Atomistic-Continuum Study of an Ultrafast Melting Process Controlled by a Femtosecond Laser-Pulse Train.

In femtosecond laser fabrication, the laser-pulse train shows great promise in improving processing efficiency, quality, and precision. This research investigates the influence of pulse number, pulse interval, and pulse energy ratio on the lateral and longitudinal ultrafast melting process using an experiment and the molecular dynamics coupling two-temperature model (MD-TTM model), which incorporates temperature-dependent thermophysical parameters. The comparison of experimental and simulation results under single and double pulses proves the reliability of the MD-TTM model and indicates that as the pulse number increases, the melting threshold at the edge region of the laser spot decreases, resulting in a larger diameter of the melting region in the 2D lateral melting results. Using the same model, the lateral melting results of five pulses are simulated. Moreover, the longitudinal melting results are also predicted, and an increasing pulse number leads to a greater early-stage melting depth in the melting process. In the case of double femtosecond laser pulses, the pulse interval and pulse energy ratio also affect the early-stage melting depth, with the best enhancement observed with a 2 ps interval and a 3:7 energy ratio. However, pulse number, pulse energy ratio, and pulse interval do not affect the final melting depth with the same total energies. The findings mean that the phenomena of melting region can be flexibly manipulated through the laser-pulse train, which is expected to be applied to improve the structural precision and boundary quality.

Molecular dynamics study on the diffusion process of AuAgCuNiPd high-entropy alloy metallurgy induced by pulsed laser heating.

As novel alloy materials with outstanding mechanical properties, high-entropy alloys have a wide range of promising applications. By establishing individual Au, Ag, Cu, Ni, and Pd nanolaminates with face-centered-cubic lattice structure arrangements, molecular dynamics simulation is carried out to track the diffusion process of AuAgCuNiPd high-entropy alloy metallurgy, which is induced by pulsed laser heating. The temperature, potential energy, and kinetic energy are analyzed to evaluate the metallurgy. The snapshots and atomic fractions are presented to show the mass transfer between metallic nanolaminates. The diffusion process is firstly observed 0.3 ns after the central point for pulsed laser heating (absorbed laser energy density at 7 kJ cm-3 and pulse duration of 0.5 ns). Meanwhile, the degrees of atomic activity for Au, Ag, Cu, Ni, and Pd are assessed by calculating the mean square displacement and diffusion coefficient. Ni has a slightly larger diffusion coefficient than the other four metallic elements. Moreover, after the central point of laser irradiation, the kinetic energy of the system reduces, while the potential energy increases, which relates to the transition from nanolaminates to high-entropy alloys. A critical absorbed laser energy density of 6 kJ cm-3 with a relative error of 8.3% for the generation of AuAgCuNiPd high-entropy alloys is found. The order of constituent nanolaminates configured with the earlier initiation of diffusion between atoms in the neighboring nanolaminates speeds up the metallurgy.

Synthesis of Silver Nanoparticles Loaded onto Polymer-Inorganic Composite Materials and Their Regulated Catalytic Activity.

We present a novel approach for the preparation of polymer-TiO2 composite microgels. These microgels were prepared by the in situ hydrolysis and condensation of titanium tetrabutoxide (TBOT) in a mixed ethanol/acetonitrile solvent system, using poly(styrene-co-N-isopropylacrylamide)/poly(N-isopropylacrylamide-co-methacrylic acid) (P(St-NIPAM/P(NIPAM-co-MAA)) as the core component. Silver nanoparticles (AgNPs) were controllably loaded onto the polymer-TiO2 composite microgels through the reduction of an ammoniacal silver solution in ethanol catalyzed by NaOH. The results showed that the P(St-NIPAM)/P(NIPAM-co-MAA)-TiO2 (polymer-TiO2) organic-inorganic composite microgels were less thermally sensitive than the polymer gels themselves, owing to rigid O⁻Ti⁻O chains introduced into the three-dimensional framework of the polymer microgels. The sizes of the AgNPs and their loading amount were controlled by adjusting the initial concentration of [Ag(NH3)2]⁺. The surface plasmon resonance (SPR) band of the P(St-NIPAM)/P(NIPAM-co-MAA)-TiO2/Ag (polymer-TiO2/Ag) composite microgels can be tuned by changing the temperature of the environment. The catalytic activities of the polymer-TiO2/Ag composite microgels were investigated in the NaBH4 reduction of 4-nitrophenol. It was demonstrated that the organic-inorganic network chains of the polymer microgels not only favor the mass transfer of the reactant but can also modulate the catalytic activities of the AgNPs by tuning the temperature.

Silencing of TKTL1 by siRNA inhibits proliferation of human gastric cancer cells in vitro and in vivo.

Tumorigenesis requires energy production via aerobic glycolysis (Warburg effect) in malignant tumors. Recent research has demonstrated that the pentose phosphate pathway (PPP) is augmented in some tumors, especially the non-oxidative part of the PPP which is controlled by transketolase (TKT) enzyme reactions. One TKT isoform, transketolase-like protein 1 (TKTL1), is specifically upregulated in different human cancers, and its overexpression predicts poor patient survival. To further define the function of in malignant progression, we employed the small interference RNA (siRNA) technique to knockdown gene expression of TKTL1 in the gastric cancer cell line AGS. We used TKTL1 siRNA to observe the effect of reduced TKTL1 expression on gastric cancer tumorigenesis in a nude mice xenograft model and on proliferation in vitro. Our results showed that the expression of double stranded RNA led to the efficient and specific inhibition of endogenous TKTL1 expression in AGS cells. In addition, the TKT activity was significantly deceased in the TKTL1 siRNA-treated AGS cells. TKTL1 suppression resulted in delayed cell proliferation in vitro. Furthermore, loss of TKTL1 inhibited the growth of AGS tumor xenografts. Altogether, our findings indicate that the specific inhibition of TKTL1 may be important therapeutically.