[en] The dineutron correlations and the crossover from superfluidity of neutron Cooper pairs in the ¹S₀ pairing channel to Bose–Einstein condensation (BEC) of dineutron pairs in both symmetric and neutron matter are studied within the relativistic Hartree–Bogoliubov theory, with the effective interaction PK1 of the relativistic mean-field approach in the particle–hole channel and the finite-range Gogny force in the particle–particle channel. The influence of the pairing strength on the behaviors of dineutron correlations is investigated. It is found that the neutron pairing gaps at the Fermi surface from three adopted Gogny interactions are smaller at low densities than the one from the bare nucleon–nucleon interaction Bonn-B potential. From the normal (anomalous) density distribution functions and the density correlation function, it is confirmed that a true dineutron BEC state does not appear in nuclear matter. In the cases of the Gogny interactions, the most BEC-like state may appear when the neutron Fermi momentum k_Fn∼0.3fm⁻¹. Moreover, based on the newly developed criterion for several characteristic quantities within the relativistic framework, the BCS–BEC crossover is supposed to realize in a revised density region with k_Fn∈[0.15,0.63]fm⁻¹ in nuclear matter

[en] The density dependence of nuclear symmetry energy is studied within the covariant density functional (CDF) theory in terms of the kinetic energy, isospin-singlet, and isospin-triplet potential energy parts of the energy density functional. When the Fock diagram is introduced, it is found that both isospin-singlet and isospin-triplet components of the potential energy play an important role in determining the symmetry energy. At high densities, a strong density-dependent behavior is revealed in the isospin-triplet potential part of the symmetry energy. In addition, the inclusion of the Fock terms in the CDF theory reduces the kinetic part of the symmetry energy and may lead to negative values at the supranuclear density region, which is regarded partly as the effect of the nuclear tensor-force components. The results demonstrate the importance of the Fock diagram in the CDF theory on the isospin properties of the in-medium nuclear force at high densities, especially from the isoscalar-meson coupling channels. (paper)

[en] Samples of double perovskite manganese La_2−xCa_xNiMnO₆ (x = 0, 0.05, 0.15, 0.2) are prepared by a traditional solid-state reaction. X-ray diffraction patterns show that four samples all exhibit a good uniform single phase and have perovskite crystal structures. From the temperature dependence of the magnetization in a 5 mT magnetic field (M–T) and the field dependence of the magnetization near the Curie temperature (M–H) for La_2−xCa_xNiMnO₆ (x = 0, 0.05, 0.15, 0.2), the ferromagnetism of the samples is weakened, while the antiferromagnetism is enhanced with Ca doping. Hysteresis loops at 2 K, enlarged views of the low-field hysteresis loops at 2 K under a field cooling process with a cooling field of 1T and Raman spectra at room temperature for La_2−xCa_xNiMnO₆ (x = 0, 0.05, 0.15, 0.2) show that when the Ca doping amount is x = 0.05, compared with La₂NiMnO₆, the antisite disorder degree of the system is almost the same, but the number of antiphase boundaries increases. With further Ca doping, the antisite disorders and numbers of antisite defects and antiferromagnetic antiphase boundaries increase, simultaneously strengthening the enhancement in the antiferromagnetic coupling. In addition, as the Ca doping increases, the upward deviation of the temperature-dependent χ⁻¹ ~ T for bulk La_2−xCa_xNiMnO₆ (LCNMO) from the Curie–Weiss law becomes more obvious, which shows that Ca doping enhances the long-range ferromagnetic order, antiferromagnetic clusters increase, and long-range ferromagnetic order dominates the magnetic behaviour near the ferromagnetic transition point. Finally, we discuss the magnetic entropy and electrical changes of four samples and confirm that Ca doping causes the systems to undergo a weak first-order phase transition.

