Wrapping effect of secondary phases on the grains: increased corrosion resistance of Mg–Al alloys

The discrete secondary phases usually cause severe galvanic corrosion, thereby resulting in rapid degradation for Mg–Al alloys in orthopaedics application. In this study, CaO was introduced into Mg–Al–Zn (AZ61) alloy via selective laser melting (SLM) to ameliorate the characterisations of the secondary phases, with an aim to improve its corrosion behaviour. Results revealed that CaO reacted with Mg and Al in Mg–Al alloys during SLM, suppressing the formation of coarse Mg₁₇Al₁₂ phase and promoting the formation of (Mg, Al)₂Ca phase. Meanwhile, the rapid solidification during SLM promoted the homogeneous precipitation of the second phase. As a result, inert (Mg, Al)₂Ca phase homogeneously wrapped the Mg grains, which effectively protected them from the invasion of corrosion solution. Thus, the degradation rate was remarkably reduced from 0.073 to 0.031?mg?cm^–2?h^–1. Furthermore, AZ61-9CaO exhibited good cytocompatibility. This work suggested that AZ61-9CaO was promising candidates for orthopaedics implants.     

Investigation of Ablation Efficiency of Stainless Steel Using Pulsed Lasers in Burst Mode

Due to its high corrosion resistance and mechanical properties, stainless steel is commonly used in various industrial applications. Although different types of stainless steel are similar in their chemical composition, they can differ significantly in their thermal diffusivity. This property is relevant in the ability of a material to conduct heat and thus, in laser processing. In this frame, this study compares the ablation efficiency and characteristics of polished stainless steel samples of the alloys AISI 304, AISI 420, and AISI 316Ti. They are irradiated with single ultrashort pulses having pulse durations between 250 fs and 10 ps as well as using GHz burst modii. The goal is to investigate the differences in both the ablation threshold and the ablation rate to improve the ablation efficiency. The results show that shorter pulse durations lead to a more efficient ablation process. On the other hand, GHz bursts are found to be, in general, less efficient. In addition, there is a significant difference in the surface morphology depending on the process parameters. The differences in the thermal diffusivity do not significantly influence the ablation threshold fluence but surface morphology and the ablation rate.     

Engineered Macrophages: A Safe-by-Design Approach for the Tumor Targeting Delivery of Sub-5 nm Gold Nanoparticles

Ultrasmall nanoparticles (NPs) are a promising platform for the diagnosis and therapy of cancer, but the particles in sizes as small as several nanometers have an ability to translocate across biological barriers, which may bring unpredictable health risks. Therefore, it is essential to develop workable cell-based tools that can deliver ultrasmall NPs to the tumor in a safer manner. Here, this work uses macrophages as a shuttle to deliver sub-5 nm PEGylated gold (Au) NPs to tumors actively or passively, while reducing the accumulation of Au NPs in the brain. This work demonstrates that sub-5 nm Au NPs can be rapidly exocytosed from live macrophages, reaching 45.6% within 24 h, resulting in a labile Au NP-macrophage system that may release free Au NPs into the blood circulation in vivo. To overcome this shortcoming, two straightforward methods are used to engineer macrophages to obtain “half-dead” and “dead” macrophages. Although the efficiency of engineered macrophages for delivering sub-5 nm Au NPs to tumors is 2.2–3.8% lower than that of free Au NPs via the passive enhanced permeability and retention effect, this safe-by-design approach can dramatically reduce the accumulation of Au NPs in the brain by more than one order of magnitude. These promising approaches offer an opportunity to expand the immune cell- or stem cell-mediated delivery of ultrasmall NPs for the diagnosis and therapy of diseases in a safer way in the future.     

Transient response of Bouc–Wen hysteretic system under random excitation via RBFNN method

Hysteresis normally exhibited by mechanical systems and materials is so prevalent that its response prediction under random excitation has been extensively investigated for decades. Nevertheless, the transient solution of the response, which is crucial for assessing the system’s reliability, is still a challenging topic that requires additional development. To this regard, this work proposes a semi-analytical method using the radial basis function neural network (RBFNN) to attain the transient probability density distribution of the randomly excited Bouc–Wen system. Specifically, the trial solution of the corresponding FPK equation is configured as the RBFNN with undetermined time-varying weight coefficients. By discretizing the time derivative with the Euler difference method, a loss function with time recurrence is derived and minimized to yield the time-varying optimal weight coefficients through the optimization method. Additionally, an optimized sampling strategy is adopted to reduce the burden of calculation. Finally, the Bouc–Wen hysteretic systems with softening and hardening nonlinearity are considered to investigate the performance of the adopted technique. The numerical results have shown that the evaluation process of the probability density functions(PDFs) can be captured well with sufficient accuracy and efficiency. The proposed efficient sampling technique can provide considerable efficiency improvement for the medium dimension system. The work of the paper will contribute to the reliability design of hysteretic structures in engineering.     

