Starch retrogradation, driven by reassociation and recrystallization of gelatinized amylose and amylopectin chains, induces undesirable firming, syneresis, and sensory deterioration, ultimately shortening the shelf-life of starch-based foods. Enzymatic modification has emerged as a promising route to retard retrogradation, but its efficacy critically depends on the structural features targeted by the enzyme, the susceptibility of the starch substrate, and the accessibility of catalytic sites. This review systematically interprets the structure-dependent mechanisms underlying enzymatic retrogradation regulation, covering the differential regulatory patterns of various enzyme systems. This review further clarifies the essential distinction between substrate structural susceptibility and enzyme catalytic accessibility, and summarizes advanced modification strategies based on porous starch construction and controlled starch swelling to optimize enzyme-substrate interfacial contact efficiency. In addition, mainstream detection techniques are compared based on the different levels of the studied starch structure. Finally, the practical applicability of enzymatic anti-retrogradation technologies in diverse staple and processed starch-based food systems are also summarized. We propose that the key design principle is controlled structural remodeling enabled by enzyme action within a defined processing window, rather than indiscriminate starch degradation. This work provides systematic theoretical insights and practical guidance for the quality stabilization and shelf-life extension of starch-based food products.
Abstract To investigate the ultimate overall buckling capacity of members loaded through the shear center with Q460 high-strength steel welded T-sections, three welded T-section members with slenderness ratios of 61, 82, and 102 were fabricated from Q460 high-strength steel plates, and quasi-shear-center tests were conducted with measured eccentricities of 19, 15, and 48 mm, respectively. The initial geometric imperfections and residual stresses of the members were measured in the tests; the buckling failure modes were analyzed, and the ultimate overall buckling capacity was obtained. A finite-element model (FEM) considering initial imperfections was established based on the measured data. Geometrically and materially nonlinear analysis with imperfections (GMNIA) was adopted for finite-element simulation, and the correctness of the FEM was verified by comparing the analytical results with the test results. With the aid of the FEM, the ultimate overall buckling capacity of welded T-section compression members with various cross-sectional dimensions and slenderness ratios was also calculated. The results indicated that Q460 high-strength steel welded T-section members loaded through the shear center with larger slenderness ratios undergo overall flexural buckling, while axially compressed and eccentrically compressed members experience overall flexural-torsional buckling. The overall buckling capacity of narrow-flange section compression members under shear-center compression was generally higher than that under axial compression. Therefore, in design, efforts should be made to ensure they are under shear-center compression. For compression members with medium-flange and wide-flange sections, efforts should be made to ensure they are under axial compression in design. The research conclusions are based on specific cross-sectional types and a slenderness ratio range ( λ y ≥ 80 ), which can provide a reference for the rational design of Q460 high-strength steel welded T-section compression members.
Grid-forming converters have gradually become critical equipment for supporting modern power systems. With the rapid development of distributed generation, single-phase grid-forming converters (SGFMCs) have attracted extensive attention. However, SGFMCs face the challenge of impedance modeling, which affects the stability analysis and controller design. This paper investigates the impedance modeling, interaction mechanisms, and sub-synchronous resonance (SSR) mitigation methods. Regarding the impedance modeling, SGFMCs have more complex internal relationships than three-phase grid-forming converters owning to their orthogonal signal generation unit. Existing impedance models for double-power loops SGFMCs rarely account for the mirror frequency effect (MFE), resulting in inaccurate impedance characterization. To fill this research gap, this paper adopts the harmonic linearization method to derive two single-input single-output impedance models that fully capture the MFE for two typical SGFMCs. Furthermore, the interaction mechanism between SGFMCs and grid is explicitly elucidated. Analytical results demonstrate that both SGFMCs are susceptible to SSR under strong grid conditions. To improve the system stability, an impedance shaping method is proposed to mitigate SSR for SGFMCs under strong grid conditions. Finally, experimental results verify the correctness of the theoretical analysis.
Traditional underground silos employ terrain-based “top-fill, bottom-discharge” gravity grain discharge, whereas new ones utilize “top-fill, top-discharge” upward suction technology to overcome terrain constraints. However, the mechanisms influencing bulk grain flow and silo wall lateral pressure remain unclear. This study constructed underground cylindrical silo models (700 mm in height, 600/500/400 mm in diameter), conducted six groups of upward grain suction tests at different storage heights, and employed dimensionless analysis to explore the relevant laws. Results show that grain forms a stable funnel flow during upward suction, with particles converging upward and inward to the suction pipe, differing significantly from traditional gravity discharge. In stable discharge, the grain surface inclination is close to wheat's angle of repose, increasing with higher storage height and smaller cylinder diameter. The static silo wall pressure distribution conforms to the design assumptions of GB 50077. For transitional silo conditions, taking the larger value of shallow and deep silo calculations can reasonably envelope the test results. Dynamic lateral pressure is notably amplified compared with static pressure, with its peak shifting from the silo base to the middle-upper section and controlled by relative depth, showing good dimensional consistency. Adopting the standard static lateral pressure engineering envelope and considering the storage material partial factor can cover dynamic effects in most working conditions. Conventional static design methods are still applicable for normal conditions, whereas for unfavorable conditions, such as small-diameter shallow silos, it is necessary to verify the dynamic response of the middle-upper silo wall to enhance structural safety.
n-Octadecane is considered a promising organic phase change material (PCM) for medium and low temperature latent heat storage systems, but its inherently low thermal conductivity limits practical applications. Combining nanoparticles with metal matrix structures to construct a macro-micro dual-scale conductive network is an advanced enhancement strategy for improving the latent heat storage efficiency of PCMs. This strategy has attracted considerable attention in engineering thermophysics. However, the cross-scale synergistic heat transfer mechanism between the two enhancement levels still requires more systematic and in-depth investigation. In this study, a metal matrix-nanoparticle multilevel-enhanced PCM (MNePCM) was developed to preserve natural convection as much as possible at the macroscale while improving the intrinsic thermal conductivity of the PCM through microscopic nanoparticles. Subsequently, melting-based heat storage experiments were sequentially conducted on PCMs under three enhancement strategies to identify the effects of nanoparticles and the metal matrix on the melting-based heat storage characteristics of PCMs. A coupled fluid-thermal-solid numerical model was established to elucidate the effects of the metal matrix and nanoparticles on heat conduction and natural convection during melting and to quantify their cross-scale synergistic enhancement. The accuracy of the numerical model was validated against the experimental results. The results show that the 2 & times; 2-6 & times; 6 metal matrix increased the heat storage rate by 224.66%-158.98%. At the same porosity, higher-order cofignurations accelerated initial melting through larger metal-PCM interfacial areas and shorter local PCM conduction distances, while transient spatial matching between the metal walls and the evolving solid and liquid interface produced configuration-dependent local melting rate enhancement, termed the structure-interface synchronization effect. As melting progressed, lower-order matrices achieved better overall performance because their wider liquid-flow channels and thicker continuous metal walls favored natural convection and long-range heat conduction. Nanoparticle addition further improved thermal diffusivity, with stronger enhancement at higher concentrations. Under synergistic enhancement, the 2 & times; 2 MNePCM containing 5 wt% nanoparticles increased the heat storage rate by 260.62%, although the energy storage density decreased by 18.93%. A multilevel enhancement factor (MLEF) was proposed to evaluate this trade-off. Under equal weighting, the 5 wt%-2 & times; 2 MNePCM exhibited the best overall performance. This study provides theoretical guidance for optimizing high-performance composite PCMs and thermal energy storage units for medium and low temperature latent heat storage systems.
