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•During the layer-by-layer laser remelting process, the cooling rate is increased.•The surface quality is improved after layer-by-layer laser remelting.•The microhardness and tensile ...performance are enhanced due to grain refinement.
Laser Powder Bed Fusion (LPBF) is an innovative additive manufacturing technology. But it is also limited by the defects and surface quality. In this work, the layer-by-layer laser remelting (LR) method is applied to LPBF AlSi10Mg to improve the surface quality and mechanical performance. To account for the physical mechanism of the laser remelting, a three-dimension multi-physics coupled transient model is established. The numerical results indicate that the molten pool during the LR process is significantly expanded. The larger molten pool plays a great role in removing the defects. Moreover, the temperature gradient and cooling rate are simultaneously increased during the LR process, which has a considerable impact on the microstructure transformation. The densification, surface quality, including roughness, wettability, and residual stress, microstructure, and mechanical property are investigated after LR treatment based on experiments. The experimental results show that after LR treatment, the densification can be up to 99.4%. The surface hydrophilicity is limited due to roughness reduction. The average grain size of top and side surface can be decreased by 6.74% and 28.79% due to the increasement of cooling rate. The average microhardness and ductility can be improved due to grain refinement and defect elimination.
The preparation of aluminum matrix composites (AMCs) by laser additive manufacturing (AM) technology has become an important means of improving performance of aluminum alloys. In this work, a novel ...in-situ synthesis method of selective laser melting combined combustion synthesis (SLM-CS) was used to prepare dual-phase reinforced AMCs. The feasibility of a B4C–Ti combustion synthesis reaction system to produce TiB2 and TiC ceramics by selective laser melting (SLM) was verified. AlSi10Mg alloy matrix composites with dual reinforcements were then fabricated by SLM, and systematic qualitative and quantitative phase analysis was carried out. The calculation results of the graphical-extrapolation method show that the lattice constant of α-Al matrix phase in the composites increases from 0.40466 nm to 0.40528 nm. The effects of a series of reactants with different chemical element composition ratios on the characteristics of melting process and non-equilibrium solidification microstructure were studied. The preliminary principles of the combustion chemical reaction under the rapid and continuous laser scanning were concluded from the theory and experiments results. In terms of mechanical properties, an appropriate amount of ceramic particles results in a significant improvement in the microhardness and elastic modulus, and yet composites prepared with a mixture powder amount greater than 0.7 wt % witnessing a clear drop in the tensile strength as well.
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•Composites were successfully produced via independent B4C-Ti combustion chemical reaction system in SLMed AlSi10Mg alloy.•Si released from α-Al is attributed to the formation of up to 18% Ti3SiC2 uniformly distributed in the melt pool.•The lattice constant of α-Al increases due to solid solution substitution, also indicating the scale of chemical reaction.•The chemical reaction provides additional heat input, largely influencing the size and morphology of the molten pool.•An increased amount of ceramics significantly improves the microhardness and clearly reduces the fracture strength.
The identification and classification of traditional Chinese herbal medicines demand significant time and expertise. We propose the dual-teacher supervised decay (DTSD) approach, an enhancement for ...Chinese herbal medicine recognition utilizing a refined knowledge distillation model. The DTSD method refines output soft labels, adapts attenuation parameters, and employs a dynamic combination loss in the teacher model. Implemented on the lightweight MobileNet_v3 network, the methodology is deployed successfully in a mobile application. Experimental results reveal that incorporating the exponential warmup learning rate reduction strategy during training optimizes the knowledge distillation model, achieving an average classification accuracy of 98.60% for 10 types of Chinese herbal medicine images. The model boasts an average detection time of 0.0172 s per image, with a compressed size of 10 MB. Comparative experiments demonstrate the superior performance of our refined model over DenseNet121, ResNet50_vd, Xception65, and EfficientNetB1. This refined model not only introduces an approach to Chinese herbal medicine image recognition but also provides a practical solution for lightweight models in mobile applications.
Due to the existence of cotton weeds in a complex cotton field environment with many different species, dense distribution, partial occlusion, and small target phenomena, the use of the YOLO ...algorithm is prone to problems such as low detection accuracy, serious misdetection, etc. In this study, we propose a YOLOv8-DMAS model for the detection of cotton weeds in complex environments based on the YOLOv8 detection algorithm. To enhance the ability of the model to capture multi-scale features of different weeds, all the BottleNeck are replaced by the Dilation-wise Residual Module (DWR) in the C2f network, and the Multi-Scale module (MSBlock) is added in the last layer of the backbone. Additionally, a small-target detection layer is added to the head structure to avoid the omission of small-target weed detection, and the Adaptively Spatial Feature Fusion mechanism (ASFF) is used to improve the detection head to solve the spatial inconsistency problem of feature fusion. Finally, the original Non-maximum suppression (NMS) method is replaced with SoftNMS to improve the accuracy under dense weed detection. In comparison to YOLO v8s, the experimental results show that the improved YOLOv8-DMAS improves accuracy, recall, mAP0.5, and mAP0.5:0.95 by 1.7%, 3.8%, 2.1%, and 3.7%, respectively. Furthermore, compared to the mature target detection algorithms YOLOv5s, YOLOv7, and SSD, it improves 4.8%, 4.5%, and 5.9% on mAP0.5:0.95, respectively. The results show that the improved model could accurately detect cotton weeds in complex field environments in real time and provide technical support for intelligent weeding research.
