6.1 numerical modeling method was developed in this study. The model combines the ion transmembrane migration equation with the mass transfer polarization theory, constructs an objective function to quantify the regulation error, and is validated by multifluid-field structural simulations. The results indicate the following: (1) Ion crossover induces a 3–5% electrolyte concentration deviation and a current density distribution bias reaching 11%; (2) The intensity of mass transfer polarization exhibits a linear increase with the flow rate difference between the positive and negative electrodes; (3) Ion crossover significantly degrades system performance, causing Coulombic efficiency (CE) and Energy efficiency (EE) to decrease by 1.1% and 1.5%, respectively. This research demonstrates that unlike conventional flow field optimization, our strategy quantifies the regulation error by directly compensating for the ΔQ caused by ion crossing, and further regulation minimizes the effect, providing a theoretical basis for mass transfer intensification and capacity recovery in flow batteries. Full article

Catalytic upgrading of vacuum residue (VR) is critical for enhancing fuel yield and reducing waste in petroleum refining. This study explores VR cracking over a novel cerium-loaded acidified metakaolinite catalyst (MKA800–20%Ce) prepared via calcination at 800 °C, acid leaching, and wet impregnation with 20 wt.% Ce. The catalyst was characterized using FTIR, BET, XRD, TGA, and GC–MS to assess structural, textural, and thermal properties. Catalytic cracking was carried out in a fixed-bed batch reactor at 350 °C, 400 °C, and 450 °C. The MKA800@Ce20% catalyst showed excellent thermal stability and surface activity, especially at higher temperatures. At 450 °C, the catalyst yielded approximately 11.72 g of total liquid product per 20 g of VR (representing a ~61% yield), with ~3.81 g of coke (~19.1%) and the rest as gaseous products (~19.2%). GC-MS analysis revealed enhanced production of light naphtha (LN), heavy naphtha (HN), and kerosene in the 400–450 °C range, with a clear temperature-dependent shift in product distribution. Structural analysis confirmed that cerium incorporation enhanced surface acidity, redox activity, and thermal stability, promoting deeper cracking and better product selectivity. Kinetics were investigated using an eight-lump first-order model comprising 28 reactions, with kinetic parameters optimized through a genetic algorithm implemented in MATLAB. The model demonstrated strong predictive accuracy taking into account the mean relative error (MRE = 9.64%) and the mean absolute error (MAE = 0.015) [MAE: It is the absolute difference between experimental and predicted values; MAE is dimensionless (reported simply as a number, not %. MRE is relative to the experimental value; it is usually expressed as a percentage (%)] across multiple operating conditions. The above findings highlight the potential of Ce-modified kaolinite-based catalysts for efficient atmospheric pressure VR upgrading and provide validated kinetic parameters for process optimization. Full article

The wettability of falling film flow outside multi-row horizontal tubes is a core factor determining the heat and mass transfer performance of falling film heat exchangers, which is critical for their optimized design and stable operation. A visualization experimental platform for falling film flow over ten rows of horizontal tubes was constructed, with water as the working fluid. High-definition imaging technology and image processing methods were employed to systematically investigate the liquid film distribution and wettability under three tube diameters (d = 0.016, 0.019, 0.025 m), four tube spacings (s = 0.75d, 1d, 1.25d, 1.5d), and four inter-tube flow patterns (droplet, columnar, column-sheet, and sheet flow). Two parameters, namely the “total wetting length” and the “total wetting area”, were proposed and defined. The distribution characteristics of the wetting ratio for each row of tubes were analyzed, along with the variation laws of the total wetting area of the ten rows of tubes with respect to tube diameter, tube spacing, and liquid film Reynolds number (Re_l). The following results were indicated: (1) Increasing the fluid flow rate and the tube spacing both promote the growth of the wetting length. When Re_l ≤ 505, with the increase of tube diameter, the percentage of the wetting length of the tenth tube row relative to that of the first tube row decreases under the same fluid flow rate; when Re_l > 505, this percentage first decreases and then increases. (2) The total wetting area exhibits a trend of “first increasing then decreasing” or “continuous increasing” with the tube spacing, and the optimal tube spacing varies by flow pattern: s/d = 1 for droplet flow (d ≤ 0.016 m), s/d = 1.25 for columnar flow, and s/d = 1.25 (0.016 m), 1 (0.019 m), 1.5 (0.025 m) for sheet flow. (3) The effect of tube diameter on the total wetting area is a balance between the inhibitory effect (reduced inter-tube fluid dynamic potential energy) and promotional effect (thinner liquid film spreading). The optimal tube diameter is 0.016 m for droplet flow and 0.025 m for columnar/sheet flow (at s/d = 1.25). (4) The wetting performance follows the order 0.016 m > 0.025 m > 0.019 m when Re_l > 505, and 0.025 m > 0.019 m > 0.016 m when Re_l ≤ 505. Finally, an experimental correlation formula for the wetting ratio considering the Re_l, the tube diameter, and tube spacing was fitted. Comparisons with the present experimental data, the literature simulation results, and the literature experimental data showed average errors of ≤10%, ≤8%, and ≤14%, respectively, indicating high prediction accuracy. This study provides quantitative data and theoretical support for the structural optimization and operation control of multi-row horizontal tube falling film heat exchangers. Full article

