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Laser powder bed fusion (L-PBF) is an innovative technique used to manufacture complex and customized parts. However, fabricating crack-sensitive Al–Cu–Mg alloy L-PBF parts with controlled defect levels remains challenging, as the effects of processing parameters on defect evolution are not well understood. In this study, we systematically investigated the influence of laser power, laser scanning speed, and hatching space on defect formation and evolution in L-PBF printed Al–4.1Cu–1.5Mg–0.6Mn alloy. Our findings indicate that laser power and scanning speed greatly impact the occurrence of lack-of-fusion porosity, hot cracks, and gas-induced pores. Initially, the relative density of L-PBF printed samples increases (from 97 to 99 pct) with increasing volumetric energy density (from 200 to 830 J/mm3), but then decreases with further increases in volumetric energy density (>830 J/mm3). The introduction of alloying elements Cu and Mg leads to increased laser reflectivity and heat dissipation, which in turn affects hot cracking susceptibility (HCS) and reduces the printability of Al–Cu–Mg alloy. This research provides a process map to guide the L-PBF manufacturing of crack-sensitive Al–Cu–Mg alloys. [ABSTRACT FROM AUTHOR]

The fracture behaviour of artificial metamaterials often leads to catastrophic failures with limited resistance to crack propagation. In contrast, natural materials such as bones and ceramics possess microstructures that give rise to spatially controllable crack path and toughened material resistance to crack advances. This study presents an approach that is inspired by nature’s strengthening mechanisms to develop a systematic design method enabling damage-programmable metamaterials with engineerable microfibers in the cells that can spatially program the micro-scale crack behaviour. Machine learning is applied to provide an effective design engine that accelerate the generation of damage-programmable cells that offer advanced toughening functionality such as crack bowing, crack deflection, and shielding seen in natural materials; and are optimised for a given programming of crack path. This paper shows that such toughening features effectively enable crack-resisting mechanisms on the basis of the crack tip interactions, crack shielding, crack bridging and synergistic combinations of these mechanisms, increasing up to 1,235% absorbed fracture energy in comparison to conventional metamaterials. The proposed approach can have broad implications in the design of damage-tolerant materials, and lightweight engineering systems where significant fracture resistances or highly programmable damages for high performances are sought after.Due to the complex, stochastic nature, fracture is a key challenge of artificial materials causing catastrophic failures. The authors overcame this by designing metamaterials that program damage and translate crack-resisting mechanisms [ABSTRACT FROM AUTHOR]

Large temperature gradient will produce high residual stress during laser powder bed fusion (LPBF). In metal matrix composites (MMCs), the thermal-induced stress distributes complexly. It is indispensable to study the interfacial stress of MMCs during LPBF process. In this study, a multi-phase finite element model was established to reveal the temperature and stress distributions of TiB2/Al-Si composites fabricated by LPBF. Influences of particulate geometries on the residual stress were also analyzed in the model. The numerical results indicate that the residual stress in the composites was induced by high temperature gradient and coefficient of thermal expansion mismatch simultaneously. TiB2 reinforcing particles suffer large compressive stress perpendicular to the interface. In the matrix, the stress component at the interface is negative and increases rapidly with distance from the particle increases. The interfacial compressive stress lessens the mean tension stress in the nearby regions of the matrix. Maximum von Mises stress is generated at the interface in the matrix, which may cause defects and cracks. High interfacial stress was generated in the vicinity of the vertex of cubic particles and the internal stress large in ellipsoidal particles, indicating that particles with fewer edges and smaller slenderness ratio possess greater thermal shock resistance. [ABSTRACT FROM AUTHOR]

This research aimed to investigate effects of different yeast culture (YC) levels on in vitro fermentation characteristics and bacterial and fungal community under high concentrate diet. A total of 5 groups were included in the experiment: control group without YC (CON), YC1 (0.5% YC proportion of substrate dry matter), YC2 (1%), YC3 (1.5%) and YC4 (2%). After 48 h of fermentation, the incubation fluids and residues were collected to analyze the ruminal fermentation parameters and bacterial and fungal community. Results showed that the ruminal fluid pH of YC2 and YC4 groups was higher (P < 0.05) than that of CON group. Compared with CON group, the microbial protein, propionate and butyrate concentrations and cumulative gas production at 48 h of YC2 group were significantly increased (P < 0.05), whereas an opposite trend of ammonia nitrogen and lactate was observed between two groups. Microbial analysis showed that the Chao1 and Shannon indexes of YC2 group were higher (P < 0.05) than those of CON group. Additionally, YC supplementation significantly decreased (P < 0.05) Succinivibrionaceae_UCG-001, Streptococcus bovis and Neosetophoma relative abundances. An opposite tendency of Aspergillus abundance was found between CON and YC treatments. Compared with CON group, the relative abundances of Prevotella, Succiniclasticum, Butyrivibrio and Megasphaera elsdenii were significantly increased (P < 0.05) in YC2 group, while Apiotrichum and unclassified Clostridiales relative abundances were decreased (P < 0.05). In conclusion, high concentrate substrate supplemented with appropriate YC (1%) can improve ruminal fermentation and regulate bacterial and fungal composition. [ABSTRACT FROM AUTHOR]

