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The results yield insights into the origin of a dynamical crossover, which is observed when lowering the temperature along isobars and was previously interpreted in terms of a fragile-to-strong transition. Our findings imply that the effect does not involve two liquid phases with an exceptionally large difference of the fragility but rather a high temperature dependence near the LLCP results from a rapid conversion from HDL-like environments with faster dynamics to LDL-like ones with slower dynamics.Transition metal nitrides have attracted great interest due to their unique crystal structures and applications. Here, we predict two N-rich iridium nitrides (IrN4 and IrN7) under moderate pressure through first-principles swarm-intelligence structural searches. The two new compounds are composed of stable IrN6 octahedrons and interlinked with high energy polynitrogens (planar N4 or cyclo-N5). Balanced structural robustness and energy content result in IrN4 and IrN7 being dynamically stable under ambient conditions and potentially as high energy density materials. read more The calculated energy densities for IrN4 and IrN7 are 1.3 kJ/g and 1.4 kJ/g, respectively, comparable to other transition metal nitrides. In addition, IrN4 is predicted to have good tensile (40.2 GPa) and shear strengths (33.2 GPa), as well as adequate hardness (20 GPa). Moderate pressure for synthesis and ambient pressure recoverability encourage experimental realization of these two compounds in near future.The thermal conductivity of model argon nanowires over a wide range of temperatures from 20 K to 70 K has been calculated using the formula obtained by solving the Boltzmann equation and independently by molecular dynamic (MD) simulations. The theoretical predictions for thermal conductivity take into account the effect of phonon confinement and boundary scattering. Two known theoretical approaches were used. The first approach is based on the solution of the Boltzmann equation with given boundary conditions and uses bulk acoustic phonon dispersion and neglects the phonon confinement effect. The second approach includes also the modification of acoustic phonon dispersion due to spatial confinement. In simulations, the square and circular shapes of wire with the transverse size of nanowires from 4.3 nm to 42.9 nm have been considered. It was found that MD simulation results match the theoretical predictions reasonably well. The obtained results showed that the phonon confinement effect influences the thermal conductivity of nanowires, but the dominant factor decreasing the thermal conductivity with the thickness of nanowires is boundary scattering. Moreover, the values of the interface specular parameter indicate that the specular phonon-boundary scattering prevails over diffuse phonon-boundary scattering.Thin films of trinitrotoluene (TNT) were shock compressed using the ultrafast laser shock apparatus at Los Alamos National Laboratory. Visible (VIS) and mid-infrared (MIR) transient absorption spectroscopies were simultaneously performed to probe for electronic and vibrational changes during shock compression of TNT. Three shock pressures (16 GPa, 33 GPa, and 45 GPa) were selected to observe no reaction, incipient reaction, and strongly developed reactions for TNT within the experimental time scale of less then 250 ps. Negligible absorption changes in MIR or VIS absorptions were observed at 16 GPa. At 33 GPa, MIR absorptions in the 3000 cm-1-4000 cm-1 range were observed to increase during the shock and continue to increase during the rarefaction, in contrast to the VIS absorption measurements, which increased during the shock and almost fully recovered during rarefaction. At 45 GPa, both VIS and MIR absorptions were strong and irreversible. The intense and spectrally broad MIR absorptions were attributed to short lived intermediates with strong, spectrally broad absorptions that dominate the spectral response. The MIR and VIS absorption changes observed at 33 GPa and 45 GPa were credited to shock induced chemistry, most likely including the formation of a very broad hydrogenic stretch feature. The results from these experiments are consistent with the chemical mechanisms that include O-H or N-H formation such as CH3 oxidation or C-N homolysis.The external voltage-driven polymer translocation through a conical pore (with a large opening at the entry and a small tip at the exit) is studied by using the Langevin dynamics simulation in this paper. The entire translocation process is divided into an approaching stage and a threading stage. First, the approaching stage starts from the polymer entering the large opening and ends up at a terminal monomer reaching the pore tip. In this stage, the polymer will undergo the conformation adjustment to fit the narrowed cross-sectional area of the pore, leading to three approaching modes the non-stuck mode with a terminal monomer arriving at the pore tip smoothly, the weak-stuck mode for the polymer stuck inside the pore for a short duration with minor conformational adjustments, and the strong-stuck mode with major conformational changes and a long duration. The approaching times (the duration of the approaching stage) of the three approaching modes show different behavior as a function of the pore apex angle. Second, the threading stage describes that the polymer threads through the pore tip with a linear fashion. In this stage, an increase in the apex angle causes the reduction of the threading time (the duration of the threading stage) due to the increase in the driving force with the apex angle at the tip. Moreover, we also find that with the increase in the apex angle or the polymer length, the polymer threading dynamics will change from the quasi-equilibrium state to the non-equilibrium state.Site-selective C-H functionalization in chemical feedstocks is a challenging and useful reaction in the broad field of chemical research. Here, we report a modular photochemical platform for the site-selective C-H pyridylation of unactivated hydrocarbons via the unique synergistic effects of triplet excited anthraquinone and an amidyl radical-based reverse hydrogen atom transfer (RHAT) agent. The selective pyridylation of tertiary and secondary C(sp3)-H bonds in abundant chemical feedstocks was achieved by employing various N-aminopyridinium salts in a highly selective fashion, thus providing a new catalytic system for the direct construction of high-value-added compounds under ambient reaction conditions. Moreover, this operationally simple protocol is applicable to a variety of linear-, branched-, and cyclo-alkanes and more complex molecules with high degrees of site selectivity under visible-light conditions, which provides rapid and straightforward access to versatile synthons for upgrading feedstocks under mild, metal-free reaction conditions.