In this work, the photocatalytic reduction of CO₂ was innovatively tested with the simultaneous removal and mineralization of a textile contaminant, methylene blue (MB), which acts as a sacrificial agent. The process was carried out in a flow regime under atmospheric conditions, using a liquid-phase photoreactor under UVA illumination with a duration of 24 h per test. Two commercial TiO₂-based photocatalysts, P25 and P90 from Evonik, were used and surface modified through the photodeposition of metallic nanoparticles of Pt, Au, and Pd, as they did not show gas-phase products from CO₂ reduction on their own. The optimal pH was 5, the decreasing order of activity by metal was Pt > Au > Pd, and the optimal MB concentration was 20 ppm. The major products were CH₄ and H₂ in the gas phase. The presence of CH₄ was only detected in the presence of a CO₂ flow. In the liquid phase, carboxylic acids were also detected in small amounts, and in the test, 100 ppm of MB ethanol was additionally detected. A 100% degradation of MB and 72.5% mineralization was achieved under the conditions of highest CH₄ production (20 ppm MB at pH 5 with 4 g·L⁻¹ P25-0.70%Pt). Full article

Humans have been using lipids for many centuries; these are oils found in plants, particularly in seeds. However, relatively recently, it has become clear that lipids are the primary metabolites of any living organism. Fatty acids (FAs) are a structural component of lipids, and their role in building the framework of the lipid bilayer cannot be overstated. They participate in maintaining homeostasis by controlling membrane permeability. Changes in the FA composition of lipid bilayers can modulate the transition of the membrane from a liquid crystalline to a gel-like state. Thus, knowledge of a plant’s FA profile can aid in understanding the physiological mechanisms underlying their interaction with the environment and the ways in which they adapt to various stress factors. Throughout the colonization of terrestrial habitats, plants evolved, and new phylogenetic groups appeared; at present, some features of the FA composition of their individual representatives are known. However, the overall change in the composition of lipid FAs during the evolution of higher plants is still not understood. Our analysis of the literature showed that the FA diversity tends to decrease from mosses to angiosperms, mainly due to a reduction in polyunsaturated very-long-chain FAs, while the average acyl chain length remains unchanged. It is important to recognize the trends in this process in order to understand the adaptive capabilities of higher plants. This knowledge can be useful not only from a fundamental point of view, but also in practical human activities. Full article

Epoxy resins are valuable in aerospace, electronics, and high-performance industries; however, their inherently low thermal conductivity (TC) limits applications requiring effective heat dissipation. Recent reports suggest that certain liquid crystalline or partially crystalline epoxy formulations can achieve higher TC, even exceeding 1 W/(m·K). To investigate this, 17 epoxy formulations were prepared, including the commonly used diglycidyl ether of bisphenol A (DGEBA) and two custom-synthesized diepoxides: TME4, which contains rigid aromatic ester linkages with a C4 aliphatic spacer, and LCE-DP, featuring rigid imine bonds. Thermal conductivity was measured using four techniques: laser flash analysis (LFA), modified transient plane source (MTPS), time-domain thermoreflectance (TDTR), and displacement thermo-optic phase spectroscopy (D-TOPS). Additionally, small-angle and wide-angle X-ray scattering (SAXS/WAXS) were performed to detect crystalline or liquid crystalline domains. All formulations exhibited TC values ranging from 0.13 to 0.32 W/(m·K). The TME4–DDS systems, previously reported to be near 1 W/(m·K), consistently measured between 0.26 and 0.30 W/(m·K). Thus, under our synthesis and curing conditions, the elevated TC reported in prior studies was not reproduced, and no strong evidence of crystallinity was observed; indications of local ordering did not translate into higher conductivity. Variations in TC among methods often matched or exceeded the gains attributed to mesophase formation. More broadly, evidence for crystallinity in epoxy thermosets appears weak, consistent with the notion that crosslinking suppresses long-range ordering. Full article

