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关键词： Tensile strength  

摘要： BS-PA-Al, BS-PA-Ni and BS-PA-Zn hydrogel flame retardant coating materials were prepared respectively using polyvinyl alcohol (PVA)/chitosan (CS) including aluminum hypophosphite (AHP) as hydrogel matrix, and employing basalt (BS) after NaOH pretreatment, KH550 grafting modification and phytic acid co-precipitation act as flame retardant filler. The effects of modified basalt/hydrogel composite coating on flame retarding and mechanical properties of wood were analyzed by thermogravimetric test, cone calorimetric test and vertical combustion test after coating on wood surface respectively. The results show that， due to the dilution of combustible gas and the increase of carbon layer density, the flame retardant properties of BS-PA-Al, BS-PA-Ni and BS-PA-Zn hydrogel flame retardant coated wood have been significantly improved. Among them, the flame retardant properties and mechanical properties of BS-PA-Ni have reached the best, and its UL-94 test has reached V-0 level. The residual carbon rate increased to 27.3%, while the peak heat release rate (pHRR), total heat release (THR) and total smoke release (TSR) decreased by 64.2%, 32.7% and 51.3%, respectively. In addition, when the thickness of the coating is 300 μm, the mechanical properties (tensile strength) of BS-PA-Ni enhanced to 80.4%, and the adhesion strength of the hydrogel on the wood reaches 3.4 MPa. © 2025 Beijing University of Aeronautics and Astronautics (BUAA). All rights reserved.

关键词： Wear resistance  

摘要： Objective Cr12MoV cold work die steel is widely used in the roll industry owing to its advantages such as low deformation, high abrasion resistance, and large bearing capacity. However, Cr12MoV rolls exhibit high hardness and brittleness, making them prone to spalling, pitting, cracking, and other microarea damage under service conditions. The harsh operational environment of rolls often involves substantial impact, extrusion, and external friction, leading to localized damage such as large-area spalling and cracking, ultimately resulting in roll scrap. Laser repair is a key method for restoring damaged rolls. This technique enables the formation of dense microstructures and metallurgical bonds at the interface, making it an important technology for repairing damaged Cr12MoV rolls. However, the surface hardness of the repaired layer exhibits fluctuations under the conventional laser mode, particularly in the interfacial transition zone. These variations negatively affect the rolling accuracy of high-precision plates and shorten the service life of rolls. This study explores the application of swing laser beams in welding to promote the transformation of columnar crystals to equiaxed crystals, addressing issues related to non-uniform surface hardness in repaired Cr12MoV rolls. This method aims to minimize hardness fluctuations in the interfacial transition zone, reduce metallurgical defects, and establish a framework for high-quality surface repair of Cr12MoV rolls. Methods The surface of a Cr12MoV roll was machined into a trapezoidal damage repair groove using fine engraving technology. The damaged area was then repaired at conventional laser and figure-8 swing laser modes. The following steps were undertaken: 1) comparing the repair layer molding quality at two laser modes;2) analyzing and comparing the microstructure of the cross-section at the same depth of the repair layer using metallographic microscopy;3) analyzing and comparing the phase composition of the re

关键词： Intracranial aneurysm   Hemodynamics   Flow pattern   Neck width   Particle image velocimetry  

摘要： Intracranial aneurysm (IA) is a prevalent cerebrovascular disease associated with high mortality and disability rates upon rupture. The hemodynamics of IA, which are significantly influenced by geometric parameters, directly impact its rupture. This study focuses on investigating the transient flow characteristics in saccular IA models fabricated using a water droplet-based method, specifically examining the influence of neck widths. Particle image velocimetry technique and numerical simulation were employed to investigate the dynamic evolution of flow structures within three IA models. The results reveal that neck width (W) has a substantial effect on flow characteristics in the neck region, subsequently impacting the deep flow inside the sac. Three distinct patterns were observed during flow evolution inside the sac: for W = 2 mm, two vortices occur and then disappear with relatively low average flow velocity;for W = 4 mm, enhanced effects of a high-speed jet result in periodic pulsatile flow velocity distribution while maintaining stable vortex core position;for W = 6 mm, significant changes in flow velocity occur due to size expansion and intensity increase of vortices. These findings demonstrate that neck widths play a complex role in influencing transient flow characteristics within IAs. Overall, this research contributes to further understanding transient flow behaviors in IAs.

