Modern Physics Letters B

The crystallization and growth of in situ crystals during non-equilibrium laser rapid melting/solidification process is an important research topic in the fields of both Applied Physics and Materials Science. The present paper studies the development mechanisms of in situ formed Al₄SiC₄ ceramic phase within the selective laser melted SiC/AlSi10Mg composites. Two different-structured Al₄SiC₄ having strip and particle morphologies were disclosed and their growth mechanisms were influenced by laser linear energy density (LED). An elevated LED resulted in a larger degree formation of strip-structured Al₄SiC₄ with the gradually coarsened crystal sizes in its length and thickness. The homogeneously dispersed particle-shaped Al₄SiC₄ exhibited a considerably refined nanostructure with a proper increase in LED, but showing a significant coarsening of particles at an excessive LED.

In this paper, we propose an extended helicopter's rescuing model to explore the effects of multiple rescuing points on each helicopter's flying behavior during the whole rescuing process from the numerical perspective. The numerical results show that the proposed model can describe the qualitative effects of multiple rescuing points on each helicopter's speed, running trail and safe region.

A planar waveguide is demonstrated in the Yb³⁺-doped tellurite glass, using (5+6) MeV O³⁺ ion implantation with doses of (4+8)×10¹⁴ ions/cm². The implantation process of O³⁺ ions into the Yb³⁺-doped tellurite glass is simulated by the stopping and range of ions in matter (SRIM) 2010 code. The dark-mode spectra are measured by the prism-coupling system at λ = 632.8 nm. The reflectivity calculation method and the finite-difference beam propagation method are used to calculate the refractive index profile and the modal profile of transverse electric (TE) mode of the fabricated waveguide, respectively. The absorption spectra show that the transmission properties are not affected by the waveguide fabrication process.

Based on density functional theory, calculations were performed for geometrically optimized N-doped TiO₂ models. The effect of N dopant and its increasing doping concentration on the band structure are elucidated. N doping narrowed the band gap of TiO₂ and introduced isolated N 2p states within the band gap. The location of N 2p states within the band gap can be optimized by N doping concentration. All N-doped TiO₂ models shifted the absorption edge of TiO₂ toward visible light region and increasing N doping concentration improved the visible light absorption. N-doped TiO₂ model having reduced band gap without any isolated states will improve the photocatalytic response. Our results provide strong theoretical background for existing experiments.

In this paper, a new immunization strategy was established to prevent the epidemic spreading based on the principle of "Multi-granularity" and "Pre-warning Mechanism", which send different pre-warning signal with the risk rank of the susceptible node to be infected. The pre-warning means there is a higher risk that the susceptible node is more likely to be infected. The multi-granularity means the susceptible node is linked with multi-infected nodes. In our model, the effect of the different situation of the multi-granularity immunizations is compared and different spreading rates are adopted to describe the epidemic behavior of nodes. In addition the threshold value of epidemic outbreak is investigated, which makes the result more convincing. The theoretical analysis and the simulations indicate that the proposed immunization strategy is effective and it is also economic and feasible.

The crystal structure of the semiconductors TlFeSe₂ and TlFeS₂ has been studied by mean of neutron diffraction at room temperature and high pressure up to 4.2 GPa and 5.2 GPa, respectively. The chain-like monoclinic crystal structure with space group C2/m remains unchanged in both compounds in the entire pressure range. The anisotropic lattice compression and the large difference in the bulk modulus and the compressibility coefficients of the structural parameters of the two compounds have been observed. The mechanism of the observed phenomena was discussed. The enhancement of the one-dimensional antiferromagnetic and metallic character was predicted.

A simple theoretical model has been proposed to study the diameter-dependent properties of metallic nanoparticles, i.e. Ag, Au, Al, Ni, Pb, Cu and Fe. The diameter-dependent thermodynamic properties includes melting temperature, Debye temperature, evaporation temperature, melting enthapy and melting entropy. The model is also extended to study the diameter-dependent elastic properties including bulk modulus, Young's modulus and thermal expansion coefficient. On comparison with available experimental findings and other theoretical approaches, the results obtained with the present formulation depict a close agreement and demonstrate the validity of the method proposed in the present paper.

Sn-doped silicon nanocrystals (Si-NCs) embedded in silicon nitride was synthesized by post-annealing of silicon-rich silicon nitride (SRN) films deposited by co-sputtering. The effects of Sn impurity on the Si crystallization behavior and photoluminescence (PL) in SRN films were investigated. Doping with Sn dopants enhances phase separation in SRN and thus accelerates the crystallization of silicon nanoparticles. It was also found that the existence of Sn decreases crystallization temperature, and could be as low as 800°C. In the Sn-doped samples, the crystalline volume fraction increases monotonically from 16.2% to 78.5% with increasing annealing temperature and the area densities of about ~2.2×10¹² cm^-2 can be achieved after annealing at 1100°C. In addition, the intensity of PL of the SRN film could be enhanced by adding Sn impurity.