In-situ synthesis of ceramics hybrid reinforced Al matrix composites (AMCs) by laser powder bed fusion (L-PBF) induced combustion reaction is a promising strategy to strengthen Al alloys. However, ...the in-situ formed microstructures are highly sensitive to the stability of mixed multi-powder feedstocks, which is a challenge to fabricate AMCs. This work develops a novel approach to obtain B4C coated Ti particles (hereafter as B4C@Ti) by collosol spraying to prepare (B4C@Ti)/AlSi10Mg composite powders. L-PBF technique was used to design and manufacture (TiB2+TiC)/AlSi10Mg composites by collosol coated powders. The effects of the coating process on the powder characteristics and phase structural evolution were systematically investigated, and the microstructures and dynamic microhardness of associated composites were monitored to reveal its underlying in-situ formation mechanism. Results indicate that the introduced B4C@Ti particles reduced the laser reflectivity of AlSi10Mg powders by 2.0 % and improved the K-M absorption factor by 4.8 %. The formation of Ti3SiC2 transition phase in the as-built composites was inhibited, and the supersaturated Si dissolution resulted in the lattice constant (a = 4.0466 Å) and interplanar spacing (d(111) = 2.3363 Å) of α-Al matrix phase increasing to 4.0504 Å and 2.3385 Å, respectively. The nanoscale TiB2 and TiC ceramic phases were in-situ formed within the elemental transition zone (ETZ) around the residual B4C particles, and the limited titanium source in the AlSi10Mg molten pool generated only TiB2 rather than TiB. The average values of dynamic microhardness of the L-PBF as-built composites concomitantly increased from 1.37 ± 0.08 GPa to 1.80 ± 0.13 GPa.
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•A coated composite powder for L-PBFed (TiB2 +TiC)/AlSi10Mg composite was prepared.•The L-PBFed composite with coated powder have higher dynamic microhardness than uncoated powder.•The limited Ti in the molten pool caused the formation of TiB2 rather than TiB.•Ti3SiC2 generation relies on whether the precipitated Si will react with B4C-Ti.
In single-step metal Additive Manufacturing (AM) processes, thermal cycling resulting from inappropriate scanning length and deposition height will eventually cause the cracking and deformation of ...the deposits, which will significantly damage object performance and intended applications. In this work, a unique altering thermal cycling pathway is proposed to efficiently control the cracking and deformation of AMed CuSi3Mn alloys without either using any auxiliary equipment or adjusting the alloy composition. With the help of the Intrinsic Heat Treatment (IHT) caused by secondary or multiple heating and cooling between the subsequent layers and the previous layers, a crack-free cylindric part fabricated by the Gas Metal Arc assisted Directed Energy Deposition (GMA-DED) based on Surface Tension Transfer (STT) is finally obtained, at the same time, the experimental results were verified by the numerical simulation. This further contributes to a superior deposition strategy to control the crack and deformation behavior on the metal AM.
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•CuSi3Mn cylindric parameters are sensitive to cracking built by DED.•A suitable deposition strategy was determined by the principle of thermal cycle.•The segregation of silicon and the solution of manganese are crucial to cracks.•The deposition height has a stronger effect on cracking than the scanning length.•The scanning length has a greater effect on deformation than the deposition height.
Pulsed laser micropropulsion (PLMP) offers a promising avenue for miniature space craft, yet conventional propellants face challenges in balancing efficiency and stability. An optical-propulsion ...metastructure strategy using metal-organic frameworks (MOFs) is presented to generate graphene-metal metastructures (GMM), specifically GMM-(HKUST-1), which significantly enhances PLMP performance. This novel approach leverages the unique interaction between pulsed lasers and the precisely engineered GMMs-comprising optimized metal nanoparticle size, graphene layers, and inter-particle gaps-to boost both propulsion efficiency and stability. Experimental and numerical analyses reveal that GMM-(HKUST-1) achieves aspecific impulse of 1072.94 s, ablation efficiency of 51.22%, and impulse thrust per mass of 105.15 µN µg-1, surpassing traditional propellants. With an average particle size of ≈12 nm and a density of 0.958 g cm-3, these metastructures exhibit 99% light absorption efficiency and maintain stability under atmospheric and humid conditions. The graphene nanolayer efficiently absorbs and converts laser energy, while the metal nanostructures enhance light-matter interactions, promoting energy transfer and material stability. These findings suggest that this GMM-based optical-propulsion strategy can revolutionize microspacecraft propulsion and energy systems, offering significant advancements across various domains.Pulsed laser micropropulsion (PLMP) offers a promising avenue for miniature space craft, yet conventional propellants face challenges in balancing efficiency and stability. An optical-propulsion metastructure strategy using metal-organic frameworks (MOFs) is presented to generate graphene-metal metastructures (GMM), specifically GMM-(HKUST-1), which significantly enhances PLMP performance. This novel approach leverages the unique interaction between pulsed lasers and the precisely engineered GMMs-comprising optimized metal nanoparticle size, graphene layers, and inter-particle gaps-to boost both propulsion efficiency and stability. Experimental and numerical analyses reveal that GMM-(HKUST-1) achieves aspecific impulse of 1072.94 s, ablation efficiency of 51.22%, and impulse thrust per mass of 105.15 µN µg-1, surpassing traditional propellants. With an average particle size of ≈12 nm and a density of 0.958 g cm-3, these metastructures exhibit 99% light absorption efficiency and maintain stability under atmospheric and humid conditions. The graphene nanolayer efficiently absorbs and converts laser energy, while the metal nanostructures enhance light-matter interactions, promoting energy transfer and material stability. These findings suggest that this GMM-based optical-propulsion strategy can revolutionize microspacecraft propulsion and energy systems, offering significant advancements across various domains.
