ABSTRACT
AgNbO3 (AN) antiferroelectrics (AFEs) are regarded as a promising candidate for high-property dielectric capacitors on account of their high maximum polarization, double polarization-electric field (P-E) loop characteristics, and environmental friendliness. However, high remnant polarization (Pr) and large polarization hysteresis loss from room-temperature ferrielectric behavior of AN and low breakdown strength (Eb) cause small recoverable energy density (Wrec) and efficiency (η). To solve these issues, herein, we have designed Sm3+ and Ta5+ co-doped AgNbO3. The addition of Sm3+ and Ta5+ reduces the tolerance factor, polarizability of B-site cations, and domain-switching barriers, enhancing AFE phase stability and decreasing hysteresis loss. Meanwhile, adding Sm3+ and Ta5+ leads to decreased grain sizes, increased band gap, and reduced leakage current, all contributing to increased Eb. As a benefit from the above synergistic effects, a high Wrec of 7.24 J/cm3, η of 72.55%, power density of 173.73 MW/cm3, and quick discharge rate of 18.4 ns, surpassing those of many lead-free ceramics, are obtained in the (Ag0.91Sm0.03)(Nb0.85Ta0.15)O3 ceramic. Finite element simulations for the breakdown path and transmission electron microscopy measurements of domains verify the rationality of the design strategy.
ABSTRACT
The dissimilar metal welding joint is connected by the metallurgical bond of intermetallic compounds at the interface, which easily causes stress concentration at the interface and cracks continuously along the interface, resulting in low reliability in impact environments. A novel multi-layer plug and bolt connection for TC4/7A52 dissimilar metal butt joints is proposed in this manuscript and analyzes the influence mechanism of the structural design on impact toughness. The impact toughness of the Ti/Al composite butt joint is 30.3 J/cm2, which is 2.6 times that of the 7A52 BM. The layered toughening design significantly reduces stress concentrations for the butt joint at impact for the Ti/Al composite butt joint. Upon impact, the Ti/Al composite butt joint does not fracture continuously at the V-notch and exhibits significant macroscopic plastic deformation. For the microstructure of each TC4 and 7A52 layer in the impact fracture, more intragranular slip systems are activated and show a higher dislocation density. Therefore, this structural design can enable dissimilar metals to absorb more impact energy during the impact process.
ABSTRACT
In this study, Al-Mg and Al-Mg-Sc ER5356 welding wires were adopted, and the effects of the Sc element on the wetting behavior of the molten metal and the porosity of the deposited metal were investigated. Al-Mg-Sc and Al-Mg welding wires exhibit wetting angles of 17.2 and 12.4°, respectively, and their porosities of deposited metal were 0.885 and 0.454%, respectively. Adding the Sc element to ER5356 welding wires reduced the surface tension and then increased the pore difference pressure, wettability, and spreadability of the molten pool, which is beneficial for pore overflow. Besides, adding Sc elements could increase the molten droplet size and the metallic vapor recoil for the ER5356 wire and then stabilize droplet transfer.
ABSTRACT
Ants use chemical signals to communicate for various purposes related to colony function. Social organization in the red imported fire ant, Solenopsis invicta, is determined by the Sb supergene, with colonies of the monogyne (single-queen) form lacking the element and colonies of the polygyne (multiple-queen) form possessing it. Polygyne workers accept new reproductive queens in their nest, but only those carrying Sb; young winged queens lacking this genetic element are executed as they mature sexually in their natal nest or as they attempt to enter a foreign nest to initiate reproduction after mating and shedding their wings. It has been suggested that queen supergene genotype status is signaled to workers by unsaturated cuticular hydrocarbons, while queen reproductive status is signaled by piperidines (venom alkaloids). We used high-throughput behavioral assays to study worker acceptance of paper dummies dosed with fractions of extracts of polygyne queens, or blends of synthetic counterparts of queen cuticular compounds. We show that the queen supergene pheromone comprises a blend of monoene and diene unsaturated hydrocarbons. Our assays also reveal that unsaturated hydrocarbons elicit discrimination by polygyne workers only when associated with additional compounds that signal queen fertility. This synergistic effect was obtained with a polar fraction of queen extracts, but not by the piperidine alkaloids, suggesting that the chemical(s) indicating queen reproductive status are compounds more polar than cuticular hydrocarbons but are not the piperidine alkaloids. Our results advance understanding of the role of chemical signaling that is central to the regulation of social organization in an important invasive pest and model ant species.