This study examines the determinants of capital structure in small agricultural enterprises in Serbia, with a particular emphasis on the external context shaped by circular economy (CE) indicators. Using a balanced panel of 254 firms between 2014 and 2022 (2286 firm-year observations), we estimate random-effects models with panel-corrected standard errors. The dependent variable is financial leverage, while explanatory variables include internal firm characteristics (liquidity, debt ratio, profitability, and asset tangibility) and territory-level CE indicators (municipal waste generated per capita, municipal waste recycling rate, and greenhouse-gas emissions from production activities). The model is statistically significant (χ² = 82.49; p < 0.01) and explains 33.7% of leverage variation. The results show that debt ratio positively and strongly relates to leverage, whereas profitability exhibits a negative and significant association, consistent with the pecking-order theory. Regarding the CE context, higher waste generation and higher GHG emissions are associated with lower leverage, while a higher recycling rate has a positive, marginal effect, suggesting that improved circular performance may ease access to external finance by lowering perceived risk among creditors. These findings highlight that environmental performance and local circularity conditions matter for financing decisions in agriculture. Policy implications include promoting CE practices and local recycling capacities to support sustainable financing. Future research should test dynamic specifications and enterprise-level CE metrics. Full article

Natural convection of liquid metals under magnetic fields is a phenomenon of interest in various industrial and scientific applications, including fusion reactor blankets and magnetohydrodynamic (MHD) power systems. While the application of a magnetic field generally suppresses convection and reduces the heat transfer rate, recent studies have reported cases where the Nusselt number increases under certain magnetic field conditions. In this study, we conduct numerical simulations of natural convection in an annular container filled with a liquid metal, subject to a circumferential static magnetic field. The governing equations, incorporating both temperature and electromagnetic fields, are solved using a high-order finite difference scheme. The results show that, within a specific range of parameters, the Nusselt number increases at moderate Hartmann numbers, even under low Rayleigh number conditions. Notably, this enhancement in heat transfer occurs alongside a reduction in kinetic energy, indicating that convective strength is not necessarily the dominant factor. Further analysis confirms that this phenomenon weakens and eventually vanishes as the Rayleigh number approaches 10⁶. These findings provide evidence that magnetic field-induced heat transfer enhancement can occur without a corresponding increase in convective motion, thereby challenging conventional assumptions in magnetoconvection theory. Full article

In order to investigate the adsorption characteristics of Cu²⁺, Zn²⁺, and Mn²⁺ on natural diatomite in liquid/solid systems and to provide reliable theoretical support for the application of these materials, we conducted a series of adsorption studies. The results revealed a non-monotonic relationship between the adsorption capacity of natural diatomite and ion concentration. The maximum adsorption capacities for Cu²⁺, Zn²⁺, and Mn²⁺ were found to be 3.56, 6.23, and 3.82 mg·g⁻¹, at concentrations of 200, 500, and 300 mg·L⁻¹. Optimal adsorption conditions were determined by investigating environmental factors such as pH and temperature: pH 6, temperature 30 °C, and contact time 40 min. The adsorption kinetics were found to be in accordance with the pseudo-second-order model (R² > 0.997). Fitting adsorption isotherms for Cu²⁺, Zn²⁺, and Mn²⁺ using various models revealed that the Langmuir (R² > 0.993), Temkin (R² > 0.953), and Freundlich (R² > 0.997) models most accurately describe their adsorption behaviour. Thermodynamic analysis confirmed that adsorption is a spontaneous, endothermic, physical process (ΔG° < 0, ΔH° > 0, ΔS° > 0) and that the overall adsorption rate is limited by micropore adsorption. Consequently, natural diatomaceous earth can serve as an efficient, low-cost adsorbent for removing heavy metals from contaminated water. Full article

The experimental study has been carried out using advanced computer vision methods in order to visualize the moment of excitation and further propagation of a non stationary isotropic domain in a hybrid aligned nematic (HAN) microsized volume under the effect of a laser beam focused on a bounding liquid crystal surface. It has been shown that, when the laser power exceeds a certain threshold value, in bulk of the HAN microvolume, an isotropic circular domain is formed. We also observed a structure of alternating concentric rings around the isotropic circular region, which increases with distance from the center of the isotropic domain. The formation of a sequence of rings in a polarizing microscopic image indicates the formation of a complex topology of the director field in the HAN cell under study. The following evolution of the texture can be represented by two modes. Firstly, the “fast” heating mode, which is responsible for the formation and explosive expansion of an isotropic zone in bulk of the HAN microvolume with characteristic time ${\tau }_1$ due to a laser spot heating on the upper indium tin oxide (ITO) layer. Secondly, the “slow” heating mode, when an isotropic zone and concentric rings slowly expand with characteristic time ${\tau }_2$ mainly due to the finite thermoconductivity of ITO layer. When the laser power significantly exceeds the threshold value, damped oscillations of the isotropic domain are observed. We also introduced the metrics that allows quantitatively estimate the behavior of texture observed. The results obtained form an experimental basis for further investigation of thermomechanical force appearing in the LC system with coupled gradients of temperature and director fields. Full article