[en] Nowadays, many investigations have been done for the synthesis of carbon nanotubes by diffusion flame using a variety of carbon sources. However, the change law of the temperature required for the reaction is the lack of attention. Carbon nanotubes have been synthesized from methane on a Fe–Mo/Al₂O₃ catalyst by a V-shape pyrolysis flame in this paper. The effect of pyrolysis temperature on the growth of the carbon nanotubes has been studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The optimum pyrolysis temperature of pyrolysis-flame-synthesized carbon nanotubes using methane as the carbon source has been confirmed to be 1100 degrees C, at this pyrolysis temperature, the yield of CNTs was the higher, the diameter was the smaller and the graphitization degree was the higher. Four optimum pyrolysis temperatures using different carbon sources (CH₄, C₂H₄, C₂H₂, and CO) have been compared and analyzed. The variation of the optimum pyrolysis temperature was consistent with the change of the chemical bond energy of the four carbon sources. And the ionization rate coefficients of these gas molecules in an electric field have been calculated to verify that breaking the chemical bonds of the different gas molecules required corresponding amounts of energy. Therefore chemical bond energy directly affected the pyrolysis temperature for these carbon sources during the synthesis of CNTs. (paper)

[en] Array of TiO₂ dendritic structure with nanotubes was constructed on transparent conductive fluorine-doped tin oxide glass (FTO) with titanium potassium oxalate as titanium source. Sb₂S₃ nanocrystals were successfully deposited on the TiO₂ substrate via spin-coating method. Furthermore, TiO₂/Sb₂S₃/P3HT/PEDOT:PSS composite film was prepared by successively spin-coating P3HT and PEDOT:PSS on TiO₂/Sb₂S₃. It was demonstrated that the modification of TiO₂ dendritic structure with Sb₂S₃ could enhance the light absorption in the visible region. The champion hybrid solar cell assembled by TiO₂/Sb₂S₃/P3HT/PEDOT:PSS composite film achieved a power conversion efficiency (PCE) of 1.56%. (paper)

[en] The dispersion equations of bulk modes and surface modes in a rectangular waveguide of semiconductor metamaterial are derived by a modified ''Marcatili's method^. The cutoff frequencies of the lowest TM bulk mode are discussed, and the Brillouin diagrams of different bulk modes are drawn. They demonstrate that different heights correspond to different guidance frequency ranges which have no superposition with each other and a waveguide with a larger height possesses a wider passband of light. In addition, tendencies of degeneracy for different modes are observed. Finally, the existence of surface modes is verified by a graphical method. (semiconductor devices)

[en] Hopf bifurcation and chaos of a nonlinear electromechanical coupling relative rotation system are studied in this paper. Considering the energy in air-gap field of AC motor, the dynamical equation of nonlinear electromechanical coupling relative rotation system is deduced by using the dissipation Lagrange equation. Choosing the electromagnetic stiffness as a bifurcation parameter, the necessary and sufficient conditions of Hopf bifurcation are given, and the bifurcation characteristics are studied. The mechanism and conditions of system parameters for chaotic motions are investigated rigorously based on the Silnikov method, and the homoclinic orbit is found by using the undetermined coefficient method. Therefore, Smale horseshoe chaos occurs when electromagnetic stiffness changes. Numerical simulations are also given, which confirm the analytical results. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)

[en] High speed impact experiments of rectangular plate-shaped Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 bulk metallic glass (BMG) were performed using a two-stage light gas gun. Under spherical shock waves with impact velocities ranging from 0.503 km/s to 4.917 km/s, obvious traces of laminated spallation at the back (free) surface and melting (liquid droplets) at the impact point were observed. The angles about 0°, 17°, 36°, and 90° to the shocking direction were shown in the internal samples because of the interaction between the compressive shock waves and the rarefaction waves. The compressive normal stress was found to induce the consequent temperature rise in the core of the shear band. (condensed matter: structural, mechanical, and thermal properties)

[en] We theoretically investigate the hybrid plasmonic modes of cylindrical nanocables with gold nanocore and two dielectric nanolayers (SiO₂ and BN). By solving a complete set of Maxwell's equations, the propagation constants and effective radii depending on geometrical parameters are numerically calculated. By declining a trade-off between propagation length and light confinement, high quality hybrid modes which can travel a long range of 120–200λ with a subwavelength effective radius are obtained at the optical wavelength. These modes in one-dimensional cylindrical waveguides should have potential applications in nanoscale optical device designs. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

[en] Hypervelocity impact on rectangular plate-shaped Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 bulk metallic glass (BMG) is performed by a two-stage light gas gun. The targets used in the experiment are BMG plates with a thickness of 5 mm. The projectile, spherical aluminum (3.1 mm in diameter), is accelerated up to various velocities; the light is detected with a radiometer. The emission lasts from 200 μs up to 1500 μs and the intensity increases from 44 to 900 W/(Sr·μm). The duration and intensity of a light emission seem to depend on the impact velocity and the extent of target destruction through the formation of impact craters or penetration. (condensed matter: structure, mechanical and thermal properties)