Direct numerical simulations for assessment of gas-solid drag models in two-dimensional random arrays of particles

The momentum exchange between the phases plays a vital role in modelling of gas–solid flows and it is mathematically described by drag models. However, no consensus exists on which drag model gives the most accurate prediction of the drag force, and, despite the increase in available computing power, the same drag models are used in two-dimensional and three-dimensional simulations. In this study, direct numerical simulations of gas flow through multiple random configurations of static monodisperse particles are performed. The variations of solid volume fraction and particle Reynolds number are in the ranges of 0.05–0.4 and 13.7–136.9, respectively. The drag force exerted on particles is calculated and properly averaged. Based on the simulation results, thirteen drag models are compared and correction factors are introduced using the stochastic gradient descent algorithm. The correction factors provide a simple adjustment for the models to be used in 2D modelling.     

Colloidal Quantum Dot Infrared Lasers Featuring Sub-Single-Exciton Threshold and Very High Gain

The use of colloidal quantum dots (CQDs) as a gain medium in infrared laser devices has been underpinned by the need for high pumping intensities, very short gain lifetimes, and low gain coefficients. Here, PbS/PbSSe core/alloyed-shell CQDs are employed as an infrared gain medium that results in highly suppressed Auger recombination with a lifetime of 485 ps, lowering the amplified spontaneous emission (ASE) threshold down to 300 µJ cm⁻², and showing a record high net modal gain coefficient of 2180 cm⁻¹. By doping these engineered core/shell CQDs up to nearly filling the first excited state, a significant reduction of optical gain threshold is demonstrated, measured by transient absorption, to an average-exciton population-per-dot 〈N^th〉_g of 0.45 due to bleaching of the ground state absorption. This in turn have led to a fivefold reduction in ASE threshold at 〈N^th〉_ASE = 0.70 excitons-per-dot, associated with a gain lifetime of 280 ps. Finally, these heterostructured QDs are used to achieve near-infrared lasing at 1670 nm at a pump fluences corresponding to sub-single-exciton-per-dot threshold (〈N^th〉_Las = 0.87). This work brings infrared CQD lasing thresholds on par to their visible counterparts, and paves the way toward solution-processed infrared laser diodes.     

First-principles calculations of binary Al compounds: Enthalpies of formation and elastic properties

Systematic first-principles calculations of energy vs. volume (E-V) and single crystal elastic stiffness constants (c_ij’s) have been performed for 50 Al binary compounds in the Al-X (X = Co, Cu, Hf, Mg, Mn, Ni, Sr, V, Ti, Y, and Zr) systems. The E-V equations of state are fitted by a four-parameter Birch-Murnaghan equation, and the c_ij’s are determined by an efficient strain-stress method. The calculated lattice parameters, enthalpies of formation, and c_ij’s of these binary compounds are compared with the available experimental data in the literature. In addition, elastic properties of polycrystalline aggregates including bulk modulus (B), shear modulus (G), Young’s modulus (E), B/G (bulk/shear) ratio, and anisotropy ratio are calculated and compared with the experimental and theoretical results available in the literature. The systematic predictions of elastic properties and enthalpies of formation for Al-X compounds provide an insight into the understanding and design of Al-based alloys.     

Modeling of thermodynamic properties of ABr-PrBr3 (A=Li-Cs ) systems

The thermodynamic properties of ABr-PrBr₃(A=Li-Cs) systems were assessed by the CALPHAD method. The liquid phase in the systems was described by the non-stoichiometric associate model. The entropies of mixing in the liquid were evaluated from experimental liquidus and enthalpy of mixing data. For the pseudobinary compounds A₃PrBr₆,APr₂Br₇, and A₂PrBr₅ (A=K,Rb) and Cs₃PrBr₆ and CsPr₂Br₇, the dependences of Gibbs energies of formation on temperature were calculated. The anomalies of sequences of thermodynamic properties in RbBr-PrBr₃ were observed and discussed. The nature of the liquid phase and precision of calculations of the Rb₂PrBr₅(s) compound were discussed.