Using the method of laser ablation in liquid, submicron-sized particles of zero-valent amorphous selenium (Se SMPs) were created. A number of composite polymer materials were manufactured based on polyurea and Se SMPs at concentrations ranging 0.1–2.5 wt.%. The manufactured materials showed no significant surface or internal defects at either the macro or micro level. It was found that the Se SMPs were not uniformly distributed inside the polymer, but formed ordered areas with slightly higher and lower concentrations of the particles. It was demonstrated that the manufactured materials did not generate a significant amount of active oxygen species, which could damage biological objects such as protein molecules and DNA, while also exhibiting pronounced bacteriostatic properties without significantly affecting the growth and reproduction of mammalian cells. Materials containing 0.25 and 1% Se SMPs, when added to soil, improved the morphometric parameters of radish plants (Raphanus sativus var. sativus). These polymer composite materials based on polyurea with the addition of Se SMPs are promising functional materials for agriculture due to their antibacterial activity. Full article

Vegetarians must rely on supplements to meet the recommended daily intake of vitamin B12. Therefore, it is essential to establish a rapid, inexpensive, and reliable method of determining B12 levels in order to accurately characterize and assess the quality of supplements. This study describes a methodology for quantifying vitamin B12 in the form of methylcobalamin and cyanocobalamin following 2 min of ultrasound-assisted extraction performed at pH 4. Vitamin B12 was determined using UV-Vis spectrophotometry and liquid chromatography-tandem mass spectrometry. Thus, LC-MS/MS validated the cost-effective UV-Vis method. The content and form of vitamin B12 in the tested supplements were investigated, and serious discrepancies were found in the content or form of vitamin B12 in three out of ten supplements. To verify the quality of the analyzed supplements, the presence of metal impurities (as Cd, Hg, and Pb) was also assessed using high-resolution continuum source electrothermal atomic absorption spectrometry. No risk associated with the presence of these metals has been noted. Nevertheless, our findings underscore the need for stricter quality control in supplement manufacturing. Full article

In this paper, we propose a novel optimization model for portfolio selection that integrates the classical mean–variance criterion with a second-order Tsallis entropy term. This approach enables a trade-off between expected return, risk, and diversification, extending Markowitz’s theory to account for non-Gaussian characteristics and heavy-tailed distributions that are typical in financial markets—especially in cryptocurrency assets. Unlike the first-order Tsallis entropy, the second-order version amplifies the effects of distributional structure and allows for more refined penalization of portfolio concentration. We derive the analytical solution for the optimal weights under this extended framework and demonstrate its performance through a case study using real data from selected cryptocurrencies. Efficient frontiers, portfolio weights, and entropy indicators are compared across models. This novel combination may improve portfolio selection under uncertainty, especially in the context of volatile assets such as cryptocurrencies, as the proposed model can provide a more robust and diversified portfolio structure compared to conventional theories. Full article

Background/Objectives: This study investigated the effect of storage conditions on mRNA-LNPs in situ via identification of the formulation traits necessary for improving storage stability. Methods: We synthesized an ionizable lipid, namely TOT-28, which has a hydrolysis-susceptible ester bond in its hydrophilic head group that allows it to act as an indicator of the hydrophilic environment within the mRNA-LNPs. LNPs were stored either at 4 or 25 °C for up to 8 weeks to investigate the effect of pH and temperature on ester hydrolysis, internal mRNA integrity, physicochemical properties of the LNPs, and mRNA gene expression. Results: The results indicate that, at 25 °C, a lower buffer pH increases ester hydrolysis, whereas an opposite trend slightly occurs in ester hydrolysis with storage at 4 °C. We also found that TOT-28-based LNPs were less hydrated and microviscosity was higher at 4 °C compared with storage temperature at 25 °C. Therefore, TOT-28-based LNPs seem less sensitive to external buffer solutions because of a higher-order structure when stored at lower temperatures. In addition, we found that LNPs with different ionizable lipid structures exhibit distinct responses to pH changes at specific storage temperatures. Conclusions: Our findings provide novel insights into the appropriate conditions for long-term storage of the mRNA-LNPs as a liquid formulation. Full article

Two cholesterol-based liquid crystalline materials were synthesized by incorporating perfluorinated acyl chains of different lengths with the help of epichlorohydrin and copper(I)-mediated azide-alkyne 2+3 dipolar cycloaddition chemistries. These materials were characterized by differential scanning calorimetry, cross-polarized optical microscopy and powder X-ray diffraction. The compound with the longer perfluorinated chain exhibited a smectic A (SmA) phase as confirmed by XRD and POM, while the shorter-chain derivative exhibited diffraction peaks suggestive of both simple SmA* ordering as well as lamellar solid phase exhibiting multilayer ordering. Full article