Crystalline polysaccharides are useful for important and rapidly growing applications ranging from advanced energy storage, green electronics, and catalyst or enzyme supports to tissue engineering ...and biological devices. However, the potential value of chitin in such applications is currently neglected because of its poor swellability, reactivity, and solubility in most commonly used solvents. Here, a high‐efficiency, energy‐saving, and “green” route for the fabrication of extremely strong and transparent chitin films is described in which chitin is dissolved in an aqueous KOH/urea solution and neutralized in aqueous ethanol solution. The neutralization temperature, ethanol concentration, and chitin solution deacetylation time are critical parameters for the self‐assembly of chitin chains and for tuning the morphology and aggregate structures of the resulting chitin hydrogels and films. Moreover, the drawing orientation can produce extremely strong and tough chitin films with a tensile strength, Young's modulus, and work of fracture of 226 MPa, 7.2 GPa, and 20.3 MJ m−3, respectively. The method developed here should contribute to the utilization of seafood waste and, thereby, to the sustainable use of marine resources.
Extremely strong and transparent chitin films are prepared using a high‐efficiency, energy‐saving, and “green” route in which chitin is dissolved in an aqueous KOH/urea solution. The chitin films exhibit high strength and high toughness with a tensile strength, Young's modulus, and work of fracture of 226 MPa, 7.2 GPa, and 20.3 MJ m−3, respectively. This method should contribute to the development of sustainable marine resources.
Polysaccharide‐based hydrogels have multiple advantages because of their inherent biocompatibility, biodegradability, and non‐toxicic properties. The feasibility of using polysaccharide‐based ...hydrogels could be improved if they could simultaneously fulfill the mechanical property and cell compatibility requirements for practical applications. Herein, the construction of double‐cross‐linked (DC) cellulose hydrogels is described using sequential chemical and physical cross‐linking, resulting in DC cellulose hydrogels that are mechanically superior to single‐cross‐linked cellulose hydrogels. The formation and spatial distribution of chemically cross‐linked domains and physically cross‐linked domains within the DC cellulose hydrogels are demonstrated. The molar ratio of epichlorohydrin to anhydroglucose units of cellulose and the concentration of the aqueous ethanol solution are two critical parameters for obtaining mechanically strong and tough DC cellulose hydrogels. The mechanical properties of the DC cellulose hydrogels under loading‐unloading cycles are described using compression and tension models. The possible toughening mechanism of double‐cross‐linking is discussed.
Double‐cross‐linked (DC) cellulose hydrogels are fabricated by a sequential chemical and physical cross‐linking strategy. The irreversible covalent cross‐linkings, cellulose II crystallite hydrates, together with the chain entanglements and strong hydrogen bonding interactions between cellulose chains endow the DC cellulose hydrogels with high strength, high toughness, and good recoverability.
Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer featured with high intra-tumoral heterogeneity and poor prognosis. To comprehensively delineate the PDAC ...intra-tumoral heterogeneity and the underlying mechanism for PDAC progression, we employed single-cell RNA-seq (scRNA-seq) to acquire the transcriptomic atlas of 57,530 individual pancreatic cells from primary PDAC tumors and control pancreases, and identified diverse malignant and stromal cell types, including two ductal subtypes with abnormal and malignant gene expression profiles respectively, in PDAC. We found that the heterogenous malignant subtype was composed of several subpopulations with differential proliferative and migratory potentials. Cell trajectory analysis revealed that components of multiple tumor-related pathways and transcription factors (TFs) were differentially expressed along PDAC progression. Furthermore, we found a subset of ductal cells with unique proliferative features were associated with an inactivation state in tumor-infiltrating T cells, providing novel markers for the prediction of antitumor immune response. Together, our findings provide a valuable resource for deciphering the intra-tumoral heterogeneity in PDAC and uncover a connection between tumor intrinsic transcriptional state and T cell activation, suggesting potential biomarkers for anticancer treatment such as targeted therapy and immunotherapy.
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