Although the power conversion efficiency values of perovskite solar cells continue to be refreshed, it is still far from the theoretical Shockley-Queisser limit. Two major issues need to be addressed, including disorder crystallization of perovskite and unbalanced interface charge extraction, which limit further improvements in device efficiency. Herein, we develop a thermally polymerized additive as the polymer template in the perovskite film, which can form monolithic perovskite grain and a unique "Mortise-Tenon" structure after spin-coating hole-transport layer. Importantly, the suppressed non-radiative recombination and balanced interface charge extraction benefit from high-quality perovskite crystals and Mortise-Tenon structure, resulting in enhanced open-circuit voltage and fill-factor of the device. The PSCs achieve certified efficiency of 24.55% and maintain >95% initial efficiency over 1100 h in accordance with the ISOS-L-2 protocol, as well as excellent endurance according to the ISOS-D-3 accelerated aging test. Disorder crystallization of perovskite and unbalanced charge extraction limit the performance of perovskite solar cells. Here, the authors develop self-polymerizing additive to form monolithic perovskite grains with mortise-tenon structure, achieving efficiency over 24% and long device stability. [ABSTRACT FROM AUTHOR]

Market impact costs are important factors to portfolio management, which always lead to adverse price fluctuations in trading. As the practical trading volume becomes increasingly large, the Problem of Portfolio Optimization with Market Impact Costs (MICPOP) has become more important. Traditional MICPOPs involve seeking an optimal allocation of capital to a limited number of assets with respect to either additional constraints or a weighted sum of objectives (net return, investment risk). We suggest solving MICPOPs with Multi-Objective Evolutionary Algorithms (MOEAs). Specifically, we formulate MICPOPs as a bi-objective optimization problem. The advantages of MOEAs over state-of-the-art single objective approaches to MICPOPs will be shown through empirical studies. Our study has revealed that a well-known MOEA, namely Nondominated Sorting Genetic Algorithm II (NSGA-II), fails to provide satisfactory solution quality sometimes. Hence, a memetic MOEA for Portfolio Optimization with Market Impact costs (POMI-MOEA), which inherits the global search capability of NSGA-II while introducing a new local search operator, is proposed and evaluated in this paper. Comprehensive experimental studies on 11 portfolio cases have shown the superiority of POMI-MOEA over NSGA-II and other two MOEAs for MICPOPs. [ABSTRACT FROM AUTHOR]

Realizing high performance of ordinary robots is one of the core problems in robotic research. Improving the performance of ordinary robots usually relies on the collaborative development of multiple research fields, resulting in high costs and difficulty to complete some high-precision tasks. As a comparison, humans can realize extraordinary overall performance under the condition of limited computational-energy consumption and low absolute precision in sensing and controlling each body unit. Therefore, developing human-inspired robotic systems and algorithms is a promising avenue to improve the performance of robotic systems. In this review, the cutting-edge research work on human-inspired intelligent robots in decision-making, cognition, motion control, and system design is summarized from behavior- and neural-inspired aspects. This review aims to provide a significant insight into human-inspired intelligent robots, which may be beneficial for promoting the integration of neuroscience, machinery, and control, so as to develop a new generation of robotic systems. [ABSTRACT FROM AUTHOR]

Broad-spectrum resistance has great values for crop breeding. However, its mechanisms are largely unknown. Here, we report the cloning of a maize NLR gene, RppK, for resistance against southern corn rust (SCR) and its cognate Avr gene, AvrRppK, from Puccinia polysora (the causal pathogen of SCR). The AvrRppK gene has no sequence variation in all examined isolates. It has high expression level during infection and can suppress pattern-triggered immunity (PTI). Further, the introgression of RppK into maize inbred lines and hybrids enhances resistance against multiple isolates of P. polysora, thereby increasing yield in the presence of SCR. Together, we show that RppK is involved in resistance against multiple P. polysora isolates and it can recognize AvrRppK, which is broadly distributed and conserved in P. polysora isolates. Southern corn rust (SCR) caused by Puccinia polysora is a major maize disease that can result in major yield loss. Here, the authors report the expression of a CC-NB-LRR type of R gene RppK results in SCR resistance in susceptible maize lines and it can recognize the effector AvrRppK produced by P. polysora. [ABSTRACT FROM AUTHOR]