关键词： Hydrogen bonds  

摘要： Carbon fiber reinforced composites (CFRP) have the advantages of light weight, high strength, corrosion resistance, fatigue resistance and wear resistance, and have become a new advanced structural materials for marine engineering. In this paper, the effects of hygrothermal aging on the thermal/mechanical (tensile, flexural and short-beam shear properties) and frictional wear properties of CFRP were investigated. Combined with the analysis of micro-morphology and structure, the degradation mechanisms of mechanical and frictional wear properties of CFRP immersed in the distilled water at 60℃ for up to 90 d were revealed. It was found that the maximum degradation amplitudes of CFRP tensile, flexural and short-beam shear strengths were 5.8%, 13.0%, and 20.9%, due to the destruction of hydrogen bonds and partial covalent bonds of polymer resin chains by water molecules during the hygrothermal aging process, which resulted in the defect creation and the lateral restraint loss of the fiber bundles within the CFRP, ultimately leading to the de-bonding of fiber/resin interfaces. In addition, the thermodynamic and viscoelastic behavior of CFRP in the hygrothermal environment exhibited a nonlinear change, attributing to the coupling effects of positive resin post-curing and negative hygrothermal aging. Compared with those before immersion, the average coefficient of frictions (COFs) of CFRP aged for 15, 30, 60, and 90 d decreased by 23.8%, 35.0%, 43.7% and 53.8%, respectively, which was attributed to the friction lubrication of water molecules inside the diffused CFRP acting as friction lubricants during friction, alleviating the wear of the CFRP/abrasive ball interface. The wear rate (Ws) and wear scar width (WSW) of CFRP aged for 90 d increased by 254.6% and 114.9% compared with that before aging, which was attributed to the fact that the water molecules forming new hydrogen bonds with the resin matrix were in the bonded water state, reducing inter-chain force between resin

关键词： 人工智能  

ISBN: (纸本)9787122475879

摘要： 本书解析了DeepSeek在职场办公、文案创作、数据分析、营销推广、生活管理、跨工具协作等十多个领域的深度应用，介绍了DeepSeek的使用与提效技巧。

关键词： Spontaneous combustion  

摘要： In order to explore the effective method of reducing the shrinkage of spontaneous combustion coal gangue concrete, seven groups of samples were designed with the different dosage of super absorbent polymers (SAP) and polypropylene (PP) fibers, the drying shrinkage test and the internal humidity test were carried out. The effect of SAP and PP fibers on shrinkage performance of spontaneous combustion coal gangue concrete was investigated, the influence of SAP and PP fibers on the internal humidity of the matrix was analyzed, and the law of change between the drying shrinkage strain and the internal relative humidity of the matrix was revealed. The shrinkage prediction model of spontaneous combustion coal gangue concrete was proposed. The results show that the addition of SAP and PP fibers can significantly reduce the drying shrinkage of spontaneous combustion coal gangue concrete. The shrinkage value of the matrix first decreases and then increases with the increasing of the SAP addition;The shrinkage value of the matrix gradually decreases with the increment of PP fibers dosage. At the age of 90 d, when the content of SAP is 0.2wt%, the shrinkage reduction effect of matrix is the best, and the shrinkage strain of the sample is reduced by 31.3% compared with the plain concrete. The addition of SAP and PP fibers can inhibit the decay of the internal humidity;The shrinkage strain and the internal relative humidity of the matrix vary linearly. By introducing the influence coefficient of spontaneous combustion coal gangue aggregate, the AFREM shrinkage prediction model is modified, the predicted results are in good agreement with the experimental results, and the modified shrinkage model can be used for the calculation of dry shrinkage of spontaneous combustion coal gangue aggregate concrete. © 2025 Beijing University of Aeronautics and Astronautics (BUAA). All rights reserved.