The non-castable Al alloy can hardly be printed by additive manufacturing (AM), because of the serious hot cracking problem induced by the wide solidification range. Here, the in-situ mixing salt method in combination with gas atomization, which is suitable for mass AM production, is first proposed to produce the powders of conventional non-castable alloy, behaving with excellent printability. For example, the non-castable Al4Cu1.6Mg0.6Mn (A0T) alloy and the pre-decorated TiB2/Al4Cu1.6Mg0.6Mn (A2T) alloy powders are prepared and their printability is evaluated in the powder bed fusion technique. The results show that the cracks are eliminated in the as-printed A2T alloy caused by the introduction of TiB2 particles. In detail, the as-printed A2T alloy shows the novel fine equiaxed-columnar bimodal grain microstructure. It has the average grain size of the printed A2T alloy is ~ 5.2 μm, which is significantly reduced to ~ 38.8 μm in the as-printed A0T alloy. Therefore, the as-printed A2T alloy exhibits the improved ultimate tensile strength (~ 371.6 MPa) and total elongation at fracture (~ 7.1 pct). Generally, this manuscript suggests a roadmap to improve the printability of the non-castable alloy for mass AM production. [ABSTRACT FROM AUTHOR]

Laser powder deposition (LPD), as one of the most widely used additive manufacturing methods for metals, is an important rapid prototype manufacturing and repairing method for large components. However, great challenges exist in LPD of aluminum alloy due to the high reflectivity to laser, the poor fluidity of the powder, the high porosity in the printed component, and the crack sensitivity, which blocks the performance of the printed structure and limits its application. Recently, various researchers have focused on LPD of aluminum alloys and explored its potential mechanism. This paper reports on the recent advances in this area and highlights the key topics requiring attention, presenting the knowledge gaps in this industry. Our work aims to develop a comprehensive understanding of the interrelation among the various aspects of the subject suggesting directions for improvement in producing aluminum alloy structure with LPD. [ABSTRACT FROM AUTHOR]

During the additive manufacturing (AM) process, energy is transferred from the energy beam to the processed material. The high-energy input and uneven temperature distribution result in the high-temperature gradient, large thermal stress, and warping deformation. The scanning strategy, one of the representative AM processing parameters, plays an important role in the microstructures, mechanical properties, and residual stresses of 3D printed parts. It is necessary to review the current state of research about scanning strategy in additive manufacturing, and this paper seeks to address this need. This review mainly focuses on the scanning strategies in selective laser melting process. Various scanning strategies and their effects on mechanical properties, microstructures, and residual stresses of selective laser melted parts are summarized. Finally, some suggestions on the optimization of scanning strategy for better performance are provided based on the above analysis. [ABSTRACT FROM AUTHOR]

The colour of water-jet rewritable paper (WJRP) is difficult to be expanded via single hydrochromic molecule, especially black. Here, inspired by the amazing phenomenon of bound-water in cells enabling various biological transformations via facilitating synergistic inter-/intra-molecular proton transfer, we present a simple strategy toward WJRP based on binary systems containing less-sensitive acidochromic dyes and mild proton donors (or developers). With such a binary system containing commercial black dye as the colouring agent, benzyl 4-hydroxybenzoate as the developer, and biomimetic bound-water as proton-transferring medium, we successfully achieve the long-awaited black WJRP. Printed images on such WJRP have excellent performances and long retaining time (>1 month). In addition, the robustness, durability and reversibility of WJRP could be increased distinctly by using polyethylene terephthalate as substrate. This strategy significantly expands hydrochromic colours to entire visible range in an eco-friendly way, which opens an avenue of smart materials for practical needs and industrialization. Water based inks used for water-jet rewritable paper (WJRP) are an environmental friendly alternative to conventional printing, but black colour in WJRP could not be realized so far. Here the authors demonstrate black as well as other colour WJRP based on binary systems containing less-sensitive acidochromic dyes and mild proton donors. [ABSTRACT FROM AUTHOR]

In this manuscript, weld pool dynamics in laser welding of various series of aluminum alloys were investigated by the in situ X-ray phase contrast imaging system. The experimental results showed that metal irradiated by laser was evaporated immediately, which generated the keyhole. Then metal surrounding the keyhole was melted gradually with the heat from keyhole. The growth rate of keyhole depth had a positive linear correlation with the total content of low boiling temperature elements (TCE), so did the keyhole depth and diameter at the stable stage. Longitudinal view area of the molten pool had a negative linear correlation with the thermal conductivity of aluminum alloy. The measured laser absorption rate had the same variation trend with the ratio of keyhole depth to diameter, and the highest absorption rate of 58% appeared in laser welding of aluminum alloy with TCE equal to 2.1%. Violent fluctuation in keyhole shape was avoided in aluminum alloy with TCE lower than 2.1%, where the surface tension and recoil pressure of metal vapor were balanced. To sum up, the effect of alloy element on weld pool dynamics in laser welding of aluminum alloys was firstly quantified in this manuscript. [ABSTRACT FROM AUTHOR]