关键词： Metabolites  

摘要： To improve the biomass and spore rate of Bacillus licheniformis HK, influences of lactate on cell growth and metabolism and spore production were investigated at a 20 L bioreactor, and lactate addition was conducted by coupling with pH7.0 from 16 h to 32 h. Basing on the data differences in transcriptome and metabolome, the metabolic regulation mechanism of lactate was analyzed. The results showed that a peak biomass (30 h) of 5.43×1010 CFU/mL was obtained in lactate supplement group, which was 54.3% higher than that of basic fermentation group (control). Meanwhile, the spore number was 5.36×1010 CFU/mL, which was 60.0% higher than the control. Compared with the control, expressions of key genes in gluconeogenesis and pentose phosphate pathway (ldh, pckA, gapB, zwf, and tkt) were up-regulated by 2.8~9.3 fold in the lactate supplement group, the abundance of marker metabolites (pyruvate, fructose-6-phosphate, glyceric acid-1,3diphosphate, 6-phosphate-gluconate, 5-phosphate-ribulose, and sedoheptulose 7-phosphate) in the pathways were increased by 1.55~12.6 fold compared with the control. Additionally, expressions of key genes in TCA cycle and oxidative phosphorylation system (citZ, icd, citB, odhB, atpAB, ndh, yumB, qcrABC, ctaODC, ythA, and sdhAB) were down-regulated by 34.2%~96.8%, while nitrate respiration metabolism gene (nasBCD) was up-regulated by 107.4~287.3 fold compared with the control. Abundances of corresponding key metabolites, such as aconitate, isocitrate and citrate, were decreased by 52.6%~62.5%, while the abundances of NAD+ and NADH were increased by 1.6~2.7 fold. Meanwhile, the precursors abundances of teichoic acid (glycerol-3-phosphate) and peptidoglycan (UDP-N-acetylmuramic acid, UDP-Nacetylmuramyl-L-alanine-D-glutamate) were increased by 1.5~14 fold compared with the control. Moreover, gene expressions involved in sporogenesis, such as phrAC, cotP, cotA, yeek, yheD, tasA, gerQ, yuzJ, were up-regulated by 1.4~5.7 fold, while rapAB, abrB, yisI, y

关键词： Hardening  

摘要： Recently, seismically isolated buildings are required to secure a safety margin against extreme ground motion. The hardening characteristics of members used in seismic isolation layer may suppress excessive displacement of the seismic isolation layer. In this paper, the influence of the hardening characteristics on the seismic response characteristics is investigated. Furthermore, the prediction method for the maximum displacement of the isolation layer is derived based on momentary input energy. © 2025 Architectural Institute of Japan. All rights reserved.

关键词： High temperature corrosion  

摘要： Objective H13 steel (4Cr5MoSiVl), a hot-working die steel, exhibits excellent wear resistance, hardness, and heat fatigue resistance. It is a crucial material for manufacturing hot extrusion and die-casting molds, which operate under high-temperature conditions and are subject to wear, corrosion, and other failure modes. These can lead to premature failure, reduced service life, significant economic losses, and resource wastage. Therefore, extending the service life of molds by repairing damaged sections, restoring geometry, and ensuring mechanical properties that are comparable to or exceed those of new molds is highly significant. The quality of the cladding layer (including geometric dimensions, dilution rate, macroscopic defects, and mechanical properties) depends not only on the matrix material and cladding powder but also on process parameters such as laser power, scanning speed, and powder feed rate. Excessive laser power may induce high residual stress, leading to cracks in the cladding layer, while insufficient laser power results in inadequate matrix melting and poor bonding strength between the matrix and cladding layer. Identifying the optimal combination of process parameters is, therefore, critical to achieving high-quality cladding layers. However, most existing studies utilize circular light spots, and fewer studies focus on large-size rectangular light spots due to challenges in their energy distribution. Circular spots typically require multi-pass overlapping cladding due to their limited irradiation size. Rectangular broadband spots, on the other hand, enhance cladding efficiency and allow for investigations into the impact of overlap rate on surface flatness under different conditions. Method The matrix material used is H13 steel, and the powder material is H13 powder, ensuring minimal thermal and physical property differences to avoid cracking of the cladding layer. Laser power, scanning speed, powder feed rate, and overlap rate are considered a

关键词： Aspect ratio  

摘要： Superhydrophobic modification of wood surfaces can effectively limit the shrinkage and swelling of wood, thereby extending the service life of wood products. However, the practical application of superhydrophobic modification of wood surfaces is limited due to the poor stability of the superhydrophobic coating. The stability of the superhydrophobic coating is affected by the microscopic morphology of inorganic nanoparticles in the wood superhydrophobic layer. However, few research has systematically discussed this issue. In this paper, three types of hydroxyapatite nanomaterials (nanospheres, nanorods and nanowires), were used as raw materials for the superhydrophobic modification of wood surfaces by compounding with polydimethylsiloxane and spraying onto the wood surface. The effect of hydroxyapatite morphology on the stability of the superhydrophobic layer on wood was investigated through sandpaper wear, tape stripping, and chemical corrosion tests. The results demonstrate that hydroxyapatite nanospheres with smaller aspect ratios and sizes can efficiently penetrate the cellular walls and cavities of wood. As a result, the superhydrophobic layer prepared from these nanospheres exhibits better hydrophobicity and stability, and the obtained coatings can maintain superhydrophobicity after 15 cycles of sandpaper wearing and tape peeling. These findings provide a theoretical foundation for the development of high-performance and stable wood superhydrophobic coatings. © 2025 Beijing University of Aeronautics and Astronautics (BUAA). All rights reserved.